WO2012171486A1

WO2012171486A1 - Methods of rapid preparation of silver nanowires with high aspect ratio

Info

Publication number: WO2012171486A1
Application number: PCT/CN2012/077015
Authority: WO
Inventors: Qingkui Jiang; Zhenyu Chang; Jianbao DING
Original assignee: Zhejiang Kechuang Advanced Materials Co., Ltd
Priority date: 2011-06-16
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: CN102259190A; US20140102254A1

Abstract

Disclosed is a method suitable for efficiently producing silver nanowires with high aspect ratio. In this method, silver nanowires with aspect ratio of more than 300 and purity of more than 80% are produced through an acid compound mediated microwave-assisted wet chemistry method. Such silver nanowires are especially suitable for the application in the flexible transparent electrodes, as they can simultaneously improve the electrical conductivity and transparency.

Description

METHODS OF RAPID PREPARATION OF SILVER NANO WIRES WITH HIGH ASPECT

RATIO

1. Field of the Invention

The present invention pertains to the microwave-assisted wet chemistry methods of efficiently preparing metal nanowires, while controlling the purity and aspect ratio of the same.

2. Introduction

Nanomaterials can differ markedly from their analogous bulk counterparts. In particular, the physical and chemical properties of nanomaterials correlate strongly with their size, shape and morphology. Hence, material scientists pay great attention on developing simple and effective methods for synthesis of nanomaterials with controllable morphology (including shapes and sizes), hence tailoring their properties.

Silver, for the excellent electrical and thermal conductivity, are widely used in electronic industry, especially used to fabricate conductive adhesives, inks, electrodes, etc. Some of the recent reports have been directed to adaptations of the polyol process for the production of various selected nanostructures, including multiply twinned particles, silver nanopyramids, silver nanocubes, silver nanowires, etc (See, for example: Sun et al., Nano Letters, 3(7): 955-960 (2003); Wiley et al., Langmuir, 21(18): 8077-8080 (2005); Wiley et al., Chem. Eur. J., 11 : 454-463 (2005); and Wiley et al., Acc. Chem. Res., 40: 1067-1076 (2007)).

With the emergence of new flexible transparent conductive film (TCF) to replace the indium tin oxide (ITO), scientists pay great attention on the new transparent conductors, such as conductive polymers, carbon nanotubes, graphene, metal grids, and the random networks of metallic nanowires (See, e.g., Cheng I. C. et al., Vol. 11, Springer, (2009), Crawford G.P., Flexible Flat Panel Displays,Ed: P. C. Gregory (2005); Fehse K. et al., Adv. Mat. 19: 441(2007); Taylor P. G. et al., Adv. Mat. 21 : 2314(2009); Jung Y. C. et al., Adv. Mat. 20:4509 (2008). Gu H. et al., Adv. Mat. 20: 4433 (2008); Wu Z.C., et al., Science 305: 1273 (2004); Lee J.H. et al., Adv. Mat. 21 : 4383 (2009). Kim K.S. et al., Nature 457:706 (2009). Kang M. G. et al., Adv. Mat. 20:4408(2008). Among which, Ag possesses excellent malleability, mechanical robustness, the highest electrical conductivity (1.6x 10 Ω cm) and the silver nanowires-based TCFs have been believed to be leading one.

There are studies for transparent electrodes based on solution-processed CNT films that indicate smaller bundles and longer CNTs improve electrode performance. (Hecht D. et al., Appl. Phys. Lett. 2006, 89, 133122.). The same idea can be applied to Ag NW electrodes. The longer and thinner nanowires would significantly decrease the percolation threshold in surface conductance (Hu, L. et al., Nano. Lett. 2004, 4, 2513-2517). Benjamin J. Wiley and Jonathan N Coleman groups systematically researched the diameter and length effect on the conductivity and transmittance of silver nanowires films and also convince the above idea (Stephen M. Bergin et al, Nanoscale, 2012,4, 1996-2004. Sophie S. et al, Nanotechnology 23 : 185201.). Consequently, the effective and reproducible preparation of silver nanowires with high purity and high aspect ratios are of great importance for their potential application in the flexible transparent conductive film.

Xia and co-workers successfully synthesized high-quality silver nanowires in a "polyol" process that ethylene glycol (EG) solutions of AgN0₃ and poly(vinylpyrrolidone) (PVP) are dropwisely added at 148 °C or above within long time. When using this method, they found low

l reagent concentration and slow addition rate are necessary for controlling the quality of the Ag nanowires; otherwise, seed crystals with specific structures or metal salt seasoning agents are necessary. See, e.g., Sun, Y. et al., Science, 298, 2176(2002); Sun, Y. et al., Nano. Lett. 2, 165(2002); Sun, Y. et al., Adv. Mater. 14, 833(2002); Kim, F. et al., Angew. Chem. Int. Ed. 116, 3759(2004); and U.S. Published Application 2005/0056118, Wiley, B. et al., Nano Lett. 4(9), 1733-1739(2004), Sun, Y. et al., Chem. Mater. 14, 4736-4745(2002). Recently, US patent 7922787 claims production of silver nanowires by using compound comprising Fe(II) and/or Fe(III) and they successfully synthesized silver nanowires at lower temperature and/or at higher concentration, US patent with application number 2011/0185852 discloses synthesis of silver nanowires with high aspect ratio (mean diameter 62nm, and length 43micron) and high purity by making the reaction temperature occurred at lower temperatures within longer time (See e.g., 80°C for 2 weeks in the example 6 of US2011/0185852), which is quite time-consuming. US patent with application number 2011/0048170 Al discloses a method for controlling metal nanowires morphologies by purging inert gas, which makes the processes complicated and troublesome.

The drawbacks of time-comsuming is actually also a common problem for traditional polyol process. Moreover, the addition sequence and adding rate of the reactants still have remarkable influence on the morphology of the final product. Sometimes, using such method, one will obtain mixed nanostructures (e.g., the silver nanowires were accompanied by the formation of silver nanoparticles). Additional separation steps are therefore necessary to obtain monodispersed nanostructures.

Microwave-assisted polyol method is efficacious on rapid synthesis of silver nanostructures. (See, e.g., Tsuji Masaharu, et al, Crystal Growth & Design 7 (2): 311-320 (2007); Liu F. K. et al, Chemistry Letters33 ( 8): 1050-1051 (2004); Liu F. K. et al, Journal of Materials Research 19( 2): 469-473(2004); Tsuji Masaharu, et al, Chem. Eur. J. 11 :440-452 (2005); Zhu Y.J. et al, Materials Letters 58: 1517-1519(2004); Zhu J.F. et al, J. Phys. Chem. B 110: 8593-8597 (2006); Gou L.F. et al, Chem. Mater. 19: 1755-1760 (2007). Zhu et al. Materials Letters 58: 1517-1519(2004)) reported the microwave-mediated synthesis of Ag nanowires by reducing Ag₂0 in 1,2-ethanedithiol (10 min, 80-140°C), whereas in ethylene glycol, the reaction produces spherical particles. Using H₂PtCl₆ as a source of Pt seeds, Tsuji's research group successfully achieved the microwave synthesis of Ag nanorods and wires in ethylene glycol in 8 min (Tsuji Masaharu, et al, Chem. Eur. J.11 :440-452 (2005)). In a movement to aqueous solution, Liu et al. and Yu et al. reported the microwave-assisted formation of Ag nanorods and Ag/C nanocables within 10 and 20 min, respectively (Liu, F.K.et al., J. Mater. Res. 2004, 19, 469-473. Yu, J. C. et al., Chem. Commun. 2704-2706 (2005). In both cases, high-pressure vessels were required, as reaction temperatures exceeded 100 °C. Another problem is complicated reaction conditions and still producing mixed nanostructures (e.g., the silver nanowires were accompanied by the formation of silver nanoparticles, or impurities introduced by the seed "Pt"). Gou et al. simplified the microwave assisted polyol process by benchtop dissolution of NaCl and AgN0₃ (ratio 1 :6 to 1 :3) in ethylene glycol and subsequent heating using microwave irradiation (320W) in the presence of PVP to obtain nanowires in -80% yield in 3.5 min. (Gou L.F. et al., Chem. Mater. 19, 1755-1760 (2007)). Such high yielding preparation does not require any external seed crystals, precursors, or mechanical stirring and is conducted under ambient (¾ conditions, leading to significant potential for the large-scale fabrication of Ag nanowires using this simple approach. In this case, however, only silver nanowires with low aspect ratio is synthesized (See, e.g. silver nanowires with dimensions of 45nm in diameter and 4~12micron in length is obtained which lead to the aspect ratio is between 89-266).

There remains a great need in the art to fabricate silver nanowires with high purity and high aspect ratio in an effective and reproducible fashion.

