Preparation of carbon-doped TiO2 / bismuth sulfide composite material and application thereof in electrochemical corrosion protection

Abstract

The application relates to a preparation method of a carbon-doped TiO2 / bismuth sulfide composite material and application thereof in electrochemical corrosion prevention. The carbon-doped TiO2 / bismuth sulfide composite material is prepared from a titanium metal organic framework through a low-temperature one-step hydrolysis method. The photoanode constructed by the composite material generates photo-induced electrons which migrate and enrich to the surface of the protected metal under illumination, so that the metal cathode is polarized to reach a thermodynamic stable state, and then the metal corrosion is inhibited, thereby constructing a metal corrosion prevention method of photoelectrochemical cathode protection. The combined modification method of carbon doping and composite narrow-band-gap bismuth sulfide semiconductors is adopted to overcome the defects of titanium dioxide, such as only absorbing ultraviolet light and photo-induced electron-hole easy recombination.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation of carbon-doped TiO2 / bismuth sulfide composite material and its application in electrochemical corrosion protection, in particular to a preparation method and application of a metal-organic framework-based carbon-doped titanium dioxide (C-TiO2) / bismuth sulfide (Bi2S3) composite photoelectric material for photoelectrochemical corrosion protection, and belongs to the field of photoelectric materials and electrochemical corrosion protection. BACKGROUND

[0002] Metal materials are widely used in various fields such as construction, transportation, aerospace, energy, medical devices, etc. due to their excellent performance and rich application scenarios. However, the thermodynamic instability of metals makes them inevitably prone to corrosion during use. Metal corrosion is the damage to the structure of metal materials caused by chemical changes, electrochemical changes or physical dissolution after contacting corrosive media such as liquids, gases or microorganisms. According to statistics, the economic loss caused by metal corrosion in China accounts for 3%-4% of GDP every year. The hazards caused by metal corrosion mainly include material waste, environmental pollution caused by metal ion dissolution and serious safety accidents caused by corrosion. Therefore, metal corrosion protection is of great significance to industrial development, reduction of economic losses and hazards caused by corrosion. Current common corrosion protection measures include coating, sacrificial anode cathodic protection and impressed current cathodic protection, which can provide protection, but have problems such as energy consumption, environmental pollution, and failure of protective layer.

[0003] Photoelectrochemical cathodic protection technology is a new type of environmentally friendly corrosion protection technology, which combines the unique advantages of semiconductor photoelectrochemical properties and electrochemical cathodic protection. The photogenerated electrons generated by light excitation of semiconductor materials are enriched on the metal surface, resulting in a negative shift of the metal potential, thereby achieving corrosion protection of the metal. The electrical energy of the photoelectrode in photoelectrochemical cathodic protection comes from solar energy, avoiding energy consumption. Moreover, the photoelectrode can provide long-term photoelectrons without consuming itself and releasing metal ions into the environment. Therefore, photoelectrochemical cathodic protection is a green, environmentally friendly and widely potentially applicable corrosion protection measure.

[0004] The core of photoelectrochemical cathodic protection method is photoelectric material, which plays the role of photoelectric conversion center. Because of low cost, environmental protection and stable photoelectrochemical performance, TiO2 photoelectric material is widely used in the field of photoelectrochemical cathodic protection. However, in practical application, it is found that TiO2 photoelectric material has some inherent defects. The wide band gap (3.2eV) leads to the limitation of TiO2 in the field of photoelectrochemical cathodic protection, such as only absorbing ultraviolet light, and the easy recombination of photoinduced electron-hole pairs. In order to overcome the above problems, the combined modification method of doping and compounding, such as doping non-metallic elements such as C, N and B to modify TiO2 and pairing with narrow band gap semiconductors to form composite materials, has attracted the attention of many researchers. Carbon-doped TiO2 can adjust the valence band and band gap of TiO2 by affecting the O 2p orbital, forming an intermediate energy level above the top of the O 2p valence band, which will expand the light response range of TiO2 from the ultraviolet region to the visible region, and promote the separation of electron-hole pairs, thereby improving the photoelectrochemical performance of TiO2. The compounding modification is to compound TiO2 with narrow band gap semiconductors to form heterojunctions to reduce the band gap, thereby improving the utilization rate of visible light; in addition, the formed heterojunctions can effectively promote the transfer and separation of photoinduced electrons.

