Professor and B. Seymour Rabinovitch Endowed Chair in Chemistry
Adjunct Professor of Chemical Engineering
Adjunct Professor of Physics
Ph.D. University of Texas at Austin, 1979
(Nanoscience, Environmental Catalysis, Physical, and Bioanalytical Chemistry)
The Campbell group pursues basic experimental research concerning energy-related and environmental catalysis, interfaces in solar cells and microelectronics, and array-based biochemical analyses. The main unifying themes of this broad-ranging work are: 1) development of tools that measure effects at surfaces more sensitively than anywhere else in the world; 2) reactivity and physical chemistry at solid surfaces; and 3) kinetics and energetics of elementary steps in energy-related catalytic reactions on solid surfaces.
Energy-Related and Environmental Catalysis
Chemical reactions catalyzed by solid surfaces dramatically improve the world in which we live. Still, the need for basic and applied research in catalysis is stronger than ever. Improving catalysts, for example, could minimize the use of fossil fuels, thus helping solve the energy crisis while decreasing greenhouse gases. Since there is a correlation between areas with high cancer mortality rates and those with high densities of pollution, an important approach to cancer reduction is the “greening” of industrial and automotive chemical processes to minimize pollution, again by modifying existing catalysts or inventing new ones. Improved catalysts do this either directly, by minimizing polluting side products, or indirectly, by minimizing requirements for feedstocks that themselves create pollution upon production. One goal of the Campbell research group is to clarify why catalyst modifiers act to promote catalytic activity or selectivity, and how nanoscale features of the catalyst surface can tuned to make better catalysts.
Transition metal catalysts are typically in the form of particles dispersed across the surface of some oxide or carbon support. Metal chemical reactivity can be tuned by varying the metal particle size. When the particles are only a few nanometers across, they can be much more active and selective in catalysis than larger particles. Unfortunately, such metal nanoparticles often sinter (i.e., combine with nearby particles and grow larger) under reaction conditions. The Campbell group is trying to improve environmental catalysts to resist sintering. For example, substantial NOx reduction could be realized if catalysts for the complete combustion of methane with low NOx emissions could be found. While Pd nanoparticles on alumina are excellent for this reaction, their resistance to sintering needs improvement before they realize this dream. Over 90% of the pollution from cars in the U.S. comes out in the first five minutes after start-up, since the Pt and Pd catalysts in our catalytic converters do not work until they get very hot. Since supported Au nanoparticles can oxidize CO at room temperature, they might solve this so-called cold-start-up problem, but they suffer sintering problems. We study these systems with a wide array of experimental techniques. Theoretical calculations (DFT, kinetic Monte-Carlo, etc.) supply important complimentary energetic and dynamical insights.
Photovoltaic Devices: Metal / Polymer and Metal / Semiconductor Interfaces
In solar cells or photovoltaic devices, charge injection and extraction occurs at the interface between a metal or other conductor and one of the semiconducting materials (inorganic materials in most current commercial devices, but hopefully more cost effective polymer films in the future). The Campbell group studies the energetics and electronic properties of these all-important interfaces, and is the only group in the world that can measure the energetics of the surface reactions occurring during thin metal film growth or molecular beam epitaxy (MBE). They are applying their unique calorimeter that does this, together with other surface characterization techniques like electron and ion spectroscopies, to study problems at specific metal/polymer and metal/Si interfaces that are of importance not only in making solar cells, but also in making microelectronics, LEDs, electro-optic modulators, and opto-electric devices.
Thermodynamics and Kinetics of Nanomaterials for Energy Technologies
As the ability to produce nanomaterials such as nanodots and nanowires has advanced, it becomes more important to understand how the energy of the atoms in these materials is affected by their reduced dimensions. The Campbell group’s single-crystal adsorption calorimeter, this country’s first, has proven powerful in this respect, with calorimetric measurements revealing that metal energies vary with particle size much more strongly than predicted by the Gibbs-Thomson relation as taught in undergraduate physical chemistry textbooks. This has already been found to be crucial for accurate modeling of long-term sintering rates of metal nanoparticles in catalysts, but will no doubt also prove important in understanding the rapidly-developing field of nanomaterials and nanoelectronics.
