Recently ionic nanoparticle networks (INN) were reported in the frame of the remarkable development of new inorganic-organic hybrid materials based on nanoparticle assembly. The original method we developed to synthesize 3-D networks is based on the functionalization of metal oxide nanoparticles with ionic linkers, the bridging ligands containing imidazolium units. Recent publications pointed out the powerful synergy of ionic species with nanoparticles. Such synergy makes those new inorganic-organic hybrid materials promising candidates for many applications such as catalysis or luminescent devices, as will be exemplified in this communication.
Focusing on catalysis for CO2 activation reactions, the combination of high imidazolium content with the presence of metal centers, also able to coordinate to CO2 molecules, makes the hybrid materials INN highly promising catalysts. In addition the imidazolium bridging units in the final hybrid material renders the INN tailorable, while the INN materials are solid, which allows an easy separation of the catalyst after reaction. Thus, INN materials, with mono- and di-imidazolium bridging units as well as with various counter anions, were investigated as catalysts for the cycloaddition of CO2 into different starting epoxides.
The photoluminescent properties of INN were also studied. It appears that INN materials are luminescent in the visible range. The excitation wavelength as well as the wavelength of maximum emission can be tailored when modifying the imidazolium linker used to link the nanoparticles. In parallel, the short-range order of the network was investigated via small-angle X-ray scattering. This short-range order was interpreted as originating from self-organization of the aromatic rings of the ligands bridging the nanoparticles by means of pi-pi stacking. This hypothesis was validated by luminescence investigations on the hybrid materials.
Institute for Materials Chemistry, Vienna University of Technology, 1060 Vienna, Austria