Search

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. Unlabelled Image • Biochar could degrade organic pollutants by activating O 2 to produce OH. • The degradation of organic pollutants was promoted by low contents of Cr(VI). • The reduction of Cr(VI) by biochar was promoted by organic pollutants. • Cr(VI) could react with organic pollutants via the mediation of biochar. • Defects of biochar facilitated the reaction between organic pollutants and Cr(VI). [ABSTRACT FROM AUTHOR]

In this study, the photogeneration of OH and 1O 2 and the degradation mechanism of organic pollutants in biochar suspension under the simulated solar light irradiations were investigated. Biochar derived from rice husk with 550 °C of charring temperature (R550) was selected to degrade benzoic acid. It was found that 10 g/L of R550 could degrade 78.7% of benzoic acid within 360 min at pH 3, and the degradation efficiency was promoted to 95.2% as ultraviolet (UV) presented. By checking the production of p-hydroxybenzoic acid, UV accelerated the production of OH, which was confirmed by the enhanced degradation efficiency of 59.2% caused by the evaluated OH as UV appeared. The furfuryl alcohol loss in the R550 suspension under light irradiations testified to the production of 1O 2 , which contributed to 9.3% of benzoic acid degradation. Oxidization treatment using gradient concentrations of H 2 O 2 was employed to enhance the ageing process of biochar. As the ageing processed, the biochar possessed a declined performance towards OH production from O 2 activation and the radical degradation of organic pollutants. As a contrast, the evaluated content of 1O 2 and enhanced non-radical degradation of organic pollutants was reached as UV presented. The further study indicated that phenolic hydroxyl groups on biochar facilitated the production of OH via the electron transfer, and quinone like structures (C=O) on biochar boosted the generation of 1O 2 via the energy transfer. Moreover, upon eliminating the BA degradation, persistent free radicals were formed on biochar, which was enhanced owing to the presence of UV. Unlabelled Image • Degradation of organic contaminants by biochar was enhanced by UV. • UV triggered the production of OH and 1O 2 from biochar suspension. • Quinone-type structures on biochar induced the production of 1O 2. • The ageing favored the production of 1O 2 under light irradiations. • The ageing retarded OH formation and radical degradation of organic contaminants. [ABSTRACT FROM AUTHOR]