WO2018138486A1

WO2018138486A1 - Membrane

Info

Publication number: WO2018138486A1
Application number: PCT/GB2018/050189
Authority: WO
Inventors: Tim Harper; Miao Yu
Original assignee: G2O Water Technologies Limited
Priority date: 2017-01-27
Filing date: 2018-01-23
Publication date: 2018-08-02
Also published as: WO2018138486A8; GB201701406D0

Abstract

There is described acomposite membrane. The composite membrane is formed of a porous support and a polyamide layer on the support. The polyamide layer comprises graphene oxide quantum dot (GOQD) moieties. The membranes are especially useful for the desalination or salt water.

Description

MEMBRANE

FIELD

[01 ] The present invention relates to a composite membrane. More specifically, the present invention relates to a reverse osmosis thin film nanocomposite membrane.

BACKGROUND

[02] The availability of clean water resources is a growing issue despite the presence of a large amount of sea water on the earth. Sea water desalination, therefore, represents a viable solution to provide usable water for daily life and industrial processes.

[03] Owing to its high energy efficiency, reverse osmosis has become a widely applied desalination technology. Moreover, reverse osmosis can be simple to design compared to other types of desalination processes and can produce high quality clean water.

[04] In reverse osmosis, a liquid, typically water, moves from a solution having a relatively high solute concentration to a solution having a relatively low solute concentration by passing through a membrane. In order to act against osmotic pressure an external pressure having a pressure level higher than an osmotic pressure level must be applied. In this manner, water may be separated from various ions, bacteria and organic materials.

[05] To achieve the desired water quality in an efficient manner, it is desirable that a reverse osmosis membrane can provide a high level of water permeability at low levels of pressure. It is also important that the membrane has a high salt rejection rate at the boundary of a membrane. The membrane should also show good structural integrity, in particular at high temperature.

[06] Thin film composite (TFC) membranes containing two or more layered materials are currently considered to be a favourable type of reverse osmosis membrane. TFC membranes are typically formed of a polymeric layer arranged over a porous support. One type of TFC membrane are polyamide composite membranes fabricated by interfacial polymerization. Interfacial polymerisation involves dipping the support in an aqueous solution of a multifunctional amine then coat it with an non-polar organic solution of an amine-reactive reactant, such as trimesoyi chloride (TMC) such that the multifunctional amine layer contacts the amine-reactive reactant and is thereby polymerized at an interface between the non-polar organic solution and the polar aqueous solution to form the polyamide layer.

[07] Nanoadditives have been added to the polyamide TFC membranes in an attempt to improve the permeability and stability properties of the membranes. Membranes containing such additives are known as thin film nanocomposite (TFN) membranes. For example, additives including inorganic nanoparticles, such as zeolite (M. Fathizadeh, et. al. J. Membrane Sci., 201 1 , 375, 88-95); titanium dioxide (Ti0₂) (S. Y. Lee, et. al. Polymer. Adv. Tech., 2007, 18, 562-568); silicon dioxide (Si0₂) (G. L. Jadav, et. al. J. Colloid. Interf. Sci., 2010, 351 , 304-314); functionalized carbon nanotube (S. Inukai, et. al., Sci. Rep., 2015, 5); graphene oxide (GO) (J. Yin, et. al. Desalination, 2016, 379, 93-101 , S. J. Xia, et. al., Chem. Eng. J., 2015, 280, 720- 727); and reduced GO (rGO) (M. Safarpour, et. al., J. Membrane Sci., 2015, 489, 43-54, and H. R. Chae, et. al. J. Membrane Sci., 2015, 483, 128-135) have been tested.

[08] There is a desire to still further improve the properties of reverse osmosis composite membranes. In particular, increasing in the permeability is desirable to further improve the efficiency of the membrane by enabling more water to be separated without being required to increase the pressure and therefore energy expenditure. To provide a high standard of clean water it is also desirable that an increase in water permeability is not at the expense of a high level of salt rejection or the stability of the membrane. Furthermore, the use of additives can increase the complexity of the manufacturing process. As such, it is also desirable to provide an improved composite membrane without significantly increasing the difficulty of existing manufacturing processes.

[09] It is therefore an object of aspects of the present invention to address one or more of the above mentioned or other problems.

SUMMARY

[10] According to a first aspect of the present invention there is provided a composite membrane comprising:

(i) a porous support; and

(ii) a polyamide layer on the support;

wherein the polyamide layer comprises graphene oxide quantum dot (GOQD) moieties.

[1 1 ] According to a second aspect of the present invention there is provided a composite membrane comprising

(i) porous support; and

(ii) a polyamide layer on the support;

wherein the polyamide layer comprises graphene oxide quantum dot (GOQD) residues;

and wherein the composite membrane is a reaction product of:

(a) a solution of a multifunctional amine-reactive reactant in an organic solvent contacted with an aqueous dispersion on a porous support; wherein the aqueous dispersion comprises a multifunctional amine and GOQD particles; and

(b) drying of the product of step (a).

[12] According to a third aspect of the present invention there is provided a method of preparing a composite membrane comprising the steps of: (a) contacting a solution of a multifunctional amine-reactive reactant in an organic solvent with an aqueous dispersion on a porous support, wherein the aqueous dispersion comprises a multifunctional amine and GOQD particles; and

(b) drying the product of step (a) to form the composite membrane.

[13] According to a fourth aspect of the present invention there is provided the use of graphene oxide quantum dot (GOQD) particles in a polyamide composition, suitably in a polyamide composite membrane.

[14] According to a fifth aspect of the present invention, there is provided a water treatment module comprising at least one membrane according to the first or second aspect of the present invention.

[15] According to an sixth aspect of the present invention there is provided a water treatment device comprising at least one or more water treatment modules according to the fifth aspect of the present invention.

[16] The composite membrane of any aspect of the present invention is typically a thin film nanocomposite (TFN) membrane. Preferably, the composite membrane of any aspect of the present invention is a reverse osmosis thin film nanocomposite membrane.

[17] The support may comprise pore sizes that are of sufficient size to permit the passage of permeate but not so large that the polyamide layer become ineffective. For example, if the pores are too large the polyamide layer can sag into the pores, affecting the performance of polyamide layer. The support is typically a microporous membrane or an ultrafiltration membrane, preferable an ultrafiltration membrane. The pore size of the support may range from 1 to 500nm, such as between 2 and 400nm, 3 and 300nm, 4 and 200nm, 5 and 100nm, 6 and 75nm, 7 and 50nm, 8 and 40nm or 9 and 35nm or 10 and 30nm.

[18] The support may have any suitable thickness. The thickness of the support may be between 25 to 125 μηι, such as between 30 and 100μηι, between 35 and 85μηι preferably between 40 to 75 μηι.

