Current Research

Sustainable Catalysis

Renewable Energy

Actinide Sequestration

Nanomedicine

Sustainable Catalysis

Heterogeneous catalysis with inorganic porous materials such as zeolites is of paramount importance for the production of many large-scale commodity products, but has rather limited success in fine chemical synthesis. We envisioned in 2001 that MOFs are particularly suited to generating single-site solid catalysts with unprecedentedly uniform catalytic sites and open channels for shape-, size-, chemo-, and stereo-selective reactions by taking advantage of the ability to assemble well-defined molecular building blocks into solid materials. The molecular origin of MOF catalysts significantly broadens the scope of reactions that porous solids can successfully catalyze, and allows for the systematic tuning of catalytic activities. On the other hand, MOF-based solid catalysts can simply be recovered and reused, yielding reductions in cost of catalyst regeneration and product purification in industrial processes.

In the past decade, we and other have shown that MOFs indeed provides an excellent platform for designing single-site solid catalysts for a large range of organic transformations that cannot be accomplished with inorganic porous materials.  For example, we reported the first chiral MOF capable of catalyzing highly enantioselective reactions in J. Am. Chem. Soc., 2005, 127, 8940.  We are actively pursuing the rational design of MOF-based asymmetric catalysts for many important stereoselective organic reactions.  We are also interested in combining light-harvesting properties of MOFs to develop highly efficient photocatalytic systems for thermodynamically uphill organic transformations.  Lastly, we are taking advantage of unique attributes of MOFs to design earth abundant metal-based single-site solid catalysts.

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Renewable Energy

Solar energy is one of the few alternative energy sources that could be scaled up to meet our future needs. The amount of solar energy that reaches our planet in one hour is more than enough to fuel the world for one year at the current consumption rate. We are designing novel hybrid materials to address the three fundamental steps that are needed to convert sunlight into solar fuels: a) sunlight absorption by the antenna to efficiently generate charge-separated excited states; b) efficient conversion of excited states to electrochemical energy as redox equivalents; and c) the use of redox equivalents (electrons and holes) to carry out energy-gaining chemical reactions (such as water splitting). Although each fundamental step can be studied separately, a device (system) encompassing all components is needed to produce solar fuels.

We surmise that MOFs can serve as a unique material platform to integrate different molecular components into a functional water splitting system. Different types of molecular and nanoparticle (NP) components can be incorporated into the MOF framework in a sequential and ordered manner to carry out the three fundamental steps of solar fuels production. Such a molecule-based solar fuel system is akin to the UV-driven TiO2–based water splitting device reported by Honda and Fujishima, but each functional component can be readily fine-tuned to maximize the efficiencies of sunlight absorption and energy storing reactions. We have incorporated light-harvesting molecules such as Ru(bpy)32+ into MOFs to study exciton transport in molecular solids and catalyze light-driven organic transformations. We have also incorporated water oxidation and proton/carbon dioxide reduction catalysts into MOF structures to catalyze water oxidation and proton/CO2 reduction half reactions, respectively. Through these projects, we hope to gain in-depth understanding of the three fundamental steps that are needed to convert sunlight into solar fuels and to design hierarchical MOF assemblies comprising multiple functional components to achieve solar energy harvesting and storage.

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Actinide Sequestration

While efficient solar power generation can provide a long-term, sustainable solution to the global energy need, nuclear power remains the only mature, large-scale, non-intermittent, and carbon-neutral means to meet the growing global energy demand in the coming decades (and centuries). Development of stable and clean energy supplies through nuclear power is a responsible pursuit. There are however two critical hurdles for sustained, large-scale nuclear energy production.  First, the uranium in terrestrial ores is limited. It is estimated that the currently available terrestrial uranium will sustain nuclear energy production for <100 years with the present nuclear power technology. Second, the nuclear waste decontamination technology is lacking.  We are working on designing novel porous materials to address both of these issues.

The oceans contain 4.5 billion tons of uranium, equivalent to 1000 times the currently available terrestrial uranium that can be economically mined, albeit at an infinitesimally low concentration of ~3 ppb.  Efficient extraction of uranium from seawater represents an attractive solution for the development of sustainable nuclear fuel cycles.  We are developing advanced sorbents for uranium extraction from seawater, specifically focused on the development of advanced porous supports with incorporated selective binding sites for uranyl ions. By increasing surface areas, maximizing binding site densities, and enhancing mass transport properties, we hope to develop novel sorbents for efficient and economical extraction of uranium from seawater.  We are also extending this approach to designing robust porous materials for sequestering radionuclides from nuclear wastes.

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Nanomedicine

Cancer is a major public health problem in the United States and around the world. The mortality rates of many types of cancers have changed very little in the past 3 decades. The high cancer mortality rates can be attributed to the lack of early diagnosis techniques and effective therapies as conventional diagnostic and therapeutic agents suffer from several drawbacks, including limited blood circulation time, non-specific toxicity, and drug resistance. We are developing nanoparticle imaging and therapeutic agents in order to overcome these limitations. Nanoparticles can have prolonged circulation half-lives, high payloads, and the ability to actively target cancer cells and to bypass drug resistance mechanisms.

We have developed novel nanoparticles for targeted delivery of anticancer therapeutics and multimodal contrast agents for optical imaging, X-ray computed tomography, and magnetic resonance imaging. In particular, nanoscale coordination polymers (NCPs) or nanoscale metal organic frameworks (NMOFs) developed in our lab have several distinctive advantages and have been shown to be effective anticancer agents in vivo. NCPs/NMOFs can also accommodate multiple types of therapeutic agents (chemotherapeutics, siRNAs, photodynamic and photothermal agents, etc.) for synergistic effects and enhanced cancer therapy. Their ability to integrate both imaging and therapy components into one single formulation has also allowed us to explore their theranostic properties. We are actively working on translating the most promising NCP/NMOF systems into the clinic.

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