Patent Application
20230241558
The present invention relates to graphene oxide-based porous composite membranes with an improved stability to humidity and resistance to water-swelling, a method of producing the same and uses thereof notably in gas separation systems and processes for separating H2 from a gas stream.
In the present document, the numbers between brackets ({ }) refer to the List of References provided at the end of the document.
Graphene oxide (GO), which is cheaply sourced through controlled oxidation and exfoliation of graphite, has recently emerged as a promising 2D nanomaterial to make high-performance membranes for important applications. GO has long been known for its ability to form ultra-permeable hydrogen membranes with high selectivity (α) to hydrogen (H2) against many gases including carbon dioxide. In the early 2010's, ultrathin graphene oxide (GO) was proposed as a step-change material for the separation of hydrogen and carbon dioxide via membrane separation processes. Selectivities of up to 1000 and triple-digit (˜000 GPU) permeances were reported. These capabilities are ideal for highly efficient H2 separation, to reach purity levels required for immediate use in fuel cells.
However, GO is also highly hygroscopic, and has a natural tendency to swell in the presence of humidity, that is, absorb water into the GO channel and form an enlarged interlayer spacing (d-spacing). As such, GO films are highly hygroscopic and swell in the presence of humidity, catastrophically losing sieving capability. When the GO membranes are exposed to a humid environment, the hydrated GO sheets become negatively charged and will come apart due to the electrostatic repulsion in which promotes the GO membranes delamination. As such, the water swelling severely impairs the separation capability of layer-stacked GO membranes. Such catastrophic swelling is the Achilles heel of GO membranes, presenting an un-resolved obstacle to the practical implementation of this exciting technology.
The foregoing shows that there is an unmet need for GO-based membranes with improved stability to humidity and resistance to water-swelling; and for a method of imparting water stability and improved resistance to water-swelling to GO-based membranes.
Thus it is an object of the invention to provide a GO-based membrane with improved stability to humidity and resistance to water-swelling.
Improving upon known GO-based membranes it is proposed according to the invention a porous composite membrane comprising:
The present invention also provides a method of manufacturing a porous composite membrane according to the invention, comprising the steps of:
In another aspect, the present invention also provides a gas separation system comprising a porous composite membrane in fluidic communication with a gas stream containing a mixture of at least two separable gases including H2, wherein the porous composite membrane comprises:
In yet another aspect, the present invention provides a process for separating H2 from a gas stream, comprising a step of permeating a mixture of at least two separable gases through a porous composite membrane of claim 1, wherein the gas mixture comprises at least H2.
In still another aspect, the present invention also provides a process for reducing H2O swelling in a graphene oxide-based membrane comprising associating nanoparticles in electrostatically and/or Van der Waals binding interaction with graphene oxide sheets constituting the graphene oxide-based hydrogen membrane.
Throughout the Drawings, data illustrated for pristine GO membranes and GO-based composite membranes with negatively charged nanoparticles (e.g., ND−, POSS−) are provided as comparative data, whereas data relative to GO-based composite membranes with positively charged nanoparticles (e.g., ND+, POSS+) are provided to illustrate exemplary embodiments of the invention.
Note to
The dispersion D was calculated according to a reported protocol based on TEM images1. First, 10×10 equal distance horizontal and vertical grid lines were overlayed onto the TEM images. Then, the free path spacing between adjacent ND+s were accurately measured. The number of measurements N was about 200 for each sample. Next, these values were plotted into a histogram and fit with lognormal distribution function.
The dispersion D was calculated using the following equation:
Where x is the size of the free path spacing:
where μ and σ are the mean and standard deviation, respectively.
In the range of μ±0.1μ, the dispersion D0.1 is
In the range of μ±0.2μ, the dispersion D0.2 is
Higher values of D0.1 and D0.2 indicate more spacing data falling into the range of μ±0.1μ and μ±0.2μ, respectively, which means more uniform distribution of the ND+ particles.
Unless defined otherwise, all the technical and scientific terms used herein have the same meaning as those generally understood by one of ordinary skill in the art to which the invention pertains. Generally, the nomenclature used herein and the experiment methods, which will be described below, are those well-known and commonly employed in the art.
To facilitate an understanding of the present invention, a number of terms and phrases are defined below:
As used herein other than the claims, the terms “a,” “an,” “the,” and/or “said” means one or more. As used herein in the claims, when used in conjunction with the words “comprise,” “comprises” and/or “comprising,” the words “a,” “an,” “the,” and/or “said” may mean one or more than one. As used herein and in the claims, the terms “having,” “has,” “is,” “have,” “including,” “includes,” and/or “include” has the same meaning as “comprising,” “comprises,” and “comprise.” As used herein and in the claims “another” may mean at least a second or more.
The phrase “a combination thereof” “a mixture thereof” and such like following a listing, the use of “and/or” as part of a listing, a listing in a table, the use of “etc.” as part of a listing, the phrase “such as,” and/or a listing within brackets with “e.g.,” or i.e., refers to any combination (e.g., any sub-set) of a set of listed components, and combinations and/or mixtures of related species and/or embodiments described herein though not directly placed in such a listing are also contemplated. Such related and/or like genera(s), sub-genera(s), specie(s), and/or embodiment(s) described herein are contemplated both in the form of an individual component that may be claimed, as well as a mixture and/or a combination that may be described in the claims as “at least one selected from,” “a mixture thereof” and/or “a combination thereof.”
The term “graphene oxide” as used herein does not deviate from the conventional meaning of the term in the art and refers to the exfoliation product of graphite oxide. It refers to a compound comprising carbon, oxygen, and hydrogen in suitable ratios, and the graphene oxide may include carbon as main component constituting greater than about 50 wt %, greater than about 60 wt %, greater than about 70 wt %, greater than about 80 wt %, greater than about 90 wt %, greater than about 95 wt %, or greater than about 99 wt % of the total weight of the graphene oxide. Graphene oxide may include functional groups containing oxygen, such as epoxy, hydroxyl, or carboxyl groups.
