<p>In this study, carbonaceous porous materials were produced from sunflower shells (SS), an agricultural waste, via ZnCl₂-assisted chemical activation, and their performance in removing Cr(VI) from aqueous solutions was investigated. The ZnCl₂/SS impregnation ratio (IR) was changed in the range of 1:1–4:1, and the carbonization temperature was changed in the range of 400–600 °C. The surface, pore, and surface chemistry properties of the produced materials were analyzed. For this purpose, N₂ adsorption–desorption isotherms, FTIR, SEM, EDS, Boehm titration, and point of zero charge pH analyses were performed. The highest BET surface area and total pore volume were 1501 m²/g and 0.842 cm³/g, respectively, in the H4-500 sample produced at 500 °C with a 4:1 (IR). The highest Cr(VI) removal efficiency for the H3-500 sample was 98.06% at an adsorbent dose of 3 g/L and at approximately pH 2. Equilibrium data are more appropriately represented by the Langmuir isotherm model, and adsorption kinetics are represented more appropriately by the pseudo-second-order kinetic model. The maximum monolayer adsorption capacity, calculated from the Langmuir model, was 111.11 mg/g at 45 °C. The thermodynamic results indicated that the adsorption process can occur spontaneously in the temperature range studied and is endothermic. Among the eluents examined in the desorption experiments, the 1 M HCl solution achieved the highest performance, and the H3-500 sample showed reuse potential over two adsorption–desorption cycles. The results show that ZnCl₂-activated carbonaceous porous materials of SS origin can be considered as effective adsorbents in Cr(VI) removal.</p>