Composition and method of removing contaminants using the composition

Abstract

A composition comprising MOF nanosheets spaced apart by magnetic nanoparticles intercalated between the nanosheets.

Description

[0001] THE from a liquid medium, their preparation method, and methods for removing contaminants from a liquid medium using said compositions. BACKGROUND OF THE INVENTION Environmental pollution is a significant contributor to diseases in living organisms, with water being crucial to humans, plants, and aquatic’s survival. However, removing both solid and dissolved contamination from a liquid medium, including water, remains a significant challenge. Molecular contaminants as well as small size suspended solids, such as microplastics (MPs), are most concerning due to the difficulty in detecting and removing them using current separation technologies, especially when they are both present in a liquid medium. The small size of microplastics is a particular concern, as they are untraceable and small invertebrates can ingest them. Moreover, microplastics can adsorb pollutants due to their high specific surface area, which can then be ingested by aquatic animals and ultimately consumed by humans, posing an unpredictable health risk. Current techniques for removing contaminants from liquid media include traditional filtration, photodegradation, adsorption, and membrane separation. However, conventional filters (paper or metal mesh) are limited to discriminate around 20 μm size particles and are therefore ineffective for separation of smaller microplastic and dissolved molecular contaminants. More specialised filtration procedures such as nano- or micro-filtration has also been trialled. However, those processes are only effective when the pore-size distribution of their membranes is tailored to each pollutant's size, dramatically reducing their versatility. Also, slow filtration rates, difficult recovery, and high-pressure requirements involved in those filtration techniques increase their operational cost, which inherently confines their use in highly specialised applications. Physico-chemical decontamination such as photo-degradation in the presence of photo- catalysts has also been found effective. However, those approaches are inefficient due to their low removal rate and inherently require significant decontamination time. For reference, photo-degradation over zinc oxide photo-catalysts only affords 65% photodegradation of 150 μm size polypropylene (PP) in over 450 hours, an operational time that is unacceptable by industrial standards. While photo-degradation may be faster in the case of smaller plastic particles, it was nevertheless found to produce dangerous carbon emissions (e.g. CO), effectively rendering photo-degradation unappealing on a large scale. There remains therefore an opportunity to develop decontamination means that address one or more limitations of existing ones. SUMMARY OF THE INVENTION The present invention provides a composition comprising Metal-Organic Framework (MOF) nanosheets spaced apart by magnetic nanoparticles intercalated between the nanosheets. The composition of the invention presents as a nanosheet-based structure that is stable with minimal to no tendency to delaminate. A challenge in the production of two-dimensional MOF sheets is that of minimising three-dimensional growth and preventing staking of two- dimensional MOF nanosheets. In that regard, and without wanting to be limited by theory, it is postulated that intercalated magnetic nanoparticles between MOF nanosheets can effectively stabilise the MOF in its two-dimensional coordination state and minimise delamination by anchoring to the metal nodes of the MOF framework. Intercalated magnetic nanoparticles can therefore allow to advantageously harness inherent qualities of two-dimensional MOFs, especially for use in decontamination processes. It is believed that the nanoparticles can effectively act as physical spacers between the nanosheets, exposing extended inter-sheet surface for adsorption of contaminants present in a liquid medium. Due to their magnetic nature, the nanoparticles also afford quick isolation of the composition from the liquid medium by magnetic separation for contaminant removal. In this context, it will be understood that by being "magnetic" the nanoparticles in the composition of the invention are made of a material that is susceptible to an external magnetic field, such that exposing the nanoparticles to an external magnetic field affords modification and manipulation their position in space. The magnetic nanoparticles may therefore be made of a material that is paramagnetic, superparamagnetic, ferromagnetic, ferrimagnetic, and / or antiferromagnetic. In some embodiments, the magnetic nanoparticles comprise a core made of a magnetic material encapsulated by a carbon shell. Magnetic nanoparticles having a carbon shell are particularly suitable to intercalate between MOF nanosheets. It is postulated that the high physico-chemical affinity of carbon with the organic regions of the MOF contributes to improve the overall mechanical stability of the nanosheet-based structure. The resulting composition advantageously displays high contaminant removal efficiency over multiple decontamination cycles. The invention also provides a method of synthesis of a composition of the kind described herein, said method comprising dissolving MOF precursors in a liquid medium, dispersing the magnetic nanoparticles in the liquid medium, and promoting formation of MOF nanosheets. It was advantageously observed that presence of magnetic nanoparticles within the solution of MOF precursors facilitates formation of MOF in nanosheet form as opposed to conventional bulk 3D crystalline MOF. Without wanting to be bound by theory, it is believed that magnetic nanoparticles coordinate preferentially to certain crystalline planes of the forming MOF, favouring differential growth along different crystalline directions. The present invention also provides a method of removing contaminants from a liquid medium, the method comprising adding a composition of the kind described herein to a liquid medium containing contaminants, whereby at least a portion of the contaminants adsorbs on the composition, and extracting composition having contaminants adsorbed thereto from the liquid medium by magnetic separation, thereby removing contaminants from the liquid medium. The specific nanosheet-based structure of the composition of the invention advantageously affords efficient adsorption of a wide range of contaminants, including dissolved molecular contaminants as well as suspended microscopic solids, such as microplastics. Further, the magnetic character of the nanoparticles affords swift isolation of the composition from a liquid medium by simple exposure of the medium to an external magnetic field. This makes the proposed method significantly more practical that conventional isolation by filtration or centrifugation. The inherent structural stability of the composition of the invention makes the composition highly suitable for solution processing. Accordingly, following a decontamination cycle the isolated composition having adsorbed contaminants can be readily regenerated, for example by solvent washing, for reuse. Advantageously, the composition of the invention has been observed to maintain its adsorption efficiency above 90% over at least three decontamination / regeneration cycles. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be now described with reference to the following non- limiting drawings, in which: Figure 1 shows an illustration of development of an embodiment composition having 2D MOF nanosheets (MIL-100) with carbon-encapsulated FeO magnetic nanoparticles (C@FeO) intercalated between the nanosheets, adsorption process, magnetic separation and potential microplastics removal pathway, Figure 2 shows the height profile analysis representing lateral dimensions of embodiment 2D MOF (MIL-100) nanosheets with intercalated magnetic nanoparticles, Figure 3 shows XRD analysis of magnetic nanoparticles (C@FeO), 2D MOF (MIL-100) and 2D MOF@C@FeO, the latter showing diffraction peaks from both C@FeO and 2D MOF, Figure 4 shows thermal gravimetric analysis (TGA) for microplastic (1g / L) removal, Figure 5 shows UV-VIS spectroscopy for methylene blue (MB) removal, Figure 6 shows UV-VIS spectroscopy for simultaneous removal of methylene blue (MB, 50 mg / kg) and microplastics (1g / L) from water, Figure 7 shows re-usability and stability of 2D MOF@C@FeO in three adsorption cycles showing around 92% Microplastics and Methylene Blue removal in last cycle, Figure 8 shows removal of (a) 100 nm, (b) 200 nm, and (c) 500 nm from MPs (1g / L) from water using 2D MOF@C@FeO (3g / L), Figure 9 shows (A) particle size analysis of MP (1g / L) and MP after adsorption, (B) UV-Vis spectroscopy of MP (1g / L) and MP after adsorption to investigate MP removal using 2D Fe MO@C@FeO (15%) (3g / L) for one hour, and (C) particle size analysis to investigate MP removal using 2D Fe MO@C@FeO (15%) (3g / L) for one hour, Figure 10 shows (A) particle size analysis, (B) UV-Vis spectroscopy of MP (1g / L) and MP after adsorption to investigate MP removal using 2D Co MO@C@FeO (15%) (3g / L) for one hour, and (C) particle size analysis for investigation of MP removal from water using room temperature based 2D Ni MOF@C@FeO as adsorbent; the MP concentration was 1g / L, the adsorbent dosage 3g / L, and adsorption time 1 hour, and Figure 11 shows removal of amine modified polystyrene and carboxylic modified polystyrene microplastics having (a) 1000 nm size, (b) 500 nm size, and (c) 30 nm size from water; adsorption time in (b) and (c) is 1 hour; MP (Polystyrene) concentration is 1g / L, adsorbent (2D MOF@C@FeO) dosage was 3g / L. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a composition comprising MOF nanosheets. MOFs are hybrid coordination structures formed by metal clusters comprising metal ions, e.g. metal ions or metal oxides, coordinated by multi-functional organic ligands. In the case of the MOF nanosheets of the invention, said coordination results in the formation of crystalline molecular arrangements which predominantly develop in a two-dimensional space. The term “nanosheet” is therefore used herein to refer to a 2D coordination structure having a thickness that is at least one order of magnitude smaller than each of length and width, such that the nanosheet has an aspect ratio of 1:10 or less. For example, MOF nanosheets in the composition of the invention may have a thickness from about 1 nm to about 100 nm. In some embodiments, the MOF nanosheets have a thickness from about 2 nm to about 25 nm. In those instances, the composition of the invention is particularly effective in the removal of contaminants from liquid media. MOFs according to the present invention include those having at least two metal clusters coordinated by at least one organic ligand. As used herein, the expression “metal cluster” is intended to mean a chemical moiety that contains at least one atom or ion of at least one metal or metalloid. This definition embraces single atoms or ions and groups of atoms or ions that optionally include organic ligands or covalently bonded groups. Accordingly, the expression “metal ion” includes, for example, metal ions, metalloid ions, and metal oxides. Suitable metal ions that form part of a MOF structure can be selected from Group 1 through 16 metals of the IUPAC Periodic Table of the Elements including actinides, and lanthanides, and combinations thereof. The metal ion may be selected from Li+, Na+, K+, Rb+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Sc3+, Y3+, Ti4+, Zr4+, Hf4+, V5+, V4+, V3+, V2+, Nb3+, Nb5+, Ta5+, Cr6+, Cr3+, Mo6+, Mo3+, W6+, W3+, Mn4+, Mn3+, Mn2+, Re7+, Re2+, Fe3+, Fe2+, Ru4+, Ru3+, Ru2+, Os3+, Os2+, Co3+, Co2+, Rh3+, Rh2+, Rh+, Ir4+, Ir2+, Ir+, Ni2+, Pd4+, Pd2+, Pt4+, Pt2+, Cu2+, Cu+, Ag+, Pb4+, Eu3+, acid, succinic acid, glutaric acid, phtalic acid, isophtalic acid, terephthalic acid, citric acid, trimesic acid, 1,2,3-triazole, pyrrodiazole, squaric acid, imidazole, or benzene-1,4- dicarboxylate (BDC). In some embodiments, the organic ligand comprises a linear dicarboxylate aromatic compound. In some embodiments, the organic ligand is selected from trimesic acid (H3BTC) and benzene-1,4- dicarboxylate (BDC). Organic ligands suitable for the purpose of the invention comprise organic ligands listed in WO 2010 / 075610 and Filipe A. Almeida Paz, Jacek Klinowski, Sergio M. F. Vilela, João P. C. Tomé, José A. S. Cavaleiro, João Rocha, ‘Ligand design for functional metal–organic frameworks’, Chemical Society Reviews, 2012, Volume 41, pages1088–1110, the contents of which are included herein in their entirety. In some embodiments, the metal ions in the MOF of the invention are one or more of Mn2+, Fe2+, Co2+, Ni2+, Cu2+and Zn2+. In some embodiments, the MOF nanosheets have a formula M2(OH)2(L), wherein M is Mn2+, Fe2+, Co2+, Ni2+, Cu2+or Zn2+and L is a linear dicarboxylate-based organic ligand. In some embodiments, the MOF nanosheets comprise a zeolitic imidazolate framework (ZIF). ZIF frameworks feature tetrahedrally-coordinated transition metal ions (e.g. Fe, Co, Cu, Zn, Ni) connected by organic imidazolate organic ligands, resulting in three-dimensional porous solids. Similarly to zeolites, ZIFs have great thermal and chemical stability. Depending on the choice of precursors, and now, according to the invention, depending on the choice of bio-molecule, many ZIF topologies can be synthesized. In some embodiments, the MOF nanosheets comprise benzene-1,4-dicarboxylate (BDC) ligands. BDC-based frameworks feature pseudo-octahedra coordinated metal clusters linked by linear p-terephthalate (1,4-benzenedicarboxylate) linkers. A suitable example MOF in that regard includes nickel benzene-1,4- dicarboxylate (BDC), also referred to as Ni-BDC. Accordingly, MOF nanosheets in accordance with the invention may be carboxylate-based MOF nanosheets, or heterocyclic azolate-based MOF nanosheets. Specific examples of MOF nanosheets according to the present invention include those commonly known in the art as CD-MOF-1, CD-MOF-2, CD-MOF-3, CPM-13, FJI-1, FMOF-1, HKUST-1, IRMOF- 1, IRMOF-2, IRMOF-3, IRMOF-6, IRMOF-8, IRMOF-9, IRMOF-13, IRMOF-20, JUC-48, JUC-62, MIL-101, MIL-100, MIL-125, MIL-53, MIL-88 (including MIL-88A, MIL-88B, MIL-88C, MIL-88D series), MOF-5, MOF-74, MOF-177, MOF-210, MOF-200, MOF-205, MOF-505, MOROF-2, MOROF-1, NOTT-100, NOTT-101, NOTT-102, NOTT-103, NOTT-105, NOTT-106, NOTT-107, NOTT-109, NOTT-110, NOTT-111, NOTT-112, NOTT-113, NOTT-114, NOTT-140, NU-100, rho-ZMOF, PCN-6, PCN-6’, PCN9, PCN10, PCN12, PCN12’, PCN14, PCN16, PCN-17, PCN-21, PCN46, PCN66, PCN68, PMOF- 2(Cu), PMOF-3, SNU-5, SNU-15’, SNU-21S, SNU-21H, SNU-50, SNU-77H, UiO-66, UiO-67, soc-MOF, sod-ZMOF, TUDMOF-1, UMCM-2, UMCM-150, UTSA-20, ZIF-2, ZIF-3, ZIF-4, ZIF-8, ZIF-9, ZIF-10, ZIF-11, ZIF-12, ZIF-14, ZIF-20, ZIF-21, ZIF-23, ZIF- 60, ZIF-61, ZIF-62, ZIF-64, ZIF-65, ZIF-67, ZIF-68, ZIF-69, ZIF-70, ZIF-71, ZIF-72, ZIF- 73, ZIF-74, ZIF-75, ZIF-76, ZIF-77, ZIF-90, or Ni-BDC. In some embodiments, the MOF comprises iron, cobalt, nickel, zirconium, manganese, or copper. In some embodiments, the MOF is MIL-100. Those MOFs have been found to be particularly effective to achieve stable compositions that afford effective contaminant removal. The MOF nanosheets of the invention are predominantly crystalline in nature. In a crystalline MOF, the metal clusters are coordinated by the organic ligands to form a geometrically regular network made of repeating units of cluster / organic ligand arrangements. A crystalline MOF generates diffraction patterns when characterized by commonly known crystallographic characterization techniques. These include, for example, X-ray powder diffraction (XPD), grazing incidence X-ray diffraction, small angle X-ray scattering (SAXS), single crystal X-Ray diffraction, electron diffraction, neutron diffraction and other techniques that would be known to the skilled person in the field of crystallography of materials. A MOF nanosheet in the composition of the invention may have a thickness from about 1 nm to about 100 nm. In some embodiments, the MOF nanosheets have a thickness from about 2 nm to about 25 nm. In those instances, the composition of the invention is particularly effective in the removal of contaminants from liquid media. In the composition of the invention, the MOF nanosheets are spaced apart by magnetic nanoparticles. As used herein, the term “nanoparticle” refers to a particle of matter ranging in size from about 0.1 nm to about 1,200 nm, as measured in terms of its greatest