A method for separating negatively charged metal oxide nanolayers of different sizes

Abstract

The application discloses a method for separating different size negatively charged metal oxide nanolayers, which comprises the following steps: preparing a negatively charged inorganic metal oxide material; dialyzing the inorganic metal oxide material with deionized water for 24 hours, and replacing the dialysate every 6 hours to obtain a colloidal suspension; dividing the colloidal suspension into n test groups, adding dilute hydrochloric acid to each group, shaking uniformly, and then standing to form an upper dispersion liquid and a lower precipitate; testing the Zeta potential of the upper dispersion liquid and the lower precipitate respectively, and determining the test group with the maximum Zeta potential difference; collecting the upper dispersion liquid and the lower precipitate of the test group with the maximum Zeta potential difference, centrifuging and washing, and then freeze-drying to obtain metal oxide nanolayers with different sizes. The material obtained by the solution method has a thinner thickness and a larger surface area, can expose rich active sites, and has a wide application prospect in the fields of energy and catalysis.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for size separation of negatively charged metal oxide nanolayer colloids, and belongs to the field of nanomaterial preparation. BACKGROUND

[0002] In recent years, the grim environmental problems have prompted people to pay more attention to the collection and utilization of clean energy such as solar energy, wind energy, tidal energy, etc. Clean energy is often limited by factors such as region and space-time and cannot stably output electric energy. The technology of electrocatalytic reduction of small molecules can effectively utilize idle energy and convert electric energy into chemical energy, which is convenient for energy storage and transportation and can lay a foundation for the promotion of renewable energy. Therefore, it is necessary to develop high selectivity, low cost and stable catalysts to promote the large-scale application of electrocatalytic reduction technology.

[0003] Two-dimensional nanomaterials have ultra-thin nanostructures in the plane, and the nanostructures also have large specific surface area, nanopores and adjustable structures, which make the materials have highly exposed active sites. Therefore, two-dimensional nanomaterials have wide application prospects in electrocatalytic synthesis and other aspects. In recent years, researchers have made great progress in this regard. However, the yield of two-dimensional catalysts is far from meeting the requirements of industrialization and still needs to be improved.

[0004] There are various methods for synthesizing inorganic metal nanosheets, such as top-down exfoliation, bottom-up solvothermal method, microwave method, template method, etc. However, the lateral size of nanosheets synthesized by the solvothermal method is often from several hundred nanometers to several microns, and the longitudinal thickness sometimes also differs greatly. The solvothermal method is simple to operate, requires less equipment for synthesis, and is easy to adjust parameters, which is suitable for industrial production. Specifically, the microstructure of metal oxide nanosheets, including the two-dimensional size of nanosheets, thickness, crystal plane, etc., has a great influence on the electrochemical performance of the material. Generally, small-size metal oxide nanosheets are suitable for applications such as catalysis, biosensing and gas separation. In addition, large-size metal oxide nanosheets can also be restructured to form three-dimensional structures for gas and energy storage. Therefore, the technology of controlling the size of metal oxide nanosheets plays a huge role in some special applications. However, the development of size grading technology of solid metal oxide nanosheets has not been smooth. This is because the surface area of metal oxide nanosheets is large, and the nanosheets will interact with each other and aggregate into blocks during the dehydration process due to van der Waals forces. SUMMARY

[0005] The purpose of the present application is to provide a method for rapidly separating different sizes of negatively charged inorganic metal nanomaterials.

[0006] The technical solution for achieving the purpose of the present application is:

[0007] A method for separating different sizes of negatively charged metal oxide nanolayers, comprising the following steps:

[0008] Step one: preparing a negatively charged inorganic metal oxide material;

[0009] Step two: dialyzing the inorganic metal oxide material with deionized water for 24 hours, and replacing the dialysate every 6 hours to obtain a colloidal suspension;

[0010] Step three: dividing the colloidal suspension into n test groups, adding a certain amount of dilute hydrochloric acid to each group, shaking uniformly, and then allowing the solution to form an upper dispersion and a lower precipitate after standing, and testing the Zeta potential of the upper dispersion and the lower precipitate respectively to determine the test group with the largest Zeta potential difference;

[0011] Step four: collecting the upper dispersion and the lower precipitate of the test group with the largest Zeta potential difference, centrifuging and washing,

[0012] and then freeze-drying to obtain metal oxide nanolayers of different sizes.

[0013] Preferably, the negatively charged metal oxide nanomaterial is a Bi2WO6 nanolayer or a MnO2 nanosheet.

[0014] Preferably, the concentration of dilute hydrochloric acid is 1M.

[0015] Preferably, after adding a certain amount of dilute hydrochloric acid to each group, shaking uniformly, and allowing the solution to form an upper dispersion and a lower precipitate after standing for 6 hours.

