In the present study, biochar derived from cypress cones was surface modified using chitosan, a biopolymer rich in amino functional groups, in order to enhance its performance for the removal of nickel (II) ions from aqueous solutions. To investigate the possible mechanisms involved in nickel removal, both raw biochar and chitosan modified biochar were characterized using BET, FTIR, and FE SEM analyses. BET results showed that chitosan coating increased the specific surface area of biochar from 13.2 to 5.75 m²/g and reduced the average pore diameter from 10.97 to 6.26 nm. FTIR spectroscopy confirmed the appearance of new peaks at 1620 cm⁻¹ (amide C=O group) and 3430 cm⁻¹ (N–H stretching vibration), verifying the successful incorporation of amino and amide groups onto the adsorbent surface. Nickel removal was optimized using response surface methodology based on a Box–Behnken design with four variables: initial nickel concentration, pH, adsorbent dose, and contact time. The reduced cubic model, with a high coefficient of determination (0.98), exhibited excellent agreement with the experimental data for both adsorbents. Under laboratory conditions, the chitosan modified biochar achieved a nickel removal efficiency of 55%, whereas the raw biochar showed only 51% removal. This enhancement is attributed to the synergistic contribution of physical adsorption within the improved porous network, surface complexation with amino/amide functional groups, and ion-exchange interactions.The findings of this study indicate that although chitosan modification of cypress cone biochar leads to a noticeable improvement in nickel adsorption capacity, further investigations are required in real industrial wastewater.