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The occurrence of heavy metal ions in industrial wastewater discharges is a pertinent issue. Discharges that are not properly treated causes pollution to the downstream river and groundwater which are often used for drinking and irrigation in the rural area. This thesis explores the feasibility of titanate nanotube as an industrial sorbent to remove cadmium and other divalent cations from water. Nanotubes, synthesized via alkali hydrothermal process, were characterized using microscopic techniques. Empirical approaches (Langmuir equation, Kurbatov equation and hard and soft acids and bases) were used to understand the sorption behaviour of titanate nanotube on seven divalent cations. It was found that the sorbent had high selectivity for lead and cadmium. In descending order, the affinity for titanate nanotube: lead » cadmium > copper > zinc > calcium > strontium > nickel. For each cation, its sorption capacitiy was correlated with intrinsic parameters (hydrolysis constant, electronegativity, hardness and charge-size function). From linear regression analyses of six cations, with the exception of nickel, it was found that sorption capacity can be adequately correlated with hydrolysis constant and electronegativity. Due to the toxicity of cadmium, the effects of solution chemistry on cadmium uptake were studied. Sorption efficiency increased at higher pH condition, other parameters being held constant. This, in part, was due to the surface charge of titanate nanotube. Metal oxide being amphoteric had negative charge when pH > point of zero charge, thereby attracting the positively charge cadmium ions. Varying ionic strength at low order of magnitude (10-3 10-2 M), did not have significant effect on sorption uptake. At 0.1 M, significant decrease in cadmium sorbed can be observed. The sorption of cadmium was due to a combination of electrostatic forces and covalent bonding. Two complementary spectroscopic techniques were utilized to investigate the mechanisms involved in sorption of cadmium. X-ray photoelectron spectroscopy (XPS) showed an increase in cadmium at higher pH which was in accordance with behaviour exhibited in the sorption edges. In open system, cadmium precipitated to ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library

Sorption mechanisms of divalent cations with titanate nanotube