Preparation method, material and application of two-dimensional TiO2 photocatalytic material with synergistic defect structure

Abstract

The invention relates to a two-dimensional TiO2 photocatalytic material with a synergistic defect structure as well as a preparation method and application of the two-dimensional TiO2 photocatalytic material. According to the material, rare earth ion doping and subsurface oxygen vacancies are introduced into a TiO2 two-dimensional lamella, a defect configuration with a synergistic enhancement effect is constructed, and visible light response and carrier separation efficiency are remarkably improved. According to the material, a precursor film is prepared through a sol-gel or sputtering method, and a stable structure is formed in combination with reducing atmosphere heat treatment; the rare earth doping element is Eu, Ce or La, and the doping concentration and defect spacing are controllable. Density functional theory calculation shows that the structure has the advantages of band gap narrowing, H * adsorption free energy optimization and the like, and experimental characterization also proves that the photocatalytic hydrogen production performance of the structure is remarkably superior to that of an unmodified sample. The device has the characteristics of clear structure, controllable process, remarkable performance improvement and the like, and is suitable for the fields of hydrogen production by photolysis of water, pollutant degradation and the like.

Description

Technical Field

[0001] This invention relates to the field of TiO2 photocatalytic materials technology, and more specifically to a method for preparing, materials for and applications of a two-dimensional TiO2 photocatalytic material with a synergistic defect structure. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental problems, the development of efficient and sustainable clean energy conversion technologies has become a current research hotspot. Solar photocatalytic water splitting for hydrogen production is considered a promising pathway due to its mild reaction conditions and environmental friendliness. The performance of semiconductor photocatalytic materials directly determines the hydrogen production efficiency.

[0003] Titanium dioxide (TiO2), as a low-cost, stable, and non-toxic semiconductor material, has been widely used in the field of photocatalysis. However, traditional bulk TiO2 has two main problems: first, its band gap is relatively large (approximately 3.2 eV for anatase), resulting in insufficient response to visible light; second, photogenerated electrons and holes are prone to recombination, leading to low quantum efficiency.

[0004] In recent years, two-dimensional TiO2 has attracted attention due to its larger specific surface area, shorter carrier diffusion paths, and more surface active sites. Studies have shown that two-dimensional TiO2 sheets are superior to three-dimensional particulate TiO2 in terms of electronic structure and catalytic interface, and have greater application potential. However, optimizing a single structure still cannot overcome the bottleneck of photocatalytic activity.

[0005] To further enhance the photocatalytic performance of TiO2, researchers have attempted to modulate its electronic properties by introducing defect structures. Rare earth element doping (such as Eu, Ce, and La) can effectively induce impurity energy levels, regulate band edge positions, and improve carrier migration behavior. Simultaneously, oxygen vacancy defects formed through reducing atmosphere heat treatment can introduce intermediate states, broaden the light absorption range, and serve as reactive sites to promote catalytic reactions.

[0006] Existing research has shown that the synergistic effect of doping and defects has significant advantages in improving photocatalytic performance. Especially in two-dimensional TiO2 materials, the spatial configuration of dopant ions and oxygen vacancies has a decisive influence on the electronic structure and catalytic pathway. However, current technologies generally lack methods for designing and controlling the precise configuration of synergistic defects, and also lack theoretically guided structural models and feasible manufacturing processes.

[0007] Therefore, there is an urgent need to develop a two-dimensional TiO2 photocatalytic material with a well-defined structure, controllable parameters, and a clear preparation path, which can significantly improve photocatalytic performance, especially the efficiency of water splitting to produce hydrogen under visible light-driven conditions, by introducing a synergistic defect structure of doping and oxygen vacancies. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a method for preparing a two-dimensional TiO2 photocatalytic material with a synergistic defect structure, the material itself, and its applications.

[0009] To achieve the above objectives, the present invention provides the following technical solution, which mainly includes:

[0010] A method for preparing a two-dimensional TiO2 photocatalytic material with a synergistic defect structure, characterized by comprising the following steps:

[0011] (1) Using titanium tetrachloride or titanium tetraisopropoxide as the precursors, the titanium is deposited on the substrate surface under hydrolysis conditions to form an initial TiO2 film or gel precursor.

[0012] (2) Introducing a rare earth dopant into the precursor system, wherein the rare earth dopant is selected from one or more of Eu, Ce, and La, and partially occupies the Ti site in an alternative manner;

[0013] (3) The doped material is annealed in a reducing atmosphere to introduce oxygen vacancy defects. The annealing temperature is 300–600℃, the annealing time is 0.5–2 hours, and the atmosphere is a mixture of H2 and inert gas (volume ratio of 5%:95%).