[0005] At present, carbon-doped / compounded TiO2 is usually prepared by a two-step method, that is, carbon-doped TiO2 and narrow band gap semiconductors are synthesized first, and then the two are compounded to prepare carbon-doped TiO2 / narrow band gap semiconductor composite materials. Moreover, carbon-doped TiO2 needs high-temperature treatment and external carbon source, and the preparation process is complex.

[0006] Publication No. CN110817952A discloses a one-step hydrothermal method for preparing TiO2 photoelectric material with different nano-morphologies and its preparation and application: TiO2 photoelectric material is directly grown on FTO conductive glass by adjusting the solvent ratio (H2O:DEG) in the hydrothermal process to prepare TiO2 photoelectric material with different morphologies and crystal structures by one-step hydrothermal method. The one-step hydrothermal method is to synthesize titanium dioxide by heating titanium potassium oxalate raw material with water as solvent. SUMMARY

[0007] The purpose of the present application is to provide a new method for preparing carbon-doped TiO2 / bismuth sulfide composite material and its application in photoelectrochemical cathodic protection; starting from titanium metal organic framework compound, carbon-doped TiO2 / bismuth sulfide composite material is prepared by low-temperature one-step hydrolysis method, and then carbon-doped TiO2 / bismuth sulfide photoanode is constructed, and a method for photoelectrochemical cathodic protection is established.

[0008] The technical scheme of the present application is as follows: a kind of preparation of carbon-doped TiO2 / bismuth sulfide composite material and its application in electrochemical corrosion protection, carbon-doped TiO2 / bismuth sulfide composite material is prepared by low-temperature one-step hydrolysis method, and carbon-doped TiO2 / bismuth sulfide photoanode is prepared on indium tin oxide conductive glass (ITO) substrate. Carbon-doped TiO2 / bismuth sulfide has good visible light absorption performance and high photoelectron-hole separation rate. The carbon-doped TiO2 / bismuth sulfide photoanode has good photoelectrochemical cathodic protection performance for 304 stainless steel (304SS). The photo-generated electrons generated by the photoanode constructed by the composite material migrate and accumulate on the surface of the protected metal under light, forcing the metal to polarize and reach a thermodynamic stable state, thereby inhibiting metal corrosion and constructing a photoelectrochemical cathodic protection method for metal corrosion protection.

[0009] The present application provides a low-temperature one-step hydrolysis method for preparing carbon-doped TiO2 / bismuth sulfide composite material and its composite photoanode method. The steps of the method are as follows:

[0010] (1) 500-2500 mg of 2-amino terephthalic acid is added to the polytetrafluoroethylene lining of the reaction kettle, then 5-100 mL of dimethylformamide and 1-10 mL of anhydrous methanol are added, followed by ultrasonic dissolution, then 200-1500 μL of titanium isopropylate is added and stirred rapidly to disperse until the mixed solution becomes thick, then the reaction kettle is covered and reacted at 80-200 ℃ for 10-35 h, then the reaction kettle is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 30-100 ℃ for 3-20 h, then ground to obtain a titanium metal organic framework.

[0011] (2) 20-500 mg of the titanium metal organic framework obtained in (1) is placed in the polytetrafluoroethylene lining of the reaction kettle, 1-15 mL of ultrapure water is added, ultrasonic stirring is performed for 1-30 min, then 0.10-1.5 mmol of bismuth (III) nitrate and 0.10-1.5 mmol of sodium sulfide are weighed and added to the above dispersion, ultrasonic stirring is performed for 1-30 min, then the reaction kettle is covered and reacted at 80-150 ℃ for 2-35 h, then the reaction kettle is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 30-100 ℃ for 3-20 h, then ground to obtain a carbon-doped TiO2 / bismuth sulfide composite material.

[0012] (3) Take 2-50 mg of the carbon-doped TiO2 / bismuth sulfide composite material obtained in (2), add 0.2-10 mL of anhydrous ethanol and 10-100 μL of a 1-10 wt% Nafion perfluorinated resin solution, and uniformly disperse by ultrasonic treatment to obtain a carbon-doped TiO2 / bismuth sulfide composite material electrode modification liquid. 5-50 μL of the carbon-doped TiO2 / bismuth sulfide composite material electrode modification liquid is uniformly dropped and coated on a 1´1 cm 2 ITO glass electrode, and after drying under an infrared lamp, a carbon-doped TiO2 / bismuth sulfide composite photoanode is obtained.

