Carbon quantum dots induce in-situ formation of oxygen vacancies and domination of {0 0 1} facets in BiOBr microflower for simultaneous removal of aqueous tetracycline and hexavalent chromium

Crystal facet engineering and defect engineering are promising strategies to enhance the photocatalytic performance of BiOBr, but limited work has been reported to realize the simultaneous exposure of highly active facets and the introduction of oxygen vacancies by a single approach. In this work, carbon quantum dots-modified bismuth oxybromide (CQDs/BiOBr) with {0 0 1} exposed facets and surface oxygen vacancies was synthesized by a two-step hydrothermal method. The characterization and density functional theory calculation results verified that the introduction of CQDs promoted the growth of BiOBr with highly exposed {0 0 1} crystal facets and induced the in situ formation of oxygen vacancies by extracting O atoms from the [Bi2O2]2+ layer. The dual functionality of the CQDs allowed them to simultaneously remove tetracycline hydrochloride (TCH) and Cr(VI) under visible light irradiation. The photocatalytic reaction rate constants in the coexisting pollutant system were 3.71 (TCH) and 13.6-times (Cr(VI)) higher than those of the mono-pollutant systems. This work provides a candidate method to design highly efficient catalysts for environmental remediation.