TiO2 is an attractive semiconductor suitable for photocathodic protection, but its weak absorption of visible light and low quantum yield limit its usage. Here, a new heterostructured SnIn4S8 nanosheet/TiO2 nanotube photoanode was prepared and its photocathodic protection performance was analyzed. SnIn4S8 nanosheets were uniformly deposited on the surface of the TiO2 nanotube via a solvothermal treatment. The SnIn4S8/TiO2 composite exhibited better photocathodic protection performance compared with pure TiO2 nanotubes, owing to its good visible-light response and photogenerated carrier separation efficiency. Moreover, the composite exhibited a maximum photocurrent density of 100 μA cm−2 for a 6 h solvothermal reaction under visible light irradiation. The negative shift of the photoinduced potential of Q235 carbon steel connected to the composite could reach 0.45 V versus SCE. Therefore, the SnIn4S8/TiO2 composite can offer efficient photocathodic protection for Q235 carbon steel against corrosion in 3.5 wt% NaCl solution. This work provides a new approach for the development of high-efficient photoanode materials for the photocathodic protection of metals.

AgInS 2 nanoparticle and graphene nanosheet co-sensitized anatase TiO 2 nanotube array films were fabricated by a combination of hydrothermal reaction and electrochemical anodization on titanium sheets. The results showed that the co-sensitization of AgInS 2 nanoparticles and graphene nanosheets extended the photoresponse of TiO 2 nanotubes into the visible-light region, and improved the photogenerated charge separation and transfer capability. The photocurrent density of the AgInS 2 /graphene/TiO 2 composites (about 4.0 mA cm −2 ) was 20 times that of bare TiO 2 (only 0.2 mA cm −2 ) under visible-light illumination. The potential negative shift value of AgInS 2 /graphene/TiO 2 composites was up to 0.68 V versus saturated calomel electrode. The AgInS 2 /graphene/TiO 2 composites can provide Q235 carbon steel with highly efficient photocathodic protection under visible-light illumination.

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Designing heterojunction photocatalysts with matched band structure and good interface contact is an effective method to improve the photoelectrochemical activity. Herein, novel CaIn2S4/TiO2 nanotube arrays (NTAs) heterojunction photoanodes were successfully prepared by electrochemical anodization and hydrothermal method. The microstructures, compositions, crystal structures, chemical valence states and light absorption performances of the composites were evaluated by field emission scanning electron microscopy, energy dispersive x-ray spectroscopy transmission electron microscope, high-resolution transmission electron microscope, x-ray diffractometer, x-ray photoelectron spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), respectively. The photocathodic protection performances of CaIn2S4/TiO2 composites for 316 stainless steel (SS) and the influences of the CaIn2S4 content on the performances were studied. The microstructural examination revealed the uniform doping of CaIn2S4 nanofragments on the TiO2 NTAs, and the composite was made up cubic CaIn2S4 and anatase TiO2. The photogenerated electrons were transferred from the TiO2 to CaIn2S4 at the interface of the composite. Compared with pure TiO2 NTAs, CaIn2S4/TiO2 NTAs exhibited better photocathodic protection performance for 316 SS under visible light. Potential drop reached 0.78 V versus saturated calomel electrode for the 316 SS coupled with CaIn2S4/TiO2 NTAs. The photocurrent density of the 316 SS coupled with the composite photoanode (235.4 μA cm–2) was 17.4 times that of TiO2. The improved photocathodic protection property of CaIn2S4/TiO2 NTAs was ascribed to the enhanced separation efficiency of the photogenerated carriers and the strong visible light absorption of the material. The CaIn2S4/TiO2 NTAs exhibited continuous protection of the 316 SS for more than 12 h even in the dark. Therefore, the CaIn2S4/TiO2 NTAs heterojunction composite is an outstanding and efficient photoanode for the photocathodic protection of metals.

