Triphenylamine-based covalent triazine framework @ carbon nanotube complex: efficient photogenerated charges migration for metal free photocatalytic Cr(VI) reduction

Abstract

Photocatalytic hazardous hexavalent chromium Cr(VI) reduces to nontoxic trivalent chromium Cr(III) by metal free catalytic system under visible light irradiation is a promising method to harness Cr(VI) pollution. However, the rate-determining step for these systems is still charge separation and transport from semiconductor to the surface active site due to high exciton binding energy and transport Schottky barrier. Herein, we present a novel composite catalyst by situ growth of two-dimensional triphenylamine-based covalent triazine framework (TACTF) semiconductor with one-dimensional (1D) carbon nanotube (CNT) electronic conductivity mediator. The resultant TACTF@CNT complex exhibits a lower Schottky barrier, which improves lateral charge transport and interlayer exciton dissociation though interconnections TACTF layers with CNT, assuring high efficiency of photogenerated charges transfer from TACTF semiconductor to the surface active site for subsequent photocatalytic Cr(VI) reduction. The TACTF@CNT shows an excellent photocatalytic activity for Cr(VI) reduction, and 100 % removal of Cr(VI) was observed under visible light irradiation for 2 h, which is remarkably superior to those of TACTF, CNT and their physical mixture.