A tandem photocatalyst of indium oxide loaded with copper single atoms and its preparation and application

Abstract

The present invention relates to an indium oxide-loaded copper single atom tandem photocatalyst and its preparation and application. The preparation method comprises the following steps: (1) weighing In(NO3)3 and terephthalic acid, dissolving them in DMF, heating and stirring, centrifuging, washing, and drying to obtain a precursor In-MOF; (2) dispersing the precursor In-MOF in an ethanol solution, adding a CuCl2 solution, stirring, and performing ion exchange to obtain a precursor InCu-MOF; and (3) calcining the precursor InCu-MOF to obtain a loose porous microtubular morphology indium oxide-loaded copper single atom tandem photocatalyst, which is the target product. The catalyst prepared by the present invention has Cu in the form of a single atom, which coordinates with oxygen in In2O3 to form a stable low-valence state and a low-coordination mode. It has a wide light absorption range, greatly improves its ability to reduce carbon dioxide (CO2) under visible light, and shows excellent selectivity for reducing CO2 to ethanol (CH3CH2OH). At the same time, in a gas-liquid reaction system, it simultaneously oxidizes water (H2O) to oxygen (O2).

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials and relates to a tandem photocatalyst of indium oxide loaded with copper single atoms and a preparation method and application thereof. Background Art

[0002] The use of renewable solar energy to convert CO2 into high-value-added carbon-based fuels and chemical raw materials provides a way to establish carbon neutrality to alleviate the rapid consumption of fossil resources and the continuous increase of CO2 emissions. Among all the products that may be formed by CO2 reduction reactions, the multi-carbon (C 2+ ) products are considered the most promising products due to their high energy density and commercial value for industrial manufacturing. CH3CH2OH is particularly popular as a liquid fuel due to its high energy density, wide application, and the ability to leverage the existing extensive infrastructure for the storage and distribution of carbon-based fuels. A commercially viable CO2 reduction reaction requires the development of catalysts that can design reaction configurations by controlling the binding energy of reaction intermediates to guide the reaction pathway towards specific products in multiple dimensions. The conversion of CO2 to CH3CH2OH relies on the transfer of multiple protons and electrons and involves multiple intermediates, making the development of more efficient photocatalysts an important but challenging problem.

[0003] Traditional semiconductor photocatalytic materials have poor applicability in reducing CO2 to multi-carbon products due to their limited light absorption capacity, few effective photogenerated electrons, and active sites that are not conducive to the adsorption of reduction intermediates. Cu-based materials are considered to be unique catalysts that can produce a considerable amount of hydrocarbons and alcohols in addition to two-electron reduction products such as CO and formate. In particular, in the electrochemical reduction of CO2, due to its special CC coupling ability, it is considered to be the only catalyst that can reduce CO2 to C 2+ However, Cu-based catalysts rarely exhibit ideal C 2+ This is because the electron transfer density of CO2 / intermediates from the semiconductor under light is much smaller than that under bias voltage.

[0004] For example, Chinese patent ZL201910237358.9 discloses a copper-based MOF carbonization-derived catalytic material. By controlling pyrolysis conditions and utilizing organic ligands as self-sacrificial templates to in situ reduce copper ions, the catalyst material's metal active centers are highly dispersed, with a higher specific surface area than traditional supported catalysts and a richer mesoporous and microporous structure. The material in this patent is synthesized using high-temperature calcination in an inert atmosphere, making it difficult to synthesize industrially. Furthermore, the copper element in this material serves as a single active site, limiting its application value. Summary of the Invention

[0005] The purpose of the present invention is to provide a tandem photocatalyst of indium oxide loaded copper single atom and its preparation and application, so as to solve the problems of limited light absorption range, few effective photogenerated carriers, poor adsorption capacity of active sites for reaction intermediates, and Cu + At least one of the technical problems such as poor photocatalytic reduction of CO2 due to difficulty in stable existence.

