Ag / baSnO3 photocatalyst, preparation method thereof and application thereof in preparation of H2O2

Abstract

The application discloses an Ag / BaSnO3 photocatalyst, a preparation method thereof and application of the Ag / BaSnO3 photocatalyst in preparation of H2O2 and belongs to the technical field of photocatalysts. The Ag / BaSnO3 photocatalyst is prepared by loading Ag on a perovskite type BaSnO3. The preparation method of the Ag / BaSnO3 photocatalyst comprises the following steps: ultrasonic mixing of the perovskite type BaSnO3, ultrapure water and AgNO3, first stirring, obtaining a premix; dropwise addition of a NaBH4 solution, second stirring, and obtaining the Ag / BaSnO3 photocatalyst. The Ag / BaSnO3 photocatalyst is prepared by loading Ag on the perovskite type BaSnO3. 10 The silver (Ag) with the electronic structure is loaded on the perovskite type BaSnO3, the prepared Ag / BaSnO3 forms a Schottky barrier between the Ag and the BaSnO3, the separation efficiency of photo-generated carriers is effectively improved, and the Ag / BaSnO3 photocatalyst serves as a photocatalyst for photocatalytic production of H2O2.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysts, and particularly relates to an Ag / BaSnO3 photocatalyst, a preparation method thereof and application thereof in preparing H2O2. BACKGROUND

[0002] Hydrogen peroxide (H2O2) as an important chemical and green oxidant has been widely used in chemical synthesis, wastewater treatment and textile bleaching and other fields. Due to its high energy density and easy transportation advantages, H2O2 is also considered as a promising fuel that can replace fossil fuels. At present, more than 90% of H2O2 is produced by indirect oxidation of anthraquinone, but this method has the disadvantages of requiring high energy input and generating a large amount of waste. Therefore, it is of great significance to develop a low-cost, environmentally friendly large-scale production method of H2O2.

[0003] The photocatalytic synthesis of H2O2 is a green, environmentally friendly and low-cost H2O2 production process, which takes oxygen and water as precursors and takes sunlight as driving force. In order to obtain high H2O2 efficiency, it is important to enhance the 2e - Oxygen reduction reaction (ORR) or 2e - Water oxidation reaction (WOR). Due to the upward thermodynamics (1.76 V vs. standardized hydrogen electrode, NHE), the 2e - WOR path is difficult to achieve. At the same time, the synthesized H2O2 can be used as a hole trapping agent and is easy to decompose during the reaction. Instead, people have been working on the 2e - O2RR route, by adding alcohol substances to improve the formation of H2O2, which can be oxidized to aldehyde and produce protons. Therefore, the photo-generated electrons can effectively enhance the 2e - O2RR half-reaction. At the same time, improving the 4e - WOR process is also an effective method to improve H2O2. Because O2 is not only the product of 4e - WOR, but also the reactant of 2e - O2RR process. If the in-situ generated O2 can be quickly reduced to H2O2, it is beneficial to WOR. Therefore, introducing a high-activity and high-selectivity 2e - ORR site in the photocatalytic system makes the O2 produced in the WOR process quickly react with the photo-generated electrons, which is crucial for improving the production efficiency of photocatalytic H2O2.

[0004] Loading metal sites on suitable semiconductors can effectively regulate the activity and selectivity of ORR, for example, the prior art proves that Sb monomers can promote two-electron ORR by forming mu-peroxide on the Sb site, and the high concentration of holes on the adjacent N atom can oxidize water to O2, and then reduce it to H2O2. For example, Ni monomers can effectively improve 2e - ORR by enhancing the absorption of O2 and weakening the stability of O-O bond. The prior art also proves that Au monomers can promote the 2e - O2RR transfer pathway by inhibiting the dissociation of O-OH* bond. Therefore, it is urgent to construct a photocatalytic system with suitable electronic structure to effectively regulate the absorption mode of oxygen, the binding energy of intermediate and the oxygen reduction pathway.

[0005] Silver (Ag) is considered to be a very promising material for efficient photocatalytic synthesis of H2O2 due to its unique d 10 electronic structure. It can achieve effective separation of photo-generated carriers and construct reaction centers with high density of electrons / holes. In addition, due to its strong localized surface plasmon resonance (LSPR) effect, Ag modification can effectively improve the efficiency of solar energy utilization. More importantly, Ag is a good oxygen evolution reaction material and can participate in the production of photocatalytic H2O2 as a reactant.