[19] The support may comprise a polymer material. The polymer material may be selected from the group consisting of polysulfone; polyethersulfone; polycarbonate; polyethylene oxide; polyimide; polyetherimide; polyether ether ketone; polyethylene; polypropylene; polymethylpentene; poly(methyl methacrylate); polymethyl chloride; halogenated polymers, such as polyvinylidene fluoride; or combinations thereof. Preferably, the polymer material is polysulfone.

[20] Suitably, the support is formed of a layer of a polymer material on a fabric, such as a non- woven fabric. The fabric may be polyester. [21 ] For the avoidance of doubt, the polyamide layer is on the support such that the membrane comprises pores extending through the membrane. The polyamide layer of the membrane may have a thickness of 50 to 1000nm, such as 100 to 900nm, 130 to 800nm, 150 to 700nm, 160 to 600nm, 170 to 500nm, 180 to 400nm, 190 to 350nm or 200 to 300nm, such as 220 to 280nm.

[22] According to a further aspect of the present invention there is provided a polyamide composition comprising GOQD moieties.

[23] The moieties of the GOQD may be in the form of GQOD particles or residues of GOQD particles.

[24] The polyamide layer or polyamide composition typically comprises GOQD moieties arranged in the polyamide layer. Preferably, the GOQD residues are covalently bonded to the polyamide layer. Preferably, the polyamide layer is formed of polymerised residues of a multifunctional amine, a multifunctional amine-reactive reactant and GOQD particles, suitably of residues of a multifunctional amine, a multifunctional amine-reactive reactant and GOQD particles, wherein the multifunctional amine, multifunctional amine-reactive reactant and GOQD particles have been polymerised by interfacial polymerisation.

[25] The GOQD particles or residues may be present in the polyamide layer or composition in an amount of between 0.05 and 5wt%, such as between 0.1 and 4 wt% or between 0.2 and 3.5wt% or between 0.25 and 3wt% or between 0.3 and 2.5wt%, or between 0.35 and 2 wt%, such as 0.4 and 1 .9wt%, 0.45 and 1 .8wt%, 0.5 and 1 .7wt%, 0.55 and 1 .6wt% or 0.60 and 1 .5wt%, or 0.65 andl .4wt% or 0.7 and 1 .3wt%.

[26] The multifunctional amine-reactive reactant may be present in the polyamide layer or composition in an amount of between 0.5 and 20wt%, such as between 1 and 10wt%, between 1 .5 and 9.5wt%, 1 .5 and 9wt%, 2 and 8.5wt%, 2.5 and 8wt%, 3 and 7.5wt%, 3.5 and 7wt%, 4 and 6.5wt%, or 4.5 and 6wt%.

[27] The multifunctional amine may be present in the polyamide layer or composition in an amount of between 75 and 99.45wt%, such as between 86 and 98.9wt%, between 87 and 98.3wt%, 88 and 98wt%, 89 and 97.5wt%, 89.5 and 97wt%, 90 and 96.5wt%, 90.5 and 96wt%, 91 and 95.5wt%, or 91 .5 and 95wt%.

[28] The multifunctional amine is operable to polymerise with the multifunctional amine- reactive reactant, and preferably with the GOQD particles. The multifunctional amine may be a monomeric amine. The multifunctional amine may be a single type of multifunctional amine or a combination of thereof.

[29] The multifunctional amine may be selected from aromatic amines, aliphatic amines, and mixtures thereof. [30] The multifunctional amine is preferably an aromatic amine, more preferably an aromatic diamine or triamine. In such an embodiment, the multifunctional amine may be selected from the group consisting of Ν,Ν'-diphenylethylene diamine, benzidine, and xylylene diamine or a multifunctional aromatic diamine or triamine according to formula I, and mixtures thereof, preferably the multifunctional amine is selected from an amine according to formula I:

Formula I

wherein two or three of R to R⁶ are NR⁷R⁸;

R to R⁶ that are not NR⁷R⁸ are independently selected from hydrogen; halogen, such as chloride or fluoride; Cr^aliphatic; C1 - ₅heteroaliphatic; or hydroxyl, such as hydrogen, chloride, Cr^alkoxy, hydroxyl-substituted Cr^alkyl, or hydroxyl; preferably hydrogen; and

for each of R to R⁶ that is NR⁷R⁸ then R⁷ and R⁸ are independently selected from a group consisting of hydrogen, Cr^aliphatic, Cr^heteroaliphatic, C₆-C ₄aryl, and C₆- C ₄heteroaryl, such as hydrogen, Cr^alkyl, C₂-i₂alkenyl, C₂-i₂alkynyl, C₃-₈alicyclic, and C₆. ₀aryl, preferably hydrogen.

[31 ] The multifunctional amine according to formula I may be selected from the group consisting of m-phenylenediamine, p-phenylenediamine, 1 ,3,6-benzene triamine, 4-chloro-1 ,3- phenylenediamine, 6-chloro-1 ,3-phenylenediamine, 3-chloro-1 ,4-phenylenediamine, N,N- dimethyl-1 ,3-phenylenediamine, and mixtures thereof.

[32] Suitably, the multifunctional amine according to formula I is a primary amine wherein R⁷ and R⁸ are hydrogen for each R to R⁶ group that is NR⁷R⁸. As such, the multifunctional amine according to formula I may be selected from the group consisting of m-phenylenediamine, p- phenylenediamine, 1 ,3,6-benzene triamine, 4-chloro-1 ,3-phenylenediamine, 6-chloro-1 ,3- phenylenediamine, 3-chloro-1 ,4-phenylenediamine, and mixtures thereof.

[33] More preferably the multifunctional amine according to formula I is a primary diamine wherein R⁷ and R⁸ are hydrogen for each R to R⁶ group that is NR⁷R⁸ and two of R to R⁶ are NR⁷R⁸, such as R and R³ or R and R⁴. In such an embodiment, the multifunctional amine may be selected from the group consisting of m-phenylenediamine, p-phenylenediamine, 4-chloro- 1 ,3-phenylenediamine, 6-chloro-1 ,3-phenylenediamine, 3-chloro-1 ,4-phenylenediamine, and mixtures thereof.

[34] Still more preferably the multifunctional amine according to formula I is a primary diamine wherein R and R³ are NR⁷R⁸ and R⁷ and R⁸ are hydrogen. As such, more preferably, the multifunctional amine is selected from the group consisting of m-phenylenediamine, 4-chloro- 1 ,3-phenylenediamine, 6-chloro-1 ,3-phenylenediamine, and mixtures thereof. Most preferably, the multifunctional amine is m-phenylenediamine.

