U.S. patent application number 15/338407 was filed with the patent office on 2017-06-01 for sorption and separation of various materials by graphene oxides.
This patent application is currently assigned to Zonko, LLC. The applicant listed for this patent is Zonko, LLC. Invention is credited to Stepan N. Kalmykov, Dmitry V. Kosynkin, Anna Y. Romanchuk, Alexander Slesarev, James M. Tour.
Application Number | 20170151548 15/338407 |
Document ID | / |
Family ID | 47296350 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170151548 |
Kind Code |
A1 |
Tour; James M. ; et
al. |
June 1, 2017 |
Sorption And Separation of Various Materials By Graphene Oxides
Abstract
Methods of sorption of various materials from an environment are
disclosed herein. Embodiments of the materials include radioactive
elements chlorates, perchlorates, organohalogens, and combinations
thereof. Other embodiments pertain to methods of sorption of
cationic radionuclides. Compositions produced by such methods are
also disclosed herein. Embodiments of the methods may include
contacting graphene oxides with the environment and sorption of the
materials to the graphene oxides. In some embodiments, the sorption
is relatively rapid in comparison to known sorbents; even in the
presence of relatively higher concentrations of complexing agents.
In some embodiments, the methods further include separating the
graphene oxides that sorbed materials from the environment. Yet
other embodiments may include desorbing the materials from the
graphene oxides that sorbed the materials, and compositions
therefrom.
Inventors: |
Tour; James M.; (Bellaire,
TX) ; Slesarev; Alexander; (Obninsk, RU) ;
Kosynkin; Dmitry V.; (Daharan, SA) ; Romanchuk; Anna
Y.; (Moscow, RU) ; Kalmykov; Stepan N.;
(Moscow, RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zonko, LLC |
Houston |
TX |
US |
|
|
Assignee: |
Zonko, LLC
Houston
TX
|
Family ID: |
47296350 |
Appl. No.: |
15/338407 |
Filed: |
October 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14001255 |
Nov 26, 2013 |
9511346 |
|
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PCT/US2012/026766 |
Feb 27, 2012 |
|
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15338407 |
|
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61446535 |
Feb 25, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 15/08 20130101;
B01J 20/3272 20130101; B01D 61/145 20130101; B01J 20/3085 20130101;
C02F 1/4696 20130101; C02F 1/66 20130101; G21F 9/12 20130101; C02F
1/52 20130101; B01J 20/0296 20130101; C02F 1/385 20130101; C02F
9/00 20130101; C02F 2303/18 20130101; B01J 20/205 20130101; B01D
21/262 20130101; B01J 20/3204 20130101; C02F 1/441 20130101; B01J
20/3416 20130101; B03C 5/00 20130101; B01D 61/025 20130101; C02F
1/444 20130101; C02F 1/683 20130101; C02F 2101/14 20130101; C02F
1/283 20130101; B01J 20/327 20130101; B01J 20/3244 20130101; C02F
2101/206 20130101; B01J 20/00 20130101; C02F 2101/006 20130101 |
International
Class: |
B01J 20/20 20060101
B01J020/20; B01J 20/34 20060101 B01J020/34; C02F 9/00 20060101
C02F009/00; G21F 9/12 20060101 G21F009/12; B01D 15/08 20060101
B01D015/08; B01D 21/26 20060101 B01D021/26; B03C 5/00 20060101
B03C005/00; B01D 61/02 20060101 B01D061/02; B01J 20/30 20060101
B01J020/30; B01D 61/14 20060101 B01D061/14 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with government support under the
U.S. Air Force Office of Scientific Research Grant No:
FA9550-09-1-0581 and the U.S. Navy Office of Naval Research Grant
No: N000014-09-1-1066, both awarded by the U.S. Department of
Defense. The government has certain rights in the invention.
Claims
1. A method of radionuclide sequestration comprising: contacting
substantially hydrophilic graphene oxides with a solution
comprising a total initial concentration of one or more cationic
radionuclides and a total initial concentration of one or more
complexing agents, and reducing the total initial concentration of
the one or more cationic radionuclides in the solution by at least
forty percent by sorption of the one or more cationic radionuclides
to at least a portion of the substantially hydrophilic graphene
oxides.
2. The method of claim 1 wherein the total initial concentration of
the one or more cationic radionuclides is equal to or less than
2.15.times.10.sup.-7 M.
3. The method of claim 1, wherein the solution comprises an aqueous
solution.
4. The method of claim 1, wherein the contacting comprises mixing
the substantially hydrophilic graphene oxides with the
solution.
5. The method of claim 1, wherein the sorption comprises
absorption.
6. The method of claim 1, wherein the substantially hydrophilic
graphene oxides are selected from the group consisting of
functionalized graphene oxides, chemically converted graphene,
pristine graphene oxides, doped graphene oxides, reduced graphene
oxides, functionalized graphene oxide nanoribbons, pristine
graphene oxide nanoribbons, doped graphene oxide nanoribbons,
reduced graphene oxide nanoribbons, stacked graphene oxides,
graphite oxides, and combinations thereof.
7. The method of claim 1, wherein the one or more cationic
radionuclides is selected from cations of the group consisting of
thallium, iridium, fluorine, americium, neptunium, gadolinium,
bismuth, uranium, thorium, plutonium, niobium, barium, cadmium,
cobalt, europium, manganese, sodium, zinc, technetium, strontium,
polonium, cesium, potassium, radium, lead, actinides, lanthanides
and combinations thereof.
8. The method of claim 1, further comprising adjusting the pH of
the solution such that the reduction of the total initial
concentration of the one or more cationic radionuclides occurs in
about twenty minutes or less after contacting the substantially
hydrophilic graphene oxides with the solution.
9. The method of claim 1, wherein the total initial concentration
of the one or more complexing agents in the solution is in the
range of 2.4.times.10.sup.4 times and 2.6.times.10.sup.13 times the
total initial concentration of the one or more cationic
radionuclides.
10. The method of claim 1, wherein the one or more complexing
agents is selected from the group consisting of Na.sup.+,
Ca.sup.2+, NO.sub.3.sup.-, CH.sub.3COO.sup.-,
C.sub.2O.sub.4.sup.2-, SO.sub.4.sup.2-, Cl.sup.-, CO.sub.3.sup.2-,
and combinations thereof.
11. The method of claim 1, wherein the substantially hydrophilic
graphene oxides have a ratio of total oxygen functionality to
graphitic sp.sup.2 carbon in the range of 2.6:1 and 4.0:1.
12. The method of claim 1, further comprising separating the
graphene oxides from the solution.
13. The method of claim 12, wherein the separating comprises at
least one of the following: centrifugation, ultra-centrifugation,
filtration, ultra-filtration, precipitation, electrophoresis,
reverse osmosis, sedimentation, incubation, treatment with acids,
treatment with bases, treatment with chelating agents, and
combinations thereof.
14. The method of claim 12, wherein the separating comprises
precipitating the graphene oxides from the solution by the addition
of a polymer to the solution.
15. The method of claim 1, wherein the one or more cationic
radionuclides is a cationic actinide and the solution is comprised
of nuclear fission products.
16. The method of claim 15, further comprising separating the
graphene oxides from the solution after the sorption.
17. A method of radionuclide sequestration comprising: contacting
substantially hydrophilic graphene oxides with a solution
comprising nuclear fission products comprised of actinides, and
reducing the concentration of the actinides in the solution by
sorption of at least a portion of the actinides to the
substantially hydrophilic graphene oxides.
18. A method of radionuclide sequestration comprising: contacting
substantially hydrophilic graphene oxides with a solution
comprising one or more cationic radionuclides having a total
initial cationic radionuclide concentration of 2.15.times.10.sup.-7
M or less, the solution is additionally comprised of one or more
complexing agents selected from the group consisting of Na.sup.+,
Ca.sup.2+, NO.sub.3.sup.-, CH.sub.3COO.sup.-,
C.sub.2O.sub.4.sup.2-, Cl.sup.-, SO.sub.4.sup.2-, Cl.sup.-,
CO.sub.3.sup.2-, and combinations thereof; and sorbing the one or
more cationic radionuclides to at least a portion of the
substantially hydrophilic graphene oxides.
19. The method of claim 18, further comprising reducing the total
initial concentration of the one more cationic radionuclides by at
least forty percent in about twenty minutes or less after
contacting the substantially hydrophilic graphene oxides.
20. The method of claim 18, further comprising desorbing one or
more of the radionuclides from the graphene oxides that sorbed the
cationic radionuclides and separating the desorbed radionuclides
from the graphene oxides to produce radionuclide-desorbed graphene
oxides.
21. The method of claim 20, further comprising repeating the method
of claim 20 at least once wherein the graphene oxides comprise the
radionuclide-desorbed graphene oxides.
22. A composition comprising radionuclide-sorbed graphene oxides
prepared by the process of contacting substantially hydrophilic
graphene oxides with a solution comprising one or more cationic
radionuclides and one or more complexing agents, sorbing at least
forty percent of the total initial concentration of the one or more
cationic radionuclides to at least a portion of the substantially
hydrophilic graphene oxides thereby producing radionuclide-sorbed
graphene oxides, separating the radionuclide-sorbed graphene oxides
from the solution.
23. A radionuclide composition prepared by the process of
contacting substantially hydrophilic graphene oxides with a
solution comprising one or more cationic radionuclides and one or
more complexing agents, sorbing at least forty percent of the total
initial concentration of the one or more cationic radionuclides to
at least a portion of the substantially hydrophilic graphene oxides
thereby producing radionuclide-sorbed graphene oxides, separating
the radionuclide-sorbed graphene oxides from the solution, and
desorbing one or more of the radionuclides from the
radionuclide-sorbed graphene oxides.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
Utility patent application Ser. No. 14/001,255 entitled "Sorption
and Separation of Various Materials By Graphene Oxides" filed on
Nov. 26, 2013 which claims priority to International PCT
Application Serial Number PCT/US2012/026766 filed on Feb. 27, 2012
and having the same title as the previously-mentioned co-pending
application Ser. No. 14/001,255 and which claims priority to U.S.