A novel In2S3/Ag2S/TiO2 nanotube arrays (NTAs) was successfully fabricated by successive ionic layer adsorption and reaction (SILAR) method and electrochemical anodic oxidation method, and served as photoanode for photocathodic protection application. The micromorphologies, optical absorption properties, crystalline structure and elemental valence states of the composites were performed by field emission scanning electron microscopy, high resolution transmission electron microscope, UV−vis diffuse reflectance absorption spectra, X-ray diffractometer and X-ray photoelectron spectroscopy, respectively. The photocathodic protection performances of In2S3/Ag2S/TiO2 NTAs on the Q235 carbon steel (CS) were also studied. The In2S3/Ag2S/TiO2 nanocomposites show better photoelectrocatalytic and photocathodic protection performance than pure TiO2 NTAs. The photocurrent density of In2S3(9)/Ag2S(8)/TiO2 photoelectrode coupled with Q235 CS reach 211 μA cm−2, which is about 4.5 times higher than that of TiO2 NTAs. The photogenerated potential of Q235 CS coupled to In2S3(9)/Ag2S(8)/TiO2 under illumination shows a negative shift to −0.92 V vs. SCE. Results indicate that the co-sensitization of In2S3 and Ag2S could extend the light absorption of TiO2 to the visible light range and enhance its photoelectric conversion efficiency.microscope, UV−vis diffuse reflectance absorption spectra, X-ray diffractometer and X-ray photoelectron spectroscopy, respectively. The photocathodic protection performances of In2S3/Ag2S/TiO2 NTAs on the Q235 carbon steel (CS) were also studied. The In2S3/Ag2S/TiO2 nanocomposites show better photoelectrocatalytic and photocathodic protection performance than pure TiO2 NTAs. The photocurrent density of In2S3(9)/Ag2S(8)/TiO2 photoelectrode coupled with Q235 CS reach 211 μA cm−2, which is about 4.5 times higher than that of TiO2 NTAs. The photogenerated potential of Q235 CS coupled to In2S3(9)/Ag2S(8)/TiO2 under illumination shows a negative shift to −0.92 V vs. SCE. Results indicate that the co-sensitization of In2S3 and Ag2S could extend the light absorption of TiO2 to the visible light range and enhance its photoelectric conversion efficiency.

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To improve the photocathodic protection performance of traditional TiO2 photoanodes for metals, constructing a Z-scheme heterojunction is one of the most promising and creative strategies. Herein, we fabricated a novel Z-scheme MgIn2S4 nanosheets/TiO2 nanotube nanocomposite through anodization and hydrothermal method. The optimized Z-scheme MgIn2S4/TiO2 nanocomposites exhibited stronger visible light absorption, higher separation efficiency of photoelectrons and photocathodic protection performances in comparison to pure TiO2. The theoretical analysis and experimental results show that the Z-scheme heterojunction and oxygen vacancies jointly improved the separation efficiency of photogenerated electron-hole pairs and visible light absorption capacity, thereby improving the photoelectric conversion performance of the MgIn2S4/TiO2 nanocomposites. Furthermore, the influence of the precursor solution concentration on the photocathodic protection performances of the composites was investigated. As a result, when the concentration of magnesium source in the precursor solution was 0.06 mmol, the prepared MgIn2S4/TiO2-0.06 displayed the best photocathodic protection performance. In addition, the hydroxyl radicals (•OH) generated in the electron spin resonance (ESR) experiment verified the Z-scheme heterojunction mechanism of the MgIn2S4/TiO2 composite, and also demonstrated the excellent redox performance of the composite. This work provides valuable reference for the construction of high-performance Z-scheme heterojunctions for photocathode protection of metals.

CuInSe2 nanoparticles were successfully deposited on the surface of TiO2 nanotube arrays (NTAs) by a solvothermal method for the photocathodic protection (PCP) of metals. Compared with TiO2 NTAs, the CuInSe2/TiO2 composites exhibited stronger visible light absorption and higher photoelectric conversion efficiency. After 316 Stainless Steel (SS) was coupled with CuInSe2/TiO2, the potential of 316 SS could drop to −0.90 V. The photocurrent density of CuInSe2/TiO2 connected to 316 SS reached 140 μA cm−2, which was four times that of TiO2 NTAs. The composites exhibited a protective effect in the dark state for more than 8 h after 4 h of visible light illumination. The above could be attributed to increased visible light absorption, the extended lifetime of photogenerated electrons, and generation of oxygen vacancies.