An oxygen-rich vacancy porous CeO2 material, its preparation method, and its applications

Abstract

This application relates to the fields of material preparation and photocatalytic oxidation of VOCs, disclosing an oxygen-rich vacancy porous CeO2 material, its preparation method, and its application. The preparation method involves: a solution of terephthalic acid dissolved in N,N-dimethylformamide and an aqueous solution of cerium ammonium nitrate are mixed and subjected to a solvothermal reaction to obtain a suspension; the suspension is then cooled, centrifuged, washed, and vacuum dried to obtain a Ce-BDC precursor solid; urea and the Ce-BDC precursor solid are mixed, and after grinding, calcination, and cooling, the CeO2 photocatalytic material is obtained. This invention also discloses the application of the CeO2 catalyst prepared according to this method in the photocatalytic oxidation of VOCs. The CeO2 material prepared by this invention increases the specific surface area, pore volume, and pore size of CeO2, and has a relatively large number of mesopores, which can provide more active sites for the catalytic reaction and promote charge transport, thus exhibiting excellent photocatalytic deep oxidation performance of toluene under high ambient humidity.

Description

Technical Field

[0001] This invention relates to the fields of material preparation and photocatalytic oxidation of VOCs, and more specifically, to an oxygen-rich vacancy porous CeO2 material, its preparation method, and its applications. Background Technology

[0002] Volatile organic compounds (VOCs) are among the major indoor pollutants. When their concentration exceeds safe threshold levels, they can easily cause acute discomfort and chronic health damage, and even pose a carcinogenic risk, seriously threatening human health. Efficient treatment of indoor VOCs with low concentrations, low flow rates, and significant fluctuations in ambient humidity has become a research hotspot in the field of environmental catalysis, possessing both theoretical and practical value. Compared to various VOCs elimination methods, solar-driven photocatalytic oxidation technology is considered a promising green technology for treating indoor VOCs pollution due to its advantages of low energy consumption, mild conditions, safe operation, and high efficiency. Therefore, developing low-cost and high-performance photocatalytic materials for oxidizing VOCs is crucial and a key research direction in this field.

[0003] Cerium dioxide (CeO2) is a relatively abundant functional rare-earth oxide semiconductor. Due to its unique 4f electron transition, excellent oxygen storage / release capacity, high chemical stability, suitable band gap energy, and tunable surface oxygen defects, it is one of the most widely used materials for photocatalytic VOCs elimination. Despite the attention given to CeO2's unique electronic structure, its weak adsorption capacity for VOC molecules, insufficient surface active sites, and easy carrier recombination limit its application in photocatalytic oxidation of VOCs. Oxygen vacancy engineering is an important strategy for introducing active sites and improving catalytic performance, playing a crucial role in the photocatalytic oxidation of aromatic VOCs. Currently, methods such as heat treatment, acid / base etching, chemical reducing agent treatment, microwave radiation, and ion doping are commonly used to construct oxygen vacancies. Although CeO2 single crystals possess superior charge transfer capabilities, their limited specific surface area and pore structure restrict their photocatalytic activity when used as catalysts. Increasing the specific surface area and controlling the porous structure can further increase the number of oxygen vacancies and improve catalytic activity.

[0004] Therefore, further development of low-cost technologies for constructing porous structures and enriching oxygen vacancies is needed. Currently, common directions for improving porous structures include mesoporous structures and three-dimensional porous structures, while methods for enriching oxygen vacancies include low-temperature reduction treatment and elemental doping. Studies have shown that under high-temperature conditions, the chemical etching effect of urea can effectively construct and regulate oxygen vacancies. Simultaneously, the space occupied by urea itself is released, easily forming porous structures and significantly enhancing catalytic performance. Furthermore, during the thermal decomposition of metal-organic framework (MOF) materials, nanoparticles are less prone to aggregation and form a large number of ordered pores, improving chemical stability. Therefore, urea combined with MOFs can effectively induce in-situ generation of porous materials with abundant and uniform oxygen vacancies, promoting the adsorption, activation, and conversion of reactant molecules VOCs, O2, and H2O. This is an excellent modification strategy for improving the mineralization rate of CeO2 photocatalytic oxidation of VOCs.

