Ultrasound-assisted removal of carbon tetrachloride and Cr(VI) by Ni/Fe@Fe3O4 in aqueous solution: Mechanisms of pollutant interactions and ultrasound enhancement

The remediation of water bodies co-contaminated with heavy metal and chlorinated organic pollutants presented significant technical challenges. In this work, a Ni/Fe@Fe 3 O 4 and an ultrasound-assisted Ni/Fe@Fe 3 O 4 co-removal reaction system were established for the simultaneous removal of co-existing pollutants carbon tetrachloride (CT) and hexavalent chromium (Cr(VI)). Results demonstrated that CT promoted Cr(VI) removal, while Cr(III)/Fe(III) oxides/hydroxides (Cr(VI) reduction products) formed on the surface of Ni/Fe@Fe 3 O 4 effectively inhibited the CT degradation. The ultrasound significantly enhanced the Ni/Fe@Fe 3 O 4 co-removal reaction system, accelerating complete Cr(VI) removal and boosting CT removal efficiency from 69.24% to 95.62%. Ultrasound treatment improved the long-term reactivity of Ni/Fe@Fe 3 O 4 , achieving consistent 100% removal of Cr(VI) with only a marginal 5.56% decrease in CT removal efficiency over five cycles. Ultrasound and Ni/Fe@Fe 3 O 4 had a significant synergistic effect on the removal of pollutants, with a synergy index of 2.06. The enhancement mechanism of ultrasound on co-contamination removal by Ni/Fe@Fe 3 O 4 included: (1) improving nanocomposite dispersibility and optimizing the reaction interface; (2) removing the passivation layer on the surface of Ni/Fe@Fe 3 O 4 to expose more active sites.