Dr. John Westall
PROFESSOR
B.S. University of North Carolina, 1971
Ph.D. Massachusetts Institute of Technology, 1977
Dr. Westall's research is focused on the application of surface and solution chemistry to problems in environmental chemistry, electrochemistry, and analytical chemistry. Current research topics include: (i) interactions of metal ions with heterogeneous environmental complexants, such as humic substances and surfaces of soil particles, and development of models for these complex interactions; (ii) electrochemical processes in the environment, including corrosion and redox transformations of inorganic and organic pollutants; (iii) the processes that control the distribution of hydrophobic, ionogenic, and ionic organic compounds between water and environmental sorbents; (iv) electric double layer phenomena associated with environmental surfaces; (v) mathematical methods for the determination of equilibrium constants from experimental data; (vi) the application of multicomponent chemical equilibrium models to biogeochemical problems. His research is funded by grants from the Environmental Protection Agency, the Department of Energy and Battelle Pacific Northwest Laboratories, and the Department of Transportation.
Some recent research activities illustrate these areas of interest. A discrete log K spectrum model has been developed to represent the binding of protons and Co(II) to leonardite humic acid (LHA) over a wide variation of solution composition: pH 4.5 - 9.5, [NaClO4] 0.01 - 0.1 M, TCo 200 nM - 500 :M. The model is internally self consistent over the range indicated without an explicit electrostatic term. The LHA was represented by four acid sites (HLi = H+ + Li-) with a fixed pKa spectrum: pKa = 4, 6, 8, 10. From the acid-base titration data, total concentrations of these sites and Na+ binding constants (Li- + Na+ = NaLi) were obtained. From Co2+ binding as a function of pH, constants for the reaction Li- + Co2+ = CoLi+ were obtained. Total concentrations of sites and binding constants were similar to those expected from other studies. This discrete log K approach has been selected as the easiest way to parameterize "multidimensional data" (i.e., data with variations in many solution chemistry parameters) for subsequent application in transport models.
The corrosion of steel is being studied towards the goal of understanding the effectiveness of cathodic protection in reducing the corrosion of reinforcing steel in concrete. Topics under investigation include composition of concrete pore solution, ionic conductivity of concrete, oxygen permeability of concrete, the effect of chloride ion on kinetics of steel oxidation, kinetics of oxygen reduction and water reduction at steel electrodes, and kinetics of oxidation of sacrificial anodes.
The solution and surface chemistry of organic acids and bases, and ionic surfactants is being investigated with a variety of solvents and surfaces. The motivation for this research is to discover the fundamental interactions of the solutes with the solvents and surfaces, and to apply this knowledge to understand the transport of the solute compounds in a variety of porous media -- from liquid chromatography columns to groundwater aquifers. Phenomena under investigation include the effect of cosolvents on the activity and acidity of the solute in the aqueous phase; the distribution of solutes between water and immiscible organic solvents; and the solvation and association of ions in the organic solvent. Complementary work addresses the retention of the same ionic and ionogenic solutes on a variety of reverse phase liquid chromatography columns with a wide range of solvent compositions. Finally the adsorption of these solutes to the surfaces of polymers, pristine oxides, and clay minerals is under investigation. The results of these experiments are interpreted primarily in terms of the hydrophobic interaction of the solute with the solvent and the electrostatic energy of the organic ion with its environment.
In another study, the interface between insulating oxides and electrolyte solutions is being studied in two types of environments: colloidal suspensions of oxide particles and electrochemical cells of the type reference electrode / electrolyte / oxide / semiconductor / metal. The results of this basic research are applicable to research work in the development of electrochemical microsensors, the adsorption of contaminants to surfaces in the environment, and photoelectrochemical energy conversion. These studies are directed at the relationship between structure and energy at the interface, for example, whether the interface more closely resembles a gel phase or a series of discrete planes, and the dependence of the interfacial potential difference on solution composition. In association with the experimental work described above, numerical methods are being developed to solve the equations associated with multicomponent chemical equilibria, including electrostatic interactions and sorption to heterogeneous materials. Both the forward problem (determine equilibrium speciation, given the thermodynamic data) and the inverse problem (determine thermodynamic constants, given experimental data) are being considered.
