A TiO2@CuO heterojunction containing oxygen vacancies, its preparation method and application

Abstract

This invention belongs to the field of photocatalytic materials technology, specifically referring to a TiO2@CuO heterojunction containing oxygen vacancies, its preparation method, and its applications. It addresses the technical problems of low photocatalytic activity of CuO in the near-infrared light range, high recombination rate of photogenerated carriers, and the complex preparation process of its composite materials. The invention uses Ti3C2T... x Using MXene powder and Cu(CH3COO)2•H2O as precursors, TiO2@CuO heterojunctions were prepared by adding hydrogen peroxide solution to their aqueous solution. These heterojunctions exhibit a certain amount of oxygen vapor content (OVs) and a strong photoresponse to near-infrared light. When used as a photocatalyst, this heterojunction can effectively degrade tetracycline and demonstrates photocatalytic stability. This invention provides a novel strategy for modifying heterojunctions through a one-pot method with mild reaction conditions and a simple preparation method.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically referring to a TiO2@CuO heterojunction containing oxygen vacancies, its preparation method, and its application. Background Technology

[0002] Metal oxides possess controllable structures, favorable surface properties, and high crystallinity, and are easily modified and functionalized, exhibiting strong stability in aqueous solutions. Various types of semiconductor metal oxides have been widely used in photocatalytic materials. Among them, CuO with a narrow bandgap has attracted considerable attention from researchers due to its ability to absorb near-infrared light, non-toxicity, and low raw material cost, making it a crucial photocatalytic semiconductor material. However, its narrow bandgap characteristic results in a high recombination rate of photogenerated electrons and holes under illumination, severely limiting the photocatalytic performance of CuO. To promote the separation of photogenerated carriers and enable it to exhibit certain photodegradation performance in the near-infrared region, modification treatment is necessary.

[0003] Introducing oxygen vacancies is a crucial strategy for improving the performance of semiconductor materials. Methods for introducing oxygen vacancies mainly include ion implantation, annealing, hydrogen thermal treatment, high-energy radiation, and chemical etching. While these strategies are effective in creating oxygen vacancies in semiconductor materials, their preparation processes are complex, require sophisticated equipment, exhibit poor controllability, and consume significant energy. Furthermore, p-type CuO has a lower electron mobility than n-type CuO, but in its natural state, CuO is a p-type semiconductor, and its defect component is naturally copper vacancies. Conventional processes struggle to convert these copper vacancies into oxygen vacancies. Therefore, there is an urgent need to develop a simple process for introducing oxygen vacancies into CuO semiconductor materials. In addition, single semiconductor materials exhibit high photogenerated electron-hole recombination rates due to the lack of photocharge transfer, resulting in low photocatalytic efficiency when used as photocatalysts. To address this drawback, constructing type II heterojunctions between different semiconductor materials to facilitate photocharge transfer is an effective strategy.

[0004] There are many existing methods for constructing semiconductor oxide heterojunctions. CuO@TiO2 heterojunctions prepared by traditional self-assembly or sol-gel methods often struggle to form high specific surface areas and uniformly shaped coatings, which is detrimental to interfacial mass transfer in photocatalytic reactions. Heterojunctions generated by template calcination can overcome this drawback. For example, patent CN115970691A discloses a dual MOF-derived copper oxide@titanium dioxide heterojunction photocatalyst, its preparation method, and its application. This involves adding the organic ligand corresponding to HKUST-1 synthesized in situ and a copper salt to a suspension of organic ligands and titanium salt in MIL-125, followed by reaction and calcination in air to prepare the heterojunction. However, this process requires the prior preparation of a dual MOF composite material, followed by high-temperature calcination at 400-600℃ for 3-6 hours, making the preparation process complex and energy-intensive. In addition, in order to overcome the problems of narrow light absorption range, high recombination rate of photogenerated carriers and low photocatalytic efficiency of conventional photocatalysts, it is urgent to develop a photocatalytic material with simple process, wide light absorption range and certain photocatalytic activity in the near-infrared region. Summary of the Invention

[0005] To address the challenges of low photocatalytic activity, high recombination rate of photogenerated carriers, and complex fabrication processes for CuO composite materials in the near-infrared range, this invention proposes a TiO2@CuO heterojunction containing oxygen vacancies, its preparation method, and its applications.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing a TiO2@CuO heterojunction containing oxygen vacancies, comprising the following steps:

[0008] (1) Ti3AlC2 was added to a hydrofluoric acid solution, stirred, centrifuged, washed, and dried to obtain Ti3C2T. x MXene powder.

[0009] (2) Combine Cu(CH3COO)2·H2O with the Ti3C2T obtained in step (1). x MXene powder was dissolved in deionized water and reacted with hydrogen peroxide solution to prepare TiO2@CuO heterojunction containing oxygen vacancies.

