Method for synchronously removing antibiotics and Cr (VI) in sewage based on multi-heterostructure titanium dioxide photoelectrode

Abstract

The invention relates to a method for synchronously removing antibiotics and Cr (VI) in sewage based on a multi-heterostructure titanium dioxide photoelectrode, which comprises the following steps: constructing a three-electrode system by taking an Ag / AgVO3QDs / 3D TiO2 photoelectrode as a working electrode, taking 3D TiO2 as a counter electrode and taking a saturated calomel electrode as a reference electrode, taking a to-be-treated water body containing OFL, Cr (VI) and electrolyte as a treatment object, applying a bias voltage under the irradiation of a light source, and carrying out electrochemical treatment on the to-be-treated water body to obtain the antibiotics and the Cr (VI) in the sewage. And OFL and Cr (VI) are synchronously removed through photoelectrocatalysis. According to the method, OFL and Cr (VI) (Cr (VI)) combined pollution in water can be synchronously removed, 100% removal of OFL and Cr (VI) can be achieved within 30 min under simulated sunlight, the removal rates of OFL and Cr (VI) are still kept at 97.8% and 90% respectively after circulation is conducted for five times, and efficient and stable photoelectrocatalytic oxidation-reduction performance is achieved. After the types of antibiotics are expanded to norfloxacin and tetracycline, the target electrode still has good synchronous pollutant removal capability.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment and relates to a method for synchronously removing OFL and Cr(VI) (i.e. hexavalent chromium) in sewage based on multi-heterostructure titanium dioxide photoelectrodes. Background Art

[0002] Since their discovery, antibiotics have been used not only in human medicine, but also in aquaculture and animal husbandry to increase crop yields. Among them, quinolone antibiotics are a type of antibiotic with a nitrogen (hetero) bicyclic structure as its skeleton. The accumulation of quinolone antibiotics in the human body is very likely to cause neurological diseases; Cr(VI) that enters the human body through various pathways accumulates in the human body due to its strong oxidizing and complexing properties, and in severe cases will cause DNA damage. At present, various physical, chemical, and biological technologies are used to treat OFL and Cr(VI) in water, such as adsorption, flocculation, and biosorption. However, these methods have the disadvantages of low efficiency, difficulty in recovery, and easy introduction of other pollutants. In the past few decades, advanced oxidation technologies (AOPs) including Fenton oxidation, electrochemical oxidation, photocatalytic oxidation, photoelectrocatalytic technology, and ozone oxidation technology have become popular technologies for the green, efficient, and simultaneous removal of OFL and Cr(VI) in water. Studies on the simultaneous removal of OFL and Cr(VI) using photocatalysis have been reported. Photocatalysts generate photogenerated electron-hole pairs under light excitation conditions. Photogenerated holes (h + ) as a strong oxidizing substance, can degrade OFL, some h + It can react with water to form highly active ·OH, promoting the mineralization of organic pollutants; photogenerated electrons (e - ) can be used as a reducing agent to reduce Cr(VI). However, photocatalytic technology is limited by the morphology of the material, and photogenerated electrons and holes are easy to recombine, which greatly affects the redox efficiency. The electrodes of photoelectrocatalytic technology are very easy to recycle, and to a certain extent, they have achieved the goal of green and sustainable degradation of pollutants. Moreover, under the action of an external electric field, photogenerated electrons and holes are quickly separated, which significantly improves the efficiency of the photoelectrocatalytic reaction.

[0003] Titanium dioxide (TiO2), which is cheap, easy to synthesize, and non-toxic, stands out among many transition metal oxides and becomes the most studied semiconductor photocatalyst. However, TiO2 has a wide band gap and can only absorb ultraviolet light to generate photogenerated carriers. The utilization rate of sunlight is not high, only less than 5%; at the same time, there are a large number of recombination sites of electrons and holes on the surface of TiO2, and the carrier lifetime is not long, which has a certain degree of inhibition on its photocatalytic performance. In order to broaden the light absorption range, constructing a heterogeneous interface is a good method to improve the light absorption efficiency and charge separation efficiency; increasing the specific surface area can be achieved by constructing a multi-level structure, thereby improving the light absorption efficiency and charge injection efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a method for simultaneously removing antibiotics and Cr(VI) in sewage based on multi-heterostructure titanium dioxide photoelectrodes, which can significantly improve the light absorption efficiency and charge separation and transfer capacity, and realize the efficient synergistic oxidation removal of OFL and Cr(VI) pollutants in water.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A method for simultaneously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes, a three-electrode system is constructed with Ag / AgVO3 QDs@3D TiO2 photoelectrode as the working electrode, 3D TiO2 as the counter electrode, and saturated calomel electrode as the reference electrode. The water body to be treated containing antibiotics (taking OFL as an example), Cr(VI) and electrolyte is taken as the treatment object. Under the irradiation of light source, bias is applied, and photoelectrocatalysis is used to simultaneously remove antibiotics and Cr(VI) therein.

