Preparation method and application of cationic interface-regulated lead-based halide perovskite photocatalyst

Abstract

This invention discloses a method for preparing and applying a cation-interface-controlled lead-based halide perovskite photocatalyst. The method utilizes an organic solvent with low erosion of the perovskite lattice as the treatment medium. An alkali metal or alkaline earth metal cation source is briefly contacted with the prepared MAPbBr3. Through a micro-dissolution-consumption balance at the solid-liquid interface or a direct solid-solid ion exchange mechanism, cations are directionally transported and selectively anchored to surface defect sites. The resulting cation-interface-controlled lead-based halide perovskite photocatalyst is applied to the photocatalytic selective oxidation of cyclohexane to cyclohexanol and cyclohexanone, or the photocatalytic selective oxidation of benzyl alcohol to benzaldehyde. Under ambient temperature and pressure, and visible light-driven conditions, significantly improved conversion efficiency and cycling stability are achieved, providing a practical new strategy for the development of efficient and stable perovskite photocatalysts.

Description

Technical Field

[0001] This invention relates to the preparation method and application of lead-based halide perovskite photocatalysts. Background Technology

[0002] The selective catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA oil) is one of the most valuable fundamental reactions in the chemical industry. Its products are crucial intermediates in the production of high-molecular-weight materials such as nylon 6 and nylon 66. However, the saturated CH bonds in the cyclohexane molecule have high bond energy, weak polarity, and significant chemical inertness, often requiring the overcoming of extremely high energy barriers for activation. Traditional thermocatalytic processes typically require high temperature (150~300℃) and high pressure conditions to achieve effective CH bond breaking. This not only consumes a huge amount of energy but also presents a significant challenge: the CH bonds of the target product, KA oil, are more reactive than those of the feedstock cyclohexane, readily undergoing continuous oxidation to generate adipic acid, CO2, and other deeply oxidized products, making precise selectivity control difficult. Similarly, the selective oxidation of benzyl alcohol to benzaldehyde is also an important conversion process in the fine chemical and pharmaceutical industries. Benzaldehyde, as a high-value-added fragrance and pharmaceutical intermediate, has a continuously growing market demand. Although the electron-rich hydroxyl groups and α-CH bonds in benzyl alcohol make it relatively easy to activate, the core challenge of this reaction lies in precisely controlling the oxidation depth to prevent the target product, benzaldehyde, from being further oxidized to benzoic acid. This places stringent requirements on the selectivity of the catalyst. Against this backdrop, photocatalytic oxidation technology, utilizing high-energy electron-hole pairs generated by semiconductor materials under light irradiation, can drive the selective activation and transformation of the aforementioned organic substrates under ambient temperature and pressure conditions. This demonstrates significant energy-saving and consumption-reducing advantages and is considered a green and sustainable alternative technology.

[0003] In recent years, lead-based halide perovskite materials (represented by MAPbBr3) have attracted widespread attention in the fields of photovoltaic devices and photocatalysis as an emerging class of optoelectronic functional materials. These materials possess several outstanding photophysical properties: their light absorption coefficient far exceeds that of traditional metal oxide semiconductors, enabling efficient utilization of visible light; their band gap can be continuously tuned over a wide range through halogen components or cation substitution to adapt to the potential requirements of different redox reactions; simultaneously, MAPbBr3 exhibits a long carrier diffusion distance and intrinsically high defect tolerance, maintaining efficient photogenerated charge separation and transport even in the presence of structural disorder. These characteristics make lead-based halide perovskites ideal candidate materials for photocatalytic organic synthesis.

[0004] However, a fundamental bottleneck remains for these materials in their practical catalytic applications—their intrinsic structural stability is insufficient to meet the long-term durability requirements of catalytic reactions. Specifically, the lattice of MAPbBr3 is maintained by soft ionic bonds. When exposed to polar organic molecules, trace amounts of moisture, or continuous light irradiation, surface ions readily migrate, dissolve, or reconstruct, leading to localized collapse of the perovskite structure. This structural degradation results in a large amount of uncoordinated Pb on the surface. 2+ The presence of halogen vacancies forms a high-density nonradiative recombination center, causing photogenerated electrons and holes to be largely consumed before reaching the reaction interface, resulting in a sharp decline in quantum efficiency and a loss of catalytic activity. Therefore, how to effectively suppress ion migration and passivate defect sites from the material surface without damaging the bulk photoelectric properties has become a key scientific problem for promoting the practical application of lead-based halide perovskite photocatalysis.