[0006] Perovskite barium stannate (BaSnO3) as a kind of n-type semiconductor material has attracted people's attention due to its excellent photoelectric performance. For example, the prior art has developed BaSnO3 reduced graphene oxide nanocomposites and has been applied to pollutant degradation. It has been reported that Fe-doped BaSnO3 exhibits excellent activity for photocatalytic oxidation of NO. In addition, it has been proved that C3N4 / BaSnO3 heterojunction can photocatalyze water splitting into hydrogen. However, there is no report on the photocatalytic production of hydrogen peroxide by BaSnO3. SUMMARY

[0007] To solve the above technical problems, the present application provides an Ag / BaSnO3 photocatalyst, a preparation method thereof and an application thereof in preparing H2O2. Silver (Ag) with d 10 electronic structure is loaded on perovskite BaSnO3 and applied to photocatalytic synthesis of H2O2. The prepared Ag / BaSnO3 forms a Schottky barrier between Ag and BaSnO3, which can effectively improve the separation efficiency of photo-generated carriers. In addition, Ag loading can improve the oxidation ability of water, produce more oxygen and hydroxyl radicals as raw materials for the synthesis of H2O2, and provide guidance for the rational design of photocatalysts in the production of photocatalytic H2O2.

[0008] To achieve the above object, the application provides an Ag / BaSnO3 photocatalyst prepared by loading Ag on perovskite type BaSnO3.

[0009] The application further provides a preparation method of the Ag / BaSnO3 photocatalyst, comprising the following steps:

[0010] (1) ultrasonic mixing of perovskite type BaSnO3, ultrapure water and AgNO3, first stirring to obtain a premix;

[0011] (2) adding NaBH4 solution dropwise into the premix obtained in step (1), second stirring to obtain the Ag / BaSnO3 photocatalyst.

[0012] Preferably, the mixing ratio of the perovskite type BaSnO3, ultrapure water and AgNO3 in step (1) is 0.05-0.15 g: 25-75 mL: 0.00005-0.0075 g; the ultrasonic mixing frequency in step (1) is 10-40 kHz, and the ultrasonic mixing time is 5-60 min.

[0013] Preferably, the first stirring speed in step (1) is 200-2000 rpm, and the first stirring time is 10-30 min.

[0014] Preferably, the ratio of the amount of the NaBH4 solution to the amount of the perovskite type BaSnO3 in step (1) is 5-15 mL: 0.05-0.15 g; the concentration of the NaBH4 solution in step (2) is 0.03-0.07 M.

[0015] Preferably, the second stirring speed in step (2) is 200-2000 rpm, and the second stirring time is 10-30 min.

[0016] Preferably, the preparation method of the perovskite type BaSnO3 in step (1) comprises the following steps:

[0017] S1, dissolving BaCl2·2H2O and SnCl4·5H2O in ethylene glycol, then adding citric acid, stirring at 60-100 ℃ for 1-3 h to obtain a solution;

[0018] S2, heating the solution obtained in step S1 to 130-170 ℃ and keeping for 12-18 h to obtain a gel;

[0019] S3, calcining the gel obtained in step S2 at 300-700 ℃ for 2-8 h, then heating to 800-1000 ℃ and keeping for 1-3 h to obtain the perovskite type BaSnO3.

[0020] The application further provides application of the Ag / BaSnO3 photocatalyst or the Ag / BaSnO3 photocatalyst prepared by the preparation method in preparation of H2O2.

[0021] The application further provides a method for preparing H2O2 by using the Ag / BaSnO3 photocatalyst, comprising the following steps:

[0022] The Ag / BaSnO3 photocatalyst and the methanol solution are mixed to obtain a photocatalyst solution; air is continuously introduced into the photocatalyst solution under irradiation of a xenon lamp to perform a catalytic reaction, centrifugation, filtration, and H2O2 is obtained.

[0023] Preferably, the volume concentration of the methanol solution is 5-15%; the mixing ratio of the Ag / BaSnO3 photocatalyst and the methanol solution is 10-30 mg: 25-75 mL; the power of the xenon lamp is 200-400 W; and the catalytic reaction time is 0.5 h-2 h.

