CN111172559A - Ultrathin hydrotalcite-based composite photoelectrode and application thereof in photoelectric decomposition water coupling organic matter oxidation reaction - Google Patents

Ultrathin hydrotalcite-based composite photoelectrode and application thereof in photoelectric decomposition water coupling organic matter oxidation reaction Download PDF

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CN111172559A
CN111172559A CN202010188382.0A CN202010188382A CN111172559A CN 111172559 A CN111172559 A CN 111172559A CN 202010188382 A CN202010188382 A CN 202010188382A CN 111172559 A CN111172559 A CN 111172559A
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项顼
罗兰
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Abstract

The invention discloses an ultrathin hydrotalcite-based composite photoelectrode and application thereof in photoelectric decomposition water coupling organic matter oxidation reaction. The photoelectrode has the structure that a compound of two-dimensional nano flaky graphene and ultrathin hydrotalcite grows on the surface of a bismuth vanadate electrode, and is specifically represented as follows: g @ U-LDHs/BiVO4And a photoelectrode. G @ U-LDHs/BiVO is put in a closed series electrolytic cell4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one or more paired anodes and cathodes and one reference electrode form a three-electrode system, electrolyte and organic matters are added, and the three-electrode system is subjected to illumination reaction. The invention utilizes the active oxygen species generated by photoelectric water decomposition to catalyze the oxidation reaction, does not need the energy-consuming oxygen molecule activation process, and simultaneously generates hydrogen at the photocathode. The methodEffectively improves the oxidation efficiency of organic matters, and obviously improves the overall energy efficiency and the molecular reaction efficiency of the photo-electrolytic water reaction system.

Description

Ultrathin hydrotalcite-based composite photoelectrode and application thereof in photoelectric decomposition water coupling organic matter oxidation reaction
Technical Field
The invention belongs to the field of photoelectrochemical synthesis, and particularly relates to an ultrathin hydrotalcite-based composite photoelectrode and application thereof in photoelectric decomposition water coupling organic matter oxidation reaction.
Background
The human science and technology development and the social progress do not have huge requirements on energy, and the exploration and the utilization of renewable energy sources (such as solar energy, wind energy, biomass energy and the like) have important significance for realizing the sustainable development strategy of China. In various renewable energy forms, the total amount of solar energy is huge, and the use process is clean and pollution-free, and is one of important objects for renewable energy utilization. At present, among three main forms of solar energy utilization (photoelectricity, photothermal and photochemical), photochemical conversion can store light energy in molecules in the form of chemical bond energy, and the light energy can be utilized in occasions where the light energy is needed, so that the defects of solar energy intermittence and difficult storage are solved to a great extent. For example, the sunlight/photoelectric water splitting process stores solar energy in the form of stable hydrogen and oxygen molecules, and is also one of the important ways to produce hydrogen energy.
Compared with the widely researched water decomposition hydrogen production process, the research of effectively utilizing the water oxidation half reaction to release oxygen molecules is not paid enough attention. This is mainly due to the stability of oxygen molecules (oxygen-oxygen bond energy of 498kJ/mol), and the high temperature and pressure conditions usually required for the oxidation reaction involving oxygen molecules to produce chemicals, as well as the efficient activation of the oxygen molecules by the catalyst (e.g. the selective oxidation of aromatic alcohols and alkylbenzenes to the corresponding carbonyl compounds), which is a very energy-intensive process. The active oxygen species is used as a high-reaction-activity intermediate, has the advantages of wide source, no toxicity, no harm and the like, and is widely applied to the fields of energy, environment, catalysis, materials and the like. Thus, if the oxygen reactive species are utilized in the oxidation process of chemical production before the photo-electrolytic water process forms stable oxygen molecules, no secondary activation of the oxygen molecules is required, i.e.: the photoelectric decomposition water is directly coupled with the oxidation reaction, and a new high-efficiency and energy-saving way for preparing chemicals by the oxidation reaction is developed. The development of high-performance catalysts with specific structures, exposed crystal faces and surface modification is the core for realizing the high-efficiency conversion of organic matters under mild conditions.
