In this study, biochar was obtained from walnut shells (WS) using one- and two-stage pyrolysis processes at different temperatures (500, 600, 700, 700 + 700 degrees C). The biochar obtained was used as an adsorbent for the removal of naproxen, an organic pollutant, from aquatic systems. The highest removal efficiency was obtained with 700 + 700-WSB obtained by the two-stage pyrolysis method. The physicochemical properties of walnut shell biochar (WSB) were investigated using SEM-EDX, FTIR, XRD, BET, elemental analysis, and TGA. 700 + 700-WSB had a high surface area of 649 m2/g and a pronounced porous structure, according to the BET and SEM analysis results. Various experimental parameters (pH, contact time, amount of adsorbent, temperature, initial concentration, and pHpzc) were investigated to study the adsorption of naproxen by 700 + 700-WSB in an aqueous solution. The point of zero charge of the 700 + 700-WSB adsorbent was calculated as 7.15. The 700 + 700-WSB obtained at optimum parameter levels, such as 25 degrees C and 4 h time has an adsorption capacity of 58.8 mg/g. To analyze the equilibrium results, the Langmuir, Sips, Freundlich, and Temkin adsorption isotherm models were utilized. The equilibrium data fit the Langmuir (R2 = 0.984) and Sips (R2 = 0.979) models among the isotherm models. Investigating the adsorption characteristics of naproxen on WSB involved the study of the kinetic models and thermodynamic components of the adsorption process. The psuedo-second order kinetic model (PSO) was shown to be consistent with the experimental data through kinetic investigations, and the thermodynamic results (Delta G degrees = – 21.87 kJ/mol, Delta H degrees = – 29.52 kJ/mol and Delta So = – 25.73 J/mol K) indicated that the adsorption process was exothermic and spontaneous.