dimension. In some embodiments, the magnetic nanoparticles are paramagnetic, superparamagnetic, ferromagnetic, ferrimagnetic, and / or antiferromagnetic. When “paramagnetic”, the nanoparticles of the invention, when placed in a magnetic field, are magnetized parallel to the field to an extent proportional to the field. When the nanoparticles are “superparamagnetic”, they behave independently of one another in a manner similar to paramagnets, so that the particles show a net magnetization in the presence of a magnetic field, but then rapidly relax to show zero net magnetization when the applied magnetic field is removed. The magnetic nanoparticles may be made of any material making the nanoparticles magnetic. Accordingly, the magnetic nanoparticles of the invention may be made of a magnetic material that is paramagnetic, superparamagnetic, ferromagnetic, ferrimagnetic, and / or antiferromagnetic. In some embodiments, the magnetic nanoparticles of the invention comprise a magnetic metal, a magnetic metal carbide, a magnetic metal nitride, a magnetic metal sulphide, a magnetic metal phosphide, a magnetic metal oxide, or a mixture thereof. Examples of suitable magnetic materials in that regard include magnetic metals (such as iron, nickel, cobalt, lead, platinum, and neodymium) as well as magnetic metal oxides (such as iron oxide, cobalt oxide, etc.). Magnetic metal oxides in that regard may include Fe either as Fe(II), Fe(III), or a mixture of Fe(II) and Fe(III). Non-limiting examples of such oxides include FeO, Fe2O3, and Fe3O4. In some embodiments, the superparamagnetic particles may comprise chemical equivalents of iron metal oxide, such as (Fe,M)oFe2O3 where M may be, in one embodiment, Zn, Co, Ni, Mn, or Cr. In some embodiments the magnetic nanoparticles comprise a magnetic metal oxide selected from FeO, Fe2O3, and Fe3O4. In some embodiments, the iron oxide possesses a Fe2+to Fe3+ratio of about 1:1.5 to about 1:2.5. In some embodiments, the iron oxide possesses a Fe2+to Fe3+ratio of about 1:2. In those instances, the magnetic nanoparticle are particularly suitable to intercalate the MOF nanosheets and provide the resulting composition with excellent contaminant adsorption efficiency over multiple decontamination cycles. In some embodiments, the magnetic nanoparticles comprise a magnetic metal. Suitable examples of metals in that regard include iron, nickel, cobalt, lead, platinum, neodymium, or a magnetic alloy, for example comprising one or more of iron, nickel, cobalt, lead, platinum, and neodymium. Typically, magnetic nanoparticles suitable for use in the present invention have a saturation magnetisation that is typically not less than about 4 emu / g (or 4 Am2 / kg). In some embodiments, the magnetic nanoparticles have a range of coercivity from zero or near-zero up to about 500 Oe (or 40 kA / m). In some embodiments, the magnetic nanoparticles have a core-shell structure. That is, the magnetic nanoparticles may be made by a core material encapsulated by a shell material different from the core material. Typically, the core would be made of magnetic material, and the shell of a material that is conducive to the nanoparticle intercalating between MOF nanosheets. In some embodiments, the shell material comprises carbon. In some embodiments, the magnetic nanoparticles are in the form of core-shell nanoparticles having a magnetic core, for example made of a magnetic material of the kind described herein, encapsulated by a shell material comprising carbon. In some embodiments, the shell material is carbon. For example, the magnetic nanoparticles may have a core of FeO, Fe2O3, Fe3O4, iron, nickel, cobalt, lead, platinum, neodymium, or a magnetic alloy (for example, a magnetic alloy comprising one or more of iron, nickel, cobalt, lead, platinum, and neodymium) or a mixture thereof, encapsulated by a carbon shell. In some embodiments, the magnetic nanoparticles are C@FeO nanoparticles (according to a notation “shell material@core material”). Magnetic nanoparticles having a carbon shell are particularly suitable to intercalate between MOF nanosheets, in that they confer high stability to the nanosheets-based composition. The resulting composition can therefore display high contaminant removal efficiency over multiple decontamination cycles. Magnetic nanoparticles for use in the composition of the invention may have any dimension conducive to formation of stable compositions. In some embodiments, the magnetic nanoparticles have a largest dimension of between about 1 nm and about 500 nm, for example between about 10 nm and about 100 nm. In some embodiments, the magnetic nanoparticles have a largest dimension of between about 10 nm and about 50 nm. In some embodiments, the magnetic nanoparticles have a largest dimension of between about 150 nm and 1,100 nm. In the composition of the invention the MOF nanosheets are spaced apart by the magnetic nanoparticles, which are intercalated between the nanosheets. Depending on the dimensions of the nanoparticles, consecutive MOF nanosheets may have any average planar spacing conducive to the resulting composition being stable. By the combination being “stable” is meant that consecutive nanosheets remain in position relative to one another, while spaced apart by the nanoparticles, without exfoliating. In some embodiments, the composition comprises MOF nanosheets spaced apart by intercalated magnetic nanoparticles to a distance of from about 0.1 nm to about 1,200 nm. In some embodiments, the MOF nanosheets are spaced apart by intercalated magnetic nanoparticles to a distance of from about 150 nm to about 1,100 nm. For example, the MOF nanosheets may be spaced apart by intercalated magnetic nanoparticles to a distance of from about 10 nm to about 50 nm. Those ranges are found to confer the composition with high stability for contamination removal over multiple decontamination cycles. The composition of the invention may contain any amount of magnetic nanoparticles that is conducive to the composition being stable. In some embodiments, the composition contains an amount of nanoparticles between about 5 to about 75 (wt.%). The structure of the composition of the invention and the presence of magnetic nanoparticles intercalated between 2D MOF nanosheets can be assessed practically by any characterisation means known to the skilled person. For example, Transmission Electron Microscopy (TEM) and / or Scanning Electron Microscopy (SEM) imaging may be used to detect presence of the nanoparticles intercalated between MOF nanosheets in a repeating spatial arrangement and geometry. Also, height profile analysis performed on sample compositions (e.g. by Atomic Force Microscopy, AFM) can reveal the step-like height profile of MOF nanosheets spaced apart by a distance compatible with the dimension of the magnetic nanoparticles. Further, X-Ray Diffraction (XRD) analysis can be used to assess the two-dimensional nature of the MOF nanosheets, revealing preferential growth along certain crystallographic directions and allowing comparison with simulated XRD for corresponding 2D MOFs. The spatial formulation of the compositions of the invention may also be investigated through high- angle annular dark-field and bright field scanning transmission electron microscopy (HAADF-STEM, and HAABF-STEM) and Energy-dispersive X-ray spectroscopy (EDS), which can allow to appreciate the uniform spatial distribution of elements in the composition. Example characterisation procedures and corresponding result analysis is given in the Example section. As a result of the magnetic nanoparticles intercalating between the MOF nanosheets, the composition of the invention has larger surface area relative to corresponding stacked MOF nanosheets absent the magnetic particles. In some embodiments, the composition of the invention has a surface area between 10% and 50% larger than the surface area of stacked MOF nanosheets absent the magnetic nanoparticles. In some embodiments, the composition has a surface area of at least about 8 m2 / g, for example at least about 500 m2 / g, at least about 750 m2 / g, or at least about 1,500 m2 / g. In some embodiments, the surface area is about 750 m2 / g. It was advantageously found that surface areas within those ranges and values contribute to efficient adsorption of contaminants, for example relative to