U.S. patent application number 15/768706 was filed with the patent office on 2018-10-25 for method for producing stable graphene, graphite and amorphous carbon aqueous dispersions.
The applicant listed for this patent is Elisa FERREIRA, Fernando GALEMBECK. Invention is credited to Fernando GALEMBECK.
Application Number | 20180304210 15/768706 |
Document ID | / |
Family ID | 58516906 |
Filed Date | 2018-10-25 |
United States Patent
Application |
20180304210 |
Kind Code |
A1 |
GALEMBECK; Fernando |
October 25, 2018 |
METHOD FOR PRODUCING STABLE GRAPHENE, GRAPHITE AND AMORPHOUS CARBON
AQUEOUS DISPERSIONS
Abstract
The present patent application relates to a method for producing
dispersions and nanodispersions of graphite, graphene and amorphous
carbon in aqueous media without using any surfactant and without
requiring any chemical modification of the graphene, such as
oxidation to produce graphene oxide.
Inventors: |
GALEMBECK; Fernando;
(Campinas, BR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FERREIRA; Elisa
GALEMBECK; Fernando |
Campinas
Campinas |
|
BR
BR |
|
|
Family ID: |
58516906 |
Appl. No.: |
15/768706 |
Filed: |
July 22, 2016 |
PCT Filed: |
July 22, 2016 |
PCT NO: |
PCT/BR2016/050169 |
371 Date: |
April 16, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/10 20130101;
C09J 101/02 20130101; C08K 3/04 20130101; C09D 5/24 20130101; H01B
13/0036 20130101; C08K 3/042 20170501; C09D 11/17 20130101; C09D
11/037 20130101; C09J 9/02 20130101; C09D 5/32 20130101; C09D 7/45
20180101; G02B 5/003 20130101; H01M 4/625 20130101; B82Y 40/00
20130101; B01F 2215/0059 20130101; C09D 101/02 20130101; C09D 11/14
20130101; C09D 11/52 20130101; H01M 4/587 20130101; B01F 2215/006
20130101; H01B 1/04 20130101; B01F 3/1214 20130101 |
International
Class: |
B01F 3/12 20060101
B01F003/12; C09D 5/24 20060101 C09D005/24; C09D 7/45 20060101
C09D007/45; C09D 101/02 20060101 C09D101/02; C09D 11/52 20060101
C09D011/52; C09D 11/037 20060101 C09D011/037; C09D 11/14 20060101
C09D011/14; C09D 11/17 20060101 C09D011/17; C09J 9/02 20060101
C09J009/02; C09J 101/02 20060101 C09J101/02; C09D 5/32 20060101
C09D005/32; H01M 4/62 20060101 H01M004/62; H01B 1/04 20060101
H01B001/04; H01B 13/00 20060101 H01B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 2015 |
BR |
1020150264208 |
Claims
1-15. (canceled)
16. A process for dispersion of graphite and graphene in a solution
or dispersion of cellulose in alkaline aqueous medium, at a range
of concentrations from 0.001% to 50% by weight, forming dispersed
particles of graphene or graphite with nanometric thickness, the
process characterized by the use of graphite or graphene powder,
without the need to use oxidizing reagents or any other form of
chemical modification of graphite or graphene.
17. A process for spontaneous formation of dispersions of graphite
and graphene in solutions or dispersions of cellulose in alkaline
aqueous medium, at a range of concentrations from 0.001% to 50% by
weight, the process characterized by spontaneous swelling and
dispersion of the graphite, since it is immersed in the cellulose
solution and gently stirred, periodically.
18. A process of dispersion of amorphous carbons in solutions or
dispersions of cellulose in alkaline aqueous medium, at a range of
concentrations from 0.001% to 50% by weight, characterized by the
use of powdered carbon, granulate carbon or any other known form of
art, eliminating the use of oxidizing reagents or any other
chemical modification of carbon.
19. A process for spontaneous formation of amorphous carbon
dispersions in solutions or dispersions of cellulose in alkaline
aqueous medium, at a range of concentrations from 0.001% to 50% by
weight, characterized by swelling and dispersion spontaneous of the
powder or carbon grains, since they are immersed in the cellulose
solution and gently shaken, periodically.
20. A process for dispersion of others carbonaceous materials as
carbon nanotubes, fullerenes and colloidal carbons in solutions or
dispersions of cellulose in alkaline aqueous medium, at a range of
concentrations from 0.001% to 50% by weight, forming dispersions of
nanometric particles, eliminating the use of surfactants or other
dispersants.
21. A process for spontaneous formation of dispersions of other
carbonaceous materials such as carbon nanotubes, fullerenes and
colloidal carbons in solutions or dispersions of cellulose in
alkaline aqueous medium, characterized by spontaneous swelling and
dispersion of the carbonaceous solids, since they are immersed in
the solution cellulose and gently shaken, periodically.
22. The process according to claim 16, whereas the mass ratio
ranges between the cellulose and the carbonaceous materials of 1 to
60 parts of cellulose and between 99 to 40 parts of carbonaceous
materials by weight.
23. The process according to claim 22, whereas that cellulose can
be introduced into the process as solid powder or in an alkaline
solution or dispersion in water and the alkali concentration may
vary between 0 and 50% by weight of the dispersion or solution.
24. A process for simultaneous miscibilization of graphite or other
carbonaceous materials such as carbon nanotubes, fullerenes and
colloidal carbons using cellulose as dispersant, by mechanical
mixing of the dried powders producing a powder mixture that can be
dispersed in water without the need for vigorous mechanical
agitation.