[0006] Unlike existing Cu-based MOF carbonization-derived materials, this invention utilizes an In-based MOF. A bimetallic InCu-based MOF is constructed via ion exchange, followed by annealing in air to form a stable tandem photocatalyst with Cu single atoms supported on In2O3. This tandem photocatalyst comprises two active units, Cu-O and In-O, which work together to effectively promote the CC coupling reaction in the photocatalytic CO2 reduction process, enabling the conversion of CO2 to high-value ethanol using light energy.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present invention provides a method for preparing a tandem photocatalyst of indium oxide loaded with copper single atoms. + It exists stably in the form of 3-coordination with O, has a wide absorption range, and the light absorption edge can reach 470nm. The carriers are not easy to recombine. Under the irradiation of simulated sunlight with λ>420nm, the reduction rate of CO2 to CH3CH2OH in pure water system can reach up to 20.7μmol·h -1 ·g -1 , and simultaneously oxidize H2O into O2.

[0009] Specifically, the preparation method comprises the following steps:

[0010] (1) Weighing In(NO3)3 and terephthalic acid, dissolving them in DMF, heating and stirring, centrifuging, washing, and drying to obtain the precursor In-MOF;

[0011] (2) Dispersing the precursor In-MOF in an ethanol solution, adding a CuCl2 solution and stirring to perform ion exchange, thereby obtaining the precursor InCu-MOF;

[0012] (3) The precursor InCu-MOF is calcined to obtain a tandem photocatalyst of indium oxide loaded with copper single atoms with a loose porous microtubular morphology, which is the target product.

[0013] Furthermore, in step (1), the mass ratio of In(NO3)3 to terephthalic acid is (0.8-1.2):1, preferably 1:1.

[0014] Furthermore, in step (1), the heating and stirring temperature is 100-140° C., and the time is 20-40 min.

[0015] Furthermore, in step (2), the ratio of the precursor In-MOF to the CuCl2 solution is 8 mg:(3-5) mL, preferably 8 mg:4 mL, and the concentration of the CuCl2 solution is 20-30 mM, preferably 25 mM.

[0016] Furthermore, in step (2), the ion exchange treatment time is 2-5 min, preferably 2 min.

[0017] Furthermore, in step (3), the calcination temperature is 400-600°C, preferably 500°C, and the calcination time is 1-3 hours, preferably 2 hours. In addition, the overall heating rate during the calcination process can be controlled to be 1°C / min.

[0018] Furthermore, in step (3), calcination is carried out in an air atmosphere.

[0019] Copper (Cu) is an element with great application potential for CO2 reduction reaction. This application designs Cu to be loaded on In2O3 in the form of single atoms. By controlling the chemical valence of Cu through different coordination with O, it can not only adjust the band gap, but also prevent the recombination of photogenerated carriers, thus achieving CO2 reduction and H2O oxidation. Cu single atoms and In2O3 form a tandem photocatalyst. In2O3 provides high coverage of *CO. At the same time, low-coordinate Cu (3-coordinate) with Cu + The presence of the catalyst in the form of carbonylation is beneficial to the adsorption of key intermediates, effectively promoting the coupling of *CO and *COH, and realizing the reduction of CO2 to C2 fuel.

[0020] The preparation principle process of the present invention can be referred to as follows:

[0021] ① Terephthalic acid was selected as the ligand and the metal salt was In(NO3)3 to prepare In-MOF solid hexagonal prisms based on In;

[0022] ② Through ion exchange reaction, In is partially replaced by Cu to obtain InCu-MOF;

[0023] ③In2O3 / Cu-O was obtained by calcining in air x ;

[0024] ④The addition of Cu is beneficial to the adsorption of CO2 and CC coupling intermediates, thereby improving the performance of photocatalytic reduction of CO2;

[0025] ⑤In2O3 / Cu-O xThe addition of Cu causes electron redistribution, thereby changing the d-band center of the catalyst and further improving the photocatalytic reduction of CO2 performance;

[0026] ⑥In2O3 / Cu-O x The pn principle exists in the process, which can realize the simultaneous reduction of CO2 and oxidation of H2O without adding sacrificial agents.