Array-based Biochemical Analysis via SPR Microscopy
The Campbell group collaborates with biotechnologists to develop chips containing patterned microarrays of proteins which bind ligand and other protein, or DNAs whose sequences selectively bind proteins such as transcription factors, so that the chips serve as receptor arrays for sensitive, highly parallel detection of such proteins. Surface plasmon resonance (SPR) microscopy is being developed for probing large microarrays of biomolecules for their binding interactions with various partners and the kinetics of such binding. It is possible to simultaneously monitor binding kinetics on >1300 spots within a protein microarray with a detection limit of ~0.3 ng per cm2, or <50 femtograms per spot (<1 million protein molecules) with a time resolution of 1 s, and spot-to-spot reproducibility within a few percent. Such instruments should be capable of high-throughput kinetic studies of the binding of small (~200 Da) ligands onto large protein microarrays. The method is label free and uses orders of magnitude less of the precious biomolecules than standard SPR sensing. It also gives the absolute bound amount and binding stoichiometry.
Bond energies of molecular fragments to metal surfaces track their bond energies to H atoms. Karp, E. M.; Silbaugh, T. L.; Campbell, C. T. J. Am. Chem. Soc. 2014, 136, 4137−4140.
Introduction: Surface Chemistry of Oxides. Campbell, C. T.; Sauer, J. Chem. Rev. 2013, 113 (6), 3859–3862.
Energetics of Adsorbed CH3 and CH on Pt(111) by Calorimetry: Dissociative Adsorption of CH3I. Karp, E. M.; Silbaugh, T. L.; Campbell, C. T. J. Phys. Chem. C 2013, 117 (12), 6325–6336.
Karp, E. M.; Silbaugh, T. L.; Crowe, M. C.; Campbell, C. T. J. Am. Chem. Soc. 2012, 134 (50), 20388–20395.
The Entropies of Adsorbed Molecules. Campbell, C. T.; Sellers, J. R. V. J. Am. Chem. Soc. 2012, 134 (43), 18109–18115.
Surface chemistry: Key to control and advance myriad technologies. Yates, J. T., Jr.; Campbell, C. T. Proc. Natl. Acad. Sci. USA 2011, 108, 911–916.
Adsorption Microcalorimetry: Recent Advances in Instrumentation and Application. Crowe, M. C.; Campbell, C. T. Annu. Rev. Anal. Chem. 2011, 4, 41–58.
The Energy of Adsorbed Hydroxyl on Pt(111) by Microcalorimetry. Lew, W.; Crowe, M. C.; Karp, E. M.; Lytken, O.; Farmer, J. A.; Árnadóttir, L.; Schoenbaum C.; Campbell, C. T. J. Phys. Chem. C 2011, 115, 11586–11594.
Insights into Catalysis by Gold Nanoparticles and their Support Effects through Surface Science Studies of Model Catalysts. Campbell, C. T.; Sharp, J. C.; Yao, Y. X.; Karp, E. M.; Silbaugh, T. L. Faraday Discuss. 2011, 152, 227–239 (invited).
Towards Well-Defined Metal-Polymer Interfaces: Temperature-Controlled Suppression of Subsurface Diffusion and Reaction at the Calcium/Poly(3-Hexylthiophene) Interface. Bebensee, F.; Schmid, M.; Steinruck, H.-P.; Campbell, C. T.; Gottfried, J. M. J. Am. Chem. Soc. 2010, 132, 12163–12165.
Ceria Maintains Smaller Metal Catalyst Particles by Strong Metal - Support Bonding. Farmer, J. A.; Campbell, C. T. Science 2010, 329, 933–936.