Inorganic and analytical chemistry; synthesis of new materials; chemical applications of solid state materials: surface chemistry, layered materials, self-assembly, artificial photosynthesis, catalysis, environmental chemistry.
Chemistry of Nanoscale Inorganic Materials
The Mallouk group uses nanoscale assembly techniques to make complex materials with unusual properties or specific functions. Often these properties arise because the system is mesoscopic, meaning that the physical size of the object corresponds to some characteristic physical length, such as the wavelength of light, the coherence length of Cooper pairs in a superconductor, or the width of the depletion layer in a semiconductor liquid junction.
Solar Photochemistry and Photoelectrochemistry
An important goal of this aspect of our research is to develop new kinds of nanomaterials that will lead to efficient, inexpensive solar energy conversion devices. The spectral response of dye sensitized solar cells, developed nearly two decades ago by Michael Graetzel and coworkers, can be significantly enhanced by manipulating light using nanoparticle assembly to produce photonic crystals. By incorporating nanoparticles that catalyze water oxidation into dye sensitized solar cells, it is possible to split water to hydrogen and oxygen using visible light. We use transient spectroscopic techniques to understand the kinetics of electron transfer catalysis in order to optimize the quantum yield for water splitting. In a collaborative project with the Redwing and Mayer groups, semiconductor nano- and microwire arrays are being studied as photoelectrodes. Crystalline Si and compound semiconductor wire arrays can be made by vapor phase and electrochemical deposition techniques. The vertical wire morphology separates the length scales of light absorption and minority carrier diffusion, and in principle offers a low-cost route to very efficient multi-junction cells.
Several projects in the group use porous membranes as templates for growing nanowires and nanorods. Multi-segment nanowires have interesting electronic properties, such as transistor and diode behavior and in some cases unusual quasi-1D superconductivity. In collaboration with the Sen group, we are now studying the movement of multi-segment nanorods powered by spontaneous catalytic reactions. These nanorods are the first examples, outside of biological systems, of autonomously powered nano- and micromotors. The same electrochemical principles have recently been used to design catalytic micropumps.
Functional Inorganic Layered Materials
We are developing a set of soft chemical reactions that topochemically interconvert different structural families of layered and three-dimensional perovskites. Layered perovskites, metal phosphates, clays, and other lamellar solids can be grown layer-by-layer and converted to other interesting nanoscale morphologies (such as nano-scrolls and tubes) by means of intercalation, exfoliation, and restacking reactions. These materials are of particular interest to us as catalyst supports and ionic conductors in intermediate temperature fuel cells.
In-Situ Remediation of Contaminants in Soil and Groundwater Using Nanoscale Reagents
Layer-by-layer assembly on nanoparticle surfaces is being studied as a means of controlling core-shell structure and particle aggregation for optimized sub-surface transport, targeting of insoluble contaminants, and concentration of soluble contaiminants at the reactive nanoparticle surface.