Direct Z-scheme MgIn2S4/TiO2 heterojunction for enhanced photocathodic protection of metals under visible light

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.

New g-C3N4/GO/MoS2 composites as efficient photocatalyst for photocathodic protection of 304 stainless steel

Photocathodic protection is an economical and environmental metal anticorrosion method. In this research, we successfully synthesized the g-C3N4/GO (15 wt%)/MoS2 catalytic materials by a facile hydrothermal method. The results show that as-prepared g-C3N4/GO (15 wt%)/MoS2 composites prominently enhanced the photocatalytic activities for the photocathodic protection of 304 stainless steel compared with the corresponding pristine g-C3N4 and MoS2. Notably, the AC impedance results demonstrated that the Rct value of 304 SS coupled with g-C3N4/GO (15 wt%)/MoS2 decreased to 35.66 Ω•cm2, which is 29 and 37 times lower than that of g-C3N4 and MoS2 alone. In addition, g-C3N4/GO (15 wt%)/MoS2 provided the highest current density (77.19 μA•cm2) for the 304 SS, which is 4 times of pristine g-C3N4. All results indicate that as-prepared g-C3N4/GO (15 wt%)/MoS2 photocatalysts have exhibited distinct enhancement on photocathodic protection performance. An optimum decorating amount of MoS2 onto g-C3N4 forms heterojunction of g-C3N4/MoS2, which favors the separation of electrons and holes efficiently. Meanwhile, the addition of GO further promotes the separation and transfer of photo-induced carriers.