[0024] Compared with the prior art, the application has the following advantages and technical effects:

[0025] The application loads silver (Ag) with d 10 The Ag / BaSnO3 photocatalyst is prepared by using a sol-gel method and a chemical reduction method. The prepared Ag / BaSnO3 is applied to photocatalytic synthesis of H2O2, and a Schottky barrier is formed between Ag and BaSnO3, which can effectively improve the separation efficiency of photo-generated carriers. The rate of the Ag / BaSnO3 photocatalyst in preparation of H2O2 is 248.9 μmol g -1 h -1 , which is 4 times that of pure BaSnO3. In addition, the Ag loading can improve the oxidation ability of water, generate more oxygen and hydroxyl radicals, and provide guidance for rational design of photocatalysts in photocatalytic production of H2O2. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0027] Figure 1Morphology characterization of BaSnO3 and Ag / BaSnO3, wherein (a) is SEM image of BaSnO3, the scale is 500 nm, (b) is SEM image of Ag / BaSnO3, the scale is 500 nm, (c) is EDS image of Ag / BaSnO3, (d) is EDS element image of Ag / BaSnO3;

[0028] Figure 2 XRD and FTIR analysis of the crystal structure of the catalysts, wherein (a) is XRD pattern of BaSnO3 and Ag / BaSnO3, (b) is FTIR spectrum of BaSnO3 and Ag / BaSnO3;

[0029] Figure 3 XPS analysis of the elemental composition and chemical valence of Ag / BaSnO3, wherein (a) is high-resolution XPS spectrum of Sn 3d, (b) is Ba 3d, (c) is O1s, (d) is Ag 3d;

[0030] Figure 4 Photocatalytic activity of different photocatalysts, wherein (a) is comparison of photocatalytic H2O2 generation rate of different photocatalysts, (b) is effect of different preparation methods on photocatalytic H2O2 generation rate of Ag / BaSnO3, (c) is photocatalytic H2O2 generation rate of Ag / BaSnO3 with different Ag loadings, (d) is time course of H2O2 on 0.35% Ag / BaSnO3;

[0031] Figure 5 H2O2 generation performance of Ag / BaSnO3 photocatalysis, wherein (a) is comparison of photocatalytic performance in pure water and 10% CH3OH, (b) is effect of light source on photocatalytic performance;

[0032] Figure 6 Photochemical properties of the prepared catalysts, wherein (a) is UV-vis diffuse reflectance spectrum, (b) is PL spectrum of BaSnO3;

[0033] Figure 7 Electrochemical property test of the prepared catalysts, wherein (a) is EIS spectrum of the prepared photocatalysts, (b) is LSV curve of the prepared photocatalysts, (c) is Mott-schottky curve of BaSnO3, (d) is Mott-schottky curve of Ag-BaSnO3;

[0034] Figure 8 Formation mechanism of Ag / BaSnO3 photocatalytic H2O2, wherein (a) is effect of different scavengers on Ag / BaSnO3 photocatalytic H2O2, (b) is mechanism of Ag / BaSnO3 photocatalytic H2O2. DETAILED DESCRIPTION

[0035] The following detailed description of various example embodiments of the application will not be considered limiting of the application, but rather as a description of certain aspects, features and embodiments of the application.

[0036] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Additionally, for a range of values of a parameter, unless otherwise stated, each intervening value of the parameter is also specifically included within the scope of the present application. The intervening values of the parameter are combined with a stated value of the parameter in range form. These are only examples of the various embodiments of the application. Other embodiments can be utilized and other changes can be made without departing from the spirit or scope of the application. It will be readily understood to those skilled in the art that the components, methods, techniques, and obtaining described herein with respect to the various embodiments can be modified or otherwise implemented. Such alternative embodiments are considered within the scope of the present disclosure and can be carried out on the basis of the teachings contained herein.

[0037] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the case of conflict between the present specification and any document incorporated herein by reference, the present specification will control.

[0038] Various modifications and changes can be made to the specific embodiments of the application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application. Unless otherwise indicated, the materials used in the examples described herein were obtained from sources commonly known and readily available in the art.

[0039] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0040] Example 1

[0041] S1, 2 mmol BaCl2.2H2O and 2 mmol SnCl4.5H2O were dissolved in 5 mL ethylene glycol, then 20 mmol citric acid was added, stirred at 80°C for 2 h to obtain a solution;

[0042] S2, the solution was heated to 150°C for 15 h to obtain a gel;

[0043] S3, the gel was calcined at 500°C for 5 h, then heated to 900°C for 2 h to obtain perovskite BaSnO3.

[0044] (1) 0.1 g of perovskite BaSnO3, 50 mL of ultrapure water, and 0.0010 g of AgNO3 (the amount of AgNO3 is 1% of the mass of the perovskite BaSnO3), 20 kHz ultrasonic mixing for 30 min, 600 rpm first stirring for 20 min, to obtain a premix;

[0045] (2) In the premix, drop 10 mL of 0.05 M NaBH4 solution, 600 rpm second stirring for 20 min, 9000 rpm, 25°C centrifugation for 5 min, 10 -2 Pa vacuum degree, vacuum drying at 50°C for 12 h, to obtain Ag / BaSnO3 photocatalyst.