25. The process according to claim 16, characterized by the
dispersion of graphite or other carbonaceous materials, such as
carbon nanotubes, fullerenes and colloidal carbons using cellulose
as a dispersant, by mechanical mixing of the powders immersed in
water, methanol, ethanol, iso-propanol, n-propanol, acetone,
ethylene glycol, glycerol, mono-methyl ethylene glycol,
characterized by the production of stable dispersions or
homogeneous sediments, eliminating the use of vigorous mechanical
agitation.
26. Electric conductive inks based on dispersions of graphene,
graphite and other carbonaceous materials, such as carbon
nanotubes, fullerenes and colloidal carbons using cellulose as
dispersant, according to claim 16.
27. Electric conductive adhesives based on slurries or dispersions
of graphene, graphite and other carbonaceous materials, such as
carbon nanotubes, carbon fullerenes and colloidal carbons using
cellulose as dispersant, according to claim 16.
28. A process of painting, printing and writing based on the use of
inks according to claim 26.
29. A process for production of solid films, coatings and
poly-functional electric conductive adhesives and/or antistatic and
radiation absorbers in the visible, ultraviolet and infra-red based
in the dispersions as described in claim 16.
30. A process for production of solid films, coatings and
poly-functional electric conductive adhesives and/or antistatic and
radiation absorbers in the visible, ultraviolet and infra-red based
in the products described in the claim 26.
30. A process for production of solid films, coatings and
poly-functional electric conductive adhesives and/or antistatic and
radiation absorbers in the visible, ultraviolet and infra-red based
in the products described in the claims 27.
31. A process for production of nanocomposites of graphene and
other carbonaceous materials, such as carbon nanotubes, carbon
fullerenes and colloidal carbons using cellulose as dispersant with
other materials, in which cellulose is introduced previously or
during the mixture of the components of the nanocomposite.
32. A process for production of electrodes for sensors, batteries,
solar cells or industrial processes, which uses the nanocomposites
described in claim 31.
33. A process for production of electrodes for sensors, batteries,
solar cells or industrial processes, which uses the inks described
in claim 26.
34. A process for production of electrodes for sensors, batteries,
solar cells or industrial processes, which uses the solid films,
coatings and conductive adhesives described in claim 27.
35. A process for production of electrodes for sensors, batteries,
solar cells or industrial processes, which uses solid films,
coatings and conductive adhesives described in claim 28.
Description
FIELD OF THE INVENTION
[0001] The present invention relates a production process of
aqueous dispersions of graphene, graphite, nanographite and
amorphous carbon, based on the unexpected and unprecedented
property of cellulose acting as dispersant of hydrophobic particles
in aqueous medium, as agent of exfoliation of graphite particles
and amorphous carbon, spontaneously. This process avoids the use of
surfactants in the production of graphene and the step of
transformation of graphite in graphene oxide which is usually
necessary to achieve its dispersions in aqueous media.
[0002] In this invention, "cellulose" is a polymer registered under
CAS Number 9004-34-6. The term "cellulose" used here comprises
different crystalline forms of this polymer, including micro and
nanocrystalline celluloses, and arrangements of macro, micro or
nanofibres of different sizes and aspect ratios.
[0003] In this invention, "graphite" comprises and represents the
mineral graphite, with a structure composed of aromatic rings of
carbon and registered under CAS Number 7782-42-5.
[0004] In this invention, "amorphous carbon" comprises and
represents any substances or materials consisting mainly of carbon
with the predominance of conjugated aromatic rings, in particular
the compounds registered under CAS Number 7440-44-0. It includes
amorphous carbon obtained by pyrolysis of wood or other materials
of vegetable origin with activation by oxygen and/or acid or alkali
compounds, as well as mineral coals and turfs.
BACKGROUND OF INVENTION
[0005] To understand the character of novelty of this invention is
necessary to know in detail graphene, graphite and amorphous
carbon, their properties, the need of their dispersions to be used
in different applications and also the procedures currently used to
disperse graphene and graphite in water.
[0006] Graphite is a material with very unique properties: it is
formed solely of carbon atoms bonded together, forming conjugated
aromatic rings arranged in lamellas that reach macroscopic
dimensions, being one of the most known allotropic forms of carbon.
It is very nonpolar, hydrophobic and good conductor of electricity
and heat. Its acoustic and thermal properties are highly
anisotropic, since the phonons propagate rapidly along a plane or
lamella, in which atoms are covalently bonded, but not between the
planes. It has high thermal stability and only oxidizes fast in air
at high temperatures, above 700.degree. C. It is diamagnetic,
floating in the air on a magnet. Its properties ensures a large
number of applications like lubricants, pigments, electrodes,
coatings of molds and brakes, batteries, refractories, anti-flame
agents and pressure sensors in microphones and others equipments.
It also has undesirable properties, such as to facilitate corrosion
of aluminum and some steels. Moreover, its mechanical properties
are very anisotropic, preventing its use as a building or
structural materials.
[0007] Graphene is another allotropic form of carbon, having the
structural basic unit of graphite, carbon, carbon nanotubes and
fullerenes. It is formed of one or a few lamellas of atomic
thickness, each formed by hundreds or thousands of conjugated
aromatic rings. For this reason, individual graphene lamellae can
he understood as a molecule of a polycyclic aromatic hydrocarbon
with extremely large number of rings. Its mechanical properties are
remarkable, because the graphene sheets are 207 times stronger than
steel per unit mass. It conducts electricity and has important
electronic effects: bipolar transistor, ballistic transport of
charge and large quantum oscillations.
