Microwave Assisted Preparation of Thio-Functionalized Polyacrylonitrile Fiber for the Selective and Enhanced Adsorption of Mercury and Cadmium from Water

In order to overcome the drawbacks of conventional heating for performing surface modification process, such as long synthesis time, low ef ciency, and adsorption capacity, we reported a novel approach by introducing a microwave (MW) assisted method to prepare a thio-functionalized fibrous adsorbent (PANMW-Thio) for the enhanced and selective removal of Hg²⁺ and Cd²⁺ from water in this study. The properties and morphologies of the adsorbent prepared by the MW-assisted method and conventional heating were compared through FTIR, XRD, SEM characterization, and mechanical tests, and the results revealed that the MW assisted method is a satisfactory technology to enable a higher sulfur content and reinforced mechanical property for the adsorbent. The selective adsorption experiment indicated that PANMW-Thio fibers possess higher affinity toward both Hg²⁺ and Cd²⁺ in the mixed solution with Pb²⁺, Cu²⁺, Ni²⁺, and Zn²⁺. The optimum pH value for the adsorption of Hg²⁺ and Cd²⁺ was found to be 7 with maximum adsorption capacities of 322.8 mg·g–¹ and 350.6 mg·g–¹, respectively. The pseudo-second-order model and Langmuir model have revealed good fitness with the experimental data. The XPS analysis of the PANMW-Thio fibers before and after metal adsorption demonstrated the chelation adsorption mechanism between metal ions and sulfur, and parts of the metals were believed to be converted to metallic sulfate or sulfides on the surface of the fibrous adsorbent. This fibrous adsorbent could still retain more than 80% of its original adsorption capacity when regenerated by HCl solution. The facile and rapid preparation protocol, high adsorption capacity and highly retained mechanical property of PANMW-Thio indicates its possible application in selective removal of Hg²⁺ and Cd²⁺ ions from water.