Development and characterization of activated charcoal adsorbent derived from oak for efficient removal of methylene blue: functionality vs surface area

Abstract With industrial growth, environmental and water pollution have become pressing issues, requiring effective treatment solutions. Adsorption is an economical and practical method for removing dyes from textile wastewater, making the choice of a sustainable, low-cost adsorbent crucial. Although it is clear that surface area is important in adsorption, the presence of functional groups that have adsorption ability is equally important. For this purpose, locally abundant oak-derived charcoal (MK) was selected. Due to its low adsorption capacity, the charcoal was activated using concentrated sulfuric acid at 150 °C with an acid-to-sample ratio of 5:1, producing activated charcoal (SMK). The adsorbent was characterized using SEM, BET, FTIR, Boehm titration, and pHpzc analyses. Methylene blue (MB), a cationic dye, was chosen as the target pollutant, and experiments were conducted to study the effects of solution pH, adsorbent dose, initial dye concentration, and temperature on MB removal. Isotherm and kinetic analyses showed that MB adsorption on SMK fits the Langmuir isotherm model, with an adsorption capacity of 370.85 mg/g, and follows a pseudo-second-order kinetic model. Thermodynamic analysis confirmed that the process is exothermic. While MK has a surface area of 76.8 m 2 /g but no affinity for dyes, SMK, with a surface area of 6.31 m 2 /g, was effective in MB removal, highlighting the importance of surface functionality. Therefore, SMK proved to be an efficient adsorbent for MB removal from water. Graphical abstract