WO2014085863A1 - Metal ion binding polymers and uses thereof - Google Patents

Abstract

Disclosed herein is an antiscale and/or antifouling coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with an aqueous environment containing the selected metal ion the ligand binds to at least some of the selected metal ions from the aqueous environment.

Description

METAL ION BINDING POLYMERS AND USES THEREOF

PRIORITY DOCUMENTS f 001 ] The present application claims priority from:

• Australian Provisional Patent Application No. 2012905325 titled "METAL ION BINDING POLYMERS AND USES THEREOF" and filed on 5 December 2012; and

• Australian Provisional Patent Application No. 2013904428 titled "METAL ION BINDING POLYMERS AND USES THEREOF" and filed on 15 November 2013.

[002] The content of each of these applications is hereby incorporated by reference in their entirety.

TECHNICAL FIELD

[003] The present invention relates generally to surface treated materials that are able to bind selected metal ions. More specifically, the present invention relates to surface treated materials that are able to bind metal ions in one oxidation state and release the same metal ions in another oxidation state or in response to some other physical or chemical parameter of the coating and to use of these materials in antifouling coatings, for the electrowinning of value metals, and related applications.

BACKGROUND

[004] Scaling and biofouling are significant problem in many industries. For example, scale formation in the oil and gas industry with applications involving heat exchangers. Biofouling is a very significant problem for the shipping industry and static marine constructions. Scale formation and biofouling are also a problem in mariculture, membrane systems, industrial equipment for fresh and salt water applications, biomedical devices for in vivo applications, power stations and the like.

[005] Scaling and biofouling occurs when a surface comes into contact with an aqueous environment containing inorganic and organic compounds and organisms. In the case of biofouling, various organic substances, such as polysaccharides and proteins, initially adsorb to the surface. This is followed by colonisation of bacteria and unicellular algae making the surface smooth and slimy. Eventually large hard foulers, such as tubeworms, barnacles and crustose algae and large soft foulers, e.g. seaweeds, sponges, anemones, tunicates, hydroids and bryozoans cover the surface. [006] All submerged surfaces are affected by biofouling to some extent, whether the surface is from natural or man-made structures such as ship hulls and offshore installations. Beyond marine

environments, scaling and biofouling present problems in many areas where water is being managed. Typical examples are industrial and domestic water supplies and dairy product processing. There are numerous other applications where scaling and biofouling is a problem. Storage of fresh water in developing countries and the growth of deadly bacteria inside tubing in water systems, fresh-water production in desalination plants where both scaling and fouling is a major challenge on membranes, microelectrochemical drug delivery devices, papermaking and pulp industry machines, underwater instruments and fire protection system piping and sprinkler system nozzles, etc. There are many more applications where scaling and fouling prevents full efficiency or capacity.

[007] Traditionally, scaling and biofouling is combated by chemical and/or mechanical means using for example biocide-releasing or self-polishing coatings. Up until the mid-nineties biofouling was kept under control using coatings based on tributyltin (TBT). As a result of its toxic effect on the marine environment, TBT was banned in 2008. Biocidal copper and zinc oxide particles were then used in conjunction with low molecular weight organic booster biocides as alternatives. These coatings rely on continuous dissolution of the coating matrix with concomitant release of the biocide as the matrix erodes. This technology has replaced the TBT-based coatings but the environmental toxicity of these compounds remains a concern. Another problem with these coatings is the need to overcharge the matrix with biocide due to rapid initial loss of biocide.

[008] The other approach for preventing biofouling is the so-called "non-stick fouling-release" approach with ultra-smooth coatings consisting of very hydrophobic polymers with very low energy of adhesion and weak internal cohesion. Even though biofouling may still occur, any attached organisms tend to release as water passes over the surface such as when the speed of a vessel increases due to^' the adhering organisms being sheared off along with a thin layer of the polymer as the shear force exceeds the cohesive strength of the coating material. These coatings rely on movement of water over the surface to release attached organisms and, therefore, are not suitable for use in relatively still aqueous environments, such as lakes, ponds, harbours etc.

[009] Nano- and microstructured surfaces and interfaces have also been of interest for antifouling purposes. Recently Lamb et al (2013) disclosed antifouling properties of diatomaceous earths materials due to their inherent ability to bind nano- and micrometer sized air bubbles making them act as a physical barrier to organism attachment.

[010] There is a need for antiscale and antifouling coatings for structures, such as ship hulls, pylons, membranes, pipes and the like for water purification, transport and storage, and related structures that overcome one or more of the problems associated with prior art coatings. Alternatively, or in addition, there is a need for antiscale and/or antifouling coatings for structures, such as ship hulls, pylons, and the like that provide an alternative to prior art coatings.

SUMMARY

[Oi l] The present invention has arisen from our research into materials that use metal ions that are naturally abundant in seawater or other aqueous environments to act at the interface between the coating and water. In some aspects of our work, we have exploited the inherent difference in binding between different ionic oxidation states of metal ions to ligands to produce a coating that binds to naturally abundant ions in the aqueous environment and releases metal ions when required.

[012] In a first aspect, the present invention provides an antiscale and/or antifouling coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution.

[013] The present invention therefore provides a coating that selectively binds a specific metal ion. The bound metal ion may prevent fouling or scaling by deterring any organism or inorganic species from attaching and crystallising, respectively, to the coating. Alternatively, or in addition, a flux of metal ions may form on the surface of the coating and the increased concentration of metal ions adjacent the surface of the coating may prevent attachment of both inorganic species and organisms to the surface, to thereby prevent or reduce scale formation and biofouling on the surface.

[014] In a second aspect, the present invention provides an antiscale and antifouling system for surfaces or structures that are maintained in an aqueous environment, the system comprising:

- an antiscale and/or antifouling coating for the surface or structure, the coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution to form a coating having bound metal ions; and

- a release system for reducing the binding constant between the bound metal ion and the metal ion binding ligand to thereby release at least some of the bound metal ions from the coating.

[015] In embodiments, the antiscale and/or antifouling coating comprises a polymer comprising the metal ion binding ligand. In these embo'diments, the metal ion binding ligand may be part of a branched or linear polymer, or the metal ion binding ligand may be grafted onto the polymer post-polymerisation. [016] In embodiments, the solution containing the selected metal ion is an aqueous environment in which the metal ion is naturally present. The aqueous environment may be a salt or fresh water environment, such as oceans, lakes, etc.

[017] In embodiments, the selected metal ion is any one of copper, zinc, tin or silver ions. In specific embodiments, the selected metal ion is copper ions.

[018] The release system for reducing the binding constant between the bound metal ion and the metal ion binding ligand may effect release of the bound metal ion and the metal ion binding ligand by:

• altering the oxidation state of the bound metal from a first oxidation state to a second oxidation state, wherein the binding constant between the metal ion binding ligand and the metal ion is greater in the first oxidation state than it is in the second oxidation state such that the ligand binds the metal ion in the first oxidation state and releases at least some of the bound metal ion in the second oxidation state; or

• chemically or physically modifying the metal ion binding ligand with metal bound thereto to release the bound metal ion.

[019] Thus, in some embodiments the release system comprises means for chemically or physically modifying the metal ion binding ligand. In these embodiments, the release system may comprise means for altering the configuration and/or oxidation state of the ligand so as to reduce the binding constant between the metal ion binding ligand and the metal ion. For example, the means for altering the configuration and/or oxidation state of the ligand may be an acid or base, an electrochemical treatment to alter the oxidation state of binding moieties in the metal ion binding ligand and/or altering the configuration of the metal ion binding ligand, or a photochemical treatment to alter the configuration of the metal ion binding ligand.