The two-dimensional intercalation structure material, namely Layered Double Hydroxides (LDHs) transition metal ions, can be uniformly distributed and stably combined on an LDHs laminate, and the transition metal of a host laminate and interlayer guest anions are adjustable, so that the preparation method has wide application in the field of photo/photoelectrocatalysis. The ultrathin LDHs obtained by adjusting the thickness of the LDHs lamella has low surface ion transmission energy barrier, excellent electron transfer performance and fully exposed active sites, rich hydroxyl groups on the surface can increase the adsorption on reaction substrates, and the separation of photogenerated carriers can be promoted and the catalytic conversion performance of organic matters can be effectively improved after the ultrathin LDHs is combined with semiconductor materials, so that the ultrathin LDHs is a thin-layer two-dimensional nano material with a great prospect.
The current reports focus mainly on photocatalytic aromatic alcohol or alkylbenzene selective oxidation and require O2And the catalyst is used as an oxidizing agent to participate in the reaction. Document 1: h, Li, F, Qin, Z, P, Yang, X, M, Cui, J, F, Wang, L, Z, Zhang, J, Am, chem, Soc, 2017,139,3513-3521, gold nanoparticles (Au-BiOCl-OV) loaded on bismuth oxychloride rich in oxygen vacancies as a photocatalyst to oxidize benzyl alcohol, irradiating the bismuth oxychloride with visible light for 8 hours and performing O-oxidation at 0.1MPa2Under the condition of serving as an oxidizing agent, the yield of benzaldehyde is 0.945mmol g-1h-1. Document 2: X.S.Sun, X.Luo, X.D.Zhang, J.F.Xie, S.jin, H.Wang, X.S.ZHEN, X.J Wu, Y.Xie.J.Am.chem.Soc.2019,141,3797-3801, using indium sulfide (In) with rich sulfur vacancies2S3) Photocatalyst, 0.1MPa O under visible light irradiation for 5h2As the oxidizing agent, the selective oxidation of benzyl alcohol to benzaldehyde was carried out in a yield of 0.71g-1h-1. Document 3: X.Cao, Z.Chen, R.Lin, W.Cheng, S.Liu, J.Zhang, Q.Peng, C.Chen, T.Han, X.Tong, Y.Wang, R.Shen, W.Zhu, D.Wang, Y.D.Li.Nature Catalysis,2018,1,704-710 using amorphous bismuth oxychloride (BiOCl) and bismuth tungstate (Bi. Zhu)2WO6–x) Bonding, irradiating with visible light for 6h, 0.1MPa O2Under the condition of serving as an oxidant, the yield of the benzene oxidation to the benzaldehyde is 1.46 mmoleg-1h-1。
TABLE 1 comparison of photocatalytic oxidation performance of aromatic alcohol and alkylbenzene
Figure BDA0002414992430000021
Disclosure of Invention
The invention aims to prepare an ultrathin hydrotalcite-based composite photoelectrode and use the ultrathin hydrotalcite-based composite photoelectrode for photoelectric decomposition water coupling organic matter oxidation reaction, active oxygen species generated in the ultrathin LDHs-based photoelectrode by photoelectric water decomposition are used for catalytic oxidation reaction, an energy-consuming oxygen molecule activation process is not needed, and hydrogen is generated at a photocathode. The method effectively improves the oxidation efficiency of organic matters, and obviously improves the overall energy efficiency and the molecular reaction efficiency of the photo-electrolytic water reaction system.
The structure of the ultrathin hydrotalcite-based composite photoelectrode is that a two-dimensional nano flaky graphene and ultrathin hydrotalcite composite grows on the surface of a bismuth vanadate electrode, and the structure is specifically represented as follows: g @ U-LDHs/BiVO4The photoelectrode, wherein, G is graphite alkene, and U-LDHs is ultra-thin hydrotalcite, and its chemical formula is: [ M ] A2+ 1－xM3+ x(OH)2]x+(An－)x/n·mH2O，M2+Represents a divalent metal ion, M2+Is Ni2+、Co2+、Zn2+One or two of (A), (B), (C), (3+Represents a trivalent metal ion, M3+Is Al3+、Fe3+One or two of (A)n－Is an interlayer anion, An－Is one or two of nitrate, sulfate and carbonate, n is 1 or 2, m is the number of water molecules, m is 5-15, x is 1/3-1, the grain size of the ultrathin hydrotalcite is 3-5 μm, and the thickness of the lamella is 3-4 nm.
