A method for preparing La-doped TiO2 photocatalysts using a high-pressure assisted sol-gel method and the La-TiO2 photocatalyst thereof.

Abstract

The application discloses a method for preparing a La-doped TiO2 photocatalyst by a high-pressure assisted sol-gel method, and the La-doped TiO2 photocatalyst is prepared by a high-pressure assisted sol-gel reaction method. The prepared Yb-TiO2 photocatalyst is in an anatase phase crystal form, has good crystallinity and dispersibility, has a larger specific surface area, has more active sites for surface reaction, and has a higher content of hydroxyl groups on the surface of the catalyst than that of intrinsic TiO2, so that the prepared La-TiO2 photocatalyst has good photocatalytic activity and stability. Through structural analysis of the La-TiO2 photocatalyst, it can be found that the specific surface area of the La-TiO2 is obviously larger than that of the intrinsic TiO2.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, specifically to a method for preparing La-doped TiO2 photocatalysts using a high-pressure assisted sol-gel method and the La-TiO2 photocatalyst thereof. Background Technology

[0002] Advanced oxidation technology using TiO2 is a typical and commonly used photocatalyst, possessing advantages such as stability, green and non-toxic properties, and economic and environmental friendliness, making it suitable for treating various wastewaters. Of particular note is the relatively large band gap of TiO2 (E... gThe photocatalytic activity of TiO2 is approximately 3.0-3.2 eV, and it only responds to ultraviolet light. Furthermore, intrinsic TiO2 exhibits a high recombination rate of photogenerated electrons and holes. Therefore, the solar energy utilization efficiency and reactivity of TiO2 in the photocatalytic treatment of wastewater are not ideal, necessitating targeted modification to improve them. In recent years, domestic and international scholars have developed various strategies to enhance the photocatalytic activity of TiO2, including noble metal composites (Au, Ag, Ru, Pt, etc.), transition metal doping (Cu, Fe, Mn, etc.), non-metallic element doping (N, C, S, etc.), and rare earth metal doping (Er, Ce, Eu). Among these methods, rare earth metals, due to their unique 4f electronic structure, can form a transition state between the conduction and valence bands of TiO2, effectively reducing the recombination probability of photogenerated electrons and holes and extending its reaction lifetime. Simultaneously, rare earth metal doping into TiO2 can alter the conduction and valence band positions, reducing its bandwidth and expanding its light absorption range. Furthermore, rare earth metal doping occupies some sites in TiO2 crystals, which can promote its interaction with various Lewis bases (such as amines, aldehydes, alcohols, thiols, etc.), enhance the adsorption of organic pollutants on the surface of TiO2 photocatalysts, and improve subsequent photocatalytic degradation activity. Among the many rare earth metal doped TiO2 photocatalysts, La-doped TiO2 exhibits excellent photocatalytic activity. However, it should be noted that although various methods for preparing La-doped TiO2 photocatalysts have been developed, these methods all have some shortcomings. Taking the most typical sol-gel method and hydrothermal method as examples: the sol-gel method mainly involves the hydrolysis of titanium alkoxides to form a sol-gel, followed by drying to obtain nano-sized TiO2; however, this method is easily affected by temperature during preparation. When the temperature is low, the hydrolysis and condensation rate of the titanium alkoxide solution slows down, resulting in insufficient gel formation and low sample yield; in addition, the crystallinity of TiO2 synthesized by the sol-gel method is not high, and amorphous and crystalline phases often coexist. The hydrothermal method primarily utilizes the high-temperature, high-pressure hydrothermal reaction of titanium salts to obtain crystalline TiO2 samples. However, controlling the morphology and size of the samples using this method is challenging. These issues all affect the catalytic activity and stability of TiO2. Catalyst surface morphology refers to the characteristics of the catalyst surface, including its structure, crystal morphology, pore distribution, and surface species. It directly influences the catalyst's reactivity, selectivity, and stability. Surface morphology affects the quality of the catalyst surface and the rate of chemical reactions, altering the location, binding energy, structure, electron distribution, and charge transport properties of active centers. For example, pore structure and particle size can affect chemisorption and diffusion, thus influencing the reaction rate constant; surface crystal morphology affects surface structure and electrical properties, altering surface characteristics and playing a crucial role in redox catalysts; surface oxide content, crystal surface configuration, and defects can effectively affect the electronic state and energy of active centers on the catalyst surface, significantly impacting the catalytic activity. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing La-doped TiO2 photocatalysts by high-pressure assisted sol-gel method and the La-TiO2 photocatalyst thereof. The prepared La-TiO2 photocatalyst has anatase phase crystal form, good crystallinity, good dispersibility, and a larger specific surface area, resulting in more active sites for surface reactions. Furthermore, the hydroxyl content on the catalyst surface is higher than that of intrinsic TiO2. Therefore, the prepared La-TiO2 photocatalyst has good photocatalytic activity and stability.

