Claims:1. A membrane comprising patterned binder and graphene oxide (GO) film.
2. The membrane as claimed in claim 1, wherein the binder is selected from a group comprising epoxy resin, polyurethane, cyanoacrylate, clay binder and combinations thereof.
3. The membrane as claimed in claim 1, wherein the patterned binder has pattern selected from a group comprising linear pattern with orthogonal orientation and periodic array.
4. The membrane as claimed in claim 1, wherein the patterned binder is in contact with the graphene oxide film, wherein the contact is on one surface the graphene oxide film or on both surfaces of the graphene oxide film.
5. The membrane as claimed in claim 1, wherein the graphene oxide film has thickness ranging from about 100 nm to 10000 nm; and wherein the graphene oxide film has surface area ranging from about 0.1 cm2 to 100 cm2.
6. The membrane as claimed in claim 1, wherein the membrane has permeation rate for solution ranging from about 1 L m-2h-1bar-1 to 10 L m-2h-1bar-1
7. The membrane as claimed in claim 1, wherein the membrane has ion/solute permeation rate ranging about 1 µmol h-1cm-2M-1 to 100 µmol h-1cm-2M-1 measured in the feed: permeate diffusion geometry.
8. The membrane as claimed in claim 1, wherein d-spacing/interlayer spacing of the graphene oxide film is ranging from about 6 Angstroms to 10 Angstroms.
9. The membrane as claimed in claim 1, wherein the membrane optionally comprises filter paper supporting the graphene oxide film.
10. The membrane as claimed in claim 1, wherein the membrane has surface area ranging from 5% to 50% of the surface area of the GO film for permeation of solution.
11. The membrane as claimed in any of the preceding claims, wherein the solution is water having solute selected from a group comprising salts of calcium, potassium, magnesium, sodium, bicarbonate, sulfate, chloride, nitrate and combinations thereof.
12. A method of preparing the membrane as claimed in claim 1, said method comprising- coating the binder on a metal mask placed on the graphene oxide film, followed by removing the metal mask and curing the binder coated graphene oxide film to obtain the membrane.
13. The method as claimed in claim 12, wherein the curing of the patterned binder coated graphene oxide film is carried out in an atmosphere having relative humidity ranging from about 0% to 30%.
14. The method as claimed in claim 12, wherein the graphene oxide film prior to coating with the binder is subjected to an atmosphere having relative humidity ranging from about 0 % RH to 30 % RH, for a duration of at least 15 minutes.
15. A method for separating solute from solution, said method comprising-passing the solution through the membrane as claimed in claim 1 and collecting solution with reduced solute content.
16. The method as claimed in claim 15, wherein the solute reduced in the solution is selected from a group comprising salts of calcium, potassium, magnesium, sodium, bicarbonate, sulfate, chloride, nitrate, and combinations thereof.
17. The method as claimed in claim 15, wherein the passing of the solution is carried out under pressure ranging from about 0 bar (pure diffusion) to 25 bar.
18. The method as claimed in claim 15, wherein the solute permeation rate through the membrane is reduced by at least 70% in comparison with a membrane with absence of the patterned binder.
19. The method as claimed in claim 15, wherein area available for passing of the solution in the membrane is ranging from about 5% to 50% of the surface area of the GO film.
20. The method as claimed in claim 15, wherein the solution is water having solute selected from a group comprising salts of calcium, potassium, magnesium, sodium, bicarbonate, sulfate, chloride, nitrate, and combination thereof.
21. A device comprising the membrane as claimed in claim 1 for separating solute from solution. , Description:TECHNICAL FIELD
The present disclosure relates to the field of filtration membrane. The present disclosure particularly relates to a membrane comprising patterned binder and graphene oxide (GO) film. The disclosure also relates to method of separating solutes from solution and/or purifying water using said membranes and method of preparing said membranes. The disclosure also relates to a device comprising the said membrane for separating solute from solution and/or for purifying water.

