CN1624211A

CN1624211A - Large scale in situ preparation method of ternary NaV6O15 single crystal nanometer needle

Info

Publication number: CN1624211A
Application number: CN 200410061000
Authority: CN
Inventors: 余家国; 程蓓; 余济美
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2004-10-26
Filing date: 2004-10-26
Publication date: 2005-06-08
Anticipated expiration: 2024-10-26
Also published as: CN1287012C

Abstract

A process or in-situ preparing the nanoneedles of three-element NaV6O15 monocrystal in large scale by in-situ reaction-crystallizing-etching method includes such steps as hydrothermal reaction between V2O5 powder, the aqueous solution of poly(styrene-alt-maleic acid, sodium salt (PSMA-Na) and catalyst HF at 120-200 deg.C, separating product, washing and distilled water and then absolute alcohol, and vacuum drying. It is possible to use sodium polystyrenesulfonate and sodium polyacrylate to replace PSMA-Na.

Description

Ternary NaV6O15Large-scale in-situ preparation method of single crystal nanoneedle

Technical Field

The invention relates to a one-dimensional ternary NaV₆O₁₅A large-scale in-situ preparation technology of single crystal nano needle, in particular to a mixtureAnd valence of vanadium oxide A_xV₂O₅A preparation method of the type vanadium bronze compound.

Background

One-dimensional nanostructured materials have attracted considerable interest due to their unique geometries, novel physical and chemical properties, and their potential applications in a variety of fields such as nanoelectronics and optoelectronics. The nanoneedle attracts special attention due to its sharp curvature property, which makes it potentially applicable to high spatial resolution probes and field emission heads. However, nanoneedles with a small amount of binary components such as ZnO, CdO and GaN are synthesized only by physical methods. Chemical synthesis of ternary-component nanoneedles remains a difficult and challenging task.

In previous studies, we used V₂O₅And NaF as raw materials, and synthesizing multi-component Na by a simple hydrothermal method₂V₆O₁₆·3H₂However, the simple method has no power in synthesizing reduced vanadium compounds, thus, a weak reduction atmosphere is urgently needed to be introduced in hydrothermal reaction to obtain mixed-valence vanadium oxide, and recently, the mixed-valence vanadium bronze compound β -Na_0.33V₂O₅Due to various novel characteristics of phase transformation, magnetoelectric sequencing, pressure-induced low-temperature superconduction and the like, people attract extensive attention. Mixed oxide NaV composed of +4 and + 5V₆O₁₅Is a typical one of A_xV₂O₅Type vanadium bronze compounds, which are generally prepared by high temperature solid phase reaction or self-fluxing methods.

Disclosure of Invention

According to the current research situation at home and abroad and the feasibility of the preparation method of the one-dimensional nanoneedle, the invention provides a simple and effective one-dimensional ternary NaV₆O₁₅Large-scale in-situ preparation method of single crystal nanoneedle, abbreviated as 'in-situ reaction-crystallization-etching' methodThe method is carried out.

Ternary NaV of the invention₆O₁₅The large-scale in-situ preparation method of the single crystal nanometer needle comprises the following steps:

1 at V₂O₅Taking the powder and the high molecular sodium salt as raw materials, taking HF as a catalyst, and carrying out hydrothermal treatment at 120-200 ℃ for 5-48 hours;

2, separating the product obtained in the step 1, and washing the product with distilled water and absolute ethyl alcohol respectively;

3, drying the cleaning product obtained in the step 2 at 40-100 ℃ for 6 hours in vacuum to obtain the required ternary NaV₆O₁₅A single crystal nanoneedle;

wherein the high molecular sodium salt is 30 wt% aqueous solution of polystyrene discontinuous maleic acid sodium salt, and the average weight average molecular weight is 120,000 (PSMA-Na for short), and V in the hydrothermal treatment substance₂O₅The concentration of the powder is 1-25 gL^-1Preferably 5-15gL^-1The concentration of the sodium salt of polystyrene discontinuous maleic acid is 0.1-15 gL^-1Preferably 0.5 to 5gL^-1，V₂O₅The concentration ratio of the powder to the polystyrene discontinuous sodium maleate salt is 1-10,the molar concentration of the HF is 0.05-3 ML^-1. During the hydrothermal reaction, HF is not only NaV₆O₁₅A catalyst for nanowire formation, and it facilitates the transformation of nanowires into nanoneedles. The sodium salt PSMA-Na can be replaced by sodium polystyrene sulfonate (poly (sodium 4-styrene-sulfonate)) and sodium polyacrylate (poly (acrylic acid)).

