Method for synergistically removing bisphenol a and hexavalent chromium in sewage based on titanium dioxide composite photoelectrode

Abstract

The present application relates to a kind of based on titanium dioxide composite photoelectrode method for removing bisphenol A and hexavalent chromium in sewage cooperatively, with 3D BQD@TiO2 photoelectrode as working electrode, 3D TiO2 as counter electrode, saturated calomel electrode as reference electrode to construct three-electrode system, with the water body to be treated containing bisphenol A, hexavalent chromium and sodium sulfate as electrolyte solution, under light source irradiation, bias is applied, photoelectrocatalytic removal bisphenol A and hexavalent chromium in water body to be treated.The present application can realize the simultaneous removal of bisphenol A (BPA) and hexavalent chromium (Cr (VI)) complex pollution in water, 100% removal of BPA and Cr (VI) can be realized within 30 min under simulated sunlight, after 5 times of cycle, the removal rate of BPA and Cr (VI) still maintains 99.1% and 95.6% respectively, with efficient and stable photoelectrocatalytic oxidation and reduction performance.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology and relates to a method for the synergistic removal of bisphenol A and hexavalent chromium from wastewater based on titanium dioxide composite photoelectrodes. Background Technology

[0002] Currently, the main technologies for removing BPA from water include biodegradation, physical adsorption, and chemical oxidation. While these technologies have achieved some success, they still face challenges such as long processing times and the potential for secondary pollution. More importantly, the removal of BPA from wastewater through oxidation and mineralization, and the reduction of Cr(VI) to Cr(III) (an essential trace element for microorganisms) to reduce toxicity, significantly increase the complexity and difficulty of simultaneous treatment due to the two different removal principles. In the past decade or so, advanced oxidation technologies, including photocatalysis and photoelectrocatalysis, have developed rapidly. These technologies, by generating reactive oxygen species, offer high reaction rates and mild experimental conditions, making them promising methods for water remediation. Research on the simultaneous removal of BPA and Cr(VI) using photocatalysis has been reported, where photogenerated electrons and holes on the catalyst surface drive the oxidation and reduction reactions, respectively. Although photocatalysis has achieved some success, its oxidation-reduction efficiency is greatly affected by the morphology of the powder material, where photogenerated electrons and holes accumulate on the same surface, resulting in a lack of directionality in charge separation. Furthermore, the regeneration and recovery of the catalyst remain unresolved. Compared to photocatalysis, photoelectrocatalysis, by combining an external electric field, can rapidly and completely separate photogenerated electrons and holes, significantly improving the efficiency of the photoelectrocatalytic reaction. Furthermore, the independent existence of the anode and cathode spaces in the photoelectrocatalytic reaction system provides more favorable conditions for efficient and synergistic removal of BPA through efficient oxidative mineralization at the anode and Cr(VI) through efficient reduction at the cathode. Simultaneously, the photoelectrode materials can be recycled and reused, greatly reducing usage costs. Currently, there are few research reports on the simultaneous removal of BPA and Cr(VI) through photoelectrocatalysis, and the focus is mostly on the development of anode materials, while cathode materials are mostly carbon cloth, carbon felt, or metallic titanium plates. The joint development of anode and cathode materials has not yet begun. Therefore, obtaining anode and cathode materials with excellent photoelectrocatalytic activity is key to achieving efficient simultaneous removal of BPA and Cr(VI).

