Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2000-12-11
2003-07-15
Lovering, Richard D. (Department: 1712)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C428S391000, C428S404000, C435S803000, C501S012000, C502S407000, C502S527240, C516S100000, C516S111000, C530S417000
Reexamination Certificate
active
06592764
ABSTRACT:
BACKGROUND OF THE INVENTION
Large pore size molecular sieves are in high demand for reactions or separations involving large molecules and have been sought after for several decades. Due to their low cost, ease of handling, and high resistance to photoinduced corrosion, many uses have been proposed for mesoporous metal oxide materials, such as SiO
2
, particularly in the fields of catalysis, molecular separations, fuel cells, adsorbents, patterned-device development, optoelectronic devices, and chemical and biological sensors. One such application for these materials is the catalysis and separation of molecules that are too large to fit in the smaller 3-5 Å pores of crystalline molecular sieves, providing facile separation of biomolecules such as enzymes and/or proteins. Such technology would greatly speed processing of biological specimens, eliminating the need for time consuming ultracentrifugation procedures for separating proteins. Other applications include supported-enzyme biosensors with high selectivity and antigen expression capabilities. Another application, for mesoporous TiO
2
, is photocatalytic water splitting, which is extremely important for environmentally friendly energy generation. There is also tremendous interest in using mesoporous ZrO
2
, Si
1−x
Al
x
O
y
, Si
1−x
Ti
x
O
y
as acidic catalysts. Mesoporous WO
3
can be used as the support for ruthenium, which currently holds the world record for photocatalytic conversion of CH
4
to CH
3
OH and H
2
. Mesoporous materials with semiconducting frameworks, such as SnO
2
and WO
3
, can be also used in the construction of fuel cells.
Mesoporous materials in the form of monoliths and films have a broad variety of applications, particularly as thermally stable low dielectric coatings, non-linear optical media for optical computing and self-switching circuits, and as host matrices for electrically-active species (e.g. conducting and lasing polymers and light emitting diodes). Such materials are of vital interest to the semiconductor and communications industries for coating chips, as well as to develop optical computing technology which will require optically transparent, thermally stable films as waveguides and optical switches.
These applications, however, are significantly hindered by the fact that, until this invention, mesoscopically ordered metal oxides could only be produced with pore sizes in the range (15~100 Å), and with relatively poor thermal stability. Many applications of mesoporous metal oxides require both mesoscopic ordering and framework crystallinity. However, these applications have been significantly hindered by the fact that, until this invention, mesoscopically ordered metal oxides generally have relative thin and fragile channel walls.
Since mesoporous molecular sieves, such as the M41S family of materials, were discovered in 1992, surfactant-templated synthetic procedures have been extended to include a wide variety of compositions and conditions for exploiting the structure-directing functions of electrostatic and hydrogen-bonding interactions associated with amphiphilic molecules. For example, MCM-41 materials prepared by use of cationic cetyltrimethylammonium surfactants commonly have d(100) spacings of about 40 Å with uniform pore sizes of 20-30 Å. Cosolvent organic molecules, such as trimethylbenzene (TMB), have been used to expand the pore size of MCM-41 up to 100 Å, but unfortunately the resulting products possess less resolved XRD diffraction patterns. This is particularly the case concerning materials with pore sizes near the high-end of this range (ca. 100 Å) for which a single broad diffraction peak is often observed. Pinnavaia and coworkers, infra, have used nonionic surfactants in neutral aqueous media (S
0
I
0
synthesis at pH=7) to synthesize worm-like disordered mesoporous silica with somewhat larger pore sizes of 20-58 Å (the nomenclature S
0
I
0
or S
+
I
−
are shorthand notations for describing mesophase synthesis conditions in which the nominal charges associated with the surfactant species S and inorganic species I are indicated). Extended thermal treatment during synthesis gives expanded pore sizes up to 50 Å; see D. Khushalani, A. Kuperman, G. A. Ozin,
Adv. Mater.
7, 842 (1995).