[35] The multifunctional amine-reactive reactant is operable to polymerise with the multifunctional amine, and preferably with the GOQD particles. The multifunctional amine- reactive reactant may be a monomer. The multifunctional amine-reactive reactant may be a single type of multifunctional amine-reactive reactant or a combination thereof. The multifunctional amine-reactive reactant may be selected from one or more of the group consisting of a multifunctional acyl halide, a multifunctional sulfonyl halide and a multifunctional isocyanate. Suitably, the multifunctional amine-reactive reactant is a multifunctional acyl halide, preferably an aromatic multifunctional acyl halide, more preferably an aromatic di- or tricarboxylic acid halide, for example selected from the group consisting of trimesoyi chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride (TPC), and combinations thereof. Most preferably, the multifunctional amine-reactive reactant is an aromatic tricarboxylic acid halide, suitably trimesoyi chloride (TMC).

[36] The GOQD particles, residues or moieties according to any aspect of the present invention may have a diameter of between 1 to 100nm, such as between 1 to 75nm, 1 to 50nm, 1 to 40nm, 1 to 30nm, 1 to 25nm, 2 to 20nm, 3 to 20nm, or 4 to 15nm, preferably 5 to 10nm. Suitably, the size distribution of the GOQD particles, residues or moieties is such that at least 30wt% of the GOQD particles, residues or moieties have a diameter of between 1 to 100nm, such as between 1 to 75nm, 1 to 50nm, 1 to 40nm, 1 to 30nm, 1 to 25nm, 2 to 20nm, 3 to 20nm, or 4 to 15nm, preferably 5 to 10nm, more preferably at least 40wt%, 50wt%, 60wt%, 70wt% and most preferably at least 80wt% or at least 90wt% or 95wt% or 98wt% or 99wt%. The diameter of the GOQD particles, residues or moieties and size distribution may be measured using transmission electron microscopy (TEM, JEM-2100F, JEOL Ltd. Japan).

[37] The GOQD particles, residues or moieties may be formed of single, two or few layers of graphene oxide, wherein few may be define as between 3 and 10 layers. Suitably, the GOQD particles, residues or moieties comprise between 1 to 8 layers, such as between 2 to 6 layers or 3 to 5 layers. Suitably, at least 30wt% of the GOQD particles, residues or moieties comprise between 1 to 8 layers, such as between 2 to 6 layers or 3 to 5 layers, more preferably at least 40wt%, 50wt%, 60wt%, 70wt% and most preferably at least 80wt% or at least 90wt% or 95wt% or 98wt% or 99wt%. The number of layers in a GOQD particle, residue or moiety may be measured using Atomic Force Microscopy (AFM or transmission electron microscopy (TEM)) (TT-AFM, AFM workshop Co., CA, USA).

[38] Suitably, the d-spacing between adjacent lattice planes in the GOQD particles, residues or moieties is between 1 to 10A, such as between 2 and 8A, between 2.5 and 6A or 3 and 5A.

[39] Preferably, the GOQD particles, residues or moieties of any aspect of the present invention are nitrogen-doped GOQD (NGOQD).

[40] The nitrogen groups of the NGOQD particles, residues or moieties may be in the form of amine groups such as nitrogen-containing heterocyclic groups and/or primary amines. Typically, the NGOQD particles, residues or moieties comprise nitrogen-containing heterocyclic groups, suitably nitrogen-containing heterocyclic groups in the graphene moiety of the NGOQD particles, residues or moiety. As such, preferably the NGOQD particles, residues or moiety comprise nitrogen-containing heterocyclic groups covalently bonded to at least two, typically at least three or four, cyclohexyl groups or other nitrogen-containing heterocyclic groups; and/or nitrogen-containing heterocyclic groups wherein the nitrogen is a tertiary nitrogen. Said nitrogen-containing heterocyclic groups may comprise pyrrole and/or pyridine residues.

[41 ] The oxide groups of the GOQS particles, residues or moiety may be in the form of carboxylic acid groups; hydroxyl groups; and/or epoxide groups, suitably at least carboxylic acid groups.

[42] Typically, the nitrogen and/or oxide groups of the GOQD particles, residues or moiety are operable to form covalent bonds with the multifunctional amine and/or multifunctional amine reactive reactant, suitably in an interfacial polymerisation reaction. More preferably, the NGOQD particles, residues or moiety comprise at least one oxide group that is operable to form covalent bonds with the multifunctional amine and at least one amine group that is operable to form covalent bonds with the multifunctional amine reactive reactant. Suitably, the amine and oxide groups are selected from primary amines; carboxylic acid groups; hydroxyl groups; and/or epoxide groups. Preferably, primary amines and carboxylic acid groups.

[43] Typically, the GOQD particles, or optionally the moieties, are operable to crosslink the polyamide chains of the polyamide resin. As such, preferably the GOQD residues or, optionally, the moieties, are crosslinkers such that they crosslink the polyamide chains of the polyamide resin. Accordingly, preferably, the GOQD particles comprises at least three, preferably, at least four, five or six, groups selected from amine and/or oxide groups operable to form covalent bonds with the multifunctional amine and with the multifunctional amine reactive reactant, suitably at least four, five or six, groups selected from primary amine and carboxylic acid groups. [44] The nitrogen-doped graphene oxide quantum dot particles, residues or moieties of any aspect of the present invention may be a reaction product of heating an aqueous solution comprising citric acid and ammonia.

[45] According to a seventh aspect of the present invention there is provided a method for preparing nitrogen-doped graphene oxide quantum dot particles, comprising the steps of:

(a) forming an aqueous solution comprising citric acid and ammonia

(b) heating the aqueous solution of step (a) to form nitrogen-doped graphene oxide quantum dot particles.

[46] The concentration of citric acid in the aqueous solution may be between 20 and 140 mg/ml, such as 30 and 130 mg/ml, 40 and 120 mg/ml, 50 and 1 10 mg/ml, 60 and 100 mg/ml, 65 and 95 mg/ml, 70 and 90 mg/ml or between 75 and 85 mg/ml.

[47] The concentration of ammonia in the aqueous solution may be between 1 and 20% v/v, such as between 2 and 18% v/v, between 2.5 and 16% v/v, between 3 and 14% v/v, between 3.5 and 12% v/v, between 4 and 10% v/v, between 4.5% v/v and 9.5% v/v, such as between 5% v/v and 9% v/v.

[48] The aqueous solution may be heated at between 100 and 250°C, such as between 120 and 230°C, between 140 and 210°C, between 160 and 190°C, preferably for between 5 and 40 hours, such as between 10 and 35 hours, or between 14 and 33 hours, such as 16 and 31 hours, 18 and 29 hours or 20 and 27 hours or between 21 and 26 hours.

[49] The reaction or method may comprise a further step of removing impurities and/or excess ammonia, preferably subjecting the heated solution of citric acid and ammonia to dialysis.

