U.S. patent application number 12/227716 was filed with the patent office on 2010-02-25 for non-metallic nano/micro particles coated with metal, process and applications thereof.
Invention is credited to Ajay Prabhakar Malshe, Vinod Chintamani Malshe.
Application Number | 20100047546 12/227716 |
Document ID | / |
Family ID | 38779150 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100047546 |
Kind Code |
A1 |
Malshe; Vinod Chintamani ;
et al. |
February 25, 2010 |
Non-Metallic Nano/Micro Particles Coated with Metal, Process and
Applications Thereof
Abstract
The present invention provides a simple and economical process
for preparation of metal-coated non-metallic nano/micro particles.
The nano/micro particles are composed of a core and metallic coat
over the core using silver or other transition/noble metals. The
core of the non-metallic nano/micro particles are selected from
inorganic material such as silica, calcium carbonate, barium
sulfate, or emulsion grade polyvinyl chloride and other polymers
prepared by emulsion process including porous polymers. The metal
coating is selected from the transition/noble metals such as
copper, nickel, silver, palladium, platinum, osmium, ruthenium,
rhodium, and such other metals and their combinations that are
easily reducible to elemental metal.
Inventors: |
Malshe; Vinod Chintamani;
(Mulund, IN) ; Malshe; Ajay Prabhakar;
(Springdale, AR) |
Correspondence
Address: |
J. CHARLES DOUGHERTY
200 WEST CAPITOL AVE, SUITE 2300
LITTLE ROCK
AR
72201
US
|
Family ID: |
38779150 |
Appl. No.: |
12/227716 |
Filed: |
May 21, 2007 |
PCT Filed: |
May 21, 2007 |
PCT NO: |
PCT/US07/11998 |
371 Date: |
July 6, 2009 |
Current U.S.
Class: |
428/221 ;
264/239; 427/212; 427/217; 427/222; 428/403; 428/404; 428/407;
977/773 |
Current CPC
Class: |
C23C 18/40 20130101;
C23C 18/1635 20130101; Y10T 428/2991 20150115; C08K 9/02 20130101;
C08K 9/02 20130101; B22F 1/025 20130101; C08L 27/06 20130101; B22F
9/24 20130101; C08L 23/04 20130101; C23C 18/34 20130101; C23C
18/1662 20130101; C23C 18/1639 20130101; B22F 2999/00 20130101;
C08K 9/02 20130101; C08K 9/02 20130101; C08K 9/02 20130101; B22F
2999/00 20130101; C08K 2201/011 20130101; C23C 18/1676 20130101;
Y10T 428/2993 20150115; C23C 18/44 20130101; Y10T 428/249921
20150401; Y10T 428/2998 20150115; C23C 18/1658 20130101; C23C 18/31
20130101; C08L 23/10 20130101; B22F 1/025 20130101; C08L 25/04
20130101 |
Class at
Publication: |
428/221 ;
428/403; 428/404; 428/407; 427/212; 427/217; 427/222; 264/239;
977/773 |
International
Class: |
B32B 15/04 20060101
B32B015/04; B32B 27/04 20060101 B32B027/04; B32B 5/02 20060101
B32B005/02; B01J 13/02 20060101 B01J013/02; B05D 7/00 20060101
B05D007/00; B29C 70/00 20060101 B29C070/00; B22F 1/00 20060101
B22F001/00; C09K 3/00 20060101 C09K003/00; C09C 3/06 20060101
C09C003/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2006 |
IN |
772/MUM/2006 |
Claims
1. A nano/micro particle, comprising: (a) a core comprising a
non-metallic material; and (b) an overlayer comprising a
transition/noble metal, wherein said overlayer comprises about 1 to
2 percent of said nano/micro particle by weight.
2. The nano/micro particle of claim 1, wherein said non-metallic
material of said core is selected from the group consisting of
silica, calcium carbonate, barium sulfate, and polyvinyl
chloride.
3. The nano/micro particle of claim 1, wherein said non-metallic
material of said core comprises an emulsion-grade polymer.
4. The nano/micro particle of claim 1, wherein said non-metallic
material of said core comprises a porous polymer.
5. The nano/micro particle of claim 1, wherein said
transition/noble metal of said overlayer is selected from the group
consisting of copper, nickel, silver, palladium, platinum,
ruthenium, gold, osmium, and rhodium.