[0004] The present invention relates to a high-pressure assisted sol-gel method for preparing La-doped TiO2 photocatalysts, which employs a combination of sol-gel method and high-pressure hydrothermal reaction method to prepare La-doped TiO2 photocatalysts.

[0005] Further, the process includes the following steps: fully dissolving the titanium source and glacial acetic acid in an organic solvent and adding a certain amount of deionized water, then adding La(NO3)3 and stirring until homogeneous, and then adding the mixture to a high-pressure hydrothermal reactor placed in a forced-air drying oven to obtain a gel;

[0006] Furthermore, the drying oven is set for 8-16 hours.

[0007] Furthermore, the temperature of the blower drying oven is set to 80-160℃;

[0008] Furthermore, the titanium source is tetrabutyl titanate, and the organic solvent is anhydrous ethanol;

[0009] Furthermore, it also includes drying and grinding the obtained gel into powder, and calcining the powder to obtain Yb-TiO2 photocatalyst;

[0010] Furthermore, the calcination temperature is 400-600℃, and the calcination time is 2-4 hours;

[0011] The present invention also discloses a La-TiO2 photocatalyst, which is prepared by a high-pressure assisted preparation method for La-doped TiO2 photocatalyst.

[0012] Furthermore, the La-TiO2 photocatalyst has a well-crystallized anatase phase crystal form.

[0013] The beneficial effects of this invention are as follows: The method for preparing La-doped TiO2 photocatalysts using the high-pressure assisted sol-gel method disclosed in this invention, and the resulting La-TiO2 photocatalyst, exhibits anatase phase crystal structure, good crystallinity, good dispersibility, and a larger specific surface area, resulting in more active sites for surface reactions. Furthermore, the hydroxyl content on the catalyst surface is higher than that of intrinsic TiO2, thus the prepared La-TiO2 photocatalyst possesses better photocatalytic activity and stability. Structural analysis of the La-TiO2 photocatalyst reveals that the specific surface area of ​​La-TiO2 is significantly larger than that of intrinsic TiO2. This indicates that a larger specific surface area results in more active sites for surface reactions, which is more conducive to improving photocatalytic performance. In addition to its excellent photocatalytic performance, 0.02% Yb-TiO2 still exhibits high photocatalytic activity after five cycles of photocatalytic degradation of MO dye. After five cycles, the degradation rate decreased by less than 5%, demonstrating good stability. Free radical capture experiments on this photocatalyst show that ·O2… - ·OH, h + All three types of reactive free radicals play a role in the degradation of MO, with ·O2 playing the most significant role. - The active groups eventually decompose and mineralize the dye, ultimately degrading it. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0015] Figure 1 The degradation effect of 0.05% La-TiO2 photocatalyst at different calcination temperatures is shown in the graphs.

[0016] Figure 2 The degradation effect of 0.15% La-TiO2 photocatalyst under different calcination times is shown in the figure.

[0017] Figure 3 The degradation effect of 0.10% La-TiO2 photocatalyst at different high pressure temperatures is shown in the graph.

[0018] Figure 4 The degradation effect of 0.2% La-TiO2 photocatalyst under different high pressure times is shown in the figure.

[0019] Figure 5 (a) XRD patterns of intrinsic TiO2 and La-TiO2 samples, (b) XRD patterns of intrinsic TiO2 and La-TiO2 samples magnified locally;

[0020] Figure 6 FTIR spectra of intrinsic TiO2 and 0.2% La-TiO2 samples;

[0021] Figure 7 (a) UV–vis diffuse reflectance absorption spectra of intrinsic TiO2 and La-TiO2; (b) photon energy spectrum.

[0022] Figure 8 (a) SEM image of a 0.2% La-TiO2 sample, (bc) TEM image of a 0.2% La-TiO2 sample.

