Plasmon / hematite heterojunction material for efficiently catalyzing epoxidation of styrene olefins as well as preparation method and application of plasmon / hematite heterojunction material

Abstract

The invention provides a plasmon / hematite heterojunction material for efficiently catalyzing epoxidation of styrene olefins as well as a preparation method and application of the plasmon / hematite heterojunction material. The preparation method of the plasmon / hematite heterojunction material comprises the following steps: a) preparing an alpha-Fe2O3 photo-anode; b) preparing an Ag (at) AgCl-C3N4 catalyst; and c) preparing the Ag (at) AgCl-C3N4-alpha-Fe2O3, namely the plasmon / hematite heterojunction material. According to the method, an Ag-coated AgCl nano material with a plasmon light absorption effect, C3N4 and alpha-Fe2O3 are assembled to construct a three-electrode system with Ag-coated AgCl-C3N4-alpha-Fe2O3 as a working electrode, and the three-electrode system is used for chloride ion mediated styrene olefin photoelectrocatalysis epoxidation. The method is simple, easy to operate and low in cost, and has certain universality for styrene substrates.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectrocatalysis, and in particular to a plasmon / hematite heterojunction material for efficiently catalyzing the epoxidation of styrene-based olefins, a preparation method thereof, and an application thereof in chlorine-mediated olefin epoxidation. Background Art

[0002] Epoxides are widely used in the synthesis of functional polymers and drugs. The usual synthetic route is direct epoxidation of C=C bonds, which requires toxic strong oxidants and precise control of reaction temperature and pressure, high cost and many side reactions. In addition, in actual operation, olefin substrates will undergo peroxidation, so how to achieve selective oxidation of olefins is a major challenge. Photoelectrochemical indirect olefin epoxidation, using water as the oxygen source and halogen as the redox medium, has become an effective way to synthesize epoxides because of its green, sustainable and low energy consumption characteristics.

[0003] α-Fe for photoelectrochemical indirect olefin epoxidation 2 O 3 Photoanode is considered to be a promising semiconductor photoelectrode material due to its advantages of absorbing visible light, excellent stability, and low cost. 2 O 3 The absorption efficiency is low (the absorption coefficient α is 8*10 at 550nm) 4 cm -1 ), the hole diffusion length is short (2-4nm), and the excited state lifetime is very short (~10 -12 s), resulting in serious recombination of photogenerated electrons and holes and low photoelectrocatalytic efficiency. 2 O 3 The absorption properties and carrier separation and transport are the key to improving the olefin epoxidation activity. Summary of the invention

[0004] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0005] A method for preparing a plasmon / hematite heterojunction material, the preparation method comprising the following steps:

[0006] a) Preparation of α-Fe 2 O 3 Photoanode;

[0007] b) Preparation of Ag@AgCl-C 3 N 4 catalyst;

[0008] c) Preparation of Ag@AgCl-C 3 N 4 -α-Fe 2O 3 , that is, the plasmon / hematite heterojunction material.

[0009] According to an embodiment of the present invention, in step a), the α-Fe 2 O 3 The preparation method of the photoanode includes: preparing β-FeOOH by hydrothermal reaction of an iron source, and then calcining at high temperature to obtain α-Fe 2 O 3 Photoanode. For example, the α-Fe 2 O 3 The preparation method of the photoanode includes: placing a titanium foil in a reactor containing a mixed solution of an iron source (such as ferric chloride), a nitrate (such as sodium nitrate) and a titanium salt (such as titanium chloride), preparing β-FeOOH through a hydrothermal reaction, and then calcining it at a high temperature in a muffle furnace to obtain α-Fe 2 O 3 Photoanode.

[0010] According to an embodiment of the present invention, in step a), the titanium foil may also be pretreated. Preferably, the pretreatment includes, for example: ultrasonication in acetone, ethanol and water in sequence (e.g., ultrasonication time is fifteen minutes), and then etching in concentrated hydrochloric acid at 80°C (e.g., etching time is forty minutes).

[0011] According to an embodiment of the present invention, in step a), the iron source is added in the form of a solution. For example, an aqueous solution of the iron source (anhydrous ferric chloride) is first prepared, and then sodium nitrate is added to the aqueous solution. The mixed solution is also stirred (for example, the stirring speed can be set to 500 rpm to 1000 rpm).