[0008] Amorphous carbons are a large group of substances derived
from graphite, but with many chemical and structural defects which
produce interesting properties. The property that gives the highest
number applications is the high adsorption capacity, responsible
for the extensive use of so-called activated carbon in the
treatment of water, water effluents and gases. Other important
properties are the mechanical reinforcement and absorption of
ultra-violet light, which make the colloidal carbons or carbon
blacks required components of many plastics and rubber articles,
particularly tires used in automotive vehicles.
[0009] A large part of the applications of graphite, graphene,
amorphous carbon and derived substances, such as carbon nanotubes
and fullerenes, requires that they are obtained in dispersions,
aqueous or not, or dispersed and mixed with other solids.
[0010] For this reason, a great effort of research and development
has been devoted to obtain dispersions and nanodispersions of
graphite, graphene, and amorphous carbon, mainly in aqueous media.
An evidence of the importance of this issue is the repercussion of
an article describing the obtainment of graphene in aqueous medium,
published by an Australian group (Li, D., Muller, M. B.; Gilje, S.
Kaner, R. B. and Wallace, G. G.), entitled "Processable aqueous
dispersions of graphene nanosheets" and published in Nature
Nanotechnology, volume 3, pages 101-105, in 2008. This article has
been cited more than 4500 times in the scientific literature, a
number that exceeds the total number of citations obtained by many
productive scientists throughout their life. This work has inspired
many patents, for example, the patent application USPTO
20130197158, deposited on 2013 Jan. 8, which claims a process of
production of nanocomposites of graphene with polyurethanes.
[0011] On the other hand, the diversity of applications and the
need for concentrated dispersions of graphene led to the use of
exotic dispersants, as the article of Ayan-Varela et al, published
in ACS Applied Materials Interfaces, volume 7, pages 10293-10307,
2015, in Which the authors describe the obtainment of concentrated
dispersions (5%) of graphene using as dispersant one
flavonucleotide, which is a complex and expensive substance.
[0012] Sang-Soo Lee, Kyunghee Kim, Soon Ho Lim, Min Park, Jun Keung
Kim, Heesuk Kim, Hyunjung Lee; in the U.S. Pat. No. 8,178,201, May
15, 2012, teach two methods for obtain graphene from graphite:
mechanical delamination made by sticking an adhesive tape on
graphite and physicochemical delamination, described by Sang-Soo
and collaborators as: "Such common method for preparing graphene
from graphite is roughly separated into two types of mechanical and
physicochemical delaminations. The mechanical delamination repeats
the process of attaching and detaching an adhesive tape on graphite
lump to peel graphene off there from. The physicochemical
delamination comprises the steps of dispersing graphite having
laminated structure in an appropriate solvent subjecting the
graphite in solvent to oxidation reaction to extend the space
between the laminates of the graphite, and, thus to obtain the
graphene oxide; and subjecting the graphene oxide to reduction
reaction to obtain graphene."
[0013] The present invention describes a surprising fact, which is
the efficient action of microcrystalline cellulose as exfoliating
agent, dispersing and stabilizing of graphite, graphene and
substances related to these, such as amorphous carbon. This result
is unexpected because the cellulose is not recognized as surfactant
or used as dispersant of powder particles in aqueous media and is
itself well-known for its insolubility in any common liquids. On
the other hand, dispersants are amphiphilic substance and cellulose
is not recognized as amphiphilic by most researchers, engineers and
technicians, although this characteristic of cellulose is supported
by some research groups in the world. The results of this present
invention are even more surprising because it does not depend on of
the oxidation steps of carbon compounds, forming graphene lamellas,
which in the current state of the art are necessarily followed by a
step of reduction and stabilization with surfactants. The formation
of the graphene oxide and its reduction forming graphene again are
steps that introduce chemical and structural imperfections in the
resultant products, which damage their use properties.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a novel process to produce
aqueous dispersions of graphene stabilized by cellulose, offering a
new alternative to the current methods of dispersion of graphene.
The process which is the object of this invention has the following
advantages: a) it uses cellulose as dispersant that is
biodegradable, renewable, recyclable, nontoxic and compatible with
the environment and it is often used in industrial process in
alkaline median and even in the absence of alkali; b) the graphene
stabilized with cellulose in alkaline medium becomes unstable when
in contact with natural waters, precipitating and therefore being
easily removed or concentrated; c) in some implementations of this
invention, the graphene dispersed in cellulose in alkaline medium
has high adhesion to various solid substrates, especially
cellulosic materials such as textile fibers and papers, what is
desirable in applications in printed electronic circuits, in other
words, electronic/photonic devices mounted on paper or fabrics; d)
this process does not requires any chemical modification or
oxidation of graphite or graphene, which is part of the state of
art but presents the disadvantage of destroy partially the graphene
structure, damaging its conductive and optical properties; e) in
some implementations of this invention, the solids obtained by
drying of the dispersions, once dried, can be redispersed in
aqueous alkaline solution; f) even when alkaline dispersions are
used, the films obtained by drying are dispersions only mildly
alkaline or neutral, because the alkali used in the forming of the
dispersion is neutralized by atmospheric CO.sub.2.
[0015] The invention also contemplates the products obtained with
these dispersions, such as: conductive inks, conductive adhesives
or other products obtained with dispersions of graphene and
nanographite stabilized by cellulose.
