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

Abstract

The application discloses a method for preparing Yb-doped TiO2 photocatalyst by a high-pressure assisted sol-gel method, and Yb-doped TiO2 photocatalyst is prepared by the high-pressure assisted sol-gel 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 Yb-TiO2 photocatalyst has good photocatalytic activity and stability.

Description

Technical Field

[0001] This invention relates to the field of TiO2 photocatalysts, specifically to a method for preparing Yb-doped TiO2 photocatalysts using a high-pressure assisted sol-gel method and the resulting Yb-TiO2 photocatalyst. 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 the subsequent photocatalytic degradation activity. Among the many rare earth metal doped TiO2 photocatalysts, Yb-doped TiO2 has high photocatalytic activity and is worthy of attention and research. However, it should be noted that although various methods for preparing Yb-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 forms a sol-gel by hydrolyzing titanium alkoxide, and then drying it 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 will be slowed down, the gel formation will be insufficient, and the sample yield will be low; 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 Yb-doped TiO2 photocatalysts by high-pressure assisted sol-gel method and the resulting Yb-TiO2 photocatalyst. The prepared Yb-TiO2 photocatalyst has anatase phase crystal form, good crystallinity, good dispersibility, a larger specific surface area, more active sites for surface reactions, and a higher hydroxyl content on the catalyst surface than the intrinsic TiO2 content. Therefore, the prepared Yb-TiO2 photocatalyst has good photocatalytic activity and stability.

[0004] The high-pressure assisted preparation method of Yb-doped TiO2 photocatalyst of the present invention uses a sol-gel method combined with a high-pressure hydrothermal reaction method to prepare Yb-doped TiO2 photocatalyst.

[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 Yb(NO3). 3· Stir the mixture thoroughly with 5H2O, then add the mixture to a high-pressure hydrothermal reactor placed in a forced-air drying oven to obtain a gel.

[0006] Furthermore, the drying time of the blower drying oven is set to 6-36 hours.

[0007] Furthermore, the temperature of the blower drying oven is set to 80-180℃;

[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 500-750℃, and the calcination time is 2-4.5h.

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

[0012] Furthermore, the Yb-TiO2 photocatalyst has anatase phase crystal structure and sharp peaks without impurity peaks;

[0013] Furthermore, the particle size of the Yb-TiO2 photocatalyst is 10-13 nm.

[0014] The beneficial effects of this invention are as follows: The method for preparing Yb-doped TiO2 photocatalysts using the high-pressure assisted sol-gel method disclosed in this invention, and the resulting Yb-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 Yb-TiO2 photocatalyst possesses better photocatalytic activity and stability. Structural analysis of the Yb-TiO2 photocatalyst reveals that the specific surface area of ​​Yb-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. In addition to its excellent photocatalytic performance, 0.09% 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 8%, 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

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0016] Figure 1 The graph shows the photocatalytic degradation effect of 0.06% Yb-TiO2 at different calcination temperatures.

[0017] Figure 2 The graph shows the photocatalytic degradation effect of 0.07% Yb-TiO2 under different calcination times.

[0018] Figure 3 The graph shows the photocatalytic degradation effect of 0.08% Yb-TiO2 under different high pressure temperatures;

[0019] Figure 4 The graph shows the photocatalytic degradation effect of 0.06% Yb-TiO2 under different high pressure times.

[0020] Figure 5 In the image, (a) XRD patterns of intrinsic TiO2 and 0.09% Yb-TiO2 under optimized conditions, and (b) magnified XRD patterns.

[0021] Figure 6 SEM images of intrinsic TiO2 and Yb-TiO2;

[0022] Figure 7(ab) TEM spectrum of 0.09% Yb-TiO2, (cd) high-resolution spectrum of 0.09% Yb-TiO2;

[0023] Figure 8 EDS spectrum of 0.09% Yb-TiO2 catalyst;

[0024] Figure 9 Energy-dispersive X-ray elemental and atomic analysis of intrinsic TiO2 and Yb-TiO2;

[0025] Figure 10 (a) Nitrogen adsorption-desorption isotherms of intrinsic TiO2 and 0.09% Yb-TiO2, (b) Intrinsic TiO2 and 0.09% Yb-TiO2 nitrogen adsorption-desorption isotherms.