[0046] The method for preparing H2O2 by using Ag / BaSnO3 photocatalyst includes the following steps: in a 100 mL beaker, 20 mg of Ag / BaSnO3 photocatalyst is dispersed in 50 mL of 10% methanol solution by 20 kHz ultrasonic for 10 min, to obtain a photocatalyst solution; under the irradiation of a 300 W xenon lamp, air is continuously introduced into the photocatalyst solution for catalytic reaction for 2 h, 9000 rpm, 25°C centrifugation for 3 min, and the supernatant is taken to obtain H2O2.

[0047] Example 2

[0048] S1, 2 mmol of BaCl2·2H2O and 2 mmol of SnCl4·5H2O are dissolved in 5 mL of ethylene glycol, then 20 mmol of citric acid is added, and stirred at 60°C for 3 h to obtain a solution;

[0049] S2, the solution is heated to 130°C and kept for 18 h to obtain a gel;

[0050] S3, the gel is calcined at 300°C for 8 h, and then heated to 800°C and kept for 3 h to obtain perovskite BaSnO3.

[0051] (1) 0.1 g of perovskite BaSnO3, 25 mL of ultrapure water, and 0.0020 g of AgNO3 (the amount of AgNO3 is 2% of the mass of the perovskite BaSnO3), 20 kHz ultrasonic mixing for 30 min, 600 rpm first stirring for 10 min, to obtain a premix;

[0052] (2) In the premix, drop 5 mL of 0.05 M NaBH4 solution, 600 rpm second stirring for 10 min, 9000 rpm, 25°C centrifugation for 5 min, 10 -2 Pa vacuum degree, vacuum drying at 60°C for 12 h, to obtain Ag / BaSnO3 photocatalyst.

[0053] The method for preparing H2O2 by using Ag / BaSnO3 photocatalyst comprises the following steps: 10 mg of Ag / BaSnO3 photocatalyst is ultrasonically dispersed in 20 mL of methanol solution with a volume concentration of 10% in a 100 mL beaker for 5 min to obtain a photocatalyst solution; air is continuously introduced into the photocatalyst solution for catalytic reaction under the irradiation of a 200 W xenon lamp for 2 h; the solution is centrifuged at 9000 rpm and 25 ℃ for 3 min, and the supernatant is taken to obtain H2O2.

[0054] Example 3

[0055] S1, 2 mmol of BaCl2·2H2O and 2 mmol of SnCl4·5H2O are dissolved in 5 mL of ethylene glycol, and then 20 mmol of citric acid is added, and the solution is stirred at 100 ℃ for 1 h;

[0056] S2, the solution is heated to 170 ℃ and kept for 12 h to obtain a gel;

[0057] S3, the gel is calcined at 700 ℃ for 2 h, and then heated to 1000 ℃ and kept for 1 h to obtain perovskite BaSnO3.

[0058] (1) 0.1 g of perovskite BaSnO3, 75 mL of ultrapure water and 0.0050 g of AgNO3 (the amount of AgNO3 is 5% of the mass of perovskite BaSnO3) are ultrasonically mixed for 40 min at 20 kHz, and then stirred at 600 rpm for 30 min to obtain a premix;

[0059] (2) 15 mL of NaBH4 solution with a concentration of 0.05 M is added dropwise into the premix, and then stirred at 200 rpm for 30 min, centrifuged at 9000 rpm and 25 ℃ for 5 min, and the supernatant is taken to obtain H2O2. -2 Pa vacuum degree, and vacuum dried at 60 ℃ for 12 h to obtain Ag / BaSnO3 photocatalyst.

[0060] The method for preparing H2O2 by using Ag / BaSnO3 photocatalyst comprises the following steps: 10 mg of Ag / BaSnO3 photocatalyst is ultrasonically dispersed in 20 mL of methanol solution with a volume concentration of 10% in a 100 mL beaker for 5 min to obtain a photocatalyst solution; air is continuously introduced into the photocatalyst solution for catalytic reaction under the irradiation of a 200 W xenon lamp for 2 h; the solution is centrifuged at 9000 rpm and 25 ℃ for 3 min, and the supernatant is taken to obtain H2O2.