[0005] Existing technical solutions and their limitations: Regarding the aforementioned challenge of synergistically improving the stability and activity of lead-based halide perovskites, the solutions reported in current literature and patents can be mainly summarized into the following categories:

[0006] The first strategy is the surface inert shell coating method. This involves epitaxially growing a dense, inert protective layer (such as SiO2, Al2O3, TiO2, or organic polymers) on the surface of perovskite particles to physically block the erosion by external polar molecules and moisture. For example, coating a few nanometers thick layer of silica onto the surface of MAPbBr3 using atomic layer deposition or sol-gel methods can, to some extent, slow down the decomposition rate of the material in aqueous phases or polar solvents. However, this method has an inherent contradiction: while the dense coating layer blocks corrosive substances, it inevitably prevents direct contact between reactant molecules and catalytically active sites, increasing interfacial charge transport resistance and causing a decrease in catalytic activity instead of an increase; while thinning the shell layer is beneficial for maintaining activity, it is difficult to provide sufficient structural protection.

[0007] The second strategy is the sacrificial agent addition method. Hole sacrificial agents (such as triethanolamine, ascorbic acid, etc.) or electron sacrificial agents are introduced into the photocatalytic reaction system to suppress the photocorrosion reaction of the material itself by preferentially consuming some of the photogenerated charges. This method can extend the catalyst's lifetime to some extent, but the introduction of sacrificial agents increases the complexity of the reaction system and the cost of product separation. Furthermore, it essentially shifts the stability problem from the material end to the operational end, without fundamentally improving the inherent chemical fragility of the perovskite surface.

[0008] The third strategy is bulk doping. This involves introducing small amounts of heterovalent metal cations (such as Mn) into the perovskite precursor. 2+ Zn 2+ Bi 3+ (etc.), partially replacing Pb 2+ or MA+ Sites are used to stabilize the crystal lattice. Although this method can improve intrinsic stability to some extent, harsh conditions such as high-temperature calcination or long-term solvothermal synthesis often lead to inhomogeneous doping, bulk structure distortion, and even the introduction of new defect energy levels, which have an uncontrollable impact on photoelectric properties.

[0009] The common shortcoming of the three strategies mentioned above is that none of them directly and precisely tailor and reconstruct the inherent coordination unsaturation states and high-density surface defects of perovskites at the atomic / ionic microenvironment level. These surface states are precisely what dominate key interfacial steps in the catalytic process, such as adsorption, activation, and charge transfer of reactant molecules. More importantly, there are no reports in the current technology of using mild post-treatment methods to directly perform defect-targeted passivation and interfacial protection on the formed perovskite surface with alkali metal or alkaline earth metal cations.

[0010] Furthermore, existing sporadic reports involving cation post-treatment almost all employ water or highly polar solvents to prepare the treatment solution to ensure complete salt dissolution. However, water molecules themselves have a strong corrosive effect on the perovskite lattice, easily inducing secondary structural damage during treatment. Therefore, exploring a mild method that can achieve effective cation interface modification while avoiding the corrosion of the perovskite bulk phase by the treatment medium itself, and clarifying the cation transport and anchoring mechanisms involved, is of significant scientific importance and application value for advancing the practical application of efficient and stable perovskite photocatalysts. Summary of the Invention

[0011] The purpose of this invention is to address two major pain points faced by existing MAPbBr3 photocatalysts in practical applications: one is the presence of a large number of uncoordinated Pb on the surface. 2+ Defects such as halogen vacancies constitute severe nonradiative recombination centers, leading to rapid recombination of photogenerated carriers and low quantum efficiency. Secondly, in organic reaction systems containing polar molecules, the structure is unstable and the surface is easily eroded, resulting in ion migration, phase separation, or even decomposition, causing a sharp decline in catalytic activity. Therefore, this paper provides a method for preparing and applying lead-based halide perovskite photocatalysts with cation interface regulation.

[0012] To address the problems existing in the prior art, the core concept of this invention lies in: utilizing alkali metal cations (K... + Na + Li + Cs + ) or alkaline earth metal cations (Ca 2+ Mg 2+ Ba 2+ 、Sr 2+A simple contact treatment medium is used to treat the prepared MAPbBr3, constructing a stable cation passivation layer on its surface. This treatment medium is preferably an organic solvent (such as isopropanol) with low corrosiveness to the perovskite lattice. Even if some cation salts are suspended rather than completely dissolved in it, directional transport and anchoring of cations to surface defect sites can still be achieved through micro-dissolution-consumption equilibrium at the solid-liquid interface or direct solid-solid ion exchange. This strategy does not change the main crystal structure of the material and simultaneously solves the problem of balancing activity and stability by precisely controlling the interfacial microenvironment.