[0026] Pore ​​size distribution of Yb-TiO2;

[0027] Figure 11 Structural properties of intrinsic TiO2 and 0.09% Yb-TiO2;

[0028] Figure 12 (a) All-purpose, (b) Ti2P, (c) Yb4d, (d) O1s

[0029] Figure 13 Fluorescence spectra of intrinsic TiO2 and 0.09% Yb-TiO2 catalysts (excitation wavelength 325 nm)

[0030] Figure 14 (a) Degradation effect of intrinsic TiO2 and Yb-TiO2 under visible light irradiation; (b) Degradation kinetic curves of intrinsic TiO2 and Yb-TiO2 on methyl orange dye; (c) Comparison of degradation rates of intrinsic TiO2 and Yb-TiO2 photocatalysts.

[0031] Figure 15 A review of kinetic data on the degradation of methyl orange dye by intrinsic TiO2 and different Yb-TiO2 photocatalytic materials; Figure 16 (a) Degradation stability data of 0.09% Yb-TiO2 sample, (b) Cyclic stability data of 0.09% Yb-TiO2 sample

[0032] Image showing the effect of ring degradation;

[0033] Figure 17 XRD patterns of 0.09% Yb-TiO2 photocatalysts A before degradation and B after degradation;

[0034] Figure 18 (a) Effects of ammonium oxalate, (b) p-benzoquinone, and (c) isopropanol on the removal of methyl orange. Detailed Implementation

[0035] The high-pressure assisted preparation method for Yb-doped TiO2 photocatalysts in this embodiment employs a sol-gel method combined with a high-pressure hydrothermal reaction method. This invention does not use a simple combination of the existing sol-gel and high-pressure hydrothermal methods. In the prior art, both the sol-gel and high-pressure hydrothermal methods have problems affecting the catalytic activity and stability of TiO2 photocatalysts. Therefore, even combining the existing sol-gel and high-pressure hydrothermal methods cannot solve their respective problems, and the issues affecting the catalytic activity and stability of TiO2 photocatalysts remain unresolved.

[0036] In this embodiment, the following steps are included: fully dissolving the titanium source and glacial acetic acid in an organic solvent and adding a certain amount of deionized water, and then adding Yb(NO3). 3· The mixture was stirred thoroughly with 5H2O, and then added to a high-pressure hydrothermal reactor placed in a forced-air drying oven to obtain a gel. The self-pressurization time of the high-pressure hydrothermal reactor was 6-36 h, and the temperature of the high-pressure hydrothermal reactor was 80-180℃. The titanium source was tetrabutyl titanate, and the organic solvent was anhydrous ethanol. The optimal synthesis conditions for Yb-doped TiO2 prepared by the high-pressure assisted sol-gel method were: calcination temperature of 650℃, calcination time of 3 h, high-pressure temperature of 120℃, and high-pressure time of 18 h. Under these optimal conditions, when the Yb doping strength was 0.09%, the photocatalytic performance of the Yb-doped TiO2 photocatalyst reached its peak under visible light irradiation, achieving a degradation rate of 95% for methyl orange within 160 min, which is 25 times that of intrinsic TiO2. Structural analysis of the Yb-TiO2 photocatalyst revealed that the specific surface area of ​​Yb-TiO2 was 76.1651 μm. 2 The specific surface area of ​​ / g is significantly greater than that of intrinsic TiO2, which is 65.4728m². 2 / g. This shows that a larger specific surface area results in more active sites for surface reactions, which is more conducive to improving photocatalytic performance. Besides its excellent photocatalytic performance, the stability of 0.09% Yb-TiO2 was also investigated. The synthesized 0.09% Yb-TiO2 still exhibited high photocatalytic activity after five cycles of photocatalytic degradation of MO dyes. After five cycles, the degradation rate only decreased by 8%, demonstrating good stability.

[0037] In this embodiment, the process further includes drying and grinding the obtained gel to obtain powder, and then calcining the powder to obtain a Yb-TiO2 photocatalyst. The calcination temperature is 500-750℃. The obtained gel is dried in a vacuum drying oven, ground to obtain powder, and then transferred to a muffle furnace for calcination at times of 2h, 2.5h, 3h, 3.5h, 4h, and 4.5h, respectively. The calcination temperatures are 500℃, 550℃, 600℃, 650℃, 700℃, and 750℃, respectively.

