In situ oxidation of ethylene glycol coupled with Bi2O3 epitaxial growth to prepare Bi2O3/BiOCOOH heterojunctions with oxygen vacancies for efficient photocatalytic lignin degradation

Papermaking wastewater has large output and high chemical oxygen demand (COD), which seriously affects the water environment. As a by-product of papermaking industry, lignin is the main contaminant that causes excessive COD value. Bismuth oxide is a potential catalyst for photocatalytic degradation of lignin-contained wastewater because of its high charge conduction performance and light corrosion resistance. However, the high electron-hole recombination rate and poor surface chemical state of pure Bi2O3 seriously hinder the degradation efficiency. Herein, we designed an OV-Bi2O3/BiOCOOH heterojunction with oxygen vacancies and heterojunction coexisting for photocatalytic degradation of lignin. Temperature induced the oxidation of ethylene glycol into formic acid, resulting in the epitaxial growth of Bi2O3 and forming a Bi2O3/BiOCOOH heterojunction. The heterojunction presents a tight interface by sharing the Bi-O tetrahedron, and provides a highway for the charge transfer. Meanwhile, the oxidation of ethylene glycol induces oxygen vacancies (OVs) on Bi2O3/BiOCOOH surface, forming charge trapping centers to promote electron transport and surface reactions. The degradation efficiency of OV-Bi2O3/BiOCOOH is approximately 3 and 16 times that of Bi2O3 and BiOCOOH, respectively. The improvement of photocatalytic performance can be attributed to the synergy of heterojunction and oxygen vacancy, and the stability is attributed to covalent bonds tightly connected.