A preparation method and application of hematite photoanode for photoelectrochlorination reaction

Abstract

The application belongs to the field of photoelectrocatalysis, and particularly relates to a preparation method of hematite photoanode for photoelectrochlorination and application thereof. The preparation method comprises the following steps: S1: performing hydrothermal reaction on a first mixed solution comprising iron salt, nitrate salt and doped metal salt in an environment with a conductive substrate to obtain a first iron oxyhydroxide electrode and annealing to obtain a hematite electrode; S2: adding the hematite electrode into a second mixed solution containing iron salt, nitrate salt, doped metal salt and ammonium salt to perform hydrothermal reaction to obtain a second iron oxyhydroxide electrode and annealing to obtain a hematite photoanode. The application can realize efficient photoelectrocatalytic electrophilic chlorination, can efficiently and selectively oxidize chloride ions to form active chlorine positive species (HClO), can inhibit water oxidation side reactions, can have high electrophilic chlorination selectivity (up to 99%) and can have high current efficiency (FE up to 90%).

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis, and particularly relates to a method for preparing a hematite photoanode for photoelectro-chlorination reactions and its application, especially in the application of efficiently activating chloride ions to achieve electrophilic chlorination reactions. Background Technology

[0002] Electrophilic chlorination is an important chemical process used to synthesize valuable organochlorides, such as benzene ring chlorides and chlorohydrin compounds. These organochlorides are widely used in pharmaceuticals, agrochemicals, and organic materials to modify their biological or physicochemical properties. Simultaneously, these chlorides are crucial raw materials for cross-coupling reactions and play a vital role in industrial-scale epoxidation reactions.

[0003] Traditionally, the synthesis of organochlorides usually requires the use of excess chlorine gas (Cl2). Cl2 is a bulky chemical substance. Although it can be obtained through the chlor-alkali industry, directly using excess Cl2 for chlorination reactions has drawbacks such as harsh processing, low chlorine atom utilization, and the generation of corrosive hydrochloric acid, which limit its development.

[0004] In recent years, electrically driven organic matter conversion has shown great potential. Among them, electrochemical oxidative chlorination technology has made breakthrough progress. Its characteristics are the use of inert and readily available chlorine sources, such as sodium chloride (NaCl), and the effective control of the Cl2 formation rate by adjusting electrochemical parameters, ensuring optimal Cl2 utilization and minimizing Cl2 escape, which facilitates the post-processing of the chlorination reaction; at the same time, it couples with "green energy" reactions such as hydrogen evolution, reducing carbon emissions.

[0005] However, due to the high thermodynamic potential required for Cl2 formation (E = 1.36 V vs. RHE), triggering the chlorine evolution reaction (CER) still requires a high applied potential and thus depends on a large amount of energy input. Solar energy is the most abundant renewable energy source and is considered the ultimate solution to the global energy problem. Therefore, solar photoelectrochemical catalysis (PEC) chlorination is a promising green chemistry technology that can significantly reduce energy input. Currently, photoelectrochemical chlorination reactions are rarely reported, and the selective control of the chlorine activation process leads to the simultaneous generation of multiple active chlorine species (·Cl, Cl2, HClO) and competitive reactive oxygen species (·OH, H2O2) formed by water oxidation, resulting in unsatisfactory photoelectrochemical chlorination activity. Therefore, how to achieve a more efficient and environmentally friendly photoelectrochemical chlorination reaction is an urgent problem to be solved. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for preparing a hematite photoanode for photoelectro-chlorination reactions and its application. This method enables highly efficient photoelectro-catalyzed electrophilic chlorination reactions, efficiently and selectively oxidizing chloride ions to form active chlorine species (HClO), suppressing water oxidation side reactions, and exhibiting high electrophilic chlorination selectivity (up to 99%) and high current efficiency (FE up to 90%).

[0007] In a first aspect, the present invention provides a method for preparing a hematite photoanode for photoelectrochlorination reactions, comprising the following steps:

[0008] S1. Hematite photoanode is prepared by a two-step hydrothermal-annealing method. A first mixed solution including iron salt, nitrate and doped metal salt is subjected to hydrothermal reaction in an environment with a conductive substrate to obtain a first hydroxyl iron oxide electrode, which is then annealed to obtain a hematite electrode.

