CN117524586A - Method for preparing conductive material by recycling silver nanowire byproducts and conductive material - Google Patents

Abstract

The invention discloses a method for preparing a conductive material by recycling silver nanowire byproducts, which comprises the following steps: adding deionized water into the pre-prepared silver nanowire stock solution, shaking uniformly, and then placing the mixture into a positive pressure filter; repeatedly executing the filtering step for preset times by utilizing the PTFE filter membrane and the positive pressure filter; collecting silver nanowires on the PTFE filter membrane, and dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid; centrifuging the collected total waste liquid, taking out the lower precipitate, and dissolving the lower precipitate in deionized water to obtain byproduct dispersion; mixing the obtained bacterial cellulose solution with the nano cellulose solution to obtain a mixed cellulose solution; and obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing pre-freezing and freeze-drying treatment to obtain the prepared conductive material, wherein the conductive material comprises a byproduct aerogel film or byproduct aerogel foam. The method can realize green recovery of the silver nanowire solid particle byproducts and prepare the conductive material, can be used as an electromagnetic protection material, and has practical value.

Description

Method for preparing conductive material by recycling silver nanowire byproducts and conductive material

Technical Field

The invention belongs to the field of silver nanowires, and particularly relates to a method for preparing a conductive material by recycling silver nanowire byproducts and the conductive material.

Background

At present, one-dimensional nano materials are paid attention to because of their excellent conductive properties, and can be prepared into conductive films. For the conductive mode, the one-dimensional nano material forms a conductive network through lap joint, so that the characteristics of low filling, high conductivity and the like are realized, and special functions of flexibility, transparency and the like can be realized. Among them, silver nanowires, which are typical representatives of one-dimensional nanomaterials, have excellent properties such as high stability (i.e., high chemical stability, environmental stability, and flexibility and stretch resistance), high electrical conductivity, high thermal conductivity, and antibacterial properties, and are currently one of the best choices for research and application of flexible conductive materials, for example, they can be applied to directions such as stretchable transparent electrodes, electromagnetic shielding, strain sensing, and food preservation.

The polyol method is one of the most effective methods for preparing nano silver, and can accurately regulate the appearance of silver particles and the growth of crystal faces. Starting from the birth of nano silver, the nano silver is always one of research hotspots in the academic and industrial circles. The general idea of the silver nanowire synthesized by the method is that silver salt is reduced in polyalcohol and grows into a nanowire along one dimension under the assistance of a surfactant. The basic mechanism of the method is as follows: the method comprises the steps of adopting heated glycol to reduce silver ions into silver atoms, polymerizing the silver atoms and growing the silver atoms into crystal nuclei, and directionally growing the crystal nuclei into nanowires with specific sizes under the directional coating of polyvinylpyrrolidone (PVP) in combination with the regulation and control of halogen ions. Due to the introduction of morphology control agents (including PVP, halide ions, etc.), the reaction not only synthesizes the nanowires, but also produces a large number of silver nanoparticles, silver nanorods, silver nanowires (referring to length <10 um), and silver-silver halide cluster microparticles. These byproducts are produced in a rapid increase in the amount as the nanowire diameter becomes smaller and the reaction conditions become more stringent.

The current methods for byproduct recovery are still limited to conventional silver ion reduction-nanowire regrowth methods, but do not effectively recycle large amounts of solid particulate byproducts. For example, patent CN110270693a and Zhao Huang et al working Simple Recycling of Ag +, surfactant, and Solvent for Repeatable Synthesis of Silver Nanowires for Applications as Flexible Transparent Heaters at ACS Applied Nano materials initially recovered unreduced silver ions in solution, but did not treat residual solid particles.

In addition, patent CN114620879a discloses a method for recycling silver nanowire production waste liquid. The method is used for efficiently treating the waste liquid generated in the preparation of the silver nanowires by the polyol method, can recycle and utilize silver in the waste liquid in multiple stages, and simultaneously, can recycle and utilize low-boiling point solvents and high-boiling point alcohol solvents contained in the waste liquid. The introduced strong acid and strong alkali are contrary to the core concept of green chemistry, the raw material safety cannot be ensured, and the treatment of solid particles is still limited to a means of decomposing and retreating by using strong acid, and the solid particles are not directly upgraded and utilized.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a method for preparing a conductive material by recycling silver nanowire byproducts and the conductive material. The technical problems to be solved by the invention are realized by the following technical scheme:

in a first aspect, embodiments of the present invention provide a method for preparing a conductive material using silver nanowire byproduct recovery, the method comprising:

adding deionized water into the pre-prepared silver nanowire stock solution, shaking uniformly, and placing the mixture into a positive pressure filter;

repeatedly executing a filtering step for preset times, wherein the filtering step comprises the steps of filtering the mixed liquid in the positive pressure filter by utilizing a PTFE filter membrane to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid; placing the PTFE filter membrane attached with the sediment in an ethylene glycol solution containing PVP for shaking washing, dissolving the sediment to obtain mixed liquid, and adding the mixed liquid into the positive pressure filter;

collecting silver nanowires on a PTFE filter membrane, and dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid; centrifuging the total waste liquid collected in a preset time, and taking out the lower precipitate to dissolve in deionized water to obtain byproduct dispersion;

mixing the obtained bacterial cellulose solution with the nano cellulose solution to obtain a mixed cellulose solution;

obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing prefreezing and freeze drying treatment on the mixed solution to obtain a prepared conductive material; wherein the conductive material comprises a byproduct aerogel film or a byproduct aerogel foam.