[0010] In step (1), the mass-to-volume ratio of Ti3AlC2 to hydrofluoric acid solution is 0.03-0.1 g / mL.

[0011] The stirring time in step (1) is 12-24 hours; the cleaning method is to repeatedly wash with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH value is close to neutral.

[0012] In step (2), Cu(CH3COO)2·H2O and Ti3C2T x The mass ratio of Mxene powder is (8-12):1.

[0013] In step (2), the mass-to-volume ratio of Cu(CH3COO)2·H2O to deionized water is 0.02-0.16 g / mL.

[0014] The mass fraction of hydrogen peroxide solution in step (2) is 10%-30%.

[0015] In step (2), the volume ratio of hydrogen peroxide solution to deionized water is 1:(0.5-2).

[0016] The reaction in step (2) is carried out at room temperature for 10-20 minutes.

[0017] The above preparation method produces a TiO2@CuO heterojunction containing oxygen vacancies.

[0018] The above-mentioned TiO2@CuO heterojunction containing oxygen vacancies is used in the photocatalytic degradation of organic matter.

[0019] The specific preparation steps of the TiO2@CuO heterojunction containing oxygen vacancies of the present invention are as follows:

[0020] (1)Ti3C2T x Preparation of MXene: HF was measured and poured into a polytetrafluoroethylene beaker. Ti3AlC2 was slowly added to the HF solution while stirring at low speed. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. x MXene powder is dried and stored for later use.

[0021] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, Cu(CH3COO)2·H2O and Ti3C2T x MXene powder was added to deionized water and stirred until homogeneous. Then, H₂O₂ was poured into the suspension and stirred. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0022] The formation principle of TiO2@CuO heterojunction containing oxygen vacancies is as follows:

[0023] Ti3C2T xWhen MXene powder and Cu(CH3COO)2·H2O are added to H2O2 solutions of varying concentrations, a rapid and intense chemical reaction occurs, accompanied by heat and the generation of numerous bubbles. The C layer is oxidized to produce CO or CO2 gas, while the Ti layer is oxidized to form a TiO2 plate-like structure. Simultaneously, H2O2 reacts with some copper ions adsorbed on the TiO2 to form black CuO. During the formation of CuO particles, the chemical reaction is extremely rapid, resulting in some Cu ions not fully combining with O ions. In other words, vacancies appear where oxygen atoms should be present in CuO, forming CuO with oxygen vacancies.

[0024] The beneficial effects of this invention are:

[0025] (1) This invention uses a simple one-pot method to prepare TiO2@CuO heterojunctions containing oxygen vacancies. The reaction conditions are mild and the preparation method is simple, providing a new strategy for the preparation of modified heterojunctions.

[0026] (2) Pure CuO particles are large in size and have poor uniformity. However, after forming the TiO2@CuO heterojunction, the CuO particles are not only better dispersed on the TiO2 surface, but their size is also significantly reduced. This indicates that the TiO2 plate-like structure is an excellent support, which can reduce the size and diameter of CuO particles and increase the specific surface area of ​​the composite catalyst.

[0027] (3) The TiO2@CuO heterojunction prepared by this invention has a narrow band gap and a low degree of photogenerated charge recombination, resulting in excellent photocatalytic performance. The 1.00 eV band gap and narrow band gap effectively improve light absorption and utilization. The TiO2@CuO heterojunction absorbs sunlight more strongly than CuO and exhibits a stronger photoresponse in the near-infrared band. Furthermore, in the TiO2@CuO heterojunction containing oxygen vacancies, TiO2 and CuO form a type II band structure, which facilitates the separation and transfer of photogenerated charges and increases the concentration of photogenerated carriers.

[0028] (4) The hydrophilic groups on the surface of the oxygen-vacancy-containing TiO2@CuO heterojunction prepared in this invention are beneficial for the adsorption of pollutants. Furthermore, thanks to its excellent photocatalytic activity, the prepared oxygen-vacancy-containing TiO2@CuO heterojunction exhibits a certain photocatalytic degradation ability of tetracycline under sunlight irradiation at different wavelengths. Under near-infrared light irradiation, the removal efficiency of tetracycline by TiO2@CuO reaches 66.8%. Moreover, after the photodegradation reaction, the Cu... 2+ The valence state of the ions did not change, indicating their good photostability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 XRD patterns (a) and Raman diagrams (b) of OVs-TiO2@CuO prepared in Example 1 and CuO prepared in Comparative Example 1.

[0031] Figure 2 Ti3C2T prepared in Example 1 x SEM images of MXene (a), CuO prepared in Comparative Example 1 (b), and OVs-TiO2@CuO (c) prepared in Example 1, and (dg) is a distribution diagram of Cu, Ti, O, and C elements in the OVs-TiO2@CuO heterojunction.

