Environmental Chemistry

David E. Bergbreiter (Green Chemistry: Homogeneous Catalysis & Polymer Chemistry) In our group, undergraduates will help develop new strategies to use soluble polymers as catalyst supports. These new strategies and new ways of using existing catalysts have led to a general approach to homogeneous catalysis that minimizes waste, that minimizes by-product formation and that simplifies reaction workup - ideas and concepts that have been externally recognized as part of a mix of chemistry and technology called Green Chemistry. Undergraduates will synthesize new polymers or new polymer derivatives necessary for this work. They will characterize these polymers using a mixture of spectroscopic procedures. For the most part, these syntheses use established chemistry. Separate synthesis of ligands containing amino or carboxyl groups or of dyes that serve as surrogates for catalysts will be followed by attachment of these species to the reactive sites that have been included in the polymers. Undergraduates will then study catalysis, focusing on selectivity, recyclability and yield in standard transition metal or organocatalysis.

John W. Bevan (Environmental Chemistry: Investigations into the Greenhouse Effect) The control of greenhouse gas emissions and the reduction of potential global warming which would result is a research area of active interest. The semiconductor industry incorporates numerous low pressure operations during the manufacture of semiconductor wafers such as chemical etch which uses perfluorocompounds (PFCs i.e. CF4, CHF3, C2F6). Such PFCs are potent global warming compounds that are vital to the semiconductor industry but there are currently no alternative substitute chemicals to effectively replace them. Increasingly, these environmentally harmful compounds are emitted into the atmosphere where they can impact the climate for tens of thousands of years. In response to the US Climate Change Action plan, the industry is actively evaluating various options such as alternative chemistries, process optimization, recycle and recovery, and abatement. However, only abatement of exhaust emissions at individual semiconductor manufacturing tools appears close to providing an effective solution. We have developed an innovative non-thermal plasma based technology capable of treating PFCs for a specific etch process with destruction and removal efficiencies (DREs) >99.998 % under conditions commonly found in semiconductor manufacture (i.e. flow rates, pressures, compositions etc). These initial studies need to be generalized for application to all semiconductor manufacturing processes. This involves characterizing and optimizing the chemistry of the processes involved. Undergraduate students would be involved in quantitative analysis of initial and final products, and also reactive intermediates that are needed to model the fundamental physical chemistry of these non-equilibrium plasma processes using state-of-the-art spectroscopic techniques.

Donald J. Darensbourg (Green Chemistry) A major focus of our research program is the investigation of catalytic processes in environmentally benign media, namely liquid or supercritical carbon dioxide or water. These studies will provide ample opportunity for the training of undergraduates whose goals are either to enter industrial positions upon completing their degree or to further their education in graduate school in chemistry.  One area of study involves CO2/epoxide copolymerization to afford polycarbonates, where CO2 is both a reactant and solvent, we have uncovered soluble zinc phenoxide complexes that are very effective catalysts for this process. The undergraduate studentís involvement here will involve the synthesis and characterization (NMR, IR, X-ray crystallography) of catalysts and potential catalysts employing air- and moist-sensitive techniques. In addition carefully supervised high pressure polymerization reactions will be performed in stainless-steel reactors and polymer products analyzed by IR, NMR, and viscometry.

Jaan Laane (Spectroscopic Investigation of Nitrogen Oxides in Their Electronic Excited States) A major group of air pollutants consists of the NOX species of various nitrogen oxides (NO, NO2, NxOy, etc.) which undergo photochemical reactions and contribute to atmospheric smog. The photochemical processes take place in the electronic excited states of these molecules. Hence it is highly desirable to understand the nature of these states for the various nitrogen oxides and the reaction intermediates that are formed. A direct way of doing this involves the spectroscopic identification of the vibrational quantum states for the electronic excited states and then the determination of the potential energy surfaces which govern the photochemical changes. In this research both electronic absorption spectroscopy and laser induced fluorescence (LIF) spectroscopy will be utilized to investigate the various types of nitrogen oxide molecules in the gas phase. A high-resolution fourier transform spectrometer in conjunction with long-path multi-reflection cells will record the absorption spectra while a pulsed, tunable Nd:YAG driven optical paramagnetic oscillator (OPO) system will be used for the LIF studies. Both systems operate under computer control. Several computer programs will then be used to calculate the potential energy surfaces which play fundamental roles in controlling the photochemistry of these nitrogen oxides. This information will help to better understand the chemical reactions leading to air pollution and thereby will help to find remediation and prevention methods.

