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

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 (K_D ~ 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 (C_o = 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.