Photocatalytic conversion of nitric oxide (NO) in ambient air was studied in a continuous-flow photoreactor system at room temperature using different TiO2 catalysts prepared with different titanium precursors of Ti(SO4)(2), TiOSO4, and Ti(O-BU)(4) by either a moderate-temperature hydrothermal process or a hydrothermal reflux process. The physicochemical properties of the prepared catalysts were characterized by XRD, BET, FTIR, and SEM. Analytical results showed that the crystallinity, morphology, nitrogen adsorption-desorption isotherms, specific surface area, and pore size distribution of catalysts were significantly affected by the precursors and hydrothermal processes. but the crystal structure and crystal size of catalysts were not significantly influenced. The NO conversion experiments demonstrated that the TiO2 catalysts prepared by the moderate-temperature hydrothermal process without ammonia pretreatment could effectively reduce NO to different low levels, in which the catalysts with longer aging time of more than 12 It performed better than the catalysts with shorter aging time. However, it was found that the NO2 concentration in outlet gas was gradually increased with extension of an experimental period. Two TiO2 catalysts (TOSO-NH3 and TOB-NH3) prepared by the hydrothermal reflux process with ammonia pretreatment demonstrated a very good performance in NO conversion and also maintained a low level of NO2 concentration in outlet gas. This study indicated that using the TiO2 catalysts modified with ammonia pretreatment in photocatalytic reaction could provide a good approach to effectively eliminate the accumulation of NO2 product from NO oxidation in the system and to achieve a sustainable process, which may be applicable for NO elimination in ambient air environment. (C) 2004 Elsevier B.V. All rights reserved.