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

[0008] Hydrochloric acid, hydrogen peroxide and water were added to the autoclave in sequence, and then a titanium mesh was placed in the autoclave for gas phase hydrothermal reaction. After the reaction was completed, the autoclave was cooled to room temperature to obtain a 1D TiO2 electrode.

[0009] The 1D TiO2 electrode was placed in a mixed solution of hydrochloric acid, titanium trichloride solution and deionized water for a secondary hydrothermal reaction, followed by a heat treatment in an air atmosphere to obtain a 3D TiO2 electrode.

[0010] Furthermore, the titanium mesh was subjected to the following pretreatment before the gas phase hydrothermal reaction: water, nitric acid (≥99.0%) and hydrofluoric acid (≥38wt%) were mixed in a volume ratio of 50:10:2 to obtain a chemical polishing solution, the titanium mesh was immersed in deionized water and ethanol for 30s, and ultrasonicated twice in turn for 3-5min.

[0011] Furthermore, during the gas phase hydrothermal reaction, the volume ratio of hydrochloric acid, hydrogen peroxide and water is 1:(0.25-0.35):(4.5-5.5), the mass fraction of hydrochloric acid is 36-38%, the mass fraction of hydrogen peroxide is 30%, and the gas phase hydrothermal temperature is 180-220°C;

[0012] During the secondary hydrothermal reaction, the volume ratio of hydrochloric acid, titanium trichloride solution and deionized water satisfies (0.2-0.25):(0.1-0.15):(22-28), the mass fraction of hydrochloric acid is 36-38%, the concentration of titanium trichloride solution is 15-20wt%, and the temperature of the secondary hydrothermal reaction is 70-90°C;

[0013] The temperature of the heat treatment is 400-550°C.

[0014] Furthermore, the preparation process of the Ag / AgVO3 QDs@3D TiO2 photoelectrode is as follows:

[0015] S1. Add solid ammonium metavanadate to the silver nitrate solution, stir under light, then adjust the solution pH to 7, transfer to a high-pressure reactor, put in a 3D TiO2 electrode, perform a hydrothermal reaction, and after the reaction is completed, cool to room temperature to obtain an AgVO3 QDs@3DTiO2 electrode;

[0016] S2. Place the AgVO3 QDs@3D TiO2 electrode in a AgNO3 solution, shield it from light and stir it, and then perform a photodeposition reaction under simulated sunlight. After the reaction, wash the electrode with deionized water and dry it to obtain Ag / AgVO3QDs@3D TiO2 photoelectrode material.

[0017] Furthermore, in S1, the concentration of the silver nitrate solution is 1.0-2.0 mM, preferably 1.5 mM, the molar ratio of silver nitrate to ammonium metavanadate is 1:1, and the light-shielded stirring time is more than 1 hour.

[0018] Furthermore, in S1, the temperature of the hydrothermal reaction is 150-250°C, and the time is 5-7h.

[0019] Furthermore, in S2, the concentration of AgNO3 solution is 0.05-0.5M, the illumination time in the photodeposition reaction is 10-20min, and the light intensity of the light source is 50-200mW / cm 2 .

[0020] Furthermore, in the water to be treated, the concentrations of antibiotics (preferably OFL, i.e., ofloxacin) and Cr(VI) are both 2-5 mg / L, and the concentration of the electrolyte is 0.1-0.4 mol / L.

[0021] Furthermore, the electrolyte is sodium sulfate.

