Innovative Biochar-Coated Cocoon-Based Adsorbent for the Removal of Organic and Inorganic Pollutants from Water

The present study describes the development of an innovative adsorbent based on Bombyx mori silkworm cocoons for the removal of organic and inorganic pollutants from water. The material was prepared by coating raw silkworm cocoons with biochar derived from the same biomass through pyrolysis under nitrogen followed by KOH activation and subsequently incorporating the coated cocoons into a sodium alginate matrix using dip-coating and calcium crosslinking. The materials were characterised using SEM, BET, DFT, FTIR, and TGA analyses. KOH activation substantially improved the porosity of biochar, increasing its specific surface area from 1.56 to 1178 m2/g and producing a predominantly microporous structure. The final biochar-coated cocoon compound exhibited a specific surface area of 422.29 m2/g. SEM observations confirmed the preservation of the fibrous cocoon morphology after coating, while FTIR and TGA analyses provided information on surface functional groups and thermal behaviour. Adsorption performance was evaluated for Pb(II) and phenol under static and dynamic conditions. The Langmuir model provided a slightly better fit for Pb(II) adsorption than the Freundlich model, whereas phenol adsorption was more clearly described by the Langmuir model. Dynamic column experiments showed higher removal efficiency and longer breakthrough times for Pb(II) than for phenol. A single regeneration cycle resulted in partial recovery of adsorption performance, particularly for Pb(II), although further consecutive adsorption–desorption cycles are needed to establish long-term reusability and stability. Overall, the results demonstrate the potential of this cocoon-based biochar composite as a sustainable adsorbent for water treatment, particularly for Pb(II) removal under batch and flow conditions.