Pristine and Ultra-reduced Graphene Oxide as a Carrier for Enzymes and Catalysts

Abstract

The introduction of graphene as a carrier for enzymes and catalysts is disclosed.

Claims

1. A method of providing a carrier for enzymes, biocides, and catalysts, the method comprising the steps of: providing pristine graphene, wherein the pristine graphene is chosen from the group consisting of particles, sheets, and plates; and dispersing the pristine graphene in a dispersion.

2. The method of claim 1, wherein the pristine graphene is graphene plates, wherein the graphene plates have a thickness of between about 1.7 nm and about 2.8 nm, wherein the graphene plates have substantially no reactive groups.

3. The method of claim 1, wherein the pristine graphene has a particle size of about 50 nm to about 10 microns.

4. The method of claim 2, wherein the graphene plates are intercalated, wherein the dispersion has stacks of graphene plates from about two to about six layers.

5. The method of claim 1, wherein enzymes are immobilized.

6. The method of claim 1, wherein catalysts are immobilized.

7. The method of claim 6, wherein heterogeneous catalyst systems are supported.

8. The method of claim 7, wherein the heterogeneous catalyst systems are chosen from the group consisting of bi-functional, hybrid, oxide, and nano.

9. The method of claim 1, wherein catalytic immobilization results in less stearic hindrance around reaction sites.

10. The method of claim 1, wherein a biocide is in suspension with the pristine graphene.

11. The method of claim 10, wherein the pristine graphene is graphene plates, wherein the graphene plates have a thickness of between about 1.7 nm and about 2.8 nm, wherein the graphene plates have substantially no reactive groups.

12. The method of claim 10, wherein the pristine graphene has a particle size of about 50 nm to about 10 microns.

13. The method of claim 11, wherein the graphene plates are intercalated, wherein the dispersion has stacks of graphene plates from about two to about six layers.

14. The method of claim 10, wherein degree of dispersion is increased and the suspension is homogenized.

Description

III. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present teachings are described hereinafter with reference to the accompanying drawings.

[0019] FIG. 1 depicts ultra-reduced graphene oxide with only minor levels of edge —COOH groups;

[0020] FIG. 2 depicts the potential states of Graphene: Exfoliated, Intercalated, Flocculated In a Nanocomposite System.

IV. DETAILED DESCRIPTION

[0021] Applications for graphene and specifically inert and partially inert graphene, also referred to as pristine graphene, can include environmentally acceptable “green” building materials, high strength coatings, bio-pharma uses as an inert carrier, bio-plastics, health care, safe food (distribution remains the greatest challenge), impermeable bio-plastic food wrap, and clean water (filtration).

EXAMPLE 1

[0022] Three grades of pristine graphene are described as carriers for both enzymes in bio-systems and as catalysts (Table 1). Though not limited to this, there are three commercial grades of graphene under the commercial name of Prophene™ considered in this Example. [0023] Grade PS50 with particle, sheet, or plate sizes of about 50 nm to about 5 microns; [0024] Grade PS100 with particle, sheet, or plate sizes of about 100 nm to about 5 microns, with increasing conductivity; and [0025] Grade PS150 with particle, sheet, or plate sizes of about 150 nm to about 10 microns.

[0026] Properties in rubber nanocomposites include electrical conductivity and thermal conductivity, improved nanocomposite compound hysteresis, tear strength, abrasion resistance, and reduction in permeability or gas flow.

[0027] The specific types or grades of graphene described herein render their application suitable in bio- and catalysis systems for the following, non-limiting reasons: [0028] 1. No, to very limited, functionality on the graphene plate surface: functionality defined as the presence of reactive groups such as carboxylic acids, aldehyde groups, ketones, quinones, and alcohols and other oxygenated entities, and surface defects such as electronic vacancies in the graphene 6-membered aromatic rings; [0029] 2. Potential plate edge minor functionality lending the plates suited to partial immobilization of entities such as catalysts and enzymes (FIG. 1); [0030] 3. Very large aspect ratio of graphene, with plates up to ten to fifteen microns; and [0031] 4. Ease of exfoliation in many suspension and solution systems.

[0032] Table 1 shows the properties of proposed graphenes as carriers.

TABLE-US-00001 TABLE 1 Properties of Proposed Graphenes for Carriers Grade PS 50 PS 100 PS 150 Form Light powder Light powder Light powder Color Dark grey/ Dark grey/ Dark grey/ Black Black Black Odor None None None Resistivity ohm <50 <100 <150 (Powder) cm Particle size nm 50 nm-5 μm 100 nm-5 μm 150 nm-10 μm Particle max 1.7 nm 2.5 nm 2.8 nm thickness Layer count <10 <15 <16 Density g/cm.sup.3 2.200 2.200 2.200 Specific m.sup.2/g 250.0 180.0 100.0 surface area

EXAMPLE 2

[0033] In rubber nanocomposite systems the graphene plates are believed to be exfoliated, or at a minimum an intercalated state is obtained, i.e., where the graphene is very well dispersed but there are still stacks of pristine graphene plates 2 to 6 layers deep (FIG. 2). The high level of dispersion results in increased shear during composite blending, which is due to the very large aspect ratio of the graphene plates. The quality, uniformity, and homogeneity of the dispersion is thus improved.

