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Research Interests

I. Nanomaterials: Synthesis and functionalization of nanocrystals for applications in energy and biology

Semiconductor nanocrystal quantum dots or 'NQDs' are solution-grown, nanometer-sized particles comprised of a crystalline core coated by a surface layer of organic ligands. NQDs exhibit broad and intense absorption spectra, narrow and size-tunable emission energies (UV to near-IR), high photoluminescence-efficiency and stability, and are even capable of undergoing carrier multiplication (a process by which one absorbed photon generates multiple electron-hole pairs or 'excitons'). NQDs are thus promising materials for a wide-range of applications including solar energy harvesting, lighting, and biological imaging. Unfortunately however, two frequent obstacles towards these applications have been: (1) Limited choice over NQD composition, size and quality, and (2) lack of control over NQD surface properties, specifically over the functionality at the layer of organic ligands on the NQD surface.

To overcome these limitations, our group is working on: (1) Developing reproducible routes to highly crystalline, mono-disperse NQDs with well-defined compositions and a significantly expanded size range, and (2) investigating the post-synthesis chemical modification of NQD surfaces via modern chemistry methods (olefin metathesis, 'click' chemistry, among others). Specific targets include: (a) Relatively small ('tiny' < 2 nm) and large ('giant' ≥ 15 nm) NQDs whose total volume is well outside the typical NQD size regime, (b) fused (continuously-crystalline) and non-fused (ligand-coupled) NQD–NQD', NQD–nanowire, and NQD–metal-nanoparticle hybrid hetero-structures, as well as (c) NQD–small molecule assemblies. We focus on these specific targets based on their relevance and application to photoinduced-charge separation and extraction (in solar cells or photovoltaics), photocatalytic assemblies, light emitting devices (LED's), and bio-labels.

II. Polymer chemistry: Synthesis of added-value polymers from readily available feedstocks

Expanding middle classes across a world of definite proportions have lead to a steady increase in raw material and energy costs. Right in the middle between the two most talked about, extreme scenarios of a global economy based mostly on fossil fuels versus one based solely on renewable sources, a more likely scenario emerges where both types of sources will be increasingly used in a concerted fashion for years to come. It is thus clear that we need new fundamental paradigms that will expand our ability to convert already available as well as emergent chemical feedstocks into high-end, added-value products in ways that are both energy- and atom-efficient (they must involve minimal energy input and zero waste generation).

Our current efforts in this area are directed at exploring how second-sphere coordination and supra-molecular interactions can affect the extent, stereochemistry, and functional group-tolerance of catalytic olefin-enchainment; a fundamental type of C-C bond forming reaction that is already in use in an industrial scale to produce everyday polymers such as polyethylene. In particular, we are (1) synthesizing hetero-bimetallic complexes containing an insertion-active metal center (iron- or nickel-based) in close proximity to an insertion-inactive, weakly acidic-metal center (lithium-, magnesium- or zinc-based). Physical organic considerations and recent mechanistic evidence suggest that introducing the acidic metal will stabilize the necessary intermediates that will lead to successful incorporation of polar monomers (for example: acrylates or vinyl-halides, but also biomass-derivable feedstocks such as hydroxy-terminated alpha-olefins) into functionalized polyolefins. We are also (2) studying the effect that catalyst encapsulation inside supra-molecular cavities has on the size-selectivity of olefin oligomerization catalysts as well as on the stereoselectivity of catalytic assymmetric hydrovinylation reactions.

III. Organometallic chemistry and catalysis: Mechanism and application of novel metal-mediated transformations

We have a long-standing interest in investigating the kinetics, mechanism, and catalytic application of organometallic reactions that are relevant to biology and materials science. Current efforts in this area are directed at: (1) Generating or activating small molecules such as H2, N2, O2, CO, and CO2, (2) investigating new catalytic processes that can transform lignocellulosic biomass and its derivatives into useful products and materials, (3) understanding the microscopic mechanism by which discrete organometallic precursors 'decompose' into colloidal nanocrystals, and (4) exploring the kinetics and mechanism of dopant mobility and diffusion in such colloidal nanocrystals.

Research environment and training opportunities
Research in our group involves multidisciplinary projects as well as frequent collaborations with different physical, analytical, biological, and engineering groups. Students in our group acquire a broad and unique set of skills in the synthesis and characterization of small molecules (organic and inorganic alike), polymers, colloids, nanocrystals, and classical (bulk) solid-state materials. Specific techniques they learn include using inert-atmosphere/vacuum manifolds (Schlenk lines) and 'dry' glove boxes, nuclear magnetic resonance spectroscopy (NMR), transmission and scanning electron microscopies (TEM and SEM), X-ray diffraction, mass spectrometry, absorption and photoluminescence spectroscopies, dynamic light scattering, thermal analysis, size exclusion-chromatography, etc.

We are always looking for the best and brightest students and scientists to join our lab!
If you are a prospective graduate student, please feel free to contact us with questions. Every applicant to our PhD program receives a fair evaluation and is seriously considered for admission. You can find general information about our graduate admissions process online by going to http://www.chem.iastate.edu/graduate/

If you are an undergraduate or high school student and are interested in doing research within our laboratory, please contact Dr. Vela directly.