Keywords

• Radiochemistry; actinide chemistry
• Nuclear materials
• Materials characterization

Focus areas

• Environmental/atmospheric
• Materials/polymer

Research interests 

Fundamental actinide chemistry

Actinides have fascinating chemical properties due to the complex nature of their 5f electrons that may lead to unique catalytic, electronic, and optical properties.  Of particular interest is the development of novel actinide complexes to improve advanced separations technologies, long-term storage of nulcear materials, and environmental remediation  We use a variety of low-temperature synthesis techniques to create novel materials containing uranium (²³⁸U), and neptunium (²³⁷Np) that are characterized by single-crystal X-ray diffraction, NMR, Raman and IR spectroscopy, and thermogravimetric analysis.  We are specifically focused on high valent actinides (+5 and +6) that form the actinyl cation because these states are most relevant to nuclear waste and environmental systems.  The actinyl cation contains the Np or U cation bonded to two oxygen atoms to create a nearly linear triatomic species.  Due to these strong bonds, the oxygen atoms are typically considered passivated, but they can become more reactive depending on the oxidation state of the actinide cation, the strength of intermolecular forces, presence of radical species, and light flux.  The Forbes research group focuses on understanding the reactivity of the actinyl oxo group under a range of conditions to develop means to control the chemical and physical properties of the actinide elements.

Development of metal organic nanotubes

The development of novel nanomaterials with unique water transport and storage properties is important to technological advances in separations, catalysis, drug delivery, and environmental remediation. Development of novel hybrid materials, such as metal-organic nanotubes (MONs) are of particular interest as they are amenable to structural engineering strategies and may exhibit unique properties based upon the presence of inorganic components. The Forbes Research Group has recently synthesized and structurally characterized a unique U(VI) MON that displays permanent porosity and thermal stability. The compound contains ordered water that structurally resembles I_h ice and exhibits low-temperature, reversible water adsorption that can be controlled by solvent polarity. “Ice channels” within single-walled carbon nanotubes have been predicted by computational methods, but the structural nature of nanoconfined water has yet to be determined experimentally.  We are currently developing novel MONs based upon actinide, main-group, and transition metals that can be developed into novel water purification membranes and separations technologies.  This research is supported by NSF Career Award – Division of Solid State and Materials Chemistry.

Transport of nuclear waste and heavy metals in environmental systems

Actinides are a major source of radioactivity associated with nuclear waste and their transport in environmental systems is enhanced through adsorption onto small (1-5 nm) nanoparticles.  The Forbes research group synthesizes novel actinide nanomaterials that are used as geochemical model compounds to enhance our understanding of the mobility of nuclear materials in environmental systems.   Single-crystal X-ray diffraction and synchrotron techniques, such as high-energy X-ray scattering, are used to provide a molecular-level understanding of the structural characteristics of the ²³²Th and ²³⁸U complexes that will aid in the development of novel remediation methods for nuclear materials.

We also investigate the adsorption of heavy metals onto small aluminum and iron oxyhydroxide particles to provide a molecular level understanding of contaminant transport in environmental systems by synthesizing and structurally characterizing geochemical model compounds.  These compounds are also investigated by computational methods through collaborations with Dr. Sara Mason in the Physical Chemistry Division.  In addition, the transport of these particles through geologic media is being explored through collaborations with Dr. Adam Ward in the Department of Earth and Environmental Sciences.  This research is currently supported by the Nuclear Regulatory Commission, Faculty Development Award.

Recent publications 

• Kravchuk, D. V. and T. Z. Forbes* “In Situ Generation of Organic Peroxide to Create a Nanotubular Uranyl Peroxide Phosphate.” (2019) Angewandte Chemie International Edition, 51, 18429-18433. DOI: 10.1021/acs.cgd.8b01735
• Pyrch, M. M., J. M. Williams, and T. Z. Forbes* “Exploring Crown-ether functionalization on the stabilization of hexavalent neptunium.” (2019) ChemComm 55, 9319-9322. DOI:10.1039/C9CC04393D
• Bjorklund, J.L., M. M. Pyrch, M. C. Basile, S.E. Mason, and T. Z. Forbes* “Actinyl-cation interactions:  Experimental and theoretical assessment of [U(VI)O2Cl4]2- and [Np(VI)O2Cl4]2- in solid state and aqueous solutions.” (2019) Dalton Transactions 48, 8861-8871.  DOI:10.1039/C9DT01753D
• Payne, M. K., Pyrch, M. M. Jubinsky, M., Basile, M.C., and T.Z. Forbes* “Impact of oxo groups on actinyl materials:  Highlight on thermal expansion behaviour.” (2018) ChemComm 54, 10828-10831.  DOI: 10.1039/C8CC05240A
• Basile, M., E. Cole and T.Z. Forbes* “Impacts of oxo interactions within neptunyl crown ether complexes.”  (2018) Inorganic Chemistry, 57, 6016-6028.  DOI:10.1021/acs.inorgchem.8b00488
• Jayasinghe, A., M. Payne, D. Unruh, A. Johns, J. Leddy, and T.Z. Forbes* “Diffusion and selectivity of water confined within metal-organic nanotubes.” (2018) Journal of Materials Chemistry A, 6, 1531-1539.  DOI: 10.1039/C7TA06741K
• Eitrheim, E. S., D. May, M. K., Schultz, T.Z. Forbes* and A. W. Nelson “Mobility of naturally-occurring radioactive materials in drill cuttings from unconventional drilling operations.” (2016) Environmental Science and Technology Letters 3, 425-429.  DOI: 10.1021/acs.estlett.6b00439
• Fairley, M, K. Corum, A. Johns, D.K. Unruh, M. Basile, S.E. Mason, and T. Z. Forbes “Isolation and characterization of the [Ga2Al18O8(OH)36(H2O)12]8+ cluster:  cationic variations on the Wells-Dawson topology.” (2015) Chemical Communications 51, 12467-12469.  DOI: 10.1039/C5CC03069B
• Basile, M., D.K. Unruh, K. Gojdas, E. Flores, L. Streicher, and T. Z. Forbe* “Chemical controls on uranyl citrate speciation and the self-assembly of nanoscale macrocycles and sandwich complexes in aqueous solutions.” (2015) Chemical Communications (Emerging Young Investigator Edition) 51, 5306-5309.  DOI: 10.1039/C4CC08657K
• Sahu, S. K., D.K. Unruh, T.Z. Forbes, and A. Navrotsky “Energetics of formation and hydration of a porous metal organic nanotube.” (2014) Chemistry of Materials 26, 5105-5112.  DOI: 10.1021/cm5024053
• Unruh, D. K., K. Gojdas, A. Libo, and T. Z. Forbes “Synthesis and characterization of metal-organic nanotubes exhibiting reversible adsorption of confined “ice channels”.  (2013) Journal of the American Chemical Society 135(20), 7398-7401.  DOI:10.1021/ja400303f

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