[0061] Experimental example

[0062] 1.1 Materials used in the experiment

[0063] Barium chloride (BaCl2, 99.5%), tin chloride pentahydrate (SnCl4.5H2O, 99%), citric acid (C6H8O7, 99.5%), p-benzoquinone (p-BQ, >99.8%), potassium hydrogen phthalate (C8H5KO4, >99.8%), potassium iodide (KI, >99.8%), sodium borohydride (NaBH4, 95%), sodium sulfate (Na2SO4, >99.8%), ethylene glycol (C2H6O2, 99%), silver nitrate (AgNO3, 99.5%).

[0064] The Ag / BaSnO3 photocatalyst used was prepared according to Example 1.

[0065] 1.2 Characterization

[0066] The morphology of the Ag / BaSnO3 photocatalyst prepared according to Example 1 was studied by scanning electron microscopy (SEM, ZEISS Sigma 300).

[0067] The crystal phase of the Ag / BaSnO3 photocatalyst prepared according to Example 1 was analyzed by X-ray diffractometry (XRD, Rigaku SmartLab SE).

[0068] The chemical composition and chemical state of the sample were analyzed by X-ray photoelectron spectroscopy (XPS, Thermo-Scientific K-Alpha).

[0069] The structure of the Ag / BaSnO3 photocatalyst prepared according to Example 1 was studied by Fourier-transform infrared spectroscopy (FTIR, Thermo-Scientific Nicolet iS10).

[0070] The light absorption was analyzed by ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS, Shimadzu UV-2600). The separation ability of the photocatalyst support was studied by fluorescence spectroscopy (PL, Edinburgh instruments Ltd. FLS980).

[0071] The electrochemical performance was tested in 0.5 M Na2SO4 with a Pt wire as the counter electrode, the FTO conductive glass loaded with the photocatalyst as the working electrode, and a saturated calomel electrode as the reference electrode on an electrochemical workstation (Chenhua, CHI660D). The electrochemical impedance spectroscopy was analyzed at an open circuit potential of 0.1-105 Hz. The Mott-Schottky curves were obtained at a potential range of -0.5 V to 0.5 V and a frequency of 1000 Hz, 1500 Hz, and 2000 Hz. The voltage scanning range of the linear sweep voltammetry curves was -0.5-1.3 V, and the scanning rate was 0.01 V s-1 .

[0072] 1.3 Photocatalytic Experiment

[0073] In a 100 mL beaker, 20 mg of Ag / BaSnO3 photocatalyst was ultrasonically dispersed (ultrasonic parameters 20 kHz, 10 min) in 50 mL of 10% methanol solution to obtain a photocatalyst solution. Under irradiation with a 300 W xenon lamp, air was continuously bubbled into the photocatalyst solution to carry out the catalytic reaction for 2 h. After centrifugation at 9000 rpm and 25 °C for 3 min, the solution was filtered through a 0.22 μm filter membrane, and the concentration of hydrogen peroxide in the supernatant was measured.

[0074] The concentration of H₂O₂ was determined using iodometric titration. The supernatant was diluted to 2 mL and added to a 2 mL mixed solution of 0.1 M potassium hydrogen phthalate (C₈H₅KO₄) and 0.4 M potassium iodide (KI). After reacting for 30 min, the absorbance was measured at 350 nm. The concentration of H₂O₂ was determined according to the following equation: H₂O₂ + 3I⁻ - +2H→I3 - +2H2O.

[0075] 2.1 Characterization of photocatalysts

[0076] The surface morphology of the Ag / BaSnO3 photocatalyst prepared in Example 1 was characterized using scanning electron microscopy. Figure 1 SEM images of BaSnO3 prepared in Example 1 and Ag / BaSnO3 prepared in Example 1. From... Figure 1 As can be seen in (a), BaSnO3 exhibits a needle-like morphology with sizes ranging from hundreds of nanometers to several micrometers. Meanwhile, the Ag / BaSnO3 surface is loaded with numerous nanoparticles (such as...). Figure 1 (b)). EDS (e.g.) Figure 1 (c) and EDS element diagram (e.g.) Figure 1 (d) shows that O, Ba, Sn and Ag elements are uniformly dispersed in the obtained Ag / BaSnO3.

[0077] The crystal phase structure of the Ag / BaSnO3 photocatalyst prepared in Example 1 was analyzed by X-ray diffraction. Figure 2 As shown in (a), the diffraction peaks are located at 30.7°, 43.9°, 54.6°, 63.9°, and 72.5°, corresponding to the (110), (200), (211), (220), and (311) crystal planes of cubic BaSnO3 (PDF#15-0780), respectively. This indicates that cubic perovskite BaSnO3 was successfully synthesized. However, Ag in Ag / BaSnO3 showed no characteristic peaks due to its low content, making it undetectable.