An object of the present invention is to overcome such problems by providing an acid compound mediated microwave assisted polyol method to produce silver nanowires with high aspect ratio and high purity from a silver salt solution. Acid compound is added, by which the length of the products can be significantly improved. Except the whole microwave process, the traditional heating source (furnace, oven, oil bath or heating mantle) combined with microwave assisted wet chemistry method is also presented here.

Thermodynamically, silver nanowires are formed by initial formation of the numerous twinned nuclei and subsequently the growth of the nuclei. The twinned nuclei are more favorable for silver nanowires formation compared with single crystal structures, which is demonstrated by Xia et al. (See, e.g., Sun, Y. et al., Science, 298, 2176(2002); Sun, Y. et al., Nano. Lett. 2, 165(2002); Sun, Y. et al., Adv. Mater. 14, 833(2002)). By manipulating the reaction kinetics, one can control the nucleation and growth process of nanomaterials to get required structures or morphologies. (See, e.g., Zeng, J. et al., Angew. Chem. Int. Ed., 51 : 2512. : Y. Xia and co-workers show shape-selectively growth of bimetallic palladium-silver nanocrystals through controlling the nucleation and growth processes.). Following this idea, the nuclei approving silver nanowires formation can be obtained by manipulating the nucleation step. Corresponding to the present invent, the nucleation step comprising heating the reaction mixture under microwave irradiation to a temperature between 100~170°C is employed to prepare the nucleus seeds approving silver nanowires formation and then growth of the nuclei can be further processed at a temperature between 100~170°C by microwave irradiation or other the traditional heating source (such as furnace, oven, oil bath or heating mantle). The rationality of the present procedures can also be supported by results in the previous literatures: Reports on the synthesis of silver nanowires by traditional heating source from an AgNCVClVPVP/EG solution demonstrate that it is necessary to remove the oxygen dissolved in the reaction solution in order to achieve the growth of silver nanowires (See, e.g. Wiley, B.et al., Nano Letters, 4(9): 1733-1739 (2004); Wiley et al., Langmuir, 21(18): 8077-8080 (2005); Campbell, C. T. et al., Science 157(1): 43-60(1985); deMongeot, F. B.et al., Chemical Physics Letters 270 (3-4): 345-350 (1997). For example, Xia's experiment has demonstrated that the addition of chloride causes enhanced oxidation and preferential etching of twinned particles, leaving only single-crystal particles (or seeds) to grow. They also carried out experiments under argon which supplied an anoxic condition and the twinned particles that formed in the early stage of the reaction could grow into uniform nanowires. However, Tsuji and Gou's results indicate this mechanism is not applicable to the synthesis of Ag nanowires under rapid microwave(MW)-polyol method in the presence of CI^" anions They did the experiments to fabricate Ag nanostructures under bubbling air or N₂ gas and obtained silver nanowires in high yield (>90% without isolation) under bubbling air, while mixtures of cubes, bipyramids, and wires under bubbling N₂ gas. Although the physical mechanism underlying the differences of the two process is not well know, one would find nuclei formed by the microwave assisted wet chemistry method with open-air condition is significantly important for the growth of nanowires.

The properties of nanostructured materials is intensively dependent on the structure, due to the nano scale matches with some physical characteristic lengths such as wavelength of light, De Broglie wave and coherence length of superconducting state, which causes the damage of the cyclical boundary condition of crystal, decrease of atomic density around superficial layer of nanoparticles and the contraction of mean free path of electron and increasing localization and coherence of electron. The factors such as size, geometric shape, and crystalline degree will significantly affect properties. The morphology controlling of nanomaterials becomes one of the key tools for material scientists to find a new material with unique abilities. The morphology of material can divide into square, pyramid, one-dimensional silver nanaowires, nanorod and nanoplate etc. One-dimensional silver nanaowires become a hot focus because of its unique optical and electrical property.

With the emergence of new flexible transparent conductive film to replace the indium tin oxide (ITO), scientists pay great attention on the new transparent conductors. Because of its characteristics such as high conductivity and easy preparation, silver nanaowires have become a focus and first priority material to prepare flexible transparent conductive film. The silver nanowires with well-defined diameter and high aspect ratio, easy to batch produce and high production efficiency are of great importance for their potential application in the flexible transparent conductive film. Large aspect ratios can be favored for obtaining a transparent conductor layer since they may enable more efficient conductive networks to be formed while permitting lower overall density of wires for a high transparency. To prepare silver nanowires with high aspect ratio and suitable diameter becomes important key technology in producing flexible transparent conductive film. The needs for silver nanowires with higher aspect ratio grow intensively.

Currently, known methods of manufacturing silver nanowires are mainly template-assistant method, polybasic alcohol method, plasma physics method etc. Papers below can be viewed as references: Chem.Commun., 699(1999), 700; Science, 294 (2001), 348; Chem. Material., 14(2002), 4736; J.Phys.Chem.B, 108(2004), 12877 etc. Although all the methods above can be used to prepare silver nanowires, the reaction conditions are complicated, the reaction needs 2~3hours, the aspect ratio of silver nanowires and also the output is low. Some methods need platinum nanopaticles as catalyst, which cause the impurity of silver nanowires. Microwave assisted methods make rapid synthesis silver nanowires possible. Some Chinese patents are as follows: (1)A large-batch preparation method for silver nanowires (Application number: 200810019828.6), (2)A large-batch preparation method for noble metal nanowires (Application number: 200810163102.X), (3)A microwave assisted preparation method for silver nanostructures with different morphologies(Application number: 20091000613 l.X), (4) A cationic control microwave assisted preparation method for diameter controlled silver nanowires(Application number: 201010559335.9). Although the microwave assisted wet chemistry methods mentioned above could prepare silver nanaowires, the diameter is less than 30micron and the aspect ratio is low. In this case, while at the same filling rate to prepare electrodes, the number of mesh conjuctions with low aspect ratio is much more than the ones with high aspect ratio and the conductivity is lower by more than an order of magnitude. So how to rapidly produce silver nanowires with high aspect ratio in large scale is the main factor to the industrialization of flexible transparent electrodes.

3. References: All literature and similar materials cited in this application, including but not limited to patents, patent applications, articles, books and treatises, regardless of the format of such literature or similar material, are expressly incorporated by reference herein in their entirety for any and all purposes.

US Patent References:

Other References:

1. E. Majidi and B.D. Gates, Optimizing Growth Rates and Thermal Stability

of Silver Nanowires, Mater. Res. Soc. Symp. Proc, vol. 1017, ID: 1017-DD18-12, 6 pages total(2007).

2. Y. Sun et al. Uniform Silver Nanowires Synthesis by Reducing AgN03 with Ethylene Glycol in the Presence of Seeds and Poly(Vinyl Pyrrolidone), Chem. Mater., , vol. 14, pp.

4736-4745(2002).

3. Fievet et al., "Homogeneous and Heterogeneous Nucleations In The Polyol Process For The Preparation of Micron and Submicron Size Metal Particles", Solid State Ionics, 32/33:

198-205 (1989). Ducamp-Sanguesa et al., "Synthesis and Characterization of Fine

Monodisperse Silver Particles of Uniform Shape", Journal of Solid State Chemistry, 100: 272-280 (1992).

Sun et al., "Crystalline Silver Nanowires by Soft Solution Processing", Nano Letters, 2(2): 165-168 (2002).

Sun et al., "Large-Scale Synthesis of Uniform Silver Nanowires Through a Soft, Self-Seeding, Polyol Process", Adv. Mater., 14(11): 833-837 (2002).

Sun et al., "Uniform Silver Nanowires Synthesis by Reducing AgN03 with Ethylene Glycol in the Presence of Seeds and Poly(Vinyl Pyrrolidone", Chem. Mater., 14: 4736-4745 (2002). Sun et al., Shape-Controlled Synthsis of Gold and Silver Nanoparticles, Science, 298:

2176-2179 (2002).

Sun et al., "Polyol Synthesis of Uniform Silver Nanowires: A Plausible Growth Mechanism and the Supporting Evidence", Nano Letters, 3(7): 955-960 (2003).

Wiley et al., "Polyol Synthesis of Silver Nanostructures: Control of Product Morphology with Fe(II) or Fe (III) Species", Langmuir, 21(18): 8077-8080 (2005).

Wiley et al., "Shape-Controlled Synthesis of Metal Nanostructures: The Case of Silver", Chem. Eur. J., 11 : 454-463 (2005).

Wiley et al., "Maneuvering the Surface Plasmon Resonance of Silver Nanostructures Through Shape-Controlled Synthesis", J. Phys. Chem. B, 110: 15666-15675 (2006).

Wiley, B et al. Synthesis and Electrical Characterization of Silver Nanobeams. Nano Lett. 6, 2273(2007).

Xia Y. N. et al One-Dimensional Nanostructures: Synthesis, Characterization, and Applications.. Adv. Mater. 15 :353(2003).