[0003] Semiconductor photocatalysts, represented by TiO2, possess advantages such as high activity, low cost, stable physicochemical properties, and non-toxicity, and are commonly used to degrade organic pollutants. However, TiO2's low electron transfer efficiency and rapid electron-hole recombination rate limit its large-scale application. Over the past decade, researchers have frequently employed structural and interface engineering techniques to accelerate charge transfer in TiO2 and reduce electron-hole recombination rates, such as metal / non-metal doping, defect construction, noble metal modification, and semiconductor coupling. For example, patent CN202110178404.X discloses a titanium dioxide photoelectrode with three-dimensional crystal plane junction properties, its preparation, and its application. The preparation process of the photoelectrode is as follows: using a titanium mesh as the titanium source, hydrochloric acid as the morphology control agent, and hydrogen peroxide as the oxidant, one-dimensional upright rutile TiO2 nanorods with exposed {111} crystal planes at the top are grown in situ on the titanium mesh substrate by a gas-phase hydrothermal method; then, {101} and {111} nanocones are grown outside the nanorods by a secondary hydrothermal process to form a three-dimensional crystal plane junction structure, which is the FH-{111}TiO2 / Ti target electrode. This patented electrode has high photoelectric degradation performance of single bisphenol A; however, TiO2 itself is still limited by the limited photoresponse range. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode, which can significantly improve light absorption efficiency and charge separation and transfer capability, and achieve efficient synergistic oxidation removal of bisphenol A and hexavalent chromium pollutants in water.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on titanium dioxide composite photoelectrodes is proposed. A three-electrode system is constructed using a 3DBQD@TiO2 photoelectrode as the photoanode, 3D TiO2 as the cathode, and a saturated calomel electrode as the reference electrode. The water containing bisphenol A and / or hexavalent chromium is used as the treatment target. Under the illumination of a light source such as a xenon lamp, a bias voltage is applied to remove bisphenol A and hexavalent chromium from the water through photoelectrocatalysis.

[0007] Furthermore, the preparation process of the 3D TiO2 is as follows:

[0008] After pretreatment, the titanium mesh was placed in a mixed solution of hydrochloric acid, hydrogen peroxide and water, and rutile TiO2 nanorods were obtained through gas-phase hydrothermal reaction. The volume ratio of hydrochloric acid, hydrogen peroxide and water was (4.2-5.3):1:17, the mass fraction of hydrochloric acid was 36-38%, and the mass fraction of hydrogen peroxide was 30%.

[0009] More preferably, the specific process of titanium mesh pretreatment is as follows: water, nitric acid (≥99.0%) and hydrofluoric acid (≥38wt%) are mixed in a volume ratio of 50:10:2 to obtain a chemical polishing solution, the titanium mesh is soaked for 30s, and then deionized water and ethanol are ultrasonically treated for 3-5min in sequence.

[0010] Rutile TiO2 nanorods were placed in a mixed solution of hydrochloric acid, titanium trichloride solution and deionized water for hydrothermal reaction, and then heat-treated in an air atmosphere to obtain a 3D TiO2 electrode with a three-dimensional nanotree structure and multiple crystal planes.

[0011] Furthermore, in the preparation of 3D TiO2, the volume ratio of hydrochloric acid, titanium trichloride solution and deionized water is 1:(0.2~2.4):120, the mass fraction of hydrochloric acid is 36~38%, the concentration of titanium trichloride solution is 15~20wt%, the hydrothermal reaction temperature is 80℃ and the time is 2~5h, and the heat treatment temperature is 400~550℃ and the time is 1~3h.

[0012] Furthermore, the fabrication process of the 3D BQD@TiO2 photoelectrode is as follows:

[0013] Bismuth nitrate ethylene glycol solution and ammonium metavanadate aqueous solution were prepared separately and mixed evenly. Hydrochloric acid was added to obtain a mixed solution. Then, a 3D TiO2 electrode was placed in the mixed solution for hydrothermal reaction. After cleaning and drying, a bismuth vanadate quantum dot modified titanium dioxide composite photoelectrode was obtained, which is the 3D BQD@TiO2 photoelectrode.

[0014] Furthermore, in the preparation process of the 3D BQD@TiO2 photoelectrode, the concentration of the bismuth nitrate ethylene glycol solution is 0.1-1.0 mM, preferably 0.5 mM, the concentration of the ammonium metavanadate aqueous solution is 0.1-1.0 mM, preferably 0.5 mM, and the volume ratio of the bismuth nitrate ethylene glycol solution to the ammonium metavanadate aqueous solution is (1-1.5):1.

[0015] Furthermore, the amount of hydrochloric acid used is 25–150 μL, preferably 25 μL, and the mass fraction of hydrochloric acid is 36–38%.

[0016] Furthermore, the hydrothermal reaction temperature is 140–200°C, preferably 160°C, and the time is 4–6 hours, preferably 5 hours.

