Highly efficient adsorption of strontium ions by carbonated mesoporous TiO2

Abstract

In this study, mesoporous carbonated TiO2 nanoparticles were synthesized by sol-gel route using a complex [Ti(OH2)6]3+·3Cl− and a modifying agent Na2CO3 and used as an adsorbents for Sr(II) removal from aqueous medium. The characterization of nanoadsorbents was accomplished using XRD, SEM, EDS, TEM, TG-DTG-DTA, IR, BET, pHPZC analyses. It was found that the sizes of carbonated TiO2 nanoparticles was ~4 nm. The presence of mononuclear bidentate carbonate groups on the titania surface was approved by IR spectroscopy. The kinetic data was analyzed by pseudo-first-order, pseudo-second-order, Elovich, and an intraparticle diffusion models. The adsorption isotherms were fitted by using Langmuir, Freundlich, and Dubinin–Radushkevich models. The fittings show that the pseudo-second-order kinetics and Langmuir isotherm are suitable models for the adsorption process. The sample with 4% (wt.) of carbonate groups showed the best adsorption performance towards Sr(II) cations. The mesoporous carbonated samples demonstrated a higher adsorption capacity for strontium ions than the basic TiO2. The adsorption capacities of modified 2C-TiO2, 4C-TiO2 and 8C-TiO2 samples were 170.4, 204.4, 190.8 mg/g respectively, while it was 70.9 mg/g for the unmodified TiO2 towards Sr(II). Higher removal of Sr(II) was observed in the alkaline medium due to the formation of SrОН+ cations. A mechanism for Sr(II) adsorption was described and the number of chemosorbed ≡Ті(О2СО) groups and active adsorption centers onto unmodified and modified TiO2 surface were calculated. The titania adsorbents have high reusability and retain their adsorption capacity during five adsorption-desorption cycles. The presented results indicated that the mesoporous carbonated adsorbents were appropriate materials for the removal of Sr(II) from aqueous medium.