[0012] According to an embodiment of the present invention, the volume of the reactor can be selected from volumes known in the art, for example, larger than the volume of the reaction solution; illustratively, the volume of the reactor is 15 mL, and the volume of the reaction solution can be 7.5 mL.

[0013] According to an embodiment of the present invention, in step a), the temperature of the hydrothermal reaction is 90-100° C., exemplarily 100° C., and the time of the hydrothermal reaction is 10-12 hours, exemplarily 10 hours. For another example, after the hydrothermal reaction, the temperature is naturally lowered to obtain β-FeOOH.

[0014] According to an embodiment of the present invention, in step a), after obtaining β-FeOOH, rinsing may be performed. For example, the rinsing solvent is water. For another example, the rinsing time may be 10 seconds, 20 seconds or longer, until the surface is rinsed clean.

[0015] According to an embodiment of the present invention, in step a), the high temperature calcination refers to calcining β-FeOOH, for example, placing it in a porcelain boat and placing it in a muffle furnace for calcination. Preferably, the calcination is a primary calcination, the primary calcination temperature is 500-600°C, exemplarily 550°C; the primary calcination time is 2-4 hours, exemplarily 2 hours; and the α-FeOOH is obtained after natural cooling. 2 O 3 Photoanode.

[0016] Preferably, in step a), the heating rate of the primary calcination may be no greater than 20° C. / min, for example, 10° C. / min.

[0017] According to an embodiment of the present invention, in step b), the Ag@AgCl-C 3 N 4 The preparation method of the catalyst comprises: first preparing C 3 N 4 Powder (such as sintering an appropriate amount of urea to obtain C 3 N 4 powder); then C 3 N 4 The powder is mixed with an organic chloride (such as hexadecyltrimethylammonium chloride CTAC), and then an Ag source (such as AgNO 3 ) solution, stirring and then irradiating with light for reaction (such as irradiating with a xenon lamp for reaction); filtering, washing (such as washing with deionized water), drying, and calcining to obtain Ag@AgCl-C 3 N 4 catalyst.

[0018] According to an embodiment of the present invention, the preparation of C 3 N 4 The powder includes, for example, a carbon and nitrogen source (such as urea) sintered to obtain C 3 N 4 Powder; wherein the mass of the urea is 8 to 10 g, exemplarily 9 g; sintering comprises placing the urea in a crucible and placing it in a muffle furnace. Preferably, the sintering temperature is 500 to 600°C, exemplarily 550°C; the sintering time is 8 to 10 hours, exemplarily 8 hours; and after natural cooling, C 3 N 4 powder.

[0019] According to the embodiment of the present invention, when the Ag source solution is added, the concentration of the Ag source solution can be adjusted to prepare Ag@AgCl-C with different Ag contents. 3 N 4Catalyst: Preferably, the concentration of the Ag source solution is 0.05-0.5 M, exemplary concentrations are 0.05 M, 0.1 M, 0.2 M, 0.3 M, 0.5 M, and the volume is 2.2 mL; stirring for 1 hour.

[0020] According to an embodiment of the present invention, the time of the light irradiation reaction is no more than 120 minutes, for example, 30 minutes.

[0021] Preferably, the xenon lamp is selected from a xenon lamp known in the art, such as a 300W xenon lamp; further, the light intensity of the xenon lamp can be selected from a light intensity known in the art, such as 200mW / cm 2 .

[0022] According to an embodiment of the present invention, the drying may be performed in a vacuum oven at an exemplary temperature of 80° C. for 8 hours.

[0023] According to an embodiment of the present invention, calcination to obtain Ag@AgCl-C 3 N 4 When the catalyst is used, the calcination temperature is 250-350°C, exemplarily 300°C; the calcination time is 2-4 hours, exemplarily 3 hours. Preferably, the temperature is naturally lowered after calcination to obtain Ag@AgCl-C 3 N 4 catalyst.

[0024] According to an embodiment of the present invention, step c) specifically comprises the following steps: 3 N 4 Catalyst modified on α-Fe 2 O 3 On the surface of the photoanode, Ag@AgCl-C was obtained by oxygen-free calcination. 3 N 4 -α-Fe 2 O 3 .

