Analytical / Environmental / Inorganic / Materials / Physical
Surface Chemistry of pyrite, FeS2 (Funding: DOE-basic Energy Sciences)
The objective of the research has been to understand important fundamental aspects of the surface chemistry of pyrite (and other environmentally relevant metal sulfides), such as charge development, reactivity, surface stoichiometry, surface structure, and interaction with dissolved constituents (sorption). Our ultimate goal is to provide insight into the role of pyrite as reactant, sorbent, and (photo)catalyst in environmentally and geologically relevant environments. One such environment is present during coal-mining operations, where the oxidation and subsequent decomposition of pyrite in the environments leads to a severe environmental problem known as Acid-mine drainage. About 1 million dollars per day is spent on this problem.
Our program uses sophisticated surface sensitive probes to study the microscopic details of the oxidation process on pyrite. Techniques available in our laboratory include x-ray photoelectron spectroscopy (XPS), Attenuated
total reflection (ATR) FTIR (see Figure 1), ion scattering spectroscopy (ISS), electron energy loss spectroscopy (EELS), and temperature programmed desorption (TPD). We also carry out a significant amount of research at the National Synchrotron Light Source (NSLS) at Brookhaven National laboratory. We typically carry out high-resolution photoelectron spectroscopy (PES) and near-edge absorption fine structure (NEXAFS) at the NSLS. A future goal is to develop a research effort employing scanning probe microscopies to image the mineral surface.
Our research has had numerous successes that have shed light on the nature of reactive sites on the mineral surface, and the effect of short and long-range order of the mineral surface. Current research is concentrated on using our knowledge to modify the pyrite surface to inhibit oxidation under environmentally relevant conditions. Our program is also expanding to investigate other important metal sulfide and metal oxide surfaces.
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 (Fig. 2). Up to 4500 Fe atoms are mineralized and stored within this protein cage as a nanoparticle of the ferric oxyhydroxide ferrihydrite (Fe(O)OH) (see Fig. 3). 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 (Fig. 4). 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 (see Fig 5). 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 catalytic reactions.
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?
Kubicki, J.D.; Paul, K.W.; Kabalan, L.; Zhu, Q.; Mrozik, M.K.; Aryanpour, M.; Pierre-Louis, A.M.; Strongin, D.R. "ATR-FTIR and Density Functional Theory Study of the Structures,
Energetics, and Vibrational Spectra of Phosphate Adsorbed onto Goethite". Langmuir 28(41): 14573-14587 (2012).
Bhandari, N.; Reeder, R.J.; Strongin, D.R. "Photoinduced Oxidation of Arsenite to Arsenate in the Presence of Goethite ". Environmental Science and Technology 46(15): 8044-8051 (2012).
Singireddy, S.; Gordon, A.D.; Smirnov, A.; Vance, M.A.; Schoonen, M.A.A.; Szilagyi, R.K.; Strongin, D.R. "Reduction of Nitrite and Nitrate to Ammonium on Pyrite ". Origins of Life and Evolution of Biospheres 42(4): 275-294 (2012).
Schoonen, M.A.A.; Sklute, E.C.; Dyar, M.D.; Strongin, D.R. "Reactivity of sandstones under conditions relevant to geosequestration:
1. Hematite-bearing sandstone exposed to supercritical carbon dioxide
commingled with aqueous sulfite or sulfide solutions ". Chemical Geology 296: 96-102 (2012).
Lammers, K.; Murphy, R.; Riendeau, A.; Smirnov, A.; Schoonen, M.A.A.; Strongin, D.R. "CO2 Sequestration through Mineral Carbonation of Iron Oxyhydroxides ". Environmental Science and Technology 45(24): 10422-10428
Harringston, R.; Hausner, D.B.; Xu, W.Q.; Bhandari, N.; Michel, F.M.; Brown, G.E.; Strongin, D.R.; Parise, J.B. "Neutron Pair Distribution Function Study of Two-Line Ferrihydrite". Environmental Science and Technology 45(23): 9883-9890 (2011).
Murphy, R.; Lammers, K.; Smirnov, A.; Schoonen, M.A.A.; Strongin, D.R. "Hematite reactivity with supercritical CO2 and aqueous sulfide ". Chemical Geology 283(3-4): 210-217 (2011).
Xu, W.Q.; Hausner, D.B.; Harrington, R.; Lee, P.L.; Strongin, D.R.; Parise, J.B. "Structural water in ferrihydrite and constraints this provides on possible structure models". American Mineralogist 96(4): 513-520 (2011).
Bhandari, N.; Reeder, R.J.; Strongin, D.R. "Photoinduced Oxidation of Arsenite to Arsenate on Ferrihydrite ". Environmental Science and Technology 45(7): 2783-2789 (2011).
Bhandari, N.; Hausner, D.B.; Kubicki, J.D.; Strongin, D.R. "Photodissolution of Ferrihydrite in the presence of Oxalic Acid: An In Situ ATR-FTIR/DFT Study". Langmuir 26(21): 16246-16253 (2010).
Schoonen, M.A.A.; Harrington,, A.D.; Laffers, R.; Strongin D.R. "Role of Hydrogen peroxide and hydroxyl radical in pyrite oxidation by molecular oxygen". Geochimica ET Cosmochimica ACTA 1800(8): 871-885 (2010).
Murphy, R.; Lammers, K.; Smirnov, A.; Strongin D.R. "Ferrihydrite phase transformation in the presence of aqueous sulfide and supercritical CO2". Chemical Geology 271(1-2): 26-30 (2010).
Debnath, S.; Hausner, D.B.; Strongin, D.R.; Kubicki, J.D. "Reductive dissolution of ferrihydrite by ascorbic acid and the inhibiting effect of phospholid". Journal of Colloid and Interface Science 341(2): 215-223 (2010).
Smirnov, A.; Hausner, D.; Laffers, R.; Strongin, D.R. "Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle". Geochemical Transactions 9: Art. No. 5 (2008).
Michel, F.M.; Ehm, L.; Antao, S.M.; Lee, P.L.; Chupas, P.J.; Liu, G.; Strongin, D.R.; Schoonen, M.A.A.; Phillips, B.L.; Parise, J.B. "The structure of ferrihydrite, a nanocrystalline material". Science 316(5832): 1726-1729 (2007).
Michel, F.M.; Ehm, L.; Liu, G.; Han, W.Q.; Antao, S.M.; Chupas, P.J.; Lee, P.L.; Knorr, K.; Eulert, H.; Kim, J.; Grey, C.P.; Celestian, A.J.; Gillow, J.; Schoonen, M.A.A.; Strongin, D.R.; Parise, J.B. "Similarities in 2-and 6-line ferrihydrite based on pair distribution function analysis of X-ray total scattering". Chemistry of Materials 19(6): 1489-1496 (2007).
Hausner, D.B.; Reeeder, R.J.; Strongin, D.R. "Humidity-induced restructuring of the calcite surface and the effect of divalent heavy metals". Journal of Colloid and Interface Science 305(1): 101-110 (2007).