Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound
Reexamination Certificate
2001-06-29
2003-11-11
Le, H. Thi (Department: 1773)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
C423S023000, C423S265000, C423S266000, C075S010620, C075S370000, C075S371000, C075S373000
Reexamination Certificate
active
06645444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal nanocrystals and the synthesis thereof, and more particularly to soluble metal nanocrystals and a scalable synthesis therefor.
BACKGROUND OF THE INVENTION
Metal nanocrystals are widely used as catalysts, and are increasingly being explored as single electron devices, self-assembled monolayers, and thin film precursors. A limitation on the applications of metal nanocrystals is the impracticality of scaling existing syntheses to an industrial scale. Cluster deposition in vacuum is characterized by low throughput, difficulty in stabilizing nanocrystals towards coalescence, and complex synthetic systems. (P. Jensen,
Reviews of Modern Physics,
71(5), (1999) 1695-1734). Colloidal syntheses of metal nanocrystals are well established, yet suffer from low yields per volume and difficulty in removing colloidal stabilizers after synthesis. An early preparation for colloidal metal includes combination of a dilute solution of hydrazine hydrate (1:2000) with an ammoninical copper sulfite solution (1:1000) in the presence of gum arabicum. Careful heating yields a hydrosol which after four days of dialysis against distilled water yields a hydrosol that is red in reflection and blue in optical transmission (A. Gutbeir, G. Hoffineyer, Z.
Anorg. Allgem. Chem.,
44, (1905) 227). Other colloidal syntheses have developed that retain the characteristics of low concentration and a polymeric or surfactant stabilizer. (H. H. Huang et al., Langmuir, 13 (1997) 172-175; I. Lisiecki and M. P. Pileni,
J. Phys. Chem.,
99 (14) (1995) 5077-5082; and Nanoparticles and Nanostructured Films, J. H. Fendler, Wiley-VCH, 1998, Chapter 4.) Shuttle molecules have also been employed to transfer metal ions to an organic phase prior to reduction in the presence of a solubilizing passivating agent. While this method is attractive for producing metal ions from an otherwise acidic acid solution, the cost of shuttle molecules such as tetraalkyl ammonium salts is considerable. (Brust et al.,
J. Chem. Soc. Commun.
. (1994) 801.) An additional group of metal nanocrystal syntheses has used an organic reducing agent as a ligand to complex a metal ion intended for reduction. While such methods produce good yields of metal nanoparticulate, such methods are characterized by particle agglomeration. (N. Arul Dhas et al.,
Chem. Mater.
10 (1998) 1446-1452.)
The ability to produce economically large quantities of metal nanocrystals that are soluble in a given solvent affords numerous opportunities to develop novel catalytic and materials systems. Thus, there exists a need for a metal nanocrystal synthesis that affords soluble nanocrystals by a process that is readily scalable to produce gram and kilogram quantities.
SUMMARY OF THE INVENTION
A process for forming metal nanocrystals includes the steps of complexing a metal ion and an organic ligand in a first solvent and introducing a reducing agent to reduce a plurality of metal ions to form the metal nanocrystal associated with the organic ligand. The organic ligand has the formula A—L—(Q)
n
or
where L is C
1
to C
30
alkyl, C
5
to C
30
cycloalkyl, C
2
to C
30
alkenyl, C
6
to C
30
cycloalkenyl, C
6
to C
40
aromatic; Q is a heteroatom containing moiety capable of coordinating a metal ion, the heteroatom including oxygen, nitrogen or sulfur; the heteroatom being present as an alcohol, carbonyl, carboxyl, phosphatidyl, sulfonyl, sulfinyl, nitrosyl, amino, imido, azide, thiol, ester, ether, secondary amino, thioester, thioether, silanol, siloxyl; and A is a solubility imparting moiety illustratively including hydrogen, alcohol, sulfonyl, sulfhydryl, amino, secondary amino, phosphatidyl, carboxyl, phenyl, nitro-, ester, ether, thioester and thioether; n is an integer between 1 and 4. A process for forming a copper containing crystal in particular includes the steps of forming a complex between a copper ion and an organic ligand in a solvent and introducing a reducing agent illustratively including hydrogen gas, hydrides and hydrazines to reduce the copper ions to form a copper nanocrystal associated with the organic ligand. Optionally, the ligand is chosen to impart solubility on the copper nanocrystal associated therewith in a second solvent immiscible with the reaction solvent so as to transport the copper nanocrystals into the second solvent and thereby leave the reaction byproducts in the reaction solvent. A solution includes a plurality of copper nanocrystals having an average domain size in between 1 and 50 nanometers, each nanocrystal having a surface passivated with an organic ligand having a molecular weight of less than 400 atomic units and a solvent having an affinity for a portion of the ligand extending from the copper nanocrystal surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a reductive synthesis of a metal ion complex where the metal ion complex ligands following reaction serve to prevent agglomeration and impart solubility to the resulting metal nanocrystal. The resulting metallic nanocrystals preferably form kinetically stable solutions, in contrast to suspensions.
As used herein, “nanocrystal” defines a crystalline domain having dimensions along at least one axis of between 1 nanometer and 100 nanometers.
As used herein, “solubility” is defined as a substance dispersed in a liquid that is able to pass through a 0.2 micron filter and remain in the liquid for 24 hours after centrifugation at 7000 rpm for ten minutes.
A process for forming metallic nanocrystals according to the instant invention includes forming a complex between a metal ion and an organic ligand in a solvent. It is appreciated that the entire coordination sphere of the metal ion need not be filled by organic ligands; rather, spectator ions, solvent molecules and solvent ions may also form coordinate bonds to the metal ion. A reducing agent is then introduced to the metal ligand complex. The reducing agent is selected to have an electrochemical potential sufficient to reduce the metal ion from a positive oxidation state to a zero oxidation state metal atom or produce metal hydrides that in turn reduce to zero oxidation state metals. The result of metal ion reduction in the presence of the organic ligand-metal ion complex is the formation of a metal nanocrystal having associated therewith the organic ligand. The association of the organic ligand with the metal nanocrystal arrests nanocrystal growth, limits nanocrystal agglomeration, and preferably is selected to impart solubility on the resulting nanocrystal.
According to the present invention a metal nanocrystal is formed of a metallic element including beryllium, magnesium, aluminum, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, thallium, lead, bismuth, polonium, thorium, protactinium, uranium, neptunium, and plutonium. Typically, an inorganic metal salt is chosen as the source of metal ions for reduction to form a nanocrystal. The choice of metal ion counter anion largely being dictated by solubility and compatibility with the solvent. Metal ion counter anions operative herein illustratively include halides, such as fluoride, chloride, bromide and iodide; nitrate; phosphate; perchlorate; formate; acetate; borate; hydroxide; silicate; carbonate; sulfite; sulfate; nitrite; phosphite; hydrates thereof; and mixtures thereof.
It is appreciated that a plurality of different metal ions are reduced simultaneously so as to form a metal alloy or metal ion doped metal nanocrystal, provided the predominant metal ion reagent based on atomic percent is present as a metal ion ligand complex. A dopant metal ion typically is uncoordinated and reduce
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Le H. Thi
Nanospin Solutions
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