[0032] Figure 3 The images show TEM and HRTEM images of OVs-TiO2@CuO prepared in Example 1, where (a) is a TEM image of OVs-TiO2@CuO; (b) is an HRTEM image of OVs-TiO2@CuO labeled region b; and (c) is an HRTEM image of OVs-TiO2@CuO labeled region c.

[0033] Figure 4 The images are XPS spectra, including (a) the full XPS spectra of samples CuO and OVs-TiO2@CuO, (b) the high-resolution XPS spectra of the O1s orbitals of CuO and OVs-TiO2@CuO, (c) the high-resolution XPS spectra of the Cu 2p orbitals of CuO and OVs-TiO2@CuO, and (d) the high-resolution XPS spectra of the Ti 2p orbitals in the OVs-TiO2@CuO heterojunction.

[0034] Figure 5 The image shows the EPR spectrum of OVs-TiO2@CuO prepared in Example 1.

[0035] Figure 6 The UV-Vis absorption spectra (a) and band gap curves (b) of OVs-TiO2@CuO prepared in Example 1 and CuO prepared in Comparative Example 1 are shown.

[0036] Figure 7 The FTIR spectra of OVs-TiO2@CuO prepared in Example 1 and CuO prepared in Comparative Example 1 are shown.

[0037] Figure 8The PL spectra of OVs-TiO2@CuO prepared in Example 1 and CuO prepared in Comparative Example 1 are shown.

[0038] Figure 9 AC impedance curves (a) of OVs-TiO2@CuO prepared in Example 1, CuO prepared in Comparative Example 1, and Mott-Schottky curve of sample CuO at 1000 Hz.

[0039] Figure 10 The photodegradation TC curves of OVs-TiO2@CuO prepared in Example 1 and CuO prepared in Comparative Example 1 under (a) simulated sunlight, (c) UV, (e) Vis and (g) NIR light irradiation are shown. (b, d, f and h) are the corresponding pseudo-first-order kinetic curves.

[0040] Figure 11 The OVs-TiO2@CuO heterojunction prepared in Example 1 was subjected to photodegradation experiments. (a) XPS full spectrum, (b) high-resolution XPS spectra of O1s, (c) Cu 2p and (d) Ti 2p, and (e) Auger electron spectrum of Cu. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] The preparation method of a TiO2@CuO heterojunction containing oxygen vacancies in this embodiment includes the following steps:

[0044] (1)Ti3C2T x Preparation of MXene: 40 mL of HF was poured into a polytetrafluoroethylene beaker, and 2 g of Ti3AlC2 was slowly added to the HF solution. The mixture was stirred at low speed for 24 h. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. x MXene powder is dried and stored for later use.

[0045] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, 0.4g Cu(CH3COO)2·H2O and 0.04g Ti3C2T xMXene powder was added to 5 mL of deionized water and stirred until homogeneous. Then, 5 mL of 15% (w / w) H₂O₂ solution was added to the suspension and stirred for 10 min. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0046] Example 2

[0047] The preparation method of a TiO2@CuO heterojunction containing oxygen vacancies in this embodiment includes the following steps:

[0048] (1)Ti3C2T x Preparation of MXene: 40 mL of HF was poured into a polytetrafluoroethylene beaker, and 1.2 g of Ti3AlC2 was slowly added to the HF solution. The mixture was stirred at low speed for 12 h. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. x MXene powder is dried and stored for later use.

[0049] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, 0.4g Cu(CH3COO)2·H2O and 0.04g Ti3C2T x MXene powder was added to 5 mL of deionized water and stirred until homogeneous. Then, 5 mL of 10% (w / w) H₂O₂ solution was added to the suspension and stirred for 15 min. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0050] Example 3

[0051] The preparation method of a TiO2@CuO heterojunction containing oxygen vacancies in this embodiment includes the following steps:

[0052] (1)Ti3C2T x Preparation of MXene: 40 mL of HF was poured into a polytetrafluoroethylene beaker, and 4 g of Ti3AlC2 was slowly added to the HF solution. The mixture was stirred at low speed for 18 h. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. xMXene powder is dried and stored for later use.

[0053] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, 0.4g Cu(CH3COO)2·H2O and 0.04g Ti3C2T x MXene powder was added to 5 mL of deionized water and stirred until homogeneous. Then, 5 mL of 30% (w / w) H₂O₂ solution was added to the suspension and stirred for 10 min. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0054] Example 4

[0055] The preparation method of a TiO2@CuO heterojunction containing oxygen vacancies in this embodiment includes the following steps:

[0056] (1)Ti3C2T x Preparation of MXene: 40 mL of HF was poured into a polytetrafluoroethylene beaker, and 2 g of Ti3AlC2 was slowly added to the HF solution. The mixture was stirred at low speed for 24 h. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. x MXene powder is dried and stored for later use.

