Preparation method of rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst

Abstract

This invention belongs to the field of photocatalytic materials and new energy technology, and discloses a method for preparing a Rh-modified Cs₂AgBiBr₆ / CdS heterojunction photocatalyst. The method includes: preparing Cs₂AgBiBr₆ nanoparticles via antisolvent precipitation, preparing CdS nanorods via hydrothermal method, subsequently constructing a heterojunction through in-situ growth, and loading a Rh co-catalyst using photoreduction. This invention effectively overcomes the technical bottleneck of structural instability of traditional perovskites in polar solvents by introducing a Cs₂AgBiBr₆ double perovskite with a rigid lattice structure. Experiments show that the catalyst retains its structural integrity after immersion in ethanol for 168 hours and under different atmospheres, and exhibits excellent performance in the photocatalytic dehydrogenation of ethanol, with a hydrogen production rate as high as 49.15 mmol·g⁻¹. ‑1 ·h ‑1 The apparent quantum efficiency at 420 nm is 22.5%, and it remains stable during a 60-hour continuous reaction. This invention provides a new strategy for developing efficient and stable lead-free perovskite photocatalytic systems.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photocatalytic materials and new energy technologies, and particularly relates to a preparation method of a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst. BACKGROUND

[0002] Halide perovskite materials have great application potential in the fields of solar cells, light-emitting diodes and photocatalysis due to their excellent light absorption coefficient, long carrier diffusion length, adjustable band gap and high defect tolerance. In particular, in the field of photocatalysis, such as water splitting for hydrogen production and carbon dioxide reduction, their wide spectral response and high charge separation capacity make them ideal photocatalyst candidates.

[0003] However, the intrinsic instability of traditional halide perovskites (such as CsPbBr3), especially in polar solvent environments, seriously restricts their practical application. The soft lattice characteristics of the perovskite lead to ion migration, lattice distortion and rapid chemical decomposition in humidity, light, especially in polar solvents containing hydroxyl groups (such as water and alcohols). For example, the accelerated aging test of the National Renewable Energy Laboratory (NREL) shows that the lifetime of perovskite components in a humid and hot environment is much lower than the commercial requirements; in polar solvents, the degradation rate is extremely high, resulting in a sharp decline in catalytic activity within a few tens of hours. This stability bottleneck makes it difficult for traditional perovskite materials to be widely used in valuable liquid-phase photocatalytic reactions such as ethanol dehydrogenation.

[0004] To improve the stability of perovskites, researchers have adopted various strategies, including component engineering, crystallization control, defect passivation and interface engineering. For example, by introducing specific ions or molecules to suppress phase transitions, or using materials such as zeolite molecular sieves for external encapsulation to isolate water and oxygen. These methods have improved the operational stability of devices to some extent, but they focus on surface / interface protection mechanisms and do not fundamentally solve the soft lattice dynamic characteristics of the octahedral framework and its derived intrinsic instability. Under the penetration and solvation of polar solvents, the PbX6 octahedral framework of traditional perovskites still faces fundamental problems such as bond length distortion and reduction of phase transition energy barrier, leading to the contradictory phenomenon that the existing photocatalytic system is stable on the surface / interface but unstable in the bulk phase, making it difficult to maintain long-term catalytic activity.

[0005] Compared with typical ABX3-type perovskites, double perovskites (such as Cs2AgBiBr6) have B-site heterovalent metal cations (such as Ag + and Bi 3+) have more rigid three-dimensional skeleton structures, and theoretically have higher intrinsic stability. However, at present, the stability mechanism of double perovskites in a polar solvent environment lacks systematic and in-depth theoretical and experimental verification, and how to construct an efficient and stable heterojunction photocatalytic system based on the stability advantage and apply it to actual polar solvent photocatalytic reactions (such as ethanol dehydrogenation) is still a difficult problem to be solved.

[0006] Therefore, developing a lead-free perovskite heterojunction catalyst with excellent solvent stability and high photocatalytic activity is of great significance for breaking through the application bottleneck of halide perovskites in the field of photocatalysis and promoting the development of solar-driven biomass refining technology. SUMMARY

[0007] In view of the defects of the prior art in the background art, the core technical problem to be solved by the present application is to overcome the defects that the existing halide perovite is not stable in the intrinsic structure in a polar solvent and is prone to degradation, thereby limiting its application in a liquid-phase photocatalytic system.

[0008] To solve the above problems, the present application provides a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst. The catalyst is constructed by building an intrinsically stable double perovskite structure to resist solvent erosion, and by utilizing the synergistic effect of the heterojunction and the noble metal, efficient separation and utilization of photo-generated carriers are achieved.