[0013] A method for preparing a lead-based halide perovskite photocatalyst with cation interface regulation is specifically carried out according to the following steps:

[0014] I. Preparation of lead-based halide perovskite MAPbBr3:

[0015] ① Under ice-water bath conditions, methylamine and hydrogen bromide are mixed and stirred, then evaporated and crystallized, washed, recrystallized, and dried under vacuum to obtain methylammonium bromide;

[0016] ② Adjust the pH of N,N-dimethylformamide to 9 using ammonia water, then add PbBr2 and methylammonium bromide, stir to form a viscous solution, and then dry to obtain lead-based halide perovskite MAPbBr3;

[0017] II. Preparation of lead-based halide perovskite photocatalysts with cation interface regulation:

[0018] Alkali metal halides or alkaline earth metal halides are added to isopropanol and stirred to obtain a suspension. MAPbBr3 is added to the suspension, sealed, shaken well, allowed to stand, and the supernatant is discarded. The resulting precipitate is dried to obtain a lead-based halide perovskite photocatalyst with cation interface regulation.

[0019] The principle of this invention:

[0020] This invention overcomes the shortcomings of the prior art and provides a simple, mild and controllable post-treatment method for cation interface regulation. Specifically, it uses an organic solvent (preferably isopropanol) with low corrosiveness to the perovskite lattice as the treatment medium to conduct a short-term contact treatment between an alkali metal or alkaline earth metal cation source (even if it is in a suspended state rather than completely dissolved) and the prepared MAPbBr3. Through the micro-dissolution-consumption balance at the solid-liquid interface or the direct solid-solid ion exchange mechanism, the directional transport and selective anchoring of cations to surface defect sites are achieved.

[0021] Advantages of this invention:

[0022] I. This invention provides a mild and controllable method for passivating interface defects: Without relying on harsh conditions such as high-temperature annealing and inert atmosphere protection, this invention effectively reduces defect density and significantly improves the separation and transport efficiency of photogenerated carriers by selectively anchoring uncoordinated sites on the surface by cations.

[0023] II. This invention constructs a surface ion protection layer while passivating defects: This invention uses low-corrosive solvents such as isopropanol as treatment media to avoid the corrosive damage of water molecules to the perovskite lattice, and significantly enhances the long-term chemical stability of the material in the photocatalytic reaction system without damaging the bulk structure.

[0024] Third, this invention applies the above-mentioned interface regulation strategy to different types of photocatalytic organic oxidation reactions: For the selective oxidation of the inert CH bond of cyclohexane, this invention achieves efficient conversion to cyclohexanol and cyclohexanone under mild conditions by synergistically improving carrier utilization efficiency and structural durability; In addition, this invention extends the application scope to the photocatalytic selective oxidation of substrates containing easily oxidizable functional groups such as benzyl alcohol, verifying the universality of the strategy of this invention for different reaction types, and providing a practical and widely applicable technical solution for the development of efficient and stable perovskite-based photocatalysts; Attached Figure Description

[0025] Figure 1 A comparison of the photocatalytic performance of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different anions.

[0026] Figure 2 A comparison of the photocatalytic performance of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations;

[0027] Figure 3 XRD comparison of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations;

[0028] Figure 4 The image shows a comparison of FTIR spectra of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations.

[0029] Figure 5 Comparison of X-ray photoelectron spectra of MAPbBr3 and MAPbBr3-KCl;

[0030] Figure 6 This is a comparison of the cyclic stability of cyclohexane oxidation by MAPbBr3 and MAPbBr3-KCl. Detailed Implementation

[0031] Specific Implementation Method 1: This implementation method is a method for preparing a lead-based halide perovskite photocatalyst with cation interface regulation, specifically completed according to the following steps:

[0032] I. Preparation of lead-based halide perovskite MAPbBr3:

[0033] ① Under ice-water bath conditions, methylamine aqueous solution and hydrogen bromide aqueous solution are mixed and stirred, then evaporated and crystallized, washed, recrystallized, and vacuum dried to obtain methylammonium bromide;

[0034] ② Adjust the pH of N,N-dimethylformamide to 9 using ammonia water, then add PbBr2 and methylammonium bromide, stir to form a viscous solution, and then dry to obtain lead-based halide perovskite MAPbBr3;

[0035] II. Preparation of lead-based halide perovskite photocatalysts with cation interface regulation:

[0036] Alkali metal halides or alkaline earth metal halides are added to isopropanol and stirred to obtain a suspension. MAPbBr3 is added to the suspension, sealed, shaken well, allowed to stand, and the supernatant is discarded. The resulting precipitate is dried to obtain a lead-based halide perovskite photocatalyst with cation interface regulation.

[0037] Unlike traditional methods that rely on homogeneous treatment where the cationic salt is completely dissolved in water or highly polar solvents, this embodiment proposes and verifies that even when the cationic salt has extremely low solubility in the treatment medium and exists in a heterogeneous suspension, efficient interfacial cationic modification can still be achieved through an extremely gentle process of suspension contact, rapid removal, and drying. Protection of this method should be independent of the specific type of cation or anion, and should be presented as a separate method claim.

