ZIF-8 derived carbon/g-C3N4 – an all-carbon heterojunction for effective photo-decontamination of Cr(VI) from water

Abstract

Carbon-based heterojunctions, because of their low toxicity and non-polluting properties, are considered as metal-free alternatives to the traditional metal oxide semiconductors for energy and environmental applications especially in acidic conditions. In this work, an all-carbon heterojunction using exfoliated graphitic carbon nitride (GCN) and porous carbon derived from zeolitic imidazolate framework (CZ8) is developed for chromium (VI) decontamination. The enhanced charge-transfer in the GCN:CZ8 heterojunctions, due to the suppressed electron-hole pair recombination, is evidenced from photoluminescence (PL) spectroscopy, transient photocurrent (TP) measurements and electrochemical impedance spectroscopy (EIS). This phenomenon significantly contributes towards improving the photo-induced decontamination of the noxious Cr(VI). Moreover, the band gap of the optimized GCN:CZ8 heterojunction is 2.48 eV which is relatively narrow than that of the GCN (2.79 eV). Nearly 100 % removal is achieved with the as-synthesized GCN:CZ8 heterojunction even with chromium solution of 100 ppm concentration. The X-Ray photoelectron spectroscopy (XPS) results suggest the facile reduction of Cr(VI) to Cr(III) under the influence of incident photons, and most importantly, the performance efficiency of the heterojunction is maintained ∼100 % up to five continuous cycles. Herein, the optimized GCN:CZ8 heterojunction is established as a potential material towards efficient decontamination of Cr(VI) from water.