Ternary composite photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photoelectrocatalytic degradation, and discloses a ternary composite photocatalyst and a preparation method and application thereof.The method comprises the steps that 1, titanium dioxide nanotubes are formed on the surface of a titanium mesh through an anodic oxidation method, and a substrate material I is obtained; (2) sintering the substrate material I to obtain a substrate material II; the average pore size of the titanium dioxide nanotube is 80-90 nm, the average length of the titanium dioxide nanotube is 10-15 [mu] m, and the average thickness of the tube wall of the titanium dioxide nanotube is 10-18 nm; and (3) immersing the substrate material II into a mixed solution for hydrothermal reaction to prepare the ternary composite photocatalyst. Compared with a powdery photocatalyst, the ternary composite material provided by the invention is easier to recover, the catalytic efficiency and stability of the photocatalyst are remarkably improved, and the ternary composite material is more suitable for large-scale actual production.

Description

Technical Field

[0001] The invention relates to the technical field of photoelectrocatalytic degradation, and in particular to a ternary composite photocatalyst and a preparation method and application thereof. Background Art

[0002] Ordinary TiO 2 The relatively wide bandgap (about 3.2 eV) results in low solar energy utilization efficiency and poor response to visible light (about 43% of the total solar energy), which cannot effectively excite TiO 2 , can only absorb and utilize ultraviolet (UV), which accounts for only 5% of the total incident solar energy. On the other hand, the rapid recombination of photogenerated electrons and holes is another major factor limiting its photocatalytic activity and practical application. Therefore, it is necessary to modify ordinary titanium dioxide. The common modification methods are: (1) Surface noble metal deposition: When TiO 2 When the semiconductor is in contact with the noble metal, the TiO 2 New energy levels will be formed in the band gap, and a Fermi level difference will be formed between the two, resulting in carrier redistribution. Electrons are transferred from the semiconductor to the surface of the noble metal, inhibiting the recombination of photogenerated electrons and holes. However, the disadvantages of this method are high cost, poor stability, and difficulty in promotion. (2) Ion modification: During the modification process, it is difficult to determine the amount of doping substances required, resulting in defects that are difficult to solve, and there is still a high cost problem. (3) Surface photosensitization: The photoactive sensitizer is attached to the TiO by physical or chemical means. 2 However, the photoactive sensitizer is easily affected by the external environment and causes decomposition or shedding.

[0003] In summary, the most common TiO 2 The photocatalysts obtained by the modification method have low efficiency, and there is an urgent need for a photocatalyst with excellent photocatalytic efficiency and the ability to utilize both visible light and ultraviolet light. Summary of the invention

[0004] The purpose of the present invention is to provide a photocatalyst which can utilize a wider range of light wavelengths, has high photocatalytic efficiency and good stability.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a ternary composite photocatalyst, the method comprising:

[0006] (1) forming titanium dioxide nanotubes on the surface of the titanium mesh by an anodic oxidation method to obtain a base material I;

[0007] (2) sintering the base material I to obtain base material II; the titanium dioxide nanotubes have an average pore diameter of 80-90 nm, an average length of 10-15 μm, and an average tube wall thickness of 10-18 nm;

[0008] (3) Immerse the substrate material II into the mixed solution for hydrothermal reaction to prepare a ternary composite photocatalyst;

[0009] The mixed solution contains bismuth nitrate, sodium molybdate, graphene quantum dots, ethylene glycol and a surfactant; in the mixed solution, the concentration of bismuth nitrate is 30-35 mmol / L, the concentration of sodium molybdate is 15-20 mmol / L, and the concentration of graphene quantum dots is 10-20 μg / L.

[0010] The second aspect of the present invention provides a ternary composite photocatalyst prepared by the method described in the foregoing first aspect.

[0011] The third aspect of the present invention provides the application of the ternary composite photocatalyst described in the foregoing second aspect in the degradation of organic pollutants.

[0012] The technical solution provided by the present invention has at least the following advantages:

[0013] The ternary composite photocatalyst (Bi 2 MoO 6 / GQDs / TiO 2 photocatalyst) provided by the present invention has a double Z-scheme heterojunction, wherein graphene quantum dots (GQDs) serve as a transfer medium for photo-generated electrons, improving the utilization rate of sunlight and reducing the recombination rate of photo-generated electron-hole pairs. The double Z-scheme heterojunction photocatalyst exhibits excellent photocatalytic degradation performance for TC (tetracycline hydrochloride).

