Phenyl Hypophosphorous Acid-Assisted Synthesis of Carbon-Modified Anatase-Brookite Bicrystal TiO2 Nanoparticles with Enhanced Visible-Light Photocatalytic Performance

Carbon-modified anatase-brookite bicrystal TiO2 nanoparticle (C/TiO2) photocatalysts were successfully synthesized by a facile hydrothermal method using phenyl hypophosphorous acid (PA) as a ligand to mediate the physicochemical properties and as a source of carbon. The carbon species were insitu formed and loaded on TiO2 surface via carbonization of PA. The characterization results show that the morphology, phase structure, crystal size, chemical states of elements and photocatalytic activity of the C/TiO2 vary with the amount of PA used. The photocatalytic performance of C/TiO2 is significantly improved compared with pure TiO2 because (1) carbon decoration of TiO2 surface extends the light absorption to the visible-light range; (2) charge transfer between anatase and brookite nanocrystals increases the quantum efficiency; and (3) small C/TiO2 nanocrystals yield stronger adsorption capability resulting in an increase in photocatalytic activity. Visible-light photocatalytic degradation of methyl orange (MO) by the C/TiO2 photocatalyst was successfully achieved. The MO concentration was reduced by 78% after exposure to visible light for 180 min. The C/TiO2 photocatalyst was highly stable after four successive experimental runs.