[0005] In this regard, the present invention provides an oxygen-rich vacancy porous CeO2 material, its preparation method, and its application. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a CeO2 material with well-developed pore structure and high oxygen vacancies by using urea and MOFs as pore-forming agents and oxygen vacancy inducers; another technical problem to be solved by the present invention is to provide a specific preparation method for the aforementioned oxygen-vacancy-rich porous CeO2 photocatalyst.

[0007] To achieve the above-mentioned objectives, this application adopts the following technical solution: A method for preparing an oxygen-rich vacancy porous CeO2 material, wherein the preparation method comprises: A suspension was obtained by solvothermal reaction of a solution of terephthalic acid dissolved in N,N-dimethylformamide and an aqueous solution of cerium ammonium nitrate. The suspension was cooled, centrifuged, washed, and vacuum dried to obtain the precursor Ce-BDC solid. The CeO2 photocatalytic material is obtained by mixing urea and the precursor Ce-BDC solid, followed by grinding, calcination and cooling. The mass ratio of urea to the precursor Ce-BDC solid is (0.1~12):1.

[0008] Furthermore, the molar ratio of terephthalic acid to cerium ammonium nitrate is 1:1.

[0009] Furthermore, the mass ratio of urea to the precursor Ce-BDC solid is (0.5–3):1.

[0010] Furthermore, the mass ratio of urea to the precursor Ce-BDC solid is (1-1.5):1.

[0011] Furthermore, in the solvothermal reaction, the temperature is at least 120 °C and the thermal reaction time is at least 15 min.

[0012] Furthermore, in the centrifugal washing process, the washing solvents are N,N-dimethylformamide and acetone, and the number of centrifugal washing cycles is at least 3 times.

[0013] Furthermore, in the vacuum drying process, the vacuum drying temperature is at least 80 °C, and the drying time is at least 12 h.

[0014] Furthermore, the mechanical grinding time of the mixture of the precursor Ce-BDC solid and urea is at least 10 minutes.

[0015] Furthermore, in the roasting process, the roasting method is segmented roasting, and the atmosphere for segmented roasting is air; The first stage of roasting was at a temperature of 400 ℃ with a heating rate of 5 ℃ / min. The second stage of roasting was at a temperature of 700 ℃ with a heating rate of 2 ℃ / min and a roasting time of 3 h.

[0016] A CeO2 catalyst prepared by a method for preparing the oxygen-rich vacancy porous CeO2 material.

[0017] Application of CeO2 catalyst in photocatalytic oxidation of VOCs.

[0018] In summary, this application has the following beneficial effects: (1) The method for preparing oxygen-rich vacancy porous CeO2 material provided by the present invention increases the specific surface area, pore volume, and pore size of CeO2, and has a relatively large number of mesopores, which can provide more active sites for catalytic reactions and promote charge transport. In addition, the oxygen-rich vacancy porous CeO2 material provided by the present invention has a shorter charge transport path, which can effectively suppress the recombination of photogenerated carriers and has lower resistance to charge, effectively promoting the separation and transfer of photogenerated charges, and has a fast carrier separation and transfer efficiency.

[0019] (2) The oxygen-rich porous CeO2 material provided by the present invention has abundant oxygen vacancies and moderate hydrophilicity, which can effectively inhibit H2O from competing for adsorption and oxidation sites, and facilitate the adsorption and activation of toluene, O2 and H2O molecules. Its well-developed pore structure promotes mass transfer and charge transport, thereby efficiently mineralizing toluene pollutant molecules under high ambient humidity, and greatly improving the photocatalytic deep oxidation performance of toluene.

