A ZnO-TiO2 photocatalytic material for low-concentration methane removal and a preparation method and application thereof

Abstract

The application belongs to the field of photocatalytic materials and low-concentration methane treatment technology, and discloses a ZnO-TiO2 photocatalytic material for removing low-concentration methane, and a preparation method and application thereof. The material comprises anatase TiO2 nanocrystalline matrix and a ZnO component loaded on the surface of the matrix, and a ZnO / TiO2 contact interface is formed between the ZnO component and the TiO2 nanocrystalline; the TiO2 nanocrystalline is preferably a nanocrystalline mainly exposing TiO2 (100) or TiO2 (101) crystal faces, and the theoretical loading amount of ZnO is 0.5-10 wt%. The preparation method comprises preparing TiO2 crystal face nanocrystalline, dispersing the nanocrystalline in a solution containing a zinc source to perform impregnation contact, drying, and calcining in air to obtain a ZnO-modified TiO2 sample. The material can be used for removing ppm-level low-concentration methane, exhaust gas or air containing methane under the conditions of room temperature, normal pressure, ultraviolet light irradiation and a wet state, and the loading of ZnO can significantly improve the apparent removal rate of low-concentration methane by TiO2, and the ZnO / TiO2 (101) interface is beneficial to the separation of photo-generated charges, the activation of water and oxygen, and the generation of active oxygen species.

Description

Technical Field

[0001] This invention belongs to the fields of photocatalyst materials, low-concentration methane treatment and coal mine exhaust gas reduction technology, and specifically relates to a ZnO-TiO2 photocatalyst material for low-concentration methane removal, its preparation method and application. Background Technology

[0002] Methane is an important greenhouse gas and a potential carbon resource. In coal mine ventilation gas, goaf areas, tunnels, mining work spaces, and enclosed or semi-enclosed monitoring chambers, methane is often continuously emitted or locally accumulated in low concentrations. Low-concentration methane typically has low partial pressure, weak surface adsorption, and high CH bond energy, making activation difficult at room temperature and atmospheric pressure. Therefore, its removal and reduction present significant technical challenges.

[0003] Traditional methane catalytic combustion or thermocatalytic oxidation usually requires high temperatures or precious metal active components, resulting in high energy consumption and material costs. Furthermore, for low-concentration methane systems at the ppm level, the methane partial pressure is low, the mass transfer driving force is weak, and the absolute amount of product is low, making it difficult to simply apply the logic of high-concentration methane conversion or product-oriented conversion.

[0004] Semiconductor photocatalysis technology can drive surface redox processes using photogenerated electrons and holes at room temperature and pressure, and has potential application value in the treatment of low-concentration methane. TiO2 has the advantages of stability, low cost and environmental friendliness, and is a commonly used photocatalytic material. However, pure TiO2 has limited activation ability for nonpolar CH4, and photogenerated electrons and holes are prone to recombination. ZnO-based materials can participate in methane adsorption, surface oxygen species regulation and interfacial charge migration, but single ZnO or ordinary ZnO composite systems still cannot simultaneously achieve low-concentration methane capture, interfacial charge separation, water and oxygen activation and reaction site recovery.

[0005] Several existing technologies exist for the removal of low-concentration methane or the catalytic oxidation of methane. For example, Chinese invention patent application CN111545197A discloses a Ru-ZnO photocatalyst, its preparation method, and its application. ZnO is prepared by annealing zinc oxalate, followed by a redox reaction and annealing with ruthenium chloride, used for catalytic purification of low-concentration methane in the air. Chinese invention patent authorization announcement CN111054391B discloses a Pd-supported NiCo2O4 spinel catalyst and its preparation method, utilizing PdO and NiCo2O4 spinel as active materials to catalyze the complete oxidation of methane at relatively low temperatures. Other related technologies disclose high-temperature resistant catalysts for the combustion of low-concentration methane or exhaust gas methane, and their preparation methods.

