TiO2 / CeO2 S-type heterojunction photocatalytic material with high {001} active crystal face exposure ratio as well as preparation method and application of TiO2 / CeO2 S-type heterojunction photocatalytic material

Abstract

The invention relates to the technical field of UDMH degradation, and particularly provides a TiO2 / CeO2S type heterojunction photocatalytic material with a {001} active crystal face high exposure ratio as well as a preparation method and application of the TiO2 / CeO2S type heterojunction photocatalytic material. The catalytic material is synthesized through a solvent hydrothermal-photo-assisted method, by means of the crystal face effect and the synergistic effect of S-type heterojunction, the absorption range of visible light by the catalyst is effectively widened, rapid separation and migration of photon-generated carriers are promoted, then the oxidation-reduction capacity of the photocatalyst is remarkably enhanced, and the photocatalytic performance of the photocatalyst is greatly improved. The preparation method is simple, the prepared photocatalyst can efficiently catalyze and degrade unsymmetrical dimethylhydrazine wastewater, generated high-toxicity intermediate products can be effectively removed, deep purification treatment of the unsymmetrical dimethylhydrazine wastewater is achieved, and the photocatalyst has important reference value for promoting wastewater treatment in the aerospace field.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a TiO2 / CeO2S type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal facets, its preparation method, and its application. Background Technology

[0002] Unsymmetrical dimethylhydrazine (UDMH), a typical high-energy liquid propellant, is widely used in the aerospace field. It is highly toxic and carcinogenic, and its oxidation process produces hundreds of toxic derivatives, such as N-nitrosodimethylamine (NDMA) and unsymmetrical hydrazone (FDMH), posing a serious threat to ecosystems and human health. To achieve deep purification of UDMH wastewater, its toxic derivatives must be completely mineralized into final products such as CO2 and H2O to eliminate environmental risks. Currently, the efficient removal of highly toxic intermediate products generated during UDMH degradation is a key challenge in UDMH treatment.

[0003] Photocatalysis, as an environmentally friendly and safe purification technology, has shown significant advantages in the treatment of organic pollutants in water. TiO2, with its non-toxic properties, cost-effectiveness, and controllable morphology, shows broad application prospects in photocatalytic pollution control. The efficiency of photocatalytic reactions is closely related to the specific crystal planes exposed on the material surface. Different atomic arrangements on different crystal planes lead to different atomic states, energy levels, and surface energies, thus affecting photocatalytic performance. The surface energy of each low-index crystal plane of anatase TiO2 is {001}(0.90 J / m²). 2 )>{100}(0.53J / m 2 )>{101}(0.44J / m 2 In the order of ), the {101} crystal plane of anatase TiO2 has the lowest surface energy (0.44 J / m). 2 Due to its better kinetic stability, it easily forms a truncated octahedral bipyramidal structure dominated by the {101} crystal plane. In contrast, the {001} crystal plane has a higher surface energy (0.90 J / m²). 2 The poor thermodynamic properties of anatase TiO2 make it difficult to achieve a high proportion of {001} crystal facet exposure. The {001} crystal facet of anatase TiO2 can enrich photogenerated holes, playing a crucial role in the selective separation of photogenerated electrons and holes, and possessing excellent potential reactivity. Therefore, synthesizing a TiO2 with a high exposure ratio of {001} active crystal faces has significant application prospects.

[0004] However, single-phase TiO2 is limited by its narrow spectral response range and insufficient separation efficiency of internal photogenerated carriers, resulting in less than ideal photocatalytic activity. Constructing heterojunction systems is considered an effective solution. S-type heterojunction systems, due to their unique charge transfer pathways, can effectively quench electron-hole pairs with weak redox capabilities while retaining holes with strong oxidizing power and electrons with strong reducing power, thus significantly improving the system's redox capacity. CeO2 possesses a unique 4f electronic structure and abundant surface oxygen defects; CeO2 contains Ce... 4+ / Ce 3+ Redox pairs can serve as excellent charge transfer mediators, effectively regulating the generation process of reactive oxygen species. TiO2 and CeO2 possess suitable band structures. Particularly noteworthy is that when {001}-faceted TiO2 and CeO2 are coupled to construct an S-type heterojunction, not only can the spectral absorption range be broadened and carrier separation efficiency improved, but a high redox potential can also be obtained. Therefore, constructing a TiO2 / CeO2 S-type heterojunction photocatalytic nanomaterial with synergistic crystal facet effects is of great significance to the development of photocatalysis technology.

[0005] There are currently some methods for preparing TiO2 / CeO2 heterojunction photocatalysts, but some shortcomings still exist.

[0006] Prior art document 1 (publication number: CN110605111A) discloses an invention entitled "A CeO2 / TiO2 heterojunction micro / nanomaterial and its preparation method and application". The CeO2 / TiO2 heterojunction micro / nanomaterial provided by this invention has a micron-scale microsphere structure, in which nano-sized CeO2 is loaded on TiO2 sheets, and numerous nano-sized TiO2 sheets aggregate to form a spherical structure with a micron size.

[0007] However, this invention has a significant limitation: its TiO2 sheets do not achieve selective exposure of the {001} crystal plane. This defect directly affects the photocatalytic performance of the material, resulting in unsatisfactory photocatalytic degradation effects. After 120 minutes of simulated visible light irradiation, the degradation rate of methyl orange by this material was only 51.7%, indicating that its photocatalytic efficiency in practical applications still has considerable room for improvement.