[0017] Furthermore, in the photoelectrocatalysis process, an AM 1.5G filter can be used to simulate the solar spectrum, with a light source intensity of 50–200 mW / cm². 2 The applied bias voltage was +0.2 to +1.0 V, the degradation time was 0.5 to 2 h, and the sodium sulfate solution concentration was 0.1 mol / L.

[0018] Furthermore, in the photoelectrocatalysis process, 3D BQD@TiO2 and 3D TiO2 can be used as the anode or cathode, respectively, to construct different photoelectrocatalytic systems. Preferably, 3D BQD@TiO2 is used as the photoanode and 3D TiO2 as the cathode.

[0019] Furthermore, in the photoelectrocatalytic process, the target pollutant can be bisphenol A alone, hexavalent chromium alone, or a coexistence of bisphenol A and hexavalent chromium. In all three cases, the concentration of the pollutant is 2–10 mg / L, and the concentration ratio of bisphenol A to hexavalent chromium in the coexisting system is (0.5–5):1 (the mass concentration of hexavalent chromium here is calculated as K₂Cr₂O₇, the same below). Preferably, the target pollutant is a coexistence of bisphenol A and hexavalent chromium.

[0020] In this invention, a titanium mesh substrate serves as the titanium source, providing sites for in-situ growth of titanium dioxide. The uniform, upright nanorods grown via hydrothermal phase facilitate rapid electron transfer. Secondary hydrothermal nanocones form a three-dimensional structure with the nanorods, enhancing charge transfer and reaction mass transfer efficiency. Further hydrothermally loaded BiVO4 quantum dots, due to their narrower bandgap, broaden the light absorption range of the photoelectrode material, effectively improving light absorption efficiency. Furthermore, the formed BiVO4 / TiO2 heterojunction promotes rapid separation of photogenerated charges, enabling photogenerated electrons to transfer from BiVO4 to TiO2 and ultimately to the counter electrode via the titanium mesh substrate. This 3D BQD@TiO2 photoelectrode exhibits highly efficient and stable photoelectrocatalytic performance under simulated sunlight, achieving 100% removal rates of bisphenol A and hexavalent chromium within 30 minutes.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) Using 3D TiO2 as the substrate electrode, its three-dimensional structure and multiple crystal planes help to quickly and efficiently separate photogenerated carriers in a selective space, while its high specific surface area provides abundant loading sites.

[0023] (2) Loading BiVO4 quantum dots onto the 3D TiO2 surface, the narrow bandgap of BiVO4 and the quantum confinement effect of the quantum dots help improve the light absorption capability of the TiO2 photoelectrode, broadening the light absorption range to the visible light region, and the quantum dot size provides more active sites. At the same time, the size of BiVO4 quantum dots does not obscure the active crystal planes of TiO2. Furthermore, the band matching between BiVO4 and TiO2 forms a heterojunction, which promotes the transfer of holes to BiVO4 and the transport of photogenerated electrons to TiO2. The synergistic effect of the BiVO2 / TiO2 heterojunction and the TiO2 crystal plane junction further promotes the separation and transfer of photogenerated carriers.

[0024] (3) The 3D BQD@TiO2 photoelectrode prepared in this invention exhibits excellent stability and cyclicity in removing coexisting pollutants such as bisphenol A (BPA) and hexavalent chromium (Cr(VI)) from water. In conventional photocatalytic systems, photogenerated electrons and holes are located on the photocatalyst. In this invention, by applying an external bias voltage, the photogenerated electrons of the 3D BQD@TiO2 photoanode are further transferred to the cathode through a titanium mesh substrate, effectively improving the separation and utilization efficiency of photogenerated charges. After 5 cycles, the removal rates of BPA and Cr(VI) still reach 99.1% and 95.6%, respectively. In addition, the applied bias voltage is low, resulting in low energy consumption, which is beneficial for practical applications.

