Electroactive Modified Carbon Nanotube Filter for Simultaneous Detoxification and Sequestration of Sb(III)

Herein, we rationally designed a dual-functional electroactive filter system for simultaneous detoxification and sequestration of Sb­(III). Binder-free and nanoscale TiO₂-modified carbon nanotube (CNT) filters were fabricated. Upon application of an external electrical field, in situ transformation of Sb­(III) to less toxic Sb­(V) can be achieved, which is further sequestered by TiO₂. Sb­(III) removal kinetics and capacity increase with applied voltage and flow rate. This can be explained by the synergistic effects of the filter’s flow-through design, electrochemical reactivity, small pore size, and increased number of exposed sorption sites. STEM characterization confirms that Sb were mainly sequestered by TiO₂. XPS, AFS, and XAFS results verify that the Sb­(III) conversion process was accelerated by the electrical field. The proposed electroactive filter technology works effectively across a wide pH range. The presence of sulfate, chloride, and carbonate ions negligibly inhibited Sb­(III) removal. Exhausted TiO₂–CNT filters can be effectively regenerated using NaOH solution. At 2 V, 100 μg/L Sb­(III)-spiked tap water generated ∼1600 bed volumes of effluent with >90% efficiency. Density functional theory calculations suggest that the adsorption energy of Sb­(III) onto TiO₂ increases (from −3.81 eV to −4.18 eV) and Sb­(III) becomes more positively charged upon application of an electrical field.