Vanadosilicate Mesoporous SBA-15 Molecular Sieves Incorporated with N-Alkylphenothiazines
| Autor: | Jae Young Bae, Larry Kevan, Zhaohua Luan |
|---|---|
| Rok vydání: | 2000 |
| Předmět: |
chemistry.chemical_classification
General Chemical Engineering Inorganic chemistry Vanadium chemistry.chemical_element General Chemistry Mesoporous silica Molecular sieve Vanadium oxide Square pyramidal molecular geometry law.invention chemistry law Materials Chemistry Electron paramagnetic resonance Mesoporous material Alkyl |
| Zdroj: | Chemistry of Materials. 12:3202-3207 |
| ISSN: | 1520-5002 0897-4756 |
| DOI: | 10.1021/cm000318q |
| Popis: | Mesoporous silica SBA-15 molecular sieves have been incorporated with various amounts of vanadium via incipient-wetness impregnation with vanadium oxide triisopropoxide in hexane followed by calcination. The products (VSBA-15) have been characterized by nitrogen adsorption and diffuse reflectance UV-visible and electron spin resonance spectroscopies. The results show that the vanadium exists as isolated tetrahedral V 5+ ions in dehydrated VSBA-15 with Si/V ≥ 40 while vanadium chains develop as vanadium loading increases. Upon hydration a large fraction of the vanadium is transformed to square pyramidal and distorted octahedral V 5+ ions by additional coordination to water molecules, suggesting an interior wall surface location for these V 5+ ions. Upon CO reduction or incorporation of N-alkylphenothiazines (PC n ), part of the V 5+ is reduced to vanadyl VO 2+ ions. While incorporation of PC n into VSBA-15 in the dark generates some PC n + cation radicals, ultraviolet photoionization at room temperature further increases the yield for Si/V = 80 and 40. The PC n + radicals are more stable in VSBA-15 than in siliceous SBA-15, and the photoyield increases with vanadium loading. The photoyield and stability of PC n + also increase with increasing alkyl chain length of the N-alkylphenothiazines. |
| Databáze: | OpenAIRE |
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