[0038] This embodiment also discloses a Yb-TiO2 photocatalyst, which is prepared by the high-pressure assisted preparation method for Yb-doped TiO2 photocatalysts as described in any one of claims 1-7. The Yb-TiO2 photocatalyst has an anatase phase crystal form with sharp peaks and no impurity peaks. The particle size of the Yb-TiO2 photocatalyst is approximately 10-13 nm. Analysis using XRD, FT-IR, SEM, and TEM reveals that the prepared Yb-TiO2 photocatalyst has an anatase phase crystal form with good crystallinity, sharp peaks, no impurity peaks, a particle size of approximately 10-13 nm, good dispersibility, and slight agglomeration. Furthermore, the hydroxyl content on the catalyst surface is higher than that of intrinsic TiO2, resulting in improved photocatalytic activity.

[0039] Example

[0040] Yb-TiO2 was prepared by high-pressure assisted sol-gel method:

[0041] Tetrabutyl titanate and glacial acetic acid were dissolved in anhydrous ethanol and stirred continuously for 10 min. Then, a certain amount of deionized water was added dropwise, followed by a certain amount of Yb(NO3)3·5H2O. Stirring was continued for another hour. The mixture was then rapidly transferred to a 100 mL hydrothermal autoclave and placed in a forced-air drying oven at temperatures of 80℃, 100℃, 120℃, 140℃, 160℃, and 180℃ for self-pressurization times of 6 h, 12 h, 18 h, 24 h, 30 h, and 36 h. The resulting gel was dried in a vacuum drying oven, ground into powder, and then calcined in a muffle furnace for 2 h, 2.5 h, 3 h, 3.5 h, 4 h, and 4.5 h at calcination temperatures of 500℃, 550℃, 600℃, 650℃, 700℃, and 750℃. Intrinsic TiO2 samples were prepared using the same method.

[0042] All major reagents used in the synthesis were AR grade and required no further purification. Acetic acid, ytterbium nitrate pentahydrate, ethanol, and tetrabutyl titanate were purchased from Shanghai Aladdin Chemical Reagent Co., Ltd. All chemicals were used as is, without further purification. Deionized water was used in all reactions and processing.

[0043] 1. Effect of calcination temperature on the synthetic materials

[0044] This thesis investigated the effect of different calcination temperatures on the photocatalytic performance of TiO2. Under the conditions of 0.06% Yb doping, a high-pressure time of 18 h, a high-pressure temperature of 120 °C, and a calcination time of 3 h, 0.06% Yb-TiO2 was prepared at calcination temperatures of 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, and 750 °C. Figure 1 The figure shows the photocatalytic degradation effect of 0.06% Yb-TiO2 prepared at different calcination temperatures. It can be seen from the figure that the degradation effect varies with different calcination temperatures. Under visible light irradiation, the degradation rates of methyl orange within 160 min were 24%, 20%, 14%, 26%, 17%, and 14%, respectively. Therefore, it can be concluded that the photocatalytic performance is best at a calcination temperature of 650℃.

[0045] 2. Effect of calcination time on the synthesized materials

[0046] Based on the above experimental results, under the same conditions (0.07% Yb, calcination temperature 650℃, high-pressure temperature 120℃, high-pressure time 18h), 0.07% Yb-TiO2 with calcination times of 2h, 2.5h, 3h, 3.5h, 4h, and 4.5h were synthesized. Figure 2 The figure shows the photocatalytic degradation effect of 0.07% Yb-TiO2 synthesized under different calcination times. As can be seen from the figure, the photocatalytic degradation efficiency of methyl orange changed with the calcination time, with degradation efficiencies of 12%, 7%, 16%, 10%, 14%, and 9% within 160 min. The degradation efficiency of MO did not vary significantly with different calcination times. A calcination time of 3 h represents the optimal synthesis environment for Yb-doped TiO2.

[0047] 3. Effects of high pressure and temperature on synthetic materials

[0048] To investigate the effect of different high-pressure temperatures on the synthesized materials, based on the above research results, under the conditions of a calcination temperature of 650℃, a calcination time of 3 hours, and a doping amount of 0.08%, high-pressure temperatures of 80℃ were used to prepare 0.08% Yb-TiO2 with high-pressure temperatures of 100℃, 120℃, 140℃, 160℃, and 180℃. Figure 3 The figure shows the photocatalytic degradation effect of 0.08% Yb-TiO2 under different high-pressure temperatures. The photocatalytic degradation effect changed with increasing temperature. Under visible light irradiation for 160 min, the degradation rates were 34.5%, 30%, 40%, 19%, 31%, and 25%, respectively. The results indicate that the degradation effect is most ideal at a high-pressure temperature of 120℃.