[0008] Prior art document 2 (publication number: CN118079892A) discloses an invention entitled "A Composite Photocatalytic Material and Its Preparation Method and Application". The composite photocatalytic material involved in this invention is a supported three-dimensional core-shell structure CC / TiO2 NRs@CeO2 NPs, which is a type II heterojunction. Under simulated sunlight irradiation test conditions, the CC / TiO2 NRs@CeO2 NPs in prior art document 2 achieved a degradation rate of 97.5% for unsymmetrical dimethylhydrazine (UDMH) within 210 min, which is a relatively long time required for the degradation process.

[0009] Furthermore, this invention has significant limitations: it only limits the research scope to the primary degradation process of unsymmetrical dimethylhydrazine (UDMH), and lacks in-depth and systematic research on the conversion mechanism and degradation efficiency of its highly toxic intermediate products—N-nitrosodimethylamine (NDMA) and unsymmetrical hydrazone (FDMH). At the same time, the mineralization degree of UDMH has not been systematically studied, resulting in the failure to achieve deep purification treatment of UDMH wastewater, which poses potential environmental risks in practical applications. Summary of the Invention

[0010] To comprehensively address the aforementioned issues, this invention proposes a TiO2 / CeO2S heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces and its preparation method. This addresses the problems of low visible light catalytic efficiency and poor pollutant degradation performance of existing photocatalytic materials. In particular, it relates to the application of this composite material for the deep purification of unsymmetrical dimethylhydrazine wastewater, which can compensate for the shortcomings of existing technologies and contribute a practical and feasible strategy to solving environmental pollution problems.

[0011] The TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal facet prepared in this invention can effectively promote the spatial separation and transfer of photogenerated carriers and the interaction between photogenerated holes and O2 under the synergistic effect of crystal facet modulation and S-type heterojunction. - The main active species with strong oxidizing properties can directly oxidize organic pollutant molecules and mineralize them into water molecules and carbon dioxide. The developed photocatalytic system not only has the ability to efficiently photocatalytically degrade unsymmetrical dimethylhydrazine (UDMH), but can also carry out deep mineralization treatment of the highly toxic intermediate products generated during its degradation process, thereby achieving deep purification of unsymmetrical dimethylhydrazine (UDMH) wastewater.

[0012] To achieve the above objectives, the first aspect of the present invention provides a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces, comprising: a TiO2 / CeO2 S-type heterojunction with a high exposure ratio of {001} active crystal faces.

[0013] The second aspect of this invention provides a method for preparing a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces, comprising:

[0014] Step 1: Using titanium tetrafluoride, tetrabutyl titanate and tert-butanol as raw materials, TiO2 nanosheets with high exposure ratio of {001} active crystal facets were prepared by hydrothermal method.

[0015] Step 2: Using TiO2 nanosheets, cerium nitrate hexahydrate and triethanolamine as raw materials, a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal facets was prepared by a photo-assisted method.

[0016] Preferably, step 1 includes:

[0017] Step 1.1: Add titanium tetrafluoride and tetrabutyl titanate to tert-butanol solution and stir to obtain a uniform milky white solution. Then transfer this solution to a hydrothermal reactor for reaction.

[0018] Step 1.2: After the reaction is complete, let the hydrothermal reactor cool naturally to room temperature, then remove the product for separation, washing and drying to obtain a white solid;

[0019] Step 1.3: The white solid from Step 1.2 is soaked in NaOH solution to remove residual fluorine on the surface. The product is taken out, separated, washed, dried in an oven and ground. The white powder obtained is TiO2 nanosheets with a high exposure ratio of {001} active crystal faces, denoted as 001-TiO2.

[0020] Preferably, step 2 includes:

[0021] Step 2.1: Weigh 001-TiO2 and cerium nitrate hexahydrate into a beaker, add deionized water and triethanolamine, and disperse by ultrasonication to form a uniform suspension;

[0022] Step 2.2: Transfer the suspension to a quartz glass reactor, place it on a photocatalytic degradation reaction platform, and irradiate it with ultraviolet light.

[0023] Step 2.3: After the reaction is complete, the solid product is collected by vacuum filtration and dried to obtain the precursor; the precursor is calcined and cooled to room temperature in the furnace.

[0024] Step 2.4: The calcined product is washed repeatedly with deionized water and anhydrous ethanol to remove residual impurities. After drying, it is ground into a uniform powder to obtain the target product, a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal face, denoted as 001-TiO2 / CeO2.

[0025] Preferably, the hydrothermal reaction in step 1.1 is carried out at a temperature of 200–300°C for 240–360 min.

[0026] Preferably, in step 1.1, the total molar concentration of titanium in the solution is 0.05 mol / L to 0.5 mol / L, and the molar ratio of titanium tetrafluoride to tetrabutyl titanate is 2:1 to 1:4.

[0027] Preferably, the molar ratio of 001-TiO2 to cerium nitrate hexahydrate is 7:1 to 1:1.

[0028] Preferably, the ultraviolet light wavelength in step 2.2 is between 200 nm and 380 nm; the calcination temperature in step 2.3 is between 400 °C and 600 °C, and the reaction time is between 6 and 12 h.