[020] In other embodiments the release system is a redox system for reducing or oxidising the bound metal ion from the first oxidation state to the second oxidation state. In embodiments, the redox system is a macroscopic metal surface having an electrochemical potential applied thereto. In other embodiments, the redox system is an electroactive particle system, such as carbon nanotubes or a conducting polymer. In each case, the redox system may be coupled with an electron source such as an electric power source, a photocatalyst or a sacrificial anode.

[021] In specific embodiments, the coating selectively binds the metal ion in a first oxidation state. Advantageously, the metal ion in the first oxidation state may be naturally present in an aqueous environment in which the antiscale and/or antifouling coating is to be used, such as in sea water (marine applications) or in fresh water (drinking water, etc) applications. The metal ion in the first oxidation state will bind, via the metal ion binding ligand, to the antiscale and/or antifouling coating. The redox system will then either reduce or oxidise the metal ion to the second oxidation state and, as a result of the lower level of binding between the ligand and the metal ion in the second oxidation state, at least some of the metal ion in the second oxidation state will be released from the coating to form a biocidal or scale preventing or reducing interface on the surface of the coating.

[022] The metal ion binding ligand may be attached to a surface by covalent bonding, ionic bonding or adsorption. The metal ion binding ligand may be part of a linear or branched polymer attached to the surface, or it may be grafted onto a polymer post-polymerisation.

[023] The metal ion binding ligand may be attached directly or indirectly to the surface. In the latter case, a spacer molecule or intermediate coating may be attached to the surface and the metal ion binding ligand subsequently attached to the spacer molecule or intermediate coating by covalent bonding, ionic bonding or adsorption.

[024] The antiscale and/or antifouling coating may comprise carrier particles onto which the metal ion binding ligand is bound or attached. The carrier particles may have a particle surface that enables strong surface adsorption either by covalent or physical modification. The carrier particles can be formed from naturally abundant materials, such as diatomaceous earth materials or from synthetic materials, such as solid or porous silica particles or PMMA-based particles.

[025] In a third aspect, the present invention provides a coating composition comprising an aqueous medium or an organic solvent based medium and an antiscale and/or antifouling composition comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution.

[026] In a fourth aspect, the present invention provides a coated surface or substrate comprising a surface or substrate and a coating according to the first aspect of the invention thereon.

[027] In a fifth aspect, the present invention provides a method for preventing or reducing scale and/or biofouling on a surface that is maintained in an aqueous environment, the method comprising coating the surface with the antiscale and/or antifouling coating of the first aspect of the invention or the antiscale and/or antifouling system of the second aspect of the invention.

[028] In a sixth aspect, the present invention provides a method for forming an antiscale and/or antifouling coating on a surface, the method comprising coating the surface of the substrate with a coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution.

[029] It will be evident from the foregoing discussion that the coating materials described herein could be used to selectively bind to a metal ion of interest that is present in an aqueous environment. The selectivity for the metal ion of interest can be used to separate metal ions of interest from aqueous environments that are complex mixtures of inorganic and organic materials.

[030] Thus, in a seventh aspect the present invention provides a metal ion extraction process comprising contacting an aqueous solution comprising a metal ion of interest with a surface comprising a metal ion binding ligand to bind the metal ion thereto, separating the surface comprising the metal ion binding ligand with the metal ion bound thereto from the aqueous environment, and releasing the bound metal ion from the metal ion binding ligand.

[031 ] In embodiments, the bound metal ion is released from the surface by changing the oxidation state of the bound metal ion from a first oxidation state to a second oxidation state in which the binding constant of the metal ion in the second oxidation state is less than it is in the first oxidation state.

[032] In other embodiments, the bound metal ion is released from the surface by chemically or physically modifying the ligand to release the bound metal ion. The ligand may be modified by treatment with an acid or base, by electrochemical treatment of the ligand to alter the oxidation state of binding moieties in the ligand and/or altering the configuration of the ligand, or by photochemical treatment to alter the configuration of the ligand.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

[033] Illustrative embodiments of the present invention will be discussed with reference to the accompanying figures wherein:

[034] Figure 1 shows a schematic illustration showing two approaches that can be used to form copper binding antiscale and/or antifouling coatings of embodiments of the invention. Ligands can be spin coated and crosslinked or plasma polymerized followed by coupling of ligands.

[035] Figure 2 shows AFM images of spin coated films (0.1 % PEI in EtOH, 2000rpm for 60s) on Au. (A) 3-D images showing the pores in the film which were exploited to determine coating thickness. (B) In-phase image where the different mechanical properties between the coating and the bottom of the pores proves that the pores penetrate the film down to the Au surface. (C) 3-D surface showing surface morphology' and pores on a larger scale. (D) Colour coded 2-D topographic surface image illustrating the pores to be about 15 nm deep.

[036] Figure 3 shows a plot of time v Cu/N ratio for the copper uptake of crosslinked PEI films, prepared from 0.05% PEl in EtOH, from 200 ppb copper in MilliQ-water and artificial seawater (error bars = one standard deviation).

[037] Figure 4 shows a plot of time v Cu N ratio for the copper uptake of crosslinked PEI films, prepared from 0.05% PEI in EtOH, from artificial seawater containing 200 ppb Cu and molar equivalent concentrations of Al, Cd, Co, Cr, Fe, n, Ni, Pb, Zn, Mo, V (error bars = one standard deviation).

[038] Figure 5 shows a plot of copper concentration v N/Cu ratio for the copper uptake of crosslinked PEI films, prepared from 0.05% PEI in EtOH, after three days in real seawater (error bars = one standard deviation).

[039] Figure 6 shows representative XPS spectra of the Si 2p region for Si-wafer with and without PEI film after submersion in seawater for three days. The PEI films were crosslinked after preparation from 0.05% PEI in EtOH. Leftmost spectrum: Si-wafer with no coating after 3 days in sea water. Middle spectrum: PEI coating on Si-wafer, as prepared. Rightmost spectrum: PEI coating on Si-wafer after 3 days in sea water.

[040] Figure 7 shows an EQCMD sensogram of crosslinked PEI prepared from 0.05% PEI in EtOH, no loaded copper. At t = 67 s the following program of applied potentials was initiated: 5 min OC, 5min 0V, 30 min OC, 5min-200mV, 30min OC, 5 min -400m V, 30 min OC, 5min -600mV, 30min OC, 5 min -800 mV, 30 min OC, 5 min 0V, 30 min OC, 5 min 200mV, 30 min OC, 5min 400mV, 30 min OC, 5min 600mV, 30min OC. OC = open circuit potential, that is, no applied potential. The left-hand y-axis corresponds to frequency change data and the right-hand axis corresponds to the dissipation data.

[041] Figure 8 shows an EQCMD sensogram of crosslinked PEI prepared from 0.05% PEI in EtOH, no loaded copper. At t = 61 s the following program was initiated: 0V to 600 mV, (600 mV to -800 mV to 600 mV)x 5, all @10mV/s. The left-hand y-axis corresponds to frequency change data and the right-hand axis corresponds to the dissipation data.

