Four methods, fast titration, salt addition, mass titration, and ζ potentiometry, were employed to determine the point of zero charge (PZC) and isoelectric point (IEP) of NiO. However, this work mainly focuses on the fast titration method because it limits the release of Ni from the substrate. Furthermore, the fast titration is simple, rapid, and accurate and requires a small quantity of substrate as compared to the salt addition and mass titration techniques. The similarity between the PZC and IEP values rules out the specific adsorption of the bulk electrolyte onto the NiO surface. However, the PZC values shift downward with the increase in Cd ion concentration, which indicates the specific adsorption of Cd onto the NiO. In addition, temperature has a mild effect on the deprotonation constants and PZC of NiO. It was also observed that the thermodynamic parameters favor the deprotonation of NiO. ' MATERIALS AND METHODSMaterials. Analytical grade reagents were used in this study. All glassware and polyethylene bottles were rinsed with 10%

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An efficient and cost effective adsorbent, activated carbon (UTAC) derived from used tea (UT) for the removal of As(III) from aqueous solutions was developed. To increase adsorption, UTAC was then impregnated with (magnetite) iron oxide particles (Fe-UTAC). The prepared adsorbents were characterized by XRD, SEM/EDX, FTIR and surface area analyzer. A comprehensive kinetic study of arsenite adsorption onto Fe-UTAC was conducted at 298-318 K and pH 8. The Richenberg model confirmed film diffusion to be the main rate limiting step. The removal of As(III) from aqueous solution onto Fe-UTAC was carried out as a function of temperature, concentration and pH. The sorption capacity (mol g -1 ) of Fe-UTAC was observed to increase with increase in arsenite concentration while a decrease in the As(III) uptake was observed by increasing the temperature of the system. The sorption capacity of Fe-UTAC was almost three and six times larger than that of UTAC and UT respectively. The effect of pH on the arsenite adsorption was significant in the pH range 7-8 which may be correlated with the stability of Fe-UTAC as no release of iron from Fe-UTAC was observed. The mean free energy calculated from DR mechanism confirmed adsorption to be chemisorption and followed ligand exchange mechanism. The thermodynamic parameters confirmed adsorption to be exothermic, spontaneous and favorable.