[0029] A third aspect of the present invention provides the use of the S-type 001-TiO2 / CeO2 heterojunction photocatalyst as described above for the preparation of unsymmetrical dimethylhydrazine degradation catalysts.

[0030] Preferred methods include:

[0031] S1: Prepare 40 ml of unsymmetrical dimethylhydrazine wastewater with a concentration of 100 mg / L to 110 mg / L;

[0032] S2: Add 2g of TiO2 / CeO2 S-type heterojunction photocatalyst material with high exposure ratio of {001} active crystal face to unsymmetrical dimethylhydrazine wastewater in S1, and place it in a light-proof reaction chamber for static reaction for 20min;

[0033] S3: Using a xenon lamp light source, place the quartz tube 10cm away from the light source to start the photocatalytic reaction.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention utilizes a hydrothermal method to prepare TiO2 nanosheets with a high exposure ratio of the {001} active crystal facets. It has the following advantages:

[0036] In the field of photocatalysis research, the preparation of TiO2 nanosheets with highly exposed (001) crystal planes, which possess both structural stability and excellent photocatalytic performance, is currently a hot topic. In traditional preparation methods, hydrofluoric acid is often used as a capping agent to promote a high proportion of exposure of the (001) crystal planes of TiO2. However, hydrofluoric acid is highly toxic and its use carries a high risk. Although existing technologies have developed a series of hydrothermal and solvothermal (ethanol or isopropanol) systems for preparing such TiO2 nanosheets, problems such as high risk, complex preparation processes, and unsatisfactory product morphology still exist.

[0037] (1) Innovative raw material and solvent system: This invention is the first to use tert-butanol as a solvent to prepare anatase TiO2 nanosheets using titanium tetrafluoride and tetrabutyl titanate as raw materials. The resulting product has a regular morphology, high purity, large size, good dispersibility, and extremely high (001) crystal plane exposure ratio. This preparation method is efficient, safe, highly reproducible, and easy to operate, and has the potential for large-scale industrial production.

[0038] (2) Synergistic advantages of solvent and titanium source: Compared with solvents such as water, isopropanol, and cyclohexanol used in traditional methods, the low polarity of tert-butanol used in this invention is more conducive to the stable existence of the (001) crystal plane. Titanium tetrafluoride can be used as both a partial titanium source and a structure control agent for TiO2 nanosheets. Compared with hydrofluoric acid, it has the advantages of low toxicity and mild reaction conditions. The synergistic effect of the dual titanium source system composed of titanium tetrafluoride and tetrabutyl titanate can effectively increase the exposure ratio of the (001) crystal plane of TiO2 nanosheets.

[0039] (3) Excellent photocatalytic performance: Benefiting from the unique structural advantage of the high exposure ratio of the (001) crystal facet, the TiO2 nanosheets combined with CeO2, as a photocatalytic material, exhibit excellent performance in the photocatalytic degradation of unsymmetrical dimethylhydrazine (UDMH). When the molar ratio of 001-TiO2 to CeO2 is 3:1, the photocatalytic degradation activity of UDMH is optimal, with a degradation rate as high as 98.4%. In addition, the 001-TiO2 / CeO2-3:1 photocatalyst exhibits long-lasting cycling stability during the photocatalytic process.

[0040] 2. This invention successfully prepared a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal facet. It has the following advantages:

[0041] (1) The interfacial bonding strength is high, forming an S-shaped heterostructure.

[0042] Existing TiO2 / CeO2 composite materials are mostly prepared by impregnation or mechanical mixing methods. CeO2 particles are physically adsorbed onto the TiO2 surface, resulting in weak interfacial bonding, easy detachment, low charge transfer efficiency, and the resulting heterojunction composites are mostly traditional type II heterojunctions. This invention employs a solvent hydrothermal-photoassisted method. First, TiO2 nanosheets with a high (001) crystal plane exposure ratio are prepared using a solvent hydrothermal method. Then, a 001-TiO2 / CeO2 S-type heterojunction is prepared using a photoassisted method. Under ultraviolet light excitation, 001-TiO2 generates photogenerated electrons and holes. Triethanolamine (TEA) acts as a sacrificial agent to capture the photogenerated holes, promoting the photogenerated electrons to transfer CeO2 particles from the solution. 3+ The particles are reduced to CeO2 nanoparticles, which directly nucleate on the surface of TiO2 nanosheets, forming Ti-O-Ce chemical bonds with tight interfacial bonding. The heterojunction structure after calcination is stable, with no particle agglomeration or detachment.

[0043] (2) Synergistic effect of crystal plane manipulation and S-type heterostructure

[0044] The 001-TiO2 / CeO2 S-type heterojunction composite photocatalyst material synthesized by a solvothermal-photoassisted method retains the morphological characteristics and advantageous crystal facet exposure of 001-TiO2 while forming a rich TiO2-CeO2 heterointerface. Based on this, the 001-TiO2 / CeO2 S-type heterojunction composite material prepared in this invention achieves efficient separation and directional migration of photogenerated charges through a synergistic strategy of crystal facet manipulation and S-type heterojunction. This strategy extends the lifetime of photogenerated carriers, optimizes the interfacial charge transport path, and enables high-throughput photogenerated charges to overcome the limitations of bulk recombination and rapidly migrate to the catalyst surface to participate in the photocatalytic reaction, thus exhibiting excellent photocatalytic activity.

