An electro-optical catalytic material electrode, preparation method and application

Abstract

The present invention relates to the technical field of photocatalytic materials, and specifically relates to a photocatalytic material electrode, a preparation method and an application thereof. The electrode is prepared by this method. The method includes preparing a cellulose nanofiber hydrogel doped with titanium suboxide; after the cellulose nanofiber hydrogel doped with titanium suboxide is subjected to a first pretreatment, titanium strips after a second pretreatment are respectively pasted on the front and back surfaces of one end thereof to obtain a cellulose nanofiber hydrogel electrode sheet doped with titanium suboxide; the part of the electrode sheet below the titanium strip is immersed in a MOFs dispersion solution, and a loading treatment is carried out under stirring to obtain a three-dimensional structure photocatalytic material electrode. The application is the application of the electrode in the degradation of tetracycline wastewater. The present invention can solve the problems of the low reaction rate of the existing photoelectrode to tetracycline antibiotics and the easy loss of titanium suboxide powder and MOFs powder.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly relates to a photocatalytic material electrode, a preparation method and an application thereof. Background Art

[0002] Tetracycline antibiotics are one of the most widely used antibiotics due to their low price, high applicability and excellent bactericidal and bacteriostatic effects. Since wastewater containing tetracycline is directly discharged into the environment without treatment, it will damage the water ecosystem, affect the survival and reproduction of aquatic organisms, and the presence of tetracycline residues and tetracycline resistance genes may pose a potential threat to human health. By treating tetracycline wastewater, the exposure of tetracycline to humans can be reduced, and the transmission risk of tetracycline resistance can be lowered, thus protecting public health.

[0003] In recent years, photocatalytic technology has been gradually used for the degradation of organic pollutants, which has obvious advantages in terms of recyclability and reproducibility. However, the treatment efficiency of the photoanode for tetracycline antibiotics often shows a low reaction rate due to the limited active area of the electrode and its mutual restriction with the height of the treatment liquid surface. In addition, the light response characteristics, stability and charge separation efficiency of the photoanode during the photocatalytic process are all important factors affecting the photocatalytic efficiency. Therefore, the selection of the electrode substrate and catalyst and the optimization of their performance are crucial for the implementation of photocatalytic technology.

[0004] Titanium-based compounds are one of the most promising electrode materials in the field of photocatalysis. Magnéli phase titanium suboxide (Ti4O7) has attracted the attention of researchers due to its small band gap, good visible light response and high stability. However, the original titanium suboxide has a low charge separation rate and limited degradation ability for pollutants, and it needs to be doped with elements or compounded with single atoms / compounds to increase the charge separation efficiency of the titanium suboxide electrode. MOFs have a large specific surface area, rich active sites, adjustable band gap structures and unique three-dimensional structural characteristics, that is, they have metal clusters and organic ligands, and show the ability to absorb ultraviolet or visible light. This light absorption process stimulates the generation of photoinduced electron-hole pairs, and the photoinduced electrons / holes can be effectively spatially separated under suitable conditions, demonstrating the potential of MOFs as photocatalysts or optoelectronic materials. Compared with other MOFs, Fe-based MOFs have higher physical and chemical stability, thermal stability and water stability. In addition, Fe(III) oxides are more easily excited by visible light irradiation, and Fe element, as one of the most abundant metal elements in the earth's crust, has broad application prospects in the field of photocatalysis.

[0005] However, titanium suboxide powder and MOFs powder are prone to loss, making recycling difficult and liable to cause secondary pollution and other problems. Therefore, there is an urgent need to find an environmentally friendly, stable in performance and excellent in structure electrode substrate to broaden the application of titanium suboxide and MOFs in the field of photocatalytic degradation of organic pollutants.

[0006] In summary, there is a need to provide a photocatalytic material electrode, a preparation method and an application thereof to solve the problems of low reaction rate of existing photoanodes to tetracycline antibiotics and the easy loss of titanium suboxide powder and MOFs powder. Summary of the Invention

[0007] The purpose of the present invention is to provide a photocatalytic material electrode, a preparation method and an application thereof. The specific technical solutions are as follows:

[0008] In the first aspect, the present invention provides a preparation method of a photocatalytic material electrode, including:

[0009] Step S1, preparing a cellulose nanofiber hydrogel doped with titanium suboxide;

[0010] Step S2, after the cellulose nanofiber hydrogel doped with titanium suboxide is subjected to a first pretreatment, titanium strips after a second pretreatment are respectively pasted on the front and back surfaces of one end thereof to obtain a cellulose nanofiber hydrogel electrode sheet doped with titanium suboxide;

[0011] Step S3, immersing the part of the electrode sheet below the titanium strip into a MOFs dispersion solution, and performing a loading treatment under stirring to obtain a three-dimensional structure photocatalytic material electrode.

[0012] Optionally, in step S1:

[0013] First, prepare a hydrogel solution A. Specifically, 20-40 g of cellulose nanofiber hydrogel, 0.3-0.6 g of agar powder and 16-32 mL of deionized water are mixed, and then subjected to a water bath treatment and a continuous first stirring treatment to obtain the hydrogel solution A;

[0014] Secondly, under the water bath treatment and the continuous first stirring treatment, 0.25-0.35 g of titanium suboxide powder is added to the hydrogel solution A and mixed evenly;

[0015] Subsequently, under the condition of room temperature, a continuous second stirring treatment is carried out until completely dissolved to obtain a solution B;

[0016] Finally, pour the solution B into a petri dish, add an acidifying agent and a crosslinking agent, and after drying treatment, obtain the cellulose nanofiber hydrogel doped with titanium suboxide.

