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

Abstract

The application discloses a method for preparing Yb-La co-doped TiO2 photocatalyst by a high-pressure assisted sol-gel method, and Yb-La co-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-La-TiO2 photocatalyst has very good photocatalytic activity and stability. Through structure analysis of the Yb-La-TiO2 photocatalyst, it can be found that the specific surface area of the Yb-La-TiO2 is obviously larger than that of the intrinsic TiO2. It can be seen that the larger the specific surface area is, the more the active sites for surface reaction are, and the more favorable the improvement of the photocatalytic performance is.

Description

Technical Field

[0001] This invention relates to the field of photocatalysts, specifically to a method for preparing Yb and La co-doped TiO2 photocatalysts using a high-pressure assisted sol-gel method and the resulting Yb-La-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 and La co-doped TiO2 photocatalysts by high-pressure assisted sol-gel method and the resulting Yb-La-TiO2 photocatalyst. The prepared Yb-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 Yb-La-TiO2 photocatalyst has good photocatalytic activity and stability.

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

[0005] Further, the process includes the following steps: fully dissolving titanium source and glacial acetic acid in an organic solvent and adding a certain amount of deionized water, then adding La(NO3)3 and YbN3O9·5H2O and stirring evenly, 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 time of the blower drying oven is set to 6-16 hours.

[0007] Furthermore, the temperature of the forced-air drying oven is set to 60-160℃;

[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 450-650℃, and the calcination time is 2-4 hours.

[0011] This invention also discloses a Yb-La-TiO2 photocatalyst, which is prepared by a high-pressure assisted sol-gel method for preparing Yb and La co-doped TiO2 photocatalysts;

[0012] Furthermore, the Yb-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 Yb and La co-doped TiO2 photocatalysts using the high-pressure assisted sol-gel method disclosed in this invention, and the resulting Yb-La-TiO2 photocatalyst, exhibits anatase phase crystal structure with good crystallinity and dispersibility. A larger specific surface area indicates more active sites for surface reactions, and the hydroxyl content on the catalyst surface is higher than that of intrinsic TiO2. Therefore, the prepared Yb-La-TiO2 photocatalyst possesses excellent photocatalytic activity and stability. Structural analysis of the Yb-La-TiO2 photocatalyst reveals that the specific surface area of ​​Yb-La-TiO2 is significantly larger than that of intrinsic TiO2. This demonstrates 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 dyes. After five cycles, the degradation rate decreased by less than 8%, demonstrating good stability. Free radical capture experiments on this photocatalyst showed 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 Graphs showing the effect of different calcination temperatures on photocatalytic degradation;

[0016] Figure 2 The effect of different calcination times on photocatalytic degradation of the product is shown in the graph.

[0017] Figure 3 The graph shows the effect of different high pressure times on photocatalytic degradation.

[0018] Figure 4 Graphs showing the effects of different high pressure temperatures on photocatalytic degradation;

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

[0020] Figure 6 The composition includes intrinsic TiO2 and 0.09% Yb-TiO2, 0.2% La-TiO2, and 0.09% Yb-0.25% La-TiO2.

[0021] FTIR spectrum of the sample;

[0022] Figure 7 SEM images of (ab) intrinsic TiO2 and (cd) 0.09% Yb-0.25% La-TiO2;

[0023] Figure 8 (ad) TEM image of 0.09%Yb-0.25%La-TiO2, (e) energy dispersive spectroscopy image of 0.09%Yb-0.25%La-TiO2;

[0024] Figure 9 (a) Adsorption-desorption isotherms of intrinsic TiO2 and Yb-La-TiO2, La-TiO2, Yb-TiO2; (b) Pore size distribution of intrinsic TiO2 and Yb-La-TiO2, La-TiO2, Yb-TiO2.

[0025] Figure 10 XPS full spectrum of (a) 0.09% Yb-0.25% La-TiO2 sample, (b) Ti 2p, (c) Yb 4d.

[0026] (d)La 3d, (e)O1;

[0027] Figure 11 (a) UV–vis diffuse reflectance absorption spectra of intrinsic TiO2 and Yb-La-TiO2; (b) photon energy spectrum.