PUBLICATIONS REPRESENTATIVE OF CURRENT WORK
G. Furrer, P. Sollins, J. Westall, "The Study of Soil Chemistry Through Quasi-Steady-State Models: II. Acidity of Soil Solution" Geochim. Cosmochim. Acta, 54, 2363-2374, 1990.
B. Brownawell, H. Chen, J. Collier, J. Westall, "Adsorption of Organic Cations to Natural Materials," Environ. Sci. Technol., 24, 1234-1241, 1990.
C. Annette Johnson and John C. Westall. "Distribution of Hydrophobic Ionogenic Organic Compounds between Octanol and Water: Organic Bases" Environ. Sci. Technol., 24, 1869-1875, 1990.
B. J. Brownawell, H. Chen, W. Zhang, J. C. Westall, "The Adsorption of Surfactants," in Organic Substances and Sediments in Water - Processes and Analytical, R. A. Baker, Ed. Lewis, Boca Raton, 1991.
D. S. Jayasinghe, B. J. Brownawell, H. Chen, J. C. Westall, "Determination of Henry's Constants of Compounds of Low Volatility: Methylanilines in Methanol-Water" Environ. Sci. Technol., 26, 2275-2281, 1992.
J. Wagner, H. Chen, B. J. Brownawell, J. C. Westall, "Use of Cationic Surfactants to Modify Soil Surfaces To Promote Sorption and Retard Migration of Hydrophobic Organic Compounds" Environ. Sci. Technol., 28, 231-237, 1994.
M. Cernik, M. Borkovec, J. C. Westall, "Regularized Least-squares Methods for the Calculation of Discrete and Continuous Affinity Distributions for Heterogeneous Sorbents," Environ. Sci. Technol., 29, 413-425, 1995.
John C. Westall, John D. Jones, Gary D. Turner, John M. Zachara, "Models for Association of Metal Ions with Heterogeneous Environmental Sorbents: I. Complexation of Co(II) by Leonardite Humic Acid as a Function of pH and NaClO4 Concentration," Environ. Sci. Technol., 29, 951-959, 1995.
John C. Westall, "Modeling of the Association of Metal Ions with Heterogeneous Environmental Sorbents," Materials Research Soc. Proc., 353, 937-950, 1995.
M. Borkovec, U. Rusch, M. Cernik, G. Koper, J. C. Westall, "Affinity Distributions and Acid-Base Properties of Homogeneous and Heterogeneous Sorbents: Exact Results versus Experimental Data Inversion," Colloids and Surfaces, 107, 285-296, 1996.
T. L. Lemmon, J. C. Westall, J. D. Ingle, Jr., "Development of Redox Sensors for Environmental Applications Based on Immobilized Redox Indicators," Analyt. Chem., 68, 947-953, 1996.
PUBLICATIONS WITH BACKGROUND INFORMATION
J. Westall, H. Hohl, "Comparison of Models for the Oxide-Solution Interface," Adv. Coll. Interfac. Sci., 12, 265-294, 1980.
R. Schwarzenbach, and J. Westall, "Transport of Nonpolar Organic Compounds from Surface Water to Groundwater: Laboratory Sorption Studies," Environ. Sci. Technol., 15, 1360-1367, 1981.
J. Westall, "Reactions at the Oxide-Solution Interface: Chemical and Electrostatic Models," in Chemical Processes at the Mineral Surfaces, J. Davis and K. Hayes, Eds., American Chemical Society Symposium Series No. 323, American Chemical Society, Washington, 1986, pp. 54-78.
J. Westall, "Adsorption Mechanisms in Aquatic Chemistry" in Aquatic Surface Chemistry, W. Stumm, Ed., John Wiley & Sons, NY, 1987, pp. 3-32.