[0016] Preferably, before testing the Zeta potential of the upper dispersion and the lower precipitate, the dispersion and the precipitate are first ultrasonically treated for 5 minutes respectively.

[0017] Compared with the prior art, the present application has the following advantages: (1) the method is suitable for different negatively charged metal oxides, and is a universal size separation method for metal oxide nanolayers; (2) the separation operation is simple, only hydrochloric acid is required as raw material, there is no environmental pollution, and it has the prospect of large-scale application; (3) the small size nanolayers separated can expose more active sites, and exhibit excellent electrocatalytic activity for water electrolysis, nitrogen reduction and electrocatalytic reduction of CO2. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a flow process schematic diagram of the present application for separating different sizes of negatively charged metal oxide nanolayers.

[0019] Figure 2are scanning electron microscope and transmission electron microscope images of Bi2WO6 of different sizes separated from the embodiment 1 of the present application, wherein a is the scanning electron microscope image of Flaky Bi2WO6, b is the scanning electron microscope image and size distribution of Lamellar Bi2WO6.

[0020] Figure 3 are X-ray photoelectron spectroscopy (A) and X-ray diffraction (B) images of Bi2WO6 nanosheets in the embodiment 1 of the present application.

[0021] Figure 4 are Zeta potential fold line graphs of Bi2WO6 nanosheet aqueous solutions of different sizes separated from the embodiment 1 of the present application, with the amount of 1M dilute hydrochloric acid added as the variable.

[0022] Figure 5 are electrochemical graphs of the material prepared in the embodiment 1 of the present application, which are LSV graphs of the Bi2WO6 nanosheet catalyst separated in the embodiment 1 under N2 and CO2 atmospheres respectively.

[0023] Figure 6 are scanning electron microscope images of MnO2 of different sizes prepared in the embodiment 2 of the present application, A is S-MnO2, and B is L-MnO2.

[0024] Figure 7 are Fourier transform infrared (A) spectrogram and X-ray diffraction (B) images of MnO2 nanosheets of different sizes separated from the embodiment 2 of the present application. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with the drawings and embodiments.

[0026] In combination with Figure 1 , the present application provides a method for separating negatively charged metal oxide nanosheets of different sizes, which comprises the following steps:

[0027] Step 1: preparing a negatively charged inorganic metal oxide material.

[0028] Step 2: dialyzing the inorganic metal oxide material with deionized water for 24 hours, and replacing the dialysate every 6 hours to obtain a colloidal suspension;

[0029] Step 3: dividing the above colloidal suspension into 12 parts, each 5 mL, and marking them as test group 1, test group 2, …, test group 12, and adding 0 μL, 10 μL, 20 μL, 40 μL, 60 μL, 80 μL, 100 μL, 120 μL, 140 μL, 160 μL, 180 μL, and 200 μL of 1M dilute hydrochloric acid respectively, shaking uniformly, and standing for 6 hours.

[0030] Step four: After 12 suspensions form upper layer dispersion and lower layer precipitate, first ultrasonic the dispersion and precipitate for 5 min respectively, then test their Zeta potential respectively, observe the Zeta potential difference between upper and lower layers, find out the test group with the largest Zeta potential difference.

[0031] Step five: Separate and collect the upper and lower layer solutions of the test group with the largest Zeta potential difference, centrifugal wash, then freeze-dry to obtain metal oxide nanolayers of different sizes.

[0032] Example 1

[0033] Take Bi2WO6 nanolayer as an example for size separation:

[0034] Step one: Dissolve 484.98 mg Bi (NO3) 2·5H2O and 494.8 mg Na2WO4·2H2O in 60 mL deionized water, then put the solution into a 100 mL reaction kettle, heat at 150℃ for 20 h, after the reaction kettle is cooled, pour out the solution, centrifugal wash the solution to obtain Bi2WO6 nanolayer. Figure 3 The XPS spectrum and XRD pattern of the Bi2WO6 nanolayer are shown in the figure, and the elements and orbits corresponding to the five peaks in the XPS spectrum are W 4f (35.08 eV), Bi 4f (160.45 eV), C 1s (285.11 eV), Bi 4d (443.57 eV) and O 1s (531.66 eV).

[0035] Step two: Ultrasonic the centrifugal washed white turbid solution for 3.5 h, then make the solution into a colloidal suspension with a concentration of 0.05 mg / mL.

[0036] Step three: Put the solution into a dialysis bag and dialyze for 24 h, replace the water every 12 h, 6 h and 2 h.

[0037] Step four: Take 60 mL Bi2WO6 dispersion, divide it into 12 parts of 5 mL, put them into 5 mL size glass bottles, and add 0, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 μL of 1M dilute hydrochloric acid respectively.