[0045] (3) Expand the light response range to the visible light region

[0046] Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) shows that the light absorption edge of the composite material is redshifted to 650 nm, extending the absorption wavelength of the photocatalyst into the visible light region and achieving a broad-spectrum response characteristic matching the solar spectrum. Simultaneously, it forms a trapping center for photogenerated electrons, exhibiting high separation efficiency between photogenerated electrons and holes. This enhancement effect originates from the formation of new Ti-O-Ce bonds after composite formation, introducing Ce 4f energy levels into the conduction band (CB) and valence band (VB) of TiO2.

[0047] 3. The TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal facets of this invention is used for the deep purification of UDMH wastewater. It has the following advantages:

[0048] Previous inventions related to UDMH wastewater treatment have only focused on the primary degradation efficiency of UDMH, without systematically studying the transformation mechanism and mineralization process of its highly toxic intermediate products (such as FDMH and NDMA). This application, based on the study of UDMH primary degradation efficiency, aims to achieve deep purification of UDMH wastewater and has developed a 001-TiO2 / CeO2 S-type heterojunction composite photocatalytic material. Solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and high-performance liquid chromatography (HPLC) are used to qualitatively and quantitatively analyze the highly toxic intermediate products FDMH and NDMA, and promote their complete mineralization into final products such as CO2 and H2O, thereby completely eliminating environmental risks. This is something that previous inventions related to UDMH wastewater treatment have not addressed. Attached Figure Description

[0049] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0050] In the attached diagram:

[0051] Figure 1001-TiO2 / CeO2 sample preparation process schematic diagram;

[0052] Figure 2 TEM image of the product prepared in the example of this invention;

[0053] Figure 3 Nitrogen adsorption-desorption isotherms and pore size distribution of the products prepared in the examples of this invention.

[0054] Figure 4 XRD patterns of the products prepared in the examples of this invention;

[0055] Figure 5 XPS spectra of the products prepared in the examples of this invention;

[0056] Figure 6 (a) Transient photocurrent response (It curve); (b) Electrochemical impedance spectroscopy; (c) Steady-state photocurrent spectrum; (d) Fluorescence lifetime spectrum of the products prepared in this invention example;

[0057] Figure 7 A graph showing the photocatalytic degradation curve of UDMH by the product prepared in the example of this invention;

[0058] Figure 8 A graph showing the TOC treatment effect of the product prepared in this invention example;

[0059] Figure 9 GC-MS analysis results and degradation effect diagram of FDMH and NDMA;

[0060] Figure 10 The UV-vis spectrum of the product prepared in the example, (αhν) 1 / 2 vs. hν curve. Detailed Implementation

[0061] The following combination Figures 1-10 The preferred embodiments of the present invention will be described herein. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0062] Example 1:

[0063] A TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces, comprising: a TiO2 / CeO2 S-type heterojunction with a high exposure ratio of {001} active crystal faces.

[0064] Example 2:

[0065] like Figure 1A method for preparing a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces, comprising:

[0066] Step 1: Using titanium tetrafluoride and tetrabutyl titanate as raw materials, TiO2 nanosheets with high exposure ratio of {001} active crystal faces are prepared by hydrothermal method; specifically including:

[0067] Step 1.1: Add 2.5 ml of titanium tetrafluoride and 12.5 ml of tetrabutyl titanate dropwise to tert-butanol solution to obtain a homogeneous solution. After stirring continuously for 1 hour, transfer the suspension to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene and react at 200°C for 6 hours.

[0068] Step 1.2: After the hydrothermal reactor has cooled to room temperature naturally, filter the mixture and wash it repeatedly with deionized water and anhydrous ethanol. Then, centrifuge it at 6000 r / min for 50 min using a high-speed centrifuge to obtain a white solid.

[0069] Step 1.3: After washing the white solid alternately with deionized water and anhydrous ethanol several times, it was soaked in 1 mol / L NaOH solution for 2 hours to remove residual fluorine on the surface. After washing it alternately with deionized water and anhydrous ethanol again, it was dried in an oven at 80°C and ground. The white powder obtained was TiO2 nanosheets with a high exposure ratio of {001} active crystal faces, denoted as 001-TiO2.

[0070] Step 2: Using 001-TiO2 and cerium nitrate hexahydrate as raw materials, a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal facet was prepared by a photo-assisted method. This includes:

[0071] Step 2.1: Weigh 1.6g of 001-TiO2 and 8.68g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) into a beaker, add 160mL of deionized water and 20mL of triethanolamine (TEA), and disperse by ultrasonication for 30min to form a uniform suspension.

[0072] Step 2.2: Transfer the suspension to a quartz glass reactor, place it on a photocatalytic degradation reaction platform, and irradiate it with ultraviolet light (λ=365nm) for 3h;

[0073] Step 2.3: After the reaction is complete, the solid product is collected by vacuum filtration and dried at 100℃ for 12h to obtain the precursor; the precursor is placed in a crucible and calcined in a muffle furnace at 400℃ for 6h, and then cooled to room temperature with the furnace.