Graphene oxide for use in the context of the invention may be made by any means known in the art. For example, graphene oxide may be obtained by oxidizing graphene (a carbon material suitably in the form of a single, planar, two-dimensional, and honey-comb like lattice). For example, graphite oxide can be prepared from graphite flakes (e.g. natural graphite flakes) by treating them with potassium permanganate and sodium nitrate in concentrated sulphuric acid. This method is called Hummers method. Another method is the Brodie method, which involves adding potassium chlorate (KClO3) to a slurry of graphite in fuming nitric acid. Individual graphene oxide (GO) sheets can then be exfoliated by dissolving graphite oxide in water or other polar solvents with the help of ultrasound, and bulk residues can then be removed by centrifugation and optionally a dialysis step to remove additional salts.
The term “nanodiamond” as used herein refers to a diamond or a particle thereof having a size in nanometer scale, for example, having a size (e.g. cross-sectional dimension) less than about 999 nm, less than about 900 nm, less than about 800 nm, less than about, less than about 700 nm, less than about 600 nm, less than about 500 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, less than about 100 nm, or less than about 50 nm. The nanodiamond is not particularly limited in its shape, color, grade, composition, chemical modification formed thereon, or the like. In addition, the nanodiamond may include carbon as a main component constituting, for example, greater than about 50 wt %, greater than about 60 wt %, greater than about 70 wt %, greater than about 80 wt %, greater than about 90 wt %, greater than about 95 wt %, or greater than about 99 wt % of the total weight thereof. An exemplary embodiment of the present invention provides a composite comprising graphene oxide and at least one nanodiamond. In particular, the nanodiamond may be non-covalently bonded on a surface of the graphene oxide. For instance, the nanodiamond may be bonded on the surface of the graphene oxide via comprise electrostatic and/or Van der Waals interactions.
As used herein, “zeta potential” when referring to GO flake or particle surface charge does not deviate from the conventional meaning of the term in electrochemistry and refers to the potential difference between the GO flake or particle surface and the stationary layer of fluid attached to the GO flake or particle surface. The zeta potential typically depends from the nature of the material surface, and characteristics of the fluid that is in contact with the material surface (e.g., pH, ion concentration, ionic force, . . . ). The zeta potential may be determined out using an electrokinetic analyzer. Zeta potential may be determined using the Smoluchowski model.
Throughout the specification, unless otherwise defined, “average diameter” refers to an average of the longest diameter of each particle in the group.
As used herein, the term “fluidic communication” means that a fluid can pass through a first component and travel to and through a second component or more components regardless of whether they are in physical communication or the order of arrangement.
The term “microscale” and the related prefix “micro-” as used herein is intended to refer to items that have at least one dimension that is one or more micrometers and less than one millimeter.
The term “nanoscale” and the related prefix “nano-” as used herein (for example in “nanoparticle”) is intended to refer to measurements that are less than one micrometer.
The term “nanoparticle” includes, for example, “nanospheres,” “nanorods,” “nanocups,” “nanowires,” “nanoclusters,” “nanofibers,” “nanolayers,” “nanotubes,” “nanocrystals,” “nanobeads,” “nanobelts,” and “nanodisks.” Nanoparticles useable in the context of the present invention may be solid particles of nanoscale size.
The term “weight percent,” “wt. %,” “wt-%,” “percent by weight,” “% by weight,” and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100.
As used herein, “about” refers to any inherent measurement error or a rounding of digits for a value (e.g., a measured value, calculated value such as a ratio), and thus the term “about” may be used with any value and/or range. As used herein, the term “about” can refer to a variation of ±5% of the value specified. For example, “about 50” percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term “about” can include one or two integers greater than and/or less than a recited integer. Unless indicated otherwise herein, the term “about” is intended to include values, e.g., weight %, temperatures, proximate to the recited range that are equivalent in terms of the functionality of the relevant individual ingredient, the composition, or the embodiment.
As used herein, the term “and/or” means any one of the items, any combination of the items, or all of the items with which this term is associated.
As will be understood by the skilled artisan, all numbers, including those expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth, are approximations and are understood as being optionally modified in all instances by the term “about.” These values can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the descriptions herein. It is also understood that such values inherently contain variability necessarily resulting from the standard deviations found in their respective testing measurements.
As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible subranges and combinations of subranges thereof, as well as the individual values making up the range, particularly integer values. A recited range (e.g., weight percents, temperature, . . . ) includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.
As will also be understood by one skilled in the art, all language such as “up to,” “at least,” “greater than,” “less than,” “more than,” “or more,” and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into subranges as discussed above. In the same manner, all ratios recited herein also include all subratios falling within the broader ratio. Accordingly, specific values recited for radicals, substituents, and ranges, are for illustration only; they do not exclude other defined values or other values within defined ranges for radicals and substituents.
One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Additionally, for all purposes, the invention encompasses not only the main group, but also the main group absent one or more of the group members. The invention therefore envisages the explicit exclusion of any one or more of members of a recited group. Accordingly, provisos may apply to any of the disclosed categories or embodiments whereby any one or more of the recited elements, species, or embodiments, may be excluded from such categories or embodiments, for example, as used in an explicit negative limitation.
The methods, systems, apparatuses, and compositions of the present invention may comprise, consist essentially of, or consist of the components and ingredients of the present invention as well as other ingredients described herein. As used herein, “consisting essentially of” means that the methods, systems, apparatuses and compositions may include additional steps, components or ingredients, but only if the additional steps, components or ingredients do not materially alter the basic and novel characteristics of the claimed methods, systems, apparatuses, and compositions.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments or examples. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
Although the present disclosure will be described in terms of specific embodiments, it will be readily apparent to those skilled in this art that various modifications, rearrangements and substitutions may be made without departing from the spirit of the present disclosure. The scope of the present disclosure is defined by the claims appended hereto.
For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the present disclosure as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the present disclosure.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. The word “example” may be used interchangeably with the term “exemplary.”
Illustrative embodiments are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The GO-based composite membranes, systems and process in accordance with the present application overcome one or more of the above-discussed problems commonly associated with conventional GO-based membrane technology and processes. Specifically, the GO-based composite membranes of the present application exhibit increased water stability and resistance to water-swelling. This and other unique features of the GO-based composite membranes are discussed below and illustrated in the accompanying drawings.