6. A method for preparing a nano/micro particle, comprising the
method steps of: (a) dissolving a metallic salt in a liquid
solvent; (b) dispersing a quantity of non-metallic nano/micro
particles in the solvent; (c) evaporating the solvent to produce a
slurry comprising a plurality of coated nano/micro particles; (d)
adding a reducing agent to the slurry; and (e) drying the
slurry.
7.-8. (canceled)
9. The method of claim 6, wherein said metallic salt comprises a
metal selected from the group consisting of copper, nickel, silver,
palladium, platinum, ruthenium, gold, osmium, and rhodium.
10. The method of claim 6, wherein said non-metallic nano/micro
particles comprise a material selected from the group consisting of
silica, calcium carbonate, barium sulfate, and polyvinyl
chloride.
11. The method of claim 6, wherein said non-metallic nano/micro
particles comprise an emulsion-grade polymer.
12. The method of claim 6, wherein said non-metallic nano/micro
particles comprise a porous polymer.
13.-54. (canceled)
55. An anti-microbial material, comprising: (a) a packaging
material; and (b) a plurality of nano/micro particles impregnated
in said packaging material, each such nano/micro particle
comprising a non-metallic core and a metallic overlayer, wherein
said overlayer comprises about 1 to 2 percent of said nano/micro
particle by weight.
56. The anti-microbial packaging material of claim 55, wherein said
plastic material is selected from a group consisting of
polyethylene, polypropylene, polyvinyl chloride, and
polystyrene.
57. The anti-microbial packaging material of claim 55, wherein said
plastic material is formed by one of extrusion, blowing,
calendaring, compression, and injection molding.
58. A method of producing an anti-microbial packaging material,
comprising the steps of: (a) producing a plurality of nano/micro
particles; (b) mixing the plurality of nano/micro particles with
plastic granules; (c) heating the resulting mixture until the
plastic granules are melted; and (d) cooling the mixture to form a
solid plastic material impregnated with nano/micro particles.
59. The method of claim 58, wherein the plurality of nano/micro
particles each comprise a non-metallic core and a metallic
overlayer.
60. (canceled)
61. The method of claim 59, wherein the metallic overlayer
comprises about 1 to 2 percent of each nano/micro particle by
weight.
62. The method of claim 59, wherein the non-metallic core is
selected from the group consisting of silica, calcium carbonate,
barium sulfate, and polyvinyl chloride.
63. The method of claim 59, wherein the non-metallic core comprises
an emulsion-grade polymer.
64. The method of claim 59, wherein the non-metallic core comprises
a porous polymer.
65. (canceled)
66. The method of claim 59, wherein the metallic overlayer
comprises a metal selected from the group consisting of copper,
nickel, silver, palladium, platinum, ruthenium, gold, osmium, and
rhodium.
67.-101. (canceled)
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of the earlier
filing date of an Indian provisional patent entitled "Non-metallic
nano/micro particles coated with metal and process thereof,"
application number 772/MUM/2006, filed May 22, 2006, the disclosure
of which is incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention generally relates to non-metallic nano/micro
particles coated with metal, particularly to nano/micro particles
of silica, barium sulfate, calcium carbonate, solid polymer
particles or high-area porous polymeric nano/micro particles coated
with silver or other transition/noble metals. The invention also
relates to a simple and economical process for preparation and
application of the same. This invention also relates to a unique
process mechanism enabling applications for a sustainable
environment.
BACKGROUND
[0003] Micro- and nanotechnologies are at the centre of numerous
investigations and huge investments, particularly in the areas of
information technologies, food and health care. Coupling the skills
in mineral synthesis, organic synthesis, physical-chemistry of
complex media, and physics of materials has been the key for the
success of these developments. Nano and micro particles in
particular have a wide range of industrial applications such as in
healthcare, medical, and photographic emulsions. In other
applications, nano/micro particles have been used as nucleation
centers, which may be used to form larger particles with specific
constructions.
[0004] Silver has long been considered a powerful and natural
antibiotic and antibacterial. The combination of silver and
nano/micro particles is extremely attractive in many areas. The
extremely small size of silver nano and micro particles means they
exhibit high surface to volume ratios, and thus enhanced surface
related properties such as catalysis when compared with bulk
silver. This allows them to easily and aggressively interact with
the environment, including microorganisms as well as other
environmental agents, thus increasing their antibacterial
efficiency.