[0014] The present invention uses a titanium mesh as a substrate, and combines an anodic oxidation method to form titanium dioxide nanotubes on the surface of the titanium mesh. By controlling the reaction conditions, the morphology of the titanium dioxide nanotubes is controlled. The prepared ternary composite material is easier to recycle than the powdered photocatalyst, and significantly improves the catalytic efficiency and stability of the photocatalyst, making it more suitable for large-scale actual production.

[0015] The technical solution provided by the present invention realizes photo-electrochemical combined catalytic degradation. On the basis of photocatalysis, after introducing a bias voltage, the performance of the photo-electrochemical catalysis (PEC) process is improved. The bias voltage promotes the separation of photo-generated electron-hole pairs and makes the photocatalyst easier to reuse, which is crucial for practical applications. Description of the Drawings

[0016] Figure 1 For the photocatalytic degradation performance curves of BGT-2 material, TiO 2 material, BGT-0 material, BGT-1 material and BGT-3 material;

[0017] Figure 2 For the BGT-2 material, TiO 2Photocurrent result diagrams of materials, BGT-0 material, BGT-1 material, and BGT-3 material;

[0018] Figure 3 is BGT-2 material, TiO 2 EIS result diagrams of material and BGT-0 material;

[0019] Figure 4 is BGT-2 material, TiO 2 LSV result diagrams of material and BGT-0 material;

[0020] Figure 5 is BGT-2 material, TiO 2 material, BGT-0 material, and Bi 2 MoO 6 XRD diagrams of material;

[0021] Figure 6 is TiO 2 SEM diagrams of material;

[0022] Figure 7 SEM diagrams of BGT-0 material;

[0023] Figure 8 SEM diagrams of BGT-2 material;

[0024] Figure 9 EDS energy spectrum diagrams of BGT-2 material;

[0025] Figure 10 Element distribution diagrams of BGT-2 material;

[0026] Figure 11 TEM diagrams of BGT-2 material;

[0027] Figure 12 HRTEM diagrams of BGT-2 material;

[0028] Figure 13 is BGT-2 material, TiO 2 XPS diagrams of material and BGT-0 material;

[0029] Figure 14 is BGT-2 material and TiO 2 Infrared spectra of material;

[0030] Figure 15 is BGT-2 material and TiO 2 Raman spectra of material;

[0031] Figure 16 is BGT-2 material, TiO 2PL result diagrams of the material and BGT-0 material;

[0032] Figure 17 It is the stability curve of the photoelectrocatalytic degradation performance of the BGT-2 material. Specific implementation manners

[0033] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0034] As described above, the first aspect of the present invention provides a method for preparing a ternary composite photocatalyst, and the method includes:

[0035] (1) Forming titanium dioxide nanotubes on the surface of a titanium mesh by anodic oxidation to obtain a substrate material I;

[0036] (2) Sintering the substrate material I to obtain a substrate material II; the average pore diameter of the titanium dioxide nanotubes is 80 - 90 nm, the average length is 10 - 15 μm, and the average wall thickness is 10 - 18 nm;

[0037] (3) Immersing the substrate material II in a mixed solution for hydrothermal reaction to prepare a ternary composite photocatalyst;

[0038] The mixed solution contains bismuth nitrate, sodium molybdate, graphene quantum dots, ethylene glycol, and a surfactant; in the mixed solution, the concentration of bismuth nitrate is 30 - 35 mmol / L, the concentration of sodium molybdate is 15 - 20 mmol / L, and the concentration of graphene quantum dots is 10 - 20 μg / L.

[0039] Preferably, in step (1), the average diameter of the mesh holes of the titanium mesh is 60 - 90 μm, preferably 70 - 80 μm.

[0040] The present invention has no particular limitation on the shape and area size of the titanium mesh. Those skilled in the art can select a titanium mesh with a suitable shape and size according to actual needs. The present invention exemplarily provides a preferred specific implementation manner hereinafter. Exemplarily, the titanium mesh is a 2 cm × 2 cm square titanium mesh, and those skilled in the art should not understand it as a limitation to the present invention.

[0041] According to a preferred specific implementation manner, the method of the present invention further includes: before performing step (1), first performing a pretreatment operation of degreasing and removing the oxide film on the titanium mesh.

[0042] The present invention has no particular limitation on the pretreatment operations of degreasing and removing the oxide film of the titanium mesh. Those skilled in the art can select according to the known technical means in the art. However, in order to obtain a ternary composite photocatalyst with higher photocatalytic efficiency and better stability, the present invention preferably adopts the following method for the pretreatment operation.

[0043] Preferably, the operations of the pretreatment include: successively immersing the titanium mesh to be treated in n-propanol, ethanol and isopropanol, and ultrasonically cleaning each for 5 - 15 min. Then immerse the cleaned titanium mesh in a mixed acid solution containing acetic acid and hydrofluoric acid simultaneously, where the volume ratio of acetic acid to hydrofluoric acid is 6 - 9:1, and soak for 4 - 8 min to obtain the pretreated titanium mesh.