The GO-based composite membranes, systems and process will be understood, both as to its structure and operation, from the accompanying drawings, taken in conjunction with the accompanying description. Several embodiments of the GO-based composite membranes, systems and process are presented herein within
As noted above, there is an unmet need for GO-based membranes with improved stability to humidity and resistance to water-swelling; and for a method of imparting water stability and improved resistance to water-swelling to GO-based membranes.
The present invention meets this need by providing a porous composite membrane comprising:
The non-covalent interactions comprise electrostatic and/or Van der Waals interactions. As used herein, the term “Van der Waals interactions” refers generally to any non-covalent interactions between materials. Van der Waals forces include dipole-dipole, dipole-induced dipole forces, and London dispersion forces. Hydrogen bonding being a dipole-dipole force, it is encompassed by Van der Waals forces.
The composite membrane may include a plurality of stacked graphene oxide sheets, and the nanoparticles may be intercalated between the stacks of graphene oxide sheets. Concerning the characterization of GO sheets, a series of characterization experiments may be performed to understand the unique shape, functionality, and other physicochemical properties of GO sheets. These experiments may include calculations related to zeta-potential analyzer for charge, Raman spectroscopy for G/D ratio, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) for functional groups, X-ray diffraction (XRD) for crystalline structure, and atomic force microscopy (AFM), SEM, and transmission electron microscopy (TEM) for size and shape. In particular, SEM and AFM techniques may be used to measure the size of GO flakes and thickness of the membranes.
The graphene oxide sheets in composite membranes according to the invention, may have an interlayer distance or d-spacing about 0.6-1.2 nm. For example, the GO sheet interlayer distance may range between 0.7-1.0 nm, for example 0.8-0.9 nm. The d-spacing can be determined by x-ray powder diffraction (XRD), using Bragg's law: d=λ/2 sin(θ) (1) where θ is half of diffraction angle and A is the wavelength of X-ray source. As will be understood by the reader, the d-spacing or the lattice spacing refers to the distance between the parallel planes of GO. In principle, XRD measures the average spacings between layers or rows of atoms. Accordingly, the GO interlayer distance or d-spacing reported herein refers to average values. Typically, the interlayer space between stacked GO sheets comprise hydrophilic domains, and hydrophobic domains. The GO sheet interspace hydrophilic domains are generally located where there are oxygen functionals groups at the edge and/or on the basal plane of GO sheets. By affinity with hydrophilic domains, water molecules may intercalate in the hydrophilic domains of stacked GO sheets. Without wishing to be bound by any particular theory, it is believed that the intercalation of nanoparticles between GO stacks creates or stabilizes areas in the GO sheet stacking where the hydrophobicity of the walls of the internal pores limits the penetration of water molecules, thereby imparting to the GO-based composite membrane less water affinity and greater resistance to water swelling. The graphene oxide sheets may have an average lateral size about 200 nm to 15 μm, for example 1 to 10 μm, for example about 1 to 6 μm. The graphene oxide sheet average lateral size may be determined using SEM. The nanoparticles may for example carry an overall positive charge, particularly on the outer surface of the nanoparticle, which is in electrostatic/Van der Waals interaction with the graphene oxide sheet surface. This positive charge is believed to favor electrostatic and/or Van der Waals interactions between the graphene oxide surface and the nanoparticles. Without wishing to be bound by any particular theory, it is believed that the presence of positively charged nanoparticles at the surface of the GO sheets contribute to neutralizing the negative charge of the stacked GO sheets (the GO sheets are not charged in dry state, but after exposure to water, GO sheets' surface becomes negatively charged mainly due to the deprotonation of hydroxyl groups) and stabilize the resulting membrane against humidity. For example, the nanoparticles may have a positive charge of not less than 30 mV Zeta potential at pH 7. The nanoparticle zeta potential may be determined using an electrokinetic analyzer. Suitable positively charged nanoparticles include, for example positively charged nanodiamonds, cationic POSS particles, cationic dyes, metal cations and double hydroxides. Nanoparticles useable in the context of the invention may be different from clay nanoparticles or MOF nanoparticles
Additional nanoparticles useable in the context of the invention may comprise metal nanocrystals such as Ag nanocrystals, porphyrins such as meso-(p-hydroxyphenyl) porphyrin nanocrystals and/or melamine nanoparticles. The adsorption of metal nanoparticles, porphyrins and melamine on GO sheet surface via non-covalent interaction has been described for example in refs {32-34}, respectively (2-dimensional assembly of a GO sheet with metal nanoparticles, porphyrins and melamine via non-covalent adsorption of the nanoparticles on the GO surface). However, the reports never considered the possibility of applying the non-covalent adsorption phenomenon to three-dimensional GO-based composite constructs, let alone that these may be used as membranes with sieving capacity. Composite GO-based membranes according to the present invention, using metal nanocrystals such as Ag nanocrystals, porphyrins such as meso-(p-hydroxyphenyl) porphyrin nanocrystals and/or melamine, as nanoparticles may be prepared according to the teachings of the present disclosure. For example, methods described in the Examples may be used, by substituting NDs with Ag nanocrystals, porphyrins nanoparticles and/or melamine nanoparticles.
The nanoparticles may have an average diameter of about 3 to 10 nm, for example 3 to 5 nm, for example about 3 nm or about 4 nm. If the nanoparticles have irregular shapes, some averaging may be made to report an average diameter. Known methods for measuring nanoparticle diameter, average diameter, and nanoparticle size distribution may be used. For example, nanoparticle average diameter may be measured using light scattering and Transmission electron microscopy methods (cf. Carvalho, Patricia M., et al. “Application of light scattering techniques to nanoparticle characterization and development.” Frontiers in chemistry 6 (2018): 237.), including some statistical analysis using a model such as the cumulant method (cf. {35}), for nanoparticles that do not all have the same size and/or geometry.
