Modified tiO2 composite photocatalyst, its preparation method and application in photocatalytic reduction of cr(vi)
By growing β-AgVO3 quantum dots on TiO2 nanosheets to form a direct Z-type heterojunction, the problem of photogenerated carrier recombination in the Cr(VI) reduction process of TiO2 photocatalyst was solved, achieving high efficiency in photocatalytic reduction of Cr(VI) and improving the photocatalytic activity and Cr(VI) reduction ability of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2023-11-03
- Publication Date
- 2026-06-09
Smart Images
Figure CN117504874B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a photocatalyst, its preparation method and application, and particularly to a modified TiO2 composite photocatalyst, its preparation method and its application in the photocatalytic reduction of Cr(VI). Background Technology
[0002] Heavy metal ions are non-biodegradable and, once in the environment, can only migrate and undergo form transformation, not disappear, thus persisting in the environment for a long time. Cr(VI) itself is highly soluble in water, highly mobile, and inherently stable and difficult to degrade. Furthermore, Cr(VI) is extremely toxic, more than 100 times more toxic than Cr(III), and therefore, contact with humans may cause skin sensitivities, and long-term exposure may increase the probability of genetic diseases and cancer. Therefore, finding a friendly and effective method to treat heavy metal Cr(VI) in wastewater is of great significance for mitigating and controlling environmental pollution. Among various water treatment technologies, photocatalysis has received widespread attention from researchers due to its simple operation, cleanliness, and high efficiency.
[0003] Titanium dioxide (TiO2) is a classic semiconductor photocatalyst. Its advantages, such as low price, high efficiency, and environmental friendliness, make it irreplaceable and a long-standing research hotspot in the field of photocatalysis. However, problems such as easy recombination of photogenerated carriers and low light utilization have affected its performance in the photocatalytic reduction of Cr(VI), limiting its widespread application in practical applications. Furthermore, although there are reports in the prior art of titanium dioxide being modified by composites with other materials, such as Liu Y, Liu N, Lin M, et al. Straightforward synthesis and mechanism insight of TiO2 / α′-AgVO3 heterostructure with enhanced photocatalytic activity[J]. Semiconductor Science and Technology, 2022, 38(1):015016, Kaur A, Kansal SK, Umar A. β-AgVO3 nanowires / TiO2 nanoparticles heterojunction assembly with improved visiblelight driven photocatalytic decomposition of hazardous pollutants and mechanism insight[J]. Separation and Purification Technology, 2020, 251:117271, and patent CN116422332A, the titanium dioxide-modified composite materials reported in the prior art are not used for photocatalytic reduction of heavy metal ions. Currently, there are few reports on the use of titanium dioxide modified composite materials for the efficient catalytic reduction of heavy metal Cr(VI), and the catalytic efficiency needs to be further improved. Summary of the Invention
[0004] Objective of the invention: This invention aims to provide a modified TiO2 composite photocatalyst for the efficient photocatalytic reduction of heavy metal ions; this invention also aims to provide a method for preparing the modified TiO2 composite photocatalyst for the photocatalytic reduction of heavy metal ions; this invention further aims to provide an application of the modified TiO2 composite photocatalyst in the photocatalytic reduction of Cr(VI), with a photocatalytic reduction efficiency of up to 99%.
[0005] Technical solution: The modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions described in this invention includes TiO2 nanosheets as a support and β-AgVO3 quantum dots grown on TiO2 nanosheets.
[0006] Furthermore, TiO2 nanosheets form a direct Z-type heterojunction structure with β-AgVO3.
[0007] The preparation method of the modified TiO2 composite photocatalyst includes the following steps:
[0008] (1) TiCl4 is dissolved in an organic solvent and water is added to carry out a hydrothermal reaction to obtain TiO2 nanosheets; in this step, titanium tetrachloride is hydrolyzed to generate titanium hydroxide, and titanium hydroxide is hydrothermally reacted to generate TiO2 during the hydrothermal reaction.
