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Access Type
WSU Access
Date of Award
January 2024
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Stephanie L. Brock
Abstract
Photocatalytic water splitting reaction is a promising method to produce hydrogen fuel, the fuel of the future that is estimated to substitute fossil fuels as the main energy source globally. However, the lack of efficient photocatalysts limits the production of hydrogen from the water splitting. In efforts to improve the efficiency of photocatalysts for hydrogen evolution reaction, we were motivated to evaluate CdS QD gels as photocatalysts and explore structure property relationships that improve the materials activity. This thesis shows the influence of the CdS crystal structure (zincblende, zb- vs. wurtzite, w-) on ~3.2-3.3 nm CdS QDs, with quick (16 h) thermodynamic aggregation of the wCdS QDs that deactivated the H2 production rate from from 1,221 (fresh) to 162 (16 h aged) µmol H2 h–1 g–1, while zbCdS QDs did not lose activity upon ageing, producing 1,458 µmol H2 h–1 g–1. The oxidative assembly of CdS QDs into QD gels was also evaluated, with the gels showing improvement of the materials catalytic activity: from 1,458 (QD) to 6,650 (AG) µmol H2 h–1g–1 on zbCdS and from 1,221 (QD) to 3,325 (AG) µmol H2 h–1g–1 on wCdS. Thermal processing the materials up to 250 °C improved even further their performance by increasing exciton delocalization effect, although annealing past 250 °C caused sintering and stark deactivation due to surface area loss. Producing composites made of Pt NPs with CdS QD gels showed good increase on the material performance. The 0.5% w/w Pt/CdS AG made with co-gelation method was the most active photocatalyst achieving 6,810 µmol H2 h–1 g–1, compared to 4,565 µmol H2 h–1 g–1 of the wet loaded 0.5% Pt/CdS AG and 3,690 µmol H2 h–1 g–1 of pure CdS AG. Additionally, small and ultrasmall CdS QDs and QD gels were synthesized, and both size-dependent electronic and structural properties were measured. Trap state recombination was found to be the most prominent recombination pathway in particles lower than 4.0 nm, and band edge recombination the most predominant in past 4.0 nm. The gels surface area was found to decrease with the QD diameter decrease as well. Data about the materials VBM and CBM are being studied to fully characterize the band structure of these materials.
Recommended Citation
Alevato Neves, Vinicius, "Cds Quantum Dot Aerogels: Exploring Structure-Property Relationships To Improve Photocatalytic Water Splitting Activity" (2024). Wayne State University Dissertations. 4131.
https://digitalcommons.wayne.edu/oa_dissertations/4131