The bismuth vanadate electrode is formed by growing or coating BiVO on one side of conductive glass4Particles.
The preparation method of the ultrathin hydrotalcite-based composite photoelectrode comprises the following steps: putting bismuth vanadate electrode into the container containing M2+、M3+In a mixed solution of urea, ammonium fluoride, graphene and acetone, and carrying out hydrothermal reaction to obtain G @ U-LDHs/BiVO4And a photoelectrode.
The prepared ultrathin hydrotalcite-based composite photoelectrode is applied to photoelectric decomposition water coupling organic matter oxidation reaction. The conditions of the oxidation reaction of the photoelectric decomposition water coupling organic matter are as follows: g @ U-LDHs/BiVO is put in a closed series electrolytic cell4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and matched with a power supply, and one or more matched anodes and cathodes and one reference electrode form three electrodesIn the electrode system, phosphate buffer solution is used as electrolyte, organic matters or organic matter solution is added and mixed uniformly, one of the cathodes is isolated from other electrodes by adopting a proton membrane, nitrogen is introduced into the mixed solution to exhaust air, and then the mixed solution is subjected to illumination reaction for 1 to 24 hours under bias voltage of 0.6 to 1.6V verses RHE; standing for layering after the reaction is finished, and separating an upper organic phase product.
The organic matter is aromatic alcohol or alkylbenzene.
The illumination direction is to illuminate the non-conductive surface of the anode.
The preparation method of the ultrathin hydrotalcite-based composite photoelectrode comprises the following specific operation steps:
A. mixing soluble divalent metal salt, soluble trivalent metal salt, urea and NH4F preparing a mixed solution, wherein the concentration of total metal ions is 30-50mmol/L, the molar ratio of divalent metal ions to trivalent metal ions is 2:1-4:1, the concentration of urea is 50-80mmol/L, and NH is added4The concentration of F is 20-40 mmol/L; then adding the graphene aqueous dispersion into the mixed solution, stirring at normal temperature, and carrying out ultrasonic treatment to form a uniform solution;
B. putting the bismuth vanadate electrode in a hydrothermal kettle liner with the conductive surface facing upwards and leaning upwards, adding 3-6mL of the solution prepared in the step A, and then adding 3-6mL of acetone to enable BiVO to grow on the electrode4The part of the electrode is completely immersed in the solution, the hydrothermal reaction is carried out for 4 to 10 hours after the ultrasonic treatment is carried out for 5 to 15 minutes and the temperature is raised to 100 to 120 ℃, after the electrode is naturally cooled, the electrode is taken out, washed by ethanol and deionized water, and dried at 70 to 100 ℃ to obtain the ultrathin hydrotalcite-based composite photoelectrode.
The soluble divalent metal salt is selected from nitrates or sulfates of Ni, Co and Zn, and the soluble trivalent metal salt is selected from nitrates or sulfates of Al and Fe.
The invention has the following remarkable effects:
(1) the ultrathin LDHs have low surface ion transmission energy barrier, excellent electron transmission performance and fully exposed active sites, and the reaction performance of the composite photoelectrode is remarkably improved.
(2) The technical method for coupling the photo-electrolysis water with the oxidation of the organic matter has the advantages of simple and convenient operation, high atom economy, mildness and greenness, and the coupling reaction provides a new way for preparing oxygen-containing chemicals with high added values in an efficient and energy-saving manner.
(3) The technical method does not need to add an oxidant, fully utilizes the active oxygen species generated in situ by the water oxidation half reaction to catalyze and oxidize the aromatic alcohol and the alkylbenzene, does not need the secondary activation process of oxygen molecules, and greatly improves the overall energy efficiency and the molecular reaction efficiency of the photoelectrolysis water reaction system. The main product of benzyl alcohol oxidation is benzaldehyde, the selectivity is more than 99%, other para-substituted benzyl alcohols are oxidized to mainly generate corresponding aldehyde-based products, and the selectivity is over 96%; toluene oxidation was carried out with benzaldehyde and benzyl alcohol as the main products (selectivity 88%).
Drawings
FIG. 1: atomic force microscopy of ultrathin U-LDHs prepared in example 1.
FIG. 2: example 1 photoelectric decomposition water coupling benzyl alcohol oxidation series electrolytic cell apparatus diagram.