Provisional Patent Application Ser. No. 61/446,535, filed on Feb.
25, 2011, The entirety of the above-identified applications are
each incorporated herein by reference.
BACKGROUND
[0003] Current methods of purifying various environmental
contaminants (including radioactive elements and halogenated
compounds) have numerous limitations in terms of efficacy, costs,
and efficiency. Therefore, a need exists for the development of
improved methods for purifying such contaminants from various
environments.
BRIEF SUMMARY
[0004] In some embodiments, the present invention provides methods
of sorption of various materials from an environment. Such methods
generally include contacting graphene oxides with the environment.
This in turn leads to the relatively rapid rate or rates of
sorption of the materials to the graphene oxides. In some
embodiments, rapid sorption of the materials to graphene oxide
occurs even in the presence of relatively high concentrations of
complexing agents. Complexing agents are agents that may compete
with graphene oxide, or otherwise prevent or interfere with
graphene oxide sorbing materials from the environment. In some
embodiments, the materials sorbed from the environment comprise at
least one of radioactive elements, chlorates, perchlorates,
organohalogens, and combinations thereof. In some embodiments the
complexing agents may be one or more of Na.sup.+, Ca.sup.2+,
NO.sub.3.sup.-, CH.sub.3COO.sup.-, C.sub.2O.sub.4.sup.2-,
SO.sub.4.sup.2-, Cl.sup.-, CO.sub.3.sup.2-, and combinations
thereof.
[0005] In some embodiments, the methods of the present invention
also include a step of separating the graphene oxides from the
environment after the sorption of the materials to the graphene
oxides. In various embodiments, the separation step may occur by
centrifugation, ultra-centrifugation, filtration, ultra-filtration,
precipitation, electrophoresis, reverse osmosis, sedimentation,
incubation, treatment with acids, treatment with bases, treatment
with chelating agents, and combinations of such methods.
[0006] Various methods may also be used to contact graphene oxides
with the environment. In some embodiments, the contacting occurs by
mixing the graphene oxides with the environment. In some
embodiments, the contacting occurs by flowing the environment
through a structure that contains the graphene oxides (e.g., a
column).
[0007] The sorption of materials to graphene oxides may also occur
by various methods. In some embodiments, the sorption includes an
absorption interaction of the materials in an environment to the
graphene oxides. In some embodiments, the sorption includes an
ionic interaction between the materials in an environment and the
graphene oxides. In some embodiments, the sorption includes an
adsorption interaction between the materials in an environment and
the graphene oxides. In some embodiments, the sorption includes a
physisorption interaction between the materials in an environment
and the graphene oxides. In some embodiments, the sorption includes
a chemisorption interaction between the materials in an environment
and the graphene oxides. In some embodiments, the sorption includes
a covalent bonding interaction between the materials in an
environment and the graphene oxides. In some embodiments, the
sorption includes a non-covalent bonding interaction between the
materials in an environment and the graphene oxides. In some
embodiments, the sorption includes a hydrogen bonding interaction
between the materials in an environment and the graphene oxides. In
some embodiments, the sorption includes a van der Waals interaction
between the materials in an environment and the graphene oxides.
The aforementioned interactions are non-limiting and herein
referred to as sorption.
[0008] Various graphene oxides may also be utilized in the methods
of the present invention. For instance, the graphene oxides may be
at least one of functionalized graphene oxides, pristine graphene
oxides, doped graphene oxides, reduced graphene oxides,
functionalized graphene oxide nanoribbons, pristine graphene oxide
nanoribbons, doped graphene oxide nanoribbons, reduced graphene
oxide nanoribbons, stacked graphene oxides, graphite oxides, and
combinations thereof. In some embodiments, the graphene oxides may
be functionalized with functional groups that comprise at least one
of carboxyl groups, esters, amides, thiols, hydroxyl groups,
carbonyl groups, aryl groups, epoxy groups, phenol groups,
phosphonic acids, amine groups, polymers and combinations thereof.
In some embodiments, the graphene oxides may be functionalized with
polymers, such as polyethylene glycols, polyvinyl alcohols,
poly(ethylene imines), poly(acrylic acids), polyamines and
combinations thereof.
[0009] Furthermore, the methods of the present invention may be
utilized to purify various materials from various environments. For
instance, in some embodiments, the environment is an aqueous
solution, such as contaminated water. In some embodiments, the
environment is an atmospheric environment, such as air. In some
embodiments, the environment is a solution comprising nuclear
fission products.
[0010] In some embodiments, the materials to be purified include
radioactive elements. In some embodiments, the radioactive elements
comprise at least one of metals, salts, metal salts, radionuclides,
actinides, lanthanides, and combinations thereof. In more specific
embodiments, the radioactive elements in the environment include
radionuclides, such as thallium, iridium, fluorine, americium,
neptunium, gadolinium, bismuth, uranium, thorium, plutonium,
niobium, barium, cadmium, cobalt, europium, manganese, sodium,
zinc, technetium, strontium, carbon, polonium, cesium, potassium,
radium, lead, actinides, lanthanides and combinations thereof. In
some embodiments, the radionuclide is actinide.
[0011] In some embodiments, the materials to be purified include
chlorates, such as ammonium chlorate, barium chlorate, cesium
chlorate, fluorine chlorate, lithium chlorate, magnesium chlorate,
potassium chlorate, rubidium chlorate, silver chlorate, sodium
chlorate, and combinations thereof. In some embodiments, the
materials to be purified include perchlorates, such as ammonium
perchlorate, barium perchlorate, cesium perchlorate, fluorine
perchlorate, lithium perchlorate, magnesium perchlorate, perchloric
acid, potassium perchlorate, rubidium perchlorate, silver
perchlorate, sodium perchlorate, and combinations thereof. In
additional embodiments, the materials to be purified include
organohalogens, such as polychlorinated biphenyls (PCB) and
halogenated flame retardants.
[0012] In more specific embodiments, the methods of the present
invention are used for the sorption of actinides from a solution
comprising nuclear fission products. Such methods may also include
a step of separating the graphene oxides from the solution
comprising nuclear fission products after the sorption step.
[0013] The methods of the present invention provide various
advantages, including the effective separation of various
radioactive elements from various environments. For instance, in
some embodiments, the methods of the present invention may be used
to reduce radioactive elements in a solution by at least about
70%.
[0014] The methods of the present invention also provide various
applications. For instance, in some embodiments, the methods of the
present invention may be used for waste water treatment and
environmental remediation applications.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIGS. 1A-1C show data relating to the removal of various
radionuclides by graphene oxide. FIG. 1A shows the kinetics of
U(VI), Am(III), Th(IV) and Pu(IV) sorption onto graphene oxide,
indicating that steady state conditions are reached within 5
minutes. FIG. 1B shows pH-sorption edges for Th(IV), U(VI), Pu(IV)
and Am(III). FIG. 1C shows pH-sorption edges for Sr(II), Tc(VII),
and Np(V) at steady state. With respect to the data shown in FIGS.
1A-1C, the concentrations are listed in Example 10.
[0016] FIG. 2A shows sorption isotherms for U(VI) in 0.01 M
NaClO.sub.4. FIG. 2B shows sorption isotherms for Sr(II) in 0.01 M
NaClO.sub.4. FIG. 2C shows sorption isotherms for Am(III) in 0.01 M
NaClO.sub.4. Isotherms were fitted with both Langmuir (solid line)
and Freundlich (dashed line) formalism. Parameters of fitting and
sorption capacity (Q.sub.max) are shown in Table 1 (Example 3). The
concentrations of the elements for sorption, and of the graphene
oxides are listed in Example 10.
[0017] FIGS. 3A and 3B show sorption efficiencies of different
materials that are compared along with the coagulation properties
of graphene oxide solutions. FIG. 3A shows the removal of U(VI)
from simulated liquid nuclear waste (see Table 2) by graphene oxide
and also by some routinely used sorbents at equal mass
concentrations. FIG. 3B show the removal of Pu(IV) from simulated
liquid nuclear waste (see Table 2) by graphene oxide and also by
some routinely used sorbents at equal mass concentrations. FIG. 3C
shows coagulation of graphene oxide in a simulated nuclear waste
solution. The left panel of FIG. 3C shows the initial graphene
oxide suspension (labeled as 1), and the coagulated graphene oxide
(labeled as 2). The mid-right panel of FIG. 3C shows a scanning
transmission electron microscope (STEM) image of the coagulated
graphene oxide (labeled as 2) and the corresponding EDX spectrum on
the far right. The highlighted section in the STEM image in FIG. 3C
shows the formation of nanoparticulate aggregates containing
cations from simulated nuclear waste solution (Si and P are trace
contaminants in graphene oxide from its preparation, as described
in Example 5).
[0018] FIG. 4A shows micrographs and analyses of Pu/graphene oxide
coagulates. The left side panel of FIG. 4A is a STEM image of
Pu(IV) on graphene oxide. The right side panels of FIG. 4A show the
EDX spectra corresponding to the different areas labeled 1, 2 and 3
as indicated on the STEM image. Pu-containing particles in graphene
oxide could be observed by Z contrast of the STEM image in FIG. 4A
and as shown in the EDX spectra of the highlighted regions of the
STEM image labeled 1, 2 and 3. FIG. 4B is a high-resolution
transmission electron microscopy (HRTEM) image of
PuO.sub.2+x.nH.sub.2O nanoparticles together with the FFT of
individual nanoparticles from the highlighted region, indicating
the cubic structure typical for PuO.sub.2+x.
