A visible light responsive composite photocatalyst and its preparation method and application

Abstract

The present invention relates to a visible light-responsive composite photocatalyst, its preparation method, and application. The preparation method comprises the following steps: mixing Bi4TaO8Br nanosheets, a cobalt source, urea, and a solvent, uniformly dispersing the mixture, and reacting the mixture; collecting the precipitate, drying it, and calcining it under an inert atmosphere to obtain a CoO / Bi4TaO8Br composite photocatalyst. Compared to a single Bi4TaO8Br photocatalyst, the CoO / Bi4TaO8Br composite photocatalyst prepared in the present invention exhibits a wider visible light absorption range, faster photogenerated charge separation and transfer efficiency, and extremely high photocatalytic oxygen production activity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and in particular to a visible light responsive composite photocatalyst and a preparation method thereof. Background Art

[0002] With fossil fuels dwindling, the development and utilization of renewable resources has become a key priority for social development. Solar energy, as an inexhaustible, renewable, clean energy source, has become a top priority. Consequently, the use of photocatalysts to directly convert solar energy into chemical energy has attracted significant attention. However, conventional photocatalysts are mostly wide-bandgap semiconductors that absorb only ultraviolet light, which accounts for approximately 3% of the solar spectrum. Since visible light accounts for approximately 50% of the solar spectrum, photocatalysts must be able to absorb visible light in order to effectively utilize sunlight. Therefore, the development of photocatalysts that respond to visible light is of great significance.

[0003] Bi4TaO8Br is a novel bismuth-based layered compound that has been selected as a candidate for photocatalytic dye degradation and solar decomposition to produce hydrogen and oxygen due to its unique crystal structure and excellent electronic and optical properties. However, its photocatalytic activity is limited by the high carrier recombination rate of single photocatalysts. Summary of the Invention

[0004] The purpose of the present invention is to overcome at least one of the defects of the above-mentioned prior art and to provide a CoO / Bi4TaO8Br composite photocatalyst with high photocatalytic efficiency, good stability and visible light response and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] One of the objectives of the present invention is to provide a method for preparing a visible light-responsive composite photocatalyst, comprising the following steps: mixing Bi4TaO8Br nanosheets, a cobalt source, urea, and a solvent, dispersing them uniformly, and then reacting them; collecting the precipitate, drying it, and calcining it under an inert atmosphere to obtain a CoO / Bi4TaO8Br composite photocatalyst. Urea can reduce the surface tension of the reaction solution, reducing the mutual repulsion between the reactants, and improving the efficiency and stability of the reaction.

[0007] Specifically:

[0008] (1) Prepare Bi4TaO8Br nanosheets for later use;

[0009] (2) Bi4TaO8Br nanosheets, Co(NO3)2·6H2O and urea were added to the aqueous solution in proportion and transferred to a stainless steel high-pressure reactor for ultrasonic dispersion treatment. The reactor was then placed in an oven for reaction.

[0010] (3) Separate and precipitate the suspension obtained in step (2), and vacuum dry it to obtain a powder sample.

[0011] (4) The powder sample obtained by the reaction in step (3) is placed in a tube furnace, introduced into a N2 atmosphere, and calcined at a certain temperature to obtain a CoO / Bi4TaO8Br composite photocatalyst.

[0012] Among them, the preparation steps of Bi4TaO8Br are: Bi2O3, Ta2O5, BiOBr, NaCl and KCl are weighed and ground evenly according to the molar ratio of 1.5:0.5:1.0:10.0:10.0, the ground mixture is heated to 800°C and maintained for 14 hours, then immediately taken out and naturally cooled, and then washed with deionized water, separated and precipitated, and vacuum dried to obtain Bi4TaO8Br nanosheets.

[0013] Furthermore, the molar ratio of the Bi4TaO8Br nanosheets, the cobalt source and the urea is 1:(0-0.3):(0-0.3).

[0014] Furthermore, the cobalt source is Co(NO3)2·6H2O.

[0015] Furthermore, the solvent is water; the reaction is a hydrothermal reaction, the reaction temperature is 100-180° C., and the reaction time is 5-14 hours.

