The photocatalytic decomposition of toluene gas was investigated using TiO2 prepared by atomic layer deposition (ALD) on nanodiamond (ND) under UV irradiation. The photocatalytic activities of ND-supported TiO2 catalysts were compared with that of P-25. The photocatalytic activity of P-25 was rapidly decreased with time due to the accumulation of reaction intermediates formed on the surface as a result of partial oxidation of toluene. Comparing to P-25, deactivation of ND-supported TiO2 catalysts was less pronounced. It is suggested that ND surface facilitates total oxidation of toluene on TiO2 and reduces poisoning of TiO2 surface with time. (C) 2011 Elsevier B.V. All rights reserved.