[0027] The second technical solution of the present invention provides a tandem photocatalyst of indium oxide loaded with copper single atoms, which is prepared by the preparation method described above. The tandem photocatalyst has a loose porous microtubular morphology.

[0028] The third technical solution of the present invention provides an application of an indium oxide-supported copper single atom tandem photocatalyst, which is used for visible light photocatalytic reduction of CO2 to CH3CH2OH. In addition, the tandem photocatalyst is an indium oxide-supported copper single atom structure with different coordination (In2O3 / Cu-O x ), containing three elements: In, O, and Cu. The etching caused by the addition of Cu and the carbon reduction caused by annealing in air give the material a loose, porous microtubular morphology. The different coordinations of Cu are mainly controlled by the ion exchange time. The optimal ion exchange time is 2 minutes, which can obtain a three-coordinated Cu with a valence of +1, namely In2O3 / Cu-O3. The absorption edge of In2O3 / Cu-O3 can reach 470nm, and the carriers are not easy to recombine. Under simulated sunlight with λ>420nm, the reduction rate to CH3CH2OH can reach up to 20.7μmol·h -1 ·g -1 .

[0029] Furthermore, when the catalyst is used for visible light photocatalytic reduction of CO2 to CH3CH2OH, it can be carried out in pure water without adding a sacrificial agent, and H2O can be simultaneously oxidized to O2.

[0030] The loose porous microtubular indium oxide-loaded copper single atom tandem photocatalyst of the present invention is a new type of photocatalyst and has the following advantages in the application of photocatalytic reduction of CO2:

[0031] 1) The formation of loose porous microtube morphology is conducive to the adsorption of CO2, thereby improving the photocatalytic reduction of CO2 performance;

[0032] 2) The addition of Cu facilitates the adsorption of CO2 and CC coupling intermediates, thereby improving the photocatalytic reduction of CO2 performance;

[0033] 3) In2O3 / Cu-O x The addition of Cu causes electron redistribution, which changes the d-band center of the catalyst and thus improves the photocatalytic reduction of CO2 performance.

[0034] 4) In2O3 / Cu-O x The pn principle exists in the process, which can realize the simultaneous reduction of CO2 and oxidation of H2O without adding sacrificial agents.

[0035] The present invention discloses a tandem photocatalyst of indium oxide loaded with copper single atoms in a loose porous microtubular morphology, which is obtained by an in-situ introduction method, realizes the absorption and utilization of ultraviolet-visible light, promotes the development of photocatalysts, and has significant practical applications for more fully utilizing sunlight.

[0036] The present invention discloses a tandem photocatalyst of indium oxide loaded with copper single atoms in a loose porous microtubular morphology. Compared with pure In2O3, the photocatalyst has high CO2 reduction performance and can reduce CO2 to a C2 product CH3CH2OH with higher added value. The photocatalyst also has the characteristics of low resistivity, rapid self-charge transfer capability, high photogenerated carrier separation capability, low carrier recombination rate, and good CO2 reduction cycle stability.

[0037] The present invention discloses a tandem photocatalyst of indium oxide loaded with copper single atoms in a loose porous microtubular morphology, which uses InCu-MOF obtained by ion exchange as a precursor, and obtains In2O3 / Cu-O by annealing in air. x The morphology is characterized by a uniform, loose, porous microtubular distribution, providing a high specific surface area for the material to better absorb sunlight, achieving excellent CO2 reduction photocatalytic activity and selectivity. Therefore, the preparation process is very simple, suitable for industrial-scale production, and has high economic and practical value.

[0038] The present invention discloses a tandem photocatalyst of indium oxide loaded with copper single atoms in a loose porous microtubular morphology. The addition of Cu forms a tandem catalyst, causing electron redistribution, effectively changing the electron transfer path, promoting the adsorption of intermediates, and facilitating the formation of *OC-COH intermediates. It exhibits high efficiency and selective reduction of CO2 to CH3CH2OH, and exhibits good photocatalytic activity in the ultraviolet-visible light region and excellent cyclic stability. At the same time, it can achieve the oxidation of H2O to O2, such as Figure 11 As shown. Under visible light irradiation, the rate of reducing CO2 to CH3C H2OH can reach up to 20.7μmol·h -1 ·g -1 .

