A novel CaIn ₂ S ₄ /TiO ₂ NTAs heterojunction photoanode for highly efficient photocathodic protection performance of 316 SS under visible light

Abstract

Designing heterojunction photocatalysts with matched band structure and good interface contact is an effective method to improve the photoelectrochemical activity. Herein, novel CaIn₂S₄/TiO₂nanotube 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/TiO₂composites for 316 stainless steel (SS) and the influences of the CaIn₂S₄content on the performances were studied. The microstructural examination revealed the uniform doping of CaIn₂S₄nanofragments on the TiO₂NTAs, and the composite was made up cubic CaIn₂S₄and anatase TiO₂. The photogenerated electrons were transferred from the TiO₂to CaIn₂S₄at the interface of the composite. Compared with pure TiO₂NTAs, CaIn₂S₄/TiO₂NTAs 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/TiO₂NTAs. The photocurrent density of the 316 SS coupled with the composite photoanode (235.4<i>μ</i>A cm^-2) was 17.4 times that of TiO₂. The improved photocathodic protection property of CaIn₂S₄/TiO₂NTAs was ascribed to the enhanced separation efficiency of the photogenerated carriers and the strong visible light absorption of the material. The CaIn₂S₄/TiO₂NTAs exhibited continuous protection of the 316 SS for more than 12 h even in the dark. Therefore, the CaIn₂S₄/TiO₂NTAs heterojunction composite is an outstanding and efficient photoanode for the photocathodic protection of metals.