Fig. 5. (a) Schematic illustrations for nonanal adsorption and aldol condensation events on the ZnO nanowire surface (left), ZnO/CuO nanowire surface (middle) and (Cu, Zn)O nanowire surface (right). (b) FTIR spectra of nonanal-adsorbed ZnO nanowires, ZnO/CuO nanowires and (Cu, Zn)O nanowires. (c) Adsorption structure of C O at the Cu²⁺ site (ν₁), –OH site (ν₂) and Zn²⁺ site (ν₃). (d–f) Temperature dependent variations of FTIR spectra for nonanal adsorbed on (d) ZnO nanowires, (e) (Cu, Zn)O nanowires and (f) ZnO/CuO nanowires after baking at a given temperature for 5 min. For all FTIR spectra, background signals from the nanowires are subtracted. For ZnO/CuO nanowires, the CuO shell thickness is 10 nm. For (Cu, Zn)O nanowires, the CuO shell thickness is varied in the range of 3–20 nm. ‘NWs’ and ‘RT’ represent ‘nanowires’ and ‘room temperature’, respectively.