BACKGROUND OF THE DISCLOSURE
Graphene oxide (GO) is a layered material, where the distance between adjacent layers is typically sub-nanometre in size. The water flow can be controlled by tuning the density of the functional groups or even by using external electric fields. Importantly, this layered system provides for a potential platform where the interlayer separation can be adjusted to allow the permeation of water molecules while restricting the flow of ions. The confined water interlocked between the layer of GO can either be in a mobile form or it could be locked onto the oxygen rich functional groups such as hydroxide, epoxy or carboxylic acid groups present on the basal plane and edges of GO. The mobile form of water is also believed to be superpermeating in nature, a property that refers to rapid conduction of water molecules through sp2 rich hydrophobic pathways formed from graphene-like regions between the GO layers. While the precise density of such pathways is unknown, some estimates suggest that they form a percolating network where the large capillary pressure arising from the Van der Waals attraction between the walls serves to conduct the water rapidly. Water molecules follow a tortuous path that traverse across the different layers of GO flakes through gaps or openings between intra-layer flake arrangement. Depending upon the flake size, for a micron thickness membrane, the path length of water can be in millimetres to centimetres. In literature studies, the water permeation rate through GO membrane has been measured to be quite high, driven by a superpermeation process analogous to that for water channel inside the pores of the carbon nanotubes. In case of GO, a thermodynamic model explains rapid permeation by noting water molecule favorably intercalates between the sp3 rich walls of the GO layers, whereas the absence of water is favored within sp2 rich. Thus, water molecule can easily enter the system from bulk water mediated by sp3 rich regions, which also serves as spacers for creating the nanowidth larger than the graphitic spacing. However, they are rapidly driven through percolating sp2 capillary networks, resulting in very large estimated diffusion constant. The cation-selective permeation process associated with the surface charge of GO in solution has been shown. Despite this impressive nanoscopic dimension which is further tunable in nature, GO membranes are yet to find applications in purification and filtration industry. The rejection ratio of small salts reported in GO is small, only about 26% for 10 mM NaCl together with water permeation of 0.5 to 5 Lm-2h-1bar-1. While some enhancement in the rejection ratio was noted for smaller concentration, it is still quite low when compared to conventional RO membranes.

Thus, new strategies are needed to overcome the factors that limit salt rejection, while enhancing flow of water. Reduction of the functional groups of GO, by thermal annealing, for example, causes the interlayer spacing to reduce but at the same time it also leads to microstructural disorder wherein the GO film is split up into small crystallites, along the direction normal to the plane of the layered arrangement. The space between these crystallites, termed as ‘voids’ can rapidly conduct both ions and water. Polymers have been used to create a hybrid or composite system with GO where the rejection ratio of small salts was found to be enhanced from about 30% to 40% to 50%.

The main factors limiting the performance are two-fold: i) GO membranes have a hierarchical microstructure, where well-ordered crystallite form lamellae thickness of about 100 nm. These lamellae further assemble to form the membrane, but voids or space larger than the subnanometre interlayer spacing exists between the lamellae. These spaces are detrimental for ion filtration especially if they get interconnected; ii) GO membranes can swell in presence of water, as more layers of water intercalates between the layers, following which the ion or molecular size dependent filtration is adversely affected. When GO membranes are placed in a solution, the intercalation of layers of water can swell the membrane and increase the interlayer spacing by a large factor, thereby rendering the membrane unsuitable for filtration application.

Further, complete encapsulation of GO membrane by epoxy based resin binder over their entire surface area while leaving a tiny opening of few microns dimension matching the thickness of the film was studied. Though binders including epoxy binders diminished swelling of the GO film, the binders employed are water impermeable. For instance, GO films prepared by vacuum filtration are 47 mm in diameter, yet the application of binder makes the large surface unusable. Thus, water cannot be inlet through this large surface area, where in the inlet flow is transverse to the GO layer arrangement. Only a small cross section opening on the side of the membrane with lateral dimension of few microns as determined by the membrane thickness is found be available for entry and flow of water parallel to the layered arrangement of GO film. Since, the opening available has a negligible small cross section area, the absolute volume of water transported is consequently tiny. Thus, the existing GO based membranes has no potential industrial scalability and application.

Therefore, there exists a need for improving the GO membranes for filtration application which overcomes the limitations described above.

STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure provides for a membrane comprising patterned binder and graphene oxide (GO) film, wherein the patterned binder restricts the swelling of the GO film and the openings of patterns serve to conduct water and/or solution. The described membrane provides for improved water and/or solution flowability and provides enhanced restriction for ion permeation.

The present disclosure further relates to method of preparing the membrane described above, said method comprising- coating the binder on a metal mask placed on the graphene oxide film, followed by removing the metal mask and curing the binder coated graphene oxide films at relative humidity ranging from about 0% to 50%.

The present disclosure further relates to a method for separating solute from solution, said method comprising- passing the solution through the membrane described above and collecting solution with reduced solute content.

The disclosure further relates to a device comprising the membrane described above for separating solute from solution or for purifying water.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:

Figure 1: a) illustrates schematics of patterning of graphene oxide (GO) film; b) patterned binder encapsulating GO film; and c) X-ray powder diffraction (XRD) for the membrane comprising patterned binder encapsulated GO film at different relative humidity (RH%).

Figure 2: a) schematic diagram illustrating the ion permeation setup; b) digital photograph of the ion permeation setup; and c) plot illustrating change in ionic conductivity of permeate cell with time for GO membrane (unpatterned) of different thickness.

Figure 3: a) plot illustrating ionic conductivity of permeate cell vs. time for membrane comprising patterned binder and GO film prepared at different relative humidity (RH%); and b) plot illustrating change of water permeation rate time through the membrane prepared at about 20% relative humidity at about 1 bar.