Reyes-Gasga et al., On the Structure of Nanorods and Nanowires with Pentagonal Cross-sections", Journal of Crystal Growth, 286: 162-172 (2006).

Wiley et al., "Syntheis of Silver Nanostructures with Controlled Shape Properties", Acc. Chem. Res., 40: 1067-1076 (2007).

Chen et al., "One-Dimensional Nanostructures of Metals: Large-Scale Synthesis and Some Potential Applications", Langmuir, 23: 4120-4129 (2007).

Zhang et al., "High-Concentration Preparation of Silver Nanowires: Restraining in Situ Nitric Acidic Etching by Steel-Assisted Polyol Method", Chem. Mater., 20: 1699-1704 (2008).

Deiphion Summary of Chinese patent application CN— 2007/010046510.2 including English title and abstract— 2 pages, Published Jul. 16, (2008).

English Translation of Chinese Patent Application Disclosure No: CN 101220506A, published Jul. 16, 2008— Reference Bl— Originally filed on Feb. 25, (2009) in Chinese. Korte et al., Rapid Synthesis of silver nanowires through a CuCI- or CuCI2 -mediated polyol process, Journal of Materials Chemistry 18: 437-441 (2008).

Tsuji Masaharu et al. Rapid synthesis of silver nanostructures by using microwave-polyol method with the assistance of Pt seeds and polyvinylpyrrolidone. CRYSTAL GROWTH & DESIGN 7 (2): 311-320 ( 2007).

Liu F. K. et al., Preparation of silver nanorods by rapid microwave heating , CHEMISTRY LETTERS 33 ( 8): 1050-1051 ( 2004).

Liu F. K. et al., Microwave-assisted synthesis of silver nanorods, JOURNAL OF MATERIALS RESEARCH 19( 2): 469-473 ( 2004).

25. Tsuji Masaharu, et al., Microwave-Assisted Synthesis of Metallic Nanostructures in Solution, Chem. Eur. J. 11, 440 - 452 (2005).

26. Zhu. YJ. et al., Microwave-assisted polythiol reduction method: a new solid-liquid route to fast preparation of silver nanowires. Materials Letters 58: 1517- 1519 (2004).

27. Zhu J. F. et al., Microwave-Assisted One-Step Synthesis of Polyacrylamide Metal (M Ag, Pt, Cu) Nanocomposites in Ethylene Glycol, J. Phys. Chem. B 110: 8593- 8597 (2006).

28. Gou L.F. et al., Convenient, Rapid Synthesis of Ag Nanowires, Chem. Mater. 19, 1755-1760 (2007).

29. Zeng J. et al., Controlling the Nucleation and Growth of Silver on Palladium Nanocubes by Manipulating the Reaction Kinetics. Angew. Chem. Int. Ed., 51 : 2512 (2012).

PROBLEM TO BE OVERCOME BY THE INVENTION

There is no report on microwave-assisted polyol method for producing silver nanowires with high aspect ratio and high purity simultaneously. Therefore, an object of the present invention is to overcome such problems by providing an acid compound mediated microwave assisted polyol method to produce silver nanowires with high aspect ratio and high purity from a silver salt solution. Acid compound is added, by which the length of the products can be significantly improved. The traditional heating source (furnace, oven, oil bath or heating mantle) combined with microwave assisted polyol method is also presented here. The first nucleation step comprising heating the reaction mixture under microwave irradiation to a temperature between 100~170°C to is employed to prepare the nucleus seeds approving silver nanowires formation and then the traditional heating source is employed to supply enough temperature and/or energy for the growth of silver nanowires. This reasonability of the present procedure can also supported by the previous results.

3. Definitions

For the purposes of interpreting this specification, the following definitions will apply and whenever appropriate, terms used in the singular will also include the plural and vice versa. In the event that any definition set forth below conflicts with the usage of that word in any other document, the definition set forth below shall always control for purposes of interpreting the scope and intent of this specification and its associated claims.

The use of "or" means "and/or" unless stated otherwise or where the use of "and/or" is clearly inappropriate. The use of "a" means "one or more" unless stated otherwise or where the use of "one or more" is clearly inappropriate.

The use of "comprise", "comprises", "comprising", "include", "includes", and "including" are interchangeable and not intended to be limiting. Furthermore, where the description of one or more embodiments uses the term "comprising" those skilled in the art would understand that in some specific instances, the embodiment or embodiments can be alternatively described using language "consisting essentially of and/or "consisting of.

As used herein, 'aspect ratio' should be interpreted differently depending on whether it is being used with reference to an individual nanostructure or to the general characteristics of bulk material. With respect to an individual nanostructure, 'aspect ratio', as used herein, refers to the length divided by diameter of the individual nanostructure. For example, a nanowire having a length of 30,000 nanometers (30 μπι) and a diameter of 50 nanometers would have an aspect ratio of 600 (30,000/50=600). With respect to bulk material, 'aspect ratio' refers to the averaged aspect ratio that is characterized based on the average length and diameter dimensions obtained by sampling individual nanostructures contained in the bulk material. For example, the "aspect ratio" of bulk product silver nanowires can be determined as follows: This method is based upon collecting measurement data from individual nanostructures in a population using electron microscopy (FIG. 2). The lengths are obtained using low magnification electron microscopy (although other methods such as optical microscopy could also be used), and the diameters are determined using electron microscopy (although other methods could be used). The diameters and lengths are determined from a sampling taken from the bulk material which contains the produced nanostructures. We define, for this invention, nanorods as materials that have a width of ~1±100 nm and aspect ratios greater than 1 but less than 20; and we call nanowires analogous materials that have aspect ratios greater than 20. We define "silver nanowires with high aspect ratio" as the value of individual or bulk samples not less than 300. Using this process, approximately 500 nanostructures are measured to determine the lengths, and more than 50 nanostructures are measured to determine the diameters. An average length and average diameter is determined for the nanostructures examined. It is also to be understood that the selection of 500 and 50 nanostructures, respectively, referred to above is arbitrary and not intended to be a limitation. Rather, the number of nanostructures selected for analysis can depend on the characteristics (e.g. homogeneity) of the bulk material and the accuracy desired for estimating the properties of the bulk material. With reference to Table 1 and Table 2, the average length column (the 'Average Length') is the average length of the measured nanowire population. With reference to Table 1, the average diameter column (the 'Average Diameter' plot) is the average diameter of the measured nanowire population. With reference to aspect ratio of bulk samples, the aspect ratio is determined by dividing the average length of the nanowires to the average diameter of the nanowires (average length, average diameter and average aspect ratio are listed in Table 1 and Table 2.

As used herein, the "purity" of the silver nanowires is defined as the weight percent of silver nanowires with aspect ratio no less than 100 in the total amount of the silver nanostructures produced. Silver nanostructures including but no limited to silver nanoparticles, silver nanorods or silver nanowires with aspect ratio less than 100, are defined as impurities. We define, for this invention, high purity means the percent of silver nanowires with high aspect ratio is no less than 50%. In practice, this can be determined by statistically calculating the weight percent of silver nanowires with aspect ratio greater than or equal to 100 in the total silver nanostructures in a SEM pictures, assuming the diameter is the same. For example, there are total 100 individual silver nanostructures in a SEM picture with average diameter 50nm, among which 60 silver nanowires with average length 20micron and aspect ratio of the each individual silver nanowire is greater than or equal to 100, 20 silver nanowires with average length 4 micron and aspect ratio of the each individual silver nanowire is less than 100, 20 silver nanoparticles with average diameter 50nm, so the purity can be estimated to be 60 X 20/(60 X 20+20 X 4+20 X 0.05) ¾ 93.7%. With reference to Table 1, the purity of bulk samples is by the same calculating process as the above example.

As used herein, the "yield" of the silver nanowires is defined as the output of silver nanowires in per unit time and per unit volume of polyols.

As used herein with respect to practice of the methods, the terms "added", "mixed" or "combined" are generally interchangeable and refer to the act of adding, mixing or combining one or more of the reactants with one or more other reactants. This can occur by adding reactants to, or mixing or combining the reactants in, the reaction vessel and/or with each other.

As used herein, 'halide ion' refers to fluoride ion, chloride ion, bromide ion or iodide ion.

As used herein 'reaction temperature' refers to the temperature of the heat source applied to the reaction vessel or the actual temperature of the reaction mixture during the reaction as determined by direct monitoring. For example, the reaction temperature could be the temperature of the reaction mixture as determined by a thermometer or thermocouple inserted into said reaction mixture.

SUMMARY OF THE INVENTION

It is an object of the present invention to produce silver nanowires with a scalable process and with high manufacturing efficiency. The instant method is an acid compound mediated microwave assisted polyol method to produce silver nanowires with high aspect ratio and high purity.