[0013] The photoelectric current response of the carbon-doped TiO2 / bismuth sulfide composite photoanode and the photoelectrochemical cathodic protection metal anticorrosion method are as follows:

[0014] When testing the photoelectric current response of the carbon-doped TiO2 / bismuth sulfide composite photoanode, a three-electrode system of a single electrolytic cell is used, in which the prepared photoanode (effective area 1´1 cm 2 ) is used as the working electrode, Ag / AgCl is used as the reference electrode, and a Pt column is used as the counter electrode. A 500 W xenon lamp is used to simulate visible light (λ ≥400 nm, and light below 400 nm is filtered out using a filter) and vertically irradiate the surface of the photoanode. The electrolytic cell is a quartz electrolytic cell. The electrolyte is a 0.1 mol / L Na2S and 0.2 mol / L NaOH solution, and the i-t test is performed on different photoanodes under a bias of 0 V (vs. Ag / AgCl).

[0015] When testing the photoelectrochemical cathodic protection performance of the prepared photoanode, a H-shaped double electrolytic cell is used, including a photolysis cell and a corrosion cell. The electrolyte in the photolysis cell is a 0.1 mol / L Na2S and 0.2 mol / L NaOH solution, and the corrosion cell is filled with a 3.5 wt% NaCl solution to simulate a seawater environment. The two electrolytic cells are connected through a Nafion proton exchange membrane (N117), and a 500 W xenon lamp is used to simulate visible light (λ ≥400 nm, and light below 400 nm is filtered out using a filter). A conventional three-electrode system is used, in which the 304 stainless steel electrode (electrode area 1´1 cm 2 ) in the corrosion cell is coupled to the working electrode clamp of the electrochemical workstation through a copper wire after being coupled to the photoanode in the photolysis cell, and the Ag / AgCl electrode and the Pt column electrode in the corrosion cell are used as the reference electrode and the counter electrode, respectively.

[0016] Open circuit potential test is the most intuitive and effective method to evaluate the photoelectrochemical cathodic protection performance of the prepared material photoanode. When light irradiates the surface of the photoanode, the photo-generated electrons of the photoanode material are excited to jump transition due to the absorption of light energy, and the photo-generated electrons can effectively migrate to the metal surface coupled with the photoanode and accumulate, so that the open circuit potential of the coupled metal is shifted to the negative direction and the cathode is polarized, thereby entering the thermodynamic stable state and being protected. The more photo-generated electrons are produced, the more negative the open circuit potential of the coupled metal is, and the better the photoelectrochemical cathodic protection performance is. The open circuit potential of 304SS is -0.207 V (vs. Ag / AgCl), and the open circuit potential of 304SS coupled with the carbon-doped titanium dioxide / bismuth sulfide composite photoanode is shifted to -464 mV (vs. Ag / AgCl).

[0017] To further evaluate the photoelectrochemical cathodic protection performance of the carbon-doped TiO2 / bismuth sulfide composite photoanode on 304SS, the Tafel polarization curve of the photoanode coupled with 304SS was tested under visible light irradiation, and the self-corrosion potential of 304SS was -0.202 V (vs. Ag / AgCl). After being coupled with the carbon-doped TiO2 / bismuth sulfide composite photoanode, the self-corrosion potential of 304SS was shifted to -0.498 V (vs. Ag / AgCl). In summary, the titanium dioxide / bismuth sulfide composite photoanode shows good photoelectrochemical cathodic protection performance on 304SS.

[0018] The beneficial effects of the present application are that the carbon-doped TiO2 / bismuth sulfide composite material is prepared by a low-temperature one-step hydrolysis method, and the photoanode constructed by the composite material is used for photoelectrochemical cathodic protection of metals, providing a simple preparation method of composite photoelectric material and a metal corrosion prevention method of photoelectrochemical cathodic protection. The one-step hydrolysis method of the present application is different from the one-step hydrothermal method in the background art. The one-step hydrothermal method is to synthesize titanium dioxide by heating titanium potassium oxalate raw material with water as solvent, while the one-step hydrolysis method of the present application is to first synthesize titanium metal organic framework, and then to obtain the carbon-doped titanium dioxide / bismuth sulfide composite material by hydrolysis decomposition. They are different in material synthesis method and material.

[0019] The present application adopts the combined modification method of carbon doping and composite narrow-bandgap bismuth sulfide semiconductor to overcome the defects of titanium dioxide, such as only absorbing ultraviolet light and photo-generated electron-hole being easy to recombine.