The reaction mechanism may be: PSMA-Na is first hydrolyzed to NaOH, then V₂O₅Reacting with NaOH in solution to form water-soluble NaVO₃Meanwhile, a small amount of V is generated due to the weak reduction characteristic of PSMA-Na under the hydrothermal treatment condition₂O₅Is reduced into VO₂(ii) a Finally, NaVO₃，V₂O₅And VO₂Further reaction to form NaV by homogeneous or heterogeneous nucleation₆O₁₅Single crystal nanowire, parallel [001 ]]And (4) directionally growing. The whole reaction processThe procedure is as follows:

(1)

(2)

(3)

(4)

F^-the etching characteristics of the ions result in NaV₆O₁₅And forming the nano needle. In the hydrothermal process, due to F^-The etching characteristic of the ions, vanadium atoms can be removed from NaV₆O₁₅The surface of the nanowire dissolves. Also, the rough portion and both ends of the nanowire are more easily etch-dissolved due to the greater surface free energy than the smooth surface of the nanowire, which results in NaV₆O₁₅The formation of nanoneedles, with smooth surface of the middle trunk and sharp ends at both ends. NaV₆O₁₅Details of the mechanism of nanoneedle formation remain to be further investigated.

The crystal phase of the sample is characterized by an X-ray diffractometer (XRD, Bruker D8 advanced XRD with Cu K α radiation), the acceleration voltage and the applied current are 40kV and 40mA respectively, X-ray photoelectron spectroscopy is carried out on a PHIQUANTUM 2000 XPS system, a monochromatic A1K α emission source is used in the experiment, the electron binding energy is referenced to the CLs peak 284.8eV of the oil-contaminated carbon element on the surface, the surface morphology of the sample is characterized by a scanning electron microscope with the acceleration voltage of 20kV (SEM, LEO 1450 VP with energy-dispersive X-ray fluorescence analyzer), Transmission Electron Microscope (TEM) and high-resolution transmission electron microscope (HRTEM) pictures are obtained by a JEOL-TEM F2010 high-resolution transmission electron microscope, the acceleration voltage is 200kV, and the morphology and the size of the sample are observed and determined.

FIG. 1 is a view at V₂O₅Taking PSMA-Na and HF as raw materials, and carrying out hydrothermal reaction at 180 +/-5 ℃ for 24 hours to obtain an XRD (X-ray diffraction) pattern of a product. All diffraction peaks of the product can be assigned to NaV₆O₁₅Monoclinic phase [ space group: a2/m (12)]The unit cell parameters are calculated to be 10.06 Å, 3.60 Å, 3.42 15.42 Å and 109.23, which are very consistent with JCPDS No.86-120₆O₁₅The crystallization state of the nanoneedle is good.

FIG. 2 is a view taken at V₂O₅PSMA-Na and HF as raw materials are subjected to a hydrothermal reaction at 180 +/-5 ℃ for 24 hours to obtain an X-ray photoelectron spectrum (XPS) full spectrum (1) of a product and an X-ray photoelectron spectrum high-resolution spectrum (2) of a V2p region, and the X-ray photoelectron spectrum full spectrum analysis shows that the product consists of Na, V and O, the atomic ratio of the Na, V and O is 1: 5.99: 15.3, and an F element is not found in the product. In addition, the high resolution XPS spectrum of the V2p region (FIG. 2(2)) can be fitted with two peaks at 517.4 and 515.9eV, corresponding to V respectively⁵⁺2p_3/2 and V⁴⁺2p_3/2，V⁴⁺∶V⁵⁺Is about 1: 5. In addition, FourierNo PSMA-Na was detected by infrared (FTIR) analysis. XPS and FTIR results further demonstrate that the product is NaV₆O₁₅。

FIG. 3 shows a diagram with V₂O₅And carrying out hydrothermal reaction on the PSMA-Na and HF which are used as raw materials at 180 +/-5 ℃ for 24 hours to obtain a scanning electron microscope photo of a product. It can be seen from FIG. 3 that the product is almost needle-shaped, with a tip diameter of about several to 50nm at both sides, a middle portion of about 50 to 250nm, and a length of about 5 to 20 μm. This indicates well-defined NaV₆O₁₅Nanoneedles are easily synthesized under the experimental conditions we propose. X-ray energy dispersive spectroscopy (EDX) analysis also indicated that no F was present in the product. Based on SEM, XRD and XPS analyses, we estimated the yield and purity of the nanoneedle product to be approximately 95 and 90%, respectively.

