A COMPOSITION, A METHOD OF MAKING A COMPOSITION, AND A FILTRATION MEMBRANE

Abstract

The present invention relates to a filter and a method of making a filter. The filter includes a porous substrate and a graphene oxide membrane and can be used to filter fluids.

Claims

1-46. (canceled)

47. A method of making a composition containing graphene oxide sheets, wherein the method includes: an adding step that includes adding a modifying agent to a graphene oxide feed suspension containing graphene oxide sheets, hereinafter referred to as the feed suspension, to form the composition; and a modifying step that includes modifying the composition under elevated temperature conditions so that the modifying agent reacts with the graphene oxide sheets to create imperfections in the graphene oxide sheets, wherein progress of the reaction is stopped by reducing the temperature of the composition so the composition stabilises and can be applied to a substrate to form a filter having a graphene oxide membrane.

48. The method according to claim 47, wherein the modifying step includes mixing the composition during at least part of, and suitably during all of, the elevated temperature conditions, and preferably wherein, the elevated temperature is in the range of from 50? C. o about 200? C., or preferably about 80? C. to about 150? C., or preferably in the range of 50 to 98? C., and preferably the modifying step is carried out for a period in the range of 0.5 hr to 7 hr, and preferably from 0.5 hr to 6 hrs, preferably from 1 hr to 6 hrs.

49. The method according to claim 47, wherein the method includes measuring the viscosity of the composition to determine when to stop the progress of the reaction, and preferably wherein the method includes a cooling step to stop the progress of the reaction by cooling the composition to a temperature below 50? C., and preferably to a temperature ranging from 15 to 45? C., and preferably wherein, the cooling step is carried out when the viscosity of the composition reaches a maximum, or has started reducing from a maximum viscosity, to stop the reaction between the modifying agent and the graphene oxide.

50. The method according to claim 49, wherein the modifying step is carried out for at least 1 to 5 hours after a maximum in the viscosity of the composition has occurred before the cooling step, and preferably the modifying step is carried out for at least 2 to 4 hours after a maximum in the viscosity of the composition has occurred before the cooling step.

51. The method according to claim 47, wherein the modifying agent is selected from a group consisting of peracetic acid, benzoyl peroxide, sodium perborate, ammonium hydroxide, alkali hydroxides such as sodium hydroxide and potassium hydroxide, and hydrogen peroxide, and preferably the modifying agent is hydrogen peroxide.

52. The method according to claim 47, wherein the modifying agent is hydrogen peroxide solution which is added to the graphene oxide feed suspension at a mass ratio of modifying agent to the graphene oxide mass in the feed suspension in a range of less than or equal to 15 to 1, preferably 12 to 1, preferably 10 to 1, preferably 9 to 1, preferably 8 to 1, preferably 7 to 1, preferably 6 to 1, preferably 5 to 1, preferably 4 to 1, preferably 3 to 1, preferably 2 to 1, preferably 1 to 1.

53. The method according to claim 47, wherein the method does not include removing, if present, any surplus modifying agent from the composition after the cooling step.

54. The method according to claim 47, wherein the method includes adding a crosslinking additive to the composition, the crosslinking additive being selected from a group consisting of: a molecule or polymer with an epoxide group, an alkoxysilane group, a cationic group provided by quaternary ammonium, or at least two amine groups, and preferably wherein, the molecule or polymer having the cationic group provided by quaternary ammonium is selected from the group consisting of cationic polyvinyl alcohol, cationic polyacrylamide, cationic poly-urea-ammonium-ether, cationic hydroxyethyl cellulose, cationic guar, and preferably the molecule or polymer having the epoxide group also has i) an alkoxysilane group including a hydrolysable silanol group, such as 3-glycidyloxypropl trimethoxy silane, which is also known as GLYMO, or ii) a cationic group including trimethylammonium, such as glycidyltrimethylammonium chloride, which is also known as GTAC, and preferably the molecule or polymer having the at least two amine groups is a diamine polymer, such as polyethyleneimine (PEI).

55. A method of making a filter for filtering a fluid, wherein the method includes: applying an adhesive additive to a porous substrate; and applying the composition to the porous substrate to form a filter having the membrane containing graphene oxide, wherein the composition has been made in accordance with the method of claim 47, and the adhesive additive facilitates bonding of the composition to the substrate.

56. The method according to claim 55, wherein the adhesive additive includes a quaternary ammonium group, and preferably the adhesive additive is a cationic polymer having quaternary functionality including: cationic polyvinyl alcohol, cationic polyacrylamide, cationic poly-urea-ammonium-ether, cationic hydroxyethyl cellulose, or cationic guar, and preferably the adhesive additive is a cationic polymer that includes poly diallyldimethylammonium chloride (polyDADMAC), and preferably the adhesive additive is a cationic polymer that include a modified polyvinylalcohol incorporating at least one quaternary ammonium group, such as GOHSENX? K.

57. The method according to claim 55, wherein the method includes applying a crosslinking additive to the graphene oxide membrane after the graphene oxide membrane has been applied to the substrate, and preferably after the graphene oxide membrane has dried, and preferably the adhesive additive includes a dopamine and the method includes initiating polymerisation of the dopamine prior to the adhesive additive being applied to the substrate.

58. The method according to claim 57, wherein the method includes selecting the crosslinking additive from a group comprising: i) a polymer having at least one epoxide group, ii) a molecule having at least one epoxide group, iii) a cationic polymer having at least one quaternary ammonium group, iv) a polymer having at least two amine groups, v) a molecule having at least two amine groups, and preferably the crosslinking additive includes a cationic polymer having at least one quaternary ammonium group, and preferably the cationic polymer includes at least one of: cationic polyvinyl alcohol, cationic polyacrylamide, cationic poly-urea-ammonium-ether, cationic hydroxyethyl cellulose, cationic guar, cationic polyDADMAC.

59. The method according to claim 57, wherein the method includes activating the crosslinking additive to complete crosslinking between the graphene oxide sheets, and preferably activating the crosslinking additive includes heating the substrate and the membrane on the substrate above 50? C. for at least 1 hour, and to a temperature of 75? C. for at least 2 hours, and preferably activating the crosslinking additive includes applying a catalyst, such as aluminium acetylacetonate to the graphene oxide membrane.

60. The filter made by the method according to claim 55, wherein the filter has a rejection ranging from greater than 90.0% to 99.5% under acidic conditions when measured using the Rose Bengal probe molecule in the cross-flow apparatus, and preferably the filter has a permeance ranging from 6.7 to 13.7 (L/m.sup.2/h/bar) under acidic conditions when measured using the Rose Bengal probe molecule in the cross-flow apparatus, and preferably, the filter has a rejection ranging from 65.5% to 98.8% under alkaline conditions when measured using the Rose Bengal probe molecule in the cross-flow apparatus, and preferably the filter has a permeance ranging from 10.0 to 25.1 (L/m.sup.2/h/bar) under alkaline conditions when measured using the Rose Bengal probe molecule in the cross-flow apparatus.