[0039] Compared to existing technologies, the present invention's porous indium oxide-supported copper single-atom tandem photocatalyst offers advantages such as no sacrificial agent addition, ultraviolet-visible light absorption, low photogenerated electron-hole recombination rate, absence of precious metals, high CO2 reduction performance, excellent reduction selectivity, high-value-added C2 products as reduction products, and simultaneous H2O oxidation. Furthermore, the preparation method is simple to operate, low-cost, and uses non-toxic raw materials, ensuring environmentally friendly production. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a scanning electron microscope image of the indium oxide-supported 3-coordinated copper single atom tandem photocatalyst obtained in Example 1;

[0041] Figure 2 This is a transmission electron microscopy image of the indium oxide-supported 3-coordinated copper single atom tandem photocatalyst obtained in Example 1;

[0042] Figure 3 This is a spherical aberration transmission electron microscopy image of the tandem photocatalyst of indium oxide loaded with three-coordinated copper atoms obtained in Example 1;

[0043] Figure 4 This is a transmission electron microscopy image of the element distribution of the indium oxide-supported 3-coordinated copper single atom tandem photocatalyst obtained in Example 1;

[0044] Figure 5 The X-ray electron diffraction patterns of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3;

[0045] Figure 6 X-ray photoelectron spectra of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3;

[0046] Figure 7 The Auger electron spectra of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 are shown;

[0047] Figure 8 The UV-visible diffuse reflectance images of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 are shown;

[0048] Figure 9 The photocurrent diagrams of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 under visible light irradiation are shown;

[0049] Figure 10 Graph showing the CO2 reduction and H2O oxidation performance rates of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2, and 3 under visible light irradiation;

[0050] Figure 11 Schematic diagram of the application of the photocatalyst of the present invention. DETAILED DESCRIPTION

[0051] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0052] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0053] In the present invention, the electrochemical performance is tested by an electrochemical workstation, and the electrochemical workstation used is a Chenhua electrochemical workstation, model CHI760E.

[0054] UV-visible diffuse reflectance is tested by SHMADZU-UV 2600;

[0055] X-ray electron diffraction was tested by D8 advance;

[0056] The CO2 reduction performance test uses 600M 1 H NMR and Thermofisher Trace 1310 gas chromatography measurements.

[0057] The electrochemical performance testing method in each embodiment of the present invention is as follows:

[0058] 7.5 mg of indium oxide-loaded copper single atom tandem photocatalyst, 1 mg of ethyl cellulose, 1 mL of α-terpineol, and 0.5 mL of ethanol were mixed, and then ultrasonicated at a power of 60 W and a frequency of 40 kHz for 12 h to obtain a slurry;

[0059] The slurry obtained above was coated on FTO glass with a coating thickness of 0.5-1 mm, and dried in an oven at 60° C. to obtain an electrochemical test working electrode, which was then tested on an electrochemical workstation for electrochemical performance.

[0060] Example 1

[0061] A tandem photocatalyst of indium oxide loaded with copper atoms in a loose porous microtubular morphology, mainly containing three main elements: In, O, and Cu, is prepared by a method comprising the following steps:

[0062] (1) Preparation of In-MOF

[0063] Take 60 mg of In(NO3)3 and 60 mg of terephthalic acid respectively and dissolve them in 40 mL of DMF. After stirring the solution at 120°C for 30 minutes, centrifuge with ethanol, wash and dry to obtain MIL-68(In). The speed is controlled to be 8000 r / min for centrifugation for 3 minutes, and the drying condition is vacuum drying at 80°C for 12 hours.