[0006] However, the aforementioned technical solutions mainly focus on Ru-ZnO photocatalytic systems, noble metal spinel thermocatalytic oxidation systems, or exhaust gas combustion catalytic systems. No material system has yet been disclosed that uses anatase TiO2 nanocrystals with predominantly exposed TiO2(100) or TiO2(101) crystal planes as the matrix, with ZnO components loaded on their surface to construct a ZnO / TiO2 crystal plane contact interface, for photocatalytic removal of ppm-level low-concentration methane under room temperature, atmospheric pressure, and humid conditions. Therefore, it is necessary to provide a new ZnO-TiO2 photocatalytic material and its preparation method, enabling it to exhibit high removal efficiency and a clear structure-performance relationship in the treatment of low-concentration methane, exhaust gas, or methane-containing air. Summary of the Invention

[0007] To address the problems in the prior art, this invention provides a ZnO-TiO2 photocatalytic material for the removal of low-concentration methane, its preparation method, and its application. By introducing ZnO components onto the surface of anatase phase TiO2 nanocrystals with specific crystal orientations, a ZnO / TiO2 contact interface is formed, thereby improving the material's apparent removal capacity of low-concentration methane under room temperature, normal pressure, and light irradiation conditions.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A ZnO-TiO2 photocatalytic material for the removal of low-concentration methane, the ZnO-TiO2 photocatalytic material comprising anatase TiO2 nanocrystal matrix and ZnO component supported on the surface of the TiO2 nanocrystal matrix, the TiO2 nanocrystal matrix comprising TiO2 nanocrystals mainly exposing TiO2 (101) crystal planes or TiO2 nanocrystals mainly exposing TiO2 (100) crystal planes, the ZnO component forming a ZnO / TiO2 crystal plane contact interface with the TiO2 nanocrystal matrix.

[0009] Furthermore, based on the theoretical ZnO loading, the loading of the ZnO component is 0.5-10 wt%, preferably 1-10 wt%, and more preferably 3-8 wt%. The wt% is the mass percentage of the theoretical ZnO mass relative to the theoretical total mass of the ZnO-TiO2 photocatalytic material; when describing the gas composition, % is the volume fraction; when describing the CH4 removal rate, % is the percentage decrease in CH4 concentration before and after the reaction.

[0010] Furthermore, the ZnO component is distributed on the surface of TiO2 nanocrystals in the form of highly dispersed ZnO, Zn-containing species on the surface, or a combination thereof.

[0011] Furthermore, the XRD pattern of the ZnO-TiO2 photocatalytic material shows characteristic peaks of anatase TiO2, and the main crystal phase and crystal plane characteristics of TiO2 are basically maintained after ZnO modification.

[0012] Furthermore, TiO2 nanocrystals that primarily expose the TiO2(100) crystal plane have TiO2(200) crystal plane family lattice fringes in the range of 0.15–0.25 nm in HRTEM, while TiO2 nanocrystals that primarily expose the TiO2(101) crystal plane have TiO2(101) crystal plane family lattice fringes in the range of 0.30–0.40 nm in HRTEM.

[0013] The present invention also provides a method for preparing the above-mentioned ZnO-TiO2 photocatalytic material, including preparing anatase phase TiO2 nanocrystalline matrix, contacting the TiO2 nanocrystalline matrix with a zinc source, drying and calcining to obtain ZnO modified TiO2 sample.

[0014] A method for preparing a ZnO-TiO2 photocatalytic material includes the following steps: (1) Preparation of anatase TiO2 nanocrystalline matrix; (2) The TiO2 nanocrystalline matrix is ​​dispersed in a solvent to form a TiO2 suspension; (3) Add a zinc source solution to the TiO2 suspension to bring the zinc species into contact with the surface of the TiO2 nanocrystals; (4) After drying, a zinc-containing precursor / TiO2 composite precursor was obtained; (5) The composite precursor is heat-treated in an atmosphere to obtain ZnO-TiO2 photocatalytic material.

[0015] Furthermore, the zinc source is selected from one or more of zinc nitrate, zinc acetate, zinc chloride, zinc sulfate and their hydrates; the solvent is selected from water, ethanol, isopropanol or a water / alcohol mixture; the mass-volume ratio of the TiO2 nanocrystalline matrix to the solvent is 1 g:(50-300) mL; after the zinc source solution is added, stirring is continued for 2-4 h.