[0014] (4) After cooling, a two-dimensional TiO2 thin film material with a surface doping and subsurface oxygen vacancy cooperative configuration is obtained.

[0015] In one specific embodiment, the rare earth dopant is Eu. 3+ ion.

[0016] In one specific embodiment, the TiO2 is an anatase structure with the main 001 crystal plane exposed, and the film thickness is 30–300 nm.

[0017] In one specific embodiment, the doping concentration of rare earth elements is 0.5–3.0 at.%, preferably 0.8–1.5 at.%.

[0018] In one specific embodiment, the surface density of oxygen vacancies in the material is 1.0 × 10⁻⁶. 14 –2.5×10 14 cm -2 .

[0019] A two-dimensional TiO2 photocatalytic material, wherein the material is a two-dimensional sheet-like structure of anatase TiO2 with exposed 001 / 101 crystal planes, wherein:

[0020] Rare earth ion doping exists at the Ti sites on the surface, and the doping element is selected from one or more of Eu, Ce, and La.

[0021] The subsurface layer has oxygen vacancy defects, and the in-plane distance between the rare earth ion and the nearest neighbor oxygen vacancy is 0.35–0.55 nm.

[0022] The material has a band gap of 2.35-2.55 eV and an ultraviolet-visible absorption edge at 520-560 nm.

[0023] The hydrogen production rate per unit area of ​​the material is 12-18 μmol·cm. -2 ·h -1 .

[0024] In one specific embodiment, the two-dimensional TiO2 structure is further combined with two-dimensional materials such as g-C3N4 or MXene to form a heterojunction.

[0025] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention effectively regulates the electronic structure and catalytic interface reaction characteristics of two-dimensional TiO2 materials by introducing rare earth ion doping and oxygen vacancy synergistic defect structures. The doping elements are preferably rare earth ions such as Eu, Ce, and La, which partially replace the surface Ti sites, thereby adjusting the conduction band bottom position and improving the carrier migration path without introducing deep-level traps. Complementing this, an appropriate amount of oxygen vacancy defects are introduced into the subsurface layer. These defects not only help to form catalytically active Ti in the Ti–O framework, but also... 3+ This also enhances the material's response to visible light and broadens the absorption spectrum.

[0026] More importantly, this invention explicitly proposes the spatial configuration relationship between rare-earth doped ions and oxygen vacancies. By controlling their relative spacing in the lattice, an electron-hole separation and migration channel is effectively established, reducing the recombination probability of photogenerated carriers and improving the efficiency of photogenerated electrons migrating to the surface and participating in reduction reactions. This cooperative configuration has been modeled and optimized using density functional theory calculations, demonstrating its positive improvement effects on bandgap modulation, density of states adjustment, and H* adsorption free energy.

[0027] Compared with existing technologies that rely solely on doping or introducing defects, this invention not only achieves dual optimization of material structure and electronic states but also has a clear process implementation path, enabling stable construction of the target configuration under conventional reducing atmosphere heat treatment conditions. The resulting two-dimensional TiO2 material exhibits superior hydrogen production activity compared to the comparative sample under simulated sunlight irradiation conditions, with significantly enhanced catalytic stability, demonstrating promising application prospects. Detailed Implementation

[0028] The technical solutions 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.

[0029] Example 1

[0030] This invention first involves controlling the deposition of a titanium source onto a substrate surface under liquid-phase hydrolysis conditions to form a TiO2 precursor film with a nanometer thickness. The selected titanium source can be titanium tetrachloride (TiCl4) or titanium tetraisopropoxide (TTIP), the solvent system is preferably an ethanol-water mixture, and the reaction temperature is controlled between 20°C and 50°C to avoid non-uniform deposition caused by excessively rapid hydrolysis. To obtain a good layered structure, surfactants (such as PEG or CTAB) can be added during the deposition process to adjust the particle orientation.

[0031] Next, rare earth ion dopants are introduced into the TiO2 precursor system, preferably Eu(NO3)3·6H2O or Ce(NO3)3·6H2O as the doping precursor. Doping can be achieved through blending, impregnation, or co-sputtering. In the solution method, the concentration of the rare earth precursor is controlled at 0.01–0.1 mol·L⁻¹. -1 Within the specified range, the material is dried at 60–100℃ after deposition to allow the dopant to initially enter the TiO2 framework. In the physical vapor deposition method, metal target co-sputtering is used, and the doping ratio is adjusted according to the target power and deposition time. The ultimate goal is to replace some of the surface Ti sites with rare earth elements, with the doping concentration controlled in the range of 0.5–3.0 at.%.