Using no more than the guidance provided herein and routine experimentation, one of skill in the art will be able to select conditions that produce silver nanowires using microwave-assisted polyol method, including reaction conditions that preferentially produce uniform silver nanowires having aspect ratios of at least 300 with high purity (80%).

The method comprises:

forming a reaction mixture including silver nitrate, poly(vinyl pyrrolidone) (PVP), acid compound, chloride additives in polyol(s); and select reaction conditions to form silver nanowires with aspect ratio equal or greater than 300 and purity equal or greater than 80% by reducing the silver salts in the reaction mixture fully or partially under microwave irradiation, wherein the reaction conditions comprise silver nitrate concentration, a PVP concentration, acid compound concentration, additive concentration, reaction temperature and reaction time, and/or microwave power.

(1) Polyol(s)

The polyol is used as both solvent (be used to dissolve the silver nitrate to form the silver solution) and reducing agent (be capable of reducing the silver nitrate to silver metal at the reaction temperature when present in the reaction mixture). Some useful polyols include ethylene glycol, glycerol, glucose, diethylene glycol, tri-ethylene glycol, propylene glycol, a butanediol, a dipropylene glycol and/or a polyethylene glycol.

The polyol may be a single polyol or a mixture of two or more polyols (e.g. three, four, five or more polyols). Whenever the term "polyol" is used herein, this term is meant to include both a single polyol and a mixture of two or more polyols unless used as part of the phrase "polyol or polyols" or "polyol(s)" (both of which include the singular and plural version of this term) or where use of the singular term is clearly intended or required.

(2) Silver Nitrate

According to some embodiments of this invention, it is not a requirement that the silver nitrate be added to the reaction in solution as it may be added in solid form (i.e. as a solid powder) or as a suspension.

(3) Poly(vinyl pyrrolidone) (PVP)

PVP is introduced into the polyol mediated preparation of nanostructures as an organic protective agent, It is to be understood that polyvinylpyrrolidone (PVP), having an average molecular weight of, for example, 55,000 is used as the organic protective agent, the concentration is calculated using the monomer weight and not the average molecular weight of the polymer. For example, the molar concentration of PVP solution would be calculated by dividing the grams of PVP used to make the OPA solution by 111 g/mole and not by 55,000 g/mole.

As discussed supra, the present invention also contemplates the use of two or more different types of PVP with different molecular weight. For example, the organic protective agent may comprise poly(vinyl pyrrolidone) having an average molecular weight of 55,000 and poly(vinyl pyrrolidone) having an average molecular weight of 1,300,000). Also, the organic protective agent may comprise poly(vinyl pyrrolidone) having an average molecular weight of 55,000 and poly(vinyl alcohol) having an average molecular weight of 35,000.

It is not a requirement that the organic protective agent be added to the reaction in solution as it may be added in solid form (a solid powder).

(4) Acid Compound

As used herein, 'acid compound' refers to any compound having a pK_a lower than 7. In some embodiments, the acid compound has a plv,, less than 3.5. In some embodiments, the acid compound has a pKa less than 2. In some embodiments, the acid compound has a pKa less than 1. The acid compound can be any acid that does not appreciably interfere with the reduction of the silver nitrate to silver metal or otherwise interfere with the reaction. In some embodiments, the acid compound may also be selected to avoid halide ion or iron. In some embodiments, the acid compound is intended to refer to a mixture of two or more compounds have a pKa less than 7, less than 3.5, less than 2 or less than 1. For the avoidance of any doubt however, the 'acid compound' is not intended to refer to a 'silver compound' as discussed and defined below.

According to some embodiments of this invention, an acid compound can be used as a reactant. As with the other reactants, there is no firm limitation on the order of mixing so long as the reaction produces the desired nanostructure, such as silver nanowires. The acid compound can be a liquid, solid or gas. If a liquid, it can be mixed directly in solution either dropwise or portionwise. If a solid, the acid compound can be mixed in solid form or in solution either dropwise or portionwise. If a gas, it can be bubbled into (through) the reaction.

(5) Chloride additives

"Chloride additives" refers to a salt additive comprising a cation and an anion CI . The cation and anion are associated by ionic interaction and dissociate in polar solvents such as water, alcohol, diols and polyols (including ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, glycerin, glycerol, and glucose). The cation can be organic or inorganic. The chloride additives may further include its corresponding acids, i.e., the cation is a proton.

In certain embodiments, the chloride additive is a quaternary ammonium chloride. As used herein, "quaternary ammonium chloride" refers to ammonium chloride (NH₄ ⁺C1 ) in which all four hydrogens have been replaced by an organic group. Thus, the quaternary ammonium chloride can be typically represented by formula NR₄ CI wherein each R is the same or different and independently an alkyl, alkenyl, alkynyl, aryl, or aralkyl.

In certain embodiments, the chloride additives is a quaternary phosphonium chloride. The quaternary phosphonium chloride can be typically represented by formula PR₄ CI , wherein each R is the same or different and independently an alkyl, alkenyl, alkynyl, aryl, or aralkyl. They are soluble in the reducing solvent, as defined herein. Moreover, they are compatible with PVP due to the organic moieties present.

"Alkyl" refers to monovalent saturated hydrocarbon structure of between 1 and 20 carbons, in which the carbons are arranged in either a linear or branched manner. Lower alkyl refers to alkyl groups of 1 to 5 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s- and t-butyl and the like. Examples of alkyl groups of longer chains include octyl(C8), decyl(ClO), dodecyl(C12), cetyl(C16), and the like. When an alkyl residue having a specific number of carbons is named, all geometric isomers having that number of carbons are contemplated; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl and t-butyl; propyl includes n-propyl and isopropyl.

Unless specified otherwise, the alkyl can be optionally substituted with a halogen (F, Br, CI or I), alkoxy, amine, and the like.

"Alkenyl" refers to a monovalent hydrocarbon structure of between 2 and 20 carbon atoms with at least one double bond. Examples include, without limitation: ethenyl, propenyl, butenyl, pentenyl, hexenyl, butadienyl, pentadienyl, and the like. Unless specified otherwise, the alkyl can be optionally substituted with a CI, alkoxy, amine, or the like.

"Alkynyl" refers to a monovalent hydrocarbon structure of between 2 and 20 carbon atoms with at least one triple bond. Examples include, without limitation: ethynyl, propynyl, butynyl, pentynyl, hexynyl, methylpropynyl, 4-methyl-l -butynyl, 4-propyl-2-pentynyl, and the like.

"Alkoxy" refers to a radical of the formula— O-alkyl. Examples include methoxy, ethoxy, propoxy, isopropoxy, and the like. Lower-alkoxy refers to groups containing one to five carbons.

"Aryl" refers to optionally substituted phenyl or naphthyl. Exemplary substituents for aryl include one or more of halogen, hydroxy, alkoxy, amino, mercapto, or the like.

"Aralkyl" refers to an alkyl residue substituted with at least an aryl group. The aralkyl can be typically represented by the formula aryl-alkyl-. Exemplary aralkyls include, without limitation, phenylmethyl (i.e., benzyl), or phenylethyl group.

Exemplary chloride additives therefore include, without limitation: Benzyl triphenyl phosphonium chloride (BTPC), Ethyltripheny phosphonium Chloride (ETPC), Tetrabutylphosphonium Chloride (TBPC), Diphenyl phosphinic chloride, Tributyl Tetradecyl Phosphonium Chloride (TTPC), Tetrakis(hydroxymethyl)phosphonium chloride (THPC), Methyltripheny phosphonium Chloride, Tetramethylammonium chloride (TMAC), Tetrabutylammonium chloride (TBAC), Cetyl trimethylammonium chloride (CTAC), C8-C18 alkyl dimethyl benzyl ammonium chloride, methyl trioctylammonium chloride (i.e., Aliquat 336®), and the like.

(6)Reaction Conditions

The reaction conditions selected for the polyol process are those which preferentially produce the desired silver nanowires. Thus, according to various embodiments of this invention, reactants are selected, combined and then reacted under conditions that are selected to preferentially produce silver nanowires.

It has been observed that the concentrations of the constituents in the reaction mixture have an impact on the formation of the nanostructures and their yields. For example, the concentration of the silver nitrate in the solution is in the range of 0.01-0.15 mol/L, more preferably 0.05-0.1 mol/L, for an optimal yield of nanowires.

In addition, the ratio of the mass concentration of the PVP to the mass concentration of the silver nitrate in the reaction mixture is in the range of about 15: 1 to 0.5: 1, more preferably 10: 1 to 1 : 1.

In some embodiments, the concentration ratio of the acid compounds in the reaction mixture is in the range of 0.0005-0.05mol/L, more preferably, the concentration is in the range of 0.005-0.0 lmol/L.

In some embodiments, the ratio of the molar concentration of the chloride additive to the molar concentration of the silver nitrate in the reaction mixture is in the range of 1 : 10000 ~ 1 :25, more preferably, in the range of 1 : 1000 ~ 1 :50.