[0023] (d) HR-TEM image of a 0.2% La-TiO2 sample;

[0024] Figure 9 (a) N2 adsorption-desorption isotherms of 0.2% La-TiO2 and TiO2, (b) pore size distribution images of 0.2% La-TiO2 and TiO2;

[0025] Figure 10 (a) XPS full spectrum of 0.2% La-TiO2 sample, (b) Ti 2p, (c) La 3d, (d) O 1s;

[0026] Figure 11 PL spectra of intrinsic TiO2 and La-TiO2 samples (excitation wavelength 350 nm);

[0027] Figure 12 (a) Comparison of the activity of intrinsic TiO2 and La-TiO2 photocatalysts in degrading MO under visible light; (b) Kinetic curves of intrinsic TiO2 and La-TiO2 on the degradation of dye MO; (c) Comparison of the degradation rate of intrinsic TiO2 and La-TiO2 photocatalysts.

[0028] Figure 13 (a) Degradation stability data of 0.2% La-TiO2 sample; (b) Cyclic degradation effect of 0.2% La-TiO2 sample;

[0029] Figure 14 XRD patterns of 0.02% La-TiO2 photocatalysts A before degradation and B after degradation;

[0030] Figure 15 (a) Oxalic acid, (b) Isopropanol, (c) Effect of p-benzoquinone on the removal rate of methyl orange. Detailed Implementation

[0031] This embodiment describes a high-pressure assisted sol-gel method for preparing La-doped TiO2 photocatalysts. It employs a combination of the sol-gel method and a high-pressure hydrothermal reaction method. However, this invention does not use a simple combination of existing sol-gel and high-pressure hydrothermal methods. In the prior art, both the sol-gel method and the high-pressure hydrothermal reaction method have problems affecting the catalytic activity and stability of TiO2 photocatalysts. Therefore, even combining the existing sol-gel method and the high-pressure hydrothermal reaction method cannot solve their respective problems, and the issues affecting the catalytic activity and stability of TiO2 photocatalysts remain unresolved.

[0032] This embodiment includes the following steps: titanium source and glacial acetic acid are fully dissolved in an organic solvent, and a certain amount of deionized water is added. Then, La(NO3)3 is added and stirred until homogeneous. The mixture is then added to a high-pressure hydrothermal reactor placed in a forced-air drying oven to obtain a gel. The self-pressure time of the high-pressure hydrothermal reactor is 8-16 h; the temperature of the high-pressure hydrothermal reactor is 80-160 °C; the titanium source is tetrabutyl titanate, and the organic solvent is anhydrous ethanol. The optimal synthesis conditions for La-doped TiO2 obtained by the high-pressure assisted sol-gel method are: calcination temperature 650 °C, calcination time 3 h, high-pressure temperature 120 °C, and high-pressure time 18 h. Under these conditions, when the La doping amount is 0.02%, the photocatalytic performance of the La-doped TiO2 photocatalyst reaches its optimal level under visible light irradiation, achieving a MO degradation rate of 92% within 160 min, which is 23 times that of intrinsic TiO2. Besides reactivity, the reaction stability of the photocatalyst is also an important parameter for evaluating its performance. The synthesized 0.02% La-TiO2 still exhibited high photocatalytic activity after five photocatalytic cycles to degrade MO dyes. Furthermore, the degradation rate decreased by only 5% after five cycles, demonstrating good stability. A series of free radical capture experiments showed that: ·O2 - ·OH, h + All three free radicals participated in the photocatalytic degradation experiment, and ·O2 - It is the main active substance in the photocatalytic degradation process.

[0033] In this embodiment, the process further includes drying and grinding the obtained gel into powder, and calcining the powder to obtain a Yb-TiO2 photocatalyst; the calcination temperature is 400-600℃, and the calcination time is 2-4 hours; the obtained gel is dried, ground into powder, and placed in a muffle furnace for 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours, respectively. The calcination temperatures are set to 400℃, 450℃, 500℃, 550℃, and 600℃, respectively.

[0034] This embodiment also discloses a La-TiO2 photocatalyst, which is prepared by a high-pressure assisted method for preparing La-doped TiO2 photocatalysts. The La-TiO2 photocatalyst has a well-crystallized anatase phase. Analysis of the prepared photocatalyst by XRD, FT-IR, SEM, and TEM shows that the La-TiO2 photocatalyst is anatase with good crystallinity (PDF card number: 21-1272), free of other impurities, and has good dispersibility, but with slight agglomeration. Furthermore, the characteristic peak of the La-doped TiO2 sample near 25.5° gradually shifts to lower angles as the La doping ratio increases. This may be because the La doping into TiO2 slightly alters its crystal structure. Structural analysis of the La-TiO2 photocatalyst shows that the specific surface area of ​​La-TiO2 is significantly larger than that of intrinsic TiO2. This indicates that a larger specific surface area results in more active sites for surface reactions, which is more beneficial for improving photocatalytic performance.