[0057] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, 0.32g Cu(CH3COO)2·H2O and 0.04g Ti3C2T x MXene powder was added to 16 mL of deionized water and stirred until homogeneous. Then, 8 mL of 15% (w / w) H₂O₂ solution was added to the suspension and stirred for 20 min. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0058] Example 5

[0059] The preparation method of a TiO2@CuO heterojunction containing oxygen vacancies in this embodiment includes the following steps:

[0060] (1)Ti3C2T xPreparation of MXene: 40 mL of HF was poured into a polytetrafluoroethylene beaker, and 2 g of Ti3AlC2 was slowly added to the HF solution. The mixture was stirred at low speed for 24 h. The resulting Ti3C2T... x MXene powder was repeatedly washed with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH of the waste liquid was close to neutral, yielding Ti3C2T. x MXene powder is dried and stored for later use.

[0061] (2) Preparation of TiO2@CuO heterojunction containing oxygen vacancies: At room temperature, firstly, 0.48g Cu(CH3COO)2·H2O and 0.04g Ti3C2T x MXene powder was added to 3 mL of deionized water and stirred until homogeneous. Then, 6 mL of 15% (w / w) H₂O₂ solution was added to the suspension and stirred for 18 min. As the reaction proceeded, a large number of bubbles were released from the suspension. Finally, the obtained precipitate was dried in a vacuum freeze dryer to obtain a TiO₂@CuO heterojunction containing oxygen vacancies, denoted as OVs-TiO₂@CuO.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that only Cu(CH3COO)2·H2O is used; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0064] Preparation of pure CuO: At room temperature, 0.4 g of Cu(CH3COO)2·H2O was dissolved in 5 mL of deionized water and stirred until homogeneous. Then, 5 mL of 15% (w / w) H2O2 solution was slowly added. A black precipitate quickly formed in the solution, which was then centrifuged. The black precipitate obtained after centrifugation was repeatedly washed with deionized water and anhydrous ethanol. The cleaned precipitate was then dried in a vacuum freeze dryer. The resulting black powder was stored for later use.

[0065] Implementation Results Example

[0066] Ti3C2T prepared in Example 1 x The crystal structure, surface morphology, chemical elements and their valence states, light absorption properties, functional groups, electrochemical properties, and photogenerated charge transfer of Mxene, OVs-TiO2@CuO, and CuO prepared in Comparative Example 1 were tested and analyzed.

[0067] Figure 1 (a) is the sample Ti3C2T xXRD patterns of MXene, CuO, and OVs-TiO2@CuO are shown. The figures reveal three distinct diffraction peaks in the CuO XRD curve, located at 32.6°, 35.7°, and 38.7°, corresponding to the (110) peaks of monoclinic CuO. And the (111) crystal plane (JCPDS No. 48-1548). In the XRD curve of the OVs-TiO2@CuO heterojunction, only the diffraction peak of CuO appeared, and its peak intensity was lower than that of pure CuO. This is because the proportion of CuO in the heterojunction is reduced, which further weakens its diffraction peak intensity. The characteristic peak of TiO2 did not appear in the heterojunction because the diffraction peak intensity of TiO2 is lower than that of CuO. The above results preliminarily indicate the successful preparation of CuO and OVs-TiO2@CuO heterojunctions.

[0068] The space group of CuO in the monoclinic system is Each unit cell consists of two molecules and has 12 vibrational modes, as shown in Equation 1:

[0069] Γ'=4A u +5B u +A g +2B g (1)

[0070] A and B represent two non-degenerate vibration modes, containing three acoustic modes (A... u +2B u Six infrared active modules (3A) u +3B u ) and three Raman active modes (A g +2B g ).

[0071] Figure 1 (b) is the sample Ti3C2T x Raman curves for MXene, CuO, and OVs-TiO2@CuO are shown. It can be observed that the Raman curve for CuO contains three distinct peaks, located at 278 cm⁻¹. -1 324cm -1 and 618cm -1 At these locations, they respectively correspond to the A of CuO. g and two Bs g Vibration modes. In the Raman curves of the OVs-TiO2@CuO heterojunction, vibration modes can be observed at 144 cm⁻¹. -1 There is a small characteristic peak at 278 cm⁻¹, which is characteristic of the anatase phase TiO₂. -1 324cm -1 and 618cm-1 The characteristic peaks at that location belong to CuO, further indicating the successful synthesis of the OVs-TiO2@CuO heterojunction.

