Sustainable dye removal using fish scale-derived biosorbent: performance and mechanisms

<b>Introduction:</b> In the context of sustainable methodologies for wastewater remediation, this study focuses on the development of an efficient and low-cost biosorbent derived from <i>Sardina pilchardus</i> fish scales (SPFS) for dye removal applications. <b>Methods:</b> The prepared biosorbent was characterized using physicochemical and morphological analyses to evaluate its surface properties and porosity. Batch adsorption experiments were conducted to investigate the removal of Methylene Blue (MB) and Congo Red (CR), including kinetic, isotherm, thermodynamic, and regeneration studies. <b>Results:</b> The material exhibited a porous structure and rich surface functional groups favorable for adsorption. Fast adsorption kinetics were observed, with equilibrium reached within 30 min for both dyes. The adsorption process followed the pseudo-second-order model, indicating chemisorption as the controlling mechanism. Isotherm analysis showed that the Langmuir-Freundlich model provided the best fit, suggesting a heterogeneous surface with combined monolayer and multilayer adsorption. Maximum adsorption capacities of 187.634 mg/g for CR and 129.694 mg/g for MB were achieved, placing SPFS among the most efficient bio-derived adsorbents reported. Thermodynamic parameters confirmed that the adsorption processes were spontaneous, exothermic, and favorable. <b>Discussion:</b> Although a slight decrease in adsorption efficiency was observed at higher temperatures, the biosorbent demonstrated excellent regenerability and maintained high performance over multiple cycles. These findings highlight the strong potential of fish-scale-derived biosorbents as sustainable, efficient, and reusable materials for dye removal in wastewater treatment.