Dual-route synthesis of bio-composites for rapid, high-efficiency arsenic and lead removal from water: Comparing pyrolysis and hydrothermal approaches

This study presents a dual-route synthesis of bio-composites derived from coconut fiber waste, chitosan, and FeCl₃ for the efficient removal of As(III) and Pb(II) from aqueous solutions. Two preparation methods, including pyrolysis and hydrothermal treatment, were employed to produce distinct bio-composites with tailored physicochemical properties. Material characterization via zeta potential analysis, BET surface area measurements, SEM-EDX, and XRD confirmed successful Fe functionalization and structural transformation. In addition, the ICP-OES was employed to measure the concentration of the investigated elements in this study. Adsorption experiments demonstrated that both pristine biochar and pyrolyzed bio-composites achieved nearly 100% removal of Pb(II) within 15 min. Notably, the hydrochar-based bio-composite synthesized via hydrothermal treatment exhibited superior performance for As(III) removal, reaching an efficiency of 90.39%. This enhanced arsenic adsorption is attributed to the high surface density of ferric oxides and reactive functional groups, promoting inner-sphere complexation with As(III). In contrast, Pb(II) adsorption was governed by surface porosity and functional group interactions, favoring both composite types. These findings highlight the critical role of synthesis strategy in dictating the adsorption behavior of the resulting materials. In particular, the hydrochar route offers significant promise for arsenic remediation applications, providing a sustainable and low-cost pathway for developing multifunctional water treatment adsorbents. This work advances the design of biopolymer- and agrowaste-derived composites for targeted removal of toxic metals from water.