Methylation modification of coal gasification fine slag for enhanced organic dye adsorption in wastewater

Abstract

The disposal of coal gasification fine slag (CGFS) and the treatment of dye wastewater present substantial environmental pressures. Therefore, developing cost-effective adsorbents is crucial. In this study, CGFS-based adsorbents, which are modified with dimethyl diethoxy silane (DDS-CGFS) and dodecyl trimethyl ammonium chloride (DTAC-CGFS), were prepared and applied for the removal of rhodamine B (RhB) organic dye. The adsorption performances were evaluated across different pH values, temperatures, and contact time. Under optimal conditions (pH = 7, 328.15 K, 24 h), the DDS-CGFS adsorbent exhibited a maximum adsorption capacity of 92.82 mg g⁻¹ for rhodamine B. Kinetic and isotherm analyses revealed that the adsorption involved both physical and chemical processes. The intra-particle diffusion model suggested that the adsorption kinetics were governed by boundary-layer and intra-particle diffusions. Thermodynamic parameters (ΔG° < 0, ΔH° > 0, ΔS° > 0) indicated that the adsorption was a spontaneous and endothermic process accompanied by an increase in entropy. Material characterization and model fitting suggested a synergistic adsorption mechanism, potentially involving interactions such as hydrogen bonding and π–π stacking. Overall, DDS-CGFS and DTAC-CGFS are low-cost adsorbents for remediating dye wastewater. Due to their outstanding adsorption capacity, they show potential as ideal adsorbents for dye wastewater treatment.