We further characterized the acicular nanostructure of the product by Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM). FIG. 4(a) is a typical NaV₆O₁₅Low magnification TEM pictures of nanoneedles. Nano needle middle trunk partThe size is uniform, and the diameters of both ends are gradually reduced to tips of dozens to several nanometers. This may be due to F^-As a result of the rapid dissolution caused by the etching action of the ions. The electron diffraction test shows that NaV₆O₁₅Single crystal nature of nanoneedles. The selected area electron diffraction pattern (FIG. 4(b)) of a single nanoneedle is from [100 ]]The incidence in the direction of the crystal band axis is obtained, and the result shows that the nanoneedle is in a single crystal and is along the direction of the c axis (namely the [001 ] of a monoclinic crystal lattice)]Direction) growth. Fig. 4(c) is a typical HRTEM image of the body part of the nanoneedle. From the graph, it was confirmed that the lattice spacing was 0.320nm, which corresponds to bulk NaV₆O₁₅The (111) interplanar spacings of (A) are very close, again indicating that the nanoneedle is along [001 ]]And (4) directionally growing. Fig. 4(d) is an HRTEM image of the nanoneedle tip, from which it can be determined that its lattice spacing is about 0.321 nm. HRTEM images of the nanoneedle trunk and tip both show that the individual nanoneedles are single crystalline and have the same lattice orientation, which is also consistent with the Selected Area Electron Diffraction (SAED) results described above.

Our further experimental results show that NaV in the presence of HF₆O₁₅The single crystal nanoneedle may also be prepared using other high molecular sodium salts such as sodium polystyrene sulfonate (poly (4-styrene-sulfonate)) and sodium polyacrylate (poly (acrylic acid), instead of PSMA-Na. However, without HF, we could not synthesize NaV₆O₁₅And (4) nano needles. Even in other mineral acids such as HCl, HNO₃And H₂SO₄When present, the product is always NaV₆O₁₅Nanowires and V₂O₅A mixture of particles. FIGS. 5(3) and (4) are respectively the values in V in the absence of HF₂O₅And carrying out hydrothermal reaction on the raw material PSMA-Na at the temperature of 180 +/-5 ℃ for 24 hours to obtain an XRD (X-ray diffraction) pattern and a Scanning Electron Microscope (SEM) picture of the product. The product was found to be approximately 40% NaV₆O₁₅Nanowires and 60% V₂O₅And (4) particle composition. Therefore, we consider F^-Ions not only being NaV₆O₁₅Catalyst for nanowire formation, and, due to F^-Nucleophilic substitution of the ion leads to V₂O₅Enhancement of dissolution and reactivity, F^-The presence of the ions also facilitates the nanowire to nanowire transition. Although NaV₆O₁₅The mechanism of nanoneedle formation is not well understood at present, but it is clear that the precursors for crystal growth are reaction products rather than raw materials. This is an important difference from nanoneedle growth methods based on the gas-solid (VS) process. NaV₆O₁₅The synthesis of nanoneedles may be based on an "in situ reaction-crystallization-etching" mechanism.

In conclusion, V is a novel 'in-situ reaction-crystallization-etching' method₂O₅The powder and PSMA-Na are used as raw materials, HF is used as a catalyst, and the mixture is subjected to hydrothermal treatment for 24 hours at the temperature of 180 +/-5 ℃, so that the ternary NaV is synthesized in a large amount₆O₁₅A single crystal nanoneedle. HF is not only NaV₆O₁₅A catalyst for nanowire formation, and it facilitates the transformation of nanowires into nanoneedles. We believe that the above synthetic strategy may be extended to other vanadium bronze materials by selecting appropriate polymeric salts.

Drawings

FIG. 1 is a view at V₂O₅Taking PSMA-Na and HF as raw materials, carrying out hydrothermal reaction at 180 +/-5 ℃ for 24 hours to obtain an XRD (X-ray diffraction) pattern of a product

FIG. 2 shows the X-ray photoelectron spectroscopy (XPS) full spectrum (1) of the product and the X-ray photoelectron spectroscopy high resolution spectrum (2) of the V2p region

FIG. 3 is a V₂O₅PSMA-Na and HF as raw materials, and carrying out hydrothermal reaction at 180 +/-5 ℃ for 24 hours to obtain a scanning electron micrograph of a product

FIG. 4 shows NaV₆O₁₅A Transmission Electron Microscope (TEM) picture (a) of the nano-needle, a Selected Area Electron Diffraction (SAED) atlas (b) of a single nano-needle, a high-resolution transmission electron microscope (HRTEM) picture (c) of the middle part of the nano-needle and a high-resolution transmission electron microscope (HRTEM) picture (d) of the tip of the nano-needle.