For example, an amount of about 5 to 40% wt of nanoparticles may be assembled on the graphene oxide sheet surface by electrostatic and/or Van der Waals interactions; the % wt being expressed based on the total weight graphene oxide sheets+nanoparticles. For example about 5 to 35% wt, or about 5 to 30% wt, or about 10 to 30% wt, or about 20 to 30% wt of nanoparticles may be used and be assembled on the graphene oxide sheet surface by electrostatic and/or Van der Waals interactions, to form the GO-based porous composite membrane according to the invention.
The nanoparticles may be carbonaceous nanoparticles (i.e., made of carbon atoms). This may be particularly advantageous owing to the compatibility of carbonaceous materials with graphene oxide. For example, the nanoparticles may include nanodiamonds. Nanodiamonds are carbon structures that can carry a positive charge, and are therefore particularly well suited for reducing to practice the present invention. In the present disclosure, nanodiamonds may be abbreviated “ND” to signify the presence of a positive charge that is present. When nanodiamonds are prepared so that they carry an overall negative charge, these will be designated “ND-”. Both ND+ and ND− are commercially available, for example in the form of colloidal aqueous dispersions. Mention may be made, for example, of ND+ and ND− colloidal aqueous dispersions, respectively, commercialized under the tradename of NanoAmando®. Without wishing to be bound by any particular theory, it is proposed that nanodiamonds (ND+), which feature a sp3/sp2 core-shell structure and positive surface charge, enhance the water-stability of GO membranes by reducing the electrostatic repulsive forces between hydrated GO sheets, thereby suppressing the random restacking and aggregation of GO sheets in the presence of humidity and strengthening the overall membrane structure.
Generally, a nanodiamond, as used herein, may be formed by an explosive reaction of graphite, and may be formed in fine nanoparticles having a size from about 3 to 10 nm, for example about 3 to 5 nm, for example about 3 nm or about 4 nm.
Porous GO-based composite membranes according to the invention may have a thickness ranging for example from 20-200 nm, or 25-150 nm, or 30-120 nm.
Porous GO-based composite membranes according to the invention present advantageous properties notably in terms of water stability, resistance to water-swelling, mechanical strength and separation performance.
Porous GO-based composite membrane according to the invention typically exhibit a H2 permeance >1300 GPU for example, or ≥1800 GPU, or ≥2400 GPU, or ≥3500 GPU, as measured at 25±3° C. under dry conditions with a membrane thickness ranging from 30-120 nm. As used herein, by “dry conditions” it is understood a relative humidity in the range of <20% RH and atmospheric pressure.
Porous GO-based composite membrane according to the invention may exhibit an ideal gas selectivity αH2/CO2>200 for example as measured with a continuous feed of equimolar H2/CO2 mixture at 25±3° C. under dry conditions with a membrane thickness ranging from 30-120 nm.
Porous GO-based composite membrane according to the invention may exhibit a H2 permeance >750 GPU for example, or >1300 GPU, or ≥1800 GPU, or ≥2000 GPU, or ≥2400 GPU, or ≥3300 GPU, as measured at 25±3° C. under continuous feed of equimolar H2/CO2 mixture under humid conditions of 85% relative humidity with a membrane thickness ranging from 30-120 nm.
Porous GO-based composite membrane according to the invention may exhibit a H2 permeance a ≥2× for example, or ≥3×, or ≥4×, or ≥5×, or ≥6×, or even a ≥7×, as compared to a pure graphene oxide membrane (0% wt nanoparticles) of equal thickness, as measured at 25±3° C. under continuous feed of equimolar H2/CO2 mixture under humid conditions of 85% relative humidity with a membrane thickness ranging from 30-120 nm.
Porous GO-based composite membrane according to the invention may exhibit a H2 permeance, as measured at 25±3° C. under continuous feed of equimolar H2/CO2 mixture under humid conditions of 85% relative humidity, ≥60% for example, or ≥65%, or ≥70%, or ≥75%, or ≥80%, or ≥85%, or ≥90%, or ≥95%, as compared to the membrane H2 permeance measured under dry conditions with the same temperature, membrane thickness and equimolar H2/CO2 mixture conditions with a membrane thickness ranging from 30-120 nm.
Porous GO-based composite membrane according to the invention may exhibit a H2/CO2 selectivity (αH2/CO2), as measured at 25±3° C. under continuous feed of equimolar H2/CO2 mixture under humid conditions of 85% relative humidity, ≥50% for example, or ≥60%, or ≥70%, or a 80%, or ≥90%, as compared to the membrane H2/CO2 selectivity measured under dry conditions with the same temperature, membrane thickness and equimolar H2/CO2 mixture conditions with a membrane thickness ranging from 30-120 nm.
Porous GO-based composite membrane according to the invention may exhibit a hardness ≥610 MPa for example, or ≥630 MPa, or ≥650 MPa, or ≥670 MPa, or ≥690 MPa, or ≥700 MPa; or ≥710 MPa, as measured using the nanoindentation method at 25±3° C. with a Berkovich three-sided pyramid diamond tip (radius of 100 nm) at the load of 0.05 mN, the errors of measurements being reported based on the standard error of 20 indents.
Porous GO-based composite membrane according to the invention may exhibit a Young's modulus ≥15 GPa for example, or ≥16 GPa, or ≥17 GPa, or ≥18 GPa, or ≥19 GPa, or ≥20 GPa; or ≥21 GPa, as measured using the nanoindentation method at 25±3° C. with a Berkovich three-sided pyramid diamond tip (radius of 100 nm) at the load of 0.05 mN, the errors of measurements being reported based on the standard error of 20 indents.
As discussed before, porous composite membranes according to the invention may find use in any applications where porous GO-based membranes find use. One area of special interest is gas separation, particularly H2 separation from gaseous mixtures. Accordingly, in any variant described herein, the porous GO-based composite membrane according to the present invention may be a GO-based composite hydrogen membrane, in particular a water-resistant GO-based composite hydrogen membrane.
Composite Membrane Preparation
In another aspect, the present invention provides a method of manufacturing a porous composite membrane according to the present invention, comprising the steps of:
The preparation of graphene oxide-nanoparticle composite membranes supported on a porous membrane may also be achieved using spray coating, casting, dip coating techniques, road coating, inject printing, or any other thin film coating techniques.
