In this study, activated carbon was synthesized using hydrochar obtained from lentil stalks, which is generally evaluated as animal feed, by hydrothermal method. Thus, a low value-added biomass source was transformed into a higher value-added product. Activated carbon was synthesized using ZnCl₂ activator by chemical activation method and then carbon molecular sieve was obtained by chemical vapor deposition method. Characterization of synthesized activated carbon and carbon molecular sieves was carried out using FTIR, BET and SEM analysis techniques. SEM analysis results showed that synthesized activated carbon had a more porous structure compared to hydrochar and raw lentil stalk. Synthesized activated carbon and carbon molecular sieve were used in methylene blue adsorption for the removal of organic pollutants. In this process, parameters such as pH and initial concentration affecting adsorption performance were investigated and adsorption kinetics were determined. Methylene blue adsorption equilibrium data were applied to Langmuir and Freundlich isotherms and it was determined that the system showed the best fit to Langmuir isotherm. The maximum adsorption capacity (qmax) was determined as 98 mg/g for activated carbon and 87 mg/g for carbon molecular sieve. In addition, it was concluded that the methylene blue adsorption kinetics for both adsorbents fit the pseudo-second-order kinetic model. This study reveals that agricultural wastes such as lentil stalks can be effectively used in reducing environmental pollution by converting them into high-performance adsorbent materials.