[0072] Figure 2 (a) Ti3C2T with a layered structure x Electron micrographs, the morphology of CuO is as follows Figure 2 As shown in (b), the CuO particles do not have a specific morphology and are irregular granular. The size difference between the particles is large, which is due to the rapid chemical reaction during the preparation process. Figure 2 (c) is a SEM image of OVs-TiO2@CuO. It can be seen that after CuO forms a heterojunction with the lamellar TiO2, CuO is perfectly attached to the surface of the lamellar TiO2, and the particle size is significantly smaller than that of pure CuO. Moreover, the CuO particle size is relatively uniform, and no large CuO particles appear. This is because the CuO precursor... 2+ Capable of being used by Ti3C2T x Adsorption and dispersion were relatively uniform, with no aggregation observed. Furthermore, from... Figure 2 As can be observed in the illustration of (c), the loading of CuO particles did not destroy the structure of TiO2, which still exhibited a plate-like morphology and a relatively flat structure, demonstrating the good uniformity of the OVs-TiO2@CuO heterojunction composition. Figure 2 (dg) is a distribution diagram of the elements contained in the OVs-TiO2@CuO heterojunction. It can be seen from the figure that the heterojunction contains Cu, Ti, O and C elements, and the distribution of each element has good uniformity.

[0073] Figure 3 The images show TEM and HRTEM images of OVs-TiO2@CuO. Figure 3 (a) is a TEM image of OVs-TiO2@CuO. The image shows that the TEM image of OVs-TiO2@CuO is relatively dark, indicating that the electron beam cannot easily penetrate it, suggesting that it is quite thick. Additionally, a large amount of particulate matter can be seen loaded on its surface. Figure 3 The HRTEM images of regions c and d marked with red circles in (a) are shown below. Figure 3 As shown in (b) and (c). From Figure 3 In (b), a clear lattice stripe pattern was observed on the OVs-TiO2@CuO surface. The width of the lattice stripes was 0.23 nm, corresponding to the (111) crystal plane of monoclinic CuO. This is consistent with the XRD results, indicating that CuO was successfully prepared. Figure 3 (c) shows some amorphous regions (circled in red), which are TiO2 surfaces. Additionally, CuO is also present. The crystal plane, with a corresponding lattice spacing of 0.25 nm, further confirms the successful fabrication of the OVs-TiO2@CuO heterojunction.

[0074] To analyze the elements and their valence states contained in the samples CuO and OVs-TiO2@CuO, they were characterized and analyzed by XPS. Figure 4 (a) shows the XPS full spectrum of CuO and OVs-TiO2@CuO. It can be observed that OVs-TiO2@CuO contains elements C, Cu, F, O, and Ti, while CuO contains only Cu and O, without other impurities. Figure 4 In (b), the O1s high-resolution XPS spectra of CuO and OVs-TiO2@CuO both exhibit a distinct main peak and a shoulder peak, which can be separated into two characteristic peaks after fitting. The characteristic peaks of O1s in CuO are located at 531.44 eV and 529.71 eV, attributed to OVs and lattice oxygen (OL), respectively, with a peak area ratio of approximately 2:1. This indicates that CuO contains a large amount of OVs, which is likely due to the rapid preparation process and the presence of some CuVs. 2+ Oxygen vacancies arise because the oxygen atoms cannot react with O2 in time. The characteristic peaks of O1s in the OVs-TiO2@CuO heterojunction are located at 531.26 eV and 529.48 eV, also belonging to OVs and OL. Here, OVs includes OVs from CuO and TiO2, while OL includes Cu-O and Ti-O. Comparison shows that the peak positions of OVs and OL in O1s of OVs-TiO2@CuO are shifted to lower binding energies relative to CuO by 0.18 eV and 0.23 eV, respectively. This is due to the change in charge density around the O atoms after the formation of the heterojunction. Figure 4 (c) shows the high-resolution XPS spectrum of Cu 2p. As can be observed from the figure, after peak fitting, the Cu 2p curves of both CuO and OVs-TiO2@CuO samples contain five characteristic peaks, including two main peaks and three satellite peaks (Sat.), which are typical of Cu. 2+ Characteristic. The satellite peaks are generated because electrons transfer from the ligand orbitals to the 3d orbitals of Cu, indicating that Cu... 2+ It is 3D 9 It exists in a divalent form, rather than as Cu with filled d-levels. + Or Cu 0 Species. Cu2p of CuO 3 / 2 The characteristic peak and its satellite peaks are located at 933.80 eV, 943.58 eV, and 940.80 eV, respectively, for Cu 2p. 1 / 2 The characteristic peak and its satellite peak are located at 953.71 eV and 962.10 eV, respectively. The Cu 2p of OVs-TiO2@CuO...3 / 2 The characteristic peak and its satellite peaks are located at 934.08 eV, 943.71 eV, and 940.89 eV, respectively, for Cu 2p. 1 / 2 The characteristic peak and its satellite peak are located at 953.92 eV and 962.13 eV, respectively. Compared to pure CuO, the Cu 2p peak in the heterojunction... 3 / 2 and Cu 2p 1 / 2 The characteristic peak positions shifted by 0.28 eV and 0.21 eV towards higher binding energies, respectively, indicating that the electron density around Cu decreased after the formation of the heterojunction. Cu 2p 3 / 2 and Cu 2p 1 / 2 The difference in binding energy between the characteristic peaks in CuO is 19.91 eV, while the difference in binding energy between OVs-TiO2@CuO heterojunction is 19.81 eV, further indicating that Cu exists in a divalent form. Figure 4 (d) The XPS high-resolution spectrum of the Ti 2p orbitals in OVs-TiO2@CuO is shown, with two main characteristic peaks, which are attributed to Ti 2p orbitals. 3 / 2 (458.02eV) and Ti 2p 1 / 2 (463.82 eV) indicates that Ti mainly exists in the tetravalent form. After peak fitting, the XPS curve of the Ti 2p orbital in OVs-TiO2@CuO yielded a Ti-C peak at 459.60 eV, which is attributed to TiO2.