The aqueous solvents in steps (i) and (ii) may be the same or different aqueous solvents. The aqueous solvent in steps (i) and (ii) may independently comprise water or alcohol/water mixtures, for example water. The alcohol may comprise methanol, ethanol, isopropanol, 1-butanol, tert-butanol, ethylene glycol, and the like, or a mixture of two or more of these. The aqueous solvents in steps (i) and (ii) may be one and the same aqueous solvent, and may be selected from water or alcohol/water mixtures, for example water. For example, the aqueous solvent in steps (i) and (ii) is water at pH=6-7.
Step (i) may comprise any method known in the art for dispersing graphene oxide. For example, step (i) may comprise sonicating a dispersion of graphene oxide in an aqueous solvent, the aqueous solvent being as defined in any variant herein.
Likewise, step (ii) may comprise any method known in the art for dispersing nanoparticles, including carbonaceous nanoparticles such as nanodiamonds. This may include, for example, ultrasound sonicating bath, ultrasound probe sonication, ultrasonic disruptor, high speed homogenizer, or high pressure homogenizer.
The method of manufacturing a porous composite membrane according to the present invention may further comprise a step of drying the substrate-supported graphene oxide-nanoparticle composite membrane obtained in step (iv). For example this may be carried out under vacuum at a temperature of about 50-70° C., to remove the excess aqueous solvent.
The dispersion of step (iii) may comprise an amount of for example about 5 to 40% wt of nanoparticles, or about 5 to 35% wt, or about 5 to 30% wt, or about 10 to 30% wt, or about 20 to 30% wt nanoparticles; the % wt being expressed based on the total weight graphene oxide sheets+nanoparticles.
Gas Separation System and Process
As discussed before, porous composite membranes according to the invention may find use in any applications where GO-based membranes find use. One area of special interest is gas separation, particularly H2 separation from gaseous mixtures. Accordingly, in any variant described herein, the GO-based composite membrane according to the present invention may be a GO-based composite hydrogen membrane, in particular a water-resistant GO-based composite hydrogen membrane.
As such, in another aspect, the present invention provides a gas separation system comprising a porous composite membrane according to the present invention in fluidic communication with a gas stream containing a mixture of at least two separable gases including H2, wherein the porous composite membrane comprises:
In the gas separation system according to the invention, the porous composite membrane may be disposed on a porous support substrate. The porous support substrate may be any suitable support substrate. The porous support substrate may be a woven material or it may be a porous membrane.
For example, if present, the porous support substrate material may an inorganic material. Thus, the porous material (e.g. porous support substrate) may comprise a ceramic. For example, the porous support substrate material may be alumina, zeolite, or silica.
It may be that, if present, the porous support substrate material may be a polymeric material. Thus, the porous support substrate material may be a porous polymer support, e.g. a flexible porous polymer support. The porous material (e.g. porous support substrate) may comprise a polymer. The polymer may comprise a synthetic polymer.
For example, the porous support substrate may comprise a ceramic or polymeric porous support, including porous ceramic materials such as an alumina- or silica-based porous ceramic, and hydrophilic polymeric materials such as polysulfones (PS), polyethersulfones (PES), fluoropolymers such as polyvinylidene fluoride (PVDF), or polyacrylonitrile.
If present, the porous support substrate may have a thickness of no more than a few tens of μm, and may be less than about 1 mm thick or even less than about 100 μm. For example, it may have a thickness of 50 μm or less, or of 10 μm or less. In some cases it may be less than about 1 μm thick though in exemplary embodiments it may be more than about 1 μm.
The porous support substrate should be porous enough not to interfere with solute transport/permeation but have small enough pores that graphene oxide sheets cannot enter the pores. For example, the pore size may be less than 1 μm, e.g. less than 500 nm or less than 200 nm. Typically the pore size will be greater than 1 nm, e.g. greater than 10 nm.
The gas separation system according to the invention may be equipped with a porous composite membrane as defined generally and in any variant herein. For example, the porous composite membrane may include a plurality of stacked graphene oxide sheets, and the nanoparticles may be intercalated between the stacks of graphene oxide sheets. The gas separation system according to the invention featuring stacked GO sheets may be such that a molecule, such as H2 gas, can flow through the nanochannels between GO layers while unwanted solutes are rejected by size exclusion and/or charge effects.
The gas separation system according to the invention may comprise a porous composite membrane having a hardness ≥610 MPa for example, or ≥630 MPa, or ≥650 MPa, or ≥670 MPa, or ≥690 MPa, or ≥700 MPa; or ≥710 MPa, as measured using the nanoindentation method at 25±3° C. with a Berkovich three-sided pyramid diamond tip (radius of 100 nm) at the load of 0.05 mN.
The gas separation system according to the invention may comprise a porous composite membrane having a Young's modulus ≥15 GPa for example, or ≥16 GPa, or ≥17 GPa, or ≥18 GPa, or ≥19 GPa, or ≥20 GPa; or ≥21 GPa, as measured using the nanoindentation method at 25±3° C. with a Berkovich three-sided pyramid diamond tip (radius of 100 nm) at the load of 0.05 mN.
The gas separation system according to the invention may comprise a plurality of GO-based composite membranes according to the invention. These may be arranged in parallel (to increase the flux capacity of the process/device) or in series.
The gas separation system may be for example the system showed in
As previously described, GO-based composite membranes according to the present invention may find use as H2 separation membrane. As such, the gas separation system according to the present invention may be used with gaseous mixtures of at least two separable gases comprising at least H2.
In another aspect, the invention provides a process for separating H2 from a gas stream, comprising a step of permeating a mixture of at least two separable gases through a porous composite membrane according to the invention, wherein the gas mixture comprises at least H2.
