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Lewis acid mediated hydrosilylation of alkynes and alkenes on non-oxidized hydride-terminated porous silicon derivatizes the surface with alkenyl and alkyl functionalities, respectively. A very broad range of chemical groups may be incorporated, allowing for tailoring of the interfacial characteristics of the material. The reaction is shown to protect and stabilize porous silicon surfaces from atmospheric or direct chemical attack without compromising its valuable material properties such as high porosity, surface area and visible room-temperature photoluminescence. The reaction is shown to act on alkenes and alkynes of all possible regiochemistries (terminal and internal alkynes; mono-, cis- and trans-, di-, tri-, and tetrasubstituted alkenes). FTIR as well as liquid- and solid-state NMR spectroscopies show anti-Markovnikov addition and cis stereochemistry in the case of hydrosilylated terminal alkynes. Material hydrosilylated with long-chain hydrophobic alkynes and alkenes shows a substantially slower surface oxidation and hydrolysis rate in air as monitored by long-term FTIR monitoring and chemography. BJH and BET measurements reveal that the surface area and average pore size of the material are reduced only slightly after hydrosilylation, indicating that the porous silicon skeleton remains intact. Elemental analysis and SIMS depth profiling show a consistent level of carbon incorporation throughout the porous silicon which demonstrates that the reaction occurs uniformly throughout the depth of the film. The effects of functionalization on photoluminescence were investigated and are shown to depend on the organic substituents.

Two-dimensional 13 C solid-state nuclear magnetic resonance (2D SSNMR) spectroscopy was applied to the study of three conformational polymorphs of 5-methyl-2-((2-nitrophenyl)amino)-3-thiophenecarbonitrile. The separation of sidebands by order experiment (de Lacroix, S. F.; Titman, J. J.; Hagemeyer; A.; Spiess, H. W. J. Magn. Reson. 1992, 97, 435-443) allowed the separation of isotropic and anisotropic chemical shift information over two dimensions, making it possible to distinguish individual carbon atoms and analyze the full chemical shift anisotropy patterns using magic angle spinning (MAS) at moderate spinning speeds. The C-3 carbon of the thiophene ring, R to the nitrile carbon, was chosen to probe the differences in chemical environment between forms. The three forms exhibited a large variation in both measured and theoretically predicted isotropic and anisotropic chemical shifts for this carbon site. The results summarized in this paper demonstrate the utility in using 2D SSNMR methods for studying polymorphism in crystalline compounds with moderate molecular weights.

In situ solid-state NMR methodologies have been employed to investigate the photocatalytic oxidation of trichloroethylene (TCE) over two TiO2-based catalysts, Degussa P-25 powder and a monolayer Ti...

Environmental catalysts that can efficiently degrade hazardous chemicals are of growing importance. Among these, TiO2 photocatalysts show high potential for effective degradation of harmful species, particularly chlorine containing compounds, which are chemically persistent.1-3 TiO2 photocatalysts can display efficiencies (degradation rate/unit energy) that are 1-2 orders of magnitude higher than thermal catalysts, particularly for the low chlorocarbon concentrations often encountered.4 Gassurface experiments5-10 show that reactions occur both in the gas phase and/or on the surface of TiO2 catalysts and can involve the following radical initiators: O2, OH, and Cl. Although a number of studies have been carried out by means of GC,7-9 MS,6,8 and FT-IR,5-8,10 a detailed understanding of the reaction mechanisms remains elusive. In the present work, we report a new approach to the study of photocatalysis, namely in situ solid-state nuclear magnetic resonance (SSNMR) spectroscopy.11-13 SSNMR methods are advantageous because they allow a quantitative examination of the reactions on the catalyst surface as well as in the gas phase. We have characterized the reaction of trichloroethylene (TCE) over two types of TiO2 photocatalysts and have identified new intermediates in the complex surface chemistry. Figure 1 shows proton-decoupled 13C magic angle spinning (MAS) NMR spectra obtained from photooxidation of TCE in the presence of O2 and Degussa P-25 TiO2 powder.14 The NMR spectra show the degradation of TCE, the formation of dichloroacetyl chloride (Cl2CHCOCl, DCAC), CO, phosgene (CCl2O), and pentachloroethane (C2HCl5), and their conversion to the final product CO2. The narrow line widths of the peaks indicate that these species are very mobile and most likely exchange rapidly between the surface and the gas phase. Assignment of these intermediates are confirmed by comparing 13C NMR shifts for liquid samples reported in the literature15 or prepared in our lab and from proton coupled spectra during the photoreactions. Most of the intermediates identified above are in good agreement