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

Abstract

The invention relates to preparation of a carbon-doped TiO2 / bismuth sulfide composite material and application of the carbon-doped TiO2 / bismuth sulfide composite material in electrochemical corrosion prevention, the method starts from a titanium metal organic framework, the carbon-doped TiO2 / bismuth sulfide composite material is prepared through a low-temperature one-step hydrolysis method, and photo-induced electrons generated by a photo-anode constructed by the composite material under illumination are migrated and enriched to a protected metal surface, so that the carbon-doped TiO2 / bismuth sulfide composite material is obtained. And the metal cathode is forced to be polarized to reach a thermodynamic stable state, so that metal corrosion is inhibited, and the metal corrosion prevention method for photoelectrochemical cathode protection is constructed. According to the invention, a combined modification method of carbon doping and compounding of a narrow-band-gap bismuth sulfide semiconductor is adopted to overcome the defects that titanium dioxide only absorbs ultraviolet light, photo-induced electrons-holes are easy to compound and the like.

Description

Technical Field

[0001] The present invention relates to a carbon-doped TiO 2 Preparation of / bismuth sulfide composite materials and their application in electrochemical corrosion protection, especially a metal organic framework carbon-doped titanium dioxide (C-TiO 2 ) / Bismuth Sulfide (Bi 2 S 3 ) The invention relates to a preparation method and application of composite photoelectric materials, and belongs to the field of photoelectric materials and electrochemical corrosion protection. Background Art

[0002] Metal materials are widely used in various fields such as construction, transportation, aerospace, energy, and medical devices as the backbone of industry due to their excellent performance and rich application scenarios. However, the thermodynamically unstable state of metals makes it inevitable that they tend to corrode during use. Metal corrosion is the damage to the structure of metal materials due to chemical changes, electrochemical changes, or physical dissolution after they come into contact with corrosive media (such as liquids, gases, or microorganisms). According to statistics, the economic losses caused by metal corrosion in my country account for 3% to 4% of GDP each 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 and reducing the economic losses and hazards caused by corrosion. At present, commonly used anti-corrosion measures include coatings, cathodic protection of sacrificial anodes, and cathodic protection of impressed current, which can play a protective role, but there are problems such as energy consumption, environmental pollution, and failure and rupture of the protective layer.

[0003] Photoelectrochemical cathodic protection technology is a new type of environmentally friendly anti-corrosion technology that combines the unique advantages of semiconductor photoelectrochemical properties and electrochemical cathodic protection. It enriches the photogenerated electrons generated by light-excited semiconductor materials on the metal surface, causing the metal's potential to shift negatively, thereby achieving anti-corrosion protection for the metal. In photoelectrochemical cathodic protection, the electrical energy of the photoelectrode comes from solar energy, avoiding energy consumption. In addition, the photoelectrode can provide long-term photoelectrons without consuming itself or releasing metal ions into the environment. Therefore, photoelectrochemical cathodic protection is a green, environmentally friendly anti-corrosion measure with a wide range of potential applications.

[0004] The core of the photoelectrochemical cathodic protection method is the photoelectric material, which plays the role of the photoelectric conversion center. Due to its low cost, environmental protection and stable photoelectrochemical performance, TiO 2 Photoelectric materials are widely used in the field of photoelectrochemical cathodic protection. However, in practical applications, it is found that TiO 2 Optoelectronic materials have some inherent defects. The wide bandgap (3.2 eV) results in the absorption of only ultraviolet light, and the easy recombination of photogenerated electrons and holes limits the TiO 2In order to overcome the above problems, doping / composite modification methods such as doping TiO with non-metallic elements such as C, N, and B are used to modify TiO 2 Pairing with narrow bandgap semiconductors to form composite materials has attracted the attention of many researchers. 2 Modulating TiO by affecting O 2p orbitals 2 The valence band and band gap of TiO form an intermediate energy level above the top of the O 2p valence band, which 2 The light response range of TiO2 is extended from the ultraviolet region to the visible region, and the electron-hole separation is promoted, thereby improving the photoelectrochemical performance of TiO2. 2 The bandgap width can be reduced by combining with narrow bandgap semiconductors to form a heterojunction, thereby improving the utilization of visible light; in addition, the formed heterojunction can effectively promote the transfer and separation of photoinduced electrons.