[0038] Step five: Shake the 12 dispersions evenly, then stand for 6 h, then separate the lower layer precipitate and the upper layer dispersion.

[0039] Step six: Ultrasonic the above lower layer precipitate and upper layer dispersion for 5 min respectively, then test their Zeta potential respectively.

[0040] According to the test data of step six, make a graph as follows: Figure 4As shown in the results, the Zeta potential difference between the upper and lower solutions was the largest, and the test group with 60 μL of 1 M dilute hydrochloric acid was determined to have the largest Zeta potential difference.

[0041] Step seven: The upper and lower solutions of the test group (with the largest Zeta potential difference) were separated and collected, centrifuged and washed, and then freeze-dried to obtain metal oxide nanolayers of different sizes. The upper and lower layers were Flaky Bi2WO6 and Lamellar Bi2WO6, respectively, and the corresponding scanning electron micrographs are shown in FIG. 2. Figure 2 As shown in the results, the Zeta potential difference between the upper and lower solutions was the largest, and the test group with 60 μL of 1 M dilute hydrochloric acid was determined to have the largest Zeta potential difference.

[0042] The material prepared in this example was applied to the electrocatalytic reduction of CO2, using a flow electrolytic cell as the reaction device, 1 M KOH aqueous solution as the electrolyte, 0.05 M sulfuric acid as the tail gas absorption liquid, a gas flow rate of 80 mL / min, and a peristaltic pump speed of 50 r / min. Figure 5 is the linear sweep voltammetry curve for the reduction of CO2, and the overpotential at a current density of 10 mA cm -2 is 647 mV.

[0043] Example 2

[0044] Size separation was performed using MnO2 nanosheets as an example:

[0045] Step one: 900 mg of sodium dodecyl sulfate was dissolved in 300 mL of deionized water, and then 300 μL of 0.5 M H2SO4 solution was added. The mixed solution was placed in an oven and heated to 90°C, and then a previously prepared potassium permanganate solution (30 mg dissolved in 30 mL of deionized water) was quickly added. The reaction was allowed to proceed for 3 h, and then the brown solution obtained after the reaction was filtered. The filter product was repeatedly washed with deionized water and ethanol to obtain MnO2 nanosheets.

[0046] The other steps were the same as in Example 1, and different sizes of L-MnO2 and S-MnO2 were obtained. The scanning electron micrographs are shown in FIG. 4. Figure 6 As shown in the results, the Zeta potential difference between the upper and lower solutions was the largest, and the test group with 60 μL of 1 M dilute hydrochloric acid was determined to have the largest Zeta potential difference.

[0047] Figure 7 are the Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns of L-MnO2 and S-MnO2. In the FTIR spectra, 3340 cm -1weak peaks at 1630 cm -1 peaks at 1140 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm -1 peaks at 456 cm

Claims

1. A method for separating negatively charged Bi2WO6 nanolayers of different sizes, characterized in that, The method comprises the following steps: Step 1: 484.98 mg of Bi (NO3) 2.5H2O and 494.8 mg of Na2WO4.2H2O are dissolved in 60 mL of deionized water, and then the solution is loaded into a 100 mL reaction kettle, heated at 150 DEG C for 20 h, and then the solution is centrifuged and washed to obtain a Bi2WO6 nanolayer; Step 2: the centrifuged and washed white turbid solution is ultrasonicated for 3.5 h, and then the solution is diluted to a concentration of 0.05 mg / mL of a suspension; Step 3: the suspension is loaded into a dialysis bag and dialyzed with deionized water for 24 h, and the dialysis liquid is replaced every 6 h to obtain a colloidal suspension; Step 4: 60 mL of the colloidal suspension is taken and divided into 12 portions of 5 mL, which are loaded into 5 mL glass bottles, and 0, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 μL of 1M dilute hydrochloric acid are added respectively; Step 5: the 12 portions of the dispersion are shaken uniformly, and then left to stand for 6 h, and then the lower precipitate and the upper dispersion are separated; Step 6: the lower precipitate and the upper dispersion are ultrasonicated for 5 min respectively, and then their Zeta potentials are tested respectively, and according to the test data, it is determined that the Zeta potential of the test group with 60 μL of 1M dilute hydrochloric acid added has the largest difference; Step 7: the upper and lower solutions of the test group with the largest difference in Zeta potential are separated and collected, centrifuged and washed, and then freeze-dried to obtain metal oxide nanolayers of different sizes, wherein the upper and lower layers are Bi2WO6 nanolayers with sizes of 200 nm-300 nm and Bi2WO6 nanolayers with sizes of 600 nm-1200 nm respectively.

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