[0078] The structure of the Ag / BaSnO3 photocatalyst prepared in Example 1 was characterized by Fourier transform infrared spectroscopy (FTIR), and the results are as follows: Figure 2 As shown in (b). Where 628cm -1 The characteristic peak is attributed to the symmetric tensile vibration of SnO6, 650 cm⁻¹. -1 The absorption peak is also attributed to the stretching vibration of Sn-O. The 1443 cm⁻¹ peak... -1 The peak value is attributed to the tensile vibration of the Ba-O bond. It can be observed at 3420 cm⁻¹. -1 and 1610cm -1 The two absorption peaks at 4000 cm⁻¹ are attributed to the stretching and bending vibrations of the hydroxyl groups, respectively. Furthermore, Ag / BaSnO₃ and BaSnO₃ show absorption peaks at 4000 cm⁻¹. -1 ~400cm -1 Similar absorption peaks were observed within the range. The results indicate that perovskite-type BaSnO3 was successfully prepared, and the loading of Ag had little effect on the structure of BaSnO3.

[0079] The elemental composition and chemical valence states of the Ag / BaSnO3 prepared in Example 1 were investigated using X-ray photoelectron spectroscopy (XPS). Figure 3 As shown, the prepared sample contains Sn, Ba, O, Ag, and C elements. The high-resolution spectrum of Sn 3d (e.g.) Figure 3 Image (a) consists of two peaks at 494.7 eV and 486.3 eV, attributed to Sn 3d 3 / 2 and Sn 3d 5 / 2, respectively. The binding energy difference between Sn 3d 3 / 2 and Sn 3d 5 / 2 is 8.45 eV, indicating that the valence state of Sn is +4. From the high-resolution image of Ba 3d (… Figure 3 As can be seen in (b), the binding energies of 794.9 eV and 779.5 eV are attributed to Ba 3d 3 / 2 and Ba 3d 5 / 2. The 1s spectrum (e.g.) Figure 3 The middle (c) shows four peaks at 533.0 eV, 531.2 eV, and 530.3 eV, which are attributed to absorbed oxygen, oxygen vacancies, and lattice oxygen. High resolution of Ag3d (e.g., Figure 3 The middle (d) shows that the peaks at binding energies of 373.2 eV and 367.3 eV are attributed to Ag 3d 3 / 2 and 3d 5 / 2, respectively, and the peak difference of 6.0 eV indicates that Ag is in Ag 3d 3 / 2 and 3d 5 / 2. 0 It exists in the form of.

[0080] 2.2 Evaluation of the photocatalytic performance of photocatalysts

[0081] The photocatalytic activity of the prepared photocatalyst was evaluated by measuring the rate of H2O2 production in the presence of 10% CH3OH and O2. Figure 4The middle (a) is the rate of H2O2 production using different photocatalysts. The stannate type photocatalysts (BaSnO3 and SrSnO3) can effectively photocatalytically reduce O2 to H2O2, and the H2O2 production of BaSnO3 (33.1 μmol g -1 h -1 ) is higher than that of SrSnO3 (13.5 μmol g -1 h -1 ). The introduction of Ni, NiO and other cocatalysts reduces the H2O2 production rate, and Ag, AgO promotes the production of H2O2. In order to study the influence of the preparation method of silver on the H2O2 production rate, silver is deposited on the surface of BaSnO3 by photocatalytic reduction and chemical reduction. The Ag prepared by the two methods can effectively improve the H2O2 production rate, and the Ag prepared by NaBH4 reduction method has a higher H2O2 production rate, that is, the method prepared by the present application. By introducing Ag synthesized by NaBH4 chemical reduction, the H2O2 production rate is increased by more than 4 times (such as Figure 4 (b) in the middle). The influence of silver content on photocatalytic activity is studied. As can be seen from Figure 4 (c), when the content of Ag increases from 0 to 0.35%, the formation rate of H2O2 increases. With the further increase of Ag content, the formation rate gradually decreases, because the appropriate amount of Ag can effectively promote the separation of photo-generated carriers, and the excessive Ag covers the active center of BaSnO3, resulting in the decrease of H2O2 production rate. As Figure 4 (d) is the change curve of H2O2 production rate with time on BaSnO3 and 0.35% Ag / BaSnO3. The results show that with the extension of time, the concentration of H2O2 gradually increases, and when the mass fraction of Ag / BaSnO3 is greater than 0.35%, the production rate of H2O2 is higher than that of BaSnO3.