[0016] Furthermore, the dispersion method is ultrasonic dispersion; the drying is vacuum drying, the drying temperature is 60-120° C., and the drying time is 0.5-5 h.

[0017] Furthermore, the calcination temperature is 300-500° C., and the calcination time is 0.5-5 h.

[0018] The second object of the present invention is to provide a visible light responsive CoO / Bi4TaO8Br composite photocatalyst obtained by the preparation method as described above, wherein the CoO nanoparticles in situ support the {001} crystal plane of the Bi4TaO8Br nanosheets.

[0019] The third object of the present invention is to use the CoO / Bi4TaO8Br composite photocatalyst that responds to visible light as described above, which is applied to the oxygen production reaction under visible light, including the following steps: dispersing the CoO / Bi4TaO8Br composite photocatalyst in an aqueous solution containing an electron sacrificial agent, and under the action of visible light, decomposing water to produce oxygen.

[0020] Furthermore, the electron sacrificial agent is AgNO3.

[0021] The fourth object of the present invention is to use the above-mentioned visible light responsive CoO / Bi4TaO8Br composite photocatalyst, wherein the CoO / Bi4TaO8Br composite photocatalyst is combined with Ru / SrTiO 3: Rh constructed the Z mechanism system, which was applied to the complete water decomposition reaction to produce hydrogen and oxygen under visible light, and showed good photochemical stability.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) Compared with Bi4TaO8Br single photocatalyst, CoO / Bi4TaO8Br composite photocatalyst has a wider visible light absorption range, faster photogenerated charge separation and transfer efficiency; it has extremely high photocatalytic oxygen production activity and extremely high stability.

[0024] (2) The preparation method is simple, has high product yield, good reproducibility, is very suitable for large-scale preparation, and is highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The XRD patterns of the Bi4TaO8Br prepared in Comparative Example 1 and the CoO / Bi4TaO8Br composite photocatalysts prepared in Examples 1-4 are shown;

[0026] Figure 2 This is the SEM image of the Bi4TaO8Br nanosheets prepared in Comparative Example 1;

[0027] Figure 3 This is the SEM image of the CoO / Bi4TaO8Br composite photocatalyst prepared in Example 2;

[0028] Figure 4 DRS spectra of the Bi4TaO8Br prepared in Comparative Example 1 and the CoO / Bi4TaO8Br composite photocatalyst prepared in Examples 1-4;

[0029] Figure 5 Graph showing the photocatalytic oxygen production performance of the Bi4TaO8Br prepared in Comparative Example 1 and the CoO / Bi4TaO8Br composite photocatalyst prepared in Examples 1-4;

[0030] Figure 6 Diagram of the photocatalytic water splitting of the Z-type system constructed for the CoO / Bi4TaO8Br composite photocatalyst prepared in Example 2. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Comparative Example 1

[0033] Preparation, characterization and photocatalytic performance test of Bi4TaO8Br nanosheets:

[0034] (1) Preparation: Bi2O3, BiOBr, Ta2O5, NaCl, and KCl (molar ratio of 1.5:0.5:1.0:10.0:10.0) were weighed and ground uniformly. The ground mixture was heated to 800°C and maintained for 14 hours. The mixture was then immediately removed and naturally cooled. The mixture was then washed with deionized water, the precipitate was separated, and vacuum dried to obtain Bi4TaO8Br nanosheets.

[0035] (2) Structure and morphology characterization: Bi4TaO8Br nanosheets were tested by XRD and the results were as follows: Figure 1 As shown. It can be seen that the characteristic peaks of Bi4TaO8Br nanosheets match the peaks of the Bi4TaO8Br standard card (PDF: 54-0189), indicating that the prepared sample is a single phase and no other impurities were introduced during the preparation process. The sample was then subjected to scanning electron microscopy analysis, and the results are shown in Figure 2. Figure 2 As shown, the inventors can see that the Bi4TaO8Br sample prepared by the molten salt method shows a regular nanosheet morphology with a size of 0.2-1μm and a thickness of about 100nm. The inventors then characterized the prepared sample by UV-visible diffuse reflectance absorption spectrum, as shown in Figure 2. Figure 4 As shown in the figure, it can be seen that the sample absorption edge is located at around 500nm and has strong absorption in the visible region.