[0025] (4) The photoelectrocatalytic synergistic system constructed in this invention can achieve highly efficient photoelectrocatalytic synergistic removal of bisphenol A and hexavalent chromium pollutants in water bodies through the synergistic interaction of anodic oxidation of bisphenol A and cathodic reduction of hexavalent chromium. Furthermore, it can be extended to the removal of other complex pollutants in actual water bodies, such as antibiotics and heavy metal ions, resistance genes and resistant bacteria. Attached Figure Description

[0026] Figure 1 A scanning electron microscope image of 3D BQD@TiO2 prepared in Example 1;

[0027] Figure 2 Comparison of photoelectric properties of 3D BQD@TiO2 and 3D TiO2 prepared in Example 1;

[0028] Figure 3 Fluorescence spectra and time-resolved transient fluorescence spectra of the 3D BQD@TiO2 and 3D TiO2 photoelectrodes prepared in Example 1;

[0029] Figure 4 The removal efficiency of bisphenol A and hexavalent chromium by different anode and cathode combinations of 3D BQD@TiO2 and 3D TiO2 prepared in Example 1 and the corresponding kinetic fitting curves;

[0030] Figure 5 The removal efficiency of 3D BVO@TiO2 prepared in Comparative Example 1 and 3D BQD@TiO2 prepared in Example 1 for single BPA removal and the corresponding first-order kinetic fitting curves;

[0031] Figure 6 A diagram showing the quantum size effect in nanocrystals;

[0032] Figure 7 The removal efficiency of BPA and Cr(VI) in a simultaneous removal system using 3D BQD@TiO2 prepared in Example 1 as the photoanode and platinum sheet and 3DTiO2 prepared in Example 1 as the cathode, respectively, and the corresponding kinetic fitting curves were obtained.

[0033] Figure 8 The 3D BQD@TiO2 and 3D TiO2 prepared in Example 1 were used as the anode and cathode, respectively. The removal efficiency of bisphenol A and hexavalent chromium under single pollutant and coexisting pollutant conditions and the corresponding kinetic fitting curves were used.

[0034] Figure 9 The removal efficiency of 3D BQD@TiO2 and 3D TiO2 prepared in Example 1 as anode and cathode, respectively, and the corresponding kinetic fitting curves are shown. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0036] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercial products or conventional processing techniques in the art.

[0037] Example 1

[0038] A method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on titanium dioxide composite photoelectrodes specifically includes the following steps:

[0039] (1) Chemical polishing pretreatment: The metal Ti mesh was folded into a double layer and cut into 2.5cm×4.5cm size. It was pretreated by soaking in chemical polishing solution (volume ratio: HNO3:HF:H2O=5:1:25) for 30s. Then it was ultrasonically cleaned in water and ethanol for 3-5min respectively and then soaked in ethanol for later use.

[0040] (2) Gas-phase hydrothermal: Add 5 mL of deionized water, 300 μL of hydrogen peroxide (30%) and 1.0 mL of hydrochloric acid (37.0 wt%) to a 100 mL polytetrafluoroethylene substrate reactor liner. Place the pretreated dry titanium mesh on the annular support in the liner and put the liner into the high-pressure reactor. Perform a gas-phase hydrothermal reaction at 200 °C for 5 h. After the reaction is completed, cool to room temperature, rinse the surface with deionized water and air dry naturally.

[0041] (3) Secondary hydrothermal reaction: Add 25 mL of deionized water, 210 μL of hydrochloric acid (37.0%) and 125 μL of titanium trichloride solution (18 wt%) to the liner of the reactor. Sonicate for 5 min to mix evenly. Place the electrode prepared in step (2) into the liner and place the liner into the high-pressure reactor. Perform hydrothermal reaction at 80 °C for 4 h. After the reaction is completed, cool to room temperature, rinse the surface with deionized water, and air dry naturally.

[0042] (4) Calcination was carried out in air at a temperature of 450℃, a heating rate of 3℃ / min, and a calcination time of 2h to obtain a 3D TiO2 photoelectrode.

[0043] (5) Add 15 mL of 0.5 mM bismuth nitrate ethylene glycol solution and an equal volume of 0.5 mM ammonium metavanadate aqueous solution to a 100 mL polytetrafluoroethylene substrate reaction vessel liner, then add 25 μL of hydrochloric acid. After mixing evenly, place the 3D TiO2 photoelectrode prepared in Example 1 into the vessel and perform a hydrothermal reaction at 160 °C for 5 h. After the reaction is complete, cool to room temperature, rinse the surface with deionized water, and air dry to obtain the target electrode 3D 0.5BQD@TiO2 photoelectrode. Alternatively, adjust the concentrations of the bismuth nitrate ethylene glycol solution and the ammonium metavanadate aqueous solution to 0.25 mM and 1.0 mM respectively to obtain 3D 0.25BQD@TiO2 and 3D 1.0BQD@TiO2 photoelectrodes.

