Fig. 3.

Graphene/Ag composite photocatalysts. a The C₂H₄ epoxidation activity, measured in terms of the turnover frequency (TOF) of EO generation, in a quasi-steady-state photocatalytic measurement for three different photocatalysts: Ag/Al₂O₃, G-Ag/Al₂O₃, and A-Ag/Al₂O₃. In each case, the bar height represents the average TOF from multiple cycles comprising a long photocatalytic reaction (see Supplementary Fig. 15) and the error bar represents the standard deviation of the TOF. Dot plots of the TOF for each cycle are also shown overlaid with the bar graph. b Normalized SERS spectrum of A-Ag/Al₂O₃ (after 14 h of irradiation) in air shows D and G bands, similar to G-Ag/Al₂O₃ indicating the formation of graphenic carbon on the Ag NP surface after activation. c Ultraviolet–visible extinction spectrum of Ag NP colloid in water and diffuse-reflectance absorption spectra of Ag/Al₂O_3, A-Ag/Al₂O₃ (after 14 h of irradiation), G/Al₂O₃, and G-Ag/Al₂O₃ powders. The spectra are shown normalized; representative HRTEM images (scale bars = 5 nm) of Ag NPs irradiated by 514.5 nm laser (5 mW, ×60) in C₂H₄ showing d multi-layer graphene with interlayer spacing of 0.34 nm and e the {002} planes of graphene with interplanar spacing of 0.32 nm. Lattice fringe spacings were determined from FFT of the selected regions indicated by the square. f A schematic showing the formation of graphenic carbon on Ag NP surface under photocatalytic reaction conditions