[0005] At present, carbon doping / composite joint modification of TiO 2 Usually a step-by-step preparation method is used, that is, carbon-doped TiO is first synthesized 2 , narrow bandgap semiconductors, and then the two are composited to prepare carbon-doped TiO 2 / narrow bandgap semiconductor composites. And carbon-doped TiO 2 It requires high temperature treatment and external carbon source, and the preparation process is complicated.

[0006] Publication No. CN110817952A discloses a method for preparing TiO2 with different nano-morphologies by a one-step hydrothermal method. 2 Photoelectric materials, preparation and applications: TiO 2 Photoelectric materials can be synthesized by adjusting the solvent ratio (H 2 O:DEG) was directly grown on FTO conductive glass using a one-step hydrothermal method to grow TiO with different morphologies and crystal structures. 2 Photoelectric materials. This one-step hydrothermal method synthesizes titanium dioxide by heating potassium titanium oxalate raw material with water as solvent. Summary of the invention

[0007] The purpose of the present invention is to provide a novel method for preparing carbon-doped TiO 2 / bismuth sulfide composite materials and methods for using them for photoelectrochemical cathode protection; Preparation of carbon-doped TiO from titanium metal organic framework compounds by low-temperature one-step hydrolysis 2 / bismuth sulfide composites and then construct carbon-doped TiO 2 / bismuth sulfide photoanode, establishing a method for photoelectrochemical cathodic protection.

[0008] The technical solution to realize the present invention is that a carbon-doped TiO 2Preparation of carbon-doped TiO / bismuth sulfide composite materials and their application in electrochemical corrosion protection. 2 / bismuth sulfide composites, carbon-doped TiO 2 / Bismuth sulfide photoanode. Carbon-doped TiO 2 / Bismuth sulfide has good visible light absorption performance and high photogenerated electron-hole separation rate, and carbon-doped TiO 2 / Bismuth sulfide photoanode has good photoelectrochemical cathodic protection performance for 304 stainless steel (304SS). The photoanode constructed using composite materials generates photogenerated electrons under light and migrates and accumulates on the surface of the protected metal, forcing the metal cathode to polarize and reach a thermodynamically stable state, thereby inhibiting metal corrosion and constructing a metal anti-corrosion method of photoelectrochemical cathodic protection.

[0009] The present invention proposes a low-temperature one-step hydrolysis method for preparing carbon-doped TiO 2 / bismuth sulfide composite material and composite photoanode method thereof, the method steps are as follows: (1) Add 500-2500 mg of 2-aminoterephthalic acid to the polytetrafluoroethylene liner of the reactor, then add 5-100 mL of dimethylformamide and 1-10 mL of anhydrous methanol, and then ultrasonically dissolve it. Then add 200-1500 μL of isopropyl titanate and quickly stir and disperse it until the mixed solution becomes thick. Then cover the reactor and react it at 80℃-200℃ for 10-35 h and then take it out. After the reactor is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 30℃-100℃ for 3-20 h. After grinding, a titanium metal organic framework is obtained.

[0010] (2) 20-500 mg of the titanium metal organic framework obtained in (1) was placed in a polytetrafluoroethylene liner of a reaction kettle, 1-15 mL of ultrapure water was added thereto, ultrasonicated for 1-30 min, 0.10-1.5 mmol of bismuth (III) nitrate and 0.10-1.5 mmol of sodium sulfide were weighed and added to the above dispersion, ultrasonically stirred for 1-30 min, and then the reaction kettle was covered and reacted at 80°C-150°C for 2-35 h and then taken out. After the reaction kettle was naturally cooled, the reaction product was centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 30°C-100°C for 3-20 h, and then ground to obtain carbon-doped TiO 2 / bismuth sulfide composite materials.