[0075] To further verify the presence of OVs in the OVs-TiO2@CuO heterojunction, EPR tests were performed under low-temperature conditions, and the obtained curves are shown below. Figure 5 As shown, through the direct conversion between the magnetic field and the g factor, a significant g factor signal exists at 2.003, indicating that OVs do indeed exist in OVs-TiO2@CuO, thus verifying the XPS results.

[0076] To verify the absorption performance of CuO and OVs-TiO2@CuO by sunlight, UV-Vis absorption spectroscopy tests were performed on them, and the results are as follows: Figure 6 As shown in (a), the absorption regions of CuO and OVs-TiO2@CuO extend into the near-infrared region. They still exhibit strong light absorption in the near-infrared region at 1500 nm, and the light absorption intensity of the OVs-TiO2@CuO heterojunction is stronger than that of pure CuO. This suggests that OVs-TiO2@CuO and CuO not only possess photodegradation activity in the visible light range but also in the near-infrared range. The bandgap curves of CuO and OVs-TiO2@CuO were obtained by converting their UV-Vis absorption spectra, as shown in (a). Figure 6As shown in (b), by plotting the tangents to the band gap curves of CuO and OVs-TiO2@CuO, their band gaps were found to be 1.16 eV and 1.00 eV, respectively. This is because the OVs present in CuO form defect energy levels, making it easier for electrons in the valence band to be excited. This result improves the utilization efficiency of sunlight.

[0077] To determine the functional groups on the material surface, FTIR tests were performed on samples CuO and OVs-TiO2@CuO. The results are as follows: Figure 7 As shown in the figure, the dashed boxes indicate the positions of -OH functional groups, indicating that all samples contain -OH functional groups. The characteristic peak intensity of the -OH functional group in CuO is higher than that in OVs-TiO2@CuO, indicating that CuO contains more -OH functional groups than OVs-TiO2@CuO, suggesting that CuO has superior hydrophilic properties. Similarly, OVs-TiO2@CuO also has a relatively large number of -OH functional groups. This is beneficial for the adsorption of pollutants.

[0078] To evaluate the recombination degree of photogenerated electrons and holes in samples CuO and OVs-TiO2@CuO under illumination, photoluminescence (PL) tests were performed. The excitation light source was 365nm ultraviolet light. The results are as follows: Figure 8 As shown, the low PL peak intensity indicates a low degree of photogenerated charge recombination, meaning the photocatalyst can utilize more photogenerated charges for redox reactions. The PL peak intensity of CuO is stronger than that of OVs-TiO2@CuO in the sample's PL spectrum, indicating that the formation of the heterojunction successfully suppressed photogenerated charge recombination and promoted the separation and transfer of photogenerated charges. The sample's PL peak also exhibits a certain intensity in the visible light range, mainly due to the luminescence from the OVs defects.

[0079] To test the charge transfer capabilities of samples CuO and OVs-TiO2@CuO, EIS tests were performed, and the results are as follows: Figure 9 As shown in (a), the AC impedance curves of samples CuO and OVs-TiO2@CuO show that the radius of the AC impedance curve of OVs-TiO2@CuO is smaller than that of CuO, indicating that the OVs-TiO2@CuO heterojunction has the smallest charge transfer resistance and excellent interfacial properties. Figure 9 (b) is the Mott-Schottky curve of the CuO sample. Its slope is positive, which shows the properties of an n-type semiconductor because CuO contains a large amount of OVs. n-type CuO is electronically conductive, with higher electron mobility and stronger conductivity.