DETAILED DESCRIPTION
[0019] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only, and are not restrictive of the invention, as
claimed. In this application, the use of the singular includes the
plural, the word "a" or "an" means "at least one", and the use of
"or" means "and/or", unless specifically stated otherwise.
Furthermore, the use of the term "including", as well as other
forms, such as "includes" and "included", is not limiting. Also,
terms such as "element" or "component" encompass both elements or
components comprising one unit and elements or components that
comprise more than one unit unless specifically stated otherwise.
Ranges of values stated herein include all subranges and such
ranges and subranges are included and disclosed herein.
[0020] The section headings used herein are for organizational
purposes only and are not to be construed as limiting the subject
matter described. All documents, or portions of documents, cited in
this application, including, but not limited to, patents, patent
applications, articles, books, and treatises, are hereby expressly
incorporated herein by reference in their entirety for any purpose.
In the event that one or more of the incorporated literature and
similar materials defines a term in a manner that contradicts the
definition of that term in this application, this application
controls.
[0021] The nuclear industry generates large amounts of radioactive
wastewater that must be effectively treated before it is discharged
into the environment. The toxic radioactive elements (such as
radionuclides) in the wastewater cannot be effectively removed by
current drinking water purification techniques. Furthermore,
separation techniques involving chromatographic methods can be
time-consuming and expensive. Moreover, various industries generate
large amounts of halogenated by-products, such as chlorates,
perchlorates, and organohalogens (e.g., polychlorinated biphenyls
and halogenated flame retardants). As a result, new methods are
needed for the relatively rapid and efficient removal of
radioactive and halogenated elements from various solutions and
environments, especially for waste water treatment and
environmental remediation applications wherein relatively higher
concentrations of complexing agents may be present. The present
invention addresses these needs.
[0022] In some embodiments, the present invention provides methods
of sorption of various materials from an environment. In some
embodiments, the materials to be removed from an environment
include at least one of radioactive elements, chlorates,
perchlorates, organohalogens, and combinations thereof.
[0023] Such methods generally include contacting graphene oxides
with the environment. This in turn leads to the sorption of the
materials to the graphene oxides. In some embodiments, the methods
of the present invention also include a step of separating the
graphene oxides from the environment after the sorption of the
radioactive elements to the graphene oxides.
[0024] As set forth in more detail below, the methods of the
present invention have numerous variations. For instance, the
methods of the present invention may involve the purification of
various materials from various environments by the use of various
graphene oxides.
Materials
[0025] The methods of the present invention may be utilized to
purify various materials from various environments. In some
embodiments, the materials to be purified include, without
limitation, radioactive elements, chlorates, perchlorates,
organohalogens, and combinations thereof. In more specific
embodiments, the materials to be purified include, without
limitation, polycyclic aromatics, chlorinated and brominated
dibenzodioxins and dibenzofurans, chlorinated biphenyls, lindane,
dichlorodiphenyltrichloroethane (DDT) and other similar hydrophobic
xenobiotics.
Radioactive Elements
[0026] In some embodiments, the radioactive elements to be purified
from an environment are metals, salts, metal salts, radionuclides,
actinides, lanthanides, and combinations thereof. In more specific
embodiments, the radioactive elements in the solutions include
radionuclides, such as thallium, iridium, fluorine, americium,
neptunium, gadolinium, bismuth, uranium, thorium, plutonium,
niobium, barium, cadmium, cobalt, europium, manganese, sodium,
zinc, technetium, strontium, carbon, polonium, cesium, potassium,
radium, lead, actinides, lanthanides and combinations thereof.
[0027] In more specific embodiments, the radioactive elements to be
purified from various environments include, without limitation,
americium(III), actinide(III), actinide(IV), thallium(IV),
plutonium(IV), neptunium(V), uranium(VI), strontium(II),
technetium(VII), and combinations thereof.
[0028] In more specific embodiments, the radioactive elements
include, without limitation, thallium-201, iridium-192,
fluorine-18, americium-241, americium-243, neptunium-237, Gd-153,
niobium-93, barium-133, cadmium-109, cobalt-57, cobalt-60,
europium-152, manganese-54, sodium-22, zinc-65, technetium-99,
strontium-90, thallium-204, carbon-14, polonium 210, cesium-137,
and combinations thereof.
[0029] In some embodiments, the radioactive elements may be
naturally occurring radioactive materials (NORMs). In some
embodiments, NORMs generally comprise uranium and its isotopes. In
some embodiments, NORMs may also comprise thorium and its isotopes.
In further embodiments, NORMs may also include potassium, lead, and
polonium. NORMs are not only considered in the context of their
natural abundance and distribution, but also in view of human
activities that increase potential for exposure to them. In some
cases, those human activities may also serve to concentrate the
radionuclides present, thereby resulting in what is called
technologically enhanced naturally occurring radioactive materials
(TENORMs).
[0030] NORMs or TENORMs can be produced by oil and gas production
and refining; mineral production; coal mining and combustion; metal
mining and smelting; fertilizer production; production of mineral
based building materials, including granite, stone, gypsum, and
concrete; and beneficiation of mineral sands, including rare earth
minerals, titanium and zirconium. NORMs and TENORMs are also
present in drinking water supplies, particularly in Western US and
Canada. See, e.g., http://world-nuclear.org/info/inf30.html.
[0031] While uranium and thorium-based elements are the main
isotopes of NORMs and TENORMs, K-40, Po-210, Ra-226, Ra-228, and
Pb-210 can also be present. NORMs and TENORMs can also include
actinides and lanthanides in general. Thus, some embodiments of the
present invention addresses the need for the capture and clean-up
of NORMs and TENORMs.
[0032] In more specific embodiments, the radioactive elements to be
purified include actinides. In some embodiments, the actinides are
in a solution that contains nuclear fission products.
Chlorates and Perchlorates
[0033] The methods of the present invention may also be utilized to
purify various chlorates and perchlorates. Non-limiting examples of
chlorates include ammonium chlorate, barium chlorate, cesium
chlorate, fluorine chlorate, lithium chlorate, magnesium chlorate,
potassium chlorate, rubidium chlorate, silver chlorate, sodium
chlorate, and combinations thereof. Non-limiting examples of
perchlorates include ammonium perchlorate, barium perchlorate,
cesium perchlorate, fluorine perchlorate, lithium perchlorate,
magnesium perchlorate, perchloric acid, potassium perchlorate,
rubidium perchlorate, silver perchlorate, sodium perchlorate, and
combinations thereof. In some embodiments, perchlorates may have
similar sorption profiles to various radioactive elements, such as
pertechnetate (Tc(VII)).
Organohalogens
[0034] The methods of the present invention may also be utilized to
purify various organohalogens. Organohalogens generally refer to
organic compounds that include one or more halogen groups. In some
embodiments, the organohalogen is an organochloride. In some
embodiments, the organohalogen is polychlorinated biphenyl (PCB).
In some embodiments, the organohalogen is a halogenated flame
retardant. In further embodiments, the organohalogens include,
without limitation, chloromethanes, dichloromethanes,
trichloromethanes, tetrachloromethanes, bromomethanes,
bromoalkanes, bromochloromethanes, iodoalkanes, iodomethanes,
organofluorines, organochlorines, acyclic organohalogens, cyclic
organohalogens, and combinations thereof.
Environments
[0035] In the present invention, materials may be purified from
various types of environments. In some embodiments, the environment
is an atmospheric environment, such as air. In some embodiments,
the environment is a solution, such as an aqueous solution.
Non-limiting examples of aqueous solutions include water, such as
radioactive water, contaminated water, and waste water. In some
embodiments, the solution includes nuclear fission products. In
some embodiments, the solution to be purified is a non-aqueous
solution, such as a solution containing benzenes, toluenes,
dichloromethane, and other non-aqueous solvents.
Graphene Oxides
[0036] "Functionalized graphene oxide," as used herein, refers to,
for example, graphene oxide that has been derivatized with a
plurality of functional groups. "Chemically converted graphene"
refers to, for example, graphene produced by reduction of graphene
oxide. Reduction of graphene oxide to chemically converted graphene
removes at least a portion of the oxygen functionalities present in
graphene oxide.
[0037] Various graphene oxides may be utilized in the methods of
the present invention. Suitable graphene oxides include, without
limitation, functionalized graphene oxides, pristine graphene
oxides, doped graphene oxides, reduced graphene oxides, chemically
converted graphene, functionalized graphene oxide nanoribbons,
pristine graphene oxide nanoribbons, doped graphene oxide
nanoribbons, reduced graphene oxide nanoribbons, stacked graphene
oxides, graphite oxides, and combinations thereof.
[0038] In some embodiments, the graphene oxides may be covalently
or non-covalently functionalized with various functional groups,
such as carboxyl groups, hydroxyl groups. carbonyl groups, aryl
groups, epoxy groups, phenol groups, phosphonic acids (e.g.,
RPO(OH).sub.2, where R is a carbon group linked to the graphene
scaffold), amine groups, esters, ether-based functional groups,
polymers and combinations thereof.
[0039] In some embodiments, functionalized graphene oxides may be
made from graphene oxide that has been derivatized with a plurality
of functional groups using a derivitazing agent. In some
embodiments, the derivatizing agent is a diazonium species. In some
embodiments, the derivatizing agent is an aryl diazonium species.
In some embodiments, the diazonium species may be a pre-formed
diazonium salt. In other embodiments, the diazonium species may be
a diazonium salt that is formed in situ. A diazonium species may be
formed in situ, for example, by treating an amine with an organic
nitrite such as, for example, isoamyl nitrite.