[0009] Another object of the present application is to provide a preparation method of the above-mentioned photocatalyst, which is controllable in process and can effectively construct a tight heterojunction and realize precise loading of Rh cocatalyst.

[0010] Still another object of the present application is to provide the application of the photocatalyst in photocatalytic ethanol dehydrogenation to produce hydrogen, which provides a new technical path for realizing efficient and stable solar-driven biomass refining.

[0011] The present application adopts the following technical solution: a preparation method of a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst, characterized in that it comprises the following steps: (1) preparing Cs2AgBiBr6 nanoparticles: using an anti-solvent precipitation method, a cesium source, a silver source and a bismuth source are dissolved in a polar solvent, stirred and reacted under an inert atmosphere, then an anti-solvent is added to induce precipitation, centrifuged and dried to obtain Cs2AgBiBr6 nanoparticles.

[0012] (2) preparing CdS nanorods: using a solvothermal method, a cadmium source and a sulfur source are dissolved in a diethylamine solvent, transferred to a high-pressure reaction kettle, reacted at 150-200°C for 6-12 hours, centrifuged and washed after cooling, and dried to obtain CdS nanorods.

[0013] (3) Constructing Cs2AgBiBr6 / CdS heterojunction: dispersing the Cs2AgBiBr6 nanoparticles obtained in step (1) and the CdS nanorods obtained in step (2) in an organic solvent at a mass ratio of 5-15:100, ultrasonic treatment and stirring, and making the Cs2AgBiBr6 nanoparticles uniformly loaded on the surface of the CdS nanorods by an in-situ growth strategy to form a Cs2AgBiBr6 / CdS heterojunction composite material.

[0014] (4) Loading Rh promoter: dispersing the Cs2AgBiBr6 / CdS heterojunction composite material obtained in step (3) in an ethanol solution containing a Rh precursor, stirring and reacting under visible light irradiation, centrifugal washing and drying to obtain a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst, wherein the loading amount of Rh is 2-6 wt%.

[0015] Further, in the above preparation method, the cesium source in step (1) is CsBr, the silver source is AgBr, and the bismuth source is BiBr3; the polar solvent is N,N-dimethylformamide or dimethyl sulfoxide; the anti-solvent is ethyl acetate or acetone; the reaction temperature is 50-80 ℃, and the reaction time is 1-3 hours.

[0016] Further, in the above preparation method, the cadmium source in step (2) is Cd(NO3)2 or CdCl2, and the sulfur source is thiourea or Na2S; the hydrothermal reaction temperature is 180 ℃, and the reaction time is 8 hours.

[0017] Further, in the above preparation method, the mass ratio of the Cs2AgBiBr6 nanoparticles to the CdS nanorods in step (3) is 10:100; the organic solvent is ethanol or isopropanol; the ultrasonic treatment time is 30-60 minutes, and the stirring time is 2-4 hours.

[0018] Further, in the above preparation method, the Rh precursor in step (4) is RhCl3 or Rh(NO3)3; the wavelength of visible light irradiation is 420 nm, the light intensity is 100-300 mW / cm 2 , the reaction time is 1-3 hours, and the loading amount of Rh is 4 wt%.

[0019] The application further discloses a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst, characterized by being prepared by any one of the above preparation methods, wherein Cs2AgBiBr6 and CdS form a Type-I heterojunction structure in the photocatalyst, Rh nanoparticles are preferentially anchored on the surface of Cs2AgBiBr6, and the crystal lattice structure of the photocatalyst remains complete after being soaked in an ethanol solvent for 168 hours.

[0020] Further, the above-mentioned photocatalyst has a size distribution of 2-10 nm; has a widened absorption shoulder peak in the range of 550-650 nm in the ultraviolet-visible absorption spectrum, corresponding to the surface plasmon resonance effect of Rh 3+ .

[0021] The application further discloses a method for photocatalyzing ethanol dehydrogenation, which uses the above-mentioned photocatalyst to catalyze ethanol dehydrogenation to generate hydrogen and a liquid product under visible light irradiation, wherein the liquid product comprises acetaldehyde and acetal; and the reaction conditions comprise that the catalyst dosage is 1-5 mg / mL of ethanol, the reaction atmosphere is an inert gas, the light wavelength is 420-800 nm, the light intensity is 100-300 mW / cm 2 , and the reaction temperature is 25-60 DEG C.

[0022] Further, the above-mentioned method for photocatalyzing ethanol dehydrogenation has a hydrogen production rate of 40-50 mmol.g -1 .h -1 , an apparent quantum efficiency of 20-25% at a wavelength of 420 nm, and a selectivity of acetaldehyde and acetal in the liquid product of 50-70% and 30-50%, respectively.