[0009] S2. The hematite electrode is added to a second mixed solution containing iron salt, nitrate, doped metal salt and ammonium salt for hydrothermal reaction to obtain a second hydroxyl iron oxide electrode, which is then annealed to obtain a hematite photoanode.

[0010] According to an embodiment of the present invention, the molar ratio of iron salt, nitrate and doped metal salt in step S1 is 1.5:1:(0 to 0.012), for example 1.5:1:0.006.

[0011] According to an embodiment of the present invention, the temperature of the hydrothermal reaction in step S1 is 80-100°C and the time is 3-5 hours. For example, the temperature of the hydrothermal reaction is 95°C and the time is 4 hours.

[0012] According to an embodiment of the present invention, the annealing in step S1 includes the following steps: first, raising the temperature to 500-600°C and annealing for 1-3 hours, then raising the temperature to 620-700°C and annealing for 10-30 minutes, for example, first raising the temperature to 550°C and annealing for 2 hours, then raising the temperature to 650°C and annealing for 20 minutes.

[0013] According to an embodiment of the present invention, the rate of temperature increase is 1–8 °C / min. -1 For example, 5℃ min -1 .

[0014] According to an embodiment of the present invention, the molar ratio of iron salt, nitrate, doped metal salt and ammonium salt in step S2 is 1.5:1:(0-0.012):(0-3), for example 1.5:1:0.06:1.5.

[0015] According to an embodiment of the present invention, the temperature of the hydrothermal reaction in step S2 is 80-100°C and the time is 3-5 hours. For example, the temperature of the hydrothermal reaction is 95°C and the time is 4 hours.

[0016] According to an embodiment of the present invention, the annealing in step S2 includes the following steps: first, raising the temperature to 500-600°C and annealing for 1-3 hours, then raising the temperature to 620-700°C and annealing for 10-30 minutes, for example, first raising the temperature to 550°C and annealing for 2 hours, then raising the temperature to 650°C and annealing for 20 minutes.

[0017] According to an embodiment of the present invention, the rate of temperature increase is 1–8 °C / min. -1 For example, 5℃ min -1 .

[0018] According to an embodiment of the present invention, the iron salt is selected from trivalent iron salts, preferably ferric nitrate, ferric chloride, ferric acetate or ferric sulfate, such as ferric chloride.

[0019] According to an embodiment of the present invention, the nitrate is selected from at least one of alkali metal nitrates, such as sodium nitrate.

[0020] According to an embodiment of the present invention, the doped metal salt is selected from at least one of soluble titanium salt, soluble palladium salt, and soluble platinum salt, for example, titanium tetrachloride.

[0021] According to an embodiment of the present invention, the doped metal salt is used for bulk doping to improve the conductivity of the semiconductor and increase the photocurrent.

[0022] According to an embodiment of the present invention, the conductive substrate is selected from a conductive substrate containing tin oxide; for example, it is fluorine-doped tin oxide conductive glass (FTO), wherein the FTO has a length of 4cm, a width of 2cm, and a thickness of 2.2mm.

[0023] Secondly, the present invention provides a hematite photoanode prepared by the method described above.

[0024] According to an embodiment of the present invention, the hematite photoanode has a basic as follows: Figure 1 The X-ray diffraction pattern shown.

[0025] According to an embodiment of the present invention, the hematite photoanode has a basic as follows: Figure 2 The scanning electron microscope image shown.

[0026] According to an embodiment of the present invention, the hematite photoanode has a basic as follows: Figure 3 The titanium metal doping dispersion diagram shown is shown.

[0027] According to an embodiment of the present invention, the hematite photoanode has a nanorod stacked structure at the microscale.

[0028] Thirdly, the present invention also provides an electrolytic cell for photoelectrochlorination reaction, the electrolytic cell comprising the hematite photoanode as described above.

[0029] According to an embodiment of the present invention, the hematite photoanode is the working electrode.

[0030] According to an embodiment of the present invention, the electrolytic cell further includes a reference electrode and a counter electrode. The reference electrode is selected from silver chloride, saturated calomel electrode, etc., and the counter electrode is selected from platinum, graphite rod, nickel foam, copper foam, etc.; for example, the reference electrode is saturated silver chloride, and the counter electrode is platinum wire.