[50] The reaction or method may comprise a further step of removing agglomerates from the heated solution of citric acid and ammonia, suitably by centrifuge.

[51 ] Suitably, supernatant liquid comprising the NGOQD particles is collected from the aqueous dispersion after heating.

[52] Advantageously, the bottom-up method of producing the NGOQD of the present invention allows for simple production of the desired small particle diameter and narrow size distribution. Furthermore, the particles produced show excellent dispersion properties in precursor solutions, thereby reducing agglomeration and allowing for NGOQD to be arranged in the polyamide layer substantially as single particles.

[53] In step (a) of the composite membrane reaction according to the second aspect of the present invention or the method of preparing a composite membrane according to the third aspect of the present invention contact of the organic solvent solution with the aqueous dispersion leads to interfacial polymerisation of the multifunctional amine-reactive reactant, multifunctional amine and GOQD particles. [54] Step (a) of the composite membrane reaction according to the second aspect of the present invention or the method of preparing a composite membrane according to the third aspect of the present invention may comprise the steps of

(a') forming on a porous support an aqueous layer comprising the aqueous dispersion of multifunctional amine and GOQD particles; and (a") contacting the aqueous layer with the solution comprising the multifunctional amine-reactive reactant in organic solvent.

[55] The aqueous layer of step (a') may be formed by contacting the porous support with an aqueous dispersion comprising a multifunctional amine and GOQD particles.

[56] The multifunctional amine is typically present in the aqueous layer or aqueous dispersion in an amount in the range of from about 0.1 to 20 w/v% of the layer or dispersion, preferably 0.5 to 8w/v%, such as 0.75 to 6w/v%, or 1 to 4w/v% or 1 .5 to 3w/v%.

[57] The GOQD particles are typically present in the aqueous layer or aqueous dispersion in an amount in the range of from about 0.001 to 0.5 w/v% of the dispersion, preferably 0.002 to 0.2 w/v%, such as 0.0022 to 0.15w/v%, or 0.0025 to 0.1w/v%, more preferably 0.004 to 0.8w/v%, or 0.005 to 0.06w/v%, most preferably 0.007 to 0.05w/v%.

[58] The aqueous dispersion comprising the multifunctional amine and GOQD particles may be prepared by contacting, suitably mixing, an aqueous solution comprising the multifunctional amine with an aqueous dispersion comprising the GOQD particles. Suitably, the aqueous dispersion comprising GOQD particles has been subjected to ultra-sonication.

[59] The multifunctional amine-reactive reactant is typically present in the organic solvent in an amount in the range of from about 0.005 to 5w/v% of the solution, preferably 0.01 to 1w/v%, 0.05 to 0.5w/v% or 0.08 to 0.3w/v%.

[60] The organic solvent may comprise any organic liquid immiscible with water. Suitably, the organic solvent is selected from one or more of the group consisting of hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, Iso- Par (Exxon), ISOL-C (SK Chem), and ISOL-G (Exxon). Preferred organic solvents are hexane, cyclohexane, heptane, octane, nonane, most preferably hexane.

[61 ] The aqueous layer may be formed on the support or the aqueous dispersion may be contact the support using any suitable method. For example, by spraying, coating, dipping, dripping, and the like may be used. Preferably, the support is reversibly attached to an immersion support member and immersed in the aqueous dispersion, suitably for between 1 and 5 minutes.

[62] Preferably, the support is saturated with the aqueous dispersion. However, excessive aqueous dispersion may be removed from the support before addition of the organic solvent solution. It can be advantageous to remove excess aqueous dispersion and multifunctional amine in order to improve stability and uniformity of the polyamide layer after polymerisation. The removal of excess aqueous dispersion may be performed by hand or with continuous operation, and may use a sponge, an air knife, nitrogen gas blowing, natural drying, a press roll, such as a soft rubber roller, or the like.

[63] The organic solvent solution may be contacted with the aqueous layer or aqueous dispersion using any suitable method. The organic solvent solution may be contacted with the aqueous layer by dipping, spraying, coating, and the like. The organic solvent solution is contacted with the aqueous layer for an amount of time sufficient to allow for polymerisation to occur, suitably in the range of from about 5 seconds to about 10 minutes, preferably about 20 seconds to 4 minutes, such as 30 seconds to 2 minutes. With contact of the organic solvent solution the multifunctional amine, multifunctional amine-reactive reactant and the GOQD react with each other to form a wet polyamide layer by interfacial polymerization. By "wet" it is meant that the polyamide layer comprises water and/or organic solvent.

[64] The product of step (a), typically the wet polyamide layer, may be cleaned by rising with an organic solvent to remove unreacted monomers, suitably the organic solvent is the same solvent used in the organic solvent solution.

[65] In step (b), the product of step (a), typically the wet polyamide layer, may be dried at a raised temperature of between 30 to 130C, 35-100, 40° C. to 80° C, 50 to 70C, suitably in an oven, and preferably for between 1 to 10 minutes, preferably between 3 to 8 minutes.

[66] The composite membranes of the present invention advantageously provide improved water permeability. Furthermore, the improved water permeability can be achieved whilst maintaining excellent salt rejection levels. It has also surprisingly been found that the composite membranes of the present invention can display improved thermal stability. The membrane manufacturing method of the present invention further advantageously provides a simple adaption to the normal method for the formation of reverse osmosis membranes, thereby enabling improved performance with only a small addition to existing manufacture processes.

[67] The term aliphatic herein means a hydrocarbon moiety that may be straight chain, branched or cyclic, and may be completely saturated, or contain one or more units of unsaturation, but which is not aromatic. The term "unsaturated" means a moiety that has one or more double and/or triple bonds. The term "aliphatic" is therefore intended to encompass alkyl, alicyclic, alkenyl or alkynyl groups. An aliphatic group preferably contains 1 to 15 carbon atoms, such as 1 to 14 carbon atoms, 1 to 13 carbon atoms, that is, an aliphatic group with 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13 carbon atoms.

[68] An alkyl group contains 1 to 15 carbon atoms. Alkyl groups may be straight or branched chained. The alkyl group preferably contains 1 to 14 carbon atoms, 1 to 13 carbon atoms, that is, an alkyl group with 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13 carbon atoms. Specifically, examples of an alkyl group include methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec- butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n- tridecyl, n-tetradecyl, n-pentadecyl, 1 ,1 -dimethylpropyl, 1 ,2-dimethylpropyl, 2,2-dimethylpropyl,

1 - ethylpropyl, n-hexyl, 1 -ethyl-2-methylpropyl, 1 ,1 ,2-trimethylpropyl, 1 -ethylbutyl, 1 -methylbutyl,

2- methylbutyl, 1 ,1 -dimethylbutyl, 1 ,2-dimethylbutyl, 2,2-dimethylbutyl, 1 ,3-dimethylbutyl, 2,3- dimethylbutyl, 2-ethylbutyl, 2-methylpentyl, 3-methylpentyl and the like, and isomers thereof.

