Type
Text
Type
Dissertation
Advisor
Parise, John B | Gersappe, Dilip | Koga, Tadanori | Whitaker, Matthew L.
Date
2017-05-01
Keywords
Materials Science -- Chemistry -- Inorganic chemistry | Ammonolysis, Band Gap, High Pressure Synthesis, Oxynitride, Photocatalysis
Department
Department of Materials Science and Engineering
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76136
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Solar water splitting, a photocatalytic process where water is directly split into hydrogen and oxygen using sunlight absorbing semiconductor materials, is one of the most sought after methods to make hydrogen economy a reality. Oxynitrides containing d0 and d10 cations tend to have the appropriate band structure required for solar water splitting. So far, reported efficiencies are not high enough for practical use and synthesizing an oxynitride showing high enough efficiency remains necessary. In this dissertation, we discuss the synthesis of oxynitrides and studying their optical and photocatalytic properties with a particular emphasis on utilizing exploratory high pressure synthesis. High pressure synthesis is an interesting route to synthesize oxynitrides as this can stabilize reactants that tend to decompose at ambient pressure, helping to achieve the intended stoichiometry. For synthesis, we selected candidate compositions from published theoretical studies. Reactions were carried out at pressures around 1-3 GPa and at temperatures up to 1300⠰C in a multi-anvil large volume press. Phase changes were observed with in situ X-ray scattering. In these experiments, we found that most d0 and d10 cations tend to reduce in the high pressure reaction environment as temperature increases, but Zr4+, Hf4+, and Ta5+ tend to retain their oxidation state. This information will be helpful in future theoretical studies to accurately predict stable oxynitrides synthesizable at high pressure. We synthesized (GaN)1–x(ZnO)x solid solution in the entire composition range at 1 GPa, 1150⠰C. The material showed photocatalytic H2 evolution activity even without surface modification with co catalysts, first such observed for this system. The minimum band gap of 2.65 eV and the highest H2 evolution activity of 2.31 μmol/h were observed at x = 0.51. On our initial investigation on the synthesis of gallium oxynitride spinel (Ga3O3N3) at high pressure, we found that the material could be formed by direct ammonolysis of gallium nitrate hydrate at ambient pressure. The formed product was nanocrystalline and exhibited an indirect band gap of 2.5 eV. The material photocatalytically evolved H2 at an initial rate 8 μmol/ h, but the activity diminished after five hours due to degradation forming gallium oxide hydroxide. | 107 pages
Recommended Citation
Dharmagunawardhane, Hingure Arachchilage Naveen, "Synthesis of oxynitride materials for solar water splitting: investigations with ambient pressure and high pressure synthesis techniques" (2017). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2084.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2084