Figure 4: a) provides schematic diagram of vacuum filtration step; b) provides schematic diagram illustrating the orientation of GO flakes on a substrate along with chemical structure of an individual GO flake; c) digital photograph of vacuum filtration Buchner funnel; d) digital photograph of vacuum filtration set up; and e) GO film on nylon filter paper.

Figure 5: illustrates X-ray powder diffraction (XRD) characterization of GO film preparing using vacuum filtration technique, wherein peaks marked ‘#’ correspond to the Nylon filter paper.

Figure 6: a) illustrates X-ray powder diffraction (XRD) plot showing (002) peak of the membrane comprising epoxy resin encapsulated GO film processed at different relative humidity (RH%) environments; and b) plot showing change in the d-spacing with different relative humidity (RH%) [Inset: FWHM vs RH% of (002) peak].

Figure 7: a) illustrates X-ray powder diffraction (XRD) plot of (002) peak for membrane comprising polyurethane encapsulated GO film; b) illustrates X-ray powder diffraction (XRD) plot of (002) peak for membrane comprising cyanoacrylate encapsulated GO film; and c) illustrates X-ray powder diffraction (XRD) plot of (002) peak for membrane comprising clay binder encapsulated GO film.

Figure 8: a) illustrates schematic diagram and digital photograph of water permeation setup; and b) illustrates a plot for water permeation rate vs time through the GO film with two different active areas at about 5 bar drive pressure.

Figure 9: a) plot illustrating ionic conductivity vs. time of permeate cell through the membrane comprising patterned binder and GO film on filter paper prepared at different relative humidity (RH%); and b) plot illustrating variation of water permeation rate with time through the membrane comprising patterned binder and GO film on filter paper prepared at 50% relative humidity.

Figure 10: plot illustrating ionic conductivity vs. concentration for KCl for calibration.

Figure 11: a) illustrates thickness profile of the membrane comprising patterned binder and GO film using optical profilometry, wherein the thickness was about 557 nm; and b) illustrates the surface roughness of the membrane.

Figure 12: illustrates thickness profile of the membrane comprising patterned binder and GO film using optical profilometry, wherein the thickness was about 4.36 µm.

DETAILED DESCRIPTION OF THE DISCLOSURE
Definitions:
Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included for better understanding of the present disclosure.

As used herein, the singular forms ‘a’, ‘an’ and ‘the’ include both singular and plural referents unless the context clearly dictates otherwise.

The term ‘comprising’, ‘comprises’ or ‘comprised of’ as used herein are synonymous with ‘including’, ‘includes’, ‘containing’ or ‘contains’ and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed.

The present disclosure relates to a membrane comprising patterned binder and graphene oxide (GO) film.

In some embodiments of the present disclosure, the binder is selected from a group comprising epoxy resin, polyurethane, cyanoacrylate, clay binder and combinations thereof.

In some embodiments of the present disclosure, the patterned binder has pattern selected from a group comprising linear pattern with orthogonal orientation, periodic arrays, and combinations thereof.

In some embodiments of the present disclosure, the patterned binder is in contact with the graphene oxide film, wherein the contact is on one surface of the graphene oxide film.

In some embodiments of the present disclosure, the patterned binder is in contact with the graphene oxide film, wherein the contact is on both surfaces of the graphene oxide film.

In some embodiments of the present disclosure, the graphene oxide film is encapsulated by the patterned binder.

In an exemplary embodiment of the present disclosure, the membrane comprises patterned epoxy resin and graphene oxide film.

In another exemplary embodiment of the present disclosure, in the membrane, the patterned epoxy resin is in contact with the graphene oxide film, wherein the contact is on one surface of the graphene oxide film or on both surfaces of the graphene oxide film.

In some embodiments of the present disclosure, the GO film is in contact with the binder having linear patterns with orthogonal orientations on opposite surface.

In some embodiments of the present disclosure, the binder is patterned with any available pattern designs but not limiting only to linear patterns with orthogonal orientations and periodic arrays.

In some embodiments of the present disclosure, the sides of the membrane are sealed.

In some embodiments of the present disclosure, the GO film has thickness ranging from about 100 nm to 10000 nm, including all values or ranges derivable therefrom, for instance 100 nm, 101 nm, 102 nm and so on and so forth, up to 10000 nm.

In some embodiments of the present disclosure, the GO film has surface area ranging from about 0.1 cm2 to 100 cm2, including all values or ranges derivable therefrom, for instance 0.1 cm2, 0.2 cm2, 0.3 cm2 and so on so forth, up to 100 cm2.

In some embodiments of the present disclosure, the membrane has open (active) surface area ranging from about 5% to 50% of the surface area of the film for permeation of solution/solvent.