[0016] Furthermore, the drying temperature is 60-100℃; the heat treatment temperature is 300-450℃; the heat treatment time is 1-4 h; and the heat treatment atmosphere is one of air, oxygen, nitrogen, or an inert atmosphere, preferably air.

[0017] Furthermore, by adjusting the amount of zinc source added, the theoretical loading of ZnO in the obtained ZnO-TiO2 photocatalytic material is 0.5-10 wt%, preferably 1-10 wt%; wherein the amount of zinc source added is determined based on the type of zinc source, the target loading of ZnO and the amount of TiO2 nanocrystalline matrix used, and the wt% is a mass percentage.

[0018] Furthermore, the TiO2 nanocrystals with the main exposed TiO2(101) crystal planes are prepared by a titanium alkoxide precursor-assisted hydrothermal method, comprising: mixing titanium alkoxide and water at a volume ratio of (8-12):1 to form a titanium-containing emulsion precursor; subjecting the titanium-containing emulsion precursor to hydrothermal treatment; and after cooling, performing solid-liquid separation, water / ethanol washing, drying, and heat treatment to obtain TiO2(101) nanocrystals; wherein the hydrothermal treatment temperature is 170-190℃, the hydrothermal treatment time is 24-28 h, the drying temperature is 50-80℃, the heat treatment time is 1-3 h, and the heat treatment temperature is 450-550℃.

[0019] Furthermore, the titanium alkoxide is selected from titanium isopropoxide, tetrabutyl titanate, or a combination thereof; the hydrothermal treatment is carried out in a closed polytetrafluoroethylene-lined reactor.

[0020] Furthermore, the TiO2 nanocrystals with the main exposed TiO2(100) crystal planes are prepared by a Ti(OH)4 precursor-assisted hydrothermal method, comprising: hydrolyzing and neutralizing a titanium chloride solution at a low temperature of 0-10℃ to obtain a Ti(OH)4 precursor; dispersing the Ti(OH)4 precursor in a water / alcohol mixed solvent, adding a sulfate auxiliary agent, homogenizing and then performing hydrothermal treatment, cooling and then performing solid-liquid separation, water / ethanol washing and drying to obtain TiO2(100) nanocrystals; wherein the hydrothermal treatment temperature is 170-190℃ and the hydrothermal treatment time is 20-28 h.

[0021] Furthermore, the titanium chloride is titanium tetrachloride; the neutralized pH is 6.0-7.0; the alcohol solvent is isopropanol, ethanol, or a combination thereof; the sulfate auxiliary is selected from ammonium sulfate, sodium sulfate, potassium sulfate, or a combination thereof, preferably ammonium sulfate; the mass-to-volume ratio of the Ti(OH)4 precursor to the water / alcohol mixed solvent is 1 g:(10-30) mL.

[0022] The present invention also provides the application of the above-mentioned ZnO-TiO2 photocatalytic material in the removal of low-concentration methane, wherein the low-concentration methane includes methane-containing air, coal mine exhaust gas, ventilation gas, methane-containing gas in goaf areas, and methane-containing gas in closed or semi-closed spaces.

[0023] Furthermore, the ZnO-TiO2 photocatalytic material is used in the removal of low-concentration methane.

[0024] Furthermore, the low-concentration methane refers to methane-containing air, coal mine exhaust gas, ventilation gas, methane-containing gas in goaf areas, or methane-containing gas in enclosed or semi-enclosed spaces.

[0025] Furthermore, the initial concentration of the low-concentration methane is 50-2000 ppm, preferably 100-1000 ppm, and more preferably about 400 ppm; ppm is a unit of volume concentration.

[0026] Furthermore, the removal is carried out under normal or near-normal pressure, 20-40°C, and ultraviolet light or simulated sunlight irradiation conditions; the reaction atmosphere is air, an oxygen / nitrogen mixture, or an oxygen-containing atmosphere, wherein the volume fraction of O2 is preferably 15-25%.