In one embodiment of the invention, the conductive material is used as an electromagnetic shielding material.

In one embodiment of the present invention, after the prepared conductive material is obtained, the method further includes:

crushing the conductive material, and then dissolving the crushed conductive material in deionized water to form conductive material dispersion liquid;

and pouring the conductive material dispersion liquid into a mould for the pre-freezing and freeze-drying treatment to obtain the same conductive material prepared again.

In one embodiment of the present invention, after adding the pre-prepared silver nanowire stock solution into deionized water and shaking the mixture uniformly, placing the mixture in a positive pressure filter, wherein the method comprises the following steps:

15mL of the pre-prepared silver nanowire stock solution is added with deionized water to 40mL, and then the mixture is shaken uniformly and poured into a 1000mL barrel type positive pressure filter.

In one embodiment of the invention, the filtering step comprises:

controlling the vacuum pressure gauge number of an air compressor in the positive pressure filter to be 20kPa, filtering the mixed liquid in the positive pressure filter by using a PTFE filter membrane at a speed of 1 drop/s to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid;

the sediment-attached PTFE filter membrane was put into 50mL of a glycol solution of 0.2 to 1wt% of PVP having a molecular weight of 55000 to be sloshed to dissolve the sediment, and the resulting mixed liquid was added to the positive pressure filter.

In one embodiment of the present invention, the parameters used for the centrifugation process include:

the speed of centrifugal treatment is 3500-6000 rpm/min; the duration of the centrifugal treatment is 5-15 min.

In one embodiment of the present invention, the mixing the obtained bacterial cellulose solution with the nanocellulose solution to obtain a mixed cellulose solution includes:

mixing 0.5-0.8wt% bacterial cellulose solution and 0.5-1wt% nano cellulose solution according to the volume ratio of 1:2-1:1, and uniformly stirring to obtain mixed cellulose solution.

In one embodiment of the present invention, the preparing a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing pre-freezing and freeze-drying processes on the mixed solution to obtain a prepared conductive material, includes:

uniformly mixing 2-6wt% of the byproduct dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution;

and (3) performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the prepared conductive material which is the by-product aerogel film.

In one embodiment of the present invention, the preparing a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing pre-freezing and freeze-drying processes on the mixed solution to obtain a prepared conductive material, includes:

forming a mixed dispersion by 0.5 to 1wt% of the byproduct dispersion and 0.1 to 1wt% of the silver nanowire dispersion;

uniformly mixing the mixed dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution;

and (3) performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the prepared conductive material which is the by-product aerogel foam.

In a second aspect, an embodiment of the present invention provides a conductive material, which is prepared by using the method for preparing a conductive material by recycling silver nanowire byproducts according to the first aspect.

The invention has the beneficial effects that:

compared with the prior art that solid particle byproducts generated by silver nanowire preparation are not effectively recycled or are decomposed and recycled in a chemical mode, the embodiment of the invention carries out centrifugal treatment on the collected total waste liquid containing the solid particle byproducts, takes out the lower sediment to dissolve in deionized water to obtain byproduct dispersion liquid, mixes the obtained bacterial cellulose solution with the nano cellulose solution to obtain mixed cellulose solution, obtains the mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and carries out pre-freezing and freeze-drying treatment to obtain the prepared conductive material, including byproduct aerogel films or byproduct aerogel foams. The invention adopts a physical mode to obtain the byproduct dispersion liquid, and the introduced bacterial cellulose solution and nanocellulose solution are green and safe raw materials, so that a novel method for recycling the silver nanowire solid byproducts is realized, green recycling can be realized, the conductive material with high conductivity is prepared, the application field is wide, and the method has practical value.

Further, after the conductive material is crushed, the conductive material is stirred and dissolved at normal temperature to form conductive material dispersion liquid, and the conductive material can be recast into the same aerogel conductive material (by-product aerogel film or by-product aerogel foam) before crushing, so that the conductive material prepared by the method has extremely strong recoverability, and can greatly promote the green recovery and utilization of the conductive material.

Further, the conductive material may be used as an electromagnetic shielding material. The byproduct aerogel film has ultrahigh conductivity and ultrahigh electromagnetic shielding effect; the by-product aerogel foam has ultrahigh conductivity, electromagnetic shielding and microwave absorption capacity, and realizes the design of the multifunctional electromagnetic protection material on the basis of the amount of the solid by-product of the green recovered silver nanowire.

Drawings

Fig. 1 is a schematic flow chart of a method for preparing a conductive material by recovering silver nanowire byproducts according to an embodiment of the present invention;

FIG. 2 is a schematic illustration of a silver nanowire deposited PTFE membrane after filtration in accordance with an embodiment of the present invention;

FIG. 3 is a schematic illustration of a by-product aerogel film prepared in accordance with example one of the present invention;

FIG. 4 is a comparison of electromagnetic shielding effectiveness EMI SE and theoretical calculation of a by-product aerogel film in accordance with an embodiment of the present invention;

FIG. 5 is a graph showing the comparison of the front and back side incident EMI SE of a by-product aerogel film in accordance with example one of the present invention;

FIG. 6 is a schematic illustration of a film after a by-product aerogel film has been broken and recycled in accordance with one embodiment of the present invention;