[0025] Preferably, Ag@AgCl-C 3 N 4 Catalyst modified on α-Fe 2 O 3 The method on the photoanode surface includes: configuring an appropriate concentration of Ag@AgCl-C 3 N 4 The ethanol dispersion solution is spin-coated on the α-Fe 2 O 3 on the surface of the photoanode.

[0026] According to an embodiment of the present invention, in step c), the Ag@AgCl-C 3 N 4 The concentration of the ethanol dispersion solution is 1 g / L.

[0027] According to an embodiment of the present invention, in step c), the spin coating is performed on a spin coater. Preferably, the spin coating specifically comprises: 2 O 3 The photoanode is fixed on a workbench, the rotation rate of the workbench is set to 2000-4000r, exemplarily 3000r, and the time is set to 3 minutes; the volume of the drop coating solution is 50-150μL, exemplarily 100μL.

[0028] According to an embodiment of the present invention, in step c), the oxygen-free calcination is carried out in a tube furnace. Preferably, the oxygen-free calcination is carried out under inert atmosphere conditions, such as argon.

[0029] Preferably, the temperature of the oxygen-free calcination is 300-400° C., exemplarily 350° C.; the time of the oxygen-free calcination is 1-3 hours, exemplarily 2 hours.

[0030] Preferably, natural cooling may be performed after the oxygen-free calcination.

[0031] The present invention also provides a plasmon / hematite heterojunction material, and the plasmon / hematite heterojunction material is obtained by the above preparation method.

[0032] The present invention also provides the use of the above-mentioned plasmon / hematite heterojunction material in photoelectrolysis, preferably as a photoanode.

[0033] The present invention also provides an electrolysis system, which comprises a photoanode, and the photoanode is selected from the above-mentioned plasmon / hematite heterojunction material.

[0034] According to an embodiment of the present invention, the electrolysis system further comprises a counter electrode, and the counter electrode can be a counter electrode known in the art. Exemplarily, the counter electrode is a platinum wire.

[0035] According to an embodiment of the present invention, the electrolysis system further comprises a reference electrode, and the reference electrode can be a reference electrode known in the art. Exemplarily, the reference electrode is a silver chloride electrode.

[0036] According to an embodiment of the present invention, the electrolysis system further comprises an electrolyte. Preferably, the electrolyte comprises a solvent (such as acetonitrile), water and an electrolyte. Further, the content of the water is 25% to 75%, for example 50%. Further, the concentration of the electrolyte can be 0.05 to 0.2M, exemplified by 0.1M. In the present invention, the unit M of concentration refers to mol / L, for example 0.1M refers to a concentration of 0.1mol / L.

[0037] Preferably, the electrolyte is selected from chlorides, such as sodium chloride.

[0038] The present invention also provides application of the electrolysis system in preparing epoxide.

[0039] A method for preparing epoxides comprises subjecting a styrene olefin substrate to a photoelectrochemical epoxidation reaction using the electrolysis system to prepare the epoxides.

[0040] According to an embodiment of the present invention, the styrene olefin substrate is preferably selected from at least one of the compounds having the following structural formula:

[0041]

[0042] According to an embodiment of the present invention, the concentration of the styrene olefin substrate is 0-5 mM, such as 1 mM, 2 mM, 3 mM, 4 mM, 5 mM. In the present invention, the unit of concentration mM refers to mmol / L, such as 1 mM means a concentration of 1 mmol / L.

[0043] According to an embodiment of the present invention, the photoelectrochemical epoxidation reaction is electrolyzed under light conditions. Preferably, the light intensity can be selected from conditions known in the art, such as 300 mW / cm 2 .

[0044] According to an embodiment of the present invention, the light source used in the photoelectrochemical epoxidation reaction may be a light source known in the art, such as an LED white light.

[0045] According to an embodiment of the present invention, the photoelectrochemical epoxidation reaction is electrolyzed under constant potential conditions. Preferably, the constant potential can be selected under conditions known in the art, such as an applied voltage of 0.8 V vs. Ag / AgCl.

