Preparation and potential application of amino-functionalized titanosilicates to removal of Th(IV) in aqueous solutions: optimization using response surface methodology (RSM)

Mesoporous titanosilicates (TiSil) with a size of almost 25 nm were prepared by an alkali-assisted hydro-thermal route, as an choice for developing efficient adsorbents of Th(IV) ions. TiSil were functionalized with the amino functional group (-NH2) from 3-aminopropyltriethoxysilane (APTES) by post-preparation method. The obtained amino-grafted titanosilicates (TiSilNH(2)) were characterized by Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) techniques. Adsorption of Th(IV) ions on TiSilNH(2) was examined in aqueous solution. Response surface methodology (RSM) based on central composite design (CCD) was applied to optimize the four essential process variables namely initial pH and initial concentration of Th(IV) ions of aqueous solution, amount of adsorbent, and adsorption process temperature for the Th(IV) removal. The adequacy of the model was investigated, and it was deemed to be statistically significant. The optimal predicted adsorption capacity of TiSilNH(2) for Th(IV) ions was 83.04 mg/g and the actual value was 84.8 mg/g. The equilibrium adsorption data were fitted to Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The equi-librium data were best re-presented by Langmuir isotherm model, showing maximum monolayer adsorption capacity of 87.71 mg/g. The thermodynamic parameters indicated that the Th(IV) adsorption on the TiSilNH(2) was a spontaneous, and endo-thermic process at the studied temperatures and occurred via physisorption. Adsorbent recovery by using 0.5 M HNO3 solution for adsorbent reuse indicated that the adsorbent was regenerable and could be employed frequently.