[0049] 4. Effect of high pressure time on the synthesized materials

[0050] To investigate the effect of high-pressure time on the photocatalytic performance of TiO2, based on the above discussion, under the conditions of 0.06% Yb doping, a high-pressure temperature of 120℃, a calcination time of 650℃, and a calcination time of 3 hours, 0.06% Yb-TiO2 photocatalysts with high-pressure times of 6h, 12h, 18h, 24h, 30h, and 36h were prepared. Figure 4 The figure shows the degradation effect of 0.06% Yb-TiO2 on MO. As can be seen from the figure, the photocatalytic activity of the sample changes with the change in high pressure and time. The degradation rates of MO within 160 min are 26%, 19%, 31%, 25%, 19%, and 18%, respectively. This indicates that the photocatalytic degradation effect is better within 6–24 h, with the optimal photocatalytic degradation effect at 18 h.

[0051] 5. Effect of Yb doping amount on the synthesized material

[0052] Based on the above discussion, it can be concluded that the calcination temperature and time, as well as the high-pressure temperature and time, all affect the photocatalytic activity of TiO2. To maximize the photocatalytic activity of TiO2, TiO2 photocatalysts with different Yb doping amounts were prepared under optimal conditions (calcination temperature 650℃, calcination time 3 hours, high-pressure temperature 120℃, and high-pressure time 18 hours), and the effect of Yb doping amount on the photocatalytic performance of TiO2 was systematically investigated.

[0053] 5.1 XRD Analysis

[0054] like Figure 5 Figure a shows the XRD patterns of intrinsic TiO2 and Yb-TiO2 samples. As can be seen from the figure, the XRD patterns of all samples are basically consistent, indicating the formation of a single anatase phase (PDF card number: 21-1272), without other impurity peaks.

[0055] 5.2 Scanning Electron Microscopy (SEM) Analysis

[0056] like Figure 6 Figures a and 6b show SEM images of intrinsic TiO2 calcined at 650℃ for 3 hours. The images show that the intrinsic TiO2 sample exhibits an irregular polygonal morphology, with relatively uniform dispersion but slight agglomeration, which may be due to insufficient hydrolysis during sample preparation. Figure 6c and 6d are SEM images of 0.09% Yb-TiO2. As can be seen from the images, 0.09% Yb-TiO2 has the same morphology as intrinsic TiO2, both exhibiting irregular shapes. However, the aggregation of the 0.09% Yb-TiO2 sample is reduced, and the sample is more uniformly dispersed. Compared with intrinsic TiO2, the particle size is significantly smaller, which is more conducive to contact with MO and thus promotes the reaction, thereby improving photocatalytic activity.

[0057] 5.3 Transmission Electron Microscopy (TEM) Analysis

[0058] To observe the microstructure of the sample, we performed TEM testing. Figure 7 (ab) are TEM images of the 0.09% Yb-TiO2 sample. The images show that the sample is relatively uniformly dispersed, with obvious granular texture and irregular shape. The average grain size is about 10-13 nm. Figure 7 (cd) shows the HRTEM image of the 0.09% Yb-TiO2 sample. The lattice diffraction fringes are clearly visible in the image. Based on these clear lattice fringes, the interplanar spacings were measured to be 0.35 nm and 0.232 nm, corresponding to the (101) and (103) crystal planes of anatase TiO2. Yb particles were not directly observed in the HRTEM image, but the presence of Yb was confirmed by EDS spectroscopy. Figure 8 As shown in the figure, this indicates that the Yb particles are well dispersed in the doped sample.

[0059] 5.4 EDS Analysis

[0060] like Figure 8 The EDS spectrum of the 0.09% Yb-TiO2 sample is shown. Based on the TEM results, Figure 8 The Ti Ka fluorescence signal of the 0.09% Yb-TiO2 sample was obtained by EDX analysis. It provides qualitative and quantitative information on the elemental and atomic percentages in the 0.09% Yb-TiO2 sample, such as... Figure 9 As shown. From Figure 8 The presence of Yb in the sample is clearly visible. Although no peaks related to Yb-Ti-O or Yb-O were found in the XRD pattern, this indicates that a small number of dopant ions are uniformly dispersed in the TiO2 crystal. However, the EDS spectrum of the dopant with a larger ionic radius (0.09%-Yb-TiO2) clearly shows the signal of rare earth ions, indicating that this rare earth dopant is located near the surface. Since it has a significantly larger ionic radius than Ti4+, it is not incorporated into the TiO2 lattice, which is consistent with the XRD analysis. Figure 9 The composition of the dopant by weight and atomic percentile is shown, with titanium and oxygen being the main components, and the remaining components being due to the gold sputtering treatment of the sample during the testing process.