[0020] (3) The entire preparation method of the present invention is simple and easy to operate, with a short cycle and low raw material cost. It can be mass-produced on a large scale and has great application prospects in the efficient and deep elimination of indoor VOCs. Attached Figure Description

[0021] Figure 1 These are the XRD spectra of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1; Figure 2 middle Figure 2 A, Figure 2 B are N2 adsorption-desorption curves and pore size distribution diagrams of CeO2-xU samples prepared in Examples 1 to 3 and Comparative Example 1, respectively. Figure 3 middle Figure 3 A, Figure 3 B are the Raman spectra and oxygen vacancy concentration diagrams of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1, respectively. Figure 4 These are water contact angle diagrams of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1; Figure 5 yes Figure 5 A, Figure 5 B represents the bandgap energy spectrum and EIS spectrum of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1, respectively. Figure 6 AB shows the catalytic performance of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1 under full-spectrum irradiation for the oxidation of toluene. Figure 6 C is the 12-hour lifetime result of the CeO2 sample in Example 3 for photocatalytic oxidation of toluene. Figure 6 D is a graph showing the results of three cycles of photocatalytic oxidation of toluene in the sample of Example 3. Detailed Implementation

[0022] The technical solutions and effects of this application will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention, not the entire structure.

[0023] When CeO2 is used as a photocatalytic material, its low specific surface area and unsatisfactory pore structure limit the exposure of active sites and reactant transport, thus restricting its photocatalytic performance. For CeO2, "establishing a porous structure" and "increasing oxygen vacancies" are two core approaches to improving catalytic / photocatalytic performance, and these two approaches are often used in combination. Therefore, this invention provides a method for preparing an oxygen-vacancy-rich porous CeO2 material.

[0024] A method for preparing an oxygen-rich vacancy-porous CeO2 material is as follows: a solution of terephthalic acid dissolved in N,N-dimethylformamide and an aqueous solution of cerium ammonium nitrate are mixed and subjected to a solvothermal reaction to obtain a suspension; the suspension is cooled, centrifuged, washed, and vacuum dried to obtain a precursor Ce-BDC solid; then urea and Ce-BDC solid are mixed, and after grinding, calcination, and cooling, the oxygen-rich vacancy-porous CeO2 photocatalytic material is obtained.

[0025] In this preparation method, a cerium-based metal-organic framework (MOF) or precursor solid, namely the precursor Ce-BDC solid, is obtained by self-assembly of raw materials (terephthalic acid, cerium ammonium nitrate, and N,N-dimethylformamide). This precursor has a microporous / mesoporous structure, a high specific surface area, and thus high porosity. Furthermore, Ce ions are dispersed within the organic framework, resulting in a uniform metal distribution. The precursor Ce-BDC solid is subsequently ground and mixed with urea, followed by high-temperature calcination to obtain CeO2. This CeO2 is a porous nanostructure with oxygen-rich vacancies.

[0026] The molar ratio of terephthalic acid to cerium ammonium nitrate is 1:1.

[0027] The solvothermal reaction temperature is controlled at 120 °C, and the solvothermal reaction time is maintained at 15 min.

[0028] In the centrifugal washing process, the washing solvents are N,N-dimethylformamide and acetone, and each is washed 3 times.

[0029] In the vacuum drying process, the vacuum drying temperature is 80 ℃ and the time is 12 h.

[0030] The mechanical grinding time of the mixture of the precursor Ce-BDC solid and urea is at least 10 min.

[0031] The roasting atmosphere is air, and the roasting is carried out in stages. The first stage roasting temperature is 400 ℃, the roasting heating rate is 5 ℃ / min, the second stage roasting temperature is 700 ℃, the roasting heating rate is 2 ℃ / min, and the roasting time is 3 h.

[0032] It should be noted that, compared with the existing methods for MOF-derived CeO2, the preparation method of this invention focuses on a specific combination of processes and limits the ratio of urea to the precursor Ce-BDC solid. In other words, by using specific segmented heating and calcination to control the MOF decomposition kinetics and CeO2 crystallization process, a CeO2 material with both high crystallinity and mesoporous structure can be obtained compared with existing CeO2.