In some embodiments, the silver solution can be mixed with the polyol (e.g. a third portion of the polyol) before the PVP solution is mixed. In some embodiments, the PVP solution can be mixed with the polyol (e.g. a third portion of the polyol) before the silver solution is mixed. In some embodiments, part of one of either the PVP solution or silver solution can be added, then part of the other of the PVP solution or silver solution can be added, or vice versa. This process can then be repeated on a second part, third part, etc. until the entirety of each solution has been mixed with the polyol (e.g. a third portion of the polyol). In some embodiments, the silver solution and the PVP solution can be mixed together and then this mixture can be added to the polyol (or portion of the polyol).

In some embodiments, the polyol may be added to the PVP solution and/or the silver solution. In some embodiments, the silver nitrate and/or PVP can be mixed in solid form. This addition can be continuous over a period of time or portionwise. Similar to the discussion pertaining to solutions, the order of addition of the solids is not limiting as the reactants can be combined in any way that produces the desired silver nanowires. Applicants have determined that it is not necessary to use dropwise addition as one can add the reagents portionwise (e.g. pour one or more reagents into a mixture over a period of about 1 to 30 seconds) or use the reagents in solid form.

The reaction can be controlled either by microwave power and irradiation time or reaction temperature and reaction time.

The reaction time is measured from the time that at least a portion of each of the reactants to be reacted and then extends through any time where a continued combining of the reactants occurs until the time when all reactants have been added to the reaction. The reaction time also includes the time after all of the reactants have been combined during which nanostructures are produced. The reaction time also includes the time period when nanostructures are produced. In general the reaction is complete when the silver nitrate has formed nanostructures. In practice, reaction times can be from about 5 minutes to about 24 hours. In some embodiments, reaction times can be from about 30 minutes to about 5 hours. Thus, in some embodiments, using no more than the disclosure provided herein and routine experimentation, one of skill in the art can select an appropriate reaction time to preferentially produce silver nanowires as compared with other nanostructures.

The microwave power combined with irradiation time influences the yields and length of the metal nanowires formed. Typically, the silver nitrate, PVP, acid compound and the chloride additives are mixed homogeneously in a polyol solvent (e.g., ethylene glycol or propylene glycol). The reaction mixture is then irradiated under typically 240-2000W microwave power within sufficient time period until the reaction is finished or partially finished. The time is depending on the total volume of the reaction mixture.

The reaction temperature influences the yields and length of the metal nanowires formed. Typically, the silver nitrate, PVP, acid compound and the chloride additives are mixed in a polyol solvent (e.g., ethylene glycol or propylene glycol) at a first temperature to provide a reaction mixture. The first temperature can be in the range of from 10°C to 50°C. The reaction mixture is thoroughly mixed before it is heated to a second temperature and maintained at a third temperature by high microwave power (e.g. 320W-2000W), and then the temperature is maintained by adjusting the microwave power to a low point (80-400W). The second temperature and the third temperature can be the same or different and independently, are in a range of about 80°C to 200°C, more typically, in a range of about 100° C to 170°C.

In some embodiments, the silver nitrate, PVP, acid compound and the chloride additives are mixed in a polyol solvent (e.g., ethylene glycol or propylene glycol) at a first temperature to provide a reaction mixture. The first temperature can be in the range of about 10°C to 50°C. And then the reaction mixture is heated to a second temperature by high microwave power (e.g. 560W-2000W), and then the reaction mixture was transferred to an oven or oil bath setted at a third temperature. The second temperature and the third temperature can be the same or different and independently, are in a range of about 80°C to 200°C, more typically, in a range of about 100° C to 170°C.

In some embodiments, PVP and silver nitrate are thoroughly mixed in a polyol solvent (e.g., ethylene glycol or propylene glycol) at a first temperature before heated to a second temperature. The first temperature is typically maintained in a range of about 10° C. to 50 ^°C, Subsequently, the acid compound and the chloride additives solution is then added and then the mixture is then heated to a third temperature. The second temperature and the third temperature can be the same or different and independently, are in a range of about 80°C to 200°C, more typically, in a range of about 100° C to 170°C.

BRIEF DESCRIPTION OF THE DRAWIGNS

The skilled artisan will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the present teaching in any way.

In the drawings, the sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles may not be drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn may not be intended to convey any information regarding the actual shape of the particular elements, and may have been selected solely for ease of recognition in the drawings.

FIGS. 1(A) low magnification and 1(B) high magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Example 1.

FIGS. 2(A) low magnification and 2(B) high magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Example2.

FIGS. 3(A) low magnification and 3(B) high magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Example 3.

FIGS. 4(A) low magnification and 4(B) high magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Example4.

FIGS. 5(A) low magnification and 5(B) high magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Comparative Example 1.

FIG.6 low magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Comparative Example 2. FIG.7 low magnification of scanning electronic microscope (SEM) image of silver nanowires as prepared in Comparative Example 2.

FIG.8 X-ray diffraction pattern of silver nanowires as obtained in Example 1. The sample was made by pasting silver nanowires on silicon substrate.

Fig. 9 is the SEM picture of the silver nanowires synthesized in example 12;

Fig. 10 is the SEM picture of the silver nanowires synthesized in example 13;

Fig. 11 is the SEM picture of the silver nanowires synthesized in example 14;

Fig. 12 is the SEM picture of the silver nanowires synthesized in example 15;

Fig. 13 is the SEM picture of the silver nanowires synthesized in comparative example 8;

Fig. 14 is the SEM picture of the silver nanowires synthesized in comparative example 9;

Fig. 15 is the XRD pattern of the silver nanowires synthesized in example 12;

EXAMPLES

Aspects of the present teachings can be further understood in light of the following examples, which should not be construed as limiting the scope of the present teachings in any way.

The chemicals used are listed here:

a) Purified ethylene glycol ("EG" from "aladdin-reagent" )

b) Purified glycerol ( from "aladdin-reagent" )

c) Purified propylene glycol ( from "aladdin-reagent" )

d) Silver nitrate ('AgN03', from "aladdin-reagent")

e) Poly (vinyl pyrrolidone) ('PVP', 55,000 MW, "aladdin-reagent")

f) Poly (vinyl pyrrolidone) ('PVP', 130,000 MW, "aladdin-reagent")

g) Standard HC1 solution (1.0mol/L from "aladdin-reagent")

h) TBAC powder (TBAC from "aladdin-reagent")

i) Nitrate Acid (FINO₃ ) solution (FINO₃ weight percent 70%, from "aladdin-reagent" ) j) Manganese chloride (MnC¾) powder (MnC¾_, from "aladdin-reagent")

k) Tetrabutyl phosphonium chloride powder (TBPC from "aladdin-reagent")

Examplel

The following solutions were prepared using said chemicals:

0.14g HC1 (0.0038 mol) solution in 100ml EG (the 'HCl Solution')

O. lg HNO₃ (0.0016 mol) solution in 2ml EG (the 'HN0₃ Solution')

2.55g AgN0₃ (0.015 mol) in 100 ml EG (the 'AgN0₃ Solution'— made up to be homogeneous at least 30 min before adding to the reaction)

2.55 g PVP (0.0225) (55,000 MW) in 70 ml EG (the 'PVP Solution') Procedure:

To a 100 mL glassy beaker, was added the PVP solution, 0.7mL of the HCl solution, 1.5ml FINO₃ solution, 10ml AgN0₃ solution. The mixture was then vigorous stirred for homogeneity. The reaction mixture was then transferred to a microwave oven and then treated with microwave irradiation using 320W within 5 min. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 250 mL of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP. Figs. 1A and IB is the SEM picture of the sample synthesized under low and high magnification. The average length, average diameter, aspect ratio and purity information for the silver nanowires obtained is listed in Table 1. The XRD pattern is also showed in Fig. 8.

Example 2

The following solutions were prepared using said chemicals:

1.2g NaCl (0.02mol) in 100ml Glycerol (the 'NaCl Solution')

lg HN0₃ 0.016 mol) solution in 20ml Glycerol (the 'HN0₃ Solution')

0.34g AgN0₃ (0.002 mol) in 10 ml Glycerol (the 'AgN0₃ Solution'— made up to be homogeneous at least 30 min before adding to the reaction)

3 g PVP (0.027 mol) (13,0000 MW) in 20mL Glycerol (the 'PVP Solution') Procedure:

To a 50 ml glassy beaker, was added the PVP solution, 5mL of the NaCl solution, 1ml FINO₃ solution, 10ml AgN0₃ solution. The mixture was then vigorous stirred for homogeneity at 25 ^°C . The reaction mixture was then transferred to a microwave oven and then treated with microwave irradiation using 400W. The irradiation is keeping on until the temperature of the reaction mixture gets to 150°C, and then the temperature of the reaction mixture is maintained for another lhours by moving the reaction mixture to a oven settled at 150°C . The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 300 ml of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP. Figs. 2A and 2B is the SEM picture of the sample synthesized under low and high magnification. The average length, average diameter, aspect ratio and purity information for the silver nanowires obtained is listed in Table 1.

