Bio-inspired membranes for adsorption of arsenic via immobilized L-Cysteine in highly hydrophilic electrospun nanofibers

Abstract

Arsenic is a concern for its ubiquity in the environment and its accumulative and toxic properties. Water is often contaminated with this chemical, so developing simple, scalable, and green water treatment technologies is urgently needed. We show here that the ability of the L-Cysteine biomolecule to form complexes with arsenic inspires its use as a natural bio-inspired sorbent to develop advanced functional materials. We establish for the first time a way to chemically anchor L-Cysteine (L-Cys) inside highly hydrophilic nanofibers to create a membrane capable of lowering As(V) concentration below the WHO limit of 10 μg/L. A homogeneous precursor mixture of an aqueous solution of PVA and L-Cys (5 wt% and 10 wt% of L-Cys with respect to PVA) was electrospun to obtain a nanofibrous membrane. Successful immobilization of L-Cys within PVA nanofibers is achieved during heat treatment at 190 °C. It occurs through esterification reactions between the hydroxyl group on the PVA chain and the carboxylic acid on L-Cys. Arsenic sorption (as As(V)) was assessed by batch experiments in aqueous media and at a controlled pH range. The maximum removal efficiency was achieved at pH 7, supporting the formation of thiolate complexes as the primary mechanism for arsenic sorption. We show that L-Cys confinement makes arsenic diffusion inside the nanofibers a rate-limiting process in adsorption kinetics, following the pseudo first order equation. Overall, this work establishes a novel arsenic remediation strategy and encourages the research of nature-mimicking adsorbents and biodegradable polymers to develop functional materials in water remediation.