[0005] In addition to having an antibacterial effect, silver has
antifungal and deodorizing effects that have been recently
exploited commercially. A study from the University of Texas and
Mexico University was recently published in the journal
Nanotechnology that showed silver nanoparticles are able to kill
HIV-1. This study looked at the effect of silver nanoparticles in
the range of 1-100 nm on Gram-negative bacteria using high angle
annular dark field (HAADF) scanning transmission electron
microscopy (STEM). Their results indicated that the bactericidal
properties of the nanoparticles were size dependent, since the only
nanoparticles that presented a direct interaction with the bacteria
preferentially have a diameter of .about.1-10 nm. The authors have
postulated that the nanoparticles could kill other viruses in
addition to HIV-1. The benefits of silver nanoparticles continue to
be explored. Researchers are optimistic that nanoengineered silver
may be the solution to controlling many types of viruses. Silver
may now come under consideration as an alternative to drugs when it
comes to fighting previously untreatable viruses such as the
Tamiflu-resistant Avian flu.
[0006] Worldwide there is a very significant economic loss in
discarded foods due to spoilage. For example, one source reports
that the food industry annually discards $35 billion worth of
spoiled goods. Fifty-six percent of all supermarket store shrink is
reported to come from perishables, according to a 2003 survey.
Currently the trend in the food growing and retail industry is to
engineer the sustainable supply chain. This entails extending and
measuring the usable life of fruits and other produce as well the
process of saving energy required for continuously cooling fruits
and other produce to preserve the freshness by keeping the
bacterial count low. Synergistically, industry trends are towards
an increase in healthier lifestyles by consuming more fresh-cut
produce with a demand for eco-friendly sustainable packaging that
can sense, monitor, communicate and extend the useable life of
foods. In particular, current methods used for extending the
useable life of these products include pesticides, fertilizers and
picking the produce before it is ripe. Other methods include
various packaging alternatives, which include control of
respiration and the depleting of area ethylene.
[0007] Various processes to produce nano/micro particles are known.
For example, U.S. Pat. No. 7,128,816 issued to Denes, et al.
discloses a process for producing colloidal dispersions of
nanoparticles of electrically conducting materials. The colloidal
dispersions are produced in a dense media plasma reactor that has
at least one static electrode and at least one rotating electrode.
Minute particles are sputtered off of the electrically conducting
material from which the electrodes are made.
[0008] Indian patent 192012 describes an emulsion process for
preparing porous polymer nanoparticles.
[0009] International patent application publication WO9106036
discloses methods of coating a nanoparticle with one or more layers
of various types of materials. It also discloses a method for
preparation of metal-coated nanoparticles, in which the metal
halide nanoparticles are prepared and exposed to ultraviolet light
to change the metal halide to metal to form metal coatings over
individual nanoparticles. In another process variant, silver-coated
particles are prepared by a process by providing silver ion source
and halide ion source to produce silver halide coated nanoparticles
and subsequently exposing the silver halide nanoparticles to
ultraviolet light in EDTA to reduce the silver halide coating to
silver-coated nanoparticles. In a further process variant, silver
halide coated particles and an electron scavenger are contained in
an anaerobic liquid carrier and uniformly distributed therein, such
that exposing the liquid carrier to light of sufficient strength
and for a sufficient time reduces the silver halide coating to
metallic silver.
[0010] In Cong et al., "Hollow Cu-NP Spheres Made from Electroless
Cu Deposition with Colloidal Particles as Templates," a process is
described for producing hollow copper spheres in the nanoparticle
range using SiO.sub.2 and PSMA nanoparticles as a template core.
The core is removed to yield a hollow metal nanoparticle. Wall
thickness on the SiO.sub.2-produced particles was measured to be
about 30 nm, and wall thickness on the PSMA-produced particles was
measured to be about 55 nm, although the thinner-walled
SiO.sub.2-produced particles were less likely to break during core
removal.
