BiOCl / TiO2 photocatalyst prepared by electrochemical method as well as preparation method and application of BiOCl / TiO2 photocatalyst

Abstract

The invention discloses a BiOCl / TiO2 photocatalyst prepared by an electrochemical method as well as a preparation method and application thereof, and the preparation method of the BiOCl / TiO2 photocatalyst comprises the following steps: 1) placing a Ti sheet subjected to surface pretreatment in an aqueous solution containing F <-> for anodic oxidation, and then placing the Ti sheet in a muffle furnace for heat treatment to obtain an anatase type TiO2 nanotube; 2) taking the TiO2 nanotube as a working electrode, and obtaining Bi nanocrystals in a water solution containing Bi (NO3) 3 with a certain concentration, lignin calcium benzenesulfonate and an emulsifier OP-10 by adopting a pulse electrodeposition method; 3, the sample with the Bi nanocrystals deposited is subjected to electrooxidation in a Cl <-> solution under the specific pH condition, and the BiOCl / TiO2 photocatalyst is obtained.The BiOCl / TiO2 photocatalyst prepared through the electrochemical method has the advantages of being stable in structure, high in CO2 photocatalytic reduction activity and high in product selectivity.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and photocatalysis, and particularly to a BiOCl / TiO2 photocatalyst prepared by an electrochemical method, its preparation method, and its application. Background Technology

[0002] BiOCl, as a ternary p-type semiconductor material, has attracted widespread attention due to its unique structure and optical properties, as well as its excellent photocatalytic activity, making it a promising candidate for applications in pollutant control, water splitting, carbon dioxide photoreduction, and N2 fixation.

[0003] Currently, BiOCl is mainly synthesized using chemical synthesis methods such as acid-base reaction, redox method (sodium hypochlorite as chlorine source), and solvothermal method. BiOCl powder prepared by these methods often has problems such as uneven particle size distribution or agglomeration, resulting in poor morphology controllability and easy introduction of impurities, which affects the photocatalytic performance of BiOCl.

[0004] Furthermore, the light absorption range of a single BiOCl catalyst is narrow, only absorbing and utilizing a small proportion (4%) of ultraviolet light in sunlight. This low solar energy utilization rate limits its practical application. Secondly, there is the problem of low charge transfer efficiency; after BiOCl photocatalysts are irradiated, most of the photogenerated electrons generated within them are lost. - and h + The process of recombining during migration to the catalyst surface results in only a small amount of photogenerated electrons. - and h + BiOCl-based composite catalysts participate in photocatalytic reactions. Therefore, developing highly efficient BiOCl-based composite catalysts, broadening their photoresponse range to the visible light region, and improving the separation and migration efficiency of photogenerated carriers are effective strategies for realizing their application in the field of photocatalysis. Summary of the Invention

[0005] To address the aforementioned technical problems of existing bismuth oxychloride catalysts, the present invention aims to provide an electrochemically prepared BiOCl / TiO2 photocatalyst, its preparation method, and its applications. The electrochemical method for preparing the BiOCl / TiO2 photocatalyst employed in this invention features stable processes, low energy consumption, and environmental friendliness, and exhibits high selectivity for the carbon dioxide reduction products. Organic additives are introduced during the Bi electrodeposition process to promote electrocrystallization nucleation and refine grain size, facilitating the deposition of Bi nanocrystals within the nano-TiO2 tubes and forming a stable embedded structure. Simultaneously, the electrodeposited Bi nanocrystals can be further electro-oxidized to form BiOCl with photocatalytic properties. By loading BiOCl onto a TiO2 substrate to form a PN junction, the separation and transport of photogenerated charges can be effectively promoted, photocatalytic efficiency improved, and stability and durability ensured.

