Enhanced performance for Hg(II) removal using biomaterial (CMC/gelatin/starch) stabilized FeS nanoparticles: Stabilization effects and removal mechanism

Iron sulfide (FeS) nanoparticles with large specific surface area and abundant pore structure have been recognized as effective Hg(II) adsorbents. However, bare FeS nanoparticles can aggregate easily, which greatly limited their engineering applications. In this study, FeS nanoparticles were stabilized by biomaterials, including sodium carboxymethyl cellulose (CMC), gelatin and starch, and thoroughly investigated for the stabilization effects. Results demonstrated that the three biomaterial stabilized FeS nanoparticles namely CMC-FeS, gelatin-FeS and starch-FeS enhanced the adsorption efficiency significantly. The maximum adsorption capacities of CMC-FeS, gelatin-FeS and starch-FeS (mass ratio of stabilizer to FeS was 1:6) achieved similar to 1726 mg/g, similar to 1939 mg/g and similar to 1989 mg/g respectively, which were over twice of the bare FeS. TEM images suggested that biomaterial-FeS nanoparticles were dispersed more uniformly than bare FeS. The removal processes of the three materials obeyed pseudo-second-order kinetic model (R-2 >= 0.9986), implying that the rate-limiting step was the chemical sorption process. High removal efficiency of biomaterial-FeS nanoparticles was observed in the initial pH range of 6-11. The presence of Cl-could accelerate the reaction process, whereas the presence of humic acid (HA) could inhibit Hg(II) uptake. In addition, high concentration of coexisting cations (30 mM as Cd2+, Pb2+, Cu2+, and Ca2+) had no significant effect on Hg(II) removal.