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 in situ 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.