[0036] (3) Photocatalytic oxygen production test: Photocatalytic water splitting experiments were conducted in a top-radiation reactor connected to a closed gas circulation and evacuation system (Perfect Light, Labsolar-IIIAG). An online gas chromatograph with a thermal conductivity detector and a 300 W Xe lamp (λ ≥ 420 nm) equipped with a UV cutoff filter was used as the light source to detect the gas components generated in the reactor. In a typical procedure, 25 mg of photocatalyst powder was dispersed in 100 mL of aqueous solution containing 0.05 M AgNO3 as a sacrificial agent, and the oxygen content generated by the system was monitored online every 30 min.

[0037] Example 1

[0038] Preparation, characterization and photocatalytic performance test of 0.25wt% CoO / Bi4TaO8Br composite photocatalyst:

[0039] (1) The preparation method of Bi4TaO8Br nanosheets is consistent with that in Example 1.

[0040] (2) 0.2 g of Bi4TaO8Br nanosheets were placed in the inner container of an autoclave, added to 30 mL of water and ultrasonically dispersed for about 30 min. 0.5 mg of Co(NO3)2·6H2O and 0.5 mg of urea solution were then added to the above solution, ultrasonically dispersed, and stirred for 60 min. The stainless steel autoclave was then placed in a vacuum oven and reacted at 120°C for 5 h. After the reaction, the resulting powder was washed and dried, then placed in a long porcelain boat, introduced into a N2 atmosphere, and calcined in a tube furnace at 400°C for 1 h to obtain a 0.25 wt% CoO / Bi4TaO8Br composite photocatalyst.

[0041] The 0.25 wt % CoO / Bi4TaO8Br composite photocatalyst was subjected to XRD, SEM, DRS characterization and photocatalytic oxygen production performance test, and the test steps and conditions were consistent with those of Comparative Example 1.

[0042] Example 2

[0043] Preparation, characterization and photocatalytic performance test of 0.5wt% CoO / Bi4TaO8Br composite photocatalyst:

[0044] (1) The preparation method of Bi4TaO8Br nanosheets is consistent with that in Example 1.

[0045] (2) 0.2 g of Bi4TaO8Br nanosheets were placed in an autoclave, added to 30 mL of water, and ultrasonically dispersed for approximately 30 min. 1 mg of Co(NO3)2·6H2O and 1 mg of urea solution were then added to the solution, ultrasonically dispersed, and stirred for 60 min. The stainless steel autoclave was then placed in a vacuum oven and reacted at 120°C for 5 h. After the reaction, the resulting powder was washed and dried, then placed in a long porcelain boat, introduced into a N2 atmosphere, and calcined in a tube furnace at 400°C for 1 h to obtain a 0.5 wt% CoO / Bi4TaO8Br composite photocatalyst.

[0046] The 0.5wt% CoO / Bi4TaO8Br composite photocatalyst was subjected to XRD, SEM, DRS characterization and photocatalytic oxygen production performance test. The test steps and conditions were consistent with those of Comparative Example 1. The sample was subjected to scanning electron microscopy analysis, and the results are as follows: Figure 3 As shown, it can be seen that CoO nanoparticles are uniformly loaded on Bi4TaO8Br nanosheets.

[0047] Example 3

[0048] Preparation, characterization and photocatalytic performance test of 1wt% CoO / Bi4TaO8Br composite photocatalyst:

[0049] (1) The preparation method of Bi4TaO8Br nanosheets is consistent with that in Example 1.

[0050] (2) 0.2 g of Bi4TaO8Br nanosheets were placed in an autoclave, added to 30 mL of water, and ultrasonically dispersed for approximately 30 min. Then, 2 mg of Co(NO3)2·6H2O and 2 mg of urea solution were added to the above solution, ultrasonically dispersed, and stirred for 60 min. The stainless steel autoclave was then placed in a vacuum oven and reacted at 120°C for 5 h. After the reaction, the resulting powder was washed and dried, then placed in a long porcelain boat, introduced into a N2 atmosphere, and calcined in a tube furnace at 400°C for 1 h to obtain a 1 wt% CoO / Bi4TaO8Br composite photocatalyst.