[0027] Furthermore, water vapor is introduced into the reaction atmosphere. The water vapor is provided by a water bath, humidifier, or moisture generator. The water vapor introduction temperature is preferably 20-30°C to promote the activation of H2O / O2 and generate active oxygen species that participate in the removal of low-concentration methane.

[0028] Compared with the prior art, the present invention has the following beneficial effects: First, ZnO loading significantly enhances the apparent removal capacity of TiO2 nanocrystals for low-concentration methane. Second, the TiO2 (101) crystal facet exhibits a more pronounced crystal facet advantage within the theoretical ZnO loading range of 0-5 wt%. Third, wet conditions are generally superior to dry conditions, indicating that water-related surface species can participate in and promote the removal of low-concentration methane. Fourth, the ZnO / TiO2 interface can promote photogenerated charge separation, H2O / O2 activation, and the interaction of •OH and •O2. - The generation of reactive oxygen species improves the photocatalytic reduction effect of low-concentration methane. Attached Figure Description

[0029] Figure 1 XRD patterns of T(100), T(101), 5 wt% ZnO-T(100) and 5% ZnO-T(101); Figure 2 TEM / HRTEM morphology and STEM-EDS elemental distribution of T(100), T(101), 5 wt%ZnO-T(100) and 5%ZnO-T(101); Figure 3 The O1 s XPS high-resolution spectra before and after the reaction of 5%ZnO-T(100) and 5%ZnO-T(101); Figure 4 The graph shows the photocatalytic removal performance of low-concentration CH4 from ZnO-supported TiO2 nanocrystals. Figure 5This is a schematic diagram of the band alignment and possible charge transfer paths of ZnO / TiO2. Figure 6 The results of PL, transient photocurrent and EIS characterization of ZnO-supported TiO2 nanocrystals are shown. Figure 7 Characterization results of CH4-TPD and CO2-TPD adsorption / retention behavior of ZnO-supported TiO2 nanocrystals; Figure 8 EPR characterization diagram of ZnO-supported TiO2 nanocrystals; Figure 9 A schematic diagram illustrating the possible mechanisms for photocatalytic removal of low concentrations of CH4 from ZnO-TiO2 with different crystal planes. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. In the present invention, the percentage of ZnO loading is a theoretical mass percentage, calculated as ZnO theoretical mass / (TiO2 mass + ZnO theoretical mass) × 100%; the percentages of O2 and N2 in the gas are volume fractions; the CH4 removal rate percentage is the percentage decrease in CH4 concentration before and after the reaction. Equivalent adjustments made by those skilled in the art to the type of raw materials, dosage range, drying temperature, calcination temperature, and testing conditions without departing from the essential content of the present invention should all fall within the scope of protection of the present invention.

[0031] Example 1: Preparation of TiO2(101) nanocrystals TiO2(101) nanocrystals were prepared using a hydrothermal method assisted by a titanium alkoxide precursor. Specifically, 10 mL of titanium isopropoxide was slowly added to 1.0 mL of deionized water under stirring conditions, making the volume ratio of titanium alkoxide to water 10:1. Stirring was continued for 20-30 min to form a homogeneous emulsion precursor. The obtained precursor was transferred to a polytetrafluoroethylene-lined reactor, sealed, and hydrothermally treated at 180℃ for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature, and the white solid was collected by centrifugation or filtration. The solid was washed three times with deionized water and ethanol, dried at 60℃ for 12 h, and then heat-treated at 500℃ for 2 h in air to obtain TiO2(101) nanocrystals. The above feed amounts can be scaled up or down proportionally.

[0032] Example 2 Preparation of TiO2(100) nanocrystals TiO2(100) nanocrystals were prepared via a Ti(OH)4 precursor-assisted hydrothermal method. First, 5 mL of titanium tetrachloride was slowly added dropwise to 50 mL of ice water under stirring conditions at 0-10 °C. After the addition was complete, stirring continued for 30 min, and the pH of the system was adjusted to approximately 6.5 with dilute ammonia or sodium hydroxide solution to obtain a white Ti(OH)4 precipitate. The precipitate was collected by centrifugation, washed with deionized water until the washing solution was nearly neutral, and then dried at 60 °C for later use.

