Enhancing photocathodic protection with Bi quantum dots and ZIF-8 nanoparticle co-sensitized TiO₂nanotubes

Since hole trapping agents do not persist in the marine environment, it is more practical to test metal protection in 3.5 wt% NaCl solution so that the photocathodic protection (PCP) technique can be effectively applied in an actual marine environment. In this paper, Bi quantum dots (QDs) and ZIF-8 nanoparticles (NPs) were successfully deposited on TiO₂by hydrothermal and impregnation methods. The PCP performances of ZIF-8/Bi/TiO₂composites in the marine environment without hole trapping agents were evaluated, and compared with the performances of pure TiO₂, Bi/TiO₂and ZIF-8/TiO₂. The electrochemical impedance spectrum (EIS) fitting results demonstrate that theR_ctvalue of the ZIF-8/Bi/TiO₂composite coupled with 316 stainless steel (SS) decreased from 7678 Ω cm²to 519.3 Ω cm²in 3.5 wt% NaCl solution, which is a decrease of about 14.8-fold compared with TiO₂under the same conditions. This indicates that the deposition of Bi QDs and ZIF-8 NPs on TiO₂nanotubes can improve the electron transport efficiency, which in turn slows down the rate of corrosion of 316 SS and significantly improves the PCP performance. This is not only attributable to the Schottky junction and heterojunction structures formed by Bi QDs and ZIF-8 NPs with TiO₂, but also to the surface plasmon resonance effect of Bi QDs and the N-Ti-O bond structure formed between ZIF-8 and TiO₂, leading to a lower electron-hole recombination efficiency and a higher electron transfer efficiency.