[0011] International patent application publication WO9106036
discloses methods of coating a nanoparticle with one or more layers
of various types of materials. It also discloses a method for
preparation of metal-coated nanoparticles, in which the metal
halide nanoparticles are prepared and exposed to ultraviolet light
to change the metal halide to metal to form metal coatings over
individual nanoparticles. In another process variant, silver-coated
particles are prepared by a process by providing silver ion source
and halide ion source to produce silver halide coated nanoparticles
and subsequently exposing the silver halide nanoparticles to
ultraviolet light in EDTA to reduce the silver halide coating to
silver-coated nanoparticles. In a further process variant, silver
halide coated particles and an electron scavenger are contained in
an anaerobic liquid carrier and uniformly distributed therein, such
that exposing the liquid carrier to light of sufficient strength
and for a sufficient time reduces the silver halide coating to
metallic silver.
[0012] All of the processes discussed in the above application for
preparing silver-coated nanoparticles are tedious and lengthy. They
are also limited in that they could only produce coated
nanoparticles having a coat of a certain size or greater. Silver
bromide is insoluble in water, the medium that is being used in
these processes for the deposition from a silver nitrate or a
soluble silver salt. It requires a very high gelatin concentration
to hold the particle size to the nanoparticle range, which is a
very well known method of producing high-speed photographic films.
If the gelatin concentration is low, and the silver concentration
is high, say about 1%, then the bromide precipitates in a very
coarse particle size. Thus if one were depositing a silver film,
the result would be the deposit of silver particles of almost
matching dimensions, and therefore a mixture of nanoparticles and
large particles.
[0013] The processes discussed in the above applications for
preparing coated silver nano/micro particles are tedious and
lengthy. It would be desirable to provide an efficient, less
tedious method of coating the nano/micro particles that also
increases the effective surface area of the silver several-fold,
allowing reduction of total used silver and production in a shorter
amount of time.
DISCLOSURE OF THE INVENTION
[0014] The present invention provides a simple and economical
process for preparation of metal-coated non-metallic nano/micro
particles. As used herein, the term "nanoparticle" means any
particle or structure having a diameter or dimension of about 100
nm or less. "Microparticle" means a tiny particle that is larger
than a nanoparticle, and the term "nano/micro particle" includes
particles of both size ranges. These terms as used herein include
particles of all shapes, including but not limited to spheres,
cylinders, and rods. The particles of the present invention
comprise a core and metallic coat over the core using silver or
other transition/noble metals. The core of the non-metallic
particles are selected from material such as, but not limited to,
silica, calcium carbonate, barium sulfate, or emulsion grade
polyvinyl chloride and other polymers prepared by an emulsion
process including porous polymers.
[0015] The present invention describes non-metallic nano/micro
particles coated with transition/noble metals such as, but not
limited to, copper, nickel, silver, palladium, platinum, osmium,
ruthenium, rhodium and such other metals which are easily reducible
to elemental metal. Advantageously, the nano/micro particles of the
present invention may be prepared with reduced manufacturing cost,
and with increased industrial applicability.
[0016] In accordance with the present invention, nano/micro
particles comprise a non-metallic core and a layer of elemental
metal disposed over the core. These coated nano/micro particles are
equivalent to hollow nano/micro particles of metal, where all the
metal and some part of the core will participate in the desired
mechanism and be used up in the life cycle of the product.
[0017] The particles coated with silver of a preferred embodiment
of the present invention have numerous industrial applications such
as an anti-ripening agent in the agricultural industry. The silver
particles of the preferred embodiment exhibit excellent algaecide
and bacteriostatic properties with sustained release activity. It
has been found that if silver-coated nano/micro particles are
placed in an environment where fruits are ripening, the silver
effectively enables the conversion of ethylene to ethylene oxide by
a unique mechanism. Thus in a controlled environment, as ethylene
is converted to ethylene oxide, biological species such as fungi,
bacteria and spores are effectively destroyed. The process of
ripening is retarded and the process of spoilage is dampened and
thus nearly stopped. Unlike other approaches, this invention is
unique in using a well-understood mechanism that uses orders of
magnitude less silver, showing similar or higher efficiency,
dramatically lower cost, and the combination of silver with
enhanced surface area and an eco-friendly core material in
nano/micro particle form.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a cut-away elevational view of a particle
according to a preferred embodiment of the present invention.
