Eco-friendly treatment of toxic reactive textile dyestuffs using biogenic eggshell powder

Abstract Increasing environmental concerns related to dye-contaminated wastewaters have intensified the demand for sustainable and cost-effective treatment approaches. In this study, eggshells (ES) were investigated as a low-cost adsorbent for the removal of Reactive Red-195 (Red-195) and Remazol Brilliant Orange (RBO) from aqueous solutions. The physicochemical properties of ES were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. Under optimized batch adsorption conditions (0.1 g ES, 30 min contact time, 25 °C, pH 4), maximum removal efficiencies of 87.98% for Red-195 and 74% for RBO were achieved. Nonlinear isotherm and kinetic modeling, supported by error analysis, revealed that the adsorption behavior of both dyes was best described by the Langmuir isotherm (R 2 RBO = 0.996, R 2 Red-195 = 0.987) and the pseudo-second-order kinetic model (R 2 RBO = 0.995, R 2 Red-195 = 0.991). These results indicate monolayer adsorption on energetically heterogeneous sites, with the process predominantly governed by physisorption mechanisms. Thermodynamic parameters confirmed that the adsorption was spontaneous (ΔG° < 0), exothermic (ΔH° < 0), and entropy-driven (ΔS° > 0). Additionally, inhibition of Escherichia coli was found to be influenced by dye concentration, solution pH, and the surface characteristics of ES. Overall, the findings highlight the potential of eggshells as an efficient and environmentally friendly adsorbent for the removal of textile dyes and related pollutants from water. Graphical abstract