[0017] Optionally, the temperature used in the water bath treatment is 85-90 °C; the rotation speed used in the first stirring treatment is 400-500 rpm, and the stirring time is 3-5 min; the rotation speed used in the second stirring treatment is 1000-1100 rpm, and the stirring time is 2-3 h.

[0018] Optionally, the acidifying agent includes sulfuric acid; the concentration of the acidifying agent is 0.5-2.0 mol / L, and the volume is 3-4 mL; the crosslinking agent includes N,N'-methylenebisacrylamide solution; the mass concentration of the N,N'-methylenebisacrylamide solution is 3.5-4.5 wt%, and the volume is 3-4 mL; the drying temperature used in the drying treatment is 50-80 °C, and the drying time is 45-60 min.

[0019] Optionally, the first pretreatment includes sequentially performing deionized water cleaning and cutting treatment on the doped titanium suboxide cellulose nanofiber hydrogel; the second pretreatment includes first ultrasonically removing impurities on the surface of the titanium sheet and then cutting it into titanium strips; the binder includes an ethanol solution of polyvinylpyrrolidone.

[0020] Optionally, the MOFs dispersion solution is obtained by dispersing 0.02-0.04 g of MIL-100(Fe) nanoparticles in 50 mL of deionized water and performing a third stirring treatment; the rotation speed used in the third stirring treatment is 200-250 rpm, and the stirring time is 12-18 h.

[0021] Optionally, the preparation steps of the MIL-100(Fe) nanoparticles include:

[0022] (1) Dissolve ferric chloride hexahydrate and 1,3,5-benzenetricarboxylic acid in a molar ratio of 2:1-1:2 in 50-100 mL of N,N-dimethylformamide, and stir until completely dissolved to obtain solution C; wherein, the molar concentrations of ferric chloride hexahydrate and 1,3,5-benzenetricarboxylic acid are both 1.0-3.0 mmol / L;

[0023] (2) Pour solution C into a stainless steel autoclave lined with polytetrafluoroethylene, and perform heat treatment at 120-180 °C for 12-14 h, wash, dry, and grind to obtain MIL-100(Fe) nanoparticles;

[0024] The washing is sequentially performed with N,N-dimethylformamide and ethanol; the drying temperature is 60-80 °C, and the drying time is 12-24 h.

[0025] In a second aspect, the present invention provides a photo-electrocatalytic material electrode, which is prepared by using the preparation method of the photo-electrocatalytic material electrode.

[0026] In a third aspect, the present invention provides an application of the above-mentioned photo-electrocatalytic material electrode in the degradation of tetracycline wastewater. The photo-electrocatalytic material electrode is used as the anode, a platinum sheet electrode is used as the counter electrode, and a saturated calomel electrode is used as the reference electrode. They are placed in tetracycline wastewater containing an electrolyte for a photo-electrocatalytic reaction to complete the degradation treatment of the tetracycline wastewater.

[0027] Optionally, the photo-electrocatalytic reaction is carried out under light conditions. The voltage used in the photo-electrocatalytic reaction is 1.5 - 2V, and the reaction time is 1 - 3h; the electrolyte includes sodium sulfate; the pH value of the tetracycline wastewater is 4.5 - 5.0; the concentration of tetracycline in the tetracycline wastewater is 10 - 20mg / L, and the electrolyte concentration is 25 - 50mmol / L.

[0028] Applying the technical solution of the present invention has at least the following beneficial effects:

[0029] (1) The preparation method of a photo-electrocatalytic material electrode provided by the present invention combines cellulose nanofiber hydrogel with titanium suboxide and MOFs to obtain a green, efficient, and stable photo-electrochemical material, which can further promote the development and application of photo-electrocatalytic technology in the treatment of tetracycline wastewater, and provide a new guarantee for the up-to-standard discharge and reuse of tetracycline wastewater. Specifically, the cellulose nanofiber hydrogel used in the present invention has a densely stacked and entangled nanofiber network structure, which can provide more catalytic active sites; at the same time, its good mechanical properties enable the catalyst MOFs to be firmly fixed in the three-dimensional network structure of the hydrogel, reducing the loss of the catalyst and ensuring the efficiency of continuous catalytic degradation. The self-assembly of MOFs inside and at the contact interface of the cellulose nanofiber hydrogel can achieve chemical bonding inside and at the interface of the two to form an intertwined network structure, obtaining a "double three-dimensional" structure. In addition, the highly entangled cellulose nanofiber hydrogel scaffold at the nanoscale can fully disperse MOFs and improve its ductility, providing a "self-supporting" effect for the structural stability of the photoelectrode under a relatively high applied voltage.

[0030] (2) The dual three-dimensional structure photoelectrocatalytic material electrode prepared by the present invention uses a cellulose nanofiber hydrogel doped with titanium suboxide as the electrode substrate, and MIL-100(Fe) nanoparticles are uniformly loaded on the electrode substrate, solving the problems of easy loss of catalyst powder, difficult recovery and easy generation of secondary pollution. Moreover, the successful combination of titanium suboxide and MIL-100(Fe) improves the charge separation efficiency of titanium suboxide, increases the separation efficiency of photogenerated carriers of the electrode, and realizes the efficient degradation of tetracycline under visible light conditions. In addition, the dual three-dimensional network structure composed of cellulose nanofiber hydrogel and MIL-100(Fe) supports each other, effectively avoiding the problem of framework collapse during the photoelectrocatalytic process, improving the stability of the photoelectrocatalytic material electrode, and making the electrode have high popularization value and application prospect in the actual treatment of tetracycline wastewater.