[0035] Example

[0036] La-TiO2 samples were prepared using a high-pressure assisted sol-gel method. Tetrabutyl titanate (10 mL) and glacial acetic acid (6 mL) were dissolved in 45 mL of anhydrous ethanol. After continuous stirring for 10 minutes, 3 mL of deionized water was added, followed by the addition of a certain amount of La(NO3)3 during stirring. The resulting mixture was then rapidly transferred to a 100 mL hydrothermal reactor and subjected to self-pressure at temperatures of 80℃, 100℃, 120℃, 140℃, and 160℃ for 8 h, 10 h, 12 h, 14 h, and 16 h, respectively, in a forced-air drying oven. The resulting gel was dried, ground into powder, and placed in a muffle furnace for 2 h, 2.5 h, 3 h, 3.5 h, and 4 h, respectively. The calcination temperatures were 400℃, 450℃, 500℃, 550℃, and 600℃, respectively. Intrinsic TiO2 samples were also prepared using the same method.

[0037] 1. The effect of calcination temperature of the product on the synthesized material

[0038] This thesis investigated the effect of the calcination temperature of the later-stage products on the photocatalytic performance of TiO2. Under the conditions of 0.05% La doping, a high-pressure time of 10 h, a high-pressure temperature of 80 °C, and a calcination temperature of 3 h, 0.05% La-TiO2 photocatalysts with calcination temperatures of 400 °C, 450 °C, 500 °C, 550 °C, and 600 °C were prepared. Figure 1The figure shows the degradation effect of 0.05% La-TiO2 at different temperatures. It can be seen from the figure that the photocatalytic degradation effect varies with different calcination temperatures under visible light irradiation. After 160 min of irradiation, the degradation rates were 30%, 71%, 42%, 54%, and 37%, respectively. Therefore, the photocatalytic performance is optimal at a calcination temperature of 450℃.

[0039] 2. Effect of calcination time of the product on the synthesized material

[0040] Based on the above experimental results, under the conditions of calcination temperature of 450℃, high pressure time of 10h, high pressure temperature of 80℃, and La doping amount of 0.15%, 0.15% La-TiO2 photocatalysts with calcination times of 2h, 2.5h, 3h, 3.5h, and 4h were prepared. Figure 2 The graph shows the degradation effect of 0.15% La-TiO2 synthesized at different calcination times under visible light. The graph shows that the catalysts synthesized at different calcination times have different effects on MO degradation, with degradation rates of 44%, 36%, 49%, 40%, and 27% within 160 min, respectively. Therefore, the optimal calcination time for the catalyst is 3 h.

[0041] 3. The effect of different high pressure temperatures on the synthesized materials

[0042] Figure 3 The image shows the photocatalytic degradation effect of 0.1% La-TiO2 synthesized at different high-pressure temperatures. To discuss the effect of high-pressure temperature on the photocatalytic performance of TiO2, based on the optimal results discussed above, 0.1% La-TiO2 was synthesized at calcination temperatures of 450℃, calcination time of 3 h, and La doping concentration of 0.1%, yielding high-pressure temperatures of 80℃, 100℃, 120℃, 140℃, and 160℃. Figure 3 The figure shows the degradation effect of 0.10% La-TiO2 synthesized at different high-pressure temperatures under visible light irradiation. The photocatalytic degradation ability varies significantly with increasing temperature. The degradation rates within 160 min are 44.7%, 66.6%, 51.7%, 39.4%, and 41.2%, respectively. This indicates that the photocatalytic performance is best at a high-pressure temperature of 100℃.

[0043] 4. The effect of different high pressure times on the synthesized materials

[0044] Figure 4The figures show the photocatalytic degradation effects of 0.2% La-TiO2 synthesized under different high-pressure times. To discuss the effect of high-pressure time on the photocatalytic degradation effect of TiO2, based on the optimal conditions discussed above, 0.2% La-TiO2 photocatalysts were prepared under the conditions of a muffle furnace calcination temperature of 450℃, a calcination time of 3h, and a high-pressure temperature of 100℃, with high-pressure times of 8h, 10h, 12h, 14h, and 16h. Under visible light irradiation, the photocatalytic degradation effect of methyl orange did not differ significantly with increasing time; the degradation rates of MO within 160min of irradiation were 43%, 36%, 45%, 34%, and 37%, respectively. Therefore, a high-pressure time of 12h yielded the best photocatalytic effect.