[0022] Furthermore, during the photoelectrocatalytic process, a xenon lamp light source with an AM 1.5G filter can be used to simulate the solar spectrum, with a light intensity of 50 to 200 mW / cm 2 , the applied bias voltage is +0.2~+1.0V, and the degradation time is 20~40min.

[0023] The titanium source in the present invention is a titanium mesh, which can be used as a site for the in-situ growth of titanium dioxide. The rapid transfer of electrons depends on the uniform upright nanorods obtained by gas phase hydrothermal. Nanocones are grown on the nanorods to form a three-dimensional structure through secondary hydrothermal treatment, and the charge transfer and reaction mass transfer efficiency can be greatly improved. Further, AgVO3 quantum dots are loaded through hydrothermal reaction. AgVO3, as a narrow-band semiconductor, broadens the light absorption range of the material after combining with TiO2, and the light absorption efficiency is improved; the pn junction formed by AgVO3 and TiO2 helps to separate and quickly transfer photogenerated electrons and holes. The photogenerated electrons are transferred to TiO2 via AgVO3 on the photoanode, and then transferred to the photocathode through an external circuit. Further, Ag quantum dots are loaded through photodeposition, and the surface plasmon effect is used to further improve the light absorption efficiency of the electrode material, and the introduction of Ag can enhance the conductivity of the electrode, and the efficiency of electron transfer can be improved to a certain extent. This Ag / AgVO3 QDs@3D TiO2 photoelectrode can achieve 100% removal of OFL and Cr(VI) within 30 min under simulated sunlight.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) With 3D TiO2 as the substrate electrode, the high specific surface area of ​​its three-dimensional structure and the crystal plane heterojunction composed of three highly exposed crystal planes ({111}, {101} and {110}) not only improve the efficiency of fast and efficient selective spatial separation of electrons and holes generated by photogeneration, but also increase the high specific surface area of ​​the material and provide abundant active sites.

[0026] (2) AgVO3 quantum dots are loaded on the surface of 3D TiO2. AgVO3, as a narrow bandgap semiconductor, helps to improve the light absorption capacity of the substrate electrode and effectively broaden the light absorption range. In addition, the quantum dots are small in size and will not block the active crystal surface while providing active sites. At the same time, AgVO3 and TiO2 have matching energy bands and can form a heterojunction, which promotes the transfer of holes to AgVO3 and the transfer of photogenerated electrons to TiO2. The synergistic effect of the AgVO3 / TiO2 heterojunction and the TiO2 polycrystalline surface heterojunction greatly increases the separation and transfer rate of photogenerated carriers.

[0027] The surface plasmon effect of Ag quantum dots helps to expand the light absorption range of TiO2 electrodes, and the loading of Ag enhances the conductivity of TiO2, increases the transfer rate of photogenerated electrons, and enhances the separation ability of photogenerated carriers.

[0028] (3) The present invention constructs a photoelectrocatalytic system based on the prepared Ag / AgVO3 QDs@3D TiO2 photoelectrode, and utilizes the effect of external bias to further promote the transfer of photogenerated electrons, thereby effectively improving the separation efficiency and utilization efficiency of photogenerated charges. At the same time, through the synergy of anodic oxidation of OFL and cathode reduction of Cr(VI), efficient photoelectrocatalytic synergistic removal of two pollutants, OFL and Cr(VI), can be achieved in water. This photoelectrocatalytic system.

[0029] (4) The photoelectrocatalytic synergistic system constructed by the present invention has excellent stability and cyclicity in the simultaneous removal of OFL and Cr(VI) complex pollutants in water. After 5 cycles, the removal rate of OFL by the target electrode still reached 97.8%, and the removal rate of Cr(VI) still reached 92.5%. In addition, it can be extended to the removal of other antibiotics and Cr(VI) complex pollution in actual water bodies, such as norfloxacin and tetracycline. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Scanning electron microscope images of 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 prepared in Example 1;

[0031] Figure 2 A comparison chart of the photoelectric properties of 3D TiO2, Ag QDs@3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3QDs@3D TiO2 prepared in Example 1;

[0032] Figure 3 The fluorescence spectra and time-resolved transient fluorescence spectra of the 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 photoelectrodes prepared in Example 1;

[0033] Figure 4 UV-vis-DRS spectra, open circuit voltage and light absorption efficiency curves of 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 photoelectrodes prepared in Example 1

