Preparation and application of a novel adsorbent from red calliandra hydrochar for pollutant remediation

•Red calliandra is declared as a new candidate for activated carbon material.•The narrowing of the pore diameter is responsible for the adsorption improvement.•Superheated steam produced the highest BET surface area and pore volume of 766 m2/g and 0.45 cm3/g, respectively.•Inherent property recovery by superheated steam results in the optimum capture for all pollutant species.•The adsorption abilities of activated carbon for benzene, chloroform, MB, and iodine species were 146, 240, 81, and 618 mg/g, respectively.