[0009] (2) The above TiO2 nanosheets were dispersed in AgNO3 solution, and then NH4VO3 solution was added dropwise. The pH of the solution was adjusted to neutral, and the TiO2 modified composite photocatalyst was obtained after ultrasonic reaction.
[0010] Preferably, in step (1), the temperature of the hydrothermal reaction is 75-175°C, the reaction time is 4-12h, and the volume ratio of TiCl4, solvent and water is 0.1-10:1-180:0.1-10.
[0011] Preferably, in step (2), the mass ratio of Ti, Ag, and V is 6–16:1.8–2.2:0.9–1.1, the mass-volume ratio of AgNO3, NH4VO3, and water is (0.03–0.08) g:(0.02–0.06) g:(40–100) mL, the dropping rate of the NH4VO3 solution is 0.5–1.2 mL / h, the ultrasonic reaction time is 0.5–1 h, and the temperature is 60–100 °C.
[0012] The modified TiO2 composite photocatalyst can be used in the photocatalytic reduction of Cr(VI). The modified TiO2 composite photocatalyst converts Cr(VI) into Cr(III) by light irradiation, and the photocatalytic reduction efficiency of Cr(VI) is up to 99%.
[0013] Invention Mechanism: Zero-dimensional AgVO3 quantum dots have attracted widespread attention due to their unique advantages such as small size (<10nm), large specific surface area, short effective charge transfer length, and tunable photoelectrons. However, their practical applications are limited by defects such as easy aggregation and structural instability. One way to solve these problems is to load quantum dots onto ultrathin TiO2 two-dimensional nanomaterials to form 0D / 2D nanocomposite materials. More importantly, the suitable band structure of AgVO3 can form a direct Z-shaped heterostructure with TiO2. Constructing a direct Z-shaped heterostructure can achieve effective spatial separation of photogenerated electrons and holes without affecting the redox activity of TiO2, which is a simple and effective control strategy to improve the photocatalytic activity of materials.
[0014] The modified TiO2 composite photocatalyst prepared in this invention forms a direct Z-shaped heterojunction between TiO2 and β-AgVO3. In the photocatalytic reduction of Cr(VI), due to the built-in electric field at the interface of the direct Z-shaped heterojunction, photoexcited electrons in the conduction band of TiO2 spontaneously transfer to the valence band of β-AgVO3, consuming the residual holes in β-AgVO3. This achieves efficient spatial separation of photogenerated electrons and holes and maintains the system's strongest redox capability, thereby enhancing the system's photocatalytic reduction performance of Cr(VI). Furthermore, by utilizing the difference in band structure to suppress the rapid recombination of electron-hole pairs, the utilization rate of light and the adsorption capacity for Cr(VI) are improved, thus enhancing the photocatalytic reduction capability of Cr(VI).
[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The modified TiO2 composite photocatalyst can convert Cr(VI) into Cr(III) by light irradiation, and the photocatalytic reduction efficiency of Cr(VI) can reach up to 99%, which is beneficial to significantly reduce the chemical activity and toxicity of Cr in the environment; (2) The modified TiO2 composite photocatalyst forms a direct Z-type heterojunction with β-AgVO3 and TiO2, which effectively inhibits the recombination of photogenerated electrons and holes and improves the utilization rate of light while maintaining the redox performance of TiO2, and improves the utilization rate of light to obtain high-efficiency photocatalytic activity; (3) The preparation method of the modified TiO2 composite photocatalyst is simple, the raw material cost is low and the yield is abundant, which has the premise of being put into large-scale production in the future. Attached Figure Description
[0016] Figure 1 Scanning electron microscope image of the modified TiO2 composite photocatalyst prepared in Example 4;
[0017] Figure 2 and Figure 3 Transmission electron microscopy image of the modified TiO2 composite photocatalyst prepared in Example 4;
[0018] Figure 4 X-ray diffraction pattern of the modified TiO2 composite photocatalyst prepared in Example 4;
[0019] Figure 5 The graph shows the photocatalytic reduction efficiency of Cr(VI) of the modified TiO2 composite photocatalysts prepared in Examples 1-4 under xenon lamp irradiation.
