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RISS 인기검색어
- 검색키워드
- 저자 : Tongying, Pornthip (검색결과 2 건)
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Nano-hetero functional materials for photocatalytic hydrogen generation
Tongying, Pornthip University of Notre Dame 2015 해외박사(DDOD)
This dissertation focuses on designing nanomaterials and investigating their photocatalytic response for H2 generation. Hydrogen has gained a lot of attention as a new source of sustainable energy. It can be used to directly generate power in fuel cells and to produce liquid fuels such as methanol. Water splitting is an ideal (clean) way of producing H2 because it uses water and sunlight, two renewable resources. To explore the use of nanostructures and particularly nanostructure heterojunctions for photocatalytic H2 generation, four different systems have been synthesized: (i) CdSe nanowires (NWs), (ii) CdSe/CdS core/shell NWs, (iii) CdSe NWs decorated with Au or Pt nanoparticles, and (iv) CdSe/CdS NWs decorated with Au or Pt nanoparticles. This is motivated by (a) the fact that CdSe NWs absorb light from the UV to the near infrared (b) the NW morphology simultaneously enables us to explore the role of nanoscale dimensionality in photocatalytic processes (c) a CdS coating can enhance photogenerated carrier lifetimes, and (d) metal nanoparticles are catalytically active and can also enhance charge separation efficiencies. Charge separation and charge transfer across interfaces are key aspects in the design of efficient photocatalysts for solar energy conversion. Femtosecond transient differential absorption (TDA) spectroscopy has been used as a tool to reveal how semiconductor/semiconductor and metal/semiconductor heterojunctions affect the charge separation and hydrogen generation efficiencies of these hybrid photocatalysts. The use of this technique in concert with hydrogen evolution tests also reveal how CdS, CdSe and metal NP interact within metal NP decorated CdSe and CdSe/CdS NWs during photocatalytic hydrogen generation reactions. Electron transfer events across both semiconductor/semiconductor and metal/semiconductor heterojunctions are followed to identify where H 2 is evolved and the role each heterojunction plays in determining a system's overall efficiency. To extend my study beyond 1D CdSe NWs, 2D CdSe nanosheets (NSs) have been synthesized. The use of cation exchange allows synthesizing micrometer-sized crystalline thin CdSe nanosheets (NSs), otherwise difficult to produce directly through solution-based methods. Starting from cubic-phased Cu2-xSe NSs as a template, CdSe NSs are obtained by cation exchange of copper to cadmium. This exchange reaction preserves the 2D morphology of the starting NSs and also retains the cubic crystal structure. Resulting CdSe NSs have a lateral size up to 6 mum and an average of thickness approximately 6 nm. Such large lateral dimensions are advantageous for single sheet optical measurements and for applications in optical and electronic devices.
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