[0031] According to an embodiment of the present invention, the electrolytic cell is provided with an electrolyte, the electrolyte comprising an alkali metal halide and a supporting electrolyte, wherein the alkali metal halide is selected from at least one of sodium chloride, potassium chloride, lithium chloride, etc., and the supporting electrolyte comprises at least one of sodium perchlorate, lithium perchlorate, tetraethylammonium tetrafluoroborate, etc., for example, sodium chloride and sodium perchlorate.

[0032] According to an embodiment of the present invention, the concentration of the alkali metal halide in the electrolyte is 10-200 mM, preferably 50-150 mM, and more preferably 80-120 mM.

[0033] As an example, the alkali metal halide is selected from a sodium chloride solution, wherein the concentration of sodium chloride in the sodium chloride solution is 100-200 mM.

[0034] As an example, the supporting electrolyte is selected from a sodium perchlorate solution, wherein the concentration of sodium perchlorate in the sodium perchlorate solution is 0-100 mM.

[0035] According to an embodiment of the present invention, the solvent in the salt solution is selected from salt and good solvents for organic substrates, preferably a mixed solution containing water and organic solvent, such as an acetonitrile-water mixed solution with a volume ratio of 1:1.

[0036] According to an embodiment of the present invention, the electrolytic cell further includes a light-illuminating mechanism, which is used to simulate sunlight and illuminate the electrolytic cell to provide a light source for the photoelectric reaction.

[0037] According to an embodiment of the present invention, in order to prevent interference between the cathode and anode reactions, a dual-chamber electrolytic cell separated by a proton exchange membrane is required, preferably with an electrolyte volume of 10 ml in each of the cathode and anode chambers.

[0038] Fourthly, the present invention also provides a method for photoelectrochlorination reaction, comprising the following steps:

[0039] The reaction substrate is added to the electrolytic cell as described above, and a voltage is applied under light to perform photoelectrolysis to obtain the chlorinated product.

[0040] According to embodiments of the present invention, the reaction substrate is selected from aromatic compounds and olefin compounds with electron-rich substituents. Aromatic compounds include anisole, acetanilide, toluene, and trimethoxybenzene; olefin compounds include styrene, p-methylstyrene, p-chlorostyrene, p-bromostyrene, α-methylstyrene, such as acetanilide and styrene.

[0041] According to an embodiment of the present invention, the concentration of the reaction substrate in the electrolyte is 0.05 to 0.3 mmol, for example, 0.1 mmol.

[0042] According to an embodiment of the present invention, the voltage value is 0.6 to 1.1 V vs. Ag / AgCl.

[0043] According to an embodiment of the present invention, the light intensity is 50–300 mW / cm². -2 For example, 100mW cm -2 .

[0044] According to an embodiment of the present invention, the photoelectrolysis time is 1 to 4 hours, for example, 2 hours.

[0045] According to an embodiment of the present invention, under illumination and applied voltage conditions, the photogenerated holes generated by the hematite photoanode selectively oxidize chloride ions to form active chlorine cations (“Cl…”). + ) species, simultaneously reacting with the substrate and the resulting active "Cl + "Species (e.g., HClO) react to produce chlorinated products."

[0046] As an example, when the electrolyte contains 10 mM sodium chloride and 90 mM sodium perchlorate solution, compared to a solution containing only 100 mM sodium perchlorate supporting the electrolyte, the light intensity is 100 mW cm⁻¹. -2 At 1.0V vs. Ag / AgCl, the photocurrent decreased from 0.7 mA cm⁻¹. -2 Increased to 1.1 mA cm -2 This indicates that chloride ions can be selectively and preferentially oxidized, suppressing water oxidation side reactions.

[0047] According to an embodiment of the present invention, the electrophilic Faraday efficiency (FE) of the photoelectrochlorination reaction is greater than or equal to 85%, preferably ≥88%, for example 90%.

[0048] According to an embodiment of the present invention, the photoelectrochlorination reaction has high selectivity, preferably para-chlorination selectivity for monosubstituted chlorinated products of electron-rich benzene rings, wherein the selectivity is ≥90%, preferably greater than or equal to 95%, for example 98%, and for example, the ortho / para ratio of the chlorinated product is 1:1.6.