[0023] Further, the above-mentioned method for photocatalyzing ethanol dehydrogenation has a hydrogen production activity of the photocatalyst of more than 90% of the initial activity after 60 hours of continuous reaction; and in the reaction, hydrogen atoms are derived from the activation of an alpha-C-H bond of an ethanol molecule, and isotopic tracing experiments prove that deuterium gas (D2) is generated when full deuterated ethanol is used as a substrate.

[0024] The application has the beneficial effects that: 1. The instability problem of perovskite in a polar solvent is solved: the Cs2AgBiBr6 double perovskite is constructed by using the strategy of replacing the metal cation with a different valence to replace the traditional CsPbBr3, and the rigid crystal lattice structure improves the solvent erosion resistance. Experiments show that after the material is soaked in ethanol for 168 hours and subjected to light treatment in different atmospheres (inert atmosphere Ar and oxidizing atmosphere Air), the crystal structure, morphology and optical properties remain complete.

[0025] 2. High photocatalytic activity: by constructing a Cs2AgBiBr6 / CdS heterojunction and loading a Rh cocatalyst, the charge separation and transmission are promoted. The hydrogen production rate of the catalyst reaches 49.15 mmol.g -1 .h -1 , and the apparent quantum efficiency under a single wavelength of 420 nm is 22.5%.

[0026] 3. Clear multi-component synergy: In this system, CdS is mainly responsible for light absorption, Cs2AgBiBr6 provides a stable interface and regulates the reaction path, and Rh serves as a hydrogen evolution site, all of which synergistically improve the carrier separation efficiency and surface reaction kinetics.

[0027] 4. Controllable product selectivity: Through the synergy of heterojunction and Rh, the distribution of liquid-phase products of ethanol dehydrogenation can be regulated, and the selectivity of acetaldehyde and acetal can be adjusted.

[0028] 5. Good stability: The catalyst maintains stable hydrogen production performance in 60 hours of continuous reaction, showing application potential in polar solvent reaction systems.

[0029] 6. Environmentally friendly and expanding applications: Lead-free perovskite is used, and the application range of perovskite photocatalysts is successfully expanded to polar solvent reaction systems containing hydroxyl groups. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The evolution of the perovskite interface structure during ethanol molecule adsorption process (N=1, N=3 and N=4): (a) CsPbBr3 interface, (b) Cs2AgBiBr6 interface; (c) Cs-Br bond length distribution of CsPbBr3 interface, (d) Cs2AgBiBr6 interface; (e) Comparison of the average absolute error (MAE) of Cs-Br bond length at the CsPbBr3 and Cs2AgBiBr6 interfaces before and after ethanol adsorption; (f) Adsorption energy of ethanol molecules on the CsPbBr3 and Cs2AgBiBr6 interfaces; (g) Solvation energy of CsPbBr3 and Cs2AgBiBr6 in ethanol solution.

[0031] Figure 2Structural evolution and optical property changes of Cs2AgBiBr6 and CsPbBr3 nanocrystals in ethanol solution during standing: (a) Schematic diagram of structural evolution of Cs2AgBiBr6 in ethanol solution during standing for 168 h; (b-d) Transmission electron microscopy (TEM) images of Cs2AgBiBr6 dispersed in ethanol solution after standing (b) 0 h (fresh sample), (c) 72 h, and (d) 168 h; (e) Schematic diagram of structural evolution of CsPbBr3 in ethanol solution during standing for 168 h; (f-h) TEM images of CsPbBr3 dispersed in ethanol solution after standing (f) 0 h (fresh sample), (g) 72 h, and (h) 168 h; (i) X-ray diffraction (XRD) patterns of Cs2AgBiBr6 and CsPbBr3 dispersed in ethanol solution after standing for 0 h and 168 h; (j) Pseudo-color map of the XRD patterns of perovskite materials in (i); (k) UV-Vis absorption spectra of Cs2AgBiBr6 and CsPbBr3 dispersed in ethanol solution after standing for 0 h and 168 h; the insets are optical photographs of the corresponding samples at different standing times.

[0032] Figure 3 XPS spectra of Cs2AgBiBr6 powder dispersed in ethanol for 0 h and 168 h, respectively: (a) Cs 3d, (b) Ag 3d, (c) Bi 4f, and (d) Br 3d.

[0033] Figure 4 Characterization results of Cs2AgBiBr6 powder in ethanol before and after light treatment under different atmospheres (argon / air): (a) XRD patterns, (b) UV-Vis diffuse reflectance absorption spectra (the inset is a photograph of the Cs2AgBiBr6 reaction solution before and after reaction under argon / air).

