Paper SS-TuP5
Self-Catalyzed Gas-Phase Cycloaddition on “Clickable” Nanostructured CuO Surface

Tuesday, October 22, 2019, 6:30 pm, Room Union Station B

The surface functionalization of nanostructured metal oxides (CuO, ZnO, TiO₂, CeO₂) has attracted substantial attention due to their extensive applications in sensing, photo-catalysis, electronics, and energy conversion. A number of studies have been reported to achieve the surface sensitization of these metal oxides with organic or organometallic compounds in order to expand their versatile properties by introducing designated functionality. However, the most common approach to achieve this functionality utilizes sensitizer molecules reacting with oxide surfaces via carboxylic (COOH) or phosphonic (P(O)(OH)₂) anchor groups or by silylation (such as with R-Si(X)₃, where the X could be Cl or -OCH₃), which potentially leads to agglomeration, multilayer growth, or surface etching. Our recent research developed a two-step functionalization approach utilizing exposure of the oxide materials to prop-2-ynoic acid (HC≡C-COOH, prop-2-ynoic acid) in the gas phase as a first step, followed by second step of post-modification exploiting the created C≡C to introduce any pre-designed functionality to the surface via Cu(I)-catalyzed “click” chemistry with azides (R-N₃). More importantly, this approach requires no additional presence of the copper catalyst for nanostructured CuO due to the reduction of surface copper from prop-2-ynoic acid modification. As a result, the second step of this functionalization can be achieved through self-catalyzed cycloaddition with gas-phase species. The morphology preservation and selective covalent attachment of the carboxylic acid onto the metal oxide surfaces have been confirmed by the combination of microscopic and spectroscopic investigations including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and solid-state nuclear magnetic resonance spectroscopy (ss-NMR) that were used to follow the process and to compare with the traditional liquid-phase modification schemes. Vienna Ab Initio Simulation Package (VASP) calculations were used to explore the reaction mechanism and key intermediates.