Porous composite membrane according to the present invention are suitable for separation of H2 from any gas mixtures comprising hydrogen gas. For example, composite membrane according to the present invention may be used for the separation of H2 gas from H2/CO2, H2/Ammonia, H2/O2, H2/N2, H2/CH4 or H2/CH3CH3 mixtures. For example, the gas stream may be natural gas. The use of porous composite membranes according to the invention in the separation of H2 from H2/O2 gas mixtures is particularly interesting since O2 and H2 are formed by electrolysis of water.
In yet another aspect, the invention relates to a process for reducing water-swelling in a graphene oxide-based hydrogen membrane, the process comprising associating nanoparticles in electrostatically and/or Van der Waals binding interaction with graphene oxide sheets constituting the graphene oxide-based hydrogen membrane.
It is to be understood that all the variants described above, notably for the various elements constituting the GO-based composite membrane according to the invention are applicable mutatis mutandis to each and every one of the sections above concerning “composite membrane preparation”, “gas separation process and system”, “process for reducing water-swelling”, and will be understood to apply to the compositions/methods/processes/systems/uses defined in the present disclosure. This includes all the variants described in the “D
The representative examples that follow are intended to help illustrate the invention, and are not intended to, nor should they be construed to, limit the scope of the invention. Indeed, various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including the examples which follow and the references to the scientific and patent literature cited herein. It should further be appreciated that the contents of those cited references are incorporated herein by reference to help illustrate the state of the art.
The following examples contain important additional information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and the equivalents thereof.
The composite membranes of this invention and processes for their preparation can be understood further by the examples that illustrate some of the processes by which these composite materials are prepared or used. It will be appreciated, however, that these examples do not limit the invention. Variations of the invention, now known or further developed, are considered to fall within the scope of the present invention as described herein and as hereinafter claimed.
GO: graphene oxide
ND: nanodiamond
ND+: positively charged nanodiamond
ND−: negatively charged nanodiamond
POSS−: Octa(tetramethylammonium) functionalized Polyhedral Oligomeric Silsesquioxanes, which is negatively charged.
POSS+: Octa(tetramethylammonium) functionalized Polyhedral Oligomeric Silsesquioxanes, which is positively charged.
GOαND+ membrane: GO-nanodiamond composite membrane according to the invention, a representing the weight concentration of ND+ particles in the composite membrane.
GOαND− membrane: GO-ND− composite membrane, α representing the weight concentration of ND− particles in the composite membrane.
GOαPOSS− membrane: GO-POSS− composite membrane, α representing the weight concentration of negatively charged Polyhedral Oligomeric Silsesquioxanes particles in the composite membrane.
GOαPOSS+ membrane: GO-POSS+ composite membrane according to the invention, α representing the weight concentration of positively charged Polyhedral Oligomeric Silsesquioxanes particles in the composite membrane.
Materials
Graphite powder was obtained from Qingdao Nanshu Graphite Co., Ltd.
The aqueous colloidal solutions of positively and negatively charged nanodiamond (ND) particles, respectively, each with an average size of 3.8±0.7 nm in water (2.5 wt. %), NanoAmando®, were supplied by Nano Carbon Research Institute Co., Ltd (Japan).
The octa(tetramethylammonium)- and octa(ammonium)-functionalized water-soluble Polyhedral Oligomeric Silsesquioxane (POSS) particles with the chemical formulas of Ca2H96N8O20Si8 (negatively charged) and C24H72Cl8N8O2Si8 (positively charged), respectively, were supplied by Hybrid Plastics Inc. (Hattiesburg, US).
10 mL of GO, ND, and POSS dispersions were freeze-dried to measure the concentration of the original dispersions precisely using an ultramicrobalance.
Characterization
The as-prepared membranes were characterized by FTIR spectroscopy (Shimadzu IRTracer-100 spectrometer, Japan) in the range of 4000-600 cm−1. The X-ray diffraction (XRD) patterns were collected at BL02B2 of SPring-8 (A=0.999190 A), Japan Synchrotron Radiation Research Institute (JASRI). The crystalline structure of membranes was determined by wide-angle XRD analysis (Rigaku, Smartlab). The samples were scanned at the rate of 10° per min over a 29 range of 4-40° using a Cu Kα anode under a voltage of 40 kV and a current of 200 mA. X-ray photoelectron spectroscopy (XPS) measurements were obtained using an X-ray Photoelectron Spectrometer (ESCA-3400, Shimadzu). The binding energy of the impurity carbon (1s) peak (the C1s peak) was adjusted to 284.6 eV to correct the chemical shifts of each element. Raman microspectroscopy was performed using a 532 nm excitation laser with 20-25 mV (Horiba XploRa, Japan).
The morphology of membranes was observed by Field Emission Scanning Electron Microscopy (FESEM instrument, Hitachi S-4800). Transmission electron microscope (TEM) images were collected on a JEOL JEM 1400 plus (120 kV) and JEM-2200FS setup (JEOL) (200 kV). The samples were freeze-fractured in liquid nitrogen and briefly sputter-coated with osmium to prevent electron charging. The morphologies of the GO-based membranes were measured by atomic force microscopy (AFM, NanoWizard III, JPK Instruments, Japan) in tapping mode.
SEM and AFM measurements were also conducted to measure the lateral size and thickness of the GO nanosheets.
Particle size distributions and zeta potential values of membrane precursors were measured using a Malvern Zetasizer Nano instrument (Malvern Panalytical Ltd.).
H2, CO2 and N2 adsorption isotherms of the membranes were recorded up to 1 bar at 298 K or 77K using BELSORP-Max (BEL-Japan Inc.). Samples were degassed offline at 80° C. for 24 hr under dynamic vacuum (10-5 bar) before analysis.
The Young's modulus (E) and indentation hardness (H) were measured at room temperature using a nanoindentation tester (ENT 2100, Elionix) equipped with a Berkovich three-sided pyramid diamond tip (radius of 100 nm) at the load of 0.05 mN. For PM0.3 rejections, the as-prepared or water-immersed (and air-dried) membranes were studied using a handheld particle counter KC-51 (RION. Co., Ltd.). The rejection values were reported based on the average values of three separate measurements of different membrane samples.
