Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Including organic component
Reexamination Certificate
1998-02-06
2001-12-04
Griffin, Steven P. (Department: 1723)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Including organic component
C502S060000, C502S063000, C502S064000, C502S065000, C423S701000, C423S705000, C423S708000
Reexamination Certificate
active
06326326
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a surface functionalized mesoporous material (SFMM) and method of making same. More specifically, the SFMM has an ordered or organized array of functional molecules containing specific functional groups, with the functional molecules attached to the available surface area of the mesoporous substrate. The surface functionalized mesoporous material is useful for but not limited to chemical separations, chemical delivery, and catalysis. As used herein the term “monolayer molecule(s) is a subset of “functional molecule(s)” both including organic, inorganic molecules and combinations thereof. An assembly or array of functional molecule(s) may include one (mono) or more (multi) layers of functional molecules. Within the category of organic molecules are included straight chain hydrocarbons, organometallics, and combinations thereof.
BACKGROUND OF THE INVENTION
Chemical separations, chemical delivery and catalysis have all experienced improvements when accomplished at the mesoporous scale. However, widespread commercial use of mesoporous materials has been limited because mesoporous materials lack specific functionality on their surfaces. Mesoporous materials
FIG. 1
a
are made of a solid substrate
100
that has been templated to form mesopores
102
which are pores having a diameter or characteristic cross section dimension from about 1.3 nm to about 50 nm.
Surface functionalized materials have also been proposed for chemical separations. Functional molecules
FIG. 1
b
are formed on a substrate
110
wherein functional molecules
112
are attached to the substrate
110
with an attaching group
114
, usually a siloxane group. The terminal end of the functional molecule may have a functional group
116
that binds to the chemical of interest for separation. The performance of surface functionalized materials is limited by (1) surface area of the substrate
110
and (2) the functional group density or coverage of the substrate surface area.
Attaching organosilanes on a ceramic oxide surface involves a complex series of reversible and irreversible chemical processes. In order for these molecules to bind to the ceramic surface, it is critical that either the surface or the organosilane be in appropriate (hydroxylated) chemical form to undergo the condensation chemistry necessary for the anchoring process. This can be accomplished in one of several ways, and water is critical to all of them.
In the usual method of attaching functional molecules on glass or silicon wafers, the substrate is cleaned and hydrated in such a way that virtually all of the silicon atoms on the surface bear a hydroxyl group (such a group is called a surface silanol). This level of coverage amounts to approximately 5×10
18
silanols per square meter. In addition, due to the hydrophilicity of this interface and the fact that the cleaning process is usually carried out in aqueous media, there is usually a significant amount of water associated with the silanol interface. Exposure of such an interface to a solution of organosilanes (e.g. alkoxy, chloro, etc.) results in hydrolysis of the silane to afford the corresponding hydroxysilane, which is strongly hydrogen bound to the hydrated silica surface. This hydroxysilane then undergoes facile condensation with the neighboring surface silanol, resulting in covalent attachment of the organosilane to the silica surface. Any remaining chlorides or alkoxides on the organosilane can also undergo similar hydrolysis (secondary hydrolysis) and condensation to provide crosslinking between the silane molecules bound to the silica surface. This crosslinking significantly enhances the stability of the monolayer coating by linking adjacent silanes to one another, thereby providing secondary points of attachment.
If the cleaned silica surface is dried, then reaction of the organosilane can take place directly with the surface silanols. However, since the surface silanols are substantially less nucleophilic than water and there is a significant kinetic barrier for this reaction, this chemistry is very slow and inefficient relative to the hydrolysis/condensation chemistry described above. In addition, the lack of surface water precludes any secondary hydrolysis and condensation, thereby preventing any crosslinking. Thus, the monolayers obtained by this method are less stable and therefore of lesser quality.
The calcination step in the preparation of the mesoporous silica severely desiccates the silica surface, both in terms of adsorbed water molecules and in terms of surface silanols. All surface water is removed during the calcination step, and the vast majority of surface silanols undergo condensation to form siloxane bridges, leaving only a small number of isolated silanols. Based on our experiments, we estimate this number of remaining silanols to be about only 10% of the silicon atoms on the surface, or about 5×10
17
silanols per square meter.
Mesoporous materials have been made according to methods set forth in U.S. Pat. Nos. 5,264,203, 5,098,684, 5,102,643, and 5,238,676 (Mobil Oil Corporation, Fairfax, Va.) as well as U.S. Pat. No. 5,645,891 (Battelle Memorial Institute, Richland, Wash.)
In the Mobil patents, a calcined silica surface is treated with an organosilane with no water present to induce hydrolysis of the silane. The only nucleophiles present capable of reaction with the silane are the small number of silanols left on the surface after the calcination process. This limits surface coverage to approximately 5×10
17
organosilanes per square meter (approximately 10% of available silanols). In addition, since there is no water present for secondary hydrolysis and condensation, there can be no crosslinking to enhance the stability of the monolayer.
The Mobil patents report derivatizing 90% of the available silanols. It is critical to note, however, that their work was performed on a calcined silica surface with no added water. Therefore, there were very few silanols (approximately 5×10
17
per square meter) and no water on the silica surface. They were successful in derivatizing 90% of these silanols, incorporating approximately 4.5×10
17
silanes per square meter or only about 9% of the silicon atoms on the surface. Again, since there was no water on the surface, no secondary hydrolysis could take place, so there could be no stability-enhancing crosslinking of the monolayer.
Accordingly, there is a need for mesoporous materials with greatly increased number of the functional molecules to greatly increase the separative, catalytic and chemical delivery capability of mesoporous materials.
Chemical separations are relied upon in a wide range of industries. Various industrial, military, agricultural, medical and research activities have resulted in severe contamination, especially metal contamination, of the environment. Chemical separations are particularly useful for cleanup and remediation of contaminated waste sites. In the case of mercury, contamination may be from fossil fuel combustion; chlorine, caustic soda cement, and lime production; waste and sewage sludge incineration; and mining and benificiation operations. Contamination may be present in the air, water, sludge, sediment, and soil.
Mercury appears in three primary forms:
(1) metallic mercury: Hg
0
,
(2) inorganic mercury: divalent mercury, Hg
2+
; monovalent mercury, Hg
2
2+
; neutral mercury compounds, HgCl
2
, Hg(OH)
2
and
(3) organic mercury: phenylmercury, C
6
H
5
Hg
+
, C
6
H
5
HgC
6
H
5
; alkoxyalkyl mercury, CH
3
O—CH
2
—CH
2
—Hg
+
; methylmercury, CH
3
Hg
+
, CH
3
HgCH
3
.
These compounds can be ranked in order of decreasing toxicity as: methylmercury, mercury vapor, inorganic salts of mercury and a number of organic forms such as phenylmercury salts (Mitra, Mercury in the Ecosystem, 1986, Trans Tech Publications). Methylmercury, the most toxic form, is formed mainly by methylation of mercury by methanogenic bacteria which are widely distributed in the sediments of ponds and in
Feng Xiangdong
Fryxell Glen E.
Liu Jun
Battelle (Memorial Institute)
Griffin Steven P.
Ildebrando Christina
Zimmerman Paul W.
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