[0034] Figure 5 The removal efficiency of OFL and Cr(VI) by different photoelectrocatalytic systems composed of 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 prepared in Example 1 and the corresponding kinetic fitting curves;

[0035] Figure 6The removal efficiency of other antibiotics and Cr(VI) by the photoelectrocatalytic system composed of Ag / AgVO3 QDs@3D TiO2 and 3D TiO2 prepared in Example 1 and the corresponding kinetic fitting curves;

[0036] Figure 7 Cyclic test of the photoelectrocatalytic system composed of Ag / AgVO3 QDs@3D TiO2 and 3D TiO2 prepared in Example 1 for OFL oxidation and Cr(VI) reduction;

[0037] Figure 8 Cyclic performance test of the photoelectrocatalytic system composed of Ag / AgVO3 QDs@3D TiO2 and 3D TiO2 in Example 1 DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0039] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercial products or conventional processing techniques in the art.

[0040] Example 1

[0041] A method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes, specifically comprising the following steps:

[0042] (1) Chemical polishing pretreatment: Fold the 80-mesh titanium mesh into a double layer and cut it into a size of 2.5 cm × 3 cm. Mix HNO3 (≥99.0%), HF (≥38 wt%) and H2O in a volume ratio of 5:1:25 to prepare a chemical polishing solution. Soak the cut titanium mesh in the solution for 30 seconds as a pretreatment. After the treatment, ultrasonically clean it twice in water and ethanol for 3-5 minutes respectively, and then soak it in ethanol for later use.

[0043] (2) Gas-phase hydrothermal reaction: 5 mL of deionized water, 300 μL of hydrogen peroxide (30%), and 1.0 mL of hydrochloric acid (37.0 wt%) were added sequentially to the inner lining of a reactor with a 100 mL polytetrafluoroethylene substrate and a 7 cm high ring support. The pretreated dry titanium mesh was placed on the ring support in the inner lining. The inner lining was placed in a high-pressure reactor and subjected to gas-phase hydrothermal reaction at 200 °C for 5 h. After the reaction was completed, the reactor was cooled to room temperature, the electrode was taken out, the surface was rinsed with deionized water, and the electrode was naturally dried to obtain a 1D TiO2 photoelectrode.

[0044] (3) Secondary hydrothermal treatment: Add 25 mL of deionized water, 210 μL of hydrochloric acid (37.0%) and 125 μL of titanium trichloride solution (18 wt%) to the inner lining of a 100 mL polytetrafluoroethylene-based reactor, shake to mix the solution evenly, place the 1D TiO2 photoelectrode prepared in step (2) therein, place the inner lining in a high-pressure reactor, and perform a hydrothermal reaction at 80°C for 4 h. After the reaction is completed, cool to room temperature, take out the electrode, rinse the surface with deionized water, and dry it naturally.

[0045] (4) The photoelectrode prepared in step (3) is placed in a muffle furnace and calcined at 450°C in an air atmosphere at a heating rate of 3°C / min for 2 hours. After the calcination is completed, the photoelectrode is cooled to room temperature and the electrode is taken out to obtain a 3D TiO2 photoelectrode.

[0046] (5) Prepare 30 ml of 1.5 mM silver nitrate solution, add the same amount of solid ammonium metavanadate, shade the solution and stir for more than 1 h, then adjust the solution pH to 7 with NaOH solution (concentration of 2.5 mol / L), add the above solution to the lining of a 100 mL polytetrafluoroethylene-based reactor, place the 3D TiO2 photoelectrode prepared in step (4) therein, place the lining in a high-pressure reactor, and perform a hydrothermal reaction at 200 °C for 6 h. After the reaction is completed, cool to room temperature, take out the electrode, rinse the surface with deionized water, and dry it naturally to obtain the AgVO3 QDs@3D TiO2 photoelectrode.

[0047] (6) Prepare 20 ml of 0.1 M silver nitrate solution, place the AgVO3QDs@3D TiO2 photoelectrode prepared in step (5) in it, shield from light and stir for 20 min, then place under simulated sunlight (light source intensity of 100 mW / cm 2 ) for 15 min. After the reaction, the electrode was taken out, the surface was rinsed with deionized water, and dried naturally to obtain the target electrode Ag / AgVO3QDs@3D TiO2.

