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. In this study, saturated and superheated agents were used to produce activated carbon from red calliandra (Calliandra calothyrsus) hydrochar. Proximate, ultimate, XRD, FTIR, thermal gravity analyzer, and SEM were used to characterize the prepared activated carbon. Chemical pollutants, such as benzene, chloroform, methylene blue (MB), and iodine, were used to test the adsorption ability. The hydrothermal and activation procedures were conducted at 250 °C and 800 °C, respectively. The activation of superheated agents effectively increased the BET surface area compared to saturation and thermal methods alone. The BET surface areas were measured as 470, 759, and 766 m²/g for thermal, saturation, and superheated methods, respectively. The superheated method preserved tiny mesopores (2–10 nm), while saturation produced large mesopores (20–50 nm), and the thermal method was more favorable for macropore development (>50 nm). Analyses of the structure of superheated activated carbon (HC–SS) showed that the aromatic layer (Lc) was thinner, which led to pores that were smaller. The adsorption test confirmed the superiority of the superheated method. For the pollutant species benzene, chloroform, MB, and iodine, HC–SS exhibited adsorption abilities of 146, 240, 81, and 618 mg/g, respectively.