Fig. 4. UV-vis/NIR spectra of Co3O4 NPs dispersed in heptane. (a) Absorption spectrum of OA-stabilized cuboidal Co3O4 NPs dispersed in heptane (Cb13) in the spectral range from 200–2000 nm (black line). For comparison, reference spectra of pure OA (blue line), as well as heptane (yellow line), are shown. (b) Series of absorption spectra for NPs with diameters between 2.8 and 10.9 nm showing size-dependent absorbance. Inset: photograph of cuvettes containing NP dispersions (left to right: increasing NP size from 2.8–10.9 nm). Intensification of colouration is observed with increasing NP size.