[0048] (7) The prepared 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 were used to form different photoelectrocatalytic systems to remove simulated wastewater containing OFL and Cr(VI). The specific process is as follows:

[0049] The photoelectrocatalytic experiment was carried out in a 50 mL cuboid quartz degradation cell. A three-electrode system was used. Different dual-photoelectrode photoelectrocatalytic systems were constructed based on 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3D TiO2 as photoanodes and 3D TiO2 as photocathodes. A saturated calomel electrode was used as the reference electrode. The distance between the working electrode and the counter electrode was 5 cm, and the effective photoelectrode area was 2.5 × 3 cm. 2 The simulated wastewater is 0.1 mol·L -1 A mixed solution of sodium sulfate, 5mg / LOFL and 5mg / LCr(VI) with a volume of 45mL. The light source is a 300W xenon lamp with a light intensity of 100mW / cm 2 The distance between the sample pool and the light source was 25 cm, the bias voltage was +0.4 V (relative to the saturated calomel electrode), the photoelectrocatalytic experiment was carried out, the reaction time was 40 min, sampling was performed at regular intervals, and the concentrations of OFL and Cr(VI) contained in the samples were tested by UV-1800 ultraviolet spectrometer. The specific degradation results are shown in Figure 4 shown. Figure 4 In the figure, (a) and (c) represent the removal curves of OFL and Cr(VI), respectively, and (b) and (d) represent the corresponding kinetic curves.

[0050] Figure 4 The test results show that the Ag / AgVO3 QDs@3D TiO2-3D TiO2 photoelectric system successfully achieved efficient photoelectrocatalytic simultaneous removal of wastewater containing OFL and Cr(VI). After 30 minutes of reaction, the removal rates of OFL and Cr(VI) both reached 100%, indicating that the synergistic photoelectrocatalytic system constructed by Ag / AgVO3 QDs@3D TiO2 photoanode and 3D TiO2 photocathode achieved efficient and simultaneous removal of OFL and Cr(VI) pollutants in water.

[0051] Performance Testing

[0052] 1. Scanning Electron Microscope Analysis

[0053] The microstructure of the electrode was characterized by field emission scanning electron microscopy (Hitachi S-4800). Figure 1 , Figure 1 The clear structure of each electrode prepared in Example 1 is shown. First, 1D TiO2 with a one-dimensional nanorod structure grown on the titanium mesh substrate can be observed. Secondly, evenly distributed nanocones are observed growing on the surface of the nanorods, which is 3D TiO2 with a three-dimensional configuration. The loading of Ag and AgVO3 quantum dots does not destroy the three-dimensional configuration, but the edges of the nanocones become blunt.

[0054] 2. Photoelectrochemical performance test

[0055] The photoelectrode prepared in Example 1, 3D TiO2, Ag QDs@3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3QDs@3D TiO2, was used to study the photoelectrocatalytic oxidation performance. The specific steps are as follows:

[0056] The specific preparation process of Ag QDs@3D TiO2 is as follows:

[0057] The 3D TiO2 photoelectrode prepared in Example 1 was placed in 20 ml of 0.1 M silver nitrate solution, shielded from light and stirred for 20 min, and then exposed to simulated sunlight (light source intensity of 100 mW / cm 2 ) for 15 min. After the reaction, the electrode was taken out, the surface was rinsed with deionized water, and dried naturally to obtain Ag QDs@3DTiO2.

[0058] The photoelectrocatalytic performance test was carried out in a square quartz reaction cell. The electrolyte solution was 0.1 mol / L sodium sulfate solution. A three-electrode system was used, with 3D TiO2, Ag QDs@3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3D TiO2 as working electrodes, platinum as counter electrode, saturated calomel electrode as reference electrode, and Chenhua CHI660C electrochemical workstation was used to test transient photocurrent response curve, linear sweep voltammetry curve, Mott-Schottky curve and AC impedance spectrum. A xenon lamp was used as the light source, and the distance between the light source and the working electrode was 1 cm. The test results are shown in Figure 2. Figure 2 The results show that under illumination conditions, the photoresponse performance of the Ag / AgVO3QDs@3D TiO2 electrode is better than that of Ag QDs@3D TiO2, AgVO3QDs@3D TiO2 and 3D TiO2. The photocurrent density of the Ag / AgVO3 QDs@3D TiO2 electrode can reach 0.85 mA / cm 2 , which is 1.7 times that of 3D TiO2, with an impedance value of approximately 408Ω, and a calculated carrier concentration of 6.33×10 20 cm -3 .