[0044] Preferably, the electrolyte used in the anodic oxidation method includes ethylene glycol, water and ammonium fluoride; the ammonium fluoride accounts for 0.4 - 0.6% of the total mass of the electrolyte, and the volume ratio of ethylene glycol to water is 30 - 35:1. The inventors found in the research that by using the electrolyte under the preferred conditions, titanium dioxide nanotubes with regular tube orifice shapes, uniform tube diameters, longer lengths and larger tube diameters can be grown.

[0045] Preferably, the conditions of the anodic oxidation method include: the voltage is 55 - 65 V and the time is 1.5 - 2.5 h.

[0046] More preferably, the operation of the anodic oxidation is controlled to be carried out under the condition of 25 - 35 °C.

[0047] The present invention has no particular limitation on the temperature control method during the anodic oxidation treatment process. Exemplarily, water bath refrigeration is used for temperature control, which is not elaborated herein in the present invention, and those skilled in the art should not consider it as a limitation to the present invention.

[0048] Preferably, in step (2), the conditions of the sintering treatment include: the temperature is 480 - 520 °C and the time is 1.5 - 2.5 h. By controlling the sintering temperature under the preferred conditions, anatase titanium dioxide can be generated, which has a better photocatalytic effect.

[0049] Preferably, in step (3), in the mixed solution, the molar concentration ratio of sodium molybdate to bismuth nitrate is 1:1.8 - 2.2, and more preferably 1:2.

[0050] Preferably, in step (3), the surfactant is selected from at least one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, and polyethylene glycol. The surfactant is particularly preferably polyvinylpyrrolidone.

[0051] Preferably, the concentration of the surfactant in the mixed solution is 4 - 6 g / L.

[0052] Preferably, in step (3), the conditions of the hydrothermal reaction include: temperature of 150-170° C. and time of 13-15 h.

[0053] According to a preferred embodiment, in step (3), the method for preparing the mixed solution comprises:

[0054] S1: Under stirring conditions, a bismuth nitrate solution in ethylene glycol and a sodium molybdate solution in ethylene glycol are first mixed to obtain a mixture I;

[0055] S2: performing a second mixing of the mixture I and an ethylene glycol solution of a surfactant to obtain a mixture II;

[0056] S3: performing a third mixing of the mixture II and graphene quantum dots to obtain the mixed solution.

[0057] Preferably, in step S1, the first mixing conditions include: a stirring speed of 400-500 rpm and a time of 10-20 min.

[0058] Preferably, in step S2, the second mixing specifically comprises: stirring and mixing the mixture I with the ethylene glycol solution of the surfactant at 400-500 rpm for 12-20 min, then ultrasonically mixing for 8-12 min, and then stirring and mixing at 300-400 rpm for 4-8 min to obtain the mixture II.

[0059] Preferably, in step S3, the third mixing conditions include: a stirring speed of 300-400 rpm and a time of 10-20 min.

[0060] The present invention has no particular restrictions on the specific source and type of the graphene quantum dots. Those skilled in the art can commercially obtain them according to product types known in the art, or can make graphene quantum dots by themselves. The graphene quantum dots can be prepared in the form of solid powder, or in the form of solution or suspension. The present invention will not be repeated here, and those skilled in the art should not be construed as limiting the present invention.

[0061] As mentioned above, the second aspect of the present invention provides a ternary composite photocatalyst prepared by the method described in the first aspect.

[0062] Preferably, the usable light wavelength range of the ternary composite photocatalyst is 400-760 nm.

[0063] The ternary composite photocatalyst provided by the present invention has a wider light wave utilization range, and can not only absorb and utilize ultraviolet rays, but also utilize visible light, thereby greatly improving the utilization efficiency of solar energy.

[0064] As described above, the third aspect of the present invention provides the application of the ternary composite photocatalyst described in the second aspect above in the degradation of organic pollutants.

[0065] Preferably, the degradation rate of the ternary composite photocatalyst to the organic pollutants is ≥76%, preferably ≥78%.

[0066] Preferably, the organic pollutants are selected from at least one of tetracycline hydrochloride, methyl orange, methyl blue, and methylene blue.

[0067] More preferably, the organic pollutant is tetracycline hydrochloride. The inventors found in the research that the ternary composite photocatalyst provided by the present invention has more excellent catalytic efficiency for tetracycline hydrochloride and higher catalytic stability.

[0068] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are all commercially available products.

[0069] Graphene quantum dots: liquid, concentration of 1 mg / L, purchased from Xianfeng Nano Company, CAS number is 7440-44-0.