FIG. 5 is a V₂O₅And PSMA-Na as raw material, but without adding HF, hydrothermal reacting at 180 +/-. deg.C for 24 h to obtain XRD pattern of product3) And scanning electron micrograph (4)

Detailed Description

Example 1

With V₂O₅Powder and PSMA-Na as raw materials, HF as catalyst, 0.91g V₂O₅The powder and 5mL of 4M HF solution were added to 70mL of 3.0gL^-1After stirring the aqueous solution of PSMA-Na solution for 2 minutes. The resulting suspension was transferred to a 100ml hydrothermal kettle. Sealing, carrying out hydrothermal treatment at 180 +/-5 ℃ for 24 hours, and then naturally cooling to room temperature. After the reaction, the solution had a pH of about 3.5, and the yellowish green reaction product was collected and washed 5 times with distilled water and absolute ethanol, respectively. Finally, vacuum drying for 6 hours at 80 +/-5 ℃ to obtain the one-dimensional ternary NaV₆O₁₅A single crystal nanoneedle product. The XRD spectrum, X-ray photoelectron spectrum, scanning electron micrograph and transmission electron micrograph of the obtained product are respectively shown in figure 1, figure 2, figure 3 and figure 4.

Example 2

To examine the effect of precursor concentration on nanoneedle quality, remove precursor V₂O₅The concentrations of the powders and PSMA-Na were different, and other experimental conditions such as hydrothermal treatment temperature and time, HF concentration, etc. were exactly the same as in example 1. As a result, it was found that: when V is₂O₅The concentration of the powder and PSMA-Na is too high, being more than 25 and 15gL respectively^-1When the concentration is too high and the viscosity is too high, NaV is mainly formed in the solution₆O₁₅A mixture of nanoneedles, nanowires and particles, and is difficult to disperse; on the contrary, if V₂O₅The molar concentrations of the powder and PSMA-Na were too low to be below 1 and 0.1gL, respectively^-1The NaV produced by the reaction₆O₁₅Because the supersaturation degree is too small to be in a metastable state, NaV cannot be formed₆O₁₅And (4) nano needles. When NaV₆O₁₅At a concentration in between, can form NaV₆O₁₅And (4) nano needles.

Example 3

To check V₂O₅Concentration ratio between powder and PSMA-Na to NaV₆O₁₅Influence of nanoneedle quality and yield, except for V₂O₅Except for the concentration ratio between the powder and PSMA-Na, other experimental conditions such as HF concentration, hydrothermal reaction temperature and time, vacuum drying temperature and time, etc. were all the same as in example 1. As a result, it was found that: when V is₂O₅When the concentration ratio of the powder to the PSMA-Na is less than 1, the obtained product is mainly NaV due to the high concentration of PSMA-Na in the precursor solution₆O₁₅The gel of the nanometer needle and the PSMA-Na macromolecule can not be well dispersed. On the contrary, if V₂O₅When the concentration ratio of the powder to the PSMA-Na is greater than 10, V is generated due to too low concentration of PSMA-Na in the precursor solution₂O₅The powder is not completely converted into NaV₆O₁₅The product is mainly composed of V₂O₅And NaV₆O₁₅Two phases are formed.

Example 4

To examine HF concentration versus NaV₆O₁₅Influence of nanoneedle quality, other than the HF concentration, other experimental conditions such as hydrothermal treatment temperature and time, V₂O₅The concentrations of the powder and PSMA-Na were the same as in example 1. As a result, it was found that NaV was observed when the HF concentration was 0.05 to 3M₆O₁₅The nanometer needle shape is best and the yield is highest. When the HF concentration is less than 0.05M, the product contains V₂O₅And (3) granules. When the HF concentration is higher than 3M, NaV cannot be formed due to the low pH value and high acidity of the solution₆O₁₅And (4) nano needles.

Example 5

For testing the kind of acid on NaV₆O₁₅Influence of nanoneedle quality and yield by other mineral acids such as HCl, HNO₃And H₂SO₄In place of HF concentration, other experimental conditions such as hydrothermal reaction temperature and time, V₂O₅The concentrations of the powder and PSMA-Na were the same as in example 1. As a result, it was found that when other inorganic acids such as HCl, HNO were used₃And H₂SO₄When used as a catalyst, the product is always NaV₆O₁₅Nanowires and V₂O₅The XRD pattern and scanning electron micrograph of the mixture of particles, the resulting product are shown in FIGS. 5(3) and (4), respectively.

