Facile preparation of porous activated carbon under ultrasonic assistance for the Methylene blue removal from aqueous environment: characterization, isothermal, kinetic and thermodynamic studies

Powdered Peganum Harmala activated carbon (PPAC) was synthesized by a new activation method using ultrasonic waves (with a frequency of 37 KHz for 1 h) after carbonization and application to remove methylene blue (MB) from aqueous solutions. In this experiment, the characteristics of the PPAC were examined through BET, FESEM, and FTIR spectrum. The effects of the initial pH (2–12), the adsorbent's dose (0.5–4 g L⁻¹), reaction time (2–80 min), initial concentration of the dye (50–300 mg l⁻¹), mixing rate (0–300 rpm), and the solution's temperature (10 °C–50 °C) in adsorption process were investigated. The results indicated that ultrasonic waves have the significant effect on the carbon activating process. BET analysis indicated that the specific surface area of PPAC before activation was 0.776 m² g⁻¹ and had increased to 442.14 m² g⁻¹ following activation by ultrasonic waves. FESEM images showed that significant elevation of the porosity level and development of numerous pores in the activated carbon. FTIR analysis indicates that following the activation, –OH groups have been developed onto the PPAC surfaces. The adsorption isotherms and kinetics were well fitted by the Freundlich and pseudo-second order model. Investigation of thermodynamic parameters indicated that adsorption process of MB by PPAC is spontaneous, endothermic, and physical. (paper)