[0020] Figure 6 The modified TiO2 composite photocatalyst prepared in Example 4 and the catalysts prepared in Comparative Examples 1-3 are shown in the photocatalytic reduction efficiency of Cr(VI) under xenon lamp irradiation.
[0021] Figure 7The X-ray diffraction patterns of the modified TiO2 composite photocatalyst prepared in Example 4 before and after the reaction are shown below.
[0022] Figure 8 and Figure 9 The images show the photocurrent and electrochemical impedance spectroscopy of the modified TiO2 composite photocatalyst prepared in Example 4. Detailed Implementation
[0023] The technical solution of the present invention will be further described below with reference to the embodiments.
[0024] Example 1
[0025] The modified TiO2 composite photocatalyst of the present invention is prepared by the following steps:
[0026] (1) Add 1 mL TiCl4 to 20 mL ethylene glycol solution, stir evenly, add 0.5 mL pure water, transfer the completely dissolved mixed solution to a hydrothermal reactor, and carry out a constant temperature thermal reaction at 110 °C for 10 h. After the reaction is completed, wash the obtained product repeatedly with ultrapure water and anhydrous ethanol, centrifuge and vacuum dry to obtain TiO2 nanosheets.
[0027] (2) 60 mg of the prepared TiO2 nanosheets were ultrasonically dispersed in 20 mL of 5 mmol / L AgNO3 solution for 0.3 h. Then, 20 mL of 5 mmol / L NH4VO3 solution was added to the system at a rate of 1 mL / min. After stirring for 0.5 h, the pH was adjusted to 8 with ammonia water, and the mixture was ultrasonically reacted at 60 °C for 0.8 h. After the reaction, the mixture was naturally cooled to room temperature. The resulting precipitate was separated by centrifugation, washed three times each with ultrapure water and anhydrous ethanol, and dried under vacuum to obtain the modified TiO2 composite photocatalyst TAV-1.
[0028] Example 2
[0029] The modified TiO2 composite photocatalyst of the present invention is prepared by the following steps:
[0030] (1) Add 5 mL TiCl4 to 150 mL ethylene glycol solution, stir evenly, add 5 mL pure water, transfer the completely dissolved mixture to a hydrothermal reactor, and carry out a constant temperature thermal reaction at 150 °C for 5 h. After the reaction is completed, wash the obtained product repeatedly with ultrapure water and anhydrous ethanol, centrifuge and vacuum dry to obtain TiO2 nanosheets.
[0031] (2) 150 mg of the prepared TiO2 nanosheets were ultrasonically dispersed in 40 mL of 8 mmol / L AgNO3 solution for 1.6 h. Then, 40 mL of 8 mmol / L NH4VO3 solution was added to the system at a rate of 0.8 mL / min. After stirring for 1 h, the pH was adjusted to 7 with ammonia water, and the mixture was ultrasonically reacted at 80 °C for 1 h. After the reaction, the mixture was naturally cooled to room temperature. The resulting precipitate was separated by centrifugation, washed three times each with ultrapure water and anhydrous ethanol, and dried under vacuum to obtain the modified TiO2 composite photocatalyst TAV-2.
[0032] Example 3
[0033] The modified TiO2 composite photocatalyst of the present invention is prepared by the following steps:
[0034] (1) Add 0.5 mL TiCl4 to 50 mL ethylene glycol solution, stir evenly, add 2 mL pure water, transfer the completely dissolved mixed solution to a hydrothermal reactor, and carry out a constant temperature thermal reaction at 90 °C for 8 h. After the reaction is completed, wash the obtained product repeatedly with ultrapure water and anhydrous ethanol, centrifuge and vacuum dry to obtain TiO2 nanosheets.
[0035] (2) 320 mg of the prepared TiO2 nanosheets were ultrasonically dispersed in 40 mL of 10 mmol / L AgNO3 solution for 1 h. Then, 40 mL of 10 mmol / L NH4VO3 solution was added to the system at a rate of 1 mL / min. After stirring for 0.8 h, the pH was adjusted to 6 with ammonia water, and the mixture was ultrasonically reacted at 80 °C for 1 h. After the reaction, the mixture was naturally cooled to room temperature. The resulting precipitate was separated by centrifugation, washed three times each with ultrapure water and anhydrous ethanol, and dried under vacuum to obtain the modified TiO2 composite photocatalyst TAV-3.