Example 3

The following solutions were prepared using said chemicals:

0.25g (0.002 mol) MnCl₂ in 100ml ethylene glycol (the 'MnCl₂ Solution')

0.3g HNO₃ (0.0048 mol) solution in 100ml Glycerol (the 'HN0₃ Solution')

2.5g AgN0₃ (0.0147 mol) in 100 ml ethylene glycol (the 'AgN0₃ Solution'— made up to be homogeneous at least 30 min before adding to the reaction)

5 g PVP (13,0000 MW) (0.045 mol) and 5 g PVP (55,000 MW) (0.045 mol)in 200 ml Glycerol (the 'PVP Solution')

Procedure:

To a 500 ml glassy beaker, was added the PVP solution, 20mL of the MnC¾ solution, 50ml FINO₃ solution, 100ml AgN0₃ solution. The mixture was then vigorous stirred for homogeneity at 25°C. The reaction mixture was then transferred to a microwave oven and then treated with microwave irradiation using 1200W. The irradiation is keeping on until the temperature of the reaction mixture gets to 140°C, and then the temperature of the reaction mixture is maintained for another 3hours by moving the reaction mixture to a oven settled at 140°C . The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 1L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP. Figs. 3 A and 3B is the SEM picture of the sample synthesized under low and high magnification. The average length, average diameter, aspect ratio and purity information for the silver nanowires obtained is listed in Table 1. Example 4

The following solutions were prepared using said chemicals:

8.5g (0.003 mol) AgN03 in 500 ml Glycerol (the 'AgN0₃ Solution'— made up to be homogeneous at least 30 min before adding to the reaction)

50 g PVP (13,0000 MW) (0.45 mol) and 50 g PVP (55,000 MW) (0.45) in 2000 ml propylene glycol (the 'PVP Solution')

0.5g CTAC (0.0015 mol) in 20ml propylene glycol (CTAC solution)

lg HNO₃ (0.016 mol) solution in 20ml propylene glycol (the 'HNO₃ Solution')

Procedure:

To a 1000 ml glassy beaker, was added PVP solution, 2mL of the CTAC solution, 0.1ml HNO₃ solution. The mixture was then vigorous stirred for homogeneity at 25°C. The reaction mixture was then transferred to a microwave oven and then treated with microwave irradiation using 800W. The irradiation is keeping on until the temperature of the reaction mixture gets to 120°C. After that, 500ml AgN0₃ solution was poured into the mixture and then stirred homogeneously. The whole reaction mixture is transferred to an oven settled to 150°C and maintained for another 3hours . The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 3 L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP. Figs. 4A and 4B is the SEM picture of the sample synthesized under low and high magnification. The average length, average diameter, aspect ratio and purity information for the silver nanowires obtained is listed in Table 1.

Example 5

The following solutions were prepared using said chemicals:

(1) 25.5g AgNC-3 (0.15 mol) and 51g PVP(13,0000 MW) (0.46 mol) in 1000 ml Glycerol (the 'AgN0₃-PVP Solution'— made up to be homogeneous at least 30 min before adding to the reaction)

(2) O. lg MnCl₂ (0.0008 mol) in 20ml EG

(3) lg HNO₃ (0.016 mol) solution in 20ml Glycerol (the 'HN0₃ Solution') Procedure:

To a 2000 ml glassy beaker, was added the AgN0₃-PVP solution, 12ml of the MnC^solution, 1ml HNO₃ solution. The mixture was then vigorous stirred for homogeneity at 25 ^°C . The reaction mixture was then transferred to a microwave oven and then treated with microwave irradiation using 800W. The irradiation is keeping on until the temperature of the reaction mixture gets to 120°C, and then the temperature of the reaction mixture is maintained for another 3hours by moving the reaction mixture to a oven settled at 120°C. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 3 L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP.

Example 6

3.4g AgNC-3 powder, 1.7g PVP (13,0000 MW) powder, 0.02g TBPC powder, O. lg HN0₃ solution and 500 mL 1,3 -propylene glycol and 500ml 1,2-propylene glycol were added into a 1000 mL glassy beaker, The mixture was then vigorous stirred for homogeneity at 25°C. Then the reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 800W. The irradiation is keeping on until the temperature of the reaction mixture gets to 135^°C, and then the microwave power is adjusted to 160W to keep the temperature constant for another 30min. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 3 L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVR

Example 7

1.7g AgNC-3 (0.01) powder, 25.5g (0.05 mol) PVP(55000 MW) powder, 0.07g TBPC (0.00024 mol) powder, 0.0315g HN0₃ (0.0005 mol) and 1000 mL glycerol were added into a 1000 mL glassy beaker, The mixture was then vigorous stirred for homogeneity at 25°C. Then the reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 800W. The irradiation is keeping on until the temperature of the reaction mixture gets to 135°C, and then the microwave power is adjusted to 240W to heat the reaction mixture to 150°C and make the temperature constant for another 30min. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 3 L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP.

Example 8

O.Olmol silver nitrate was dissolved into 90 ml glycerol under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (55000 MW) were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP -glycerol complex solution, 0.3mmol MnCl₂ powder was added into 10ml glycerol and uniformly MnCl₂ glycerol solution was formed after a short period of ultrasonic treatment. The above 10ml MnCl₂ solution and 0.005mol HNO₃ were added into the solution prepared. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 400W within 5 min. The silver slurry was thus obtained and then washed with ethanol after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol.

Example 9

O.Olmol silver nitrate was dissolved into 90 ml glycerol under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (55000 MW) were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP -glycerol complex solution, 0.4mmol NaCl powder was added into 10ml glycerol and uniformly NaCl glycerol solution was formed after a short period of ultrasonic treatment. The above 10ml NaCl solution and O. lmmol HNO₃ were added into the solution prepared. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 7min. The silver slurry was thus obtained and then washed with ethanol after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol.

Example 10

34g AgN0₃ (0.2 mol) powder, lOOg PVP(55000 MW) (0.9 mol) powder, 0.02mmol TBPC powder, 1.575g HNO₃ (0.025 mol) and 5000 mL glycerol were added into a 10000 mL glassy beaker, The mixture was then vigorous stirred for homogeneity at 25 ^°C . Then the reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 20KW. The irradiation is keeping on until the temperature of the reaction mixture gets to 100^°C, and the reaction mixture is transferred to an oven settled to 110^°C and make the temperature constant for another 24hours. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 30 L of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP.

Example 11

0.002mol AgN0₃ powder, 0.008 mol PVP(55000 MW) powder, 0.02mmol TBPC powder, 0.001 mol HNO₃ solution and 50 mL glycerol were added into a 100 mL glassy beaker, The mixture was then vigorous stirred for homogeneity at 25 ^°C . Then the reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 800W. The irradiation is keeping on until the temperature of the reaction mixture gets to 130°C, and then the microwave power is adjusted to 800W to heat the reaction mixture to 170°C and make the temperature constant for another lOmin. The silver nanowires solution was thus obtained and the reaction was permitted to cool to room temperature. The silver nanowires solution was poured into 300 ml of ethanol. Centrifugalization is used to remove unnecessary solvent and PVP.

Comparative Example 1

Without acid compound

O. lmol silver nitrate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP 55,000) MW were dissolved into the above solution containing Ag ion to get the silver-PVP- EG complex solution, ( 2 ) 0. lmmol sodium chloride (NaCl) powder was added into 20ml ethylene glycol and uniformly NaCl EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml NaCl solution was added into the solution in step (1) and mixed homogeneously. Then the prepared reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 400 W within 14 min. The silver slurry was thus obtained and then washed with ethanol after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol. Fig. 5 is the SEM picture of the sample synthesized.

Comparative Example 2

Without acid compound O. lmol silver nitrate powder was dissolved into 500 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. 0.3 mol polyvinyl pyrrolidone (PVP 130,000 MW) with and O. lmmol MnC^were dissolved into 500 ml ethylene glycol (PG). The above solution were then mixed together to get the silver-PVP- EG-PG complex solution, Then, the reaction mixture was transferred to a microwave oven and then treated with microwave irradiation using 320W within 30 min. The silver slurry was thus obtained and washed with ethanol after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol. Fig. 6 is the SEM picture of the sample synthesized.