[0031] (3) When the present invention uses the photoelectrocatalytic material electrode to degrade tetracycline wastewater, a visible light-responsive dual three-dimensional structure photoelectrocatalytic material electrode is used as the anode, a platinum sheet electrode is used as the counter electrode, and a saturated calomel electrode is used as the reference electrode, and they are placed in tetracycline wastewater containing an electrolyte for photoelectrocatalytic reaction, so as to realize the catalytic degradation of tetracycline in the wastewater. Compared with the modified cellulose nanofiber hydrogel without loaded MOFs, the degradation efficiency of the visible light-responsive dual three-dimensional structure photoelectrocatalytic material electrode for treating tetracycline-containing wastewater is increased by 3.86 times; the synergy factor of the photoelectrocatalytic process reaches 6.66; after 4 cycles, the degradation ability of the visible light-responsive dual three-dimensional structure photoelectrocatalytic material electrode for tetracycline has not decreased, showing the advantages of good light response performance, excellent catalytic effect, stable use performance, and environmental friendliness, and has broad application prospects in the field of photoelectrocatalytic degradation of tetracycline wastewater.

[0032] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The following will refer to the drawings for a further detailed description of the present invention. Description of the Drawings

[0033] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0034] Figure 1a It is a scanning electron microscope image of the cellulose nanofiber hydrogel electrode CNF prepared in Comparative Example 1;

[0035] Figure 1b It is a scanning electron microscope image of the cellulose nanofiber hydrogel electrode Ti4O7@CNF doped with titanium suboxide prepared in Comparative Example 2;

[0036] Figure 1cScanning electron microscopy image of the cellulose nanofiber hydrogel electrode MIL-100(Fe)@CNF loaded with MIL-100(Fe) prepared in Comparative Example 3;

[0037] Figure 1d Scanning electron microscopy image of the dual three-dimensional structure photoelectrocatalytic material electrode MIL-100(Fe) / Ti4O7@CNF prepared in Example 1;

[0038] Figure 2 X-ray diffraction patterns of the respective photoanodes prepared in Example 1 and Comparative Examples 1-3;

[0039] Figure 3a UV-Vis diffuse reflectance spectra of the respective photoanodes prepared in Example 1 and Comparative Examples 1-3;

[0040] Figure 3b Band gap energy diagrams of the respective photoanodes prepared in Example 1 and Comparative Examples 1-3;

[0041] Figure 4 Electrochemical impedance spectra of the respective photoanodes prepared in Example 1 and Comparative Examples 1-3.

[0042] Figure 5a Degradation effect diagrams of the respective photoanodes prepared in Example 1 and Comparative Examples 1-3 on tetracycline wastewater;

[0043] Figure 5b For Figure 5a The corresponding (pseudo) first-order kinetic curve diagram;

[0044] Figure 6a Degradation effect diagrams of Example 2 and Comparative Examples 4-5 on tetracycline wastewater under different application conditions;

[0045] Figure 6b For Figure 6a The corresponding (pseudo) first-order kinetic curve diagram;

[0046] Figure 7a Degradation effect diagrams of Example 3 and Comparative Examples 6-10 on tetracycline wastewater under different pH conditions;

[0047] Figure 7b For Figure 7a The corresponding (pseudo) first-order kinetic curve diagram;

[0048] Figure 8a Degradation effect diagrams of Example 4 and Comparative Examples 11-13 on tetracycline wastewater under different voltage conditions;

[0049] Figure 8b For Figure 8a The corresponding (pseudo) first-order kinetic curve diagram;

[0050] Figure 9a It is the degradation effect diagram of tetracycline wastewater under different photon fluxes in Examples 5 - 8;

[0051] Figure 9b is Figure 9a the corresponding pseudo - first - order kinetic curve diagram;

[0052] Figure 10a It is the degradation effect diagram of each photo - electrode prepared in Example 1 and Comparative Example 14 on tetracycline wastewater;

[0053] Figure 10b is Figure 10a the corresponding pseudo - first - order kinetic curve diagram;

[0054] Figure 11a It is the degradation effect diagram of each photo - electrode prepared in Example 1 and Comparative Example 15 on tetracycline wastewater;

[0055] Figure 11b is Figure 11a the corresponding pseudo - first - order kinetic curve diagram. Detailed implementation manners

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0057] Example 1:

[0058] A preparation method of a photo - electrocatalytic material electrode includes:

[0059] Step S1, prepare cellulose nanofiber hydrogel doped with titanium sub - oxide;

[0060] Step S2, after the cellulose nanofiber hydrogel doped with titanium sub - oxide is subjected to a first pretreatment, titanium strips after a second pretreatment are respectively pasted on the front and back of one end thereof to obtain a cellulose nanofiber hydrogel electrode sheet doped with titanium sub - oxide;

[0061] Step S3, immerse the part of the electrode sheet below the titanium strip in the MOFs dispersion solution, and perform a loading treatment under stirring to obtain a double three - dimensional structure photo - electrocatalytic material electrode (abbreviated as photo - electrode, named MIL - 100(Fe) / Ti4O7@CNF).

[0062] In step S1:

[0063] First, configure the hydrogel solution A. Specifically, mix 20 - 40 g (specifically 20 g) of cellulose nanofiber hydrogel, 0.3 - 0.6 g (specifically 0.3 g) of agar powder, and 16 - 32 mL (specifically 16 mL) of deionized water. After water bath treatment and continuous first stirring treatment, hydrogel solution A is obtained;

[0064] Secondly, under the water bath treatment and continuous first stirring treatment, add 0.25 - 0.35 g (specifically 0.3 g) of titanium suboxide powder into the hydrogel solution A and mix evenly;

[0065] Subsequently, under room temperature conditions (specific temperature is 25 °C), carry out continuous second stirring treatment until completely dissolved to obtain solution B;

[0066] Finally, pour the solution B into a petri dish, add an acidifying agent and a crosslinking agent, and after drying treatment, obtain the cellulose nanofiber hydrogel doped with titanium suboxide.

