How is aluminum oxide activated?

• A. Oxygen and heat
• B. Sulfuric acid and heat
• C. Heat and washing with sodium hydroxide
• D. Carbon dioxide wash with HCl and heat

Answer: (C)

Activation of aluminum oxide means conditioning the material so its surface can reliably adsorb contaminants. This is done by heating to drive off moisture and organize the porous structure, then washing with sodium hydroxide to create the active surface sites. The heat step makes the surface accessible and stable, while the NaOH wash deprotonates surface hydroxyl groups, forming Al–O− sites that can attract and exchange contaminants like fluoride and arsenate in water. Without the heat, the surface stays hydrated and less available for adsorption; without the base wash, there aren’t enough active sites, so adsorption capacity is limited. Using oxygen, acid, or other washes would not produce the same activated surface chemistry and could reduce adsorption effectiveness.