[0028] Figure 12 The PL spectra of three doped photocatalysts (excitation wavelength 320 nm) are shown.

[0029] Figure 13 (a) Comparison of the activities of intrinsic TiO2 and Yb-La-TiO2 photocatalysts in degrading methyl orange under visible light; (b) Kinetic curves of intrinsic TiO2 and Yb-La-TiO2 on the degradation of dye MO; (c) Comparison of the degradation rates of intrinsic TiO2 and Yb-La-TiO2 photocatalysts.

[0030] Figure 14 The graph shows the degradation stability data of (a) the 0.09% Yb-0.25% La-TiO2 sample, and (b) [the graph is missing from the original text].

[0031] Graph showing the cyclic degradation effect of a 0.09% Yb-0.25% La-TiO2 sample;

[0032] Figure 15 The XRD patterns of 0.09% Yb-0.25% La-TiO2 photocatalysts A before degradation and B after degradation are shown.

[0033] Figure 16 The photocatalytic degradation mechanism of Yb-La-TiO2 is described. Detailed Implementation

[0034] This embodiment describes a high-pressure assisted sol-gel method for preparing Yb and La co-doped TiO2 photocatalysts. It employs a combination of the sol-gel method and a high-pressure hydrothermal reaction method. However, this invention does not simply combine existing sol-gel and high-pressure hydrothermal methods. In the prior art, both the sol-gel method and the hydrothermal reaction method have problems affecting the catalytic activity and stability of TiO2 photocatalysts. Therefore, even combining the existing sol-gel method and the hydrothermal reaction method cannot solve their respective problems, and the issues affecting the catalytic activity and stability of TiO2 photocatalysts remain unresolved.

[0035] This embodiment includes the following steps: fully dissolving titanium source and glacial acetic acid in an organic solvent and adding a certain amount of deionized water, then adding La(NO3)3 and YbN3O9·5H2O and stirring evenly, then adding the mixture to a hydrothermal reactor and placing it in a forced-air drying oven to obtain a gel; the time set in the forced-air drying oven is 6-16 hours; the temperature set in the forced-air drying oven is 60-160℃; the titanium source is tetrabutyl titanate, and the organic solvent is anhydrous ethanol; the embodiment also includes drying and grinding the obtained gel to obtain powder, and calcining the powder to obtain Yb-TiO2 photocatalyst; the calcination temperature is 450-650℃, and the calcination time is 2-4 hours. The optimal conditions for preparing Yb-La-TiO2 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, the photocatalyst synthesized under visible light irradiation showed the highest photocatalytic activity when La was 0.25% and Yb was 0.09%, with a degradation rate of 97.3% for MO within 140min. XRD results showed that the prepared Yb-La-TiO2 had a typical anatase phase, and significant characteristic peaks of TiO2 were observed in the FT-IR image. The lattice diffraction fringes of the sample were clearly visible in the SEM and TEM images, indicating that the photocatalyst has good crystallinity. After Fourier transform, the interlayer spacings of 0.35nm and 0.241nm were clearly seen for the (101) and (103) crystal planes of TiO2, respectively. EDX and XPS analyses confirmed the presence of four elements: Ti, La, O, and Yb in the sample. UV-Vis DRS analysis showed that the doping of Yb and La altered the band gap of intrinsic TiO2, resulting in higher photocatalytic activity. In cyclic degradation experiments, the synthesized 0.09%Yb-0.25%La-TiO2 maintained high photocatalytic activity after five cycles of photocatalytic degradation of MO dye. Furthermore, the degradation rate decreased by only 4.3% after five cycles, demonstrating good stability. Free radical capture experiments were conducted on the MO dye. (·O2) - ·OH, h + Analysis of the capture experiments of three free radicals showed that during the degradation of MO, O2... - ·OH, h + Under the influence of three active groups, it gradually decomposes and mineralizes, with ·O2 playing the main role. - Active free radicals.