[0006] The technical solution adopted in this invention is as follows: An electrochemical method for preparing BiOCl / TiO2 photocatalysts includes the following steps: Step 1: After surface pretreatment, the titanium sheet is used as the anode, and another conductive material is used as the cathode. In an electrochemical device, HF aqueous solution is used as the electrolyte, and anodic oxidation is performed under current. The anodic oxidized titanium sheet is placed in a tube furnace for heat treatment to obtain anatase TiO2 nanotubes on the surface of the titanium sheet. Step 2: Using the TiO2 nanotubes obtained in Step 1 as the cathode and another conductive material as the anode, the cathode and anode are placed in an acidic environment containing Bi. 3+ Bi nanocrystals / TiO2 were obtained by pulse electrodeposition in a deposition solution containing ions, organic additives with surface-active properties, and emulsifiers. Step 3: Using the Bi nanocrystals / TiO2 obtained in Step 2 as the anode and another conductive material as the cathode, in an acidic environment containing Cl... - Electrolytic oxidation was performed in an aqueous solution to obtain a BiOCl / TiO2 photocatalyst.

[0007] Further, in step 1, the surface pretreatment of the titanium sheet is as follows: first, it is polished step by step with sandpaper of different grits until there are no coarse scratches on its surface; then, it is chemically polished in an aqueous solution containing 70~80 g / L CrO3 and 1~5wt% HF at a reaction temperature of 45-55℃ for 10~20 min until the surface is bright.

[0008] Furthermore, the titanium sheet used in step 1 has a titanium content of 99.5 wt% or higher. It is polished step by step with 400-grit, 600-grit, 800-grit, and 1000-grit sandpaper until there are no large scratches on its surface.

[0009] Furthermore, in step 1, the process conditions for anodizing are as follows: the electrolyte is an aqueous solution containing 1~5wt% HF, the pretreated titanium sheet is used as the anode, the graphite electrode or platinum electrode is used as the cathode, the anodizing voltage is 15~35V, the time is 20~30min, and the temperature is 10~30℃.

[0010] Furthermore, the heat treatment process in step 1 involves controlling the heating rate to be 5~20℃ / min, raising the temperature from room temperature to a constant temperature heat treatment temperature of 350~550℃, and holding the temperature for 2~4 hours.

[0011] Furthermore, in step 2, Bi is adjusted using one of Bi(NO3)3, BiCl3, or Bi2(SO4)3. 3+ Ion concentration, Bi in the deposition solution 3+The ion concentration ranges from 0.3 to 0.7 mol / L, preferably from 0.4 to 0.5 mol / L, and the pH of the sediment is in the range of 1 to 3.

[0012] Further, in step 2, the solvent of the sedimentation solution is water, and the organic additive is selected from one or more of calcium lignin benzenesulfonate, sodium dodecylbenzenesulfonate, and epichlorohydrin. The final concentration of the organic additive in the sedimentation solution is 0.2~0.8 g / L, preferably 0.4~0.6 g / L. The emulsifier is emulsifier OP-10, which can assist in the dissolution of the organic additive. Its final concentration in the sedimentation solution is 0.8-5 mL / L.

[0013] In this invention, the organic additives have surface-active properties, which can improve the electrode surface environment and promote electrochemical reactions. The emulsifier OP-10 has no direct effect on the electrochemical reaction, but it can assist the dissolution of organic compounds such as calcium lignin benzenesulfonate, sodium dodecylbenzenesulfonate, and epichlorohydrin in solution, thereby indirectly affecting the reaction.

[0014] Furthermore, in step 2, Bi nanocrystals are deposited in situ within TiO2 nanotubes using pulsed electrodeposition, with a pulse peak current of -50 to -90 mA / cm². 2 The pulse period is 1-2 seconds, the duty cycle is 60%-90%, and the deposition time is 10-30 minutes. The preferred pulse peak current is -70 to -80 mA / cm². 2 The pulse period is 1.2~1.5s, the duty cycle is 75%~85%, and the deposition time is 20~25min.