[0020] The present application is suitable for preparing composite photoelectric material and composite photoanode for photoelectrochemical cathodic protection of metals. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Preparation flow chart of the doped TiO2 / bismuth sulfide composite photoelectrode of the present application;

[0022] Figure 2 Scanning electron microscope image of the titanium metal-organic framework prepared in this invention;

[0023] Figure 3 X-ray diffraction pattern of the titanium metal-organic framework prepared in this invention;

[0024] Figure 4 This is a scanning electron microscope image of carbon-doped titanium dioxide.

[0025] Figure 5 Scanning electron microscope image of bismuth sulfide;

[0026] Figure 6 Scanning electron microscope image of carbon-doped TiO2 / bismuth sulfide composite material;

[0027] Figure 7 X-ray diffraction patterns of carbon-doped titanium dioxide, bismuth sulfide, and carbon-doped TiO2 / bismuth sulfide composite materials;

[0028] Figure 8A XPS full spectrum of carbon-doped titanium dioxide / bismuth sulfide composite material; Figure 8B High-resolution spectra of C in carbon-doped titanium dioxide / bismuth sulfide composites; Figure 8C High-resolution spectrum of O in carbon-doped titanium dioxide / bismuth sulfide composite material; Figure 8D High-resolution spectra of Ti in carbon-doped titanium dioxide / bismuth sulfide composites; Figure 8E High-resolution spectra of Bi in carbon-doped titanium dioxide / bismuth sulfide composites; Figure 8F High-resolution spectrum of S in carbon-doped titanium dioxide / bismuth sulfide composite material;

[0029] Figure 9A The UV-Vis diffuse reflectance spectra of carbon-doped titanium dioxide, bismuth sulfide, and carbon-doped TiO2 / bismuth sulfide are shown. Figure 9B Tauc diagram of bismuth sulfide; Figure 9C Tauc diagram of carbon-doped titanium dioxide; Figure 9D Tauc plot of carbon-doped TiO2 / bismuth sulfide;

[0030] Figure 10 Photocurrent response of carbon-doped TiO2 / bismuth sulfide photoanode;

[0031] Figure 11 Open circuit potential of 304SS coupled with bismuth sulfide, carbon-doped titanium dioxide and carbon-doped TiO2 / bismuth sulfide photoanodes;

[0032] Figure 12 Polarization curves of 304SS coupled with bismuth sulfide, carbon-doped titanium dioxide and carbon-doped TiO2 / bismuth sulfide photoanodes. Detailed Implementation

[0033] The application will be described in detail below through specific examples, which are helpful for those skilled in the art to further understand the application, but by no means limit the protection scope of the application.

[0034] Figure 1 The preparation flow chart of the TiO2-doped / bismuth sulfide composite photoelectrode in this embodiment is shown.

[0035] Embodiment 1

[0036] This embodiment is based on the preparation of carbon-doped TiO2 / bismuth sulfide composite material by low-temperature one-step hydrolysis of titanium metal organic framework.

[0037] (1) 1265 mg of 2-amino terephthalic acid was added to the polytetrafluoroethylene lining of the reaction kettle, then 10 mL of dimethylformamide and 3 mL of anhydrous methanol were added, followed by ultrasonic dissolution, then 300 μL of isopropyl titanate was added and rapidly stirred and dispersed until the mixed solution became thick, then the reaction kettle was covered and reacted at 90°C for 20 h, after which the reaction kettle was naturally cooled, the reaction product was centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 60°C for 20 h, and then ground to obtain a titanium metal organic framework.

[0038] (2) 30 mg of the titanium metal organic framework obtained in (1) was placed in the polytetrafluoroethylene lining of the reaction kettle, 2 mL of ultrapure water was added thereto and ultrasonicated for 5 min, then 0.20 mmol of bismuth (III) nitrate and 0.30 mmol of sodium sulfide were weighed and added to the above dispersion, ultrasonicated and stirred for 5 min, then the reaction kettle was covered and reacted at 90°C for 25 h, after which the reaction kettle was naturally cooled, the reaction product was centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 80°C for 15 h, and then ground to obtain a carbon-doped titanium dioxide / bismuth sulfide composite material.

[0039] Embodiment 2

[0040] This embodiment is based on the preparation of carbon-doped TiO2 / bismuth sulfide composite material by low-temperature one-step hydrolysis of titanium metal organic framework.

[0041] (1) 1086 mg of 2-amino terephthalic acid was added to the polytetrafluoroethylene lining of the reaction kettle, then 18 mL of dimethylformamide and 2 mL of anhydrous methanol were added, followed by ultrasonic dissolution, then 960 μL of isopropyl titanate was added and rapidly stirred and dispersed until the mixed solution became thick, then the reaction kettle was covered and reacted at 150°C for 24 h, after which the reaction kettle was naturally cooled, the reaction product was centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 60°C for 12 h, and then ground to obtain a titanium metal organic framework.

