The Eastern Illinois University Chemistry Department has a Master's program usually with about ten graduate students enrolled at any given time. Undergraduates are also encouraged to participate in research. Thus in the large scale of things my program is a relatively modest affair, but we do what we can to make a contribution. A list of publications relating to the work described below is provided in my CV.
Organosilane-modified Silica Surfaces
The chemical modification of silica surfaces using organofunctional silanes is important for the synthesis of materials with a wide range of useful properties. We have put our efforts into understanding the kinetics and mechanism of these reactions from organic solution in heterogeneous phase. In studying the reaction of methymethoxysilanes with silica it was found that the direct condensation of unhydrolyzed silane with silica surface silanols does not occur at room temperature.
Si(s)-OH + (CH3)3SiOCH3 --> No reaction
With surface adsorbed water present however a small amount of reaction occurs as a result of methoxysilane hydrolysis followed by reaction with silica surface silanols.
Si(s)-OH + Surface H2O
+ (CH3)3SiOCH3 --> (CH3)3SiOH
(CH3)3SiOH + Si(s)-OH --> Si(s)-O-Si(CH3)3 + H2O
When this reaction is carried out in the presence of an
amine a strong catalytic effect is observed. We have determined that the
amine adsorbs onto the relatively acidic surface silanols rendering the oxygen
attached to the surface silicon atom highly nucleophilic. This oxygen
then attacks the relatively electrophilic silane silicon resulting in surface
silylation. This work was published in the later 1980's in JACS and the
J. Colloid Interface Sci. It has been widely accepted and applied to a
variety of industrial processes.
After a multi-year hiatus we have come back to work in this field. Currently our work involves developing realistic models to understand the kinetics of these silica surface silylation reactions. New insights into the reasons for the general behavior of an initial fast reaction, followed by a slower uptake over a period of hours and days, were obtained. Details can be found in the J. Colloid Interface Sci. paper published in 2000. This project has continued using homogeneous organosilanol and silsesquioxane solution models to understand the kinetics of silylation of various surface functional groups. This project along with computational modeling has yielded some very interesting results which will be submitted for publication in the near future.
Another project involves synthesizing modified fumed silica and silica gel surfaces with a variety of organosilanes to different extents. These materials were then characterized by nitrogen adsorption and other methods, the results theoretically modeled to determine physical characteristics of these modified surfaces. This work, in collaboration with Vladimir Gun'ko and others, has resulted in a number of publications since 2002. This work has been extended to study the chelation of metal ions in aqueous solutions, the results of which were presented and published at a NATO Advanced Research Workshop in 2005 in
Chemically modified silica surfaces as olefin polymerization catalysts
Silica supported olefin polymerization catalysts are used in industrial processes to make millions of pounds of polyolefins each year. Very little work has been done to understand how the nature of the silica gel surface can be used to modify the structure and behavior of these catalysts. This work takes the view that the silica gel surface is a reagent in the catalyst synthesis, not simply an inert high surface area "rock" to support polymerization active species. We have found that by variation of silica gel surface chemistry different metals can be reacted with the surface with different structures. This provides a method to study the role of structure on catalytic properties for these technically relevant systems.
The silica gel surface consists of both non-hydrogen bonded and hydrogen bonded surface hydroxyl (silanol) groups, easily detected and differentiated by diffuse reflectance infrared spectroscopy. Heating the silica to 600oC condenses the hydrogen bonded silanols leaving the non-hydrogen bonded silanols available for further reaction.
/ / / 600oC /
O O O -----> O O + H2O (g)
| | | | / \
Si Si Si Si Si Si
If silica gel is reacted with hexamethyldisilazane (HMDS), the HMDS reacts
primarily with hydrogen bonded silanols leaving the non-hydrogen bonded
silanols available for further reaction.
H H H Si H H
/ / / HMDS | / /
O O O -----> O O O
| | | | | |
Si Si Si Si Si Si
Also, if the 600oC silica is reacted with hexamethyldisilazane,
then a silica gel with no surface silanols is synthesized.
/ HMDS |
O O -----> O O
| / \ | / \
Si Si Si Si Si Si
Reaction of these modified silica surfaces with reagents such as TiCl4, Mg(C4H9)2, Al(Et)3, BCl3 and other reagents provides the opportunity to examine how various species react with different groups on the silica gel surface. The first of these series of papers was pubished in 1992 in Colloids & Surfaces. Subsequent studies have been published in the Microchemical Journal (1996), Langmuir (1998), New Advances in Polyolefins, and The Journal of Physical Chemistry B (2005). This work has been a mainstay of our group for nearly 10 years, and a handful of publications remain to be completed, but we are not planning to focus our efforts here in the future.
Spectroelectrochemistry of Organometallic Cluster Compounds
This work was accomplished at the Chemistry Department at
A project jointly written by Prof. Doug Klarup of EIU and myself was funded by the NSF. This work utilizes inquiry based laboratories to emphasize the complementarity of various types of analytical instrumentation employed in Instrumental Analysis. Developed projects are discussed in more detail in the Instrumental Analysis section of this web site. Doug Klarup and I have also published a paper in the Journal of Chemical Education (2002) concerning an experiment which was developed using FT-IR to understand various aspects related to signal-to-noise ratio. Also two publications in 2006 with Dan Sheeran concern the use of an inexpensive diode array UV/Visible spectrometer, which we have found quite useful in a variety of undergraduate educational settings.