FIG. 7 is a schematic illustration of the EMI SE of the film after the by-product aerogel crush cycle reconstitution in accordance with the first embodiment of the present invention;

FIG. 8 is a side product aerogel foam produced in example two of the present invention;

FIG. 9 is an SEM image of the internal nanoparticle composition of a byproduct aerogel foam in accordance with example II of the invention;

FIG. 10 is an SEM image of the internal pores of a by-product aerogel foam according to a second embodiment of the invention;

FIG. 11 is a graph showing by-product aerogel foam thickness versus wave absorption loss for a second embodiment of the invention;

FIG. 12 is a schematic illustration of a by-product aerogel foam EMI SE in accordance with embodiment II of the invention;

FIG. 13 is a schematic representation of foam after a by-product aerogel crush cycle reconstitution in accordance with example two of the present invention;

FIG. 14 is a schematic diagram of the absorption loss of foam after a by-product aerogel crush cycle reconstitution in accordance with example two of the present invention;

FIG. 15 is a schematic illustration of the EMI SE of a foam after a by-product aerogel crush cycle reconstitution in example two of the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In a first aspect, an embodiment of the present invention provides a method for preparing a conductive material using silver nanowire byproduct recovery, as shown in fig. 1, the method may include the steps of:

s1, adding deionized water into a pre-prepared silver nanowire stock solution, shaking uniformly, and placing the mixture in a positive pressure filter;

the silver nanowire stock solution prepared in advance can be prepared by any existing method for preparing silver nanowires, and the method is not limited.

For example, taking a polyol process as an example, an alternative process for preparing a silver nanowire stock solution is given below as an example, specifically including the following steps a1 and a2:

step a1, preparing A, B, C three glycol solutions;

a:0.4 to 0.6g NaBr+20mL EG (national medicine);

b:0.2 to 0.4g NaCl+20mL EG (national medicine);

c: 1.5-2 g PVP (sigma 360 k) +30mL EG (national drug);

wherein NaBr is sodium bromide; naCl is sodium chloride; PVP is polyvinylpyrrolidone; EG is Ethylene Glycol, representing Ethylene Glycol; the Chinese medicine represents the relevant brands.

The prepared A, B, C three glycol solutions were placed in a drying cabinet with a humidity of 20%. Then, 0.5-1 g of silver nitrate (national medicine) is taken and poured into 15mL of glycol (national medicine), and after being put into a 100Hz ice bath (0-8 ℃) for 1min, ultrasonic treatment is carried out for 5.0-6.0 min (complete dissolution), thus obtaining colorless silver nitrate solution.

Step a2, taking 110-120 mL EG (national drug) solvent by using a cylinder, placing the solvent into a single-neck round-bottom flask (250 mL), immersing the solvent into an oil bath, and starting an oil bath stirring function; simultaneously adding mechanical stirring with the speed set to be 100-500 rmp/min; sequentially taking 1mL of solution A, 2mL of solution B and 15mL of solution C by a pipetting gun, injecting the solution into the round-bottomed flask, and finally injecting the silver nitrate solution prepared in the step a1, and starting timing for 30min at the same time; the heating temperature is 178-182 ℃, the temperature can be set to 165-175 ℃ after the heating to 180 ℃, the mechanical stirring speed is reduced to 50-120 rpm/min, and the stirring is stopped after the timing is carried out for 10min again; and (3) timing again, taking out the silver nanowire after reacting for 1h (hour), and placing the silver nanowire in cold water for quenching for standby, and taking the silver nanowire as a prepared silver nanowire stock solution.

For S1, a proper volume of silver nanowire stock solution can be selected according to the requirement, deionized water is added to form a certain volume, and the silver nanowire stock solution is uniformly shaken and then placed in a positive pressure filter so as to conveniently execute the subsequent filtering step.

In an alternative embodiment, S1 may include:

15mL of the pre-prepared silver nanowire stock solution is added with deionized water to 40mL, and then the mixture is shaken uniformly and poured into a 1000mL barrel type positive pressure filter.

S2, repeatedly executing the filtering step for preset times;

the filtering step comprises the steps of filtering the mixed liquid in the positive pressure filter by utilizing a PTFE filter membrane to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid; placing the PTFE filter membrane attached with the sediment in an ethylene glycol solution containing PVP for shaking washing, dissolving the sediment to obtain mixed liquid, and adding the mixed liquid into the positive pressure filter;

the PTFE filter membrane is the polytetrafluoroethylene filter membrane, and the PTFE filter membrane with the diameter of 100 mm@10 um can be selected for standby in the embodiment of the invention, and the PTFE filter membrane is subjected to water bath at the temperature of 90 ℃ for 30min in advance, so that the S2 is used for standby. Of course, the diameter and pore size of the PTFE filter membrane may be selected as required, and are not limited to those shown above.

And for the first time, executing the filtering step, wherein the mixed liquid in the positive pressure filter is the mixed liquid obtained by adding the silver nanowire stock solution in the S1 into deionized water and shaking the mixture, and for the second time and later executing the filtering step, the mixed liquid in the positive pressure filter is the mixed liquid added into the positive pressure filter when the filtering step is executed last time, namely, the mixed liquid obtained by dissolving the sediment after shaking and washing the PTFE filter membrane attached with the sediment in the ethylene glycol solution containing PVP.

