In-situ multi-step pulsed vapor phase surface functionalization of zirconia nanoparticles via copper-free click chemistry

We report on multi-step copper-free vapor phase azide-alkyne click reactions for the functionalization of metal oxide nanopowders, automated with the atomic layer deposition (ALD) technique. The synthetic approach consists of the following reaction steps: chemisorption of propiolic acid (PA) to ZrO2 from the gas phase, followed by the formation of a triazole ring through a click reaction with 1,4-bis(azidomethyl)benzene (BisA), and, in the final step, click-coupling of the pendant azide groups with a second dose of propiolic acid (PA). The chemical composition and nature of the chemical bonding in the samples obtained after each of the ALD processing steps were investigated in detail by ATR-FTIR and XPS. As confirmed by an additional ALD deposition of ZnO, the latter reaction step introduces free polar carboxylic acid functionalities to the nanomaterial surface, which enhance the stability of the chemically modified zirconia in ethanolic dispersion. This proof-of-concept study offers great potential toward the fabrication of functional organic layers on metal oxide surfaces by sequential azide-alkyne cycloadditions performed in ALD.