FIG. 3: example 1 photo-amperometric graph of the photo-electric decomposition of water coupled benzyl alcohol oxidation.
Detailed Description
Example 1
A. 0.306g of Co (NO) is weighed out3)2·6H2O、0.132g Al(NO3)3·9H2O, 0.424g urea, 0.07gNH4And F, adding 70mL of deionized water into a 250mL beaker, uniformly mixing, adding 1mL of graphene water dispersion with the concentration of 1mg/mL, performing ultrasonic treatment and stirring to form a uniform solution, wherein the ultrasonic power is 50W, the time is 10min, and the temperature is 20 ℃.
B. BiVO (bismuth oxide) is added4The conductive surface of the electrode is inclined upwards by 45 degrees, and is placed into a hydrothermal kettle liner, 4mL of the solution prepared in the step A and 3mL of acetone (the mass fraction is more than or equal to 99.9 percent) are added, so that BiVO grows4The part is completely immersed in the solution, the ultrasonic power is 50W, the time is 5min, the mixture is fully and uniformly mixed, the hydrothermal reaction is carried out for 4h at the temperature of 100 ℃, after the mixture is naturally cooled, the electrode is taken out, the ethanol is used for washing for 3 times, 10mL is used for each time, finally the deionized water is used for washing, and the washed electrode is placed in a 60 ℃ drying oven for drying for 1 h to obtain G @ U-LDHs/BiVO4And a photoelectrode.
C. At normal temperatureNext, 8mL of a phosphate buffer solution (pH 7, 0.1mol/L) was weighed into a closed series electrolytic cell, 2mmol of benzyl alcohol was added, a cylindrical magnetic stirring magneton was added, the electrolytic cell was sealed and covered, magnetic stirring was performed for 10 minutes (rotation speed: 700r/min) to obtain a uniformly mixed colorless mixed solution, and nitrogen gas was continuously introduced into the mixed solution for 30 minutes to purge air. G @ U-LDHs/BiVO4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and paired with a power supply, 2 paired anodes and cathodes form a three-electrode system with one reference electrode, a naphthol proton membrane is adopted to isolate one cathode from other electrodes, a xenon lamp light source (simulated sunlight) provided with an AM1.5G optical filter is used for irradiating a non-conducting surface of the anode, and the light intensity is 100mW/cm2. The reaction was carried out at room temperature using a current-time (i-t) mode with the application of a voltage using an electrochemical workstation (CHI 660E), in which the potential E isRHETime was set to 14400 seconds at 1.2V. (RHE represents a reversible hydrogen electrode)
D. After the reaction, the mixture was allowed to stand for 30 minutes, the reaction solution was divided into upper and lower layers, the electrode was taken out, and the upper organic phase liquid was separated.
The BiVO4The preparation method of the electrode comprises the following steps: 0.485g of Bi (NO) is weighed3)3Dissolving in 100mL of ethylene glycol and 50mL of aqueous solution to dope fluorine with SnO2Immersing a conductive glass FTO sheet serving as a working electrode into the solution, taking a Pt wire as a cathode, taking Ag/AgCl as a reference electrode, and depositing for 10-15min under the constant potential of-0.4-0.8V versus RHE to obtain a Bi/FTO electrode sheet; dripping 200 mu L of 0.1-0.4mol/L dimethyl sulfoxide solution of vanadium acetylacetonate on a Bi/FTO electrode sheet, putting the Bi/FTO electrode sheet into a muffle furnace for calcination, keeping the Bi/FTO electrode sheet at 450 ℃ for 2 hours, heating at the rate of 2-5 ℃/min, cooling to room temperature, washing and stirring the obtained product with 0.5-1mol/L NaOH aqueous solution for 10-30 minutes, taking out the obtained product, washing the obtained product with deionized water for 3-5 times, and drying the obtained product in a vacuum drying oven at 70 ℃ for 2 hours to obtain BiVO4An electrode sheet.