[0015] Further, in step 3, one or more of NaCl, KCl, and NH4Cl are added to the electrolytic oxidation solution, preferably NaCl or Cl. - The ion concentration is controlled at 1~3 mol / L, preferably 2~2.5 mol / L. HCl is also added to the electrolytic oxidation solution to control the H2O content of the solution. + The concentration is 0.5~2 mol / L, preferably 0.8-1 mol / L.

[0016] Furthermore, in step 3, the Bi / TiO2 prepared in step 2 is electrochemically oxidized using a DC regulated power supply, with an oxidation current of 60~80 mA / cm². 2 Preferably, it is 65~70 mA / cm 2 The oxidation time is 10~30s, preferably 20~30s, and the oxidation temperature is 20~40℃.

[0017] The present invention also discloses the application of the BiOCl / TiO2 photocatalyst in the photocatalytic reduction of carbon dioxide to ethanol. The specific process is as follows: in a quartz reaction apparatus, deionized water and the prepared BiOCl / TiO2 photocatalyst are added, CO2 is introduced, the pressure is 0.8~1.2 Bar, and the reaction is continuously catalyzed under ultraviolet light irradiation. The composition of the liquid phase product is measured, and the photocatalytic performance is measured by the yield of ethanol produced.

[0018] The above-described solution of the present invention has the following beneficial effects: 1. This invention synthesizes BiOCl / TiO2 catalysts via a two-step process of electrochemical deposition and electrooxidation, such as... Figure 2 The XRD pattern shows that the sample exhibits high-intensity BiOCl characteristic diffraction peaks, and no characteristic peaks of metallic Bi were detected, indicating that after electro-oxidation treatment, the Bi nanocrystals in the precursor were completely transformed into the BiOCl phase, with no unreacted Bi residue. Meanwhile, the characteristic diffraction peaks of TiO2 are still clearly observed in the pattern, indicating that BiOCl did not continuously coat the TiO2 substrate to form a BiOCl / TiO2 composite structure. This process is stable, produces catalysts with uniform particle size, and solves the problems of uneven powder particle size distribution and agglomeration existing in traditional chemical synthesis methods.

[0019] 2. To promote Bi deposition within TiO2 nanotubes, this invention incorporates organic additives into the deposition solution. These additives refine the Bi grains generated by electroreduction and ensure their uniform loading within the TiO2 nanotubes. Figure 1 As shown, Bi is tightly deposited on the wall of TiO2 nanotubes, and the resulting embedded structure is beneficial to the stability of BiOCl nanoparticles.

[0020] 3. The BiOCl / TiO2 composite catalyst prepared in this invention utilizes the high specific surface area and ordered nanochannels of TiO2 to promote the transport of photogenerated carriers, enhance visible light absorption and optimize surface reaction pathways, effectively suppress electron-hole recombination, and improve photocatalytic performance.

[0021] 4. The BiOCl / TiO2 composite catalyst prepared by the electrochemical method in this invention significantly improves the reaction efficiency and selectivity of carbon dioxide photocatalytic reduction to ethanol, which is beneficial to the processing and utilization of subsequent products. Attached Figure Description

[0022] Figure 1 The images show SEM and EDS images of the Bi nanocrystals / TiO2 samples prepared by pulse electrodeposition according to this invention. Figure 2 The image shows the XRD pattern of the BiOCl / TiO2 photocatalyst prepared in Example 1 of this invention. Figure 3The macroscopic morphology and SEM image of BiOCl / TiO2 prepared in Example 1 of this invention; Figure 4 The macroscopic morphology and SEM image of BiOCl / TiO2 prepared in Comparative Example 1 of this invention are shown. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] In this embodiment of the invention, the pretreatment process of the titanium substrate is as follows: S1: The titanium sheet used has a titanium content of over 99.5 wt%. It is polished step by step with 400 grit, 600 grit, 800 grit and 1000 grit sandpaper until there are no large scratches on its surface.

