Facile synthesis of functionalized porous carbon from bitumite mixed with waste powder char for excellent wastewater purification

Waste powder char (WPC) is harmful to the environment and abundant in the production process of the coal chemical industry, but produces relatively low heat energy and releases large amounts of coal ash if it is burned directly. To efficiently solve this issue and create high value materials, three-dimensional hierarchical porous carbons (HPCs) with abundant oxygen-containing groups were prepared from Yulin bitumite (YL) mixed with WPC by combined pyrolysis carbonization and steam activation. The effects of preparation parameters, including WPC doping amount, activation temperature, and activation time, on pore structure development and adsorption capacity of methylene blue from wastewater were explored in detail. The obtained HPCs are microporous structures with additional mesopores and their largest specific surface area (SSA) reached 1299.75 m2 g−1 (8-YLHPC-950–3). Furthermore, 8-YLHPC-900–3 presents a high oxygen content of 15.92 wt%. The SSA and total pore volume (1081.67 m2 g−1 and 0.685 cm3 g−1) of the HPC with 8 wt% WPC doping are larger than those without WPC doping (1155.36 m2 g−1 and 0.755 cm3 g−1). Moreover, these HPCs show superior adsorption of methylene blue in aqueous solution (301 mg g−1 for 8-YLHPC-900–3 compared with 198 mg g−1 for 0-YLHPC-900–3), especially when the HPC was prepared with a WPC doping amount of 8 wt%, activation temperature of 900 °C, steam flow of 0.8 mL g−1 h−1, and activation time of 3 h. These conditions give an optimal adsorption capacity of 301 mg g−1 methylene blue adsorption value (MBV). We introduce a value-added utilization approach for coal-based solid waste and a potential feedstock for adsorption material in the purification of wastewater. The results achieved in this study provide a green and environmentally friendly method for the preparation of HPCs from waste powder char that not only is an industrial reference for the removal of methylene blue from wastewater by HPCs but also contributes to sustainable development in the coal chemical industry.