compositions made of stacked MOF nanosheets with no intercalated magnetic particles. The present invention also provides a method of synthesis of the composition described herein. The method comprises a step of dissolving MOF precursors in a solvent to form a solution of said MOF precursors. MOF precursors suitable for use in the method of the invention comprise a metal ion precursor and a multi-dentate organic ligand having at least two chemical moieties capable of coordinating a metal ion. MOF precursors for use in the method of the invention may include those known in the art that provide the metal ions listed herein in the solution within a suitable solvent. In some embodiments, the metal ion precursor comprises a salt of said metal ion selected from a metal-chloride, -nitrate, -acetate, -sulphate, -hydrogen sulphate, -bromide, -carbonate, - phosphate, and derivatives thereof, and the organic ligand has at least two chemical moieties comprising a carboxylate, a phosphonate, a sulphonate, a N-heterocyclic group, and a combination thereof. Examples of suitable metal salt precursors include, but are not limited to, cobalt nitrate (Co(NO3)2·xH2O), zinc nitrate (Zn(NO3)2·xH2O), iron(III) nitrate (Fe(NO3)3·xH2O), aluminium nitrate (Al(NO3)3·xH2O), magnesium nitrate (Mg(NO3)2·xH2O), calcium nitrate (Ca(NO3)2·xH2O), manganese(II) nitrate (Mn(NO3)2·xH2O), cobalt chloride (CoCl2·xH2O), zinc chloride (ZnCl2·xH2O), iron(III) chloride (FeCl3·xH2O), iron(II) chloride (FeCl2·xH2O), aluminium chloride (AlCl3·xH2O), magnesium chloride (MgCl2·xH2O), calcium chloride (CaCl2·xH2O), manganese(II) chloride (MnCl2·xH2O), cobalt acetate (Co(CH3COO)2·xH2O), zinc acetate (Zn(CH3COO)2·xH2O), iron(III) acetate (Fe(CH3COO)3·xH2O), iron(II) acetate (Fe(CH3COO)2·xH2O), aluminium acetate (Al(CH3COO)3·xH2O), magnesium acetate (Mg(CH3COO)2·xH2O), calcium acetate (Ca(CH3COO)2·xH2O), manganese(II) acetate (Mn(CH3COO)2·xH2O), cobalt sulphate (CoSO4·xH2O), zinc sulphate (ZnSO4·xH2O), iron(III) sulphate (Fe2(SO4)3·xH2O), iron(II) sulphate (FeSO4·xH2O), aluminium sulphate (Al2(SO4)3·xH2O), magnesium sulphate (MgSO4·xH2O), calcium sulphate (CaSO4·xH2O), cobalt hydroxide (Co(OH)2·xH2O), zinc hydroxide (Zn(OH)2·xH2O), iron(III) hydroxide (Fe(OH)3·xH2O), iron(III) oxide:hydroxide (FeO(OH)·xH2O), Iron(II) hydroxide (Fe(OH)2·xH2O), aluminium hydroxide (Al(OH)3·xH2O), magnesium hydroxide (Mg(OH)2·xH2O), calcium hydroxide (Ca(OH)2·xH2O), manganese(II) hydroxide (Mn(OH)2·xH2O), cobalt bromide (CoBr2·xH2O), zinc bromide (ZnBr2·xH2O), iron(III) bromide (FeBr3·xH2O), iron(II) bromide (FeBr2·xH2O), aluminium bromide (AlBr3·xH2O), magnesium bromide (MgBr2·xH2O), calcium bromide (CaBr2·xH2O), manganese(II) bromide (MnBr2·xH2O), cobalt carbonate (CoCO3·xH2O), zinc carbonate (ZnCO3·xH2O), iron(III) carbonate (Fe2(CO3)3·xH2O), aluminium carbonate (Al2(CO3)3·xH2O), magnesium carbonate (MgCO3·xH2O), calcium carbonate (CaCO3·xH2O), manganese(II) carbonate (MnCO3·xH2O), and mixtures thereof, where x ranges range from 0 to 12. MOF precursors for use in the invention also include organic ligands of the kind described herein that coordinate the metal ion clusters in the MOF framework. The organic ligands include molecules that have at least two chemical moieties capable of coordinating a metal ion. In some embodiments, these groups comprise carboxylates, phosphonates, sulphonates, N-heterocyclic groups, and combinations thereof. Suitable organic ligands include those ligands listed in WO 2010 / 075610 and Filipe A. Almeida Paz, Jacek Klinowski, Sergio M. F. Vilela, João P. C. Tomé, José A. S. Cavaleiro, João Rocha, Ligand design for functional metal–organic frameworks, Chemical Society Reviews, 2012, Volume 41, pages1088–1110, the contents of which are included herein in their entirety. Examples of organic ligand precursors include, but are not limited to, 4,4′,4″-[benzene-1,3,5- triyl-tris(ethyne-2,1-diyl)]tribenzoate, biphenyl-4,4′-dicarboxylate, 4,4′,4″-[benzene-1,3,5- triyl-tris(benzene-4,1-diyl)]tribenzoate, 1,3,5-benzenetribenzoate, 1,4- benzenedicarboxylate, benzene-1,3,5-tris(1H-tetrazole), 1,3,5-benzenetricarboxylic acid, terephthalic acid, imidazole, benzimidazole, 2-nitroimidazole, 2-methylimidazole (HmIm), 2-ethylimidazole, 5-chloro benzimidazole, purine, fumaric acid, α-cyclodextrin, β- cyclodextrin, γ-cyclodextrin 1,4-Bis(1-imidazolyl)benzene), 4,4’-Bispyridyl, 1,4- Diazabicyclo[2.2.2]octane, 2-amino-1,4-benzenedicarboxylate, 2-amino-1,4- benzenedicarboxylic acid, 4,4’-Azobenzenedicarboxylate, 4,4’-Azobenzenedicarboxylic acid, Aniline-2,4,6-tribenzoate, Aniline-2,4,6-tribenzic acid, Biphenyl-4,4’-dicarboxylic acid, 1,1’-Biphenyl-2,2’,6,6’-tetracarboxylate, 1,1’-Biphenyl-2,2’,6,6’-tetracarboxylic acid, 2,2′-Bipyridyl-5,5′-dicarboxylate, 2,2′-Bipyridyl-5,5′-dicarboxylic acid, 1,3,5-Tris(4- carboxyphenyl)benzene, 1,3,5-Tris(4-carboxylatephenyl)benzene, 1,3,5- Benzenetricarboxylate, 2,5-Dihydroxy-1,4-benzenedicarboxylate, 2,5-Dihydroxy-1,4- benzenedicarboxylic acid, 2,5-Dimethoxy-1,4-benzenedicarboxylate, 2,5-Dimethoxy-1,4- benzenedicarboxylic acid, 1,4-Naphthalenedicarboxylate, 1,4-Naphthalenedicarboxylic acid, 1,3-Naphthalenedicarboxylate, 1,3-Naphthalenedicarboxylic acid, 1,7- Naphthalenedicarboxylate, 1,7-Naphthalenedicarboxylic acid, 2,6- Naphthalenedicarboxylate, 2,6-Naphthalenedicarboxylic acid, 1,5- Naphthalenedicarboxylate, 1,5-Naphthalenedicarboxylic acid, 2,7- Naphthalenedicarboxylate, 2,7-Naphthalenedicarboxylic acid, 4,4’,4’’-Nitrilotrisbenzoate, 4,4′,4′′-Nitrilotrisbenzoic acid, 2,4,6-Tris(2,5-dicarboxylphenylamino)-1,3,5-triazine, 2,4,6- Tris(2,5-dicarboxylatephenylamino)-1,3,5-triazine, 1,3,6,8-Tetrakis(4- carboxyphenyl)pyrene, 1,3,6,8-Tetrakis(4-carboxylatephenyl)pyrene, 1,2,4,5-Tetrakis(4- carboxyphenyl)benzene, 1,2,4,5-Tetrakis(4-carboxylatephenyl)benzene, 5,10,15,20- Tetrakis(4-carboxyphenyl)porphyrin, 5,10,15,20-Tetrakis(4-carboxylatephenyl)porphyrin, adenine, adeninate, fumarate, 1,2,4,5-benzenetetracarboxylate, 1,2,4,5- benzenetetracarboxylic acid, 1,3,5-benzenetribenzoic acid, 3-amino-1,5- benzenedicarboxylic acid, 3-amino-1,5-benzenedicarboxylate, 1,3-benzenedicarboxylic acid, 1,3-benzenedicarboxylate, 4,4′,4″-[benzene-1,3,5-triyl-tris(ethyne-2,1-diyl)]tribenzoic acid, 4,4′,4″-[benzene-1,3,5-triyl-tris(benzene-4,1-diyl)]tribenzoic acid, oxalic acid, oxalate, fumaric acid, fumarate, maleic acid, maleate, trans,trans-muconic acid, trans,trans- muconate, cis,trans-muconic acid, cis,trans-muconate, cis,cis-muconic acid, cis,cis- muconate, pyrazole, 2,5-dimethylpyrazole, 1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, pyrazine, 2,5-dimethylpyrazine, hexamethylentetraamine, nicotinic acid, nicotinate, isonicotinic acid, isonicotinate, 4-(3,5-dimethyl-1H-pyrazole)-benzoic acid, 2,5- furandicarboxylic acid, 2,5-furandicarboxylate, 3,5-dimethyl-4-carboxypyrazole, 3,5- dimethyl-4-carboxylatepyrazole, 4-(3,5-dimethyl-1H-pyrazol-4-yl)-benzoic acid, 4-(3,5- dimethyl-1H-pyrazol-4-yl)-benzoate, and mixtures thereof. Suitable coordinating organic ligands can be derived from oxalic acid, malonic acid, succinic acid, glutaric acid, phtalic acid, isophtalic acid, terephthalic acid, citric acid, trimesic acid, 1,2,3-triazole, pyrrodiazole, squaric acid, imidazole, or benzene-1,4-dicarboxylate (BDC). In some embodiments, the organic ligand comprises a linear dicarboxylate aromatic compound. In some embodiments, the organic ligand is selected from trimesic acid (H3BTC) and benzene-1,4- dicarboxylate (BDC). It will be understood that the organic ligands can also be functionalised organic ligands. For example, any one of the organic ligands listed herein may be additionally functionalised by amino-, such as 2-aminoterephthalic acid, urethane-, acetamide-, or amide-. The organic ligand can be functionalised before being used as precursor for MOF formation, or alternatively the assembled MOF itself can be chemically treated to functionalise its bridging organic ligands. A skilled person will be aware of suitable chemical protocols that allow functionalizing MOFs with functional groups, either by pre-functionalizing organic ligands used to synthesize MOFs or by post-functionalizing pre-formed MOFs. Suitable functional groups that may be provided on the MOF include -NHR, -N(R)2, -NH2, -NO2, -NH(aryl), halides, aryl, aralkyl, alkenyl, alkynyl, pyridyl, bipyridyl, terpyridyl, anilino, -O(alkyl), cycloalkyl, cycloalkenyl, cycloalkynyl, sulfonamido, hydroxyl, cyano, - (CO)R, -(SO2)R, -(CO2)R, -SH, -S(alkyl), -SO3H, -SO3-M+, -COOH, COO-M+, -PO3H2, - PO3H-M+, -PO32-M2+, -CO2H, silyl derivatives, borane derivatives, ferrocenes and other metallocenes, where M is a metal atom, and R is C1-10alkyl. There are no particular restrictions on the solvents that can be used to prepare the solution of the MOF precursors, provided that the MOF precursors are soluble in the solvent. Examples of solvent that may be used include methanol, ethanol, dimethyl sulfoxide (DMSO), acetone, water, and mixtures thereof. Provided the MOF forms, there is no particular limitation regarding the concentration of MOF precursors present in the solution. For example, concentrations of MOF precursors in the solution can include a range from about 0.001 M to about 1 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.2 M, from about 0.02 M to about 0.2 M, from about 0.02 M to about 0.15 M, from about 0.05 M to about 0.15 M, from about 0.08 M to about 0.16 M. The values refer to concentration of organic ligand as well as concentration of metal salt, relative to the total volume of the solution containing the MOF precursors. The ratio between the concentration of organic ligands and the concentration of metal salts is not limited, provided the ratio is adequate for the formation of MOF. In some embodiments, the organic ligand to metal salt ratio may range from 60:1 to 1:60 (mol : mol), from 30:1 to 1:30, from 10:1 to 1:10, from 5:1 to 1:5, from 2.5:1 to 1:2.5, from 2:1 to 1:2, or from 1.5:1 to 1:1.5. The method of the invention comprises a step of dispersing the magnetic nanoparticles in the solvent. Dispersion of the magnetic nanoparticles in the solvent may be achieved by any means known to the skilled person that afford a stable suspension of the magnetic nanoparticles in the solvent. For example, the magnetic nanoparticles may be dispersed in the solvent by mechanical stirring, magnetic stirring, or ultra-sonication. In some embodiments, dispersion of the magnetic nanoparticles in the solvent is performed by mechanical stirring, magnetic stirring, or ultra-sonication for a duration of at least about 1 minute, at least about 10 minutes, at least about 30 minutes, at least about 60 minutes, at least about 2 hours, or at least about 3 hours. The method of the invention comprises a step of promoting formation of MOF nanosheets. Promoting formation of MOF nanosheets may achieved by any means known to the skilled person. For example, formation of MOF nanosheets may be achieved by heating the solution. Heating the solution may be performed under ambient pressure, or under pressure above ambient pressure, for example using an autoclave. In some embodiments, the MOF nanosheets precipitate spontaneously under ambient conditions after the MOF precursors coexist in the solution for some time. In some embodiments, formation of the MOF nanosheets is promoted at a temperature of from about 5°C to about 300°C. In some embodiments, formation of the MOF nanosheets is promoted at a temperature of between about 5°C and 250°C. For example, formation of the MOF nanosheets is promoted at a temperature of from about 10°C to about 300°C, from about 20°C to about 300°C, from about 100°C to about 250°C, from about 100°C to about 200°C, for example at about 160°C. In some embodiments, formation of the MOF nanosheets is promoted at room temperature. As used herein, the expression "room temperature" will be understood as encompassing a range of temperatures between about 15°C and 25°C, with an average within about 20-23°C. In some embodiments, formation of the MOF nanosheets is promoted in an autoclave. In some embodiments, formation of the MOF nanosheets is promoted for at least 10 hours, for example about 12 hours, about 24 hours, or about 36 hours. In some embodiments, formation of the MOF nanosheets is promoted for a duration of from about 1 second to about 24 hours. In the method of the invention it was advantageously observed that presence of magnetic nanoparticles within the solution of MOF precursors facilitates formation of MOF in nanosheets form as opposed to conventional 3D crystalline MOF. Without wanting to be bound by theory, it is believed that magnetic nanoparticles coordinate preferentially to certain crystalline planes of the forming MOF, favouring differential growth along different plane directions. The magnetic nanoparticles may be used in any amount conducive to formation of MOF nanosheets spaced apart by the magnetic nanoparticles intercalated between the nanosheets to form a stable composition. In some embodiments, the magnetic nanoparticles are used in weight amount of at least 5% the weight of the MOF nanosheets precursors. For example, the magnetic nanoparticles are used in weight amount of at least 20%, at least 30%, at least 50%, or at least 70% the weight of the MOF nanosheets precursors. In some embodiments, the magnetic nanoparticles are used in weight amount of from about 5% to about 75% relative to the weight of the MOF nanosheets precursors. It was found those ranges and values are particularly conducive to effective intercalation of the metal particles between the MOF nanosheets. In some embodiments, the magnetic nanoparticles are used in weight amount of from about 20% to about 40%, for example 30% relative to the weight of the MOF nanosheets precursors. It was found those ranges and values are particularly conducive to effective intercalation of the metal particles between the MOF nanosheets. The composition of the invention has been found to be particularly suitable for removal of contaminants from liquid media. Accordingly, the present invention also provides a method of removing contaminants from a liquid medium. Contaminants in that regard may include any substance that pollutes said liquid medium, is poisonous, and / or makes said liquid medium impure. In this context, contaminants would be understood to include dissolved as well as dispersed or suspended contaminants. Dissolved contaminants include molecular compound that are dissolved in the liquid medium, and dispersed or suspended contaminants include contaminants that do not dissolve in the liquid medium. Examples of dispersed or suspended contaminants include microplastics. In some embodiments, the contaminant comprises a microplastic. By "microplastic" is meant herein plastic particulate having a unit size of about 5 mm or less, for example from about 30 nm to about 5 mm. In some embodiments, the microplastics have a unit size of from about 30 nm to about 1 µm. The microplastic may be made of any polymer that adsorbs on the composition of the invention. In some embodiments, the microplastics are made of a polymer comprising polystyrene, polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE, including high-density polyethylene (HDPE), and low-density polyethylene (LDPE)), polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), or a mixture thereof. In some embodiments, the microplastic comprises a charged polymer. That is, the microplastic may present a charge distribution, resulting in discrete positively and / or negatively charged zones within its structure. Advantageously, microplastics comprising a charged polymer adsorb readily on the composition of the invention, therefore affording efficient removal from the liquid medium. Without wanting to be limited by theory, it is postulated that adsorption is favoured by direct coordination of charges in the polymer and adsorption sites on the composition of the invention. In some embodiments, the contaminants comprise molecular contaminants. Said molecular contaminant may be anionic or cationic in nature. As in the case of charges polymers, anionic and / or cationic molecular contaminants can readily adsorb on the composition of the invention by direct coordination of charges in the contaminant and adsorption sites on the composition. The molecular contaminant may be any molecular contaminant that can dissolve in the liquid medium and adsorb on the composition of the invention. Suitable examples of molecular contaminants in that regard include contaminants containing a non-azo group (for example Methylene Blue) and contaminants containing an azo group (for example Congo Red (CR) and Orange II (OR)). In some embodiments, the