[69] Alkenyl and alkynyl groups each contain 2 to 12 carbon atoms, such as 2 to 1 1 carbon atoms, 2 to 10 carbons atoms, such as 2 to 9, 2 to 8 or 2 to 7 carbon atoms. Such groups may also contain more than one carbon-carbon unsaturated bond.

[70] Alicyclic groups may be saturated or partially unsaturated cyclic aliphatic monocyclic or polycyclic (including fused, bridging and spiro-fused) groups which have from 3 to 15 carbon atoms, such as 3 to 14 carbon atoms or 3 to 13 carbon atoms, that is an alicyclic group with 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13 carbon atoms. Preferably, an alicyclic group has from 3 to 12, more preferably from 3 to 1 1 , even more preferably from 3 to 10, even more preferably from 3 to 9 carbon atoms, or from 3 to 8 carbons atoms or from 3 to 7 or 3 to 6 carbon atoms. The term "alicyclic" encompasses cycloalkyl, cycloalkenyl and cycloalkynyl groups. It will be appreciated that the alicyclic group may comprise an alicyclic ring bearing one or more linking or non-linking alkyl substituents, such as -CH₂-cyclohexyl. Specifically, examples of C_3-15 cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, isobornyl and cyclooctyl.

[71 ] An aryl group is a monocyclic or polycyclic group having from 6 to 14 carbon atoms, such as 6 to 13 carbon atoms, 6 to 12, or 6 to 1 1 carbon atoms. An aryl group is preferably a "C₆. ₂ aryl group" and is an aryl group constituted by 6, 7, 8, 9, or 10 carbon atoms and includes condensed ring groups such as monocyclic ring group, or bicyclic ring group and the like. Specifically, examples of "C₆. ₀ aryl group" include phenyl, biphenyl, indenyl, naphthyl or azulenyl and the like. It should be noted that condensed rings such as indan and tetrahydro naphthalene are also included in the aryl group.

[72] The use of the term "hetero" in heteroaliphatic and heteroaryl is well known in the art. Heteroaliphatic and heteroaryl refers to an aliphatic or aryl group, as defined herein, wherein one or more carbon atoms has been replaced by a heteroatom in the chain and/or ring of the group, as applicable, respectively. The heteroatom(s) may be one or more of sulphur and/or oxygen.

[73] The heteroatom(s) may be in any form that does not remove the ability of the amine groups of the multifunctional amine to react with the multifunctional amine-reactive. The heteroatom(s) may be in the form of an ether group, such as C^C^ alkoxy; if terminal, a hydroxyl group; sulphur and oxygen heterocycles; and/or a polysulphide group, such as a polysulphide containing at least two sulphur atoms. [74] Preferably, the alkoxy group contains from 1 to 8 carbon atoms, and is suitably selected from methoxy, ethoxy, propoxy, butoxy, pentlyoxy, hexyloxy, heptyloxy, octyloxy, and isomeric forms thereof.

[75] All of the features contained herein may be combined with any of the above aspects in any combination.

EXAMPLES

[76] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the following experimental data.

[77] Synthesis of NGOQD particles and example membranes

[78] Trimesoyl chloride (TMC) (98%), m-phenylenediamine (MPD) (flakes, 99%), n-hexane (laboratory reagent, >95%), dichloromethane (anhydrous, >99.8%, 40-150 ppm amylene as stabilizer), citric acid (99%), ammonia (28.0-30.0% NH₃ solution), and sodium chloride (NaCI, >99%) were purchased from Sigma Aldrich and used without further purification. Polysulfone (PS) ultrafiltration membrane (P35, Nanostone Co., Minnesota, USA) was used as the support in the comparative and inventive examples.

[79] NGOQD particles were synthesized by carbonization of citric acid with ammonia through hydrothermal treatment. 80 ml_ of a citric acid aqueous solution (100 mg/mL) and 20 ml_ of the ammonia aqueous solution was transferred into a Teflon-lined autoclave and heated at 180 °C for 24 hours. The resulting light yellow solution was dialyzed using a dialysis tubing (3000 Da, Spectrum Lab. Inc.) soaked in deionised water for 4 hours to remove impurities and excess ammonia. After dialysis, the aqueous dispersion was centrifuged at 10,000 rpm to remove any agglomerates. The supernatant liquid containing the NGOQD particles was collected for subsequent membrane preparation, as described below.

[80] The example membranes were produced using interfacial polymerisation on the PS support. To prepare the comparative membrane the PS support was taped on a glass plate and immersed in a 2.0 w/v% MPD aqueous solution for 2 min. Excess aqueous MPD solution was removed from the PS support surface by a soft rubber roller. The saturated PS support was soaked in a 0.1 w/v% of TMC in n-hexane solution for 1 min. The resulting membrane was washed by hexane to remove unreacted monomers, cured at 60°C for 6 min, and then stored in a lightproof water bath. To prepare membranes according to the present invention, the MPD aqueous solution was replaced by an aqueous dispersion of MPD and N-GOQD. To prepare the aqueous dispersions of MPD and NGOQD particles, several aqueous dispersions containing NGOQD particles produced according to the above method were formed and subjected to ultra- sonication. The NGOQD dispersions were then mixed with appropriate amounts of MPD aqueous solutions to obtain final dispersion with a MPD concentration of 2.0 w/v% and N- GOQD concentrations from 0 to 0.07 w/v% (Table 1). The membrane preparation procedure was the same as described above for the comparative membranes.

Table 1 - Concentrations of MPD, TMC and N-GOQD

[81 ] Characterisation and testing

[82] A series of methods were used to characterise and test the example membranes. X-ray Photoelectron Spectroscopy (XPS) (Kratos Axis Ultra DLD instrument equipped with a monochromated Al Ka X-ray source and hemispherical analyzer capable of an energy resolution of 0.5 eV) and X-Ray Diffraction (XRD) (Rigaku D/Max 2100 Powder X-ray Diffractometer (Cu Ka radiation)) measurements were conducted to characterize the elemental composition and structure of the NGOQD. The functional groups of the membrane surfaces and NGOQD were measured by Fourier Transform Infrared (FTIR) measurements in Attenuated Total Reflection (ATR) mode (Thermo Scientific, Waltham, MA, USA) with 4 cm^"1 resolution over a wave number range of 600-4,000 cm^"1.

