Nanostructured hydrous titanium(IV) oxide: Synthesis, characterization and Ni(II) adsorption behavior

The synthetic oxide was characterized as hydrated and agglomerated nanocrystallite (11–13 nm) titanium(IV) oxide (NHTO), which was used for Ni(II) adsorption from aqueous solution. The variable parameters investigated were the effects of pH, contact time, metal concentration and temperature on reaction. The optimum pH fixed was 5.0 (±0.1) for Ni(II) adsorption. The kinetic data described the pseudo-first order equation well and, film diffusion governed the reaction. The Redlich–Peterson equation described well the equilibrium isotherm data of all temperatures. The Fe(III) showed negative influence on Ni(II) adsorption. The negative Gibbs free energy (−ΔG° = 13.90–16.30 kJ mol−1) and positive enthalpy change (+ΔH° = 6.15 kJ mol−1) indicated spontaneous and endothermic nature of the reaction, respectively, and took place with increasing entropy (ΔS° = +0.07 kJ mol−1 K−1). The mean energy of adsorption (EDR = 13.25–16.35 kJ mol−1 at T = 288–328 K) predicted physisorption nature of Ni(II) on NHTO. The dilute (0.1 M) mineral acids desorbed 95–98% of adsorbed metal from the NHTO surface.