[0033] In the first stage of calcination, at 400℃, the BDC ligands in the Ce-BDC solid begin to decompose in large quantities, removing organic ligands and preventing framework collapse by avoiding a violent one-time combustion, thus initially forming CeO2 nanocrystal nuclei. Compared to directly heating to 700℃, which is prone to local overheating, pore structure collapse, and particle sintering, the 400℃ stage actually plays a role in "pre-oxidation + pre-nucleation". In the second stage of calcination, the heating rate is relatively slow, allowing the CeO2 crystals to grow further, thereby increasing crystallinity. Moreover, during the heating process, slow heating is conducive to the gradual release of gases and reduces pore wall rupture. Therefore, the segmented calcination mode usually results in a higher pore structure retention rate than the rapid heating mode.

[0034] It should also be noted that the mass ratio of urea to the precursor Ce-BDC solid is (0.1–12):1, and can be further limited to (0.5–3):1. Preferably, the mass ratio of urea to the precursor Ce-BDC solid is controlled within the range of 1–1.5:1 to obtain CeO2 materials with both high specific surface area and abundant oxygen vacancies. The best effect is achieved when the mass ratio is approximately 1.14:1, and the resulting CeO2 material exhibits a better porous structure and a higher oxygen vacancy content.

[0035] Specifically, the detailed steps for preparing the above-mentioned oxygen-rich vacancy porous CeO2 material are as follows: (1) Weigh terephthalic acid and put it into a heat-resistant glass bottle containing N,N-dimethylformamide. After sonication for 30 min, a uniformly dispersed transparent solution is obtained. Then, cerium ammonium nitrate aqueous solution is added dropwise to the heat-resistant glass bottle to obtain an orange-red mixed solution. (2) The heat-resistant glass bottle containing the orange-red mixed solution obtained in step (1) was sealed and placed in an oven. After a constant temperature solvothermal reaction at 120 °C for 15 min, it was naturally cooled to room temperature to obtain a light yellow suspension. (3) The pale yellow suspension obtained in step (2) was washed three times each by centrifugation with N,N-dimethylformamide and acetone, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain Ce-BDC solid.

[0036] (4) Mix the Ce-BDC solid obtained in step (3) with urea and put them into a mortar and grind them mechanically for 10 min to obtain a uniform powder mixture.

[0037] (5) Disperse the powder mixture obtained in step (4) in a ceramic boat, place it in a muffle furnace, and calcine it at a rate of 5 °C / min to 400 °C in an air atmosphere, and then at a rate of 2 °C / min to 700 °C for 3 h. After the calcination is completed, allow it to cool naturally to room temperature to obtain the oxygen-rich vacancy porous CeO2 photocatalyst.

[0038] The oxygen-rich vacancy porous CeO2 catalyst can be prepared using the above-described method. It should be noted that different ratios of urea and Ce-BDC solid have different effects on the final CeO2 prepared. Therefore, the present invention provides the following Examples 1-3 and Comparative Example 1.

[0039] Example 1 The preparation method of oxygen-rich vacancy porous CeO2-0.05U material by solvothermal method is as follows: (1) Accurately weigh 0.354 g of terephthalic acid and put it into a heat-resistant glass bottle containing 12 mL of N,N-dimethylformamide. After ultrasonic treatment for 30 min, a uniformly dispersed transparent solution is obtained. Then, 1.168 g of cerium ammonium nitrate solid dissolved in 4 mL of deionized water is added dropwise to the heat-resistant glass bottle to obtain an orange-red mixed solution. (2) The heat-resistant glass bottle containing the orange-red mixed solution obtained above was sealed and placed in an oven. After a constant temperature solvothermal reaction at 120°C for 15 min, it was naturally cooled to room temperature to obtain a pale yellow suspension. (3) The pale yellow suspension was washed three times each by centrifugation with N,N-dimethylformamide and acetone, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain 0.44 g Ce-BDC solid.

