Modification of H3PO4-activated Pomelo Peel Biochar with Cetyltrimethylammonium Bromide for Methyl Orange Removal: Adsorption Performance and Mechanism

Abstract

The biochar obtained from pomelo peel with phosphoric activation (A-PBC) was modified using a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The percentage of CTAB in biochar significantly affects the physicochemical characteristics of the obtained biochar. The specific surface area of CTAB-modified biochar could remarkably increase up to 2150.61 m²/g. The surface charge of biochar significantly changed with the point zero charge pH_pzc = 6.49. The biochar modified with 2 wt% of CTAB (CTAB2@A-PBC) was the best adsorbent for methyl orange (MO) removal. The maximum adsorption capacity of MO calculated by the Langmuir model reached 534.23 mg/g at 30 °C. The result of the isotherm study indicates that the adsorption process of MO on the modified biochar is well fitted with Langmuir and Temkin models, meaning homogeneous rather than heterogeneous adsorption. The kinetic result revealed that the Elovich kinetic model could predict the adsorption process better than the pseudo-first model as well as the pseudo-second model. It suggests that the MO adsorption mechanisms by CTAB2@A-PBC could be involved by electrostatic attraction, pore-filling, p-p interaction, and hydrogen bonding.