[042] Figure 9 shows an EQCMD sensogram of crosslinked PEI prepared from 0.05% PEI in EtOH, pre-loaded with copper in 10 mM CuS0₄. The following electrochemical manipulation was performed: t = 60 s, CV; t = 300 s, TP; t = 780 s, CV; t = 1021 s, TP; t = 1500 s, CV; t = 1740 s, TP; t = 2220 s, CV; t = 2485 s, TP; 2937 s, CV; t = 3180 s, TP; t = 3660 s. CV. CV = (600 mV to -700 mV to 600 mV)x2, @50mV/s. TP = 600 mV to -700 mV @50 raV/s, -700 mV to 0 mv @50 mV/s, hold for 300s at 0 mV, 0 mV to 600 mV @50mV/s. The left-hand y-axis corresponds to frequency change data and the right-hand axis corresponds to the dissipation data.

[043] Figure 10 shows a plot of time v coating thickness for the deposition of propionaldehyde plasma polymer on silicon wafers. Power was 40W and monomer pressure was 0.2 torr.

[044] Figure 1 1 shows a QCMD sensogram of aldehyde plasma polymer film with applied PEI and Cu²⁺. The left-hand y-axis corresponds to frequency change data and the right-hand axis corresponds to the dissipation data. The 5th overtones are graphed (F5 and D5).

[045] Figure 12 shows a plot of Cu/N ratios showing copper remaining after QCM or eQCM experiments. The analysed sample was crosslinked PEI prepared from 0.05 PEI in EtOH, loaded by soaking in 200 ppb Cu solution.

[046] Figure 13 shows a graph showing a cyclic voltammogram obtained for PEI film pre-soaked with copper, thoroughly washed and analysed using the electrochemical cell in the QCM-D.

[047] Figure 14 shows a plot for the electrochemical manipulation while analysing films in the QCM- D. CV indicates 3 sweeps from 500 mV to -500 mV to 500 mV @50mV/s. From the CVs, the relative copper content at each time was calculated from the area of the oxidation peak. Additional

electrochemical manipulation was performed, but has been excluded for clarity.

DESCRIPTION OF EMBODIMENTS

[048] Before proceeding to describe the present invention, and embodiments thereof, in more detail it is important to note that various terms that will be used throughout the specification have meanings that will be understood by a skilled addressee.

[049] As used herein, the term "antifouling", and related terms, is intended to mean compounds, coatings, or other materials which substantially reduce or eliminate the growth of organisms that attach to surfaces or structures in contact with aqueous environments. Standard tests can be used to determine whether or not a surface is antifouling and the tests vary with the application. Suitable tests for ship hulls, membranes, etc. are available in the literature.

[050] As used herein, the term "antiscale", and related terms, is intended to mean compounds, coatings, or other materials which substantially reduce or eliminate the growth of inorganic materials that attach to surfaces or structures in contact with aqueous environments. Standard tests can be used to determine whether or not a surface is antiscale and the tests vary with the application. Suitable tests for membranes, etc. are available in the literature.

[051 ] As used herein, the term "polymer" is intended to mean a molecule composed of repeating structural units. The term "prepolymer" is intended to mean a polymer of relatively low molecular weight that is intermediate between a monomer and a final polymer. A prepolymer is capable of further polymerisation by reactive groups to a fully cured final polymer. The term "monomer" is intended to mean a relatively low molecular weight molecule that is capable of reacting with other molecules to form a polymer.

[052] As used herein, the term "spacer" is intended to mean a molecule capable of attaching strongly, preferably covalently, to a metal surface.

[053] As used herein, the term "ligand" is intended to mean a molecule that is capable of binding to a metal atom to form a coordination complex. A ligand may be "selective" for a specific metal in which case the ligand has different affinities with different metals such that at least one metal can bind to the ligand preferentially over other metals. A selective ligand does not necessarily have to be 100% selective for a particular metal ion of interest.

[054] As used herein, the term "binding constant" is intended to mean a constant that describes the bonding affinity between a metal ion and a ligand at equilibrium. The binding constant (also known as association constant or affinity constant) for the binding of a ligand to a metal is described by the following equation (note: Keq = A):

[Mi]

K^eq ~ [M][L]

[055] where Keq is the equilibrium constant for the reaction, [ML] is the concentration of the metal ligand complex, [M] is the concentration of the metal ion, and [L] is the concentration of the ligand.

[056] As discussed, the present invention provides an antiscale and/or antifouling coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution.

[057] The antiscale and antifouling coating of the present invention may be used on any surface or structure that is normally maintained in an aqueous environment and may be subjected to fouling by inorganic species and water borne organisms. For example, antifouling compositions are commonly used on: the hulls of ships and other water craft; pylons of structures such as jetties, over water decks, oil and gas rigs, etc; pipes and other pumping components; surfaces in desalination plants, such as membranes and other surfaces in contact with both fresh and salt water; surfaces in contact with blood, either in treatment outside the body, cleaning of blood for instance, or in biomedical devices used inside the human body; and processing equipment in the dairy and food industries.

[058] The metal ion binding ligand may be any moiety that is capable of binding a metal ion of interest. The metal ion binding ligand may comprise one or more function groups containing primary, secondary, tertiary or aromatic heteroatoms such as nitrogen, sulphur and/or oxygen. Suitable functional groups include alcohols, aldehydes, esters, carboxylic groups, amines, amides, ketones, aldehydes, and hydrazides. The metal ion binding ligand may be a small organic molecule. Suitable small organic molecules include imidazole, ethylenediaminetetracetic acid (EDTA), pyridyls, terpyridines, hydroxamates, catechols, pyranones, hydroxy pyridinones, etc containing compounds. Alternatively, or in addition, the metal ion binding ligand may be part of a polymer. In these embodiments, the functional group(s) that bind the metal may be part of the polymer backbone and/or the polymer side chain.

[059] In some embodiments, the heteroatoms of the metal ion binding ligand are selected from the group consisting of: O, S and N.

[060] In some embodiments, the metal ion binding ligand comprises 2, 3, 4, 5 or 6 heteroatoms capable of binding to the metal.

[061] The metal ion binding ligand may be attached directly to a surface. For example, the metal ion binding ligand may comprise a functional group having a high affinity for the particular surface material. For example, the ligand may comprise a charged functional group that is able to bond to a complementary charged group on the surface. Alternatively, the metal ion binding ligand may be deposited on the surface by plasma deposition.

[062] Alternatively, the metal ion binding ligand may be attached indirectly to the surface via a spacer molecule or intermediate layer. The spacer may be covalently linked to the surface and the metal ion binding ligand attached to the spacer molecule by covalent bonding or adsorption. In embodiments, the spacer having a metal ion binding ligand is formed by reacting a spacer molecule with the metal ion binding ligand or precursor thereof to covalently attach the metal ion binding ligand to the spacer. The spacer may have a reactive group that is able to form a covalent bond with a complementary reactive group on the metal ion binding ligand. Examples of suitable spacers for use in these embodiments are bifunctional oligoethylene oxides, epoxides, maleimides, and similar. Optimal spacers can be selected for specific applications, such as the types of micro-organisms that cause fouling and their enzymatic secretions. [063] In another alternative, the substrate surface may be functionalised and the functionalised surface may be reacted with the metal ion binding ligand or precursor thereof to covalently bond the metal ion binding ligand to the surface or to adsorb the metal ion binding ligand to the surface. In embodiments of this aspect, the surface of the substrate may be functionalised by contacting the surface with a compound having a reactive functional group that can then be reacted with the metal ion binding ligand. For example, the surface may be treated by plasma polymerisation of an alkyl aldehyde to form an aldehyde functionalised surface which can then be reacted with the metal ion binding ligand. This is particularly suitable when the metal ion binding ligand contains nitrogen. In embodiments, the surface of the substrate is treated with propionaldehyde by plasma deposition, and the coated substrate then treated with allylamine to form the coating.

