Preparation method of calcium hydroxystannate material based on topography reconstruction to enhance intrinsic light absorption

Abstract

The application relates to the technical field of photocatalytic material preparation, and discloses a preparation method of calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption, which comprises the following steps: firstly, a regular polyhedral calcium hydroxystannate precursor powder is prepared by adopting a liquid phase precipitation method; subsequently, deionized water and anhydrous ethanol are mixed to construct a solvent cage medium, and a low-concentration etching working solution is prepared by adding an organic weak acid; the precursor is added into the working solution for constant-speed stirring, morphology reconstruction is carried out on the crystal surface by using the solvent cage shielding effect and acid etching effect, and solid-liquid separation is carried out immediately after the reaction is completed; the obtained precipitate is washed and dried to obtain the calcium hydroxystannate material with a surface micro-rough structure. Through a mild and limited etching process, a defect layer rich in oxygen vacancies is constructed in situ on the crystal surface, the micro-morphology is reconstructed into an octagonal shape, the band gap width is effectively reduced, the light absorption edge is red-shifted, carrier recombination is inhibited, and therefore the photocatalytic mineralization performance of the material under visible light is improved.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic material preparation technology, specifically to a method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption. Background Technology

[0002] Calcium hydroxystannate (CaSn(OH)6), as a chemically stable and environmentally friendly n-type semiconductor material, has potential applications in photocatalytic degradation of organic pollutants, environmental purification, and photocatalytic water splitting for hydrogen production. The efficiency of photocatalytic reactions is mainly limited by the material's light-trapping ability and the separation efficiency of photogenerated carriers. However, intrinsic calcium hydroxystannate prepared by conventional liquid-phase precipitation methods exhibits regular cubic or polyhedral micron-sized particles with a large band gap, primarily responding to the ultraviolet region, and showing extremely low utilization of visible light, which constitutes the highest energy proportion of sunlight. Furthermore, the intrinsic material lacks effective charge-trapping sites both internally and on its surface, leading to a rapid recombination rate of photogenerated electrons and holes, which restricts its quantum efficiency and actual mineralization performance.

[0003] To improve the light absorption and catalytic performance of calcium hydroxystannate, existing technologies employ modification methods such as elemental doping, construction of semiconductor heterojunctions, or noble metal deposition. While introducing impurity ions or heterojunctions can broaden the spectral response range to some extent, these methods involve complex fabrication processes and high costs. More importantly, exogenous doping easily introduces deep-level defects within the crystal lattice. These defects, in turn, become recombination centers for photogenerated carriers, reducing photocatalytic activity. Therefore, enhancing the intrinsic light absorption capacity by controlling the material's microstructure and surface state is considered a more direct and effective approach to improving photocatalytic performance.

[0004] Currently, research on the morphology regulation of calcium hydroxystannate focuses on constructing nanosheets, hollow structures, or multi-level assemblies using hydrothermal methods, template methods, or strong acid-base etching methods. However, hydrothermal synthesis is time-consuming and energy-intensive; template methods require the use of difficult-to-remove surfactants, which can easily cause secondary pollution and hinder active sites; and traditional acid-base etching processes are difficult to precisely control reaction kinetics. In particular, when using acid for surface etching, the lack of effective constraints on mass transfer processes leads to excessively fast reaction rates, which can easily cause over-dissolution of the crystal framework or even structural collapse. It is difficult to obtain specific geometric morphologies (such as octagonal structures) with high specific surface areas and abundant and stable surface defects while maintaining the integrity of the crystal structure. This results in existing modified materials still suffering from insufficient adsorption sites, weak visible light driving ability, and low mineralization efficiency when facing low concentrations and high stability of gaseous pollutants (such as volatile organic compounds, VOCs). Therefore, developing a mild, controllable preparation method that can optimize band structure and microstructure is of great significance for enhancing the photocatalytic application value of calcium hydroxystannate. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing calcium hydroxystannate materials based on morphology reconstruction to enhance intrinsic light absorption. This method solves the problems of existing calcium hydroxystannate materials having a large bandgap leading to a narrow visible light response range, a fast recombination rate of photogenerated carriers, and the difficulty of accurately constructing surface defects while maintaining the integrity of the crystal structure using conventional morphology control methods, which result in low mineralization efficiency for highly stable gaseous pollutants.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing calcium hydroxystannate materials based on morphology reconstruction to enhance intrinsic light absorption, employing the following technical solution:

[0008] Regular polyhedral calcium hydroxystannate precursor powder was prepared by liquid-phase precipitation.

[0009] A low-concentration etching working solution is prepared by uniformly mixing deionized water and anhydrous ethanol as a solvent cage medium and adding an organic weak acid to the solvent cage medium.

[0010] The regular polyhedral calcium hydroxystannate precursor powder was added to the low-concentration etching working solution and stirred at a constant speed. The surface morphology of the regular polyhedral calcium hydroxystannate precursor powder was reconstructed by utilizing the solvent cage shielding effect in combination with acid etching. After the reaction was completed, the solid and liquid phases were separated immediately. The resulting solid precipitate was washed and dried to obtain the calcium hydroxystannate material with a micro-rough surface structure.

[0011] By employing the above technical solution, this invention utilizes a solvent cage medium system constructed from deionized water and anhydrous ethanol, combined with a low-concentration weak organic acid, to achieve confined etching of the crystal surface, thereby obtaining a calcium hydroxystannate material with enhanced photocatalytic activity. Its main mechanism of action and beneficial effects are as follows:

[0012] First, anhydrous ethanol molecules interact with the hydroxyl groups on the surface of calcium hydroxystannate crystals via hydrogen bonds, forming a solvation shielding layer (i.e., solvent cage effect) at the solid-liquid interface. This shielding layer increases the mass transfer resistance of hydrogen ions to the crystal surface and reduces the local dielectric constant of the reaction interface, thereby confining the acid etching reaction to the kinetically controlled region and preventing excessive dissolution or collapse of the crystal framework.

[0013] Secondly, the weak organic acid undergoes incomplete ionization in the solvent cage medium, slowly releasing hydrogen ions that pass through the shielding layer and preferentially react with bridging hydroxyl groups or lattice oxygen on crystal edges and high-energy surfaces. This process is in metastable equilibrium, capable of removing only surface atoms while completely preserving the regular polyhedral structure of the bulk phase.

[0014] Finally, with the stripping of surface atoms, the coordination environment on the crystal surface rearranges, generating oxygen vacancy defects in situ. The specific reaction process is as follows: the tin hydroxyl groups on the crystal surface first combine with adsorbed hydrogen ions to become surface protonated hydroxyl groups, then undergo a dehydration reaction to remove one water molecule, exposing coordinately unsaturated tin sites and forming oxygen vacancies. This process introduces defect energy levels into the band structure, reducing the band gap of the material and causing a redshift in the light absorption edge to enhance visible light absorption. Simultaneously, the formed oxygen vacancies act as electron traps, effectively separating photogenerated electrons and holes and extending carrier lifetime.

[0015] Preferably, the preparation method of the regular polyhedral calcium hydroxystannate precursor powder includes the following steps:

[0016] Sodium hydroxide solid was dissolved in deionized water, and tin source powder was added and stirred until dissolved to obtain solution A.

[0017] Solution B was obtained by dissolving the solid calcium source in deionized water.

[0018] Solution B was added dropwise to solution A at a set rate. After the addition was complete, the mixture was stirred under constant temperature. After the reaction was completed, stirring was stopped and the mixture was allowed to stand and age. The precipitate was collected, washed, dried, and ground to obtain the regular polyhedral calcium hydroxystannate precursor powder.

[0019] By adopting the above technical solution, the coordination form of the tin source is controlled by an alkaline environment to generate a hexahydroxystannate octahedron as the growth unit; combined with the slow addition and aging process of calcium ions, the crystal is controlled to grow according to a specific crystal plane orientation, thereby obtaining a regular polyhedral precursor with high crystallinity, smooth surface and uniform morphology, which provides a stable structural basis for subsequent surface etching and reconstruction.

[0020] Preferably, the tin source powder is tin tetrachloride pentahydrate, and the calcium source solid is anhydrous calcium chloride; the molar ratio of sodium hydroxide to tin tetrachloride pentahydrate in solution A is controlled between 6.0:1 and 6.5:1; the molar ratio of anhydrous calcium chloride in solution B to tin tetrachloride pentahydrate in solution A is controlled between 0.9:1 and 1.1:1.

[0021] By adopting the above technical solution, the molar ratio of sodium hydroxide to tin source is controlled to be close to the stoichiometric ratio and slightly in excess, maintaining the system at a suitable degree of supersaturation to avoid the formation of impurity phases; the calcium-tin ratio is controlled to be close to 1:1 to ensure the purity of the chemical composition of the product.

[0022] Preferably, the temperature of the constant temperature condition is controlled between 20°C and 30°C; the set rate is controlled between 2 mL / min and 4 mL / min; the stirring reaction time is controlled between 3.5 hours and 4.5 hours; and the standing aging time is controlled between 10 hours and 14 hours.

[0023] By adopting the above technical solution, the appropriate reaction temperature and slower drop rate help to form and grow crystal nuclei uniformly; the aging process uses the Ostwald ripening mechanism to eliminate small grains, making the precursor particle size distribution narrower and the crystal face development more complete.

[0024] Preferably, when preparing the low-concentration etching working solution, the deionized water and the anhydrous ethanol are mixed at a volume ratio of 1:0.8 to 1:1.2.

[0025] By employing the above technical solution, this volume ratio can balance the shielding effect of ethanol and the solubilizing ability of water. If the ethanol ratio is too low, insufficient shielding will lead to an excessively fast etching rate and damage to the crystal; if the ethanol ratio is too high, the hydrogen ion dissociation will be too low, making it difficult to initiate the etching reaction. This ratio range helps to achieve nanoscale control over the etching depth.

[0026] Preferably, the organic weak acid is glacial acetic acid; the concentration of the organic weak acid in the low-concentration etching working solution is controlled between 0.008 mol / L and 0.012 mol / L.

[0027] By employing the above technical solution, glacial acetic acid is selected as the proton donor, utilizing its weak acidity to maintain an extremely low concentration of free hydrogen ions in the reaction system. The millimolecular-level acid concentration controls the reaction rate at the solid-liquid interface, which is beneficial for preferentially etching highly reactive crystal edges and defect sites, forming anisotropic surface textures.

[0028] Preferably, the ratio of the mass of the regular polyhedral calcium hydroxystannate precursor powder to the volume of the low-concentration etching working solution is controlled between 0.72g:115mL and 0.72g:460mL.

[0029] By adopting the above technical solution and using a lower solid-liquid ratio, on the one hand, the concentration of acid components is kept relatively constant during the reaction process, avoiding uneven etching due to local acid depletion; on the other hand, it ensures that the crystal particles are in full contact with the solvent environment.

[0030] Preferably, during the morphology reconstruction, the constant rotation speed is controlled between 450 rpm and 550 rpm; the temperature of the stirring reaction is controlled between 20°C and 30°C; and the stirring reaction time is controlled between 0.5 hours and 1.5 hours.

[0031] By adopting the above technical solution, a short-time reaction is carried out at room temperature and medium speed stirring. The shear force of fluid dynamics is used to promote the desorption of surface products, while preventing particle agglomeration or physical breakage due to mechanical collision, ensuring that the morphology reconstruction process is mainly dominated by chemical etching.

[0032] Preferably, the solid-liquid phase separation method is centrifugation, with the centrifugation speed set between 4000 rpm and 6000 rpm and the centrifugation time set between 2 minutes and 5 minutes; the drying temperature is set between 50°C and 70°C and the drying time is set between 6 hours and 10 hours.

[0033] By adopting the above technical solution, rapid centrifugation can quickly terminate the etching reaction and prevent residual acid from continuing to corrode the crystal; the mild drying conditions remove physically adsorbed solvent molecules while avoiding excessive dehydration of surface hydroxyl groups or lattice collapse caused by high temperature, thereby maintaining the stability of the micro-rough structure.

[0034] Preferably, the calcium hydroxystannate material with a surface micro-roughness structure exhibits an octagonal microstructure; the surface micro-roughness structure includes oxygen vacancy defects introduced by confined etching, which are used to trap photogenerated electrons and suppress carrier recombination.

[0035] By employing the above technical solution, the obtained material retains its octagonal geometric shape, maintaining its mechanical stability and dispersibility. The micro-roughness of the surface and oxygen vacancy defects increase the reaction surface area, providing more active adsorption sites. In the photocatalytic reaction, photogenerated electrons are captured by oxygen vacancies, reducing adsorbed oxygen molecules to superoxide radicals, while holes oxidize surface hydroxyl radicals to generate hydroxyl radicals, thereby achieving the oxidative removal of organic pollutants and nitrogen oxides.

[0036] This invention provides a method for preparing calcium hydroxystannate materials based on morphology reconstruction to enhance intrinsic light absorption. It has the following beneficial effects:

[0037] 1. This invention utilizes the solvation shielding effect of the ethanol-water mixed solvent system, combined with low-concentration glacial acetic acid, to construct a confined etching environment, thereby regulating the diffusion and reaction rate of hydrogen ions. This process can preferentially etch the high-energy angular regions of the crystal, transforming the conventional polyhedral precursor into a calcium hydroxystannate material with an octagonal microstructure. This specific geometric structure, while retaining the mechanical stability of the crystal framework, increases the reaction specific surface area, providing a sufficient contact interface for subsequent photocatalytic reactions.

[0038] 2. This invention constructs a micro-rough defect layer rich in oxygen vacancies in situ on the crystal surface through a mild acid etching process. The introduction of oxygen vacancies forms defect energy levels in the band structure, reducing the band gap of calcium hydroxystannate and causing a redshift of the light absorption edge, thereby expanding the material's response range to visible light. At the same time, these surface defect sites act as trapping traps for photogenerated electrons, suppressing the recombination of electrons and holes, prolonging carrier lifetime, and improving photonic quantum efficiency.

[0039] 3. Benefiting from the optimized band structure and morphology, the material obtained in this invention exhibits a higher reaction rate and mineralization rate when photocatalytically degrading highly stable gaseous pollutants such as volatile organic compounds (VOCs). Furthermore, the preparation process employed in this invention is mild and simple to operate, avoiding the problems of crystal structure collapse or over-dissolution that are easily caused by traditional strong acid etching, thus ensuring the uniformity and repeatability of product quality and demonstrating promising application prospects. Attached Figure Description

[0040] Figure 1 X-ray diffraction patterns of calcium hydroxystannate materials prepared in different embodiments of the present invention;

[0041] Figure 2 The O1s high-resolution X-ray photoelectron spectra of the embodiments and comparative samples of the present invention are shown below.

[0042] Figure 3 The electron paramagnetic resonance spectra of the embodiments and comparative samples of this invention are shown below.

[0043] Figure 4 The ultraviolet and visible diffuse reflectance spectra of the embodiments and comparative samples of this invention are shown below;

[0044] Figure 5 The steady-state photoluminescence spectra of the embodiments and comparative samples of the present invention are shown below.

[0045] Figure 6 The transient photocurrent response spectra of the embodiments and comparative samples of the present invention are shown below;

[0046] Figure 7 The graphs show the changes in VOCs photocatalytic mineralization rate with light exposure time for different embodiments and comparative samples of the present invention.

[0047] Figure 8 This is a bar chart comparing the VOCs photocatalytic mineralization rates of different embodiments and comparative samples of the present invention.

[0048] Figure 9 This is a graph showing the cyclic stability test results of the samples in this embodiment of the invention.

[0049] Figure 10This is a comparison chart of the photocatalytic removal rates of samples from embodiments of the present invention at different toluene to nitrogen dioxide concentration ratios;

[0050] Figure 11 The electron paramagnetic resonance spectrum of the sample capturing superoxide radicals in an embodiment of the present invention;

[0051] Figure 12 The electron paramagnetic resonance spectrum of the sample capturing hydroxyl radicals in an embodiment of the present invention;

[0052] Figure 13 This is a low-magnification scanning electron microscope image of the calcium hydroxystannate material prepared in an embodiment of the present invention;

[0053] Figure 14 This is a high-magnification scanning electron microscope image of the calcium hydroxystannate material prepared in an embodiment of the present invention. Detailed Implementation

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Preparation Examples 1-3:

[0056] Preparation Example 1:

[0057] This preparation example provides a method for preparing a regular polyhedral calcium hydroxystannate precursor, including the following steps:

[0058] Add 200 mL of deionized water to the reaction vessel, turn on the magnetic stirrer and control the temperature at 25 °C, add 2.40 g of sodium hydroxide solid and stir until completely dissolved; add 3.51 g of tin tetrachloride pentahydrate powder to the obtained solution and continue stirring until completely dissolved to obtain solution A; separately, dissolve 1.11 g of anhydrous calcium chloride in 20 mL of deionized water to prepare solution B; adjust the stirring speed to 600 rpm, add solution B dropwise to solution A at a rate of 3 mL / min, and continue stirring at 25 °C for 4 hours after the addition is complete; after the reaction is completed, stop stirring and let the system stand for 12 hours; collect the precipitate by centrifugation, wash it three times each with deionized water and anhydrous ethanol, dry it in a 60 °C oven for 12 hours, and grind it to obtain calcium hydroxystannate precursor powder.

[0059] Preparation Example 2:

[0060] This preparation example provides a method for preparing a regular polyhedral calcium hydroxystannate precursor, including the following steps:

[0061] Add 180 mL of deionized water to the reaction vessel, turn on the magnetic stirrer and control the temperature at 20 °C, add 2.20 g of sodium hydroxide solid and stir until completely dissolved; add 3.16 g of tin tetrachloride pentahydrate powder to the obtained solution and continue stirring until completely dissolved to obtain solution A; separately, dissolve 1.00 g of anhydrous calcium chloride in 15 mL of deionized water to prepare solution B; adjust the stirring speed to 550 rpm, add solution B dropwise to solution A at a rate of 2 mL / min, and continue stirring at 20 °C for 3.5 hours after the addition is complete; after the reaction is completed, stop stirring and let the system stand for 10 hours; collect the precipitate by centrifugation, wash it three times each with deionized water and anhydrous ethanol, dry it in a 55 °C oven for 10 hours, and grind it to obtain calcium hydroxystannate precursor powder.

[0062] Preparation Example 3:

[0063] This preparation example provides a method for preparing a regular polyhedral calcium hydroxystannate precursor, including the following steps:

[0064] Add 220 mL of deionized water to the reaction vessel, turn on the magnetic stirrer and control the temperature at 30 °C, add 2.70 g of sodium hydroxide solid and stir until completely dissolved; add 3.86 g of tin tetrachloride pentahydrate powder to the obtained solution and continue stirring until completely dissolved to obtain solution A; separately, dissolve 1.22 g of anhydrous calcium chloride in 25 mL of deionized water to prepare solution B; adjust the stirring speed to 650 rpm, add solution B dropwise to solution A at a rate of 4 mL / min, and continue stirring at 30 °C for 4.5 hours after the addition is complete; after the reaction is completed, stop stirring and let the system stand for 14 hours; collect the precipitate by centrifugation, wash it three times each with deionized water and anhydrous ethanol, dry it in a 65 °C oven for 14 hours, and grind it to obtain calcium hydroxystannate precursor powder.

[0065] Examples 1-3:

[0066] Example 1:

[0067] This embodiment provides a method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption, including the following steps:

[0068] Deionized water and anhydrous ethanol were mixed evenly at a volume ratio of 1:1.2 to serve as the solvent cage medium. Glacial acetic acid was added to prepare a low-concentration etching working solution with an acetic acid concentration of 0.008 mol / L. 0.72 g of the calcium hydroxystannate precursor powder obtained in Example 1 was weighed and placed in a reaction vessel. 115 mL of the above-prepared etching working solution was added. A magnetic stir bar was placed in the vessel, and the mixture was stirred at a constant speed of 500 rpm for 1 hour at 25°C. The strong shielding effect of the solvent cage and the low dose of acid were used to perform shallow etching on the crystal surface. After the reaction was completed, the suspension was immediately transferred to a centrifuge tube and centrifuged at 5000 rpm for 3 minutes. The supernatant was discarded. The resulting solid precipitate was washed twice each with deionized water and anhydrous ethanol, and then dried in a 60°C oven for 8 hours. The calcium hydroxystannate material with a micro-rough surface structure was collected.

[0069] Example 2:

[0070] This embodiment provides a method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption, including the following steps:

[0071] Deionized water and anhydrous ethanol were mixed evenly at a volume ratio of 1:1 to serve as a solvent cage medium. Glacial acetic acid was added to prepare a low-concentration etching working solution with an acetic acid concentration of 0.01 mol / L. 0.72 g of the calcium hydroxystannate precursor powder obtained in Example 1 was weighed and placed in a reaction vessel, and 345 mL of the above-prepared etching working solution was added. A magnetic stir bar was placed in the vessel, and the mixture was stirred at a constant speed of 500 rpm at 25 °C for 1 hour. Under these conditions, the acid content was close to the stoichiometric critical point, and the appropriate solvent cage effect enabled precise directional etching of the crystal edges. After the reaction was completed, the suspension was immediately transferred to a centrifuge tube and centrifuged at 5000 rpm for 3 minutes. The supernatant was discarded. The resulting solid precipitate was washed twice each with deionized water and anhydrous ethanol, and then dried in a 60 °C oven for 8 hours to obtain a uniformly morphological octagonal calcium hydroxystannate material.

[0072] Example 3:

[0073] This embodiment provides a method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption, including the following steps:

[0074] Deionized water and anhydrous ethanol were mixed evenly at a volume ratio of 1:0.8 to serve as the solvent cage medium. Glacial acetic acid was added to prepare a low-concentration etching working solution with an acetic acid concentration of 0.012 mol / L. 0.72 g of the calcium hydroxystannate precursor powder obtained in Example 1 was weighed and placed in a reaction vessel. 460 mL of the above-prepared etching working solution was added. A magnetic stir bar was placed in the vessel, and the mixture was stirred at a constant speed of 500 rpm at 25 °C for 1 hour. At this time, the acid content in the system was slightly excessive and the solvent cage shielding effect was slightly weak. The stoichiometric limitation was used to prevent the framework from disintegrating and to achieve deep etching. After the reaction was completed, the suspension was immediately transferred to a centrifuge tube and centrifuged at 5000 rpm for 3 minutes. The supernatant was discarded. The resulting solid precipitate was washed twice with deionized water and twice with anhydrous ethanol, and then dried in a 60 °C oven for 8 hours. The deeply etched octagonal calcium hydroxystannate material was collected.

[0075] Comparative Examples 1-5:

[0076] Comparative Example 1:

[0077] Compared with Example 2, the difference is that no etching process is performed, and the calcium hydroxystannate precursor powder obtained in Preparation Example 1 is directly used as the final product, while the rest are the same.

[0078] Comparative Example 2:

[0079] Compared with Example 2, the difference is that the solvent matrix of the etching working solution is all deionized water, and no anhydrous ethanol is added, that is, no solvent cage system is constructed. All other aspects are the same.

[0080] Comparative Example 3:

[0081] Compared with Example 2, the difference is that the concentration of acetic acid in the etching working solution is increased to 0.2 mol / L, while the rest are the same.

[0082] Comparative Example 4:

[0083] Compared with Example 2, the difference is that the solvent base of the etching working solution is all anhydrous ethanol, without the addition of deionized water, while the rest are the same.

[0084] Comparative Example 5:

[0085] Compared with Example 2, the difference is that hydrochloric acid is used instead of glacial acetic acid to prepare the etching working solution, and the acid concentration is kept at 0.01 mol / L. All other aspects are the same.

[0086] Test Examples 1-6:

[0087] Test Example 1: Analysis of Crystal Structure Integrity and Phase Evolution

[0088] This test case aims to verify the stability and phase purity of the calcium hydroxystannate crystal framework under different etching degrees using X-ray diffraction (XRD) technology, and to confirm the regulatory effect of the stoichiometric confinement strategy on the crystal structure.

[0089] Experimental steps:

[0090] Take the samples prepared in Examples 1-3 (corresponding to the attached samples). Figure 1 CSOH-0.1, CSOH-0.2, CSOH-0.3, and the untreated sample prepared in Comparative Example 1 (corresponding to the attached sample). Figure 1 CSOH) and the excess acid etched sample prepared in Comparative Example 3 (corresponding to the attached sample). Figure 1 CSOH-0.4) was placed in an agate mortar and ground until there was no obvious grainy texture.

[0091] The ground powder sample is spread evenly in the groove of the glass sample holder, and then compacted and leveled with a glass slide to ensure that the test surface is flat and flush with the reference surface.

[0092] The tests were conducted using a Bruker D8 Advance X-ray diffractometer with Cu Kα rays (λ=0.15406nm) as the radiation source, tube voltage set to 40kV, and tube current set to 40mA.

[0093] Set the scanning mode to continuous scanning, the scanning range (2θ) to cover 10° to 80°, the step size to 0.02°, and the scanning speed to 6° / min.

[0094] After acquiring diffraction data, baseline correction and smoothing were performed using MDI Jade 6.5 software, and phase retrieval and cell parameter analysis were conducted by referring to standard PDF card #09-0030.

[0095] Experimental data:

[0096] Table 1: Statistical table of XRD crystal structure parameters for each sample

[0097]

[0098] Note: The (200) crystal plane represents a specific family of planes in crystallography that uses Miller indices to label the atomic arrangement within a crystal. The (200) crystal plane represents a specific set of parallel atomic layers. In X-ray diffraction (XRD) patterns, specific diffraction peaks appear when X-rays diffract with this set of crystal planes. In this test example, the diffraction peaks corresponding to the (200) crystal plane with higher intensity and independence are selected as reference standards for calculating grain size (Scherrer formula) and monitoring the integrity and changes of the crystal structure during the etching process.

[0099] In the CSOH-0.4 line, "-" indicates that the crystal structure of the sample has broken down into an amorphous state due to excessive etching. No obvious sharp diffraction peaks are found in the XRD pattern, so crystallographic parameters such as peak position and full width at half maximum cannot be read.

[0100] In line #09-0030 of PDF, "-" indicates that the data source is a standard database card, which only provides theoretical peak position references and does not include actual physical state parameters such as experimentally measured full width at half maximum (FWHM), crystallinity, or grain size.

[0101] in conclusion:

[0102] Based on the data in Table 1 and the appendix Figure 1 The diffraction pattern analysis shown shows that Comparative Example 1 (CSOH) exhibits sharp and high-intensity diffraction peaks. All characteristic peak positions (such as 19.3°, 22.4°, 32.1°, etc.) highly coincide with the cubic phase CaSn(OH)6 standard card (PDF#09-0030), indicating that the precursor has a complete long-range ordered crystal structure.

[0103] In the spectra of Examples 1 (CSOH-0.1) to 3 (CSOH-0.3), the positions of the characteristic peaks did not shift significantly, and no impurity phase diffraction peaks such as SnO2 or CaO were detected. This indicates that although morphology reconstruction occurred during the solvent cage-mediated weak acid etching process, the basic stoichiometry and Ca-Sn-OH framework structure of the material were preserved, and no decomposition reaction occurred.

[0104] From CSOH to CSOH-0.3, as the etching depth gradually increased, the intensity of the (200) crystal plane diffraction peak showed a decreasing trend, and the full width at half maximum (FWHM) increased from 0.241° to 0.482°. The relative crystallinity of the CSOH-0.2 sample decreased to 27.8%, and that of the CSOH-0.3 sample further decreased to 9.4%. This peak intensity attenuation and broadening phenomenon confirms that the orderliness of the crystal surface and subsurface regions is reduced, and the grain size is reduced. The example samples retained some characteristic diffraction peaks, indicating that the internal framework is still intact, and a disordered layer is formed on the surface. This composite structure of crystal nuclei and amorphous shells effectively preserves the bulk carrier transport channels.

[0105] In contrast, the diffraction curve of Comparative Example 3 (CSOH-0.4) tends to be flat, and the characteristic peaks almost completely disappear, indicating that when the acid content exceeds the stoichiometric limit and the solvent cage shielding effect is insufficient, the crystal structure disintegrates and transforms into an amorphous state. In summary, this invention, through precise control of the reaction system, successfully introduces surface defect structures while maintaining the integrity of the crystal framework, avoiding structural collapse caused by excessive corrosion.

[0106] Test Example 2: Characterization of Surface Chemical States and Electron Spin Structure

[0107] This test case utilizes X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) techniques to quantitatively analyze the elemental coordination environment and unpaired electronic states on the sample surface, in order to verify the mechanism of solvent cage confined etching strategy in inducing and stabilizing oxygen vacancy defects.

[0108] Experimental steps:

[0109] The CSOH-0.2 sample prepared in Example 2 and the CSOH sample prepared in Comparative Example 1 were selected and treated in a vacuum drying oven at 60°C for 4 hours to remove physically adsorbed water. Then, they were ground and pressed into thin sheets with a diameter of 5 mm on a tablet press at a pressure of 10 MPa. Some powder samples were loaded into quartz capillaries for testing.

[0110] The thin-section sample was fed into the XPS analysis chamber through the pre-evacuation chamber, while the background vacuum level of the analysis chamber was maintained at 1.0 x 10⁻⁶. - 9 The energy levels were on the order of mbar. A monochromatic Al Kα ray source (hν = 1486.6 eV) with a spot diameter of 400 µm was used. High-resolution fine spectra of the O1s ray were acquired using an energy analyzer with a pass energy of 30 eV and a step size of 0.1 eV. All binding energy data were charge-corrected using the C1s peak (284.80 eV) as a reference.

[0111] Background subtraction (Shirley type) and peak fitting were performed on the original spectra using Avantage software. The binding energy and relative content of different oxygen species were analyzed using the Gaussian-Lorentz mixture function (G / L ratio=30%).

[0112] A quartz capillary tube containing powder was placed in the resonant cavity of the Bruker EMX plus electron paramagnetic resonance spectrometer. At room temperature, the microwave frequency was set to X-band (~9.85 GHz), microwave power to 2.0 mW, modulation amplitude to 1.0 G, and modulation frequency to 100 kHz. A central magnetic field scan was performed within a magnetic field range of 2000 G to 4000 G, and a differential signal spectrum was recorded.

[0113] Experimental data:

[0114] Table 2: Summary of XPS fitting parameters and EPR spin parameters of oxygen species on sample surface

[0115]

[0116] Note: The "-" in the CSOH row indicates that no effective resonance signal was detected in the EPR test (i.e., the spectrum is linear noise), which means that the sample does not contain unpaired electrons and exhibits diamagnetism;

[0117] In the CSOH-0.2 line, " "and" The corresponding "-" indicates that the g-factor is a physical quantity measured based on the overall magnetic response of the entire sample, and is already shown in the first row of the sample ( The rows are listed, and do not correspond to a single XPS peak species.

[0118] in conclusion:

[0119] According to Table 2 and appendix Figure 2 High-resolution XPS spectra of O1s show that the untreated CSOH sample exhibits typical metal hydroxide characteristics, with its main peak located at 531.36 eV, attributed to lattice oxygen in the Ca-O and Sn-O bonds. The relative content is as high as 94.47%; only weak surface-physically adsorbed water or loosely bound oxygen exists at 532.94 eV. The signal indicates that the surface atoms of Comparative Example 1 are arranged in a regular manner and are in a state of stoichiometric saturation.

[0120] The CSOH-0.2 sample treated in Example 2 of this invention exhibited significant chemical shifts and peak splitting in its O1s spectrum. Firstly, the lattice oxygen main peak shifted towards lower binding energy to 530.86 eV (a shift of approximately 0.5 eV). This enhanced shielding effect suggests an increase in electron density around the Sn atom, a typical characteristic of reduced metal cations or decreased coordination numbers. More importantly, a novel high-intensity characteristic peak (labeled as...) was separated at 532.04 eV. Its relative content reaches 23.02%. This binding energy range corresponds to oxygen atoms near low-coordinated oxygen species or oxygen vacancies. Due to the solvent cage effect of ethanol molecules during etching, which restricts the deep diffusion of anions, the reaction is confined to the solid-liquid interface, resulting in the selective stripping of oxygen atoms in the surface lattice, thereby inducing a surface oxygen vacancy defect concentration as high as 23%.

[0121] Appendix Figure 3 The EPR test results further confirmed the above analysis. The EPR spectrum of the CSOH sample showed a flat noise baseline, indicating diamagnetism and the absence of unpaired electrons in the sample. The CSOH-0.2 sample, however, exhibited a significant resonance signal near a magnetic field strength of approximately 3400 G, yielding a Landé factor g = 2.0291. This g value deviates significantly from the free electron value (ge ≈ 2.0023), representing a typical characteristic signal of a single electron trapped by an oxygen vacancy.

[0122] Combining XPS chemical environment analysis and EPR electron spin detection, it can be confirmed that the confined etching strategy of this invention successfully constructed a defect structure rich in oxygen vacancies on the surface of CaSn(OH)6 crystals. These vacancies not only act as charge trapping centers, altering the electronic structure of the material, but the intermediate energy levels they introduce also provide a structural basis for the subsequent separation of photogenerated carriers and the adsorption and activation of reactants.

[0123] Test Example 3: Intrinsic Light Absorption Characteristics Test

[0124] This test example uses ultraviolet and visible diffuse reflectance spectroscopy to compare and analyze the light response range and absorption intensity of the sample in the ultraviolet and visible light regions, in order to verify the effect of crystal surface defect structure on band structure.

[0125] Experimental steps:

[0126] Prepare the CSOH-0.2 sample prepared in Example 2 and the CSOH sample prepared in Comparative Example 1. At the same time, prepare high-purity barium sulfate (BaSO4) powder as a total reflection standard reference.

[0127] The sample powder and BaSO4 powder are respectively filled into the round hole of the powder sample holder for the integrating sphere, and the surface is compacted with a quartz glass plate to ensure that the sample surface is flat and without specular reflection.

[0128] Turn on the Shimadzu UV-2600 spectrophotometer with integrating sphere attachment and allow it to warm up for 30 minutes until the light source stabilizes. Set the scanning mode to diffuse reflection mode, the scanning wavelength range to 200nm to 800nm, the sampling interval to 1.0nm, and the slit width to 2.0nm.

[0129] First, a standard white board (BaSO4) was scanned to collect baseline data for background subtraction. Then, CSOH and CSOH-0.2 samples were scanned respectively, and reflectance data (R%) were recorded.

[0130] The instrument's built-in software automatically converts reflectance data into absorbance values ​​based on the Kubelka-Munk function, and exports spectral data for plotting and band gap calculation.

[0131] Experimental data:

[0132] Table 3: Absorbance values ​​and calculated band gap parameters of samples at different wavelengths

[0133]

[0134] Note: "-" indicates optical band gap. The energy value (in eV) is calculated by extrapolating the absorption edge tangent using the Kubelka-Munk function transformation and Tauc plotting method, and is not a specific sampling wavelength point during the spectral scanning process.

[0135] in conclusion:

[0136] Based on the data in Table 3 and the appendix Figure 4 The spectral curve analysis shown indicates that Comparative Example 1 (CSOH) exhibits significant intrinsic absorption only in the deep ultraviolet region with wavelengths less than 300 nm. Its absorbance drops sharply to below 0.2 at 300 nm, exhibiting a steep absorption edge. This suggests that untreated calcium hydroxystannate has a wide bandgap (calculated to approximately 3.92 eV), primarily responds to short-wavelength photons, and has low light energy utilization.

[0137] The spectral curve of Example 2 (CSOH-0.2) showed significant changes. First, in the ultraviolet region from 200 nm to 270 nm, its overall absorbance remained high, above 1.0, without the premature intensity decay seen in the CSOH sample. Second, a noticeable redshift occurred at the absorption edge, with the inflection point of absorbance decrease delayed to around 340 nm, and the calculated optical bandgap decreased to 3.45 eV. Furthermore, in the near-ultraviolet to visible light boundary region from 320 nm to 400 nm, CSOH-0.2 exhibited a distinct tailing absorption characteristic.

[0138] This enhanced light absorption performance is directly related to the solvent cage-confined etching mechanism of this invention. The introduction of surface oxygen vacancies disrupts the periodic potential field of the crystal lattice, introducing discrete defect energy levels (intermediate energy levels) in the band gap between the valence band top and the conduction band bottom. These intermediate energy levels serve as intermediate transition states for electron transitions, allowing even lower-energy photons to excite electrons to jump from the valence band to the defect energy level, or from the defect energy level to the conduction band. Therefore, CSOH-0.2 not only broadens the photoresponse range but also improves the light trapping efficiency, providing an energy basis for generating more photogenerated electron-hole pairs.

[0139] Test Example 4: Photogenerated Carrier Separation and Transport Behavior Test

[0140] This test case uses steady-state photoluminescence spectroscopy (PL) and transient photocurrent response techniques to evaluate the electron-hole separation efficiency and migration performance inside and on the surface of the material, in order to verify the inhibitory effect of surface defect structure on photogenerated charge recombination behavior.

[0141] Experimental steps:

[0142] Photoluminescence (PL) spectroscopy testing: The CSOH-0.2 sample prepared in Example 2 and the CSOH sample prepared in Comparative Example 1 were selected and filled into solid sample cells, respectively, with smooth and dense surfaces. Testing was performed using an F-7000 fluorescence spectrophotometer. The excitation wavelength was set to 320 nm, the emission spectrum scanning range was 350 nm to 700 nm, the excitation and emission slit widths were both set to 5 nm, the photomultiplier tube voltage was set to 400 V, and the scan rate was 1200 nm / min.

[0143] Working electrode preparation: 5 mg of the sample powder was dispersed in a mixed solvent consisting of 1 mL ethanol and 10 μL Nafion solution (5 wt%), and ultrasonically dispersed for 30 minutes to form a homogeneous suspension. 100 μL of this suspension was drop-coated onto a cleaned conductive glass (FTO) surface, controlling the coating area to be 1 cm². 2 After air drying, it is annealed in a vacuum oven at 60℃ for 1 hour to make a photoanode working electrode.

[0144] Photoelectrochemical testing system setup: A standard three-electrode system was used for photoelectrochemical testing, with the prepared FTO photoanode as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. The electrolyte was a 0.5M sodium sulfate (Na2SO4) aqueous solution.

[0145] Transient photocurrent testing: The three-electrode system was connected to an electrochemical workstation (CHI 660E), and a 0V (vs. SCE) bias voltage was applied. A 300W xenon lamp equipped with an AM 1.5G filter was used as the light source, and the light intensity was adjusted to 100mW / cm². 2 The light source switch was controlled by a mechanical chopper, with a switching cycle of 20 seconds, and the current-time curve was recorded over a total duration of 1400 seconds.

[0146] Experimental data:

[0147] Table 4: Statistical Table of Steady-State Fluorescence Emission Intensity Peak Value and Photocurrent Density

[0148]

[0149] Note: "Blue shift" refers to the shift of the center position of the spectral peak toward a shorter wavelength (i.e., a shift toward higher energy).

[0150] @Peak indicates that the data is read from the vertical axis value of the emission intensity at the maximum value (i.e., the peak) in the steady-state photoluminescence spectrum (PL), which corresponds to the wavelength of the "emission peak center" listed in the table, and is used to characterize the strongest point of electron-hole recombination;

[0151] @1000s indicates that the data was read from the instantaneous current density value at 1000 seconds into the transient photocurrent versus time test curve. This time point was selected to eliminate interference from unstable signals at the beginning of the test and to accurately reflect the steady-state photoelectric conversion performance of the material after multiple light and dark cycles.

[0152] "-" indicates that the variation range is not applicable to the simple difference calculation of this item, which reflects the stability difference of the photoelectrode under long-term illumination.

[0153] in conclusion:

[0154] Based on the data in Table 4 and the appendix Figure 5 As shown, Comparative Example 1 (CSOH) exhibits an extremely strong broad peak emission signal near 468 nm. Photoluminescence mainly originates from the radiative recombination of photogenerated electrons and holes. The high-intensity PL signal directly proves that there is a serious charge recombination phenomenon inside the untreated crystal, and that photogenerated charge carriers have already recombinated in large quantities before migrating to the surface to participate in the reaction.

[0155] In contrast, the PL spectrum waveform of Example 2 (CSOH-0.2) remained consistent, but the overall relative intensity decreased, with the peak intensity reduced by approximately 42.9%. This weakening of fluorescence intensity was not due to a decrease in light absorption, but rather attributed to an increase in the efficiency of photogenerated electron-hole separation. The present invention utilizes surface oxygen vacancies introduced through confined etching to act as shallow electron traps. These defect sites effectively intercept photogenerated electrons before they fall back to the valence band and recombine with holes, thereby blocking the radiative recombination path.

[0156] Appendix Figure 6 The transient photocurrent response curves further confirm the above-mentioned charge separation mechanism and visually demonstrate the differences in photoelectric stability of the samples:

[0157] in, Figure 6 In the spectrum, "On" corresponds to the region where the current jumps upward. In this state, the chopper is turned on, the light source illuminates the sample surface, the sample is excited to generate photoelectrons, and the external circuit detects the photocurrent signal. "Off" corresponds to the region where the current falls back to the baseline in the spectrum. In this state, the chopper blocks the light source, the illumination stops, the photogenerated carriers are no longer generated, and the detected signal returns to the dark current level.

[0158] Optical response speed and waveform characteristics: such as Figure 6As shown, when the light source switches to the "On" state, the photocurrent density of the CSOH-0.2 sample exhibits a steeper rising edge, indicating that its photogenerated carriers can be rapidly generated and separated. In the "Off" state, both currents drop rapidly, indicating no significant continuous dark current interference. It is worth noting that the CSOH sample (solid line) shows a sharp overshoot peak in the early stage of the "On" phase, followed by a rapid drop, forming a sawtooth waveform. This characteristic usually indicates that the accumulated charge on the surface cannot be discharged in time, resulting in severe bulk recombination; while the photocurrent waveform of CSOH-0.2 is more square, with a more obvious flat-top feature, indicating that its surface charge transport is more efficient.

[0159] Steady-state current density comparison: In the initial stage of the test (<200 seconds), the peak current of CSOH-0.2 reached 0.048μA / cm. 2 It is significantly higher than 0.032 μA / cm at CSOH. 2 As the testing period progresses (as shown in the attached document)... Figure 6 (At 1000 seconds on the x-axis), the current in the CSOH sample decayed significantly, dropping to 0.009 μA / cm. 2 The CSOH-0.2 sample also showed some attenuation, but eventually stabilized at 0.023 μA / cm; while the CSOH-0.2 sample also showed some attenuation, but eventually stabilized at 0.023 μA / cm. 2 The level is higher than that of CSOH samples in the same period, which is more than 2.5 times higher.

[0160] In summary, the dual improvement in photocurrent density and stability of the CSOH-0.2 sample confirms that the surface defect layer not only provides charge trapping sites but also constructs a low-impedance interfacial transport channel, effectively suppressing carrier recombination and promoting the continuous injection of photogenerated carriers into the electrolyte interface.

[0161] Test Example 5: Photocatalytic Deep Purification Performance Test of Gaseous Complex Pollutants

[0162] This test case simulates a real atmospheric environment where volatile organic compounds (VOCs) and nitrogen oxides (NOx) coexist. Toluene (C7H8) and nitrogen dioxide (NO2) are used as model pollutants to investigate the photocatalytic degradation efficiency, deep mineralization capacity, and cycle stability of the material under dynamic flow field.

[0163] Experimental steps:

[0164] Sample coating: Weigh 0.1g of the photocatalyst powder to be tested (a series of samples prepared in Examples 1-3 and Comparative Example 1), disperse it in anhydrous ethanol to make a suspension, spread it evenly on the bottom of a glass culture dish with a diameter of 50mm, and dry and fix it at 60℃ to make a catalyst film.

[0165] Reaction system setup: A glass dish loaded with catalyst was placed in the center of a continuous flow gas-phase photocatalytic reactor (300 mL volume). A 300 W xenon lamp with a filter was placed above the reactor, and the light intensity was adjusted to 100 mW / cm². 2 An external circulating condensate jacket is connected to maintain the reaction temperature at 25±2℃.

[0166] Single pollutant test (C7H8): Standard toluene gas (initial concentration approximately 500 ppm) equilibrated with dry air was introduced via a mass flow meter at a total flow rate of 50 mL / min. Dark adsorption was first performed for 30 minutes under light-protected conditions. After the outlet gas concentration stabilized, the light source was turned on for photocatalytic reaction, which lasted for 60 minutes. The residual C7H8 concentration and the generated CO2 concentration at the outlet were monitored in real time using an online gas chromatograph and infrared gas analyzer.

[0167] Cyclic stability test: For the CSOH-0.2 sample with the best performance, after completing one C7H8 degradation experiment, the reactor was purged with clean air for 30 minutes, and then the next round of dark adsorption and photodegradation cycle was restarted. A total of 5 consecutive cycle tests were carried out.

[0168] Combined pollutant test (C7H8 and NO2): By changing the inlet gas composition and adjusting the flow ratio of the C7H8 gas path to the NO2 gas path, five operating conditions were set with volume ratios of 4:0, 3:1, 2:2, 1:3, and 0:4 (while keeping the total flow rate constant). For the CSOH-0.2 sample, the removal rates of C7H8 and NO2 were recorded after 60 minutes of illumination under different mixed atmospheres.

[0169] Experimental data:

[0170] Table 5: Record of Photocatalytic Degradation Performance and Mineralization Parameters of Gaseous Pollutants

[0171]

[0172] Note: The "-" in the NO2 removal rate column corresponds to the experimental groups with an inlet gas composition of "4:0 (pure C7H8)". Since only toluene gas was introduced into the reaction system during this test phase and no NO2 component was introduced, there was no NO2 removal behavior, therefore no relevant detection data is available.

[0173] The "-" in the C7H8 removal rate, CO2 generation rate, and mineralization rate columns corresponds to the experimental group with an inlet gas composition of "0:4 (pure NO2)". Since no carbon-containing organic source (toluene) was introduced into the reaction system during this test phase, there was no process of photocatalytic oxidation of organic matter to produce CO2; therefore, the calculation of C7H8 removal and mineralization parameters is not applicable. The "-" in the mineralization rate column corresponding to the mixed atmosphere group indicates:

[0174] In a complex pollution system where C7H8 and NO2 coexist, the experiment mainly investigated the competitive adsorption behavior and simultaneous removal efficiency of the two pollutants on the catalyst surface. Due to the complex reaction mechanism in the complex system, which generates trace amounts of intermediate byproducts such as organic nitrates, the mineralization rate calculated solely based on CO2 production is no longer used as the core evaluation indicator for this specific competitive adsorption experimental stage.

[0175] in conclusion:

[0176] Based on the data in Table 5 and the appendix Figure 7-10 The experimental results can provide an in-depth analysis of the mechanism by which the surface defect structure of crystals enhances the treatment performance of complex gaseous pollutants such as C7H8 and NO2.

[0177] First, refer to the appendix Figure 7 and attached Figure 8 Regarding the mineralization performance of a single C7H8 pollutant, the untreated CSOH sample, while exhibiting some photocatalytic activity, only achieved a mineralization rate of 51.3%, indicating that most C7H8 was only partially oxidized to intermediate products rather than completely mineralized into CO2 and H2O. With increasing restricted etching depth, the mineralization performance of the samples showed a trend of first increasing and then decreasing. Among them, the CSOH-0.2 sample exhibited the best catalytic performance, with a peak mineralization rate of 116.6%, achieving not only complete removal of C7H8 but also demonstrating extremely high CO2 selectivity. This indicates that an appropriate amount of oxygen vacancies not only promotes the separation of photogenerated charges but also acts as an adsorption activation center for O2 molecules, significantly enhancing the adsorption of surface superoxide radicals (·O2). - The generation rate of ) is increased, thereby endowing the material with oxidizing ability to open the benzene ring structure of C7H8.

[0178] Secondly, appendix Figure 9 The stability of the CSOH-0.2 sample under long-term operation was demonstrated. In five consecutive cycles with a cumulative duration exceeding 400 minutes, the mineralization rate of C7H8 remained consistently high, between 100% and 110%, while the amount of CO products (byproducts) generated remained stable and at a low level. This proves that the defective photocatalyst prepared in this invention has excellent resistance to photocorrosion, and that the highly reactive oxygen species on the surface can promptly oxidize and remove adsorbed organic intermediates, effectively preventing catalyst poisoning and deactivation.

[0179] Finally, see the attached document. Figure 10For the C7H8 and NO2 co-polluting system, CSOH-0.2 exhibited both competitive adsorption and synergistic purification characteristics. Under a pure NO2 atmosphere, the removal rate was 37.2%; however, after introducing C7H8 (e.g., a 3:1 ratio), the NO2 removal rate increased to 83.62%, suggesting the existence of a dual-channel reaction mechanism of electrons and holes in the coexisting system. That is, while C7H8 consumes holes and is oxidized, NO2 consumes electrons and is reduced, forming a complementary reaction kinetic. However, when the NO2 concentration was too high (e.g., 2:2 and 1:3 ratios), the strong adsorption of NO2 molecules on the catalyst surface occupied some active sites, leading to a certain decrease in the C7H8 removal rate (down to 66.3% and 75.5%, respectively), but still better than traditional catalysts. Overall, CSOH-0.2 maintained high simultaneous removal efficiency under complex atmospheres, confirming its application potential in practical environmental purification.

[0180] Test Example 6: Detection of Active Species in Photocatalytic Reaction

[0181] This test case utilizes electron spin resonance spectroscopy (ESR) to capture and analyze short-lived reactive oxygen species (ROS) generated in the photocatalytic reaction system in situ. By comparing the signal differences under dark and light conditions, as well as the signal intensity of different samples, the regulatory mechanism of surface defect structure on the redox reaction pathway is revealed.

[0182] Experimental steps:

[0183] Scavenger preparation: 5,5-Dimethyl-1-pyrrolline-N-oxide (DMPO) was used as the spin scavenger. Two dispersion systems were prepared for different free radical detection methods.

[0184] Superoxide radicals (·O2) - Detection system: Accurately weigh 4 mg of CSOH-0.2 sample prepared in Example 2 and CSOH sample prepared in Comparative Example 1, disperse them in 2 mL of chromatographic grade methanol solvent, add 20 μL of DMPO stock solution, mix evenly by ultrasonication, and take a small amount of suspension into a quartz capillary tube.

[0185] Hydroxyl radical (·OH) detection system: Take 4 mg of each of the above two samples, disperse them in 2 mL of deionized water, add 20 μL of DMPO stock solution, sonicate and then aspirate into a quartz capillary.

[0186] Spectral Acquisition: The capillary tube containing the sample was placed inside the resonant cavity of the Bruker EMXplus spectrometer. First, the background signal was recorded in the "Dark" state under completely dark conditions. Then, a 300W xenon lamp (equipped with a 420nm cutoff filter) was turned on to irradiate the sample in situ. The ESR spectrum in the "Light" state was recorded after 5 minutes of illumination (corresponding to the attached label "Light on 5min").

[0187] Instrument parameter settings: central magnetic field set to 3500G, sweep width 100G, microwave frequency 9.85GHz, microwave power 20mW, modulation amplitude 1.0G.

[0188] Experimental data:

[0189] Table 6: Statistical Table of Relative Intensities of ESR Characteristic Signal Peaks of Active Free Radicals

[0190]

[0191] Note: "-" indicates that the data in this row is based on the ratio of the signal intensity of CSOH-0.2 to that of the CSOH sample under the "Light on 5min" condition (quantitative analysis), rather than independent experimental test conditions or qualitative spectral waveform descriptions (such as quartet characteristics), and therefore is not applicable to the classification description of this column.

