Reduction–responsive sulfur–monoterpene polysulfides in microfiber for adsorption of aqueous heavy metal

Sulfur-containing polymers such as those with polysulfide linkages in their backbone have attracted strong interest due to the ease of modifying the structure and properties of these materials. Electrospun fiber membranes have large specific surface areas, adjustable microstructures and chemical properties, and recovery. Consequently, these materials are promising candidates for applications as sorbents for heavy metal enrichment and water remediation. Herein, polymeric sulfur–monoterpene (PST) was loaded into a polyvinylidene/poly(methyl methacrylate) (PVDF/PMMA) polymer matrix by electrospinning technology to obtain a uniform and continuous fiber-based membrane. It was found that treatment with a reducing agent increased the thiol group content in PST. Then, by using the coordination and binding effect between sulfhydryl groups and metal ions, it was found that the adsorption of Cd(II), Cr(III), Ni(II) and Hg(II) ions onto the membrane was enhanced under the stimulation of reduction. The results indicated that the reduction-responsive adsorption of Hg(II) and Cd(II) was the best, with maximum adsorption values of 58 and 34 mg g−1 for each of these respective ions. In addition, the presence of sodium ions did not interfere with the adsorption of Hg(II) or Cd(II) ions. The adsorption kinetics of Hg(II) and Cd(II) ions on the reduced membrane at different times were also studied. The results revealed that the adsorption of Hg(II) and Cd(II) ions onto the reduced membrane conforms to the pseudo-second-order kinetic model. These results indicated that PST can removal of heavy metal ions from wastewater via a convenient and reusable adsorption process.