contaminants comprise at least one of a microplastic and a molecular contaminant. The liquid medium may be any liquid medium that can dissolve and / or suspend molecular contaminants and / or microplastics. In some embodiments, the liquid medium is water. The method of removing contaminants from a liquid medium comprises adding a composition of the kind described herein to a liquid medium containing contaminants. Addition of the composition to the liquid medium may be made according to any means known to the skilled person. The composition of the invention may be added to the liquid medium contaminant in accordance with any amount conducive to adsorb at least a portion of the contaminant onto the composition. In some embodiments, the composition of the kind described herein is added to the liquid medium to a concentration of 50 g / kg or less (g composition / kg liquid medium), for example 35 g / kg or less, 25 g / kg or less, 10 g / kg or less, 5 g / kg or less, or 1 g / kg or less. In some embodiments, the composition is added to the liquid medium to a concentration of 6 g / kg or less, for example from about 3 to about 6 g / kg. In some embodiments, the composition is added to the liquid medium to a concentration of 6 g / kg or less, for example from about 3 to about 6 g / kg, for a concentration of microplastics of about 1 g / kg (g microplastics / kg liquid medium). In some embodiments, the composition is added to the liquid medium to a concentration of about 3 g / kg for a concentration of microplastics of about 1 g / kg. In the method of removing contaminants from a liquid medium, addition of the composition of the invention to the liquid medium results in the contaminants adsorbing on the composition. Adsorption of the required amount of contaminant can be advantageously fast. In some embodiments, adsorption of the required amount of contaminant is achieved after 60 minutes or less following addition of the composition to the liquid medium. For example, adsorption of the required amount of contaminant is achieved after 45 minutes or less, after 30 minutes or less, or after 15 minutes of less. In some embodiments, the composition is left in the liquid medium for 60 minutes or less before being isolated from the medium. The method of removing contaminants from a liquid medium also comprises a step of isolating composition having contaminants adsorbed thereto from the liquid medium by magnetic separation. Magnetic separation may be achieved by any means known to the skilled person. In that regard, the expression “magnetic separation” as used herein refers to a process that involves exposing the liquid medium to an external magnetic field, resulting in preferential attraction (or repulsion) of the composition of the invention to a confined space within the liquid medium, or outside of the liquid medium, where it can be readily isolated. Examples of suitable procedures for magnetic separation for use in the method of the invention include magneto-collection, magneto-flocculation, and magneto-anisotropic sorting. Isolation of the composition from the liquid medium results in effective removal of contaminants from the liquid medium. The method of removing contaminants from a liquid medium of the present invention as advantageously efficient. Typically, the method affords removal of at least 90% of the contaminants present in the liquid medium after 60 minutes from the addition of the composition to the liquid medium. In some embodiments, the method affords removal of at least about 50%, at least about 75%, at least about 80%, at least about 90%, or at least about 98% of contaminants from the liquid medium. Following isolation of the composition from the liquid medium, the composition having contaminants adsorbed thereon can be regenerated for further removal of contaminant from the liquid medium. Regeneration may be achieved by any means known to the skilled person. For example, isolated composition having contaminants adsorbed thereon may be regenerated by washing with one or more suitable solvents, for example, water and an alcohol (e.g. ethanol), followed by drying. In some embodiments, regeneration of the composition comprises at least one washing cycle with water and ethanol, followed by drying. Water and ethanol may be used in a mixture, or used sequentially as discrete washing solvents. A regenerated composition is particularly stable and effective for repeated removal of contaminants from the liquid medium. For example, the use of regenerated composition can afford removal of up to 100% contaminants in a second decontamination cycle, and at least 90% in a second decontamination cycle, following a second regeneration. In some instances, the composition of the invention affords complete removal (i.e.100%) of microplastics and molecular contaminants from the liquid medium in 60 minutes. Specific embodiments of the invention will now be described with reference to the following non limiting examples.

[0002] EXAMPLES EXAMPLE 1 Synthesis of magnetic nanoparticles Parr reactor 5500 was used to produce carbon encapsulated iron oxide (C@FeO) by using 1:0.5 ratio of olive waste: iron chloride, respectively, in 300 mL water and treated hydrothermally at 250℃ for 90 minutes. Synthesis of example composition (2D MOF@C@FeO) For the preparation of the 2D MOF@C@FeO, 9 mmol of iron nitrate nonahydrate (Fe (NO3)3·9H2O) and 6 mmol of trimesic acid (H3BTC) were dissolved in a 15 mL distilled water to form a solution A, followed by 40 min magnetic stirring. Afterwards, 30%, 50% or 70% C@FeO with respect to iron salt were added in 3mL distilled water and mixed with solution A and stirred for 1 hr to form the homogenous solution B (18 mL). Then this solution B was transformed into the 50mL Teflon-lined stainless-steel autoclaves and kept at 160 °C for 12 hr in the furnace and allowed to cool down to room temperature. The obtained powders were washed with ethanol and water at room temperature several times to remove the unreacted reactants. Finally, the product was dried overnight at 113 °C in a Vacuum oven. Similarly, the above-mentioned steps were followed in order to produce pristine 2D MOF except for the addition of C@FeO. A schematic representation of the synthesis procedure and resulting nanosheet-based structure of the composition is shown in the schematic of Figure 1 (left side). EXAMPLE 2 Decontamination Procedure Batch microplastic (MP) removal experiments were carried out by using 5 mL of MP in water at 0.2-1g / kg concentrations with the abovementioned material for different exposure times (30-90 minutes). Methylene blue (MB) concentration in water at 50 mg / kg was used with different adsorbent dosages (1-3 g / L) for 30 minutes for adsorption experiments. In binary system, equal volume of MB (50 mg / kg) solution, and MP suspension (1g / kg) were added to prepare a 20 mL of mixed-pollutant suspension which then had 2D MOF@C@FeO at 3g / L added to that and kept for 60 minutes adsorption time. 2D MOF@C@FeO stability was tested by recycling it in three adsorption cycles using adsorbent dosage at 3g / L and exposure time of 30 min for binary system consisting of MB and MP. After each cycle 2D MOF@C@FeO was recovered using an external magnet washed several times with water and ethanol and dried for 4 hours at 105 ℃ before using it in subsequent cycles. To investigate MP removal quantity, three different techniques were used based on particle size, weight and wavelength. Differential Light Scanning (DLS) method using Malvern Zetasizer Nano ZS analyser was used to quantify MP presence in the solution for the change of intensity in the peak of particle size between 1000 ± 30 nm range compared to milli Q water as standard. For a weight based approach, TGA from 30 ℃ to 100 ℃ (held for 30 minutes) using 20 ℃ heating rate was used to quantify MP based on weight difference observed between original MP solution and solution after adsorption to calculate removal percentage. UV-vis spectrophotometer Shimadzu UV-2700 was utilised from 200-800 nm wavelength where MP (250-295 nm) and MB (665 nm) peaks were investigated for both single and binary systems. A schematic representation of a decontamination cycle is shown in Figure 1 (right side). Contaminants (molecular or microscopic) are dispersed in the liquid medium having suspended composition of the