[0045] 5. Effect of La doping amount on the synthesized material

[0046] In the process of synthesizing materials, the calcination temperature, calcination time, high-pressure temperature, and high-pressure time of the product all have a certain impact on the photocatalytic performance of La-TiO2. Based on the above discussion, 0.05%-0.25% La-TiO2 was prepared under the optimized preparation conditions (calcination temperature of 450℃, calcination time of 3h, high-pressure temperature of 100℃, and high-pressure time of 12h) to systematically explore the effect of La doping amount on the photocatalytic performance of TiO2.

[0047] 1) XRD analysis

[0048] The XRD patterns of the intrinsic TiO2 and La-TiO2 samples are shown below. Figure 5 As shown in (a). Overall, the XRD diffraction patterns of all samples are essentially consistent, indicating that they are all typical anatase phases (PDF card number: 21-1272) and contain no other impurities. The images show that the La-TiO2 sample has better crystallinity than intrinsic TiO2. For example... Figure 5 As shown in (b), the characteristic peak of TiO2 with different La doping ratios around 25.5° gradually shifts to a lower angle as the La doping ratio increases. This may be because the introduction of La doping into TiO2 slightly alters its crystal structure.

[0049] 2)FT-IR analysis

[0050] Figure 6 To obtain the FT-IR spectra of intrinsic TiO2 and 0.2% La-TiO2. A broad absorption peak was observed at 3421.154 cm⁻¹. -1 and 1633.437cm -1These peaks are related to hydroxyl groups on the sample surface and physically adsorbed water molecules, respectively. After La doping, the intensities of these two peaks are significantly stronger than the intrinsic TiO2 peaks, indicating an increase in the number of surface hydroxyl groups and improved photocatalytic activity. (1300-1000 cm⁻¹) -1 It is a newly formed Ti-OC bond. Meanwhile, the absorption band is at 700 cm⁻¹. -1 up to 400cm -1 The peaks between these peaks correspond to the Ti-O and Ti-O-Ti composites of TiO2, indicating that the catalyst has the characteristic of absorbing light.

[0051] 3) UV-Vis DRS analysis

[0052] Figure 7 As can be seen from this, intrinsic TiO2 does not absorb visible light, while some La-TiO2 samples exhibit significant absorption of visible light in the 400–500 nm range. To analyze the effect of different La doping ratios on the bandgap of TiO2, the Kubelka-Munk method was used to convert UV-Vis diffuse reflectance data into the bandgap width of the samples for direct comparison. Figure 7 As shown in b, the intrinsic bandgap of TiO2 is 3.22 eV. After doping with different proportions of La, the bandgap of TiO2 changed. Specifically, the bandgaps for 0.05% La-TiO2, 0.10% La-TiO2, 0.15% La-TiO2, 0.20% La-TiO2, and 0.25% La-TiO2 are 3.15 eV, 2.88 eV, 2.87 eV, 2.80 eV, and 2.85 eV, respectively. This indicates that the absorption edge of the La-doped TiO2 samples exhibits a significant red shift, and the light absorption of some samples extends into the visible light region. The reason for the red shift in the absorption edge of TiO2 due to La doping may be that La doping causes some Ti in the TiO2 lattice to... 4+ The site was La 3+ Substitution may cause changes in the positions of the conduction band and valence band, or the formation of impurity energy levels between them.

[0053] 4) Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis

[0054] Figure 8 Image a shows the SEM image of 0.2% La-TiO2. The sample is relatively uniformly dispersed, but exhibits an irregular shape and slight agglomeration, which may be due to the rapid addition of deionized water during the synthesis process. To obtain the microstructure and grain size of the La-doped TiO2 particles, we performed TEM analysis. Figure 8bc are TEM images of the 0.2% La-TiO2 sample. As can be seen from the images, the 0.2% La-TiO2 exhibits a polygonal distribution, with stacked grains and a distinct granular texture. The grain size is approximately 8-10 nm. Additionally, as shown... Figure 8 Figure d shows the HR-TEM image of 0.2% La-TiO2. Clear lattice diffraction fringes are visible in the image, with interplanar spacings of 0.35 nm and 0.233 nm, corresponding to the (101) and (103) planes of the anatase TiO2, respectively. While La particles were not directly observed in the HR-TEM image, XPS confirmed their presence. This indicates that La particles are well dispersed in the doped sample.