[0040] (4) Mix the obtained 0.44 g Ce-BDC solid and 0.05 g urea in a mortar and grind mechanically for 10 min to obtain a uniform powder mixture.

[0041] (5) The obtained powder mixture was dispersed in a ceramic boat and placed in a muffle furnace. Under an air atmosphere, the temperature was first raised to 400 ℃ at a rate of 5 ℃ / min, and then raised to 700 ℃ at a rate of 2 ℃ / min for 3 h. After the calcination was completed, the mixture was allowed to cool naturally to room temperature to obtain 0.19 g of oxygen-rich vacancy porous CeO2-0.05U photocatalyst.

[0042] Example 2 The preparation method of oxygen-rich vacancy porous CeO2-0.5U material by solvothermal method is as follows: (1) Accurately weigh 0.354 g of terephthalic acid and put it into a heat-resistant glass bottle containing 12 mL of N,N-dimethylformamide. After ultrasonic treatment for 30 min, a uniformly dispersed transparent solution is obtained. Then, 1.168 g of cerium ammonium nitrate solid dissolved in 4 mL of deionized water is added dropwise to the heat-resistant glass bottle to obtain an orange-red mixed solution. (2) The heat-resistant glass bottle containing the orange-red mixed solution obtained above was sealed and placed in an oven. After a constant temperature solvothermal reaction at 120°C for 15 min, it was naturally cooled to room temperature to obtain a pale yellow suspension. (3) The pale yellow suspension was washed three times each by centrifugation with N,N-dimethylformamide and acetone, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain 0.44 g Ce-BDC solid.

[0043] (4) Mix the obtained 0.44 g Ce-BDC solid and 0.5 g urea in a mortar and grind mechanically for 10 min to obtain a uniform powder mixture.

[0044] (5) The obtained powder mixture was dispersed in a ceramic boat and placed in a muffle furnace. Under an air atmosphere, the temperature was first raised to 400 ℃ at a rate of 5 ℃ / min, and then raised to 700 ℃ at a rate of 2 ℃ / min for 3 h. After the calcination was completed, the mixture was allowed to cool naturally to room temperature to obtain 0.19 g of oxygen-rich vacancy porous CeO2-0.5U photocatalyst.

[0045] Example 3 The preparation method of oxygen-rich vacancy-rich porous CeO2-4U material by solvothermal method is as follows: (1) Accurately weigh 0.354 g of terephthalic acid and put it into a heat-resistant glass bottle containing 12 mL of N,N-dimethylformamide. After ultrasonic treatment for 30 min, a uniformly dispersed transparent solution is obtained. Then, 1.168 g of cerium ammonium nitrate solid dissolved in 4 mL of deionized water is added dropwise to the heat-resistant glass bottle to obtain an orange-red mixed solution. (2) The heat-resistant glass bottle containing the orange-red mixed solution obtained above was sealed and placed in an oven. After a constant temperature solvothermal reaction at 120°C for 15 min, it was naturally cooled to room temperature to obtain a pale yellow suspension. (3) The pale yellow suspension was washed three times each by centrifugation with N,N-dimethylformamide and acetone, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain 0.44 g Ce-BDC solid.

[0046] (4) Mix the obtained 0.44 g Ce-BDC solid and 4 g urea in a mortar and grind mechanically for 10 min to obtain a uniform powder mixture.

[0047] (5) The obtained powder mixture was dispersed in a ceramic boat and placed in a muffle furnace. Under an air atmosphere, the temperature was first raised to 400 ℃ at a rate of 5 ℃ / min, and then raised to 700 ℃ at a rate of 2 ℃ / min for 3 h. After the calcination was completed, the mixture was allowed to cool naturally to room temperature to obtain 0.19 g of oxygen-rich vacancy porous CeO2-4U photocatalyst.