BRIEF DESCRIPTION OF FIGURES
[0016] FIG. 1 is a photographic image that shows aqueous
dispersions containing different concentrations of graphite,
cellulose and NaOH, after 24 hours of decantation. The
concentrations (w/w) of each dispersion are: 1) 1% NaOH, 2%
cellulose and 2% graphite; 2) 1% NaOH, 2% cellulose and 5%
graphite; 3) 1% NaOH, 5% cellulose and 2% graphite; 4) 1% NaOH, 5%
cellulose, 5% graphite; 5) 7% NaOH, 2% cellulose and 2% graphite;
6) 7% NaOH, 2% cellulose and 5% graphite; 7) 7% NaOH, 5% cellulose,
and 2% graphite; 8) 7% NaOH, 5% cellulose, 5% graphite; 9) 0% NaOH,
5% cellulose 5% graphite; 10) 0% NaOH, 0% cellulose and 5%
graphite; 11) 7% NaOH, 0% cellulose and 5% graphite; 12) 0% NaOH,
0% cellulose and 5% graphite.
[0017] FIGS. 2A and 2B show images of transmission electron
microscopy of a dispersion containing 7% NaOH, 5% cellulose and 5%
graphite. The images were obtained from the same experiment, where
the FIG. 2B was acquired using a 25 eV energy filter for better
distinction of the areas of cellulose and graphite.
[0018] FIG. 3 shows shear stress versus shear rate curves of
different mixtures containing cellulose, sodium hydroxide and
graphite. The shear stress of the cellulose solution in a
concentration of 2% by weight varies linearly with the shear rate,
even in the presence of graphite. However, the addition of graphite
in an alkaline solution with 5% cellulose causes a sharp increase
in viscosity, which is an evidence of graphite exfoliating in
lamellar structures containing few sheets.
[0019] FIG. 4 is a photographic image of aqueous dispersions
containing different concentrations of amorphous carbon, cellulose
and NaOH, after 24 hours of decantation. The concentrations by
weight of each dispersion are: 1) 1% NaOH, 2% cellulose and 2%
coal; 2) 1% NaOH, 2% cellulose and 5% carbon; 3) 1% NaOH, 5%
cellulose and 2% coal; 4) 1% NaOH, 5% cellulose and 5% carbon; 5)
7% NaOH, 2% cellulose and 2% coal; 6) 7% NaOH, 2% cellulose and 5%
carbon; 7) 7% NaOH, 5% cellulose and 2% coal; 8) 7% NaOH, 5%
cellulose and 5% carbon; 9) 0% NaOH, 5% cellulose and 5% coal; 10)
0% NaOH, 0% cellulose and 5% carbon; 11) 7% NaOH, 0% cellulose and
5% coal; 12) 0% NaOH, 0% cellulose and 5% coal.
[0020] FIG. 5 is a descriptive flowchart of the method shown in
Example 1.
DETAILED DESCRIPTION OF FIGURES
[0021] FIG. 1 is a photographic image that shows aqueous
dispersions containing different concentrations of graphite,
cellulose and NaOH, after 24 hours of decantation. The
concentrations (w/w) of each dispersion are: 1) 1% NaOH, 2%
cellulose and 2% graphite; 2) 1% NaOH, 2% cellulose and 5%
graphite; 3) 1% NaOH, 5% cellulose and 2% graphite; 4) 1% NaOH, 5%
cellulose, 5% graphite; 5) 7% NaOH, 2% cellulose and 2% graphite;
6) 7% NaOH, 2% cellulose and 5% graphite; 7) 7% NaOH, 5% cellulose
and 2% graphite; 8) 7% NaOH, 5% cellulose, 5% graphite; 9) 0% NaOH,
5% cellulose, 5% graphite; 10) 0% NaOH, 0% cellulose and 5%
graphite; 11) 7% NaOH, 0% cellulose and 5% graphite; 12) 0% NAM, 0%
cellulose and 5% graphite.
[0022] For the preparation of mixtures 1 to 8 solutions and
alkaline dispersions of cellulose were initially prepared. First,
the sodium hydroxide was solubilized in water and the solution was
cooled to 0.degree. C., using an ice bath. The cellulose was added
to the NaOH solution and the mixture was homogenized in a disperser
at 6500 rpm for 5 min at 0.degree. C. The mixture was kept at
-20.degree. C. in a freezer for 2 h. After the preparation of
cellulose solutions and dispersions, the samples 1 to 8 received
additions of graphite resulting in the concentrations listed above.
The mixtures 9 to 12 were prepared by additions of the components
in the water. All mixtures were made in plastic centrifuge tubes
with lid and the mixtures were shaken on a reciprocal motion shaker
at 360 oscillations per minute with a displacement of 2 cm, during
15 h. The mixtures have remained static for 24 h at room
temperature (24.degree. C) and were photographed after the period
of decantation.
[0023] The mixtures 9 and 10 show that graphite is not dispersed in
water without the presence of cellulose, and most of the material
remained in contact with the hydrophobic wall of the vial.
[0024] In contrast, the system 3 shows total sedimentation of the
solids, forming a clear supernatant. The absence of graphite on the
wall of the plastic bottle shows that the graphite becomes
hydrophilic due to contact with the cellulose. In addition,
macroscopic separation of the constituents, cellulose and graphite,
in the sediments has not occurred despite the difference of density
between them, showing their chemical compatibility.
[0025] Mixtures 7 and 8 show dispersions which remained stable
after 24 hours, wherein the solids remain in suspension, without
the formation of macroscopic domains of each species. These systems
show that the cellulose is a dispersant of graphite in water.
[0026] FIGS. 2A and 2B show images of transmission electron
microscopy of a dispersion containing 7% NaOH, 5% cellulose and 5%
graphite. For the sample preparation, the dispersion of cellulose
and graphite was diluted with water and applied immediately on the
specimen holder. The images were obtained at 80 kV and in the same
region, and the FIG. 2B was obtained using a 25 eV energy filter
for better distinction of the areas of cellulose and graphite. In
the images it was possible to check the contact, at the microscopic
level, of cellulose films with the graphite sheets. The chemical
compatibility between the two species is visible and no segregation
of the components was observed.
