TiO₂−Graphene Nanocomposites for Gas-Phase Photocatalytic Degradation of Volatile Aromatic Pollutant: Is TiO₂−Graphene Truly Different from Other TiO₂−Carbon Composite Materials?

Abstract

The nanocomposites of TiO₂−graphene (TiO₂−GR) have been prepared <i>via</i> a facile hydrothermal reaction of graphene oxide and TiO₂ in an ethanol−water solvent. We show that such a TiO₂−GR nanocomposite exhibits much higher photocatalytic activity and stability than bare TiO₂ toward the gas-phase degradation of benzene, a volatile aromatic pollutant in air. By investigating the effect of different addition ratios of graphene on the photocatalytic activity of TiO₂−GR systematically, we find that the higher weight ratio in TiO₂−GR will decrease the photocatalytic activity. Analogous phenomenon is also observed for the liquid-phase degradation of dyes over TiO₂−GR. In addition, the key features for TiO₂−GR including enhancement of adsorptivity of pollutants, light absorption intensity, electron−hole pairs lifetime, and extended light absorption range have also been found in the composite of TiO₂ and carbon nanotubes (TiO₂−CNT). These strongly manifest that TiO₂−GR is in essence the same as other TiO₂−carbon (carbon nanotubes, fullerenes, and activated carbon) composite materials on enhancement of photocatalytic activity of TiO₂, although graphene by itself has unique structural and electronic properties. Notably, this key fundamental question remains completely unaddressed in a recent report (ACS Nano 2010, 4, 380) regarding liquid-phase degradation of dyes over the TiO₂−GR photocatalyst. Thus, we propose that TiO₂−GR cannot provide truly new insights into the fabrication of TiO₂−carbon composite as high-performance photocatalysts. It is hoped that our work could avert the misleading message to the readership, hence offering a valuable source of reference on fabricating TiO₂−carbon composites for their application as a photocatalyst in the environment cleanup.