Synthesis and characterization of radiation sensitive TiO₂/monazite photocatalyst

Abstract

A TiO₂/monazite photocatalyst was prepared by embedding TiO₂ nanoparticles into a monazite substrate surface. TiCl₄ hydrolysis/citric acid chelating procedure under acidic conditions were used to synthesize the nanophase TiO₂ particles. The anatase TiO₂/monazite photocatalyst surface area, morphology, crystalline and elemental concentrations were characterized using Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Monazite contains a large amount of Ce-, La-, Nd- and Th-PO₄ compounds; it has been known as a natural mineral material with minor radioactivity. TiO₂-CeO₂ composite is a kind of radiation sensitive photocatalyst in which the radiations of thorium nuclides give energy to trigger TiO₂ and cerium ions which play an energy absorber with charge separator. The result showed that methylene blue and phenol were spontaneously photocatalytic decomposed by TiO₂/monazite composite even in a dark environment. A synergistic effect was also examined with applied exterior UV or ⁶⁰Co irradiation. A hybrid mechanism is proposed; according by the radioluminescence (RL) from excited Ce ion by γ-radiation soliciting CeO₂/TiO₂ heterojunction (HJ). This seems to be a possible mechanism to explain this self-activated photo-catalytic behavior.