[0036] This embodiment also discloses a Yb-La-TiO2 photocatalyst, which is prepared by a high-pressure assisted sol-gel method for preparing Yb and La co-doped TiO2 photocatalysts. The Yb-La-TiO2 photocatalyst has a well-crystallized anatase phase. Structural analysis of the Yb-La-TiO2 photocatalyst reveals that the specific surface area of ​​Yb-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. Furthermore, the Yb-La co-doped TiO2 photocatalyst was systematically characterized to demonstrate that Yb-La-TiO2 exhibits higher photocatalytic degradation activity than Yb-TiO2 or La-TiO2 single-doped photocatalysts.

[0037] Example

[0038] Yb-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. During stirring, a certain amount of La(NO3)3 and YbN3O9·5H2O were added. The mixture was then transferred to a 100 mL hydrothermal reactor and subjected to high-pressure treatment in a forced-air drying oven at temperatures of 60℃, 80℃, 100℃, 120℃, 140℃, and 160℃ for 6 h, 8 h, 10 h, 12 h, 14 h, and 16 h. The resulting gels were dried, ground, and then calcined in a muffle furnace for 2 h, 2.5 h, 3 h, 3.5 h, and 4 h at calcination temperatures of 450℃, 500℃, 550℃, 600℃, and 650℃. Meanwhile, intrinsic TiO2 samples were prepared using the same method.

[0039] All major reagents used in the synthesis were AR grade and required no further purification. Acetic acid, lanthanum nitrate, 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 steps.

[0040] 1. Effect of product calcination temperature on the synthesized material

[0041] In the experiment, the calcination time was set to 2.5 h, the high-pressure temperature to 80 °C, and the high-pressure time to 10 h. The doping amounts of Yb and La were 0.09% and 0.5%, respectively. 0.09% Yb-0.5% La-TiO2 photocatalysts were prepared with calcination temperatures of 450 °C, 500 °C, 550 °C, 600 °C, and 650 °C. Figure 1The figures show the photocatalytic degradation curves of 0.09% Yb-0.5% La-TiO2 samples synthesized at different calcination temperatures. The degradation levels varied depending on the calcination temperature. The degradation rates within 160 min of illumination were 33%, 34%, 36%, 40%, and 29%, respectively. Therefore, the optimal photocatalytic degradation effect was observed at 600℃.

[0042] 2. Effect of product calcination time on the synthesized material

[0043] Based on the above experimental results, under the conditions of a calcination temperature of 600℃, a high-pressure temperature of 80℃, a high-pressure time of 10h, and Yb and La doping amounts of 0.09% and 0.5%, respectively, 0.09% Yb-0.5% La-TiO2 catalysts with calcination times of 2h, 2.5h, 3h, 3.5h, and 4h were prepared. Figure 2 The figure shows the degradation effect of the 0.09%Yb-0.5%La-TiO2 photocatalyst prepared under different calcination times. Different calcination times have different effects on the photocatalytic degradation of MO. The degradation rates within 160 min of illumination are 42%, 46%, 30%, 35%, and 43%, respectively. Therefore, the photocatalytic degradation effect is optimal at a calcination time of 2.5 h.

[0044] 3. Effect of high pressure time on the synthesized materials

[0045] This thesis investigated the effect of high pressure time on the photocatalytic degradation of TiO2. Based on the above experimental studies, 0.09% Yb-0.5% La-TiO2 was prepared under the conditions of calcination temperature of 600℃, calcination time of 2.5h, and high pressure temperature of 80℃, with high pressure times of 6h, 8h, 10h, 12h, and 14h. Under visible light irradiation, the photocatalytic degradation effects of different high pressure times showed some differences. The photocatalytic degradation efficiencies within 160min of light irradiation were 34%, 42%, 45%, 36%, and 33%, respectively. Therefore, it can be determined that the photocatalytic degradation effect is best after 10h of high pressure.