[0011] (3) Weigh 2~50 mg of carbon-doped TiO obtained in (2) 2 / bismuth sulfide composite material, add 0.2~10mL anhydrous ethanol, 10~100μL 1~10wt% Nafion perfluororesin solution, and disperse evenly by ultrasonic to obtain carbon-doped TiO 2 / bismuth sulfide composite electrode modification solution. Pipette 5~50μL carbon-doped TiO 2 / bismuth sulfide composite electrode modification solution is evenly dropped on a 1´1cm 2 On the ITO glass electrode, carbon-doped TiO 2 / bismuth sulfide composite photoanode.

[0012] The present invention is based on carbon-doped TiO 2 The photocurrent response of the / bismuth sulfide composite photoanode and the photoelectrochemical cathodic protection metal corrosion protection method are as follows: Testing carbon-doped TiO 2 The photocurrent response of the bismuth sulfide / composite photoanode was determined using a single electrolytic cell three-electrode system, in which the prepared photoanode (effective area 1´1 cm 2 ) was used as the working electrode, Ag / AgCl was used as the reference electrode, and the Pt column was used as the counter electrode. A 500 W xenon lamp was used to simulate visible light (λ ≥400 nm, and a filter was used to filter out light below 400 nm) and irradiate the photoanode surface vertically. The electrolytic cell was a quartz electrolytic cell. The electrolyte was 0.1 mol / L Na 2 S and 0.2 mol / L NaOH solution, and it was tested on different photoanodes at a bias of 0 V (vs. Ag / AgCl).

[0013] The photoelectrochemical cathodic protection performance of the prepared photoanode was tested using an H-type double electrolytic cell, including a photolysis cell and a corrosion cell. The electrolyte in the photolysis cell was 0.1 mol / L Na 2 S and 0.2 mol / L NaOH solution, the corrosion cell was filled with 3.5 wt% NaCl solution to simulate the seawater environment, the two electrolytic cells were connected through a Nafion proton exchange membrane (N117), and a 500 W xenon lamp was used to simulate visible light (λ ≥400 nm, and a filter was used to filter out light below 400 nm). A traditional three-electrode system was used, in which the 304 stainless steel electrode in the corrosion cell (electrode area 1´1 cm 2 ) was 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 Pt column electrode placed in the corrosion cell served as the reference electrode and counter electrode, respectively.

[0014] The open circuit potential test is the most intuitive and effective method to evaluate the photoelectrochemical cathodic protection performance of the prepared material. When light irradiates the surface of the photoanode, the electron-hole pairs of the photoanode material are excited by the absorption of light energy and generate photogenerated electrons. If the photogenerated electrons can effectively migrate to the metal surface coupled with the photoanode and accumulate, the open circuit potential of the coupled metal will shift negatively and the cathode will polarize, thus entering a thermodynamically stable state and being protected. The more photogenerated electrons are generated, 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 carbon-doped titanium dioxide / bismuth sulfide composite photoanode shifts negatively to -464 mV (vs. Ag / AgCl).

[0015] To further evaluate the carbon-doped TiO 2 The photoelectrochemical cathodic protection performance of the TiO2 / bismuth sulfide composite photoanode for 304SS was tested by the Tafel polarization curve of the photoanode coupled with 304SS under visible light irradiation. The self-corrosion potential of 304SS was -0.202 V (vs.Ag / AgCl), which was comparable to that of carbon-doped TiO 2 After coupling with the titanium dioxide / bismuth sulfide composite photoanode, the self-corrosion potential of 304SS shifted negatively to -0.498 V (vs. Ag / AgCl). In summary, the titanium dioxide / bismuth sulfide composite photoanode exhibited good photoelectrochemical cathodic protection performance for 304SS.

