Synthesis of hydrochloric acid-assisted coconut trunk biochar and evaluation of its adsorption capacity for methyl red and copper ions

Abstract

In this study, biochar derived from coconut tree biomass was successfully synthesized with the assistance of a hydrochloric acid solution. The structural and morphological characterizations of the material were obtained by X-ray diffraction, SEM, EDS, BJH, BET method. The prepared biochar exhibited a specific surface area of 166 m²/g and adsorption capacities of 41.63 mg/g for methyl red and 35.86 mg/g for Cu(II), demonstrating effective adsorption performance toward both organic and inorganic pollutants. The density functional theory calculations using the PBE functional and the def2-TZVP basis set were performed to simulate the molecular interactions between the biochar structure and the methyl red and copper ion. The results revealed that methyl red adsorption is mainly stabilized through hydrogen-bond interactions with surface hydroxyl groups, whereas Cu(II) adsorption involves coordination with oxygen-containing functional groups, resulting in stronger adsorption. The combined experimental and theoretical results provide molecular-level insights into the adsorption behavior of hydrochloric acid-assisted coconut trunk biochar and demonstrate its potential as a sustainable adsorbent for wastewater treatment.