Gas Permeation Tests
The gas permeation measurements were conducted by a homemade membrane permeation/separation setup (
For hydrated gas permeation tests, the equimolar H2/CO2 mixture was passed through a gas bubbler filled with saturated solutions of LiCl (12% RH), MgCl2 (33% RH), NaCl (75% RH) and water (85% RH) and a humidity sensor prior to the permeation cell. For the simulated water splitting test, the 90 mL min−1 of H2:O2 (2:1) was prior passed through a water bubbler (85% RH) to the permeation cell. Gas permeation behaviors of the membranes at different temperatures were studied at a temperature-controlled chamber. The membranes were kept at each temperature for more than 3 h. A calibrated gas chromatograph (Shimadzu GC-2014) was used to analyze the composition of the permeate gas.
The gas permeance (Pi, GPU) was calculated using the following equation:
The ideal selectivity (αi/j) is defined as the permeance of gas “i” relative to that of gas “j” and is expressed by:
αi/j=Pi/Pj (2)
For mixed gas, the separation factor αi/j was defined as the molar ratio of two-component in the permeate and feed side:
Synthesis of GO
Single-layered graphene oxide (GO) was prepared by a modified hummers' method. Briefly, 1 g of graphite powder (mesh size 50, Qingdao Nanshu Graphite Co., Ltd.) was added to a 9:1 (v/v) mixture of concentrated H2SO4/H3PO (120:14 mL) in an ice bath and stirred for 20 min. Then, 6 g of KMnO4 was gradually added to the reaction media, and the mixture was stirred at 50° C. for 4 h, 8 h, and 24 h for the large-size GO (LGO), (medium-size) GO, and small-size GO (SGO), respectively. The reaction was cooled to room temperature and poured slowly onto 150 mL of cold water (0-2° C.), then 2 mL of 30% H2O2 was added dropwise until the color of the solution turns to pale yellow. The product was filtered with 10% aqueous HCl (750 mL) and thoroughly washed with distilled water until the pH value reached 6-7.
10 mL of GO dispersions were freeze-dried to measure the concentration of the original dispersions precisely using an ultramicrobalance.
Membrane Preparation
The as-prepared Hummers product was sonicated at 40 W for 1 hr (Branson 1510E-MT) to exfoliate the GO sheets. Upon sonication, the resulting dispersions were subjected two times (each time 30 min) centrifugation at 5,000 r.p.m. to remove un-exfoliated and large flakes. The supernatant was further centrifuged at 10,000 r.p.m. for 40 min to remove small-size GO flakes and obtain GO dispersion. The un-exfoliated particles were eliminated from LGO dispersion by 3 min of bath sonication, followed by centrifugation at 3,000 r.p.m. for 20 min. Then, repeat centrifugation at 5,000 r.p.m. for 30 min to collect the sediment. For SGO, 4 h sonication and 10,000 r.p.m. for 1 h were conducted to collect the supernatant. To obtain a uniform membrane, a certain amount of GO dispersion was pre-diluted to 0.001 mg/mL and then vacuum filtrated (GCD-051X, ULVAC vacuum pump) at 10 Pa vacuum pressure through the anodic aluminum oxide (AAO) filters (pore size: 20 nm, diameter: 25 mm, Whatman) or polyethersulfone (PES, pore size: 30 nm, diameter: 25 mm, Sterlitech Co., Ltd.). The fresh positively charged ND+ dispersion was centrifuged at 10,000 r.p.m. for 1 h to remove any aggregates A calculated amount of ND+suspension (5 to 35 wt %) was added into the diluted GO dispersions under bar stirring for 10 min. Resulting GO-ND+ dispersions were then subjected to mild bath sonication for 10 min at 23 W just before depositing composite GOαND+ membranes by vacuum filtration. The total mass of GO and GOαND were kept the same for all samples (0.03 mg). The resulting membranes were vacuum-dried at 60° C. for 24 hr to remove the residual water before further characterizations. For PM0.3 rejections, the GO-based membranes (total mass: ˜0.01 mg) were vacuum filtrated on polyethersulfone substrate (100 kDa, diameter: 25 mm, Synder Co.).
For comparison, a specific amount of negatively charged POSS particles was firstly dispersed in water and sonicated for 5 hr. The GOαPOSS− membranes were fabricated using the same method as the GO-based composite membranes of Example 1.
For comparison, Example 1 was repeated using negatively charged ND (ND−) dispersions.
For comparison, Comparative Example 2 was repeated using positively charged POSS particles.
Results
GO membranes were prepared, by a common vacuum filtration method of a dispersion of single-layer GO sheets (
3 nm-sized ND+s were controllably introduced into the membrane by adding them to the GO dispersions before vacuum filtration (
H2 Permeance
On ceramic supports, the produced native GO membranes were found to have performances comparable to, or slightly better than, those reported in the literature with initial H2 permeance of around 1150 GPU and ideal gas selectivity of ˜282 against CO2 (Tables 2 and 3). However, when exposed to a water-saturated equimolar mixed-gas feed, the GO membrane performances dramatically deteriorated over a 100-hr test at room temperature. Permeances and selectivity dropped by 55% and 70% respectively (
H
186 ± 175.0
± 1.1
aThe gas permeances are reported based on the average values of three separate measurements of different membrane samples. GPU is gas permeation unit; 1 GPU = 3.35 × 10−10 mol m−2 s−1 Pa−1
indicates data missing or illegible when filed
/CO
/N
/CH
/C
H
indicates data missing or illegible when filed
The results show that ND+s could stabilize the performance of the GO-based membranes.
Composite Membrane Morphology—GO/ND+ Interaction
A detailed examination of the interaction of the ND+s with the GO sheets was performed.
The ND+ particles were positively charged (+45 mV), while the GO sheets carry a net negative charge (˜48 mV) at pH=7 (
X-ray diffraction of the GO and GOαND+ samples were particularly revealing. The sharp peak of the GO membrane at 20=6.15° suggests highly ordered stacking of GO laminates with the d-spacing of 0.93 nm (
The X-ray diffraction peak of the GO based membranes, corresponding to the interlayer spacing of GO sheets stacks and can be calculated by using Bragg's equation:
Bragg's law: d=λ/2 sin(θ) (1)
where θ is half of diffraction angle and λ is the wavelength of X-ray source.
