Liquid purification or separation – Processes – Chromatography
Reexamination Certificate
1999-09-15
2001-06-26
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Chromatography
C210S660000, C210S681000, C210S198200, C210S502100, C210S635000, C502S400000, C502S407000, C502S408000, C502S439000, C501S039000
Reexamination Certificate
active
06251280
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to molecular imprint coating techniques. More particularly, the invention relates to the use of molecular imprint coating techniques for the synthesis of mesoporous sorbents and the use of such sorbents for adsorption, separation, and sensing of molecules.
BACKGROUND
One of the major problems facing industries such as mining, precious metals, and energy (e.g., coal mining and coal-fired power plants) is removal of toxic metal ions from process effluents. Stringent standards for the maximum level of pollutants in water that is funneled into domestic and ground water systems are being promulgated by federal and state agencies. Thus, there is a need in the art for simple and effective methods for the removal of such metals from process effluents.
Polymerization of metal alkoxides in the presence of molecular assemblies of surfactants or related substances, acting as structure directors, has resulted in several novel classes of mesoporous and macroporous inorganic materials with extremely high surface areas and ordered mesostructure. The mechanism for the organization of such mesostructure involves electrostatic interactions and charge matching between micellar assemblies of quaternary ammonium cations and anionic silicate oligomer species. These materials have now found extensive applications as catalyst supports and chromatographic resins.
Many applications of mesoporous materials require functionalization of the material's silanol surfaces. Presently, extensive research is being conducted to develop procedures to introduce functional silane ligands into the surfaces of the ordered mesoporous materials
Feng et. al. (Science: 276, 923-926; 1997) and Mercier and Pinnavaia (Advanced Materials: 9, 500-503; 1997) have developed new, effective mesoporous sorbents for the removal of toxic metal ions based on mesoporous materials as supports. Their methodology involves coating surfaces of hexagonally packed mesoporous silica with organic functional groups to enhance their affinities for metal ions. High capacities and fast kinetics have been observed for these new sorbents. The selectivity of these materials relies solely on the affinity of the surface-coated functional ligand for a specific metal ion, with no consideration of the stereochemical interactions between the ligand and the metal ion. Thus, there is a need in the art for mesoporous sorbents having stereochemical specificity.
Bulk molecular imprinting methods based on the template approach have been used in crosslinked polymers, as well as in silica gels, to prepare polymeric supports possessing solid-state organized structures. Imprinting processes generally involve three steps: (1) selection of a target molecule as a template; (2) incorporation of the template into rigid solid networks through in situ copolymerization; and (3) removal of the template, leaving cavities with a predetermined number and arrangement of ligands that later “recognize” or selectively rebind the template or target molecule. These imprinted organic polymers have been used to resolve racemates and separate mixtures of metal cations. One major drawback associated with this bulk molecular imprinting technique is that the kinetics of the sorption-desorption process are unfavorable, as the template and ligand are totally embedded in the bulk polymer matrices and the mass transfer must take place through nonpolar, microporous channels. Furthermore, molecular imprinting studies have thus far all been conducted in disordered polymers or amorphous sol-gel matrices where the inhomogeneity of the cavities produced by the molecular imprinting reduces the selectivity of the final imprinted materials. Thus, there is a need for a bulk molecular imprinting technique that provides favorable sorption-desorption kinetics.
The generally accepted mechanism for such direct coating methods involves the initial hydrolysis of siloxane groups in the functional silane ligand followed by condensation with the surface silanol groups to produce ligands that are covalently bound or “tethered” to the surfaces. Drawbacks associated with this coating method are the time-consuming reflux syntheses and low loading of the functional silane ligands. Thus, a simpler and more efficient method for imprint coating is needed.
SUMMARY OF THE INVENTION
The present invention relates generally to mesoporous sorbent materials having high capacity, high selectivity, fast kinetics, and molecular recognition capability. The sorbent materials of the present invention exhibit significantly greater target ion binding selectivities than sorbents prepared by conventional coating methods. These sorbent materials are built upon the unique environments of ordered, hexagonally-packed mesopore surfaces and provide superior performance when compared to conventional sorbents. The mesoporous substrates of the invention exhibit many beneficial properties. These properties include circularly curved, extremely rigid pore surfaces, with optimum pore diameters of 20 Å to 500 Å that match the stereochemical requirements for surface imprinting of four or six coordinated metal ions, and a very uniform pore size distribution, which allows the generation of the uniform imprints and limits the possible choices of coordination environments.
The present invention also relates to a process for preparing these mesoporous substrates through molecular imprinting techniques. Surface imprinting was conducted in cylindrical concave surfaces, thereby successfully organizing ligand functional groups according to the sizes of the template. In general, the present process is different from conventional processes in that a template molecule is bound to one end of more than one bifunctional ligand to form a complex. This is the template binding end of the bifunctional ligand. This complex is then bound to the substrate through the free functional group of the bifunctional ligands. This is the substrate binding end of the bifunctional ligand. The template molecule is then removed from the sorbent creating ligand imprints. This coating methodology allows precise control of the stereochemical arrangement of ligands on the surfaces of mesopores, which in turn optimizes the binding of the targeted template molecule, such as a metal ion, through the creation of a tailored binding site which reflects both the size and stereochemical signature of the template molecule. This structure leads to template molecule recognition and subsequent selective binding of the template molecule from mixtures containing the template molecule.
The present invention also relates to methods of using the mesoporous sorbent materials. These uses include, but are not limited to the following: separation of toxic metals from process effluents, paints, and other samples; selective separation of specific ions from industrial process streams; removal of heavy metals from acid mine drainage, electroplating, wastewater, and municipal landfill leachate; detection of target molecules, such as ions, amino acids, drugs, herbicides, fertilizers, and trinitrotoluene (TNT) in samples; separation and/or detection of substances using chromatography; separation of enantiomeric mixtures of chemicals, such as pharmaceuticals; imaging agents; sensors; coatings; and composites. Thus, the sorbent materials of the present invention are useful in such industries as the airline, automotive, waste water management, recycling, mining, nuclear, pharmaceutical, chemical, and biological industries.
Therefore, it is an object of the present invention to provide mesoporous sorbent materials having improved stereochemical specificity.
Another object of the present invention is to provide mesoporous sorbent materials exhibiting high selectivity for a specific target molecule so that these materials may selectively remove a specific target molecule from a complex mixture or solution of different molecules.
It is another object of the present invention to provide mesoporous sorbent materials having improved kinetics.
It is yet another
Burleigh Mark C.
Dai Sheng
Shin Yongsoon
Kilpatrick & Stockton LLP
Therkorn Ernest G.
University of Tennessee Research Corporation
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