| Summary: | Two-dimensional (2D) heterostructures, characterized by their extensive interfacial area, hold remarkable potential as exceptionally efficient photocatalysts. In this thesis, microscale uniform 2D heterostructures with designed thickness and structure as well as controlled surfaces can be prepared via template-assisted bottom-up or top-down fabrication. The magnetic attributes of Fe3O4 templates provide notable advantages, making it possible to easily separate the resulting 2D heterostructures from other components in the solution using magnetic forces.
First, utilizing Fe3O4 microplates as templates, a bottom-up fabrication approach was employed to construct 2D heterostructures involving TiO2 and polymeric carbon nitride (PCN). This process involved the sequential layer-by-layer growth of ultra-thin layers of PCN and TiO2 onto the microplate surfaces, followed by the removal of the template. An average combined thickness of 25 nm was observed in the resulting 2D PCN/TiO2 heterostructures. Remarkably, these structures exhibited exceptional photocatalytic hydrogen generation capabilities, achieving a rate of 11.1 mmol h-1 g-1. This performance surpassed that of independent 2D PCN and TiO2, together with bulk PCN/TiO2 heterojunctions. The notable enhancement in photocatalytic activity can be ascribed to the extensive contact area between PCN and TiO2, which facilitates the efficient separation and transportation of photo-exited electrons and holes across the PCN/TiO2 interfaces.
Second, the top-down construction process of 2D heterostructures composed of TiO2 and BaTiO3 involved utilizing Fe3O4 microplates as a template, initiating the construction with the growth of a ~40nm thick layer of titanium hydroxide on the microplate surface. Subsequently, the conversion of BaTiO3 and TiO2 is achieved through the intercalation of Ba2+ ions followed by calcination. The 2D TiO2/BaTiO3 heterostructures, obtained with a combined thickness of around 40 nm, demonstrated a remarkable photocatalytic hydrogen generation rate of 31.0 mmol h-1 g-1 under the influence of ultrasonic vibration. This rate far exceeded those of individual TiO2 and BaTiO3 nanosheets, together with the bulk and commercial TiO2/BaTiO3 heterojunctions. This enhanced photocatalytic activity can be attributed to the optimized interfacial area between TiO2 and BaTiO3, facilitating the efficient separation and transfer of photo-induced electron-hole pairs. Notably, the charge separation and transfer at the BaTiO3 side undergo further enhancement through the application of piezoelectric polarization induced by ultrasonication.
This thesis offers novel insights into the realm of template-assisted bottom-up and top-down approaches for designing and constructing diverse 2D heterostructures for photocatalysis.
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