The filtering step is performed by controlling an air compressor in the positive pressure filter and using a PTFE filter membrane laid flat on a liquid surface, and in an alternative embodiment, the filtering step may include:

step b1, controlling the vacuum pressure representation number of an air compressor in the positive pressure filter to be 20kPa, filtering the mixed liquid in the positive pressure filter by using a PTFE filter membrane at a speed of 1 drop/s to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid;

and b2, placing the PTFE filter membrane attached with the sediment in 50mL of ethylene glycol solution with 0.2-1 wt% of PVP molecular weight of 55000, washing in a shaking way to dissolve the sediment, and adding the obtained mixed liquid into the positive pressure filter.

Wherein the deposited PTFE membrane, i.e. the PTFE membrane deposited with silver nanowires after filtration, can be seen in FIG. 2.

The preset times can be set according to the needs, for example, 1-5 times.

The filtering step is repeatedly carried out for preset times, so that the content of byproduct particles in the target product silver nanowires is reduced through multiple times of filtering, and purer silver nanowires can be filtered out on a final PTFE filter membrane. Meanwhile, the method can effectively separate and obtain the total waste liquid so as to be convenient for subsequent use, and it is understood that the total waste liquid contains a large amount of solid particles of silver.

S3, collecting silver nanowires on a PTFE filter membrane, and dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid; centrifuging the total waste liquid collected in a preset time, and taking out the lower precipitate to dissolve in deionized water to obtain byproduct dispersion;

wherein, the parameters adopted by the centrifugal treatment can be set according to the needs, for example, in an optional implementation manner, the parameters adopted by the centrifugal treatment can include:

the speed of centrifugal treatment is 3500-6000 rpm/min; the duration of the centrifugal treatment is 5-15 min.

Compared with the prior art that solid particles containing a large amount of silver in the waste liquid are not treated or are recycled in a chemical way, the embodiment of the invention carries out centrifugal treatment on the total waste liquid to take out the lower sediment to dissolve in deionized water to obtain the byproduct dispersion liquid, and the byproduct dispersion liquid is recycled in a physical treatment way, so that the method has the advantages of being green and safe.

S4, mixing the obtained bacterial cellulose solution with the nano cellulose solution to obtain a mixed cellulose solution;

according to the embodiment of the invention, a bacterial cellulose solution with a certain mass percentage can be obtained in advance through purchasing, configuration and other modes and mixed with the nano cellulose solution to obtain a mixed cellulose solution. Such as:

in an alternative embodiment, the mixing the obtained bacterial cellulose solution with the nanocellulose solution to obtain a mixed cellulose solution includes:

mixing 0.5-0.8wt% bacterial cellulose solution and 0.5-1wt% nano cellulose solution according to the volume ratio of 1:2-1:1, and uniformly stirring to obtain mixed cellulose solution.

It will be appreciated by those skilled in the art that both bacterial cellulose solution and nanocellulose solution are green and safe raw materials, and thus, recovery of silver nanowire byproducts using the resulting mixed cellulose solution is safe.

S5, obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing prefreezing and freeze drying treatment on the mixed solution to obtain a prepared conductive material;

wherein the conductive material comprises a byproduct aerogel film or a byproduct aerogel foam.

In the embodiment of the invention, when the mode of obtaining the mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution is different, a byproduct aerogel film or a byproduct aerogel foam can be obtained respectively, and the preparation method can be carried out according to the needs.

In an alternative first embodiment, the preparing a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing prefreezing and freeze drying on the mixed solution to obtain the prepared conductive material includes:

step c1, uniformly mixing 2-6wt% of the byproduct dispersion liquid and the mixed cellulose solution according to a volume ratio of 1:1 to obtain a mixed solution;

and c2, performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the aerogel film with the prepared conductive material as a byproduct.

In an optional second embodiment, the preparing a conductive material based on the byproduct dispersion liquid and the mixed cellulose solution to obtain a mixed solution, and performing prefreezing and freeze drying on the mixed solution to obtain the prepared conductive material, including:

step d1, forming a mixed dispersion liquid by 0.5-1 wt% of the byproduct dispersion liquid and 0.1-1 wt% of the silver nanowire dispersion liquid;

step d2, uniformly mixing the mixed dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution;

and d3, performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the aerogel foam with the prepared conductive material as a byproduct.

The same manner can be adopted for the pre-freezing treatment of the obtained mixed solution and the freeze-drying treatment of the mixed solution by using a freeze dryer for the step c2 and the step d3, and specific parameters of the pre-freezing treatment and the freeze-drying treatment can be set according to the needs. For example, in an alternative embodiment, the pre-freezing treatment of the obtained mixed solution and the freeze-drying treatment by using a freeze dryer may include:

step e1, pre-freezing the obtained mixed solution for 2-12 hours at the temperature of-10-50 ℃;

and e2, performing freeze drying treatment on the pre-frozen substance by using a freeze dryer, wherein the temperature of the freeze dryer is minus 60 ℃, the air pressure is 10Pa, and the freeze drying time is 12-48 hours.

As can be seen, when preparing a byproduct aerogel film, only the byproduct dispersion liquid and the mixed cellulose solution are used for mixing, and when preparing a byproduct aerogel foam, the silver nanowire dispersion liquid is used in addition to the byproduct dispersion liquid and the mixed cellulose solution; and, the mass percentages of the byproduct dispersions are different when preparing the byproduct aerogel film and the byproduct aerogel foam.