[0067] The temperature used for the water bath treatment is 85 - 90 °C (specifically 90 °C); the rotation speed used for the first stirring treatment is 400 - 500 rpm (specifically 450 rpm), and the stirring time is 5 min; the rotation speed used for the second stirring treatment is 1000 - 1100 rpm (specifically 1000 rpm), and the stirring time is 2 - 3 h (specifically 2 h).

[0068] The acidifying agent is sulfuric acid; the concentration of the acidifying agent is 1 mol / L, and the volume is 3 - 4 mL (specifically 4 mL); the crosslinking agent is N,N′-methylenebisacrylamide solution; the mass concentration of the N,N′-methylenebisacrylamide solution is 4 wt%, and the volume is 3 - 4 mL (specifically 4 mL); the drying temperature used for the drying treatment is 60 °C, and the drying time is 45 min.

[0069] The first pretreatment includes sequentially performing deionized water cleaning and cutting treatment (cut into square flakes with a side length of 3 cm) on the cellulose nanofiber hydrogel doped with titanium suboxide; the second pretreatment includes first ultrasonically removing impurities on the surface of the titanium sheet, and then cutting it into a titanium strip with a length of 3 cm and a width of 0.5 cm; the surface ultrasonic impurity removal is to ultrasonically treat the titanium sheet with acetone, ethanol, and deionized water for 15 min each to remove impurities on the surface of the titanium sheet; the binder is an ethanol solution of polyvinylpyrrolidone, where the mass fraction of polyvinylpyrrolidone in the ethanol solution is 5 wt%.

[0070] The MOF-dispersed solution is prepared by dispersing 0.02 - 0.04 g (specifically 0.03 g) of MIL-100(Fe) nanoparticles in 50 mL of deionized water, and the MOF-dispersed solution is obtained after the third stirring treatment; the rotation speed used in the third stirring treatment is 200 - 250 rpm (specifically 220 rpm), and the stirring time is 12 - 18 h (specifically 18 h).

[0071] The preparation steps of the MIL-100(Fe) nanoparticles include:

[0072] (1) Dissolve ferric chloride hexahydrate and 1,3,5-benzenetricarboxylic acid in a molar ratio of 1:1 in 50 mL of N,N-dimethylformamide, and stir until completely dissolved to obtain solution C; wherein, the molar concentrations of both ferric chloride hexahydrate and 1,3,5-benzenetricarboxylic acid are 2.5 mmol / L;

[0073] (2) Pour solution C into a stainless-steel autoclave lined with polytetrafluoroethylene, and perform heat treatment at 150 °C for 12 - 14 h (specifically 12 h), then wash, dry, and grind to obtain MIL-100(Fe) nanoparticles;

[0074] The washing is sequentially carried out by washing twice with N,N-dimethylformamide and once with ethanol; the drying temperature is 60 - 80 °C (specifically 60 °C), and the drying time is 12 - 24 h (specifically 18 h).

[0075] Comparative Example 1:

[0076] Different from Example 1, only the cellulose nanofiber hydrogel electrode (named CNF) is prepared, that is, the use of titanium suboxide powder and the MOF-dispersed solution is cancelled.

[0077] Comparative Example 2:

[0078] Different from Example 1, the cellulose nanofiber hydrogel electrode doped with titanium suboxide (named Ti4O7@CNF) is prepared, that is, the use of the MOF-dispersed solution is cancelled.

[0079] Comparative Example 3:

[0080] Different from Example 1, the cellulose nanofiber hydrogel electrode loaded with MIL-100(Fe) (named MIL-100(Fe)@CNF) is prepared, that is, the use of titanium suboxide powder is cancelled.

[0081] The respective photoelectrodes prepared in Example 1 and Comparative Examples 1 - 3 are subjected to scanning electron microscopy tests. The test results are as follows:

[0082] Figure 1aScanning electron micrograph of the cellulose nanofiber hydrogel electrode CNF prepared in Comparative Example 1. It can be seen that the CNF has a cross-linked structure, a smooth surface, and wavy folds.

[0083] Figure 1b Scanning electron micrograph of the doped titanium suboxide cellulose nanofiber hydrogel electrode Ti4O7@CNF prepared in Comparative Example 2. It can be seen that in Ti4O7@CNF, CNF wraps and fixes titanium suboxide, presenting a stacked and folded structure. Such a structural feature is beneficial to the loading of MIL-100(Fe) in the solution on Ti4O7@CNF, improving the loading amount of MIL-100(Fe) nanoparticles.

[0084] Figure 1c Scanning electron micrograph of the cellulose nanofiber hydrogel electrode MIL-100(Fe)@CNF loaded with MIL-100(Fe) prepared in Comparative Example 3. It can be seen that the surface of MIL-100(Fe) introduced with pure CNF is rough, presenting an irregular octahedral structure.

[0085] Figure 1d Scanning electron micrograph of the dual three-dimensional structure photoelectrocatalytic material electrode MIL-100(Fe) / Ti4O7@CNF prepared in Example 1. It can be seen that the MIL-100(Fe) nanoparticles on the surface of MIL-100(Fe) / Ti4O7@CNF, and a complete octahedron can be clearly observed.