[0074] Step 2.4: The calcined product is washed repeatedly with deionized water and anhydrous ethanol to remove residual impurities. After drying in an oven at 80°C, it is ground into a uniform powder to obtain the target product 001-TiO2 / CeO2, namely TiO2 / CeO2 S-type heterojunction with a high exposure ratio of {001} active crystal plane.

[0075] Furthermore, by adjusting the molar ratio of Ce(NO3)3·6H2O to TiO2 (nCe:nTi), and using a 1:1 molar ratio as the baseline, gradient sample series were designed: 001-TiO2 / CeO2-1:1, 001-TiO2 / CeO2-3:1, 001-TiO2 / CeO2-5:1, and 001-TiO2 / CeO2-7:1.

[0076] Example 3:

[0077] The use of an S-type TiO2CeO2 heterojunction photocatalyst, as described in Example 1, for the preparation of unsymmetrical dimethylhydrazine degradation catalysts.

[0078] Comparative example:

[0079] (1) P25 was purchased from Degussa.

[0080] (2) Preparation of P25 / CeO2: P25 / CeO2 was prepared by photo-assisted method.

[0081] A method for preparing an S-type P25 / CeO2 heterojunction photocatalyst, comprising:

[0082] Step 1: Prepare P25 / CeO2 using a photo-assisted method. This includes:

[0083] Step 1.1: Weigh 1.6g of P25 and 8.68g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) into a beaker, add 160mL of deionized water and 20mL of triethanolamine (TEA), and disperse by ultrasonication for 30min to form a uniform suspension;

[0084] Step 1.2: Transfer the suspension to a quartz glass reactor, place it on a photocatalytic degradation reaction platform, and irradiate it with ultraviolet light (λ=365nm) for 3h;

[0085] Step 1.3: After the reaction is complete, the solid product is collected by vacuum filtration and dried at 100℃ for 12h to obtain the precursor; the precursor is placed in a crucible and calcined in a muffle furnace at 400℃ for 6h, and then cooled to room temperature with the furnace.

[0086] Step 1.4: The calcined product was washed repeatedly with deionized water and anhydrous ethanol to remove residual impurities. After drying in an oven at 80°C, it was ground into a uniform powder to obtain the target product P25 / CeO2, namely P25 / CeO2 heterojunction photocatalyst.

[0087] The accompanying drawings further illustrate how the various embodiments of the present invention embody the purpose of the present invention and achieve its beneficial effects.

[0088] Experimental results and characterization:

[0089] I. TEM test results:

[0090] Please see Figure 2 TEM characterization showed that 001-TiO2 exhibited truncated octahedral ultrathin nanosheets, approximately 3.20 nm thick, with lateral dimensions ranging from 50 to 150 nm. Figure 2 (a) and (b) in 2); the 0.352 nm interplanar spacing in the HRTEM image corresponds to the (101) crystal plane of anatase TiO2, indicating that the synthesis of anatase TiO2 nanosheets with highly exposed (001) crystal planes ( Figure 2 (c) TEM characterization showed that CeO2 consisted of irregular particles with particle sizes ranging from several to tens of nanometers. Figure 2 The HRTEM image (d) shows that the interplanar spacing is 0.311 nm, which matches the cubic CeO2 (111) crystal plane, indicating that the cubic CeO2 nanoparticles were successfully synthesized. Figure 2 (e). HRTEM images of 001-TiO2 / CeO2 show ellipsoidal CeO2 nanocrystals uniformly loaded on the crystal faces and edges of large-sized nanosheets, forming a heterogeneous interface. Figure 2 (f and g in 2); enlarged view of the part ( Figure 2 The two sets of lattice fringes shown in h) correspond to the CeO2 (111) crystal plane at 0.311 nm and the TiO2 (101) crystal plane at 0.351 nm. Figure 2 (i). TEM characterization showed that TiO2 and CeO2 in 001-TiO2 / CeO2 had good crystallization properties, forming a rich TiO2-CeO2 heterostructure interface, and CeO2 modification did not change the morphology of 001-TiO2 or the exposure of the dominant crystal faces.

[0091] II. XRD Analysis and Testing

[0092] Please see Figure 3 The crystal structure of the prepared photocatalyst was analyzed by XRD. Figure 3As shown in Figure a, 001-TiO2 exhibits characteristic diffraction peaks of the (101), (004), and (200) crystal planes of anatase TiO2 at 2θ values ​​of 25.3°, 37.5°, and 48.2°, consistent with PDF#21-1272. The sharp peaks and significant intensity indicate high crystallinity. The CeO2 diffraction peaks match those of the cubic CeO2 standard card (PDF#81-0792). 001-TiO2 / CeO2 retains the characteristic diffraction peaks of both 001-TiO2 and CeO2, with no other impurity peaks observed, indicating successful recombination of 001-TiO2 and CeO2. (The magnified local spectrum...) Figure 3 As shown in b), the diffraction peaks of TiO2 and CeO2 in the composite material are slightly shifted compared to the monomer, indicating that there is an electronic interaction between the two phases, forming a strongly coupled heterostructure. Combined with electron microscopy characterization, this proves that the 001-TiO2 / CeO2 heterostructure was successfully constructed.