Comparative Example 3

Using traditional heating source (oil bath) without microwave irradiation

The reactants are added or mixed together at room temperature without dropwise or portionwise addition at high temperature

0.02 AgN0₃ (0.02 mol) powder, 0.08 PVP (13,0000 MW) powder, O.lmmol FeCl₃ powder, 1.6mmol HNO₃ solution and 1000ml 1,2-propylene glycol were added into a 1000 mL glassy beaker, The mixture was then vigorous stirred for homogeneity at 25°C. Then the reaction mixture was poured into a round bottomed flask settled in an oil bath with temperature fixed at 135°C. The reaction mixture was mechanically stirred and maintained at 135°C for 3-5hours. The solution containing abundant silver nanoparticles and few silver nanowires was thus obtained and the reaction was permitted to cool to room temperature. Fig. 7 is the SEM picture of the sample synthesized.

Comparative Example 4

Without Chloride Additive

As a comparison, the reaction of Example 1 but without the chloride additive was carried out. Only nanoparticles were obtained.

Comparative Example 5

With Bromide Additive

As a comparison, the reaction of Example 1 with potassium bromide additive instead of HC1 was carried out. Only nanoparticles were obtained.

Comparative Example 6

With silver acetate instead of silver nitrate

As a comparison, the reaction of Example 1 with silver acetate instead of silver nitrate was carried out. Only nanoparticles were obtained.

Comparative Example 7

With Polyvinyl Acetate (PVA) instead of PVP As a comparison, the reaction of Example 1 was carried out with PVA instead of PVP. Only nanoparticles were obtained.

Table 1 list the average lengths and average diameters, aspect ratio, purity of the silver nanowires synthesized in Example 1 ~ Example 4 and the Comparative Example 1~ Comparative Example 2. From this work, we can definitely find that the acid compound mediated micro-wave assisted wet chemistry method is a wonderful way for the mass production of silver nanowires with high aspect ratio and high purity.

The invention is also offering a pH value mediated microwave assisted wet chemistry method for large-scale rapid preparation of silver nanowires with high aspect ratio. The detailed steps comprise:

(a) Adding silver nitrate or silver acetate into polyol to form a reactive solution with silver ion, then adding capping agents into this solution to prepare a solution with silver ion.

(b) Adding water soluble halide into polyol and stirring it to form a transparent solution.

(c) Adding the above transparent solution prepared in step2 and acid compounds into reactive solution prepared in stepl and stirring to form a precursor suspension.

(d) Put the suspension under microwave irradiation for minutes to get silver nanowires; then centrifugalizing and washing them by deionized water or ethanol for several times; re-dispersing in ethanol or deionized water to get the final dispersant.

Silver nitrate and silver acetate mentioned in step (a) is industrial-grade silver salts and the pureness is above 98%.

The capping agents mentioned in step (a) is polyvinyl pyrrolidone (PVP), polymerization degree of which is preferable K^30.

The polyhydroxy liquid organic compounds mentioned in step (a), is ethylene glycol, glycerol or mixture of ethylene glycol and glycerol.

The water soluble halide mentioned in step (b), is industrial-grade sodium chloride (NaCl), manganese chloride (MnC^), ferric chloride(FeCl₃), potassium chloride (KC1), magnesium chloride (MgCy, zinc chloride (ZnC^), potassium bromide(KBr), sodium bromide (NaBr), cetyltriethyl ammnonium bromide(CTAB) or their mixture.

The acid compound mentioned in step (c) is highly concentrated HN03, highly concentrated HC1 or highly concentrated H₂SO₄.

The mol concentration of the silver nitrate or silver acetate in the reaction mixture prepared in step (1) is in the range of 0.02-0.3 mol/L

The mol ratio between silver salts and the capping agent in the reaction mixture prepared in step (1) is 1 : 1-1 :6

The mol ratio between cationic control agent added in step (c) and silver salts is 1 : 1000 ~ 1 :25.

The acid compound added in step (c) in the reaction mixture is about 0.005-0.05mol/L and after its addition, the pH value of the reaction mixture is 1.3-2.3.

The power of microwave is 320W-560W, the irradiation time is 6~30min.the frequency of the microwave is 2.45GHz.

In this method, silver nanowires with diameters of 80~500nm and lengths of 30~150microns,and simultaneously aspect ratio over 100 can be obtained.

In this method, silver nanowires with high aspect ratio are washed three or four times by deionized water or ethanol, acetone and then dispersed in them to form silver nanowire suspension.

Examples of producing the silver nanowires with high aspect ratio according to the present invention will be described below in detail.

EXAMPLE 12

According to the process: ( 1) 0. lmol silver nitrate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0. lmmol sodium chloride (NaCl) powder was added into 20ml ethylene glycol and uniformly NaCl EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml NaCl solution and 0.01 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.02mol/L. So the pH value is 1.7. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 400 W within 14 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and then the nanowires are well dispersed in ethanol or deionized water. Fig. 9 is the SEM picture of the sample synthesized. The silver nanowires show high aspect ratio more than 150, with its length more than 50micron, and diameter about 320nm. In a lot, more than 80% of the silver nanowires reached high aspect ratio above 150. The production efficiency is as high as 65g(L*h).The XRD pattern is also showed in Figure 15.

EXAMPLE 13

According to the process: ( 1) O. lmol silver acetate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2 ) 0.5mmol manganese chloride (Μη(¾) powder was added into 20ml ethylene glycol and uniformly MnCl₂ EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml MnCl₂ solution and 0.0125 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.025mol/L. So the pH value is 1.6. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 480 W within 15 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. Fig. 10 is the SEM picture of the sample synthesized. The silver nanowires show high aspect ratio more than 200, with its length more than 40micron, and diameter about 160nm. In a lot, more than 90% of the silver nanowires reached high aspect ratio above 200. The Production efficiency is as high as 73g(L*h).

EXAMPLE 14

According to the process: ( 1) 0.05mol silver nitrate were dissolved into 240 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.2 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2 ) 0.2mmol manganese chloride (MnC^) powder was added into 10ml ethylene glycol and uniformly MnCl₂ EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 10ml MnCl₂ solution and 0.0125 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.05mol/L. So the pH value is 1.3. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 17 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. Fig. 11 is the SEM picture of the sample synthesized. The silver nanowires show high aspect ratio more than 200, with its length more than 25micron, and diameter about UOnm. In a lot, more than 70% of the silver nanowires reached high aspect ratio above 200. The Production efficiency is as high as 57g(L*h).

EXAMPLE 15

According to the process: ( 1) O.Olmol silver acetate were dissolved into 90 ml glycerol under strong stirring to form a transparent solution with Ag ion. And then 0.01 mol polyvinyl pyrrolidone (PVP) with K=90 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP -glycerol complex solution, (2 ) 0.3mmol ferric chloride (FeC^) powder was added into 10ml glycerol and uniformly FeCl₃ glycerol solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 10ml FeClj solution and 0.001 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about O.Olmol/L. So the pH value is 2. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 7min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. Fig. 12 is the SEM picture of the sample synthesized. The silver nanowires show high aspect ratio more than 250, with its length more than 25micron, and diameter about 90nm. In a lot, more than 68% of the silver nanowires reached high aspect ratio above 250. The Production efficiency is as high as 49g(L*h).

EXAMPLE 16

According to the process: ( 1) 0.005mol silver acetate and 0.015 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into 45 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) O. lmmol manganese chloride (MnC^) powder was added into 5ml glycerol and uniformly MnCl₂ glycerol solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 5ml MnCl₂ solution and 0.00025 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.005mol/L. So the pH value is 2.3. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 6 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 300, with its length more than 40micron, and diameter about 1 lOnm.

EXAMPLE 17

According to the process: ( 1) 0.15mol silver nitrate and 0.15mol silver acetate were dissolved into 900 ml ethylene glycol (EG) under strong stirring to form a transparen solution with Ag ion. And then 0.9 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0.3mmol manganese chloride (MnC^) powder was added into 100ml glycerol and uniformly MnCl₂ glycerol solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 100ml MnCl₂ solution and O.Olmol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about O.Olmol/L. So the pH value is 2. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 30 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 200, with its length more than 35micron, and diameter about 160nm.

EXAMPLE 18

According to the process: ( 1) 0.02mol silver acetate and 0.06mol polyvinyl pyrrolidone (PVP) with K=90 were dissolved into 900 ml glycerol under strong stirring to form a transparent solution with Ag ion. Then we can get the silver-PVP- glycerol complex solution, (2 ) 0.2mmol ferric chloride (FeCy powder and 0.2mmol sodium chloride (NaCl) powder was added into 100ml ethylene glycol and uniformly FeCl₃ and NaCl mixed EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 100ml solution and 0.015 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.015mol/L. So the pH value is 1.82. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 560W within 17 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 300, with its length more than 34micron, and diameter about l lOnm.

EXAMPLE 19

According to the process: ( 1) 0.05mol silver acetate were dissolved into 240 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.05 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2) 0.2mmol potassium bromide (KBr) powder was added into 10ml ethylene glycol and uniformly KBr EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 10ml KBr solution and 0.0025 mol highly concentrated HC1 were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HQ in the solution is about O.Olmol/L. So the pH value is 2. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 400W within 8 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 350, with its length more than 30micron, and diameter about 80nm.