[0042] (2) The titanium metal organic framework of 100 mg obtained in (1) was placed in a reaction kettle polytetrafluoroethylene lining, 3 mL of ultrapure water was added thereto, and ultrasonic treatment was performed for 10 min. Then, 0.50 mmol of bismuth (III) nitrate and 0.50 mmol of sodium sulfide were added to the dispersion liquid, and ultrasonic stirring was performed for 15 min. Then, the reaction kettle was covered, and the reaction was performed at 100°C for 9 h. After the reaction kettle was naturally cooled, the reaction product was centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 60°C for 12 h. After grinding, the carbon-doped titanium dioxide / bismuth sulfide composite material was obtained.

[0043] Example 3

[0044] In this example, a composite photoanode was constructed based on the carbon-doped TiO2 / bismuth sulfide composite material.

[0045] The carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification liquid was obtained by adding 0.5 mL of anhydrous ethanol and 90 μL of a 6wt% Nafion perfluoro resin solution to 20 mg of the carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 1, and uniformly ultrasonicating. Then, 15 μL of the carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification liquid was uniformly drop-coated on a 1´1 cm ITO glass electrode, and the carbon-doped titanium dioxide / bismuth sulfide composite photoanode was obtained after drying under an infrared lamp. 2

[0046] Example 4

[0047] In this example, a composite photoanode was constructed based on the carbon-doped TiO2 / bismuth sulfide composite material.

[0048] The carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification liquid was obtained by adding 1 mL of anhydrous ethanol and 60 μL of a 5wt% Nafion perfluoro resin solution to 10 mg of the carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 2, and uniformly ultrasonicating. Then, 20 μL of the carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification liquid was uniformly drop-coated on a 1´1 cm ITO glass electrode, and the carbon-doped titanium dioxide / bismuth sulfide composite photoanode was obtained after drying under an infrared lamp. 2

[0049] Example 5

[0050] The titanium metal organic framework obtained in Example 2 was subjected to scanning electron microscope and X-ray diffraction characterization tests.

[0051] The titanium metal organic framework obtained in Example 2 was subjected to morphology characterization by scanning electron microscope. As shown in FIG. 1, the titanium metal organic framework obtained in Example 2 was a porous structure with a pore size of about 1 μm. Figure 2 ​​As can be seen, the titanium metal-organic frameworks prepared by the solvothermal method exhibit a hexagonal, grain-like shape with regularity. The structure of the titanium metal-organic frameworks was characterized using X-ray diffraction. Figure 3 As can be seen, the characteristic diffraction peaks appearing at 11.6°, 15.36°, 16.51°, 17.84°, 18.92°, 19.52°, 22.52°, 23.36°, 24.24°, and 26.12° correspond to the (211), (220), (310), (103), (222), (312), (213), (400), (004), and (422) crystal planes of the titanium metal-organic framework synthesized from 2-aminoterephthalic acid and titanium, respectively, indicating the successful preparation of the titanium metal-organic framework.

[0052] Example 6

[0053] The carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 2 was characterized.

[0054] Following the method of Example 2, carbon-doped titanium dioxide was obtained by hydrolysis without the addition of bismuth nitrate and sodium sulfide, and bismuth sulfide was synthesized without the addition of a titanium metal-organic framework. Scanning electron microscope (SEM) images of carbon-doped titanium dioxide, bismuth sulfide, and the carbon-doped titanium dioxide / bismuth sulfide composite material are shown below. Figure 4 , Figure 5 , Figure 6 .

[0055] from Figure 4 It is evident that carbon-doped titanium dioxide exists in the form of nanoparticles; from Figure 5 As can be seen, bismuth sulfide is needle-shaped; from Figure 6 It can be seen that carbon-doped titanium dioxide nanoparticles are dispersed around the nano-needle-shaped bismuth sulfide to form a carbon-doped titanium dioxide / bismuth sulfide composite material.

