Effect of microwave radiation on the (Raman) lattice phonons in selected titanium dioxide solid specimens

Abstract

The effects of 2.45-GHz microwave radiation on the Raman-active lattice phonons of two selected (Wako) anatase and rutile specimens and on Degussa P-25 TiO 2 nanoparticles were probed by in situ microscopic Raman spectroscopy in the solid phase with samples subjected to microwave irradiation (MW) or in combination with UV illumination (UV/MW). Significant changes were seen in the Raman band intensities for the pure anatase E g mode at 143 cm −1 and for the rutile vibration at 446 cm −1, whereas only negligible changes in intensity were observed for the 144 cm −1 band of P-25 nanoparticles exposed to MW and UV/MW radiation. It is deduced that microwaves have a negligible impact on the lattice vibrational modes (phonons) of P-25 titania, even though this specimen was thermally heated by the microwaves. The photodegradation of phenol was re-visited to examine the photoactivity of the TiO 2 specimens selected for the in situ Raman study, as attested by the number of OH radicals produced (DMPO spin trap ESR) under UV versus UV/MW irradiations, and by the related enhanced dynamics under UV/MW irradiation relative to UV alone or UV/CH.