I have broad research interests in the general areas of geochemistry and mineralogy, with an emphasis on the molecular-level structure of minerals and their surfaces. Environmental Molecular Science: A primary goal of my current research efforts is to understand the processes and reaction mechanisms operating at mineral-water interfaces, and the control that surface chemistry exerts on the rates of surface-controlled reactions such as dissolution, precipitation, and coprecipitation of impurities. The composition of fluids in near-surface environments are modified through reactions with minerals. The rates of these reactions determines how quickly contaminants can be transferred between fluid and solid phases, whether they can be effectively locked up in mineral phases, and how quickly they can be re-released upon change in fluid chemistry. Our research makes extensive use of Nuclear Magnetic Resonance (NMR) spectroscopic techniques to determine the the molecular-level structure of minerals and their surfaces, and for measuring kinetics of reactions for dissolved complexes. We are particularly interested in determining the structure of impurities in minerals, such as organic molecules, as models for how these ions and molecules bind to mineral surfaces. Our research group is affiliated with the Center for Environmental Molecular Science (CEMS), which is a collaboration among researchers at Stony Brook, Brookhaven National Laboratory, Penn State University, and Temple University.

Kinetics of Oxygen Exchange Reactions
Structural and chemical properties of mineral surfaces provide some of the most fundamental constraints on reactions that result in mass transfer between solid and fluid phases, such as sorption, coprecipitation, crystal growth, and dissolution . Fundamental processes at mineral surfaces are difficult to study directly because of the heterogeneous nature of the mineral surface and of the surface/fluid interface.An alternative approach is to study dissolved complexes that contain structural elements similar to those thought to occur on exposed mineral surfaces. One class of molecules that fit this description are the Al-oxyhydroxide polymers based on the Al₁₃ molecule:


These molecules contain a central 4-coordinated metal (Al, Ga, or Ge) surrounded by a shell of 12 6-coordinated Al in edge-sharing configurations similar to the structure of Al-hydroxide and 1:1 clay minerals. This molecule exposes oxygens in bridging (bonded to two Al) and terminal configurations similar to those expected for simply terminated crystals and exhibits charge densities similar to those of Al-oxyhyroxides at near-neutral to slightly acidic conditions. The rates at which these oxygens exchange with oxygens in the bulk solution can be measured in situ by ¹⁷O-NMR techniques, giving time scales for bond-breaking reactions and how they change with change in chemistry. For example, we have found that substitution of fluoride ion onto an oxygen site makes the other oxygens more reactive by a factor of 100.

Nuclear Magnetic Resonance (NMR) Spectroscopy
NMR spectroscopy can provide information on the structure of minerals in terms of the distribution of distinct atomic configurations and complements techniques, such as X-ray diffraction, that yield average atom positions. The structural information from NMR is related to the immediate coordination environment of the atom of interest and is isotopically specific. This makes NMR very useful for disordered materials such as amorphous (non-crystalline) phases and mineral surfaces, where the structure varies over short (nm) distance scales. For example, the white precipitate in this image is an amorphous aluminum-oxyhydroxide that results from neutralization of acid mine drainage in a stream:

Oxyhydroxide flocs of Fe (orange) and Al (white) formed at a stream-bed spring of acid mine water. Yuba county, California.

Using ²⁷Al NMR spectroscopy we could determine the distribution of Al coordination environments, which provided information on the precursor molecules from which the precipitate probably forms.

Selected Publications 

Phillips, B.L., Houston, J.R., Feng, J., and Casey, W.H. (2006) Observation of ¹⁰³Rh NMR by cross-polarization.  J. Am. Chem. Soc., in press

Casey, W.H., Olmstead, M.M., and Phillips, B.L. (2005)  A new aluminum-hydroxide octamer.  Inorg. Chem., 44:4888-4890.

Phillips, B.L., Lee, Y.J., Reeder, R.J. (2005) Organic coprecipitates with calcite: an NMR spectroscopic study.  Env. Sci. Technol.,  39:4533-4539.

Swaddle, T.W., Rosenqvist, R., Yu, P.,  Bylaska, E., Phillips, B.L., Casey, W.H. (2005), Kinetic evidence for five-coordination in AlOH²⁺(aq) ion.  Science, 208:1450-1453.

Tangeman, J.A., Phillips, B.L., Nordine, P.C., and Weber, J.K.R. (2004) Thermodynamics and structure of single- and two-phase yttria-alumina glasses.  J. Phys. Chem. B, 108:10663-10671.

Loring, J.; Yu, P.; Phillips, B.L.; Casey, W.H. (2004) Activation volumes for oxygen exchange between the GaO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁺(aq) (GaAl₁₂) polyoxocation and aqueous solution from variable pressure ¹⁷O NMR spectroscopy.  Geochim. Cosmochim. Acta, 68:2791-2798.

Phillips, B.L., Lee, A.P., and Casey, W.H. (2003)  Rates of oxygen exchange between the Al₂O₈Al₂₈(OH) ₅₆(H₂O)₂₄¹⁸⁺ (aq) (Al₃₀) molecule and aqueous solution. Geochim. Cosmochim. Acta, 67:2725-2733.

Yu, P., Lee, A., Phillips, B.L., and Casey, W.H. (2003) Potentiometric and ¹⁹F nuclear magnetic resonance spectroscopic study of fluoride substitution in the GaAl₁₂ polyoxocation:  Implications for aluminum (hydr)oxide mineral surfaces. Geochim. Cosmochim. Acta, 67:1065-1080.

Furrer, G., Phillips, B.L., Ulrich, K.-W., Pothig, R., and Casey, W.H. (2002) The origin of aluminum flocs in polluted streams.  Science, 297:2245-2247.

Lee A.P., Phillips B.L., Olmstead M.M., Casey W.H. (2001)  Synthesis and characterization of the GeO₄Al₁₂(OH)₂₄(OH₂)₁₂⁸⁺  polyoxcation. Inorg. Chem.,  40:4485-4487.

Tangeman, J.A., Phillips, B.L., Navrotsky, A., and Weber, J.K.R. (2001) Vitreous forsterite (Mg₂SiO₄):  Synthesis, structure, and thermochemistry.  Geophys. Res. Lett., 28:2517-2520.

Casey W.H., and Phillips, B.L. (2001)  The kinetics of oxygen exchange between sites in the GaO₄Al₁₂(OH)₂₄(OH₂)₁₂⁷⁺ (aq)  molecule and aqueous solution.   Geochim. Cosmochim. Acta, 65:705.

Phillips, B.L., Casey, W.H., and Karlsson, M. (2000) Bonding and reactivity at oxide mineral surfaces from model aqueous complexes. Nature, 404:379-382.

Nordin, J.P., Sullivan, D.J., Phillips, B.L., and Casey, W.H. (1999)  Mechanisms for F-promoted dissolution of Bayerite [b-Al(OH)₃(s)] and Boehmite [g-AlOOH]: ¹⁹F NMR spectroscopy and experimental surface chemistry. Geochim. Cosmochim. Acta 63:3513-3524.