Enhanced simulated sunlight photocatalytic reduction of an aqueous hexavalent chromium over hydroxyl-modified graphitic carbon nitride

Hydroxyl-modified graphitic carbon nitride (HUCN) with interconnected open-framework is fabricated by hydrolysis of urea-derived graphitic carbon nitride (UCN) in an aqueous NaOH solution followed by a self-assembly in dialysis process. Compared with bulk graphitic carbon nitride (UCN), HUCN possesses more advantages such as plentiful exposed active sites, fast photogenerated charge carrier separation rate and more negative conduction band edge potential. These advantages bestow the HUCN remarkably higher simulated sunlight photocatalytic reduction ability towards an aqueous Cr(VI) as compared with UCN. By the combination of the experimental results including photoelectrochemistry and electron scavenger with the DFT calculated electrostatic potential (ESP) distribution, a possible reaction mechanism for the simulated sunlight photocatalytic reduction of highly toxic and carcinogenic Cr(VI) to non-toxic Cr(III) is put forward tentatively.