The preparation of films and monolithic silicates using acidic sol-gel processing methods is an active research field, and has been studied for several decades. Many studies have focused on creating a variety of hybrid organic-silicate materials, such as Wojcik and Klein's polyvinyl acetate toughening of TEOS monoliths (Wojcik, Klein; SPIE,
Passive Materials for Optical Elements II
, 2018, 160-166 (1993)) or Lebeau et al's organ ic-inorgan ic optical coatings (B. Lebeau, Brasselet, Zyss, C. Sanchez;
Chem Mater.,
9, 1012-1020 (1997)). The majority of these studies use the organic phase to provide toughness or optical properties to the homogeneous (non-mesostructured) monolithic composite, and not as a structure-directing agent to produce mesoscopically ordered materials. Attard and coworkers have reported the creation of monoliths with ~40 Å pore size, which were synthesized with low molecular weight nonionic surfactants, but did not comment on their thermal stability or transparency; see G. S. Attard; J. C. Glyde; C. G. G61tner, C. G.
Nature
378, 366 (1995). Dabadie et al. have produced mesoporous films with hexagonal or lamellar structure and pore sizes up to 34 Å using cationic surfactant species as structure-directing species; see Dabadie, Ayral, Guizard, Cot, Lacan;
J. Mater Chem.,
6, 1789-1794, (1996). However, large pore size (>50 Å) monoliths or films have not been reported, and, prior to our invention, the use of block copolymers as structure-directing agents has not been previously explored (after our invention, Templin et al. reported using amphiphilic block copolymers as the structure-directing agents, aluminosilicate mesostructures with large ordering lengths (>15 nm); see Templin, M., Franck, A., Chesne, A. D., Leist, H., Zhang, Y., Ulrich, R., Schädler, V., Wiesner, U. Science 278, 1795 (Dec. 5, 1997)). For an overview of advanced hybrid organic-silica composites, see Novak's review article, B. Novak;
Adv. Mater.,
5, 422-433 (1993).
While the use of low-molecular weight surfactant species have produced mesostructurally ordered inorganic-organic composites, the resulting materials have been in the form of powders, thin films, or opaque monoliths. Extension of prior art surfactant templating procedures to the formation of nonsilica mesoporous oxides has met with only limited success, although these mesoporous metal oxides hold more promise in applications that involve electron transport and transfer or magnetic interactions. The following mesoporous inorganic oxides have been synthesized with small mesopore sizes (<4 nm) over the past few years:
MnO
2
(Tian, Z., Tong, W., Wang, J., Duan, N., Krishnan, V. V., Suib, S. L.
Science.
Al
2
O
3
(Bagshaw, S. A., Pinnavaia, T. J.
Angew. Chem. Int. Ed. Engl.
35,1102 (1996)),
TiO
2
(Antonelli, D. M., Ying, J. Y.
Angew. Chem. Int. Ed. Engl.
34, 2014 (1995)),
Nb
2
O
5
(Antonelli, D. M., Ying, J. Y.
Chem. Mater.
8, 874 (1996)),
Ta
2
O
5
(Antonelli, D. M., Ying, J. Y.
Chem. Mater.
8, 874 (1996)),
ZrO
2
(Ciesla, U., Schacht, S., Stucky, G. D., Unger, K. K., Schüth, F.
Angew. Chem. Int. Ed. Engl.
35, 541 (1996)),
HfO
2
(Liu, P., Liu, J., Sayari, A.
Chem. Commun.
557 (1997)), and reduced Pt (Attard, G. S., Barlett P. N., Coleman N. R. B., Elliott J. M., Owen, J. R., Wang, J. H. Science, 278, 838 (1997)).
However these often have only thermally unstable mesostructures; see Ulagappan, N., Rao, C. N. R.
Chem Commun.
1685 (1996), and Braun, P. V., Osenar, P., Stupp, S. I.
Nature
380, 325 (1996).
Stucky and co-workers first extended the surfactant templating strategy to the synthesis of non-silica-based mesostructures, mainly metal oxides. Both positively and negatively charged surfactants were use
Chmelka Bradley F.
Feng Jianglin
Fredrickson Glenn H.
Huo Qisheng
Lukens, Jr. Wayne
Fulbright & Jaworski L.L.P.
Lovering Richard D.
The Regents of the University of California
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