61. The filter made by the method in accordance with claim 47, wherein the crosslinking additive is one of the following: cationic polyacrylamide (lg/L), cationic poly urea-ammonium-ether (5 g/L), cationic polyacrylamide (lg/L), cationic hydroxyethyl cellulose (lg/L), cationic guar (lg/L), cationic polyDADMAC (5 g/L), and polyamine (5 g/L), and wherein the filter has ranges of rejection values from acid conditions to alkaline conditions measured using the Rose Bengal probe molecule in the cross-flow apparatus as shown in the following table: TABLE-US-00011 Crosslinking Rejection (%) additive Acidic Alkaline Class conditions conditions Cationic 96.3% 91.9% polyacrylamide Cationic poly urea- 99.3% 98.4% ammonium-ether Cationic 98.6% 95.8% polyacrylamide Cationic 95.8% 76.7% hydroxyethyl cellulose Cationic guar 91.9% 65.5% Cationic 99.5% 98.8% polyDADMAC Polyamine 98.7% 95.7% and preferably the filter has ranges of permeance values from acidic conditions to alkaline conditions measured using the Rose Bengal probe molecule in the cross-flow apparatus as shown in the following table: TABLE-US-00012 Permeance Crosslinking (L/m.sup.2/h/bar) additive Acidic Alkaline Class conditions conditions Cationic 6.7 10.9 polyacrylamide Cationic poly urea- 6.9 10.0 ammonium-ether Cationic 9.0 12.9 polyacrylamide Cationic 11.0 16.3 hydroxyethyl cellulose Cationic guar 11.6 19.8 Cationic 13.7 25.1 polyDADMAC Polyamine 9.8 17.6 and preferably the porous substrate is selected from the group comprising a metallic substrate, a ceramic substrate, or a polymeric substrate such as polyvinylidene difluoride.

62. The filter made by the method in accordance with claim 47, wherein the crosslinking additive is a cationic polymer and the adhesive additive is cationic polyvinylalchohol (such as GOHSENX? K), when exposed to 10,000 ppm.h of chlorine, the filter has a permeance value ranging from 13.7 to 29.8 (L/m.sup.2/h/bar) and a rejection value ranging from 90.7% to 98.5% under alkaline conditions, and preferably the filter has a permeance value ranging from 11.0 to 23.8 L/m.sup.2/h/bar and a rejection value ranging from 86.6% to 99.5% under acidic conditions, and preferably the porous substrate is selected from the group comprising a metallic substrate, a ceramic substrate, or a polymeric substrate such as polyvinylidene difluoride.

63. The filter made by the method in accordance with claim 55, wherein the crosslinking additive is a diamine polymer with at least two reactive amine groups, and the adhesive additive is cationic polyvinylalchohol (such as GOHSENX? K), and when exposed to 10,000 ppm.h of chlorine, the filter has a rejection value at least 85%, and suitably a rejection in the range of 85% to 88% and a permeance value ranging from 13 to 15 L/m.sup.2/h/bar, and suitably a permeance value of approximately 14.5 L/m.sup.2/h/bar under acid conditions, and preferably the porous substrate is selected from the group comprising a metallic substrate, a ceramic substrate, or a polymeric substrate such as polyvinylidene difluoride.

64. A composition containing graphene oxide sheets that can be applied to a porous substrate to make a filter, wherein the graphene oxide sheets have been modified by reacting with a modifying agent to create imperfections in the graphene oxide sheets at an elevated temperature wherein progress of the reaction is stopped by reducing the temperature of the composition to form a stable composition that can be applied to a substrate to form a graphene oxide filtration membrane, and preferably the modifying agent is selected from a group consisting of peracetic acid, benzoyl peroxide, sodium perborate, ammonium hydroxide, alkali hydroxides such as sodium hydroxide and potassium hydroxide, and hydrogen peroxide, and preferably the modifying agent is hydrogen peroxide, and preferably the modifying agent is hydrogen peroxide and was added to the graphene oxide feed suspension at a mass ratio of modifying agent to the graphene oxide mass in the feed suspension in a range of less than or equal to 15 to 1, preferably 12 to 1, preferably 10 to 1, preferably 9 to 1, preferably 8 to 1, preferably 7 to 1, preferably 6 to 1, preferably 5 to 1, preferably 4 to 1, preferably 3 to 1, preferably 2 to 1, preferably 1 to 1.

65. The composition according to claim 64, wherein the composition is stable without removing the modifying agent from the composition.

66. The composition according to claim 64, wherein the composition includes a crosslinking additive in which the crosslinking additive is selected from a group consisting of: a molecule or polymer with an epoxide group, an alkoxysilane group, a cationic group provided by quaternary ammonium, or at least two amine groups, and preferably the molecule or polymer having the cationic group is provided by quaternary ammonium is selected from the group consisting of cationic polyvinyl alcohol, cationic polyacrylamide, cationic poly-urea-ammonium-ether, cationic hydroxyethyl cellulose, cationic guar, and preferably the molecule or polymer having the epoxide group also has i) an alkoxysilane group including a hydrolysable silanol group, such as 3-glycidyloxypropl trimethoxy silane, which is also known as GLYMO, or ii) a cationic group such as glycidyltrimethylammonium chloride, which is also known as GTAC, and preferably the molecule or polymer having the at least two amine groups is a diamine polymer, such as polyethyleneimine (PEI).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] Embodiments of the present invention will now be described with reference to the accompanying Figures which may be summarised as follows.

[0125] FIG. 1 is a block diagram of the steps for making a composition according to a preferred embodiment and a method of making a filter by applying the composition to a substrate.

[0126] FIG. 2 is a block diagram of the steps for making a composition according to another embodiment and a method of making a filter by applying the composition to a substrate.

[0127] FIG. 3 is a block diagram of the steps for making a composition according to yet another embodiment and a method of making a filter by applying the composition to a substrate.

[0128] FIG. 4 is a schematic cross-sectional view of the filter that can be made according to an embodiments shown in FIGS. 1 to 3.

DESCRIPTION OF THE DRAWINGS

[0129] With reference to FIG. 1, the suitability of a graphene oxide feed suspension for making a composition that can be applied such as printed to form a graphene oxide filtration membrane 90 on the substrate 110 is a function of many variables. One possible variable is the level or concentration of impurities in the feed suspension. Step 10 of FIG. 1 can include selecting a feed suspension and optionally determining the suitability of the feed suspension by assessing the level of impurities in the feed suspension. One method for assessing the level of impurities is measuring the electrical conductively of the feed suspension. Step 10 of FIG. 1 may optionally also include preparing a suitable feed suspension, including combining dry graphite oxide with water and mixing, or combining dry graphene oxide with water and mixing. For example, a feed suspension may be prepared by combining a graphene oxide cake containing 43?5 wt % graphene oxide with water and mixing. Water may be added to the feed suspension to adjust the graphene oxide concentration into a range of 0.1 to 15 wt %.

[0130] Step 20 of FIG. 1 can include treating the feed suspension to create imperfections in the graphene oxide. Specifically, Step 20 includes adding an active modifying agent to the feed suspension to form a composition, and mixing the composition under elevated temperature and then reducing the temperature of the composition to stop progress of the reaction between the modifying agent and the graphene oxide so as to form a stable composition. In this situation all of, or nearly all of, the modifying agent may have reacted with the graphene oxide sheets. Step 20 can include determining the amount of modifying agent(s) to be added to the feed suspension, including determining a desired mass ratio of modifying agent to the graphene oxide sheets in the feed suspension. In addition, Step 20 can be carried out under heated conditions, which may or may not be accompanied by pressurised conditions, to increase the reaction rate between the modifying agent(s) and the graphene oxide. The period of mixing the composition may be reduced by increasing the temperature and pressure conditions of Step 20. Conversely the period of mixing the composition may be increased by lowering the temperature to ambient temperature.