[0046] 4. Effects of high pressure and temperature on the synthesized materials

[0047] To investigate the effect of high pressure and temperature on the photocatalytic performance of TiO2, based on the results of the above experimental studies, 0.09%Yb-0.5%La-TiO2 was prepared at high pressure temperatures of 60℃, 80℃, 100℃, 120℃, and 140℃ under the following conditions: calcination temperature of 600℃, calcination time of 2.5h, high pressure time of 10h, and Yb and La doping amounts of 0.09% and 0.5%, respectively. Figure 4The figure shows the photocatalytic degradation effect of 0.09%Yb-0.5%La-TiO2 samples prepared under different high pressure and time conditions. Under visible light irradiation, the photocatalytic degradation performance varies significantly with changes in high pressure and temperature. The degradation rates within 160 min are 38%, 45%, 29%, 32%, and 27%, respectively. This indicates that the photocatalytic effect is best at a high pressure and temperature of 80℃.

[0048] 5. Effects of Yb and La doping amounts on TiO2 performance

[0049] Based on the above discussion, calcination time, calcination temperature, high-pressure time, and high-pressure temperature all significantly affect the performance of TiO2. To improve the photocatalytic activity of TiO2, we prepared TiO2 photocatalysts with different Yb and La doping amounts under the optimal conditions of the high-pressure assisted sol-gel method (calcination temperature 600℃, calcination time 2.5h, high-pressure time 10h, and high-pressure temperature 80℃). The effects of Yb and La doping amounts on the photocatalytic performance of TiO2 were systematically investigated.

[0050] 1) XRD analysis

[0051] Figure 5 The XRD patterns of intrinsic TiO2 and TiO2 doped with La and Yb at different doping ratios are shown below, obtained under the conditions of 600℃, calcination time of 2.5h, high pressure temperature of 80℃, and high pressure time of 10h. From the images, we can see that the XRD diffraction patterns of all samples are basically consistent, indicating that they are typical anatase phase titanium dioxide (PDF card number: 21-1272) without other impurity peaks. However, after careful peak calibration, it was found that the characteristic peaks of TiO2 doped with La and Yb at different ratios around 25.5° gradually shifted slightly to lower angles as the La and Yb doping ratios increased. This may be because the La doping into TiO2 slightly alters its crystal structure. However, compared with intrinsic TiO2, the diffraction peaks of the Yb-La-TiO2 samples are sharper and clearer, indicating better crystallinity.

[0052] 2)FT-IR analysis

[0053] Figure 6 These are intrinsic TiO2, 0.2% La-TiO2, 0.09% Yb-TiO2, and 0.09% Yb-0.25% La-TiO2, respectively. The figure shows 3430.261 cm⁻¹. -1 The two strong broad absorption peaks are due to the stretching vibrations of surface hydroxyl groups in water molecules physically adsorbed on the catalyst surface. The peak at 1626.18 cm⁻¹ is [missing information]. -1The peaks at these locations are caused by the bending vibrations of physically adsorbed water (HOH). After doping, the intensities of these two peaks significantly increased, indicating a marked increase in the number of surface hydroxyl groups, thereby further enhancing its photocatalytic activity. Additionally, at 2334.892 cm⁻¹... -1 The absorption at this point is due to CO2 on the sample surface. However, the peak is obvious in intrinsic TiO2, and it gradually disappears with the doping of rare earth elements La and Yb. The absorption peak is at 500 cm⁻¹. -1 Up to 900cm -1 The vibrations are caused by the bending vibrations of the Ti-O-Ti bonds in anatase TiO2. At 1379.366 cm⁻¹ -1 The absorption peak at that location belongs to the carboxyl group.

[0054] 3) Scanning electron microscopy (SEM) analysis

[0055] Figure 7 SEM images of intrinsic TiO2 and 0.09% Yb-0.25% La-TiO2 photocatalysts. Figure 7 Images a and 7b are SEM images of intrinsic TiO2. The images show severe aggregation and uneven dispersion of intrinsic TiO2. Figure 7 Images c and 7d are SEM images of Yb and La co-doped TiO2. The images show that the co-doped sample is more uniformly dispersed than the intrinsic TiO2 and Yb and La mono-doped TiO2 samples, indicating that co-doping further improves the sample's dispersibility. Furthermore, the agglomeration phenomenon is significantly improved; the sample appears as slightly solid spheres with some irregularly sized shapes, which may be due to insufficient grinding.