[0044] (6) The simulated wastewater containing bisphenol A and hexavalent chromium was removed using the 3D TiO2 and 3D 0.5BQD@TiO2 photoelectrode (hereinafter referred to as 3DBQD@TiO2) prepared above. The specific process is as follows:

[0045] The photoelectrocatalytic experiments were conducted in a 50 mL cuboid quartz degradation cell using a three-electrode system. Different dual-photoelectrode photoelectrocatalytic systems were constructed based on 3D BQD@TiO2 and 3D TiO2. A saturated calomel electrode served as the reference electrode, the distance between the working electrode and the counter electrode was 25 cm, and the effective photoelectrode area was 2.5 × 3 cm². 2 The simulated wastewater was 0.1 mol·L⁻¹. -1 A 45 mL solution of sodium sulfate, 5 mg / L bisphenol A, and 5 mg / L hexavalent chromium was prepared. The light source was a 300 W xenon lamp with an illuminance of 100 mW / cm². 2 A bias voltage of +0.4V (relative to a saturated calomel electrode) was applied for photoelectrocatalysis experiments. The reaction time was 1 hour, and samples were taken periodically. The concentration of bisphenol A in the samples was measured using an Agilent 1260 high-performance liquid chromatography (HPLC), and the concentration of hexavalent chromium in the samples was measured using UV 1800. Specific degradation results are as follows: Figure 4 As shown. Figure 4 In the figure, (a) and (c) represent the removal curves of bisphenol A and hexavalent chromium, respectively, and (b) and (d) represent the corresponding first-order kinetic curves.

[0046] Figure 4Test results show that the 3D BQD@TiO2 photoelectrode successfully achieved highly efficient photoelectrocatalytic oxidation-reduction of wastewater containing bisphenol A and hexavalent chromium. After 1 hour of reaction, the removal rates of both bisphenol A and hexavalent chromium reached 100%, indicating that the synergistic photoelectrocatalytic system constructed by the 3D BQD@TiO2 photoanode and the 3D TiO2 photocathode achieved efficient and simultaneous removal of bisphenol A and hexavalent chromium pollutants from water.

[0047] Performance testing

[0048] 1. Scanning electron microscopy analysis

[0049] The microstructure of the electrodes was characterized using field emission scanning electron microscopy (Hitachi S-4800), see [see details]. Figure 1 , Figure 1 This indicates that the TiO2 prepared in Example 1 has a three-dimensional structure. One-dimensional nanorods with a diameter between 150 and 250 nm are grown on the titanium mesh substrate. Nanocones are grown on the surface of the nanorods and are uniformly distributed on the nanorods to form a three-dimensional high-order configuration and a multi-faceted crystal structure. The loaded BiVO4 quantum dots make the edges of the two-dimensional nanocones rounded without destroying the three-dimensional configuration and are uniformly distributed on the TiO2 surface.

[0050] 2. Photoelectrochemical performance testing

[0051] The photoelectrocatalytic oxidation performance of the 3D TiO2 and 3D BQD@TiO2 photoelectrode prepared in Example 1 was studied. The specific steps are as follows:

[0052] The photoelectrocatalytic performance was tested in a square quartz reaction cell using a 0.1 mol / L sodium sulfate solution. A three-electrode system was employed, with 3D TiO2 and 3D 0.5BQD@TiO2 as working electrodes, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. Linear sweep voltammetry, Mott-Schottky curves, transient photocurrent response curves, and AC impedance spectroscopy were measured using a Chenhua CHI660C electrochemical workstation. A xenon lamp was used as the light source, with a distance of 1 cm between the light source and the working electrode. The test results are as follows: Figure 2 As shown, the results indicate that under illumination, the photoresponse performance of the 3D BQD@TiO2 electrode is significantly better than that of 3D TiO2, with a photocurrent density reaching 0.8 mA / cm². 2 It is 2.67 times that of 3D TiO2, with an impedance of approximately 600Ω, which is about 0.5 times smaller than that of 3D TiO2. The calculated carrier concentration is 5.96 × 10⁻⁶. 20 cm -3 It is ~518 times better than 3D TiO2.