[0046] According to an embodiment of the present invention, the area of ​​the photoanode in the electrolysis system may be an area known in the art, for example, 2×4 cm 2 .

[0047] According to an embodiment of the present invention, the reaction temperature of the photoelectrochemical epoxidation is not higher than 40°C, for example, 25°C.

[0048] According to an embodiment of the present invention, the photoelectrochemical epoxidation is carried out in a single cell. For example, the concentration of the styrene olefin substrate in the single cell is 5 mM; the speed of the reaction in the single cell is 1000 rpm; and the volume of the reaction solution in the single cell is 15 mL. The epoxidation performance is best when the water content in the single cell reaction is 50%.

[0049] Beneficial effects of the present invention:

[0050] The present invention provides a plasmon / hematite heterojunction material for efficient catalysis of styrene olefin epoxidation and a preparation method thereof. The present invention utilizes Ag@AgCl nanomaterials with plasmon absorption effect and C 3 N 4 and α-Fe 2 O 3 The plasmon / hematite heterojunction material is assembled and constructed. 3 N 4 -α-Fe 2 O 3 The invention discloses a three-electrode system with a photoanode as a working electrode, and uses the system to carry out a method for chloride ion-mediated photoelectrocatalytic epoxidation of styrene olefins. Under stirring, the chloride ions are oxidized on the surface of the photoanode to generate hypochlorous acid, and then the hypobromous acid oxidizes the olefin substrate to generate epoxide with high selectivity and high Faradaic efficiency.

[0051] The plasmon / hematite heterojunction material of the present invention is simple to prepare, easy to operate, and has high stability, and can use visible light under mild conditions to convert styrene olefin compounds into corresponding oxidized styrene compounds with high selectivity. The method of the present invention is simple, easy to operate, and low in cost, and has certain universality for styrene substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The Ag@AgCl-C prepared in Example 1 3 N 4 -α-Fe 2 O 3 XRD pattern of .

[0053] Figure 2 The Ag@AgCl-C prepared in Example 1 3 N 4 -α-Fe 2 O 3 XPS graph.

[0054] Figure 3 The α-Fe prepared in Example 1 2 O 3 and Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 Solid-state UV-visible absorption comparison of the photoelectrode.

[0055] Figure 4 The α-Fe prepared in Example 1 2 O 3 and Ag@AgCl-C 3 N4 -α-Fe 2 O 3 Comparison of incident photon-to-electron conversion efficiency (IPCE) of photoelectrodes.

[0056] Figure 5 In Application Example 1, α-Fe 2 O 3 , C 3 N 4 -α-Fe 2 O 3 and Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 Linear sweep voltammetry (LSV) curves of each of them as working electrode under chlorine-mediated olefin epoxidation conditions.

[0057] Figure 6 For the Ag@AgCl-C in Application Example 2 3 N 4 -α-Fe 2 O 3 Photoelectrocatalytic activity of chlorine-mediated styrene epoxidation as a function of Ag loading.

[0058] Figure 7 For the Ag@AgCl-C in Application Example 3 3 N 4 -α-Fe 2 O 3 Substrate conversion and epoxide product selectivity of photoelectrocatalytic chlorine-mediated styrene epoxidation at different applied potentials.

[0059] Figure 8 For the Ag@AgCl-C in Application Example 4 3 N 4 -α-Fe 2 O 3 Results on conversion and selectivity of photoelectrocatalytic epoxidation of styrene substrates with various substituents in a single cell. DETAILED DESCRIPTION

[0060] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0061] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0062] The photoelectrochemical epoxidation reaction in the following examples was carried out in an electrochemical workstation, the model of which was PGSTAT302N (Autolab, Metrohm).

[0063] Example 1

[0064] Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 Preparation of photoanode:

[0065] (1) α-Fe 2 O 3 - Preparation of Ti photoanode: Place the purchased titanium foil in acetone and ethanol for 10 minutes each, and then etch it in concentrated hydrochloric acid in an 80°C oil bath for 40 minutes to obtain the treated titanium foil. 0.27g urea, 10mL titanium trichloride and 1.22g ferric chloride are added to 60mL deionized water and stirred to obtain a precursor solution. The treated titanium foil is then placed in a 20mL polytetrafluoroethylene liner, and then 10mL of the above precursor solution is added to the liner. The reactor is tightened and placed in an oven for hydrothermal reaction at 100°C for 10 hours to obtain hydroxyl iron (β-FeOOH) grown on the titanium foil. Finally, the titanium foil is placed in a muffle furnace and calcined at 550°C for 2 hours and cooled naturally to obtain α-Fe 2 O 3 -Ti photoanode. The heating rate to 550°C was 10°C / min.