In some embodiments of the present disclosure, the membrane has open (active) surface area of about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45% or about 50% of the surface area of the film for permeation of solution/solvent.

In some embodiments of the present disclosure, d-spacing/interlayer spacing of the graphene oxide film is ranging from about 6 Å to 10 Å.

In some embodiments of the present disclosure, d-spacing/interlayer spacing of the graphene oxide film is about 6 Å, about 7 Å, about 8 Å, about 9 Å or about 10 Å.

In some embodiments of the present disclosure, d-spacing/interlayer spacing of the graphene oxide film is smaller by 0.5 Å when the GO film is in contact/coated with the patterned binder at low relative humidity ranging from about 0.1% to 20% when compared to contacting/coating at relative humidity of about 50%.

In some embodiments of the present disclosure, the patterned binder in the membrane diminishes the swelling of the GO film when in contact with solution/solvent at least by about 0.5 Å when compared to bare GO film.

In some embodiments of the present disclosure, the membrane additionally comprises component including but not limited to filter paper supporting the GO film.

In some embodiments of the present disclosure, the patterned binder in the membrane allows flow of water and/or solution from the openings in planar surface area of the GO film.

In some embodiments of the present disclosure, the patterned binder upon contacting the GO film restricts swelling of the GO film, while the openings of the pattern serve to conduct solution and/or water through the membrane. As a result, the membrane demonstrates enhanced filtration ability while allowing reasonable absolute water flow rate through the pattern openings on large surface area of the membrane.

In some embodiments of the present disclosure, ion permeation through the membrane is reduced by about 70% to 80% when compared to GO film without patterned binder (control GO film/bare GO film), while still retaining water permeation rate ranging from about 1 L m-2 h-1 bar-1 to 10 L m-2 h-1 bar-1. Establishing that the membrane comprising the patterned binder and the GO film is efficient in restricting the permeation of ion through the membrane, as a result, providing efficient filtration capabilities.

In an exemplary embodiment of the present disclosure, in the membrane, the patterned binder allows flow of water from the open space in the large surface of the dead-end membrane rather than from the cross-sectional area. Average ion permeation rate for 10 mM KCl in water, measured in feed-permeate geometry is reduced up to about 80% when compared to pristine graphene oxide membranes. This significant reduction in ion permeation is attributed to patterned binder in contact with the GO film and to low relative humidity of about 20% which helps in maintaining low interlayer spacing in the GO film.
In some embodiments of the present disclosure, superior filtration efficiency of the membrane for ions is achieved by contacting patterned binder with the GO film stored under relative humidity ranging from about 0.0 % to 30%.

In some embodiments of the present disclosure, superior filtration efficiency of the membrane for ions is achieved by contacting patterned binder with GO film stored under relative humidity of about 0%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29% or about 30%.

In some embodiments of the present disclosure, the membrane has permeation rate for solution ranging from about 1 L m-2 h-1 bar-1 to 10 L m-2 h-1 bar-1.

In some embodiments of the present disclosure, the membrane has permeation rate for solution ranging from about 1 L m-2 h-1 bar-1, about 2 L m-2 h-1 bar-1, about 3 L m-2 h-1 bar-1, about 4 L m-2 h-1 bar-1, about 5 L m-2 h-1 bar-1, about 6 L m-2 h-1 bar-1, about 7 L m-2 h-1 bar-1, about 8 L m-2 h-1 bar-1, about 9 L m-2 h-1 bar-1 or about 10 L m-2 h-1 bar-1.

In some embodiments of the present disclosure, the membrane has permeation rate for water ranging from about 1 L m-2 h-1 bar-1 to 10 L m-2 h-1 bar-1.

In some embodiments of the present disclosure, the membrane has permeation rate for water ranging from about 1 L m-2 h-1 bar-1, about 2 L m-2 h-1 bar-1, about 3 L m-2 h-1 bar-1, about 4 L m-2 h-1 bar-1, about 5 L m-2 h-1 bar-1, about 6 L m-2 h-1 bar-1, about 7 L m-2 h-1 bar-1, about 8 L m-2 h-1 bar-1, about 9 L m-2 h-1 bar-1 or about 10 L m-2 h-1 bar-1.

In some embodiments of the present disclosure, the membrane has ion permeation rate ranging from about 1 µmol h-1 cm-2 M-1 to 100 µmol h-1 cm-2 M-1, including all values or ranges derivable therefrom.

In some embodiments of the present disclosure, the ions that are filtered by the membrane belong to salt selected from a group comprising calcium salt, potassium salt, magnesium salt, sodium salt, bicarbonate salt, sulfate salt, chloride salt, nitrate salt and combinations thereof.

In some embodiments of the present disclosure, the membrane permits flow of water and/or solution through the active area in dead end geometry.