[0131] In a situation in which the modifying agent comprises hydrogen peroxide in isolation with no other modifying/active agent, we have found that a 30 wt % hydrogen peroxide solution can be added to the feed suspension at a ratio of equal to or less than 5 parts hydrogen peroxide to 1 part suspension. In this embodiment the suspension comprises approximately 1 mg/mL of graphene oxide. When used in this range, the hydrogen peroxide is reacted with the graphene oxide for sufficient reaction time. These conditions provide a graphene oxide with the required permeance, avoids subsequent separation of excess modifying agent from the feed suspension, and can be readily scaled up into commercial operating batches. Step 20 may be carried out in a batch operation.

[0132] Step 20 of FIG. 1 may include determining when the reaction between the modifying agent and the graphene oxide has progressed far enough by measuring, for example, any one or a combination of the viscosity of the composition, colour and colour changes of the composition, and infrared spectrum analysis of the composition. The reaction between the modifying agent and the graphene oxide may also produce a gas, such as carbon dioxide, and determining whether the reaction has progressed far enough may be determined by measuring the amount of the gas produced during the mixing step.

[0133] The composition may then be treated in optional Step 30 of FIG. 1 to facilitate the composition being used as a printable composition using microgravure printing machines or other application methods. Properties of the composition, such as viscosity and surface tension may then be measured and adjusted in Step 30. For example, the surface tension may be controlled using surfactants such as Triton-available from DOW Inc. In another example, the viscosity of the composition may also be controlled by adding polyphenol and/or ethanol. Adjusting the viscosity and/or the surface tension enables the composition to be applied as a filtration membrane using high speed printing machinery, such as gravure printing or micro-gravure printing. In other words, not only is the composition suitable for making filtration membranes, but in addition, the composition can be applied at a manufacturing speed at a large scale.

[0134] One of the benefits of the method shown in FIG. 1 is that no cross-linking materials need to be added to the composition prior to applying the composition to the substrate.

[0135] Step 60 of FIG. 1 can include selecting a porous substrate 110 such as a porous film including polymeric, metallic or ceramic films. Selecting an appropriate substrate, is typically based on the desired permeance and flexibility.

[0136] Step 70 of FIG. 1, which is optional, can include modifying the substrate 110 to improve the adhesion of the graphene oxide membrane 90 to the porous substrate 110. For example, an adhesive additive 100, such as either one or a combination of, adhesives such as polyDADMAC, GOHSENXT? K and dopamine can be applied to the substrate in Step 70, and dried. The rate at which the adhesive dries may be increased by heating once the additive has been applied to the substrate. The adhesive additive 100 may be applied using dip coating, printing, spraying, or other suitable techniques.

[0137] Step 40 of FIG. 1 can include applying and preferably printing the composition prepared in Steps 20 and/or 30 to the substrate 110 to form a filter 200 having a graphene oxide membrane 90 provided by the composition. This may be done by a gravure printing machine including micro-gravure printing, or other techniques such as dip coating, rod coating, knife coating, blade coating, vacuum filtration or spraying to form a membrane 90 of the composition on the substrate 110. Step 40 may include drying the composition which may be done in ambient conditions. However ideally, the rate at which the composition dries may be increased by exposure to radiant heat or by convection, for example, by means of a stream of heated air. The adhesion of the composition to the substrate 110 is less prone to degradation as a result of the adhesive additive 100 applied in Step 70.

[0138] Step 50 of FIG. 1 is optional and can include a post treatment of the filter 200 by applying a crosslinking additive 120 such as polyDADMAC to the dried graphene oxide membrane 90. The crosslinking additive 120 provides a level of pH resistance to the graphene oxide membrane 90. The term pH resistance refers to the rejection of the filter 200 being less variable over a broader pH range than if no crosslinking additive 120 was added to the composition. Step 50 of FIG. 1 may optionally also include a permeance-enhancing or permeance setting step by exposing the membrane 90 to a solution of sodium hypochlorite for a period of time. For example, the membrane 90 can be submerged in a 10 g/L solution of sodium hypochlorite for a period of 30 minutes (5,000 ppm.h) to increase the permeance.

[0139] FIG. 2 is a block diagram of an embodiment for making a composition that can be applied to a substrate, such as printed, to form a graphene oxide filtration membrane 90 on the substrate 110. FIG. 2 has particular steps relating to the addition of epoxy containing crosslinker 120 to the composition prior to the composition being applied to the substrate, and subsequent activation of the crosslinker in a post-treatment step after the composition has been applied to the substrate. Step 10 of FIG. 2 can include the same procedures described above in relation to Step 10 of FIG. 1. Ideally, the feed suspension has or is adjusted to have a graphene oxide concentration into a range of 0.1 to 15 wt %.

[0140] Step 20 of FIG. 2 can include the same procedures described above in relation to Step 20 of FIG. 1. That is Step 20 includes treating the feed suspension to create imperfections in the graphene oxide to form a composition. For instance, Step 20 can include adding an active modifying agent to the feed suspension to form a composition, and mixing the composition under elevated temperature and then reducing the temperature of the composition to stop progress of the reaction between the modifying agent and the graphene oxide to form a stable composition. In this situation all of, or nearly all of, the modifying agent may have reacted with the graphene oxide. In addition, Step 20 of FIG. 2 can include determining whether the reaction can be stopped to form a stable composition.

[0141] For instance, Step 20 of FIG. 2 may include determining when the reaction between the modifying agent and the graphene oxide has progressed far enough by measuring, for example, any one or a combination of the viscosity of the composition, colour and colour changes of the composition, and infrared spectrum analysis of the composition. The reaction between the modifying agent and the graphene oxide may also produce a gas, such as carbon dioxide, and determining whether the reaction has progressed far enough may be determined by measuring the amount of the gas produced during the mixing step.

[0142] The composition may then be treated in Step 30 of FIG. 2 to facilitate the composition being used as a printable composition using microgravure printing machines or other application methods. For instance, viscosity and surface tension may then be measured and adjusted in Step 30 by adding surfactants such as Triton-available from DOW Inc. The viscosity of the composition may also be controlled by adding polyphenol and/or ethanol. Adjusting the viscosity and/or the surface tension enables the composition to be applied as a filtration membrane using high speed printing machinery, such as gravure printing or micro-gravure printing.

[0143] In addition, Step 80 of FIG. 2 may optionally include adding crosslinking additives 120 to the composition such as either one or a combination of epoxide containing crosslinkers, such as GLYMO or GTAC (glycidyl trimethylammonium chloride). These crosslinking additives 120 provide stabilization to the rejection properties of the filter 120 over a broader range of pH than if no crosslinking additive was included. At a structural level the crosslinkers 120 manage the spatial separation between the graphene oxide sheets.

[0144] Step 60 of FIG. 2 can include the same procedures described above in relation to Step 60 of FIG. 1. Specifically, Step 60 can include selecting a porous substrate 110 such as a porous film including polymeric, metallic or ceramic films.

