Photocatalytic oxidation of organic compounds with nanocatalysts

Alhar, Munirah Sulaiman (2021) Photocatalytic oxidation of organic compounds with nanocatalysts. Doctoral thesis (PhD), University of Sussex.

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Abstract

This study focuses on the development of high efficiency nanostructures and their applications in the photocatalytic oxidations of organic molecules in a single phase and two phases.
Through in-situ precipitation techniques, cubic Ag3PO4 nanocrystals and particle Ag3PO4 were successfully synthesised. The precipitation method was used for the preparation of Ag3PO4 nanocrystals by reacting with Na2HPO4 and using ammonia as the mediate agent to control their morphologies. Furthermore, Ag3PO4/TiO2 nanocomposite containing a different proportion of TiO2-P25 and Ag3PO4 nanocomposites were synthesised. The optimal nanocomposites mixture ratio was determined by investigating their photocatalytic activities by photocatalytic degradation methylene blue. In addition, the relationship between the catalysts morphologies, stability and their photocatalytic activity were studied.
The indirect oxidation of benzyl alcohol (BA) to benzyl aldehyde (BAD) was investigated using Electrochemical (ECO) and Photocatalytic electrochemical oxidation methods (PECO) in two-phase reactions. For the ECO, the oxidation of BA to BAD under different conditions was achieved using a batch reactor set up and using stainless steel as electrodes. While for PECO, TiO2 nanotubes were synthesised via electrochemical anodization process in fluoride-containing organic electrolytes. Furthermore, the TiO2 nanotubes were used as photoanode for photocatalytic selective oxidation of benzyl alcohol to benzaldehyde. PECO showed higher BA conversion as well as BAD selectivity comparing to ECO.
Application of biphasic systems can significantly improve the selectivity production. Photocatalytic oxidation of BA to BAD using a TiO2 photocatalyst and Cl-ion as a radical mediator in a biphasic reaction method. An aqueous suspension of commercial TiO2 -P25 catalyst was used for the oxidation in a batch photo-reactor set up in the photocatalytic oxidation of BA to BAD. The effect of various reaction parameters and conditions on the TiO2 photo-reactivity were tested. The two phases (organic and aqueous) ratio plays an important role as well as the pH. The effect of catalyst loading, and different types of acid were also studied. The mechanism of the photocatalytic oxidation of BA to BAD was proposed. Finally, the effect phenyl-ring substitution groups on the photocatalytic activity were investigated. Borrowing hydrogen (BH) or hydrogen autotransfer (HA) methodologies were traditionally used for the production of amines from alcohols. This study investigated photocatalysis's feasibility as an alternative greener process for the N-alkylation of amines using TiO2-P25 as the photocatalyst. In the BH or HA process, hydrogen is extracted temporarily by alcohol to form corresponding the intermediate aldehyde or ketone by photocatalyst, making alcohol as an alkylating agent. By condensation with an amine in situ, such an intermediate is converted into an imine. Subsequent addition of converts the imine intermediate to the amine product with a newly formed C-N bond. Initial findings were positive, with low imine intermediate yields indicating that the photocatalytic reaction worked, but the benzylaniline effect was not observed. Optimization experiments were performed, where pH 2 was determined to be the optimal condition for BA oxidation. In addition, aniline was gradually added to the reaction mixture over time by a liquid pump. This controls the increasing feeding of aniline to react with the produced benzaldehyde to avoid aniline's excessive oxidation at the early stage. Finally, the final benzylaniline product was made by reacting with the H2 gas added into the reaction mixture. Therefore, the photocatalysis is established for the first time as a viable technique for amine N-alkylation.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry
Depositing User: Library Cataloguing
Date Deposited: 14 Sep 2021 09:09
Last Modified: 14 Sep 2021 09:09
URI: http://sro.sussex.ac.uk/id/eprint/101565

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