[0061] 5.5 Specific Surface Area (BET) and Pore Size (BJH) Analysis

[0062] The N2 adsorption-desorption isotherms of intrinsic TiO2 and 0.09% Yb-TiO2 are as follows: Figure 10 As shown in a. Figure 10 a shows that the N2 adsorption-desorption isotherm of the sample is a typical type IV curve, and the curves of all samples show hysteresis loops of type H2, indicating the presence of mesoporous structures in the samples. Figure 10 b shows the pore size distribution curves for intrinsic TiO2 and 0.09% Yb-TiO2. The pore size of TiO2 is approximately 7 nm, and the pore size of 0.09% Yb-TiO2 is approximately 6.25 nm. We also discussed the specific surface area of ​​the samples before and after doping, such as... Figure 11 The figures show the specific surface area and pore volume of intrinsic TiO2 and 0.09% Yb-TiO2. The specific surface area of ​​intrinsic TiO2 is 65.47 m². 2 The specific surface area of ​​0.09% Yb-TiO2 is 76.16 m² / g. 2 / g. The results show that the specific surface area of ​​Yb-doped TiO2 is significantly larger than that of intrinsic TiO2. This indicates that Yb-doped TiO2 has a stronger adsorption capacity and a larger specific surface area for reactions. This may be due to the increased specific surface area of ​​TiO2 resulting from the construction of a porous structure. A larger specific surface area means more active sites for surface reactions, which is more conducive to improving photocatalytic performance.

[0063] 5.6XPS Analysis

[0064] The chemical composition and elemental valence states of the prepared 0.09% Yb-TiO2 were analyzed using XPS analysis, and the results are as follows: Figure 12 As shown. We analyzed the full spectrum and four different elements (C, Ti, O, Yb) on the surface of a 0.09% Yb-TiO2 material. The C1s binding energy of deposited carbon (284.8 eV) was used as an internal calibration. Figure 12 Figure a shows the full XPS spectrum. The XPS signals of Ti, Yb, O, and C are clearly visible, indicating that Yb is present in the sample. The C1s peak at 284.28 eV is the calibration peak of carbon used to fix the sample during XPS analysis. No other impurity peaks were detected, proving that the obtained sample has high purity. Figure 12 b shows the high-resolution XPS spectrum of the Ti 2p region. Peaks were observed at 458.38 eV and 464.08 eV, indicating that the peaks are caused by Ti 2p. 3 / 2 and Ti 2p 1 / 2 This is caused by the difference in spin orbital splitting energies between the two peaks, which is 5.7 eV, indicating that the material is TiO2. Figure 12 c shows the high-resolution XPS spectrum of the Yb 4d region.5 / 2 The peak value is concentrated at the binding energy of 185.28 eV. The results indicate that the Yb 4d... 3 / 2 The peak centers are 193.08 eV and 199.18 eV, respectively, which may be due to Yb₂O₃ or Yb in the Yb-O-Ti bond. 3+ The results in the O1s region are as follows: Figure 12 As shown in d, one strong peak and two weak peaks can be observed. The strong binding energy peak at 529.58 eV is the peak of Ti-O bond forming TiO2, and the peaks at 531.38 eV and 532.68 eV are the OH bond and CO bond, respectively.

[0065] 5.7PL Analysis

[0066] from Figure 13 As can be seen, the Yb-doped TiO2 catalyst exhibits a broad diffraction peak in the 370-600 nm region. No new PL peak appeared after doping. Its luminescence intensity decreases from top to bottom. This indicates that Yb doping may suppress the recombination of photogenerated electron-hole pairs, leading to an increase in fluorescence intensity and a decrease in photocatalytic activity. 3+ The ions have a unique 4f electron configuration, which can temporarily trap photogenerated electrons and tend to be released into acceptors such as O2 adsorbed on the surface to form O. 2- This suppresses the recombination of photoelectrons and holes. Different Yb doping ratios have different suppressive effects on fluorescence intensity, thus there exists an optimal doping concentration. In this study, the Yb doping concentration was 0.09% when the light intensity was low, indicating that the photocatalytic activity was highest at this doping level.