[0082] The photocatalytic H2O2 production performance in pure water and 10% CH3OH is compared. As shown in Figure 5 (a), in pure water, H2O2 can be formed on the surface, and the formation rate of H2O2 on BaSnO3 and Ag / BaSnO3 is 20.8 μmol g -1 h -1 and 70.6 μmol g -1 h -1 , respectively. In 10% methanol solution, the H2O2 production rate is higher, which is 40.9 μmol g -1 h -1 and 248.9 μmol g -1 h -1This is because CH3OH can act as a sacrificial agent for photogenerated holes, producing more free electrons that can react with O2 to generate H2O2. The effect of the light source was studied, and the results are as follows: Figure 5 As shown in (b), under visible light irradiation, the H2O2 formation rates on BaSnO3 and Ag / BaSnO3 were 23.4 μmol g⁻¹, respectively. -1 h -1 and 43.8 μmol g -1 h -1 Full-spectrum excitation can increase the generation rate of H2O2 because the higher the light utilization rate, the more photogenerated carriers participate in the generation of H2O2.

[0083] The photoelectric properties of a photocatalyst determine its photocatalytic performance. To explore the reasons for the different photocatalytic activities of BaSnO3 and Ag / BaSnO3, the photoelectric properties of the prepared samples were studied in detail.

[0084] Light absorption by a photocatalyst is a crucial factor affecting its photocatalytic activity. The light response range of the samples was investigated using ultraviolet-visible diffuse reflectance spectroscopy. Figure 6 As shown in Figure (a), the absorption band edges of BaSnO3 and Ag / BaSnO3 are approximately 410 nm. According to the Tauc equation, the band gaps of BaSnO3 and Ag / BaSnO3 are 3.06 eV and 3.01 eV, respectively. This indicates that the introduction of Ag can reduce the band gap of BaSnO3, meaning that the introduction of Ag can effectively improve the utilization rate of solar energy and generate more charge carriers.

[0085] Photogenerated carriers in the samples were studied using photoluminescence (PL) spectroscopy. The weaker the photoluminescence intensity, the higher the separation efficiency of the photogenerated carriers. For example... Figure 6 As shown in (b), the luminescence intensity of Ag / BaSnO3 is significantly lower than that of BaSnO3, indicating that Ag / BaSnO3 has a stronger ability to separate photogenerated carriers. Therefore, Ag modification can improve the separation efficiency of photogenerated carriers.

[0086] To investigate the interfacial electrochemical properties of Ag / BaSnO3, electrochemical impedance spectroscopy (EIS) was performed in 0.5 M Na2SO4. Figure 7 In figure (a), the electrochemical impedance spectroscopy (EIS) spectrum of the synthesized photocatalyst is shown. The semicircular arc of Ag / BaSnO3 is smaller than that of BaSnO3, indicating that Ag deposition is beneficial for electron transfer. The effect of Ag on water oxidation activity was investigated using linear sweep voltammetry (LSV). Figure 7Figure (b) shows the LSV curves of the prepared photocatalyst. The LSV curves indicate that Ag / BaSnO3 exhibits higher water oxidation activity than BaSnO3, suggesting that Ag deposition enhances water oxidation capacity. An oxidation peak at 0.24 V was also observed, which is attributed to the oxidation of Ag.

[0087] Mott-Schottky curves were measured at frequencies of 500, 1000, and 1500 Hz to explore the optimal semiconductor properties of BaSnO3 and Ag / BaSnO3. Figure 7 (c) and Figure 7 As shown in (d), they all exhibit C -2 The positive slope of the values ​​(relative to the applied potential) indicates that BaSnO3 and Ag / BaSnO3 are n-type semiconductors. The flat band potential of BaSnO3 is -0.55V, while that of Ag / BaSnO3 is -0.38V. Therefore, the flat band potential after Ag modification exhibits a positive shift. Since the conduction band potential is close to the flat band, the valence band potential can be calculated based on the band gap energies of BaSnO3 and Ag / BaSnO3. The band gap energies of BaSnO3 and Ag / BaSnO3 are essentially the same; after Ag modification, the valence band energy of BaSnO3 increases by 0.1V. Therefore, compared to BaSnO3, Ag / BaSnO3 has a stronger ability to oxidize water and a higher H2O2 generation rate.