[0066] In the above step (1), the titanium foil has a size of 2 cm×4 cm and an effective working area of ​​2 cm×2 cm.

[0067] (2) Ag@AgCl-C 3 N 4 Preparation: Weigh 9g urea into a crucible, sinter at 550℃ for 8h and cool naturally to obtain C 3 N 4 The temperature of the powder was raised to 550°C at a rate of 10°C / min. Then 0.2 g of C 3 N 4 0.32 g of hexadecyltrimethylammonium chloride (CTAC) was mixed in 100 mL of deionized water, stirred for 30 min, and ultrasonicated for 30 min; then 2.2 ml of 0.2 M AgNO was quickly added to the above solution. 3 The solution was stirred for 1 h and irradiated under a 300 W xenon lamp for 30 min (the light intensity was set to 200 mW / cm 2 ); filter and wash with deionized water; finally, dry in an oven at 80°C for 8 h, calcine in a muffle furnace at 300°C for 3 h and cool naturally to obtain Ag@AgCl-C3 N 4 The temperature of the powder was raised to 300 °C at a rate of 10 °C / min.

[0068] (3)C 3 N 4 -α-Fe 2 O 3 Preparation of photoanode: weigh 10 mg C 3 N 4 The powder was dissolved in 10 mL of ethanol and the α-Fe 2 O 3 -Ti was fixed on the workbench of the spin coater, and 100 μL C 3 N 4 The ethanol solution was dropped onto the α-Fe 2 O 3 -Ti, and then calcined in a tube furnace at 350°C in an Ar atmosphere for 2 h. The rate of heating to 350°C was 5°C / min.

[0069] (4) Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 Preparation of photoanode: Weigh 10 mg of Ag@AgCl-C prepared in step (2) above. 3 N 4 The powder was dissolved in 10 mL of ethanol and the α-Fe 2 O 3 -Ti was fixed on the workbench of the spin coater, and 100 μL of Ag@AgCl-C was drawn with a pipette. 3 N 4 The ethanol solution was dropped onto the α-Fe 2 O 3 -Ti, and then calcined in a tube furnace at 350°C in an Ar atmosphere for 2 h. The rate of heating to 350°C was 5°C / min.

[0070] In the above steps, the rotation speed of the spin coater was set to 3000 r and the time was 5 min.

[0071] Example 2

[0072] In this example, Ag@AgCl-C with different Ag loading amounts were prepared with reference to Example 1. 3 N 4 -α-Fe 2 O 3 The only difference is that in step (2), Ag@AgCl-C 3 N 4When adjusting the AgNO 3 The concentrations of Ag@AgCl-C with different loading amounts of Ag are 0.05M, 0.1M, 0.2M, 0.3M, and 0.5M, respectively. 3 N 4 -α-Fe 2 O 3 photoelectrodes, denoted as Ag@AgCl-C 3 N 4 (0.05M)-α-Fe 2 O 3 、Ag@AgCl-C 3 N 4 (0.1M)-α-Fe 2 O 3 、Ag@AgCl-C 3 N 4 (0.2M)-α-Fe 2 O 3 、Ag@AgCl-C 3 N 4 (0.3M)-α-Fe 2 O 3 、Ag@AgCl-C 3 N 4 (0.5M)-α-Fe 2 O 3 .

