Jonathan P. Blitz

Fundamental and applied aspects of chemically modified surfaces

Siloxane-anchored monolayers as templates for oxide film deposition synthesis and characterization of self-organized microstructures with chemically active surfaces and evaluation of their technical utility Thiol-modified phthalocyanines and their self-assembled monolayers on gold surfaces modification of particle surfaces by grafting of functional polymers grafting processes studied with a nanotip - silane molecules and polymers grafted on silica and silanized silica surfaces multilayer dendrimer-poly(anhydride) nanocomposite films conductivity enhancement of polymer composites through admicellar polymerization of pyrrole on particulate surfaces filler surface characterization and its relation to mechanical properties of polymer composites grafting of crystalline polymers onto carbon black surface and its application for gas sensors surface modifications to support materials for HPLC, HPCE and electromatography synthesis, characterization and application of new bonded phases for HPLC microscale synthesis and screening of combinatorial libraries of new chromatographic stationary phases the alkylation of drugs at ion exchange sites on the surface of solid phase extraction columns connection between surface modification of fumed silica, its particle size distribution, and electrophoretic mobility in aqueous suspensions highly efficient acid-gas-removing shaped fibre filters maximizing the extent of hexamethyldisilazane reaction with silica - an experimental design study surface modification of highly dispersed titania/silica, and efficiency of their applications surface modification of micron-size powders by a plasma polymerization process effect of water plasma on silica surfaces - synthesis, characterization and applications. (Part contents)

Structural and adsorption characteristics and catalytic activity of titania and titania-containing nanomaterials.

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.

Functionalized O-alkyldithiocarbonates: a new class of ligands designed for luminescent heterometallic materials.

The new ligand 4-PyCH(2)OCS(2)Na, that combines two different donor groups in one molecule (a soft -CS(2)(-) group and a hard pyridine moiety), has been synthesized. The ligand coordinates to a [(bipy)Re(CO)(3)](+) center in a monodentate fashion through one of its soft sulfur atoms, leaving the hard pyridine terminus free for further coordination chemistry. Using a Ni(II) dithiophosphonate linker, the heterometallic {[CH(3)OCH(2)CH(2)OP(An)S(2)](2)Ni}[4-PyCH(2)OCS(2)Re(bipy)(CO)(3)](2) complex is obtained, through the coordination of two pyridine groups to the Ni(II) center. This simple, high-yield stepwise strategy toward heterometallic complexes could be easily transferable to other 1,1-dithiolate ligands and used in combination with a large variety of luminescent metallic systems.

Post-synthesis surface-modified silicas as adsorbents for heavy metal ion contaminants Cd(II), Cu(II), Cr(III), and Sr(II) in aqueous solutions.

To analyze the influence of silica surface modification and confined space effects on specific interactions of divalent and trivalent metal cations with surface functionalities, three different high surface area silicas with different pore size distributions were modified with the following organosilanes: 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-(trimethoxysilylpropyl)diethylenetriamine, N-(triethoxysilylpropyl)ethylenediaminetriacetic acid (EDTrA), and 3-(2,4-dinitrophenylamino)propyltriethoxysilane. The silicas were characterized by N(2) adsorption and reflectance FTIR spectroscopy before and after surface modification. N(2) adsorption and pore size distributions showed an increase in the pore width for all EDTrA-modified silicas, opposite to what occurred with the other organosilanes. Adsorption isotherms of Cd(II), Cr(III), Cu(II), and Sr(II) obtained from aqueous solutions were compared and analyzed by silica type, organosilane functional group, and metal adsorbed. Reflectance FTIR spectroscopy was used to probe the acetate functionality in EDTrA as a function of adsorbed metal content. A band shift to higher energy for Cr(III) on the wide pore silica studied indicated that the interaction with the acetate groups can be probed in this manner. In general, the wider pore distribution silica provided larger adsorption maxima, whereas the narrower pore distribution silica provided more favorable ΔG because of stronger binding of the cations. Cr(III) and Cu(II) exhibited larger adsorption maxima compared to Cd(II) and Sr(II), with the grafted organosilanes studied since the first cations have a greater charge/radius ratio than the second ones that provide a greater binding energy.