[0145] The method of FIG. 2 may optionally include Step 70 which includes modifying the substrate 110 to improve the adhesion of the graphene oxide membrane 90 to the porous substrate 110. For example, an adhesive additive 100, such as either one or a combination of, adhesives such as polyDADMAC, GOHSENXT? K and dopamine can be applied to the substrate in Step 70, and dried. The rate at which the adhesive dries may be increased by heating once the adhesive additive 100 has been applied to the substrate. The adhesive additive 100 may be applied using dip coating, printing, spraying, or other suitable techniques.

[0146] Step 70 of FIG. 2 can include the same steps as Step 70 described in relation to FIG. 1. For instance, Step 70 of FIG. 2 can include applying the composition, such as printing, that has been prepared in Steps 20 or 30 to the substrate to form a filter 200 having a graphene oxide membrane 90 provided by the composition. This may be done by a gravure printing machine including micro-gravure printing, or other techniques such as dip coating or spraying so as to form a membrane of the composition on the substrate.

[0147] Step 40 may include drying the composition which may be done in ambient conditions.

[0148] The method of FIG. 2 may optionally include Step 50 which can include a post treatment step in which the epoxide containing crosslinking additive 120, such as GLYMO, of Step 30 are activated to complete the crosslinking between the graphene oxide sheets. In one example, activation can be carried out by heating the substrate and composition on the substrate above 50? C. for at least 1 hour, and suitably to a temperature of 75? C. for at least 2 hours. In another example, a catalyst such as aluminium acetylacetonate (1 g/L in 2-propanol) can be applied to the graphene oxide membrane by dip-coating, gravure printing, microgravure printing, or rod coating. For dip-coating, a coupon of the graphene oxide membrane 200 was submerged in a bath of the catalyst solution for a period of 5 minutes, after which the membrane 200 was removed from the bath and dried at ambient temperature without washing. Step 50 of FIG. 2 can also include a permeance-enhancing step of exposing the membrane 200 to a solution of sodium hypochlorite for a period of time. For example, the membrane 200 can be submerged in a 10 g/L solution of sodium hypochlorite for a period of 30 minutes (5,000 ppm.h) to increase the permeance.

[0149] FIG. 3 is a block diagram of an embodiment for making a composition that can be applied to a substrate, such as printed, to form a graphene oxide filtration membrane 90 on a porous substrate 110. FIG. 3 has particular steps relating to the addition of diamine crosslinkers to the composition prior to the composition being applied to the substrate. Step 10 of FIG. 3 can include the same procedures described above in relation to Step 10 of FIG. 1. Ideally, the feed suspension has or is adjusted to have a graphene oxide concentration into a range of 0.1 to 15 wt %.

[0150] Step 20 of FIG. 3 can include the same procedures described above in relation to Step 20 of FIG. 1. That is Step 20 includes treating the feed suspension to create imperfections in the graphene oxide to form a composition. For instance, Step 20 can include adding an active modifying agent to the feed suspension to form a composition, and mixing the composition under elevated temperature and then reducing the temperature of the composition to stop progress of the reaction between the modifying agent and the graphene oxide so as to form a stable composition. In which case all of, or nearly all of, the modifying agent may have reacted with the graphene oxide. In addition, Step 20 of FIG. 2 can include determining whether the reaction can be stopped to form a stable composition as outline in Step 20 of FIG. 1.

[0151] For instance, Step 20 of FIG. 2 may include determining when the reaction between the modifying agent and the graphene oxide has progressed far enough by measuring, for example, any one or a combination of the viscosity of the composition, colour and colour changes of the composition, and infrared spectrum analysis of the composition. The reaction between the modifying agent and the graphene oxide may also produce a gas, such as carbon dioxide, and determining whether the reaction has progressed far enough may be determined by measuring the amount of the gas produced during the mixing step.

[0152] The composition may or may not then be treated in Step 30 of FIG. 3 to facilitate the composition being used as a printable composition using gravure printing machines including microgravure or other application methods. Step 3 may not be required depending on the inherent properties of the composition. If required, viscosity and surface tension may then be measured and adjusted in step C by adding surfactants such as Triton-available from DOW Inc. The viscosity of the composition may also be controlled by adding polyphenol and/or ethanol. Adjusting the viscosity and/or the surface tension enables the composition to be applied as a filtration membrane using high speed printing machinery, such as gravure printing or microgravure.

[0153] In addition, Step 80 of FIG. 3 can include adding crosslinking additives 120 containing diamine, such as PEI (polyethyeleneimine), prior to application of the composition to the substrate 110. Diamine crosslinkers provide stabilization to the rejection properties of the filter 200 over a broader range of pH.

[0154] Step 60 of FIG. 3 can include the same procedures described above in relation to Step 60 of FIG. 1 or 2. Specifically, step 60 can include selecting a porous substrate 110 such as a porous film including polymeric, metallic or ceramic films.

[0155] Step 70 of FIG. 3 can include modifying the substrate 110 to improve the adhesion of the graphene oxide to the porous substrate as described in relation to FIG. 1 or 2. For example, an adhesive additive 100, such as either one or a combination of polyDADMAC, GOHSENXT? K and dopamine can be applied to the substrate 110 in step E, and dried. The rate at which the adhesive additive 100 dries may be increased by heating once the adhesive additive 100 has been applied to the substrate. The adhesive additive 100 may be applied using dip coating, printing, spraying, or other suitable techniques.

[0156] Step 40 of FIG. 3 can include the same steps as Step 40 described in relation to FIGS. 1 and 2. For instance, Step 40 of FIG. 2 can include printing or applying the composition prepared in step 30 to the substrate to form a filter 200 having a graphene oxide membrane 90 provided by the composition. This may be done by a gravure printing machine such as a microgravure printing machine, or other techniques such as dip coating or spraying so as to form a membrane 90 of the composition on the substrate 110. Step 40 may include drying the composition which may be done in ambient conditions.

[0157] Step 50 of FIG. 1 can include a permeance-enhancing step of exposing the membrane to a solution of sodium hypochlorite for a period of time. For example, the membrane 90 can be submerged in a 10 g/L solution of sodium hypochlorite for a period of 30 minutes (5,000 ppm.h) to increase the permeance.

[0158] FIG. 4 is a schematic cross-section view of the filter including a graphene oxide membrane 90 applied to a substrate 110. The substrate 110 can be selected in accordance with Step 60 and optionally modified in accordance with Steps 70 by applying an adhesive additive 100. The graphene oxide membrane 90 that is applied to the substrate 110 includes the suspension or composition of Step 10, and the composition may optionally be further characterised by the Steps 20 and 30. The composition applied to the substrate may include a crosslinking additive 120 which is suitably applied to a dried graphene oxide membrane 90 formed on the substrate 110 in accordance Step 50. In addition, or alternatively, the crosslinking additive 120 may be added to the composition containing the graphene oxide prior to the composition being applied to the substrate 110, such as in Steps 30 and 80.

Examples:Example 1

[0159] In this example, a composition and a filtration membrane were made in accordance with the Steps of FIG. 1. The permeance and the rejection of this filtration membrane were measured, in accordance with the membrane performance test described below, to be 14 L/m.sup.2/h/bar and 96% respectively. These measurements are included in Table 3A.

[0160] A composition containing modified graphene oxide (8.6 g/L), i.e., the GO composition, was prepared by reacting graphene oxide (10 g/L) with hydrogen peroxide (5:1 mass ratio H.sub.2O.sub.2:GO) for 6.0 hr at 90? C. in an autoclave.