[0073] Application Example 1

[0074] Study on α-Fe 2 O 3 , C 3 N 4 -α-Fe 2 O 3 and Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 Linear sweep voltammetry (LSV) curves of three photoanodes in chlorine-mediated epoxidation system:

[0075] In a single-chamber three-electrode system, the α-Fe 2 O 3 , C 3 N 4 -α-Fe 2 O 3 and Ag@AgCl-C 3 N 4 -α-Fe 2 O 3The photoanode was used as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode. The solvent was a mixed solution of acetonitrile and water (volume ratio was 1:1), the electrolyte was 0.1M sodium chloride, and the solution volume was 15mL. The light source was an LED white light source, and the light intensity on the electrode surface was 300mW / cm 2 The potential range is 0-1.5V vs.Ag / AgCl. Figure 5 The LSV results of different photoanodes are compared. Figure 5 It can be seen that in C 3 N 4 After loading, the current density of the system increased slightly, and when Ag@AgCl-C 3 N 4 After loading, the current density in the system increased significantly compared to the unmodified α-Fe 2 O 3 It increased by 6 times, which shows that Ag@AgCl-C 3 N 4 The loading of α-Fe can effectively increase 2 O 3 Catalytic epoxidation activity of the photoanode.

[0076] Application Example 2

[0077] The effect of different Ag loading amounts on the enhancement of α-Fe 2 O 3 Effect of catalytic epoxidation activity.

[0078] In a single-chamber three-electrode system, the Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 The photoelectrode was used as the working electrode, Ag / AgCl as the reference electrode, platinum wire as the counter electrode, the solvent was a mixed solution of acetonitrile and water (volume ratio of 1:1), the electrolyte was 0.1M sodium chloride, and the concentration of styrene was 5mM. The light source was an LED white light source, and the light intensity reaching the electrode surface was 300mW / cm 2 The potential range is 0-1.2V vs.Ag / AgCl. Figure 6 Comparison of Ag@AgCl-C loaded with different amounts of Ag 3 N 4 -α-Fe 2 O 3 The catalytic epoxidation activity is determined by Figure 6 It can be seen that: with the use of AgNO 3 With the increase of concentration, Ag@AgCl-C 3 N 4 -α-Fe 2 O3 The catalytic epoxidation activity showed a trend of increasing first and then decreasing, and in the presence of AgNO 3 The best enhancement effect was achieved at a concentration of 0.2 M, compared with the unmodified α-Fe 2 O 3 The catalytic activity is increased by 6 times.

[0079] Application Example 3

[0080] Study on the effect of different applied potentials on Ag@AgCl-C in a single cell system 3 N 4 -α-Fe 2 O 3 Effect of FE on catalytic styrene epoxidation.

[0081] Photoelectrochemical experiment: In a single-chamber three-electrode system, the Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 The electrode is used as the working electrode, Ag / AgCl is used as the reference electrode, and platinum wire is used as the counter electrode. The volume of the reaction solution in a single cell is 15 mL. The solvent is a mixed solution of acetonitrile and water (volume ratio is 1:1), the electrolyte is 0.1 M sodium chloride, and the concentration of styrene is 5 mM. The light source is an LED white light source, and the light intensity reaching the electrode surface is 300 mW / cm 2 In a single cell system, constant potential electrolysis was performed at a rotation speed of 1000 rpm, and the reactants and products were quantified by high performance liquid chromatography at 0.9, 1, 1.1, 1.2, 1.3, 1.4, and 1.5 V vs. Ag / AgCl. After electrolysis at 15C, the reactants and products were quantified by high performance liquid chromatography ( Figure 7 ).from Figure 7 It can be seen that under the selected multi-potential, the conversion rate of styrene and the selectivity of epoxy products hardly change with the change of applied potential, and both remain at a level close to 90%. 3 N 4 -α-Fe 2 O 3 The photoelectrode has good potential compatibility for the styrene epoxidation reaction and can maintain efficient styrene epoxidation performance in a wide potential window.

[0082] Figure 7 The calculation formulas for styrene conversion and epoxide selectivity are as follows:

[0083]

[0084]

[0085] Application Example 4

[0086] Study on Ag@AgCl-C in single cell system 3 N 4 -α-Fe 2 O 3 The compatibility of the photoanode with a variety of olefin substrates, styrene substrates with different substituents are selected from the following 6 substrates of the following structural formula:

[0087]

