Design of heterostructured metal-semiconductor nanocrystal photocatalysts for enhanced photocatalytic efficiency

Abstract

Inorganic nano-semiconductors including quantum dots and metal oxides have bandgap energies that can absorb the entire range of sunlight. Their applications to photocatalysis have been actively studied. However, when these inorganic materials are employed alone, it is difficult to achieve the desired level of efficiency in the application. In this thesis, it was tried to study the synthesis and design of heterostructured nanocrystals between various material combinations suitable for applying them to photocatalysts. Heterojunctions between various inorganic nanomaterials were investigated, thereby improving photocatalytic activities or optical properties. First, potential of amorphous $TiO_2$, which is not well used due to the trap of charges, was studied as a photocatalyst. It was revealed that thin layer of $TiO_2$ on quantum dots facilitates release of electrons for $H_2$ production. Next, we proved that junction of $TiO_2$ and CuPt alloy catalysts contributed to improved selectivity and efficiency of $CH_4$ in $CO_2$ conversion. Small size of CuPt nanoparticles exposed facets on which carbon dioxide could be efficiently adsorbed, which was confirmed by molecular simulation. Finally, heterojunctions between quantum dots by cation exchange were investigated. During cation exchange, defect can be produced due to residual cations. New cation exchange method was designed using metal-ligand interaction, which improved optical properties of heterostructures. This study is expected to be used as a new synthesis method of blue-emitting quantum dots, which is an issue in light emitting diodes. This thesis provides insight on design of the heterostructure nanocrystals. The synthetic method that we developed has a positive effect on application to enhanced photocatalysis and light emitting diode.