[0036] Example 4
[0037] The modified TiO2 composite photocatalyst of the present invention is prepared by the following steps:
[0038] (1) Add 1 mL TiCl4 to 30 mL ethylene glycol solution, stir evenly, add 1.5 mL pure water, transfer the completely dissolved mixed solution to a hydrothermal reactor, and carry out a constant temperature thermal reaction at 135 °C for 4.5 h. After the reaction is completed, wash the obtained product repeatedly with ultrapure water and anhydrous ethanol, centrifuge and vacuum dry to obtain TiO2 nanosheets.
[0039] (2) 120 mg of the prepared TiO2 nanosheets were ultrasonically dispersed in 20 mL of 5 mmol / L AgNO3 solution for 0.5 h. Then, 20 mL of 5 mmol / L NH4VO3 solution was added to the system at a rate of 0.8 mL / min. After stirring for 1 h, the pH was adjusted to 7 with ammonia water, and the mixture was ultrasonically reacted at 80 °C for 0.8 h. After the reaction, the mixture was naturally cooled to room temperature. The resulting precipitate was separated by centrifugation, washed three times each with ultrapure water and anhydrous ethanol, and dried under vacuum to obtain the modified TiO2 composite photocatalyst TAV-4.
[0040] Comparative Example 1
[0041] Based on Example 4, only step (1) was performed to obtain TiO2 nanoparticles, while the other conditions remained unchanged.
[0042] Comparative Example 2
[0043] Based on Example 4, step (1) is omitted, and TiO2 nanosheets are not added in step (2). Only β-AgVO3 is synthesized, and the other conditions remain unchanged.
[0044] Comparative Example 3
[0045] This comparative example provides a TiO2 / AgVO3 composite photocatalyst and its preparation method. The main difference between this catalyst and that in Example 4 is that this catalyst is type-II. The specific preparation method is as follows:
[0046] (1) 10 mL of tetrabutyl titanate was added to a mixed solution containing 10 mL of alcohol and 3 mL of acetic acid, and the mixture was stirred in a sealed container for 2 h. Then, 1 g of vinylpyrrolidone was added to the solution, and the reaction was continued for 10 h. The resulting solution was transferred to the syringe of an electrospinning machine, and electrospinning was performed at a voltage of 15 kV and a feed rate of 1.8 mL / h. The obtained product was calcined at 500 °C for 4 h to obtain TiO2 nanorods.
[0047] Step (2) is the same as in Example 4, and TiO2 / AgVO3 composite photocatalyst is obtained.
[0048] Structural characterization:
[0049] The modified TiO2 composite photocatalyst synthesized in Example 4 was characterized structurally.
[0050] Figure 1 and Figure 2 , 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the modified TiO2 composite photocatalyst prepared in Example 4. Figure 1 , 2As shown in Figure 3, the composite catalyst exhibits the morphology of quantum dots grown on nanosheets. The intuitive morphological structure diagram initially indicates that the two materials were successfully combined, with the size of the β-AgVO3 quantum dots being <10nm.
[0051] Figure 4 The image shows the X-ray diffraction pattern of the modified TiO2 composite photocatalyst prepared in Example 4. As can be seen from the image, the characteristic peaks of TiO2 and β-AgVO3 appear simultaneously in the composite catalyst, further illustrating the close bonding between the two materials.
[0052] Performance characterization:
[0053] The photocatalytic performance of the modified TiO2 composite photocatalysts synthesized in Examples 1-4 and the catalysts synthesized in Comparative Examples 1-3 was tested.
[0054] Test method: Using a photocatalytic reactor (Nanjing Xujiang Electromechanical Plant, XPA-8), under irradiation with a 500W Xe lamp, the heavy metal Cr(VI) was reduced to Cr(III) to evaluate the catalytic ability of the prepared photocatalyst. Before all catalytic experiments, the dispersion was stirred in the dark for 30 minutes to reach adsorption equilibrium.