[0088] Photoelectrochemical experiment: In a single-chamber three-electrode system, the Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 The electrode is used as the working electrode, Ag / AgCl is used as the reference electrode, and platinum wire is used as the counter electrode. The volume of the reaction solution in a single cell is 15 mL. The solvent is a mixed solution of acetonitrile and water (volume ratio is 1:1), the electrolyte is 0.1 M sodium chloride, and the above 6 styrene substrates are taken respectively, and their concentrations are all 5 mM. The light source is an LED white light source, and the light intensity reaching the electrode surface is 300 mW / cm 2 In a single cell system, constant potential electrolysis was performed at a rotation speed of 1000 rpm. At 0.9 V vs. Ag / AgCl, the reactants and products were quantified using high performance liquid chromatography and nuclear magnetic resonance hydrogen spectroscopy after electrolysis passed 15C. The results are shown in Figure 8 .

[0089] like Figure 8 As shown in the figure, after the photoelectrochemical reaction, for styrene substrates with different substituents, the conversion rate is 70-90%, and the selectivity of the prepared epoxy product is above 60%, and the highest can reach 93%. This shows that Ag@AgCl-C 3 N 4 -α-Fe 2 O 3 The photoelectrode has excellent compatibility with styrene substrates with different substituents.

[0090] The above is a description of the exemplary embodiments of the present invention. However, the protection scope of the present application is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a plasmon / hematite heterojunction material, characterized in that: The preparation method comprises the following steps: a) preparing α-Fe2O3 photoanode; b) preparing Ag@AgCl-C3N4 catalyst; c) preparing Ag@AgCl-C3N4-α-Fe2O3, i.e. the plasmon / hematite heterojunction material.

2. The preparation method according to claim 1, characterized in that: In step a), the method for preparing the α-Fe2O3 photoanode comprises: preparing β-FeOOH by hydrothermal reaction of an iron source, and then calcining the β-FeOOH at high temperature to obtain the α-Fe2O3 photoanode. Preferably, in step a), the iron source is added in the form of a solution. Preferably, in step a), the temperature of the hydrothermal reaction is 90-100° C., and the time of the hydrothermal reaction is 10-12 hours. Preferably, in step a), the high temperature calcination refers to calcining β-FeOOH. Preferably, the calcination is a primary calcination, the primary calcination temperature is 500-600°C, and the primary calcination time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that: In step b), the preparation method of the Ag@AgCl-C3N4 catalyst includes: first preparing C3N4 powder; then mixing the C3N4 powder with an organic chloride, adding an Ag source solution thereto, stirring and then irradiating with light to react; filtering, washing, drying and calcining to obtain the Ag@AgCl-C3N4 catalyst. Preferably, the preparation of C3N4 powder comprises: sintering a carbon nitrogen source to obtain C3N4 powder. Preferably, the sintering temperature is 500-600° C. and the sintering time is 8-10 hours. Preferably, in step b), when the Ag@AgCl-C3N4 catalyst is obtained by calcination, the calcination temperature is 250-350° C. and the calcination time is 2-4 hours.

4. The preparation method according to claim 1, characterized in that: Step c) specifically includes the following steps: modifying the Ag@AgCl-C3N4 catalyst on the surface of the α-Fe2O3 photoanode, and then calcining in the absence of oxygen to obtain Ag@AgCl-C3N4-α-Fe2O3. Preferably, in step c), the oxygen-free calcination is carried out under inert atmosphere conditions. Preferably, the temperature of the oxygen-free calcination is 300-400° C., and the time of the oxygen-free calcination is 1-3 hours.

5. A plasmon / hematite heterojunction material, characterized in that: The plasmon / hematite heterojunction material is obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the plasmon / hematite heterojunction material according to claim 5 in photoelectrolysis.

7. An electrolysis system, characterized in that: The electrolysis system comprises a photoanode, wherein the photoanode is selected from the plasmon / hematite heterojunction material of claim 5.

8. The electrolysis system according to claim 7, characterized in that: The electrolysis system also includes a counter electrode. Preferably, the electrolysis system further comprises a reference electrode. Preferably, the electrolysis system further comprises an electrolyte.

9. Use of the electrolysis system according to claim 7 or 8 in the preparation of epoxides.

10. A method for preparing epoxide, comprising subjecting a styrene olefin substrate to a photoelectrochemical epoxidation reaction using the electrolysis system according to claim 7 or 8 to prepare the epoxide.

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