[0064] (2) Preparation of InCu-MOF

[0065] The In-MOF prepared in step (1) was dispersed in anhydrous ethanol, and then a CuCl2 solution was added dropwise for ion exchange to obtain InCu-MOF. The volume of anhydrous ethanol was 10 mL, the mass of In-MOF was 8 mg, the concentration of the CuCl2 solution was 25 mM, the volume of the CuCl2 solution was 4 mL, and the ion exchange time was 2 min.

[0066] (3) Preparation of indium oxide loaded with tri-coordinated copper atoms (hereinafter referred to as In2O3 / Cu-O3)

[0067] The InCu-MOF prepared in step (2) above was placed in a muffle furnace and calcined at a temperature of 500°C, a heating rate of 1°C / min, and a holding time of 2 hours to obtain In2O3 / Cu-O3 with a loose porous microtube morphology.

[0068] Comparative Example 1:

[0069] Compared with Example 1, most of the steps are the same except that step (2) is omitted.

[0070] When the calcination process of step (3) is directly carried out without adding Cu source, pure In2O3 is formed, and In2O3 / Cu-O x .

[0071] Comparative Example 2:

[0072] Compared with Example 1, most of the steps are the same except that the ion exchange time in step (2) is 5 min.

[0073] When the ion exchange time in step (2) is 5 min, more Cu replaces In, so that In2O3 / Cu-O4 is formed after calcination in step (3), and Cu in the catalyst exists in the form of +2 valence and 4 coordination.

[0074] Comparative Example 3:

[0075] Compared with Example 1, most of the steps are the same except that the ion exchange time in step (2) is 10 min.

[0076] When the ion exchange time in step (2) is 10 min, Cu completely replaces In to form Cu-MOF, so that CuO is formed after calcination in step (3). Cu in the catalyst exists in a +2 valence, 4-coordinate form, and no In2O3 crystal phase exists.

[0077] The In2O3 / Cu-O3 photocatalyst obtained above was scanned using a scanning electron microscope (model JM7900, manufactured by JEOL Electronics Co., Ltd., Japan). The obtained scanning electron microscope image is shown in FIG. Figure 1 As shown, from Figure 1 The loose porous microtubule morphology can be seen in the figure.

[0078] The In2O3 / Cu-O3 photocatalyst obtained above was scanned using a transmission electron microscope (model JEOL JEM-2100F, manufactured by JEOL Electronics Co., Ltd., Japan). The obtained transmission electron microscope image is shown in FIG. Figure 2 As shown, from Figure 2 It can be seen that In2O3 / Cu-O3 has a loose porous microtube morphology.

[0079] The In2O3 / Cu-O3 photocatalyst obtained above was scanned using a spherical aberration corrected transmission electron microscope (EM-ARM300F, manufactured by JEOL Electronics Co., Ltd., Japan). The obtained transmission electron microscope image is shown in FIG. Figure 3 As shown, from Figure 3 It can be seen that Cu exists in the form of single atoms.

[0080] The In2O3 / Cu-O3 photocatalyst obtained above was scanned using a spherical aberration corrected transmission electron microscope (model EM-ARM300F, manufactured by JEOL Electronics Co., Ltd., Japan). The element distribution obtained is as follows: Figure 4 As shown, from Figure 4 It can be seen that the material contains three elements: In, O, and Cu, and the elements are evenly distributed.

[0081] The photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 were measured using an X-ray diffractometer (model: D8 advance, manufacturer: Bruker, Germany). The obtained XRD patterns are shown in FIG. Figure 5 As shown, Figure 5 In the figure, the horizontal axis is the 2θ angle, and the vertical axis is the diffraction peak intensity, wherein In2O3 / Cu-O3 represents the indium oxide loaded 3-coordinated copper single atom photocatalyst obtained in Example 1, In2O3 represents the indium oxide photocatalyst obtained in Comparative Example 1, In2O3 / Cu-O4 represents the indium oxide loaded 4-coordinated copper single atom photocatalyst obtained in Comparative Example 2, and CuO represents the copper oxide photocatalyst obtained in Comparative Example 3. Figure 5It can be seen that Cu in In2O3 / Cu-O3 exists in the form of single atoms instead of forming an In2O3 / CuO heterojunction.

