Photocatalytic oxidation of alcohols in the presence of plasmonic metals using
oxygen as oxidizing agent is considered as a promising approach for efficient and green
chemical transformations under mild conditions. In this direction, this Thesis
demonstrates the synthesis of commercially valuable products such as benzaldehyde via
the development of plasmonic-based nanomaterials as photocatalysts, along with design
of continuous flow reactor, enabling high reaction rate and high selectivity of formed
carbonyl compounds.
Initially, the current state of photocatalytic oxidation of alcohols is summarized, the
importance and fundamentals of plasmonic metal nanoparticles is presented while
challenges and research gaps of the field are highlighted. Three experimental strategies
were adopted in the Thesis. The first experimental part of the thesis focused on
understanding the plasmonic heating effect generated by Au nanoparticles and
particularly the surface plasmon resonance of Au nanoparticles by performing a well controlled experiment using a continuous flow system. The results revealed a significant
temperature rise of Au-based nanofluids, with different Au loadings, compared to bare
TiO2 nanofluid or pure water, which arise from the localized surface plasmon resonance
effect of Au nanoparticles.
The second experimental part of the thesis aimed to investigate the performance of
plasmonic Au nanoparticles decorated on Cr2O3 microspheres towards the
photocatalytic oxidation of benzyl alcohol. It has been shown that the amount of Au
loading affected significantly the reaction efficiency, with 1.18 wt.% of Au loaded
photocatalyst converting 81.4% of benzyl alcohol to benzaldehyde with a selectivity of
98.3% after 3 hours of laser irradiation. Additionally the plasmonic heating effect of Au
nanoparticles contributed to a 26% oxidation rate enhancement using 1.18 wt.% Au.
In the third experimental part, the effect of incorporating a second noble metal like
Ag as well as the fabrication of a continuous flow reactor for comparison with a typical
batch reactor were demonstrated. Bimetallic 0.34Ag-1.21Au/Cr2O3 photocatalyst
converted 92.4% of benzyl alcohol to benzaldehyde with 98.8 % selectivity, which is
4.5 times that of pure Cr2O3 and 1.3 times of monometallic 1.18Au/Cr2O3. The results
showed that the reaction rate under continuous flow conditions was almost an order of
magnitude superior to the values achieved using batch reactor. Therefore, the findings
of this Thesis highlight the need for development and optimization of continuous flow
synthesis of carbonyl compounds in the presence of plasmonic metals, which can favour
the conversion of alcohols in terms of reaction rate and selectivity
