This work reports a facile approach to monodisperse bismuth nanospheres (Bi-NPs), which are then evenly assembled on graphene oxide (GO) via a solution-based sonication method. The resultant Bi-NPs@GO composite can serve as a robust direct plasmonic photocatalyst to remove 42.3% of ppb-level NO from a continuous flow under UV illumination. Localized surface plasmon resonance (LSPR) of Bi nanospheres were confirmed by a numerical simulations and the intense LSPR on Bi nanospheres under UV illumination accounts for the generation of energetic hot electron/hole pairs for NO removal. Experimental results combined with the density functional theory calculation analysis indicate that the abundant carboxyl groups on GO play crucial roles in whole photocatalysis: (i) form a directional carrier deliver channel: Bi -> C-graphene -> C-COOH -> O-COOH, facilitating the hot electrons transfer from the plasmonic Bi nanospheres to carboxyl groups and encouraging the carrier separation efficiency, (ii) enrich the reactant concentrations (O-2 and NO) around catalyst surface by adsorption, promoting the generation of active radicals center dot O-2(-) and the sequent oxidation of NO. Further examination of the photocatalytic NO oxidation by in situ DRIFT confirms the key roles of carboxyl groups as adsorption/reaction centers for photocatalytic NO oxidation, as well as the pathway of NO oxidation to nontoxic nitrate on the catalyst.