[0067] 5.8 Photocatalytic activity experiment

[0068] The photocatalytic degradation performance of the catalyst for methyl orange was evaluated through photocatalytic degradation experiments on the prepared samples. The degradation activity of the Yb-doped TiO2 photocatalyst was studied under the following conditions: calcination temperature of 650℃, calcination time of 3 hours, high pressure time of 18 hours, and high pressure temperature of 120℃, with Yb doping amounts of 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, and 0.11%, respectively. Figure 14 As shown in figure a, it can be seen from the figure that there is a significant difference in the degradation effect of intrinsic TiO2 and Yb-doped TiO2 samples under visible light irradiation. The image shows that intrinsic TiO2 has a relatively small degradation effect on MO, but under the same conditions, the catalyst activity gradually changes with the addition of Yb. The optimal degradation effect on MO is achieved at a doping concentration of 0.09%. Figure 14 As shown in c, the degradation rate of MO reached 95% within 160 min, which is 25 times that of intrinsic TiO2.

[0069] Based on the preceding analysis, this is likely because rare earth element Yb plays a crucial role in the degradation process. On one hand, Yb doping causes a redshift in the absorption spectrum, reducing its bandgap and expanding the light absorption range. On the other hand, the incorporation of Yb may create transition states, extending the lifetime of photogenerated electron-hole pairs and thus improving photocatalytic activity. However, when the Yb doping concentration exceeds 0.09%, the catalyst activity decreases. This may be because higher Yb doping concentrations lead to blockage and obstruction of photoparticles due to the covering of the semiconductor surface. Another reason might be that at higher loading rates, multiple capture of charge carriers may increase the likelihood of electron-hole recombination; therefore, there exists an optimal doping concentration. In this experimental study, the highest photocatalytic activity was observed at a doping concentration of 0.09%.

[0070] like Figure 14 Figure b shows the relationship between ln(C0 / C) and degradation irradiation time. According to the Langmuir-Hinshelwood (LH) principle, the photocatalytic degradation reaction follows a first-order kinetic equation, as shown below:

[0071] ln(C0 / C)=kt

[0072] in

[0073] C0 represents the initial concentration of methyl orange;

[0074] C represents the concentration of methyl orange after time t;

[0075] K represents the reaction rate constant;

[0076] t represents the reaction time

[0077] like Figure 15 As shown, compared with intrinsic TiO2, the reaction rate constant k is significantly increased after Yb doping, indicating that the kinetic rate of MO degradation catalyzed by Yb-doped TiO2 is enhanced, with Yb (0.09%)-doped TiO2 exhibiting the highest photodegradation rate constant k value. Under the same conditions, the degradation rate of MO is faster.

[0078] Besides photocatalytic activity, stability is also an important parameter for evaluating its performance. The stability of the photocatalyst was studied by photocatalytic degradation of MO when the catalyst dosage was 25 mg, the dye concentration was 10 mg / L, and the Yb doping concentration was 0.09%. We conducted five consecutive photocatalytic degradation experiments. Each time, the previous sample was centrifuged at high speed, the supernatant was removed, and the sample was washed several times with anhydrous ethanol and deionized water before being dried in an oven. The recovered catalyst was then used to degrade MO. Other parameters were kept constant. Figure 16As shown in Figure a, 0.09% Yb-TiO2 exhibited effective stability under visible light irradiation, but after the fifth cycle, as... Figure 16 As shown in b, the degradation rate decreased from 95% to 87%. Therefore, the synthesized Yb-TiO2 is a highly efficient photocatalyst with high reusability.

[0079] To further demonstrate its stability, the sample after five cycles was washed with deionized water, dried, and then subjected to XRD testing. Figure 17 As shown in the figure, both the XRD patterns before and after degradation show a single, typical anatase phase without any other impurity peaks. Furthermore, the peak shape of the XRD pattern after degradation is as sharp and clear as that before degradation, indicating that there is no significant difference between the 0.09% Yb-TiO2 catalyst before and after degradation, and the crystallinity remains good, demonstrating the good stability of 0.09% Yb-TiO2.