[0049] As an example, when the reaction substrate is acetanilide, the electrophilic Faraday efficiency is 90%, and the chlorination product includes monosubstituted acetanilide and polysubstituted acetanilide, wherein the proportion of monosubstituted acetanilide is greater than or equal to 95%, and the ratio of o-chloroacetanilide to p-chloroacetanilide is 1:1.6.

[0050] As an example, when the reaction substrate is styrene, the electrophilic Faraday efficiency is 80%, and the chlorination products include 2-chloro-1-phenylethanol and α,β-dichlorostyrene, preferably the proportion of 2-chloro-1-phenylethanol is greater than or equal to 80%.

[0051] As an example, when the reaction substrate is a mixture of sodium chloride and acetanilide, the hydrogen production rate increases from 22 μmol / h compared to when only sodium perchlorate is used. -1 Increased to 47 μmol h -1 .

[0052] According to an embodiment of the present invention, after several cycles of the photoelectrochlorination reaction, the Faraday efficiency of the electrophilic chlorination reaction is maintained at 89-91%, for example, after 6 cycles, the Faraday efficiency is maintained at 90%.

[0053] Beneficial effects

[0054] 1) The preparation method of the present invention only requires first performing a hydrothermal reaction and annealing of iron salt, nitrate and doped metal salt, and then adding iron salt, nitrate and doped metal salt and ammonium salt to perform a hydrothermal reaction and annealing again to obtain hematite anode. The reaction steps are simple, the raw materials are readily available, the cost is low, and there is no need to perform complex modifications on the obtained hematite anode.

[0055] 2) The hematite anode prepared in this invention, when used in a photoelectric chlorination reaction, selectively oxidizes chloride ions through photogenerated holes generated by the hematite photoanode to form active chlorine cations (“Cl…”). + ) species, simultaneously reacting with the substrate and the resulting active "Cl +"The reaction of species (e.g., HClO) generates chlorination products, enabling highly efficient photoelectrocatalytic electrophilic chlorination. It can efficiently and selectively oxidize chloride ions to form active chlorine species (HClO), suppress water oxidation side reactions, and achieve high electrophilic chlorination selectivity (up to 99%) and high current efficiency (FE up to 90%). Moreover, after several cycles, the Faraday efficiency of the electrophilic chlorination reaction remains at 89-91%."

[0056] 3) The photoelectric chlorination system containing hematite anode in this invention has electrophilic chlorination performance far superior to that of traditional titanium dioxide photoanodes, providing a new strategy for achieving green and efficient electrophilic chlorination reactions and efficient utilization of solar energy. Attached Figure Description

[0057] Figure 1 The X-ray diffraction pattern of the hematite photoanode (labeled as α-Fe2O3 in the figure) prepared in Example 1 is shown.

[0058] Figure 2 This is a scanning electron microscope image of the hematite photoluminescence prepared in Example 1.

[0059] Figure 3 This is a schematic diagram of titanium doping in the hematite photoanode prepared in Example 1.

[0060] Figure 4 The linear sweep voltammetric curve is shown for the hematite photoanode in Example 2.

[0061] Figure 5 This is a comparison of the benzene ring chlorination reaction performance on hematite photoanode and titanium dioxide photoanode (marked as TiO2 in the figure) in Example 3.

[0062] Figure 6 This is a comparison of the chlorohydrination reaction performance of hematite photoanode and titanium dioxide photoanode in Example 3.

[0063] Figure 7 This is a performance comparison of the hydrogen evolution reaction coupled with the electrophilic chlorination reaction and the water oxidation reaction on the hematite photoanode in Example 4.

[0064] Figure 8 This is for the confirmation of the chlorine-active species in Example 5.

[0065] Figure 9 Cyclic stability test of electrophilic chlorination reaction on hematite photoanode in Example 6. Detailed Implementation

[0066] The following detailed description, with reference to specific embodiments, illustrates the hematite photoanode used in electrophilic chlorination reactions of the present invention, its preparation method, and its application. It should be understood that the following embodiments are merely illustrative and explanatory of the invention and should not be construed as limiting the scope of protection of the invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0067] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0068] Example 1

[0069] 1.1 Weigh 2.43 g of ferric chloride and 0.86 g of sodium nitrate into 100 mL of aqueous solution, then add 120 μl of 0.5 M titanium tetrachloride aqueous solution and stir until homogeneous to obtain hydrothermal precursor solution A.

