Sub-bituminous coal as a peculiar adsorbent for dye removal from wastewater

Abstract Coal, an abundant and cost-effective adsorbent, is explored for its potential in environmentally friendly greenhouse gas storage. Herein, the adsorption of anionic (methyl orange) and cationic (methylene blue) dyes on sub-bituminous coal was intensively studied. This study is the first application of sub-bituminous coal to examine the removal of different concentrations of dyes from water. The properties of the coal were studied using advanced analytical techniques. The initial dye concentration, solution pH, and adsorbent-adsorbate contact time were investigated for their influence on the adsorption efficiency of the dyes. Adsorption kinetics were then studied by applying common kinetic models and the adsorption isotherms were modeled using relevant isotherm models. The results showed that the sub-bituminous coal was an excellent adsorbent to capture methylene blue dye but less effective for methyl orange dye, with adsorption capacities of 25 mg/g and 15.5 mg/g, respectively. The Dubinin-Radushkevich model showed a higher R 2 value (0.999) for the adsorption of methyl orange, while the adsorption of methylene blue on the Pan upper coal was better described by the Freundlich model (R 2 = 0.999). Additionally, the Pseudo-first-order kinetic model proved favorable for both adsorbates, indicating that the adsorbate molecules were transported to the solid surface by diffusion, and the adsorption process involved physisorption. This study confirms that sub-bituminous coal is a promising economic adsorbent for removing methylene blue dye.