Adding a small amount of ethanol into the organic phase liquid for dilution, filtering by adopting a nylon 66 filter membrane, and placing in a sample bottle for gas chromatography test: the gas chromatographic analysis of benzaldehyde and benzoic acid product adopts internal standard analysis methodThe internal standard was p-xylene and was measured by gas chromatography using Shimadzu GC2014, in a sample volume of 1. mu.L. As a result: under the conditions of 1.2V versusRHE and visible light irradiation for 4 hours and no oxygen, the main product of the selective oxidation of the benzyl alcohol is benzaldehyde, the selectivity is more than 99 percent, and the yield of the benzaldehyde is 14.45mmol g-1h-1。
Example 2
A. 0.343g of Ni (NO) was weighed3)2·6H2O、0.135g Al(NO3)3·9H2O, 0.435g urea, 0.07g NH4And F, adding 70mL of deionized water into a 250mL beaker, uniformly mixing, adding 1mL of graphene water dispersion with the concentration of 1mg/mL, performing ultrasonic treatment, and stirring until the mixture is mixed to form a uniform solution, wherein the ultrasonic power is 50W, the time is 10min, and the temperature is 20 ℃.
B. BiVO (bismuth oxide) is added4The conductive surface of the electrode is inclined upwards by 45 degrees, and is placed into a hydrothermal kettle liner, 4mL of the solution prepared in the step A and 3mL of acetone (the mass fraction is more than or equal to 99.9 percent) are added, so that BiVO grows4The part is completely immersed in the solution, the ultrasonic power is 50W, the time is 5min, the mixture is fully and uniformly mixed, the hydrothermal reaction is carried out for 4h at the temperature of 100 ℃, after the mixture is naturally cooled, the electrode is taken out, the ethanol is used for washing for 3 times, 10mL is used for each time, finally the deionized water is used for washing, and the washed electrode is placed in a 60 ℃ drying oven for drying for 1 h to obtain the G @ U-LDHs composite BiVO4And a photoelectrode.
C. At normal temperature, 8mL of phosphate buffer solution (pH 7, 0.1mol/L) is weighed into a closed series electrolytic cell, 2mmol of benzyl alcohol is added, a cylindrical magnetic stirring magneton is added, the electrolytic cell is sealed and covered, magnetic stirring is carried out for 10 minutes (rotating speed: 800r/min) to obtain a uniformly mixed colorless mixed solution, and nitrogen is continuously introduced into the mixed solution for 30 minutes to exhaust air. G @ U-LDHs @ BiVO4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and paired with a power supply, 3 paired anodes and cathodes form a three-electrode system with one reference electrode, a naphthol proton membrane is adopted to isolate one cathode from other electrodes, a xenon lamp light source (simulated sunlight) provided with an AM1.5G optical filter is used for irradiating a non-conducting surface of the anode, and the light intensity is 100mW/cm2. Benefit toApplying a voltage with an electrochemical workstation (CHI 660E) and performing the reaction at room temperature using a current-time (i-t) mode, wherein the potential E isRHETime was set to 14400 seconds at 1.2V.
D. After the reaction, the reaction solution was allowed to stand for 30 minutes, the reaction solution was divided into upper and lower layers, the electrode was taken out, and the upper organic phase liquid was separated.
The same evaluation method as in example 1 was used, and the evaluation results were: under the condition of 1.2V versus RHE and visible light irradiation for 4 hours, the selectivity of the main product benzaldehyde generated by the selective oxidation of the benzyl alcohol is more than 99 percent, and the yield of the benzaldehyde is 7.82mmol g-1h-1。
Example 3
A. 0.446g Zn (NO) is weighed3)2·6H2O、0.134g Al(NO3)3·9H2O, 0.426g urea, 0.068g NH4And F, adding 70mL of deionized water into a 250mL beaker, uniformly mixing, adding 1mL of graphene dispersion liquid with the concentration of 1mg/mL, performing ultrasonic treatment, and stirring until the mixture is mixed to form a uniform solution, wherein the ultrasonic power is 50W, the time is 10min, and the temperature is 20 ℃.
B. BiVO (bismuth oxide) is added4The conductive surface of the electrode is inclined upwards by 45 degrees, and is placed into a hydrothermal kettle liner, 4mL of the solution prepared in the step A and 3mL of acetone (the mass fraction is more than or equal to 99.9 percent) are added, so that BiVO grows4The part is completely immersed in the solution, the ultrasonic power is 50W, the time is 5min, the mixture is fully and uniformly mixed, the hydrothermal reaction is carried out for 4h at the temperature of 100 ℃, after the mixture is naturally cooled, the electrode is taken out, the ethanol is used for washing for 3 times, 10mL is used for each time, finally the deionized water is used for washing, and the washed electrode is placed in a 60 ℃ drying oven for drying for 1 h to obtain the G @ U-LDHs composite BiVO4And a photoelectrode.