[0040] In some embodiments of functionalized graphene oxide,
carboxylic acids, hydroxyl groups, carbonyl groups, and epoxides
comprising the graphene oxides (see, e.g., Table 3) may be
chemically transformed by the derivatizing agents in forming the
functionalized graphene oxide. In some embodiments, functionalized
graphene oxides generally contain a plurality of functional groups
attached to the graphene oxide through a covalent bond. Chemical
bonding of the functional groups may occur to the edge of the
graphene oxide, to the basal plane of the graphene oxide, or to
both the edge and the basal plane of the graphene oxide.
[0041] In some embodiments, the graphene oxides may be
functionalized with polymers, such as polyethylene glycols,
polyamines, polyesters, polyvinyl alcohols, poly(ethylene imines),
poly(acrylic acids), and combinations thereof. Examples of suitable
polyethylene glycol functional groups include, without limitation,
triethylene glycol di(p-toluenesulfonate), polyethylene glycol
methyl ether tosylate, and the like. In some embodiments,
polyethylene glycol functional groups on graphene oxides can be
further hydrolyzed to remove most or all of any tosylate groups in
order to afford terminal hydroxyl groups.
[0042] The graphene oxides of the present invention may also have
various arrangements. For instance, in various embodiments, the
graphene oxides of the present invention may be in stacked form. In
some embodiments, the stacked graphene oxides may contain from
about 2 layers to about 50 layers of graphene oxide. In some
embodiments, the graphene oxides of the present invention may form
a single sheet.
[0043] In some embodiments, the graphene oxides of the present
invention may also include one or more layers of graphene along
with the graphene oxides. Such graphenes may include, without
limitation, pristine graphenes, doped graphenes, chemically
converted graphenes, functionalized graphenes and combinations
thereof.
[0044] In further embodiments, the graphene oxides may be graphene
oxides derived from exfoliated graphite, graphene nanoflakes, or
split carbon nanotubes (such as multi-walled carbon nanotubes). In
more specific embodiments, the graphene oxides of the present
invention may be derived from split carbon nanotubes. In various
embodiments, the split carbon nanotubes may be derived from
single-walled carbon nanotubes, multi-walled carbon nanotubes,
double-walled carbon nanotubes, ultrashort carbon nanotubes,
pristine carbon nanotubes, functionalized carbon nanotubes, and
combinations thereof. In more specific embodiments, the graphene
oxides of the present invention are derived from split multi-walled
carbon nanotubes.
[0045] In addition, various methods may be used to split carbon
nanotubes. In some embodiments, carbon nanotubes may be split by
potassium or sodium metals. In some embodiments, the split carbon
nanotubes may then be functionalized by various functional groups,
such as alkyl groups. Additional variations of such embodiments are
described in U.S. Provisional Application No. 61/534,553 entitled
"One Pot Synthesis of Functionalized Graphene Oxide and
Polymer/Graphene Oxide Nanocomposites." Also see Higginbotham et
al., "Low-Defect Graphene Oxide Oxides from Multiwalled Carbon
Nanotubes," ACS Nano 2010, 4, 2059-2069. Also see Applicants'
co-pending U.S. patent application Ser. No. 12/544,057 entitled
"Methods for Preparation of Graphene Oxides From Carbon Nanotubes
and Compositions, Thin Composites and Devices Derived Therefrom."
Also see Kosynkin et al., "Highly Conductive Graphene Oxides by
Longitudinal Splitting of Carbon Nanotubes Using Potassium Vapor,"
ACS Nano 2011, 5, 968-974.
[0046] In various embodiments, the graphene oxides may be doped
with various additives. In some embodiments, the additives may be
one or more heteroatoms of B, N, O, Al, Au, P, Si or S.
[0047] In more specific embodiments, the doped additives may
include, without limitation, melamine, carboranes, aminoboranes,
phosphines, aluminum hydroxides, silanes, polysilanes,
polysiloxanes, sulfides, thiols, and combinations thereof. In more
specific embodiments, the graphene oxides may be HNO.sub.3 doped
and/or AuCl.sub.3 doped.
[0048] In various embodiments, the graphene oxides of the present
invention may also be dissolved or suspended in one or more
solvents before being contacted with environments containing
radioactive elements. Examples of suitable solvents include,
without limitation, acetone, 2-butanone, dichlorobenzene,
ortho-dichlorobenzene, chlorobenzene, chlorosulfonic acid, dimethyl
formamide, N-methyl pyrrolidone, 1,2-dimethoxyethane, water,
alcohol and combinations thereof.
[0049] In further embodiments, the graphene oxides of the present
invention may also be associated with a surfactant before being
associated with various environments. Suitable surfactants include,
without limitation, sodium dodecyl sulfate (SDS), sodium
dodecylbenzene sulfonate, Triton X-100, chlorosulfonic acid, and
the like.
[0050] The graphene oxides of the present invention may have
various properties. For instance, in some embodiments, the graphene
oxides of the present invention have an aspect ratio in
length-to-width greater than or equal to 2, greater than 10, or
greater than 100. In some embodiments, the graphene oxides have an
aspect ratio greater than 1000. In further embodiments, the
graphene oxides of the present invention have an aspect ratio in
length-to-width greater less than or equal to 2.
[0051] Furthermore, the graphene oxides of the present invention
can come in the form of variable sized sheets. Such sheets may have
lengths or diameters that range from about a few nanometers to a
few hundred microns to several centimeters. In more specific
embodiments, the graphene oxides may have lengths or diameters that
range from about 1 nanometers to about 3 centimeters.
[0052] The graphene oxides of the present invention are generally
hydrophilic and can be coagulated upon addition of cations or
surfactants. In some embodiments, the graphene oxides have a ratio
of total oxygen functionality to graphitic sp.sup.2 carbon in the
range of 2.6:1 and 4.0:1 (for example, as in Table 3 further below
Examples 6-7). All individual values and subranges within the range
of 2.6:1 and 4.0:1 are included herein and disclosed herein.
[0053] In other embodiments, the surface oxidation of the graphene
oxides can be gradually and systematically reduced to modify their
properties. Such reduction can occur through the addition of
reducing agents (e.g., hydrazine, sodium borohydride, acid or base
with heat) or thermolysis (with or without H.sub.2 being present).
In some embodiments, graphene oxide may be reduced with at least
one reducing agent to form chemically converted graphene. In some
embodiments, the at least one reducing agent for forming chemically
converted graphene from graphene oxide may be, for example,
hydrazines, iodide, phosphines, phosphites, sulfides, sulfites,
hydrosulfites, borohydrides, cyanoborohydrides, aluminum hydrides,
boranes, hydroxylamine, diamine, dissolving metal reductions,
hydrogen, and combinations thereof. In some embodiments, the at
least one reducing agent may be hydrogen. In some embodiments, the
graphene oxide may be first reduced with hydrazine or hydrazine
hydrate and thereafter reduced with a second, more powerful
reducing agent such as, for example, hydrogen. The second reduction
may further restore the sp.sup.2 structure of pristine graphene
sheets over that obtained in the first reduction. In various
embodiments, reduction of the graphene oxide with hydrogen may
involve annealing the graphene oxide in the presence of hydrogen.
In some embodiments, annealing may include an inert gas.
[0054] Hydrazine, for example, removes ketone and hydroxyl groups
from graphene oxide but leaves behind edge carboxylic acid groups
in the chemically converted graphene. The residual carboxylic acid
groups may disrupt the .pi.-conjugated network of the graphene
sheet and lower the conductivity of the chemically converted
graphene relative to that ultimately obtainable by their removal.
Hydrogen may be more efficient than hydrazine at removing
oxygen-containing functional groups from the graphene oxide, since
this reagent removes even carboxylic acid groups in addition to
carbonyl and hydroxyl functionalities. In some embodiments, borane
(BH.sub.3) may be used to reduce the graphene oxide. Borane is
particularly effective at reducing carboxylic acids to alcohols,
and the alcohols can be further removed with hydrogen and heat in a
second reduction step. In some embodiments, the chemically
converted graphene may be further reacted with a derivatizing agent
to form a functionalized, chemically converted graphene.
[0055] The graphene oxides of the present invention may also have
various forms. For instance, in some embodiments, the graphene
oxides of the present invention may be associated with various
composites. In some embodiments, such composites may include
organic materials, such as synthetic polymers, natural fibers,
nonwoven materials, and the like. In some embodiments, the graphene
oxide composites may include inorganic materials, such as porous
carbons, asbestos, Celite, diatomaceous earth, and the like. In
further embodiments, the graphene oxides of the present invention
may be in isolated and pure forms.
[0056] In more specific embodiments of the present invention, the
graphene oxides are derived from the direct oxidation of graphite.
In some embodiments, the oxidation of graphite could be through
chemical methods, electrochemical methods or combinations of
chemical methods and electrochemical methods that may occur
simultaneously or sequentially in either order. In some
embodiments, graphene oxides are derived by the chemical oxidation
of graphite. Examples of methods of oxidizing graphite are
disclosed in Applicants' prior work. See, e.g., Marcano, et al.,
"Improved Synthesis of Graphene Oxide" ACS Nano 2010, 4, 4806-4814.
Also see U.S. Provisional Patent Application Nos. 61/180,505 and
61/185,640. Also see WO 20111016889, and corresponding U.S. Patent
Application Publication No. US 2012/0129736 published May 24, 2012.
(Although stated elsewhere, each reference is hereby incorporated
by reference in its entirety). In some embodiments, the graphene
oxide may have a relatively higher level of oxidation,
hydrophilicity and degree of dispersability in relatively more
polar solvents. In some embodiments, graphene oxides readily
disperse in water.
[0057] In some embodiments, making graphene oxides may comprise
providing a graphite source, providing a solution containing at
least one acid solvent, at least one oxidant (oxidizing agent) and
at least one protecting agent, mixing the graphite source with the
solution, and oxidizing the graphite source with the at least one
oxidant (oxidizing agent) in the presence of the at least one
protecting agent to form graphene oxide.