[0053] The working electrode was replaced with 3D 0.25BQD@TiO2 or 3D 1.0BQD@TiO2, and the photoelectrocatalytic performance was tested. The test results showed that, under illumination, the photocurrent density of the 3D 0.25BQD@TiO2 electrode could reach 0.75 mA / cm². 2 The impedance is approximately 650Ω, and the carrier concentration is 5.95×10⁻⁶. 19 cm -3 The photocurrent density of the 3D 1.0BQD@TiO2 electrode can reach 0.60 mA / cm². 2 The impedance is approximately 900Ω, and the carrier concentration is 3.05×10⁻⁶. 19 cm -3 .

[0054] 3. UV-Vis Diffuse Reflectance Test

[0055] The 3D TiO2 and 3D 0.5BQD@TiO2 photoelectrode prepared in Example 1 were used for UV-Vis diffuse reflectance testing, see [see details]. Figure 3 a indicates that the loading of BiVO4 quantum dots enhances the light absorption capability of TiO2, extending its light absorption range to 500 nm. Figure 3 b indicates that calculations show that after loading BiVO4 quantum dots, the band gap of the photoelectrode becomes 2.8 eV, indicating that BiVO4 and TiO2 form a heterojunction through band matching. The resulting 3D 0.5BQD@TiO2 photoelectrode has a smaller band gap, which improves the light absorption efficiency.

[0056] 4. Fluorescence spectroscopy and time-resolved transient fluorescence spectroscopy tests

[0057] Fluorescence spectroscopy and time-resolved transient fluorescence spectroscopy were performed using the 3D TiO2 and 3D 0.5BQD@TiO2 photoelectrode prepared in Example 1. (See attached image.) Figure 3 a indicates that the loading of BiVO4 quantum dots significantly improves the separation efficiency of photogenerated charges in TiO2 and prolongs the lifetime of excited electrons (3D TiO2: 17.14 ns; 3D0.5BQD@TiO2: 19.59 ns), allowing more holes to reach the surface and participate in the oxidation reaction, thereby improving the efficiency of oxidative degradation of pollutants.

[0058] To highlight the advantages of 3D BQD@TiO2 loaded with bismuth vanadate in "quantum dot form," a "non-quantum dot form" BiVO4 coated composite photoelectrode (3D BVO@TiO2) prepared by impregnation method was used as a comparison (see Comparative Example 1 for the specific preparation process). Using 3D BQD@TiO2 and 3D BVO@TiO2 as working electrodes and platinum sheets as counter electrodes, the removal effects on single bisphenol A were as follows: Figure 5As shown, 3D BVO@TiO2 achieved a BPA removal rate of 74.8% within 20 min, with a kinetic constant of 0.081 min. -1 This is lower than the 3D BQD@TiO2 of the present invention (removing 90.4% within 20 min, k = 0.14 min). -1 This indicates that loading BiVO4 onto 3D TiO2 at the quantum dot size is more conducive to achieving efficient removal of pollutants.