[064] Alternatively, the coating may be a polymer comprising the metal ion binding ligand. The ligand may be part of the side chain of a monomer used to form the polymer, or the ligand may be grafted onto a polymer post-polymerisation. The polymer may be a natural or synthetic polymer and the metal ion binding ligand can be either adsorbed or covalently attached to the polymer.

[065] In embodiments, the polymer comprising the metal ion binding ligand is formed by reacting a polymer with a metal ion binding ligand precursor to covalently attach the metal ion binding ligand to the polymer. The polymer may have a reactive group that is able to form a covalent bond with a

complementary reactive group on the metal ion binding ligand. Examples of suitable natural polymers for use in these embodiments are polysaccharides, including but not limited to amylose, amylopectin, cellulose, chitin, pectin, and xylan. Examples of suitable synthetic polymers for use in these embodiments include, but are not limited to: polyvinylimidazole, polyvinylalcohol, polyacrylic acid,

polyhydroxyethylmethacrylate, polyethylene glycol, derivatives of any of the aforementioned polymers, and chlorine or bromine containing polymers, such as polyvinylbenzyl chloride. In specific embodiments, the polymer is polyvinylbenzyl chloride.

[066] In other embodiments, the polymer comprising the metal ion binding ligand is formed by polymerising a prepolymer or monomer having the metal ion binding ligand covalently attached thereto. Examples of prepolymers or monomers suitable for use in these embodiments include polyvinylimidazole prepolymers or imidazole monomers, polypyrrole prepolymers or pyrrole monomers, polythiophene prepolymers or thiophene monomers, and polyamine prepolymers or amine monomers.

[067] In still other embodiments, the polymer comprising the metal ion binding ligand is a preformed polymer that is used to coat the surface of the substrate. The polymer comprising the metal ion binding ligand may be selected from the group consisting of: a polyamine, a polyhhdroxy, a polysulfhydryl. The polymer comprising the metal ion binding ligand may be an aliphatic- or aromatic based polymer. [068] In embodiments that are particularly suitable for binding Cu²⁺ ions, the metal ion binding ligand is a polyamine. The polyamine may be a polyalkyleneimine. Suitable polyalkyleneimines include polyethyleneimine (PEI), polypropyleneimine, polybutyleneimine, etc. In other embodiments, the ^' polyamine is polyallylamine.

[069] In specific embodiments, the polyamine is PEI. The PEI may be a branched or linear PEI (Kobayashi et at., 1987). In embodiments, the polyamine is branched PEI and the average molecular weight (weight average molecular weight Mw) is 750,000, 2,000 or 1 ,300. In other embodiments, the polyamine is linear PEI and the average molecular weight (number average molecular weights Mn) is 10,000, 5,000 or 2,500.

[070] The polymer comprising the metal ion binding ligand may be spin coated onto a substrate to form the coating. Methods for spin coating are known in the art. For example, the polymers may be dissolved in a suitable solvent, the solution spin coated onto the substrate and the solvent removed to form a coating. Alternatively, the polymer comprising the metal ion binding ligand or a precursor thereof may be coated onto the substrate by plasma polymerisation. A suitable method is disclosed in Blattler et al. (2006).

[071 ] In other embodiments suitable for binding Cu²⁺ ions by PEI the polymer may be physically or chemically adsorbed to carrier particles. The carrier particles are solid and porous nano- and micrometer sized particles of silica, synthetic and natural. Examples of natural silica particles are diatomaceous earth materials that by themselves have shown to have antifouling properties due to their binding of air bubbles acting as a physical barrier against biofouling (Lamb et al. 2013). In these embodiments, the antiscale and/or antifouling coating has a combined metal ion flux antifouling mechanism and an inherent antifouling mechanism from the air entrapment of diatomaceous earth materials. The diatomaceous earth or other carrier particles can be surface modified with PEI using literature methods (Beatty et al. 1999).

[072] In other embodiments suitable for binding Cu²⁺ ions, the metal ion binding ligand comprises at least one imidazole group. In embodiments, the metal ion binding ligand comprises two imidazole groups. In embodiments, the metal ion binding ligand comprises three imidazole groups.

[073] Alternatively, the metal ion binding ligand may be an integral part of a larger molecule such as an enzyme (eg. a metalloenzyme), a protein (eg. a metalloprotein), a porphyrin or a dextrin.

[074] The metal ion may be an ion of any metal belonging to groups 3-13 and periods 4-7 in the periodic table. For example, the metal may be selected from the group consisting of Cu, Zn, Fe, Co, Mn, and V. Copper and zinc ions are preferred for antifouling compositions because they are well known broad-spectrum biocides and they also exist in both fresh and sea water. [075] The polymer comprising the metal binding ligand may be cross linked with a cross linking agent. Suitable cross linking agents include molecules or macromolecules containing more than one group which is reactive towards a functional group of the metal ion binding ligand, such as, but not limited to, isothiocyanate, isocyanate, sulfonyl chloride, aldehyde, ketone, carbodiimide, acyl azide, anhydride, fiuorobenzene, carbonate, NHS ester, imidoester, epoxide, fluorophenyl ester, halogenobenzene, and halogenoalkenes. Examples of suitable crosslinking agents for amine containing metal ion binding ligands are glutaraldehyde, genipin (Butler el al., 2003), disuccinimidyl suberate, bis(sulfosuccinimidyl) suberate, poly(vinylchloride), ethylenedichloride, 1.4-dibromo-butene, 1.9-dibromononane, 1.10- dibromodecane, 1.3.dibromo-2-propanol, 1.7-dibromoheptane, 1.12-dibromododecane, and 1.4-dibromo- 2.3-butanedione.

[076] We have found that cross linking improves the stability of the coating. The coating can be cross linked by contacting the spincoated substrate with a solution comprising the cross linking agent for a suitable period of time and then washing. The spincoated substrate may be contacted with the solution comprising the cross linking agent for a period of 5 to 60 minutes, such as about 30 minutes.

[077] Optionally, after cross linking any unreacted reactive groups on the cross linking agent may be capped by further treating the substrate with a solution containing the polymer comprising the metal binding ligand for a suitable period of time, such as about 30 minutes. The coated substrate can then be washed and dried.

[078] In embodiments of the invention we exploit a difference in binding constant between the metal ion of interest in a first oxidation state and the metal ion of interest in a different oxidation state to form a coating that binds the metal ion in the first oxidation state and releases at least some of the bound metal ion in the second oxidation state. Provided the metal is biocidal in at least one of the oxidation states an antiscale and/or antifouling action is achieved through flux of metal ions in both oxidation states from the coating.

[079] In these embodiments, the binding constant between the ligand and the metal ion in a first oxidation state is greater than the binding constant between the ligand and the metal ion in a second oxidation state. The metal ion may be pre-loaded to the ligand prior to the coating being applied to a surface or structure or, advantageously, the coating may be applied to a surface with no metal ion bound to the ligand and the coated surface placed in an aqueous environment whereupon the coating selectively binds to metal ions present in the water.