It can be understood that, because the byproduct dispersion liquid contains silver, and silver is a material with higher conductivity, the material prepared based on the byproduct dispersion liquid is a conductive material, specifically, the conductivity of the aerogel (i.e. the byproduct aerogel film and the byproduct aerogel foam) prepared by the method is as high as 300000S/m, and the aerogel has good flexibility, so that the aerogel can be applied to various fields of circuit design, flexible electronics and the like.

Compared with the prior art that solid particle byproducts generated by silver nanowire preparation are not effectively recycled or are decomposed and recycled in a chemical mode, the embodiment of the invention carries out centrifugal treatment on the collected total waste liquid containing the solid particle byproducts, takes out the lower sediment to dissolve in deionized water to obtain byproduct dispersion liquid, mixes the obtained bacterial cellulose solution with the nano cellulose solution to obtain mixed cellulose solution, obtains the mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and carries out pre-freezing and freeze-drying treatment to obtain the prepared conductive material, including byproduct aerogel films or byproduct aerogel foams. The invention adopts a physical mode to obtain the byproduct dispersion liquid, and the introduced bacterial cellulose solution and nanocellulose solution are green and safe raw materials, so that a novel method for recycling the silver nanowire solid byproducts is realized, green recycling can be realized, the conductive material with high conductivity is prepared, the application field is wide, and the method has practical value.

Further, after the prepared conductive material is obtained, the method further includes:

step f1, after the conductive material is crushed, the crushed conductive material is placed in deionized water to be dissolved to form conductive material dispersion liquid;

in an alternative embodiment, step f1 may include: after the conductive material is crushed, adding a magneton, and stirring for 1-12 hours at normal temperature, so that the conductive material is fully dissolved in deionized water to form conductive material dispersion liquid; a conductive material dispersion is formed based on the byproduct dispersion and the mixed cellulose solution.

And f2, pouring the conductive material dispersion liquid into a mould to perform the prefreezing and freeze drying treatment to obtain the same conductive material prepared again.

In an alternative embodiment, step f2 may include: pouring the conductive material dispersion liquid into a mould, pre-freezing for 2-12 hours at the temperature of-10-50 ℃, and then performing freeze drying treatment by using a freeze dryer to obtain the same conductive material prepared again; wherein the temperature of the freeze dryer is-60 ℃, the air pressure is 10Pa, and the freeze drying time is 12-48 hours.

After the conductive material prepared by the method is crushed, stirring and dissolving the conductive material into conductive material dispersion liquid at normal temperature, and recasting the conductive material into the same aerogel conductive material (by-product aerogel film or by-product aerogel foam) before crushing, so that the conductive material prepared by the method has extremely strong recoverability, and can greatly promote the green recovery and utilization of the conductive material.

The silver nanowire conductive material can effectively reflect electromagnetic wave interference due to high conductivity of silver, so that the sensitive unit is protected. However, high conductivity also causes severe impedance mismatch and is not suitable for preparing electromagnetic wave absorbing materials for perfect absorption. And silver halide (silver chloride and silver bromide) in byproducts of silver nanowire preparation is used as a dielectric material, so that the defects of the silver nanowire can be effectively overcome, and good impedance matching is formed. Meanwhile, the silver-silver halide cluster microparticles contain a large number of distorted lattices, amorphous metals and point defects, so that strong dipole polarization can be generated, and electromagnetic wave loss, conversion and absorption are promoted. And the interface polarization effect caused by the abundant heterojunction interface (Ag/AgCl/AlBr) existing between the silver nanowire byproduct material systems can also exacerbate electromagnetic wave absorption.

In recent years, new porous materials represented by aerogel have begun to exhibit a new angle of attack in the electromagnetic wave absorbing field. The novel structure prepared by self-assembly of the low-dimensional material has the advantages of unique three-dimensional network, high specific surface area, low density and the like, and can realize the construction of a high-efficiency conductive network under the condition of low filling quantity, thereby endowing the material with stronger electromagnetic wave attenuation capability. More interestingly, the aerogel structure is formed by utilizing silver nano particles, silver nano rods, silver halide particles and shorter silver nano wires, so that a typical aerogel internal porous structure is formed on a micrometer scale, the reflection interface of electromagnetic waves in the material is enriched, a multi-element electromagnetic protection network of particles, short rods and short wires is also formed on a nanometer scale, the roughness of the surface of the aerogel is obviously increased, and the multiple reflection loss of the electromagnetic waves is aggravated to a certain extent.

Since the wave-absorbing material must meet the special conditions of impedance matching (material input impedance zin≡free space impedance Z0), this means that the electrical conductivity of the material can be significantly affected, making it difficult to meet the electromagnetic shielding requirements (electrical conductivity > 1S/m). At present, the reported research on simultaneous application of the same material system to electromagnetic shielding and microwave absorption basically needs to complete the two tasks by changing the solid content of the nano-filler (namely, meeting the electromagnetic shielding requirement at high filling amount and meeting the microwave absorption requirement at low filling amount). This presents a small inconvenience for sample preparation and use in applications where two electromagnetic shielding requirements are required.

In the embodiment of the invention, the conductive material can be used as an electromagnetic protection material. Wherein, the by-product aerogel film has ultra-high conductivity>10 ⁵ S/m) and ultra-high electromagnetic shielding effectiveness; the by-product aerogel foam has ultrahigh conductivity, electromagnetic shielding and microwave absorption capacity.

