Potassium hydroxide activation of microalgal biochar for improved adsorption efficiency

Abstract Activated carbon was prepared from Chlorella by carbonization and potassium hydroxide activation, and its structural properties and methylene blue (MB) adsorption performance were evaluated. Raw Chlorella exhibited an adsorption capacity of 287.2 mg g −1 , which decreased to 214.8 mg g −1 after carbonization. Potassium hydroxide (KOH) activation increased the adsorption capacity to 329.7 mg g −1 , representing an increase of approximately 15% compared with the raw material and 54% relative to the biochar. This improvement was attributed to the development of a porous structure and the increase in specific surface area induced by the activation process. Adsorption isotherms were analyzed using the Langmuir, Freundlich, and Temkin models. The Langmuir model gave a maximum monolayer adsorption capacity of 379.6 mg g −1 , whereas the Freundlich model provided the best fit ( R 2 = 0.93), indicating predominance of multilayer physisorption. Temkin analysis showed strong adsorption during the initial stages, followed by a gradual decrease in adsorption heat, reflecting surface heterogeneity and a partial contribution of chemisorption. These findings demonstrate that KOH activation effectively enhances the adsorption performance of Chlorella ‐derived carbon materials and that the adsorption mechanism involves coexistence of monolayer adsorption, multilayer adsorption, and chemisorption.