Characterization and evaluation of novel nano-structured bismuth vanadate and hybrid nanomaterials as more sustainable and enhanced photocatalysts in organic transformations

• Main Author: Ng, Leonard Kia Sheun
• Other Authors: Chen Zhong
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials::Material testing and characterization; DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: https://hdl.handle.net/10356/106064; http://hdl.handle.net/10220/47892
• Institution: Nanyang Technological University

In light of the growing demand for alternative energy sources, artificial photosynthesis (AP) has shown great potential as one of the solutions in the production of chemicals by harnessing renewable solar energy from the sun. In recent years, extensive research has been done for photocatalytic (PC) processes with semiconducting metal oxides as potentially efficient, low cost, and environmentally friendly catalysts for AP to produce solar chemicals. We have synthesized and fully characterized a mesoporous bismuth vanadate-copper oxide-silica semiconductor nanocomposite (SiO2/BiVO4/CuOx) to act as a chromophore in a Z-scheme system for effective light harvesting and charge separation in the synthesis of solar chemicals. Notably, the SiO2/BiVO4/CuOx nanospheres perform seven times faster than bulk BiVO4 and provide higher yields for oxidative coupling of amines to imine products. The superior photocatalysis of SiO2/BiVO4/CuOx is attributed to the surface CuOx nanoparticles that increase the average PL lifetime from 2.3 to 4.5 ns, which improved the charge separation and decreased the unproductive recombinations of electron-hole pairs. To the best of our knowledge, this is the first report of uniform nanoparticulate BiVO4/CuOx catalysts that absorb light via a Z-scheme for photoredox organic synthesis. We envision that this work will pave the way for the use of more ideas from AP in the synthesis of fine chemicals, agrochemicals, and active pharmaceutical ingredients. Apart from being a photocatalyst, SiO2/BiVO4/CuOx nanospheres and various metal oxides including titanium dioxide (TiO2), cerium oxide (CeO2), and tungsten oxide (WO3) can be employed as light harvesting supports for the immobilization of molecular complexes to enhance the performance of their homogeneous molecular counterparts. An oxidatively stable anchoring group, maleimide, is shown to form covalent linkages with surface hydroxyl functionalities of metal oxide nanoparticles by photoclick chemistry. Definitive evidence of the active site molecular structure was achieved from a broad range of characterization techniques. The hybrid nanomaterials function with essentially quantitative oxidative conversions of internal and terminal alkenes with molecular selectivity, but can operate in a broader range of solvents, including more eco-friendly ones. In conclusion, a novel photocatalyt SiO2/BiVO4/CuOx was successfully fabricated and tested in this project. Apart from being a photocatayst, SiO2/BiVO4/CuOx has the potential to function as a light harvesting support for the immobilization of molecular complexes that can synergize the benefits of both homogeneous and heterogeneous catalysts and enhance the PC performance.