[0034] Figure 5 XPS spectra of Cs2AgBiBr6 powder in ethanol before and after light treatment under different atmospheres (argon / air): (a) Cs 3d, (b) Ag 3d, (c) Bi 4f, and (d) Br 3d.

[0035] Figure 6 SEM images of Cs2AgBiBr6 powder in ethanol before and after light treatment under different atmospheres: (a) under argon atmosphere, (b) under air atmosphere.

[0036] Figure 7Synthesis route, microstructure and elemental distribution analysis of Cs2AgBiBr6 / CdS heterojunction; (a) Schematic diagram of the synthesis process of Cs2AgBiBr6 / CdS heterojunction; (b) HRTEM image of the interface of Cs2AgBiBr6 / CdS composite material; (c, f) Enlarged Cs2AgBiBr6 and CdS regions; (d, g) FFT images corresponding to the Cs2AgBiBr6 and CdS regions; (e) XRD patterns of composite photocatalysts with different Cs2AgBiBr6 loadings (5-15 wt%); (h) HAADF and element mapping images of Cs2AgBiBr6 / CdS composite material; (i) UV absorption spectra of CdS, Cs2AgBiBr6 / CdS and Rh-Cs2AgBiBr6 / CdS.

[0037] Figure 8 Performance optimization diagram of Cs2AgBiBr6 / CdS; (a) Photocatalytic hydrogen evolution rate of introducing different proportions of Cs2AgBiBr6 on CdS nanorods, (b) Photocatalytic hydrogen evolution rate of Rh loaded in different amounts on Cs2AgBiBr6 / CdS by photo-deposition, (c) Selectivity distribution of liquid products in photocatalytic ethanol dehydrogenation reaction of CdS, Cs2AgBiBr6 / CdS and Rh-Cs2AgBiBr6 / CdS.

[0038] Figure 9 Performance stability and structural evolution of Rh-Cs2AgBiBr6 / CdS in long-time photocatalytic reaction; (a) Performance change diagram of Rh-Cs2AgBiBr6 / CdS in 60 hours of photocatalytic reaction; (b) XRD patterns before and after photocatalytic reaction; (c) and (d) are SEM images before and after reaction, respectively.

[0039] Figure 10 (a) Steady-state photoluminescence spectra; (b) Electrochemical impedance spectra; (c) Transient photocurrent response curves; (d) Linear sweep voltammetry curves; (e) Comparison of ethanol photocatalytic hydrogen evolution rates in the absence of additives and in the presence of different trapping agents, the inset is the ESR spectrum of the catalytic system under dark and visible light irradiation conditions when DMPO is used as a trapping agent; (f) Mechanism diagram of photocatalytic ethanol dehydrogenation coupling reaction of CdS, Cs2AgBiBr6 / CdS and Rh-Cs2AgBiBr6 / CdS. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the protection scope of the present application.

[0041] Example 1: Preparation of Cs2AgBiBr6nanoparticles.

[0042] Cs2AgBiBr6nanoparticles were synthesized by an anti-solvent precipitation method. The specific steps are as follows: 1 mmol of CsBr, 0.5 mmol of AgBr and 0.5 mmol of BiBr3were dissolved in 10 mL of N,N-dimethylformamide (DMF) and stirred at 60°C until completely dissolved to obtain a precursor solution. Then, the precursor solution was quickly injected into 50 mL of isopropanol (anti-solvent) under vigorous stirring, and a yellow precipitate was immediately produced. After continuing to stir for 10 minutes, the precipitate was collected by centrifugation (8000 rpm, 5 min) and washed twice with ethanol. Finally, the obtained product was dried in a vacuum drying oven at 60°C for 6 hours to obtain yellow Cs2AgBiBr6nanoparticle powder.

[0043] Example 2: Preparation of CdS nanorods.

[0044] CdS nanorods were synthesized by a hydrothermal method. The specific steps are as follows: 5 mmol of CdCl2·2.5H2O and 15 mmol of thiourea were dissolved in 60 mL of diethylamine and stirred vigorously for 30 minutes. Then, the mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reaction kettle and reacted at 160°C for 50 hours. After the reaction was completed, it was naturally cooled to room temperature, and the yellow precipitate was collected by centrifugation and washed with deionized water and anhydrous ethanol for three times, respectively. The final product was vacuum dried at 60°C overnight to obtain CdS nanorods.

[0045] Example 3: Construction of Cs2AgBiBr6 / CdS heterojunction.

