Preparation of a bismuth tungstate complex and its application in the photocatalytic synthesis of urea.

Abstract

The present invention discloses a preparation method of a bismuth tungstate complex and its application in photocatalytic synthesis of urea, belonging to the technical field of photocatalytic material synthesis. The present invention mixes a bismuth nitrate solution with a sodium tungstate solution, prepares a semiconductor material Bi2WO6 by a high-temperature hydrothermal method, and then performs a secondary hydrothermal reaction with thiourea and cadmium chloride to obtain a CdS / Bi2WO6 binary complex. The bismuth tungstate complex obtained by the present invention exhibits good photocatalytic synthesis of urea activity under visible light, and also has certain activity in carbon dioxide reduction and synthesis of ammonia, and its raw materials are easily available, the process is simple and easy to operate, the product yield is high, and it is suitable for use in a humid environment where bacteria are easy to breed, it is harmless to the human body, and the environmental pollution is small, and it has a wide range of practical value and application research prospects in production and life.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic material synthesis, and specifically relates to a cadmium sulfide / bismuth tungstate binary composite material and a preparation method thereof and application thereof in photocatalytic synthesis of urea. Background Art

[0002] In recent years, people have developed a variety of green nitrogen fixation technologies in the laboratory, including electrocatalytic nitrogen fixation, photocatalytic nitrogen fixation, and photoelectrocatalytic nitrogen fixation. Among them, photocatalytic nitrogen fixation is considered to be a very promising artificial nitrogen fixation technology. This is because the energy radiated to the earth by the sun is as high as 120 PW, which is several orders of magnitude larger than the total energy demand of human beings and can fully meet human needs. In the process of photocatalytic nitrogen fixation, sunlight can be used to reduce nitrogen to ammonia through the reaction N2+3H2O= 2NH3+3 / 2O2 under mild conditions, or oxidized to nitric acid through the reaction 2N2+5O2+2H2O=4HNO3. Photocatalytic nitrogen fixation can be traced back to 1977, when Schrauzer and Guth used the photocatalytic effect of TiO2 to realize the conversion of nitrogen into ammonia and N2H4, and found that the loading of Fe2O3 can improve the photocatalytic nitrogen fixation activity of TiO2. Since then, various semiconductor materials such as oxides, sulfides, and bismuth oxyhalides have been used for photocatalytic nitrogen fixation, and the efficiency of photocatalytic nitrogen fixation has been greatly improved. However, the light response of semiconductors is limited by their band gap, making it difficult to achieve a wide spectrum response to light. Unlike semiconductors, the resonance wavelength of localized surface plasmons (LSPs) can achieve a wide spectrum response and strong absorption of sunlight by regulating the size and aspect ratio of nanoparticles, and has therefore been applied to reactions such as photocatalytic water splitting, photocatalytic CO2 reduction, and photocatalytic nitrogen fixation. Summary of the invention

[0003] The purpose of the present invention is to provide a cadmium sulfide / bismuth tungstate binary complex and its preparation and application in photocatalytic synthesis of urea.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A cadmium sulfide / bismuth tungstate binary composite, the preparation method of which comprises the following steps:

[0006] 1) Dissolve a certain amount of bismuth nitrate in an aqueous acetic acid solution and stir vigorously for 30 minutes to mix evenly to form a bismuth nitrate solution;

[0007] 2) Dissolve a certain amount of sodium tungstate in deionized water, stir evenly to obtain a sodium tungstate solution, then add it to the bismuth nitrate solution and stir for 30 minutes to form a mixed solution;

[0008] 3) transferring the obtained mixed solution to a hydrothermal reactor, performing hydrothermal reaction, cooling, filtering, washing and drying to obtain Bi2WO6 semiconductor material;

[0009] 4) The obtained Bi2WO6 is mixed with thiourea and cadmium chloride, deionized water is added and stirred for 1 hour, and then subjected to hydrothermal reaction, cooling, and washing to obtain a CdS / Bi2WO6 binary complex.

[0010] Furthermore, in step 1), the volume ratio of acetic acid to deionized water in the acetic acid aqueous solution is 4:11.