[0161] A porous substrate membrane, which was commercially available under the trade name Solecta PVDF 400, was prepared by printing a thin film of GOHSENX? K onto the substrate using a microgravure printer to act as an adhesive additive. GOHSENX? K was in the form of a 50% aqueous ethanol (4.3 g/L) solution which was applied at a density of approximately 0.1 g/m.sup.2. After drying, a thin film of the modified GO composition was applied to the treated porous membrane support using a microgravure printer at a density of approximately 0.09 g/m.sup.2. The modified GO composition contained 4.3 g/L of modified graphene oxide. After drying, a thin film of crosslinking additive comprising polyDADMAC (average M.sub.w<100,000, Sigma-Aldrich product code 522376) was applied at a density of approximately 0.01 g/m.sup.2 to the graphene oxide membrane using a microgravure printer, from a 50% aqueous ethanol solution containing 5 g/L polyDADMAC.

Example 2

[0162] In this example, a composition and a filtration membrane were made in accordance with the Steps of FIG. 2. The permeance and the rejection of this filtration membrane were measured, in accordance with the membrane performance test described below, to be 27 L/m.sup.2/h/bar and 95% respectively. These measurements are included in Table 3A.

[0163] A composition containing modified graphene oxide (8.6 g/L) was prepared by reacting graphene oxide (10 g/L) with hydrogen peroxide (5:1 mass ratio H.sub.2O.sub.2:GO) for 6.0 h at 90? C. in an autoclave. 100 mL of the modified graphene oxide suspension was diluted to 5 g/L by adding 70 mL of 2-propanol. 0.43 g of glymo, (3-glycidyloxypropyl)trimethoxysilane, was added to the diluted suspension (dropwise), while the suspension was being vigorously stirred.

[0164] A porous membrane substrate was prepared by printing a thin film of an adhesive additive comprising GOHSENX? K onto a substrate at a density of approximately 0.1 g/m.sup.2. The substrate comprised Solecta PVDF 400 and an aqueous solution of GOHSENX? K (5 g/L) was applied using a microgravure printer. After drying, a thin film of the modified graphene oxide composition was applied to the treated porous membrane substrate using a microgravure printer at a density of approximately 0.09 g/m.sup.2. After drying, the membrane was immersed in a solution of aluminium acetylacetonate (1 g/L in 2-propanol) for 5 minutes which acts as a catalyst for the glymo to form crosslinks between the graphene sheets. The membrane was then removed from the catalyst solution and dried at ambient temperature without washing.

Example 3

[0165] In this example, a composition and a filtration membrane were made in accordance with the Steps of FIG. 3. The permeance and the rejection of this filtration membrane were measured, in accordance with the membrane performance test described below, to be 34 L/m.sup.2/h/bar and 96% respectively. These measurements are included in Table 3A.

[0166] A composition containing modified graphene oxide (8.6 g/L) was prepared by reacting graphene oxide (10 g/L) with hydrogen peroxide (5:1 mass ratio H.sub.2O.sub.2:GO) for 5.5 h at 90? C. in an autoclave. Red grape skin polyphenol (5.36 g) was added to 2.92 L of the composition whilst being stirred vigorously at a rate of 6000 rpm. The polyphenol was added slowly in stages and the composition was sheared for 15 minutes. The composition was then heated to 75? C. and stirred at 100 rpm for 1 hour. A crosslinking additive comprising polyethyleneimine (PEI, branched, average M.sub.w?800, Sigma-Aldrich product code 408719) was added at a 1:16 mass ratio to the graphene oxide composition.

[0167] An adhesive additive containing a dopamine solution (2000 mg/L in 50% aqueous ethanol) was prepared, and polymerisation was initiated by adding sodium periodate (at 4000 mg/L) and the reaction occurred for 10 minutes to form a polydopamine (PDA). A porous substrate was then prepared by applying a thin film of the polymerising solution using a microgravure printer. After drying, a thin film of the composition at a density of 0.09 g/m.sup.2 was applied to the treated porous substrate using a microgravure printer.

Example 4

[0168] In this example, a composition and a filtration membrane were made in accordance with the Steps of FIG. 1.

[0169] A graphene oxide membrane can also be formed on a hollow fibre porous support, such as an ultrafiltration or microfiltration hollow fibre made of polyvinylidene fluoride, polypropylene, polyacrylonitrile, polysulphone, or ceramic.

[0170] The fibre is dipped in an adhesive additive comprising GOHSENX? K (4 g/L in 50% aqueous ethanol) for 1 minute, then dried for 1 hour in a dehydrator at 70? C. (application of adhesive).

[0171] A composition containing modified graphene oxide (8.6 g/L) was prepared by reacting graphene oxide (10 g/L) with hydrogen peroxide (5:1 mass ratio H.sub.2O.sub.2:GO) for 5.5 h at 90? C. in an autoclave, then diluting to 1 g/L graphene oxide with water. The adhesive-coated substrate was then submerged in the composition and connected to a vacuum pump. A vacuum is applied to the adhesive-coated membrane until the permeate is colourless, indicating that a graphene oxide film had formed on the fibre substrate, preventing further passage of graphene oxide. The graphene oxide-coated fibre was then dried overnight at 70? C. in a dehydrator.

[0172] A crosslinking additive was then applied to the film of graphene oxide by being dipped in a solution of polyDADMAC (5 g/L in 50% aqueous ethanol) for 1 minute, then dried for 2 hours in a dehydrator at 70? C.

[0173] The treated hollow fibre was then submerged in a solution of Rose Bengal (?200 mg/L) and a vacuum applied. The area of the fibre was unknown so the permeance could not be calculated, but the concentration of Rose Bengal in the feed and permeate showed that the rejection was 99%.

Filtration Membrane Performance Testing

[0174] We have tested the permeance and rejection of the filtration membranes mentioned in Examples 1, 2 and 3 above, and several other samples of filtration membranes that have been made in accordance with the embodiments shown in FIGS. 1, 2 and 3. Results of the tests are summarised in Tables 3A, 3B and 3C.

[0175] The testing procedure included flat samples of the filtration membranes being held in a cross-flow mode at 2 bar transmembrane pressure using Rose Bengal (4,5,6,7-tetrachloro-2,4,5,7-tetraiodofluorescein disodium salt) as the probe molecule (200-300 mg/L) at pH 9 (unless otherwise specified) using a Sterlitech CF042 cell. The membrane area was 42.1 cm.sup.2. Rejection was calculated from the concentration of Rose Bengal in the feed and the permeate according to the following equation:

[00001]$\mathrm{Rejection}=\left[1-\left(R{B}_{\mathrm{permeate}}/R{B}_{\mathrm{feed}}\right)\right]?100\%$ [0176] Where: [0177] RB.sub.feed=concentration of Rose Bengal in the feed [0178] RB.sub.permeate=concentration of Rose Bengal in the permeate

[0179] The concentration of Rose Bengal was measured by UV-visible spectrophotometry, using the Beer-Lambert Law to convert the absorbance at 549 nm to concentration in mg/L.

[0180] The flow rates of the feed and the permeate were measured gravimetrically for calculation of the permeance using the following equation:

[00002]$\mathrm{Permeance}\left(L/m^2/h/\mathrm{bar}\right)=V_{\mathrm{permeate}}/\left(A?t?P\right)$ [0181] Where: [0182] V=volume of permeate (L) [0183] A=area of membrane (in) [0184] t=time (h) during which permeate was collected [0185] P=transmembrane pressure (bar)

[0186] NaOCl post-treatment was carried out by exposing membrane coupons to a 10,000 mg/L solution of NaOCl for 30 minutes.