[0056] X-ray diffraction characterization of carbon-doped titanium dioxide, bismuth sulfide, and carbon-doped titanium dioxide / bismuth sulfide composites can be found in [reference needed]. Figure 7As shown in the figure, the diffraction peak positions of carbon-doped titanium dioxide match the standard diffraction pattern (JCPDS No. 99-0008) of anatase TiO2, indicating that anatase-phase carbon-doped titanium dioxide was obtained by hydrolyzing the titanium metal-organic framework precursor in a one-step hydrolysis method. In the X-ray diffraction pattern of bismuth sulfide, apart from the diffraction peaks of bismuth sulfide, the diffraction peak at 10.68° belongs to the (011) crystal plane of BiONO3 precipitation, which mainly originates from the hydrolysis of bismuth sulfide, indicating the presence of impurities in the bismuth sulfide sample alone. The diffraction peaks at 2θ = 15.72°, 17.56°, 22.52°, 23.64°, 24.96°, 28.6°, 31.8°, 32.84°, 33.88°, 35.6°, 40.0°, 45.52°, 46.6°, 46.92°, and 52.6° of the carbon-doped titanium dioxide / bismuth sulfide composite material correspond to the (020), (120), (220), (101), (130), (230), (221), (301), (330), (240), (141), (002), (431), (501), and (351) crystal planes of bismuth sulfide, respectively. This indicates that the bismuth sulfide in the carbon-doped titanium dioxide / bismuth sulfide composite material belongs to the orthorhombic crystal system (JCPDS). The shoulder peaks at 25.2°, 48.6°, and 62.72° (No. 75-1306) can be attributed to the (101), (200), and (104) crystal planes of carbon-doped titanium dioxide, confirming the successful preparation of the carbon-doped titanium dioxide / bismuth sulfide composite material. Compared with bismuth sulfide alone obtained by reaction without the addition of a titanium metal-organic framework, no BiONO3 diffraction peaks appeared in the X-ray diffraction pattern of the carbon-doped titanium dioxide / bismuth sulfide composite material, indicating that the titanium metal-organic framework precursor can act as a carrier to disperse Bi. 3+ This makes it less likely to react with water alone to form impurities and precipitates.

[0057] To further investigate the elemental composition and chemical state of the prepared carbon-doped titanium dioxide / bismuth sulfide composite material, XPS analysis was performed on it. Figure 8A The image shows the XPS full spectrum of the carbon-doped titanium dioxide / bismuth sulfide composite material. As can be seen from the image, the sample contains characteristic peaks of C, O, Ti, Bi, and S elements, indicating that the carbon-doped titanium dioxide / bismuth sulfide composite material contains C, O, Ti, Bi, and S elements. Figure 8B , Figure 8C , Figure 8D , Figure 8E , Figure 8F High-resolution spectra of C, O, Ti, Bi, and S for carbon-doped titanium dioxide / bismuth sulfide composite materials are shown. Figure 8C In the O 1s spectrum, the two peaks at 529.96 eV and 531.72 eV represent the oxygen and CO bonds in the Ti-O-Ti lattice, respectively.Figure 8D In the high-resolution spectrum of Ti 2p, two peaks at 458.48 eV and 465.03 eV correspond to Ti 2p 1 / 2 and Ti 2p 3 / 2 , respectively, which are attributed to Ti 4+ ; the binding energy moves to the low energy direction, revealing the presence of Ti 3+ , indicating that the chemical state of Ti atoms and oxygen defects in the heterostructure are affected by the complexation with other semiconductors. Figure 8E In the Bi 4f spectrum, due to spin-orbit splitting, four spin-split peaks at 158.59 eV, 159.52 eV, 163.86 eV and 164.75 eV are attributed to Bi 3+ and Bi 4f5 / 2 in Bi2S3, respectively. Figure 8F In the S 2p spectrum, four spin-split peaks at 158.57 eV, 159.4 eV, 163.92 eV and 164.82 eV are attributed to S 2p 3 / 2 and S 2p 1 / 2 .

[0058] Example 7

[0059] The light absorption performance and band gap of the carbon-doped TiO2 / Bi2S3 composite material composite photoanode were tested.

[0060] In order to explore the light absorption performance of carbon-doped TiO2 / Bi2S3, the sample was tested in the wavelength range of 200~800 nm. As shown in Figure 9A , compared with Bi2S3 and carbon-doped TiO2, the composite material carbon-doped TiO2 / Bi2S3 shows strong light absorption in the range of 400~800 nm, which is caused by the introduction of narrow-bandgap semiconductor material Bi2S3. Since Bi2S3 has a narrower band gap, the band gap value of the carbon-doped TiO2 / Bi2S3 composite material is between the two, which can achieve more effective utilization of sunlight, indicating that the introduction of narrow-bandgap Bi2S3 in carbon-doped TiO2 can widen the visible light absorption range of the composite material.