[0058] In some embodiments of making the graphene oxides, and
without being bound by theory or mechanism, addition of what may be
conceptually thought of as a protecting agent operable for
protecting alcohols or diols may be included in the reaction
mixture. In some embodiments of making graphene oxides, such a
protecting agent would be, for example, phosphoric acid. Phosphoric
acid may be included in the reaction mixture to prepare graphene
oxides as provided in Examples 5-6, and Example 8. As demonstrated
in those examples, regardless of the mechanism or manner of
protection, excessive basal plane oxidation in the graphene sheets
is precluded, while the overall level of oxidation is increased
relative to that of other methods for forming graphene oxide from
bulk graphite. See, e.g., Table 3 and compare Examples 6 and 8 with
Example 7.
[0059] In various embodiments, the at least one oxidant may be an
oxidant such as, for example, permanganate, ferrate, osmate,
ruthenate, chlorate, chlorite, nitrate, osmium tetroxide, ruthenium
tetroxide, lead dioxide, and combinations thereof. For any of the
referenced oxidants that are cations or anions, any counteranion
suitable for forming a salt of the oxidant cation or anion may be
used in practicing the methods of the present disclosure. However,
one of ordinary skill in the art will recognize that certain salts
may be more advantageous than others in such properties as, for
example, their solubility and stability. In some embodiments, the
at least one oxidant is potassium permanganate. In general, the at
least one oxidant of the present disclosure is an oxidant that
mediates a cis-oxidation of double bonds.
[0060] In some embodiments, making the graphene oxides may further
include at least one acid solvent. The at least one acid solvent
may be, for example, oleum (fuming sulfuric acid), sulfuric acid,
chlorosulfonic acid, fluorosulfonic acid, trifluoromethanesulfonic
acid, and combinations thereof. In some embodiments, the at least
one acid solvent may be sulfuric acid. In some embodiments, the at
least one acid solvent is sulfuric acid and the at least one
oxidant is potassium permanganate. In various embodiments, oleum
may have a free sulfur trioxide concentration ranging from about
0.1% to about 20%. In various embodiments, sulfuric acid may have a
concentration greater than about 90% (v/v). Although Examples 5-8
employ potassium permanganate as the at least one oxidant and
sulfuric acid as the at least one acid solvent, one of ordinary
skill in the art will recognize that many different combinations of
oxidants, acid solvents and protecting agents may be used to
achieve a similar result in preparing graphene oxides in preparing
graphene oxide while operating within the spirit and scope of the
present disclosure.
[0061] In various embodiments, without meaning to be bound by any
particular theory or mechanism, the at least one protecting agent
of the present method is operable for protecting vicinal diols. In
some embodiments, the at least one protecting agent is operable for
protecting vicinal diols in the presence of at least one acid
solvent.
[0062] In some embodiments and without intending to be bound by any
theory or mechanism, the at least one protecting agent is a
non-oxidizing acid. In some embodiments, the at least one
protecting agent is an anhydride or mixed anhydride that is
convertible to a non-oxidizing acid operable for serving as a
protecting agent. Such protecting agents are operable for
protecting vicinal diols in the presence of a strong acid solvent
such as, for example, fuming sulfuric acid, sulfuric acid,
chlorosulfonic acid, fluorosulfonic acid and
trifluoromethanesulfonic acid. Illustrative protecting agents
useful in any of the various embodiments of the present disclosure
include, for example, trifluoroacetic acid, phosphoric acid,
orthophosphoric acid; metaphosphoric acid; polyphosphoric acid,
boric acid, trifluoroacetic anhydride; phosphoric anhydride,
orthophosphoric anhydride; metaphosphoric anhydride, polyphosphoric
anhydride; boric anhydride; mixed anhydrides of trifluoroacetic
acid, phosphoric acid, orthophosphoric acid, metaphosphoric acid,
polyphosphoric acid, and boric acid; and combinations thereof. In
some embodiments, the at least one protecting agent may be, for
example, phosphoric acid, boric acid, trifluoroacetic acid, and
combinations thereof. Although Example 5-6 and Example 8 each
utilize phosphoric acid as an illustrative protecting agent,
similar results have been obtained using trifluoroacetic acid and
boric acid as the protecting agent. In some embodiments, a salt of
any of the aforesaid protecting agents may be used in the various
methods presented herein.
[0063] In various embodiments, oxidizing the graphite source takes
place at a temperature between about -50.degree. C. and about
200.degree. C. In some embodiments, oxidizing takes place at a
temperature between about 0.degree. C. and about 100.degree. C. In
some embodiments, oxidizing takes place at a temperature between
about 300.degree. C. and about 85.degree. C. In some embodiments,
oxidizing takes place at a temperature between about 30.degree. C.
and about 50.degree. C. In some embodiments, oxidizing takes place
at a temperature between about 25.degree. C. and about 70.degree.
C. In some embodiments, oxidizing takes place at a temperature of
less than about 50.degree. C. In some embodiments, oxidizing takes
place at a temperature of less than about 30.degree. C.
[0064] In general, reaction times may vary as a function of the
reaction temperature and as a function of the particle size of the
starting graphite source. In various embodiments, reaction times
may vary from about 1 hour to about 200 hours. In other
embodiments, reaction times may vary from about 1 hour to about 24
hours. In other embodiments, reaction times may vary from about 1
hour to about 12 hours. In still other embodiments, reaction times
may vary from about 1 hour to about 6 hours.
[0065] At the aforesaid temperatures, a high recovery of graphene
oxide having a flake dimension approximating that of the starting
graphite flakes and only a small amount of mellitic acid and other
low molecular weight byproducts are observed. Operation at these
temperatures is advantageous to minimize decomposition of the
oxidant, particularly when the oxidant is KMnO.sub.4. In strongly
acidic media, permanganate slowly decomposes to Mn(IV) species that
are incapable of oxidizing graphite to graphene oxide. Hence, the
temperature is kept as low as possible to provide for essentially
complete conversion of graphite to graphene oxide at an acceptable
rate using only a moderate excess of KMnO.sub.4. In the theoretical
limit of infinite size graphite crystals, for each gram of graphite
being oxidized, 4.40 grams of KMnO.sub.4 are required for
stoichiometric equivalence. Losses of KMnO.sub.4 to decomposition,
formation of carboxylic acid groups and other basal plane edge
functionality, and hole formation in the basal plane make the
addition of oxidant somewhat above the theoretical amount
desirable.
[0066] In some embodiments of making graphene oxides, about 0.01 to
about 10 grams of KMnO.sub.4 per gram of graphite (0.002 to about
2.3 equiv. KMnO.sub.4) may be used.
[0067] In embodiments having sub-stoichiometric quantities of
KMnO.sub.4 or any other oxidant, a co-oxidant may also be included
to re-oxidize the primary oxidant and make the reaction proceed to
completion. Illustrative co-oxidants include, for example, oxygen
and N-methylmorpholine N-oxide (NMO). In some embodiments of the
present disclosure, about 6 grams of KMnO.sub.4 per gram of
graphite (1.4 equiv. KMnO.sub.4) may be us to obtain graphene oxide
having properties that are different than previously known forms of
graphene oxide.
[0068] In other various embodiments, methods of making graphene
oxides include providing a graphite source, providing a solution
containing at least one acid solvent, at least one oxidant and at
least one protecting agent, mixing the graphite source with the
solution, and oxidizing the graphite source with the at least one
oxidant in the presence of the at least one protecting agent to
form graphene oxide. The at least one protecting agent is operable
for protecting vicinal diols.
[0069] In still other various embodiments, methods of making
graphene oxide include providing a graphite source, providing a
solution containing at least one acid solvent, potassium
permanganate and at least one protecting agent, mixing the graphite
source with the solution, and oxidizing the graphite source with
the potassium permanganate in the presence of the at least one
protecting agent to form graphene oxide. The at least one acid
solvent may be, for example, oleum, sulfuric acid, fluorosulfonic
acid, trifluoromethanesulfonic acid, and combinations thereof. The
at least one protecting agent may be, for example, trifluoroacetic
acid; phosphoric acid; or orthophosphoric acid, metaphosphoric
acid; polyphosphoric acid; boric acid; trifluoroaceitc anhydride;
phosphoric anhydride; orthophosphoric anhydride; metaphosphoric
anhydride; polyphosphoric anhydride; boric anhydride; mixed
anhydrides of trifluoroacetic acid, phosphoric acid,
orthophosphoric acid, metaphosphoric acid, polyphosphoric acid, and
boric acid; and combinations thereof.
[0070] In some embodiments of making graphene oxides, methods of
the present disclosure further include isolating the graphene
oxide. Isolating the graphene oxide may take place by, for example,
centrifugation or filtration. In some embodiments, a poor solvent
(e.g. ether) may be added to a solution of graphene oxide to induce
precipitation. In some embodiments, the methods further include
washing the graphene oxide after isolating the graphene oxide. For
example, in some embodiments, the graphene oxide may be washed with
solvents including hydrochloric acid, water, acetone, or alcohols
to remove small molecule byproducts. In other embodiments, the
graphene oxide may be washed with solutions of bases. Washing with
solutions of bases such as, for example, sodium hydroxide, sodium
carbonate or sodium bicarbonate afford the sodium salt of
carboxylates or other acidic functional groups (e.g., hydroxyl
groups) on the graphene oxide. Similarly, other basic salts of
metal cations such as, for example, potassium, cesium, calcium,
magnesium and barium can be used.
[0071] Some embodiments of making graphene oxides may further
include purifying graphene oxide. However, in alternate
embodiments, the graphene oxide may be used in an unpurified state.