[0019] FIG. 2 is a flow diagram of a process for manufacturing a
coated particle according to a preferred embodiment of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] With reference to FIG. 1, a preferred embodiment of the
present invention may now be described. The preferred embodiment is
composed of a non-metallic nano/micro particle 10 coated with a
layer of elemental silver 12. Since silver is an expensive metal,
the production of solid silver nano/micro particles would limit
their applications. The high density (10.49 g/cc) of silver affords
very low surface area for one gram of silver even if the particle
size is only about 50 nanometers (10.sup.-9 meters). The surface
area per gram may be calculated as SA=6/.rho.D, where SA is surface
area in cm.sup.2/g, .rho. is density in g/cc, and D is diameter in
cm=6/10.49.times.0.000050=11.439 m.sup.2/g. Thus, a large amount of
silver is wasted in a solid silver particle and is not available
for the desired disinfection reaction. Also, the disinfection
surface plays a critical role, and thus it is important to
generating a coating where only desired amount of silver is used.
The surface texture of the core particle may allow an increase in
the surface area of silver, giving it the ability to increase the
effectiveness of the particles.
[0021] Several inorganic or organic polymeric particles have a
large surface area either from the surface or from the pores
present on their surface. Typically, the values range from 100-400
m.sup.2/g. These materials are an order of magnitude cheaper than
silver particles. Thus by coating these low-cost particles with
nanometer-thin silver by chemical or physical techniques, one may
produce the effect of nano/micro particles of silver at a fraction
of the cost of silver nano/micro particles. Not only is the cost
reduced, but the effectiveness of the particles would be much
higher due to a major increase in the relative surface area to
volume ratio. Finally, it is only the silver on the surface that
actively participates in the applications and is sacrificed in the
reactive ripening medium in contact at a level of 20 parts per
billon and produces the antibacterial or antiviral activity. Hence,
the present invention teaches an alternative technical approach
that replaces solid silver nano/micro particles with nano/micro
particles of non-metallic material coated with elemental silver.
This invention teaches not only an increase in the scope of the
applications, but simultaneously teaches an enhancement in
efficiency. Also, this invention describes a process to coat such
non-metallic nano/micro particles with elemental silver material
and optionally in other embodiments with other transition/noble
metals. Further, selection of suitable non-metallic materials, such
as sand or SiO.sub.2 core particles, will not only provide the
ability to be environmentally sustainable, but also could provide
functional sensitivity, such as photo-sensitivity, for example when
nano and micro TiO.sub.2 or zinc oxide or silicon particles are
selected. This may further enhance reactivity of over-coated silver
or silver-like metal(s), due to combined photo-catalytic activities
when applied in the supply chain for retail fruits.
[0022] For the purpose of metallic coating, elemental silver has
been selected as a coating material for the inorganic nano/micro
particle in the preferred embodiment described herein. The
silver-coated nano/micro particles comprise silver 1 to 2% by
weight of the particle. The silver-coated nano/micro particles of
the present invention have high silver surface area per gram of
silver employed to increase the effectiveness of the silver-coated
particles. Thus, the coated nano/micro particles of inorganic
material have only a fraction of the cost of silver nano/micro
particles, dramatically lowering the price of the coated particles
to about 1-5% of the cost of silver or 1/20.sup.th of the cost of
silver nano/micro particles. The silver coated nano/micro particles
are equivalent to hollow nano/micro particles of silver, where all
or part of the silver will be used up in the life cycle of the
product.
[0023] The preferred embodiment is also directed to a simple and
economical process for preparation of silver-coated nano/micro
particles. The coated nano/micro particles comprise a non-metallic
nano/micro particle core and a layer of elemental silver and/or
their combinations with other elements disposed over the core. The
non-metallic core is selected from inorganic material such as
silica, calcium carbonate, barium sulfate, titanium dioxide,
emulsion grade polyvinyl chloride, or porous polymeric particles
and related other materials in various sizes and shapes.