[83] Field Emission Scanning Electron Microscope (FESEM) (Zeiss Ultra Plus) was used to observe the morphology of the example membranes. Particles size and distribution of NGOQD was observed with transmission electron microscopy (TEM, JEM-2100F, JEOL Ltd. Japan). Moreover, Atomic Force Microscopy (AFM) (TT-AFM, AFM workshop Co., CA, USA) was employed to analyse surface roughness in root mean square (RMS) and relative surface area of the polyamide layer in the example membranes. AFM images were taken over a membrane

[84] The contact angle of water was measured by VCP Optima system (Optima XE) to compare the hydrophilicity of the example membranes. Water droplets (~1 μί) were dropped carefully onto the example membrane surfaces for imaging. All example membranes were dried at ambient temperature prior to characterization. [85] Thermal gravimetric analysis (TGA) was carried out to investigate the thermal stability of the example membranes. To study the thermal property of the polyamide layer the PS support of the membranes separated from the bottom non-weaven polyester. The PS support was then dissolved in dichloromethane solution, and the polyamide layer collected from solution. TGA measurement was carried out under a nitrogen atmosphere using Perkin-Elmer thermo gravimeter (Diamond TG/DTA). The flow rate of nitrogen was 20 ml/min, and the heating rate was 10 °C/min from 25 to 700 °C.

[86] A stainless-steel dead-end module with an effective permeation area of 5.1 cm² was used for salt water permeation measurements. The feed side of the module was connected to a high- pressure nitrogen tank to generate a driving force around 15 bar. Desalination performance of the example membranes was evaluated using 2,000 ppm NaCI solution at room temperature. An electronic scale (Ohaus, CS Series) was used to measure the mass of permeate over time (>3 h), which was used to calculate the volumetric water permeance (J) at steady state. The salt rejection (R=1 -C_p/C_f, where C_p and C_f are the salt concentration of permeate and feed, respectively) was calculated from the feed and permeate salt concentration. Concentration of NaCI was measured by a conductivity meter (Pour Grainger International, Lake Forest, IL, USA).

[87] Results

[88] The TEM image of Figure 1 a shows that the NGOQD particles had a relatively uniform size distribution of between 3 and 8 nm and were fully dispersed single NGOQD particles without any apparent agglomeration. The XPS spectra of Figure 1 b shows that the NGOQD particles had carbon, oxygen and nitrogen signals at 283 to 290 eV, 530 to 533 eV and 398 to 402 eV. The N1 s peaks at around 399-402 eV confirms both amine and pyridine groups in the NGOQD particles. The XRD pattern of the NGOQD particles in Figure 1 c shows a strong peak centered at 20.3°, corresponding to d-spacing of around 4.2 A.

[89] The FTIR spectrum of the NGOQD particles in Figure 1 d. contains peaks at 1709 and 1790 cm¹ corresponding to a C=0 stretch and indicating the presence of carboxylic groups. Carboxylic group bonded with aromatic ring have FTIR peaks in the range of 1700 to 1730 cm^"1 , but these peaks are expected to shift to higher wave numbers by replacing carbon with nitrogen in the aromatic ring. Moreover, the FTIR spectrum of Figure 1 d also indicates the existence of C-H (1395 cm^"1), N-H stretch of amine group (1560 cm^"1), C=C (1450 cm^"1) and C-N (1060 cm^" ) groups in the NGOQD particles. The FTIR spectrum of figure 1 d further exhibits two distinct peaks associated with oxygen functional groups at 1208 cm^"1 (C-O stretching vibrations of epoxy) and 1670 cm^"1 (C=N stretching vibrations of pyrrolic structure).

[90] The AFM results of Figure 2 show that the NGOQD particles were formed of 1 to 5 graphene oxide layers. [91 ] The ATR-FTIR spectra of the comparative and inventive membranes are presented in Fig. 3. The peaks at 1488 and 1245 cm^"1 correspond to CH₃-C-CH₃ stretching and C-O-C stretching of the support. Absorption bands at 1600-1700 and 1700-1760 cm^"1 can be attributed to the C=0 group of polyamide and ester groups, respectively. The amide bands of the comparative membrane's polyamide layer are at around 1660, 1640 and 1080 cm^"1 for C=0 stretching of carboxylic, N-H stretching of amide, and C-N stretching, respectively. The inventive examples have very wide peaks from 1600 to 1720 cm^"1 , which can be deconvoluted into three peaks, 1624 cm^"1 (N-H of amide), around 1650 cm^"1 (C=0 of carboxylic), and 1670 cm^"1 (C=N of pyrrolic). The ATR-FTIR spectrum of the comparative membrane does not show the presence of amine N-H group at wavenumber of 1560 cm^"1 , while this peak can be clearly seen in the inventive membranes.

[92] The surface roughness and contact angle measurements are provided in Table 2.

Table 2 - Surface roughness, effective surface area and contact angle

[93] The results of Table 2 show that the inclusion of NGOQD particles reduces the surface roughness of the inventive membranes whilst increasing the effective surface area.

[94] The results of Table 2 are supported by the FESEM images of Figure 4 show the surface morphology and cross section of comparative and inventive membranes. The FESEM images show that the addition of NGOQD particles leads to a smooth surface and further that the smoothness increases with higher NGOQD concentrations (comparing figures 4a, 4b and 4c). The FESEM images surface images also indicate that adding NGOQD particles changes the surface morphology from the leaf-like morphology of the comparative membrane to a hill and valley morphology. [95] The cross sectional views of the comparative and inventive membranes in Figures 4d and 4e, respectively, show an average polyamide layer thickness of around 250 nm in both membranes, indicating that the inclusion of the NGOQD particles has little, if any, effect on the membrane thickness.

[96] The results of Table 2 also show that the use of NGOQD particles in a composite membrane greatly improves the hydrophilicity of the membrane. The contact angle of water decreased from 87° in comparative example 1 to <60° with the addition of the NGOQD particles.

[97] The TGA measurements shown in Figure 6 shows the thermal stability of the comparative and inventive membranes. Two weight losses can be seen for comparative example 1 at temperatures starting at around 280 and 450°C, which are likely to be the degradation of unreacted functional groups, such as amine and acid groups, and decomposition of polyamide polymer. In contrast, the TGA curve for example 4 has no significant loss until ca. 470°C, showing that the addition of NGOQD particles produces significantly improved thermal stability in the membrane.

[98] The desalination performance of the membranes of examples 1 to 6 was evaluated and compared with the membrane of comparative example 1 . The results are shown in Figure 7. The circular markers represent the water permeability and the triangular markers represent the salt rejection level.

[99] The inventive membranes provide approximately a 3-fold increase of water permeability while maintaining similar salt rejection. Water permeability of the example membranes increased approximately linearly from 0.62 to 1 .66 L/(m² h bar) with the increase of NGOQD particle concentration from 0 to 0.02 wt/v% without sacrificing salt rejection (~93%). Further increasing N-GOQD particle concentration to 0.04 wt/v% also provided the combination of significantly improved water permeability without sacrificing salt rejection. An improved water permeability is still found for example 6, however this is at the expense of a lower salt rejection (-85%).

