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Photocatalytic hydrogen production with supported Au and Au-alloy nanoparticles

Jones, Wilm Vincent 2016. Photocatalytic hydrogen production with supported Au and Au-alloy nanoparticles. PhD Thesis, Cardiff University.
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Photocatalytic reforming reactions of simple alcohols and amines have been studied as a method of hydrogen production. The reactions were carried out with synthesised catalysts consisting of noble metal nano-particles (NP) supported on semiconductor supports. The aim was to develop an alternative environmentally friendly approach to hydrogen production. Primarily catalysts were synthesised by the sol immobilisation method, which allows for the formation of a colloidal dispersion of noble metals in solution which can then be deposited onto the surface of an appropriate support. By exploring the parameters during the sol immobilisation method a standard synthesis procedure was decided upon and used throughout this thesis. This procedure allowed for the reproducible preparation of Au and Pd NPs in the order of ~ 3 nm as well as bimetallic AgAu and Pd Au NPs on the surface of a TiO2 support. The sol immobilisation method was used to prepare two sets of bimetallic AgAu NPs supported on TiO2 (P25). AgAu-TiO2 catalysts with a 1:1 weight ratio were prepared and they were found to be more active than the monometallic Au-TiO2 and Ag-TiO2. The most active of the AgAu-TiO2 catalysts was synthesised by first preparing a Au colloid followed by reduction of the Ag precursor onto the surface of the Au to make a core-shell structure NP. A second set of AgAu-TiO2 catalysts was prepared starting with Au NPs followed by deposition of a controlled shell thickness of Ag on the surface supported on TiO2, by three different methods. Characterisation for these samples was performed by X-ray absorption spectroscopy (XAS) techniques at the Diamond light source. The deposition of thin layers of Ag onto the preformed Au NPs results in the activity being poorer than the reference catalyst of Au-TiO2. Preparation of Au NPs supported on TiO2 with the subsequent deposition of thin layers of Pd onto the surface of the Au by three methods was also undertaken, and again characterised by XAS. Here all of the PdAu-TiO2 catalysts which were made exhibited improved activity over the reference samples tested. This improvement in H2 was attributed to the NPs having a Au core and PdAu shell on the surface of TiO2. Finally graphitic carbon nitride (g-C3N4) was investigated as a visible light active semiconductor for hydrogen production by photocatalytic reforming reactions. In recent years graphitic carbon nitride has gain interest as an alternative semiconductor support for photocatalytic reactions. Direct activity comparisons between Pd loaded g-C3N4 (urea derived) and TiO2 (P25) were undertaken by performing two sets of reactions under identical conditions. The results from these reactions show that under the full arc condition of the solar simulator (150 W Xe arc lamp) TiO2 was the most active, despite having a larger band gap (3.2 eV) compared to the g-C3N4 (2.8 eV). Also investigated was the choice of molecule being reformed (or hole scavenger) by Pd-TiO2 and Pd-C3N4 with triethanolamine and methanol compared, as well as a variety of simple amines.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 25 January 2017
Last Modified: 17 Jan 2022 13:41

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