[0025] S2: Then chemically polish the surface in an aqueous solution containing 75 g / L CrO3 and 2.5 wt% HF at a temperature of 50°C for 15 min until the surface is shiny.

[0026] Example 1: Preparation method and application of an electrochemically prepared BiOCl / TiO2 photocatalyst (1) Using a pretreated titanium substrate as the anode and a graphite sheet as the cathode, anodizing was performed in an electrochemical device. The electrolyte for anodizing was an aqueous solution containing 1 wt% HF. The constant voltage was 25 V, the time was 20 min, and the temperature was 25 °C. The anodized sample was placed in a tube furnace and heated to 450 °C with the furnace. The heating rate was controlled at 10 °C / min. Then, it was kept at 450 °C for 2 h and then slowly cooled to room temperature with the furnace. TiO2 nanotubes were obtained on the surface of the titanium sheet. (2) Using the TiO2 obtained from the anodization in step (1) as the cathode and the platinum electrode as the anode, Bi nanocrystals were deposited in a deposition solution containing 1 mol / L Bi(NO3)3, 0.5 g / L calcium lignin benzenesulfonate, and 1 ml / L emulsifier OP-10 (pH=1, solvent is water) by pulse electrodeposition. The peak pulse current was -70 mA / cm. 2 The pulse period was 1.2s, the duty cycle was 80%, and the deposition time was 20min, finally obtaining Bi nanocrystals / TiO2; (3) Using the Bi nanocrystals / TiO2 obtained in step (2) as the anode and the graphite sheet as the cathode, the electrolyte is a solution containing 1 mol / L H2O. + 2mol / L Cl - Aqueous solution (using HCl to adjust H+) + The concentration was then adjusted using NaCl. -(Concentration), electrochemical oxidation was performed using a DC regulated power supply with an oxidation current of 70 mA / cm². 2 The oxidation time was 30 s, and BiOCl was generated by electro-oxidation. The oxidized sample was washed with distilled water and dried in a vacuum drying oven at 50 ℃ to obtain the BiOCl / TiO2 photocatalyst electrode.

[0027] Experiment on photocatalytic reduction of CO2: The BiOCl / TiO2 photocatalyst electrode prepared in Example 1 was added to a quartz reaction apparatus, along with 10 ml of deionized water and CO2. The pressure was controlled at 1 Bar during the reaction. Under ultraviolet irradiation conditions, the wavelength was 380 nm and the power was 5 mW / cm². 2 The photocatalytic reaction was continued for 6 hours. Under the above photocatalytic reduction conditions, the liquid products after the reaction were determined by gas chromatography, and the ethanol yield was 7.2 μmol / cm³. 2 The unit of ethanol production is the amount of ethanol that can be catalyzed and produced per square centimeter of photocatalyst surface after the reaction.

[0028] Using the TiO2 nanotubes prepared in step (1) of Example 1 as the photocatalyst, replacing the "BiOCl / TiO2 photocatalyst" prepared in Example 1, under the above photocatalytic reaction conditions, the ethanol yield was only 1.2 μmol / cm³. 2 .

[0029] Comparing the BiOCl / TiO2 photocatalyst prepared by electrochemical method in Example 1 of this invention with the TiO2 nanotube photocatalyst, it is shown that the BiOCl / TiO2 catalyst has good photocatalytic performance and can synthesize ethanol products with high selectivity.

[0030] SEM and EDS images of the Bi nanocrystals / TiO2 sample prepared in step (2) of Example 1 of this invention are shown below. Figure 1 It can be seen that the Bi grains generated by electroreduction are refined and uniformly loaded in TiO2 nanotubes. Bi is tightly deposited on the tube wall of TiO2 nanotubes, and the resulting embedded structure is beneficial to the stability of BiOCl nanoparticles.