[0070] Example 1

[0071] (1) Put the titanium mesh (2 cm × 2 cm, pore size of 75 μm) into a beaker, immerse it in n-propanol, clean it with an ultrasonic cleaner for 10 min, take it out and dry the surface, then put it into absolute ethanol and repeat the above operation. After that, put it into isopropanol solution for cleaning to complete the cleaning work of grease impurities on the surface of the titanium mesh. Put the cleaned titanium mesh into a mixed acid solution of acetic acid and hydrofluoric acid (volume ratio of 8:1), soak it for 5 min and then take it out to remove the surface oxide film, and then wash it with deionized water and ethanol in turn, and dry it and put it into a bag.

[0072] (2) The anode is the pretreated titanium mesh, the cathode is the platinum electrode, use a voltage of 60 V, and carry out anodic oxidation for 2 h in the electrolyte (485 mL of ethylene glycol, 15 mL of water and 0.5 wt% ammonium fluoride), while cooling with a water bath, and add a magnetic stirrer into the electrolyte and stir continuously to obtain the substrate material I.

[0073] (3) Put the substrate material I into a muffle furnace and bake it at 500 °C for 2 h, take it out after natural cooling to obtain the substrate material II; the average pore diameter of the titanium dioxide nanotubes is 84.13 nm, the average length is 13.25 μm, and the average wall thickness of the tube wall is 14.89 nm.

[0074] (4) Put 1 mmol of Bi(NO 3 ) 3 ·5H 2Add 10 mL of ethylene glycol and stir for 15 min to obtain an ethylene glycol solution of bismuth nitrate; Add 0.5 mmol of Na 2 MoO 4 ·2H 2 O to 10 mL of ethylene glycol and stir for 15 min to obtain an ethylene glycol solution of sodium molybdate; Add 0.15 g of polyvinylpyrrolidone (PVP) to 10 mL of ethylene glycol and stir for 15 min to obtain an ethylene glycol solution of the surfactant;

[0075] Mix the above-mentioned ethylene glycol solution of bismuth nitrate and the ethylene glycol solution of sodium molybdate and stir for 15 min to obtain mixture I; Then mix mixture I with the ethylene glycol solution of PVP and stir for 15 min. After stirring, ultrasonicate for 10 min and then stir for 5 min; Finally, add 0.4 mL of graphene quantum dots and stir for 15 min to obtain a mixed solution;

[0076] Immerse the substrate material II in the mixed solution for hydrothermal reaction (160 °C, 14 h) to prepare a ternary composite photocatalyst Bi 2 MoO 6 -GQDs-TiO 2 , named BGT-2.

[0077] Comparative Example 1

[0078] Prepare the substrate material II according to the methods of steps (1), (2) and (3) of Example 1, which is the TiO 2 material.

[0079] Comparative Example 2

[0080] Carry out in a method similar to that of Example 1. The difference is that graphene quantum dots are not added during the preparation of the mixed solution in step (4), and the rest remain unchanged, to prepare a binary composite photocatalyst, named BGT-0.

[0081] Comparative Example 3

[0082] Adopt a process similar to that of Example 1. The difference is that in step (4), the addition amount of graphene quantum dots is reduced, 0.2 mL of graphene quantum dots is added, and the rest remain unchanged, to prepare a composite photocatalytic material, named BGT-1.

[0083] Comparative Example 4

[0084] Adopt a process similar to that of Example 1. The difference is that in step (4), the addition amount of graphene quantum dots is increased, 0.8 mL of graphene quantum dots is added, and the rest remain unchanged, to prepare a composite photocatalytic material, named BGT-3.

[0085] Test Example 1

[0086] Using the BGT-2 material of Example 1, the TiO of Comparative Example 1 2 material, the BGT-0 material of Comparative Example 2, the BGT-1 material of Comparative Example 3, and the BGT-3 material of Comparative Example 4 as samples, the photocatalytic degradation performance was tested.

[0087] The photocatalytic performance of the above 5 samples was tested. The test method was as follows:

[0088] Using an electrolytic cell with an effective volume of 100 mL as the reaction vessel, the test material was placed in a 20 mg / L tetracycline hydrochloride solution and left to adsorb statically in the dark for half an hour. After that, its content was measured using an ultraviolet spectrophotometer. Then, air was sent into the solution at a flow rate of 200 mL / min using an air pump for 10 min. After that, ventilation was maintained and illumination was started, so that visible light with a light power density of 300 mw / cm 2 was irradiated on the test material, and the degradation time was 120 min. The supernatant was placed in a cuvette every 30 min to measure its content. According to the content of tetracycline hydrochloride in the solution at different time points, a photocatalytic degradation curve was plotted.