One of ordinary skill in the art will recognize that various
applications for the graphene oxide product may require different
levels of purity that might necessitate further purification.
Illustrative impurities that may remain in unpurified graphene
oxide include, for example, residual inorganic salts and low
molecular weight organic compounds.
Contacting Graphene Oxides and Environments
[0072] Various methods may also be used to contact graphene oxides
with various environments that contain materials to be purified. In
some embodiments, the contacting occurs by incubating the graphene
oxides with the environment (e.g., an atmospheric environment). In
some embodiments, the contacting occurs by mixing the graphene
oxides with the environment (e.g., an aqueous solution). The mixing
may occur by conventional methods, such as agitation, sonication,
and the like.
[0073] In some embodiments, the contacting of graphene oxides and
an environment containing materials to be purified can also occur
by flowing the environment through a structure that contains the
graphene oxides. In some embodiments, the structure may be a column
or a sheet that contains immobilized graphene oxides.
[0074] Additional methods of contacting graphene oxides with
various environments can also be envisioned. Generally, such
contacting results in the sorption of radioactive elements in the
environment to the graphene oxides.
Sorption of Materials to Graphene Oxides
[0075] The sorption of materials to graphene oxides may also occur
by various methods. In some embodiments, the sorption includes an
absorption of the materials in an environment to the graphene
oxides. In some embodiments, the sorption includes an adsorption of
the materials in an environment to the graphene oxides. In some
embodiments, the sorption includes an ionic interaction between the
materials in the environment and the graphene oxides. In some
embodiments, the sorption includes an adsorption interaction
between the materials in an environment and the graphene oxides. In
some embodiments, the sorption includes a physisorption interaction
between the materials in an environment and the graphene oxides. In
some embodiments, the sorption includes a chemisorption interaction
between the materials in an environment and the graphene oxides. In
some embodiments, the sorption includes a covalent bonding
interaction between the materials in an environment and the
graphene oxides. In some embodiments, the sorption includes a
non-covalent bonding interaction between the materials in an
environment and the graphene oxides. In some embodiments, the
sorption includes a hydrogen bonding interaction between the
materials in an environment and the graphene oxides. In some
embodiments, the sorption includes a van der Waals interaction
between the materials in an environment and the graphene oxides.
The aforementioned interactions are non-limiting and herein
referred to as sorption.
[0076] The sorption of materials to graphene oxides may also have
various effects. For instance, in some embodiments, the sorption
leads to the formation of graphene oxide-cation colloids. In some
embodiments, the sorption may lead to coagulation or
precipitation.
Separation of Graphene Oxides from Environments
[0077] In some embodiments, the methods of the present invention
also include a step of separating the graphene oxides from an
environment containing various materials. The separation step
generally occurs after the sorption of the materials to the
graphene oxides. Various methods may be used for such separation
steps. In some embodiments, the separation step may occur by
centrifugation, ultra-centrifugation, filtration, ultra-filtration,
precipitation, electrophoresis, sedimentation, reverse osmosis,
treatment with acids, treatment with bases, treatment with
chelating agents such as EDTA, and combinations of such
methods.
[0078] In some embodiments, the separation step involves
ultra-filtration. In more specific embodiments, the
ultra-filtration step may lead to the removal of formed graphene
oxide-cation colloids from an environment. In additional
embodiments, the graphene oxide-cation colloids may also be removed
by ultra-filtration, high speed centrifugation, sedimentation,
reverse osmosis, or other suitable separation procedures.
[0079] In some embodiments, the separation step involves
precipitation. In some embodiments, the precipitation can be
initiated by adding one or more polymers to an environment. For
instance, in some embodiments, cationic polyelectrolytes, such as
poly(ethylene imine), may be added to a solution. In some
embodiments, the solution may contain graphene oxide-cation
coagulants that precipitate upon the addition of polymers. The
precipitated coagulants may then be removed by filtration,
centrifugation or other methods.
[0080] The separation step may have various effects. In some
embodiments, the separation step may lead to a reduction of the
radioactive elements in the environment by at least about 70%.
[0081] In some embodiments, the separated graphene oxides may then
be processed further in order to dissociate the sorbed materials
(such as radioactive elements). For instance, in some embodiments,
the materials may be dissociated from the graphene oxides by
changing the pH or temperature of a solution. The dissociated
graphene oxides may then be reused.
Advantages and Applications
[0082] The methods of the present invention provide numerous
applications. For instance, the methods of the present invention
can be used as filters or sorbents for removal of radioactive
elements and halogenated compounds from various sources. The
methods of the present invention can also be used for nuclear waste
treatment, and remediation of contaminated groundwater. For
instance, the methods of the present invention can be used as
components of ultra-filtration and reverse osmosis technologies in
waste water treatment. The methods of the present invention may
also be used to mitigate environmental radionuclide contamination.
The methods of the present invention may also be used to separate
various human-made radionuclides from aqueous solutions of various
compositions. In some embodiments, graphene oxides may also be used
as components of reactive barriers at contaminated sites.
[0083] In some embodiments, the methods of the present invention
can be used for the sorption and separation of actinides from
nuclear fission products. A classic method for this separation
involves using the PUREX process. However, the PUREX process
involves multiple extraction and preferential solubility steps and
valence adjustments. Thus, by using graphene oxides in accordance
with the methods of the present invention, one could mitigate the
need for subsequent valence adjustments, extraction into organic
phase, valence return, back extraction to the aqueous phase, and
sometimes oxalate conversion to oxides.
[0084] To the best of Applicants' understanding, graphene oxides
were not used previously for the sorption or separation of
radioactive elements or halogenated compounds. Furthermore,
effective separation of actinides from aqueous solutions and
nuclear wastes containing strong complexing agents (such as in
nuclear fission products) were not previously reported.
[0085] In addition, the use of graphene oxides to purify
radioactive elements and halogenated compounds from various
environments provides various advantages. To begin with, graphene
oxides are comprised of two-dimensional materials that consist of
single atomic planes. Therefore, graphene oxides provide a high
surface area and a low specific mass, especially when compared to
other potential sorbents. This in turn provides graphene oxides
with optimal sorption kinetics for radioactive elements.
[0086] In addition, graphene oxides are hydrophilic materials with
oxygen-containing functionalities that form stable complexes with
many radioactive elements, including actinides and lanthanide
cations. These attributes can help lead to rapid macroscopic
aggregation and precipitation of the formed complexes from various
solutions, including water. This process can be further facilitated
by the use of additional agents, such as surfactants and
polymers.
[0087] Moreover, graphene oxides can be readily produced in mass
quantities. Furthermore, the sorbed radioactive elements and
halogenated compounds that are appended to graphene oxides can be
liberated from the graphene oxides upon the lowering of the pH in
the solution. This in turn provides for reversible leaching and
sorption of radioactive elements.
ADDITIONAL EMBODIMENTS
[0088] Reference will now be made to more specific embodiments of
the present disclosure and experimental results that provide
support for such embodiments. However, Applicants note that the
disclosure below is for exemplary purposes only and is not intended
to limit the scope of the claimed invention in any way.
[0089] The Examples below pertain to the use of graphene oxides for
effective radionuclide removal. In particular, we show the efficacy
of graphene oxide for rapid removal of some of the most toxic and
radioactively long-lived human-made radionuclides from contaminated
water, even in acidic solutions (pH<2). The interaction of
graphene oxides with cations, including Am(III), Th(IV), Pu(IV),
Np(V), U(VI) and typical fission products Sr(II) and Tc(VII) were
studied, along with their sorption kinetics. Cation/graphene oxide
coagulation occurs with the formation of nanoparticle aggregates on
the graphene oxide surface, facilitating their removal. Graphene
oxide is far more effective in removal of transuranium elements
from simulated nuclear waste solutions than other routinely used
sorbents such as bentonite clays, iron oxide and activated carbon.
These results point toward a simple methodology to mollify the
severity of nuclear waste contamination that has been spawned by
humankind, thereby leading to effective measures for environmental
remediation.
[0090] Treatment of aqueous waste effluents and contaminated
groundwater containing human-made radionuclides, among which the
transuranic elements are the most toxic, is an essential task in
the clean-up of nuclear legacy sites. The recent accident that
included radionuclide release to the environment at the Fukushima
Daiichi nuclear power plant in Japan and the contamination of the
water used for cooling its reactor cores, underscores the need for
effective treatment methods of radionuclide-contaminated water.
Such technologies should be inexpensive, swift, effective and
environmentally friendly. Graphene oxide has been known for more
than a century, but has attracted attention in the last decade due
to its conversion to graphene.
[0091] The colloidal properties of graphene oxide make it a
promising material in rheology and colloidal chemistry. The
amphiphilic graphene oxide produces stable suspensions when
dispersed in liquids and shows excellent sorption capacities.
Previously, it was shown that graphene oxide enables effective
removal of Cu.sup.2+, arsenate, and organic solvents. As a result
of oxygen functionalization, the graphene oxide surface contains
epoxy, hydroxyl and carboxyl groups (see, e.g., Table 3) that are
responsible for interaction with cations and anions. In this work,
the application of graphene oxide for the effective removal of a
variety of radionuclides from aqueous solutions is described.
Kinetics of sorption, pH sorption edges and sorption capacity were
studied in the batch sorption mode to illustrate the performance of
graphene oxide in sequestering radionuclides from solution.
Examples 1-4 described below employed the graphene oxide of Example
5. Preparation of the graphene oxide of Example 5, and also several
other examples of graphene oxide and chemically converted graphene
oxide follow thereafter.