[0016] The beneficial effect of the present invention is that the carbon-doped TiO is prepared by a low-temperature one-step hydrolysis method. 2 / bismuth sulfide composite material, the photoanode constructed by the composite material is used for the photoelectrochemical cathode protection of metals, and a simple method for preparing composite photoelectric materials and photoelectrochemical cathode protection of metals is provided. The one-step hydrolysis method of the present invention is different from the one-step hydrothermal method in the background technology. The one-step hydrothermal method is to synthesize titanium dioxide by heating potassium titanium oxalate raw material with water as solvent, while the one-step hydrolysis method of the present invention is to first synthesize a titanium metal organic framework, and then decompose it by hydrolysis to obtain a composite material of titanium dioxide / bismuth sulfide doped with carbon; the two are different in terms of material synthesis method and material.

[0017] The invention adopts a combined modification method of carbon doping and composite narrow-bandgap bismuth sulfide semiconductor to overcome the defects of titanium dioxide absorbing only ultraviolet light and easy recombination of photogenerated electrons and holes.

[0018] The invention is suitable for preparing composite photoelectric materials and composite photoanode for photoelectrochemical cathode protection of metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 For the present invention, doped TiO 2 / bismuth sulfide composite photoelectrode preparation flow chart; Figure 2 This is a scanning electron microscope image of the titanium metal organic framework prepared in the present invention; Figure 3 The X-ray diffraction pattern of the titanium metal organic framework prepared in the present invention; Figure 4 is a scanning electron microscope image of carbon-doped titanium dioxide; Figure 5 Scanning electron microscope image of bismuth sulfide; Figure 6 Carbon-doped TiO 2 SEM image of the composite material of / bismuth sulfide; Figure 7 Carbon-doped titanium dioxide, bismuth sulfide, carbon-doped TiO 2 X-ray diffraction pattern of / bismuth sulfide composite material; Fig. 8A This is the full XPS spectrum of carbon-doped titanium dioxide / bismuth sulfide composite material; Figure 8B This is the high-resolution spectrum of C in carbon-doped titanium dioxide / bismuth sulfide composites; Figure 8C High-resolution spectrum of O in carbon-doped titanium dioxide / bismuth sulfide composites; Fig.8D This is the high-resolution spectrum of Ti in carbon-doped titanium dioxide / bismuth sulfide composites; Fig. 8E This is the high-resolution spectrum of Bi in carbon-doped titanium dioxide / bismuth sulfide composites; Fig.8F High-resolution spectrum of S in carbon-doped titanium dioxide / bismuth sulfide composites; Fig. 9A Carbon-doped titanium dioxide, bismuth sulfide and carbon-doped TiO 2 / UV-visible diffuse reflectance spectrum of bismuth sulfide; Fig. 9B is the Tauc plot of bismuth sulfide; Fig. 9C is the Tauc plot of carbon-doped titanium dioxide; Fig.9D Carbon-doped TiO 2 / Tauc plot of bismuth sulfide; Fig.10 Carbon-doped TiO 2 / Photocurrent response diagram of bismuth sulfide photoanode; Fig.11 With bismuth sulfide, carbon-doped titanium dioxide and carbon-doped TiO 2 / Open circuit potential of bismuth sulfide photoanode coupled to 304SS; Fig.12 With bismuth sulfide, carbon-doped titanium dioxide and carbon-doped TiO 2 Polarization curve of 304SS coupled with bismuth sulfide photoanode. DETAILED DESCRIPTION

[0020] The present invention is described in detail below through specific examples. The following examples are helpful for those skilled in the art to further understand the present invention, but in no way limit the protection scope of the present invention.

[0021] Figure 1 The doped TiO 2 / bismuth sulfide composite photoelectrode preparation flow chart.

[0022] Example 1 In this example, carbon-doped TiO was prepared by low-temperature one-step hydrolysis of titanium metal organic frameworks. 2 / bismuth sulfide composite materials.