[0011] Furthermore, the concentration of the bismuth nitrate solution obtained in step 1) is 0.166 mol / L.

[0012] Furthermore, in step 2), the concentration of the sodium tungstate solution is 0.25 mol / L.

[0013] Furthermore, the amounts of the sodium tungstate solution and the bismuth nitrate solution used in step 2) are converted according to a molar ratio of sodium tungstate to bismuth nitrate of 1:2.

[0014] Furthermore, in step 3), the temperature of the hydrothermal reaction is 180° C. and the time is 3 h.

[0015] Furthermore, the mass ratio of Bi2WO6 to thiourea and cadmium chloride used in step 4) is 400:126.4:126.4.

[0016] Furthermore, in step 4), the temperature of the hydrothermal reaction is 180° C. and the time is 24 hours.

[0017] The cadmium sulfide / bismuth tungstate binary complex obtained above can be used for photocatalytic synthesis of urea.

[0018] The significant advantages of the present invention are:

[0019] (1) The preparation steps of the composite material of the present invention are simple, the preparation conditions are mild, the raw materials are cheap and readily available, the energy consumption is low, and it is highly environmentally friendly.

[0020] (2) The composite material obtained by the present invention exhibits good photocatalytic performance in synthesizing urea in an environment with nitrogen and carbon dioxide as raw materials, showing good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of CdS / Bi2WO6 with different loading amounts prepared in the examples.

[0022] Figure 2 SEM images of Bi2WO6 and 20% CdS / Bi2WO6 prepared in the example.

[0023] Figure 3 This is the DRS image of 20% CdS / Bi2WO6 prepared in Example.

[0024] Figure 4 Diagram of the device used for the photocatalytic synthesis of urea experiment.

[0025] Figure 5 This is a comparison chart of the catalytic activities of CdS / Bi2WO6 with different loading amounts prepared in the examples. DETAILED DESCRIPTION

[0026] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto. Example

[0027] 1) Dissolve 5mmol bismuth nitrate in a mixed solution consisting of 4ml acetic acid and 26ml deionized water, stir vigorously for 30min to mix evenly, and form a bismuth nitrate solution; dissolve 2.5mmol sodium tungstate in 10mL deionized water, stir evenly and add to the above bismuth nitrate solution. Then transfer the obtained mixed solution to a hydrothermal kettle, perform hydrothermal reaction at 180℃ for 3 hours, then cool to room temperature, filter and wash the obtained precipitate until the ion concentration of the washing liquid is below 10, then vacuum dry at 60℃ for 12h, grind carefully to powder after drying, collect the product, and obtain Bi2WO6.

[0028] 2) Take 400 mg of Bi2WO6, 126.4 mg of thiourea, and 126.4 mg of cadmium chloride in a hydrothermal reactor, add 4 ml of deionized water and stir for 1 hour, cool and wash to obtain a CdS / Bi2WO6 binary complex with a loading of 20%. In the same way, weigh the corresponding amount of Bi2WO6, thiourea and cadmium chloride to synthesize CdS / Bi2WO6 binary complexes with loadings of 10%, 30%, and 40%, respectively.

[0029] Figure 1 The XRD graphs of CdS / Bi2WO6 with different loading amounts are shown in Figure 1. As can be seen from the figure, after loading cadmium sulfide, the crystal form of the synthesized composite material has not changed, but is completely consistent with the XRD standard card of Bi2WO6. At the same time, the characteristic peaks of cadmium sulfide can be observed, indicating that CdS / Bi2WO6 has been successfully prepared and has high crystallinity.

[0030] Figure 2 The SEM images of the obtained Bi2WO6 (left) and 20% CdS / Bi2WO6 (right) are shown in Figure 1. From the comparison of the two images, it can be seen that the obtained CdS / Bi2WO6 is a spherical material of uniform size, with a diameter of about 3 microns, and cadmium sulfide particles are attached to the surface of bismuth tungstate.

