Surface Interactions between Molecules and Nanocrystals in Copper Oxalate Nanostructures

Copper oxalate (CuOx) mesocrystalline nanostructures have been synthesized by aqueous precipitation. Several morphologies of these nanostructures could be obtained with high monodispersity depending on the presence and the nature of additive molecules [glycerol, poly(ethylene glycol) (PEG), and hydroxypropyl methylcellulose (HPMC)]. A core shell structure of the CuOx mesocrystals and a radial self-assembly mechanism are deduced from the respective effects of each additive on the mesocrystal final morphologies. Additive molecules are detected by Fourier transform infrared (FTIR) spectroscopy in CuOx powders in spite of the postsynthesis washing steps. A fluorescence phenomenon occurring in CuOx synthesized with additives is highlighted by an atypical use of Raman spectroscopy. This fluorescence seems to be specific to the combination of CuOx with additive molecules. We suggest that fluorescence is generated by interactions between nanocrystals and adsorbed molecules. Additive desorption is finally both performed and real-time monitored by Raman spectroscopy by using the incident laser source.