[0187] Chlorine resistance was evaluated by exposing membrane coupons to a solution of NaOCl at the specified pH for a period of time. For example, 10,000 ppm.h=1 hour of exposure to a 10,000 mg/L NaOCl solution. Following chlorine exposure, the membrane coupon was rinsed with deionised water and then tested using Rose Bengal as above.

TABLE-US-00004 TABLE 3A Rejection of Rose Bengal with various combinations of adhesive and cross-linker Made in Adhesive additive Crosslinking Permeance Rejection accordance Sample Substrate added to substrate additive L/m.sup.2/h/bar % with: 1a Solecta PVDF400 GOHSENX-K polyDADMAC 14 96% FIG. 1 2a Solecta PVDF400 GOHSENX-K glymo 27 95% FIG. 2 3a Solecta PVDF400 polyDADMAC glymo 23 99% FIG. 2 4a Solecta PVDF400 polyDADMAC GOHSENX-K 34 98% FIG. 1 5a Solecta PVDF400 Polydopamine (PDA) PEI 34 96% FIG. 3 6a Synder Bx GOHSENX-K polyDADMAC 12 99% FIG. 1

[0188] The measurements in Table 3A shows that the filtration membranes made in accordance with FIGS. 1, 2 and 3 with combinations of adhesive and crosslinking additives have viable rejections of equal to, or greater than 90%, and in the range from 96% to 99%. In addition, the permeance is measured to range from 12 to 34 L/m.sup.2/h/bar.

TABLE-US-00005 TABLE 3B Improved permeance after NaOCl post-treatment and maintaining high rejection Made in Adhesive additive Crosslinking Post- Permeance Rejection accordance Sample Substrate added to substrate additive treatment L/m.sup.2/h/bar % with 7a Solecta GOHSENX-K glymo None 27 95% FIG. 2 PVDF400 7b Solecta GOHSENX-K glymo NaOCl 37 99% FIG. 2 PVDF400 8a Solecta GOHSENX-K polyDADMAC None 14 96% FIG. 1 PVDF400 8b Solecta GOHSENX-K polyDADMAC NaOCl 31 94% FIG. 1 PVDF400 9a Solecta polyDADMAC glymo None 14 98% FIG. 2 PVDF400 9b Solecta polyDADMAC glymo NaOCl 20 94% FIG. 2 PVDF400 10a Synder Bx GOHSENX-K polyDADMAC None 12 99% FIG. 1 10b Synder Bx GOHSENX-K polyDADMAC NaOCl 35 93% FIG. 1

[0189] Table 3B includes measurements that compare the filtration membranes without a post treatment and filtration membranes that include a bleach post treatment. The combinations of substrate, adhesive additive and crosslinking additive show that the filtration membranes were resistant to the chlorine in the bleach post treatment, whilst maintaining viable rejection rates of greater than 90%. In addition, the bleach post treatment was shown to increase the permeance of the filtration membranes.

TABLE-US-00006 TABLE 3C Stable performance across pH range when cross-linker is included in membrane Made in Adhesive Crosslinking Permeance Rejection accordance Sample Substratet additive additive pH L/m.sup.2/h/bar % with 11a Solecta Polydopamine None 4 9 96% FIG. 3 PVDF400 (PDA) 11b Solecta Polydopamine None 7 14 85% FIG. 3 PVDF400 (PDA) 11c Solecta Polydopamine None 9 28 45% FIG. 3 PVDF400 (PDA) 12a Solecta Polydopamine PEI 4 28 98% FIG. 3 PVDF400 (PDA) 12b Solecta Polydopamine PEI 7 28 98% FIG. 3 PVDF400 (PDA) 12c Solecta Polydopamine PEI 9 33 97% FIG. 3 PVDF400 (PDA)

[0190] Samples 11a, 11b and 11c were made in accordance with one of the embodiments shown in FIG. 3, in which no crosslinking additive was added to the composition and no crosslinking additive was applied to the graphene oxide membrane. Moreover, the results show that the filtration membranes of the samples 11a to 11c were suspectable to swelling with changes in pH which caused both the permeance and rejection to fluctuate considerably. However, the inclusion of crosslinking additive PEI, in samples 12a, 12b and 12c stabilised rejection and permeance of these samples.

[0191] Table 4 includes samples 17 to 23 of membranes that were prepared in accordance with the procedure outlined in Example 1 and FIG. 1 and tested for pH resistance. The membranes were prepared by coating a porous substrate comprising PVDF from TOMAC Corporation (Japan) with an adhesive additive comprising a GOHSENX? K aqueous solution. A thin film of the adhesive additive, at a density of approximately 0.1 g/m.sup.2, was applied to the substrate using a microgravure printer and dried. A thin film of the graphene oxide composition was then applied at a density of approximately 0.09 g/m.sup.2 using a microgravure printer. The membranes were then dip coated with aqueous solutions of various crosslinking additives as shown in Table 4 at a density of approximately 0.001 g/m.sup.2, and the permeance and rejection of the membranes were tested under particular pH conditions. No crosslinking additive was added to sample 24 which provided a Control.

[0192] The membranes were tested for pH resistance in the cross-flow apparatus Sterlitech CF042, using a solution of Rose Bengal, at pH 4, pH 7 and pH 10. The permeance and the rejection were measured. The data set out in Table 4 shows that all of the cationic polymers tested as crosslinking additives produced membranes with higher rejection than the Control that had no crosslinking additive at each of the pH values. That is to say, the crosslinking additives had a pronounced effect on the ability of the membranes to continue to perform under various pH conditions, specifically from pH values ranging from 4 to 10. The difference was most pronounced at pH 10, which is indicative of layers of the graphene oxide sheets swelling, which decreases rejection. The permeance increased as the rejection decreased.

TABLE-US-00007 TABLE 4 Crosslinking additive Conc Permeance (L/m.sup.2/h/bar) Rejection (%) Sample Trade name Class (g/L) pH 4 pH 7 pH 10 pH 4 pH 7 pH 10 13 SINOFLOC 680* Cationic 1 6.7 8.1 10.9 96.3% 95.0% 91.9% polyacrylamide 14 Polyquaternium-2* Cationic poly urea- 5 6.9 8.6 10.0 99.3% 99.1% 98.4% ammonium-ether 15 Hydroflux HB-2705* Cationic 1 9.0 10.4 12.9 98.6% 97.9% 95.8% polyacrylamide 16 Polyquaternium-10* Cationic hydroxyethyl 1 11.0 13.7 16.3 95.8% 92.9% 76.7% cellulose 17 Jaguar Optima* Cationic guar 1 11.6 16.1 19.8 91.9% 86.4% 65.5% 18 Polyquaternium-6* Cationic polyDADMAC 5 13.7 17.5 25.1 99.5% 99.1% 98.8% 19 PEI Polyamine 5 9.8 12.8 17.6 98.7% 97.6% 95.7% 20 N/A Control n/a- 15.8 18.8 34.3 90.0% 62.1% 36.1% *indicates quaternary functionality

[0193] In summary, when the crosslinking additive is a cationic polymer, and is preferably one selected from a group consisting of: Cationic polyacrylamide, Cationic poly urea-ammonium-ether, Cationic polyacrylamide, Cationic hydroxyethyl cellulose, Cationic guar, Cationic polyDADMAC, or is a polyamine, the filter has a rejection value greater than 90% under acid conditions. For the same crosslinking additives, the filter has a rejection value greater than 90% under alkaline conditions.