Therefore, the embodiment of the invention not only can effectively recycle the silver nanowire byproducts, but also can skillfully realize the design of the multifunctional electromagnetic protection material by means of the existing byproduct material system.

A specific example is given below for a by-product aerogel film and a by-product aerogel foam, respectively, to illustrate the preparation process.

Embodiment one:

step g1, preparing A, B, C three ethylene glycol solutions:

a:0.4572g NaBr+20mL EG (national medicine);

b:0.2466g NaCl+20mL EG (national medicine);

c:1.68g PVP (sigma 360 k) +30mL EG (national drug);

the prepared A, B, C three glycol solutions were placed in a drying cabinet with a humidity of 20%. Then, 0.6765g of silver nitrate (national medicine) is taken and poured into 15mL of glycol (national medicine), and after being put into a 100Hz ice bath (4-8 ℃) for 1min, ultrasonic treatment is carried out for 5.0-6.0 min (complete dissolution), thus obtaining colorless silver nitrate solution.

Step g2, taking 116mL EG (Chinese medicine) solvent by a measuring cylinder, placing the solvent in a single-neck round-bottom flask (250 mL), immersing the solvent in an oil bath, and starting an oil bath stirring function; simultaneously adding mechanical stirring, wherein the speed is set to 300rmp/min; sequentially taking 1mL of A, 2mL of B solution and 15mL of C solution by a pipette, injecting the solution into the round-bottomed flask, and finally injecting a new silver nitrate solution, and simultaneously starting timing for 30min; heating to 180deg.C, setting the temperature to 170deg.C, reducing the mechanical stirring speed to 120rpm/min, timing for 10min, and stopping stirring; and (3) timing again, taking out the silver nanowire stock solution after reacting for 1h, and placing the silver nanowire stock solution in cold water for quenching for standby.

Step g3, carrying out water bath for 30min at 90 ℃ on a polytetrafluoroethylene filter membrane (with the diameter of 100 mm@aperture of 10 um) for standby, and taking the polytetrafluoroethylene filter membrane as a PTFE filter membrane;

step g4, 15mL of the silver nanowire stock solution prepared in the step g2 is taken, deionized water is added to 40mL, the silver nanowire stock solution is uniformly shaken and then poured into a 1000mL barrel type positive pressure filter, the vacuum pressure gauge number of an air compressor in the positive pressure filter is controlled to be 20kPa, and the mixed liquid in the positive pressure filter is filtered by a PTFE filter membrane at the speed of 1 drop/s; obtaining a PTFE filter membrane attached with sediment, and collecting filtered waste liquid; after the end, placing the PTFE filter membrane attached with the sediment in 50mL of glycol solution with the PVP molecular weight of 55000 and 1wt percent, washing in a shaking way to dissolve the sediment, adding the obtained mixed liquid into the positive pressure filter, and repeating the step g4 for 3-5 times.

Step g5, collecting silver nanowires on the PTFE filter membrane, dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid for standby; and centrifuging the total waste liquid collected for 3-5 times at a centrifuging speed of 5000rpm/min for 15min, and taking out the lower precipitate to dissolve in deionized water to obtain byproduct dispersion liquid for later use;

step g6, mixing 0.8wt% of bacterial cellulose solution with 1wt% of nano cellulose solution according to the volume ratio of 1:1, mixing, stirring uniformly to obtain a mixed cellulose solution for standby;

step g7, uniformly mixing 5wt% of the byproduct dispersion liquid and the mixed cellulose solution in a volume ratio of 1:1 to obtain a mixed solution; pre-freezing the mixed solution at-50 ℃ for 12 hours; setting the temperature of a freeze dryer to minus 60 ℃ and the air pressure to 10Pa, and freeze-drying for 24 hours to prepare a byproduct aerogel film, as shown in figure 3; the S-parameters of the by-product aerogel films were tested and the calculated electromagnetic shielding effectiveness EMI SE is shown in fig. 4. In fig. 4, theoratical calculation represents a theoretical calculation; 0.04mm, 0.09mm, 0.12mm for blue, 0.12mm for gray, respectively, indicate the thickness of the by-product aerogel film.

Repeating the steps, changing the mass percentage of the byproduct dispersion liquid to be 2wt percent, and preparing a new byproduct aerogel film; the S-parameters were measured from the opposite direction, and the calculated electromagnetic shielding effectiveness EMI SE is shown in fig. 5, in which fig. 5, top and Down represent incidence from the front side of the aerogel (referred to herein as by-product aerogel film) and incidence from the back side of the aerogel, respectively.

Further, step g8 may be further included after step g 7: crushing the aerogel film of the byproduct obtained in the step g7, adding the magnetons, and stirring for 12 hours at normal temperature to fully dissolve the aerogel film; dissolving to form corresponding dispersion, pouring into a mold, and pre-freezing at-50deg.C for 12 hr; setting the temperature of a freeze dryer to minus 60 ℃ and the air pressure to 10Pa, and freeze-drying for 24 hours to prepare a byproduct aerogel film again, as shown in figure 6; the S parameter was measured and the electromagnetic shielding effectiveness EMI SE was calculated as shown in FIG. 7.

From the related test data of this example, the aerogel film of the by-product prepared by the example of the present invention has good electromagnetic shielding performance.