[0048] Comparative Example 1 The preparation method of ordinary CeO2-0U material without urea addition is as follows: (1) Accurately weigh 0.354 g of terephthalic acid and put it into a heat-resistant glass bottle containing 12 mL of N,N-dimethylformamide. After ultrasonic treatment for 30 min, a uniformly dispersed transparent solution is obtained. Then, 1.168 g of cerium ammonium nitrate solid dissolved in 4 mL of deionized water is added dropwise to the heat-resistant glass bottle to obtain an orange-red mixed solution. (2) The heat-resistant glass bottle containing the orange-red mixed solution obtained above was sealed and placed in an oven. After a constant temperature solvothermal reaction at 120°C for 15 min, it was naturally cooled to room temperature to obtain a pale yellow suspension. (3) The pale yellow suspension was washed three times each by centrifugation with N,N-dimethylformamide and acetone, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain 0.44 g Ce-BDC solid.

[0049] (4) The obtained 0.44 g Ce-BDC solid was placed in a mortar and mechanically ground for 10 min to obtain a uniform powder.

[0050] (5) Disperse the obtained powder in a ceramic boat, place it in a muffle furnace, and calcine it at a rate of 5 °C / min to 400 °C in an air atmosphere, and then at a rate of 2 °C / min to 700 °C for 3 h. After the calcination, allow it to cool naturally to room temperature to obtain 0.20 g of ordinary CeO2-0U photocatalyst.

[0051] Figure 1 The images show the XRD patterns of the CeO2 samples from Examples 1 to 3 and Comparative Example 1. It can be seen that all four samples exhibit the cubic fluorite CeO2 crystal phase, indicating that urea modification did not change the crystal structure of CeO2. That is, no new diffraction peaks appeared in CeO2, nor did a crystal form transformation occur, demonstrating that the introduction of urea did not alter the main crystal phase of CeO2. This is because urea does not primarily function by changing the CeO2 crystal phase. In fact, in this invention, the CeO2 sample after the co-reaction of urea and the precursor Ce-BDC solid functions by regulating the pore structure, particle size, and surface defect state of the CeO2 material. This allows for performance improvement while maintaining crystal structure stability, such as increasing oxygen vacancy concentration and specific surface area. See subsequent sections for details.

[0052] Table 1: Comparison of specific surface area, pore volume, and pore size results for CeO2 samples

[0053] Figure 2The N2 adsorption-desorption curves of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1 are shown. Figure 2 A) and aperture distribution map ( Figure 2 B). Table 1 shows the specific surface area, pore volume, and pore size results for four CeO2 samples. (Combined with...) Figure 2 As shown in Table 1, the porosity effect generated by the decomposition of urea and Ce-DBC significantly increased the specific surface area, pore volume, and pore size of CeO2. The CeO2 sample in Example 3 had the largest specific surface area, pore volume, and pore size, followed by the pore size in Example 2, and then the specific surface area and pore volume in Example 1. The sample in Example 2 had a higher number of mesopores, which provided more active sites for the catalytic reaction and promoted charge transport. Although the CeO2 sample in Example 3 had the largest specific surface area, pore volume, and pore size, its hydrophilicity was too strong. Excessive water molecule adsorption would compete with the reactants toluene and O2, thus reducing catalytic performance. Overall, the CeO2 sample in Example 2 showed the best performance.