In some embodiments of the present disclosure, the membrane permits flow of water and/or solution at a flow rate ranging from about 5 L m-2 h-1 bar-1 to 10 L m-2 h-1 bar-1 through active area of the membrane in dead end geometry.

In some embodiments of the present disclosure, the patterned binder in the membrane significantly decreases the swelling of the GO film when in contact with solution and/or water when compared to membrane without the patterned binder.

The present disclosure further relates to a method of preparing the membrane described above.

In some embodiments of the present disclosure, the method of preparing the membrane comprises- coating the binder on a metal mask placed on the graphene oxide (GO) film, followed by removing the metal mask and curing the binder coated graphene oxide film.

In some embodiments of the present disclosure, the curing of the binder coated graphene oxide film is carried out under atmosphere having relative humidity ranging from about 0 % to 30%.

In some embodiments of the present disclosure, the curing of the binder coated graphene oxide film is carried out under atmosphere having relative humidity of about 0%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29% or about 30%.

In some embodiments of the present disclosure, the graphene oxide film prior to coating with the binder is subjected to an atmosphere having relative humidity ranging from about 0 % to 30% for a duration of at least 15 minutes.
In some embodiments of the present disclosure, the graphene oxide film prior to coating with the binder is subjected to an atmosphere having relative humidity of about 0%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29% or about 30%, for at least about 15 minutes.

In an exemplary embodiment of the present disclosure, the graphene oxide (GO) film, with and without the filter paper support is patterned with Stycast epoxy resin on both sides by using a metal shadow mask in a controlled humidity environment inside a glove box. The metal mask consists of central rectangular region of dimensions of about 1.5 cm × 3.3 cm with linear metal stripes of width of about 1 mm separated by opening of width of about 1mm. The epoxy resin is applied on the GO film by painting a thin coating and the mask was lifted and the GO film was subject to curing. After curing of the binder, the membrane was flipped over and again patterned, wherein the linear binder stripes were oriented orthogonal to the original ones. Figure 1(a) illustrates the application of the patterned binder on the GO film and Figure 1(b) illustrates the membrane comprising patterned binder and GO film, wherein the patterned binder is in contact with the GO film.

In an exemplary embodiment of the present disclosure, the figure 1c illustrates X-ray powdered diffraction of the membrane comprising patterned binder and GO film prepared at about 9% relative humidity and at about 50% relative humidity (ambient), respectively. The plot under Figure 1c illustrates the (002) peak for both the membranes. According to the plot the peak shift centred at 9.85 º for ambient RH membrane is shifted to 10.46 º for membrane prepared at about 9% RH which corresponds to a d-spacing between GO layers of the membrane of about 8.45 Å and 8.97 Å for 9% RH and ambient (50% RH), respectively.

In exemplary embodiment of the present disclosure, the permeation rate for ions including but not limited to K+ and Cl- through the membrane prepared at relative humidity ranging from about 0% to 50% is reduced by about 70% to 80% when compared to the bare GO film.

In exemplary embodiment of the present disclosure, the permeation rate for ions including but not limited to K+ and Cl- through the membrane prepared at relative humidity ranging from about 0% to 30% is reduced by about 34% (on an average) when compared to the membrane prepared at relative of about 50%.

In another exemplary embodiment of the present disclosure, the permeation rate for ions including but not limited K+ and Cl- through the membrane prepared at relative humidity ranging from about 1% to 50% is reduced by about 70% to 80% when compared to pristine graphene oxide membrane having ion permeation rate about 80 µmol h-1 cm-2 M-1.

The present disclosure further relates to a method for separating solute from solution, said method comprising- passing the solution through the membrane described above and collecting solution with reduced solute content.

In some embodiments of the present disclosure, the solute reduced in the solution is selected from a group comprising salts of calcium, potassium, magnesium, sodium, bicarbonate, sulfate, chloride, nitrate and combinations thereof.

In some embodiments of the present disclosure, passing of the solution through the membrane is carried out under pressure ranging from about 0 bar (pure diffusion) to 25 bar.

In some embodiments of the present disclosure, passing of the solution through the membrane is carried out under pressure of about 0 bar (pure diffusion), about 1 bar, about 2 bar, about 3 bar, about 4 bar, about 5 bar, about 6 bar, about 7 bar, about 8 bar, about 9 bar, about 10 bar, about 11 bar, about 12 bar, about 13 bar, about 14 bar, about 15 bar, about 16 bar, about 17 bar, about 18 bar, about 19 bar, about 20 bar, about 21 bar, about 22 bar, about 23 bar, about 24 bar or about 25 bar.

In some embodiments of the present disclosure, the solute permeation rate through the membrane is reduced by at least 70% in comparison with a membrane with absence of the patterned binder.

