Adsorption of Aminophenol from Aqueous Solution Using KOH Pretreated Biochar Derived from Orange Peel Pyrolysis: Optimization, Kinetics, and Isotherm study

Abstract Biochar derived from waste biomass can remove fine concentrations of phenolic compounds from aqueous media. In this study, orange peel was pretreated with potassium hydroxide (KOH) followed by a low-temperature pyrolysis. The main aim was to investigate the effectiveness of orange peel biochar using batch and column adsorption of aminophenol from water. A novel KOH pre-treatment followed by a low-temperature pyrolysis process was used to produce orange peel biochar with enhanced properties for aminophenol adsorption from an aqueous solution. The adsorbent was characterized for its physicochemical and surface properties before and after adsorption to provide mechanistic insights into biochar role in the aminophenol adsorption process. The optimum adsorption conditions were pH 7, adsorbent dosage of 15 mg and contact time of 105 min for a 50 mg/L aminophenol concentration. Under these conditions, the adsorption efficiency and capacity were estimated at 89.12% and 59.36 mg/g, respectively. Notably, multipoint Brunauer–Emmett–Teller (BET) surface area, Barret-Joyner-Halenda (BJH) pore volume, and pore diameter of the biochar were found to be 403.05 m 2 /g, 0.099 cm 3 /g, and 3.83 nm, respectively, decreasing to 298.6 m 2 /g, 0.054 cm 3 /g, and 3.80 nm, respectively, after aminophenol adsorption. Langmuir model best fitted the experimental data with a minimum error margin of 39.42 and a correlation coefficient of 0.99. The non-linear kinetic data were estimated to be best fitted by the pseudo-second-order model (R 2 = 0.99, RMSE = 0.72, and χ 2 = 3.13). This study demonstrates that a low-temperature pretreated biochar is an efficient adsorbent for the removal of aminophenol from aqueous solutions.