[0024] Referring now to FIG. 2, a process for the preparation of
silver-coated nano/micro particles according to a preferred
embodiment of the present invention may be described. A known
quantity of silver salt is dissolved at step 14 into a quantity of
chloride-free demineralized water sufficient to soak non-metallic
nano- or micron-size polymeric or inorganic particles. The
particles are dispersed in the solution at step 16. The solution is
evaporated at step 18 to produce a thick slurry. In this process,
the silver ions are deposited on the surface of the
nano/microparticles. The slurry is further force dried at step 20
to deposit the residual silver on the particles, preferably using
an oven at 50-120.degree. C. for 2 hours. At step 22 a reducing
agent is selected from a range of organic or inorganic reducing
agents dissolved in water, and is added in commensurate quantity in
dilute form to completely cover the surface of the dried particles,
then allowed to stand for 2-4 hours and optionally heated to
100-120.degree. C. in a closed environment until reduction is
complete. Then these reduced particles are slurried in
demineralized water, filtered and washed at step 24 until free of
any residual reducing agent and finally dried. The white particles
exhibit a light-yellow tinge, which is characteristic of fine
silver particles.
[0025] The silver salt is selected from nitrate, acetate, or
ammonical silver chloride or silver sulfate, which are soluble in
water. The reducing agents of choice are solutions of hydrazine,
solution of sodium meta-bisulfite or solid meta-bisulfite or sodium
sulfite or sodium borohydride, sodium hypophosphate, elemental
hydrogen, carbon monoxide or formaldehyde or acetaldehyde or
glucose, or other reducing sugars from aldehydes and ketone
varieties and their combinations thereof.
[0026] In another preferred embodiment the invention provides a
process for the incorporation of coated nano/micro particles in
such substrates, for example plastics, by mixing the plastic
granules with coated nano/micro particles and processing by usual
method in films by extrusion, blowing, calendaring or injection
molded into products. Plastic granules are selected from various
types such as polyethylene, polypropylene, linear low density
polyethylene, poly vinyl chloride, polystyrene, and any other
commodity plastic. This combination of nano/micro particles with
substrate could further be extended to hosts such as various types
of papers and their hybrids, fibers such as jute, and any other
packaging materials. These materials could also be fabricated in
various forms, commensurate with the needs of the fruit and other
supply chains. Not only could films be used but also bags,
containers, wraps, foamed plastic wraps, sprays, and other shapes,
like the fruit itself, that are a part of the fruit shipment. In
addition to use with fruits, such a combined technical solution
could also be applied to other types of perishable items, such as
flowers, to help retain freshness and extend useable life and
reduce the degrading effect of the environment.
[0027] In another embodiment, these particles can be derived as
sensors and actuators, to sense level of gases, microbes and other
agents as well as can convert and store energy, respectively, to
provide higher level of environmental sustainability to this
invention. Another important feature of this embodiment is also in
noninvasive use of the above described silver and other elements
coated particles and their ability to function in combination with
state of the art devices such as RFID tags used in fruits and other
supply chains to track the products.
[0028] In an additional embodiment, the coating on the particles
could be passive, when for example, converting ethylene to ethylene
oxide but also could be active, for example, when scarifying
through dissolution in time or functional release modes. The later
could be effective when applied to meat or medicinal or vegetable
applications to decontaminate bacteria.
[0029] The following examples, which include preferred embodiments,
will serve to illustrate the practice of this invention, it being
understood that the particulars shown are by way of example and for
purpose of illustrative discussion of preferred embodiments of the
invention.
Example 1
[0030] Step 1: Silver nitrate loading: 100 grams (0.591 gram moles)
of silver nitrate is dissolved in demineralized water (1-2 liters)
and the silver nitrate solution is subsequently diluted by the
addition of 10-12 liters of demineralized water. Nonsurface treated
precipitated calcium carbonate (10 kg) is added to the solution
with constant stirring to ensure uniform mixing. The mixture is
dried in an oven at a temperature below 120.degree. C.
[0031] Step 2: Reduction of silver nitrate coated nano/micro
particles using hydrazine hydrate: 50 g of 85% Hydrazine hydrate
(1.325 gram mole) is dissolved in demineralized water (1 liter).
This was added to the dried silver nitrate loaded calcium carbonate
with constant stirring in a sigma mixer and allowed to react for
four hours. The mixture was dried at 100-125.degree. C. in an oven
to obtain coated silver nano/micro particles with a calcium
carbonate core. The particles were slurried in demineralized water,
filtered and washed till free of any residual reducing agent and
nitrates and finally dried.
Example 2
[0032] Step 1: Silver nitrate loading: 158.8 grams (0.934 gram
moles) of silver nitrate is dissolved in demineralized water (1-2
liters) and subsequently diluted by the addition of 100-120 liters
of demineralized water. Fumed silica (10 kg) is added to the
solution with constant stirring to ensure uniform mixing.