[0033] Subsequently, 1.0 g of the dried Ti(OH)4 precursor was weighed and dispersed in a water / alcohol mixture consisting of 10 mL of deionized water and 20 mL of isopropanol. 0.30 g of ammonium sulfate was added as a sulfate auxiliary agent, and the mixture was homogenized by ultrasonication or high-speed stirring for 20-30 min. The suspension was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally treated at 180℃ for 24 h. After natural cooling, the reaction product was collected by centrifugation, washed three times with deionized water and ethanol, and dried at 60℃ for 12 h to obtain TiO2(100) nanocrystals.

[0034] Example 3 Preparation of ZnO-modified TiO2 samples ZnO-modified TiO2 samples were prepared using an impregnation-drying-calcination method. Taking the preparation of a 5 wt% ZnO-TiO2 sample as an example, 1.00 g of TiO2 support was weighed and dispersed in 100 mL of ultrapure water. The mixture was sonicated for 10 min and magnetically stirred to form a homogeneous suspension. Separately, approximately 0.192 g of zinc nitrate hexahydrate was dissolved in 10 mL of ultrapure water to obtain a zinc-containing source solution. Under stirring conditions, the zinc-containing source solution was added dropwise to the TiO2 suspension, and stirring continued for 2 h to ensure sufficient contact between the Zn species and the TiO2 surface. The suspension was then evaporated or dried at 80 °C to obtain a Zn-containing precursor. The precursor was then ground uniformly and calcined at 350 °C for 2 h in air to obtain a 5 wt% ZnO-TiO2 sample.

[0035] Samples with different ZnO loadings were prepared using the same method, with only the amount of zinc source added varying. The resulting samples can be denoted as xwt%ZnO-T(100) and xwt%ZnO-T(101), where x represents the theoretical mass percentage loading of ZnO. Based on 1.00 g TiO2, when preparing 3 wt%, 5 wt%, and 10 wt% ZnO-TiO2 samples, the amount of zinc nitrate hexahydrate used can be approximately 0.113 g, 0.192 g, and 0.406 g, respectively; the x is preferably adjusted within the range of 0.5-10 wt% to balance ZnO / TiO2 interface construction, TiO2 crystal surface effect retention, and low-concentration methane removal performance.

[0036] Example 4: Material Structure Confirmation The samples obtained in Examples 1–3 were characterized by XRD, TEM / HRTEM, STEM-EDS, and XPS. The results showed that both T(100) and T(101) exhibited characteristic diffraction peaks of anatase TiO2, and no obvious rutile or brookite impurities were observed. The main crystal phase and crystal plane characteristics of TiO2 were basically preserved after ZnO modification.

[0037] HRTEM results showed that lattice fringes of approximately 0.19 nm were observed in the T(100) sample and its ZnO-modified sample, corresponding to the (200) crystal plane family of anatase TiO2; lattice fringes of approximately 0.35 nm were observed in the T(101) sample and its ZnO-modified sample, corresponding to the (101) crystal plane family of anatase TiO2. STEM-EDS results showed that Zn, Ti, and O elements spatially overlapped in the particle region, indicating that ZnO was successfully loaded onto the TiO2 nanocrystal surface and formed a ZnO / TiO2 contact interface.

[0038] Application Example 1: Low-concentration CH4 photocatalytic removal test The low-concentration CH4 photocatalytic removal experiment was conducted in a closed reactor with a quartz light window and a reactor volume of 31.4 mL. For each experiment, 30 mg of catalyst was weighed and evenly spread on a quartz wool disc with a diameter of about 20 mm. The disc was then placed in the central cavity of the reactor to ensure that UV light could pass through the top quartz light window and irradiate the catalyst surface.

