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

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 TiO2 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 Eg 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 TiO2 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.