[0033] Step 2: Reduction of silver nitrate nano particles using
hydrazine hydrate: 50 g of 85% Hydrazine hydrate (1.325 gram mole)
is dissolved in demineralized water (1 liter). Hydrazine hydrate
solution is added with constant stirring to the dispersion of
example 1 and kept for four hours. The mixture is dried at
50-65.degree. C. in an oven to obtain coated silver nano/micro
particles with fumed silica core. The particles are slurried in
demineralized water, filtered and washed till free of any residual
reducing agent and are used either as wet or as a flush in the
required medium. The nano silica particles tend to flocculate if
completely dried.
Example 3
[0034] 15 g Palladium chloride is dissolved in 150 cc 2 N
hydrochloric acid and diluted to 100 liters with demineralized
water. 10 kg of fumed silica is thoroughly mixed with this solution
to allow a very fine layer of palladium chloride to be deposited on
the surface of the particles. These are reduced by the addition of
100 g of hydrazine hydrate diluted to 1 liter. The reduced
particles appear slightly black in color.
Prophetic Example 1
[0035] For deposition of elements such as nickel, a surface which
is electrically conducting would be better. For this a very thin
layer of silver or copper could be deposited on the surface and the
deposition of nickel could be followed by reduction of nickel salts
with reducing agents such as sodium hypo phosphite.
[0036] The silver coated particles of the present invention have
numerous industrial applications especially in the areas of
agricultural and food industries. Industrial applications also
exist in healthcare, including biomedical instrumentation such as
coatings on medical tools. The silver nano/micro particles of the
present invention exhibit excellent algaecide and bacteriostatic
properties with sustained release and reactivity.
[0037] The poor life of fruits that ripen while in the food supply
chain is a cause of environmental concern due to the amount of
loss. Since the life after harvesting is limited to 3-4 days, the
farmer is forced to pluck the fruits when they are only 80% ripe.
The time taken for these fruits to completely ripen varies from
3-10 days, allowing for distribution to consumers. This trend is
growing in global supply chains where delays and changing
environmental conditions further increase the loss of perishable
items due to ripening and other related processes. The process of
ripening produces ethylene. Ethylene is also a catalyst for the
process of ripening. Thus, if the ethylene is not removed from the
surroundings of the fruit, the process of ripening is accelerated
and becomes out of control. During the time the fruits move through
the supply chain this process of uncontrolled ripening could be
accelerated in conditions of uncontrolled temperature and/or
humidity. This leads to a loss of fruits. Also, the uncontrolled
ripening is accompanied by the growth of fungi, bacteria and spores
on these perishable items making the situation cumulatively more
difficult.
[0038] Silver-coated nano/micro particles placed in the environment
where fruits ripen can effectively destroy the generated ethylene
and convert it to ethylene oxide. Silver is the only known catalyst
for oxidation of ethylene to ethylene oxide. Ethylene oxide is a
very well known disinfectant used even in medical surgery rooms.
Thus, in a controlled environment, as produced by the invention as
described herein, ethylene gets converted to ethylene oxide, which
effectively destroys unwanted biological species such as fungi,
bacteria and spores. The process of ripening is significantly
retarded and the process of spoilage is retarded and stopped for
practical purposes. Polyethylene bags of 100 micron thickness
containing 1% by weight of calcium carbonate particles coated with
1% silver could effectively extend the life of highly perishable
fruits such as banana and melons by as much as 120-192 hours (5-8
days), when the fruits were stored in such bags at room temperature
with air sealing. This time for extended preservation could be
further increased if the fruits are kept cold during shipping.