[0027] FIG. 3 shows data about the rheological behavior of
different mixtures of cellulose, sodium hydroxide and graphite. The
graph in this figure shows that the shear stress varies linearly
with shear rate in the cellulose solutions with a concentration of
2%, with or without graphite. However, the viscosity of the
solution with 5% cellulose decreases with the shear rate, which is
a characteristic property of non-Newtonian fluids. Therefore the
concentration of 5% by weight of cellulose is equal or greater than
its critical concentration. The addition of graphite in an alkaline
solution containing 5% cellulose causes a sharp increase of
viscosity, represented by the increase of the slope of the shear
stress versus shear rate curves. The viscosity increase due to the
addition of particles is an evidence of the exfoliation of the
graphite in lamellar structures containing a few sheets, as
nanographite or graphene. This type of dispersion has reduced its
viscosity with increasing shear rate due to the alignment of the
nanographite and graphene lamellas in the flow direction,
facilitating the movement of the fluid. For shear rates employed in
this rheological analysis, dispersions containing 2% graphite show
very high viscosity, reaching 40,000 cP, and dispersions containing
5% graphite present aspect of slurries, with viscosity up to 176000
cP.
[0028] FIG. 4 is a photographic image of 12 aqueousdispersions
containing different concentrations of commercial activated carbon,
cellulose and NaOH, after 24 hours of decantation. The
concentrations by weight of each dispersion are: 1) 1% NaOH, 2%
cellulose and 2% activated carbon; 2) 1% NaOH, 2% cellulose and 5%
activated carbon; 3) 1% NaOH, 5% cellulose and 2% activated carbon;
4) 1% NaOH, 5% cellulose and 5% activated carbon; 5) 7% NaOH, 2%
cellulose and 2% activated carbon; 6) 7% NaOH, 2% cellulose and 5%
activated carbon; 7) 7% NaOH, 5% cellulose and 2% activated carbon;
8) 7% NaOH 5% cellulose and 2% activated carbon; 9) 0% NaOH, 5%
cellulose and 5% activated carbon; 10) 0% NaOH, 0% cellulose and 5%
activated carbon; 11) 7% NaOH, 0% cellulose and 5% activated
carbon; 12) 0% NaOH 0% cellulose and 5% activated carbon.
[0029] For the preparation of mixtures 1 to 8 solutions and
alkaline dispersions of cellulose were initially prepared. First,
the sodium hydroxide was solubilized in water and the solution was
cooled to 0.degree. C. using an ice bath. The cellulose was added
to the NaOH solution and the mixture was homogenized in a disperser
at 6500 rpm for 5 min and at 0.degree. C. The mixture was kept at
-20.degree. C. in a freezer for 2 h. After preparation of the
solutions and cellulose dispersions, the mixtures 1 to 8 received
additions of commercial activated carbon resulting in the
concentrations listed above. The mixtures 9 to 12 were prepared by
adding the components to water. All mixtures were made in plastic
centrifuge tubes and shaken in a reciprocal motion shaker at 360
oscillations per minute with a displacement of 2 cm for 15 h. The
mixtures remained static for 24 h at room temperature (24.degree.
C) and were photographed after the decantation period.
[0030] The systems 9 and 10 show that carbon does not disperse in
water without the presence of cellulose, and much of the material
remained in contact with the hydrophobic wall of the vial, so it
did not get hydrophilic character, which should have been provided
by adsorption of the cellulose.
[0031] In contrast, systems 1 to 4 show sedimentation of the carbon
in the presence of cellulose, with no carbon spread on the surface
of the plastic bottle, such as the systems 9 and 10. The systems 1
to 4 show the accumulation of the aggregate material only in a few
regions of the vial, indicating that most of the carbon became
hydrophilic due to contact with the cellulose. Furthermore, no
macroscopic separation of the constituents, cellulose and carbon,
in the sediments was observed despite the density difference of
these compounds, showing the chemical compatibility between
them.
[0032] The mixtures 5 to 8 present dispersions which remain stable
after 24 hours, the solids remain in suspension, without the
formation of macroscopic domains of each species. These systems
show that cellulose disperses carbon in water.
[0033] FIG. 5 shows the flowchart of the process used in Example 1.
The first step is the preparation of an alkaline solution by
addition of sodium hydroxide in water, followed by cooling of this
solution on an ice bath. Then, microcrystalline cotton cellulose
was added to the NaOH and the mixture homogenized in a disperser at
6500 rpm for 5 mitt at The system was maintained at -20.degree. C.
for 2 h, obtaining a solution containing 5% (w/w) of cellulose and
7% (w/w) of NaOH. The alkaline cellulose solution was warmed until
the room temperature (24.degree. C.) and commercial graphite powder
was added at a concentration of 2% (w/w). After the addition, the
mixture was stirred in a homogenizer with a reciprocal movement of
360 oscillations per minute and a displacement of 2 cm for 15
hours.
DESCRIPTION OF THE INVENTION
[0034] Graphite is a material used in various applications as a
lubricant, pigment and conductor of electricity and heat, it is
highly hydrophobic, what makes its use in aqueous media difficult,
in Which it can be dispersed using dispersing agents well-known in
the area, such as surfactants and water soluble polymers. The
importance of graphite increased very recently When it was
discovered the possibility of its exfoliation producing graphene
lamellas, of monoatomic thickness. Graphene is, in the present, the
most investigated material by material researchers and also of
several technology areas that can be benefited by its exceptional
chemical, mechanical, electrical and optical properties. Amorphous
carbons are materials very common in nature, easily obtained by
incomplete combustion and pyrolisis processes. They have great
structural affinity with graphite and graphene but they are
chemically more complex, due to the oxidation degree, highly
variable. Its structure is much less regular than that of graphene
and graphite, although polynuclear aromatic domains are
prevalent.