[0031] The XRD pattern of the BiOCl / TiO2 photocatalyst prepared in Example 1 of this invention is shown below. Figure 2As shown in Figure 1, a high-intensity BiOCl characteristic diffraction peak appeared in the sample, and no characteristic peak of elemental Bi was detected. This indicates that after electro-oxidation treatment, the Bi nanocrystals in the precursor were completely transformed into the BiOCl phase, with no unreacted elemental Bi residue. Combined with Figure 1, it can be inferred that BiOCl is anchored to the surface of the TiO2 nanotube wall in a tightly deposited form, forming a BiOCl / TiO2 composite structure. This close-contact deposition method is beneficial for constructing a stable pn heterojunction. The built-in electric field at the heterojunction interface accelerates the separation and migration of photogenerated electron-hole pairs, reducing the carrier recombination probability and thus significantly improving the photocatalytic activity of the material.

[0032] Comparative Example 1: The preparation method of BiOCl / TiO2 photocatalyst in Comparative Example 1 is the same as that in Example 1, except that "the deposition solution in step (2) does not contain calcium lignin benzenesulfonate and emulsifier OP-10, and becomes a deposition solution containing 1 mol / L Bi(NO3)3 (pH=1)", and the other conditions remain unchanged, and finally BiOCl / TiO2 photocatalyst is obtained.

[0033] The photocatalytic reaction experiment in Comparative Example 1 was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Comparative Example 1 was used instead of the BiOCl / TiO2 photocatalyst in Example 1; all other conditions remained unchanged. The test results showed that the ethanol yield of Comparative Example 1 was only 3.5 μmol / cm³. 2 .

[0034] Figure 3 The macroscopic morphology and SEM image of BiOCl / TiO2 prepared in Example 1 of the present invention are shown in the figure. Macroscopically, the deposited layer is dense and flat, and microscopically, BiOCl is uniformly distributed as spherical particles on TiO2. Figure 4 The macroscopic morphology and SEM image of the BiOCl / TiO2 photocatalyst prepared in Comparative Example 1 of the present invention show poor deposition effect and local peeling on a macroscopic scale, while BiOCl is loosely distributed in a dendritic form on a microscopic scale. Figure 3 and Figure 4 The comparison shows that the addition of calcium lignin benzenesulfonate and emulsifier OP-10 to the deposition solution refines the grains generated by electroreduction and uniformly loads them within the TiO2 nanotubes. This significantly improves the uniformity and bonding strength of the final BiOCl deposition layer, which is beneficial for subsequent CO2 photocatalytic reactions.

[0035] Comparative Example 2: The preparation method of BiOCl / TiO2 photocatalyst in Comparative Example 2 is the same as that in Example 1, except that "the organic additive in the deposition solution in step (2) is changed to 0.5 g / L sodium dodecylbenzene sulfonate, and the deposition solution is changed to contain 1 mol / L Bi(NO3)3 and 0.5 g / L sodium dodecylbenzene sulfonate (pH=1)", and the other conditions remain unchanged, and finally BiOCl / TiO2 photocatalyst is obtained.

[0036] The photocatalytic reaction experiment in Comparative Example 2 was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Comparative Example 2 was used instead of the BiOCl / TiO2 photocatalyst in Example 1; all other conditions remained unchanged. The test results showed that the ethanol yield of Comparative Example 2 was only 5.1 μmol / cm³. 2 .

[0037] Comparing the test results of Example 1, Comparative Example 1, and Comparative Example 2 of this invention, it can be seen that: sodium dodecylbenzenesulfonate can promote the deposition of bismuth as fine particles, but it is prone to local enrichment leading to inhomogeneity; calcium ligninbenzenesulfonate guides metal ions to deposit uniformly and densely along preferred crystal planes, without dendrites or byproducts. Comparing the photocatalytic performance of BiOCl / TiO2 photocatalysts obtained by electro-oxidation of Bi / TiO2 prepared by these two methods, calcium ligninbenzenesulfonate and OP-10 as organic additives show better electrodeposition effects on Bi than sodium dodecylbenzenesulfonate. Furthermore, the uniformity and bonding strength of the final BiOCl deposition layer are significantly improved, which is beneficial for CO2 photocatalytic reactions.