[0061] In order to obtain the band gap values of Bi2S3, carbon-doped TiO2 and carbon-doped TiO2 / Bi2S3 composite material, the band gap of the material was analyzed by ultraviolet-visible diffuse reflectance spectroscopy through Kubelka-Munk theory and linear fitting Tauc-plot method, and the results are shown in Figure 9B , Figure 9C , Figure 9D .

[0062] The specific calculation formula is:

[0063] ;

[0064] Where α is the absorption coefficient measured in the ultraviolet-visible diffuse reflectance spectrum, and h is Planck's constant. ν h is the frequency. ν Let A be the photon energy, and A be a constant. E g denoted as the bandgap of the semiconductor; n is related to the semiconductor type, taking 1 / 2 for direct bandgap semiconductors and 2 for indirect bandgap semiconductors.

[0065] According to Formula 1, h ν (αh) is the x-axis. ν ) 1 / n Plot a Tauc plot with the ordinate as the vertical axis, perform a linear fit on the near-straight-line portion of the curve, and the intercept on the X-axis represents the bandgap width of the semiconductor. Calculations show that bismuth sulfide, carbon-doped titanium dioxide, and carbon-doped TiO2 / bismuth sulfide... E g The values ​​are 1.33 eV, 3.0 eV, and 2.72 eV, respectively. Therefore, combining it with the narrow bandgap semiconductor bismuth sulfide can further improve the utilization rate of visible light by carbon doping and enhance its absorption of visible light, thereby improving photoelectrochemical performance.

[0066] Example 8

[0067] Photocurrent response and photoelectrochemical cathodic protection performance of carbon-doped TiO2 / bismuth sulfide composite photoanodes

[0068] Figure 10 The image shows the photocurrent response of a carbon-doped TiO2 / bismuth sulfide photoanode. Under illumination, the carbon-doped TiO2 / bismuth sulfide photoanode generates a positive photocurrent, indicating that the photoelectrode produces photogenerated electrons. A higher photocurrent density means that the photoanode can provide more photogenerated electrons to the coupled 304SS.

[0069] Figure 11The open circuit potential diagram of carbon-doped TiO2, bismuth sulfide and carbon-doped TiO2 / bismuth sulfide photoanodes coupled with 304SS under intermittent visible light irradiation is shown. When there is no light, the open circuit potential of all photoanodes does not change, when there is visible light irradiation, the open circuit potential of all 304SS coupled with photoanodes starts to shift negatively, after a period of light irradiation, the potential tends to be stable and the open circuit potential value is lower than the self-corrosion potential of 304SS, among them, the open circuit potential of carbon-doped TiO2 / bismuth sulfide photoanode coupled with 304SS decreases to-464 mV under visible light irradiation. Compared with bismuth sulfide and carbon-doped TiO2, the open circuit potential of carbon-doped TiO2 / bismuth sulfide composite photoanode is the most negative, indicating that the formation of bismuth sulfide heterojunction can improve the photoelectrochemical cathodic protection performance of carbon-doped TiO2 / bismuth sulfide. After several intermittent light cycles, the open circuit potential remains stable, indicating that the prepared photoanode has good stability, when the light is turned off, the open circuit potential starts to shift positively, because no light can generate photoelectrons, the number of electrons on the surface of 304SS electrode decreases. In the dark, the open circuit potential of 304SS coupled with photoanode is still lower than its self-corrosion potential [-0.207 V (vs. Ag / AgCl)], indicating that it can also provide certain photoelectrochemical cathodic protection for 304SS in the dark.

[0070] To further evaluate the photoelectrochemical cathodic protection performance of carbon-doped TiO2 / bismuth sulfide composite photoanode on 304SS, the Tafel polarization curves of different photoanodes coupled with 304SS were tested under visible light irradiation, and the results are shown in Figure 12 It can be seen that the corrosion potential of 304SS is-0.202 V (vs. Ag / AgCl), compared with 304SS connected with bismuth sulfide and carbon-doped titanium dioxide photoanode, the corrosion potential of 304SS coupled with carbon-doped TiO2 / bismuth sulfide photoanode is the most negative.

[0071] In summary, the narrow band gap semiconductor material bismuth sulfide is compounded with carbon-doped titanium dioxide, which can expand its visible light absorption range, promote the separation of photo-generated electron-hole pairs, and improve the photoelectrochemical cathodic protection performance of carbon-doped TiO2 / bismuth sulfide.

