Adsorption of heavy metal ions by mesoporous ZnO and TiO2@ZnO monoliths: Adsorption and kinetic studies

Abstract

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.