Direct Formation of Atomically-Thin Carbon Shells on Metal Oxide for Catalytic Application

Abstract

In this thesis, direct formation of atomically-thin carbon shells on metal oxide using aromatic carboxylic acid (ACA) and their application to selective photocatalytic hydrogen peroxide (H2O2) generation were reported. Atomically-thin carbon shells are formed directly on the surface of metal oxide through pyrolytic decarboxylation of ACA such as benzoic acid (BA), 1-naphthoic acid (NA), 9-anthracnecarboxylic acid (AA), and 1-pyrnecarboxylic acid (PA). Compared to previous hybridizing metal oxide with carbon nanostructures (metal oxide@carbon nanocomposites), direct formation of carbon shell on metal oxide would have some advantages that structural stability, uniformity of nanocomposites, and efficient carrier transfer. As-obtained nanocomposites show similar D/G ratio but different D*/G ratio in their Raman spectra with respect to the type of ACA, which implies that the size of graphitic domains is almost same for all samples but carbon shell synthesized using NA contains more oxygenic species than other obtained nanocomposites. Such oxygenic species are presented majorly in the form of epoxide groups, which is observed on the attenuated total reflection infrared spectroscopy. For investigating formation process of carbon shell, several polyaromatic hydrocarbon (PAH) and ACA were pyrolized. Under heating, PAH was only vaporized without any reacted product, whereas ACA were pyrolized to carbon nanodots (CNDs). From this results, the formation of carbon shells derived by ACA would be attributed to decarboxylation of ACA. The CNDs can be synthesized using AA and PA respectively, (AA-CNDs, and PA-CNDs) and emit long wavelength light (600 nm, and 560 nm). Then orange-freestanding color filter was demonstrated using PA-CNDs whose quantum yield is 36%. The film exhibits the Commission international d’Elclairage (CIE) coordinates (0.5599, 0.43889). The carbon shells were directly formed on the surface of TiO2 nanoparticles. Then, selective photocatalytic H2O2 generation systems based on TiO2@C were successfully demonstrated. It turns out that sp2 carbon near epoxide groups in the carbon shells can act as active sites for the two-electron reduction of O2, and accordingly, TiO2@C(NA) can generate H2O2 more efficiently than TiO2@C(BA). Furthermore, the carbon shells retard the re-consumption of generated H2O2 by inhibiting the adsorption of H2O2 on the surface of TiO2 nanoparticles to improve photocatalytic efficiency of H2O2 generation.