[0038] Example 2: The preparation method of BiOCl / TiO2 photocatalyst in Example 2 is the same as that in Example 1, except that in step (2), Bi nanocrystals are deposited by electrodeposition method, but not by pulse electrodeposition method. Instead, Bi is deposited by direct current electrodeposition method with a constant current density of -70mA / cm. 2 The deposition time was 20 min, and all other conditions remained unchanged, finally obtaining the BiOCl / TiO2 photocatalyst.

[0039] The photocatalytic reaction experiment in Example 2 was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Example 2 was used instead of the BiOCl / TiO2 photocatalyst in Example 1; all other conditions remained unchanged. The test results showed that the ethanol yield was 4.2 μmol / cm³. 2 .

[0040] Comparing the test results of Examples 1 and 2 of this invention, it can be seen that the catalyst prepared by electrodepositing Bi on TiO2 using constant current mode has poor performance. This is because the electrodeposition is performed using direct current, resulting in a thick diffusion layer at the cathode-solution interface. This reduces the concentration of metal ions on the cathode surface, causing concentration polarization, which limits the electrodeposition rate, reduces current efficiency, and deteriorates the electrodeposition quality. Pulse electroplating, due to its off-time, allows the consumed metal ions to diffuse and replenish near the cathode during this period. When the next conduction time arrives, the concentration of metal ions near the cathode recovers, thereby improving the deposition quality and ultimately enhancing the photocatalytic performance of the product.

[0041] Example 3: The preparation method of BiOCl / TiO2 photocatalyst in Example 3 is the same as that in Example 1, except that the pulse peak current is changed in step (2), while the other conditions remain unchanged, and BiOCl / TiO2 photocatalyst is finally obtained.

[0042] The photocatalytic reaction experiment in Example 3 was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Example 3 was used instead of the BiOCl / TiO2 photocatalyst in Example 1, while all other conditions remained unchanged. Table 1 shows the comparison results of ethanol yield from the photocatalytic reaction of the photocatalysts prepared under different pulse peak currents in Example 3.

[0043] Table 1 .

[0044] Example 4: The preparation method of BiOCl / TiO2 photocatalyst in Example 4 is the same as that in Example 1, except that "the final concentration of Bi(NO3)3 in the deposition solution is changed in step (2)," while the other conditions remain unchanged, and BiOCl / TiO2 photocatalyst is finally obtained.

[0045] The photocatalytic reaction experiment in Example 4 was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Example 4 was used instead of the BiOCl / TiO2 photocatalyst in Example 1, while all other conditions remained unchanged. Table 2 shows the comparison results of the ethanol yield of the photocatalysts prepared in the pulse electrodeposition solution of Example 4 at different final concentrations of Bi(NO3)3.

[0046] Table 2 .

[0047] Example 5: The preparation method of BiOCl / TiO2 photocatalyst in Example 5 is the same as that in Example 1, except that "step (3) changes the H in the electrolytic oxidation solution". + Concentration, Cl -"Keep the concentration at 2 mol / L" and keep other conditions unchanged to finally obtain the BiOCl / TiO2 photocatalyst.

[0048] Example 5: The photocatalytic reaction experiment was the same as in Example 1, except that the BiOCl / TiO2 photocatalyst prepared in Example 5 was used instead of the BiOCl / TiO2 photocatalyst in Example 1; all other conditions remained unchanged. Example 5: Electrolytic oxidation solution with different H... + The results of the ethanol yield of the photocatalyst prepared at the specified concentration are shown in Table 3.

[0049] Table 3 .

