| Summary: | The photocatalytic degradation of formaldehyde, acetaldehyde, toluene, and styrene are compared using monoclinic Ga<sub>2</sub>O<sub>3</sub> and anatase TiO<sub>2</sub> nanostructures under ultraviolet-C irradiation. These Ga<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> photocatalysts are characterized using a field emission scanning electron microscope, a powder X-ray diffraction system, the Brunauer–Emmett–Teller method, and a Fourier transform infrared spectrometer. The Ga<sub>2</sub>O<sub>3</sub> shows a higher reaction rate constant (<i>k</i>, min<sup>−1</sup>) than TiO<sub>2</sub> by a factor of 7.1 for toluene, 8.1 for styrene, 3.1 for formaldehyde, and 2.0 for acetaldehyde. The results demonstrate that the photocatalytic activity ratio of the Ga<sub>2</sub>O<sub>3</sub> over the TiO<sub>2</sub> becomes more prominent toward the aromatic compounds compared with the nonaromatic compounds. Highly energetic photo-generated carriers on the conduction/valence band-edge of the Ga<sub>2</sub>O<sub>3</sub>, in comparison with that of the TiO<sub>2</sub>, result in superior photocatalytic activity, in particular on aromatic volatile organic compounds (VOCs) with a high bond dissociation energy.
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