Facile modification of graphene oxide by humic acid for enhancing hexavalent chromium photoreduction

Abstract

The removing of hexavalent chromium has received extensive attention. In this work, graphene oxide (GO) was modified by humic acid (HA), then the GO−HA composites were prepared using green methods. The sp2 carbon system was increased markedly and the reduced GO (rGO) that with rough and porous structure was formed in GO−HA composites. GO−HA has a band gap of 2.73 eV and owned an adequate aqueous dispersion. The modification of HA enhanced the performance of GO for Cr(VI) photoreduction at environmental relevant pH. GO−HA could trigger the separation of photo−generated electrons/holes under irradiation with the incident wavelength lower than 455 nm. Wherein rGO sheets, as an electron carrier, allowed photo−excited electrons quickly transferred to Cr(VI) and caused the reduction. The ∙O2- that from the excitation of HA with irradiation also could reduce Cr(VI). Meanwhile, photo−generated holes have ability to combine HA and water molecules. Hence, the depletion of photo−generated electrons and holes would enhance its catalytic ability via the separation of charge carriers. These data indicate that the modification with organic molecules is a convenient strategy to obtain GO−based catalysts, which may pave a way to new developments of the GO−based materials.