C. At normal temperature, 8mL of phosphate buffer solution (pH 7, 0.1mol/L) is weighed into a closed series electrolytic cell, 2mmol of benzyl alcohol is added, a cylindrical magnetic stirring magneton is added, the electrolytic cell is sealed and covered, magnetic stirring is carried out for 10 minutes (rotating speed: 700r/min) to obtain a uniformly mixed colorless mixed solution, and nitrogen is continuously introduced into the mixed solution for 30 minutes to exhaust air. G @ U-LDHs @ BiVO4Photoelectrode as anode, Pt filament as cathode, Ag/AgCl as reference electrode, one anode and one cathodeConnecting with power supply, pairing, forming a three-electrode system by 2 paired anodes and cathodes and a reference electrode, isolating one of the cathodes from other electrodes by adopting naphthol proton membrane, irradiating non-conducting surface of the anode by xenon lamp light source (simulated sunlight) equipped with AM1.5G optical filter, and making light intensity be 100mW/cm2. The reaction was carried out at room temperature using a current-time (i-t) mode with the application of a voltage using an electrochemical workstation (CHI 660E), in which the potential E isRHETime was set to 14400 seconds at 1.2V.
D. After the reaction, the reaction solution was allowed to stand for 30 minutes, the reaction solution was divided into upper and lower layers, the electrode was taken out, and the upper organic phase liquid was separated.
The evaluation method of example 1 was used, and the evaluation results were as follows: under the condition of 1.2V versus RHE and visible light irradiation for 4 hours, the selectivity of the main product of the selective oxidation of the benzyl alcohol, namely the benzaldehyde, is more than 98 percent, and the yield of the benzaldehyde is 5.80mmol g-1h-1。
Example 4
A. 0.305g Co (NO) was weighed out3)2·6H2O、0.131g Al(NO3)3·9H2O, 0.421g urea, 0.07g NH4And F, adding 70mL of deionized water into a 250mL beaker, uniformly mixing, adding 1mL of graphene dispersion liquid with the concentration of 1mg/mL, performing ultrasonic treatment, and stirring until the mixture is mixed to form a uniform solution, wherein the ultrasonic power is 50W, the time is 10min, and the temperature is 20 ℃.
B. BiVO (bismuth oxide) is added4The conductive surface of the electrode is inclined upwards by 45 degrees, and is placed into a hydrothermal kettle liner, 4mL of the solution prepared in the step A and 4mL of acetone (the mass fraction is more than or equal to 99.9 percent) are added, so that BiVO grows4The part is completely immersed in the solution, the ultrasonic power is 50W, the time is 5min, the mixture is fully and uniformly mixed, the hydrothermal reaction is carried out for 4h at the temperature of 100 ℃, after the mixture is naturally cooled, the electrode is taken out, the ethanol is used for washing for 3 times, 10mL is used for each time, finally the deionized water is used for washing, and the washed electrode is placed in a 60 ℃ drying oven for drying for 1 h to obtain the G @ U-LDHs composite BiVO4And a photoelectrode.
C. Dissolving 2mmol of toluene in 4mL of acetonitrile at normal temperature, weighing 8mL of phosphate buffer solution (pH 7, 0.1mol/L) in a closed series electrolytic cell, adding toluene-acetonitrile solution,adding cylindrical magnetic stirring magnetons, sealing and covering the electrolytic cell, magnetically stirring at room temperature (the rotating speed: 700r/min) for 10 minutes to obtain a uniformly mixed colorless mixed solution, and continuously introducing nitrogen into the mixed solution for 30 minutes to exhaust air; g @ U-LDHs @ BiVO4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and paired with a power supply, 1 paired anode and cathode and one reference electrode form a three-electrode system, a naphthol proton membrane is adopted to isolate one cathode from other electrodes, a xenon lamp light source (simulated sunlight) provided with an AM1.5G optical filter is used for irradiating a non-conducting surface of the anode, and the light intensity is 100mW/cm2The reaction was carried out at room temperature using a current-time (i-t) mode with the application of a voltage using an electrochemical workstation (CHI 660E), in which the potential E isRHETime was set to 21600 seconds at 1.2V.
