| Summary: | Titanium oxide (TiO<sub>2</sub>) nanostructures, the most widely used photocatalysts, are known to suffer from poisoning of the active sites during photocatalytic decomposition of volatile organic compounds. Partially oxidized organic compounds with low volatility stick to the catalyst surface, limiting the practical application for air purification. In this work, we studied the UV-driven photocatalytic activity of bare TiO<sub>2</sub> toward toluene decomposition under various conditions and found that surface deactivation is pronounced either under dry conditions or humid conditions with a very high toluene concentration (~442 ppm). In contrast, when the humidity was relatively high (~34 %RH) and toluene concentration was low (~66 ppm), such deactivation was not significant. We then modified TiO<sub>2</sub> surfaces by deposition of polydimethylsiloxane and subsequent annealing, which yielded a more hydrophilic surface. We provide experimental evidence that our hydrophilic TiO<sub>2</sub> does not show deactivation under the conditions that induce significant deactivation with bare TiO<sub>2</sub>. Conversion of toluene into dimethylacetamide was observed on the hydrophilic TiO<sub>2</sub> and did not result in poisoning of active sites. Our hydrophilic TiO<sub>2</sub> shows high potential for application in air purification for extended time, which is not possible using bare TiO<sub>2</sub> due to the significant poisoning of active sites.
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