The effect of Bi2S3/Bi2MoO6/TiO2 photoanode microstructure on solar PEC degradation on several typical dyes

Abstract

The solar photoelectrochemical (PEC) cell is designed to degrade several typical organic dyes, methylene blue (MB), Rhodamine B (Rh B), methyl orange (MO) and malachite green (MG) with two Bi₂S₃/Bi₂MoO₆/TiO₂ photoanodes in different microstructure and Pt plate counter electrode. The photoanode microstructure was modified via two different preparation routes to improve dye degradation efficiency. XRD, SEM, EDS and TEM measurements were used to characterize the elemental composition and microstructure of photoanodes. The results showed that PEC cells based on Bi₂S₃/Bi₂MoO₆/TiO₂ photoanode can exert efficient degradation on the π-π conjugated double bond system of benzene ring and N ion, while low degradation on azo structure through the comparison of UV–Vis. spectra of dye solution before and after PEC degradation. Compared with BSMT*, BSMT photoanode exhibited the highest decoloration rate on MG dye, up to 86.69 % under 2-hour one sun illumination (AM1.5,100 mW/cm²), which was attributed to thinner Bi₂MoO₆ nanocrystals and smaller Bi₂S₃ quantum dots leading to the stronger absorption in UV–Vis. region and higher bulk charge separation efficiency. Furthermore, the BSMT photoanode system exhibited high stability that decoloration rate was still 82.64 % after 5 cycles of 2-hour. It was confirmed that hydroxyl radicals, superoxide radicals and holes were the key active species in MG degradation process through active species-trapping experiments. According to all results, the thermodynamic mechanism of PEC dye degradation was illustrated based on energy level alignment in cells.