[0023] (1) Add 1265 mg of 2-aminoterephthalic acid to the polytetrafluoroethylene liner of the reactor, then add 10 mL of dimethylformamide and 3 mL of anhydrous methanol, and then ultrasonically dissolve it. Then add 300 μL of isopropyl titanate and quickly stir and disperse it until the mixed solution becomes thick. Then cover the reactor and react it at 90 °C for 20 h before taking it out. After the reactor is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 60 °C for 20 h. After grinding, the titanium metal organic framework is obtained.

[0024] (2) 30 mg of the titanium metal organic framework obtained in (1) was placed in a polytetrafluoroethylene liner of a reaction kettle, 2 mL of ultrapure water was added thereto, and ultrasonic treatment was performed 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, and ultrasonic stirring was performed for 5 min. Then, the reaction kettle was covered and reacted at 90 °C for 25 h and then taken out. After 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. After grinding, a carbon-doped titanium dioxide / bismuth sulfide composite material was obtained.

[0025] Example 2 In this example, carbon-doped TiO was prepared by low-temperature one-step hydrolysis of titanium metal organic frameworks. 2 / bismuth sulfide composite materials.

[0026] (1) Add 1086 mg of 2-aminoterephthalic acid to the polytetrafluoroethylene liner of the reactor, then add 18 mL of dimethylformamide and 2 mL of anhydrous methanol, and then ultrasonically dissolve it. Then add 960 μL of isopropyl titanate and quickly stir and disperse it until the mixed solution becomes thick. Then cover the reactor and react it at 150 °C for 24 h before taking it out. After the reactor is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 60 °C for 12 h. After grinding, the titanium metal organic framework is obtained.

[0027] (2) 100 mg of the titanium metal organic framework obtained in (1) was placed in a polytetrafluoroethylene liner of a reactor, 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 weighed and added to the above dispersion, and ultrasonic stirring was performed for 15 min. Then, the reactor was covered and reacted at 100 °C for 9 h and then taken out. After the reactor 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, a carbon-doped titanium dioxide / bismuth sulfide composite material was obtained.

[0028] Example 3 This embodiment is based on carbon-doped TiO 2 / bismuth sulfide composite materials to construct composite photoanode.

[0029] Weigh 20 mg of the carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 1, add 0.5 mL of anhydrous ethanol and 90 μL of 6wt% Nafion perfluororesin solution, and ultrasonically fractionate to obtain a carbon-doped titanium dioxide / bismuth sulfide composite electrode modification solution. Pipette 15 μL of the carbon-doped titanium dioxide / bismuth sulfide composite electrode modification solution and evenly drop it on a 1´1 cm 2 The carbon-doped titanium dioxide / bismuth sulfide composite photoanode was obtained after being dried under an infrared lamp.

[0030] Example 4 This embodiment is based on carbon-doped TiO 2 / bismuth sulfide composite materials to construct composite photoanode.

[0031] Weigh 10 mg of the carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 2, add 1 mL of anhydrous ethanol and 60 μL of 5wt% Nafion perfluororesin solution, and ultrasonically fractionate to obtain a carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification solution. Pipette 20 μL of the carbon-doped titanium dioxide / bismuth sulfide composite material electrode modification solution and evenly drop it on a 1´1 cm 2 The carbon-doped titanium dioxide / bismuth sulfide composite photoanode was obtained after being dried under an infrared lamp.

[0032] Example 5 The titanium metal organic framework obtained in Example 2 was subjected to scanning electron microscopy and X-ray diffraction characterization tests.

[0033] The morphology of the titanium metal organic framework obtained in Example 2 was characterized by scanning electron microscopy. Figure 2 It can be seen that the titanium metal organic framework prepared by the solvothermal method is in the shape of hexagonal rice grains with regular shape. The structure of the titanium metal organic framework was characterized by X-ray diffractometer. Figure 3It can be seen that 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, which indicates the successful preparation of the titanium metal organic framework.