Experiments show that such bags may be used repeatedly without
significant change in the performance property for more than one
year. The use of these bags would allow the producer to ripen a
fresh fruit crop naturally on the vine, enhance its taste, and
enable shippers and retailers to retard spoilage and increase the
shelf life of their produce. The produce distributor packaging
industry is a billion-dollar market annually and is projected to
grow globally. This growth will be fueled by rising consumer demand
for fresh produce with enhanced freshness and better taste. Even
end use of trash bags could benefit from this invention in that
incorporation of the silver-coated nano/micro particles with added
perfume in the material of the bags would result in a better
smelling bag with more antibacterial capabilities. Additionally,
this invention will address key issues related to environmental
sustainability in the following ways: (1) reduce wastage due to
premature ripening, before reaching to consumer, (2) save wastage
and thus, open up the possibility to provide saved product to a
larger population, (3) produce less crop, as the need for
compensation for premature ripening losses are not as dire, and
thus, proportionally less fertilizer will go in the soil, and (4)
the fractional amount of silver along with calcium carbonate or
SiO.sub.2 (sand) as a core non-metallic in polymer matrix, such as
poly lactic acid will make this product bio degradable, unlike any
of the current products in the industry. Thus, this invention
addresses sustainability, which is a global concern of this
century.
[0039] Similar results to extend the ripening period could be
obtained with dusting powder which could be used only once.
Experiments have shown that the palladium-coated particles also
retarded the ripening of fruits but were not able to prevent
spoilage of fruits due to fungus. In the case of silver-coated
non-metallic particles, the effectiveness is not only due to the
reduction of ethylene, similar to the palladium, which oxidizes
ethylene to acetaldehyde or carbon dioxide rather than to ethylene
oxide, but the conversion of ethylene to ethylene oxide serves to
disinfect by its reduction in the fungus population, unlike the
case of palladium.
[0040] Further, such particles may be implemented in the supply
chain in various physical forms, such as bags, containers, wraps,
blocks, spray and other related items and their combinations. For
example, spray coating or electrostatic spray coating (ESC) could
give the same results when applied on a pallet for fruit or
paper-based fruit rack separators, such as for a stack of apples. A
convenient method of delivering the spray coating could be by
canister. Additionally, the paper bedding for the produce could be
spray coated with material or could have the material embedded
within the paper bedding during the paper manufacturing itself.
[0041] In another important application, such as in the packaging
and shipping industry, heterogeneous packaging is a growing trend,
where fruits are shipped with other items such as vegetables. In
another important application, the combination of fruits with other
perishable products may extend life of other perishable items too,
as ethylene oxide will decontaminate those non-ethylene producing
products as well.
[0042] Competing technologies include a packaging method that
primarily focuses on produce respiration for fresh-cut produce,
reduction of spoilage during storage and transportation using
ethylene scrubbers designed to remove ethylene gas from the air,
modified atmosphere packaging designed to increase carbon dioxide
and reduce oxygen in the atmosphere surrounding the produce,
moisture and humidity controls as well as temperature controls.
These technologies are not completely effective in eliminating
spoilage and a newer and better technology is needed in the
industry.
[0043] Other diverse nonagricultural uses of silver and other metal
coated nano/micro particles include the use of this invention in
trash bags and trash truck or bio disposable containers.
Additionally, other uses include antimicrobial agents, perfume or
disinfectant release media, coatings of surgical instruments,
equipments, sanitary napkins, diapers, additive to talcum powders,
soaps, detergents for home use, as pigments for coatings on
textiles to prevent odors, for prevention of bad breath in tooth
paste, disinfectant coatings on walls, additive to interior and
exterior architectural finishes and paints for prevention of algae
growth. Further, this invention could be used as a catalyst with
metal-coated nano/micro particles, embedding metal-coated
nano/micro particles in membranes to prepare a membrane reactor
that may be polymeric or ceramic, an addition to paints to enhance
electrical conductivity for better electrostatic spraying, and an
addition to plastics for improved electrostatic spraying. For
instance, the silver nano/micro particles of a preferred embodiment
of the present invention may be used as bactericide pigments by
mixing in 1 to 2% along with other biocides and pigments in paints
during dispersion or can be used in the textile industry by mixing
along with pigments for printing purposes or along with finishing
agents.
[0044] It will be evident to those skilled in the art that the
invention is not limited to the details of the foregoing
illustrative examples and that the present invention may be
embodied in other specific forms without departing from the
essential attributes thereof, and it is therefore desired that the
present embodiments and examples be considered in all respects as
illustrative and not restrictive, reference being made to the
appended claims, rather than to the foregoing description, and all
changes which come within the meaning and range of equivalency of
the claims are therefore intended to be embraced therein. It should
be appreciated that certain improvements and modifications may be
practiced within the scope of the appended claims.
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