kind described herein. Following adsorption, the composition with adsorbed contaminants can be isolated by exposure to an external magnetic field (a magnet in the schematic). EXAMPLE 3 Morphology of MOF The scanning electron microscope (SEM) was utilized to explore the morphology, which suggests that the C@FeO is composed of small particles that tend to aggregate and form porous lumps. On the other hand, the SEM image of MOF shows its preferred 2D growth to produce nanosheets, but these sheets are highly stacked (not shown). But the in-situ growth of MOF sheets over C@FeO particles resulted in a very unique structure where C@FeO particles self-assembled within the sheets of 2D MOF which assist in not only overcoming the issue of C@FeO lumps but also stacking of 2D MOF; consequently synergizing the advantages of both materials. This was further investigated by transmission electron microscopy (TEM), where C@FeO particles can be seen trapped between the sheets of 2D MOF and repeating the geometry. This structure architecture increases available surface active sites and their accessibility by avoiding stacking of 2D sheets. To investigate the structure and interface of the structure, high-resolution TEM (HRTEM) analysis was carried out, which shows that 2D MOF@C@FeO exhibited Fe2O3 (d spacing of 0.36 nm related to plane (012)) related to 2D MOF. Similarly, it shows presence of Fe3O4 (d spacing of 0.16 nm related to plane (511)), and carbon confirming the presence of all components from 2D MOF and C@FeO in its heterostructure. Further, Fast Fourier transform (FFT) analysis featured polycrystalline 2D MOF@C@FeO. Atomic force microscopy (AFM) imaging was performed to further confirm the intercalated structure, and the AFM image clearly shows the sheets of 2D MOF separated by the particles of C@FeO. AFM height profile is presented in Figure 2 elucidating measurements of a typical 2D MOF thickness of ~3.4 nm and C@FeO diameter of ~16.8 nm, the inset of Figure 2 schematically represents the intercalated structure. Structural analysis was done using XRD of 2D MOF@C@FeO (Figure 3), which showed relatively less crystallinity as compared to 2D MOF and C@FeO. XRD analysis was well- matched with reported and simulated 2D MOF indicating synthesis of pristine material. XRD spectra of C@FeO showed peaks at 30.2º, 35.4º, 43.2º, 53.3º, 57.2º, and 62.8º correspond to planes (220), (311), (400), (422), (511), and (440) of Fe3O4 according to JCPDS 01-075-0449, confirming well-crystalline growth of Fe3O4NPs within carbon matrix (Figure 3). Similarly, 2D MOF@C@FeO represented peaks from both MOF and Fe3O4(C@FeO) compared to 2D-MOF. XPS analysis was performed to better understand the surface chemistry, and results suggest that 2D MOF has similar binding energies as are reported in the literature for MIL 100 Fe, confirming successful in situ growth. However, 2D MOF@C@FeO, C 1s fittings showed peaks at 285.4 eV, 286.6 eV, and 289.3 eV, respectively, representing C-C, C- O / C-N, and O-C=O groups, which overlap with C@FeO C 1s fittings and different from 2D MOF. The presence of particular C-N peak in 2D MOF@C@FeO belongs to the carbon matrix of C@FeO. Similarly, oxygen peak fittings showed similar peaks for 2D MOF, and 2D MOF@C@FeO centred at 532 eV and corresponded to Fe-O-C. Interestingly, 2D MOF peak fitting of Fe 2p show two distinct peaks at 710.7 eV, and 725.5 eV, separated by satellite peak corresponds to Fe 2p1 / 2 and Fe 2p3 / 2, respectively. On the contrary, 2D MOF@C@FeO showed peaks at 712.5 eV and 726.5 eV representing Fe2+and correspond to C@FeO, whereas peaks at 714.6 eV and 731.9 eV correspond to 2D MOF. Fe 2p peak fittings, in this case, suggest the presence of both pristine materials suggesting the development of a hybrid structure. Moreover, the distribution of these components was investigated through high-angle annular dark-field and bright field scanning transmission electron microscopy (HAADF-STEM, and HAABF-STEM) and Energy-dispersive X-ray spectroscopy (EDS) to understand the structure of 2D MOF@C@FeO, which shows uniform distribution of iron, carbon, oxygen, and nitrogen. Further, to investigate the preservation of surface functionality of 2D MOF in the heterostructure, FTIR analysis was carried out, which showed representative peaks of MOF around 457 cm-1, 712 cm-1, 759 cm-1, 1385 cm-1, 1442 cm-1, and 1631 cm-1correspond to Fe-O, C-H, C-O, -OH, and C=O, respectively in both pure 2D MOF and 2D MOF@C@FeO. Thus, confirming that intercalation architecture did not impact the surface chemistry of MOF and preserved its functionality exactly the same as it has in its pure form to make it an effective adsorbent for water pollutants. As hypothesized that intercalation structure will enhance the available surface; therefore, to investigate this, Brunauer-Emmett-Teller (BET) analysis was carried out to determine the porosity and surface area. Interestingly, the surface area of 2DMOF@C@FeO has been increased to 749.7 m2 / g compared to 571.1 m2 / g of pure 2D MOF, confirming the successful incorporation of C@FeO intercalated between the sheets of 2D MOF. Notably, the surface area of C@FeO is only 8.1 m2 / g; therefore, an increase in the surface area of 2D MOF@C@FeO heterostructure is purely based on the presence of C@FeO nanoparticles intercalated between the sheets of MOF, hence again supporting microscopic studies and validating the proposed approach to develop functional materials. Thermogravimetric analysis (TGA) explored material stability and iron content estimation. 2D MOF and 2D MOF@C@FeO represented two-step weight loss where up to around 200℃ is regarded as removal of moisture from pores. The second weight loss, up to 500℃, is attributed to the degradation of MOF ligands. The 2D MOF@C@FeO showed up to 5% less weight loss confirming increased iron content than 2D MOF, evidencing successful loading of C@FeO and 2D MOF. EXAMPLE 4 Adsorption data – Polystyrene (PS) and contaminant individually After confirming the unique structure and morphology of 2D MOF@C@FeO, it has been employed as an adsorbent to remove MP from the aqueous system. As it is well-known that it is very hard to quantify the exact removal of MP, therefore, a set of three different techniques, including DLS (Diffraction Light Scattering), UV-Vis, and TGA, was utilized to precisely determine the MP removal. The 1μm size polystyrene beads were selected as persistent model MPs because this range is relatively difficult to detect and remove in wastewater systems. A series of experiments were performed using different MP and adsorbent concentration ranges, and the optimized experiments are presented here. DLS data uses particle size to determine whether particles of a specific size are present in the system or not, where the accurate size of MPs makes this technique more effective. Interestingly, it is found that C@FeO can remove 71.7% MP (1g / L) in 60 minutes. However, at the same time, MOF and 2D MOF@C@FeO removed 100% MP, which confirms that MOF chemistry is highly suitable for such solid removal. But pure 2D MOF has a critical challenge of separation and is not possible without applying filtration / centrifuge, which makes the system very complex and retains the issue of reusability of adsorbent. While introducing C@FeO magnetic nanoparticles not only makes it an effective adsorbent but also resolves the issue of separation by simply employing an external magnet as well as reducing the overall materials use and operational cost. To further evaluate the removal and issue of leaching of materials in the system, UV-Vis spectra are recorded for all samples (raw MP solution, solution treated with C@FeO, 2D MOF, 2D MOF@C@FeO), where MP peak appeared in the 250-290 nm region. The peak of MP has disappeared in case of treatment with all adsorbents; however, overall high absorbance in the case of C@FeO shows incomplete removal of C@FeO from the solution. However, minimal overall absorbance in the case of 2D MOF@C@FeO highlights the advantage of making intercalation structures that avoid any leaching of adsorbent into water hence eliminating the chances of creating secondary pollutants. Note: pure 2D MOF UV- Vis spectrum also shows low overall absorbance because this is a filtered (not preferred) sample to remove all adsorbent as it is not magnetically removable. As UV-Vis usually is more