[0034] Example 6 The carbon-doped titanium dioxide / bismuth sulfide composite material obtained in Example 2 was characterized and tested. According to the method of Example 2, carbon-doped titanium dioxide was obtained by hydrolysis without adding bismuth nitrate and sodium sulfide, and bismuth sulfide was synthesized without adding titanium metal organic framework. The scanning electron microscopy images of carbon-doped titanium dioxide, bismuth sulfide, and carbon-doped titanium dioxide / bismuth sulfide composite materials are as follows: Figure 4 , Figure 5 , Figure 6 .

[0035] from Figure 4 It can be seen that carbon-doped titanium dioxide is in the form of nano-sized particles. Figure 5 It can be seen that bismuth sulfide is needle-shaped; Figure 6 It can be seen that nano-sized carbon-doped titanium dioxide particles are dispersed around the nano-needle-shaped bismuth sulfide to form a carbon-doped titanium dioxide / bismuth sulfide composite material.

[0036] X-ray diffraction characterization of carbon-doped titanium dioxide, bismuth sulfide, and carbon-doped titanium dioxide / bismuth sulfide composites is shown in Figure 7 As can be seen from the figure, the diffraction peak position of carbon-doped titanium dioxide is similar to that of anatase TiO 2 The standard diffraction pattern of (JCPDS No.99-0008) matches that of the titanium metal organic framework precursor (JCPDS No.99-0008), indicating that the anatase phase carbon-doped titanium dioxide was obtained by hydrolyzing the titanium metal organic framework precursor through a one-step hydrolysis method. In the X-ray diffraction spectrum of bismuth sulfide, in addition to the diffraction peak of bismuth sulfide, the diffraction peak at 10.68° is attributed to BiONO 3The (011) crystal plane of the precipitate mainly originates from the hydrolysis of bismuth sulfide, indicating the presence of impurities in the bismuth sulfide sample alone. For the carbon-doped titanium dioxide / bismuth sulfide composites, 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° 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 bismuth sulfide in the carbon-doped titanium dioxide / bismuth sulfide composites belongs to the orthorhombic system (JCPDS No.75-1306), and the shoulder peaks at 25.2°, 48.6°, and 62.72° can be attributed to the (101), (200), and (104) crystal planes of carbon-doped titanium dioxide, confirming the successful preparation of carbon-doped titanium dioxide / bismuth sulfide composite materials. Compared with the single bismuth sulfide obtained by the reaction without adding titanium metal organic framework, the X-ray diffraction spectrum of carbon-doped titanium dioxide / bismuth sulfide composite materials does not appear BiONO 3 diffraction peaks, indicating that the titanium metal organic framework precursor can act as a carrier to disperse Bi 3+ , making it difficult for it to react with water alone to form impurity precipitation.

[0037] In order to further study the elemental composition and chemical state of the prepared carbon-doped titanium dioxide / bismuth sulfide composite material, XPS test and analysis were carried out on it. Fig. 8A This is the full XPS spectrum of the carbon-doped titanium dioxide / bismuth sulfide composite material. It can be seen from the figure that 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 , Fig.8D , Fig. 8E , Fig.8F These are the high-resolution spectra of C, O, Ti, Bi and S in carbon-doped titanium dioxide / bismuth sulfide composites. Figure 8C In the O 1s spectrum, the two peaks at 529.96 eV and 531.72 eV are Ti-O-Ti lattice oxygen and CO bond, respectively. Fig.8D In the Ti 2p high-resolution spectrum, the two peaks at 458.48 eV and 465.03 eV correspond to Ti 2p 1 / 2 and Ti 2p 3 / 2 , belonging to Ti 4+ ; The binding energy moves toward the low energy direction, revealing that Ti3+ The appearance of indicates that the combination with other semiconductors will affect the chemical state of Ti atoms and the presence of oxygen defects in the heterogeneous phase. Fig. 8E In the Bi 4f spectrum, due to spin-orbit splitting, the four spin splitting peaks at 158.59 eV, 159.52 eV, 163.86 eV and 164.75 eV are respectively attributed to Bi in bismuth sulfide. 3+ Chemical states of Bi 4f7 / 2 and Bi 4f5 / 2. Fig.8F In the S 2p spectrum, the four spin split peaks at 158.57 eV, 159.4 eV, 163.92 eV, and 164.82 eV are attributed to the S 2p 3 / 2 and S 2p 1 / 2 .