[0089] The calculation method of the photocatalytic degradation rate was: (C 0 -C 120 ) / C 0 ; where C 0 represents the initial concentration of tetracycline hydrochloride, and C 120 represents the concentration of tetracycline hydrochloride after 120 minutes of degradation.

[0090] The results are shown in Table 1.

[0091] Table 1

[0092] Degradation rate of tetracycline hydrochloride Example 1 (BGT-2) 78.67％ <![CDATA[Comparative Example 1 (TiO 2 )]]> 60.35％ Comparative Example 2 (BGT-0) 74.79％ Comparative Example 3 (BGT-1) 74.83％ Comparative Example 4 (BGT-3) 70.23％

[0093] Figure 1 is the photocatalytic degradation performance curve of the BGT-2 material of Example 1, the TiO of Comparative Example 1 2 material, the BGT-0 material of Comparative Example 2, the BGT-1 material of Comparative Example 3, and the BGT-3 material of Comparative Example 4.

[0094] From Table 1 and Figure 1 it can be seen that compared with the photocatalytic degradation performance of the 4 materials of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the photocatalytic performance of the ternary composite photocatalyst BGT-2 provided by the present invention is significantly improved.

[0095] Test Example 2

[0096] For the materials prepared in the foregoing examples and comparative examples in 0.05 mol / L of Na2 SO 4 Photocurrent, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and other electrochemical performance tests were carried out in the solution. The test instrument was: CHI660E electrochemical workstation (CHInstrumentsCo., USA), and the electrochemical workstation was equipped with a three-electrode device.

[0097] In 0.05 mol / L Na 2 SO 4 The photocurrent was tested in the solution without applying an external voltage. The test time was 300 seconds. The test material was placed in the dark for 0 - 50 seconds, and irradiated with visible light with a light power density of 300 mw / cm 2 on the test material for 50 - 100 seconds. The above operation was repeated twice subsequently.

[0098] Figure 2 Photocurrent result diagrams of the BGT-2 material in Example 1, the TiO 2 material in Comparative Example 1, the BGT-0 material in Comparative Example 2, the BGT-1 material in Comparative Example 3, and the BGT-3 material in Comparative Example 4. Among all the test samples, BGT-2 had the strongest photocurrent response (9.96 μA / cm 2 ), which was 5.5 times that of undoped TiO 2 (1.81 μA / cm 2 ). It was proved that the interaction between GQDs and Bi 2 on the surface of TiO 2 nanotubes and MoO 6 significantly enhanced light absorption and promoted the separation and transport of photo-generated carriers.

[0099] The EIS test was carried out at the open circuit potential. The amplitude was 5 mV, and the frequency range was from 1×10 -2 Hz to 1×10 6 Hz. Figure 3 EIS result diagrams of the BGT-2 material in Example 1, the TiO 2 material in Comparative Example 1, and the BGT-0 material in Comparative Example 2. According to the Nyquist cycle principle, the smaller the radius of the impedance curve, the lower the resistance of the sample and the higher the conductivity. Compared with TiO 2 and BGT-0, BGT-2 had the smallest radius, indicating the smallest transfer resistance. The fitting results of the impedance analysis further confirmed this conclusion. Figure 3 The inset in it shows the impedance spectra and corresponding equivalent circuit models of pure TiO 2 , BGT-0, and BGT-2. The solution resistance (R1), the interfacial charge transfer resistance (R2), and the double-layer capacitance (CPE) between the photocatalyst and the electrolyte are shown in Table 2 specifically.

[0100] As can be seen from Table 2, the BGT-2 electrode exhibits a lower charge transfer resistance (R2). The charge transfer resistance of BGT-2 is much lower than that of pure TiO 2 , indicating that the composite material has efficient carrier transfer ability at the photocatalyst / solution interface. The EIS results show that BGT-2 has the strongest separation and transfer ability for photo-generated e - / h + , the smallest transfer resistance, which improves the PEC performance of BGT. This is consistent with the results of photocurrent tests.

[0101] Table 2: EIS data of charge transfer characteristics at the electrode / electrolyte interface

[0102] R1 (Ω) R2 (Ω) CPE1-T CPE1-P Example 1 (BGT-2) 15.02 670.1 0.0194 0.7045 <![CDATA[Comparative Example 1 (TiO 2 )]]> 20.07 6448 0.0005 0.7145 Comparative Example 2 (BGT-0) 40.91 3319 0.0035 0.774

[0103] LSV was tested in 0.05 mol / L Na 2 SO 4 solution. The starting voltage was set at -1 V, the ending voltage was 1 V, and the scanning rate was 0.05 V / s. The light power density of 300 mw / cm 2 visible light irradiation was maintained on the test material during the test.