[0046] Take 100 mg of CdS nanorods prepared in Example 2, disperse in 100 mL of absolute ethanol, and ultrasonically treat for 30 minutes to fully disperse. Then, take 10 mg of Cs2AgBiBr6 nanoparticles prepared in Example 1 (equivalent to 10 wt% of CdS), and add to the above CdS suspension. Continuously stir the mixed suspension at room temperature for 4 hours, so that the Cs2AgBiBr6 nanoparticles are loaded on the surface of the CdS nanorods by an in-situ growth strategy. After the reaction is completed, the composite material is collected by centrifugation, washed with ethanol, and vacuum dried at 60°C to obtain a Cs2AgBiBr6 / CdS heterojunction photocatalyst.

[0047] Example 4: Preparation of Rh-Cs2AgBiBr6 / CdS catalyst.

[0048] The Rh promoter is loaded by a photoreduction method. Take 50 mg of Cs2AgBiBr6 / CdS heterojunction prepared in Example 3, disperse in 50 mL of 10% ethanol aqueous solution. Then, add a certain volume of RhCl3 aqueous solution (containing Rh 1 mg / mL) to the suspension, and fully mix the catalyst with the Rh precursor by magnetic stirring. Under continuous stirring, irradiate the suspension with a LED light source with a wavelength of 420 nm (light intensity 100 mW / cm 2 ) for 2 hours, and maintain an argon atmosphere in the whole system. During the reaction, the Rh 3+ is reduced to metallic Rh by photo-generated electrons and deposited on the surface of the catalyst. After the reaction is completed, the solid product is collected by centrifugation, washed with deionized water three times, and vacuum dried at 60°C to obtain the final product Rh-Cs2AgBiBr6 / CdS photocatalyst.

[0049] By adjusting the amount of RhCl3 solution added, samples with Rh loadings of 2 wt% (Example 4a), 4 wt% (Example 4b), and 6 wt% (Example 4c) are prepared.

[0050] Test Example 1: Comparison of theoretical calculation and experimental results for structural stability.

[0051] In order to elucidate and verify the structural stability of the catalyst in a polar solvent from a mechanism, theoretical calculation and experimental comparison are carried out.

[0052] Theoretical calculation: By density functional theory (DFT) calculation, the adsorption behavior of ethanol molecules on the surface of Cs2AgBiBr6 and CsPbBr3 is studied. As shown in Figure 1 a and Figure 1 b, with the increase of the amount of adsorbed ethanol, the structural distortion of CsPbBr3 is much larger than that of Cs2AgBiBr6. The analysis of the surface Cs-Br bond length is as shown in Figure 1c and Figure 1 d, the comparison of the average absolute deviation of the bond length variation is shown in Figure 1 e, which indicates that the bond length variation of Cs2AgBiBr6 is significantly lower than that of CsPbBr3. Meanwhile, as shown in Figure 1 f and Figure 1 g, the absolute values of the adsorption energy and the solvation energy of Cs2AgBiBr6 to ethanol are lower than those of CsPbBr3, which theoretically predicts its better stability.

[0053] Experimental verification: Cs2AgBiBr6 prepared in Example 1 and CsPbBr3 as a comparison were dispersed in anhydrous ethanol and left to stand for 168 hours. The structural evolution schematic diagram is shown in Figure 2 a and Figure 2 e.

[0054] Experimental verification: Cs2AgBiBr6 prepared in Example 1 was dispersed in anhydrous ethanol and treated under inert atmosphere of argon and oxidative atmosphere of air for 4 hours of light irradiation. The structural integrity and stability before and after the light irradiation treatment.

[0055] TEM test: As shown in Figure 2 b-d and Figure 2 f-h, the morphology of Cs2AgBiBr6 particles is still complete after 72h and 168h of soaking, while the CsPbBr3 particles show serious dissolution phenomenon.

[0056] XRD test: As shown in Figure 2 i and Figure 2 j, the characteristic diffraction peaks of the Cs2AgBiBr6 sample do not change after standing, while the characteristic peak intensity of CsPbBr3 is sharply weakened and the impurity peaks of PbBr2 and CsBr appear.

[0057] UV-Vis test: As shown in Figure 2 k, the Cs2AgBiBr6 sample still maintains its original light absorption ability after standing, while the light absorption intensity of CsPbBr3 is significantly attenuated, and its macroscopic color change is shown in Figure 2 k.

[0058] XPS test: As shown in Figure 3 a-d, the chemical state of each element of the Cs2AgBiBr6 sample does not change after standing.

[0059] The above theory and experiment jointly confirm that the double perovskite Cs2AgBiBr6 has excellent structural stability in ethanol solvent.

[0060] Test Example 2: Structural stability under different atmospheres.

[0061] XRD test: As shown in Figure 4As shown in Fig. 2a, the characteristic diffraction peaks of the Cs2AgBiBr6 sample did not change before and after the light treatment under different atmosphere environments (inert atmosphere argon, oxidative atmosphere air), which confirmed that the crystal structure (including the lattice constant) of Cs2AgBiBr6 remained highly stable under the test conditions and was not affected by the type of atmosphere and light treatment.