Embodiment two:

step h1, preparing A, B, C three ethylene glycol solutions:

a:0.4572g NaBr+20mL EG (national medicine);

b:0.2466g NaCl+20mL EG (national medicine);

c:1.68g PVP (sigma 360 k) +30mL EG (national drug);

the prepared A, B, C three glycol solutions were placed in a drying cabinet with a humidity of 20%. Then, 0.6765g of silver nitrate (national medicine) is taken and poured into 15mL of glycol (national medicine), and after being put into a 100Hz ice bath (4-8 ℃) for 1min, ultrasonic treatment is carried out for 5.0-6.0 min (complete dissolution), thus obtaining colorless silver nitrate solution.

Step h2, taking 116mL EG (Chinese medicine) solvent by a measuring cylinder, placing the solvent in a single-neck round-bottom flask (250 mL), immersing the solvent in an oil bath, and starting an oil bath stirring function; simultaneously adding mechanical stirring, wherein the speed is set to 300rmp/min; sequentially taking 1mL of A, 2mL of B solution and 15mL of C solution by a pipette, injecting the solution into the round-bottomed flask, and finally injecting a new silver nitrate solution, and simultaneously starting timing for 30min; heating to 180deg.C, setting the temperature to 170deg.C, reducing the mechanical stirring speed to 120rpm/min, timing for 10min, and stopping stirring; and (3) timing again, taking out the silver nanowire stock solution after reacting for 1h, and placing the silver nanowire stock solution in cold water for quenching for standby.

Step h3, carrying out water bath for 30min at 90 ℃ on a polytetrafluoroethylene filter membrane (with the diameter of 100 mm@aperture of 10 um) for standby, and taking the polytetrafluoroethylene filter membrane as a PTFE filter membrane;

step h4, 15mL of the silver nanowire stock solution prepared in the step h2 is taken, deionized water is added to 40mL, the silver nanowire stock solution is uniformly shaken and then poured into a 1000mL barrel type positive pressure filter, the vacuum pressure gauge number of an air compressor in the positive pressure filter is controlled to be 20kPa, and the mixed liquid in the positive pressure filter is filtered by a PTFE filter membrane at the speed of 1 drop/s; obtaining a PTFE filter membrane attached with sediment, and collecting filtered waste liquid; after the end, placing the PTFE filter membrane attached with the sediment in 50mL of glycol solution with the PVP molecular weight of 55000 and 1wt percent, washing in a shaking way to dissolve the sediment, adding the obtained mixed liquid into the positive pressure filter, and repeating the step h4 for 3-5 times.

Step h5, collecting silver nanowires on the PTFE filter membrane, dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid for standby; and centrifuging the total waste liquid collected for 3-5 times at a centrifuging speed of 5000rpm/min for 15min, and taking out the lower precipitate to dissolve in deionized water to obtain byproduct dispersion liquid for later use;

step h6, mixing a bacterial cellulose solution with the weight percent of 1 and a nanocellulose solution with the weight percent of 1, wherein the volume ratio is 1:1, mixing, stirring uniformly to obtain a mixed cellulose solution for standby;

step h7, forming a mixed dispersion liquid by 1 weight percent of the byproduct dispersion liquid and 0.2 weight percent of the silver nanowire dispersion liquid; uniformly mixing the mixed dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution; pre-freezing the mixed solution at-50 ℃ for 12 hours; setting the temperature of a freeze dryer at-60 ℃ and the air pressure at 10Pa, and freeze-drying for 24 hours to prepare the by-product aerogel foam. The correlation results are shown in FIGS. 8-10; the dielectric constant of the by-product aerogel foam was tested and the reflection loss RL was calculated as shown in fig. 11; testing the S parameter, and calculating electromagnetic shielding effectiveness EMI SE, as shown in figure 12;

further, step h7 may further include step h8: crushing the aerogel foam of the byproduct obtained in the step h7, adding the magnetons, and stirring for 12h at normal temperature to fully dissolve the aerogel foam; dissolving to form corresponding dispersion, pouring into a mold, and pre-freezing at-50deg.C for 12 hr; setting the temperature of the freeze dryer to minus 60 ℃ and the air pressure to 10Pa, freeze-drying for 24 hours, and preparing the aerogel foam as a byproduct again, as shown in figure 13; the dielectric constant was measured, and the reflection loss RL was calculated as shown in FIG. 14, wherein 1.2mm, 1.3mm and 1.4mm in FIG. 14 represent the thicknesses of the by-product aerogel foam, respectively; the S parameter was measured and the electromagnetic shielding effectiveness EMI SE was calculated as shown in FIG. 15.

From the related test data of the embodiment, the by-product aerogel foam prepared by the embodiment of the invention has better electromagnetic shielding performance and wave absorbing performance.

As can be seen from the first embodiment and the second embodiment, compared with the prior art, the present invention has the following advantages:

1. silver halide (silver chloride and silver bromide) in byproducts of silver nanowire preparation is used as a dielectric material, so that the defects of the silver nanowire can be effectively overcome, and good impedance matching is formed. Meanwhile, the silver-silver halide cluster microparticles contain a large number of distorted lattices, amorphous metals and point defects, so that strong dipole polarization can be generated, and electromagnetic wave loss, conversion and absorption are promoted. And the interface polarization effect caused by the abundant heterojunction interface (Ag/AgCl/AlBr) existing between the silver nanowire byproduct material systems can also exacerbate electromagnetic wave absorption.

