The presence of dye molecules in water leads to numerous adverse effects on both human health and aquatic life. This work explores the valorization of agricultural waste through the synthesis and functionalization of date pit-based activated carbon (DP-AC) derived from Phoenix dactylifera (Ghars variety) pits collected at three distinct developmental stages. The base DP-AC was prepared via chemical activation using phosphoric acid (H₃PO₄), with the objective of enhancing its adsorption performance. The synthesized adsorbent was comprehensively characterized using N2 adsorption–desorption isotherm, FTIR, XRD, SEM, TGA, \({\text{pH}}_{\text{PZC}}\) , and Boehm titration. The BET analysis revealed that DP-AC possesses a microporous structure with a surface area of 946.68 m2/g and a total pore volume of 0.46 cm3/g. Moreover, SEM images revealed that DP-AC exhibited noticeable structural modifications, including improved surface texture and pore accessibility. These modifications translated into superior adsorption behavior. Batch adsorption experiments were conducted to evaluate the effect of pH, contact time, adsorbent dose, dye concentration, and temperature on the removal efficiency of Congo Red dye. DP-AC exhibited an equilibrium time of 120 min, with a maximum adsorption capacity of 156.04 mg/g under optimal conditions. Isotherm modeling revealed that the Langmuir model best described the adsorption process, indicating monolayer adsorption on a homogeneous surface. Kinetic analysis showed that the data fit well with the pseudo-second-order model, highlighting surface-controlled adsorption mechanisms. Kinetic analysis revealed a good agreement with the pseudo-second-order model, indicating that the adsorption process was predominantly governed by surface-controlled mechanisms. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) confirmed that the adsorption onto AC was spontaneous and endothermic in nature.