[0032] After drying and preheating, the doped sample needs to be thermally annealed in a reducing atmosphere to induce oxygen vacancies. The preferred annealing atmosphere in this invention is a mixture of hydrogen and argon (e.g., H2:Ar = 5:95 volume ratio), with an annealing temperature range of 350–500℃ and a treatment time controlled between 30–90 minutes. This heat treatment induces subsurface oxygen vacancies on the material surface, along with some Ti... 4+ Restore to Ti 3+ This forms visible light active centers. It is worth noting that the annealing time and atmosphere composition should be adjusted in tandem; excessive reduction may cause lattice collapse or too many intermediate state traps.

[0033] The obtained material exhibits a typical two-dimensional sheet-like structure with a thickness between 30 and 200 nm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed its lateral dimensions to be in the range of 200–800 nm, with a smooth surface and a polycrystalline thin film state. X-ray diffraction (XRD) analysis confirmed that the material is mainly composed of anatase phase, with crystal orientations predominantly {001} and {101}. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) detected rare earth element signals and Ti. 3+ The ratio; high-resolution transmission electron microscopy (HRTEM) combined with electron energy loss spectroscopy (EELS) can further characterize the in-plane distance between rare earth ions and nearest neighbor oxygen vacancies, with typical values ​​in the range of 0.35–0.55 nm.

[0034] UV-Vis DRS showed that the absorption edge of the material redshifted from approximately 380 nm to 520–580 nm; the time-resolved fluorescence lifetime (TRPL) was significantly higher than that of the undoped / vacancy-free samples, indicating that the lifetime of photogenerated carriers was extended. Hydrogen production performance was tested using a closed reaction apparatus and an AM1.5G solar simulator, with H2 yield recorded in an aqueous / methanol solution. The obtained hydrogen production rate per unit area was 2–3 times higher than that of the defect-free samples.

[0035] Example 2

[0036] Preparation of Two-Dimensional TiO2 Synergistic Defect Structure Materials Based on Sol-Gel Method

[0037] A certain amount of tetrabutyl titanate (Ti(OBu)4) was weighed as a precursor and slowly added dropwise to an ethanol-deionized water mixture (volume ratio 4:1). The mixture was reacted for 1 hour under constant temperature stirring (25–35℃). An appropriate amount of nitric acid was added to adjust the pH to 1–2, so that the system formed a homogeneous and stable sol. Subsequently, Eu(NO3)3·6H2O or Ce(NO3)3·6H2O was added, controlling the rare earth ion concentration to be 1.0–2.0 at.% of the molar amount of Ti.

[0038] The resulting mixed sol was aged at 80°C for 8 hours to form a gel. The gel was dried, ground, and spread onto a clean glass or FTO substrate, and a thin film was deposited using a spin-coating process (3000 rpm, 60 s). The deposited sample was pre-sintered in air (300°C, 30 min) to remove organic residues, and then annealed at 400°C for 1 hour in a 5% H2–95% Ar atmosphere to induce oxygen vacancies and form a cooperative defect configuration.

[0039] This method is suitable for low-cost, rapid sample preparation in the laboratory, yielding films with a thickness of approximately 80–150 nm, uniform surface, and grain size of approximately 10–20 nm. XPS displays Eu. 3+ Occupying the Ti site, accompanied by the formation of Ti3+ Spectrum analysis; HR-TEM revealed a relative spacing of surface dopant to subsurface vacancy in the range of 0.40–0.48 nm. The spectral response extended into the visible region (λ≈540 nm) and exhibited superior photocatalytic H2 yield compared to the control sample under simulated sunlight.

[0040] Example 3

[0041] In the preparation pathway of Example 1, Ce(NO3)3·6H2O and La(NO3)3·6H2O were used to replace the Eu precursor, respectively, to maintain a consistent doping concentration (1.2 at.%). The remaining process flow remained unchanged, including precursor film deposition, reduction annealing, and other steps.

[0042] All products exhibited a clear oxygen vacancy characteristic, with Ce in XPS. 3+ and La 3+ The signal is clearly visible. Both DFT prediction and experimental observation show that:

[0043] Ce doping is more likely to induce instability at nearby O sites, forming oxygen vacancies, resulting in a formation energy lower than that of the Eu system.

[0044] La 3+ Larger ionic radii are more likely to cause local lattice distortion, and they tend to occupy the second layer more on the {001} crystal plane.

[0045] The band gap narrowing is more significant in the Eu and Ce systems, while the charge separation efficiency is relatively low in the La system despite enhanced absorption.