[0039] Before the reaction, CH4 was mixed with air to maintain an initial CH4 concentration of approximately 400 ppm. The equilibrium gas was air, approximately 80% N2 and 20% O2, where 80% and 20% are volume fractions. In the dry-state experiment, the gas flow rate was approximately 57 ± 2 mL / min. -1 In the wet experiment, the gas flow rate was approximately 48 ± 2 mL / min. -1 The mixed gas is first introduced into the reactor for 5-6 minutes to displace any residual gas inside. Then, the outlet and inlet are closed, and the reactor is evacuated through the outlet for approximately 20 seconds using a vacuum pump. Afterward, the CH4 / air mixture is re-injected into the reactor using a 50 mL syringe, while a smaller syringe is connected to buffer pressure changes and maintain the reactor at near-atmospheric pressure.

[0040] In the wet-state experiment, water vapor was introduced into the mixed gas through a gas washing bottle containing approximately 100 mL of water before entering the reactor. The gas washing bottle was maintained at 25°C, and the outlet-to-reactor inlet pipeline was maintained at approximately 34 ± 1.5°C via insulation wire to reduce water vapor condensation. For the temperature comparison experiment between 25°C and 38°C, both groups of experiments used the same 25°C water vapor introduction method, only changing the temperature of the circulating water outside the reactor to maintain the same absolute water vapor content as much as possible.

[0041] The photocatalytic reaction was carried out under UV light irradiation for 1 h. In standard experiments, the UV lamp power was 100 W; in comparative experiments, 50 W and 100 W were used. After the reaction, gas was extracted from the reactor using a 50 mL syringe, typically yielding 15-30 mL of gas sample, which was then transferred to a gas bag for storage. The CH4 concentration was subsequently determined by GC. The apparent CH4 removal rate was calculated using the following formula: CH4 removal (%) = (C0 - C t ) / C0 × 100%, where C0 is the CH4 concentration before the reaction, C t The concentration of CH4 after the reaction is given; the percentage represents the relative decrease in concentration.

[0042] Application Example 2: CH4 Removal Results of Samples with Different ZnO Loadings and Crystal Facets Under wet conditions, the CH4 removal rates of unloaded ZnO T(100) and T(101) were 52.5% and 56.4%, respectively. As the ZnO loading increased from 0% to 10%, the CH4 removal rates of both types of TiO2 nanocrystals continued to increase, with ZnO-T(100) increasing from 52.5% to 91.9% and ZnO-T(101) increasing from 56.4% to 91.6%.

[0043] A similar enhancement trend was observed under dry conditions. With increasing ZnO loading, the CH4 removal rate of dry ZnO-T(100) increased from 43.8% to 82.6%, and that of dry ZnO-T(101) increased from 46.9% to 81.8%.

[0044] Taking the 5% ZnO-loaded sample as an example, the removal rates of 5% ZnO-T(100) and 5% ZnO-T(101) under wet conditions were 77.8% and 79.8%, respectively, while under dry conditions they were 67.9% and 69.5%, respectively. The wet condition was about 10 percentage points higher than the dry condition, indicating that water vapor participation has a promoting effect on the CH4 photocatalytic removal process in this system.

[0045] Within the theoretical loading range of 0-5 wt% ZnO, ZnO-T(101) generally exhibits higher CH4 removal capacity compared to ZnO-T(100). Specifically, under wet conditions, the time difference between 1 wt% and 2 wt% ZnO loading is approximately 13.1 and 13.5 percentage points, respectively; under dry conditions, the time difference between 1 wt% and 2 wt% loading is approximately 8.4 and 9.4 percentage points, respectively.

[0046] The results of three repeated experiments showed that the average CH4 removal rates of 5% ZnO-T(100) and 5% ZnO-T(101) under wet UV irradiation were 76.19% and 79.51%, respectively; the average CH4 removal rates of 10 wt% ZnO-T(100) and 10% ZnO-T(101) were 91.12% and 91.70%, respectively.

[0047] Table 1. Results of low-concentration CH4 removal from different samples under humid light conditions.

[0048] Application Example 3: Dark-state adsorption, temperature, and light power comparison To differentiate the contributions of dark-state adsorption and light-driven processes, the wet-state and dark-state adsorption, total light removal rate, and apparent net photocatalytic contribution of 5%ZnO-T(100) and 5%ZnO-T(101) were separated. Under wet-state and dark-state conditions, the CH4 removal rates of 5%ZnO-T(100) and 5%ZnO-T(101) were 6.88% and 8.35%, respectively, significantly lower than the total removal rate under light conditions. After deducting the contribution of dark-state adsorption, the apparent net photocatalytic contributions of the two were 69.30% and 71.16%, respectively.

