Studies of materials chemistry and heterogeneous catalysis by solid state NMR spectroscopy

My research interests are focused on the chemistry of surfaces and the study of advanced materials, primarily through the use of new high resolution solid-state NMR techniques. Some results in the area of environmental photocatalysis and thioborate based glassy fast ionic conductors are summarized below.

1. Environmental Catalysis
Heterogeneous semiconductor photocatalysis represents an emerging area of environmental catalysis with the broadly defined goal of efficiently detoxifying hazardous organic pollutants. UV initiated photooxidations of trichloroethylene, ethanol, and acetone over Degussa P-25 powder and a monolayer TiO2 catalyst dispersed on porous Vycor glass (TiO2/PVG) have been investigated using in situ solid-state NMR methodologies. 13C MAS NMR spectra obtained using an in situ optical MAS probe allow us to identify long-lived reaction intermediates and final products during the photo-reactions. The formation of surface-bound reaction intermediates was observed and identified via 13C CP/MAS experiments.

Selected Publications:
1.    S. -J Hwang, Chris Petucci, and Daniel Raftery, "In Situ Solid-State NMR Observations of Photocatalytic Surface Chemistry: Degradation of Trichloroethyulene" J. Am. Chem. Soc. Comm. 1997, 119, 7877.
2.    S. -J Hwang, Chris Petucci, and Daniel Raftery, "In Situ Solid-State NMR Studies of Trichloroethylene Photocatalysis: Formation and Characterization of Surface-Bound Intermediates" J. Am. Chem. Soc. 1998,  120, 4388.
3.    S. -J Hwang and Daniel Raftery, "In Situ Solid-State NMR Studies of Photocatalytic Oxidation of Ethanol:   Characterization of surface sites and their reactivities”  Catalysis Today, 1999, 49, 353.
4.    Sarah Pilkinton, Sonjon-Jong Hwang, and Daniel Raftery "Ethanol Photocatalysis on TiO2 Coated Optical Microfiber, Supported Monolayer, and Powdered Catalysts: An In Situ NMR Study", J. Phy. Chem. B. 1999, 103, 11152.

2. Fast Ionic Conductors

Thioborate glasses Na2S-B2S3 have high room temperature conductivity and so their potential utilization as solid state electrolytes is high. Glasses and polycrystals xNa2S + (1-x)B2S3 in the series have been prepared and studied by magic angle spinning (MAS) NMR and by two-dimensional multiple-quantum (MQ) MAS NMR of 11B and 23Na. These techniques, when applied at various magnetic fields and combined with computer simulations of the spectra, provide new insights into the structure of the polycrystalline samples. Based on NMR observations, a structural model of polycrystalline sodium dithioborate (x = 0.33) was first proposed. The MQMAS NMR method significantly enhanced the resolution in 11B spectra of xNa2S + (1-x) B2S3 glasses and proved instrumental in finding and identifying various structural units present within these materials as the modification of the B2S3 network progressed with increasing Na2S content.

Selected Publications:
1.    S.-J. Hwang, C. Fernandez, J.-P. Amoureux, J. Cho, S.W. Martin, and M. Pruski "Quantitative study of the short range oder in B2O3 and B2S3 by MAS and two- dimensional triple-quantum MAS 11B NMR." Solid State NMR , 1997, 8, 109.
2.   S.-J. Hwang, J.-W. Han, C. Fernandez, J.-P. Amoureux, J. Cho, S.W. Martin, and M. Pruski "Structural Study of xNa2S + (1-x) B2S3 polycrystallines and glasses by 11B and 23Na MAS and 2D-3Q MAS NMR spectroscopy"  J. Am. Chem. Soc. 1998, 120, 7337.

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