This paper reports a simple and environmentally benign approach for the synthesis of photocatalytically active rutile TiO₂ mesocrystals. It is a microwave-assisted hydrothermal method involving titanium(III) chloride as the only reactant. The resulting 1D rutile nanowires can easily assemble into 3D hierarchical architectures without the help of surfactants or additives. The average aspect ratio for the nanowires is 267. The BET specific surface area of the mesocrystals is 16 m² g⁻¹. The optical band energy of the product exhibits an obvious red-shift of 0.2 eV with aspect to that of pure rutile TiO₂. This red-shift effect may be ascribed to the high aspect ratio of rutile nanowires. The products show excellent photocatalytic activity for NO removal in air and the activity is well maintained after three cycles. Gold modification on the rutile TiO₂ results in a 50% improvement in the photocatalytic performance.