Preparation of biomorphic porous calcium titanate and its application for preconcentration of nickel in water and food samples.

Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol-gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol-gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4-8, but the adsorbed nickel ion could be completely eluted using 2 mol L(-1) HNO3. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g(-1) and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol(-1). At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (Ea) was 25.291 kJ mol(-1) for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.