[0104] Figure 4 It is the LSV result diagram of the BGT-2 material in Example 1, the TiO 2 material in Comparative Example 1 and the BGT-0 material in Comparative Example 2. Compared with the TiO 2 material in Comparative Example 1 and the BGT-0 material in Comparative Example 2, the potential required for BGT-2 in Example 1 to reach a given current density is the smallest. Before the photocurrent finally tends to be stable, a linear increase in the photocurrent with the applied potential bias is observed. Compared with other samples, the photocurrent density of the BGT-2 ternary composite photocatalyst material is significantly enhanced, indicating that the increase in the interface of the ternary heterojunction improves the carrier mobility. The increase in carrier mobility is beneficial to providing more reaction sites, thereby improving the performance of the catalyst.

[0105] Test Example 3

[0106] The materials obtained in the foregoing examples and comparative examples were subjected to structural characterization.

[0107] Figure 5 It is the XRD diagram of the BGT-2 material in Example 1, the TiO 2 material in Comparative Example 1, the BGT-0 material in Comparative Example 2 and the Bi 2 MoO 6 material. In the XRD patterns of BGT-0 and BGT-2, anatase phase titanium dioxide and Bi 2 MoO 6Characteristic peaks. However, the diffraction peak of GQDs could not be observed at 26.43°, which might be due to the low content of GQDs, resulting in the diffraction peak being covered by the TiO 2 diffraction peak at 25.65°. No diffraction peak of GQDs was detected in the XRD pattern of BGT-2. In addition, the intensity of the diffraction peak of the composite material decreased significantly. It might be because the generation of crystal orientation (002) in GQDs led to the reduction of the peak of TiO 2 NTs.

[0108] Figure 6 SEM image of the TiO 2 material for Comparative Example 1. The TiO 2 NTAs (titanium dioxide nanotube arrays) sample was amplified from a small magnification to a large magnification, and its microstructural morphology is shown in the figure. It can be seen from the figure that TiO 2 NTAs have a uniform and dense tubular structure, indicating that titanium dioxide nanotube arrays were successfully prepared on the surface of the titanium mesh after anodic oxidation. The titanium dioxide nanotubes obtained by anodic oxidation have an average length of 13.25 μm, an average pore size of 84.13 nm, and a wall thickness of about 14.89 nm.

[0109] Figure 7 SEM image of the BGT-0 material for Comparative Example 2. As shown in the figure, the surface of the titanium dioxide nanotubes is uniformly covered with a dense layer of Bi 2 MoO 6 ultrathin nanosheets (molar ratio 2:1).

[0110] Figure 8 SEM image of the BGT-2 material for Example 1. The Bi 2 MoO 6 nanosheets synthesized by the hydrothermal method grow in the form of microspheres. The diameter of the spheres is 0.2 - 0.3 μm. The obtained BGT-2 basically retains the spherical morphology. In contrast, the dispersion of Bi 2 MoO 6 microspheres in BGT-2 is significantly improved compared to BGT-0 without doped GQD.

[0111] Figure 9 EDS energy spectrum of the BGT-2 material for Example 1. The figure shows the elemental mapping results of the chemical composition of BGT-2 based on energy spectrum analysis, in which the peaks of Ti, O, C, Bi, and Mo elements are clearly shown.

[0112] Figure 10Element distribution map of the BGT-2 material of Example 1. As shown in the figure, energy-dispersive X-ray spectroscopy attached to the SEM also proves this result. The distributions of Ti, O, C, Bi, and Mo elements in BGT-2 are uniform, indicating the tight combination of the two materials. The above results show that Bi 2 MoO 6 / GQDs / TiO 2 heterojunction has been successfully synthesized.

[0113] Figure 11 TEM image of the BGT-2 material of Example 1, Figure 12 HRTEM image of the BGT-2 material of Example 1. Due to the limitations of the SEM equipment, GQDs cannot be imaged. The microstructure of the BGT-2 material of Example 1 was further characterized using TEM and HRTEM images. It can be clearly seen from Figure 11 that both Bi 2 MoO 6 nanosheets and GQDs are attached to TiO 2 NTAs. The HRTEM image of BGT-2 is as shown in Figure 12 . Figure 12 An obvious boundary between the two materials can be observed in the upper left figure of , indicating that Bi 2 MoO 6 nanosheets are tightly adhered to the surface of titanium dioxide nanotubes. The high-resolution transmission electron microscopy image shows two lattices with lattice spacings of 0.35 nm and 0.27 nm, corresponding to titanium dioxide (101) and Bi 2 MoO 6 (200) crystal planes respectively. Some spherical nanostructures with a diameter of 5.000 nm are interpreted as typical GQDs, corresponding to the (002) crystal plane with a lattice spacing of 0.32 nm. The obvious heterojunction boundary and the coexistence of three lattices in BGT-2 prove that the coupling of titanium dioxide with Bi 2 MoO 6 and GQDs produces a heterojunction with a tight interface and strong adhesion, which is beneficial to the transfer and migration of carriers. Therefore, the above results confirm the modification of the ternary heterojunction nanostructure induced by GQDs.

