Stepwise Deprotonation of Magnetite-Supported Gallic Acid Modulates Oxidation State and Adsorption-Assisted Translocation of Hexavalent Chromium

Recently, a synergistic strategy involving reduction of carcinogenic Cr(VI) into less toxic Cr(III) followed by Cr(III) adsorption and subsequent separation by surface-engineered magnetite nanoparticles has emerged as a promising alternative to address the environmental hazards associated with Cr(VI)-contaminated water. Despite several previous attempts exploiting this synergy, modulating the oxidation state and translocation of Cr(VI) with high spatiotemporal precision remains a major challenge. Here, we report how Cr(VI) responds accordingly in a well-defined manner to deprotonation of gallic acid covalently immobilized on magnetite nanoparticles, which proceeds through a fixed spatial sequence of distinct stages. To the best of our knowledge, this proof-of-principle study, for the first time, demonstrates that accurate spatiotemporal control over the cascading reduction-adsorption process of Cr(VI) by magnetic adsorbents is feasible, which provides guidance for rational design of more exquisite, magnetite-supported surfaces, where a predictable, and hence controllable, synergy can manifest for Cr(VI) detoxification.