Removal of methylene blue from water by low-cost activated carbon prepared from tea waste: A study of adsorption isotherm and kinetics

•Tea waste based activated carbon was synthesized using H3PO4 (H-AC), KOH (K-AC) and ZnCl2 (Z-AC).•Activating agents show significant effects on the adsorptive properties of activated carbon.•H-AC showed the highest adsorptive properties for the removal of methylene blue (MB).•The methylene blue removal from water followed pseudo-second-order kinetics.•H-AC and Z-AC followed Freundlich and K-AC followed Langmuir isotherm for the removal MB.