Enhanced photocatalytic removal of 2,4-dichlorophenoxyacetic acid in soil using biochar and graphitic carbon nitride nanocomposites optimized by central composite design

Abstract

This study optimized the remediation of 2,4-dichlorophenoxyacetic acid (2,4-D) in soil using a Rumex abyssinicus biochar/g-C 3 N 4 nanocomposite under visible-light irradiation (400–700 nm) via a central composite design. The hybrid catalyst was synthesized by ball-milling biochar and g-C 3 N 4 nanoparticles at a 2:1 ratio. Physicochemical characterization confirmed a stable fixed carbon backbone (73.6%) and an accumulation of catalytic alkaline oxides (45.71% K 2 O and 16.67% CaO). Morphological and structural analyses revealed well-distributed polymeric g-C 3 N 4 sheets embedded within porous carbon networks, yielding a specific surface area of 285.2 m 2 /g, a point of zero charge at pH 8.0, and a narrowed semiconductor bandgap of 2.30 eV. The experimental results demonstrate that the removal of 2,4-D is achieved through a synergy of adsorption and photocatalytic degradation. Under optimized treatment parameters, a maximum 2,4-D soil remediation efficiency of 94.84% was achieved within 30 days, following pseudo-first-order kinetics. Radical scavenging assays suggest that superoxide radicals, photogenerated holes, and hydroxyl radicals contribute to the photocatalytic portion of the herbicide removal. The synergy between the condensed biochar core and reactive nitrogen-bearing functionalities optimizes surface chemistry and electrostatic attraction, enhancing visible-light-responsive charge separation for efficient 2,4-D remediation in soil matrices.