Facile synthesis of sugarcane-based biochar using a non-electrical gasifier for the sequestration of 2,4-dichlorophenoxyacetic acid

The chlorinated phenoxy herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is one of the most widely applied agricultural herbicides globally and is frequently detected in surface and groundwater at concentrations that pose ecological and public-health concerns, which motivates the development of low-cost, locally produced adsorbents for its sequestration. This study aimed to synthesize biochar from sugarcane leaves using a non-electrical top-lit updraft gasifier followed by ultrasonication, to characterize its physicochemical properties, and to evaluate its performance for the sequestration of 2,4-D from aqueous solution using a Box-Behnken response surface design. Proximate analysis of the feedstock showed 70.69% volatile matter and 23.46% fixed carbon. XRD revealed a turbostratic carbon structure with a (002) peak at 22.985° and crystallite size of 8.44 Å. Elemental composition showed carbon (67.45%), oxygen (17.31%) and silicon (5.06%). SEM micrographs revealed vesicular surfaces with bubble-like cavities. FTIR confirmed hydroxyl, aromatic C C and C-O functional groups. BET specific surface area was 409.934 m²/g with a BJH pore diameter of 2.136 nm. The point of zero charge of the biochar was 7.53, consistent with a weakly basic surface. Numerical optimization predicted a maximum removal efficiency of 91.81% and an equilibrium adsorption capacity of 163.97 mg/g at pH 9.07, adsorbent dosage 0.78 g/L, initial 2,4-D concentration 86.14 mg/L and contact time 758 min. The study concludes that sugarcane leaf biochar is an effective, low-cost adsorbent for 2,4-D sequestration.