Fast, simultaneous metal reduction/deposition on electrospun a-WO3/PAN nanofiber membranes and their potential applications for water purification and noble metal recovery

Abstract

Wastewater containing metal pollutants has raised concerns owing to their accumulation in the human body and their negative effects on human health. Meanwhile, metal pollutants in wastewater are valuable resources and their removal/recovery from wastewater is essential for both environmental protection and sustainable development. However, current technologies cannot meet the requirements of high-efficiency removal/recovery of metal ions in ultralow concentrations from wastewater. Here we report the fabrication of electrospun nanofiber membranes (NFMs) with amorphous-WO₃ (a-WO₃) incorporated into polymeric nanofibers. By solar light irradiation, the NFM can be switched to a blue color reduced state. By immersing the reduced NFM in water containing metal ions, a variety of metal compounds can be reduced and homogeneously deposited on the surfaces of the nanofibers rapidly and simultaneously. More interestingly, the metal reduction/deposition process inhibits the metal ion desorption, and the strong electrostatic attraction between the negatively charged NFMs and the metal ions makes the NFMs highly efficient in removing trace amounts of metal ions from water. We show that by immersing the NFM in water, the metal concentrations dropped by two to four orders of magnitude at the ppb level within an hour. Such a NFM achieves metal removal at the ppb level without pumping water through complex filtration membranes and can potentially be a beneficial supplement of the current water purification systems. Also, the NFM can be used for noble metal recovery. The noble metals removed from water are spontaneously reduced and deposited on the NFM as elemental metal nanoparticles which can be facilely separated and recycled, converting metal pollutants into valuable materials. These NFMs are low-cost, environmentally benign and easy for large-scale production, which indicate their great potential for rapid, efficient toxic metal removal/noble metal recovery at the ppb level from wastewater.