[0056] 4) Transmission electron microscopy (TEM) and energy dispersive spectroscopy (DES) analysis

[0057] To further obtain the microstructure and grain size of the sample, we performed TEM analysis, and the results are as follows: Figure 8 The image shown (ad) depicts the microstructure of a 0.09% Yb-0.25% La-TiO2 sample. As can be seen from the image, similar to Yb and La single-doped samples, the samples aggregate into irregular particles. However, the Yb and La co-doped sample is more uniformly dispersed, with a more pronounced granular appearance, indicating that Yb and La co-doping further suppresses TiO2 particle agglomeration. Furthermore, compared to Yb and La single-doped samples, the grain diameter is slightly smaller, with an average diameter of approximately 7-10 nm. Figure 8Images (b), (c), and (d) show HR-TEM images of the 0.09% Yb-0.25% La-TiO2 sample. Clear lattice diffraction fringes indicate good crystallinity, and Fourier transforms clearly show interlayer spacings of 0.35 nm and 0.241 nm corresponding to the (101) and (103) crystal planes in TiO2, respectively. This demonstrates that the co-doping of Yb and La did not alter the phase structure of TiO2, which remains anatase. Figure 8 (e) shows the energy dispersive spectroscopy (EDS) spectrum of the 0.09% Yb-0.25% La-TiO2 sample. It provides qualitative and quantitative information on the elemental and atomic percentages in the 0.09% Yb-0.25% La-TiO2 sample, as shown in the table. The EDS spectrum shows the detection of elements Yb and La, indicating that Yb and La were successfully incorporated into TiO2.

[0058] Table 1. Energy-dispersive X-ray elemental and atomic analyses of TiO2 and 0.09%Yb-0.25%La-TiO2.

[0059] Element Weight% Atomic% Ti 50.01 28.75 O 40.31 69.37 Yb 0.97 0.15 La 8.71 1.73

[0060] 5) Specific surface area (BET) and pore size (BJH) analysis

[0061] Figure 9 a is the N2 adsorption-desorption isotherm of the Yb and La co-doped TiO2 sample prepared at a calcination temperature of 600℃, a calcination time of 2.5h, a high-pressure time of 10h, and a high-pressure temperature of 80℃. As can be seen from the image, they all belong to type IV adsorption-desorption isotherms, which indicates that the catalysts all have mesoporous structure characteristics. Figure 9 b represents the BJH pore size distribution curve. And from... Figure 9 As can be seen from graph a, within the relative pressure range of 0.5 to 0.95 (P / P0), the sample exhibits an H2-type hysteresis loop, indicating a relatively narrow sample distribution. As shown in the table, the specific surface area of ​​TiO2, based on the test results, is 65.4728 m². 2 The specific surface area of ​​0.09% Yb-0.25% La-TiO2 is 150.1227 m² / g. 2 The g / g data shows that the specific surface area of ​​TiO2 increases after doping with Yb and La. This is likely because the doping of Yb and La inhibits the growth of TiO2 grains, thus increasing the specific surface area. Figure 9 The pore size distribution curves show that after co-doping modification, the average adsorption pore size of 0.09% Yb-0.25% La-TiO2 is 5.1006 nm, while that of intrinsic TiO2 is 7.0804 nm. The increased pore size facilitates the transport and adsorption of degraded substances, thus contributing to improved photocatalytic performance of the co-doped samples.

[0062] Structural properties of intrinsic TiO2 and three catalysts.

