During the past several decades, nanotechnology and nanoscience have developed extensively in a variety of areas such as catalysis, pharmaceutical, energy conversion, and energy storage. This thesis research focuses on increasing fundamental understanding on the influence of two-dimensional (2D) semiconducting nanomaterials (graphene quantum dots, GQD) on the catalytic activity and selectivity of water-soluble palladium nanoparticles (PdNP) for alkene hydrogenation and 4-nitrophenol reduction.
The PdNP catalyst showed low catalytic activity toward the hydrogenation of hydrophobic alkene (1-octene) and allylic alcohol (1-octen-3-ol). Despite the micellar characteristics of -carboxylatehexanethiolate-capped PdNP, the biphasic reaction condition where the catalysts are in aqueous phase, while the substrate is in organic phase leads to limited reaction interface and poor catalysis results. While the activity of PdNP/GQD remains low, the selectivity of PdNP/GQD hybrid differs from that of PdNP producing more hydrogenation product. The changed electronic property of PdNP upon electron transfer from GQD or the chemical interaction of GQD with substrate is considered to be a contributing factor to this different catalytic selectivity.
The PdNP catalyst showed, however, good catalytic activity toward 4-nitrophenol reduction in the presence of NaBH4 in water. The reduction of 4-nitrophenol with 0.5 mol% PdNP reached 94% conversion in just 5 min. The presence of GQD had a negative influence on 4-nitrophenol reduction requiring at least 10 min for the reduction to complete. The reduced catalytic activity could be explained by two possible mechanisms. First, the preferential adsorption of 4-nitrophenol on GQD by molecular interactions (electrostatic and pi-pi interactions) lengthens the diffusion time for 4-nitrophenol to PdNP. Second, the static interaction of PdNP and GQD decreases the amount of active surface of PdNP for 4-nitrophenol reduction.
GQD exhibits the blue fluorescence emission property under UV light indicating the presence of excited electrons in aqueous environment. The catalytic activity of PdNP/GQD under UV light was, however, unchanged compared to that of PdNP/GQD under natural light for 4-nitrophenol reduction. The similar catalytic activity toward 4-nitrophenol reduction by PdNP/GQD with and without UV light indicated that the contribution of excited electron transfer to PdNP is insignificant.
|Commitee:||Derakhshan, Shahab, Tavassol, Hadi|
|School:||California State University, Long Beach|
|Department:||Chemistry and Biochemistry|
|School Location:||United States -- California|
|Source:||MAI 82/2(E), Masters Abstracts International|
|Subjects:||Chemistry, Nanoscience, Nanotechnology|
|Keywords:||Semiconducting nanodiscs , Colloidal catalysis, Palladium nanoparticles, Water|
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