Facile fabrication of BUC-21/g-C3N4 composites and their enhanced photocatalytic Cr(VI) reduction performances under simulated sunlight: BUC-21/g-C3N4 composites and their photocatalytic activities

A series of BUC-21/g-C3N4 composites were facilely fabricated from two-dimensional metal-organic framework BUC-21 and two-dimensional metal-free polymer semiconductor graphitic carbon nitride (g-C3N4) through ball-milling, and characterized via powder X-ray diffraction, Fourier transform infrared spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV-visible diffuse reflectance, X-ray photoelectron and photoluminescence emission spectrometry. The photocatalytic activities of B100G100 (weight ratio of BUC-21 to g-C3N4 being 1:1) towards Cr(VI) reduction were investigated upon the irradiation of simulated sunlight and real sunlight, in which the influences of various organic compounds (tartaric acid, citric acid and oxalic acid) as hole scavengers, pH values (2, 3, 4, 5, 6, 7 and 8) and foreign ions (ions in tap water and real surface water) were also investigated. The results revealed that B100G100 exhibited more outstanding photocatalytic Cr(VI) reduction than individual BUC-21 and g-C3N4, resulting from enhanced separation of photogenerated electrons and holes, which were confirmed via both photoluminescence emission and electrochemical determination. The B100G100 composite exhibited good reusability and stability after several experimental runs. Also, the corresponding mechanism of photocatalytic reaction was proposed.