Sulfur Copolymerization with Hydrophilic Comonomers as Polysulfides in Microbeads for Highly Efficient Hg²⁺ Removal from Wastewater

Repurposing of sulfur, a petroleum industry byproduct, will not only address safety issues of its storage but also advance its valorization. Herein, sulfur was directly copolymerized with 2-carboxyethyl acrylate (CEA) to synthesize a S-rich hydrophilic polysulfide (pS-CEA) for Hg²⁺ sequestration. Physicochemical properties such as the hydration number and S-content were correlated with the ability of pS-CEAs to capture Hg²⁺ in terms of the binding capacity (q) and site utilization. Results reveal that the S content in pS-CEA must be balanced carefully with its wettability to ensure an efficient Hg²⁺ sequestration. At an optimized S/CEA molar ratio, pS-CEA (6:1) exhibited an extremely high affinity towards Hg²⁺ with a distribution coefficient (K_d ∼ 26 095 mL g^–1). It attained a superior adsorption capacity q_m ∼ 989 mg Hg²⁺ g^–1 derived from the Langmuir isotherm model and followed a pseudo-second-order kinetics. pS-CEA was conveniently configured into microbeads via agar gelation and the drop-in-oil method. At its highest acceptable pS-CEA loading (150 wt %), pS-CEA/agar microbeads attained a q_m = 527 mg g^–1. The microbeads were configured into a packed bed column and successfully filtered out 99.89% Hg²⁺ from atypically high-concentration feeds (C_o = 50 mg L^–1). The filtration column can be easily regenerated by passing a stripping solution (0.5 M HCl/1 M thiourea) with nearly 100% Hg²⁺ elution efficiency. This work demonstrates the effective design and benefits of the developed polysulfide, which can be synthesized from sulfur waste as a functional material for Hg²⁺ pollution remediation.