[0114] Figure 13 XPS spectra of the BGT-2 material of Example 1, the TiO 2 material of Comparative Example 1, and the BGT-0 material of Comparative Example 2. All XPS peak positions were corrected using the C1s peak at 284.8 eV. Compared with the full spectrum of titanium dioxide, the presence of Ti, Bi, Mo, O, and C in BGT-2 is indicated, which is consistent with the SEM-EDS data ( Figure 9 ), and it can be inferred that Bi 2 MoO6 and the presence of graphene quantum dots.

[0115] Figure 14 The BGT-2 material of Example 1 and TiO of Comparative Example 1 2 materials' infrared spectra. Fourier transform infrared analysis was used to understand the structure of the nanomaterials before and after adding GQDs. Pure TiO 2 The Fourier transform infrared spectrum of NTAs shows a broad absorption band in the 500 - 800 cm -1 region, generally attributed to the Ti - O - Ti bond. Compared with TiO 2 NTAs, there is a slight red shift of this vibration band in BGT-2, which is caused by the combination of GQDs with Ti - O - C vibration. This confirms that GQDs are coordinated with TiO 2 NTAs. The peaks at 2921 cm -1 and 2291 cm -1 in the BGT-2 composite can be attributed to the stretching vibration of C - H and the vibration of the C - O - Ti bond. In addition, compared with the infrared spectrum of TiO 2 , additional infrared vibration peaks appear in the BGT-2 composite. Most of the characteristic peaks of GQDs can be found in the spectrum of the BGT-2 composite. The peaks at 1548 cm -1 , 1295 cm -1 and 1071 cm -1 can be attributed to the C═C, C - OH, and C - O functional groups respectively. These findings confirm the presence of GQDs in the hybrid sample.

[0116] Figure 15 The BGT-2 material of Example 1 and TiO 2 materials' Raman spectra. To further confirm the combination of GQDs with TiO 2 nanotubes, the Raman spectrum of BGT-2 was tested. In BGT-2, in addition to the characteristic peaks of TiO 2 and Bi 2 MoO 6 , peaks can also be found at 1240.62 cm -1 , 1306 cm -1 , 1412.4 cm -1 , 1523.4 cm -1 , 1643.6 cm -1 and 1788 cm -1Characteristic peaks of GQDs were observed and labeled as D1, D, D2, G, D3, and D4, respectively. Among them, the D peak and the G peak are typical characteristics of graphene-based materials, originating from the edge states of graphene and the in-plane vibration of sp2 hybridized carbon atoms, respectively. The type of edge arrangement of GQDs can be determined by the intensity of the D band. On the armchair edges of GQDs, the D band is very obvious, while it is absent on the zigzag edges. The D band of BGT-2 is not obvious, so the edges of GQDs in the hybrid are zigzag. The results show that GQDs were successfully added to BGT-2 through the hydrothermal process.

[0117] Figure 16 For the BGT-2 material of Example 1, TiO of Comparative Example 1 2 materials and the photoluminescence (PL) result graphs of the BGT-0 material of Comparative Example 2. In semiconductors, PL is generated due to the recombination of electrons and holes. The intensity of PL is proportional to the recombination rate of electrons and holes. The separation efficiency of photo-generated carriers can be studied using the PL spectrum. Figure 16 showing TiO 2 、BGT-0 and BGT-2 nanoheterostructures' PL spectra. TiO 2 nanotubes have two obvious emission peaks at 440 nm and 470 nm, which belong to the emission peaks of bandgap transitions. The fluorescence intensity of the BGT-0 and BGT-2 ternary composites is significantly weaker than that of the original TiO 2 , indicating that the heterostructure between TiO 2 and Bi 2 MoO 6 can effectively reduce the recombination of photo-generated carriers, thereby enhancing the photocatalytic activity.

[0118] Test Example 4

[0119] An experiment on the photoelectrocatalytic degradation stability of the BGT-2 material of Example 1 was carried out.