[0051] The 1wt% CoO / Bi4TaO8Br composite photocatalyst was subjected to XRD, SEM, DRS characterization and photocatalytic oxygen production performance test, and the test steps and conditions were consistent with those of Comparative Example 1.

[0052] Example 4

[0053] Preparation, characterization and photocatalytic performance test of 2wt% CoO / Bi4TaO8Br composite photocatalyst:

[0054] (1) The preparation method of Bi4TaO8Br nanosheets is consistent with that in Example 1.

[0055] (2) 0.2 g of Bi4TaO8Br nanosheets were placed in an autoclave, added to 30 mL of water, and ultrasonically dispersed for approximately 30 min. Then, 4 mg of Co(NO3)2·6H2O and 4 mg of urea solution were added to the above solution, ultrasonically dispersed, and stirred for 60 min. The stainless steel autoclave was then placed in a vacuum oven and reacted at 120°C for 5 h. After the reaction, the resulting powder was washed and dried, then placed in a long porcelain boat, introduced into a N2 atmosphere, and calcined in a tube furnace at 400°C for 1 h to obtain a 2 wt% CoO / Bi4TaO8Br composite photocatalyst.

[0056] The 2 wt % CoO / Bi4TaO8Br composite photocatalyst was subjected to XRD, SEM, DRS characterization and photocatalytic oxygen production performance test, and the test steps and conditions were consistent with those of Comparative Example 1.

[0057] Comparing the XRD patterns of Comparative Example 1 with those of Examples 1-4, the results are as follows: Figure 1 As shown in the figure, the hydrothermal loading of CoO on Bi4TaO8Br sample does not affect the crystal structure of Bi4TaO8Br. However, no diffraction peak corresponding to CoO is seen, which may be due to the fact that CoO x The content is too low and cannot be detected by X-ray diffraction analyzer. In addition, no other impurity peaks are observed in the XRD spectrum of CoO / Bi4TaO8Br, indicating that the sample still has high purity and crystallinity after hydrothermal deposition treatment. The UV-visible diffuse reflectance spectra of Comparative Example 1 and Examples 1-4 are compared. The results are as follows: Figure 3 As shown. Obviously, compared with Bi4TaO8Br nanosheets, the absorption rate of the loaded CoO particles in the ultraviolet and visible light ranges and the red-shifted absorption edge has been improved. In particular, among all the loading amounts, the loading amount at 0.5wt% shows the highest light absorption, which may be one of the reasons why the photocatalytic oxygen production yield of 0.5wt% CoO / Bi4TaO8Br is the highest. Comparing the photocatalytic oxygen production of Comparative Example 1 with that of Examples 1-4, the results are shown as follows. Figure 5 As shown. After 2.5h of visible light irradiation, the Bi4TaO8Br nanosheets produced 26μmol of O2. After CoO was deposited on the Bi4TaO8Br{001} surface via a hydrothermal reaction, the yield of O2 showed a very small increase. It is worth noting that the O2 production produced at a loading of 0.5wt% was even nearly 5 times higher than that of the unloaded Bi4TaO8Br nanosheets (115μmol / h), indicating the effectiveness of CoO as a modifier. However, further increasing the CoO content will lead to a rapid decrease in oxygen production. This may be because the excess CoO scatters the incident light, which is not conducive to light absorption, thereby reducing the efficiency of photocatalytic oxygen production.

[0058] Example 5

[0059] Considering the effective photocatalytic water oxidation on Bi4TaO8Br nanosheets loaded with CoO, the inventors used CoO / Bi4TaO8Br prepared in Example 2 as oxygen-producing photocatalyst, Ru / SrTiO3:Rh as hydrogen-producing photocatalyst and Fe 3+ / Fe 2+ As a redox mediator, a visible light-driven Z-mechanism water splitting reaction was constructed.