[0070] 1.2 Weigh 1.23g of ferric chloride and 0.43g of sodium nitrate and place them in 95mL of H2O. Then add 60μl of 0.5M titanium tetrachloride aqueous solution and 5mL of 0.15M ammonium fluoride aqueous solution and stir well to obtain hydrothermal precursor solution B.

[0071] 1.3 Place the cleaned FTO (fluorine-doped SnO2 conductive glass) glass into the lining of a 20ml hydrothermal reactor, add 7.5ml of precursor solution A, then tighten and place it in an oven. Set the temperature to 95℃ and hydrothermally heat for 4 hours to obtain a yellow iron hydroxyl oxide electrode.

[0072] 1.4 Rinse the obtained iron hydroxyl oxide electrode with deionized water, then place it in a muffle furnace and incubate at 5°C for 1 minute. -1 The temperature was increased to 550℃, annealed at 550℃ for 2 hours, then increased to 650℃ and annealed for 20 minutes. Finally, it was naturally cooled to room temperature to obtain a hematite electrode.

[0073] 1.5 Place the hematite electrode obtained in step 1.4 into the lining of a 20ml hydrothermal reactor, add 7.5ml of precursor solution B, then tighten and place it in an oven, set the temperature to 95℃, and hydrothermally heat for 4 hours to obtain an iron hydroxyl oxide electrode.

[0074] 1.6 Rinse the ferric hydroxide electrode obtained in step 1.5 with deionized water, then place it in a muffle furnace and incubate at 5°C for 1 minute. -1 The heating rate was increased to 550℃, annealed at 550℃ for 2 hours, then heated to 650℃ and annealed for 20 minutes. Finally, it was naturally cooled to room temperature to obtain the final hematite photoanode.

[0075] See Figure 1The figure shows the X-ray diffraction pattern of the hematite photoanode prepared in this embodiment. As can be seen from the figure, the obtained product has high crystallinity and is consistent with the PDF standard card (PDF#79-0007), which proves the successful preparation of the hematite photoanode.

[0076] See Figure 2 The image shown is a scanning electron microscope (SEM) image of the hematite photoanode prepared in this embodiment. As can be seen from the image, the hematite photoanode exhibits a nanorod-like structure.

[0077] See Figure 3 The image shown is a high-resolution transmission electron microscope image of the hematite photoanode prepared in this embodiment. As can be seen from the image, Ti metal is uniformly doped on the hematite photoanode.

[0078] Example 2

[0079] Photocurrent test: This test is performed in a standard three-electrode system.

[0080] The testing system is as follows: The hematite photoanode prepared in Example 1 was used as the working electrode, platinum wire as the counter electrode, and saturated silver chloride as the reference electrode. The light source was a 300W xenon lamp equipped with an AM 1.5G filter. The light intensity was measured to be 100 mW cm⁻¹ using a photometer. -2 The test method used was linear scanning voltammetry, with a scan range of -0.2 to 1.2 V vs. Ag / AgCl and a scan rate of 50 mV / s. -1 .

[0081] The test solutions include 0.1M sodium perchlorate, 10mM sodium chloride, 25mM sodium chloride, 50mM sodium chloride, 100mM sodium chloride, and 200mM sodium chloride.

[0082] See Figure 4 The figure shows the linear sweep voltammetry curve of the hematite photoanode prepared in Example 1. The photocurrent in 0.1M sodium perchlorate (NaClO4) represents the performance of photoelectrocatalytic water oxidation. When testing in 10mM to 50mM sodium chloride, sodium perchlorate needs to be added to support the electrolyte and improve conductivity. The amount added is 50-90mM, that is, to maintain the total Na ion concentration in the solution at 0.1M. When testing in 100mM to 200mM sodium chloride, no additional sodium perchlorate is required.

[0083] from Figure 4It can be seen that under no light conditions, there is no photocurrent in 0.1M sodium perchlorate (NaClO4) within the voltage range of -0.2V to 1.2V; under light conditions, there is a small amount of water oxidation current in 0.1M sodium perchlorate (NaClO4); the photocurrent of the hematite photoanode gradually increases with the increase of chloride ion concentration in the solution (10mM, 25mM, 50mM, 100mM, 200mM), indicating that the increased photocurrent comes from the oxidation of chloride ions.