[0046] Under uniform testing conditions (AM1.5G, methanol sacrificial agent, 20mg carrier material), the hydrogen production rate per unit area of ​​the Ce system was slightly higher than that of the Eu system. Although the La system showed enhanced absorption capacity, its lifetime improvement effect was not as good as the former two. Therefore, the preferred doping element in this invention is Eu or Ce.

[0047] Example 4

[0048] To further analyze the impact of doping-defect configuration on the performance of TiO2, a method based on density functional theory (DFT) was used to calculate the band structure and reaction pathways. The main steps are as follows:

[0049] S1. Construct a two-dimensional supercell model (4×4×1) of the anatase TiO2 (001) plane, containing 96 atoms;

[0050] S2. Replace one Ti atom with Eu at the Ti site on the surface layer to construct an Eu@Ti configuration with a doping concentration of approximately 1.0 at.%;

[0051] S3. Delete one O atom at the nearest neighbor subsurface O position of Eu to construct the Eu+V_O cooperative defect model;

[0052] S4. Optimize the structure using GGA+U (U_Ti=4.5eV, U_Eu=5.5eV);

[0053] S5. The band structure and density of states distribution of the key system are further optimized using the HSE06 hybrid functional;

[0054] S6. Use VASP to simulate the Gibbs free energy change ΔG_H of H adsorption at defect sites.

[0055] Calculations show that the band gap narrows from the intrinsic 3.2 eV to approximately 2.4 eV in the cooperative configuration, the CBM position rises by about 0.3 eV, and the VBM shifts slightly downward. In the density of states diagram, the Eu4f states are located at the lower edge of the conduction band, providing electron trapping centers, while the V_O induced states are distributed in the middle of the band gap, which is beneficial for the separation of photogenerated electrons. ΔG_H* is close to 0.05 eV in the Eu–V_O defect coexistence configuration, which is superior to the configurations with only doping or only V_O.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a two-dimensional TiO2 photocatalytic material with a synergistic defect structure, characterized in that, The method comprises the following steps: (1) using titanium tetrachloride or titanium tetraisopropoxide as the titanium source, depositing on the surface of the substrate under hydrolysis conditions to form an initial TiO2 film or gel precursor; (2) introducing a rare earth dopant into the precursor system, the rare earth dopant being selected from one or more of Eu, Ce, and La to partially occupy Ti sites in a substitutional manner; (3) annealing the doped material in a reducing atmosphere to introduce oxygen vacancy defects, wherein the annealing temperature is 300-600℃, the annealing time is 0.5-2 hours, and the atmosphere is a mixture of H2 and inert gas with a volume ratio of 5:95; (4) after cooling, a two-dimensional TiO2 film material with surface layer doping and subsurface oxygen vacancy cooperative configuration is obtained.

2. The production method according to claim 1, characterized by, The rare earth dopant is Eu 3+ ions.

3. The preparation method according to claim 1, characterized in that, The TiO2 is anatase structure with exposed 001 crystal plane, and the film thickness is 30-300 nm.

4. The method of claim 1, wherein, The doping concentration of the rare earth element is 0.5-3.0 at.%, preferably 0.8-1.5 at.%.

5. The preparation method according to claim 1, characterized in that, The surface area density of oxygen vacancies in the material is 1.0 x 10 14 - 2.5 x 10 14 cm -2 .

6. A two-dimensional TiO2 photocatalytic material, characterized in that, The material is an anatase TiO2 two-dimensional sheet structure with exposed 001 / 101 crystal planes, wherein: The surface layer Ti sites are doped with rare earth ions, and the doping element is selected from one or more of Eu, Ce, and La; The subsurface layer has oxygen vacancy defects, and the in-plane distance between the rare earth ions and the nearest neighbor oxygen vacancy is 0.35-0.55 nm; The band gap of the material is 2.35-2.55 eV, and the ultraviolet-visible light absorption edge is located at 520-560 nm; The hydrogen production rate per unit area of the material is 12-18 pmol-cm -2 ·h -1 .

7. The material of claim 6, wherein The two-dimensional TiO2 structure is further compounded with two-dimensional materials such as g-C3N4 or MXene to form a heterojunction.

8. Use of the two-dimensional TiO2 photocatalytic material according to claim 6 in the photocatalytic water decomposition reaction to produce hydrogen, characterized in that, Under AM1.5G solar light simulation conditions, the material exhibits enhanced photocatalytic hydrogen production performance under visible light irradiation with a wavelength of λ≥420 nm.

9. Use according to claim 8, characterized in that, The hydrogen production efficiency of the material attenuates by no more than 12-14% after 24 hours of continuous light irradiation.

10. Use according to claim 8, characterized in that, The free energy change ΔG_{H*} of the hydrogen intermediate (H*) of the material is in the range of –0.05 to +0.05 eV.