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Fundamental studies on solar-activated zeolite-supported photocatalysts for water splitting application

University of British Columbia

Robust calculations show that the incidence of solar energy on the earth’s surface by far exceeds all human energy needs. Undoubtedly, the most trusted way of utilizing solar energy is to convert and store it in the form of an energy carrier such as hydrogen. Semiconductors capable of absorbing light energy so-called photocatalysts can potentially drive water splitting reaction for hydrogen generation. In this research, fundamental studies on a new class of solar-activated supported photocatalysts for water splitting application are presented. This resulted in significantly higher rates of H₂ production in comparison to the existing supported TiO₂ series under visible light. The composition comprises silico-aluminates (zeolite) as the support, titanium dioxides (TiO₂) as the semiconductor, cobalt compounds as hydrogen evolution sites and heteropolyacids (HPAs) as multifunctional solid acids with excitability under visible light. Using this composition, I ended up with at least 2.6 times higher hydrogen evolution rates under visible light in comparison to Degussa P25, the best commercially available titania product. The chemical point of view of this successful combination was investigated, attributing the higher photocatalytic activity of the synthesized chemical compositions to the basicity of the matrix. The more basicity properties besides HPA presence can overcome the negative impacts of titania interactions with the zeolite which are band gap widening and anodic shift of the TiO₂ band edges. Furthermore, the effect of cobalt precursors (nitrates and chlorides) on the photocatalytic activity of the prepared photocatalysts was also investigated. Although nitrate-based photocatalysts exhibited an improvement in the UV-VIS absorbance spectra toward visible light, they caused an almost 30% lower H₂ production rate in comparison to the chloride salts. Overshadowing the poisoning and parasitic effects of Cl⁻ anions on the photooxidation sites in the zeolite-supported composition was another notable outcome of this study. This suggests emulation of the core-shell photocatalysis concept insofar with providing a reasonable distance between redox sites. The results indicate the importance of zeolite’s structural and chemical properties as the photocatalyst support. This can be addressed through the selection of suitable zeolite types, taking an important step in the development of visible-light-activated photocatalysts based on earth-abundant materials.

Text

2012-06-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42578

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/