[0034] The high level of shear thus results in a highly dispersed mixer and high level of mixture homogeneity. This allows for better mechanical properties as observed in rubber nanocomposites.

[0035] Such systems also show increased electrical conductivity due to an apparent low percolation point not observed with conventional systems, such as those containing carbon black. Such conductivity might lend itself to uses in built-in antennae for articles such as RFID sensors in tires or other applications.

EXAMPLE 3

[0036] Graphene can function as (i) an enzyme carrier, and ii) dispersion aid in a suspension or solution. Partial immobilization and full immobilization of multi-enzymes on support materials improve biocatalysts efficiency. It can also facilitate multi-enzyme immobilization. There are several reasons to use immobilized enzymes. In addition to the convenient handling of enzyme preparations, the two main targeted benefits are: (1) easy separation of enzyme from the product; and (2) reuse of the enzyme. Easy separation of the enzyme from the product simplifies enzyme applications and permits reliable and efficient reaction technology. Enzyme reuse provides a number of cost advantages, which are often an essential prerequisite for establishing an economically viable enzyme-catalyzed process. Enzyme immobilization can be divided into several categories such as the following: [0037] a. binding to a support; [0038] b. cross-linking; [0039] c. encapsulation (entrapment); [0040] d. homogeneous system dispersion; and [0041] e. lubricating by improving rheology or system flow properties.

[0042] Homogeneous enzyme system dispersion can be chosen to ensure improved efficiency. Furthermore, reduced, to no, graphene functionality ensures no side reactions or interference reactions. However, in instances where there is functionality on the graphene plate surface or edges, i.e., graphene oxides, the activity and reusability of the enzymes could be improved by controlling the extent of graphene oxide reduction. Graphene-based materials have unique optical, mechanical, and electrical properties which make them attractive for many applications. Oxidation of graphite powder to graphene oxide (GO) followed by chemical reduction to reduced graphene oxide (r-GO) is a well-established approach to generating graphene based materials. Numerous methods of chemical reduction to r-GO have been published where hydrazine hydrate, dimethylhydrazine, hydroquinone, NaBH.sub.4, HI and Fe and Zn powder have been used to reduce GO. Since the GO from different sources vary widely and contains a wide range of oxygen containing groups such as hydroxyl, carboxyl and epoxy, r-GO represents a family of material with different physical/chemical properties. Reduced graphene oxide (rGO) contains residual oxygen and other heteroatoms, as well as structural defects. Despite rGO's less-than-perfect resemblance to pristine graphene, it is still an appealing material that can definitely be sufficient in quality for various applications, but for more ahractive pricing and manufacturing processes.

[0043] The large plate size of graphene in this instance will further maximize dispersion and homogeneity thus further ensuring enzyme efficiency and utility.

EXAMPLE 4

[0044] Regarding Biocides: water supplies are stressed due to increasing demand, greater cleanliness in drinking water supplies, anti-pollution, and environmental sustainability requirements. There is also growing demand for water treatment biocides, such as glutaraldehyde and t-hydroxymethyl-phosphonium sulfate (THPS) in oil and gas applications. With pristine graphene, biocide effectiveness in many systems could be enhanced due to effective dispersion and therefore lower quantitative demands. It is understood that graphene in a suspension with biocides will increase the degree of dispersion, homogeneity of the suspension, and thus efficiency of utilization.

EXAMPLE 5

[0045] Mechanical and thermal stability allows graphene, and specifically pristine graphene, to support heterogeneous catalysts systems ranging from single to bi-functional, hybrid, oxide and nano systems. Application also widens the heterogeneous catalyst application areas, including: [0046] chemical conversion; [0047] photocatalysts; [0048] sensors; and [0049] fuel cells and energy storage.

[0050] Areas of applicability include water purification, hydrogen generation and production, and graphene-based catalysts for electrochemical carbon dioxide reduction.

[0051] Pristine graphene will facilitate improved catalyst efficiency via dispersion and creating of homogeneous suspensions or solutions. It is understood that graphene in a suspension or solution with a catalyst, either immobilized, added via graphene surface doping as describe below, or as an agent increasing suspension shear, will increase the degree of dispersion, homogeneity of the suspension, and thus efficiency of utilization.

[0052] In addition, a second technique to use pristine graphene in chemical systems is via metal doping of graphene which can increase the number of active sites for electrochemical CO.sub.2 reduction; this improvement can be ascribed to an increase in charge and spin density caused by an increase in adsorption sites of CO.sub.2 molecules. Prophene™ renders itself suitable for such utilization.

[0053] Non-limiting aspects have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of the present subject matter. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.

[0054] Having thus described the present teachings, it is now claimed: