A diatom earth loaded SnO2 / g-C3N4 nano composite photocatalyst, a preparation method and application thereof

Abstract

This invention discloses a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst, its preparation method, and its applications. This invention successfully prepared a visible light-responsive SnO2 / g-C3N4 / Dt composite photocatalyst via a hydrothermal method combined with calcination. This catalyst exhibits high purity, good crystallinity, high specific surface area, and a mesoporous structure. Its microstructure consists of a well-dispersed binary heterostructure composed of plate-like SnO2 and layered g-C3N4 on a Dt substrate. After 60 min of illumination, the degradation rates of MO, SEX, and TCH reached 94.29%, 99.63%, and 93.31%, respectively, significantly outperforming the corresponding single-component and binary composite materials, as well as related materials in existing technologies. The photocatalytic degradation process follows a pseudo-first-order reaction kinetic model, and its reaction rate constant k is 3.5 to 4.1 times higher than that of single-component and binary composite materials. •O2 ‑ •OH and h + These are key active species generated during the degradation process. Furthermore, this composite material exhibits excellent recyclability and stability, making it an environmentally friendly, inexpensive, and highly efficient photocatalyst with significant potential for practical industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, and specifically relates to a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst, its preparation method and application. Background Technology

[0002] The rapid advancement of global industrialization has brought enormous challenges to the purification of industrial wastewater containing organic pollutants. Among numerous pollution sources, wastewater from the textile, pharmaceutical, and mining industries causes particularly severe damage to ecosystems. Methyl orange (MO), a representative azo dye widely used in the textile and paper industries, has a complex aromatic structure and extremely high chemical stability, making it difficult to biodegrade naturally. Wastewater containing MO not only hinders light penetration and inhibits photosynthesis in aquatic plants, but also poses a serious biological threat: its azo bonds (-N=N-) undergo reduction and breakage under anaerobic conditions, typically generating carcinogenic aromatic amines. These toxic metabolites can bioaccumulate through food webs, posing long-term risks to aquatic ecosystems and human health. Meanwhile, the mineral processing sector has also raised significant environmental concerns, with sodium ethyl xanthate (SEX), a commonly used collector for sulfide ores, attracting widespread attention due to its enormous consumption. Besides the deterioration of local air quality caused by its foul odor, the migration and transformation behavior of SEX in the aquatic environment requires close monitoring. Studies have shown that under acidic conditions or specific degradation scenarios, sex (sex) is prone to decomposition into highly toxic substances. Other organosulfur byproducts. These derivatives are acutely toxic to aquatic plants and animals, and may pollute groundwater resources and disrupt regional ecological balance. Furthermore, antibiotic pollution, exemplified by tetracycline hydrochloride (TCH), has become a global environmental problem urgently needing to be addressed in the pharmaceutical and personal care products (PPCPs) sector. Due to its low metabolic rate in humans and animals, a large portion of TCH is released into the environment as either unchanged or active metabolites. This "pseudo-persistence" of broad-spectrum antibiotics not only causes chronic toxicity to non-target organisms, but more importantly, it acts as a persistent selective pressure, inducing the proliferation of antibiotic resistance genes (ARGs) in environmental microorganisms. The potential spread of these "superbugs" underscores the urgency of completely eliminating TCH to safeguard public health. Therefore, developing novel and efficient wastewater treatment technologies containing organic pollutants has become an urgent need to ensure ecological security and human health.

[0003] Advanced oxidation processes (AOPs), particularly photocatalysis based on semiconductor nanomaterials, have become important means to solve the aforementioned wastewater treatment problems. Unlike physical adsorption or biological treatment, which tend to saturate or produce toxic inhibition, photocatalysts utilize solar energy to generate reactive oxygen species (ROS), which can mineralize organic pollutants into bioinert inorganic substances. Among various semiconductor photocatalysts, g-C3N4 has become a promising material in the field of solar-driven environmental remediation due to its metal-free polymerization properties, excellent chemical stability, and suitable band gap of approximately 2.7 eV. Despite these advantages, the photocatalytic efficiency of bulk g-C3N4 is limited by the rapid recombination of photogenerated electron-hole pairs and the scarcity of surface active sites due to its low specific surface area. To overcome these kinetic and thermodynamic defects, constructing heterojunctions by coupling g-C3N4 with band gap-matched metal oxides has proven to be effective. SnO2, as a typical n-type semiconductor with a wide band gap and deep valence band, is an ideal choice for constructing type II heterojunctions with g-C3N4, which can promote the efficient separation of photogenerated carriers through an internal electric field. Salunkhe et al. synthesized SnO2 quantum dot heterojunctions grafted onto g-C3N4 via a sonochemical approach, achieving a 98.25% degradation efficiency for Rhodamine B (RhB) within 40 min, 28% higher than g-C3N4. Similarly, Jourshabani et al. prepared SnO2 / S-doped g-C3N4 (SnO2 / CNS) nanocomposites via an in-situ thermal condensation strategy, achieving a 94.8% removal rate for methylene blue (MB) after 150 min of irradiation, exceeding SnO2 and CNS by 39% and 42%, respectively. Furthermore, Abdulmajeed et al. constructed SnO2 / Sn-doped g-C3N4 heterojunctions using a hydrothermal method, demonstrating a 91% degradation efficiency for ibuprofen (IBP) within 90 min, representing improvements of 64% and 50% compared to SnO2 and g-C3N4, respectively. Therefore, coupling SnO2 with g-C3N4 to construct a heterojunction is indeed one of the most effective strategies for achieving high photocatalytic efficiency.

[0004] However, challenges remain. Nanoparticles with high surface energy are prone to aggregation during hydrothermal synthesis, which significantly reduces active interface contact and hinders mass transfer. To overcome this aggregation bottleneck, introducing porous supports becomes crucial. Diatomaceous earth (Dt) is a natural biogenic siliceous sedimentary rock derived from diatom fossil remains. It is characterized by its unique hierarchical porous structure, large specific surface area, and excellent chemical inertness and thermal stability. Due to its low cost, non-toxicity, and excellent physical adsorption capacity, diatomaceous earth is widely considered an ideal green porous material and is often used as an adsorbent or an excellent support for anchoring functional nanoparticles in environmental remediation applications.

[0005] Therefore, this invention provides a method for preparing a ternary SnO2 / g-C3N4 / Dt nanocomposite photocatalyst via a hydrothermal method combined with a calcination process, and evaluates its photocatalytic degradation performance of MO, SEX, and TCH. The innovations of this work are as follows: First, by utilizing the structural dispersion effect of Dt, the aggregation problem of the binary heterojunction system composed of SnO2 and g-C3N4 is effectively alleviated, increasing the number of active sites for photocatalytic reactions. Second, by utilizing the excellent adsorption capacity of Dt, a locally high-concentration reaction microenvironment is constructed on the catalyst surface, enriching pollutants in the water around the heterojunction and shortening the diffusion distance between reactive oxygen species (ROS) and pollutant molecules, thereby accelerating the surface catalytic degradation reaction. Third, given the abundant reserves, low price, and simple pretreatment of Dt, this invention provides a highly cost-effective route for the preparation of high-performance composite photocatalysts. Summary of the Invention

[0006] This invention provides a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst, its preparation method, and its application, in order to solve the problems in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst includes the following steps:

[0009] S1. Preparation of g-C3N4 nanomaterials:

[0010] g-C3N4 nanomaterials were prepared by thermal polymerization. 15 mmol of melamine was placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product was then naturally cooled to room temperature and stored for later use.

[0011] S2. Preparation of ternary SnO2 / g-C3N4 / Dt composite materials:

[0012] Solution A was prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B was prepared by dissolving 8 mmol NaOH in 20 mL of water; solution B was magnetically stirred for 10 min, and then 10 mmol g-C3N4 and 0.2 g Dt (diatomaceous earth) were added to solution A. Solution A was added dropwise to solution B while stirring continuously for 20 min. The resulting 60 mL suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 °C for 12 h. After naturally cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 °C for 12 h to obtain the ternary SnO2 / g-C3N4 / Dt composite material.

[0013] A diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by the aforementioned method.

[0014] A diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by the above preparation method is used for wastewater treatment.

[0015] A diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by the above preparation method is used for the degradation of MO, SEX and TCH.

[0016] A method for preparing SnO2 nanomaterials: SnO2 nanomaterials are synthesized by a hydrothermal method. Solution A is prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B is prepared by dissolving 8 mmol NaOH in 20 mL of water. After magnetically stirring solution B for 10 min, solution A is added dropwise to solution B under continuous stirring, and stirring is continued for 20 min. The resulting 60 mL suspension is transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 ℃ for 12 h. After naturally cooling to room temperature, the supernatant is discarded. The precipitate is collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 ℃ for 12 h to obtain SnO2 nanomaterials.

[0017] A method for preparing g-C3N4 nanomaterials is disclosed. The g-C3N4 nanomaterials are prepared by thermal polymerization. 15 mmol of melamine is placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product is then naturally cooled to room temperature to obtain g-C3N4 nanomaterials.

[0018] A method for preparing SnO2 / g-C3N4 nanocomposite material includes the following steps:

[0019] S1. Preparation of g-C3N4 nanomaterials:

[0020] g-C3N4 nanomaterials were prepared by thermal polymerization. 15 mmol of melamine was placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product was then naturally cooled to room temperature and stored for later use.

[0021] S2. Preparation of SnO2 / g-C3N4 nanocomposite materials:

[0022] SnO2 / g-C3N4 nanomaterials were synthesized via a hydrothermal method. Solution A was prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B was prepared by dissolving 8 mmol NaOH in 20 mL of water. After magnetically stirring solution B for 10 min, 10 mmol g-C3N4 was added to solution A. Solution A was then added dropwise to solution B while continuously stirring for another 20 min. The resulting 60 mL suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 °C for 12 h. After natural cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 °C for 12 h to obtain the SnO2 / g-C3N4 nanocomposite material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention successfully prepared a visible light-responsive SnO2 / g-C3N4 / Dt composite photocatalyst via a hydrothermal method combined with calcination. The catalyst exhibits high purity, good crystallinity, high specific surface area, and a mesoporous structure. Its microstructure consists of a well-dispersed binary heterostructure of plate-like SnO2 and layered g-C3N4 on a Dt substrate. After 60 min of illumination, the degradation rates of MO, SEX, and TCH reached 94.29%, 99.63%, and 93.31%, respectively, significantly outperforming the corresponding single-component and binary composite materials, as well as existing related materials. The photocatalytic degradation process follows a pseudo-first-order reaction kinetic model, with the reaction rate constant k being 3.5 to 4.1 times higher than that of single-component and binary composite materials. •O2 - •OH and h + These are key active species generated during the degradation process. Furthermore, this ternary composite material exhibits excellent recycling stability, making it an environmentally friendly, inexpensive, and highly efficient photocatalyst with significant potential for practical industrial applications. Attached Figure Description

[0025] Figure 1 This is the XRD pattern of the sample prepared in this invention; Figure 2 These are the FTIR images of the samples prepared in this invention; Figure 3 These are XPS images of SnO2 / g-C3N4 / Dt in this invention, where: (a) full spectrum, (b) Sn3d, (c) O1s, (d) C1s, (e) N1s, (f) Si2p; Figure 4 The nitrogen adsorption-desorption isotherms and corresponding pore size distribution curves of the samples in this invention are shown in the inner figure: (a) SnO2, (b) g-C3N4, (c) SnO2 / g-C3N4, (d) SnO2 / g-C3N4 / Dt; Figure 5 The FE-SEM and HR-TEM analyses in this invention include: (a) the microstructure of the sample, (b) the bright-field morphology and EDS elemental distribution of SnO2 / g-C3N4, and (c) the high-resolution (HRTEM) and selected area electron diffraction (SAED) patterns of SnO2 / g-C3N4. Figure 6 The UV-Vis DRS analysis diagrams in this invention are as follows: (a) UV-Vis DRS spectrum, (b) Tauc diagram; Figure 7 These are the cyclic voltammetry curves at different scan rates in this invention: (a) SnO2, (b) g-C3N4, (c) SnO2 / g-C3N4, (d) SnO2 / g-C3N4 / Dt, (e) scan rate of 50 mV s -1 (f) Cyclic voltammetry curves of each sample, and the relationship between the specific capacitance of each sample and the scan rate. Figure 8 Here is a summary graph of the degradation rates of three organic compounds by the samples in this invention: (a) MO, (b) SEX, (c) TCH; Figure 9 These are the photocatalytic degradation reaction kinetic curves in this invention: where: (a) MO, (b) SEX, (c) TCH; Figure 10 This is a schematic diagram of the photocatalytic mechanism of SnO2 / g-C3N4 / Dt in this invention; Figure 11 This refers to the degradation rate in the presence of different quenching agents in this invention; Figure 12 This is a summary chart of the degradation rates of MO, SEX, and TCH in the SnO2 / g-C3N4 / Dt cyclic degradation process of this invention; Figure 13 These are XRD patterns before and after the SnO2 / g-C3N4 / Dt cyclic degradation experiment in this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments.

[0027] All chemical reagents used in this invention were of analytical grade. SnCl4·5H2O, NaOH, hexadecyltrimethylammonium bromide (CTAB), and methyl orange (MO) were purchased from Aladdin Reagent Co., Ltd. Melamine was purchased from Tianjin Huasheng Chemical Reagent Co., Ltd. Tetracycline hydrochloride (TCH) and diatomaceous earth (Dt, SiO2 > 90%) were both purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Sodium ethyl xanthate (SEX) was purchased from Beijing Solarbio Technology Co., Ltd. All solutions were prepared with deionized water.

[0028] Example 1

[0029] A method for preparing a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst includes the following steps:

[0030] S1. Preparation of g-C3N4 nanomaterials:

[0031] g-C3N4 nanomaterials were prepared by thermal polymerization. 15 mmol of melamine was placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product was then naturally cooled to room temperature and stored for later use.

[0032] S2. Preparation of ternary SnO2 / g-C3N4 / Dt composite materials:

[0033] Solution A was prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B was prepared by dissolving 8 mmol NaOH in 20 mL of water; solution B was magnetically stirred for 10 min, and then 10 mmol g-C3N4 and 0.2 g Dt (diatomaceous earth) were added to solution A. Solution A was added dropwise to solution B while stirring continuously for 20 min. The resulting 60 mL suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 °C for 12 h. After naturally cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 °C for 12 h to obtain the ternary SnO2 / g-C3N4 / Dt composite material.

[0034] Comparative Example 1

[0035] Preparation of SnO2 nanomaterials: SnO2 nanomaterials were synthesized by a hydrothermal method. Solution A was prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B was prepared by dissolving 8 mmol NaOH in 20 mL of water. After magnetically stirring solution B for 10 min, solution A was added dropwise to solution B under continuous stirring, and stirring was continued for 20 min. The resulting 60 mL suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 ℃ for 12 h. After natural cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 ℃ for 12 h.

[0036] Comparative Example 2

[0037] Preparation of g-C3N4 nanomaterials: g-C3N4 nanomaterials were prepared by thermal polymerization. 15 mmol of melamine was placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product was then naturally cooled to room temperature to obtain g-C3N4 nanomaterials.

[0038] Comparative Example 3

[0039] Preparation of SnO2 / g-C3N4 nanocomposites:

[0040] S1. Preparation of g-C3N4 nanomaterials:

[0041] g-C3N4 nanomaterials were prepared by thermal polymerization. 15 mmol of melamine was placed in a ceramic crucible and calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 5 °C / min. The product was then naturally cooled to room temperature and stored for later use.

[0042] S2. Preparation of SnO2 / g-C3N4 nanocomposite materials:

[0043] SnO2 / g-C3N4 nanomaterials were synthesized using a hydrothermal method. Solution A was prepared by dissolving 2 mmol SnCl4·5H2O and 2 mmol CTAB in 40 mL of water; solution B was prepared by dissolving 8 mmol NaOH in 20 mL of water. After magnetically stirring solution B for 10 min, 10 mmol g-C3N4 was added to solution A. Solution A was then added dropwise to solution B while continuously stirring for another 20 min. The resulting 60 mL suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 ℃ for 12 h. After natural cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation (8000 r / min, 10 min), washed three times alternately with ethanol and water, and finally dried at 60 ℃ for 12 h to obtain the SnO2 / g-C3N4 nanocomposite material.

[0044] I. Experiments were conducted on Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0045] 1. Characterization techniques

[0046] The crystal structure and phase purity of the samples were analyzed using X-ray diffraction (XRD, Shimadzu, XRD-6100, Cu Kα radiation, 40 kV). Fourier transform infrared spectroscopy (FTIR, Shimadzu, Prestige-21, KBr pellet method, sample / KBr mass ratio 1:99) was used at 500–4000 cm⁻¹. -1 Spectra were recorded within a specific range to identify functional groups and chemical bonds. Surface elemental composition and chemical states were investigated using X-ray photoelectron spectroscopy (XPS, Thermo, ESCALAB 250XI). Specific surface area and pore size distribution of the products were determined using a surface area analyzer (BET, Quantachrome, Autosorb-iQ). Morphology and microstructure were observed using scanning electron microscopy (SEM, JEOL, JSM-7500F) and transmission electron microscopy (TEM, JEOL, JEM-2010). Light absorption characteristics of the samples in the 200–800 nm wavelength range were studied using UV-Vis diffuse reflectance spectroscopy (DRS, Shimadzu, UV-3600Plus). The electrochemical stability of the samples was evaluated by analyzing charge separation and migration efficiency using cyclic voltammetry. The test was performed on a CHI660E workstation using a standard three-electrode system. The working electrode was prepared by drop-coating the sample suspension onto nickel foam (1 cm × 2 cm), while a platinum sheet (1 cm × 1 cm) and a mercury / mercury oxide (Hg / HgO) electrode served as the counter and reference electrodes, respectively. A 1.0 mol L⁻¹ solution was used. -1KOH solution was used as the electrolyte. All potentials were scanned in the range of -0.5 V to 0.4 V at a scan rate of 5–100 mV / s. -1 .

[0047] 2. Photocatalytic activity test

[0048] The degradation performance of the obtained samples was systematically evaluated in a photochemical reactor (QFN-GHX-I). For SnO2, a 500 W mercury lamp (λ=315-400 nm) was used as the light source; for g-C3N4, SnO2 / g-C3N4, and SnO2 / g-C3N4 / Dt, a 500 W xenon lamp (λ=400-750 nm) was used as the light source. The degraded pollutants included MO (10 mg / L), TCH (40 mg / L), and SEX (50 mg / L). Test procedure: 30 mg of photocatalyst was dispersed in 50 mL of a solution containing the target pollutant at a specific concentration and stirred in the dark for 30 min to reach adsorption-desorption equilibrium. The light source was then turned on to begin the photocatalytic degradation reaction. To assess the reaction progress, approximately 5 mL of solution was periodically aspirated from the reaction system. The extracted solution was centrifuged (3000 r / min, 5 min) and its ultraviolet absorption spectrum was measured using a UV-Vis spectrophotometer (Puxi General, TU-1810).

[0049] 3. Calculation of photocatalytic degradation rate

[0050] In the ultraviolet absorption spectrum, the characteristic absorption peaks of MO, SEX, and TCH are located at 460 nm, 235 nm, and 353 nm on the abscissa, respectively. The height of the characteristic absorption peaks corresponds to the concentration of organic pollutants. The degradation rate I can be calculated by the following formula:

[0051] I = (1 - C / C0) × 100% (1)

[0052] In the formula, C0 is the initial concentration of organic pollutants, and C is the concentration of organic pollutants during photocatalytic degradation. The final degradation rate was calculated based on the maximum photocatalytic reaction time.

[0053] Finally, the photocatalytic ability of the samples was evaluated based on the degradation rate. For the same organic pollutant, the shorter the degradation time and the higher the degradation rate, the stronger the photocatalytic ability of the sample to degrade the organic matter.

[0054] 4. Analysis of photocatalytic degradation kinetics model

[0055] Because the surface structure and chemical properties of catalysts are prone to dynamic changes during photocatalytic reactions, and environmental factors (such as temperature, pH, and pollutant concentration) have a significant impact on the catalytic process, the reproducibility of photocatalytic experiments faces challenges. Therefore, by conducting catalytic kinetic studies on the photocatalytic reactions of pollutants using nanomaterials, and systematically analyzing the reaction rate, the contribution of active species, and key influencing factors, the reliability and regularity of experimental results can be effectively improved, providing a scientific basis for catalyst design optimization and reaction condition control.

[0056] According to the Langmuir-Hinshelwood kinetic equations

[0057] (2)

[0058] Where r is the reaction rate at a certain moment (unit: mg·L). -1 ·min -1 ); dc / dt represents the derivative of solution concentration with respect to time; k is the surface reaction rate constant; K is the adsorption equilibrium constant; C t The reactant concentration at time t (unit: mg·L) -1 ).

[0059] Finally, the photocatalytic degradation performance of a sample for a specific organic pollutant was evaluated based on the reaction rate constant k. For the same organic pollutant, a larger k indicates a faster photocatalytic degradation rate of the organic pollutant.

[0060] 5. Free radical quenching experiment

[0061] Selective scavenging of specific free radicals (such as hydroxyl radicals ·OH, photogenerated holes h) using specific quenchers + Superoxide anion O2 - (etc.) to determine its dominant role in the reaction system. 1 mmol / L benzoquinone (BQ), 1 mmol / L ammonium oxalate (AO), and 100 mmol / L isopropanol (IPA) were used as ·O2. - h +Quenching agents for ·OH radicals. In quenching experiments, the dominant free radical types were investigated when different nano-photocatalysts degraded different organic pollutants. The following example illustrates the free radical quenching experiment using the SnO2 / g-C3N4 / Dt sample photocatalyzing MO solution: 5.4 mg BQ, 6.2 mg AO, and 0.72 mL IPA solutions were added as quenchers to 50 mL of MO solution (10 mg / L) containing 30 mg of photocatalyst. After irradiation with a 500 W xenon lamp for 60 min, the UV spectra of the three solutions were measured, and the final degradation rate was calculated. If the addition of a certain quencher had the greatest impact on the final degradation rate of the MO solution, it indicates that the free radical corresponding to that quencher played a dominant role in the photocatalytic reaction when the SnO2 / g-C3N4 / Dt sample photocatalyzed the MO solution.

[0062] 6. Photocatalyst stability test

[0063] The photocatalytic stability of the prepared samples was evaluated through a cyclic degradation experiment. The specific procedure was as follows: After 60 minutes of illumination (i.e., after the photocatalytic degradation reaction was complete), the test tube was removed from the photochemical reactor. The photocatalyst was collected at the bottom of the tube by centrifugation. The supernatant was poured off, and the sample was washed three times with deionized water and ethanol to remove adsorbed organic or inorganic ions from the catalyst surface. The sample was then dried and set aside. The photocatalytic degradation experiment was then repeated four times. XRD analysis was performed on the last recovered photocatalyst to verify its photocatalytic performance and structural stability during cyclic use.

[0064] II. Results and Analysis

[0065] 1. XRD Result Analysis

[0066] The phase composition and crystal structure of the prepared samples were characterized by XRD, and the results are as follows: Figure 1As shown. For SnO2 nanomaterials, all observed diffraction peaks closely match the characteristic peak of SnO2 (JCPDS No. 01-075-2893), and no impurity peaks were detected. For the binary SnO2 / g-C3N4 composite material, a characteristic peak corresponding to the hexagonal g-C3N4 (JCPDS No. 01-087-1526) (002) crystal plane was identified at 26.5°. Due to the very close diffraction angles, this peak appears as a shoulder peak and partially overlaps with the (110) peak (2θ=26.6°) of SnO2, which is consistent with the prior art. For the ternary SnO2 / g-C3N4 / Dt composite material, a new diffraction peak appears at 21.8°, corresponding to the (101) crystal plane of the tetragonal SnO2 (JCPDS No. 01-082-0512). The characteristic peaks of all three components were clearly visible, and no impurity peaks appeared, confirming that the sample has high phase purity, excellent crystallinity, and a successful ternary system construction.

[0067] 2. FTIR Result Analysis

[0068] The surface functional groups and chemical composition of the prepared samples were characterized by FTIR, and the results are as follows: Figure 2 As shown. For SnO2, at 3470 cm⁻¹ -1 and 1630 cm -1 The broad absorption bands at 700 cm⁻¹ are attributed to the stretching and bending vibrations of the hydroxyl groups (O–H) in the adsorbed water molecules, respectively. -1 The absorption peak at 1720 cm⁻¹ corresponds to the asymmetric stretching vibration of Sn–O–Sn, confirming the formation of the metal oxide network. For g-C₃N₄, the absorption peak at 1720 cm⁻¹ corresponds to the asymmetric stretching vibration of Sn–O–Sn, confirming the formation of the metal oxide network. -1 The absorption band at 810 cm⁻¹ corresponds to the stretching vibrations of C–N and C=N, representing the framework structure of graphitic carbon nitride. Notably, the absorption band at 810 cm⁻¹... -1 The peak at 1080 cm⁻¹ is a characteristic vibrational band of the tri-s-triazine / heptazine unit, originating from the out-of-plane bending vibration or ring breathing vibration of the triazine ring. This is one of the recognized hallmark peaks of the typical g-C3N4 framework. For the SnO₂ / g-C3N₄ binary complex, these characteristics of g-C3N₄ are well preserved, indicating that the chemical structure of g-C3N₄ remains intact during complexation with SnO₂. The ternary SnO₂ / g-C3N₄ / Dt peak at 1080 cm⁻¹... -1 A new peak was observed. This peak corresponds to the asymmetric stretching vibration of Si–O–Si, confirming the presence of SnO2 in the composite material. Therefore, the coexistence of characteristic vibrational modes of Sn–O bonds, aromatic C–N heterocycles, triazine rings, and Si–O–Si groups further confirms the successful construction of the ternary composite system.

[0069] 3. XPS Result Analysis

[0070] XPS was used to investigate the surface chemical composition and electronic properties of the prepared SnO2 / g-C3N4 / Dt ternary nanocomposite material. The results are as follows: Figure 3 As shown. All binding energies in the figure are calibrated with the C1s peak at 284.8 eV as a reference. (Full spectrum) Figure 3 In (a), the presence of Sn, Si, C, N, and O is clearly observed without any impurity signals, indicating that the prepared sample has high purity. (Sn3d high-resolution spectrum) Figure 3 (b) at 486.4 eV (Sn3d 5 / 2 ) and 494.8 eV (Sn3d 3 / 2 A pair of double peaks are observed at (), with a spin-orbit splitting energy of 8.4 eV, indicating that Sn in the SnO2 lattice is in the SnO2 state. 4+ Oxidized state exists. O1s spectrum. Figure 3 (c) The spectrum was fitted to three components: the peak at 530.6 eV corresponds to lattice oxygen (Sn–O); the peak at 532.2 eV is attributed to surface hydroxyl groups (O–H); and the peak at 533.5 eV originates from surface-adsorbed water species (O). C1s spectrum Figure 3 (d) can be fitted to two distinct peaks: the peak at 284.8 eV is attributed to the exogenous carbon and sp in the graphite domains. 2 Hybrid C–C bonds; the main peak at approximately 288.2 eV corresponds to the sp structure of the N–C=N group in the triazine ring. 2 Hybridized carbon confirms the retention of the g-C3N4 framework structure. N1s spectrum. Figure 3 (e) The fitted characteristic peaks at 398.8 eV and 400.3 eV are attributed to the pyridine nitrogen (C–N=C) and amino functional groups (C–N–H) within the aromatic ring, respectively. Si2p spectrum Figure 3 (f) shows a symmetrical peak centered at 102.4 eV, which is the Si in the SiO2 network. 4+ The characteristics of this composite material are noteworthy. It is worth noting that, compared to existing single-phase SnO2 and g-C3N4 materials, the binding energies of Sn3d and N1s in the ternary composite material exhibit a slight displacement. These displacements originate from the strong interfacial coupling between the components and the built-in electric field formed, which promotes space charge separation and the transfer of photogenerated carriers.

[0071] 4. BET Result Analysis

[0072] The specific surface area and pore characteristics of the synthesized sample were determined by measuring the nitrogen adsorption-desorption isotherm, and the results are as follows: Figure 4As shown. According to IUPAC classification, all samples exhibited Type IV isotherm characteristics with an H3-type hysteresis loop. These isotherms indicate capillary condensation within the mesopores, confirming the presence of a well-defined mesoporous structure in both single-component and composite photocatalyst bulk phases.

[0073] isotherm of g-C3N4 Figure 4 (b) An H3-type hysteresis ring is observed in the relatively high pressure region (0.8 < P / P0 < 1.0), indicating the presence of slit-like pores formed by the stacking of lamellar particles, consistent with the layered two-dimensional structure of g-C3N4. In contrast, the binary SnO2 / g-C3N4 composite material... Figure 4 (c) Exhibits characteristics similar to SnO2 Figure 4 (a) Similar isotherm profiles, with hysteresis loops spanning a wide range of relative pressures. Meanwhile, the hysteresis loops shown in Figure 4(d) of the ternary SnO2 / g-C3N4 / Dt composite material cover an even wider relative pressure region (0.4 < P / P0 < 1.0), indicating that the introduction of oxide nanoparticles alters the pore structure properties. The corresponding BJH pore size distribution curves further reveal that most of the pores in the prepared samples are concentrated in the mesoporous region (3–5 nm). This mesoporous system is crucial for heterogeneous photocatalysis: it not only provides abundant accessible active sites for surface redox reactions but also promotes efficient diffusion and mass transfer of reactants and products.

[0074] 5. FE-SEM and HR-TEM Analysis

[0075] The micromorphology and microstructure of the prepared samples were studied using SEM and TEM, and the results are as follows: Figure 5 As shown in (a), g-C3N4 exhibits a typical layered morphology; SnO2 presents a plate-like morphology with a length of approximately 100 nm and a width of 10–50 nm, exhibiting uniform size and good dispersion; while Dt exhibits independent microdisc-like structures with a diameter of approximately 50 μm and a thickness of approximately 10 μm. For the binary SnO2 / g-C3N4 composite, plate-like SnO2 is attached to the layered g-C3N4. After further combining with Dt to form a ternary system, the SnO2 / g-C3N4 heterostructure is dispersed on the Dt substrate. This hierarchical assembly structure inhibits the aggregation of nanoparticles, effectively facilitating the exposure of catalytic active sites, and simultaneously enhancing the structural stability of the photocatalyst.

[0076] EDS element distribution map Figure 5 (b) Further confirmation shows that the plate-like and layered morphologies correspond to the SnO2 and g-C3N4 phases, respectively. Sn, O, C, and N are uniformly distributed within the scanning region, and no obvious signs of phase separation were found. This uniform dispersion indicates that the elements have good chemical compatibility and confirms the successful construction of the binary heterostructure system.

[0077] HRTEM Figure 5 (c) The image clearly shows the tight interface between SnO2 and g-C3N4, providing direct evidence for the formation of a strong heterojunction, which is crucial for efficient charge transfer. Clear lattice fringes with interplanar spacings of 0.334 nm, 0.351 nm, and 0.262 nm are identifiable in the image, belonging to the (002) and (101) planes of g-C3N4 and the (101) plane of SnO2, respectively. Furthermore, the diffraction spots shown in the SAED pattern correspond to the (-110), (10-1), and (1-10) planes of SnO2, and the (1-10) and (110) planes of g-C3N4. These results confirm the multiphase coexistence and high crystallinity of the synthesized composite material, consistent with the XRD results.

[0078] 6. UV-Vis DRS Analysis

[0079] The light absorption characteristics and electronic band structure of the prepared photocatalyst were studied using ultraviolet-visible diffuse reflectance spectroscopy (DRS), and the results are as follows: Figure 6 As shown, g-C3N4 exhibits a characteristic absorption boundary at approximately 450 nm; upon the introduction of SnO2, the absorption boundary of the binary SnO2 / g-C3N4 composite material shows a significant redshift compared to the single-component composition. This optical modulation provides indirect but strong evidence for the close electronic coupling between the two semiconductors, indicating that the heterojunction interface has been successfully formed.

[0080] To quantitatively assess the band gap (Eg) of the samples, the obtained reflectance data were transformed using the Kubelka-Munk function and the Tauc equation (Equation 3):

[0081] (3)

[0082] in: , and These are the absorption coefficient, photon energy, and proportionality constant, respectively. By... The slope of the linear portion in the graph relating photon energy is extrapolated to zero intercept. Figure 6 (b) Obtain the Eg of the sample. The measured SnO2 and g-C3N... 44 The Eg values ​​of SnO2 / g-C3N4 were 3.70 eV, 2.78 eV, and 2.92 eV, respectively. The Eg of the composite material fell between that of the two monomer components, indicating that the hybridization of SnO2 and g-C3N4 altered the electronic state of the composite system. This is highly beneficial for photocatalytic reactions, not only promoting the capture of visible light but also facilitating the spatial separation of photogenerated electron-hole pairs, thereby improving the overall quantum efficiency.

[0083] 7. Cyclic Voltammetry Analysis

[0084] The prepared samples were tested at 5-50 mV s. -1 The CV curves at the scan rate were used to study the charge transfer kinetics at the photocatalyst interface and the separation efficiency of photogenerated carriers. The results are as follows: Figure 7 As shown. By Figure 7 (a)- Figure 7 As can be seen, all samples exhibit a typical quasi-rectangular shape with obvious redox peaks, indicating that the total electrochemical capacitance originates from the combined contribution of electric double-layer capacitance (EDLC) and Faraday pseudocapacitance. With increasing scan rate, the current density gradually increases, and the CV curve tends to maintain its characteristic shape, indicating that the synthesized material has low internal resistance and high structural integrity, enabling rapid electron transport even at high scan rates. Figure 7 (e) The CV curves of different samples at a fixed scan rate were compared, where the area of ​​the closed loop is directly related to the charge storage capacity and the density of available active sites. It can be clearly observed that the relative closed area of ​​the composite material is much larger than that of SnO2 and g-C3N4. The binary SnO2 / g-C3N4 composite material exhibits the largest closed loop area (highest degree of charge transfer), followed by the ternary SnO2 / g-C3N4 / Dt composite material.

[0085] To quantitatively evaluate its electrochemical performance, the specific capacitance was calculated from CV data according to equation (4). ):

[0086] (4)

[0087] in, The integral area of ​​the CV curve is represented by I, where I is the current, V is the potential, and m represents the mass of the active material. Represents the scan rate. The denominator 2 represents the potential window, and the denominator 2 indicates the dual charge-discharge process. The specific capacitance values ​​calculated using this method are shown in Table 1 and... Figure 7 As shown in (f).

[0088] Table 1. Specific capacitance values ​​of samples prepared at different scan rates

[0089]

[0090] Based on the calculated data, at 5 mV s -1 At the scan rate, g-C3N4 exhibits the smallest specific capacitance, at 293.53 F. -1 The specific capacitance of SnO2 / g-C3N4 is as high as 1044.09 F g. -1It is 3.6 times that of g-C3N4; the specific capacitance of SnO2 / g-C3N4 / Dt is 602.83 F g -1 The capacitance is slightly lower than that of the binary system, mainly due to the increased interfacial resistance caused by the non-conductive Dt substrate. The significant improvement in specific capacitance strongly demonstrates that the construction of the heterojunction successfully created an efficient electron transport channel. This optimized electronic structure effectively reduces the recombination rate of photogenerated electron-hole pairs, thereby providing a higher density of electrochemically active sites for surface catalytic reactions.

[0091] 8. Analysis of photocatalytic degradation rate results

[0092] The photocatalytic activity of the prepared samples was systematically evaluated by calculating their photocatalytic degradation rates of MO, SEX, and TCH. The results are as follows: Figure 8 As shown in the figure, -30 min to 0 min corresponds to the dark adsorption stage, and 0 min to 60 min corresponds to the light irradiation stage. Calculations show that after 60 min of light irradiation, the degradation rate of MO by SnO2 / g-C3N4 / Dt was 94.29%, which was 33.62%, 39.7%, and 15.88% higher than that of SnO2, g-C3N4, and SnO2 / g-C3N4, respectively; the degradation rate of SEX was 99.63%, which was 5.83%, 6.85%, and 1.76% higher than that of SnO2, g-C3N4, and SnO2 / g-C3N4, respectively; and the degradation rate of TCH was 93.31%, which was 45.2%, 17.08%, and 5.03% higher than that of SnO2, g-C3N4, and SnO2 / g-C3N4, respectively. The lower degradation rates of SnO2 and g-C3N4 are mainly attributed to the rapid recombination of photogenerated electron-hole pairs. In contrast, the formation of the SnO2 / g-C3N4 heterojunction promotes the separation of photogenerated carriers and enhances photocatalytic activity. The ternary composite exhibits higher catalytic activity than the single-component and binary composites. This is primarily due to the Dt support, which not only endows the composite with a larger specific surface area and optimized porosity, facilitating the adsorption of organic pollutants, but also improves the dispersibility of the binary composite and promotes interphase mass transfer, ultimately increasing the yield and utilization of photoactive species.

[0093] To objectively evaluate the photocatalytic performance of the SnO2 / g-C3N4 / Dt nanocomposite material prepared in this invention, degradation rate data of some prior art nanomaterials for MO, SEX, and TCH were compiled, including commercial TiO2 (P25). The summarized data are shown in Table 2. The results show that the photocatalytic performance of the prepared SnO2 / g-C3N4 / Dt nanocomposite material is superior to that of previously reported nanomaterials and P25.

[0094] Table 2 Comparison of photocatalytic performance of the prepared products with existing catalysts

[0095]

[0096] 9. Kinetic analysis of photocatalytic reaction

[0097] To quantitatively investigate the photocatalytic reaction mechanism, a kinetic model was used to analyze the degradation data of MO, SEX, and TCH in the samples. The results are as follows: Figure 9 As shown in Table 3.

[0098] Table 3 Kinetic parameters of the photocatalytic degradation of organic pollutants by the prepared products

[0099]

[0100] Depend on Figure 9 As can be seen, the kinetic curves of all samples exhibit a clear linear trend, intuitively indicating that these 12 photocatalytic degradation processes all follow pseudo-first-order reaction kinetics. Table 3 shows that for the degradation of MO, the k value of SnO2 / g-C3N4 / Dt is 47.56 × 10⁻⁶. -3 min -1 The ternary composite material showed a 3.50-fold, 4.14-fold, and 1.95-fold increase in photocatalytic reaction rate compared to SnO2, g-C3N4, and SnO2 / g-C3N4, respectively. Similarly, for the degradation of SEX and TCH, the k-value of the ternary composite material was 1.31-7.68 times higher than that of the single-component and binary composite materials. This indicates that the photocatalytic reaction rate of the ternary composite material is significantly superior to that of the single-component and binary composite materials.

[0101] To further verify the photocatalytic reaction kinetic order, this invention also used a pseudo-second-order kinetic model to fit the experimental data, and the relevant data are shown in Table 3. The comparison revealed that R0 obtained using the pseudo-second-order reaction kinetic model... 2 The values ​​were 0.46096–0.97560, significantly lower than the 0.91913–0.99429 values ​​for the pseudo-first-order reaction kinetic model. This further confirms that the photocatalytic degradation process in this study is dominated by pseudo-first-order reaction kinetics, meaning that the reaction rate is linearly correlated with the pollutant concentration.

[0102] 10. Photocatalytic mechanism analysis

[0103] The charge transfer and photocatalytic mechanism of SnO2 / g-C3N4 / Dt composite materials after photoexcitation are as follows: Figure 10 As shown. According to literature review, the CB and VB potentials of g-C3N4 are -1.1 eV and 1.6 eV, respectively, while those of SnO2 are 0 eV and 3.6 eV, respectively. When the two recombine, they form a type II pn heterojunction. Under illumination, both SnO2 and g-C3N4 are excited, and electrons in VB are excited and transferred to CB, generating electrons. -The empty space left in VB becomes h. + This process results in the formation of a large number of equal amounts of h. + and e - Because the CB and VB potentials of g-C3N4 are lower than those of SnO2, h + The VB migrates from SnO2 to g-C3N4, while e - Then the CB migrates from g-C3N4 to SnO2. In this way, h + and e - The recombination probability during migration to the photocatalyst surface is greatly reduced, thereby significantly increasing the likelihood of photogenerated carriers reaching the photocatalyst surface.

[0104] h on the surface of photocatalyst + It has strong oxidizing properties and can oxidize H2O or OH adsorbed on the surface. - It is oxidized into highly reactive hydroxyl radicals (•OH). These highly oxidizing •OH radicals can degrade large organic molecules in solution into smaller organic or inorganic molecules. Simultaneously, e-molecules reach the surface of the photocatalyst. - It exhibits excellent reduction properties and can undergo a reduction reaction with O2 adsorbed on the catalyst surface to produce active groups with strong oxidizing capabilities, such as •O2. - HO2 • Or H2O2, thereby causing the oxidative degradation of organic macromolecules. The main reaction equations are as follows:

[0105]

[0106] It is worth noting that since Dt is an insulator, it does not have photocatalytic activity itself. Therefore, in the above photocatalytic reaction system, Dt mainly enhances the photocatalytic degradation performance of the ternary composite material by leveraging its high adsorption and high structural dispersibility.

[0107] 11. Analysis of Free Radical Quenching Experiment Results

[0108] Using SnO2 / g-C3N4 / Dt as the photocatalyst and benzoquinone (BQ), isopropanol (IPA), and ammonium oxalate (AO) as quenchers, free radical quenching experiments were conducted to determine the main active species generated during the photocatalytic degradation of different pollutants. The experimental results are as follows: Figure 11 As shown.

[0109] Depend on Figure 11It can be seen that all three free radical quenchers significantly inhibited the photocatalytic degradation of the three organic pollutants. However, different scavengers exhibited different inhibitory effects on the target pollutants. For TCH degradation, the addition of IPA resulted in the largest decrease in degradation rate, indicating that •OH is the main reactive species in this oxidation process; for MO degradation, BQ had the greatest impact on its degradation rate, indicating that •O2 ⁻ It is the main species causing the decolorization of this dye. Regarding the mineralization process of SEX, the degradation rate decreased from 99.63% before addition to 16.09% after the addition of AO, significantly higher than the effects of the other two quenchers, indicating that h + It plays a leading role in this catalytic degradation reaction.