In some embodiments of the present disclosure, the solute permeation rate through the membrane is reduced by at least 75% in comparison with a membrane with absence of the patterned binder.

In some embodiments of the present disclosure, the solute permeation rate through the membrane is reduced by at least 80% in comparison with a membrane with absence of the patterned binder.

In some embodiments of the present disclosure, the solution is water having solute selected from a group comprising salts of calcium, potassium, magnesium, sodium, bicarbonate, sulfate, chloride, nitrate and combination thereof.

In some embodiments of the present disclosure, area available for passing of the solution through the membrane is ranging from about 5% to 50% of the surface area of the GO film, including all values or ranges derivable therefrom, for instance 5%, 6%, 7% and so on and so forth up to 50%, wherein the surface area of the GO film is ranging from about 0.1 cm2 to 100 cm2, including all values or ranges derivable therefrom, for instance 0.1 cm2, 0.2 cm2, 0.3 cm2 and so on and so forth up to 100 cm2.

The present disclosure further relates to a device comprising the membrane described above for carrying out filtration.

In some embodiments of the present disclosure, the device is a filtration device comprising the membrane.

In some embodiments of the present disclosure, the filtration device may be a filter assembly, or it may be a removable and replaceable filter for use in the filter assembly.

It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES
Example 1: Preparation of GO film
GO suspension (4mg/ml, from University wafer) is diluted by adding water and filtered through a 47mm diameter nylon filter paper (Rankem, pore size 0.45µm) on a porous support in a Buchner funnel. Fig 4 (a) shows a schematic diagram of the vacuum filtration setup used for preparing the graphene oxide membrane. The system is constantly evacuated with a rotary pump during the process.Vacuum filtration is quite suited to create solution processed layered films from 2D materials since the suction process helps in stacking the flakes above the substrate while preventing random orientations [Tang et al.], as shown in fig. 4 (b). By controlling the quantity of GO in the solution one can have good control on the thickness of film and Manish et. al prepared few nanometers thin GO film using this technique. Digital photographs of the setup are shown in fig. 4 (c) and (d). Fig. 4 (e) shows a digital photograph of a prepared GO membrane with filter paper support.

Example 2: Binding ability of different binders
GO films prepared by vacuum filtration, were stored in custom-designed controlled humidity chamber (0-90% RH) for a period of 1 hour before encapsulating them with binder. Figure 6 (a) shows the XRD plots of the portion of GO membrane which is completely encapsulated by stycast adhesive binder. The plot indicates a monotonic shift in 2O peak position of (002) peak to smaller vales as the RH is tuned. The d-spacing between the GO layers estimated from the peak position found to increase from about 8 Å to about 10 Å as the RH% is increased from 0% to 90% (see figure 6 (b). This result is consistent with the observations made in literature [Abraham et al.(2017)], although some difference in the obtained value of d-spacing can be attributed to likely differences is the extent and nature of the oxygen functionalization of the GO, which depends on the parent source of the aqueous solution. The inset of figure 6(b) shows the variation of full-width-half- maximum (FWHM) of the (002) peak with RH% variation. The FWHM has lowest value of about 1.4×10-2 radian for 0% to20% range RH and highest value of about 2.3×10-2 radian for 90% RH. In general, the width of any XRD peak can be related to the size of the crystallite, a result captured in the Scherrer formula t=k?/ßCosO where t is the crystallite size, k ~ 0.9, ? is the X-ray wavelength, O is the Bragg angle and ß is the FWHM in radians. It has been shown in the work of Pranav et al., that Scherer formula slightly overestimates the mean crystallite size as compared to a more rigorous application of the scattering equation that factors the very small crystallite size in vertical direction as well as possible distribution of the crystallite sizes [Pranav et al. (2019)]. The FWHM increase with RH indicates that the microstructure disorder in the system increases, with mean crystallite size decreasing from about 9.6 nm to 6.0 nm. In the space intervening these crystallites are spacing larger than sub nanochannel widths and these are referred as voids

In addition to Stycast which is an epoxy based resin binder, various popular adhesive binders to control and preserve the nanochannel width of GO membrane was attempted. Figure 7 (a) shows the XRD plot of (002) peak of GO treated at various RH% before being encapsulated by Polyurethane based binder. Once again, the 2O values shifted from 10.18° to 9.37° as RH% changes from 0 to 70%. This corresponds to a change in the nanochannel width from 8.67 Å to 9.42 Å.

However, the data for 90% RH shows a clear departure from the trend with large 2O values of 10.14° with d-spacing of 8.71 Å. The anomaly can be reconciled by noting that the binding mechanism of polyurethane adhesive relies on the presence of surface moisture [Thota et al. (2013)], Thus at very large RH%, the adhesive may cure even before it can bind with the GO membrane. Figure 7 (b) shows the XRD plot for (002) peak of GO processed at different RH% and encapsulated with cynoacrylate based adhesive.