[0093] III. Nitrogen Adsorption-Desorption

[0094] Please see Figure 4 Nitrogen adsorption-desorption analysis was used to analyze the pore characteristics of the samples. All samples exhibited a type IV isotherm and an H3 hysteresis loop in the relative pressure range of P / P0 = 0.5–0.95, indicating that all four samples contain mesoporous structures. Figure 4 (a) Compared to pure 001-TiO2 and P25, the specific surface area of ​​the CeO2-loaded composite material decreased, which can be attributed to the partial blockage of pores caused by CeO2 nanoparticle deposition on the TiO2 surface. The pore size distribution range of 001-TiO2 / CeO2 and P25 / CeO2 is significantly wider than that of the monomers. This optimization of the mesoporous structure is conducive to the diffusion of reactant molecules, providing a more efficient mass transfer channel for photocatalytic reactions. Figure 4 (b)

[0095] IV. X-ray photoelectron spectroscopy (XPS)

[0096] Please see Figure 5 X-ray photoelectron spectroscopy (XPS) reveals the surface chemical state and interfacial charge transfer behavior of catalysts. Full-spectrum scanning ( Figure 5 (a) shows the coexistence of Ti, O, and Ce elements in the 001-TiO2 / CeO2 sample, and the Ce 3d characteristic peak at 900 eV confirms the effective recombination of CeO2 and TiO2. (Ti 2p high-resolution spectrum) Figure 5 In (b), 001-TiO2 is at 458.5 eV (Ti 2p). 3 / 2 ) and 464.4 eV (Ti2p 1 / 2 The characteristic peaks indicate that Ti atoms are in the form of Ti 4+ Mainly. Ce 3dXPS high-resolution spectrum ( Figure 5c) reveals the chemical state changes of Ce, showing that the Ce 3d orbitals can be further subdivided into 3d orbitals. 5 / 2 and 3D 3 / 2 The two spin-coupled orbitals are identified by ν and μ, respectively, and the μ″,ν″,μ,ν peaks correspond to Ce. 3+ 3D of Species 10 4f 1 The initial electronic configuration, while the remaining μ″″, ν″″, μ″′, ν″′, μ′, ν′ peaks correspond to Ce. 4+ 3D 10 4f 0 Initial electronic configuration, O 1s high-resolution XPS spectrum ( Figure 5 (d) Reveals the distribution of oxygen species on the catalyst surface. The O1s fraction of CeO2 shows characteristic peaks at 529.4 eV and 531.5 eV, corresponding to lattice oxygen (O2) and lattice oxygen (O2) respectively. latt ) and adsorbed oxygen (O ads ).

[0097] V. Fluorescence spectroscopy analysis, photoelectrochemical testing, and surface photovoltage testing

[0098] Please see Figure 6 Fluorescence spectroscopy, photoelectrochemistry, and surface photovoltage measurements provide a concrete view of the carrier generation, separation, migration, and recombination processes within the photocatalyst. Transient photocurrent (It, Figure 6 a) and electrochemical impedance spectroscopy (EIS) Figure 6 Tests in section b) show that the photocurrent density 001-TiO2 / CeO2 > P25 / CeO2 > 001-TiO2 > P25, indicating that crystal plane modulation promotes the separation of photogenerated carriers, and CeO2 loading constructs a heterojunction that enhances interfacial charge separation. EIS shows that the radius of curvature of the Nyquist curve is consistent with the order of photocurrent density, and the 001-TiO2 / CeO2 interface has the lowest charge transfer resistance, allowing photogenerated electrons to migrate rapidly to the interface and participate in the reaction.

[0099] After steady state (PL, Figure 6 c) and transient (TRPL, Figure 6(d) Fluorescence spectroscopy was used to evaluate the photogenerated carrier recombination rate of the samples. PL analysis showed that the fluorescence intensity of 001-TiO2 was significantly lower than that of P25, indicating that crystal facet modulation can effectively suppress electron-hole recombination. After recombination with CeO2, the fluorescence intensity of 001-TiO2 / CeO2 and P25 / CeO2 further decreased, indicating that the heterojunction significantly suppressed carrier recombination, and 001-TiO2 / CeO2 had the highest photogenerated electron-hole separation efficiency. TRPL analysis showed that the average fluorescence lifetime of 001-TiO2 (2.18 ns) was 18% longer than that of P25 (1.85 ns), indicating that high-index crystal facet exposure reduced the photogenerated electron-hole recombination rate. 001-TiO2 / CeO2 had the longest average fluorescence lifetime (2.89 ns) and the slowest decay rate, consistent with the PL analysis results.

[0100] Example 4:

[0101] Because the S-type 001-TiO2 / CeO2 heterojunction photocatalyst has a wide light response range, photocatalytic degradation experiments of unsymmetrical dimethylhydrazine (UDMH) were conducted under simulated solar radiation conditions. The UDMH content was detected using sodium aminoferrocyanide spectrophotometry (GB / T14376-93), and the degradation rate was calculated. The specific experiments are as follows.

[0102] A method for applying a TiO2 / CeO2 S-type heterojunction photocatalyst with a high exposure ratio of {001} active crystal faces to unsymmetrical dimethylhydrazine wastewater treatment:

[0103] S1: Prepare 100 mg / L unsymmetrical dimethylhydrazine wastewater and determine the initial concentration of unsymmetrical dimethylhydrazine using sodium aminoferrocyanide spectrophotometry.