[0059] 3. Fluorescence spectroscopy and time-resolved transient fluorescence spectroscopy tests

[0060] The 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 photoelectrodes prepared in Example 1 were used for fluorescence spectroscopy and time-resolved transient fluorescence spectroscopy tests. Figure 3, indicating that the loading of Ag and AgVO3 quantum dots significantly improved the separation efficiency of TiO2 photogenerated charges and effectively prolonged the lifetime of photogenerated electrons (3D TiO2: 13.35ns; AgVO3QDs@3D TiO2: 14.52ns; Ag / AgVO3 QDs@3DTiO2: 15.97ns), so that the rate of electron transfer was correspondingly improved, and the holes of the photoanode could participate in the oxidation reaction more efficiently, thereby theoretically improving the efficiency of oxidative degradation of OFL.

[0061] 4. UV-Vis diffuse reflection test

[0062] The 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 photoelectrodes prepared in Example 1 were used for UV-visible diffuse reflection tests. Figure 4 a, indicating that the loading of Ag and AgVO3 quantum dots promotes the light absorption ability of TiO2, and its light absorption range is extended. Figure 4 b shows that through calculation, it was found that after loading Ag and AgVO3 quantum dots, the band gap of the photoelectrode became 2.5eV, indicating that the band gap of the target photoelectrode became smaller, thereby improving the light absorption efficiency. Figure 4 The open circuit voltage drop of the target electrode in c is the largest, which further confirms the improvement of the electrode light absorption efficiency. Figure 4 d is the light absorption efficiency curve of the three electrodes. It is observed that at an operating voltage of 0.4 V, the target electrode exhibits the best light absorption efficiency, which can reach 70.64%, which is 1.44 times higher than that of the 3D TiO2 photoelectrode.

[0063] 5. Test of the removal effect of OFL and Cr(VI) using 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3QDs@3D TiO2 photoelectrodes prepared in Example 1

[0064] Different photoelectrocatalytic systems were constructed using the 3D TiO2, AgVO3 QDs@3D TiO2 and Ag / AgVO3 QDs@3DTiO2 photoelectrodes prepared in Example 1 to remove OFL and Cr(VI) in water. The results are shown in Figure 2. Figure 5 The results show that the removal rate of OFL by the target electrode reaches 100% within 20 min, and the first-order kinetic constant is 0.292×10 -3 min -1 , which is 3.52 times that of 3D TiO2; for the removal of Cr(VI), the photoelectric system composed of the target electrode and 3DTiO2 can achieve 100% removal of Cr(VI) within 30 minutes, and the secondary kinetic constant is 0.227M -1 ·min-1 , which is 3.27 times that of 3D TiO2. In summary, the target electrode can achieve efficient and simultaneous removal of OFL and Cr(VI) in water;

[0065] The types of antibiotics were expanded to norfloxacin and tetracycline, and the effects of 3D TiO2, AgVO3 QDs@3DTiO2 and Ag / AgVO3 QDs@3D TiO2 photoelectrodes on the simultaneous removal of antibiotics and Cr(VI) were investigated. Figure 6 As shown in the figure, within 40 minutes, when the target electrode system coexists with Cr(VI), the removal rate of norfloxacin and Cr(VI) reaches 100%, and when tetracycline and Cr(VI) coexist, the removal rate of tetracycline reaches 90%, and the removal rate of Cr(VI) reaches 88%. This shows that the photoelectrocatalytic system composed of the target electrode and 3D TiO2 is universal for the efficient removal of antibiotics and Cr(VI).

[0066] 6. Cyclic test of the removal effect of OFL and Cr(VI) using the Ag / AgVO3 QDs@3D TiO2 photoelectrode prepared in Example 1

[0067] The Ag / AgVO3 QDs@3D TiO2 photoelectrode prepared in Example 1 was used to construct a photoelectrocatalytic system, and the cyclic stability of the removal effect of OFL and Cr(VI) in water was tested. The results are as follows: Figure 7 As shown in the figure, after 5 cycles, the removal rate of OFL at the anode can still reach 97.8%, indicating that the target electrode has good stability. At the same time, the photoelectric cycle performance of the photoelectrocatalytic system composed of Ag / AgVO3 QDs@3D TiO2 and 3D TiO2 was tested. During the 12000s cycle test, the photoelectrocatalytic system showed a relatively stable photocurrent with an average value of 0.95mA, which further confirmed the cycle stability of the target electrode.

