Herein, a plug-flow reactor coated with one-dimensional (1D) TiO nanotube (TNT) heterostructures incorporated with g-CN (CN) and metallic Cu (CN/Cu/TNT) nanocomposite and irradiated by a daylight lamp was newly applied for the mitigation of harmful indoor organic vapors. The CN/Cu/TNT catalyst showed high mitigation efficiency for all target pollutants, followed by Cu-incorporated TNT (Cu/TNT), CN-incorporated TNT (CN/TNT), TNT, and TiO, in that order. The order of their photocatalytic activities agrees with that of the electron‒hole separation rates determined from their photoluminescence emission spectra. The mitigation efficiency of the CN/Cu/TNT catalyst increased as the CN-to-Cu/TNT percentage was increased from 1% to 10%, but subsequently decreased as the CN-to-Cu/TNT percentage increased to 20%. The mitigation efficiencies of the CN/Cu/TNT catalyst decreased with increasing relative humidity, feed pollutant concentrations, and airstream flow rates. However, in most cases, the reaction rates of the target compounds increased when the feed concentration was increased from 1 to 5 ppm. The mineralization rates of all target pollutants were lower than the corresponding photocatalytic mitigation rates, which could be ascribed to the production of CO and organic intermediates observed during the photocatalysis of the target pollutants. Nevertheless, the intermediates formed during the photocatalytic mitigation process would not cause significant adverse health effects to building occupants, because their concentrations were far below their exposure or threshold limit values. A probable mechanism for the photocatalytic mitigation of the organic vapors by the CN/Cu/TNT catalyst under daylight illumination was also proposed.