[080] Thus, in a second aspect the present invention provides an antiscale and antifouling system for surfaces or structures that are maintained in an aqueous environment, the system comprising: - an antiscale and/or antifouling coating for the surface or structure, the coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with a solution containing the selected metal ion the ligand binds to at least some of the selected metal ions from the solution to form a coating having bound metal ions; and

- a release system for reducing the binding constant between the bound metal ion and the metal ion binding ligand to thereby release at least some of the bound metal ions from the coating.

[081 ] The release system for reducing the binding constant between the bound metal ion and the metal ion binding ligand may effect release of the bound metal ion and the metal ion binding ligand by altering the oxidation state of the bound metal from a first oxidation state to a second oxidation state, wherein the binding constant between the metal ion binding ligand and the metal ion is greater in the first oxidation state than it is in the second oxidation state such that the ligand binds the metal ion in the first oxidation state and releases at least some of the bound metal ion in the second oxidation state.

[082] Alternatively, the release system for reducing the binding constant between the bound metal ion and the metal ion binding ligand may effect release of the bound metal ion and the metal ion binding ligand by chemically or physically modifying the metal ion binding ligand with metal bound thereto to release the bound metal ion.

[083] Thus, in some embodiments the release system comprises means for chemically or physically modifying the metal ion binding ligand. In these embodiments, the release system may comprise means for altering the configuration and/or oxidation state of the ligand so as to reduce the binding constant between the metal ion binding ligand and the metal ion. For example, the means for altering the configuration and/or oxidation state of the ligand may be an acid or base, an electrochemical treatment to alter the oxidation state of binding moieties in the metal ion binding ligand and/or altering the configuration of the metal ion binding ligand, or a photochemical treatment to alter the configuration of the metal ion binding ligand.

[084] In other embodiments the release system is a redox system for reducing or oxidising the bound metal ion from the first oxidation state to the second oxidation state. In embodiments, the redox system is a macroscopic metal surface having an electrochemical potential applied thereto. In other embodiments, the redox system is an electroactive particle system, such as carbon nanotubes or a conducting polymer. In each case, the redox system may be coupled with an electron source such as an electric power source, a photocatalyst or a sacrificial anode.

[085] In embodiments, the redox system comprises an electrode having an electrochemical potential applied thereto. This could for instance be the metal at which the coating is applied in the case of metal -

15 surfaces. As an example the Cu²7Cu ^" redox couple has a standard potential of +0.159 V. Therefore, an electrode requires a redox potential lower than this value in order to reduce Cu²⁺. The antiscale and/or antifouling coating can be coated onto a stainless steel surface.

[086] In other embodiments, the redox system comprises an electroactive nanoparticle or a conducting polymer. In each case, the redox system may be coupled with an electron source such as an electric power source or obtain the energy from the sunlight.

[087] In other embodiments of the invention we exploit a change in configuration of the ligand-metal complex when the metal ion of interest is reduced or oxidised from a first oxidation state to a second oxidation state such that at least some of the bound metal ion is released from the coating.

[088] The present invention therefore provides a coating that binds the metal ion in a first oxidation state. Advantageously, the metal ion in the first oxidation state may be naturally present in an aqueous environment in which the antifouling coating is to be used, such as in fresh or sea water. The metal ion in the first oxidation state will bind, via the metal ion binding ligand, to the antiscale and/or antifouling coating. The redox system will then either reduce or oxidise the metal ion to the second oxidation state and, as a result of the lower level of binding between the ligand and the metal ion in the second oxidation state, at least some of the metal ion in the second oxidation state will be released from the coating to form a biocidal interface which also acts as antiscale on the surface of the coating. Alternatively, if there is a change in configuration of the ligand-metal complex when the metal is reduced or oxidised to the second oxidation state the metal ion may then be oxidised or reduced back to the first oxidation state and released from the coating in the first oxidation state. Due to the re-establishment of equilibrium following the release of the reduced or oxidised metal ion, a 'fresh^' metal ion is bound to the free site on the ligand. Taken together these two mechanisms create a high surface concentration of metals in both states. Both can therefore act as biocidal agents.

[089] In embodiments, the metal ion is copper. In these embodiments, the metal ion in the first oxidation state is Cu²⁺ and the metal ion in the second oxidation state is Cu ' . Cu⁺ is a known biocide that has been used in antifouling coatings (Ytreberg, et <//. 2010). The antiscale and/or antifouling coating described herein may provide a high, constant, bio-available flux of copper ions across the interface, but not in the sacrificial fashion of prior art copper-releasing paints or copper plates on ships. In contrast, the metal ion binding ligand of the polymer attracts ions of a certain oxidation state from water into the coating, i.e. not only to the surface between the water and the coating, in as large concentrations as possible. Once loaded these ions are reduced or oxidized by electrochemical means to a higher or lower oxidation state, i.e. Cu²⁺ <-> Cu¹ , V²⁺ <-> V⁺, Fe³⁺ <-> Fe²⁺ etc. As the electrochemically activated ions are not as strongly coordinated to the ligands they will diffuse to the interface, and there create a flux of ions at the interface needed to prevent both scale build-up and biofouling. With regards to Cu^" it is known to interact with various biological molecules, such as respiratory redox enzymes, thereby killing microbes. Upon death of the organism, reoxidised Cu²' is released, thus attaining an environmentally sustainable closed loop.

[090] In other embodiments, the metal ion is zinc; In these embodiments, the ligand selectively binds Zn²⁺ from the aqueous environment and the bound Zn^{~ '} is then released from the coating by the action of the release system on the ligand. Suitable ligands for zinc ions include azoles (e.g. imidazole, pyrazole, 1 ,2,4-trazole, tetrazole) and polymeric amidoxime.

[091 ] In other embodiments, the metal ion is tin. In these embodiments, the metal ion in the first oxidation state is Sn⁴⁺ and the metal ion in the second oxidation state is Sn²⁺. Suitable ligands for tin ions include tartaric, citric, oxalic, and 2-mercaptopropanoic acids.

[092] In other embodiments, the metal ion is silver. Suitable ligands for silver ions include phosphenic acid polymer.

[093] In a third aspect, the present invention provides a coating composition comprising an aqueous based medium or an organic solvent based medium and an antiscale and/or antifouling composition comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with an aqueous environment containing the selected metal ion the ligand binds to at least some of the selected metal ions from the aqueous environment. The coating composition may be a liquid, emulsion or suspension of the metal ion binding ligand in an aqueous based medium such as water, or water in combination with one or more organic solvent(s). Useful organic solvents include alcohols, such as methanol, ethanol, ether, esters, and the like.

[094] The coating composition may also contain additional materials, such as dispersants, surfactants and the like.

[095] The antiscale and/or antifouling coating can be applied to the surface or substrate using known techniques. For example, the coating composition can be spray coated, dip coated, brushed, rolled or spin coated onto the surface or substrate. Once the coating composition has been applied to the surface the aqueous based medium or organic solvent based medium is evaporated to produce a surface or substrate coated with a layer of the polymer having a metal ion binding ligand. The coating may be applied to the whole of the surface or substrate or only part of the surface or substrate. For normal use, the coating is applied to any part of the surface or substrate that is regularly in contact with an aqueous environment.