[0035] Many applications of graphene, graphite and amorphous carbon
require its prior dispersion in water. For example, inks and
conductive adhesives formulated in aqueous medium require these
compounds finely dispersed and stable in the medium. The amorphous
carbons, specifically, are widely used as adsorbents of
contaminants soluble in water destinated for municipal supply, and
in this function it would be very desirable to be able to disperse
in water the powdered carbon, what is hampered by its
hydrophobicity, as in the case of graphene and graphite.
[0036] Given the importance of these materials and especially their
aqueous dispersions, many researchers have made considerable
efforts to obtain such dispersions. A proof of this is that the
United States Patent Trade Office (USPTO) registers 700 patents,
searched combining the keywords "graphene" and "cellulose". But
when are searched "(graphene or graphite) and cellulose" was
founded 18.495 patents. Moreover, the number of patent applications
filed since 2001 was 2.072 only searched combining keywords
"graphene" and "cellulose". These patents cover a large number of
specific applications in the areas of energy (solar cells, lithium
batteries and others), lighting (LEDs), information technology
(printed and flexible electronic circuits), sensors, diagnostics
and analysis devices, electrodes for industrial processes,
structural materials for engineering and construction, among
others.
[0037] The scientific publications also provide abundant evidence
of the great interest by these materials. For example, an article
that describes the dispersion of graphene in water (Li, D., Muller,
M. B., Gilje, S., Kaner, & R. B. Wallace G. G.; Processable
aqueous dispersions of graphene nanosheets. Nature NanoTechnology,
v. 3(2), p. 101-102, 2008) with more than 4.500 citations.
[0038] The methods used in the art to obtain aqueous dispersions of
graphene, graphite and amorphous carbons are based on the use of
surfactants and water-soluble polymers as dispersants. Very popular
methods such as the described by Wallace, G. G. et al. (cited in
[0037]) use a previous step of oxidation of graphene forming
graphene oxide which is easily dispersed in water. Unfortunately,
the oxidation affects many of the desirable properties of graphene,
which can be partially recovered by the reduction of the oxide in
the presence of stabilizers to prevent their reaggregation and
precipitation from the dispersion.
[0039] The almost absolute prevalence of methods for graphene
dispersion based on the formation and subsequent reduction of
graphene oxide becomes apparent when it was found few patents and
publications by eliminating of the words "graphene oxide" in the
search. A search by eliminating of these words showed only six
articles and a patent. The articles are: High Concentration and
Stable Aqueous Dispersion of Graphene Stabilized by the New
Amphiphilic Copolymer; Wu, Shengli; Shi Tiejun; Zhang, Liyuan.
Fullerenes Nanotubes and Carbon Nanostructures, v. 23, p. 974-984,
2015; Liposome-induced exfoliation of graphite to few-layer
graphene dispersion with antibacterial activity; Zappacosta, R.; Di
Giulio, M.; Ettorre, V.; et al.; Journal of Materials Chemistry B,
v. 3, p. 6520-6527, 2015; Aqueous graphene dispersions-optical
properties and stimuli-responsive phase transfer; Ager, David;
Vasantha, Vivek Arjunan; Crombez, Rene; et al., ACS NANO, v. 8, p.
11191-11205, 2014.; Interfacial engineering of
polypropylene/graphene nanocomposites: Improvement of graphene
dispersion by using tryptophan as a stabilizer"; You, Feng; Wang,
Dongrui; Li Xinxin; et al., RSC Advances, v. 4, p. 8799-8807, 2014;
Preparation of PYP-PVA-exfoliated graphite composite cross-linked
hydrogels for the incorporation of small tin nanoparticles;
Delbecq, Frederic; Kono, Fumihiko; Kawai, Takeshi; European Polymer
Journal, v. 49, p. 2654-2659, 2013; Role of poly
(N-vinyl-2-pyrrolidone) stabilizer for the dispersion of graphene
via hydrophobic interaction; Yoon, Seyoung; Journal of Materials
Science, v. 46, p. 1316-1321; 2011.
[0040] The patent mentioned in [0039]above is: Lead-acid cell
cathode lead-paste, comprehend lead powder, fiber, graphene liquid
aqueous dispersion, acetylene black, barium sulfate, sulfuric acid
and water, CN103367753, inventors Chen, T.; Gao, X; Huang, H; et
al., Shandong University. However, in this patent the graphene is
chemically modified, which is one of the ways to make it
hydrophilic.
[0041] Delbecq, Frederic; Kono, Fumihiko; Kawai, Takeshi;
Preparation of PVP-PVA-exfolied graphite cross-linked composite
hydrogels for the incorporation of small tin nanoparticles.
European Polymer Journal, v. 49, p. 2654-2659, 2013; used only
polyvinylpyrrolidone and polyvinylalcohol as exfoliating of the
graphite in aqueous medium, but with low efficiency and very dilute
solutions.
[0042] An unprecedented possibility of dispersion and stabilization
of graphite, graphene and amorphous carbons in aqueous solution is
the use of cellulose. This polymer, although abundant and well
known in the art, presents some challenges to current knowledge,
such as the problem of insolubility in practically all known
liquids. Attempts to address this problem produced in the last 150
years, several products of technological importance such as rayon,
cellophane, "artificial silk", and more recently, regenerated
cellulose fibers obtained from cellulose solutions in N-oxide of
N-methylmorpholine.