[0038] Innovation of this implementation method:

[0039] (1) An interface control strategy using an organic solvent with low corrosivity to perovskite as the treatment medium: isopropanol is used as a representative, which is different from water or highly polar solvents commonly used in the prior art; this type of solvent can achieve effective interfacial transport of cations while avoiding corrosive damage to the perovskite lattice by the treatment medium itself; the scope of protection should cover any organic solvent with low corrosivity or non-corrosivity to MAPbBr3 lattice, including but not limited to alcohols, ethers, halogenated hydrocarbons and non-polar hydrocarbon solvents;

[0040] (2) A perovskite surface defect passivation strategy based on cation-anion synergistic effect: This invention first immobilizes cations (K... + Screening different halogen anions (Cl) - ,Br - I -The study found that the catalytic activity in the oxidation of cyclohexane and benzyl alcohol showed a consistent trend of KCl>KBr>KI, thus determining that Cl... - The optimal accompanying anion; thus fixing Cl - The system verified the monovalent alkali metal cation (Li). + Na + K + Cs + ) and divalent alkaline earth metal cations (Mg 2+ Ca 2+ 、Sr 2+ Ba 2+ Both classes of metal ions can achieve effective interface modification. The scope of protection should be broadly defined as treatment processes using alkali metal or alkaline earth metal chlorides as cation sources, covering both single-salt and mixed-salt schemes;

[0041] (3) Lead-based halide perovskite material modified by the above interface: The protected object is a lead-based halide perovskite material with an interface cation modification layer and an unchanged bulk XRD structure, characterized in that the surface is anchored with a sub-monolayer amount of alkali metal or alkaline earth metal cations, the binding energy of Pb and Br shifts to the direction of lower binding energy, and the bulk structure is not changed.

[0042] (4) Application of the above interface-controlled perovskite materials in photocatalytic selective oxidation reactions: The protected objects include, but are not limited to: selective oxidation of cyclohexane to cyclohexanol and cyclohexanone under visible light-driven molecular oxygen, and selective oxidation of benzyl alcohol to benzaldehyde.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in the following ways: the mass fraction of the methylamine aqueous solution in step one ① is 30%~33%; the mass fraction of the hydrogen bromide aqueous solution is 40%; the molar ratio of methylamine to hydrogen bromide in step one ① is 1:1; the stirring time in step one ① is 2h~3h; the evaporation and crystallization temperature in step one ① is 70℃, and the time is 10h~14h. Other steps are the same as in Specific Implementation Method One.

[0044] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in the following ways: the washing described in step 1① is performed using ether 2 to 4 times; the recrystallization described in step 1① is performed using ethanol; the vacuum drying temperature described in step 1① is 60℃ to 80℃, and the vacuum drying time is 20h to 24h. Other steps are the same as in Specific Implementation Method 1 or 2.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the molar ratio of PbBr2 to methylammonium bromide in step one ② is (1~1.1):(1~1.1); the mass ratio of PbBr2 to N,N-dimethylformamide in step one ② is (2g~3g):9mL. Other steps are the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the mass fraction of ammonia water mentioned in step one to two is 25% to 28%; the stirring time mentioned in step one to two is 2 to 3 hours; and the drying temperature mentioned in step one to two is 60°C to 80°C. Other steps are the same as in Specific Implementation Methods One to Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the alkali metal halide mentioned in step two is an alkali metal chloride, alkali metal bromide, or alkali metal iodide; the alkali metal chloride is LiCl, NaCl, KCl, or CsCl; the alkali metal bromide is LiBr, NaBr, KBr, or CsBr; and the alkali metal iodide is LiI, NaI, KI, or CsI. The other steps are the same as in Specific Implementation Methods One to Five.

[0048] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the alkaline earth metal halide mentioned in step two is an alkaline earth metal chloride, alkaline earth metal bromide, or alkaline earth metal iodide; the alkaline earth metal chloride is CaCl2, MgCl2, BaCl2, or SrCl2; the alkaline earth metal bromide is CaBr2, MgBr2, BaBr2, or SrBr2; and the alkaline earth metal iodide is CaI2, MgI2, BaI2, or SrI2. The other steps are the same as in Specific Implementation Methods One to Six.

[0049] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the concentration of alkali metal halides or alkaline earth metal halides in the suspension described in step two is 0.005 mol / L; the mass ratio of MAPbBr3 to the volume of the suspension in step two is 0.5 g: 10 mL. Other steps are the same as in Specific Implementation Methods One to Seven.

[0050] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the stirring time in step two is 10-20 minutes; the settling time in step two is 15-20 minutes; and the drying temperature in step two is 60°C-80°C. Other steps are the same as in Specific Implementation Methods One to Eight.