[0086] From Figures 1a - 1d analysis, it can be concluded that the composite of MIL-100(Fe) and Ti4O7@CNF is beneficial to the formation of the regular morphology of MIL-100(Fe), thereby improving its photoelectrocatalytic performance.

[0087] The X-ray diffraction tests were respectively carried out on the photoelectrodes prepared in Example 1 and Comparative Examples 1-3. The test results are as follows:

[0088] From Figure 2 It was observed that the characteristic diffraction peaks shown by the X-ray diffraction pattern of the MIL-100(Fe) / Ti4O7@CNF composite material near 14.1° and 20.2° match those of MIL-100(Fe), proving the successful synthesis and loading of MIL-100(Fe). However, the diffraction peaks at 11.3°, 18.4° and 24.2° were not observed in the X-ray diffraction pattern. This may be due to some minor changes in the crystal structure of MIL-100(Fe) after the composite of MIL-100(Fe) and Ti4O7@CNF, resulting in the diffraction peak shift. In addition, from Figure 2Diffraction peaks were also observed at 2θ = 20.74°, 26.35°, 29.57°, 31.82°, 34.08°, 35.60°, 53.31° and 55.05° etc. for Ti4O7@CNF and MIL-100(Fe) / Ti4O7@CNF electrodes. By comparing with the X-ray diffraction standard spectrum of titanium suboxide (JCPDS no.77-1392), it can be found that these diffraction peaks highly match the characteristic diffraction peaks of titanium suboxide, proving the successful combination of titanium suboxide in the photoanode.

[0089] The ultraviolet-visible diffuse reflectance light tests were respectively carried out on the photoanodes prepared in Example 1 and Comparative Examples 1-3. The test results are as follows:

[0090] From Figure 3a it can be concluded that the absorption edges of the photoanodes prepared in Example 1 and Comparative Examples 1-3 are all in the ultraviolet light range, indicating that the four material electrodes can all well absorb ultraviolet light. Among them, both CNF and MIL-100(Fe)@CNF have obvious steep absorption edges, and the absorption edge wavelengths are 370nm and 421nm respectively. It should be noted that due to the relatively small band gap of titanium suboxide, the light absorption ability of Ti4O7@CNF and MIL-100(Fe) / Ti4O7@CNF is much better than that of MIL-100(Fe)@CNF and CNF; among them, Ti4O7@CNF has relatively strong light absorption ability, and its light absorption range extends to visible light, especially with significantly enhanced light absorption within 300nm - 800nm.

[0091] According to the Kubellka-Munk equation (i.e., Equation 1), the absorption data at different wavelengths obtained from the ultraviolet-visible diffuse reflectance light tests of the photoanode materials prepared in Example 1 and Comparative Examples 1-3 were converted into Tauc plots to evaluate the band gap energy (E g ) of each photoanode. As Figure 3b , the E g values of the samples CNF, Ti4O7@CNF, MIL-100(Fe)@CNF and MIL-100(Fe) / Ti4O7@CNF are 4.03eV, 3.75eV, 4.31eV and 3.88eV respectively; among them, the E g value of Ti4O7@CNF is the smallest, indicating that Ti4O7@CNF has relatively excellent light absorption ability, which is consistent with the conclusion drawn from the ultraviolet-visible diffuse reflectance spectrum. Although the light absorption ability of the composite MIL-100(Fe) / Ti4O7@CNF is slightly weaker than that of Ti4O7@CNF, compared with MIL-100(Fe)@CNF, the light absorption range is greatly enhanced, and it still has relatively excellent light response performance.

[0092] (αhν) 2= A(hν - E g )(Equation 1);

[0093] In Equation 1, α represents the absorption coefficient; hν represents the incident photon energy; A represents a constant related to the material properties; E g represents the band gap energy.

[0094] The photoelectrodes prepared in Example 1 and Comparative Examples 1 - 3 were respectively subjected to electrochemical impedance tests. The test results are as follows:

[0095] From Figure 4 it can be seen that the curve radius of MIL - 100(Fe) / Ti4O7@CNF is the smallest. This phenomenon indicates that the successful introduction of MIL - 100(Fe) significantly enhances the photogenerated carrier transfer efficiency of Ti4O7@CNF, making MIL - 100(Fe) / Ti4O7@CNF have the most excellent optoelectronic performance.

[0096] Example 2:

[0097] The photoelectrode (MIL - 100(Fe) / Ti4O7@CNF) prepared in Example 1 was used as the anode, a platinum sheet electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. It was placed in 100 mL of tetracycline wastewater containing sodium sulfate (the concentration of sodium sulfate in this wastewater was 50 mmol / L, the concentration of tetracycline was 20 mg / L, pH = 4.75), and a photoelectrocatalytic reaction was carried out for 120 min under the conditions of a visible light source and a constant voltage of 2 V to complete the degradation of tetracycline; among them, the photoelectrode was 10 cm away from the light source.

[0098] The photoelectrodes prepared in Comparative Examples 1 - 3 were respectively used as the anodes, and the experiments for degrading tetracycline wastewater were carried out according to the same operating conditions as in Example 2. During the 120 - minute photoelectrocatalytic reaction process, 1 mL of the sample was taken every 30 minutes (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis), passed through a 0.45 - μm filter head, and the change in the peak area at different degradation times was measured by a high - performance liquid chromatograph to determine the change in the tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photoelectrode on tetracycline. The degradation effect is as Figures 5a - 5b shown.

