High surface area activated carbon for sustainable tetracycline adsorption: Mechanism, regeneration and efficacy in realistic water matrices

Abstract

This study systematically examines the synthesis, structural properties, and adsorption performance of activated carbon prepared using Kachnar pods (KP–AC) to remove tetracycline (TC) from aqueous media. KP–AC was synthesized via H₃PO₄ activation, yielding a highly porous, heterogeneous, and functionalized adsorbent with a high BET surface area (1528.14 m²/g) and mesoporosity. Various characterization analyses revealed a rough, flake-like structure with oxygenated and phosphorus-containing functional groups that facilitate strong interactions with TC through electrostatic interactions, π–π stacking, and hydrogen bond formation. Batch adsorption experiments demonstrated pH-dependent uptake, with maximum removal at pH 4, driven by minimized electrostatic repulsion and enhanced non-covalent interactions. Adsorption kinetics followed a pseudo-second-order model, while equilibrium data fitted best to the Freundlich isotherm. The high monolayer capacity from the Langmuir model (201.3 mg/g) underscored KP–AC's strong adsorption potential. Thermodynamic parameters revealed the spontaneity and endothermic nature of adsorption. KP–AC also exhibited good regeneration performance, retaining 52.9 % of its initial removal efficiency after four adsorption–desorption cycles, and maintained robust performance across diverse real water matrices despite moderate reductions. These findings establish KP–AC as an efficient, sustainable, and regenerable adsorbent for TC remediation from water.