2. The electromagnetic shielding and microwave absorption function integration realized by utilizing the silver nanowire byproducts to prepare the electromagnetic protection material not only can realize perfect absorption (absorption rate is more than 90%) in the effective microwave absorption frequency band, but also can realize electromagnetic shielding in other frequency bands to protect sensitive devices.

In a second aspect, corresponding to the embodiment of the method, the embodiment of the invention also provides a conductive material, which is prepared by the method for preparing the conductive material by recycling the silver nanowire byproducts in the first aspect.

The conductive material prepared by the embodiment of the invention can comprise a byproduct aerogel film or byproduct aerogel foam, and can be used as an electromagnetic protective material.

Please refer to the related matters of the first aspect, and detailed descriptions thereof are omitted herein.

The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims (10)

1. A method for preparing a conductive material by recovering silver nanowire byproducts, comprising:

adding deionized water into the pre-prepared silver nanowire stock solution, shaking uniformly, and placing the mixture into a positive pressure filter;

repeatedly executing a filtering step for preset times, wherein the filtering step comprises the steps of filtering the mixed liquid in the positive pressure filter by utilizing a PTFE filter membrane to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid; placing the PTFE filter membrane attached with the sediment in an ethylene glycol solution containing PVP for shaking washing, dissolving the sediment to obtain mixed liquid, and adding the mixed liquid into the positive pressure filter;

collecting silver nanowires on a PTFE filter membrane, and dispersing the silver nanowires in water to obtain silver nanowire dispersion liquid; centrifuging the total waste liquid collected in a preset time, and taking out the lower precipitate to dissolve in deionized water to obtain byproduct dispersion;

mixing the obtained bacterial cellulose solution with the nano cellulose solution to obtain a mixed cellulose solution;

obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and performing prefreezing and freeze drying treatment on the mixed solution to obtain a prepared conductive material; wherein the conductive material comprises a byproduct aerogel film or a byproduct aerogel foam.

2. The method for preparing a conductive material using silver nanowire byproduct recovery according to claim 1, wherein the conductive material is used as an electromagnetic shielding material.

3. The method for preparing a conductive material using silver nanowire byproduct recovery according to claim 1, wherein after the prepared conductive material is obtained, the method further comprises:

crushing the conductive material, and then dissolving the crushed conductive material in deionized water to form conductive material dispersion liquid;

and pouring the conductive material dispersion liquid into a mould for the pre-freezing and freeze-drying treatment to obtain the same conductive material prepared again.

4. The method for preparing conductive material by recycling silver nanowire byproducts according to claim 1, wherein the adding deionized water into the pre-prepared silver nanowire stock solution, shaking, and placing in a positive pressure filter comprises:

15mL of the pre-prepared silver nanowire stock solution is added with deionized water to 40mL, and then the mixture is shaken uniformly and poured into a 1000mL barrel type positive pressure filter.

5. The method for preparing a conductive material using silver nanowire byproduct recovery according to claim 4, wherein the filtering step comprises:

controlling the vacuum pressure gauge number of an air compressor in the positive pressure filter to be 20kPa, filtering the mixed liquid in the positive pressure filter by using a PTFE filter membrane at a speed of 1 drop/s to obtain a PTFE filter membrane attached with sediment, and collecting filtered waste liquid;

the sediment-attached PTFE filter membrane was put into 50mL of a glycol solution of 0.2 to 1wt% of PVP having a molecular weight of 55000 to be sloshed to dissolve the sediment, and the resulting mixed liquid was added to the positive pressure filter.

6. The method for preparing a conductive material using silver nanowire byproduct recovery according to claim 5, wherein the centrifugation process employs parameters including:

the speed of centrifugal treatment is 3500-6000 rpm/min; the duration of the centrifugal treatment is 5-15 min.

7. The method for preparing a conductive material using silver nanowire byproduct recovery according to claim 5, wherein the mixing the obtained bacterial cellulose solution with the nanocellulose solution to obtain a mixed cellulose solution comprises:

mixing 0.5-0.8wt% bacterial cellulose solution and 0.5-1wt% nano cellulose solution according to the volume ratio of 1:2-1:1, and uniformly stirring to obtain mixed cellulose solution.

8. The method for producing a conductive material using silver nanowire byproduct recovery according to claim 7, wherein the obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and subjecting the mixed solution to pre-freezing and freeze-drying processes, comprises:

uniformly mixing 2-6wt% of the byproduct dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution;

and (3) performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the prepared conductive material which is the by-product aerogel film.

9. The method for producing a conductive material using silver nanowire byproduct recovery according to claim 7, wherein the obtaining a mixed solution based on the byproduct dispersion liquid and the mixed cellulose solution, and subjecting the mixed solution to pre-freezing and freeze-drying processes, comprises:

forming a mixed dispersion by 0.5 to 1wt% of the byproduct dispersion and 0.1 to 1wt% of the silver nanowire dispersion;

uniformly mixing the mixed dispersion liquid and the mixed cellulose solution according to the volume ratio of 1:1 to obtain a mixed solution;

and (3) performing pre-freezing treatment on the obtained mixed solution, and performing freeze drying treatment by using a freeze dryer to obtain the prepared conductive material which is the by-product aerogel foam.

10. A conductive material prepared by the method of any one of claims 1-9 using silver nanowire byproduct recovery.