[0054] Figure 3 These are the Raman spectra of the CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1. Figure 3 A) and oxygen vacancy concentration map ( Figure 3 B). For example... Figure 3 As shown in A, at 462, 600, and 1169 cm... -1 The peaks observed at these locations are attributed to the F-type symmetric stretching vibrations of Ce-O-Ce. 2g Mode, defect vibration mode (D) and second-order longitudinal optical phonon mode (2LO), according to ( I D + I 2LO ) / I F2g The peak intensity ratio was calculated. Figure 3 B indicates that urea treatment promotes Ce. 3+ - Formation of oxygen vacancy pairs Figure 3 Examples 1-3 in A are at 600 cm -1 The defect peaks at each location are higher than those in Comparative Example 1, combined with Figure 2 As shown in Table 1, urea promotes the formation of oxygen vacancies, indicating that there is a high concentration of oxygen vacancies and defect sites in the CeO2 material. Figure 3 Examples 1-3 in A are at 1169 cm -1 The peaks at these locations were also higher than those in Comparative Example 1, which also indicates an increase in oxygen vacancy concentration. According to ( I D + I 2LO ) / I F2g The peak intensity ratio was calculated. Figure 3 B, Figure 3 The highest value was found in Example 2 of B, indicating the highest increase in defect sites and oxygen vacancy concentrations in the material, which also demonstrates that urea treatment promoted Ce. 3+ - The formation of oxygen vacancy pairs improves the oxygen migration ability and surface activity of the material.

[0055] This shows that, in combination Figure 2 As shown in Table 1, the decomposition of urea and Ce-DBC does indeed bring more oxygen vacancies to CeO2. Specifically, compared with Comparative Example 1, the oxygen vacancies in Examples 1-3 are at least 1.2 times higher, with the CeO2-0.5U catalyst in Example 2 having an even higher oxygen vacancy concentration, up to at least 1.5 times, which is beneficial for the adsorption, activation and conversion of toluene and O2.

[0056] Figure 4 These are water contact angle diagrams for samples from Examples 1 to 3 and Comparative Example 1. It was found that the hydrophilicity of the CeO2-xU catalyst gradually increased with the increasing amount of urea inducer added to the precursor. The CeO2-0.5U catalyst in Example 2 exhibited moderate hydrophilicity, readily adsorbing H2O onto its surface, promoting the generation of reactive oxygen free radicals, which is beneficial for the photo-oxidation of toluene. However, the CeO2-4U catalyst was too hydrophilic, leading to the occupation and coverage of reactive sites, thus reducing catalytic efficiency.

[0057] Figure 5 These are the bandgap energy spectra of the samples from Examples 1 to 3 and Comparative Example 1. Figure 5 A) and EIS ( Figure 5 B) Spectrum. From Figure 5 As can be seen from A, the band gap of CeO2-0.5U (3.06 eV) is significantly narrower than that of CeO2-0.05U (3.12 eV), CeO2-4U (3.16 eV) and CeO2-0U (3.17 eV), which shortens the charge transport path and suppresses the recombination of photogenerated carriers. Figure 5 B shows that the CeO2-0.5U catalyst has lower charge resistance, which effectively promotes the separation and transfer of photogenerated charges, allowing more effective photogenerated electrons and holes to participate in the photo-oxidation of toluene, thus exhibiting highly efficient deep toluene oxidation performance.

[0058] The present invention also provides the application of oxygen-rich vacancy porous CeO2 material prepared according to the preparation method of the present invention in photocatalytic oxidation of VOCs.

[0059] Furthermore, the application of oxygen-vacancy-rich porous CeO2 materials in the photocatalytic oxidation of VOCs involves the following steps: (1) Weigh the photocatalyst sample, disperse it evenly on a 400-mesh sieve, and place it in a sealed reactor with a quartz open window at the top; (2) A mixture of 50% RH and 20 ppm toluene / air was continuously introduced into the reactor at a flow rate of 50 mL / min. After dark treatment for 40 min to reach the toluene adsorption-desorption equilibrium state, a 280 W xenon lamp was turned on to carry out the photocatalytic reaction.

