Kinetic, equilibrium and thermodynamic studies for the removal of lead (II) and copper (II) ions from aqueous solutions by nanocrystalline TiO2

Titanium dioxide nanocrystallites were synthesized as adsorbents through the hydrolysis of titanium tetrachloride as the precursor in hydrochloric acid. The product was analyzed by XRD, BET and SEM-EDX; analysis indicated that the particles were a mixture of 86.8% rutile and 13.2% anatase TiO2 with spherical shapes. The adsorption of Pb (II) and Cu (II) metal ions from aqueous solution onto nano- TiO2 were investigated with variations in pH, contact time, initial metal ion concentration and temperature. The kinetics, adsorption isotherm and adsorption thermodynamics of the heavy metals were studied. The kinetics data were analyzed by the pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models; the best correlation coefficients were obtained for the pseudo-second order kinetic model. The adsorption results obtained from equilibrium experiments were analyzed by Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherms with the Freundlich isotherm giving the best fitting isotherm to the equilibrium data. The thermodynamic parameters (ΔG°ΔG°, ΔH°ΔH° and ΔS°ΔS°) were calculated and it was found that the adsorption process is spontaneous and endothermic and is favored at higher temperature.