[0038] Example 7 In this embodiment, carbon-doped TiO 2 Light absorption properties and bandgap width of composite photoanode of / bismuth sulfide composite materials.

[0039] In order to investigate the carbon-doped TiO 2 / Bismuth sulfide light absorption performance, this example tests the sample in the 200 ~ 800 nm wavelength range of ultraviolet-visible diffuse reflectance spectrum. Fig. 9A As shown, compared with bismuth sulfide and carbon-doped titanium dioxide, the composite carbon-doped TiO 2 Bismuth sulfide shows strong light absorption in the range of 400-800 nm, which is caused by the introduction of bismuth sulfide, a narrow bandgap semiconductor material. Since bismuth sulfide has a narrow bandgap, carbon-doped TiO 2 The band gap value of the carbon-doped TiO 2 The introduction of narrow-bandgap bismuth sulfide can broaden the visible light absorption range of the composite material.

[0040] To obtain bismuth sulfide and carbon-doped TiO 2 and carbon-doped TiO 2 The bandgap width of the composite material was analyzed by UV-visible diffuse reflectance spectroscopy using the Kubelka-Munk theory and the linear fitting Tauc-plot method. The results are shown in Fig. 9B , Fig. 9C , Fig.9D shown.

[0041] The specific calculation formula is: ; Where α is the absorption coefficient measured in the UV-visible diffuse reflectance spectrum, h is Planck's constant, ν is the frequency, h ν is the photon energy, A is a constant, E g is the bandgap width of the semiconductor; n is related to the type of semiconductor. For direct bandgap semiconductors, n is 1 / 2, and for indirect bandgap semiconductors, n is 2.

[0042] According to formula 1, h ν is the horizontal axis, (αh ν ) 1 / n Draw a Tauc plot for the ordinate, perform a linear fit on the part of the curve close to the straight line, and the intercept on the X-axis is the bandgap width of the semiconductor. 2 / bismuth sulfide E g They are 1.33 eV, 3.0 eV and 2.72 eV respectively. Therefore, the composite with narrow bandgap semiconductor bismuth sulfide can further improve the utilization rate of carbon doping for visible light, enhance its absorption of visible light, and thus improve the photoelectrochemical performance.

[0043] Example 8 Carbon-doped TiO 2 Photocurrent response and photoelectrochemical cathodic protection performance of composite photoanode of bismuth / sulfide composites Fig.10 Carbon-doped TiO 2 Photocurrent response of carbon-doped TiO under light 2 / bismuth sulfide photoanode produces a positive photocurrent, indicating that the photoelectrode produces photogenerated electrons. The higher photocurrent density means that the photoanode can provide more photogenerated electrons for the coupled 304SS.