[0080] Application examples

[0081] The OVs-TiO2@CuO prepared in Example 1 and the CuO prepared in Comparative Example 1 were used as photocatalysts, and their photocatalytic degradation performance of tetracycline (TC) solution was tested and analyzed.

[0082] Specific testing procedure: Tetracycline (30 mg / L) was used as the target pollutant for evaluation. The reaction system consisted of 0.02 g of photocatalyst and 100 mL of tetracycline solution, with the temperature of the reaction system controlled at 0°C using circulating cooling water. Before the photodegradation experiment, an adsorption experiment was conducted for 40 min to allow the reaction system to reach adsorption equilibrium. The sample C-TiO₂ was then... x CuO x OVs-TiO2@CuO were placed under different light irradiations (full-spectrum sunlight, ultraviolet light (<400nm), visible light (420nm~760nm), and near-infrared light (>780nm)) at a distance of 10cm. 4mL of tetracycline solution was collected every 20min for centrifugation, and the supernatant was subjected to UV-Vis analysis. The absorption peak at 357nm was used as the characteristic peak to assess degradation efficiency. The adsorption and removal efficiency of the tetracycline solution was calculated using the C / C0 ratio, where C is the absorbance during adsorption and degradation, and C0 is the original absorbance of the tetracycline solution. Photodegradation of TC was also performed. Figure 10 As shown.

[0083] The photodegradation curves and pseudo-first-order kinetic curves of different samples CuO and OVs-TiO2@CuO on TC solution under full-spectrum simulated sunlight are shown below. Figure 10 As shown in (a) and (b), the curves reveal that the removal rates of TC solution by samples CuO and OVs-TiO2@CuO were 59.3% and 90.6%, respectively. OVs-TiO2@CuO exhibited the highest removal efficiency for TC solution, primarily due to two factors. Firstly, the OVs-TiO2@CuO heterojunction possesses strong adsorption properties, achieving an adsorption capacity of 42.2% for TC solution in the dark adsorption stage, higher than CuO's 22.1%. This indicates that OVs and -OH groups play a crucial role in TC adsorption, while the lower adsorption efficiency of pure CuO is attributed to its larger particle size and smaller specific surface area. Secondly, the OVs-TiO2@CuO heterojunction exhibits strong photodegradation properties, with pseudo-first-order kinetic constants of 6.03 × 10⁻⁶ for samples CuO and OVs-TiO2@CuO. -3 and 1.74×10 -2It can be observed that OVs-TiO2@CuO exhibits the highest photodegradation performance, while CuO shows the lowest. This is because, although CuO also contains a large amount of OVs, its non-uniform particle size results in a smaller contact area with the TC solution and fewer reactive sites. In contrast, the OVs-TiO2@CuO heterojunction, under illumination, not only absorbs photons in the near-infrared region, but the type II band structure formed by TiO2 and CuO facilitates the transfer of photogenerated electrons and holes at the interface, which is more conducive to the separation of photogenerated carriers. In summary, the OVs-TiO2@CuO heterojunction possesses excellent adsorption and photodegradation performance, making it a superior photocatalytic material.

[0084] The photodegradation TC curves and corresponding pseudo-first-order kinetic curves of different samples CuO and OVs-TiO2@CuO under ultraviolet light irradiation are shown below. Figure 10 As shown in (c) and (d), the removal efficiencies of the catalysts CuO and OVs-TiO2@CuO for TC solution were 53.3% and 80.9%, respectively, with corresponding pseudo-first-order kinetic constants of 4.49 × 10⁻⁶. -3 and 1.07×10 -2 Therefore, it can be seen that the OVs-TiO2@CuO heterojunction exhibits superior photodegradation performance under ultraviolet light compared to pure CuO. Both catalysts have narrow band gaps and are rich in OVs, meaning their valence band electrons can be excited by visible light. However, the band gap of CuO is much smaller than that of OVs-TiO2@CuO. This is because under ultraviolet light irradiation, the OVs-TiO2@CuO heterojunction not only excites a large number of photogenerated charges but also allows these charges to transfer between the heterojunctions, which is beneficial for increasing the concentration of photogenerated carriers. Therefore, the OVs-TiO2@CuO heterojunction exhibits the best photocatalytic performance.

[0085] The photodegradation TC curves and corresponding pseudo-first-order kinetic curves of different samples CuO and OVs-TiO2@CuO under visible light irradiation are shown below. Figure 10 As shown in (e) and (f), the removal efficiencies of the catalysts CuO and OVs-TiO2@CuO for TC solution were 54% and 76.9%, respectively, with corresponding pseudo-first-order kinetic constants of 4.99 × 10⁻⁶. -3 and 9.33×10 -3 It can be observed that the OVs-TiO2@CuO heterojunction exhibits the best photocatalytic performance.