D. After the reaction, the reaction solution was allowed to stand for 30 minutes, the reaction solution was divided into upper and lower layers, the electrode was taken out, and the upper organic phase liquid was separated.
Adding a small amount of ethanol into the organic phase liquid for dilution, filtering by adopting a nylon 66 filter membrane, and placing in a sample bottle for gas chromatography test: the gas chromatography analysis is performed on benzyl alcohol, benzaldehyde and benzoic acid products, an internal standard analysis method is adopted, an internal standard substance is p-xylene, the test is performed by Shimadzu GC2014 type gas chromatography, and the sample injection amount is 1 mu L. As a result: under the conditions of 1.2 Vvarsus RHE, visible light irradiation for 6 hours and no oxygen, the main product of the selective oxidation of toluene is benzaldehyde, the selectivity is 74 percent, and the generation rate of the benzaldehyde is 0.80mmol g-1h-1。
Example 5
A. 0.310g of Co (NO) is weighed out3)2·6H2O、0.135g Al(NO3)3·9H2O, 0.430g urea, 0.07g NH4And F, adding 70mL of deionized water into a 250mL beaker, uniformly mixing, adding 1mL of graphene dispersion liquid with the concentration of 1mg/mL, performing ultrasonic treatment, and stirring until the mixture is mixed to form a uniform solution, wherein the ultrasonic power is 50W, the time is 10min, and the temperature is 20 ℃.
B. BiVO (bismuth oxide) is added4The conductive surfaces of the electrodes are inclined upwards by 45 degrees and water is put inAdding 4mL of the solution prepared in the step A and 4mL of acetone (the mass fraction is more than or equal to 99.9%) into a hot kettle liner to enable BiVO to grow4The part is completely immersed in the solution, the ultrasonic power is 50W, the time is 5min, the mixture is fully and uniformly mixed, the hydrothermal reaction is carried out for 4h at the temperature of 100 ℃, after the mixture is naturally cooled, the electrode is taken out, the ethanol is used for washing for 3 times, 10mL is used for each time, finally the deionized water is used for washing, and the washed electrode is placed in a 60 ℃ drying oven for drying for 1 h to obtain the G @ U-LDHs composite BiVO4And a photoelectrode.
C. Dissolving 3mmol of toluene in 4mL of acetonitrile at normal temperature, weighing 9mL of phosphate buffer solution (pH 7, 0.1mol/L) in a closed series electrolytic cell, adding the toluene-acetonitrile solution, adding a cylindrical magnetic stirring magneton, sealing and covering the electrolytic cell, magnetically stirring at room temperature (rotating speed: 600r/min) for 15 minutes to obtain a uniformly mixed colorless mixed solution, and continuously introducing nitrogen into the mixed solution for 30 minutes to exhaust air; g @ U-LDHs @ BiVO4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and paired with a power supply, 1 paired anode and cathode and one reference electrode form a three-electrode system, a naphthol proton membrane is adopted to isolate one cathode from other electrodes, a xenon lamp light source (simulated sunlight) provided with an AM1.5G optical filter is used for irradiating a non-conducting surface of the anode, and the light intensity is 100mW/cm2The reaction was carried out at room temperature using a current-time (i-t) mode with the application of a voltage using an electrochemical workstation (CHI 660E), in which the potential E isRHETime was set to 21600 seconds at 1.2V.
D. After the reaction, the mixture was allowed to stand for 30 minutes, the reaction solution was divided into upper and lower layers, the electrode was taken out, and the upper organic phase liquid was separated.
The evaluation method of example 4 was used, and the evaluation results were as follows: under the conditions of 1.2V versus RHE and visible light irradiation for 6 hours and no oxygen, the main product of the selective oxidation of the toluene is benzaldehyde, the selectivity is 76 percent, and the generation rate of the benzaldehyde is 0.67mmol g- 1h-1。

Claims (9)

1. The ultrathin hydrotalcite-based composite photoelectrode is characterized in that the structure of the photoelectrode is two-dimensional nanometerThe compound of the flake graphene and the ultrathin hydrotalcite is grown on the surface of a bismuth vanadate electrode, and is specifically represented as follows: g @ U-LDHs/BiVO4The photoelectrode, wherein, G is graphite alkene, and U-LDHs is ultra-thin hydrotalcite, and its chemical formula is: [ M ] A2+ 1－xM3+ x(OH)2]x+(An－)x/n·mH2O，M2+Represents a divalent metal ion, M2+Is Ni2+、Co2+、Zn2+One or two of (A), (B), (C), (3+Represents a trivalent metal ion, M3+Is Al3+、Fe3+One or two of (A)n－Is an interlayer anion, An－Is one or two of nitrate, sulfate and carbonate, n is 1 or 2, m is the number of water molecules, m is 5-15, x is 1/3-1, the grain size of the ultrathin hydrotalcite is 3-5 μm, and the thickness of the lamella is 3-4 nm.