[0063]

[0064] XPS Analysis

[0065] The chemical composition and elemental valence states of the prepared 0.09% Yb-0.25% La-TiO2 were analyzed by XPS. Figure 10 Figure a shows the full XPS spectrum, where the XPS signals of five elements—Ti, La, Yb, O, and C—are clearly visible, indicating the presence of Yb and La in the sample. The C1s peak at 284.28 eV is the XPS carbon calibration peak. Figure 10 b is the XPS spectrum of Ti 2p. The characteristic peaks at 458.2 eV and 464.2 eV correspond to the Ti 2p3 / 2 and Ti 2p1 / 2 signal peaks, respectively. The difference in spin-orbit splitting energy between the two peaks is 5.70 eV, indicating that this sample is a typical anatase TiO2. Figure 10 c shows the high-resolution XPS spectrum of the Yb 4d region. The peak of Yb 4d5 / 2 is concentrated at the binding energy of 185.24 eV. The results indicate that the peak centers of Yb 4d3 / 2 in the sample are 193.04 eV and 199.15 eV, respectively, which may be due to Yb in Yb2O3 or Yb-O-Ti bonds. 3+ . Figure 10 Figure d shows the high-resolution XPS spectrum of La 3d. In the figure, 834.3 eV and 851.1 eV correspond to the La 3d5 / 2 and La 3d3 / 2 signals, respectively, while the other two satellite peaks are at 838.5 eV and 855.3 eV. The spin-orbit splitting of La 3d2 / 5 and La 3d3 / 2 occurs at 16.80 eV, a characteristic consistent with La 3d3 / 2. 3+ The typical XPS signal is basically consistent. Figure 10 The O1s XPS spectrum of the 0.09% Yb / 0.25% La-TiO2 sample is shown. The peaks at 529.48 eV and 531.28 eV are attributed to lattice oxygen and hydroxyl (-OH) respectively. A small third peak was detected at a binding energy of 532.38 eV, indicating the presence of a small amount of La-O bonds.

[0066] 7) UV-Vis DRS analysis

[0067] Depend on Figure 11It can be seen that intrinsic TiO2 has no absorption in the visible light region, and the doping of La and Yb changes the band gap width of TiO2 to varying degrees. To study the influence of different ratios of Yb and La doping on the band gap of TiO2, the Kubelka-Munk method was used to convert the UV-visible diffuse reflectance data into the band gap width of the samples for intuitive comparison. As Figure 11 shown in Fig. b, the band gap of intrinsic TiO2 is 3.22 eV. After doping with different ratios of Yb and La, the band gap of TiO2 changes. Specifically, for intrinsic TiO2, 0.06Yb%-0.1%La-TiO2, 0.07Yb%-0.15%La-TiO2, 0.08Yb%-0.2%La-TiO2, 0.09Yb%-0.25%La-TiO2, and 0.10Yb%-0.3%La-TiO2, the corresponding band gaps are 3.20 eV, 3.10 eV, 2.90 eV, 2.87 eV, 2.70 eV, and 2.78 eV, respectively. It can be seen that the absorption edge of the Yb and La doped TiO2 samples shows an obvious red shift phenomenon, and the light absorption of some samples can be extended to the visible light region. Moreover, the increase in the doping amounts of La and Yb leads to a greater decrease in the band gap. There is an optimal doping amount, and the band gap decreases the most when it is 0.09Yb%-0.25%La-TiO2.

[0068] 8) PL analysis

[0069] Figure 12 The PL emission spectra of Yb-TiO2, La-TiO2, and Yb-La-TiO2 (excitation wavelength: 320 nm) are given respectively. It can be seen from the figure that there is a broad diffraction peak at 450 nm - 500 nm, and the peak shapes are roughly the same. The PL intensities are in the order of Yb-La-TiO2 < La-TiO2 < Yb-TiO2. Since the lower the PL intensity, the lower the probability of recombination of photo-generated electron-hole pairs, which enhances the photocatalytic activity of the catalyst. Therefore, the photocatalytic activities of the three photocatalysts are in the order of: Yb-La-TiO2 > La-TiO2 > Yb-TiO2.