[0099] From Figure 5a it can be seen that for T without loading MIL - 100(Fe) i4The degradation ability of the Ti4O7@CNF electrode for tetracycline is very limited, only 24.14%, because the interfacial transfer resistance of titanium suboxide is high and the electrocatalytic activity is low. MIL-100(Fe)@CNF can degrade 66.43% of tetracycline within 120 min, while the composite MIL-100(Fe) / Ti4O7@CNF electrode can degrade 93.22% of tetracycline within 120 min, which is 3.86 times the degradation efficiency of Ti4O7@CNF.

[0100] It can be seen that Figure 5b the reaction rate of MIL-100(Fe) / Ti4O7@CNF increases significantly compared with other photoanodes, from 0.00178 min -1 of the CNF electrode to 0.02246 min -1 of the MIL-100(Fe) / Ti4O7@CNF electrode, indicating that the introduction of MIL-100(Fe) into Ti4O7@CNF significantly improves the photoelectrocatalytic performance of MIL-100(Fe) / Ti4O7@CNF.

[0101] Comparative Example 4:

[0102] Different from Example 2: The applied condition is only a visible light source.

[0103] Comparative Example 5:

[0104] Different from Example 2: The applied condition is only a constant voltage of 2V.

[0105] During the 120-min photoelectrocatalytic reaction in Example 2 and Comparative Examples 4-5, 1 mL of the sample was taken every 30 min (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis), passed through a 0.45-μm filter head, and the change in peak area at different degradation times was measured by a high-performance liquid chromatograph to determine the change in tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photoanode on tetracycline under different applied conditions. The degradation effect is as Figures 6a - 6b shown.

[0106] It can be Figure 6a seen that under the conditions of separately applying a visible light source (i.e., photocatalysis) and separately applying a constant voltage of 2V (i.e., electrocatalysis), after 120 min of reaction, the degradation rates of the MIL-100(Fe) / Ti4O7@CNF electrode for tetracycline are both relatively low, 16.20% and 23.69% respectively. While under the condition of simultaneously applying a visible light source and a constant voltage of 2V (i.e., photoelectrocatalysis), the degradation rate can be as high as 93.22%, which is significantly better than photocatalysis and electrocatalysis; this proves that there is a significant photo-electric synergistic effect during the photoelectrocatalytic process.

[0107] According to Figure 6b The synergistic factor (SF) of the photocatalytic process was calculated to be 6.66 based on the first-order kinetic constant (k) using Equation 2.

[0108]

[0109] Among them, k in Equation 2 PEC , k PC and k EC respectively represent the first-order kinetic constants of tetracycline degradation in the photocatalytic, photocatalytic, and electrocatalytic processes.

[0110] Example 3:

[0111] Different from Example 2, pH = 5.

[0112] Comparative Example 6:

[0113] Different from Example 2, pH = 1.

[0114] Comparative Example 7:

[0115] Different from Example 2, pH = 3.

[0116] Comparative Example 8:

[0117] Different from Example 2, pH = 7.

[0118] Comparative Example 9:

[0119] Different from Example 2, pH = 9.

[0120] Comparative Example 10:

[0121] Different from Example 2, pH = 11.

[0122] During the 120-min photocatalytic reaction in Example 3 and Comparative Examples 6 - 10, 1 mL of the sample was taken every 30 min (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis) and passed through a 0.45-μm filter head. The change in the peak area at different degradation times was measured by a high-performance liquid chromatograph to determine the change in the tetracycline concentration during the photocatalytic process, so as to obtain the degradation effect of tetracycline by each photoanode under different pH conditions. The degradation effect is as Figures 7a - 7b shown.

[0123] From Figure 7a and 7bIt is known that in a strong acid environment with pH = 1 and 3, the degradation rates of tetracycline by MIL-100(Fe) / Ti4O7@CNF are both about 55%. The first-order reaction kinetic constants k are 0.00657 and 0.00647 respectively, which are both relatively low. This is because the catalytic sites on the catalyst surface are limited, and under strong acidic conditions, the concentration of H + is relatively high, and H + occupies the active sites on the surface of the photoelectrode, hindering the adsorption and degradation of tetracycline. In addition, it may also be due to the fact that excessive H + reacts with ·OH, resulting in a decrease in the number of ·OH and a decrease in the degradation rate. When pH = 5, which is close to the initial pH value of the solution, 4.75, the degradation rate of tetracycline is 95.24%. This indicates that in a weak acidic environment, MIL-100(Fe) / Ti4O7@CNF can achieve efficient degradation of tetracycline. Subsequently, as the pH of the solution increases, the degradation efficiency gradually decreases. However, when the pH increases to 11, the degradation rate of tetracycline by MIL-100(Fe) / Ti4O7@CNF reaches the maximum value, and the degradation rate is as high as 96.03% within 60 min, and 100% degradation of tetracycline is achieved within 120 min. The first-order reaction kinetic constant k is as high as 0.04243. The following reasons may account for this phenomenon: 1) The nature of the target pollutant. Tetracycline is unstable in strong alkaline aqueous solutions, will undergo partial hydrolysis, and will also undergo a reversible epimerization reaction to form isomers with lactone structures; 2) There are a large number of OH - in the solution, and more active substances (such as ·OH, ·O 2- ) may be generated under the action of photoelectrocatalysis. The reaction of the active substances with tetracycline accelerates the degradation rate.

[0124] Example 4:

[0125] Different from Example 2, the voltage is adjusted to 1.5 V.

[0126] Comparative Example 11:

[0127] Different from Example 2, the voltage is adjusted to 2.5 V.

[0128] Comparative Example 12:

[0129] Different from Example 2, the voltage is adjusted to 1 V.

[0130] Comparative Example 13:

[0131] Different from Example 2, the voltage is adjusted to 0.5 V.