[0120] The specific test method is as follows: An electrolytic cell with an effective volume of 100 mL is used as the reaction vessel. The anode is the test material, and the cathode is a titanium sheet. The anode size is 2 cm × 2 cm. A mixed solution of 100 mL of 0.05 mol / L Na 2 SO 4 and 20 mg / L of tetracycline hydrochloride is prepared. The test material is placed in the mixed solution and adsorbed for half an hour and then placed in the dark. After that, its content is measured using an ultraviolet spectrophotometer. Then, air is sent into the solution at a flow rate of 200 mL / min using an air pump for 100 min. After that, ventilation is maintained and power is supplied. It is set in the constant current mode, and the current magnitude is 0.1 A. At the same time, the light power density is 300 mw / cm 2Visible light is irradiated on the test material, and the degradation time is 120 min. The supernatant is placed in a colorimetric cell every 30 min to measure its content. According to the content of tetracycline hydrochloride in the solution at different time points, a photocatalytic degradation curve is plotted. After each degradation experiment, the test sample is washed 2 - 3 times with ethanol to wash away the adsorbed organic pollutants, dried thoroughly, and then the next cycle test is carried out. The experiment is repeated 4 times. Figure 17 It is the photocatalytic degradation performance stability curve of the BGT-2 material in Example 1.

[0121] From Figure 17 It can be seen that the degradation performance of the ternary composite photocatalyst provided by the present invention is very stable. After the BGT-2 material in Example 1 is reused four times, the reduction rate of the removal rate of tetracycline hydrochloride is still within 5%, indicating that the ternary composite photocatalyst provided by the present invention has very stable photocatalytic degradation performance.

[0122] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a ternary composite photocatalyst, characterized in that: The method includes: (1) forming titanium dioxide nanotubes on the surface of the titanium mesh by an anodic oxidation method to obtain a base material I; (2) sintering the base material I to obtain base material II; the titanium dioxide nanotubes have an average pore diameter of 80-90 nm, an average length of 10-15 μm, and an average tube wall thickness of 10-18 nm; (3) immersing the substrate material II in the mixed solution for hydrothermal reaction to prepare a ternary composite photocatalyst; The mixed solution contains bismuth nitrate, sodium molybdate, graphene quantum dots, ethylene glycol and a surfactant; in the mixed solution, the concentration of the bismuth nitrate is 30-35 mmol / L, the concentration of the sodium molybdate is 15-20 mmol / L, and the concentration of the graphene quantum dots is 10-20 μg / L.

2. The method according to claim 1, characterized in that In step (1), the average mesh diameter of the titanium mesh is 60-90 μm.

3. The method according to claim 1 or 2, characterized in that: In step (1), the electrolyte used in the anodizing method includes ethylene glycol, water and ammonium fluoride; the ammonium fluoride accounts for 0.4-0.6% of the total mass of the electrolyte, and the volume ratio of the ethylene glycol to the water is 30-35:

1.

4. The method according to claim 1 or 2, characterized in that: In step (1), the conditions of the anodization method include: voltage of 55-65V, time of 1.5-2.5h; And / or, in step (2), the sintering treatment conditions include: temperature of 480-520° C. and time of 1.5-2.5 h.

5. The method according to claim 1 or 2, characterized in that: In step (3), in the mixed solution, the molar concentration ratio of the sodium molybdate to the bismuth nitrate is 1:1.8-2.2; And / or, in step (3), the surfactant is selected from at least one of polyvinyl pyrrolidone, hexadecyltrimethylammonium bromide, and polyethylene glycol; and the concentration of the surfactant in the mixed solution is 4-6 g / L.

6. The method according to claim 1 or 2, characterized in that: In step (3), the conditions of the hydrothermal reaction include: temperature of 150-170° C. and time of 13-15 h.

7. The method according to claim 1 or 2, characterized in that: In step (3), the method for preparing the mixed solution comprises: S1: Under stirring conditions, a bismuth nitrate solution in ethylene glycol and a sodium molybdate solution in ethylene glycol are first mixed to obtain a mixture I; S2: performing a second mixing of the mixture I and an ethylene glycol solution of a surfactant to obtain a mixture II; S3: performing a third mixing of the mixture II and graphene quantum dots to obtain the mixed solution.

8. A ternary composite photocatalyst prepared by the method according to any one of claims 1 to 7; And / or, the usable light wavelength range of the ternary composite photocatalyst is 400-760nm.

9. Use of the ternary composite photocatalyst according to claim 8 in the degradation of organic pollutants.

10. The use according to claim 9, characterized in that: The degradation rate of the organic pollutants by the ternary composite photocatalyst is ≥ 76%; And / or, the organic pollutant is selected from at least one of tetracycline hydrochloride, methyl orange, methyl blue and methylene blue.

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