[0070] 9) Photocatalytic activity test

[0071] The photocatalytic degradation activity is as Figure 13 shown. Among them Figure 13 Fig. a shows the photocatalytic degradation of MO by intrinsic TiO2 and different doping amounts of Yb and La. It can be seen from the figure that the self-degradation of MO is extremely weak. However, under visible light irradiation, Yb and La doped TiO2 show obvious MO degradation activity, while the activity of intrinsic TiO2 is very small. Figure 13b) uses Origin software to perform linear fitting on the data, obtaining the first-order kinetic curve of MO degradation by the catalyst. The rate constant (k) results for MO degradation are shown in the figure. It can be seen from the table that the reaction rate constant of the catalyst is significantly improved after co-doping with Yb and La. Among them, the 0.09%Yb-0.25%La-TiO2 catalyst has a higher k value. Its enhanced photocatalytic activity may be because Yb and La can act as trapping elements to enhance the separation of photogenerated electrons and holes; secondly, it may be because the doping of Yb and La can improve the adsorption of organic pollutants by the photocatalyst. Figure 13 c shows the three-dimensional effect of 0.09% Yb-0.25% La-TiO2 photocatalyst on MO degradation. Within 140 minutes, its degradation rate of MO reached 97.3%, which is 40.5 times that of intrinsic TiO2. Compared with single-doped Yb and La, the co-doped sample showed better degradation performance. As analyzed above, on the one hand, after Yb and La doping, the absorption spectrum of TiO2 undergoes a red shift, reducing the bandgap and allowing for the absorption and utilization of some visible light to drive the photocatalytic reaction; on the other hand, the incorporation of Yb and La into TiO2 effectively reduces the recombination rate of photogenerated electrons and holes, promoting the participation of more photogenerated carriers in the photocatalytic reaction. Therefore, 0.09% Yb-0.25% La-TiO2 exhibits higher photocatalytic activity for MO degradation.

[0072]

[0073] 10) Testing of photocatalytic stability

[0074] Besides photocatalytic activity, stability is also an important parameter for evaluating performance. The stability of MO was studied by photocatalytic degradation when the catalyst dosage was 25 mg, the dye concentration was 10 mg / L, and the doping amounts of La and Yb were 0.25% and 0.09%, respectively. Each reaction time was set to 140 min. In the experiment, the previously degraded photocatalyst was centrifuged at 800 r / min, the supernatant was discarded, and the resulting solid was washed several times with deionized water and ethanol. The washed solid was then dried in a drying oven. This process was repeated five times, and the absorbance was calculated for each iteration. Figure 14 As shown in a. Figure 14 b shows the effect of five cycles of degradation. The graph shows that the degradation rate dropped from 97.3% to 92%, indicating that the difference in degradation rate is very small and it shows good stability.

[0075] To further demonstrate the good stability of the prepared 0.09% Yb-0.25% La-TiO2, the remaining sample after five degradation cycles was washed several times with distilled water and then dried in an oven. After complete drying, XRD analysis was performed, and the results are as follows: Figure 15 As shown in the figure, A and B represent 0.09% Yb-0.25% La-TiO2 before and after degradation, respectively. Overall, the XRD diffraction patterns of all samples are basically consistent, indicating that they are all typical anatase phases (PDF card number: 21-1272) and contain no other impurities. This shows that the crystal structure of the samples did not change after five cycles of degradation, thus demonstrating the good stability of 0.09% Yb-0.25% La-TiO2.

[0076] 11) Photocatalytic reaction mechanism analysis

[0077] In the semiconductor photocatalytic degradation of organic pollutants, h + ·OH and ·O2 - These could all be active substances driving the reaction. To investigate the specific mechanism of the photocatalytic degradation of MO by 0.09% Yb-0.25% La-TiO2, we conducted targeted active substance capture experiments. Ammonium oxalate (AO), isopropanol (IPA), and p-benzoquinone (p-BQ) were added to the reaction system to act as active substance capture agents. Based on the above analysis, from Figure 15 a and Figure 15 As can be seen from b, when ammonium oxalate (h) is added + When either a scavenger (Yb) or isopropanol (·OH scavenger) is used, the photocatalytic degradation efficiency of MO by 0.09% Yb-0.25% La-TiO2 decreases from 97.3% to 91.7% and 92.7%, respectively. The change in reaction activity is not significant, indicating that h + Neither ·OH nor ·OH is the main active substance driving MO degradation; however, when p-benzoquinone is added, the efficiency of MO photocatalytic degradation by 0.09% Yb-0.25% La-TiO2 decreases from 97.3% to 68.2%, and the reaction activity is significantly inhibited, indicating that ·O2 - It is the main active substance driving MO degradation.