[0059] Most bismuth vanadate-loaded materials involve coating bismuth vanadate onto a substrate, utilizing its narrow-band semiconductor properties for visible light absorption, neglecting the synergistic effect of the two materials. Furthermore, bismuth vanadate's poor charge transport characteristics and short hole diffusion length (<70 nm) lead to severe charge recombination and slow reaction kinetics. Photoelectrocatalysis, as a heterogeneous catalytic interface reaction, depends on the electrode's light absorption efficiency, charge separation efficiency, and surface electron injection efficiency. A comprehensive consideration of these three efficiencies is needed to improve the overall efficiency of the photoelectrocatalysis reaction. Therefore, the 3D BQD@TiO2 electrode material prepared in this invention has the following unique advantages: Firstly, the quantum dot-sized BiVO4 does not obscure the active crystal facet of TiO2. After selective separation between BiVO4 and TiO2, photogenerated electrons and holes are further separated through the TiO2 crystal facet junction, finally reaching the counter electrode, effectively promoting charge separation and transfer. Secondly, quantum dot-sized materials exhibit quantum confinement and quantum size effects, affecting the semiconductor's energy (e.g., ...). Figure 6 As shown, the quantum dot material and the bulk material have different valence band positions. With the increase of the band gap, the conduction band edge shifts to more reduction potentials, and the valence band shifts to more oxidation potentials, which is conducive to the energy matching of BiVO4 and TiO2 to form a heterojunction and promote electron-hole separation. Therefore, the bismuth vanadate quantum dot-modified titanium dioxide composite photoelectrode can more effectively leverage the synergistic effect of the semiconductor heterojunction (BiVO4 / TiO2) and the crystal plane junction of titanium dioxide itself ({111} / {110} / {101}) to achieve efficient removal of pollutants.

[0060] Using a platinum sheet as the counter electrode, and otherwise identical to Example 1, Comparative Example 2 was constructed to simultaneously degrade bisphenol A and hexavalent chromium (see Comparative Example 2 for details). The results are as follows. Figure 7 As shown, compared to the PEC system using platinum as the counter electrode, the PEC system using 3DTiO2 as the counter electrode can increase the oxidation efficiency of BPA from 82.0% to 97.4% within 20 minutes, with the corresponding first-order kinetic constant increasing from 0.083 min. -1 Increased to 0.18 min -1The reduction efficiency of Cr(VI) increased significantly from 12.5% ​​to 99.7%, and the corresponding kinetic rate constant also increased from 8 × 10⁻⁶. -4 M -1 min -1 Increased to 0.82M -1 min -1 This demonstrates that the synergistic redox PEC system constructed based on 3DBQD@TiO2 and 3D TiO2 can simultaneously achieve efficient removal of bisphenol A and hexavalent chromium.

[0061] During the degradation process, the two pollutants "bisphenol A and hexavalent chromium" removed by this invention have a synergistic removal effect. Simulated wastewater containing only 5 mg / L bisphenol A or hexavalent chromium was removed using 3D TiO2 and 3D BQD@TiO2 photoelectrodes, with the rest being the same as in Example 1. Comparative Example 3 was constructed to separately degrade bisphenol A and hexavalent chromium (see Comparative Example 3 for details). The results are as follows... Figure 8 As shown, for BPA oxidation, the removal rate of BPA alone was 89.7% within 20 min, and the removal rate increased to 97.4% when Cr(VI) coexisted in the solution. For Cr(VI) reduction, the removal rate of Cr(VI) alone was 75.9% within 20 min, and the removal rate increased to 99.7% when BPA coexisted in the solution. This result indicates that BPA oxidation and Cr(VI) reduction have a synergistic effect, acting as hole and electron traps respectively, avoiding recombination of photogenerated carriers and improving electron-hole utilization.

[0062] Comparative Example 1:

[0063] A method for preparing a bismuth vanadate-coated titanium dioxide composite photoelectrode specifically includes the following steps:

[0064] 100 mL of 0.5 mM Bi(NO3)3·5H2O (ethylene glycol as solvent) was used as solution A, and 100 mL of 0.5 mM NH4VO3 aqueous solution (pH adjusted to 3 with nitric acid) was used as solution B. The 3D TiO2 photoelectrode prepared in Example 1 was immersed in solution A for 30 s, then immersed in solution B for 30 s. The order of solutions A and B was changed, and this process was repeated 15 times. After completion, the electrode surface was rinsed with deionized water and calcined at 500 °C in an atmospheric atmosphere for 1 h to obtain the "BiVO4 coated composite photoelectrode" 3D BVO@TiO2.

[0065] Comparative Example 2:

[0066] The two embodiments are largely the same as in Example 1, except that in this embodiment, the counter electrode in step (6) is a platinum sheet.

[0067] Comparative Example 3:

[0068] Compared with Example 1, most of them are the same, except that in this example: the simulated wastewater in step (6) is 0.1 mol·L⁻¹. -1 A mixture of sodium sulfate solution and bisphenol A (or hexavalent chromium) at a concentration of 5 mg / L.