[0082] The photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 were measured using an X-ray photoelectron spectrometer (model: Kratos Axis UltraDLD, manufacturer: Kratos, UK). The XPS patterns obtained by XPSPEAK41 software analysis are shown in FIG. Figure 6 As shown, Cu exists with a valence of +1 in In2O3 / Cu-O3, while it exists with a valence of +2 in In2O3 / Cu-O4 and CuO.

[0083] The photocatalysts obtained in Example 1 and Comparative Example 2 were measured using an Auger electron spectrometer (model: Kratos Axis UltraDLD, manufacturer: Kratos, UK). The AES graphs obtained are shown in FIG. Figure 7 As shown, Cu exists with a valence of +1 in In2O3 / Cu-O3, while it exists with a valence of +2 in In2O3 / Cu-O4 and CuO.

[0084] The photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 were measured using an ultraviolet-visible spectrophotometer (model: UV-2400, manufacturer: Shimadzu, Japan). The obtained ultraviolet-visible diffuse reflectance patterns are shown in FIG. Figure 8 As shown, Figure 8 In the equation, the horizontal axis is the wavelength and the vertical axis is the absorption rate. Figure 8 It can be seen that the addition of Cu effectively broadens the light absorption range and intensity.

[0085] The photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 were measured using an electrochemical workstation (model: CHI760E, manufacturer: Shanghai Chenhua). The photocurrent graphs obtained are shown in FIG. Figure 9 As shown, the introduction of three-coordinated Cu makes the catalyst exhibit excellent photogenerated electron separation efficiency.

[0086] The photocatalysts obtained in Example 1 and Comparative Examples 1, 2, and 3 were measured using a liquid nuclear magnetic spectrometer (model: AVANCE III HD 600MHz, manufacturer: Bruker, Germany). The CO2 reduction test process was as follows: 10 mg of the above photocatalysts were placed in a sealed reactor, 10 mL of deionized water was added, and ultrasonic waves were performed at a power of 60 W and a frequency of 40 kHz for 10 minutes. The reactor was then sealed, vacuumed, and introduced with CO2. With circulating cooling water added, the reactor was placed under irradiation with a 300 W xenon lamp (with a 420 nm cutoff filter) for CO2 reduction testing. The CO2 reduction test was performed using liquid nuclear magnetic resonance every 2 hours of illumination. Figure 10 As shown, In2O3 / Cu-O3 can reduce CO2 to CH3CH2OH.

[0087] Photocatalytic reduction of CO2 and H2O oxidation performance test

[0088] 10 mg of the photocatalysts obtained in Example 1 and Comparative Examples 1, 2 and 3 were respectively weighed and placed in sealed reactors, and 10 mL of deionized water was added. The reactors were then ultrasonically tested at a power of 60 W and a frequency of 40 kHz for 10 minutes. The reactors were then sealed, evacuated, and CO2 was introduced. Under the condition of adding circulating cooling water, the reactors were placed under irradiation of a 300 W xenon lamp (with a 420 nm cutoff filter) for CO2 reduction and H2O oxidation tests.

[0089] The above-mentioned photocatalyst was used for photocatalytic reduction of CO2. The dosage of the photocatalyst was 10 mg. The rate of catalytic reduction of CO2 to CH3CH2OH for 10 h under visible light irradiation was 20.7 μmol·g -1 ·h -1 .

[0090] The above results show that the performance of In2O3 / Cu-O3 photocatalyst in reducing CO2 is much higher than that of pure In2O3 and In2O3 / Cu-O4. The reason may be that the 3-coordinated Cu is Cu + The existence of the catalyst in this form is more conducive to adjusting the electrons of the catalyst to a position suitable for CO2 reduction.

[0091] Comparative Example 4:

[0092] Compared with Example 1, most of the steps are the same except that the calcination atmosphere in step (3) is nitrogen.

