Nanoporous Xerogel for Adsorption of Pb2+ and Cd2+

Classical xerogels are robust, inexpensive and nontoxic materials with low-ordered nanoporous structures. In water streams where the pH is higher than the Point of Zero Charge, the surface of classical xerogels such as tetraethoxy orthosilan (TEOS) xerogel is negatively charged. It was assumed that a xerogel can work as a strong adsorbent for metal ions without further modification. Therefore, the capability of TEOS xerogel for adsorption of two heavy metal ions, Pb2+ and Cd2+ , from aqueous solution was studied. The batch experiments revealed that the adsorbent has higher adsorption capacity for Pb2+ (58.82 mg/g) and Cd2+ (35.71 mg/g) as compared with the reported low-cost adsorbents. Kinetics and thermodynamic studies were employed to explain the adsorption mechanism. It was concluded that the adsorption of both ions on TEOS xerogel obey chemisorption mechanism. However, the reaction of Pb2+ with the adsorbent is thermodynamic controlled and the one of Cd2+ is kinetic controlled.