[0051] Specific Implementation Method 10: This implementation method is a lead-based halide perovskite photocatalyst with cation interface regulation for selective photocatalytic oxidation of cyclohexane to prepare cyclohexanol and cyclohexanone, or selective photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde.

[0052] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0053] All reagents: Hydrogen bromide aqueous solution (HBr, 40% by mass), lead bromide (PbBr2, 99% by mass), diethyl ether (C4H2O) 10 O (99.8% by mass), ethanol (C2H6O, 99.7% by mass), N,N-dimethylformamide (DMF, not less than 99.5% by mass), isopropanol (C3H7OH, not less than 99.5% by mass), cyclohexane (C6H 12 The following reagents are available: carbon tetrachloride (CCl4, 99.5%), lithium chloride (LiCl, 99%), sodium chloride (NaCl, ≥99.0%), potassium chloride (KCl, 99.99%), cesium chloride (CsCl, 99.5%), calcium chloride (CaCl2, 99.99%), magnesium chloride (MgCl2, 99%), barium chloride (BaCl2, 99%), and strontium chloride (SrCl2, 99.5%). All of these are products of Maclean Reagent Co., Ltd.

[0054] Example 1: The preparation method of lead-based halide perovskite MAPbBr3 is carried out according to the following steps:

[0055] First, under ice-water bath conditions, the aqueous solution of methylamine and the aqueous solution of hydrogen bromide were mixed and stirred for 2 hours. Then, the reaction solution was transferred to a vacuum drying oven and evaporated and crystallized at 70°C for 12 hours. The mixture was washed three times with diethyl ether, recrystallized with ethanol, and finally dried under vacuum at 70°C for 24 hours to obtain methylammonium bromide (MABr).

[0056] The methylamine (CH3NH2) aqueous solution mentioned in step one has a mass fraction of 30%.

[0057] The mass fraction of the hydrogen bromide (HBr) aqueous solution mentioned in step one is 40%;

[0058] The molar ratio of methylamine to hydrogen bromide mentioned in step one is 1:1;

[0059] 2. Adjust the pH of 9 mL of N,N-dimethylformamide (DMF) to 9 using ammonia water, then add 2.31 g of PbBr2 and 0.67 g of methylammonium bromide, stir for 2 h to form a viscous solution, then transfer it to an oven at 70 °C to dry, and obtain lead-based halide perovskite powder, denoted as MAPbBr3;

[0060] The ammonia solution mentioned in step two has a mass fraction of 25%.

[0061] Example 2: Preparation method and catalytic performance study of lead-based halide perovskite photocatalysts with different potassium halide anion interfaces, specifically completed according to the following steps:

[0062] KCl was added to isopropanol and stirred for 20 min to obtain a suspension with a KCl concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-KCl.

[0063] KBr was added to isopropanol and stirred for 20 min to obtain a suspension with a KBr concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-KBr.

[0064] KI was added to isopropanol and stirred for 20 min to obtain a suspension with a KI concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded. The resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-KI.

[0065] Comparative example: Treatment of MAPbBr3 with pure isopropanol, specifically carried out according to the following steps:

[0066] Add 0.5 g MAPbBr3 to 10 mL of pure isopropanol, seal and shake well, let stand for 15 min and then discard the supernatant. Dry the resulting precipitate in an oven at 70 °C to obtain the control sample treated with isopropanol alone, named MAPbBr3-IPA.

[0067] The above samples were used as catalysts in the photocatalytic oxidation of cyclohexane and benzyl alcohol, respectively. Typical conditions for cyclohexane oxidation were as follows: 50 mg of catalyst was weighed and dispersed in a mixed solution of 1 mL cyclohexane and 10 mL carbon tetrachloride, pure oxygen was introduced, and the reaction was carried out under a 300 W xenon lamp (λ > 400 nm) for 5 hours. After the reaction, the products were analyzed by gas chromatography, and the results are shown below. Figure 1 As shown;

[0068] Typical conditions for benzyl alcohol oxidation are as follows: 50 mg of catalyst is weighed and dispersed in a mixed solution of 22 μL benzyl alcohol and 3 mL carbon tetrachloride, using pure oxygen as the oxidant, and reacted under a 300 W xenon lamp (λ > 400 nm) for 4 hours. After the reaction, the products are analyzed by gas chromatography, and the results are shown below. Figure 1 As shown;

[0069] Figure 1 A comparison of the photocatalytic performance of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different anions.