Example 1. Kinetics of Radionuclide Removal
[0092] The kinetics of radionuclide removal by graphene oxide are
presented in FIG. 1A, indicating that near steady state conditions
were achieved within 5 minutes even at very low graphene oxide
concentrations (<0.1 g/L by carbon). Without being bound by
theory, it is envisioned that the fast sorption kinetics are likely
due to graphene oxide's highly accessible surface area and lack of
internal surfaces that usually contribute to the slow kinetics of
diffusion in cation-sorbent interaction. This fast kinetics are of
importance for practical applications of graphene oxide for removal
of cationic impurities, including Th(IV), U(VI), Pu(IV) and
Am(III).
Example 2. Radionuclide Removal as a Function of pH
[0093] FIGS. 1B and 1C show pH sorption edges for Sr(II), Tc(VII),
Np(V), Th(IV), U(VI), Pu(IV) and Am(III). All of the radionuclides
demonstrate typical S-shaped pH-edges for cations, except for Tc,
which exists as the pertechnetate anion, TcO.sub.4.sup.-. This
explains its sorption at low pH when the graphene oxide surface is
protonated and positively charged. For Lewis "hard" cations such as
the actinides Th(IV), Pu(IV) and Am(III), the sorption is high,
even from acidic solutions with pH<2. For these cations, the
sorption from neutral pH solutions was nearly quantitative, a
result that is indicative of the prospects of its application in
remediation of contaminated natural waters.
Example 3. Graphene Oxide's Radionuclide Sorption Capacities
[0094] Graphene oxide demonstrates high sorption capacity towards
U(VI), Sr(II) and Am(III) cations, as determined from sorption
isotherms shown in FIG. 2. Even with a graphene oxide concentration
of only 0.038 g/L, the saturation limit is not reached. The values
for sorption capacity presented in FIG. 2 are calculated from
experimental data using Langmuir formalism and Freundlich
formalism. The experimental results are summarized in Table 1.
TABLE-US-00001 TABLE 1 Parameters for sorption of U(VI), Sr(II) and
Am(III) on graphene oxide Langmuir formalism Freundlich formalism
Q.sub.max, .mu.mol/g K.sub.L, L/.mu.mol R.sup.2 K.sub.F,
mol.sup.n-1L.sup.n/g n R.sup.2 U(VI), pH = 3.5 97 .+-. 19 0.046
.+-. 0.014 0.98 0.004 .+-. 0.002 0.33 .+-. 0.04 0.95 U(VI), pH = 5
116 .+-. 5 0.035 .+-. 0.064 0.97 0.078 .+-. 0.026 0.68 .+-. 0.03
0.99 Sr(II), pH = 6.5 272 .+-. 35 0.026 .+-. 0.007 0.95 0.034 .+-.
0.017 0.55 .+-. 0.05 0.96 Am(III), pH = 3.5 2 .+-. 1 7.034 .+-.
3.125 0.97 0.05 .+-. 0.03 0.67 .+-. 0.05 0.99
[0095] The above-mentioned results were obtained, despite the fact
that the graphene oxide surface was far from saturation. While it
is difficult to directly compare the sorption performance of
different sorbents towards radionuclides since it is dependent on
the precise experimental conditions, the sorption capacity of
graphene oxide is much higher than that of activated carbon,
bentonite clay and Fe(III) oxide, but close to the value determined
for oxidized carbon nanotubes (CNTs).
[0096] However, sorption rates for oxidized CNTs are much slower
than those of graphene oxide since much of the CNT surfaces are
internal or inaccessible due to bundling, and the CNTs have been
investigated for only a limited number of radionuclides and never
with a large host of competing counterions (referred to as
complexing agents herein). Moreover, CNT synthesis and subsequent
oxidation is far more expensive than synthesis of graphene oxide,
the latter coming from the one-pot treatment of graphite, thereby
rendering graphene oxide more suitable for large-scale clean-up
operations.
Example 4. Removal of Radionuclides from Simulated Nuclear
Waste
[0097] The removal of radionuclides from waste solutions was tested
using simulated liquid nuclear wastes that contains U and Pu salts
together with Na, Ca and various complexing substances such as
carbonate, sulfate, acetate, and citrate that could potentially
complicate sorption of radionuclides. See Table 2 for the complete
list. Among the commonly used scavengers for cationic radionuclides
(such as bentonite clays, granulated activated carbon and Fe(III)
oxide), graphene oxide demonstrates the highest sorption ability
towards actinides that form strong complexes in solutions with
sulfate, citrate, carbonate and acetate. The comparison of the
sorption of different sorbents towards U(VI) and Pu(IV) are
presented in FIGS. 3A-3B. Remarkably, even for Pu(IV) that forms
strong complexes with such complexing agents in solution, the
sorption onto graphene oxide was as high as 80%.
TABLE-US-00002 TABLE 2 Composition of Simulated Nuclear Waste at pH
7.5 Concentration, M Na.sup.+ 1.500 Ca.sup.2+ 0.005 NO.sup.3- 0.806
CH.sub.3COO.sup.- 0.339 C.sub.2O.sub.4.sup.2- 0.159 SO.sub.4.sup.2-
0.014 Cl.sup.- 0.010 CO.sub.3.sup.2- 0.005
[0098] Upon the interaction of simulated nuclear waste solution
with graphene oxide, coagulation occurred that resulted in visual
changes of the suspension (FIG. 3C). A scanning transmission
electron microscope (STEM) image of the graphene oxide coagulate
with cations and a corresponding energy-dispersive X-ray (EDX)
spectrum are presented in FIG. 3C. This is in agreement with the
earlier observations that addition of such cations results in
coagulation of graphene oxide. The most important observation for
application of graphene oxide for radionuclides removal is that,
despite the presence of high concentrations of cations that could
compete with Pu for sorption sites, the sorption of Pu remains
high. Thus, it is envisioned that the coagulation of graphene oxide
suspension resulting from cations and radionuclides would enable
the effective removal of radionuclides by filtration, reverse
osmosis or sedimentation.
[0099] The interaction of Pu(VI) with graphene oxide results in its
stabilization as Pu(IV) and formation of nanoparticulate
PuO.sub.2+x.nH.sub.2O on the graphene oxide (FIG. 4A). Such
stabilization could be explained by much higher sorption affinity
of Pu(IV) towards the surfaces compared with Pu(V). The high
resolution transition electron micrograph (HRTEM) image and EDX
show that Pu is concentrated in aggregates of crystalline
nanoparticles with an average size of 2 nm (FIG. 4B). The crystal
structure of nanoparticles corresponds to cubic Fm3m lattice with
d-spacing typical for PuO.sub.2 as studied by FFT. The reduction to
Pu(IV) is also supported by solvent extraction after Pu-leaching
from graphene oxide at pH 0.7. Upon acid leaching (see Example 5),
only .about.10% of Pu(IV) was desorbed from graphene oxide after 15
minutes, indicating that Pu(IV) nanoparticles are kinetically
stable. This is in concert with the earlier published data that
Pu(IV) is minimally leached from sorbents and more kinetically
stable than Pu(V) or Pu(VI).
[0100] The experimental data verifies the ability of graphene oxide
to effectively sorb most toxic radionuclides from various
solutions. Graphene oxide is found to be much more effective
compared with bentonite days, activated carbon and Fe(III) oxide in
actinide removal from liquid nuclear wastes. Graphene oxide
containing radionuclide could be easily coagulated and
precipitated. The simplicity of industrial scale-up of graphene
oxide, its high sorption capacity, and it ability to coagulate with
cations makes it a promising new material for responsible
radionuclide containment and removal.
Experimental Protocols
Example 5: Synthesis of Graphene Oxide Used in Examples 1-4
Above
[0101] Graphene oxide Example 5 was prepared using the improved
Hummer's method. Marcano et al., ACS Nano 2010. 4:4806-4814.
Large-flake graphite (10.00 g, Sigma-Aldrich, CAS 7782-42-5, LOT
332461-2.5 KG, Batch #13802EH) was suspended in a 9:1 mixture of
sulfuric and phosphoric acids (400 mL). Next, potassium
permanganate (50.00 g, 0.3159 mol) was added in small portions over
a period of 24 hours. After 5 days, the suspension was quenched
with ice (1 kg) and the residual permanganate was reduced with
H.sub.2O.sub.2 (30% aqueous, .about.3 mL) until the suspension
became yellow. The product was isolated by centrifugation at 319 g
for 90 minutes (Sorvall T1, ThermoFisher Scientific) and
subsequently washed with 10% HCl and water. The yellow-brown water
suspension (190.0 g) was isolated, corresponding to 10 g of dry
product. Gravimetric analysis and XPS shows 81% mass fraction of
carbon in the dry product.
Example 6: Synthesis of Graphene Oxide in the Presence of a
Protecting Agent
[0102] A 9:1 mixture of conc. H.sub.2SO.sub.4:H.sub.3PO.sub.4
(360:40 mL) was added to a mixture of graphite flakes (3.0 g, 1 wt.
equiv) and KMNO.sub.4 (18.0 g, 6 wt. equiv), producing a slight
exotherm to 35-40.degree. C. The reaction was then heated to
50.degree. C. and stirred for 12 h. The reaction was cooled to RT
and poured on to ice (.about.400 mL) along with 30% H.sub.2O.sub.2
(3 mL). For work up, the mixture was sifted through a metal U.S.
Standard testing sieve (W. S. Tyler, 300 .mu.m) and then filtered
through polyester fiber (Carpenter Co.). The filtrate was
centrifuged (4000 rpm for 4 h), and the supernatant was decanted
away. The remaining solid material was then washed in succession
with 200 mL of water, 200 mL of 30% HCl, and twice with 200 mL of
ethanol. For each wash the mixture was sifted through the U.S.
Standard testing sieve and then filtered through polyester fiber.
In each case, the filtrate was centrifuged (4000 rpm for 4 h), and
the supernatant was decanted away. The material remaining after the
multiple wash process was coagulated with 200 mL of ether, and the
resulting suspension was filtered over a PTFE membrane with a 0.45
.mu.m pore size. The solid obtained on the filter was vacuum dried
overnight at room temperature. The yield was 5.8 g of a solid
having a color similar to that of peanut butter.
