Waterhouse, GeoffreyXia, Bangwei2021-01-132021-01-132020https://hdl.handle.net/2292/54204Full Text is available to authenticated members of The University of Auckland only.Graphitic carbon nitride (g-C3N4) is a polymeric semiconductor material which can readily be synthesized by the thermal condensation polymerization of melamine or urea at temperatures around 550 ℃. Owing to its narrow band gap (Eg = 2.6-2.8 eV) and favorable valence band and conduction band levels (+1.6 V and -1.1 V, respectively), g-C3N4-based photocatalysts are been actively pursued for H2 production under visible light. This research project aimed to examine the effect of g-C3N4 morphology on the performance of Pt/g-C3N4 photocatalysts for photocatalytic hydrogen evolution in 10:90 triethanolamine:water mixture under visible light (λ > 420 nm). Firstly, g-C3N4 photocatalysts in the form of nanosheets were synthesized via heating melamine or urea to 550 ℃, and holding at this temperature for 4 h. Experiments were conducted in air (A) or an N2 flow (N), with the obtained g-C3N4 photocatalysts being denoted here as ACN-urea, ACN-melamine, NCN-urea and NCN-melamine, respectively. To prepare the g-C3N4 nanotubes, melamine:urea mixtures in different weight ratios of 1:10, 1:8, 1:6, 1:4; 1:2 and 1:1 were used. On heating, these formed supramolecular complexes which guided nanotube synthesis (the obtained photocatalysts synthesized in air or N2 are denoted here as ACN-x and NCN-x respectively). As the amount of melamine in the precursor mixture increased, the aspect ratio in the g-C3N4 nanotubes decreased. Detailed characterization studies using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, elemental analysis (C,H,N,O), and UV-visible spectroscopy determined that all the g-C3N4 photocatalysts were crystalline/nanocrystalline and Nrich, with electronic band gaps in the range 2.6-2.8 eV, thus allowing photoexcitation at wavelengths below 460 nm. Next, the various g-C3N4 supports (both ACN-x and NCN-x series) were decorated with Pt nanoparticles at a nominal Pt loading of 5 wt.%. This was achieved in a two-step process involving the adsorption of cationic Pt species on the surface of the photocatalysts using a deposition-precipitation with urea method, followed by a H2 reduction step at 550 ℃ to reduce the cationic Pt species to Pt0 nanoparticles. The Pt/g-C3N4 photocatalysts were then systematically characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and other various standard methods (XRD, FT-IR, N2 physisorption, UV-vis, photoluminescence and elemental analyses). TEM revealed that the average size of Pt nanoparticles in most samples was ~1.6 nm, with the nanoparticles generally being well-dispersed over the g-C3N4 supports. Pt deposition did not alter the structure or electronic properties (e.g. band gap) of the g-C3N4 photocatalysts, though dramatically improved the H2 production performance.H2 production tests were conducted on all the Pt/ACN-x and Pt/NCN-x photocatalysts in a mixture of 10 vol.% triethanolamine and 90 vol.% Milli-Q water under 300 W Xe lamp irradiation (λ > 420 nm). In general, the nanotube-based photocatalysts prepared at the melamine:urea weight ratio of 6:1 offered the best H2 production performance (rates > 5 mmol g-1 h-1), representing some of highest rates yet reported for Pt/g-C3N4-based photocatalysts. The optimized nanotube-based photocatalysts outperformed photocatalyst based on g-C3N4 nanosheets. Results suggests that g-C3N4 nanotubes may be advantageous compared to g-C3N4 nanosheets for photocatalyst H2 production.Restricted Item. Full Text is available to authenticated members of The University of Auckland only.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmhttps://creativecommons.org/licenses/by-nc-sa/3.0/nz/Thesis2021-01-01Copyright: the authorQ112954389