Asymmetric Janus nanostructures containing a gold nanocage (NC) and a carbon-titania hybrid nanocrystal (AuNC/(C-TiO2)) are prepared using a novel and facile microemulsion-based approach that involves the assistance of ethanol. The localized surface plasmon resonance of the Au NC with a hollow interior and porous walls induce broadband visible-light harvesting in the Janus AuNC/(C-TiO2). An acetone evolution rate of 6.3 mu mol h(-1) g(-1) is obtained when the Janus nanostructure is used for the photocatalytic aerobic oxidation of iso -propanol under visible light (lambda = 480-910 nm); the rate is 3.2 times the value of that obtained with C-TiO2, and in photo-electrochemical investigations an approximately fivefold enhancement is obtained. Moreover, when compared with the core-shell structure (AuNC@(C-TiO2) and a gold-carbon-titania system where Au sphere nanoparticles act as light-harvesting antenna, Janus AuNC/(C-TiO2) exhibit superior plasmonic enhancement. Electromagnetic field simulation and electron paramagnetic resonance results suggest that the plasmon-photon coupling effect is dramatically amplified at the interface between the Au NC and C-TiO2, leading to enhanced generation of energetic hot electrons for photocatalysis.