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A novel thiosemicarbazide modified adsorbent (PAN(MW)-TSC) based on polyacrylonitrile fiber was successfully synthesized under microwave irradiation, which was applied for the uptake of Cd(II) and Pb(II) from aqueous solution subsequently. Microwave irradiation method is a new approach to achieve the modification and it turns out that just a 30min process is enough for the anchoring of functional groups in the fiber matrix. The surface characterization was performed by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) elemental analysis (EA) and thermogravimetric analysis (TGA), indicating that the modification was successfully accomplished. Batch adsorption experiments including equilibrium isotherms, kinetics and the effects of pH and temperature on the adsorption of Cd(II) and Pb(II) were systematically studied. Among three kinetic models, the pseudo-second-order kinetic model provides the best correlation for the process. The nonlinear resolution of the Langmuir isotherm equation has been found to show the closest fit to the equilibrium date. Thermodynamic parameters, involving △G, △H and △S were also calculated from graphical interpretation of the experimental data, which suggest that metal ions adsorption onto PAN(MW)-TSC fibers is spontaneous and exothermic. Regeneration of PAN(MW)-TSC fibers loaded with metal ions was efficiently done with 0.5M HNO3, by which the investigated adsorbent could be used reproductively for five times with a small decrease in sorption capacity. The feasible preparation of PAN(MW)-TSC fibers with high adsorption capacities opens a new perspective in the potential application for wastewater treatment.

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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 (PAN MW -Thio) for the enhanced and selective removal of Hg 2+ and Cd 2+ 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 PAN MW -Thio fibers possess higher affinity toward both Hg 2+ and Cd 2+ in the mixed solution with Pb 2+ , Cu 2+ , Ni 2+ , and Zn 2+ . The optimum pH value for the adsorption of Hg 2+ and Cd 2+ 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 PAN MW -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 PAN MW -Thio indicates its possible application in selective removal of Hg 2+ and Cd 2+ ions from water.

A HPEI modified biosorbent based on cellulose fiber was prepared promptly by MW irradiation.