Selective electro-induced reduction using bionic BC@SA-Nafion particle electrodes in 3D systems and phytotoxicity assessment

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Three-dimensional electrode technology (3D technology), featuring dispersed particulate electrodes is rapidly advancing in the separation of pollutants. However, in contrast to the electrochemical oxidation performance, the design of particulate electrodes for electrochemical reduction remains relatively underexplored. This study introduced a bionic particle electrode (BC@SA-Nafion) with high reducibility and selectivity, and integrated it into a 3D system. Specifically, the selective electro-induced reduction capacity of BC@SA-Nafion was examined using Cr(Ⅵ) as a model pollutant. The electrochemical reactivity of BC@SA-Nafion was found to be dependent on the amount of biochar (BC) incorporated. Furthermore, the selectivity for Cr(Ⅵ) could be fine-tuned by adjusting the Nafion content, thereby addressing the efficiency decline at lower Cr(Ⅵ) concentrations. In the 3D system, the Cr(Ⅵ) removal rate reached up to 99 % under optimal conditions (pH 2, 2 V cm−1, 30 min). The density functional theory calculations indicated that the selectivity of BC@SA-Nafion for Cr(Ⅵ) was dependent on the presence of fluorine bonds. The reduction of Cr(Ⅵ) mainly relied on direct electron transfer provided, with superoxide (·O- 2) also playing a role. Post-treatment with the 3D technology resulted in negligible phytotoxicity of the wastewater. This study introduced a novel strategy for enhancing the selectivity of particle electrodes, thereby expanding the application of the particle electrode and advancing sustainable water treatment technologies.