An investigation of the structure of stearate monolayers on Au@ZrO2 and Ag@ZrO2 core-shell nanoparticles

Monolayer protected nanoparticles, Au@ZrO2@stearate and Ag@ZrO2@stearate, in which the core-shell nanoparticles, Au@ZrO2 and Ag@ZrO2 (ZrO2 coated Au and Ag nanoparticles) are functionalized with stearic acid, have been synthesized and characterized. The air-dried powders, freely dispersible in several organic solvents (both polar and non-polar), are stable for extended periods. The materials were characterized by spectroscopic, microscopic, diffraction and thermal analysis techniques. The monolayer cover is stable up to 200 degreesC. Monolayers do not exhibit strong inter-chain interactions, unlike in the case of those on metal nanoparticles, suggesting that their surface anchoring sites are widely spaced. As a result, temperature-dependent infrared spectra of the monolayers are featureless. The oxide surface is accessible for small molecules in solution even after stearic acid coverage. Freely dispersible nanoparticles with oxide shells may offer new possibilities in catalysis, photophysics and materials science.