[0132] During the 120 - minute photoelectrocatalytic reaction in Example 4 and Comparative Examples 11 - 13, 1 mL of the sample was taken every 30 minutes (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis), passed through a 0.45 - μm filter head, and the change in peak area at different degradation times was measured by a high - performance liquid chromatograph to determine the change in tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photo - electrode on tetracycline under different voltage conditions. The degradation effect is as Figures 8a - 8b shown.

[0133] As Figure 8a known, under the conditions of voltages of 0.5 V, 1.0 V, 1.5 V, 2 V, and 2.5 V, the degradation rates of tetracycline by MIL - 100(Fe) / Ti4O7@CNF are 9.69%, 16.34%, 76.02%, 93.22%, and 96.89% respectively; as Figure 8b known, the first - order kinetic constant (k) also increases from 0.00087 min -1 at 0.5 V to 0.03002 min -1 at 2.5 V, that is, with the continuous increase of voltage, the degradation rate of tetracycline gradually increases. This may be because the increase in voltage promotes the charge transfer in the reaction system, improving the reaction activity and catalytic efficiency. However, when the voltage increases to 2.5 V, bubbles and holes appear on the surface of the photo - electrode, which is caused by the obvious enhancement of side reactions (such as hydrogen evolution and oxygen evolution reactions) in the system under a higher applied voltage. To ensure the service life of the photo - electrode and stable degradation efficiency, a voltage of 2 V is the most suitable applied voltage.

[0134] Example 5:

[0135] Different from Example 2, the distance between the photo - electrode and the light source is 6 cm.

[0136] Example 6:

[0137] Different from Example 2, the distance between the photo - electrode and the light source is 8 cm.

[0138] Example 7:

[0139] Different from Example 2, the distance between the photo - electrode and the light source is 12 cm.

[0140] Example 8:

[0141] Different from Example 2, the distance between the photo - electrode and the light source is 14 cm.

[0142] In Examples 2 and 5 - 8, the photon flux was changed by varying the distance between the light source and the photo - electrode.

[0143] During the 120 - minute photoelectrocatalytic reaction in Examples 2 and 5 - 8, 1 mL of the sample was taken every 30 minutes (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis), passed through a 0.45 - μm filter head, and the change in peak area at different degradation times was measured by a high - performance liquid chromatograph to determine the change in tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photo - electrode on tetracycline under different photon flux conditions. The degradation effect is as Figures 9a - 9b shown.

[0144] Figure 9a shows the effect of different photon fluxes on the degradation efficiency of tetracycline by the MIL - 100(Fe) / Ti4O7@CNF electrode. It can be seen that the degradation efficiency of tetracycline gradually increases as the distance between the photo - electrode and the light source decreases; when the distance is reduced to 6 cm, MIL - 100(Fe) / Ti4O7@CNF can degrade up to 98.11% of tetracycline; when the distance increases to 14 cm, the degradation efficiency of tetracycline is 91.48%.

[0145] Figure 9b is the (pseudo) first - order kinetic curve of the tetracycline degradation process under different photon flux conditions. Analyzing the obtained first - order kinetic constant (k), it can be known that the k value at high photon flux is 1.69 times that at low photon flux. This is because with the increase in photon flux, the number of electrons generated by photon excitation increases, resulting in an increase in the degradation rate of tetracycline.

[0146] Comparative Example 14:

[0147] Different from Example 1, the dosage of titanium sub - oxide powder is 0.15 g.

[0148] Comparative Example 15:

[0149] Different from Example 1, the dosage of MIL - 100(Fe) nanoparticles is 0.06 g.

[0150] Taking the photo - electrodes prepared in Example 1 and Comparative Example 14 as anodes respectively, the experiment of degrading tetracycline wastewater was carried out according to the operation conditions of Example 2. During the 120 - minute photoelectrocatalytic reaction, 1 mL of the sample was taken every 30 minutes (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis), passed through a 0.45 - μm filter head, and the change in peak area at different degradation times was measured by a high - performance liquid chromatograph to determine the change in tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photo - electrode on tetracycline. The degradation effect is as Figures 10a - 10b shown.

[0151] From Figure 10a and Figure 10bIt can be seen that when preparing the MIL-100(Fe) / Ti4O7@CNF photoanode, when the dosage of titanium suboxide powder is 0.15 g, the degradation rate of the corresponding photoanode for tetracycline within 120 min is only 44.22%, and the first-order kinetic constant is 0.00405; when the dosage of titanium suboxide powder increases to 0.3 g, the degradation rate of the corresponding photoanode for tetracycline within 120 min reaches 93.22%, and the first-order kinetic constant also increases to 0.02246. Compared with adding 0.15 g of titanium suboxide powder, the degradation efficiency increases by 2.1 times and the reaction rate increases by 5.5 times.

[0152] Taking the photoanodes prepared in Example 1 and Comparative Example 15 as anodes respectively, the experiments for degrading tetracycline wastewater were carried out according to the operating conditions of Example 2. During the 120-min photoelectrocatalytic reaction process, 1 mL of the sample was taken every 30 min (i.e., at 0 min, 30 min, 60 min, 90 min, and 120 min of catalysis) and passed through a 0.45-μm filter head, and the change in the peak area at different degradation times was measured by a high-performance liquid chromatograph to determine the change in the tetracycline concentration during the photoelectrocatalytic process, so as to obtain the degradation effect of each photoanode on tetracycline. The degradation effect is as Figures 11a - 11b shown.