[0062] UV-Vis test: As shown in Fig. 2b, the Cs2AgBiBr6 sample still retained its original light absorption ability after the light treatment under different atmosphere environments (inert atmosphere argon, oxidative atmosphere air), and its macroscopic color change was as shown in Fig. 2c. Figure 4 Figure 4 b, the HRTEM image of Fig. 2b shows that the Cs2AgBiBr6 nanoparticles were successfully grown on the surface of the CdS nanorod, and a clear and closely contacted heterojunction interface was formed between the two.

[0063] XPS test: As shown in Fig. 2d, the chemical state of the elements of the Cs2AgBiBr6 sample did not change after the light treatment under different atmosphere environments (inert atmosphere argon, oxidative atmosphere air). Figure 5

[0064] SEM test: As shown in Fig. 2e-f, the micro-morphology of the Cs2AgBiBr6 sample did not change significantly after the light treatment under different atmosphere environments (inert atmosphere argon, oxidative atmosphere air). Figure 6 The above theory and experiment together confirmed that the double perovskite Cs2AgBiBr6 also has excellent structural stability under different atmosphere and light conditions.

[0065] Test Example 3: Catalyst structure and morphology characterization.

[0066] The prepared heterojunction catalyst was systematically characterized.

[0067] Synthesis route and microstructure: The synthesis route of the Cs2AgBiBr6 / CdS composite material is as shown in Fig. 3a. As shown in Fig. 3b, the HRTEM image of the Cs2AgBiBr6 / CdS composite material shows that the Cs2AgBiBr6 nanoparticles were successfully grown on the surface of the CdS nanorod, and a clear and closely contacted heterojunction interface was formed between the two.

[0068] Figure 7 a, the HRTEM image of Fig. 3b shows that the Cs2AgBiBr6 nanoparticles were successfully grown on the surface of the CdS nanorod, and a clear and closely contacted heterojunction interface was formed between the two. Figure 7 Figure 7 c and f are local magnified images showing the (222) crystal face (d = 0.33 nm) of Cs2AgBiBr6 and the (100) crystal face (d = 0.36 nm) of CdS, respectively. The corresponding FFT images (d, 7g) show sharp diffraction spots, confirming the good crystallinity of the two phases. Figure 7 Figure 7

[0069] Phase and element analysis: As shown in Fig. 3d, the XRD pattern of the Cs2AgBiBr6 / CdS composite material shows that the crystal structure of the composite material is consistent with the standard card of the CdS nanorod (JCPDS No. 41- 1049) and the Cs2AgBiBr6 nanoparticle (JCPDS No. 71- 1477). Figure 7 ​​​​​​XRD patterns of e show that when the loading of Cs2AgBiBr6 is increased to 15 wt%, obvious characteristic diffraction peaks of Cs2AgBiBr6 can be observed at 22.37°, 31.74°, 39.26° and 45.65°, which correspond to the (022), (004), (224) and (044) crystal planes of the cubic perovskite structure, respectively, thus proving that Cs2AgBiBr6 has been successfully loaded on CdS. As shown in Figure 7 The HAADF-STEM and element Mapping images of h show that the elements Cd, S, Cs, Ag, Bi, Br, etc. are uniformly distributed in the composite material and form a clear heterojunction structure, and the Rh element is selectively deposited in the Cs2AgBiBr6 area.

[0070] Spectroscopy and surface chemistry: As shown in Figure 7 After the introduction of Rh, the Rh-Cs2AgBiBr6 / CdS shows a broadened absorption shoulder in the range of 550-650 nm, which is attributed to the plasmonic resonance effect of Rh.

[0071] Test Example 4: Photocatalytic ethanol dehydrogenation performance test.

[0072] The photocatalytic performance of the catalyst was evaluated under standard conditions: 2 mg of catalyst was dispersed in 5 mL of anhydrous ethanol and placed in a sealed photoreactor. Before the reaction, the system was purged with argon for 30 minutes to exclude air. A 300 W xenon lamp equipped with a 420 nm cutoff filter was used as the visible light source (λ > 420 nm, light intensity 300 mW / cm 2 ). The gas produced in the reaction was quantitatively analyzed by online gas chromatography.

[0073] Ethanol dehydrogenation performance test.

[0074] Heterojunction construction: First, the Cs2AgBiBr6 / CdS catalysts with different loadings of Cs2AgBiBr6 were tested. The results showed that, as shown in Figure 8 a, when the loading was 10 wt% (Example 3), the hydrogen production rate was the highest, reaching 8.25 mmol g -1 ·h -1 .

