Abstract
The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies. Chromium and arsenic are among the most prevalent heavy metal pollutants in urban and agricultural waters, with current separation processes having severe limitations due to lack of molecular selectivity. Here, we report redox-active metallopolymer electrodes for the selective electrochemical removal of chromium and arsenic. An uptake greater than 100 mg Cr/g adsorbent can be achieved electrochemically, with a 99% reversible working capacity, with the bound chromium ions released in the less harmful trivalent form. Furthermore, we study the metallopolymer response during electrochemical modulation by in situ transmission electron microscopy. The underlying mechanisms for molecular selectivity are investigated through electronic structure calculations, indicating a strong charge transfer to the heavy metal oxyanions. Finally, chromium and arsenic are remediated efficiently at concentrations as low as 100 ppb, in the presence of over 200-fold excess competing salts.
Highlights
The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies
The effectiveness of PVF as a heterogeneous, electrochemically mediated adsorbent for the removal of chromate from water was evaluated using uniform, nanostructured films of multiwalled carbon nanotubes (CNTs) and PVF prepared by a drop-casting method[23,26]
X-ray photoelectron spectroscopy (XPS) surface analysis confirmed the high uptake of chromium relative to the CNT control, in which no visible chromium adsorption was observed (Supplementary Figures 13 and 14)
Summary
The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies. Whereas trivalent Cr(III) is a naturally occurring form in the earth’s crust, hexavalent Cr(VI) is an anthropogenic chemical7—as such, the development of energy-efficient pathways for capture of Cr(VI) and conversion to Cr(III) is key to long-term environmental sustainability[2,6] Arsenic is another heavy metal in its highly soluble oxyanion form that has received strong interest both in North America and developing countries due to its acute health effects[8,9], and wide prevalence from both natural and anthropogenic sources[10]. A universal redox material platform, targeting the molecular level recognition of heavy metal oxyanions (HMOAs), would overcome a major challenge for environmental remediation, especially in the presence of competing excess anions. Our results are expected to serve as an important platform for tailoring advanced redox materials targeting heavy metal recovery and remediation
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