[100] NGOQD particles have been shown as an effective additive for reverse osmosis composite membranes to significantly improve the water permeability of the membrane. The salt rejection level can also be maintained and the thermal stability improved. Furthermore, the NGOQD particles, as well as the NGOQD-containing membranes, can be prepared by a low- cost, bottom-up method.

[101 ] Without wishing to be bound by theory, the improved water permeability may be at least partially attributable to the participation of the NGOQD particles in the interfacial polymerisation reaction. The inclusion the small particles of graphene oxide that have also been nitrogen doped appears to surprisingly form transport pathways with larger pores than those of the comparative polyamide resin, thereby further improving water permeability. Larger pores may be expected to facilitate water transport at the expense of lower salt rejection, however embodiments of the present invention have been found to provide a combination of improved water permeability in combination with maintained salt rejection levels, possibly due to the combination of favourable surface properties and an optimum number of the larger interfacial pores. The improved therma stability may also be attributable to the participation of the NGOQD particles in the interfacial polymerisation reaction due to the additional crosslinking produced in the polyamide resin.

[102] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[103] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[104] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[105] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

A composite membrane comprising:

(i) a porous support; and

(ii) a polyamide layer on the support;

A composite membrane comprising

(i) porous support; and

(ii) a polyamide layer on the support;

and wherein the composite membrane is a reaction product of:

(b) drying of the product of step (a).

3. A method of preparing a composite membrane comprising the steps of:

(a) contacting a solution of a multifunctional amine-reactive reactant in an organic solvent with an aqueous dispersion on a porous support, wherein the aqueous dispersion comprises a multifunctional amine and GOQD particles; and

(b) drying the product of step (a) to form the composite membrane.

Use of graphene oxide quantum dot (GOQD) particles in a polyamide composition, preferably in a polyamide composite membrane comprising a porous support and a polyamide layer on the support.

A membrane, method or use according to any preceeding claim, wherein the membrane is a thin film nanocomposite (TFN) membrane, preferably, a reverse osmosis thin film nanocomposite membrane.

6. A membrane, method or use according to any preceding claim, wherein the support is a microporous membrane or an ultrafiltration membrane, preferably the pore sizes of the support are from 1 to 500nm, such as between 2 and 400nm, 3 and 300nm, 4 and 200nm, 5 and 100nm, 6 and 75nm, 7 and 50nm, 8 and 40nm or 9 and 35nm or 10 and 30nm.

7. A membrane, method or use according to any preceding claim, wherein the support comprises a polymer material, preferably the polymer material is selected from the group consisting of polysulfone; polyethersulfone; polycarbonate; polyethylene oxide; polyimide; polyetherimide; polyether ether ketone; polyethylene; polypropylene; polymethylpentene; poly(methyl methacrylate); polymethyl chloride; halogenated polymers, such as polyvinylidene fluoride; or combinations thereof, more preferably, the polymer material is polysulfone.

8. A membrane, method or use according to any preceding claim, wherein the polyamide layer of the membrane has a thickness of between 50 to 1000nm, such as 100 to 900nm, 130 to 800nm, 150 to 700nm, 160 to 600nm, 170 to 500nm, 180 to 400nm, 190 to 350nm or 200 to 300nm, such as 220 to 280nm.

9. A polyamide composition comprising GOQD moieties.

10. A membrane, method, use or composition according to any preceding claim, wherein the polyamide layer or polyamide composition comprises GOQD moieties arranged in a polyamide layer, preferably the GOQD moieties are GOQD residues covalently bonded to the polyamide layer, more preferably, the polyamide layer is formed of polymerised residues of a multifunctional amine, a multifunctional amine- reactive reactant and GOQD particles.

1 1 . A membrane, method, use or composition according to any preceding claim, wherein the polyamide layer comprises GOQD moieties, particles or residues in an amount of between 0.05 and 5% by weight of the polyamide layer, such as between 0.1 and 4 wt% or between 0.2 and 3.5wt% or between 0.25 and 3wt% or between 0.3 and 2.5wt%, or between 0.35 and 2 wt%, such as 0.4 and 1 .9wt%, 0.45 and 1 .8wt%, 0.5 and 1 .7wt%, 0.55 and 1 .6wt% or 0.60 and 1 .5wt%, or 0.65 and1 .4wt% or 0.7 and 1 .3wt%.

12. A membrane, method, use or composition according to any preceding claim, wherein the polyamide layer comprises multifunctional amine-reactive reactant in an amount of between 0.5 and 20% by weight of the polyamide layer, such as between 1 and 10wt%, between 1 .5 and 9.5wt%, 1 .5 and 9wt%, 2 and 8.5wt%, 2.5 and 8wt%, 3 and 7.5wt%, 3.5 and 7wt%, 4 and 6.5wt%, or 4.5 and 6wt%.

13. A membrane, method, use or composition according to any preceding claim, wherein the polyamide layer comprises multifunctional amine in an amount of between 75 and 99.45% by weight of the polyamide layer, such as between 86 and 98.9wt%, between 87 and 98.3wt%, 88 and 98wt%, 89 and 97.5wt%, 89.5 and 97wt%, 90 and 96.5wt%, 90.5 and 96wt%, 91 and 95.5wt%, or 91 .5 and 95wt%.

14. A membrane, method, use or composition according to any preceding claim, wherein multifunctional amine is selected from aromatic amines, aliphatic amines, and mixtures thereof.

15. A membrane, method, use or composition according to any preceding claim, wherein the multifunctional amine is an aromatic amine, more preferably an aromatic diamine or triamine, still more preferably the multifunctional amine is selected from the group consisting of Ν,Ν'-diphenylethylene diamine, benzidine, and xylylene diamine or a multifunctional aromatic diamine or triamine according to formula I, and mixtures thereof, most preferably the multifunctional amine is selected from an amine according to formula I:

Formula I

wherein two or three of R to R⁶ are NR⁷R⁸;

R to R⁶ that are not NR⁷R⁸ are independently selected from hydrogen; halogen, such as chloride or fluoride; Cr^aliphatic; C1 - ₅heteroaliphatic; or hydroxyl, such as hydrogen, chloride, Cr^alkoxy, hydroxyl-substituted C_r ₅alkyl, or hydroxyl; preferably hydrogen; and

for each of R to R⁶ that is NR⁷R⁸ then R⁷ and R⁸ are independently selected from a group consisting of hydrogen, Cr^aliphatic, Cr^heteroaliphatic, C₆- C ₄aryl, and C₆-C ₄heteroaryl, such as hydrogen, Cnsalkyl, C₂-i₂alkenyl, C₂- 2alkynyl, C₃-₈alicyclic, and C₆. ₀aryl, preferably hydrogen.