[0049] Under the conditions of maintaining the same initial CH4 concentration, O2 / N2 ratio, catalyst dosage, UV light power, and absolute water vapor content, increasing the reaction temperature from 25℃ to 38℃ did not improve the CH4 removal rate, indicating that the main promoting factor in this system is not simply thermal promotion. On the contrary, increasing the UV light power can improve the CH4 removal rate, indicating that the generation of photogenerated electron-hole pairs and the subsequent formation of reactive oxygen species play an important role in CH4 removal.

[0050] Application Example 4: Characterization of Mechanism of Action PL, transient photocurrent, and EIS tests show that ZnO modification can reduce photogenerated electron-hole recombination in TiO2 and improve interfacial charge transfer. 5wt%ZnO-T(101) exhibits lower PL emission intensity, higher transient photocurrent response, and lower interfacial charge transfer resistance.

[0051] TPD results showed that the total CH4 desorption capacity of 5 wt% ZnO-T(101) was lower than that of 5% ZnO-T(100), indicating that the advantage of 5% ZnO-T(101) in removing low-concentration CH4 in wet conditions is not directly determined by its higher total CH4 adsorption capacity. CO2-TPD results showed that 5% ZnO-T(101) had a weaker tendency to retain desorbable CO2 / carbonate species, which may be beneficial for reducing the coverage of moderate-intensity carbonate species and promoting site recovery.

[0052] XPS O1 s and EPR results show that 5 wt% ZnO-T(101) has a more favorable 1 s facet hydroxyl / deficient oxygen environment and produces stronger DMPO-.OH and DMPO-.O2- signals under wet illumination, indicating that the ZnO / TiO2(101) interface is more conducive to H2O / O2 activation and reactive oxygen species generation.

[0053] In summary, the removal effect of the ZnO-TiO2 photocatalytic material of this invention on low-concentration methane is due to the synergistic effect of factors such as ZnO / TiO2 contact interface construction, enhanced photogenerated charge separation and migration, promoted water and oxygen activation, and reduced CO2 / carbonate retention.

[0054] Industrial applicability The ZnO-TiO2 photocatalytic material of this invention has a simple preparation method and readily available raw materials. Different performance levels of low-concentration methane removal materials can be obtained by adjusting the TiO2 crystal planes and ZnO loading. This material can be used for the photocatalytic reduction of methane gases in coal mine exhaust gas, ventilation gas, methane-containing gases in goaf areas, methane-containing air in confined or semi-confined spaces, and other low-concentration methane gases at the ppm level, showing promising application prospects.

[0055] In this invention, unless otherwise specified, the percentage of ZnO loading is the theoretical mass percentage, the percentage of gas composition is the volume fraction, and the percentage of methane removal rate is the percentage of relative decrease in methane concentration before and after the reaction.

[0056] 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 ZnO-TiO2 photocatalytic material for the removal of low-concentration methane, characterized in that, The ZnO-TiO2 photocatalytic material comprises anatase TiO2 nanocrystalline matrix and ZnO component loaded on the surface of the TiO2 nanocrystalline matrix, wherein the ZnO component and the TiO2 nanocrystalline matrix form a ZnO / TiO2 crystal plane contact interface; the TiO2 nanocrystalline matrix is ​​TiO2 nanocrystals with exposed TiO2 (101) crystal plane or TiO2 nanocrystals with exposed TiO2 (100) crystal plane.

2. The ZnO-TiO2 photocatalytic material according to claim 1, characterized in that, The theoretical loading of the ZnO component is 0.5-10 wt%; the wt% is the mass percentage of the theoretical mass of ZnO relative to the total theoretical mass of the ZnO-TiO2 photocatalytic material.