[0093] When the calcination atmosphere in step (3) is nitrogen, a large amount of amorphous carbon remains in the material, only a small amount of In2O3 is generated, and Cu cannot coordinate with O to maintain a stable Cu + form.

[0094] Comparative Example 5:

[0095] Compared with Example 1, most of the steps are the same, except that the calcination atmosphere in step (3) is nitrogen and the calcination temperature is 800°C.

[0096] When the calcination atmosphere in step (3) is nitrogen and the calcination temperature is 800°C, there is no In2O3 in the material, Cu cannot coordinate with O, and the material becomes CuIn loaded on graphitized carbon.

[0097] Example 2:

[0098] Compared with Example 1, most of the steps are the same except that the concentration of the CuCl2 solution is 20 mM.

[0099] Example 3:

[0100] Compared with Example 1, most of the steps are the same except that the concentration of the CuCl2 solution is 30 mM.

[0101] Example 4:

[0102] Compared with Example 1, most of the steps are the same, except that the calcination temperature in air is adjusted to 400° C. and the calcination time is adjusted to 3 h.

[0103] Example 5:

[0104] Compared with Example 1, most of the steps are the same, except that the calcination temperature in air is adjusted to 600° C. and the calcination time is adjusted to 1 h.

[0105] In summary, the present invention provides a tandem photocatalyst of indium oxide loaded with copper atoms in a loose porous microtubular morphology, which has excellent photocatalytic and electrochemical properties. When applied to the photocatalytic reduction of CO2, the product has good selectivity for CH3CH2OH, and the rate of producing CH3CH2OH can reach up to 20.7 μmol·g -1 ·h -1 The preparation method has the characteristics of simple operation and low production cost.

[0106] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a tandem photocatalyst of indium oxide loaded with copper single atoms, characterized in that: The following steps are involved: (1) Weigh In(NO3)3 and terephthalic acid and dissolve them in DMF, heat and stir, centrifuge, wash, and dry to obtain the precursor In-MOF; (2) Dispersing the precursor In-MOF in an ethanol solution, adding a CuCl2 solution and stirring to perform ion exchange, thereby obtaining the precursor InCu-MOF; (3) calcining the precursor InCu-MOF to obtain a tandem photocatalyst of indium oxide loaded with copper single atoms with a loose porous microtubular morphology, which is the target product; In step (2), the ion exchange treatment time is 2 min; In step (3), calcination is carried out in an air atmosphere; In step (2), the ratio of the precursor In-MOF to the CuCl2 solution is 8 mg: (3-5) mL, and the concentration of the CuCl2 solution is 20-30 mM; The target product is indium oxide loaded with 3-coordinated copper single atoms In2O3 / Cu-O3, wherein Cu exists in the form of single atoms rather than forming an In2O3 / CuO heterojunction.

2. The method for preparing a tandem photocatalyst of indium oxide supported copper single atoms according to claim 1, characterized in that: In step (1), the mass ratio of In(NO3)3 and terephthalic acid is (0.8~1.2):

1.

3. The method for preparing a tandem photocatalyst of indium oxide supported copper single atoms according to claim 1, characterized in that: In step (1), the heating and stirring temperature is 100-140°C and the time is 20-40 minutes.

4. The method for preparing a tandem photocatalyst of indium oxide supported copper single atoms according to claim 1, characterized in that: In step (3), the calcination temperature is 400-600°C and the calcination time is 1-3 hours.

5. A tandem photocatalyst of indium oxide loaded with copper single atoms, prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The tandem photocatalyst has a loose porous microtube morphology.

6. The use of the indium oxide-supported copper single atom tandem photocatalyst according to claim 5, characterized in that: The catalyst is used for visible light photocatalytic reduction of CO2 to CH3CH2OH.

7. Use of the indium oxide-supported copper single atom tandem photocatalyst according to claim 6, characterized in that: When the catalyst is used for visible light photocatalytic reduction of CO2 to CH3CH2OH, it is carried out in pure water without adding sacrificial agents, and H2O is simultaneously oxidized to O2.

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