Highly efficient sunlight-driven reduction of Cr(VI) by TiO2@NH2-MIL-88B(Fe) heterostructures under neutral conditions

TiO2@NH2-MIL-88B(Fe) heterostructures (TMFe-x) were successfully synthesized and used in an efficient sunlight-driven reduction towards Cr(VI) in a neutral aqueous media. Further, the prepared TMFe-x heterostructures exhibited higher photocatalytic activity when compared with those exhibited by pure TiO2 and NH2-MIL-88B(Fe) under simulated sunlight irradiation. The optical TiO2 modification content was determined to be 10 wt.% (TMFe-b), with 98.6% Cr(VI) being converted to Cr(III) within 35 min using ammonium oxalate as the hole scavenger at pH = 7. In neutral conditions, the kinetic rate constant (0.0878 min−1) was five times larger than the published values. Additionally, the photocatalytic performance of TMFe-b was maintained and Fe leaching was observed to be negligible after the completion of four reaction cycles. The superior photocatalytic property can be attributed to the high photoelectron-hole separation and migration efficiency. Subsequently, TMFe-b achieved Cr(VI) reduction under neutral conditions by capturing hydrogen from the water molecules or the hole scavengers. The photoelectrons and superoxide radicals were the main active species. Furthermore, TMFe-b was able to efficiently eliminate various pollutants through photocatalytic oxidation and reduction. This study suggests a novel strategy for the preparation of environmentally stable and efficient MOF-based photocatalysts to efficiently eliminate various pollutants. Further, there is a huge potential for the practical application of this technology to water purification.