The peak width of GO based membranes reflect the average size of the GO domains (crystallites) in each sample, which are separated by the grain boundaries and large lateral defects. The Debye-Scherer equation can be used to determine the average width crystallite width (D) of the GO domains
D=0.89λ/β cos(θ) (2)
where D is the crystallite width, β is the full peak width of the diffraction peak at half maximum height (FWHM) expressed in radians.
The average number of GO layers per domain (N) explains provides insights regarding the re-stacking ability degree of the GO nanosheets after upon the incorporation of ND particles. The combination of Bragg and Debye-Scherer equations (1 and 2) is used for calculating the average number of layers in GO stacks (stacking layers):
N=D/d+1 (3)
where D and d, are the crystallite width and inter-layer spacing, respectively.
Composite Membrane Mechanical Properties
It was found that both Young's modulus and hardness of the GOαND+ membranes also improved up to ˜25% compared to the pristine GO membrane (
Gas Separation
Primarily, the separation of H2 and CO2 is discussed in detail in this section. However, other industrially important hydrogen gas pairs were tested (H2/O2, H2/N2, H2/CH4, and H2/C2H6) performed equally well as summarized in Tables 2 and 3 (cf. supra).
The gas diffusion in the GO membrane takes place between the edges and interlayer galleries of adjacent sheets. Therefore, not only the membrane thickness but also the lateral dimension of the GO sheets (
The cross-section view of the GO membrane in
The evaluation of gas separation properties of the membranes was investigated under the mixed-gas feeds. Using equimolar H2/CO2 feed mixture, H2 permeance and H2/CO2 selectivity of the GO30ND+ membrane decreased 6% and 13%, respectively (Table 7,
/N
/CH
/C
H
indicates data missing or illegible when filed
The reduction in the permeance and selectivity of the membranes under the mixed-gas condition is, in general, due to the partial hindrance of H2 molecules transport by highly adsorbed CO2 molecules (
Stability Against Water, Humidity, and Aerosols
Compelling evidence for the stabilizing property of ND+s against humidity can be ascertained from their immersion in aqueous conditions the immersion of GO30ND+ membranes in water (
Impact of Intercalated Positively Charged ND+s
In the context of the present invention, in exemplary embodiments, GO-based composite membranes were produced at neutral or near-neutral solution conditions (pH ˜6-7): destabilization under humid conditions was minimized presumably by limiting the GO laminate's mobility that arises due to the electrostatic repulsion between the negatively charged GO sheets. An effect of the intercalation of positively charged ND+s between the GO laminates is that the negative charge of GO sheets has been partially neutralized, thereby mitigating the strong repulsion of the GO layers.
To test the generalizability of the charge compensation effect, we exploited another type of positively charged particle, POSS+. As negative controls, we also prepared ND− and POSS− incorporated GO membranes at different loadings (
The results obtained with GOαPOSS− membranes are consistent with previous reports of GO-based membranes with GO sheets intercalated with foreign particles (for example, the intercalation of MOF additives to GO systems). Invariably, the reports are of increased permeance through the intercalation, but with a loss in selectivity (
This comes in striking contrast with what was observed with the GOαND+ systems described in Example 1, which reinforces the notion that the enhanced performance of the GOαND+ systems according to the invention can be correlated to the extent of interaction of the positively charged ND+ additive and its chemical similarity with its surroundings.
Weak interactions between the negative-charged particles and GO flakes were noted by the Fourier-transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WXRD) and severe agglomeration (
We have further expanded the application space of GOαND+ membranes by the upgrading of a water-splitting product (H2O2 mixture with ˜66% H2). As shown in
In summary, the Examples illustrate the use of positively charged nanodiamonds (ND+s) or POSS+ nanoparticles that neutralize the negative charge of the stacked GO sheets and stabilize the resulting membrane against humidity. Whereas a native GO membrane lost all of its sieving capability under aggressive humidity cycling tests, GOαND+ composite membranes were found to retain up to ˜90% of their stability under the same conditions. Specifically, the Examples show the stabilization of GO-based membranes towards adverse humid conditions, whilst maintaining the membranes' overall high performance towards H2/CO2 separation. This was achieved via the intercalation of positively charged nanodiamonds (ND+s) which feature a sp3/sp2 core-shell structure and positive surface charge or POSS+ nanoparticles. The positively charged ND+s or POSS+ nanoparticles reduce the electrostatic repulsive forces between hydrated GO sheets, where their robust and GO compatible structures are intercalated between the GO laminates, strengthening the membrane structure. As a result, the random restacking and aggregation of GO sheets in the presence of humidity is suppressed (
The ND+ addition was shown to extend the permeance of the native membrane by a factor of 3 (to ˜3700 GPU) without drastically affecting the overall hydrogen selectivity of the membrane (e.g. αH2/CO2˜210). Positive results were also shown in the case of the addition of POSS+ nanoparticles.
As a control, similarly-sized but negatively charged nanodiamonds (ND-s) or polyhedral oligomeric silsesquioxanes (POSS−) additives were found to bring no enhancement to the swelling resistance of GO-based membranes.
In the present Examples, the benefit of the addition of positively charged nanoparticles, such as carbonaceous nanoparticles, has therefore been demonstrated, notably through ND+s or POSS+ nanoparticles that serve to stabilize negatively charged GO membranes against humidity and enhanced destabilization of the membrane's separation performance, whilst enhancing its intrinsic separation performance tremendously.
All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application (for example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference).
All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art, and it is intended that this information can be employed herein, if needed, to exclude (for example, to disclaim) specific embodiments that are in the prior art. For example, when a composition is claimed, it should be understood that compositions known in the prior art, including certain compositions disclosed in the references disclosed herein, are not intended to be included in the claims.
This application is the United States national phase of International Application No. PCT/IB2021/050708 filed Jan. 29, 2021 and claims priority to U.S. patent application Ser. No. 16/892,666 filed on Jun. 4, 2020, the disclosures of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/050708 | 1/29/2021 | WO |
