Efficient visible light driven photocatalysis using BiOBr/BiOI heterojunction modified by Quercetin and defect engineering via simple mechanical grinding: Experiments & first-principles analysis.

Herein we report construction of a dual heterojunction-based system consisting of simultaneous type-III and pn junction between Q/BiOBr/BiOI. The concentration of bismuth oxyhalides were varied from 0.2 to 0.8 viz. BiOBryI1-y-Q (y =0.2, 0.4, 0.5,0.6, 0.8). The as-fabricated photocatalysts were used for photochemical- disintegration of Methyl Orange (MO) and Phenol (Ph) and the best activity was found for the BiOBr0.8I0.2-Q [MO (86.01 %, 90 min); Ph (69.9 %, 180 min)] heterostructures. The fabricated heterostructures were endowed with oxygen-vacancies within 15-minutes of fabrication time. During fabrication, Quercetin was able to grow on p-type-BiOBr and n-type-BiOI due to the presence of positively charged Bi(III)ions and negatively charged Oxygen ions of Q, respectively. The formation of the pn-junction was confirmed by the Mott-Schottky plot. Significantly, the Q was not only able to reduce BiOBr/ BiOI but was also able to create surface-oxygen- vacancies, which effectually improved visible-light absorption as well as charge separation efficiency. The photocatalytic efficiency has significantly convalesced from pristine BiOBr and BiOI. First-Principles Density Functional Theory (DFT) based calculations were performed on pristine BiOBr, BiOI as well as BiOBryI1-y-Q with and without oxygen vacancies, and an insightful understanding of the heterojunction formation, effect of oxygen vacancies, physical mechanism, and superior photocatalytic performance of BiOBr0.8I0.2-Q heterostructure over other samples have been provided.