[0075] Promoter loading: Based on 10 wt% Cs2AgBiBr6 / CdS, the performance of different Rh loadings was compared. As shown in Figure 8 b, (4 wt% Rh) showed the best activity, with a hydrogen production rate of up to 49.15 mmol g -1 ·h -1 , which was significantly higher than that of the sample without Rh loading and the samples loaded with Pt and Ni.

[0076] Product selectivity: Rh-CdS mainly generated acetaldehyde (selectivity 87.2%), Cs2AgBiBr6 / CdS mainly generated diacetals (selectivity 99.1%), and the product of Rh-Cs2AgBiBr6 / CdS (c) was a mixture of acetaldehyde (60.2%) and diacetals (39.8%), indicating that the heterojunction and Rh jointly regulated the selectivity of the liquid phase product, and enhanced the selectivity of acetaldehyde. Figure 8

[0077] Test Example 5: Photocatalytic long-time reaction stability.

[0078] Stability test: the Rh-Cs2AgBiBr6 / CdS catalyst prepared by example 4b was used to carry out a continuous 60-hour light experiment under standard reaction conditions. As shown in Figure 9 a, the catalyst still maintained more than 90% of the initial hydrogen production activity after 60 hours, as shown in Figure 9 b-d, the XRD and SEM characterization before and after the reaction showed that the crystal structure and morphology did not change significantly, proving that it had excellent photocatalytic stability.

[0079] Test Example 6: Photoelectrochemical and mechanism research.

[0080] Photoelectric performance test: CdS, Cs2AgBiBr6 / CdS (example 3) and Rh-Cs2AgBiBr6 / CdS (example 4b) were characterized.

[0081] PL spectrum: as shown in Figure 10 a, the fluorescence intensity of Rh-Cs2AgBiBr6 / CdS was the weakest, indicating that it had the highest photo-generated carrier separation efficiency.

[0082] EIS spectrum: as shown in Figure 10 b, Rh-Cs2AgBiBr6 / CdS showed the smallest arc radius, indicating that it had the smallest interface charge transfer resistance.

[0083] Transient photocurrent: as shown in Figure 10 c, Rh-Cs2AgBiBr6 / CdS had the largest photocurrent density, further confirming that it had the optimal charge separation and migration ability.

[0084] LSV spectrum: as shown in Figure 10 d, Rh-Cs2AgBiBr6 / CdS had a lower overpotential, proving that it required a lower initial driving voltage to drive the reaction.

[0085] Reaction mechanism research.

[0086] ​Radical capture: The addition of hole, electron and radical scavengers in the reaction system, respectively, found that the hydrogen production rate was significantly inhibited, such as Figure 10 e shows that these active species are involved in the reaction together.

[0087] EPR test: DMPO (5, 5-dimethyl-1-pyrroline-N-oxide) as spin trapping agent, under light, detect obvious DMPO-·CH(CH3)OH (alpha-hydroxyethyl radical) complex characteristic signal, such as Figure 10 f shows that the activation of ethanol alpha-C-H bond is the starting step of the reaction.

[0088] Summary: The present application discloses the preparation method of Rh-Cs2AgBiBr6 / CdS heterojunction photocatalyst through four core embodiment systems: Cs2AgBiBr6 nanoparticles are prepared by anti-solvent precipitation method, CdS nanorods are prepared by solvothermal method, heterojunction is constructed by in-situ growth, and finally Rh cocatalyst is precisely loaded by photoreduction method. Six test examples comprehensively verify its excellent performance from theory to experiment: theoretical calculation and experimental characterization together confirm that the double perovskite material exhibits excellent stability in ethanol environment. Its structure remains intact after long-term immersion in ethanol for 168 hours, and under argon / air atmosphere and light conditions, the optical properties and crystal structure of the material can be maintained stable. The performance test of the optimal sample shows that the hydrogen production rate is 49.15 mmol·g -1 ·h -1 , the apparent quantum efficiency is 22.5%, and the introduction of Rh can regulate the distribution of acetaldehyde / acetals products; 60 hours of continuous reaction maintains more than 90% activity, confirming its long-term stability; photoelectric test and mechanism research reveal the synergistic effect of heterojunction and Rh and the reaction path of alpha-C-H bond activation. The whole set of embodiments and test examples constitute a complete technical solution from material preparation, structure characterization to performance verification and mechanism interpretation.

[0089] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples, and the changes, modifications, additions or substitutions made by the person skilled in the art within the essential scope of the present application should also belong to the protection scope of the present application.