Cage-like mesoporous organosilicas with isocyanurate bridging groups synthesized by soft templating with poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) block copolymer

Ordered large-pore organosilicas with isocyanurate bridging groups were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS) in the presence of poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) (EO(39)BO(47)EO(39)) B50-6600 template under acidic conditions. It was shown that the extraction of the B60-5500 triblock copolymer with acidified ethanol solution was insufficient to remove completely the template; however, calcination of as-synthesized and extracted samples under air atmosphere at 200 degrees C, 250 degrees C and 300 degrees C caused not only the removal of the polymer but also a substantial decomposition of the ICS groups. In contrast, the heat treatment of extracted organosilicas at 360 degrees C in flowing nitrogen was able to fully remove the residual template without degradation of the ICS bridging groups. Characterization of the resulting materials by small angle X-ray scattering (SAXS) and X-ray powder diffraction (XRD) revealed that isocyanurate-containing organosilicas have a body-centered cubic symmetry (Im3m). Argon adsorption-desorption isotherms of these organosilicas revealed cage-like mesopores, high surface areas and large pore volumes. The diameters of spherical cages were found to be very uniform in the range of 12-14 nm. A complete removal of triblock copolymer was confirmed by high-resolution thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR) and CHNS elemental analysis (EA). The latter showed that the isocyanurate rings are intact in the framework and their loading is up to 1 mmol g(-1). Moreover, these organosilicas were also synthesized using low acid concentration, double amount of polymer and sodium chloride; in this case the template was completely extracted and there was no need for additional heat treatment.

Kinetics and computational studies of an aminosilane reaction with a silsesquioxane silanol.

The reaction between (3-aminopropyl)dimethylmethoxysilane (APDMS) with silica and silsesquioxane 3,5,7,9,11,13,15-heptacyclopentylpentacyclo[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxan-1-ol was studied in hexane and tetrahydrofuran (THF) using experimental (reaction kinetics, FTIR) and quantum chemistry methods. In hexane at temperatures above 245 K, the reaction rate decreases with increasing temperature due to a reduction of prereaction complex formation at higher temperature. Below 245 K the reaction itself is rate limiting, resulting in a reaction rate decrease with decreasing temperature. The reaction occurs much faster in hexane than in THF in part because of stronger competitive effects of the O-containing polar solvent with the formation of APDMS/silsesquioxane prereaction complexes due to hydrogen bonding. Analysis of the experimental data and computational results suggest that the catalytic reaction is second-order with respect to APDMS, the second APDMS molecule plays the role of catalyst. Estimation of the activation energy using dynamic calculations give results much more in agreement with experiment than nondynamic calculations, since the limiting H(+) transfer stage occurs so quickly (approximately 15 fs) that displacements of other atoms are insignificant to the activation energy.

Interfacial phenomena at a surface of partially silylated nanosilica.

Unmodified pyrogenic silica PS300 and partially silylated nanosilica samples at a degree of substitution of surface silanols by trimethylsilyl (TMS) groups Θ(TMS)=27.2% and 37.2% were studied to elucidate features of the interfacial behavior of water adsorbed alone, or co-adsorbed with methane, hydrogen, or trifluoroacetic acid (TFAA). In the aqueous suspension modified PS300 at Θ(TMS)=37.2% forms aggregates of 50-200 nm in size and can bind significant amounts of water (up to ∼5 g/g). Only 0.5 g/g of this water is strongly bound, while the major fraction of water is weakly bound. The presence of surface TMS groups causes the appearance of weakly associated water (WAW) at the interfaces. The adsorption of methane and hydrogen onto TMS-nanosilica with pre-adsorbed water (hydration degree h=0.05 or 0.005 g/g) increases with increasing temperature. In weakly polar CDCl3 medium, interfacial water exists in strongly (SAW, chemical shift δ(H)=4-5 ppm) and weakly (δ(H)=1-2 ppm) associated states, as well as strongly (changes in the Gibbs free energy -ΔG>0.5-0.8 kJ/mol) and weakly (-ΔG<0.5-0.8 kJ/mol) bound states. WAW does not dissolve TFAA but some fraction of SAW bound to TMS-nanosilica surface can dissolve TFAA.

Reactions of palladium acetate in alkali chlorides studied by variable-temperature DRIFTS and mass spectrometry

Diffuse reflectance spectroscopy in the mid-infrared region (DRIFTS) has become an accepted technique for the analysis of powdered materials. With the advent of commercially available accessories to control atmosphere and temperature, variable-temperature (VT) DRIFTS is now used for the in situ study of a variety of chemical and catalytic reactions. We have used VT-DRIFTS, coupled both on-line and off-line with mass spectrometric detection of volatile reaction products, for the study of a variety of systems. This work has shown that the alkali halide diluent, normally KCI, can have a profound effect on the chemical reactions under study. This report describes results which illustrate the effect of various alkali chlorides on the reaction of palladium acetate [Pd(OAc)2] with an ethylene/oxygen mixture. This system is of interest to us as a model for the palladium catalyzed synthesis of vinyl acetate.

Model Silica Supported Olefin Polymerization Catalysts

Chemically modified silica surfaces have been synthesized and characterized as model olefin polymerization catalysts. By variation of silica gel pretreatments, TiC14 can be reacted with various surface bonding geometries. Most surface characterization was done acing diffuse reflectance FTIR spectroscopy. The TiC14 reacted silica gels, after reaction with Al(Et)3, give catalysts which polymerize ethylene and 1-butene with different activities and comonomer incorporation.