[0068] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes, characterized in that: A three-electrode system was constructed with Ag / AgVO3 QDs@3D TiO2 photoelectrode as the working electrode, 3D TiO2 as the counter electrode, and saturated calomel electrode as the reference electrode. The water body to be treated containing antibiotics, Cr(VI) and electrolyte was taken as the treatment object. Under the irradiation of light source, bias voltage was applied, and photoelectrocatalysis was used to simultaneously remove antibiotics and Cr(VI).

2. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 1, characterized in that: The preparation process of the 3D TiO2 is: Hydrochloric acid, hydrogen peroxide and water were added to the autoclave in sequence, and then a titanium mesh was placed in the autoclave for gas phase hydrothermal reaction. After the reaction was completed, the autoclave was cooled to room temperature to obtain a 1D TiO2 electrode. The 1D TiO2 electrode was placed in a mixed solution of hydrochloric acid, titanium trichloride solution and deionized water for a secondary hydrothermal reaction, followed by a heat treatment in an air atmosphere to obtain a 3D TiO2 electrode.

3. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 2, characterized in that: During the gas phase hydrothermal reaction, the volume ratio of hydrochloric acid, hydrogen peroxide and water is 1: (0.25-0.35): (4.5-5.5), the mass fraction of hydrochloric acid is 36-38%, the mass fraction of hydrogen peroxide is 30%, and the gas phase hydrothermal temperature is 180-220°C; During the secondary hydrothermal reaction, the volume ratio of hydrochloric acid, titanium trichloride solution and deionized water satisfies (0.2-0.25):(0.1-0.15):(22-28), the mass fraction of hydrochloric acid is 36-38%, the concentration of titanium trichloride solution is 15-20wt%, and the temperature of the secondary hydrothermal reaction is 70-90°C; The temperature of the heat treatment is 400-550°C.

4. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 1, characterized in that: The preparation process of the Ag / AgVO3 QDs@3D TiO2 photoelectrode is as follows: S1. Add solid ammonium metavanadate to the silver nitrate solution, stir under light, then adjust the solution pH to 7, transfer to a high-pressure reactor, put in a 3D TiO2 electrode, perform a hydrothermal reaction, and after the reaction is completed, cool to room temperature to obtain an AgVO3 QDs@3DTiO2 electrode; S2. Place the AgVO3 QDs@3D TiO2 electrode in a AgNO3 solution, shield it from light and stir it, and then perform a photodeposition reaction under simulated sunlight. After the reaction, wash the electrode with deionized water and dry it to obtain Ag / AgVO3QDs@3D TiO2 photoelectrode material.

5. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 4, characterized in that: In S1, the concentration of the silver nitrate solution is 1.0-2.0 mM, the molar ratio of silver nitrate to ammonium metavanadate is 1:1, and the light-shielded stirring time exceeds 1 h.

6. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 4, characterized in that: In S1, the temperature of the hydrothermal reaction is 150-250°C and the time is 5-7h.

7. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 4, characterized in that: In S2, the concentration of AgNO3 solution is 0.05-0.5M, the illumination time in the photodeposition reaction is 10-20min, and the light intensity of the light source is 50-200mW / cm 2 .

8. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 1, characterized in that: In the water to be treated, the concentrations of antibiotics and Cr(VI) are both 2-5 mg / L, and the electrolyte is sodium sulfate, and its concentration is 0.1-0.4 mol / L.

9. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 1, characterized in that: During the photoelectrocatalytic process, the light intensity of the light source is 50-200 mW / cm 2 , the applied bias voltage is +0.2~+1.0V, and the degradation time is 20~40min.

10. The method for synchronously removing antibiotics and Cr(VI) from sewage based on multi-heterostructure titanium dioxide photoelectrodes according to claim 1, characterized in that: The antibiotics are OFL, norfloxacin and tetracycline.

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