[0103] The yield of hydrophobic, under-oxidized graphite oxide
removed during the first passage through the U.S. Standard testing
sieve was 0.7 g. Visual observation of the hydrophobic,
under-oxidized graphite oxide showed the amount of recovered solid
was significantly less than that obtained by Hummers' Method
(Example 7 below) or a modification of Hummers' Method (Example 8,
further below).
Example 7. Synthesis of Graphene Oxide Via Hummers' Method
[0104] Concentrated H.sub.2SO.sub.4 (69 mL) was added to a mixture
of graphite flakes (3.0 g, 1 wt. equiv) and NaNO.sub.3 (1.5 g, 0.5
wt equiv), and the mixture was cooled to 0.degree. C. KMNO.sub.4
(9.0 g, 3 wt. equiv) was added slowly in portions to keep the
reaction temperature below 20.degree. C. The reaction was warmed to
35.degree. C. and stirred for 30 min., at which time water (138 mL)
was added slowly, producing a large exotherm to 98.degree. C.
External heating was introduced to maintain the reaction
temperature at 98.degree. C. for 15 min, and the reaction was
cooled using a water bath for 10 min. Additional water (420 mL) and
30% H.sub.2O.sub.2 (3 mL) were then added, producing another
exotherm. After air cooling, the mixture was purified as described
for Example 6. The yield was 1.2 g of a black solid. The yield of
hydrophobic, under-oxidized graphite oxide removed during the first
passage through the U.S. Standard testing sieve was 6.7 g.
Example 8: Synthesis of Graphene Oxide Via a Modification of
Hummers' Method
[0105] Graphene oxide was also synthesized by a modification of
Hummers' Method by including additional KMNO.sub.4 in the reaction
mixture. Concentrated H.sub.2SO.sub.4 (69 mL) was added to a
mixture of graphite flakes (3.0 g, 1 wt. equiv) and NaNO.sub.3 (1.5
g, 0.5 wt. equiv), and the mixture was cooled using an ice bath to
0.degree. C. KMnO.sub.4 (9.0 g, 3 wt. equiv) was added slowly in
portions to keep the reaction temperature below 20.degree. C. The
reaction was warmed to 35.degree. C. and stirred for 7 h.
Additional KMnO.sub.4 (9.0 g, 3 wt. equiv) was added in one
portion, and the reaction was stirred for 12 h at 35.degree. C. The
reaction mixture was cooled to room temperature and poured on to
ice (.about.400 mL) along with 30% H.sub.2O.sub.2 (3 mL). The
mixture was then purified as described for Example 6. The yield was
4.2 g of a black solid. The yield of hydrophobic, under-oxidized
graphite oxide removed during the first passage through the U.S.
Standard testing sieve was 3.9 g.
Solid State .sup.13C NMR Analysis of Graphene Oxide Examples
6-8
[0106] Solid state .sup.13C NMR spectra for the graphene oxides of
Examples 6-8 were obtained at 50.3 MHz, with 12 kHz magic angle
spinning, a 90.degree. .sup.13C pulse, 41 ms FID and 20 second
relaxation delay. In the .sup.13C NMR spectra, signals near 190 ppm
were assigned to carboxylates, signals near 164 ppm were
collectively assigned to ketone, ester and lactol carbonyl groups,
signals near 131 ppm were assigned to graphitic sp.sup.2 carbons
and signals near 101 ppm were assigned to sp.sup.3 carbons of
lactols. The signals near 70 ppm were assigned to alcohols, and the
upfield shoulder of this peak was assigned to epoxides. Integral
ratios are summarized in Table 3 below. Table 3 also contains
calculated integral ratios for alcohol/epoxide:sp.sup.2 graphitic
carbon and total oxygen containing functionality: sp.sup.2
graphitic carbon as a measure of the degree of oxidation.
TABLE-US-00003 TABLE 3 Summary of Integral Ratios in Solid State
13C NMR Analysis of Examples 6-8 Graphene Oxide sp.sup.3 Alcohol/
Total Oxygen Example Graphitic Alcohol/ Lactol Epoxide:Graphitic
Functionality:Graphitic No. Carbon Epoxide Carboxylate Carbonyl
sp.sup.3 sp2 Ratio sp.sup.2 Ratio 6 20 67 4 4 5 3.4:1 4.0:1 7 32 59
3 2 4 1.8:1 2.1:1 8 28 63 3 2 4 2.3:1 2.6:1
[0107] Solid state .sup.13C NMR indicated that the graphene oxide
of Example 6 was more completely oxidized than that of either
Example 7 or Example 8. The simplest measure of the degree of
oxidation is the ratio of the alcohol/epoxide peak integration to
that of the graphitic sp.sup.2 carbons. A pristine graphene plane
having no edge functionalization would have a ratio of zero, since
all carbons would be of the sp.sup.2 type. Upon oxidation to form
graphene oxide, the number of sp.sup.2 carbons in the graphene
plane decreases and oxygen-containing functionalities
correspondingly increase to produce a non-zero ratio. Higher ratios
are therefore indicative of a greater degree of oxidation. As shown
in Table 3, the graphene oxide of Example 6 was more oxidized than
that of either Example 7 or Example 8, as evidenced by its greater
alcohol/epoxide:graphitic sp.sup.2 carbon ratio and total oxygen
functionality:graphitic sp.sup.2 carbon ratio.
Example 9. Reduction of Graphene Oxide
[0108] In some cases, hydrazine hydrate reduction was followed by
annealing at 300.degree. C. in H.sub.2. In general, hydrazine
hydrate reduction was conducted by dispersing 100 mg of the
graphene oxide material in 100 ml of deionized water and stirring
for 30 minutes. Thereafter, 1.00 ml of hydrazine hydrate was added.
The mixture was then heated for 45 minutes at 95.degree. C. using a
water bath. A black solid precipitated from the reaction mixture.
The product was isolated by filtration on a 20 .mu.m PTFE filter
and as washed thereafter three times each with deionized water and
methanol.
Example 10. Sorption Experiments Using the Graphene Oxides of
Example 5
[0109] Sorption experiments using the graphene oxides of Example 5
were carried out in plastic vials for which sorption onto the vial
walls was negligible under the experimental conditions. In the
sorption experiments, radionuclides nitrates were added to graphene
oxide suspension. Next, the pH was measured by a glass combined pH
electrode (In Lab Expert Pro, Mettler Toledo) and adjusted by
addition of small amounts of dilute HClO.sub.4 or NaOH. After
equilibration, the graphene oxide suspension was centrifuged at
40000 g for 20 minutes (Allegra 64R, Beckman Coulter) to separate
radionuclides sorbed onto the graphene oxide. The sorption was
calculated from the difference between the initial activity of the
radionuclides and that measured after equilibration. The initial
total concentration of radionuclides in the kinetic experiments and
pH-dependence tests was 2.15.times.10.sup.-7 M for .sup.233U(VI),
1.17.times.10.sup.-8 M for .sup.239Pu(IV), 5.89.times.10.sup.-14 M
for .sup.234Th(IV), 3.94.times.10.sup.-10 M for .sup.241Am(III),
3.94.times.10.sup.-10 M for .sup.239Np(V), 3.94.times.10.sup.-10 M
for .sup.95Tc(VII) and 1.24.times.10.sup.-7 M for .sup.90Sr(II).
The concentration of the graphene oxide suspension was 0.077 g/L in
0.01 M NaClO.sub.4. In all cases, the total concentration of
cations was much less than the solubility limit, and the graphene
oxide/radionuclide ratio corresponded to a very high
under-saturation of graphene oxide sorption sites.
[0110] To measure the sorption capacity of graphene oxide towards
different radionuclides, the sorption isotherms were obtained using
0.038 g/L graphene oxide suspension in 0.01 M NaClO.sub.4. The
concentration of the cations was varied at constant pH values.
[0111] To demonstrate the performance of graphene oxide compared
with other routinely used sorbents for radionuclide removal,
experiments were conducted with simulated nuclear wastes containing
high concentrations of complexing agents. The concentrations of
actinides was equal to 8.times.10.sup.-8 M for .sup.233U(VI) and
3.times.10.sup.-9 M for .sup.239Pu(IV).
[0112] For HRTEM examination, the graphene oxide containing Pu
samples were prepared such that the Pu(VI) at a total concentration
of 1.14.times.10.sup.-5 M was added to the graphene oxide
suspensions having a concentration of 0.28 g/L at pH 4.8. After 18
hours, 99% of Pu was sorbed onto the graphene oxide. The
precipitated material was deposited onto a carbon-coated TEM grid
and analyzed using HRTEM (JEOL-2100F) at an accelerating voltage of
200 kV. EDX analysis was performed with a JED-2300 analyzer. For Pu
leaching tests, concentrated HClO.sub.4 was added to the
suspensions to make them pH 0.7. After 15 minutes, the
concentration of Pu in solution was measured.
[0113] Without further elaboration, it is believed that one skilled
in the art can, using the description herein, utilize the present
invention to its fullest extent. The embodiments described herein
are to be construed as illustrative and not as constraining the
remainder of the disclosure in any way whatsoever. While the
preferred embodiments have been shown and described, many
variations and modifications thereof can be made by one skilled in
the art without departing from the spirit and teachings of the
invention. Accordingly, the scope of protection is not limited by
the description set out above, but is only limited by the claims,
including all equivalents of the subject matter of the claims. The
disclosures of all patents, patent applications and publications
cited herein are hereby incorporated herein by reference, to the
extent that they provide procedural or other details consistent
with and supplementary to those set forth herein.
* * * * *
References