[0044] Fig.11 Carbon-doped titanium dioxide, bismuth sulfide and carbon-doped TiO 2 The open circuit potential diagram of the bismuth sulfide photoanode coupled with 304SS. When there is no light, the open circuit potential of all photoanodes remains unchanged. When there is visible light irradiation, the open circuit potential of all 304SS coupled with the photoanode begins 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. 2 The open circuit potential of the photoanode of bismuth sulfide / C-doped TiO decreased to -464 mV under visible light irradiation. 2 In comparison, carbon-doped TiO 2 The open circuit potential of the photoanode of the carbon-doped TiO / bismuth sulfide composite material is the most negative, indicating that the formation of heterojunction with bismuth sulfide can enhance the 2 / BiS photoelectrochemical cathodic protection performance. After several intermittent illumination cycles, the open circuit potential remained stable, indicating that the prepared photoanode has good stability. When the illumination is turned off, the open circuit potential begins to shift positively, because no photogenerated electrons can be generated without illumination, and the number of electrons on the surface of the 304SS electrode decreases. In the dark, the open circuit potential of 304SS coupled with the photoanode is still lower than its self-corrosion potential [-0.207 V (vs. Ag / AgCl)], indicating that it can also provide a certain amount of photocathodic protection for 304SS in the dark state.

[0045] To further evaluate the carbon-doped TiO 2 The photoelectrochemical cathodic protection performance of the bismuth sulfide composite photoanode on 304SS was studied. The Tafel polarization curves of different photoanodes coupled with 304SS were tested under visible light irradiation. The results are shown in Fig.12 It can be seen that the corrosion potential of 304SS is -0.202 V (vs.Ag / AgCl), which is higher than that of 304SS connected to bismuth sulfide and carbon-doped titanium dioxide photoanode. 2 The corrosion potential of 304SS coupled with bismuth sulfide photoanode is the most negative.

[0046] In summary, the composite of narrow bandgap semiconductor material bismuth sulfide and carbon-doped titanium dioxide can expand its visible light absorption range, promote the separation of photogenerated electron-hole pairs, and enhance the carbon-doped TiO 2 Photoelectrochemical cathodic protection performance of 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 a carbon-doped TiO2 / bismuth sulfide composite photoelectric material by low-temperature one-step hydrolysis, and then prepares a 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 polytetrafluoroethylene-lined reactor, and then add 5-100 mL of dimethylformamide and 1-10 mL of anhydrous methanol; then perform ultrasonic dissolution, and then add 200-1500 μL of isopropyl titanate and quickly stir and disperse until the mixed solution becomes thick; then cover the reactor, react it at 80°C-200°C for 10-35 hours, then take it out, and after the reactor is naturally cooled, centrifuge the reaction product, wash it with dimethylformamide and anhydrous ethanol, and vacuum dry it at 30°C-100°C for 3-20 hours, and grind it to obtain a titanium metal organic framework; (2) 20-500 mg of the titanium metal organic framework obtained in step (1) is placed in a polytetrafluoroethylene liner of a reaction kettle, 1-15 mL of ultrapure water is added thereto, and ultrasonication is performed for 1-30 min; 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, and ultrasonic stirring is performed for 1-30 min; then the reaction kettle is covered and reacted at 80°C-150°C for 2-35 h, and then taken out. After the reaction kettle is naturally cooled, the reaction product is centrifuged, washed with dimethylformamide and anhydrous ethanol, and vacuum dried at 30°C-100°C for 3-20 h, and then ground to obtain a carbon-doped TiO2 / bismuth sulfide composite material; (3) Weigh 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 1-10 wt% Nafion perfluororesin solution, and disperse evenly by ultrasonication to obtain a carbon-doped TiO2 / bismuth sulfide composite material electrode modification solution; pipette 5-50 μL of the carbon-doped TiO2 / bismuth sulfide composite material electrode modification solution and evenly drop-coat it on a 1×1 cm 2 On the indium tin oxide conductive glass electrode, a carbon-doped TiO2 / bismuth sulfide composite photoanode was obtained after drying under an infrared lamp; The carbon-doped TiO2 / bismuth sulfide prepared by the method has good visible light absorption performance and high photogenerated electron-hole separation rate, and the carbon-doped TiO2 / bismuth sulfide photoanode has good photoelectrochemical cathodic protection performance for 304 stainless steel.

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

3. 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 xenon lamp simulates visible light with a wavelength λ≥400 nm, and a filter is used to filter out 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 1×1 cm 2 .

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