Example 6

To check the reaction time on NaV₆O₁₅The influence of the quality and yield of nanoneedles was the same as in example 1 except that the reaction time was varied and the experimental conditions such as the concentrations of reactants and catalyst, the hydrothermal treatment temperature, etc. When the reaction time is less than 5 hours, the product consists essentially of V₂O₅And NaV₆O₁₅Two-phase composition, which is caused by too short reaction times. When the reaction time is higher than 48 hours, the product is mainly composed of NaV₆O₁₅Nano needle composition to further increase reaction time, NaV₆O₁₅The quality and yield of the nanoneedles did not change significantly. This is due to the nearly complete reaction of the reactants.

Example 7

To examine the hydrothermal reaction temperature vs. NaV₆O₁₅The influence of the quality and yield of nanoneedles was the same as in example 1 except that the reaction temperature was varied and the experimental conditions such as the concentrations of reactants and catalyst, the hydrothermal treatment time, etc. When the reaction temperature is lower than 110 ℃, the product is mainly composed of V₂O₅And NaV₆O₁₅Two-phase composition, which is caused by too low a reaction temperature and too slow a reaction rate. When the reaction temperature is higher than 200 ℃, the product is mainly composed of NaV₆O₁₅The nanoneedles are composed, but the diameter of the nanoneedles is not uniform, which is caused by excessively fast reaction rate.

Example 8

To examine the species of the high-molecular sodium salt vs. NaV₆O₁₅Influence of nanoneedle quality and yield by other high molecular sodium saltSuch as sodium polystyrene sulfonate (poly (4-styrene-sulfonate)) and sodium polyacrylate (poly (acrylic acid)) instead of PSMA-Na, and other experimental conditions such as hydrothermal reaction temperature and time, V₂O₅The concentrations of the powder and HF were the same as in example 1. As a result, it was found that when other high molecular weight sodium is usedWhen a salt such as sodium polystyrene sulfonate (poly (4-styrene-sulfonate)) and sodium polyacrylate (poly (acrylic acid)) is used in place of PSMA-Na, the product is mainly composed of NaV₆O₁₅And (4) nano needles.

Example 9

To examine the vacuum drying temperature vs. NaV₆O₁₅The influence of the quality of the nanoneedles was the same as in example 1 except that the vacuum drying temperature was different, and the experimental conditions such as the concentrations of the reactants and the catalyst, the hydrothermal treatment temperature and time, and the like were the same. When the vacuum drying temperature is lower than 40 ℃, the product is not easy to dry. When the vacuum drying temperature is higher than 100 ℃, the NaV product₆O₁₅The nanoneedles are easily broken.

Claims

1. Ternary NaV₆O₁₅The large-scale in-situ preparation method of the single crystal nanometer needle is characterized in that the method is an in-situ reaction-crystallization-etching method, and the preparation steps are as follows:

1, at V₂O₅Taking the powder and the high molecular sodium salt as raw materials, taking HF as a catalyst, and carrying out hydrothermal treatment at 120-200 ℃ for 5-48 hours;

separating the product obtained in the step 1, and washing the product with distilled water and absolute ethyl alcohol respectively;

and 3, drying the cleaning product obtained in the step 2 at 40-100 ℃ for 6 hours in vacuum to obtain the required ternary NaV₆O₁₅A single crystal nanoneedle;

wherein the high molecular sodium salt is 30 wt.% aqueous solution of polystyrene sodium salt of discontinuous maleic acid, the average weight average molecular weight is 120,000, and V in the hydrothermal treatment substance₂O₅The concentration of the powder is 1-25 gL^-1The concentration of the sodium salt of polystyrene discontinuous maleic acid is 0.1-15 gL^-1，V₂O₅The concentration ratio of the powder to the polystyrene discontinuous sodium maleate salt is 1-10, and the molar concentration of the HF is 0.05-3 ML^-1。

2. The method of claim 1The method is characterized in that the concentration of the sodium salt of polystyrene discontinuous maleic acid is 0.5-5gL^-1。

3. The method of claim 1 wherein V is₂O₅The concentration of the powder is 5-15gL^-1。

4. The method of claim 1, wherein the hydrothermal reaction temperature is 180 ± 5 ℃ and the reaction time is 24 hours.

5. The method of claim 1, wherein the sodium salt of a polymer is poly (sodium 4-styrene-sulfonate)).

6. The method of claim 1, wherein the sodium salt of a polymer is poly (acrylic acid).