Simultaneous reduction of Cr(VI) and oxidization of organic pollutants by rice husk derived biochar and the interactive influences of coexisting Cr(VI)

In this study, biochar derived from rice husk via one-spot calcination treatment at 550 °C (biochar R550), demonstrated a remarkable efficiency in the simultaneous reduction of Cr(VI) and degradation of organic pollutants. With a low Cr(VI) content (0–0.2 mM) coexisting in the biochar (10 g L−1) system, organic pollutants (1 mM) were mostly degraded via a radical process at pH 3, additionally oxidized by Cr(VI) via an electron transfer mediated by biochar, which ultimately promoted the removal of organic pollutants. While further increasing the Cr(VI) content, the radical degradation of organic pollutants was gradually restrained, but partially replaced by the accelerated oxidization of organics by Cr(VI). On the other hand, the Cr(VI) was mainly reduced to Cr (III) by the functional groups on biochar in the absence of organic pollutants. However, the coexisted organic pollutants could take the place of biochar to reduce Cr(VI), resulting in a slight change of Cr(VI) reduction. Further studies indicated that the defective sites on biochar could enhance the reaction between organic pollutants and Cr(VI). These findings are very much interesting and innovative in the ongoing biochar research and demonstrate a new dimension of biochar potential for detoxification of multiple industrial pollutants containing Cr(VI) and organics.