Caffeine adsorption on activated biochar derived from macrophytes (Eichornia crassipes)

•Biochars were sucessfully synthesized from aquatic plant (macrophytes).•CO2 physical activation improved the surface area of the biochar.•The activated material shows na adsorption capacity of 117.8 mg g−1. This work reports the use of macrophyte (Eichornia crassipes) as raw material for preparation activated biochar (ABC) from the physical activation, using CO2 as activating agent. The ABC was applied in the removal of caffeine (CAF) from the aqueous solution. The characterization of ABC showed that it has micro and mesoporosity features with BET surface area (SBET) value of 740 m2 g−1 and basic character of surface with value of pHPCZ of 8.44. CAF adsorption study demonstrated that the initial pH is not a factor that directly influences the adsorption capacity, whose qe is 161.1 ± 10.56 mg g−1. The kinetic study showed that pseudo-second-order model is that better describe the adsorption process. Adsorption equilibrium study indicated the Redlich-Peterson as the best isothermal model and that ABC has high monolayer adsorption maximum capacity of CAF (Qmax = 117.8 mg L−1). Thermodynamic studies indicated that the processo is spontaneous, endothermic and governed by chemisorption.