Functionalized mesoporous magnetic biochar for methylene blue removal: Performance assessment and mechanism exploration

To improve both adsorption and separation efficiency by increasing the mesoporous volume and stability of tea-based biochar for dye wastewater treatment, the magnetic biochar by KOH activation (MBCK), was prepared by slow pyrolysis of tea residues powder with FeCl3 solution impregnation in various ratios. The specific surface area of MBCK0.5 enhanced significantly to 409.15 m2/g with a 3-fold increase in mesopore pore volume and good magnetic properties. Using methylene blue (MB) as the dye model, a sorption capacity as high as 394.30 mg/g of 1 g/L MBCK0.5 toward 500 mg/L MB was observed in 360 min at 25 °C and pH 10.0, significantly higher than un-activated biochar MBCK0. After 5 cycles, MBCK0.5 still exhibited excellent adsorption capacity (82.81 mg/g), due to the main interactions of pore filling, hydrogen bonding, π-π interactions and electrostatic attraction. Experimental data are more consistent with the Dubinin-Radushkevich isotherm and the pseudo-second-order kinetics models. These results indicated that tea residue-based biochar has considerable scope for application in printing and dyeing wastewater remediation.