M. Sharma^a, J. Singh^b, S. Hazra^c and S. Basu^b
aDivision of Chemistry, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
^bSchool of Chemistry and Biochemistry, Thapar University, Patiala 147004, India
^cSaha Institute of Nuclear Physics, Kolkata 700064, India

Up till now, the excessive and unconstrained release of Pb²⁺ and Cd²⁺ ions in water becomes a foremost concern by way of threatening human health seriously. Therefore, for removal of heavy metal ions from waste water, adsorbent with high efficacy and low-cost technologies is most needed to alleviate the situation. In this work, robust, mesoporous ZnO & TiO₂@ZnO monoliths with the valuable surface area (120-332 m²/g) were synthesized via nanocasting process and their performance as an adsorbent for removal of heavy metal (Pb²⁺ and Cd²⁺) ions from aqueous water was successfully evaluated. The adsorption data shows better fit at pH 6 to Freundlich isotherm model. Applicability of pseudo-second order (PSO) kinetic model specifies the chemisorption process. Thermodynamic parameters confirmed that removal of Pb²⁺ and Cd²⁺ ions was an endothermic process. The maximum adsorption efficacy of Pb²⁺ ions based on monolayer adsorption was found to be 790 and 978 mg/L for ZnO and TiO₂@ZnO monoliths, respectively whereas the maximum adsorption efficacy of Cd²⁺ ions based on monolayer adsorption was found to be 643 and 786 mg/L for ZnO and TiO₂@ZnO monoliths respectively. Besides, used mesoporous ZnO & TiO₂@ZnO monoliths could be efficiently reused for at least three times after treatment with NaOH. The high uptake capacity for Pb²⁺ and Cd²⁺ ions with good reusability of ZnO & TiO₂@ZnO monoliths made them a potentially attractive adsorbent.