Eggshell-alginate composites (EACs) as eco-friendly adsorbents for Rhodamine B uptake from aqueous solutions

Abstract

The contamination of wastewater by Rhodamine B (RhB) poses a significant environmental concern due to its negative impacts on aesthetics, ecosystems, and human well-being. This study successfully synthesized eco-friendly egg-shell-alginate composites (EACs) as adsorbents by combining alginate solution, eggshell powder, and a 2% CaCl2 solu-tion. Characterization techniques including FTIR, SEM, TGA, and SAA were employed to analyze the EACs. FTIR analysis revealed characteristic absorption peaks corresponding to -OH groups, C=O groups, C-O groups, and the pres-ence of CO32-. The structural analysis confirmed the physical mixture of functional groups from eggshells and alginate, resulting in a homogeneous EACs mixture. TGA analysis demonstrated the decomposition of eggshell calcium car-bonate (CaCO3), yielding calcium oxide (CaO) and carbon dioxide (CO2) within the 700-800°C temperature range. SAA results indicated that EACs exhibited a mesoporous structure (average pore diameter: 20-500 Å) and a higher sur-face area (6.102 m2/g) compared to eggshells. The adsorption capacity of EACs for RhB was investigated by evaluating contact time, adsorbent dosage, pH, and initial concentration. Characterization results validated the successful synthesis of EACs with enhanced thermal resistance compared to Ca-alginate. Sorption studies demonstrated the potential of EACs as effective adsorbents for RhB removal from aqueous solutions, following the Langmuir isotherm model with a maximum adsorption capacity of 151.51 mg/g. Furthermore, adsorption kinetics exhibited a pseudo-second-order mod-el. Thermodynamic analysis indicated that RhB adsorption onto EACs was exothermic (negative ΔHo) and spontaneous (negative ΔGo). The results underscore the potency of EACs as highly efficient adsorbents for the remediation of RhB-contaminated water bodies.