Materials characterization and adsorption isotherm data

Nano-zirconia (ZO) was synthesized using a microwave assisted one pot precipitation route. Two biopolymers, chitosan (CTS) and carboxymethyl cellulose (CMC), were then combined with zirconia at different w/w ratios in order to identify the system with the most improved sorption properties towards Pb(II), Cd(II), As(V) and F-. The formulation with 30% w/w chitosan (ZO-CTS) was found to give enhanced uptake of F- and As(V). Improved sorption properties could not be observed for Pb(II) and Cd(II) in any of the ZO-polymer blends, with ZO being the most potent sorbent here. ZO and the lead system ZO-CTS were characterized in detail using Fourier transform infra-red spectroscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). These confirmed the formation of a composite system comprising nanoparticles with 50 nm in size in which ZO was present in the amorphous form. Interactions between Zr and the amide and hydroxide groups of chitosan were suggested from XPS. Batch adsorption studies were carried out and equilibrium adsorption data were fitted to a series of isotherm models. It was observed that the combination of ZO with CTS improved the F- and As(V) adsorption capacity most notably at pH 5.2. Fluoride adsorption by ZO-CTS followed the Freundlich isotherm model, with an adsorption capacity of 120 mg/g. Adsorption of As(V) by ZO-CTS could be fitted with both the Langmuir and Freundlich isotherm models, and was found to have a capacity of 14.8 mg/g. Gravity filtration studies were also carried out at two different pH levels to test the feasibility of ZO-CTS in real-world applications. These indicated that the sorbent could be used to filter a significant volume of water and ensure that pollutant levels remained below acceptable values.