Claims

1. A method for preparing a carbon-doped TiO2 / bismuth sulfide composite material and a composite photoanode, characterized in that, The method obtains carbon-doped TiO2 / bismuth sulfide composite optoelectronic material by low-temperature one-step hydrolysis, and then prepares carbon-doped TiO2 / bismuth sulfide photoanode using indium tin oxide conductive glass as a substrate. The method steps are as follows: (1) Add 500~2500 mg of 2-aminoterephthalic acid to a reaction vessel lined with polytetrafluoroethylene, then add 5~100 mL of dimethylformamide and 1~10 mL of anhydrous methanol; then sonicate to dissolve, then add 200~1500 μL of isopropyl titanate and stir rapidly until the mixed solution becomes thick; then cover the reaction vessel and react it at 80℃~200℃ for 10~35 h, then take it out and let the reaction vessel cool naturally. Centrifuge the reaction product, wash it with dimethylformamide and anhydrous ethanol, then vacuum dry it at 30℃~100℃ for 3~20 h, and grind it to obtain a titanium metal organic framework; (2) Place 20-500 mg of the titanium metal organic framework obtained in step (1) into the polytetrafluoroethylene liner of the reaction vessel, add 1-15 mL of ultrapure water, and sonicate for 1-30 min; then weigh 0.10-1.5 mmol of bismuth nitrate (III) and 0.10-1.5 mmol of sodium sulfide and add them to the above dispersion, and sonicate for 1-30 min; then cover the reaction vessel and react at 80℃-150℃ for 2-35 h. After that, take it out and let the reaction vessel cool naturally. Centrifuge the reaction product, wash it with dimethylformamide and anhydrous ethanol, and vacuum dry it at 30℃-100℃ for 3-20 h. After grinding, carbon-doped TiO2 / bismuth sulfide composite material is obtained. (3) take 2-50 mg of the carbon-doped TiO2 / bismuth sulfide composite material obtained in step (2), add 0.2-10 mL of anhydrous ethanol and 10-100 μL of a 1-10 wt% Nafion perfluorinated resin solution, and uniformly disperse by ultrasonic wave to obtain a carbon-doped TiO2 / bismuth sulfide composite material electrode modification liquid; take 5-50 μL of the carbon-doped TiO2 / bismuth sulfide composite material electrode modification liquid and uniformly drop coat on a 1×1 cm 2 indium tin oxide conductive glass electrode, and dry under an infrared lamp to obtain a carbon-doped TiO2 / bismuth sulfide composite photoanode; The carbon-doped TiO2 / bismuth sulfide prepared by the method has good visible light absorption performance and high photogenerated electron-hole separation rate. The carbon-doped TiO2 / bismuth sulfide photoanode has good photoelectrochemical cathodic protection performance for 304 stainless steel.

2. The TiO2 / bismuth sulfide composite photoanode prepared by the method for preparing a carbon-doped TiO2 / bismuth sulfide composite material and a composite photoanode as described in claim 1, characterized in that, The method for using the doped TiO2 / bismuth sulfide composite photoanode for electrochemical cathodic protection of metal corrosion is as follows. The photoelectrochemical cathodic protection performance method of the photoanode adopts an H-type dual electrolytic cell, including a photolysis cell and an corrosion cell. The electrolyte in the photolysis cell is a 0.1 mol / L Na2S and a 0.2 mol / L NaOH solution, and the corrosion cell is filled with a 3.5 wt% NaCl solution to simulate the seawater environment. The two electrolytic cells are connected by a Nafion proton exchange membrane, and a 500W xenon lamp is used to simulate visible light. A traditional three-electrode system is adopted, in which the 304 stainless steel electrode in the corrosion cell is coupled to the photoanode in the photolysis cell through a copper wire and then connected to the working electrode clamp of the electrochemical workstation. The Ag / AgCl electrode and the Pt column electrode placed in the corrosion cell serve as the reference electrode and the counter electrode, respectively.

3. The method for using the doped TiO2 / bismuth sulfide composite photoelectrode for electrochemical cathodic protection of metal corrosion prevention according to claim 2, characterized in that, The xenon lamp simulates visible light with a wavelength λ ≥ 400 nm, and uses a filter to remove light below 400 nm.

4. The method for using the doped TiO2 / bismuth sulfide composite photoelectrode for electrochemical cathodic protection of metal corrosion according to claim 2, characterized in that, The electrode area of the 304 stainless steel electrode is 1 x 1 cm 2 .

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