Controlled thermal treatment of NH2-MIL-125(Ti) for drastically enhanced photocatalytic reduction of Cr(VI)

Abstract

It is a challenge to achieve efficient photocatalytic activity of pure MOFs. Herein, the defective NH2-MIL-125(Ti) with adjustable linker vacancy level was successfully created by thermal treatment. The band gaps of samples decreased and the more Ti-O clusters on the surface of the samples can be achieved as the time of thermal treatment increased from 0 to 500 min, both of which facilitated the photocatalytic activity for the reduction of Cr(VI). Moreover, the ligands from the surface to the inside of the samples were successively decarboxylated, resulting in the declined specific surface area and the increased proportion of mesoporous and the defect level. The moderate defect level in NH2-MIL-125(Ti) can be obtained as the time of thermal treatment was 300 min, which facilitated the separation of photogenerated charges, contributing to the highest photocatalytic activity for reduction of Cr(VI), which was 9.2 times than that of the initial MOFs. However, the excessive linker vacancy defect level in NH2-MIL-125(Ti) may result in the seriously affected crystal structure and the retarded separation of photogenerated charges.