Chemical Protection of Material Morphology: Robust and Gentle Gas-Phase Surface Functionalization of ZnO with Propiolic Acid.

Chemical functionalization of ZnO surface with an alkyne functional group was successfully achieved by exposing ZnO nanopowder to gas-phase propiolic acid in vacuum, which left the alkyne group available for subsequent chemical modification via the azide-alkyne cycloaddition "click" reaction with benzyl azide. The highly selective formation of a bidentate carboxylate linkage and the reaction of benzyl azide were confirmed by solid-state nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Most importantly, scanning electron microscopy revealed that the surface morphology was perfectly preserved by this gas-phase modification, as opposed to the alternative protocols based on liquid phase processing. This simple and precise design can serve as a universal method for the modular functionalization of zinc oxide surface following the initial surface preparation and be further applied to thin films, nanostructures, and powders, where preserving surface morphology during chemical modification is especially important.