CO2-hierarchical activated carbon prepared from coal gasification residue: Adsorption equilibrium, isotherm, kinetic and thermodynamic studies for methylene blue removal

Mineral matter in a residue (R-CG) from coal gasification (CG) was removed by two-stage acid leaching. Hierarchical activated carbon (HAC) was prepared by activating R(CG )with CO2. The performance of HAC on removing methylene blue (MB) from an aqueous solution was investigated. HAC was characterized by N-2 adsorption-desorption isotherm, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results show that HAC exhibits hierarchical pore structure with high specific surface area (862.76 m(2).g(-1)) and total pore volume (0.684 cm(3).g(-1)), and abundant organic functional groups. The adsorption equilibrium data of MB on HAC are best fitted to the Redlich-Peterson. The kinetic data show that the pseudo-first-order model is more suitable at low MB concentration, while the advantages of the pseudo-second-orderand the Elovich models are more obvious as the concentration increases. According to the thermodynamic parameters, the HAC-MB adsorption process is spontaneous and endothermic. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.