CHE231 STUDENTS: FINAL EXAM IS IN BEURY HALL 166
Surface chemistry and structure of geochemical materials
Bioengineering routes to the production of metal and metal oxide nanoparticles for homogeneous and heterogeneous catalysis
Environmental Molecular Science Institute, NSF
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SURFACE SCIENCE STUDIES OF CATALYTIC MATERIALS
Three research projects, briefly outlined below, are underway in my laboratory at Temple University. All the projects are carried out with modern surface science techniques that include x-ray and ultraviolet spectroscopies, ion scattering, secondary ion mass spectrometry, and near-edge x-ray absorption fine structure. The latter technique is carried out at the National Synchrotron Light Source (NSLS) facility at nearby Brookhaven National Laboratory (BNL).
1. Surface chemistry
and structure of geochemical materials
We have just initiated a research program to investigate the surface chemistry of minerals. At the present time we are elucidating the surface reactivity of pyrite (i.e., FeS2). A well-ordered naturally occurring surface of this material is prepared in the ultra-high vacuum environment by a novel preparation technique developed in our laboratory [S. Chaturvedi, R. Katz, J. Guevremont, M.A.A. Schoonen and D.R. Strongin, American Mineralogist 81, 261 (1996)], allowing us to investigate the same surface that appears in the natural environment. Quite simply, this procedure allows us to obtain reproducible surfaces for experimental study. A goal of this research is to determine the reactivity of these surfaces for environmentally relevant molecules. At the moment studies in our laboratory are concentrated on the elucidation of the chemistry of water and small halogenated organic molecules on pyrite using a combined UHV/high pressure cell. These investigations will allow us to develop a fundamental understanding of the chemical reactions that are (and can) be driven in the environment by these ubiquitous materials.
Recently, photoemission of adsorbed xenon (PAX) has been for the first time applied to elucidate the effect of short-range order on the surface reactivity of pyrite. Application of this technique has suggested that the reaction of adsorbates, such as H2O and H2S, occur at sulfur anion vacancy sites. These sites allow the dissoication of the molecule and the subsequent diffusion of the reaction products to the stoichiometric surface. With regard to H2S, these results have implications for pyrite growth from the reaction H2S and FeS.
2) Bioengineering routes to the production of metal
and metal oxide nanoparticles for homogeneous and heterogeneous catalysis
(Funding: U.S. EPA and Petroleum Research Fund-AC)
The project concentrates on developing bio-mediated routes to the controlled synthesis of nano-metal oxide and nano-metal structures, and to investigate the use of these nano-structures for photo- and catalytic chemistry. Our working hypothesis is that nano-materials will provide a unique reactivity that is conducive to important chemistry, such as heterogeneous chemistry and/or environmental remediation, that cannot be obtained at more traditional spatial dimensions (i.e., > Fm).
The research is a multi-disciplinary research effort in close collaboration with a bioinorganic (Trevor Douglas, Montana State) and geochemist (Martin Schoonen, SUNY). Consequently, students are exposed to several disciplines. The goal of the research is to develop a firm understanding of the properties of nano-size metal oxide compounds within the protein shell (or cage) of the iron storage protein, ferritin. These systems are unexplored in terms of their potential use in remediation processes or as a method for synthesis of nano-scale particles of metal compounds. The entire system, consisting of the inorganic core material and protein shell, provides opportunities for the development of new catalysts by manipulating the composition and size of the core material, as well as chemically functionalizing the surrounding protein shell.
Our proposed studies focus on three important aspects, summarized as follows:
Develop a bioengineering approach to assemble nano-size particles with well-defined size and composition. Initially we are concentrating our efforts on the synthesis of metal oxide nanoparticles, and derive zero valent metal particles by reduction. Furthermore, preliminary results demonstrate our ability to reduce the iron oxide core of ferritin to yield nano-sized zero valent iron metal particles. At least one prior impediment to fully investigating and ultimately testing the utility of nano-structures has been the difficulty that their preparation and stabilization presents. Our bioengineering approach addresses and helps circumvent these difficulties.
Develop a firm understanding of the surface chemistry and electrochemistry
of the ferritin systems. We are investigating the charge development
and electronic structure (band gap, band edge position) of the ferritin-derived
systems as a function of 1) composition of the core and cage; and 2) size
of the core particles.
Investigate the potential of the synthesized nanoparticles in photochemical driven environmental remediation and heterogeneous catalysis applications. The reactivity of the different nanoparticles toward these applications will be determined, as a function of composition and size. With regard to environmental chemistry, for example, we have shown (paper has been submitted) that demonstrates that ferritin, when photoexcited, rapidly reduces environmentally toxic Cr(VI) to the immobile Cr(III) species.
Ferritins are comprised of 24 structurally similar polypeptide
subunits that self-assemble to form a protein cage structure. The
outside diameter of the cage is 120 Å, and the cage surrounds a hollow
cavity roughly 80 Å in diameter (Cross
sectional view of Ferritin.) Up to 4500 Fe atoms are mineralized
and stored within this protein cage as a nanoparticle of the ferric oxyhydroxide
ferrihydrite (Fe(O)OH) ( TEM
micrograph ). By virtue of being encapsulated within the confines of
the protein cage, this mineralization process is spatially constrained
by the reaction volume of the cage and by diffusion of species through
the 5 Å diameter channels of the protein shell. We can manipulate
this chemistry in our laboratory so that homogeneous ferrihydrite (or other
materials, such as Co and Mn oxyhydroxides) particles with diameters ranging
from 20 to 75 A can be synthesized within the protein cage (Synthetic
Routes ). Particles with diameters less than <75 Å are formed
by controlling the Fe(II) to protein concentration ratio. This protein
cage is relatively porous, having roughly 5 Å diameter pores.
Furthermore, we have recently shown in our laboratory that the homogeneous
ferrihydrite nano-particles intrinsic to ferritin can be reduced to the
zero valent metal without loss of the nano-particle morphology (SEM
micrograph ). Hence, we will extend this specific development
to synthesize nano-size zero valent nano-particles with controllable and
homogeneous dimensions. The chemical properties of these supported
metal nanoparticles are currently being investigated in a variety of heterogeneous
3) Environmental Molecular Science Institute, NSF
This Center for Environmental Molecular Science (CEMS) located at SUNY-Stony Brook has just recently been funded by the NSF. Through this institute our research group at Temple will collaborate with investigators at SUNY-Stony Brook, Penn State, and Brookhaven National Laboratory. The project has a strong interdisciplinary component, bringing together investigators from chemistry, geochemistry, physics, materials science, and biochemistry to tackle important environmental problems. The general theme of the institute is to investigate contaminant interactions with mineral, organic, and biological components in natural systems (including sulfide, carbonate, zeolite, oxide, and clay minerals). Scientific interest will be focused on how changes in the coordination of contaminants, such as toxic metals and radionuclides alter their sequestration and mobility. Special attention will also be focused on modifying mineral surfaces to alter their interactions with contaminant species. Several scientific questions that will be asked and addressed in this Center will be i) what is the molecular level step that determine the sorption and sequestration of toxic metals, actinides and metalloids by minerals and synthetic materials? ii) What is the chemical environment (bonding, electronic structure, geometric structure etc..) of contaminants on minerals? iii) What is the effect of biota on the fate of contaminant bound on natural materials?
this link for complete publication list)