[0055] 5) Specific surface area (BET) and pore size (BJH) analysis

[0056] Figure 9 a and Figure 9 b represents the N2 adsorption-desorption isotherm and pore size distribution curves for intrinsic TiO2 and 0.2% La-TiO2, respectively. Figure 9 As shown in Figure a, both adsorption-desorption isotherms belong to type IV, indicating that the prepared photocatalytic material has a mesoporous structure. The adsorption capacity increases significantly within the relative pressure range of 0.5–0.9 (P / P0), the adsorption-desorption curves do not overlap, and a significant hysteresis loop appears, both indicating H2 type adsorption-desorption. Comparing the specific surface area of ​​the samples before and after adsorption-desorption, it can be seen that the specific surface area of ​​intrinsic TiO2 is 65.4728 m² / g. 2 The specific surface area of ​​the 0.2% La-TiO2 sample was 118.9836 m² / g. 2 / g. The specific surface area of ​​the sample increased after doping with La, indicating that La participated in the synthesis of its specific surface area. After La doping modification, the growth of TiO2 grains was inhibited, thus giving it a larger adsorption capacity and reaction specific surface area. Figure 9 b represents the pore size adsorption curve of BJH. The figure shows that the average adsorption pore size distribution of intrinsic TiO2 and 0.2% La-TiO2 is between 2 and 10 nm. The pore size distributions of the two catalysts differ significantly, but both fall within the mesoporous range. As shown in the table, the pore volume after La doping is 0.2159 cm³. 3 / g is greater than the intrinsic TiO2 pore volume of 0.1484 cm³. 3 / g, the highest peak in the pore size range after La doping is significantly higher than that of intrinsic TiO2. The increased specific surface area indicates an increase in active sites, which can enhance the absorption of organic dyes and achieve the purpose of rapid degradation of organic matter.

[0057]

[0058] 6) XPS Analysis

[0059] like Figure 10 As shown, the chemical composition and elemental valence states of the 0.2% La-TiO2 sample were analyzed by XPS testing. Figure 10 Image a shows the full XPS spectrum of the sample. The XPS signal peaks for Ti, La, O, and C are clearly visible in the spectrum, indicating the presence of La in the sample. The C1s peak at 284.28 eV is the calibration peak for fixing the sample using carbon during XPS analysis. Figure 10 b shows the high-resolution XPS spectrum of the Ti2p region. Peaks were observed at 458.28 eV and 463.98 eV, indicating that the peaks are caused by Ti2p. 3 / 2 and Ti 2p 1 / 2 This is caused by the fact that the spin orbital splitting energy difference between the two peaks is 5.7 eV, indicating that the material is TiO2. Figure 10 c represents the high-resolution XPS spectrum of the La 3d region, with values ​​at 834.48 eV and 851.18 eV belonging to the La 3d region. 5 / 2 and La 3d 3 / 2 The energy level spin orbital splits, while the other two peaks at 838.58 eV and 855.68 eV are satellite peaks. La 3d 2 / 5 and La 3d 3 / 2 The spin orbitals split to 16.7 eV, therefore, La exists in the synthesized sample as La2O3. Figure 10 d represents the O1s energy level spectrum of the 0.2% La-TiO2 sample. After peak fitting, the peaks at 529.48 eV and 531.28 eV are attributed to lattice oxygen and hydroxyl groups (-OH), respectively. Furthermore, a third peak was detected at a binding energy of 532.38 eV, indicating the presence of La-O bonds.

[0060] 7) PL Analysis

[0061] Photoluminescence (PL) spectroscopy is a commonly used method for studying the carrier recombination properties of semiconductor photocatalysts. Based on this, intrinsic TiO2 and TiO2 with different proportions of La doping were characterized by PL spectra. Figure 11 The PL spectra of the obtained samples under 350 nm excitation are shown. As can be seen from the figure, all samples exhibit a clear PL peak near 540 nm, which is due to photoluminescence caused by carrier recombination in the samples. Compared to the PL peak intensity of intrinsic TiO2, the PL peak intensity of TiO2 gradually decreases after La doping, indicating that La doping suppresses radiative carrier recombination in TiO2. Among them, the PL peak intensity of TiO2 decreased the most after 0.2% La doping, indicating that its carrier recombination rate was the lowest. The reason for the decrease in carrier recombination rate of TiO2 due to La doping may be: 1. La... 3+ Partially replaces the original Ti 4+The disruption of the unit cell structure causes a charge imbalance, creating a potential difference. This situation favors electron transitions, further promoting the separation of photogenerated carriers. Secondly, it may be due to the introduction of La... 3+ The alteration of the material structure creates a transition state energy level, making it easier for electrons to jump to the conduction band. Different La doping ratios have varying degrees of suppression effect on fluorescence intensity; therefore, there is an optimal doping concentration. Analysis of the UV-Vis and PL results above shows that 0.2% La doping has the greatest impact on the properties of TiO2, which is beneficial for improving its photocatalytic activity. Therefore, this thesis focuses on comparing the photocatalytic activity of intrinsic TiO2 and TiO2 with 0.2% La doping in subsequent sections.