[0194] In addition, when the crosslinking additive is a cationic polymer, and is preferably one selected from a group consisting of: Cationic polyacrylamide, Cationic poly urea-ammonium-ether, Cationic polyacrylamide, Cationic hydroxyethyl cellulose, Cationic guar, Cationic polyDADMAC, or is a polyamine, the filter has a permeance value (L/m.sup.2/h/bar) less than 15.8 under acidic conditions, and preferably a permeance value in the range of 6.7 to 13.7. For the same crosslinking additives, the filter has a permeance value (L/m.sup.2/h/bar) less than 34.4 under alkaline conditions, and preferably a permeance value in the range of 10.0 to 25.1 under alkaline conditions.

[0195] Samples 21 to 27 of a filter were prepared in accordance with Example 1 and FIGS. 1, and a Control, sample 28, was also tested for chlorine resistance. A First set of the samples 21 to 27 were treated with a solution of sodium hypochlorite (5 g/L) at pH 4 or at pH of 10 for 2 hours, that is 10,000 ppm.h of NaOCl. The membranes were then rinsed with deionised water to remove residual NaOCl, and then tested in the cross-flow apparatus using a solution of Rose Bengal, at pH 4 and pH 10. For comparison, another set of the membranes, namely the Second Set of samples 21 to 27 were made in accordance with Example 1 and FIG. 1, and Control 24 was prepared and tested without being exposed to chlorine, that is 0 ppm.h of NaOCl. The permeance and rejection of the Second Set of samples 21 to 27 were tested in the cross-flow apparatus using a solution of Rose Bengal at pH 4 and pH 10.

[0196] Table 5 comprises performance data of the First and Second Sets of samples 21 to 28 at a pH of 10. The data of the samples having a cationic polymer as crosslinking additive produced membranes with higher rejection than the Control which had no crosslinking additive after exposure to chlorine, such as sodium hypochlorite. The data also showed that the membranes having cationic polymers with quaternary ammonium groups as crosslinking additives produced membranes with improved resistance to degradation by chlorine. Specifically, the first set of samples 1 to 13 had permeance values after exposure to 10,000 ppm.h of NaOCl ranging from 13.7 to 29.8 (L/m.sup.2/h/bar) when measured using the probe molecule Rose Bengal in the cross-flow apparatus at a pH of approximately 10, i.e. under alkaline conditions. Under alkaline conditions, i.e. a pH of approximately 10, the rejection was greater than 90% with a cross linking additive selected from cationic polyacrylamide, Cationic poly urea-ammonium-ether, Cationic polyacrylamide, polyDADMAC. By comparison, the permeance of the second set of samples 21 to 28 which were not exposed to chlorine had a permeance values ranging from 10.9 to 25.1 (L/m.sup.2/h/bar). That is to say, the permeance, of the membranes, after exposure to 10,000 ppm.h of NaOCl increased in range from 2.8 to 5.3 (L/m.sup.2/h/bar) according to the Rose Bengal cross flow under alkaline conditions, whilst rejection ranged from 45.1% to 98.5%, and suitably 61.8% to 98.5%, and even more suitably from 90% to 98.5%.

TABLE-US-00008 TABLE 5 Chlorine resistance of membranes with quaternary ammonium crosslinkers at pH 10 Second Set of samples First Set of samples Filtration at pH 10 after Filtration at pH 10 after Crosslinking additive 0 ppm .Math. h 10,000 ppm .Math. h Sample Conc Permeance Rejection Permeance Rejection numbers Trade name Class/Description (g/L) (L/m.sup.2/h/bar) % (L/m.sup.2/h/bar) % 21 SINOFLOC 680* Cationic polyacrylamide 1 10.9 91.9% 13.7 90.7% 22 Polyquaternium-2* Cationic poly urea- 5 10.0 98.4% 14.1 93.2% ammonium-ether 23 Hydroflux HB-2705* Cationic polyacrylamide 1 12.9 98.4% 16.3 91.6% 24 Polyquaternium-10* Cationic hydroxyethyl 1 16.3 76.7% 19.7 61.8% cellulose 25 Jaguar Optima* Cationic guar 1 19.8 65.5% 25.1 45.1% 26 Polyquaternium-6* Cationic polyDADMAC 5 25.1 98.8% 29.8 98.5% 27 PEI Polyamine 5 17.6 95.7% 49.1 19.3% 28 None Control 34.3 36.1% 51.3 20.5% *indicates quaternary functionality

[0197] In summary, when the crosslinking additive is a cationic polymer selected from cationic polyacrylamide, cationic poly urea-ammonium-ether, cationic hydroxyethyl cellulose, cationic guar and cationic polyDADMAC, and when exposed to 10,000 ppm.h of chlorine, the filter has rejection values ranging from 90% to 98.5% under alkaline conditions. In this instance, the filter has permeance values ranging from 13.7 to 29.8 (L/m.sup.2/h/bar) when measured using the probe molecule Rose Bengal in the cross-flow apparatus.

[0198] When the filter has a crosslinking additive including a cationic polymer and an adhesive additive including GOHSENX-K?, and when exposed to 10,000 ppm.h of chlorine, the filter has a permeance value ranging from 13.7 to 29.8 L/m2/h/bar and a rejection value ranging from 90.7% to 98.5% under alkaline conditions.

[0199] Table 6 comprises performance data at pH of 4. The data of the samples having a cationic polymer as crosslinking additive produced membranes with higher rejection than the Control which had no crosslinking additive after exposure to chlorine, such as sodium hypochlorite. The data also showed that the membranes having cationic polymers with quaternary ammonium groups as crosslinking additives produced membranes with improved resistance to degradation by chlorine. Specifically the two far right columns show that permeance values after exposure to 10,000 ppm.h of NaOCl range from 11.0 to 23.8 (L/m.sup.2/h/bar) when measured using the probe molecule Rose Bengal in the cross-flow apparatus at a pH of approximately 4, i.e. under acidic conditions. By comparison, the permeance of the Second set of samples 21 to 28, which had not been exposed to chlorine, had permeance values ranging from 10.9 to 25.1 (L/m.sup.2/h/bar). The permeance values of the membranes after exposure to 10,000 ppm.h of NaOCl increased by an amount of equal to or less than 10.1 (L/m.sup.2/h/bar), and suitably less than 5.0, and suitably by an amount in the range of 1.1 to 4.8 (L/m.sup.2/h/bar) according to the Rose Bengal cross flow under acid conditions and rejection values range from 86.9% to 99.2%, and suitably 90% to 99%, and even more suitably from 90% to 97%, and even more suitably still form 90% to 95%.