3. The ZnO-TiO2 photocatalytic material according to claim 2, characterized in that, The ZnO component is distributed on the surface of TiO2 nanocrystals in the form of highly dispersed ZnO, Zn species on the surface, or a combination thereof; the XRD pattern of the ZnO-TiO2 photocatalytic material has the characteristic peaks of anatase TiO2, and the main crystal phase and crystal face features of TiO2 are maintained after ZnO modification.

4. The ZnO-TiO2 photocatalytic material according to claim 3, characterized in that, TiO2 nanocrystals with exposed TiO2(100) crystal planes exhibit TiO2(200) crystal plane family lattice fringes in the range of 0.15-0.25 nm in HRTEM, while TiO2 nanocrystals with exposed TiO2(101) crystal planes exhibit TiO2(101) crystal plane family lattice fringes in the range of 0.30-0.40 nm in HRTEM.

5. A method for preparing the ZnO-TiO2 photocatalytic material as described in any one of claims 1-4, characterized in that, The process includes the following steps: preparing anatase TiO2 nanocrystal matrix; dispersing the TiO2 nanocrystal matrix in a solvent to form a TiO2 suspension; adding a zinc source solution to the TiO2 suspension to bring zinc species into contact with the surface of the TiO2 nanocrystals; A zinc-containing precursor / TiO2 composite precursor was obtained by drying; the composite precursor was then heat-treated in an atmosphere to obtain a ZnO-TiO2 photocatalytic material.

6. The preparation method according to claim 5, characterized in that, The zinc source is selected from one or more of zinc nitrate, zinc acetate, zinc chloride, zinc sulfate and their hydrates; the solvent is selected from water, alcohol solvents or water / alcohol mixed solvents; the mass-volume ratio of the TiO2 nanocrystalline matrix to the solvent is 1 g:(50-300) mL; after the zinc source solution is added, stirring is continued for 0.5-4 h; the drying temperature is 60-100℃, the heat treatment temperature is 300-450℃, and the heat treatment time is 1-4 h.

7. The preparation method according to claim 6, characterized in that, The TiO2 nanocrystals with exposed TiO2(101) crystal planes are prepared by a titanium alkoxide precursor-assisted hydrothermal method, which includes: mixing titanium alkoxide and water at a volume ratio of (8-12):1 to form a titanium-containing emulsion precursor; hydrothermally treating the titanium-containing emulsion precursor at 170-190℃ for 24-28 h; cooling and then performing solid-liquid separation, water / ethanol washing, drying at 50-80℃, and air heat treatment at 450-550℃ for 1-3 h to obtain TiO2(101) nanocrystals.

8. The preparation method according to claim 6, characterized in that, The TiO2 nanocrystals with exposed TiO2(100) crystal planes are prepared by a Ti(OH)4 precursor-assisted hydrothermal method, comprising: hydrolyzing titanium tetrachloride solution at a low temperature of 0-10℃ and neutralizing it to pH 6.0-7.0 to obtain Ti(OH)4 precursor; dispersing the Ti(OH)4 precursor in a water / alcohol mixed solvent and adding a sulfate auxiliary agent; after homogenization, hydrothermally treating it at 170-190℃ for 24-28 h; cooling and then performing solid-liquid separation, washing with water / ethanol and drying at 50-80℃ to obtain TiO2(100) nanocrystals.

9. The application of the ZnO-TiO2 photocatalytic material according to any one of claims 1-4 or the ZnO-TiO2 photocatalytic material prepared by the preparation method according to any one of claims 5-8 in the removal of low-concentration methane, characterized in that, The low-concentration methane refers to methane-containing air, coal mine exhaust gas, ventilation gas, methane-containing gas in goaf areas, and methane-containing gas in enclosed or semi-enclosed spaces, with an initial methane concentration of 50-2000 ppm.

10. The application according to claim 9, characterized in that, The low-concentration methane removal is carried out under normal or near-normal pressure, 20-40℃, and ultraviolet light or simulated sunlight irradiation conditions; the reaction atmosphere is air or an oxygen-containing atmosphere with an oxygen volume fraction of 15-25%, and water vapor is introduced at a temperature of 20-30℃; wherein the gas percentage is a volume fraction, and the methane removal rate percentage is the percentage of relative decrease in methane concentration before and after the reaction.

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