[0062] 8) Photocatalytic activity test

[0063] The difference in photocatalytic activity between intrinsic TiO2 and La-TiO2 samples was evaluated by experimentally testing the photocatalytic degradation of methyl orange using the prepared samples. Figure 12 Image a shows the variation of methyl orange concentration with irradiation time under visible light irradiation for intrinsic TiO2 and samples with different La doping ratios. The image shows that La-doped TiO2 significantly improves the degradation of MO compared to intrinsic TiO2. Furthermore, according to the Langmuir-Hinshewood kinetic model:

[0064] ln(C0 / C)=kt

[0065] in

[0066] C0 represents the initial concentration of methyl orange;

[0067] C represents the concentration of methyl orange after time t;

[0068] K represents the reaction rate constant;

[0069] t represents the reaction time

[0070] Linear fitting of the data using Origin software yielded the first-order kinetic curves for MO degradation by the catalyst, and the rate constant (k) results for MO degradation are shown in the figures. The table shows that doping significantly improved the reaction rate constants of the catalysts. The 0.10% La-TiO2 catalyst exhibited a higher k value. This enhanced photocatalytic activity may be due to La acting as a trapping element to strengthen the separation of photogenerated electron-hole pairs, and secondly, it may be due to La doping improving the adsorption of organic pollutants by the photocatalyst. Figure 12As shown in c, the 0.2% La-TiO2 photocatalyst exhibits high degradation efficiency, reaching 92% for MO after 160 min, which is 38.3 times that of intrinsic TiO2. Based on the preceding analysis, the La-TiO2 sample demonstrates two main reasons for its enhanced photocatalytic activity: firstly, the absorption spectrum of the La-doped sample exhibits a redshift, reducing its bandgap and expanding the light absorption range; secondly, the unique 4f electronic structure of the rare earth element La allows for the formation of impurity energy levels between the valence and conduction bands, thereby decreasing the recombination probability of photogenerated electron-hole pairs.

[0071] A review of the kinetic data on the degradation of methyl orange dye by intrinsic TiO2 and different La-TiO2 photocatalysts.

[0072]

[0073] 9) Recycling performance analysis

[0074] Besides the photocatalytic activity of the sample, stability is also an important parameter for evaluating its performance. The stability of the photocatalyst was studied by photocatalytic degradation of MO with a catalyst dosage of 25 mg, a dye concentration of 10 mg / L, and a La doping concentration of 0.2%. We conducted five consecutive experiments on the photocatalytic degradation of MO under visible light, using recovered 0.2% La-TiO2 with other parameters remaining constant. Figure 13 Table a shows that 0.2% La-TiO2 exhibits good stability under visible light irradiation. After 5 cycles of degradation, the efficiency decreased from 92% to 87%, and the degradation effect is as follows: Figure 13 As shown in b. Therefore, the prepared La-TiO2 is a highly efficient photocatalyst with high stability.

[0075] To further demonstrate the excellent stability of the La-TiO2 photocatalyst, we recovered the 0.2% La-TiO2 photocatalyst after five cycles of degradation, washed it several times with deionized water and anhydrous ethanol, and then dried it in a drying oven. The dried 0.2% La-TiO2 photocatalyst was then subjected to XRD analysis, and the results are as follows: Figure 14 As shown in the figure, the 0.2% La-TiO2 photocatalyst before degradation and the photocatalyst after five cycles of degradation both exhibit the same anatase crystal structure. Furthermore, the 0.2% La-TiO2 photocatalyst after five cycles of degradation does not contain any other impurity peaks, and its peak shape remains relatively sharp, indicating good crystallinity retention. This suggests that the degraded 0.2% La-TiO2 photocatalyst still possesses good stability.