[0043] A recent possibility of solubilizing cellulose is the use of
aqueous solutions of NaOH at low temperatures or in the presence of
urea, thiourea and some other hydrotropic additives. This
possibility is interpreted as evidence of the amphiphilic character
of cellulose, hypothesis defended by the Swedish researcher
Lindman, Bjorn (Alves, L.; Medronho, B.; Antunes, F. E.; Topgaard,
D. and Lindman, Bjorn. Dissolution state of cellulose in aqueous
systems. 1 Alkaline solvents, Cellulose, v. 23, p. 247-258, 2016)
but that is not completely accepted. According to this hypothesis,
the cellulose chains have hydrophilic and hydrophobic domains
geometrically separated and the association between the hydrophobic
domains excludes the water contact with a significant part of the
chains area, causing its insolubility in water.
[0044] This invention exploits the possibility of connect
hydrophobic domains of cellulose chains with faces of graphene
lamellas and surfaces of particles of graphite or amorphous carbon,
leaving the hydrophilic cellulose domains in contact with the
water, which should cause its stabilization.
[0045] Researches familiar with the art, should not expect success
this way for the stabilization of graphene dispersions, graphite
and amorphous carbon, for several reasons: cellulose and graphite
are known to be incompatible, even the cellulose is insoluble in
water and its amphiphilic nature is not recognized by most
practitioners of the art.
[0046] However, the experiments described in the examples provided
in this patent show that the cellulose is, surprisingly, a
dispersing and stabilizing of graphene, graphite and amorphous
carbon. The cellulose can be put in contact with the carbon
allotropes in different ways: as alkaline aqueous solution of
cellulose such as cellulose powder mixed with graphite or amorphous
carbon in dry conditions and as cellulose powder mixed with
graphite or carbon under water or another liquid compatible with
cellulose, graphite or carbon. In all cases, there is an
association between cellulose and carbonaceous compound,
characterized by the impossibility of observing, by microscopic
examination, separation of cellulose particles from the others, due
to dispersion and stability in water of the carbonaceous compound
and its rheological behavior.
[0047] When graphite is dispersed with cellulose it is possible to
exfoliate graphite forming graphene, depending on the relative
amounts, the intensity of the contact between two reactants, the
intensity of mechanical action and the temperature. The graphene
formed, when brought into contact with more cellulose, is also
stabilized by it, so that the cellulose can be used to produce
graphene stabilized, in an aqueous medium.
[0048] The dispersions and slurries of carbon materials in this
present invention comprise the use of cellulose (CAS Number
9004-34-6) or pulp composed mainly of cellulose (CAS Number
65996-61-4) dispersed partially or totally solubilized. The present
invention comprises the use of cellulose as a dispersing agent for
materials formed mainly of carbon such as graphite, nanographite,
graphene, amorphous carbons, colloidal carbons, fullerenes and
carbon nanotubes. The amounts of cellulose necessary are
conveniently expressed by the ratio of the masses of cellulose and
graphite or other carbonaceous material, and can vary from 1 part
of cellulose to 99 of graphite, nanographite, graphene, amorphous
carbon, colloidal carbon, fullerenes and carbon nanotubes and 60
cellulose for 40 graphite, nanographite, graphene, amorphous
carbon, colloidal carbon, fullerenes and carbon nanotubes.
[0049] The concentrations of graphite or other carbonaceous
materials in liquid dispersions, slurry or dry mass may vary
between 0.001% and 50% by weight of graphite on the weight of the
dispersion.
[0050] The dispersions and slurries of this invention may be
prepared in neutral or alkaline medium. Alkalis are selected from a
group comprising sodium, potassium, lithium, calcium and ammonium,
tetramethylammonium, or aluminates and zincates of alkali and its
concentration may vary between 0% and 50% by weight.
[0051] In an alternative embodiment of the invention, the
dispersion or slurry can be produced with a neutralizing additive,
such as sodium bicarbonate, borax, boric acid or other substance
with buffering action at neutral pH. Neutralizing agents will be
required to achieve the desired pH, depending on the concentration
of alkali used. The additive can be added in solid form, in
solution or in any other manner known in the art, in any convenient
concentration.
[0052] In another embodiment of the invention, the dispersion or
solution of cellulose in an alkaline medium is produced by addition
of a hydrotrope additive such as urea, thiourea, mono-, di- and
triethanolamines, glycerol, ethanol and other alcohols,
dimethylsulfoxide, toluene sulfonates, xylene sulfonates, cumen
sulfonates, lignin sulphonates, benzoates, salicylates, citrates,
acetates and other compounds known in the art. The amounts of
additives can vary between 0% and 25% by mass of solution or
dispersion of graphite or other carbonaceous compound in the
presence cellulose.
[0053] In another embodiment of the invention, the alkaline
cellulose solution or dispersion is added with oxides of zinc,
aluminum, vanadium, titaniun or germanium.
[0054] In another embodiment, the aqueous medium may be replaced
partially or completely by a polar organic liquid, such as
methanol, ethanol, iso-propanol, n-propanol, acetone, ethylene
glycol, glycerol, mono-methyl ethylene glycol, containing or not an
alkali, with concentration ranging between 0 and 50%.
[0055] The following examples represent only some embodiments of
the present invention and should not be considered, in any way, as
limiting of the scope and inventive concept of the present
invention, since there are additional possible alternatives and
arrangements.