EXAMPLE 20

According to the process: ( 1) O. lmol silver nitrate and 0.05mol silver acetate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2 ) 0.2mmol manganese chloride (MnC^) powder and 0.2mmol sodium bromide (NaBr) powder was added into 20ml ethylene glycol and uniformly mixed EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml solution and 0.0025 mol highly concentrated H₂SO₄ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of H₂SO₄ in the solution is about 0.005mol/L. So the pH value is 2. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 480 W within 15 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 300, with its length more than 30micron, and diameter about lOOnm.

EXAMPLE 21

According to the process: ( 1) O. lmol silver nitrate and 0.05mol silver acetate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP) with K=30 and O. lmol polyvinyl pyrrolidone (PVP) with K=90 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2 ) 0.2mmol Cetyltrimethyl Ammonium Bromide(CTAB) powder was added into 20ml ethylene glycol and uniformly mixed EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml solution and 0.005 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about O.Olmol/L. So the pH value is 2. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 480 W within 15 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 300, with its length more than 150micron, and diameter about 500nm.

EXAMPLE 22

According to the process: ( 1) O. lmol silver nitrate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0.2mmol magnesium chloride (MgC¾) powder was added into 20ml ethylene glycol and uniformly MgCl₂ EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml solution and 0.01 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.02mol/L. So the pH value is 1.7. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 480 W within 15 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 200, with its length more than 25micron, and diameter about 89nm.

EXAMPLE 23

According to the process: ( 1) O. lmol silver nitrate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0.4mmol potassium chloride (KC1) powder was added into 20ml ethylene glycol and uniformly KC1 EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml solution and 0.01 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.02mol/L. So the pH value is 1.7. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 480 W within 15 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 100, with its length more than 42micron, and diameter about 320nm.

EXAMPLE 24

EXAMPLE 25

According to the process: ( 1) 0.02mol silver nitrate were dissolved into 150 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.06mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, (2 ) 0.04mmol sodium bromide (NaBr) powder was added into 50ml ethylene glycol and uniformly NaBr EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 50ml solution and 0.004 mol highly concentrated HNO₃ were added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. The content of HNO₃ in the solution is about 0.02mol/L. So the pH value is 1.7. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 400W within 8 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. The silver nanowires show high aspect ratio more than 300, with its length more than 32micron, and diameter about 90nm.

Comparative example was designed according to above process, which had the different pH value compared to the above examples, while keep other parameter unchanged.

COMPARATIVE EXAMPLE8

Specifically, ( 1) 0. lmol silver nitrate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.3 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0. lmmol sodium chloride (NaCl) powder was added into 20ml ethylene glycol and uniformly NaCl EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml NaCl solution was added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 25 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. Fig. 13 is the SEM picture of the sample synthesized. The silver nanowires show low aspect ratio of 64, with its length about 14 micron, and diameter about 220nm. The Production efficiency is as high as 35g/(L*h).

COMPARATIVE EXAMPLE 9

Specifically, ( 1) O. lmol silver acetate were dissolved into 480 ml ethylene glycol (EG) under strong stirring to form a transparent solution with Ag ion. And then 0.5 mol polyvinyl pyrrolidone (PVP) with K=30 were dissolved into the above solution containing Ag ion. Then we can get the silver-PVP- EG complex solution, ( 2 ) 0. lmmol MnCl₂ powder was added into 20ml ethylene glycol and uniformly MnCl₂ EG solution was formed after a short period of ultrasonic treatment. ( 3 ) The above 20ml MnCl₂ solution was added into the solution prepared in step (1). After it, the whole solution is mixed homogeneously. Thereafter, the prepared precursor was transferred to a microwave oven and then treated with microwave irradiation using 320W within 25 min. The silver slurry was thus obtained and then washed by ethanol or deionized water after it being cooled down, Centrifugalization is used to remove unnecessary solvent and well dispersed in ethanol or deionized water. Fig. 14 is the SEM picture of the sample synthesized. The silver nanowires show low aspect ratio of 92, with its length about 11 micron, and diameter about 120nm.

Table 2 includes average diameter, average length, average aspect ratio and yield of silver nanowires synthesized in example 12 to 15, comparative example 8 to 9.

Claims

1. A method of rapid preparation of silver nanowires with high aspect ratio and high purity comprising:

forming a reaction mixture including silver nitrate, poly(vinyl pyrrolidone) (PVP), acid compound, chloride additives in polyol(s) at a first temperature, then the reaction mixture is heated to second temperature by microwave irradiation, subsequently the reaction mixture was heated to third temperature and maintained for times to form silver nanowires.

2. The method of claim 1, wherein the concentration of the silver nitrate in the solution is in the range of 0.01-0.15 mol/L

3. The method of claim 1, wherein the ratio of the mass concentration of the PVP to the mass concentration of the silver nitrate in the reaction mixture is in the range of 15: 1 to 0.5: 1.

4. The method of claim 1, wherein the polyol is ethylene glycol, 1,2-propylene glycol, 1,3 -propylene glycol, or glycerol.

5. The method of claim 1, acid compound refers to hydrochloric acid, nitric acid, the ratio of the acid compounds in the reaction mixture is 0.0005-0.05mol/L.

6. The method of claim 1, chloride additive refers to sodium chloride (NaCl), manganese chloride (MnCl₂), ferric chloride (FeCl₃).

7. The method of claim 1, chloride additive refers to quaternary ammonium chloride by formula NR₄ CI , or quaternary phosphonium chloride by formula PR₄ CI . Each R in the NR₄ CI and/or PR₄ CI is the same or different and independently refers to an alkyl, alkenyl, alkynyl, aryl, or aralkyl.

8. The method of claim 1 or claim 2, wherein the ratio of the molar concentration of the chloride additive to the molar concentration of the silver nitrate in the reaction mixture is in the range of 1 : 10000 —1 :25.

9. The method of claim 1, wherein the first temperature is in the range from 10°C to 50°C, the second temperature is in the range from 100°C to 170°C, the third temperature is in the range from 100°C to 170°C.

10. The method of claim 1, wherein the third temperature of the reaction mixture can be obtained by microwave irradiation or furnace or oven, or oil bath or heating mantle.

11. The method of claim 1, wherein the maintenance time of third temperature is in the range from 5 minutes to 24hours.

12. The method of claim 1, wherein the silver nanowires obtained exhibit aspect ratio equal or greater than 300 and purity equal or greater than 80%

13. The method of claim 1, wherein it contains the method for large-scale rapid preparation of silver nanowires with high purity, consisting of forming a reaction mixture including silver nitrate, poly(vinyl pyrrolidone) (PVP), acid compound, chloride additives in polyol(s) at a first temperature, The detailed steps comprise:

a) Adding silver nitrate or silver acetate into polyol to form a reactive solution with silver ion, then adding capping agents into this solution to prepare a solution with silver ion.

b) Adding water soluble halide into polyol and stirring it to form a transparent solution.

c) Adding the above transparent solution prepared in step2 and acid compounds into reactive solution prepared in step 1 and stirring to form a precursor suspension. Then, the reaction mixture is heated to second temperature by microwave irradiation, subsequently the reaction mixture was heated to third temperature and maintained for times to form silver nanowires. The detailed steps comprise:

d) Put the suspension under microwave irradiation for minutes to get silver nanowires; then centrifugalizing and washing them by deionized water or ethanol for several times; re-dispersing in ethanol or deionized water to get the final dispersant.

14. The method of claim 13, wherein the silver nitrate and silver acetate refer to industrial-grade silver salts and the purisity is above 98%. The mol concentration of the silver salts in the reaction mixture is in the range of 0.02-0.3 mol/L.

15. The method of claim 13, wherein the capping agents refer to polyvinyl pyrrolidone (PVP), polymerization degree of which is preferable K^30. The mol ratio between silver salts and the capping agent in the reaction mixture is 1 : 1-1 :6.

16. The method of claim 13, wherein the polyols refer to ethylene glycol, glycerol or mixture of ethylene glycol and glycerol.

17. The method of claim 13, wherein the water soluble halides refer to sodium chloride (NaCl), manganese chloride (Μη(¾), ferric chloride(FeCl₃), potassium chloride (KC1), magnesium chloride (MgCl₂), zinc chloride (ZnCl₂), potassium bromide(KBr), sodium bromide(NaBr), cetyltriethyl ammnonium bromide(CTAB) or their mixture. The mol ratio between halide and silver salts is 1 : 1000 ~ 1 :25.

18. The method of claim 13, wherein the acid compounds, they refer to highly concentrated HNO₃, highly concentrated HC1 or highly concentrated H₂SO₄. The acid compounds in the reaction mixture is about 0.005-0.05mol/L and after its addition, the pH value of the reaction mixture is 1.3-2.3.