2. The ultra-thin hydrotalcite-based composite photoelectrode of claim 1, wherein the bismuth vanadate electrode is BiVO grown or coated on one side of conductive glass4Particles.
3. The preparation method of the ultrathin hydrotalcite-based composite photoelectrode is characterized in that a bismuth vanadate electrode is placed in a cathode containing M2+、M3+In a mixed solution of urea, ammonium fluoride, graphene and acetone, and carrying out hydrothermal reaction to obtain G @ U-LDHs/BiVO4A photoelectrode; m2+Represents a divalent metal ion, M2+Is Ni2+、Co2+、Zn2+One or two of (A), (B), (C), (3+Represents a trivalent metal ion, M3+Is Al3+、Fe3+One or two of them.
4. The method for preparing the ultrathin hydrotalcite-based composite photoelectrode according to claim 3, characterized in that the method comprises the following specific operation steps:
A. mixing soluble divalent metal salt, soluble trivalent metal salt, urea and NH4F preparing a mixed solution with a total metal ion concentration of 30-50mmol/L, the molar ratio of divalent metal ions to trivalent metal ions is 2:1-4:1, the concentration of urea is 50-80mmol/L, NH4The concentration of F is 20-40 mmol/L; then adding the graphene aqueous dispersion into the mixed solution, stirring at normal temperature, and carrying out ultrasonic treatment to form a uniform solution;
B. putting the bismuth vanadate electrode in a hydrothermal kettle liner with the conductive surface facing upwards and leaning upwards, adding 3-6mL of the solution prepared in the step A, and then adding 3-6mL of acetone to enable BiVO to grow on the electrode4The part of the electrode is completely immersed in the solution, the hydrothermal reaction is carried out for 4 to 10 hours after the ultrasonic treatment is carried out for 5 to 15 minutes and the temperature is raised to 100 to 120 ℃, after the electrode is naturally cooled, the electrode is taken out, washed by ethanol and deionized water, and dried at 70 to 100 ℃ to obtain the ultrathin hydrotalcite-based composite photoelectrode.
5. The method for preparing the ultrathin hydrotalcite-based composite photoelectrode as claimed in claim 4, wherein the soluble divalent metal salt is selected from nitrates or sulfates of Ni, Co and Zn, and the soluble trivalent metal salt is selected from nitrates or sulfates of Al and Fe.
6. The application of the ultrathin hydrotalcite-based composite photoelectrode prepared according to the method of claims 3-5 in photoelectric decomposition water coupling organic matter oxidation reaction.
7. The use of claim 6, wherein the conditions for the oxidation reaction of the photovoltaically decomposed water-coupled organic matter are as follows: in a closed series electrolytic cell, phosphate buffer solution is used as electrolyte, organic matter or organic matter solution is added and mixed evenly, nitrogen is introduced into the mixed solution to exhaust air, and G @ U-LDHs/BiVO is added4The photoelectrode is used as an anode, the Pt wire is used as a cathode, the Ag/AgCl is used as a reference electrode, one anode and one cathode are connected and paired with a power supply, one or more paired anodes and cathodes and one reference electrode form a three-electrode system, a proton membrane is adopted to isolate one of the cathodes from other electrodes, and the light irradiation reaction is carried out for 1 to 24 hours under the bias voltage of 0.6 to 1.6V verses RHE; standing for layering after the reaction is finished, and separating an upper organic phase product.
8. Use according to claim 7, characterized in that the organic substance is an aromatic alcohol or an alkylbenzene.
9. Use according to claim 7, characterised in that the direction of the light irradiation is to irradiate the non-conducting face of the anode.
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