[0076] 10) Analysis of Active Free Radical Scavenging Experiments

[0077] like Figure 15The figure shows the inhibitory effect of 0.02% La-TiO2 photocatalyst on MO degradation under different concentrations of free radical scavengers. The figure clearly shows that different active free radicals play different roles in the photocatalytic degradation of MO, as indicated by the results. Figure 15 As shown. Figure 15 The AO radical scavenger added to a is for h + Capture of active free radicals. The figure shows that the degradation rate was not significantly inhibited with increasing AO concentration. Under the same conditions, the degradation rate decreased by only 4% compared to the case without AO. This indicates that there is a certain degree of inhibition during the catalytic degradation process. + It generates active free radicals, but its inhibitory effect is relatively small.

[0078] Figure 15 Figure b shows the degradation experiment with the addition of IPA radical scavenger. As can be seen from the figure, the inhibition of MO degradation rate is relatively small with increasing IPA scavenger concentration. Compared to the case with IPA scavenger, the degradation rate only decreased by 5%. This indicates that ·OH reactive free radicals are generated during the catalytic degradation process, but their role in the catalytic degradation process is very small and can be ignored. Figure 15 Figure c shows the addition of p-BQ as a reactive free radical scavenger. As can be seen from the figure, the degradation rate of MO was significantly inhibited with increasing p-BQ concentration. The inhibition of MO degradation reached its maximum when the concentration increased to 0.2 mmol / L. The MO removal rate decreased by 45% compared to the p-BQ addition. This indicates the presence of O2 during the catalytic degradation process. - The generation of free radicals, and compared with other reactive free radicals, ·O2 - Free radicals have the strongest oxidizing effect.

[0079] in conclusion:

[0080] This invention prepares La-doped TiO2 photocatalysts via a high-pressure assisted sol-gel method. The main conclusions drawn from the systematic characterization of the effects of calcination temperature and time, high pressure, and time on the photocatalytic performance of La-TiO2 are as follows:

[0081] (1) The optimal synthesis conditions for La-doped TiO2 prepared by high-pressure assisted sol-gel method are: calcination temperature 650℃, calcination time 3h, high pressure temperature 120℃, and high pressure time 18h. Under these conditions, when the doping amount of La is 0.02%, the photocatalytic performance of La-doped TiO2 photocatalyst reaches the best under visible light irradiation. The degradation rate of MO reaches 92% within 160min, which is 23 times that of intrinsic TiO2.

[0082] (2) Analysis of the prepared photocatalyst by XRD, FT-IR, SEM and TEM showed that the prepared La-TiO2 photocatalyst was anatase phase with good crystallinity (PDF card number: 21-1272), contained no other impurities, and had good dispersibility, but with slight agglomeration. In addition, the characteristic peak of the La-doped TiO2 sample near 25.5° gradually shifted to a lower angle as the La doping ratio increased. This may be because the La doping into TiO2 slightly changed its crystal structure.

[0083] (3) Structural analysis of the La-TiO2 photocatalyst revealed that the specific surface area of ​​La-TiO2 is 150.1227 m². 2 The specific surface area of ​​ / g is significantly greater than that of intrinsic TiO2, which is 65.4728m². 2 / g. This shows that the larger the specific surface area, the more active sites there are on the surface, which is more conducive to improving photocatalytic performance.

[0084] (4) Besides reactivity, the reaction stability of photocatalysts is also an important parameter for evaluating their performance. The synthesized 0.02% La-TiO2 still exhibited high photocatalytic activity after five photocatalytic cycles to degrade MO dyes. Moreover, the degradation rate only decreased by 5% after five cycles, demonstrating good stability.

[0085] (5) A series of free radical capture experiments showed that: ·O2 - ·OH, h + All three free radicals participated in the photocatalytic degradation experiment, and ·O2 - It is the main active substance in the photocatalytic degradation process.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for degrading methyl orange using a La-doped TiO2 photocatalyst prepared by a high-pressure assisted sol-gel method, characterized in that: A La-doped TiO2 photocatalyst was mixed with the dye methyl orange for the degradation of methyl orange. The La doping amount in the TiO2 photocatalyst was 0.02%. The TiO2 photocatalyst was prepared by the following method: 10 mL of tetrabutyl titanate and 6 mL of glacial acetic acid were dissolved in 45 mL of anhydrous ethanol and stirred continuously for 10 minutes. Then, 3 mL of deionized water was added, followed by the addition of a certain amount of La(NO3)3 during stirring. The resulting mixture was then rapidly transferred to a 100 mL hydrothermal reactor and dried in a forced-air drying oven at 100 °C for 12 h to obtain a gel. The gel was dried, ground into powder, and calcined in a muffle furnace at 450 °C for 3 h to obtain the La-TiO2 photocatalyst. The La-TiO2 photocatalyst is anatase phase crystal form.

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