[096] Alternatively, the coating composition of the invention may be incorporated into a polymer base that is suitable for coating or manufacturing an object that may be immersed in an aqueous environment. For example, a latex coating material or a polyethylene-based polymer may be used as a polymer base for the antifouling and/or antiscale composition.

[097] The antifouling and/or antiscale coating of the invention may have a thickness in the range of from about 1 micron to about 500 microns.

[098] Thus, the present invention also provides a method for forming an antiscale and/or antifouling coating on a surface, the method comprising coating the surface of the substrate with a coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with an aqueous environment containing the selected metal ion the ligand binds to at least some of the selected metal ions from the aqueous environment.

[099] In another aspect, the present invention relates to a coated surface or substrate comprising a surface or substrate and a coating according to the first aspect of the invention thereon. The surface or substrate may be made from any material including, but not limited to metal, plastic, wood and ceramic. The surface or substrate may be used in: marine applications such as shipping (metal hulls), leisure craft (plastic and wooden hulls), engines, marine platforms, underwater constructions, ocean laying pipes, underwater instruments, rigs, desalination plants, oceanic structures such as marine oil and gas rigs; fresh water applications such as water storage, groundwater wells, drinking water distribution, waste water treatment, sewage water systems; industrial applications, such as cooling water cycles, heat exchangers, power stations, oil pipelines, membranes, fluid flow, fuel, food processing, brewery, winery, pharmaceutical manufacturing, papermaking, paint production, pulp industry machines; and medical or biological applications such as orthopaedic implants, respirators, contact lenses, catheters, haemodialysis, teeth/dental implants, biosensors, and microelectrochemical drug delivery devices.

[0100] From the foregoing description it will be evident that the present invention also provides a method for preventing or reducing scale and/or biofouling on a surface that is maintained in an aqueous environment, the method comprising coating the surface with the antiscale and/or antifouling system of the second aspect of the invention.

[0101 ] The present invention further provides a metal ion extraction process comprising contacting an aqueous solution comprising a metal ion of interest with a surface having a metal ion binding ligand to bind the metal ion thereto, separating the surface having the metal ion binding ligand with the metal ion bound thereto from the aqueous environment, and releasing the bound metal ion from the metal ion binding ligand.

[0102] The metal ion binding ligand may be any of the ligands known in the art to be suitable for their strong ability to bind to the selected transition metal ions. By way of examples, suitable ligands for copper ions include azoles (e.g. imidazole, pyrazole, 1 ,2,4-trazole, tetrazole), polymeric amines (polyethyleneimine (PEI), polyallylamine, polymeric amidoxime) and others such as 1 ,1 ,4,7, 10,10- hexamethyltriethylenetetramine, 1 , 1 ,4,6,6-pentamethyldiethylenetriamine, tris[2- (dimethylamino)ethyl]amine, and the protein stellacyanin. Suitable ligands for zinc ions include azoles (e.g. imidazole, pyrazole, 1,2,4-trazole, tetrazole) and polymeric amidoxime. Suitable ligands for tin ions include tartaric, citric, oxalic, and 2-mercaptopropanoic acids. Suitable ligands for silver ions include phosphenic acid polymer.

[0103] In embodiments, the metal ion binding ligand is PEI. We have found that PEI has the capacity to adsorb a large amount of copper. Therefore, these embodiments of the invention may be used for the mining of copper from sea water and in the purification of water by extraction of copper (e.g. extraction of copper from water in mining processes.

EXAMPLES

[0104] Two approaches that can be used to form coatings are shown in Figure 1 . Ligands were spin coated and crosslinked or plasma polymerized followed by coupling of ligands.

[0105] Example 1 - General methods

[0106] Coating thickness determination

[0107] Coating thicknesses were determined using a multi-angle spectroscopic ellipsometer (V-VASE, J.A. Wollam Co., Inc.) for coatings on gold-coated substrates, and silicon wafers. The wavelength of incident light was scanned between 250 to 1 100 nm in 10 nm steps and angles were varied between 65° to 75° in steps of 5°. Data were fit to a Cauchy overlayer on an infinitely thick generic gold substrate for polymer coatings on gold electrodes or gold coated QCM-substrates. For polymers on Si-wafers, the optical parameters of the substrate were first separately determined and fixed and then used as the substrate layer.

[0108] Coating morphology and validation of ellipsometry model

[0109] The coating morphology was investigated by atomic force microscopy (AFM) using a muttimode 8 with a nanoscope 5 controller (Bruker). Pinholes in the coatings were used to validate that the thickness values from the ellipsometer model were realistic.

[01 10] Quartz crystal microbalance with dissipation monitoring (QCMD) and electrochemical (E)QCMD. [011 1] The mass increase and mechanical properties of the coatings in solution and when subjected to electrochemical manipulation were monitored using a QCMD (Q-Sense E4, Q-Sense), using either normal flow cells, or for EQCMD an electrochemical cell connected to a IM6ex Zahner elektrik potentiostat. Coatings were prepared on gold QCM-substrates. The solvent used was 100 mM KC1 in MilliQ-water. For EQCM a platinum plate was used as the counter electrode and an AgCl electrode was used as reference, all potentials are given versus AgCl. Where applicable the coatings were loaded with copper by three different approaches: in the QCM using 10 mM CuS0₄ solution; by incubation in excess 10 mM CuS0₄ for > I h; or by incubation in 200 ppb CuS0₄ in MilliQ-water over night.

[0112] Elemental composition of coatings and metal uptake quantification

[0113] The elemental composition of the coatings was determined using X-ray photoelectron spectroscopy (XPS) using a Kratos Axis Ultra DLD spectrometer equipped with a monochromatic Al Ka source. The metal content of the coatings was evaluated as the ratio between metal and nitrogen, this as nitrogen are responsible for the metal binding of the coatings and this ratio eliminates influence from coating thickness, surface adsorbed hydrocarbons or coating imperfections.

[01 14] Metal uptake by coated substrates

[01 15] Metal uptake studies were conducted for copper in 200 ppb CuS04 in MilliQ-water or in artificial seawater. Competitive uptake studies were conducted in artificial seawater containing 200 ppb Cu and molar equivalent concentrations of Al, Cd, Co, Cr, Fe, Mn, Ni, Pb, Zn, Mo, V, prepared using the following metal salts: Aluminium chloride hexahydrate (Sigma-Aldrich), Cadmium nitrate tetrahydrate (Sigma-Aldrich), Cobalt(II) chloride hexahydrate (Sigma-Aldrich), Chromium(III) nitrate nonahydrate (Sigma-Aldrich), Copper (II) sulfate pentahydrate (Chem-Supply), Iron(II) sulfate heptahydrate (Sigma- Aldrich), Manganese(II) sulfate monohydrate (Sigma-Aldrich), Nickel(II) nitrate hexahydrate (Sigma- Aldrich), Lead(II) nitrate (May & Baker (Australia) Pty Ltd), Zinc chloride (Scharlau, Scharlab S.L), Sodium molybdate dihydrate (Sigma-Aldrich), Vanadium(III) chloride (Sigma-Aldrich).

[0116] The used artificial seawater was prepared as previously described (Handa et al., 2006), but excluding sodium azide. In addition, metal uptake from real seawater was determined. Seawater samples were collected from Outer Harbour (North Haven, South Australia) at three different sites approximately 100 m apart. The concentration of selected metals in the seawater was quantified using an Agilent 7500ce inductively coupled plasma mass-spectrometer (ICPMS) with an octopole reaction system. Substrates with polymeric coatings were submerged for three days before being rinsed, dried with N₂ and analysed.

