The effect of pH on the adsorption capacity of activated carbon for the removal of a specific pollutant from an aqueous solution can be significant and depends on the nature of the pollutant and the properties of the activated carbon. The pH of the solution can influence the adsorption process through several mechanisms:1. Surface charge of activated carbon: The surface of activated carbon has various functional groups that can ionize at different pH values, leading to a change in the surface charge. At low pH, the surface is more positively charged, while at high pH, it becomes more negatively charged. This change in surface charge can affect the adsorption of pollutants, especially if they are charged species.2. Speciation of the pollutant: The pH of the solution can also affect the speciation of the pollutant, which means that the pollutant may exist in different forms e.g., ionized or non-ionized depending on the pH. Some forms of the pollutant may have a higher affinity for the activated carbon than others, leading to a change in adsorption capacity.3. Electrostatic interactions: The pH can influence the electrostatic interactions between the pollutant and the activated carbon surface. For example, if the pollutant is anionic negatively charged and the activated carbon surface is positively charged at a specific pH, the electrostatic attraction between them can enhance the adsorption capacity. Conversely, if both the pollutant and the activated carbon surface have the same charge, electrostatic repulsion can reduce the adsorption capacity.4. Hydrogen bonding and other interactions: Changes in pH can also affect hydrogen bonding and other interactions between the pollutant and the activated carbon surface. For example, at low pH, the abundance of protons H+ in the solution can compete with the pollutant for adsorption sites on the activated carbon, reducing the adsorption capacity.In summary, the effect of pH on the adsorption capacity of activated carbon for the removal of a specific pollutant from an aqueous solution is complex and depends on the properties of both the activated carbon and the pollutant. Optimal pH conditions for maximum adsorption capacity can vary depending on the specific pollutant and activated carbon used.