[0110] 12. Stability and Reusability Analysis

[0111] Reusability and structural stability are two key attributes of photocatalysts for practical industrial applications. Therefore, this invention evaluates the photocatalytic stability of the prepared ternary SnO2 / g-C3N4 / Dt composite material through cyclic degradation experiments. The cyclic degradation experiment process is described in section 8, "Photocatalytic Degradation Rate." The degradation rates of TCH, MO, and SEX after four cycles of degradation of the SnO2 / g-C3N4 / Dt composite material are summarized with the degradation rate before recycling. The results are as follows: Figure 12 As shown.

[0112] Depend on Figure 12 It was found that after four cycles, the degradation rates of TCH, MO, and SEX decreased by only 2.38%, 2.67%, and 2.42%, respectively. This slight decrease in photocatalytic performance is attributed to the slow accumulation of recalcitrant intermediates at the active sites, rather than actual catalyst deactivation. To assess structural stability, XRD analysis was performed on the used catalyst (collected after the fourth cycle) and compared with fresh samples. Figure 13 The results showed that the characteristic peak positions and intensities of the used sample were almost identical to those of the original material in terms of qualitative characteristics. This indicates that the SnO2 / g-C3N4 / Dt composite material exhibits excellent structural stability throughout the photocatalytic reaction process.

[0113] In summary, this invention successfully prepared a visible light-responsive SnO2 / g-C3N4 / Dt composite photocatalyst via a hydrothermal method combined with calcination. This catalyst exhibits high purity, good crystallinity, high specific surface area, and a mesoporous structure. Its microstructure consists of a well-dispersed binary heterostructure of plate-like SnO2 and layered g-C3N4 on a Dt substrate. After 60 min of illumination, the degradation rates of MO, SEX, and TCH reached 94.29%, 99.63%, and 93.31%, respectively, significantly outperforming the corresponding single-component and binary composite materials, as well as existing related materials. The photocatalytic degradation process follows a pseudo-first-order reaction kinetic model, and its reaction rate constant k is 3.5 to 4.1 times higher than that of single-component and binary composite materials. •O2 ⁻ •OH and h + These are key active species generated during the degradation process. Furthermore, this ternary composite material exhibits excellent recycling stability, making it an environmentally friendly, inexpensive, and highly efficient photocatalyst with significant potential for practical industrial applications.

[0114] This invention presents a novel ternary nanocomposite photocatalyst, SnO2 / g-C3N4 / Dt, prepared via a hydrothermal method combined with calcination. This design fully utilizes the high photocatalytic activity of SnO2 and g-C3N4, along with the high dispersibility of diatomaceous earth (Dt), to successfully construct a stable heterojunction system. Characterization results show that this ternary composite material possesses a large specific surface area, optimized pore structure, and abundant active sites, effectively inhibiting nanoparticle aggregation. Under simulated visible light irradiation, the ternary composite material exhibits highly efficient and broad-spectrum photocatalytic activity: after 60 min of irradiation, the degradation rates of methyl orange (MO, dye), sodium ethyl xanthate (SEX, mineral processing reagent), and tetracycline hydrochloride (TCH, antibiotic) reached 94.29%, 99.63%, and 93.31%, respectively, significantly outperforming single-component and binary materials. The photocatalytic degradation process follows pseudo-first-order kinetics, with a degradation rate 3.5-4.1 times higher than that of single-component and binary materials. The results of the cyclic degradation experiment show that the ternary composite photocatalyst has good stability for recycling and has good application prospects in the field of industrial wastewater treatment containing organic pollutants.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst, characterized in that, Includes the following steps: S1. Preparation of g-C3N4 nanomaterials: g-C3N4 nanomaterials were prepared by thermal polymerization, in which melamine was placed in a ceramic crucible and calcined in a muffle furnace; the product was then naturally cooled to room temperature and stored for later use. S2. Preparation of ternary SnO2 / g-C3N4 / Dt composite materials: SnCl4·5H2O and CTAB were dissolved in water to form solution A; NaOH was dissolved in water to prepare solution B. After magnetic stirring of solution B, g-C3N4 and Dt were added to solution A. Solution A was added dropwise to solution B while stirring continuously. The resulting suspension was transferred to a polytetrafluoroethylene-lined stainless steel autoclave for reaction. After natural cooling to room temperature, the supernatant was discarded. The precipitate was collected by centrifugation, washed, and finally dried to obtain the ternary SnO2 / g-C3N4 / Dt composite material.

2. The preparation method of the diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst according to claim 1, characterized in that, In step S1, the amount of melamine used is 15 mmol.

3. The preparation method of the diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst according to claim 1, characterized in that, In step S1, the calcination temperature is 500 ℃, the heating rate is 5 ℃ / min, and the calcination time is 2 h.

4. The preparation method of the diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst according to claim 1, characterized in that, In step S2, solution A contains 2 mmol of SnCl4·5H2O, 2 mmol of CTAB, and 40 mL of water; solution B contains 8 mmol of NaOH, 20 mL of water, 10 mmol of g-C3N4, and 0.2 g of Dt.

5. The preparation method of the diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst according to claim 1, characterized in that, In step S2, the mixture is magnetically stirred for 10 min; stirring is continued for 20 min; the resulting 60 mL suspension is transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave, the reaction temperature in the autoclave is 180℃, and the reaction time is 12 h; the centrifugation speed is 8000 r / min, and the centrifugation time is 10 min; the precipitate is washed three times with alternating ethanol and water; the drying temperature is 60 ℃, and the drying time is 12 h.

6. The diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by any one of the preparation methods according to claims 1-5.

7. The diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by any one of the preparation methods according to claims 1-5 is used for wastewater treatment.

8. The diatomaceous earth-supported SnO2 / g-C3N4 nanocomposite photocatalyst prepared by the method according to claim 7 is used for the degradation of MO, SEX and TCH.

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