Recent Trends in the Application of Silk-Based Composites for Remediation of Toxic Contaminants from Wastewater

The utilization of harmful chemicals, such as ions of heavy metals, organic and inorganic dyes, and oils, has expanded dramatically due to rapid industrialization and urbanization. The haphazard discharge of these chemicals has menaced the terrain and aquatic bodies, causing transfiguration for aquatic and non-aquatic life. Frequently used techniques like membrane filtration and reverse osmosis for effluent removal have impediments such as toxic sludge generation, erratic pollutant removal, and an expensive process that is annihilated using the most efficient technique of effluent treatment, 'Adsorption'. Conventional adsorbents, like activated carbon, generate secondary sludge and are challenging to reactivate post-treatment. Hence, an abundantly accessible natural material like silk fibroin is used as an adsorbent with superior mechanical properties, biodegradability, and regenerability. The silk fibers obtained post-degumming are then functionalized and used with several engineered biomaterials forming composites, exhibiting excellent adsorption efficiencies for removing metal ions and dyes and separating oil from water. With adsorption efficiencies of greater than 90% for copper ions, 93.75% for lead ions, and adsorption capacities of 88.5 mg/g for acid-yellow 11, and 74.63 mg/g for naphthol orange, functionalized silk composites can be employed to discard pollutants. This review emphasizes the characteristics of functionalized silk fibroins for the removal of various heavy metal ions. Furthermore, it discusses the optimal parameters required for adsorption and kinetics and isotherms, followed by the thermodynamic evaluation, which gives insights into the reaction's spontaneity.