[0084] Example 3

[0085] Photoelectrolysis experiment: The test system used in this embodiment is the same as that in embodiment 2. At the same time, a titanium dioxide anode is set as a comparative example.

[0086] The testing method was changed to chronoamperometry: 0.1 mmol of acetanilide or styrene was added as the reaction substrate, the applied voltage was set to 1.0 V vs. Ag / AgCl, and the testing time was set to 2 h. The test system was placed under simulated sunlight, and the voltage was applied to start photoelectrolysis. After 2 h of photoelectrolysis, the conversion products of the reaction substrate were quantitatively analyzed using liquid chromatography, and the Faradaic efficiency of each product was calculated. The reaction equations are as follows:

[0087]

[0088] See Figure 5 The figure shows a performance comparison of the benzene ring chlorination reaction (acetanilide chlorination reaction) on the hematite photoanode prepared in Example 1 and the traditional titanium dioxide photoanode. It can be clearly seen from the figure that the benzene ring chlorination activity on the hematite photoanode is significantly higher than that on the titanium dioxide photoanode. The chlorination Faradaic efficiency (FE) can reach 90%, and the selectivity of the monosubstituted benzene ring chlorination product can reach more than 95%. Among them, the ortho / para position of the chlorinated product is 1:1.6, which shows high para chlorination substitution selectivity.

[0089] See Figure 5 The figure shows a comparison of the performance of the chlorohydrin reaction on the hematite photoanode prepared in Example 1 and the traditional titanium dioxide photoanode. As can be seen from the figure, the chlorohydrin reaction activity on the hematite photoanode is significantly higher than that on the titanium dioxide photoanode. The chlorination Faraday efficiency (FE) on the hematite photoanode can reach 80%, and the chlorohydrin product selectivity can reach more than 80%.

[0090] Example 4

[0091] "Green hydrogen" generation performance: The test system was the same as in Example 2, with the addition of a mixture of reaction substrate sodium chloride (0.1 mM) and acetanilide (0.1 mmol), or sodium perchlorate (0.1 mM) as the supporting electrolyte. The applied voltage was set to 1.0 V vs. Ag / AgCl, and the test time was set to 2 h. The test system was placed under simulated sunlight, and the voltage was applied to start photoelectrolysis. After 2 h of photoelectrolysis, the hydrogen production was quantitatively analyzed using a gas chromatograph.

[0092] from Figure 7 It can be seen that the photocurrent and hydrogen production rate of the photocatalytic electrophilic chlorination reaction on the hematite photoanode are significantly greater than those of the simple water splitting reaction, with the hydrogen production rate increasing from 22 μmol / h. -1 Increased to 47 μmol h -1 .

[0093] Example 5

[0094] Identification of chlorine-reactive species: Electrophilic chlorination reactions mainly depend on the electrophilic "Cl" + "To achieve the chlorination reaction, HClO was directly used as the electrophilic chlorinating reagent. After 2 hours of reaction, the product was analyzed by liquid chromatography and compared with the product distribution and selectivity of acetanilide chlorination on the hematite photoanode to determine the active chlorine species formed on the hematite photoanode."

[0095] from Figure 8 As can be seen, the benzene ring chlorination activity on the hematite photoanode is consistent with the product selectivity and ortho / para ratio (p / o) when HClO is used as an electrophilic chlorinating agent, indicating that the selective formation of HClO species on the hematite photoanode achieves a highly efficient benzene ring chlorination reaction.

[0096] Example 6

[0097] Cyclic stability test: The test system, test method and reaction substrate were the same as in Example 2. The applied voltage was set to 1.0V vs. Ag / AgCl, and the test time was set to 2h. The test system was placed under simulated sunlight and the voltage was applied to start photoelectrolysis. This process was repeated 6 times, and the electrolysis current and Faraday efficiency were recorded each time.

[0098] Figure 9 Cyclic stability tests were conducted on the hematite photoanode during the chlorination reaction of acetanilide. As can be seen from the figure, after 6 cycles, the photocurrent did not decrease significantly, and the electrophilic chlorination Faraday efficiency (FE) remained at around 90%.