[0060] Photocatalytic water splitting experiments were conducted in a top-radiation reactor connected to a closed gas circulation and evacuation system (Perfect Light, Labsolar-IIIAG). The gas components generated in the reactor were detected using an online gas chromatograph with a thermal conductivity detector and a 300 W Xe lamp (λ ≥ 420 nm) equipped with a UV cutoff filter as the light source.

[0061] The specific steps are as follows: 50 mg of CoO / Bi4TaO8Br prepared in Example 2 and 50 mg of Ru / SrTiO3:Rh were ultrasonically dispersed in 100 mL of FeCl3 aqueous solution (2 mM). The pH of the solution was adjusted to 2.5 by adding a small amount of HCl aqueous solution. The solution was stirred under vacuum for 1 hour to balance the Fe 3+ and Fe 2+ The concentration is then adjusted, and then illumination is carried out. The oxygen and hydrogen content produced by the system is detected online every 30 minutes.

[0062] like Figure 6 As shown, the simultaneous release of H₂ and O₂ in a stoichiometric ratio of 2:1 was successfully observed under visible light, with H₂ and O₂ yields as high as 22.0 μmol / h and 11.0 μmol / h. The photocatalytic durability and photostability of the Z-mechanism system were also investigated by periodically evacuating the generated gases. Figure 6 The results show a steady increase in H₂ and O₂ with irradiation time in each cycle. The gas production rate was maintained even after a long reaction time (9 hours), confirming the durability and photostability of the CoO / Bi₄TaO₄Br composite photocatalyst. These impressive photocatalytic properties indicate that the CoO / Bi₄TaO₄Br prepared by the inventors is a promising candidate for photocatalytic water oxidation, even in the presence of redox mediators, by constructing a Z-mechanism system for overall water splitting via interaction with appropriate hydrogen-producing photocatalysts.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for preparing a composite photocatalyst responsive to visible light, characterized in that: The steps include: Bi4TaO8Br nanosheets, a cobalt source, urea, and a solvent are mixed and uniformly dispersed before reacting; the precipitate is collected, dried, and calcined under an inert atmosphere to obtain a CoO / Bi4TaO8Br composite photocatalyst; The reaction is a hydrothermal reaction; In the CoO / Bi4TaO8Br composite photocatalyst, CoO nanoparticles in situ support the {001} crystal planes of Bi4TaO8Br nanosheets.

2. The method for preparing a visible light responsive composite photocatalyst according to claim 1, characterized in that: The molar ratio of the Bi4TaO8Br nanosheets, the cobalt source and the urea is 1:(0-0.3):(0-0.3).

3. The method for preparing a visible light responsive composite photocatalyst according to claim 1, characterized in that: The cobalt source is Co(NO3)2·6H2O.

4. The method for preparing a composite photocatalyst responsive to visible light according to claim 1, characterized in that: The solvent is water; the reaction temperature is 100-180° C., and the reaction time is 5-14 h.

5. The method for preparing a composite photocatalyst responsive to visible light according to claim 1, characterized in that: The dispersion method is ultrasonic dispersion; the drying is vacuum drying, the drying temperature is 60-120° C., and the drying time is 0.5-5 h.

6. The method for preparing a composite photocatalyst responsive to visible light according to claim 1, characterized in that: The calcination temperature is 300-500°C, and the calcination time is 0.5-5 h.

7. Use of a visible light responsive composite photocatalyst obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The method is applied to the oxygen production reaction under visible light, and includes the following steps: dispersing the CoO / Bi4TaO8Br composite photocatalyst in an aqueous solution containing an electron sacrificial agent; under the action of visible light, water is decomposed to produce oxygen.

8. The use of a visible light responsive composite photocatalyst according to claim 7, characterized in that: The electron sacrificial agent is AgNO3.

9. An application of a visible light responsive composite photocatalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The CoO / Bi4TaO8Br composite photocatalyst and Ru / SrTiO3:Rh construct a Z mechanism system, which is applied to the complete decomposition of water to produce hydrogen and oxygen under visible light.

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