[0060] The CeO2 materials prepared in Examples 1-3 and Comparative Example 1 were applied to the photocatalytic oxidation of toluene. The experimental steps were as follows: The photocatalytic oxidation of toluene was tested in a continuous flow reactor. 50 mg of photocatalyst sample was weighed, uniformly dispersed on a 400-mesh sieve, and placed in a 650 mL stainless steel reactor. A stainless steel lid with a 4.5 cm diameter quartz window was placed on top. A toluene / air mixture of 20 ppm (50% RH, controlled by the proportion of water vapor introduced into the reactor via high-purity air bubbling) was continuously introduced into the reactor at a flow rate of 50 mL / min. After a 40-min dark treatment to reach toluene adsorption-desorption equilibrium, a 280 W xenon lamp was turned on to initiate the photocatalytic reaction. The reaction times for activity, cycle life, and lifetime tests were 1 h and 12 h, respectively. The products were analyzed periodically (10 min) by an online gas chromatograph (GC-7920). The toluene conversion rate and toluene mineralization rate were calculated using the following formula: (1) (2) In the formula: [Toluene]in and [Toluene]out are the toluene concentrations (ppm) at the reactor inlet and outlet, respectively, and [CO2]out is the CO2 concentration (ppm) at the reactor outlet.

[0061] Figure 6 Figure AB shows the catalytic oxidation performance of CeO2 samples prepared in Examples 1 to 3 and Comparative Example 1 under full-spectrum irradiation for 1 h. It was found that the conversion rate and mineralization rate of photocatalytic oxidation of toluene by urea-modified CeO2-0.5U (85%, 81%), CeO2-4U (81%, 75%), and CeO2-0.05U (76%, 61%) were significantly higher than those of CeO2-0U (61%, 54%). Among them, the conversion rate and mineralization rate of photocatalytic oxidation of toluene by CeO2-0.5U sample in Example 2 were at least 50% higher than those in Comparative Example 1. Figure 6 C represents the 12-hour lifetime result of the CeO2-0.5U sample for photocatalytic oxidation of toluene. Its conversion rate of toluene remained at around 85%, while the toluene mineralization rate decreased slightly to 76%. Overall, the CeO2-0.5U catalyst exhibits good stability. Figure 6D is the result of three cycles of photocatalytic oxidation of toluene using the CeO2-0.5U sample, which further illustrates the excellent photochemical stability and reusability of CeO2-0.5U in Example 2.

[0062] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing an oxygen-rich vacancy porous CeO2 material, characterized in that, The preparation method is as follows: A suspension was obtained by mixing a terephthalic acid solution dissolved in N,N-dimethylformamide and an aqueous solution of cerium ammonium nitrate, followed by a solvothermal reaction. The suspension was cooled, centrifuged, washed, and vacuum dried to obtain the precursor Ce-BDC solid. The precursor Ce-BDC solid and urea are mixed, and after grinding, calcination and cooling, CeO2 photocatalytic material is obtained. The mass ratio of urea to the precursor Ce-BDC solid is (0.1~12):

1.

2. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 1, characterized in that, The molar ratio of terephthalic acid to cerium ammonium nitrate is 1:

1.

3. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 2, characterized in that, The mass ratio of urea to the precursor Ce-BDC solid is (0.5~3):

1.

4. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 3, characterized in that, The mass ratio of urea to the precursor Ce-BDC solid is (1-1.5):

1.

5. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 1, characterized in that, In the solvothermal reaction, the temperature is at least 120 °C and the thermal reaction time is at least 15 min.

6. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 1, characterized in that, In the centrifugal washing process, the washing solvents are N,N-dimethylformamide and acetone, and the centrifugal washing is performed at least 3 times.

7. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 1, characterized in that, In the vacuum drying process, the vacuum drying temperature is at least 80 °C and the drying time is at least 12 h.

8. The method for preparing oxygen-rich vacancy porous CeO2 material according to claim 1, characterized in that, In the roasting process, the roasting method is segmented roasting, and the atmosphere for segmented roasting is air; The first stage of roasting was at a temperature of 400 ℃ with a heating rate of 5 ℃ / min. The second stage of roasting was at a temperature of 700 ℃ with a heating rate of 2 ℃ / min and a roasting time of 3 h.

9. A CeO2 catalyst prepared by the method for preparing oxygen-rich vacancy porous CeO2 material according to any one of claims 1-8.

10. The application of the CeO2 catalyst according to claim 8 in the photocatalytic oxidation of VOCs.

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