[0070] from Figure 1 It can be seen that the conversion rates of all potassium salt-treated samples in Example 2 were significantly higher than those of MAPbBr3 and MAPbBr3-IPA in the comparative example, but there were significant differences in activity among the three. In the oxidation of cyclohexane and benzyl alcohol, a consistent trend was observed: MAPbBr3-KCl > MAPbBr3-KBr > MAPbBr3-KI. Specifically, the cyclohexane conversion rate of the MAPbBr3 sample was 3.2%, the MAPbBr3-IPA conversion rate was 3.5%, while the MAPbBr3-KCl sample had the highest cyclohexane conversion rate at 7.0%. Similarly, the benzyl alcohol conversion rate of the MAPbBr3 sample was 26.3%, the MAPbBr3-IPA conversion rate was 30.2%, showing no significant change, while the MAPbBr3-KCl sample had the highest benzyl alcohol conversion rate at 67.4%, approximately 2.6 times higher than that of MAPbBr3. These differences are mainly attributed to the different halogen anions affecting the Br2 on the MAPbBr3 surface. - The vacancy repair efficiency differs: MAPbBr3 surface has a large number of halogen vacancy defects, among which Br... - Vacancies are most abundant. When treated with potassium salts of different halide anions, K... + As cations, they are captured and anchored by surface defect sites, while the accompanying halide anions (Cl...) - ,Br - I - These halogens may occupy or fill surface halogen vacancies, and the two work together to passivate surface defects. - The ionic radius is smaller than that of Br. - It has stronger electronegativity, and it fills surface vacancies or interacts with uncoordinated Pb. 2+The coordination effect of [the substance] may be more effective, and the repair of defect states may be more thorough, thereby suppressing carrier nonradiative recombination to the greatest extent. In contrast, I […]. - The ionic radius is greater than that of Br. - The matching degree with the perovskite surface lattice is poor, resulting in relatively low passivation efficiency. Based on the above screening results, the optimal accompanying anion was determined to be Cl. - .

[0071] Different alkali metal and alkaline earth metal chloride interfaces regulate the catalytic performance of MAPbBr3.

[0072] In Example 2, Cl was determined - Based on the optimal accompanying anion, the interfacial regulation effect of different metal cations was further systematically investigated. Monovalent alkali metal chlorides (LiCl, NaCl, KCl, CsCl) and divalent alkaline earth metal chlorides (CaCl2, MgCl2, BaCl2, SrCl2) were selected for treatment.

[0073] Example 3: A method for preparing a lead-based halide perovskite photocatalyst with cation interface regulation, specifically carried out according to the following steps:

[0074] KCl was added to isopropanol and stirred for 20 min to obtain a suspension with a KCl concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-KCl.

[0075] LiCl was added to isopropanol and stirred for 20 min to obtain a suspension with a LiCl concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-LiCl.

[0076] NaCl was added to isopropanol and stirred for 20 min to obtain a suspension with a NaCl concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-NaCl.

[0077] CsCl was added to isopropanol and stirred for 20 min to obtain a suspension with a CsCl concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-CsCl.

[0078] CaCl2 was added to isopropanol and stirred for 20 min to obtain a suspension with a CaCl2 concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-CaCl2.

[0079] MgCl2 was added to isopropanol and stirred for 20 min to obtain a suspension with a MgCl2 concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-MgCl2.

[0080] BaCl2 was added to isopropanol and stirred for 20 min to obtain a suspension with a BaCl2 concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded and the resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-BaCl2.

[0081] SrCl2 was added to isopropanol and stirred for 20 min to obtain a suspension with a SrCl2 concentration of 0.005 mol / L. 0.5 g MAPbBr3 was added to 10 mL of the suspension, sealed and shaken well. After standing for 15 min, the supernatant was discarded. The resulting precipitate was dried in an oven at 70 °C to obtain a lead-based halide perovskite photocatalyst with cation interface regulation, denoted as MAPbBr3-SrCl2.

[0082] Comparative example: Treatment of MAPbBr3 with pure isopropanol, specifically carried out according to the following steps:

[0083] Add 0.5 g MAPbBr3 to 10 mL of pure isopropanol, seal and shake well, let stand for 15 min and then discard the supernatant. Dry the resulting precipitate in an oven at 70 °C to obtain the control sample treated with isopropanol alone, named MAPbBr3-IPA.

[0084] The above samples were used as catalysts in the photocatalytic oxidation of cyclohexane and benzyl alcohol, respectively. Typical conditions for cyclohexane oxidation were as follows: 50 mg of catalyst was weighed and dispersed in a mixed solution of 1 mL cyclohexane and 10 mL carbon tetrachloride, pure oxygen was introduced, and the reaction was carried out under a 300 W xenon lamp (λ > 400 nm) for 5 hours. After the reaction, the products were analyzed by gas chromatography, and the results are shown below. Figure 2 As shown;

[0085] Typical conditions for benzyl alcohol oxidation are as follows: 50 mg of catalyst is weighed and dispersed in a mixed solution of 22 μL benzyl alcohol and 3 mL carbon tetrachloride, using pure oxygen as the oxidant, and reacted under a 300 W xenon lamp (λ > 400 nm) for 4 hours. After the reaction, the products are analyzed by gas chromatography, and the results are shown below. Figure 2 As shown;

