Surfactant-free one-pot synthesis of CeO2, TiO2 and Ti@Ce oxide nanoparticles for the ultrafast removal of Cr(vi) from aqueous media.

Cerium oxide (CeO2), titanium oxide (TiO2) and titanium oxide impregnated with cerium oxide (Ti@Ce oxide) nanoparticles were synthesized using a simple one-pot surfactant-free method. The synthesized adsorbents were tested against the removal of Cr(vi) from aqueous medium. Comprehensive characterization methods like BET, XRD, SEM, EDAX, HR-TEM, SAED, HR-XPS and FT-IR were performed at different stages of the adsorption process and synthesis. A N2-BET study revealed the large surface area (268 m2 g-1) and pore size (6.8 nm) of CeO2 nanoparticles, which decreased after impregnation of titania. An XRD study demonstrated the phase transformation of TiO2 from the anatase phase to the rutile phase after the impregnation with CeO2 by lowering the phase transformation temperature from >550 °C to 400 °C. Ti0.3@Ce0.7 oxide nanoparticles showed 81% removal of Cr(vi) within 2.5 min of initiating the adsorption process while more than 92% removal of Cr(vi) was achieved within 10 min of adsorption. A HR-XPS study indicated the dual oxidation states of ceria and titania metals, which helped to convert the more toxic Cr(vi) ions to less toxic Cr(iii) ions during the adsorption process. The adsorption pattern depicted the monolayer behavior of Cr(vi) obeying the Redlich-Peterson isotherm and followed pseudo second-order kinetics. An intraparticle diffusion model disclosed the surface and pore resistance diffusion of Cr(vi) on the surface of adsorbents.