Enhanced removal of hexavalent chromium from aqueous solution by nano-TiO2 modified zero valent iron under UV light irradiation: Performance, reaction kinetic and the role of iron oxide interfacial layers

Abstract

The major problem for nano-zero valent iron (nZVI) application is the degradation of performance due to the continuous oxidation during reaction process. A composite has been prepared, which was developed by coating TiO2 nanoparticles onto the surface of nZVI (TiO2@nZVI). A series of experiments were used to examine the effects of TiO2 loading, ultraviolet–visible (UV) light, initial concentration, pH of aqueous solution on the hexavalent chromium (Cr(VI)) removal. The results show that TiO2 and UV irradiation could slow down the oxidation of nZVI during removing Cr(VI). The TiO2@nZVI with UV irradiation have dramatically higher Cr(VI) removal efficiencies than TiO2 and nZVI (increased by 78.5% and 39.9%, respectively). More Fe(II) instead of Fe(III) into the suspension and a slower oxidation rate of nZVI should be responsible for the enhanced Cr(VI) removal. Kinetic studies reveal that Cr(VI) adsorption process is accordant with the pseudo-second-order model, which suggests that chemisorption was the dominant adsorption mechanism. Langmuir isotherm adsorption model describes the Cr(VI) adsorption better and the maximum adsorption capacity of 62.80 mg·g−1. Finally, a possible removal and enhanced mechanism of Cr(VI) by TiO2@nZVI is proposed. Our study would provide ideas for the modification of nZVI and improve its removal efficiency for pollutants.