[0086] Figure 2 A comparison of the photocatalytic performance of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations;

[0087] Figure 2 The results showed that after treatment with different alkali metal and alkaline earth metal chlorides, the conversion rates of cyclohexane and benzyl alcohol in all samples were significantly improved compared with MAPbBr3. Among them, the cyclohexane conversion rate of MAPbBr3-KCl reached the highest of 7.0%, and the benzyl alcohol conversion rate reached 67.4%, confirming that the conversion rate of cyclohexane and benzyl alcohol was significantly improved by fixing Cl-. - Under the condition of accompanying anions, various alkali metal and alkaline earth metal cations can effectively achieve interface defect passivation and catalytic performance enhancement.

[0088] Figure 3 XRD comparison of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations;

[0089] like Figure 3 As shown, the diffraction peaks of MAPbBr3 can all be attributed to the typical cubic perovskite structure. No new impurity phase diffraction peaks appeared in any of the samples treated with different cation suspensions. The peak positions and peak shapes were not significantly different from those of MAPbBr3, indicating that the cation modification only acts on the material surface and does not destroy the bulk crystal structure.

[0090] Figure 4 The image shows a comparison of FTIR spectra of MAPbBr3 and lead-based halide perovskite photocatalysts regulated by different cations.

[0091] from Figure 4 It can be seen that the characteristic absorption peak positions of all samples treated with different cation suspensions are basically consistent with those of MAPbBr3, indicating that cation regulation did not change the main chemical framework structure and functional group structure of the material.

[0092] Figure 5 Comparison of X-ray photoelectron spectra of MAPbBr3 and MAPbBr3-KCl;

[0093] from Figure 5 It can be seen that, compared with MAPbBr3, the Pb 4f and Br 3d binding energies of MAPbBr3-KCl undergo a measurable shift towards lower binding energies, indicating an increase in the surrounding electron density. This is due to the electronegative KCl structure. + Cations anchored to uncoordinated Pb on the surface 2+ Direct spectroscopic evidence of electron injection into the Pb-Br octahedral framework after the addition of electron-deficient defect sites such as halogen vacancies; the C 1s and N 1s binding energies remain essentially unchanged, confirming that the cation modification does not affect the bulk methylamine cation. Corresponding characteristic signals can be detected in the K 2p and Cl 2p regions, but the peak shapes exhibit asymmetric and broadened characteristics, reflecting K... + and Cl - Multiple coordination environments exist at various defect sites on the surface. Combined with the absence of new diffraction peaks detected by XRD, it can be confirmed that KCl species are anchored to the outermost layer of the material only at a sub-monolayer level, without bulk diffusion or new phase formation.

[0094] Photocatalytic oxidation cycle stability test:

[0095] MAPbBr3 and MAPbBr3-KCl were used as catalysts in the photocatalytic oxidation of cyclohexane. Typical conditions for cyclohexane oxidation were as follows: 50 mg of catalyst was weighed and dispersed in a mixed solution of 1 mL cyclohexane and 10 mL carbon tetrachloride. Pure oxygen was introduced, and the reaction was carried out under a 300 W xenon lamp (λ > 400 nm) for 5 hours. After the catalytic reaction, the catalyst was centrifuged, washed with isopropanol, dried at 70 °C, and then recycled back into the cyclohexane oxidation reaction system under the same conditions for cycle testing. (See attached diagram). Figure 6 As shown;

[0096] Figure 6 A comparison of the cyclohexane oxidation cycle stability of MAPbBr3 and MAPbBr3-KCl;

[0097] The results showed that the cation-regulated catalyst MAPbBr3-KCl maintained good catalytic activity after five cycles, achieving a conversion rate of 6.6%, which was 95.6% of the initial conversion rate. In contrast, MAPbBr3 showed a significant decline in cyclohexane oxidation performance under the same conditions (a conversion rate of 2.8% after five cycles, representing 87.5% of the initial conversion rate). This is attributed to the ion-protective layer constructed on the surface by the cations, which effectively prevented the polar molecules in the reaction system from eroding the perovskite lattice.

