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

Abstract

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.