Claims

1. A method for preparing a BiOCl / TiO2 photocatalyst by an electrochemical method, characterized in that The method comprises the following steps: Step 1: the titanium sheet is pre-treated on the surface, and then is used as an anode in an electrochemical device with another conductive material as a cathode and an aqueous HF solution as an electrolyte, and is anodized under electricity, and the titanium sheet after anodic oxidation is heat-treated in a tubular furnace to obtain anatase TiO2 nanotubes on the surface of the titanium sheet; Step 2: The TiO2nanotubes obtained in Step 1 are used as cathode and another conductive material is used as anode, and the cathode and anode are subjected to pulse electrodeposition in a deposition solution containing Bi 3+ nanocrystals / TiO2is obtained. Step 3: Electrolytic oxidation was carried out in a pH acidic Cl - aqueous solution with the Bi nanocrystals / TiO2 obtained in step 2 as anode and another conductive material as cathode to obtain BiOCl / TiO2 photocatalyst.

2. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 1, the surface pre-treatment of the titanium sheet comprises the following steps: firstly, the titanium sheet is polished by using sandpaper with different mesh numbers until the surface is free of rough scratches; and then the titanium sheet is chemically polished in an aqueous solution containing 70-80 g / L CrO3 and 1-5 wt% HF, the reaction temperature is 45-55℃, and the reaction time is 10-20 min until the surface is bright.

3. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 1, the process conditions of anodic oxidation are as follows: the electrolyte is an aqueous solution containing 1-5 wt% HF, the pre-treated titanium sheet is used as an anode, a graphite electrode or a platinum electrode is used as a cathode, the voltage of anodic oxidation is 15-35 V, the time is 20-30 min, and the temperature is 10-30℃.

4. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 1, the heat treatment process is as follows: the temperature rising rate is controlled to be 5-20℃ / min, the temperature is raised from room temperature to a constant temperature heat treatment temperature, the constant temperature heat treatment temperature is 350-550℃, and the holding time is 2-4 h.

5. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 2, Bi is adjusted with one of Bi(NO3)3, BiCl3, Bi2(SO4)3 3+ Ion concentration, Bi in the deposition solution 3+ Ion concentration range 0.3-0.7 mol / L, preferably 0.4-0.5 mol / L, pH of the deposition solution in the range 1-3; In step 2, the solvent of the deposition solution is water, the organic additive is selected from one or more of calcium lignosulfonate, sodium dodecylbenzenesulfonate and epichlorohydrin, the final concentration of the organic additive in the deposition solution is 0.2-0.8 g / L, and preferably 0.4-0.6 g / L; the emulsifier is emulsifier OP-10, which can assist the dissolution of the organic additive, and the final concentration of the emulsifier OP-10 in the deposition solution is 0.8-5 mL / L.

6. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 2, Bi nanocrystals are in-situ deposited in the TiO2 nanotubes by pulse electrodeposition with a pulse peak current of -50 to -90 mA / cm 2 , a pulse period of 1 to 2 s, a duty cycle of 60% to 90%, and a deposition time of 10 to 30 min.

7. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 3, one or more of NaCl, KCl, NH4Cl is added to the electrolytic oxidation solution, and Cl - The ion concentration is controlled at 1-3 mol / L, and HCl is added to the electrolytic oxidation solution to control the H + The concentration is controlled at 0.5-2 mol / L, preferably 0.8-1 mol / L.

8. The method for preparing BiOCl / TiO2 photocatalyst by electrochemical method according to claim 1, characterized in that In step 3, a direct current stabilized power supply is used to electrochemically oxidize the Bi / TiO2 prepared in step 2, the oxidation current is 60-80 mA / cm 2 , the oxidation time is 10-30 s, and the oxidation temperature is 20-40℃.

9. The BiOCl / TiO2 photocatalyst prepared by the method according to any one of claims 1-8.

10. The application of the BiOCl / TiO2 photocatalyst according to claim 9 in photocatalytic reduction of carbon dioxide to synthesize ethanol.

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