The variation in 2O value and d-spacing is very slight and the result can be reconciled by noting the moisture sensitivity of cynoacrylate binding reaction which fails at both very low and very high humidity [Shantha et al. (1989)]. Figure 7 (c) shows the corresponding XRD data where clay binder kept at ambient RH is used. While clay encapsulation was unsuccessful at 90% RH, experiments could be performed for GO stored at 0% and 50% RH. The d-spacing at both these relative humidities was almost identical to about 7 Å. The lack of departure on RH% may arise from the fact that clay is a natural desiccant. Thus, any water intercalated in GO layers from moisture will get transferred to pore sites within clay particles or the interstices between the clay layers [Odom et al. (1984)]. However, the obtained d-spacing is the lowest among all samples. For instance, if Stycast encapsulation results in d spacing of about 8 Å at 0% RH, the same value is 1 Å lower for the clay encapsulation. The low value of nanochannel width for clay encapsulation may appear lucrative for filtration application to note 6 Å is the minimal d-spacing needed for the accommodating one monolayer of water molecules [Nair et al. (2012)] and thus 7 Å spacing could potentially help filter the smallest of the ions.

Example 3: Binder contacting/patterning on GO membrane
The GO film, with and without the filter paper support, was patterned with Stycast epoxy resin on both sides by using a metal shadow mask in a controlled humidity environment inside glove box. The metal mask consists of central rectangular region of dimensions about 1.5 cm × 3.3 cm with linear metal stripes of width of about 1 mm separated by opening of width of about 1 mm. The binder was applied on the GO film by painting a thin coating and the mask was lifted. After curing of the binder, the membrane was flipped over and again patterned in the same manner except that linear binder stripes were oriented orthogonal to the original ones. Since the binder was in a viscous state before drying, the actual separations obtained between the linear patterns were smaller. The coating of the GO film was realized that contained array of windows which served for permeation of water. A photograph of a representative patterned membrane is shown in figure 1(b). The complete encapsulation of the GO membrane prepared under different RH% preserved the d-spacing when XRD was measured under ambient humidity condition. Along the same lines, XRD of the patterned binder encapsulated GO prepared at low RH (9%) and ambient (~50% RH). The position of (001) peak for both cases is plotted in fig. 1(c). The peak shift centered at 9.85° for ambient RH patterned sample is shifted to 10.46° for low RH patterned sample. This corresponds to a d-spacing between GO-layers of 8.45 Å and 8.97 Å for 9% and ambient (~ 50%) respectively. The swelling of the GO membrane exposed to ambient RH is therefore reduced by ~0.5Å when it is encapsulated by a patterned binder at low RH%.

Example 4: Ion and water permeation through the Membrane
GO film patterned with binder on one side were peeled off from the filter paper support and cross pattern was applied to the reverse side after the former has cured. After coating/contacting the patterned binder with GO film and curing of the edges, the membrane was mounted with O-ring support in the feed permeate setup. Six patterned binder enclosed GO films were prepared for ion permeation study; 4 processed in ambient relative humidity (about 50 % RH) environment (labeled GOPAHi, where i = 1, 2, 3, 4) and 2 processed in an environment of relative humidity (RH) about 9% (labeled GOPLHi, where i = 1, 2). The permeation of ions from about 0.01 M KCl in the feed cell was monitored as a function of time as in figure 3 (a). It was observed that the membrane prepared at about 9% RH had the smallest increase in the conductivity, normalized with the average area of the linear periodic opening on the binders. The mean conductivity change at t = 48h was 9.3 ± 0.93µS cm-3 for membrane prepared at about 9% RH and 16.2 ± 5.6 µS cm-3 for membrane prepared at about 50% RH patterned, this corresponds to 0.8 mmol cm-2 M-1 and 1.4 mmol cm-2 M-1 permeation through low RH patterned and ambient RH patterned sample respectively. In the linear region (7- 46 hours) of the permeation curves in figure. 3 (a), the corresponding molecular permeation rate of 16.4 ± 0.9 µmol h-1cm-2M-1 for the former and 24.6 ± 9.8 µmol h-1cm-2M-1 for the latter case was obtained. These numbers are 3-4 times smaller than the permeation rate without pattern [see figure 2 (c)] demonstrating that the application of binder pattern significantly reduced the ion permeation process. From nanochannel model the area for ion diffusion increases proportional to the square d-spacing and the calculated effective diffusion constant for KCl salt ions comes out five orders of magnitude larger than bulk diffusion constant. The reason for such a high value of diffusion constant is due to presence of highly saturated salt solution inside the GO film. From the above results, it is noted that the patterned binder restricts the swelling of GO film when exposed to KCl. Figure 3 (b) shows the water permeation through a representative sample at 1 bar drive pressure, where the area is taken to be the active area (unexposed) area of the membrane. The saturation water permeation rate achieved was 5 L m-2 h-1 bar-1 which is comparable to permeation of commercial RO membrane [Li et al., (2017)].