[0117] Example 2 - Preparation of a polyethtyleneimine coating by spin coating [01 18] The goal was to prepare films thinner than 15 nm so that electrons could tunnel across the films during the electrochemical experiments, otherwise the films would act insulating.

[0119] Spin coating

[0120] Coatings were deposited on gold or silicon wafer substrates by spin coating of polyethyleneimine (PE1) dissolved in ethanol at 2000rpm for 60 seconds using a Karl Suss Delta 80 Spin Coater (SUSS MicroTec), followed by baking on a hotplate at 60 °C for 5 minutes.

[0121] Crosslinking of spin coated films

[0122] Subsequent to the spin coating, the stability of the coatings was improved by crosslinking using the following protocol:

• Submerse the substrate comprising the spincoated substrate in 5 ml glutaraldehyde solution (0.5 wt% in water) for 30 min.

• Wash the sample by dipping into 5 ml MilliQ-water three times.

• Submerse the sample in 5 ml polyethyleneimine solution (2 mg/mL in water) for 30 min.

• Wash the sample by dipping into 5 ml MilliQ-water three times.

Dry the sample using a nitrogen stream. [0123] Results

[0124] The spin coating followed by crosslinking provided a means to prepare films with well-defined thickness, as seen in Table 1.

[0125] Table 1- Film thicknesses, for spin-coated PEI films prepared from different concentrations on different substrates, before and after crosslinking.

[PEI] in

Substrate Before crosslinking After crosslinking preparation (%)

Average STDEV Average STDEV

0.05 Si 6.2 0.7 8.0 1.1

0.05 Au 1 1.7 3.8 14.3 4.5 0.1 Si 1 1.5 0.5 14.5 0.8

0.1 Au 22.5 2.9 22.3 2.9

[0126] Characterization of spin coated films using AFM revealed the films to be very smooth and dense, with the exception of some areas with pinholes. Furthermore, the AFM analysis confirmed the thickness values from the ellipsometry to be reasonable, as seen in Figure 2.

[0127] Copper uptake

[0128] It was found that the films rapidly take up copper from model solutions (200 ppb copper in MilliQ-water and artificial seawater), reaching close to equilibrium in about three hours (Figure 3).

[0129] It was further surprisingly found that the films selectively took up copper from artificial seawater containing a mix of metal ions. Initially some other metals could be observed, but at later time-points (4h) only copper was observed (Figure 4).

[0130] It was found that the films, largely selectively, accumulated copper from real seawater (Figure 5).

[0131] Film stability during submersion and electrochemical manipulation

[0132] Based on film thickness measurements before and after submersion of samples in copper containing (200 ppb) MilliQ-water and artificial seawater and the signal from the Si (substrate) in XPS for samples submerged for three days in seawater, it was concluded that the films were stable during submersion (Table 2 and Figure 6).

[0133] Table 2 - Stability of crosslinked films prepared from 0.05% PEI in EtOH upon copper loading.

Before crosslinking After crosslinking After Cu loading

128 hours 200

ppb

Average S.D. Average S.D. Average S.D.

Milli Q water 5.3 0.45 7.2 0.93 6.7 0.25

Artificial Seawater 6.1 0.05 7.5 0.48 8.2 0.61 [0134] Based on behaviour during EQCMD, that is generally no significant mass loss as determined from frequency change, it was concluded that the films are stable also during electrochemical manipulations in the range of investigated potentials (-800 mV to +600 mV), see figures below. To put the frequency change in perspective with film mass: The Sauerbrey equation for rigid films can be used to calculate the mass change:

CAf

Am =

n

[0135] where A is the mass change, C = 17.7 ng Hz^'1 cm^"2 for a 5 MHz quartz crystal, Δ/is the frequency change and n is the overtone number. The frequency change in Figures 7, 8 and 9 is typically less than +5 Hz (already normalized for overtone number). This corresponds to a mass loss of less than 90 ng/cm². Given that the dry films had a thickness of about 14 nm, corresponding to 1 .4 ug / cm² if assuming a density of 1 gram / cm³, and that they should swell to become even thicker in water, this small mass loss is negligible.

[0136] Example 3 - Coating preparation by plasma polymerization

[0137] The deposition of a polymeric coating onto gold or silicon wafer substrates by plasma polymerization was performed as previously described (Blattler et al., 2006) using a custom built reactor (Griesser, 1989). The reactor was operated with a 13.56 MHz radio-frequency power generator and matching network. Power and reaction time were varied to determine the functional group incorporation and film thickness (see results section). Propionaldehyde vapours produced a deposited plasma polymer with functional aldehyde groups forming a reactive interlayer which allowed facile conjugation of nucleophiles (i.e. ligands of interest) to be coupled onto the substrates. Polyethyleneimine (PEI) or polyallylamine were reacted with aldehyde groups in the coating.

[0138] Results

[0139] The relationship between aldehyde plasma polymer thickness and polymerization time was investigated. A linear relationship was apparent for polymerization times longer than 10 seconds (Figure 10). Based on this data, a plasma polymerization time of 15 s was selected to generate functional coatings of approx. 10 nm.

[0140] A typical experiment proving the binding of ligand containing polymers to the aldehyde plasma polymer is illustrated in Figure 1 1. The reduction in frequency corresponds to increase in mass, which is from the, in this case, PEI binding to the aldehyde plasma polymer. [0141] Pethyleneimine (PEI) or polyallylamine conjugated coatings were then incubated with a 10 mM solution of copper ions in water, extensively washed, and analysed for the presence of copper on the surface using XPS. The polymeric ligands were able to bind copper as seen in Table 3.

[0142] Table 3 - Copper binding to plasma polymerized polyallylamine and PEI samples

[0143] Example 4 - Electrochemical manipulation to stimulate copper release

[0144] From EQCM followed by electrochemical manipulation it was found that the release of copper from the films could be largely accelerated by electrochemical manipulation.

[0145] A series of cyclic voltammetry programs were run over the course of approximately 2 hours according to the parameters shown in Table 4. The scans started at a potential of 600 mV ('oxidising'). The fluid flow was 0.1 ml/min. The results are shown in Figure 12.

[0146] Table 4 - Experimental details of electrochemical program 1.

[0147] In a second electrochemical program, a series of cyclic voltammetry programs were run over the course of approximately 2 hours according to the parameters shown in Table 5. The direction of the scan was determined by the starting potential and was either 600 mV ('oxidising') or -800 mV ('reducing'). Additionally, the fluid flow was chosen to be either slow (0.1 ml/min) or fast (0.4 ml/min). [0148] Table 5 - Experimental details of electrochemical program 2.

[0149] During the electrochemical experiments- copper peaks were observed in the cyclic

voltammograms of copper loaded samples (Figure 13).

[0150] Additional

[0151] During EQCM analysis of non-crosslinked PEI films prepared from 0.1% PEI in EtOH, it was found that the decrease in copper concentration at the electrode, as determined by the integrals of the copper peaks in the voltammograms, correlated with dissolution of the polymer film (Figure 14). This behaviour indicates that copper was released together with PEI. Such a film could be useful as an electrochemically activated, copper containing, self-polishing coating.

