Apblett Research Interests
The research efforts of Professor Apblett's research group are concerned with the application of metallo-organic and inorganic materials chemistry to the multitude of problems that are faced by industry today. Such challenges as improved methods of extracting minerals and recycling waste materials, the direct "one-pot" conversion of minerals to useful commodity chemicals and polymers, new catalytic processes, pollution prevention and remediation and novel processing techniques and products, are all addressed by our research. Target products include high technology materials, artificial bone, catalysts, ion exchange materials, inorganic polymers, medical detectors, and metallo-organic compounds that are therapeutic agents for cancer treatment.
The application of metallo-organic compounds as precursors for catalysts and high-technology materials can provide improvement of the product's chemical and phase purity and compositional homogeneity, greater control of microstructure, and lower temperature synthesis and processing. Our research efforts in this area are focused on the preparation and characterization of metallo-organic precursors and inorganic polymers that may find use in catalytic, electronic, optical, structural, and environmental applications.
One aspect of this research is the development of low temperature precursors for ceramic films, fibers and bodies. These precursors tend to be metal carboxylates that are specifically designed to readily decompose to the desired metal oxide and small, volatile organic fragments (for example metal 2-oximinopropionates shown below). Depending on the processing conditions used, these precursors can be used to prepare very high surface area powders that are excellent for use as catalysts or sintering into ceramic bodies or they may be applied to the preparation of ceramic thin films on a variety of substrates including heat-sensitive plastics. Target materials include structural ceramics, catalysts, electronic and magnetic materials, superconductors, and bioceramics including artificial bone. We also design precursors for bimetallic electronic and magnetic materials which crystallize with the metals "fixed" in the proper ratio. Since the useful properties of such materials depend dramatically on the correct stoichiometry of the metals, we are able to synthesize superior electronic-grade materials. It was also discovered by the Apblett research group that ion-exchange materials can be converted to spherical aggregates of nanoparticles of metal oxides. These materials are ideally shaped for water treatment or catalysis and have already proven to be effective for removal of arsenic from water.
Scanning electron micrographs for (A) hematite particles 150 X magnification (B) initial Dowex 650C resin bead 150 X magnification and (C) hematite particles 700 X magnification
Recently, we discovered a new class of metal carboxylates that are liquids at room temperature. These liquids are excellent solvents for other metal ions and have significant applications as electrolytes for batteries and in the processing of ceramic materials. Using these compounds we have produced foamed ceramics that may be useful for high-temperature insulation or preparation of metal-ceramic composites, protective ceramic coatings, and novel processing methods for ceramic synthesis. For example, a mixture of a ceramic powder with a liquid precursor has been found to yield a highly moldable putty that converts to a ceramic with very little shrinkage while maintaining the same shape.
Another aspect of the research is the development of inorganic polymers that possess a metal-oxygen backbone. These are prepared directly in a one step reaction from common minerals including ones that are found on Mars (suggesting that colonization of space might take advantage of these unique polymers). Target macromolecules are those with beneficial properties for application as ceramic precursors, magnetic materials, electrical or ionic conductors, medical imaging agents, and structural polymers. One particularly useful application is the use magnetically-active polymers to absorb toxic compounds from water and allow their separation by magnetic filtration. A slightly different approach has also been used to prepare successful "magnetic extractants" by grafting organic or organosilicon moieties to magnetite cores. Additionally, magnetic activated carbons have been synthesized by incorporating iron or nickel oxide precursors in standard recipes for activated carbon. Preliminary results indicate that these materials can revolutionize wastewater treatment, decolorization of sugar extracts, and breaking of oil-in-water emulsions, and separation of petrochemicals and organic pollutants from water.
We are also developing methods for growing films and particles of photovoltaic materials (materials that can convert sunlight to electricity). These methods involve either the design of low-temperature precursors or solution-growth of thin films. The latter technique involves slow, controlled generation of reactive species in solution either by hydrolysis of reactive molecules or by the action of enzymes. It is an excellent environmentally-friendly method for preparing these materials since the solvent is water and little waste is generated.
The desire to remediate pollution and to minimize industry's impact on the environment has created the need to develop novel strategies for both clean up of pollution and attenuation of the production of hazardous waste by industry. Much of the chemistry described above is performed in water and the developed processes may be used to replace conventional processes that depend on the use of environmentally-unacceptable organic solvents. Other research in the environmental area includes methods by which inorganic pollutants such as heavy metals and actinides may be removed from the environment and immobilized in a ceramic matrix that mimics the minerals that normally serve as a repository for the elements in nature. In this fashion, we can be assured that the toxic metals are locked away from the biosphere and no longer constitute a threat to living organisms. We are also developing inexpensive ion-exchange materials (including the magnetic polymers described above) that are capable of replacing toxic metal ions with environmentally-benign ones. Our efforts in catalyst preparation have resulted in several promising processes that are capable of destroying chlorocarbon pollutants such as herbicides, pesticides, solvents, chemical weapons and freons. Additionally, our ability to prepare superior metal oxide catalysts for use in selective oxidation, combustion, waste gas treatment, and petroleum cracking may lead to both improved economics and reduction of the environmental impact of industry. We are also developing environmentally-acceptable methods for extraction and refinement of metals from ores and waste materials (such as coal ash) in which all of the ore or waste material is completely converted to marketable chemicals without generating any waste.