The permeation rate of K+ and Cl- through the membrane patterned at low RH% (1% to 30% RH) is found to be smaller than patterned at high RH% (greater than 30%), and furthermore, the permeation rates were about 70 to 80 % smaller than that for a pristine graphene oxide membrane of identical thickness. Pressure-driven water permeation, measured for about 1 to 5 bar differential pressure, was high during the first 2 hours, similar to the case for pristine graphene oxide membranes (comparative membrane) and it converged to a value ranging from 5-10 L m-2 h-1 bar-1 at longer timescales when scaled with active area. Thus, the membrane comprising the patterned binder and the GO film maintains good water flow in the industrially relevant range, even as the ion permeation was diminished by about 80%.

Example 5: Ion and water permeation through an unpatterned GO film
In this experiment, flow of ions through as-prepared GO films (bare GO film) is assessed. For this experiment, a feed: permeate cell setup was used, as popularly employed in literature to study ion permeation through GO based membrane systems [Joshi et al. (2014)]. Figure 2(a) and 2(b) shows a schematic diagram and a digital photograph of the setup, respectively. The GO membrane is sealed with a rubber O-ring and tested for being leak-proof. An aqueous solution of about 10 mM KCl was used as the feed solution and DI water (Millipore) was used in permeate side. The permeation is driven by concentration gradient between the two sides. The conductivity of the solution on permeate side is periodically monitored with a conductivity meter (PWT, Hanna Instruments; see our calibration data in Annexure-E). Figure 2(c) shows the plot of conductivity vs. time for the permeation of K+ and Cl- ions through GO membrane. The rate of increase of conductivity is higher during the initial time and diminishes to a smaller rate after a time of about 10 hours. These conductivity values can be converted to molecular permeation rates. Even though GO membranes are noted to be cation selective, the rate of both K+ and Cl- proceeds at an equal stoichiometric rate governed by that of slower ionic species, due to charge neutrality requirement [Joshi et al. (2014)]. The rate of conductivity was almost linear, but it slightly decreased with time and latter may be attributed to decrease in the concentration gradient. From the slope of the linear fit to data in figure 2 (c), molecular permeation rate after 46 hours was obtained as about 81.4 µmol h-1cm-2 M-1 for about 500 nm thick membrane and about 10.8 µmol h-1cm-2 M-1 for about 4.5 µm thick GO membrane and these permeation rates on pristine (un-patterned) GO membranes match previously reported values [Joshi et al. (2014)]. The permeation through the unpatterned film is about 81.4 µmol h-1cm-2 M-1 and for ambient and low RH patterned membrane it is about 24.6 µmol h-1cm-2 M-1 and about 16.2 µmol h-1cm-2 M-1 respectively. So the decrease in the ion permeation for patterned membranes is about 56.8 µmol h-1cm-2 M-1 and about 65.2 µmol h-1cm-2 M-1 for ambient patterned and low RH% patterned membrane respectively, which is about 70% and about 80% of the permeation through bare GO film.

Example 6: Water flow through bare (unpatterned) GO membranes
This experiment describes measuring of water permeation rates through GO film (unpatterned). Figure 8 (a) shows a schematic diagram and digital photograph of Sterlitech HP 4750 high pressure cell that uses compressed gas to apply pressure on the water column with 300 ml water. The liquid is driven through the GO membrane: filter paper system kept on a porous ceramic support at the pressure difference from about 1 to 5 bar. The rate of collection of liquid at the outlet is monitored as a function of time to obtain the water permeation rate for the membrane. Figure 8(b) shows a plot of time dependent water permeation rate through a GO membrane having thickness of about 500 nm for two different exposed areas 11.37 cm2 and 3.35 cm2. The variation in the area was achieved by using the reducer in pressure cell. Very large flow rate of about 4 to 5 L m-2 h-1 bar-1 were recorded during the initial time interval. This rapid initial permeation was caused by presence of voids in the GO membrane. As shown in the inset of figure 6(b), the X-ray peaks have significant width which originates from the site of GO crystallites. These crystallite forms lamella structures with voids separating the two lamellae [Chong et al. (2018), Ravishankar et al. (2019)]. The water is rapidly conducted through the voids, but the latter get compactified after prolonged water exposure and a saturation flow rate is achieved after about 2hrs. In this case, this value is 0.33 L m-2 h-1 bar-1 and 0.40 L m-2 h-1 bar-1 for 11.37 cm2 and 3.35 cm2 surface area, respectively. The areal dependence of the saturation flow rate is weak, and it is this flow rate that may comprise the nanochannels driven flow process.

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