[0099] The specific embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hematite photoanode for photoelectrochlorination reaction, characterized in that, Includes the following steps: S1: A first mixed solution comprising iron salt, nitrate and doped metal salt is subjected to a hydrothermal reaction in an environment with a conductive substrate to obtain a first hydroxyl iron oxide electrode, which is then annealed to obtain a hematite electrode. The doped metal salt is a soluble titanium salt; S2. The hematite electrode is added to a second mixed solution containing iron salt, nitrate, doped metal salt and ammonium salt for hydrothermal reaction to obtain a second hydroxyl iron oxide electrode, which is then annealed to obtain a hematite photoanode. The ammonium salt is ammonium fluoride.

2. The method for preparing the hematite photoanode for photoelectrochlorination reaction according to claim 1, characterized in that, The molar ratio of iron salt, nitrate and doped metal salt in step S1 is 1.5:1:(0~0.012).

3. The method for preparing the hematite photoanode for photoelectrochlorination reaction according to claim 1, characterized in that, The hydrothermal reaction in step S1 is carried out at a temperature of 80~100℃ for 3~5 hours.

4. The method for preparing a hematite photoanode for photoelectrochlorination reaction according to any one of claims 1-3, characterized in that, The annealing in step S1 includes the following steps: first, raise the temperature to 500~600℃ and anneal for 1~3 hours, then raise the temperature to 620~700℃ and anneal for 10~30 minutes.

5. The method for preparing the hematite photoanode for photoelectrochlorination reaction according to claim 1, characterized in that, The molar ratio of iron salt, nitrate, doped metal salt and ammonium salt in step S2 is 1.5:1:(0~0.012):(0-3).

6. The method for preparing a hematite photoanode for photoelectro-chlorination reaction according to any one of claims 1-3, characterized in that, The hydrothermal reaction in step S2 is carried out at a temperature of 80~100℃ for 3~5 hours.

7. The method for preparing a hematite photoanode for photoelectrochlorination reaction according to any one of claims 1-3, characterized in that, The annealing in step S2 includes the following steps: first, raise the temperature to 500~600℃ and anneal for 1~3 hours, then raise the temperature to 620~700℃ and anneal for 10~30 minutes.

8. The method for preparing a hematite photoanode for photoelectrochlorination reaction according to any one of claims 1-3, characterized in that, The iron salt used is a trivalent iron salt; And / or, the nitrate is selected from alkali metal nitrates; And / or, the conductive substrate is selected from a conductive substrate containing tin oxide.

9. A hematite photoanode prepared by the method of any one of claims 1-8.

10. An electrolytic cell for photoelectrochlorination reaction, the electrolytic cell comprising a hematite photoanode prepared by any one of claims 1-8 or the hematite photoanode of claim 9, wherein the hematite photoanode is the working electrode.

11. The electrolytic cell according to claim 10, characterized in that, The electrolytic cell also includes a reference electrode and a counter electrode.

12. The electrolytic cell according to claim 10, characterized in that, The electrolytic cell is provided with an electrolyte, which contains an alkali metal halide and a supporting electrolyte. The alkali metal halide is selected from at least one of sodium chloride, potassium chloride, and lithium chloride. The supporting electrolyte includes at least one of sodium perchlorate, lithium perchlorate, and tetraethylammonium tetrafluoroborate.

13. The electrolytic cell according to claim 12, characterized in that, The concentration of alkali metal halide in the electrolyte is 10~200 mM.

14. The electrolytic cell according to any one of claims 10-13, characterized in that, The electrolytic cell also includes a lighting mechanism, which is used to simulate sunlight and illuminate the electrolytic cell to provide a light source for the photoelectric reaction.

15. A method for photoelectrochlorination reaction, characterized in that, Includes the following steps: Add the reaction substrate to the electrolytic cell according to any one of claims 10-14, apply voltage under light to perform photoelectrolysis, and obtain the chlorination product; The reaction substrate is selected from aromatic compounds and olefin compounds with electron-rich substituents, and the concentration of the reaction substrate in the electrolyte is 0.05~0.3 mmol.

16. The method for photoelectrochlorination reaction according to claim 15, characterized in that, The electrophilic Faraday efficiency FE of the photoelectrochlorination reaction is greater than or equal to 85%; And / or, the photoelectrochlorination reaction has para-chlorination selectivity for monosubstituted chlorinated products of electron-rich benzene rings, wherein the selectivity is ≥90%.

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