EXAMPLES
Example 1--Preparation of Aqueous Dispersion Containing 2% of
Graphite, 5% of Cellulose and 7% of NaOH
[0056] An alkaline solution was prepared by adding sodium hydroxide
in water and the solution was cooled to 0.degree. C. in an ice
bath. Microcrystalline cotton cellulose was added in NaOH solution
and the mixture was homogenized in a disperser at 6500 rpm for 5
min and at 0.degree. C. The system was kept at -20.degree. C. for 2
h, obtaining a solution containing 5% (w/w) cellulose and 7% (w/w)
NaOH. The alkaline cellulose solution was warmed to room
temperature (24.degree. C.) and commercial graphite was added at a
concentration of 2% (w/w). After the addition, the mixture was
stirred in a disperser with reciprocal movement to 360 oscillations
per minute with a displacement of 2 cm for 15 hours.
[0057] The dispersion stability was evaluated by keeping the system
standing for 24 h. After this period, there was no settling of
solids and appearance of the dispersion remained unchanged. Also,
it was not observed distinct domains of cellulose and graphite,
indicating that there was no separation of the two species, despite
the density difference (graphite from 2.09 to 2.23 g/cm.sup.3 and
cellulose 1.5 g/cm.sup.3), showing the compatibility of the
compounds.
[0058] The dispersion was centrifuged at 3000 rpm for 1 h at
20.degree. C. and it was obtained a sediment volume of 3.5 ml of a
total volume of approximately 5 mL. It was not observed
heterogeneity in the sediment or its separation in graphite and
cellulose.
Example 2--Preparation of Aqueous Dispersion Containing 5% of
Graphite, 5% of Cellulose and 7% of NaOH
[0059] An alkaline solution containing 5% of cellulose was prepared
as in example 1. The alkaline cellulose solution was warmed to room
temperature (24.degree. C.) and commercial graphite was added at a
concentration of 5% (m/m). The mixture was homogenized as in
example 1, turning into a slurry.
[0060] The dispersion stability was evaluated by keeping the system
standing for 24 h. After this period, there was no settling of the
solids, as in example 1.
[0061] 5 ml of the dispersion were centrifuged at 3000 rpm for 1 h
at 20.degree. C., and it was obtained 3.6 ml of sediment
volume.
Example 3--Preparation of Aqueous Dispersion Containing 2% of
Graphite, 5% of Cellulose and 1% of NaOH
[0062] A dispersion containing 5% (w/w) of cellulose and 1% (w/w)
of NaOH was prepared as in examples 1 and 2. The cellulose
dispersion was warmed to room temperature (24.degree. C.) and
commercial graphite was added at a concentration of 2% (w/w). After
the addition, the mixture was stirred as in examples 1 and 2.
[0063] The dispersion stability was evaluated by keeping the system
standing for 24 h. After this period, the solids were sedimented
and a clear supernatant was formed with no deposit of material on
the wall of a plastic bottle, as occurred in the graphite
dispersion in water. The sedimentation of the particles indicates
that graphite and cellulose are in contact and there are no
macroscopic domains of both, and furthermore, the solids remain in
the aqueous medium, like a water-cellulose system.
[0064] 5 ml of the dispersion was centrifuged at 3000 rpm for 1 h
at 20.degree. C., and a sediment volume of 1.0 ml was obtained.
Example 4--Preparation of Aqueous Dispersion Containing 5% of
Activated Carbon, 2% of Cellulose and 7% of NaOH
[0065] A solution containing 2% (w/w) cellulose and 7% (w/w) NaOH
was prepared as in examples 1-3. The cellulose solution was warmed
to room temperature (24.degree. C.) and the activated carbon was
added at a concentration of 5% (m/m). After the addition, the
mixture was stirred as in examples 1-3.
[0066] The dispersion stability was evaluated by keeping the system
standing for 24 h. After the period, there was no settling of
solids, and the system remained unchanged. Also, it was not
observed different domains of cellulose and activated carbon,
indicating that there was no separation of the two species, despite
the density difference (activated carbon 2.0 to 2.1 g/cm.sup.3 and
cellulose 1.5 g/cm.sup.3), showing the compatibility of compounds
and, therefore, that the alkaline cellulose is a good dispersing of
activated coal in water.
Example 5--Preparation of Aqueous Dispersion Containing 5% of
Activated Coal, 5% of Cellulose and 1% of NaOH
[0067] A dispersion containing 5% (w/w) of cellulose and 1% (w/w)
of NaOH was prepared as in examples 1-4. The cellulose dispersion
was warmed to room temperature (24.degree. C.) and the activated
carbon was added at a concentration of 5% (m/m). After the
addition, the mixture was stirred as in examples 1-4.
[0068] The dispersion stability was evaluated by keeping the system
standing for 24 h. After this period, the solids were sedimented
forming a clear supernatant without an uniform distribution of
carbon in the wall of the plastic bottle, as observed in the
activated carbon dispersion in aqueous NaOH solution. The
sedimentation of the particles indicates that the activated carbon
and cellulose are in close contact, because it was not observed
macroscopic domains of both.
Example 6--Preparation of Aqueous Dispersion Containing 5% of
Activated Coal, 5% of Cellulose and 7% of NaOH
[0069] A solution containing 5% (w/w) of cellulose and 7% (w/w) of
NaOH was prepared as in examples 1-5. The cellulose solution was
warmed to room temperature (24.degree. C.) and activated carbon was
added at a concentration of 5% (m/m). After the addition, the
mixture was stirred as in examples 1-5, turning it into a
slurry.
[0070] The dispersion stability was evaluated by keeping the system
standing for 24 h. After the period, there was no settling of
solids and the system remained unchanged. Also, it was not observed
different domains of cellulose and activated carbon indicating that
there was no separation of the two species, despite the density
difference (activated coal 2.0 to 2.1 g/cm.sup.3 and cellulose 1.5
g/cm.sup.3), showing the chemical compatibility of the compounds,
where the alkali cellulose is the dispersant of the activated
carbon in water.
* * * * *