[0088] Studying the major active species in the photocatalytic H2O2 formation process is crucial for understanding the formation mechanism of H2O2. Disodium ethylenediaminetetraacetate, isopropanol, and p-benzoquinone were used to capture holes (h+) and superoxide anions (·O2), respectively. 2- Active species of hydroxyl radicals (·OH). Figure 8 As shown in (a), the rate of H2O2 formation decreases after adding disodium ethylenediaminetetraacetate, isopropanol, and p-benzoquinone to the photocatalytic system. p-benzoquinone was introduced into the photocatalytic system. Therefore, it can be concluded that superoxide radicals are a necessary condition for H2O2 formation. This also indicates that holes (h+) and superoxide anions (·O2) are also necessary for H2O2 formation. 2- ) and hydroxyl groups (·OH) participate in the formation of H2O2. Based on this, a possible formation mechanism for the photocatalytic production of hydrogen peroxide from BaSnO3 is proposed. Figure 8In the middle (b). Under light, electrons are excited to the lowest unoccupied molecular orbital (LUMO) of BaSnO3, while holes are retained on the highest occupied molecular orbital (HOMO) and generate photo-generated carriers, i.e. photo-generated holes and electrons. Holes can react with adsorbed water to generate O2 and ·OH. O2 is reduced to superoxide radicals, which react with two electrons and two protons to form H2O2. Due to the difference between Ag and BaSnO3, a Schottky barrier can be formed, and electrons are transferred from Ag to BaSnO3, promoting the separation of photo-generated carriers, and more free electrons participate in the formation of H2O2. In addition, the valence band of BaSnO3 is raised, and the oxidation of water is enhanced. Therefore, the generation rate of H2O2 is improved by Ag modification.

[0089] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for preparing an Ag / BaSnO3 photocatalyst, characterized by, The Ag / BaSnO3 photocatalyst is prepared by loading Ag on perovskite BaSnO3; The method comprises the following steps: (1) ultrasonic mixing perovskite BaSnO3, ultrapure water and AgNO3, first stirring to obtain a premix; (2) adding NaBH4 solution dropwise into the premix obtained in step (1) and second stirring to obtain the Ag / BaSnO3 photocatalyst; The preparation method of the perovskite BaSnO3 in step (1) comprises the following steps: S1, dissolving BaCl2·2H2O and SnCl4·5H2O in ethylene glycol, then adding citric acid, stirring at 60-100 ℃ for 1-3 h to obtain a solution; S2, heating the solution obtained in step S1 to 130-170 ℃ and keeping for 12-18 h to obtain a gel; S3, calcining the gel obtained in step S2 at 300-700 ℃ for 2-8 h, then heating to 800-1000 ℃ and keeping for 1-3 h to obtain the perovskite BaSnO3.

2. The method of claim 1, wherein, The mixing ratio of the perovskite BaSnO3, ultrapure water and AgNO3 in step (1) is 0.05-0.15 g: 25-75 mL: 0.00005-0.0075 g; the ultrasonic mixing frequency in step (1) is 10-40 kHz, and the ultrasonic mixing time is 5-60 min.

3. The preparation method according to claim 1, characterized in that, The first stirring speed in step (1) is 200-2000 rpm, and the first stirring time is 10-30 min.

4. The preparation method according to claim 1, characterized in that, The ratio of the amount of the NaBH4 solution to the amount of the perovskite BaSnO3 in step (1) is 5-15 mL: 0.05-0.15 g; the concentration of the NaBH4 solution in step (2) is 0.03-0.07 M.

5. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. The second stirring speed in step (2) is 200-2000 rpm, and the second stirring time is 10-30 min.

6. The application of the Ag / BaSnO3 photocatalyst prepared by the preparation method in any one of claims 1-5 in preparing H2O2.

7. A method for preparing H2O2 using the Ag / BaSnO3 photocatalyst according to claim 1, characterized by, The method comprises the following steps: Mixing the Ag / BaSnO3 photocatalyst and a methanol solution to obtain a photocatalyst solution; under the irradiation of a xenon lamp, continuously bubbling air into the photocatalyst solution to perform a catalytic reaction, centrifuging, filtering to obtain H2O2.

8. The method of claim 7, wherein the H202 is produced at a rate of at least 0.1 g H202 / g catalyst / hr. The volume concentration of the methanol solution is 5-15%; the mixing ratio of the Ag / BaSnO3 photocatalyst and the methanol solution is 10-30 mg: 25-75 mL; the power of the xenon lamp is 200-400 W; and the catalytic reaction time is 0.5-2 h.

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