Coupling of metals and hydrogenated TiO2 (HT) to bare TiO2 may improve synergistically the photocatalytic activity of TiO2 for pollutant decomposition. Herein, we address this issue by investigating the photocatalytic performances of Cu-loaded HT (CuHT)/bare TiO2 (CuHTT) heterojunction nanocomposites for the degradation of harmful n-butanol under simulated solar light illumination. CuHTT with a CuHT-to-TiO2 composition ratio of 0.1 showed a photocatalytic efficiency exceeding those of four reference photocatalysts, exhibiting the advantages of improved visible light absorption efficiency, charge carrier separation, and adsorption capacity. Increasing the CuHT-to-TiO2 ratio from 0.01 to 0.1 improved the photocatalytic efficiency of CuHTT, whereas a further increase to 0.9 resulted in a decreased photocatalytic efficiency. Moreover, the photocatalytic efficiency improved as relative humidity increased from 20% to 70%, decreasing upon its further increase to 95%. The efficiencies of n-butanol to CO2 conversion over CuHTT were lower than the corresponding decomposition efficiencies. Incompletely oxidized CO and three organic vapors (butanal, propanal, and 1-propanol) were determined as major intermediates. A possible mechanism for CuHTT-catalyzed photodegradation under simulated solar illumination was proposed.