Use of fibroin polypeptide from silk processing waste as an effective biosorbent for heavy metal removal

Abstract

AbstractSilk fibroin was extracted from Bombyx mori cocoon and used as a biosorbent to remove Pb2+, CrO42−, Cu2+, and Co2+ from aqueous solutions. The sorption isotherms for the metals in fibroin were determined, and a thermodynamic analysis (ΔG°, ΔH°, and ΔS°) of the sorption process showed that the metal sorption in fibroin was physical, spontaneous, and endothermic. The sorption kinetics data was found to match well with the modified pseudo‐second‐order rate model, and the sorption rate constant was determined based on a rectified approach of model fitting. It was shown that the sorption rate constant was largely independent of the initial sorbate concentration, which was expected because it is a specific quantity characterizing the relationship between sorbate concentration and the rate of sorption. The metal‐loaded fibroin could be regenerated easily by stripping the metal off fibroin using ethylenediamine tetraacetic acid, and the sorption performance of the regenerated fibroin remained the same as pristine fibroin. When used repeatedly over 10 sorption‐regeneration cycles, the fibroin biosorbent showed no change in sorption capacity, which demonstrates the excellent stability and reusability of the fibroin biopolymer for metal capture from water.