(71h) Supramolecule-Directed Immobilization of Nanoparticles on Solid Surfaces
We have developed an in situ synthesis route for preparation of a layer of immobilized nanoparticles on a solid surface by employing covalently tethered supramolecular layer as a directing agent. The nanoparticles were immobilized and stabilized by a calixhydroquinone monolayer which in turn was immobilized on the substrate surface by covalent layer-by-layer assembly. The calixhydroquinone moiety served as a nano-reactor, container and template in the in situ synthesis process. The nanoparticles were formed by reduction of the metallic ions by the hydroquinone form of the calixarene. The size of the nanoparticles can be tuned continuously up to islands of 100 nm by repeated application of the redox properties of calixarene. A variety of metals can be formed as nanoparticles by this process, including Ag, Pt, Pd, Cu and Au. Metallic ions with less charges, lower oxidation state in the reaction and higher standard redox potential provided better yield. Bimetallic nanoparticles with a core-shell structure were synthesized by a sequential deposition of different metals on the same monolayer. The process is applicable to flat surfaces as well as to those with irregular topography. A significant advantage derived by this method of formation and assembly is its surfactant-free nature that enables access to the active surface of the nanoparticle. The process of in situ synthesis under controlled conditions, together with calibrated variation of particle size has the potential to serve as building blocks for electronic nano-devices, nano-catalysts, etc.