[0098] Based on the above results, the inventors discovered that although the macroscopic solubility of the aforementioned alkali metal and alkaline earth metal chlorides in isopropanol is low, and some metal chlorides (such as sodium chloride and potassium chloride) cannot form homogeneous solutions in the traditional sense, efficient cation interface passivation can still be achieved by mixing perovskite powder with an isopropanol suspension containing cationic salt particles and then drying it. The mechanism is as follows: under isopropanol wetting and 70°C thermal driving conditions, the suspended salt particles are in close contact with the perovskite surface, and the trace amounts of dissolved cations are absorbed by the highly active uncoordinated defect sites on the perovskite surface (such as Br₂). - Vacancy, Pb 2+ The continuous consumption and capture of dangling bonds (and other components) drives the sustained dissolution of the salt and the directional migration of cations to the interface. The key advantages of this heterogeneous treatment method are: isopropanol has almost no corrosive effect on the MAPbBr3 lattice, effectively protecting the bulk structure; simultaneously, the extremely low solubility of the salt constitutes a self-confining mechanism, avoiding excessive cation doping or the formation of new interfacial phases, enabling atomic / ionic level interface modification precision. This method achieves surface confinement modification under mild conditions, providing a new strategy for the development of efficient and stable perovskite photocatalysts.

Claims

1. A method for preparing a lead-based halide perovskite photocatalyst with cation interface regulation, characterized in that, The preparation method is specifically carried out according to the following steps: I. Preparation of lead-based halide perovskite MAPbBr3: ① Under ice-water bath conditions, methylamine aqueous solution and hydrogen bromide aqueous solution are mixed and stirred, then evaporated and crystallized, washed, recrystallized, and dried under vacuum to obtain methylammonium bromide; ② Adjust the pH of N,N-dimethylformamide to 9 using ammonia water, then add PbBr2 and methylammonium bromide, stir to form a viscous solution, and then dry to obtain lead-based halide perovskite MAPbBr3; II. Preparation of lead-based halide perovskite photocatalysts with cation interface regulation: Alkali metal halides or alkaline earth metal halides are added to isopropanol and stirred to obtain a suspension. MAPbBr3 is added to the suspension, sealed, shaken well, allowed to stand, and the supernatant is discarded. The resulting precipitate is dried to obtain a lead-based halide perovskite photocatalyst with cation interface regulation.

2. The method for preparing a cation interface-regulated lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The methylamine aqueous solution in step 1① has a mass fraction of 30%~33%; the hydrogen bromide aqueous solution has a mass fraction of 40%; the molar ratio of methylamine to hydrogen bromide in step 1① is 1:1; the stirring time in step 1① is 2h~3h; the evaporation and crystallization temperature in step 1① is 70℃, and the time is 10h~14h.

3. The method for preparing a cation interface-regulated lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The washing described in step 1① involves washing with ether 2 to 4 times; the recrystallization described in step 1① involves crystallization with ethanol; the vacuum drying temperature described in step 1① is 60℃ to 80℃, and the vacuum drying time is 20h to 24h.

4. The method for preparing a lead-based halide perovskite photocatalyst with cation interface regulation according to claim 1, characterized in that, The molar ratio of PbBr2 to methylammonium bromide in step 1② is (1~1.1):(1~1.1); the mass ratio of PbBr2 to N,N-dimethylformamide in step 1② is (2g~3g):9mL.

5. The method for preparing a cation interface-regulated lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The mass fraction of ammonia water mentioned in step 1② is 25%~28%; the stirring time mentioned in step 1② is 2h~3h; the drying temperature mentioned in step 1② is 60℃~80℃.

6. The method for preparing a cation interface-controlled lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The alkali metal halide mentioned in step two is an alkali metal chloride, alkali metal bromide, or alkali metal iodide; the alkali metal chloride is LiCl, NaCl, KCl, or CsCl; the alkali metal bromide is LiBr, NaBr, KBr, or CsBr; and the alkali metal iodide is LiI, NaI, KI, or CsI.

7. The method for preparing a cation interface-controlled lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The alkaline earth metal halide mentioned in step two is an alkaline earth metal chloride, alkaline earth metal bromide, or alkaline earth metal iodide; the alkaline earth metal chloride is CaCl2, MgCl2, BaCl2, or SrCl2; the alkaline earth metal bromide is CaBr2, MgBr2, BaBr2, or SrBr2; and the alkaline earth metal iodide is CaI2, MgI2, BaI2, or SrI2.

8. The method for preparing a cation interface-controlled lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The concentration of alkali metal halides or alkaline earth metal halides in the suspension in step two is 0.005 mol / L; the mass ratio of MAPbBr3 to the volume of the suspension in step two is 0.5 g: 10 mL.

9. The method for preparing a cation interface-regulated lead-based halide perovskite photocatalyst according to claim 1, characterized in that, The stirring time in step two is 10 min to 20 min; the settling time in step two is 15 min to 20 min; and the drying temperature in step two is 60℃ to 80℃.

10. The application of a cation interface-regulated lead-based halide perovskite photocatalyst as described in any one of claims 1 to 9, characterized in that... A lead-based halide perovskite photocatalyst with cation interface regulation is used for the selective photocatalytic oxidation of cyclohexane to prepare cyclohexanol and cyclohexanone, or for the selective photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde.

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