Water-insoluble hydrophilic polysulfides as microfibrous composites towards highly effective and practical Hg2+ capture

Abstract

Polysulfides (PS) are emerging S-rich materials with unique properties attractive for various applications including Hg2+ capture. However, PS have yet to offer competitive Hg2+ binding capacities (q) due to their poor hydration and intractable structures. Herein, neoteric PS were developed by reacting molten sulfur with oxygenous co-monomers containing acryl-, methacryl-, and allyl groups. The PS products were thoroughly examined in terms of their consistency, rheology, solvent solubility, hydrophilicity and morphology. Their composition and chemical structures were proposed based on elemental analysis, FTIR, GC-MS, 2D NMR (HSQC) and XPS analyses. The best PS achieved high q ~ 835 mg g−1 (vs. q < 26 mg g−1 of conventional PS) due to enhanced utilization of the sulfide-rich and hydrophilic regions for Hg2+ capture. The PS can be conveniently electrospun into microfibrous (MF) composites with polyacrylonitrile (PAN) matrix, which further increased the Hg2+ binding site utilization especially for the S-rich region (~92%). These highlight the combined benefits of simple yet very effective methods in overcoming the current limitations on PS-based Hg2+ capture. The PS/PAN MF is highly Hg2+-selective (KD ~ 1.10 × 107 mL g−1), can remove ~99.91% Hg2+ and can retain only 1.0 μg L−1 even at low feed concentration (Co = 1 mg L−1). It can be regenerated and re-used as a membrane filter, with consistent performance and Hg2+ stripping efficiency. Considering sulfur as an abundant industrial waste, inexpensive PS-based membrane filters can be developed for practical high-volume treatment of Hg2+ contaminated water.