PROPHETIC EXAMPLES

[0152] N'-[(E)-2-Pyrimidinylmethylene]benzohydrazide (I) is a ligand that strongly binds Cu^{2 '} selectively, but not Cu⁺. The ligand is available commercially and can be modified with coupling groups such as carboxylic or amine groups in positions X or Y to allow for covalent attachment of the ligand to a polymer.

(I)

[0153] Prophetic Example 1 - Polymer modification

[0154] The polymer backbone that the ligand can be attached to is based on polyvinylbenzyl chloride (PVBC), as shown below. The main advantage with this polymer is that the synthetic route for the modification is known and according to literature works at high yield and mild conditions.

[0155] The resulting polymer, assuming an amine coupling, is shown below.

[0156] Prophetic Example 2 - Redox agent

[0157] The simplest and most straightforward approach to establish a Cu²7Cu' dynamic equilibrium at the surface of the coating is the direct, electrochemical reduction of Cu²⁺ within the coating. The establishment of a dynamic Cu²⁺/Qf equilibrium can be monitored and quantified by an increased electrical current (a quasi-corrosion current) at the coating (the working electrode in this case). In electrochemistry, such an increase in current is sometimes called autocatalytic cycle. Autocatalytic currents can be used to quantify and optimize the coating. Generally, a higher autocatalytic current corresponds with a higher Cu²7Cu^r flux.

[0158] Prophetic Example 3 - Characterization

[0159] Surface characterization

[0160] The physico-chemical characterization, such as hydrophobicity, surface roughness, swelling in water etc. can be carried out by known surface techniques such as light microscopy, contact angle, QCM- D and SEM.

[0161] Copper loading characterization

[0162] After spin-coating or plasma-mediated coating of the polymer, or spacer treatment, on a suitable surface the adsorbed amount and rate of water can be studied by QCM-D. Cu^2÷ adsorption experiments can also be carried out at varying concentrations of Cu ⁺. In parallel, the Cu^2* uptake can be monitored electrochemically by application of a specifically tailored stripping voltammetry technique.

[0163] Prophetic Example 4 - Bacterial testing of antifouling efficiency

[0164] Prior to testing the coatings against colonization by marine organisms, their resistance to biofouling can be tested by evaluating their ability to resist the formation of bacterial biofilms. This model is relevant to coatings intended for prevention of marine biofouling because many bacteria, including the Staphylococcus species that we have considerable experience with, are sensitive to Cu⁺ ions in the same way that marine organisms are. Cu ' ions are known to exhibit antibacterial properties; they probably act in the same way that Ag⁺ ions do, by entering the bacterial cytoplasmic space and interfering with bacterial redox enzymes essential for the oxidative respiratory burst metabolism. Analogous redox enzymes are found in a wide variety of organisms, thereby making Ag and Cu ions broad spectrum antimicrobial compounds. [0165] Prophetic Example 5 -Testing ofantiscaling efficiency

[0166] The coatings can be evaluated for their ability to resist the formation of scaling by exposing them to supersaturated brine, containing for example CaC0₃ and HC1. Coatings applied on stainless steel samples can be used as substrates and in order to observe scaling tendency the samples are weighed before and after an experiment. Temperature and pH are parameters that influence the formation of scaling and they can be altered during an experiment. The experiments can be done using, for example, a Rotating Cylinder Electrode (RCE) or a heat exchanger cell and the surface can be analysed by using SEM (scanning electron microscope).

[0167] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

[0168] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0169] All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of each claim of this application

REFERENCES

[0170] Beatty, S.T., Fischer, R. J., Rosenberg, E. Comparison of novel and patented silica-polyamine composite materials as aqueous heavy metal ion recovery materials. Separation science and technology, 1999, 34(14), 2723-2739

[0171 ] T.M. Blattler, S. Pasche, M. Textor, H.J. Griesser, High Salt Stability and Protein Resistance of Poly(l-lysine)-g-poly(ethylene glycol) Copolymers Covalently Immobilized via Aldehyde Plasma Polymer Interlayers on Inorganic and Polymeric Substrates, Langmuir, 22 (2006) 5760-5769.

[0172] M.F. Butler, Y-F. Ng, P.D.A. Pudney, Journal of Polymer Science: Part A: Polymer Chemistry, 41 (2003) 3941 -3953.

[0173] H.J. Griesser, Small scale reactor for plasma processing of moving substrate web, Vacuum, 39 (1989) 485-488.

[0174] P. Handa, C. Fant, M. Nyden, Antifouling agent release from marine coatings-ion pair fonnation/dissolution for controlled release, Progress in Organic Coatings, 57 (2006) 376-382.

[0175] Shiro Kobayashi , Kazuhisa Hiroishi , Masazumi Tokunoh , Takeo Saegusa, Chelating properties of linear and branched poly(ethylenimines); Macromolecules, 1987, 20 (7), pp 1496-1500.

[0176] Lamb, R., Wu, A. H-F., Nakanishi, K., Diatom attachment inhibition: limiting surface accessibility through air entrapment, Biointerfaces 2013, 8:5

[0177] E. Ytreberg, et al., Science of the Total Environment 408 (2010) 2459-2466.

Claims

1. An antiscale and/or antifouling coating comprising a metal ion binding ligand having an affinity for a selected metal ion such that when the coating is in contact with an aqueous environment containing the selected metal ion the ligand binds to at least some of the selected metal ions from the aqueous environment.

2. The antiscale and/or antifouling coating of claim 1 , wherein the metal ion binding ligand is a polymer comprising nitrogen, sulphur and/or oxygen heteroatoms.

3. The antiscale and/or antifouling coating of claim 2, wherein the metal ion binding ligand comprises 2, 3, 4, 5 or 6 heteroatoms capable of binding to the metal.

4. The antiscale and/or antifouling coating of claim 3, wherein the polymer comprising the metal ion is a polyamine.

5. The antiscale and/or antifouling coating of claim 4, wherein the polyamine is a polyalkyleneimine.

6. The antiscale and/or antifouling coating of claim 5, wherein the polyalkyleneimine is

polyethyleneimine.

7. The antiscale and/or antifouling coating of any one of claims 4 to 6, wherein the polyamine is cross linked with a cross linking agent.

8. An antiscale and'or antifouling system for surfaces or structures that are maintained in an aqueous environment, the system comprising: the antiscale and/or antifouling coating of any one of claims 1 to 7; and a release system for reducing the binding constant between the bound metal ion and the ligand to thereby release at least some of the bound metal ions from the coating.

9. The antiscale and/or antifouling system of claim 8, wherein the release system is a redo system.

10. The antiscale and/or antifouling system of claim 9, wherein the redox system is a metal surface having an electrochemical potential applied thereto.

1 1. The antiscale and/or antifouling system of claim 9, wherein the redox system is an electroactive nano- or micron-sized particle or a conducting polymer.

12. The antiscale and/or antifouling coating of any one of claims 1 to 7 or the ant iscale and/or antifouling system according to any one of claims 8 to 1 1 , wherein the metal ion is copper.

13. A method for preventing or reducing scale formation and/or biofouling on a surface that is maintained in an aqueous environment, the method comprising coating the surface with the antiscale and/or antifouling system of any one of claims 8 to 1 1.

14. A metal ion extraction process comprising contacting an aqueous solution comprising a metal ion of interest with a surface having a metal ion binding ligand to bind the metal ion thereto, separating the surface having the metal ion binding ligand with the metal ion bound thereto from the aqueous environment, and releasing the bound metal ion from the metal ion binding ligand.