Mechano-synthesized TiO2/g-C3N4 composites for rapid photocatalytic removal of perrhenate

Pertechnetate (TcO4-), an ionic radioactive contaminant, poses a threat to environmental safety due to its high solubility and mobility. Photocatalytic reduction of TcO4- to low-soluble TcO2·nH2O is a novel ecological method, but the photocatalysts currently available are insufficiently efficient. Herein, a heterojunction TiO2/g-C3N4 photocatalyst was synthesized using a simple ball-milling method. Under simulated sunlight irradiation, the removal rate of ReO4- (a surrogate for TcO4-) over 30-GT (30 wt% g-C3N4) reached over 95% in 10 min, a value noticeably faster than other photocatalysts. The enhanced light adsorption of 30-GT is due to the transformation of more antimagnetic Nb- species from N-TiO2 into paramagnetic species Nb·. The Z-type heterojunction containing TiO2/g-C3N4 could facilitate the transfer and separation efficiency of photo-generated carriers. Rapid Re(VII) reduction activity for 30-GT is attributed to the transfer of more secondary species ·OH, with subsequent oxidation of HCOOH to provide strongly reducing radicals ·CO2-, resulting in the subsequent reduction of Re(VII). This study shows how ball-milling can be used to create a variety of high-performance, low-cost heterojunction photocatalysts.