16. A membrane, method, use or composition according to claim 16, wherein the multifunctional amine according to formula I is a primary amine wherein R⁷ and R⁸ are hydrogen for each R to R⁶ group that is NR⁷R⁸, preferably the multifunctional amine according to formula I is a primary diamine wherein R⁷ and R⁸ are hydrogen for each R to R⁶ group that is NR⁷R⁸ and two of R to R⁶ are NR⁷R⁸, such as R and R³ or R and R⁴, more preferably the multifunctional amine according to formula I is a primary diamine wherein R and R³ are NR⁷R⁸ and R⁷ and R⁸ are hydrogen, most preferably, the multifunctional amine is m-phenylenediamine.

17. A membrane, method, use or composition according to any preceding claim, wherein the multifunctional amine-reactive reactant is selected from one or more of the group consisting of a multifunctional acyl halide, a multifunctional sulfonyl halide and a multifunctional isocyanate, preferably the multifunctional amine-reactive reactant is a multifunctional acyl halide, more preferably an aromatic multifunctional acyl halide, still more preferably an aromatic di- or tricarboxylic acid halide, for example selected from the group consisting of trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride (TPC), and combinations thereof, most preferably, the multifunctional amine-reactive reactant is an aromatic tricarboxylic acid halide, suitably trimesoyl chloride (TMC).

18. A membrane, method, use or composition according to any preceding claim, wherein the GOQD particles, residues or moieties have a diameter of between 1 to 100nm, such as between 1 to 75nm, 1 to 50nm, 1 to 40nm, 1 to 30nm, 1 to 25nm, 2 to 20nm, 3 to 20nm, or 4 to 15nm, preferably 5 to 10nm.

19. A membrane, method, use or composition according to any preceding claim, wherein at least 30wt% of the GOQD particles, residues or moieties have a diameter of between 1 to 100nm, such as between 1 to 75nm, 1 to 50nm, 1 to 40nm, 1 to 30nm, 1 to 25nm, 2 to 20nm, 3 to 20nm, or 4 to 15nm, preferably 5 to 10nm, more preferably at least 40wt%, 50wt%, 60wt%, 70wt% and most preferably at least 80wt% or at least 90wt% or 95wt% or 98wt% or 99wt%.

20. A membrane, method, use or composition according to any preceding claim, wherein the GOQD particles, residues or moieties are formed of single, two or few layers of graphene oxide, preferably the GOQD particles, residues or moieties comprise between 1 to 8 layers, such as between 2 to 6 layers or 3 to 5 layers.

21 . A membrane, method, use or composition according to any preceding claim, wherein at least 30wt% of the GOQD particles, residues or moieties comprise between 1 to 8 layers, such as between 2 to 6 layers or 3 to 5 layers, more preferably at least 40wt%, 50wt%, 60wt%, 70wt% and most preferably at least 80wt% or at least 90wt% or 95wt% or 98wt% or 99wt%.

A membrane, method, use or composition according to any preceding claim, wherein the GOQD particles, residues or moieties are nitrogen-doped GOQD (NGOQD).

A membrane, method, use or composition according to claim 22, wherein the nitrogen groups of the NGOQD particles, residues or moieties are in the form of amine groups such as nitrogen-containing heterocyclic groups and/or primary amines, preferably the NGOQD particles, residues or moieties comprise nitrogen- containing heterocyclic groups, suitably nitrogen-containing heterocyclic groups in the graphene moiety of the NGOQD particles, residues or moiety, more preferably said nitrogen-containing heterocyclic groups comprise pyrrole and/or pyridine residues.

A membrane, method, use or composition according to any preceding claim wherein the oxide groups of the GOQS particles, residues or moiety are in the form of carboxylic acid groups; hydroxyl groups; and/or epoxide groups, suitably at least carboxylic acid groups.

A membrane, method, use or composition according to claim 22 or 23, wherein the nitrogen-doped graphene oxide quantum dot particles, residues or moieties are a reaction product of heating an aqueous solution comprising citric acid and ammonia.

A method for preparing nitrogen-doped graphene oxide quantum dot particles, comprising the steps of:

(a) forming an aqueous solution comprising citric acid and ammonia

A membrane, method, use or composition according to claim 25 or 26, wherein the concentration of citric acid in the aqueous solution is between 20 and 140 mg/ml, such as 30 and 130 mg/ml, 40 and 120 mg/ml, 50 and 1 10 mg/ml, 60 and 100 mg/ml, 65 and 95 mg/ml, 70 and 90 mg/ml or between 75 and 85 mg/ml.

28. A membrane, method, use or composition according to any of claims 25 to 27, wherein the concentration of ammonia in the aqueous solution is between 1 and 20% v/v, such as between 2 and 18% v/v, between 2.5 and 16% v/v, between 3 and 14% v/v, between 3.5 and 12% v/v, between 4 and 10% v/v, between 4.5% v/v and 9.5% v/v, such as between 5% v/v and 9% v/v.

29. A membrane, method, use or composition according to any preceding claim, wherein step (a) of the composite membrane reaction according to claim 2, or step (a) of the method according to claim 3 comprises the steps of

30. A membrane, method, use or composition according to claim 29, wherein the aqueous layer of step (a') is formed by contacting the porous support with an aqueous dispersion comprising a multifunctional amine and GOQD particles.

31 . A membrane, method, use or composition according to any preceding claim, wherein the multifunctional amine is present in the aqueous layer or aqueous dispersion in an amount in the range of from about 0.1 to 20 w/v% of the layer or dispersion, preferably 0.5 to 8w/v%, such as 0.75 to 6w/v%, or 1 to 4w/v% or 1 .5 to 3w/v%.

32. A membrane, method, use or composition according to any preceding claim, wherein the GOQD particles are present in the aqueous layer or aqueous dispersion in an amount in the range of from about 0.001 to 0.5 w/v% of the dispersion, preferably 0.002 to 0.2 w/v%, such as 0.0022 to 0.15w/v%, or 0.0025 to 0.1w/v%, more preferably 0.004 to 0.8w/v%, or 0.005 to 0.06w/v%, most preferably 0.007 to 0.05w/v%.

33. A membrane, method, use or composition according to any preceding claim, wherein the multifunctional amine-reactive reactant is typically present in the organic solvent in an amount in the range of from about 0.005 to 5w/v% of the solution, preferably 0.01 to 1w/v%, 0.05 to 0.5w/v% or 0.08 to 0.3w/v%.

34. A water treatment module comprising at least one membrane according to any preceding claim. A water treatment device comprising at least one or more water treatment modules according to claim 34.