The photophysics surrounding the electron and hole trapping in TiO2 do not have a scientific consensus. Herein, we studied the steady-state photoluminescence and time-resolved spectroscopy features from TiO2 and TiO2/Au nanoparticles (NPs). In TiO2/Au NPs, time-resolved photoluminescence indicates that the electrons from bandgap excitation decay slower (∼30 ps) than in TiO2 (<24 ps). We conclude this as a result of the band bending passivation effect on the surface electron traps. Meanwhile, electron trapping is proved as the dominant surface depopulation process because of the easy-fill characteristics of surface hole traps even under low excitation density, which also interprets the slow surface hole trapping (∼2 ns) in TiO2. Through plasmon-assisted electron injection, we distinguished the electron and hole behaviors at varied photon fluences and then obtained the intrinsic bulk trapping of electrons and holes in the ∼50 and ∼400 ps time range, respectively.

Plasmonic systems convert light into electrical charges and heat that mediate catalytic transformations. However, the debate about the involvement of hot carriers in the catalytic process remains shredded in controversy. Here, we demonstrate the direct use of plasmon hot electrons in the hydrogen evolution with visible light. A plasmonic nanohybrid system consisting of NiO/Au/[CoII(phen-NH2)2(H2O)2] (phen-NH2 = 1,10-Phenanthrolin-5-amine) that is unstable at water thermolysis temperatures was consciously assembled, ensuring that the plasmon contribution to the catalytic process is solely from hot carriers. With the combination of photoelectrocatalysis and advanced in situ spectroscopies, one could establish the reaction mechanism, which consisted of electron injection into the phenanthroline-ligands followed by two quick, concerted proton-coupled electron transfer steps resulting in the evolution of hydrogen. Light-driven hydrogen evolution with plasmons provides a sustainable route for producing green hydrogen, which modern society strives to achieve.