Date of Completion

2018

Thesis Type

College of Arts and Science Honors

Department

Chemistry

First Advisor

Dr. Christopher Landry

Keywords

heterogeneous, photocatalysis, catalysis, conjugated, semiconductor, photoluminescence

Abstract

Heterogeneous photocatalysts are of interest for their use in applications such as environmental remediation. WO3 is a known photocatalyst, and mesoporous WO3 offers a higher surface area than the bulk material, and thus a greater concentration of active sites. By covalently attaching 𝜋-conjugated organic molecules to the surface of metal oxides, sensitization of the semiconductor is possible through charge transfer between the molecule and the solid. In this work, mesoporous WO3 particles, synthesized via a hard-templating method from mesoporous SiO2, are modified by attachment of either folic acid or 3,3′′′-dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (DH4T) to the surface of the particles. Covalent attachment of these molecules to the metal oxide is achieved by use of a silane anchoring group, aminopropyltriethoxysilane (APTES), which attaches to the surface by a condensation reaction with the surface hydroxides. The amine group of APTES then allows for peptide coupling with FA or the carboxylated thiophene tetramer, DH4T-COOH, yielding WO3-APTES-FA or WO3‑APTES-DH4T. The optical properties of the synthesized materials were studied by photoluminescence (PL) spectroscopy under 405 nm laser excitation. WO3-APTES-FA showed no change in spectrum from WO3, possibly due to small surface concentration of the molecule, or the fact that 405 nm is not resonant with any electronic transitions of FA. WO3-APTES-DH4T showed an intense PL emission when excited at 405 nm. Fitting of the spectrum revealed contribution from the molecular emission, as well as transitions involving oxygen vacancy (OV) states in WO3. Photophysical mechanisms of the sensitization of WO3­ by DH4T are proposed, and possible implications for photocatalysis are discussed.

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