Synergistic effect of adsorption and photocatalysis of BiOBr/lignin-biochar composites with oxygen vacancies under visible light irradiation

Effective utilization solar energy through photocatalysis is an ideal way to solve environmental problems and achieve sustainable development. Herein, a novel BiOBr/Lignin-Biochar photocatalyst has been successfully synthesized by a simple hydrothermal method. The number of oxygen vacancies of BiOBr increased after C doping, which improves visible-light absorbance, reduces the recombination of photo-generated carriers and promotes O2 activation to produce O2−. UV–vis DRS result demonstrated that the visible-light absorption capacity of BiOBr improved significantly with the addition of lignin. Compared with BiOBr, the adsorption and photocatalytic ability of BiOBr/Lignin-Biochar composites were greatly enhanced due to enriched oxygen vacancies and the congenerous effect between BiOBr and lignin-biochar. The RhB removal with pure BiOBr and BiOBr/Lignin-Biochar under visible-light irradiation at 60 min was 54.5% and 99.2%, respectively, owing to the interface interaction between BiOBr and lignin-biochar promoted the separation between electron and holes and the enrichment of RhB around the photocatalysts. Notably, the bandgap of BiOBr/Lignin-Biochar composites decreased from 2.65 eV to 2.56 eV after C doping, useful for visible-light-driven photocatalysis. The superoxide radical anions (O2−) were the main active species, as demonstrated by free radical capture experiments and ESR characterization results. Hence, the present work provides new insights into constructing cost-effective, high-efficiency composite materials for environmental remediation.