Enhancing photocathodic protection with Bi quantum dots and ZIF-8 nanoparticle co-sensitized TiO₂ nanotubes

Abstract

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 the actual marine environment. In this paper, Bi quantum dots (QDs) and ZIF-8 nanoparticles (NPs) were successfully deposited on TiO2 by hydrothermal and impregnation methods. The PCP performances of ZIF-8/Bi/TiO2 composites in the marine environment without hole trapping agents were evaluated, and compared to the performances of pure TiO2, Bi/TiO2 and ZIF-8/TiO2. The electrochemical impedance spectrum (EIS) fitting results demonstrate the Rct value of the ZIF-8/Bi/TiO2 composite coupled with 316 stainless steel (SS) decreased from 7678 Ω·cm2 to 519.3 Ω·cm2 in 3.5 wt% NaCl solution, which is a decrease of about 14.8-fold as compared to TiO2 under the same conditions. This indicates that the deposition of Bi QDs and ZIF-8 NPs on TiO2 nanotubes can improve the electron transport efficiency, which in turn slows down the corrosion rate of 316 SS and significantly improves the PCP performance. This is not only attributed to the Schottky junction and heterojunction structures formed by Bi QDs and ZIF-8 NPs with TiO2, but also due to the SPR 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.