Dietz, Mark



Ph.D., University of Arizona

Research Areas

Few analytical methods are truly specific for a single species. As a result, problems in chemical analysis frequently involve a preliminary separation step to isolate the species of interest from matrix constituents and from potential interferents. Chemical separations play an equally important role in many preparative and process-scale applications, the preparation of high-purity radiopharmaceuticals and the reprocessing of spent nuclear fuel representing just two of many possible examples.

In general terms, the goal of our research is to devise improved reagents, media, and processes for the separation and preconcentration of metal ions and organic molecules, and to explore the fundamental chemistry underlying their use. Of particular interest is the development of environmentally benign approaches to chemical separations. Within this broad framework lie two specific areas of study: room-temperature ionic liquids (RTILs) and supercritical fluids (SCFs). Supercritical fluids comprise a unique class of solvents with properties intermediate between those of a liquid and a gas.

Fig. 1. Phase diagram for carbon dioxide.

Ionic liquids, unlike SCFs or conventional molecular solvents, consist entirely of ions, and as a result, exhibit a wide variety of interesting and useful properties.

Fig. 2. A representative room-temperature ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate

Both classes of solvents show enormous potential as replacements for the toxic and volatile organic solvents employed in many separation processes, in part a result of their extraordinary tunabililty. In the case of SCFs, simply changing the temperature or pressure can significantly alter the solvent properties of the fluid. Similarly, for RTILs, minor changes in the nature of the cation or anion comprising the solvent can lead to dramatic changes in its behavior. It is this tunability that we seek to exploit in developing improved methods of separation.

Our recent work in this area has focused on three topics:

    • Preparation and characterization of "inorganic liquids", a novel sub-class of ionic liquids incorporating at least one inorganic component (e.g., a polyoxometalate anion), and evaluation of their potential utility in separations.
Fig. 3. The 1-ethyl-3-methylimidazolium salt of the Lindqvist anion.
    • Elucidation of the factors (e.g., RTIL cation and anion structure) determining the mode of metal ion transfer from aqueous solution into an ionic liquid in the presence of various types of ligands (e.g., crown ethers).
Fig. 4. Possible partitioning modes for metal ions in biphasic aqueous-RTIL systems in the presence of a macrocyclic polyether.
    • Development of alternatives to fluorination as a means of improving the compatibility of organic extractants with supercritical carbon dioxide.
Fig. 5. A trimethylsilylpropyl esterified diphosphonic acid.

Progress in these areas is expected to provide the basis of efficient and selective "green" approaches to the separation of metal ions and organic molecules from a variety of complex matrices.

Selected Publications

Dietz, Mark L., and Hawkins, Cory A. “Extraction with ionic liquids: Metals.” Handbook of Separation Science: Liquid Phase Extraction. Ed. Colin Poole. Elsevier Science, (2019).
Dietz, Mark L., and Hawkins, Cory A. “Task-specific ionic liquids for metal ion extraction: Progress, challenges, and prospects.” Ion Exchange and Solvent Extraction. Changing the Landscape in Solvent Extraction 23. Ed. Bruce A Moyer. CRC Press, (2019): 83-113.
Kaul, Michael J., Qadah, Diab, Mandella, Victoria, and Dietz, Mark L. “Systematic evaluation of hydrophobic deep- melting eutectics as alternative solvents for the extraction of organic solutes from aqueous solution.” RSC Advances 9. (2019): 15798-15804.
Momen, Md A., and Dietz, Mark L. “High-capacity extraction chromatographic materials based on polysulfone microcapsules for the separation and preconcentration of lanthanides from aqueous solution.” Talanta 197. (2019): 612-621.
Kaminski, Michael, Sandi, Giselle, Dietz, Mark L., and Park, Anthony. “Optimization of a tandem ion exchange—extraction chromatographic scheme for the recovery of strontium from raw urine.” Separation Science and Technology. (2019).
Smith, Charles D., Downs, Ryan P., Carrick, Jesse D., and Dietz, Mark L. “Determination of extractant solubility in ionic liquids by thermogravimetric analysis.” Solvent Extraction & Ion Exchange 36.3 (2018): 304-314.
Hawkins, Cory A., Rigney, Madison L., Rud, Anna, and Dietz, Mark L. “Solvent water content as a factor in the design of metal ion extraction systems employing ionic liquids.” Solvent Extraction & Ion Exchange 36.2 (2018): 191-205.
Hawkins, Cory A., Momen, Md A., and Dietz, Mark L. “Application of ionic liquids in the preparation of extraction chromatographic materials for metal ion separations: Progress and prospects.” Separation Science and Technology 53.12 (2017): 1820-1833.
Wankowski, James L., and Dietz, Mark L. “Ionic liquid (IL) cation and anion structural effects on metal ion extraction into quaternary ammonium-based ILs.” Solvent Extraction and Ion Exchange 34.1 (2016): 48-59.
Momen, M. A., and Dietz, Mark L. “Sol-gel glass-encapsulated crown ethers for the separation and preconcentration of strontium from acidic media.” Separation Science and Technology 50.18, SI (2015): 2873-2880.
Hawkins, Cory A., Rud, Anna, Guthrie, Margaret L., and Dietz, Mark L. “Rapid quantification of imidazolium-based ionic liquids by hydrophilic interaction liquid chromatography: Methodology and an investigation ofthe retention mechanisms.” Journal of Chromatography A 1400. (2015): 54-64.
Hawkins, Cory A., Momen, M. A., Garvey, Sarah L., Kestell, John, and Dietz, Mark L. “Evaluation of solid-supported room-temperature ionic liquids containing crown ethers as media for metal ion separation and preconcentration.” Talanta 135. (2014): 115-123.