The pH of the solution plays a significant role in the adsorption efficiency of activated carbon for pollutants such as methylene blue. The adsorption process is influenced by the pH due to its effect on the surface charge of the activated carbon and the ionization state of the pollutant.At low pH values acidic conditions , the surface of the activated carbon becomes protonated, leading to a positively charged surface. Methylene blue, being a cationic dye, will experience electrostatic repulsion with the positively charged surface, resulting in lower adsorption efficiency.As the pH increases alkaline conditions , the surface of the activated carbon becomes deprotonated, leading to a negatively charged surface. This enhances the electrostatic attraction between the negatively charged surface and the cationic methylene blue, resulting in higher adsorption efficiency.However, at very high pH values, the methylene blue molecule may undergo deprotonation, forming a neutral or anionic species, which can reduce the adsorption efficiency due to the lack of electrostatic attraction with the activated carbon surface.In summary, the adsorption efficiency of activated carbon for methylene blue is generally higher under alkaline conditions, but it may decrease at very high pH values due to the changes in the ionization state of the pollutant. Optimal pH conditions for maximum adsorption efficiency should be determined experimentally for each specific activated carbon and pollutant system.