[0104] S2: Take 2.0 g of 001-TiO2 / CeO2-7:1, 001-TiO2 / CeO2-5:1, 001-TiO2 / CeO2-3:1, 001-TiO2 / CeO2-1:1, P25, and P25 / CeO2 prepared in Examples 1-2 and the comparative example, respectively, and add them to a quartz tube containing 40 ml of 100 mg / L unsymmetrical dimethylhydrazine wastewater. Place the tube in a light-protected reaction chamber and let it stand for 30 min. Detect the content of unsymmetrical dimethylhydrazine using sodium aminoferrocyanide spectrophotometry.

[0105] S3: Using a xenon lamp light source, place the quartz tube 10cm away from the light source to begin the photocatalytic reaction. Take samples for analysis every 1 hour, and set the lamp radiation power to 100W / cm². 2 The concentration of unsymmetrical dimethylhydrazine was determined by sodium aminoferrocyanide spectrophotometry.

[0106] During the photocatalytic reaction, samples were taken every 20 minutes for analysis to determine the concentration of unsymmetrical dimethylhydrazine in the wastewater.

[0107] Results analysis:

[0108] 1. Evaluation of photocatalytic performance

[0109] Please see Figure 7 The photocatalytic performance of the prepared materials was evaluated under simulated sunlight irradiation. After 30 min of dark reaction, the UDMH concentration of each sample decreased slightly due to weak adsorption on the sample surface. After 120 min of simulated sunlight irradiation, the degradation rate of P25 was 43.3%, while that of 001-TiO2 increased to 54.7%, attributed to the efficient separation and transfer of photogenerated carriers promoted by crystal facet modulation. The degradation rate of the composite material 001-TiO2 / CeO2-3:1 was as high as 98.4%, while that of P25 / CeO2-3:1 was only 79.8%. Figure 7 (a) The difference stems from the synergistic effect of crystal plane modulation and heterojunction, which promotes the separation and migration of photogenerated carriers, improves quantum efficiency, and enhances photocatalytic activity. The degradation rates of the composite materials 001-TiO2 / CeO2-7:1, 001-TiO2 / CeO2-5:1, 001-TiO2 / CeO2-3:1, and 001-TiO2 / CeO2-1:1 are 82.3%, 90.2%, 98.4%, and 77.4%, respectively, with 001-TiO2 / CeO2-3:1 showing the best activity. With the increase of the CeO2 composite ratio, the photocatalytic activity first increases and then decreases. Figure 7 (b) Figure 7 The results show that the photocatalytic reaction follows first-order kinetics, and the degradation rate constant of 001-TiO2 / CeO2-3:1 is 5.2 and 3.7 times that of P25 and 001-TiO2, respectively. Stability testing ( Figure 7 (d) indicates that after five reuses, the degradation rate of 001-TiO2 / CeO2-3:1 decreased slightly, but it still exhibited excellent reusability, with a UDMH degradation rate of 91.6%.

[0110] 2. Mineralization Capacity Assessment

[0111] Please see Figure 8 Total organic carbon (TOC) analysis was performed on the 001-TiO2 / CeO2-3:1 photocatalytic degradation system for UDMH. After 140 min of photocatalytic reaction, 12.4 mg / L of unoxidized TOC was still detected in the system, with a TOC removal rate of only 65.6%. This indicates that the degradation process of UDMH is accompanied by the generation of various secondary oxidation products. After 300 min of reaction, the TOC decreased to 6.67 mg / L, and the TOC removal rate increased to 84.5%, suggesting that under simulated sunlight, the secondary products can be further mineralized into CO2 and H2O.

[0112] 3. Active species driving the photocatalytic degradation of UDMH

[0113] Please see Figure 9 To assess the completeness of UDMH degradation, qualitative and quantitative analyses were performed on the highly toxic intermediates FDMH and NDMA. Solid-phase microextraction-gas chromatography-mass spectrometry (SPE-GC-MS) was used to analyze the solution after 140 min of reaction. Characteristic peaks were detected at retention times of approximately 5.5 min (m / z = 72, relative content 43.5%) and 9.4 min (m / z = 74, relative content 1.2%), which were confirmed as FDMH by mass spectrometry comparison. Figure 9 a) NDMA Figure 9 (d). Further comparison of retention times between high-performance liquid chromatography (HPLC) and the standard substance confirmed that the intermediate product with m / z = 72 and 74 was FDMH. Figure 9 (b) NDMA Figure 9 (e). HPLC quantitative analysis ( Figure 9 As shown in Figures c and f), the initial UDMH waste liquid contained trace amounts of FDMH and NDMA. With the oxidation and decomposition of UDMH, the concentrations of both first increased and then decreased, with FDMH generation significantly higher than NDMA. The peak concentrations of both occurred around 60 min, and they were essentially completely degraded after 240 min of photocatalytic reaction. This indicates that the developed photocatalytic system can efficiently remove UDMH and deeply mineralize highly toxic intermediates, demonstrating excellent pollutant degradation capabilities.