The design of single-source precursors for multi-metallic oxides is another important pursuit of the Apblett research group. The 2-oximinopropionates mentioned above are amenable to this task since it is possible to form solid solutions with various divalent transition metals. A more challenging problem, however, is the combination of two dissimilar metals into a single source precursor. Considerable success was achieved using the reaction of metal 2-hydroxycarboxylates with vanadium pentoxide or molybdenum trioxide to yield bimetallic complexes. These have been useful for the synthesis of a variety of vanadate or molybdate-based catalysts and electronic materials. Complexes formed between calcium or zinc gluconate and molybdenum trioxide were demonstrated to be both flame-retardants and corrosion inhibitors.
During the testing of metal molybdates for catalytic hydrolytic dechlorination of halocarbons, it was discovered that molybdenum hydrogen bronze (HMoO3 formed by reduction of molybdate) is a reagent for reduction of chlorocarbons to alkanes. Since that discovery, HMoO3 and related tungsten hydrogen bronzes have been applied to chloromethane destruction and reductive coupling of α-chloroalkylbenzenes. During the course of this investigation it was found that these materials are unique reagents for a variety of organic transformations. These include conversion of nitriles to amides or alkynes to ketones, cyclotrimerization of alkynes, and coupling of cyclopentene to decalin. A recent triumph was the direct conversion of dimethylcyanamide to altetramine, an anti-cancer drug, in a one-step reaction. Molybdenum hydrogen bronze was also tested for its ability to absorb heavy metals and actinides from water. It was found that it is an extremely selective agent for absorption of metals with large radii but the mechanism was not an ion-exchange process but a topotactical reaction with the bronze to give layered or three-dimensional molybdate salts. Therefore, molybdenum trioxide was tested for direct reaction with aqueous metal solutions. Again, it is very selective for acinides such as uranium but unreactive towards light metals such as calcium. The use of molybdenum trioxide as a very inexpensive heavy metal absorbant has the potential to revolutionize water treatment and industrial metal separations. MoO3 might also prove useful for prevention of heavy metal emissions from coal combustion and other industrial processes.
Recently, the Apblett research group has developed a new process for synthesis of ceramic oxides called the Sol-Jello process. This process involves addition of gelatin to a hot aqueous solution of metal chlorides followed by cooling to 10°C. This leads to formation of a homogeneous gel that is then placed in a chamber containing concentrated ammonium hydroxide. Hydrolysis of the metal cations then occurs as ammonia diffuses through the gel. The by-products ammonium chloride and gelatin can be removed by heating to 600°C to yield the final metal oxide. Depending on the gelatin concentration, nanoparticulate oxides (high gelatin) or porous 3-dimensional metal oxide products (low gelatin) can be synthesized. So far the process has been used to synthesize spinel and yttrium aluminum garnet but it will be useful for a very large range of materials.
- A.W. Apblett, L.E. Reinhardt, and E. H. Walker "The Application of Liquid Metal Carboxylates to the Preparation of Aluminum-Containing Ceramics" Comments in Inorganic Chemistry, 20, 83-99, 1998.
- A.W. Apblett, M.L. Breen, and E. H. Walker "Synthesis of Nickel Ferrite Using Liquid Metal Carboxylates" Chem. Mater., 10, 1265-1269, 1998.
- A.W. Apblett and E.M. Holt "Structure of Potassium Methoxyacetate Tetrahydrate" Acta. Cryst., C55, 539-542, 1999.
- Allen W. Apblett, B.P. Kiran, and Katie Oden "Reductive Dechlorination of Chloromethanes Using Tungsten and Molybdenum Hydrogen Bronzes or Sodium Hypophosphite" in Chlorinated Solvents and DNAPLS; Reactive Permeable Barriers and Other Innovations, (ACS Book Series, Washington, DC, 2002), 154-164.
- E.J. Eisenbraun, K.W. Payne, J.S. Bymaster, A. Iob, and A. Apblett "An Improved Method for Dehydrating Alcohols Using Inorganic Sulfates Supported on Silica in Refluxing Octane" Industrial & Engineering Chemistry, 41, 2611-2616 (2002).
- A.W. Apblett, S. M. Al-Fadul, M. Chehbouni, and T. Trad "Ceramic-Derived Magnetic Extractants for Waste Water Treatment" Ceram. Trans., 143,15-22 (2003).
- A,W. Apblett, Sol-Gello Process for Synthesis of Yttrium Aluminum Garnet, Ceram. Trans. 135, 97-104 (2002).
- A.W. Apblett, M. Chehbouni, and B.P. Kiran. Absorption of Heavy Metals and Radionuclides from Water in a Direct-to-Ceramic Process, Ceramic Transactions 143. (2003).
- Satish Kuriyavar, B.P. Kiran, and Allen Apblett "Preparation of Micron-Sized Spherical Porous Iron Oxide Particles" J. Mater. Chem., 13, 983-985 (2003).