[0078] Based on the above findings, we can derive the specific mechanism of the photocatalytic degradation of MO by 0.09% Yb-0.25% La-TiO2 as follows (see...). Figure 16 As shown): (1) After the band gap of 0.09%Yb-0.25%La-TiO2 changes, it can absorb the corresponding visible light. After absorbing visible light, it will generate photogenerated electron-hole pairs; (2) The photogenerated electrons transfer to the surface of 0.09%Yb-0.25%La-TiO2 and react with dissolved oxygen in the solution to generate highly active ·O2. - (3)·O2 -It reacts with MO adsorbed on the surface of 0.09%Yb-0.25%La-TiO2, gradually degrading and mineralizing MO into small molecule compounds such as CO2 and H2O. At the same time, photogenerated holes in 0.09%Yb-0.25%La-TiO2 degrade and mineralize a small amount of MO by reacting directly with MO, or by first reacting with water molecules to generate ·OH, which then reacts with MO.

[0079] Conclusion: Yb-La-TiO2 photocatalysts were prepared using the high-pressure assisted sol-gel method. After systematic characterization, the main conclusions are as follows:

[0080] (1) The optimal conditions for preparing Yb-La-TiO2 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 La is 0.25% and Yb is 0.09%, the photocatalytic activity of the photocatalyst reaches its highest level under visible light irradiation, and the degradation rate of MO reaches 97.3% within 140min. The XRD test results show that the prepared Yb-La-TiO2 has a typical anatase phase, and significant characteristic peaks of TiO2 are observed in the FT-IR image. The lattice diffraction stripes of the sample can be clearly seen in the SEM and TEM images, indicating that the photocatalyst has good crystallinity. After Fourier transform, the interlayer spacing of 0.35nm and 0.241nm is clearly seen to correspond to the (101) and (103) crystal planes in TiO2, respectively. EDX and XPS analyses confirmed the presence of four elements in the sample: Ti, La, O, and Yb. UV-Vis DRS analysis indicated that the doping of Yb and La elements altered the band gap width of intrinsic TiO2, resulting in higher photocatalytic activity.

[0081] (2) Structural analysis of the Yb-La-TiO2 photocatalyst revealed that the specific surface area of ​​Yb-La-TiO2 is 124.231 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.

[0082] (3) In the cyclic degradation experiment, the synthesized 0.09%Yb-0.25%La-TiO2 still exhibited high photocatalytic activity after five photocatalytic cyclic degradations of MO dye. Furthermore, the degradation rate decreased by only 4.3% after five cycles, demonstrating good stability.

[0083] (4) Free radical capture experiments were conducted on the MO dye. ·O2 - ·OH, h +Analysis of the capture experiments of three free radicals showed that during the degradation of MO, O2... - ·OH, h + Under the influence of three active groups, it gradually decomposes and mineralizes, with ·O2 playing the main role. - Active free radicals.

[0084] 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, La co-doped TiO2 photocatalyst prepared by a high-pressure assisted sol-gel method, characterized in that: A TiO2 photocatalyst doped with Yb and La was mixed with the dye methyl orange for the degradation of methyl orange. The doping amounts of La and Yb in the TiO2 photocatalyst were 0.25% and 0.09%, respectively. The 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. After stirring continuously for 10 minutes, 3 mL of deionized water was added. During stirring, a certain amount of La(NO3)3 and Yb(NO3)3·5H2O were added. The mixture was then transferred to a 100 mL hydrothermal reactor and dried in a forced-air drying oven at a high pressure temperature of 80 °C for 10 h to obtain a gel. The gel was dried and ground, and then calcined in a muffle furnace at a calcination temperature of 600 °C for 10 h to obtain a Yb-La-TiO2 photocatalyst. The Yb-La-TiO2 photocatalyst is anatase phase crystal form.

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