[0055] Figure 5 The graph shows the photocatalytic reduction efficiency of heavy metal Cr(VI) in wastewater by the modified TiO2 composite photocatalysts prepared in Examples 1-4 under xenon lamp irradiation. The photocatalytic reduction efficiencies of the modified TiO2 composite photocatalysts TAV-1, TAV-2, TAV-3 and TAV-4 prepared in Examples 1-4 within 180 min were 91%, 98%, 94% and 99%, respectively.
[0056] Figure 6 The graph shows the photocatalytic reduction efficiency of heavy metal Cr(VI) in wastewater under xenon lamp irradiation for the modified TiO2 composite photocatalyst prepared in Example 4 and the catalysts prepared in Comparative Examples 1-3. In the absence of sacrificial agents and photosensitizers, the modified TiO2 composite photocatalyst prepared in Example 4 exhibited excellent photocatalytic reduction efficiency of Cr(VI), reaching 99%. Under the same experimental conditions as in Example 4, and without sacrificial agents and photosensitizers, the reduction efficiencies of Comparative Examples 1, 2, and 3 were 18%, 54%, and 63%, respectively.
[0057] The modified TiO2 composite photocatalysts prepared in Examples 1-4 of this invention have significantly better catalytic efficiency than the catalysts synthesized in Comparative Examples 1-3, indicating that the combination of TiO2 and β-AgVO3 has an excellent catalytic effect on the catalyst.
[0058] Figure 7The X-ray diffraction patterns of the modified TiO2 composite photocatalyst prepared in Example 4 before and after the reaction are shown in the figure. As can be seen from the figure, the crystal structure of the catalyst remains unchanged before and after the photocatalytic reaction, indicating that it has excellent stability.
[0059] Figure 8 and Figure 9 The images show the photocurrent and electrochemical impedance spectroscopy of the modified TiO2 composite photocatalyst prepared in Example 4. Figure 8 and Figure 9 It can be seen that the composite material exhibits a significant increase in photocurrent intensity and a decrease in impedance compared to the two monomer materials TiO2 and β-AgVO3, indicating that the construction of the Z-shaped heterojunction suppresses the recombination rate of photogenerated electron-hole pairs.
Claims
1. A modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions, characterized in that, The catalyst comprises a TiO2 nanosheet support and β-AgVO3 quantum dots grown on the TiO2 nanosheet, wherein the TiO2 nanosheet and the β-AgVO3 quantum dots form a direct Z-type heterojunction structure.
2. A method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions as described in claim 1, characterized in that, The method includes the following steps: (1) TiCl4 was dissolved in an organic solvent and water was added to carry out a hydrothermal reaction to obtain TiO2 nanosheets; (2) The above TiO2 nanosheets were dispersed in AgNO3 solution, and then NH4VO3 solution was added dropwise. The pH of the solution was adjusted to 6-8, and the TiO2 modified composite photocatalyst was obtained after ultrasonic reaction.
3. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (1), the temperature of the hydrothermal reaction is 75~175℃ and the reaction time is 4~12 h.
4. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (1), the volume ratio of TiCl4, solvent and water is 0.1~10:1~180:0.1~10.
5. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (2), the mass ratio of Ti, Ag and V is 6~16:1.8~2.2:0.9~1.
1.
6. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (2), the mass-volume ratio of AgNO3, NH4VO3 and water is 0.03~0.08 g: 0.02~0.06 g: 40~100 mL.
7. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (2), the dropping rate of the NH4VO3 solution is 0.5~1.2 mL / h.
8. The method for preparing the modified TiO2 composite photocatalyst for photocatalytic reduction of heavy metal ions according to claim 2, characterized in that, In step (2), the ultrasonic reaction time is 0.5~1 h and the temperature is 60~100 ℃.
9. The application of the modified TiO2 composite photocatalyst according to claim 1 in the photocatalytic reduction of Cr(VI).