[0031] To explore the light absorption of the catalyst, DRS test was further performed, and the results are shown in Figure 3 .Depend on Figure 3 It can be seen that bismuth tungstate has very strong absorption under visible light. After being modified with cadmium sulfide, the absorption wavelength of bismuth tungstate is red-shifted, which indicates that the light absorption of bismuth tungstate is enhanced, proving that after being loaded with cadmium sulfide, the performance of bismuth tungstate is significantly improved.

[0032] Application Examples

[0033] The photocatalytic activity of Bi2WO6 and a series of CdS / Bi2WO6 composite samples for the synthesis of urea was tested in Figure 4 The photocatalytic reactor shown in the figure is carried out, and the specific operation is as follows: 50 mg of the prepared catalytic material is weighed and placed in a small weighing bottle, and an appropriate amount of deionized water is added to evenly disperse it, and then dried. Then the obtained catalyst is evenly spread in a small weighing bottle again and placed in a photocatalytic reactor. Before the reaction, a vacuum pump is used to evacuate the reactor for 30 minutes, and then vacuum grease is used to seal the reactor at the air inlet and outlet to prevent air leakage in the reactor. During the reaction, 40 microliters of deionized water is drawn with an injection needle and injected into the reactor through the injection port. At the same time, a mixed gas of N2 and CO2 (1:1, v / v) is introduced, and the photocatalytic reactor is moved to a visible light (420nm) light source. After 1 hour of irradiation, the illumination is terminated, and about 1 ml of the sample is taken and transferred to a glass bottle. The color is developed using a color developer according to the diacetyl monoxime (DAMO) method. The color development temperature needs to be maintained at 100°C for 15 minutes, and then the sample is taken out and cooled to room temperature. After comparison with deionized water, the data is tested using an ultraviolet spectrophotometer, and then the yield data is calculated according to the standard curve to finally obtain the urea yield.

[0034] from Figure 5 The obtained catalyst activity data show that the activity of bismuth tungstate is significantly improved after being compounded with cadmium sulfide. When the proportion of cadmium sulfide is 20%, the activity reaches the peak, and its urea production efficiency is 5.9894μmol ▪g -1 h -1 , is the urea production efficiency of a single bismuth tungstate component (0.735 μmol ▪g -1 h -1 ) is 8.15 times.

[0035] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. Application of a cadmium sulfide / bismuth tungstate binary composite in photocatalytic synthesis of urea, characterized in that: The preparation method of the cadmium sulfide / bismuth tungstate binary composite comprises the following steps: 1) Dissolve a certain amount of bismuth nitrate in an aqueous acetic acid solution and stir vigorously for 30 minutes to mix evenly to form a bismuth nitrate solution; 2) Dissolve a certain amount of sodium tungstate in deionized water, stir evenly to obtain a sodium tungstate solution, then add it to the bismuth nitrate solution and stir for 30 minutes to form a mixed solution; 3) subjecting the obtained mixed solution to hydrothermal reaction, cooling, filtering, washing and drying to obtain Bi2WO6 semiconductor material; 4) Mix the obtained Bi2WO6 with thiourea and cadmium chloride, add deionized water and stir for 1 hour, then perform hydrothermal reaction, cool and wash to obtain CdS / Bi2WO6 binary complex; The mass ratio of Bi2WO6 to thiourea and cadmium chloride used in step 4) is 400:126.4:126.

4.

2. The use according to claim 1, characterized in that: Step 1) The volume ratio of acetic acid to deionized water in the acetic acid aqueous solution is 4:11, and the concentration of the obtained bismuth nitrate solution is 0.166 mol / L.

3. The use according to claim 1, characterized in that: Step 2) The concentration of the sodium tungstate solution is 0.25 mol / L.

4. The use according to claim 1, characterized in that: The amounts of the sodium tungstate solution and the bismuth nitrate solution used in step 2) are converted based on a molar ratio of sodium tungstate to bismuth nitrate of 1:

2.

5. The use according to claim 1, characterized in that: Step 3) The temperature of the hydrothermal reaction is 180°C and the time is 3 hours.

6. The use according to claim 1, characterized in that: Step 4) The temperature of the hydrothermal reaction is 180°C and the time is 24 hours.

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