[0069] Examples 2 to 3

[0070] Compared with Example 1, most of them are the same, except that in this example, the hydrothermal reaction time in step (5) is 4h and 6h respectively.

[0071] Examples 4 to 5

[0072] Compared with Example 1, most of them are the same, except that in this example, the hydrothermal reaction temperatures in step (5) are 140°C and 180°C respectively.

[0073] Examples 6 to 7

[0074] Compared with Example 1 above, most of them are the same, except that in this example, the concentrations of bisphenol A and hexavalent chromium were adjusted to 2 mg / L and 10 mg / L, respectively, for photoelectrocatalysis experiments.

[0075] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode, characterized in that, A three-electrode system was constructed using a 3D BQD@TiO2 photoelectrode as the photoanode, a 3D TiO2 photocathode, and a saturated calomel electrode as the reference electrode. The water containing bisphenol A and hexavalent chromium was used as the treatment target. Under the illumination of the light source and the application of a bias voltage, photoelectrocatalysis was used to synergistically remove bisphenol A and hexavalent chromium from the water. The fabrication process of the 3D BQD@TiO2 photoelectrode is as follows: Bismuth nitrate ethylene glycol solution and ammonium metavanadate aqueous solution were prepared separately and mixed evenly. Hydrochloric acid was added to obtain a mixed solution. Then, a 3D TiO2 electrode was placed in the mixed solution for hydrothermal reaction. After cleaning and drying, a bismuth vanadate quantum dot modified titanium dioxide composite photoelectrode was obtained, which is the 3D BQD@TiO2 photoelectrode. During the preparation of the 3D BQD@TiO2 photoelectrode, the concentration of the bismuth nitrate ethylene glycol solution is 0.1–1.0 mM, the concentration of the ammonium metavanadate aqueous solution is 0.1–1.0 mM, and the volume ratio of the bismuth nitrate ethylene glycol solution to the ammonium metavanadate aqueous solution is (1–1.5):

1. The amount of hydrochloric acid used is 25–150 μL, and the mass fraction of hydrochloric acid is 36–38%. The hydrothermal reaction temperature is 140–200℃, and the time is 4–6 h; the total concentration of bisphenol A and hexavalent chromium in the water to be treated is 2–10 mg / L, and the concentration ratio of bisphenol A to hexavalent chromium is (0.5–5):

1.

2. The method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode according to claim 1, characterized in that, The preparation process of the 3D TiO2 is as follows: After pretreatment, the titanium mesh was placed in a mixed solution of hydrochloric acid, hydrogen peroxide and water, and rutile TiO2 nanorods were obtained through gas-phase hydrothermal reaction. The volume ratio of hydrochloric acid, hydrogen peroxide and water was (4.2-5.3):1:17, the mass fraction of hydrochloric acid was 36-38%, and the mass fraction of hydrogen peroxide was 30%. Rutile TiO2 nanorods were placed in a mixed solution of hydrochloric acid, titanium trichloride solution and deionized water for hydrothermal reaction, and then heat-treated in an air atmosphere to obtain a 3D TiO2 electrode with a three-dimensional nanotree structure and multiple crystal planes.

3. The method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode according to claim 2, characterized in that, During the preparation of 3D TiO2, the volume ratio of hydrochloric acid, titanium trichloride solution and deionized water is 1:(0.2~2.4):120, the mass fraction of hydrochloric acid is 36~38%, and the concentration of titanium trichloride solution is 15~20wt%. The hydrothermal reaction was carried out at a temperature of 80℃ for 2–5 hours. The heat treatment temperature is 400–550℃, and the time is 1–3 hours.

4. The method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode according to claim 1, characterized in that, During the photoelectrocatalysis process, the water to be treated also contains sodium sulfate at a concentration of 0.1–0.4 mol / L.

5. The method for synergistic removal of bisphenol A and hexavalent chromium from wastewater based on a titanium dioxide composite photoelectrode according to claim 1, characterized in that, In the photoelectrocatalysis process, the light intensity of the light source is 50–200 mW / cm². 2 The applied bias voltage is +0.2 to +1.0V, and the degradation time is 0.5 to 2 hours.

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