Claims

1. A method for preparing a Rh-modified Cs 2AgBiBr 6 / CdS heterojunction photocatalyst, characterized in that, The method comprises the following steps: (1) preparing Cs2AgBiBr6 nanoparticles: a cesium source, a silver source and a bismuth source are dissolved in a polar solvent, ultrasonic stirring is performed to disperse them uniformly, then the solution is added to an anti-solvent to induce precipitation, centrifugal separation is performed and drying is carried out, thereby obtaining Cs2AgBiBr6 nanoparticles; (2) preparing CdS nanorods: a cadmium source and a sulfur source are dissolved in a diethylamine solvent, the solution is transferred to a high-pressure reaction kettle, reaction is carried out at 150-200 °C for 6-12 hours, after cooling, centrifugal washing and drying are carried out, thereby obtaining CdS nanorods; (3) constructing a Cs2AgBiBr6 / CdS heterojunction: the Cs2AgBiBr6 nanoparticles obtained in step (1) and the CdS nanorods obtained in step (2) are dispersed in an organic solvent at a mass ratio of 5-15:100, ultrasonic treatment and stirring are performed, the Cs2AgBiBr6 nanoparticles are uniformly loaded on the surface of the CdS nanorods by an in-situ growth strategy, thereby forming a Cs2AgBiBr6 / CdS heterojunction composite material; (4) loading a Rh cocatalyst: the Cs2AgBiBr6 / CdS heterojunction composite material obtained in step (3) is dispersed in an ethanol solution containing a Rh precursor, stirring reaction is carried out under visible light irradiation, centrifugal washing and drying are carried out, thereby obtaining a Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst, wherein the loading amount of Rh is 2-6 wt%.

2. The production method according to claim 1, characterized by, In step (1), the cesium source is CsBr, the silver source is AgBr, and the bismuth source is BiBr3; the polar solvent is N,N-dimethylformamide or dimethyl sulfoxide; the anti-solvent is ethyl acetate or acetone; the reaction temperature is 50-80 °C, and the reaction time is 1-3 hours.

3. The preparation method according to claim 1, characterized in that, In step (2), the cadmium source is Cd(NO3)2 or CdCl2, and the sulfur source is thiourea or Na2S; the solvothermal reaction temperature is 180 °C, and the reaction time is 8 hours.

4. The method of claim 1, wherein, In step (3), the mass ratio of the Cs2AgBiBr6 nanoparticles to the CdS nanorods is 10:100; the organic solvent is ethanol or isopropanol; the ultrasonic treatment time is 30-60 minutes, and the stirring time is 2-4 hours.

5. The preparation method according to claim 1, characterized in that, The Rh precursor in step (4) is RhCl3 or Rh(NO3)3; the wavelength of visible light irradiation is 420 nm, and the light intensity is 100-300 mW / cm 2 , the reaction time is 1-3 hours, and the loading of Rh is 4 wt%.

6. A Rh-modified Cs2AgBiBr6 / CdS heterojunction photocatalyst, characterized in that, The photocatalyst is prepared by the method of any one of claims 1-5, a Type-I heterojunction structure is formed between Cs2AgBiBr6 and CdS in the photocatalyst, Rh nanoparticles are anchored on the surface of Cs2AgBiBr6, and the crystal lattice structure of the photocatalyst remains intact after the photocatalyst is soaked in an ethanol solvent for 168 hours.

7. The photocatalyst according to claim 6, wherein The size distribution is 2-10 nm; in the UV-visible absorption spectrum there is a broadened absorption shoulder in the range 550-650 nm, corresponding to the surface plasmon resonance effect of Rh 3+ .

8. A method of photocatalytic dehydrogenation of ethanol, characterized by, The photocatalyst of claim 6 or 7 is used to catalyze the dehydrogenation of ethanol to produce hydrogen and liquid phase products, including acetaldehyde and acetal, under visible light irradiation; the reaction conditions include: the catalyst dosage is 1-5 mg / mL of ethanol, the reaction atmosphere is inert gas, the light wavelength is 420-800 nm, the light intensity is 100-300 mW / cm 2 , and the reaction temperature is 25-60 ℃.

9. The method of claim 8, wherein, The hydrogen production rate of the photocatalytic ethanol dehydrogenation reaction is 40-50 mmol·g -1 ·h -1 The apparent quantum efficiency at a wavelength of 420 nm is 20-25%; the selectivity of acetaldehyde and acetal in the liquid phase product is 50-70% and 30-50%, respectively.

10. The method of claim 8, wherein, The hydrogen production activity of the photocatalyst remains above 90% of the initial activity after continuous reaction for 60 hours; in the reaction, hydrogen atoms are derived from the activation of an α-C-H bond of an ethanol molecule, and it is verified by an isotopic tracing experiment that deuterium gas is generated when per-deuterated ethanol is used as a substrate.

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