Biosilica/Silk Fibroin/Polyurethane biocomposite for toxic heavy metals removal from aqueous streams

Development of green, eco-friendly, and efficient adsorbents for wastewater treatment is highly researched to mitigate the alarming rate of water pollution. In this work, a novel biocomposite of biosilica (BS)/silk fibroin (SF)/polyurethane foam (PUF) was prepared and studied for the adsorptive recovery of toxic copper (Cu²⁺) and chromium (Cr^6＋) ions from synthetic wastewater. XRD and FTIR studies confirmed the formation of biocomposite with amorphous structure and –OH, –NH, C=O surface functionalities. SEM results confirmed the successful incorporation of SF and PUF into BS. The biocomposite possessed a specific surface area of 751.9 m²/g and a mean pore size of 7.21 nm. Further, effects of pH, adsorbent dose, contact time, and initial metal ion concentration on the adsorptive removal of Cu²⁺ and Cr^6＋ metal ions by the BS/SF/PUF biocomposite were studied in detail. Equilibrium and kinetic analysis showed that the metal ions sequestration by the BS/SF/PUF biocomposite followed the Freundlich isotherm and Elovich model, respectively. Maximum adsorption capacities of 331.69 mg/g and 201.56 mg/g were estimated for the Cu²⁺ and Cr^6＋ ions, respectively. A plausible mechanism for the adsorption of the metal ions onto BS/SF/PUF biocomposite is postulated. Reusability studies of the biocomposite using EDTA eluent showed that the biocomposite could be efficiently reused up to four consecutive adsorption/desorption cycles. Thus, this study provides comprehensive data for applying the BS/SF/PUF biocomposite to treat Cu²⁺ and Cr^6＋ metal ions polluted wastewater streams.