[0080] 5.8 Experiment on the capture of active free radicals

[0081] Many free radicals are generated during photocatalytic reactions, and these free radicals typically possess strong oxidizing properties. Among them, h... + O2 - ·OH is considered to be the main free radical in photocatalytic reactions. In this study, the existence of these three free radicals was verified through free radical capture experiments, and their roles in the degradation process were analyzed through experiments on the degradation of MO.

[0082] Figure 18 Figure a shows the effect of different concentrations of AO on the removal rate of MO. As can be seen from the figure, the degradation rate of MO was affected to some extent after adding different concentrations of AO. The overall inhibitory effect of AO on MO degradation was very weak after increasing the concentration. When the AO concentration increased to 0.5 mmol / L, the degradation rate decreased by 7% compared with the sample without AO. This indicates that the inhibitory effect of AO on MO degradation is not significant. This suggests that there is a certain degree of inhibition in the degradation of MO. + The presence of reactive free radicals is present, but their role is not significant.

[0083] Figure 18 Figure b shows the effect of different concentrations of p-BQ on the removal rate of MO. As can be seen from the figure, the degradation rate of MO was significantly inhibited after adding different concentrations of p-BQ. When the concentration of p-BQ reached 0.14 mmol / L, under the same conditions, the degradation rate with p-BQ added decreased by 39% compared to the degradation rate without p-BQ. Figure 18As shown in Figure c, the degradation rate of MO was also somewhat inhibited with the addition of different concentrations of IPA. Under the same conditions, the degradation rate decreased by 6% compared to the addition of IPA. This indicates that O2 is present during the degradation of methyl orange. - The presence of ·OH demonstrates, through experiments, that ·O2, compared to other active free radicals, plays a more significant role in the catalytic degradation process. - It has the strongest oxidizing effect.

[0084] in conclusion:

[0085] (1) The optimal synthesis conditions for Yb-doped TiO2 prepared by high pressure assisted sol-gel method are: calcination temperature of 650℃, calcination time of 3h, high pressure temperature of 120℃, and high pressure time of 18h. Under these optimal conditions, when the doping power of Yb is 0.09%, the photocatalytic performance of Yb-doped TiO2 photocatalyst reaches the best under visible light irradiation. The degradation rate of methyl orange reaches 95% within 160min, which is 25 times that of intrinsic TiO2.

[0086] (2) Combined with XRD, FT-IR, SEM and TEM analysis, it can be found that the prepared Yb-TiO2 photocatalyst is anatase phase crystal form with good crystallinity, sharp peaks, no impurity peaks, and a particle size of about 10 to 13 nm. It has good dispersibility and slight agglomeration. Moreover, the hydroxyl content on the catalyst surface is higher than that of intrinsic TiO2, which leads to the improvement of photocatalytic activity.

[0087] (3) Structural analysis of the Yb-TiO2 photocatalyst revealed that the specific surface area of ​​Yb-TiO2 is 76.1651 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.

[0088] (4) In addition to its good photocatalytic performance, the stability of 0.09% Yb-TiO2 was also investigated. The synthesized 0.09% Yb-TiO2 still exhibited high photocatalytic activity after five photocatalytic degradation cycles of MO dye. After five cycles, the degradation rate only decreased by 8%, demonstrating good stability.

[0089] 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 Yb-doped TiO2 photocatalyst prepared by a high-pressure assisted sol-gel method, characterized in that: A Yb-doped TiO2 photocatalyst was mixed with the dye methyl orange for the degradation of methyl orange. The Yb doping content in the TiO2 photocatalyst was 0.09%. The TiO2 photocatalyst was prepared by the following method: tetrabutyl titanate and glacial acetic acid were dissolved in anhydrous ethanol and stirred continuously for 10 min. Then, a certain amount of deionized water was added dropwise, followed by a certain amount of Yb(NO3)3·5H2O. The mixture was stirred for another hour. The mixture was then quickly transferred to a 100 mL hydrothermal reaction pressure vessel. The pressure vessel was placed in a forced-air drying oven at a temperature of 120 °C for 18 h to obtain a gel. The obtained gel was dried in a vacuum drying oven and ground into powder. The powder was then calcined in a muffle furnace at a temperature of 650 °C for 3 h to obtain the Yb-TiO2 photocatalyst. The Yb-TiO2 photocatalyst had anatase phase crystal form and a particle size of 10-13 nm.

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