A novel, reusable biomass-derived adsorbent biochar material, referred to as WS, was developed by pyrolyzing ball-milled walnut shell powder under an inert gas atmosphere, followed by chemical activation with sodium hydroxide (NaOH). The resulting biochar WS demonstrated rapid adsorption capabilities for trinitrotoluene (TNT) from wastewater, achieving equilibrium within 30 min. The maximum adsorption capacity was determined to be 107.0 mg·g⁻¹. Adsorption data were well-described by the Langmuir isotherm model and the pseudo-second-order kinetic model, indicating favorable adsorption characteristics. The efficient removal of TNT by WS was attributed to a synergistic mechanism involving electrostatic attraction and chemisorption.