[0086] The photodegradation curves and corresponding pseudo-first-order kinetic curves of TC solutions obtained by different samples of CuO and OVs-TiO2@CuO under near-infrared light irradiation are shown below. Figure 10The results (g) and (h) show that their removal efficiencies for TC solution were 50% and 66.8%, respectively, with pseudo-first-order kinetic constants of 4.12 × 10⁻⁶. -3 and 5.5×10 -3 The OVs-TiO2@CuO heterojunction exhibits the strongest degradation performance against TC solution, followed by CuO. Their absorption spectra show that both CuO and OVs-TiO2@CuO show a photoresponse to the infrared spectrum.

[0087] To analyze the stability of the sample after photodegradation, XPS analysis and Auger electron spectroscopy of Cu were performed on the OVs-TiO2@CuO heterojunction after degradation (full-spectrum simulated sunlight). Figure 11 As shown. In Figure 11 In (a), the OVs-TiO2@CuO heterojunction after photodegradation contains the elements Cu, F, O, Ti and C, which are the same as the elements before the photodegradation reaction. Figure 11 (b) is the high-resolution spectrum of O1s. After curve fitting analysis, it can be observed that the characteristic peaks of O1s in the OVs-TiO2@CuO heterojunction are located at 531.48eV and 529.70eV, which belong to OVs and OL, and there are still a large number of OVs. Figure 11 (c) is the XPS high-resolution spectrum of Cu 2p. From the fitted image, it can be observed that the Cu 2p curve of OVs-TiO2@CuO still contains five characteristic peaks, including two main peaks and three satellite peaks (Sat.). No other extra peaks appear, indicating that Cu... 2+ The Cu ions remained in their divalent form after photodegradation, with no other valence states appearing, fully demonstrating the sample's good photostability. Figure 11 In (d), after fitting analysis, the curve of the Ti 2p orbital still follows the Ti 2p orbital. 1 / 2 Ti 2p 3 / 2 Cu exists in the form of Ti-C bonds. To more accurately analyze the valence of Cu, Auger electron spectroscopy was performed, such as... Figure 11 As shown in (e), the characteristic peak obtained after testing is located at 569.48 eV, and no other peaks appear. This characteristic peak is generated by divalent Cu atoms, possibly because photogenerated electrons are transferred from CuO to TiO2, avoiding Cu... 2+ It is reduced. Based on the above analysis, OVs-TiO2@CuO exhibits excellent photostability.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a TiO2@CuO heterojunction containing oxygen vacancies, characterized in that, The steps are as follows: (1) Ti3AlC2 is added to a hydrofluoric acid solution, stirred, centrifuged, washed, and dried to obtain Ti3C2T x MXene powder; (2) Cu(CH3COO)2•H2O and Ti3C2T prepared in step (1) are mixed to prepare a CuO@Ti3C2T suspension; wherein, the mass ratio of Cu(CH3COO)2•H2O to Ti3C2T is 1: (8-12); the mass ratio of Cu(CH3COO)2•H2O to deionized water is 0.02-0.16 g / mL; the volume ratio of Cu(CH3COO)2•H2O to deionized water is 1: (0.5-2); and the volume ratio of Cu(CH3COO)2•H2O to deionized water is 1: (0.5-2). x MXene powder is dissolved in deionized water, 10%-30% hydrogen peroxide solution is added, and the mixture is reacted at room temperature for 10-20 min to prepare TiO2@CuO heterojunction containing oxygen vacancies; wherein, the mass ratio of Cu(CH3COO)2•H2O to Ti3C2T is 1: (8-12); the mass ratio of Cu(CH3COO)2•H2O to deionized water is 0.02-0.16 g / mL; and the volume ratio of hydrogen peroxide solution to deionized water is 1: (0.5-2). x The mass ratio of Mxene powder is (8-12): 1; the mass ratio of Cu(CH3COO)2•H2O to deionized water is 0.02-0.16 g / mL; and the volume ratio of hydrogen peroxide solution to deionized water is 1:

2. The production method according to claim 1, characterized by, The mass-volume ratio of Ti3AlC2 to hydrofluoric acid solution in the step (1) is 0.03-0.1 g / mL.

3. The preparation method according to claim 2, characterized in that, The stirring time in the step (1) is 12-24 h; the cleaning method is repeated cleaning with anhydrous ethanol and deionized water, accompanied by ultrasonic treatment, until the pH value is close to neutral.

4. The TiO2@CuO heterojunction containing oxygen vacancies prepared by the preparation method of any one of claims 1-3.

5. The application of the TiO2@CuO heterojunction containing oxygen vacancies in claim 4 in photocatalytic degradation of organic matter.

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