Stephen A. Miller (Chemistry of biorenewable feedstocks) The worldís consumption of fossil fuels is made up of two distinct components:  the combustion of fossil fuels for energy and the transformation of fossil fuel biomass into the worldís supply of chemical feedstocks.  Because 86% of the worldís energy supply is linked to the combustion of fossil fuels,  only minority amounts of petroleum, natural gas, and coal are reserved for the preparation of bulk, intermediate, and fine chemicals, which ultimately become important consumer products such as drugs and plastics.  Given our limited supply of fossil fuels, it is clear that chemists need to develop a new encyclopedia of reactions to transform renewable biomass sources into the bulk, intermediate, and fine chemicals upon which people depend. The Miller research group has recently begun a broad-based research project designed to utilize readily available organic molecules from Nature.  To date, our efforts have involved:  using biomolecules as monomers in polymerization reactions; converting biomolecules into other useful organic feedstocks; transforming biomolecules into chiral ligands for transition metal catalysts; and using certain biomolecules as catalysts themselves.  The overriding target is the development of novel chemical pathways designed ultimately to supplant fossil fuels as the progenitor of pharmaceuticals, polymers, fuels, and other commercial products.  The current and proposed research efforts seek to exploit several specific renewable biomass sources, all of which can be obtained in large and sustainable quantities:  carbon dioxide, furfural, vanillin, glucose, and triglycerides.

Simon W. North (Atmospheric and Environmental Chemistry: Hydrocarbon Oxidation and Stratospheric Halogen Chemistry ) Our research group is interested in understanding photo-initiated chemical reactions that occur in the atmosphere. Our experiments combine molecular beam and state-resolved ionization techniques with angle-resolved time-of-flight to determine the identity and energy content of photochemical products in the absence of secondary collisions. Studies will focus on the ultraviolet photolysis of brominated halocarbons, transient oxides of bromine such as Br2O and BrO2, and the important reservoir species BrONO2. Atom-for-atom bromine is now thought to be 100 times more efficient at destroying stratospheric ozone than chlorine yet the chemistry of bromine in the atmosphere is not nearly as well characterized. Our studies seek to establish quantitative trends in the wavelength dependent photochemistry of these molecules and aid in assessing their atmospheric significance. These experiments are ideally suited to undergraduate researchers, who will participate under the guidance of experienced graduate students.

We are also interested in the oxidation of troposheric hydrocarbons has major implications for local and regional air quality. In collaboration with the Atmospheric Sciences Department we study the reactions of a wide range of hydrocarbons with OH, NO3 and O3 in order to identity the rates, reactive intermediates, and final products using a combination of chemical ionization mass spectrometry and laser photolysis/laser induced fluorescence.

Marvin Rowe We have developed a plasma-chemical extraction method for removing carbon from perishable organic archaeological artifacts. This permits us to non destructively obtain radiocarbon and stable carbon isotopic analyses in rare and valuable artifacts such as papyrus, skins, leather, grass, straw mats, hair, etc. Microscopy has failed to show any visible change in selected samples. We are currently obtaining radiocarbon dates on materials selected because of their inherent interest, but with previously determined radiocarbon dates for comparison with the non destructive analyses. Results so far are very promising.
 

For more information, write the Graduate Student Advisor: gradmail@mail.chem.tamu.edu.

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Last Updated date 02/09/00