[0192] in conclusion:

[0193] Appendix Figure 11 and attached Figure 12 In the diagram, "Dark" indicates the test baseline in a dark environment where the light source is not turned on; "Light on 5min" indicates the in-situ test signal after the xenon lamp has been turned on for 5 minutes.

[0194] Based on the data records in Table 6 and appendices Figure 11 and attached Figure 12 The ESR spectral characteristics shown can confirm the source of the photocatalytic activity of the material of the present invention from the perspective of microscopic reaction mechanism.

[0195] Observe the spectral lines marked "Dark" in the attached figure. Both CSOH and CSOH-0.2 samples appear as flat straight lines in the dark (the values ​​in Table 6 are extremely low and are only instrument noise), indicating that free radicals cannot be spontaneously generated on the material surface when there is no light excitation.

[0196] After the light source was turned on for 5 minutes, the system underwent significant changes:

[0197] Superoxide radicals (·O2) - ): In the appendix Figure 11A 1:1:1:1 quartet signal was detected. Comparing the intensities of the two spectral lines, the peak signal (4215 a.u.) of Example 2 (CSOH-0.2, dashed line) was significantly higher than that of Comparative Example 1 (CSOH, solid line, 1843 a.u.), with an intensity approximately 2.3 times higher. This indicates that after photogenerated electrons migrate to the material surface, they are effectively captured by surface oxygen vacancies, thereby adsorbing oxygen molecules (O2). - It is reduced to superoxide radicals.

[0198] Hydroxyl radical (·OH): in the attached Figure 12 In the study, a 1:2:2:1 quartet signal was detected. Similarly, the signal intensity of CSOH-0.2 (2780 a.u.) was much higher than that of CSOH (956 a.u.), with an increase of nearly 3 times. This is because after electrons are consumed by oxygen vacancies, the lifetime of photogenerated holes in the valence band is extended, thus providing more opportunities to oxidize surface-adsorbed water or hydroxyl groups into hydroxyl radicals.

[0199] In summary, the defect structures constructed on the CSOH-0.2 surface directly serve as active sites for surface catalytic reactions. ESR results confirm that this structure not only inhibits carrier recombination but also enhances the activity of ·O2 in the system. - The steady-state concentrations of the two types of strong oxidizing free radicals, ·OH, are consistent with the aforementioned conclusions regarding the enhancement of photocurrent and the improvement of the mineralization performance of organic pollutants in terms of mechanism.

[0200] To visually demonstrate the effect of the preparation process of this invention on the control of the microstructure of the material, the prepared calcium hydroxystannate material was characterized by scanning electron microscopy (SEM), and the results are shown in the appendix. Figure 13 and attached Figure 14 As shown in the attached document. Figure 13 As shown, after restricted etching with a low-concentration organic weak acid, the material exhibits a uniform octagonal structure. The central region of the originally regular polyhedral precursor crystal faces becomes concave, forming a unique framework morphology. Furthermore, the particles are well dispersed, with no obvious agglomeration. Further observation... Figure 14 The high-magnification images reveal that the particle surface is no longer smooth but rather covered with micro-rough structures. This etching-induced surface reconstruction significantly increases the specific surface area of ​​the material, providing abundant active sites for photocatalytic reactions. The English parameters and symbols at the bottom of the image explain the test conditions: 1μm and 500nm in the lower left corner are image scales, representing the surface area of ​​the particles, respectively. Figure 13 The length of this line segment corresponds to an actual size of 1 micrometer. Figure 14The value corresponds to 500 nanometers; EHT=10.00kV indicates that the electron beam acceleration voltage is 10 kilovolts; Signal A=InLens indicates that a secondary electron detector inside the lens is used to acquire signals to obtain clear surface details; Mag=20.00KX and 55.00KX represent image magnification of 20,000x and 55,000x respectively; ZEISS is the identifier of the microscope equipment manufacturer.

Claims

1. A method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption, characterized in that, Includes the following steps: Regular polyhedral calcium hydroxystannate precursor powder was prepared by liquid-phase precipitation. A low-concentration etching working solution is prepared by uniformly mixing deionized water and anhydrous ethanol as a solvent cage medium and adding an organic weak acid to the solvent cage medium. The regular polyhedral calcium hydroxystannate precursor powder was added to the low-concentration etching working solution and stirred at a constant speed. The surface morphology of the regular polyhedral calcium hydroxystannate precursor powder was reconstructed by utilizing the solvent cage shielding effect in combination with acid etching. After the reaction was completed, the solid and liquid phases were separated immediately. The resulting solid precipitate was washed and dried to obtain the calcium hydroxystannate material with a micro-rough surface structure.

2. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, The preparation method of the regular polyhedral calcium hydroxystannate precursor powder includes the following steps: Sodium hydroxide solid was dissolved in deionized water, and tin source powder was added and stirred until dissolved to obtain solution A. Solution B was obtained by dissolving the solid calcium source in deionized water. Solution B was added dropwise to solution A at a set rate. After the addition was complete, the mixture was stirred under constant temperature. After the reaction was completed, stirring was stopped and the mixture was allowed to stand and age. The precipitate was collected, washed, dried, and ground to obtain the regular polyhedral calcium hydroxystannate precursor powder.

3. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 2, characterized in that, The tin source powder is tin tetrachloride pentahydrate, and the calcium source solid is anhydrous calcium chloride. The molar ratio of sodium hydroxide to tin tetrachloride pentahydrate in solution A is controlled between 6.0:1 and 6.5:

1. The molar ratio of anhydrous calcium chloride in solution B to tin tetrachloride pentahydrate in solution A is controlled between 0.9:1 and 1.1:

1.

4. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 2, characterized in that, The temperature under the constant temperature condition is controlled between 20°C and 30°C; The set rate is controlled between 2 mL / min and 4 mL / min; The stirring reaction time is controlled between 3.5 hours and 4.5 hours; The settling and aging time is controlled between 10 and 14 hours.

5. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, When preparing the low-concentration etching working solution, the deionized water and the anhydrous ethanol are mixed at a volume ratio of 1:0.8 to 1:1.

2.

6. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, The organic weak acid is glacial acetic acid. The concentration of the organic weak acid in the low-concentration etching working solution is controlled between 0.008 mol / L and 0.012 mol / L.

7. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, The ratio of the mass of the regular polyhedral calcium hydroxystannate precursor powder to the volume of the low-concentration etching working solution is controlled between 0.72g:115mL and 0.72g:460mL.

8. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, During the morphology reconstruction, the constant rotation speed is controlled between 450 rpm and 550 rpm; The temperature of the stirring reaction is controlled between 20°C and 30°C; The stirring reaction time is controlled between 0.5 hours and 1.5 hours.

9. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, The solid-liquid phase separation method is centrifugation, with the centrifugation speed set between 4000 rpm and 6000 rpm and the centrifugation time set between 2 minutes and 5 minutes. The drying temperature is set between 50°C and 70°C, and the drying time is set between 6 hours and 10 hours.

10. The method for preparing calcium hydroxystannate material based on morphology reconstruction to enhance intrinsic light absorption according to claim 1, characterized in that, The calcium hydroxystannate material with a surface micro-roughness structure exhibits an octagonal microstructure. The surface micro-roughness structure includes oxygen vacancy defects introduced by confined etching, which are used to trap photogenerated electrons and suppress carrier recombination.

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