[0153] It can be seen from Figure 11a and Figure 11b that when preparing the MIL-100(Fe) / Ti4O7@CNF photoanode, when the dosages of MIL-100(Fe) nanoparticles are 0.03 g and 0.06 g respectively, the degradation rates of the corresponding photoanodes for tetracycline within 120 min are 93.22% and 92.66% respectively, and the first-order kinetic constants are 0.02246 and 0.02324; since the degradation efficiencies obtained when the addition amount of MIL-100(Fe) nanoparticles is 0.03 g and 0.06 g are both above 90% and the difference is not significant, in order to save production costs, the dosage of MIL-100(Fe) nanoparticles is preferably 0.03 g.

[0154] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a photoelectrocatalytic material electrode, characterized in that Including: Step S1: Prepare a cellulose nanofiber hydrogel doped with titanium suboxide. Step S2: After the cellulose nanofiber hydrogel doped with titanium suboxide undergoes a first pretreatment, titanium strips after a second pretreatment are respectively pasted on the front and back of one end thereof to obtain a cellulose nanofiber hydrogel electrode sheet doped with titanium suboxide. Step S3: Immerse the part of the electrode sheet below the titanium strip in a MOFs dispersion solution, and perform a loading treatment under stirring to obtain a double three-dimensional structure photocatalytic material electrode.

2. The preparation method of the photo-electrocatalytic material electrode according to claim 1, characterized in that, In step S1: First, prepare hydrogel solution A. Specifically, mix 20 - 40 g of cellulose nanofiber hydrogel, 0.3 - 0.6 g of agar powder, and 16 - 32 mL of deionized water, and obtain hydrogel solution A after a water bath treatment and a continuous first stirring treatment. Second, under the water bath treatment and the continuous first stirring treatment, add 0.25 - 0.35 g of titanium suboxide powder to the hydrogel solution A and mix well. Subsequently, perform a continuous second stirring treatment at room temperature until completely dissolved to obtain solution B. Finally, pour the solution B into a petri dish, add an acidifying agent and a crosslinking agent, and obtain the cellulose nanofiber hydrogel doped with titanium suboxide after a drying treatment.

3. The preparation method of the photo-electrocatalytic material electrode according to claim 2, characterized in that, The temperature used for the water bath treatment is 85 - 90 °C; the rotation speed used for the first stirring treatment is 400 - 500 rpm, and the stirring time is 3 - 5 min; the rotation speed used for the second stirring treatment is 1000 - 1100 rpm, and the stirring time is 2 - 3 h.

4. The preparation method of the photoelectrocatalytic material electrode according to claim 2, characterized in that, The acidifying agent includes sulfuric acid; the concentration of the acidifying agent is 0.5 - 2.0 mol / L, and the volume is 3 - 4 mL; the crosslinking agent includes an N,N′-methylenebisacrylamide solution; the mass concentration of the N,N′-methylenebisacrylamide solution is 3.5 - 4.5 wt%, and the volume is 3 - 4 mL; the drying temperature used for the drying treatment is 50 - 80 °C, and the drying time is 45 - 60 min.

5. The preparation method of the photo-electrocatalytic material electrode according to claim 1, characterized in that, The first pretreatment includes sequentially performing deionized water cleaning and cutting treatment on the cellulose nanofiber hydrogel doped with titanium suboxide; the second pretreatment includes first ultrasonically removing impurities on the surface of the titanium sheet and then cutting it into titanium strips; the binder includes an ethanol solution of polyvinylpyrrolidone.

6. The preparation method of the photo-electrocatalytic material electrode according to claim 1, wherein, The MOFs dispersion solution includes dispersing 0.02 - 0.04 g of MIL-100(Fe) nanoparticles in 50 mL of deionized water, and obtaining the MOFs dispersion solution after a third stirring treatment; the rotation speed used for the third stirring treatment is 200 - 250 rpm, and the stirring time is 12 - 18 h.

7. The preparation method of the photoelectrocatalytic material electrode according to claim 6, characterized in that, The preparation steps of the MIL-100(Fe) nanoparticles include: (1) Dissolve ferric trichloride hexahydrate and 1,3,5-benzenetricarboxylic acid in a molar ratio of 2:1 - 1:2 in 50 - 100 mL of N,N-dimethylformamide, and stir until completely dissolved to obtain solution C; wherein, the molar concentrations of the ferric trichloride hexahydrate and the 1,3,5-benzenetricarboxylic acid are both 1.0 - 3.0 mmol / L. (2) Pour solution C into a stainless-steel autoclave lined with polytetrafluoroethylene, and perform heat treatment at 120 - 180 °C for 12 - 14 h, then wash, dry, and grind to obtain MIL-100(Fe) nanoparticles; The washing is successively carried out with N,N-dimethylformamide and ethanol; the drying temperature is 60 - 80 °C, and the drying time is 12 - 24 h.

8. An optoelectrocatalytic material electrode, characterized in that, It is prepared by using the preparation method of the photo-electrocatalytic material electrode according to any one of claims 1 - 7.

9. Application of a photoelectrocatalytic material electrode as described in claim 8 in the degradation of tetracycline wastewater, characterized in that, Use the photo-electrocatalytic material electrode as the anode, a platinum sheet electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, and place them in tetracycline wastewater containing an electrolyte for a photo-electrocatalytic reaction to complete the degradation treatment of the tetracycline wastewater.

10. The application according to claim 9, characterized in that The photo-electrocatalytic reaction is carried out under light conditions, the voltage used in the photo-electrocatalytic reaction is 1.5 - 2 V, and the reaction time is 1 - 3 h; the electrolyte includes sodium sulfate; the pH value of the tetracycline wastewater is 4.5 - 5.0; the concentration of tetracycline in the tetracycline wastewater is 10 - 20 mg / L, and the electrolyte concentration is 25 - 50 mmol / L.

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