Modeling 2,4-dichlorophenoxyacetic acid adsorption on candle bush pod-derived activated carbon: Insights from advanced statistical physics models

The widespread usage of 2,4-Dichlorophenoxyacetic acid (2,4-D) as an herbicide has led to alarming levels of environmental pollution, presenting severe risks to ecosystems and human health. This study aimed to synthesize a new adsorbent, activated carbon from candle bush pods (CBAC) via low-temperature phosphoric acid activation and investigate its ability for adsorptive elimination of 2,4-D. The setup of a new adsorption system requires the experimental determination of adsorption isotherms and their thorough modeling, which is achieved through advanced statistical physics models (ASPMs). The characterization of CBAC revealed a porous morphology with a remarkable specific surface area (415.31 m²/g). XRD revealed graphitic carbon structures, while XPS detected phosphate groups, graphitic structures, and oxygen-containing functional groups. Double layer with single energy (DLSE) model – one of the ASPMs revealed both non-parallel and parallel orientation of 2,4-D molecules on CBAC, with saturation adsorption capacity values increasing with temperature (up to 252.35 mg/g) at pH 2. The adsorption was physisorption (ΔE = 12.62–16.26 kJ/mol) and spontaneous and endothermic. Hence, the findings herein demonstrate the potential of CBAC as a sustainable and effective adsorbent for mitigating environmental pollution caused by 2,4-D.