[0114] 4. Light absorption characteristics and band structure of photocatalysts

[0115] Please see Figure 10 To further investigate the light absorption characteristics and band structure of photocatalysts, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) analysis was performed on the samples, such as... Figure 10 The UV-Vis DRS results showed that P25 and pure 001-TiO2 exhibited significant light absorption only in the ultraviolet region, while the light absorption edge of the 001-TiO2 / CeO2 and P25 / CeO2 composite materials red-shifted to 650 nm, demonstrating a broadened visible light response range. Figure 10 In Figure b, the band gap energies (Eg) of the semiconductors calculated using the Tauc plot method show that the band gap energies of 001-TiO2, CeO2, and 001-TiO2 / CeO2 are 3.15 eV, 2.87 eV, and 2.76 eV, respectively. The results indicate that 001-TiO2 / CeO2 has the lowest band gap value. The synergistic effect of the S-type heterojunction and crystal plane modulation jointly reduces the band gap, making it easier for valence band electrons to be excited to the conduction band and generate photogenerated holes. Strongly oxidizing holes and their solution-derived active substances are the main active species for the photocatalytic degradation of UDMH, which is beneficial for improving photocatalytic performance.

[0116] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces, characterized in that, The composition is: a TiO2 / CeO2 S-type heterojunction with a high exposure ratio of the {001} active crystal plane.

2. The preparation method of a TiO2 / CeO2 S-type heterojunction photocatalytic material with high exposure ratio of {001} active crystal facets as described in claim 1, characterized in that, include Step 1: Using titanium tetrafluoride, tetrabutyl titanate and tert-butanol as raw materials, TiO2 nanosheets with high exposure ratio of {001} active crystal facets were prepared by hydrothermal method. Step 2: Using TiO2 nanosheets, cerium nitrate hexahydrate and triethanolamine as raw materials, a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal facets was prepared by a photo-assisted method.

3. The method for preparing a TiO2 / CeO2S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces according to claim 2, characterized in that, Step 1 includes: Step 1.1: Add titanium tetrafluoride and tetrabutyl titanate to tert-butanol solution and stir to obtain a uniform milky white solution. Then transfer this solution to a hydrothermal reactor for reaction. Step 1.2: After the reaction is complete, let the hydrothermal reactor cool naturally to room temperature, then remove the product for separation, washing and drying to obtain a white solid; Step 1.3: The white solid from Step 1.2 is soaked in NaOH solution to remove residual fluorine on the surface. The product is taken out, separated, washed, dried in an oven and ground. The white powder obtained is TiO2 nanosheets with a high exposure ratio of {001} active crystal faces, denoted as 001-TiO2.

4. The preparation method of a TiO2 / CeO2S-type heterojunction photocatalytic material with high exposure ratio of {001} active crystal facets according to claim 3, characterized in that, Step 2 includes: Step 2.1: Weigh 001-TiO2 and cerium nitrate hexahydrate into a beaker, add deionized water and triethanolamine, and disperse by ultrasonication to form a uniform suspension; Step 2.2: Transfer the suspension to a quartz glass reactor, place it on a photocatalytic degradation reaction platform, and irradiate it with ultraviolet light. Step 2.3: After the reaction is complete, the solid product is collected by vacuum filtration and dried to obtain the precursor; the precursor is calcined and cooled to room temperature in the furnace. Step 2.4: The calcined product is washed repeatedly with deionized water and anhydrous ethanol to remove residual impurities. After drying, it is ground into a uniform powder to obtain the target product, a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of the {001} active crystal face, denoted as 001-TiO2 / CeO2.

5. The method for preparing a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces according to claim 4, characterized in that, The hydrothermal reaction described in step 1.1 is carried out at a temperature of 200–300°C for 240–360 minutes.

6. The method for preparing a TiO2 / CeO2S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces according to claim 5, characterized in that, In step 1.1, the total molar concentration of titanium in the solution is 0.05 mol / L to 0.5 mol / L, and the molar ratio of titanium tetrafluoride to tetrabutyl titanate is 2:1 to 1:

4.

7. The method for preparing a TiO2 / CeO2S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces according to claim 6, characterized in that, The molar ratio of 001-TiO2 to cerium nitrate hexahydrate is 7:1 to 1:

1.

8. The method for preparing a TiO2 / CeO2S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces according to claim 7, characterized in that, The ultraviolet light wavelength mentioned in step 2.2 is between 200 nm and 380 nm; the calcination temperature in step 2.3 is between 400 °C and 600 °C, and the reaction time is between 6 and 12 h.

9. The use of a TiO2 / CeO2 S-type heterojunction photocatalytic material with a high exposure ratio of {001} active crystal faces as described in claim 1 for the preparation of unsymmetrical dimethylhydrazine degradation catalysts.

10. The use of the TiO2 / CeO2 S-type heterojunction photocatalyst material with a high exposure ratio of the {001} active crystal facet according to claim 9 for the preparation of a catalyst for the degradation of unsymmetrical dimethylhydrazine, characterized in that, Specific methods include: S1: Prepare 40 ml of unsymmetrical dimethylhydrazine wastewater with a concentration of 100 mg / L to 110 mg / L; S2: Add 2g of TiO2 / CeO2 S-type heterojunction photocatalyst material with high exposure ratio of {001} active crystal face to unsymmetrical dimethylhydrazine wastewater in S1, and then place it in a light-proof reaction chamber and let it stand for 20min. S3: Using a xenon lamp light source, place the quartz tube 10cm away from the light source to start the photocatalytic reaction.

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