Microwave hydrothermal synthesis of a Bi2SiO5/Bi12SiO20 heterojunction with oxygen vacancies and multiple charge transfer for enhanced photocatalytic activity

Abstract

A novel Bi2SiO5/Bi12SiO20 heterojunction photocatalyst was synthesized by microwave hydrothermal synthesis using Bi(NO3)3 and nano-SiO2 as precursors. The as-prepared Bi2SiO5/Bi12SiO20 heterojunction exhibited more efficient charge separation and higher ultraviolet (UV) light photocatalytic activity in the degradation of rhodamine B (Rh-B) and methylene blue (MB). The optimal reaction rate constant of the Bi2SiO5/Bi12SiO20 heterojunction photocatalyst is 3 and 4.3 times higher than that of Bi12SiO20, respectively. Experimental results reveal that the high photocatalytic performance of Bi2SiO5/Bi12SiO20 could be attributed to its larger specific surface area, good crystallinity, smaller particle morphology, and remarkable improvement of charge separation ability via the heterojunctions. The influence of Bi2SiO5/Bi12SiO20 on the charge separation efficiency and optical properties was investigated by electrochemical impedance spectroscopy and photocurrent analysis. Basis on DMPO-ESR spin trapping and radical scavenger experiments, the active species produced from the Bi2SiO5/Bi12SiO20 heterojunction under UV light irradiation were superoxide radicals (O2−) and holes (h+). Additionally, the possible photocatalytic mechanism of the Bi2SiO5/Bi12SiO20 heterojunction was discussed, and finally, a photocatalytic degradation mechanism based on multiple charge transfer channels was proposed. Furthermore, the Bi2SiO5/Bi12SiO20 heterojunction sample still displayed a high photochemical stability even after 5 times of recycling.