TABLE-US-00009 TABLE 6 Chlorine resistant or membranes with quaternary ammonium cationic crosslinkers at pH 4 Second Set of samples First Set of samples Filtration at pH 4 after Filtration at pH 4 after Crosslinking additive 0 ppm .Math. h 10,000 ppm .Math. h Sample Conc Permeance Rejection Permeance Rejection number Trade name Class/Description (g/L) (L/m.sup.2/h/bar) % (L/m.sup.2/h/bar) % 21 SINOFLOC 680* Cationic polyacrylamide 1 6.7 96.3% 11.3 93.3% 22 Polyquaternium-2* Cationic poly urea- 5 6.9 99.3% 11.0 95.0% ammonium-ether 23 Hydroflux HB-2705* Cationic polyacrylamide 1 9.0 98.6% 13.8 93.9% 24 Polyquaternium-10* Cationic hydroxyethyl 1 11.0 95.8% 12.1 90.9% cellulose 25 Jaguar Optima* Cationic guar 1 11.6 91.9% 13.7 86.9% 26 Polyquaternium-6* Cationic polyDADMAC 5 13.7 99.5% 23.8 99.2% 27 PEI Polyamine 5 9.8 98.7% 14.5 87.8% 28 None Control 15.8 90.0% 20.2 88.2% *indicates quaternary functionality

[0200] In summary, the crosslinking additive is a cationic polymer selected from cationic polyacrylamide, cationic poly urea-ammonium-ether, Cationic hydroxyethyl cellulose, Cationic guar, and cationic polyDADMAC, and when exposed to 10,000 ppm.h of chlorine, the filter has rejection value ranging from 86.9% to 99.2% under acid conditions.

[0201] When the cross linking additive is selected from cationic polyacrylamide, cationic poly urea-ammonium-ether, Cationic hydroxyethyl cellulose, and cationic polyDADMAC, and when exposed to 10,000 ppm.h of chlorine the filter has rejection values greater than 90% to 99.2, under acid conditions. The filter has permeance values ranging from 11.0 to 23.8 (L/m.sup.2/h/bar) when measured using the probe molecule Rose Bengal in the cross-flow apparatus.

[0202] When the filter has a crosslinking additive including a cationic polymer and an adhesive additive including GOHSENXT? K, and when exposed to 10,000 ppm.h of chlorine, the filter has a permeance value ranging from 11.0 to 23.8 L/m2/h/bar and a rejection value ranging from 86.6% to 99.5% under acidic conditions

[0203] When the filter has a crosslinking additive including a diamine polymer with at least two reactive amine groups, and an adhesive additive for adhering the membrane to the porous substrate and the adhesive additive includes GOHSENX? K, and when exposed to 10,000 ppm.h of chlorine, the filter has a rejection value of at least 85%, and suitably a rejection in the range of 85% to 88% and a permeance value ranging from 13 to 15 L/m2/h/bar, and suitably a permeance value of approximately 14.5 L/m2/h/bar under acid conditions.

[0204] In addition, the composition prepared in accordance with Example 1 and FIG. 1 was also prepared to determine the point at which the reaction between a modifying and the graphene oxide sheets had progressed sufficiently far enough so the temperature of the composition can be reduced to form a stable composition. That is to say, all of, or nearly all of, the modifying agent had reacted with the graphene oxide sheets.

[0205] The procedure included adding i) 2.5L of graphene oxide at a concentration of 10 g/L and ii) 420 mL of H.sub.2O.sub.2 at a concentration of 30 wt % to an autoclave which was stirred at 500 rpm and heated up to 90? C. at 0.8? C./min, and then held at 90? C. for 7 hours. Once the temperature reached 90? C., samples of the composition was withdrawn at time equals zero hrs. At this point, there had been no appreciable reaction between the graphene oxide and the modifying agent and graphene oxide is regarded as unmodified. Samples of the composition were withdrawn at one hour intervals until the reaction was stopped after 7 hours by turning off the heater and turning on the chiller.

[0206] The viscosity of the samples was measured at 20? C. using a Brookfield LVT viscometer. Due to the shear thinning nature of the graphene oxide composition, the reported viscosity is the apparent viscosity at a shear rate of 30 rpm.

[0207] Filter membranes were then prepared using the samples of the composition in accordance with Example 1 and FIG. 1 and are labelled as Samples 29 to 36 in Table 7 below. Filter membranes were prepared using TOMAC PVDF for the porous substrate, GOHSENXT? K for the adhesive additive and polyDADMAC for the crosslinking additive. The Samples 29 to 36 comprised coupons of 42.1 cm.sup.2 in area and the permeance and rejection of each were tested using a 300 ppm solution of Rose Bengal in a cross-flow apparatus operating at 2 bar.

TABLE-US-00010 TABLE 7 Apparent viscosity of unmodified and modified graphene oxide composition and performance of membranes prepared therefrom Reaction Apparent time viscosity Rejection Permeance Sample hr mPa .Math. s % L/m.sup.2/h/bar 29 0 104 96.4% 6.5 30 1 830 99.5% 9.6 31 2 1800 N/A N/A 32 3 1160 99.8% 8.6 33 4 470 97.1% 17.8 34 5 170 95.5% 17.8 35 6 30 96.2% 17.8 36 7 <30 95.9% 16.9

[0208] Table 7 shows that the viscosity increases as the reaction proceeds, up to a maximum after 2 hours of reaction time and thereafter the viscosity decreases. The data shows that a functioning membrane can be produced from any of samples 25 to 32, each having a rejection of Rose Bengal greater than 90%. That is to say, a stable composition was obtained for each. In addition, for the filter to have an increased permeance, the viscosity of the composition has ideally reached and passed a maximum viscosity. A maximum in the viscosity occurred somewhere in between 1 and 3 hours. For instance, a total reaction time of 4, 5, 6 and 7 hrs is preferrable. In other words, the modifying step was carried out for at least 1 to 5 hours after a maximum in the viscosity of the composition has occurred. Suitably, the modifying step was carried out for at least 2 to 4 hours after a maximum in the viscosity of the composition has occurred. In the case of sample 27, the high viscosity of the composition prevented the composition from being printed onto the substrate

[0209] The method of making the composition and/or filtration membrane may include optional steps such as the following.

Optional Steps/Features

[0210] This step involves adding and mixing a reducing solution with the GO composition. Specifically, a reducing solution containing an amount of red grape skin polyphenol equal to 25% of the GO mass in the composition can be measured and added to the composition whilst the composition is being mixed/sheared. Typically, 5.36 g of polyphenol is added to the 2.917 L of the composition while stirring vigorously at a rate of 6000 rpm. The polyphenol is added slowly in stages and the composition is mixed for 15 minutes or until the composition is homogeneous and a desired viscosity is achieved.

[0211] The composition was then heated to 75? C. and stirred at 100 rpm for 1 hour.

[0212] To provide a composition that is conducive to printing, an organic solvent can be added. For example, 100 mL of a graphene oxide composition containing 8.57 g/L of graphene oxide was mixed with 100 mL of ethanol to form a 50% aqueous ethanol suspension. This resulted in changes to viscosity and surface tension that improved the application of the graphene oxide to the porous substrate.

[0213] Finally, fine control of the permeance of the substrate was carried out with a NaOCl treatment. Specifically, setting the permeance may include treating the filtration membrane by submerging the substrate in a solution of NaOCl for a period. For example, submerging the substrate in a solution of 10,000 mg/L NaOCl for period of 30 minutes, increased the permeance of a PVDF-GO membrane e.g. from 20 to 30 L/m.sup.2/hr/bar.

[0214] Those skilled in the art of the present invention will appreciate that many variations and modification can be made to the example described herein without departing from the spirit and scope of the present invention.

[0215] In the claim which follows, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.