Novel effect of significant enhancement of gas-phase photocatalytic efficiency for nano ZnO

Nano ZnO photocatalysts were prepared and characterized with XRD, BET, TEM, photocurrent measurement, and positron annihilation spectroscopy (PAS). It has been found that the photocatalytic activity for the gas-phase photocatalytic oxidation of acetone on the nano ZnO photocatalysts significantly increases with increasing reaction temperature. Temperature-dependent photocurrent measurement of the nano ZnO samples reveals that the significant enhancement of photocatalytic activity is attributed to a great enhancement in the separation efficiency of photogenerated charge carriers with increasing temperature. This enhancement is most probably attributed to the effects of the ionized impurity scattering and dislocation scattering, and the increased conductivity of the nano ZnO samples with the elevation of temperature. The PAS result indicates the presence of defects such as monovacancies and vacancy clusters in the nano ZnO samples, which probably leads to the temperature effect of the ionized impurity scattering and dislocation scattering. The novel strategy of improving photocatalytic activity of nano ZnO is facilely realized by coating nano ZnO on the surface of a high-pressure Hg lamp without using additional heater, under which nano ZnO was co-excited by both UV irradiation and thermal energy from the Hg lamp. Under such photothermocatalytic condition, nano ZnO exhibits an excellent durability for the gas-phase photodegradation of acetone, which is in striking contrast to the photoinstability of nano ZnO in liquid-phase photodegradation. (C) 2012 Elsevier B.V. All rights reserved.