qualitative and harder to precisely quantify the removal amount, the quantification was carried out using TGA studies. TGA analysis quantified MP removal based upon weight difference in recovered solution. The MP solution was analyzed and taken as standard, followed by the analysis of adsorption solution after removing the absorbent. Results exhibited 100% removal of MP for 2D MOF (filtered) and 2D MOF@C@FeO (magnetically collected) in only 60 minutes (Figure 4). EXAMPLE 5 Polystyrene (PS) and contaminants together To further evaluate the capability of the developed, engineered structure in the presence of both solid and dissolved pollutants, initially, MB removal was investigated individually for the unary system. It is found that C@FeO and 2D MOF showed minimal MB (50 mg / kg) removal (under 10%) in 30 minutes; on the other hand, 2D MOF@C@FeO removed ~100% MB (50 mg / kg) in just 30 minutes, outperforming both individual materials due to its unique intercalation sheets architecture. Figure 5 shows data for MB removal by all adsorbents tested (C@FeO, MOF, MOF@C@FEO. Apart from MP, the MB removal ability of 2D MOF@C@FeO is better as compared to other reported materials, such as, sulfur doped graphdiyne which removed 81.1% of 5-times less concentrated MB (10 mg / kg) than 2D MOF@C@FeO in 1 hour. This excellent removal efficiency inspired the utilization of 2D MOF@C@FeO for binary (MP+MB) system, and interestingly it was able to completely remove both simultaneously in 60 minutes, proving the high efficiency and superiority of 2D MOF@C@FeO (Figure 6) as compared to C@FeO and 2D MOF. Figure 6 relates to MB + MP removal by all three adsorbents (C@FeO, MOF, MOF@C@FEO). On the contrary, C@FeO and 2D MOF removed 42% and 68.5% MP +MB respectively in a binary system. The poor removal efficiency of 2D MOF in binary systems compared to 2D MOF@C@FeO heterostructures further highlight the advantages of constructing such intercalation architectures. EXAMPLE 6 Cyclic use In order to study the stability and re-useability in water, 2D MOF@C@FeO was used in three adsorption cycles where it was magnetically recovered each time after adsorption (Figure 7). The 100% removal in two cycles and 91% in a third cycle represents excellent stability of 2D MOF@C@FeO, which can be linked to its material stability. The slightly reduced efficacy in the third cycle can be attributed to covering of the active functional sites with pollutants via chemisorption. An ex situ microscopic study of magnetically recovered 2D MOF@C@FeO was investigated to visualize MP adsorption. Amazingly, the MP particles are attached to the surface. This surface attraction and aggregation of MP on 2D MOF@C@FeO can be linked with the hydrophobic nature between both surfaces and electrostatic interactions, as discussed below. It is also worth noting that MP particles are attached without any surface change showing simple adsorption, not demineralization, which normally results in second pollutants such as toxic gases and dissolvable chemicals. EXAMPLE 7 Adsorption mechanism To further investigate the adsorption process, ex situ XPS of magnetically recovered 2D MOF@C@FeO after adsorption of MP and MB in both systems was carried out. The peak at 285.7 eV, which resembles 286.6 eV in 2D MOF@C@FeO for MP removal, are shifted due to adsorption and showed almost double intensity C-O and / C-N bonds participated in MP removal. Similarly, the O 1s peak at 532 eV showed around 24% increased intensity, corresponding to the Fe-O-C bond, indicating the interaction of iron with MP. MP interaction with different metals has been reported due to oxygenated and phenyl groups on the MP surface, making it more reactive alongside the pi-electron system, which tends to make pi-pi interactions with 2D MOF@C@FeO and increase MP adsorption. Interestingly, iron peak intensity was found higher for 2D MOF@C@FeO after adsorption, supporting our argument that electrostatic interaction between negatively charged MP and positive iron ions enhances adsorption. In the case of MB, the carboxylic group peak around 288.8 eV was shifted and depicted enhanced intensity representing its participation in MB removal. A new peak ~292 eV can be seen, attributed to pi-pi aromatic stacking. Moreover, a new peak around ~529 eV was raised, corresponding to the M-O peak suggestion that iron oxide also participated in MB removal. This can be supported by Fe 2p spectra, where iron peak intensity was increased, delineating that Fe-O can bind with hydrogen during adsorption. An additional nitrogen peak in 2D MOF@C@FeO after adsorption is found and is attributed to C-N depicting nitrogen role in adsorption. Further electrostatic interaction can be another possible MB removal mechanism. To illustrate this, surface zeta potential analysis was carried out, revealing that C@FeO has the highest negative surface charge with a -31.9 mV value as compared to 2D MOF, which represented only a -1.8 mV charge. The 2D MOF@C@FeO, however, showed intermediate values amongst two (-16.8 mV), which tend to increase electrostatic interaction between cationic MB and negatively charged 2D MOF@C@FeO. This negative charge can be attributed to the presence of carbonyl and carboxylic groups. In the case of simultaneous removal, similar results were found with increased intensities of C-C, and Fe3+, and the formation of new peaks, which include C-H, C=O, pi-pi interaction, Fe-O peak, and Fe-N, suggesting a similar mechanism as discussed above. EXAMPLE 8 Different size microplastic particles Removal of microplastics (MPs) of various sizes was also investigated utilising the method of the present invention. The MPs tested ranged in size from 30 nm to 1000 nm. Removal efficiency of the MP particles ranged from 15 to 100%. More than 90% and up to 100% of MPs of sizes 30 nm and 1000 nm were removed, while at least 45% of MPs of sizes in between 30 nm to 1000 nm were removed. In these examples, the microplastic concentration was 1g / L, the adsorbent dosage was 3g / L and the adsorption time was 1 hour. Figure 8 shows removal of different sizes of MPs from water in addition to the 1000 nm size which is used in Example 1. Figure 8(a) shows removal of 40% of 100 nm size microplastic particles at 100 nm, Figure 8(b) shows removal of 15.8%, of 200 nm size microplastic particles at 200 nm and Figure 8(c) shows removal of 44.7% of 500 nm size of MP at 500 nm. Each graph represents MP particle size analysis before and after adsorption. For example, in Figure 8(a), it can be seen that the intensity drops significantly at around the 100 nm size, that is, there is a bigger gap between the two curves (MP intensity and MP after adsorption intensity) showing removal of MP occurring. The wider the gap between the lines the more removal of MPs has occurred. The data shows that 2D MOF@C@FeO has the ability to remove MPs with a wide range of sizes from water. EXAMPLE 9 Different types of MOFs in addition to MIL-100 were investigated to verify the general applicability of the proposed synthesis methodology to other types of MOF-based compositions. Fe-MOF@C@FeO A 2D Fe-ZIF was synthesized at room temperature in the presence of carbon-encapsulated FeO magnetic nanoparticles (C@FeO). The synthesis was performed at room temperature and resulted in the successful formation of an intercalation structure termed herein "2D Fe- MOF@C@FeO", which intercalation structure was verified through TEM (not shown). The structure is made of 2D Fe-MOF (Fe-ZIF) nanosheets spaced apart by the magnetic C@FeO nanoparticles intercalated between the nanosheets. In a typical synthesis, in beaker A, 15-75 mg (15-75% to metal salt) C@FeO nanoparticles were suspended in 45 mL deionised water and stirred for 5 minutes. In a separate beaker (beaker B), 45 mg imidazole was dissolved in 22 mL deionised water by mechanical stirring for 5 minutes. Imidazole is an aromatic heterocycle, classified as a diazole, whereas the previous linker used for synthesis of 2D MOF@C@FeO (MIL-100, in Example 1) was a carboxylic linker. In beaker C, iron nonahydrate (100 mg) was dissolved in 22 mL water and stirred for 5 minutes. The contents of beakers B and C were then poured into beaker A, and the resulting mixture was left stirring for at least 6 hours. Suspended MOF intercalated nanosheets were then sonicated to remove solid particles and vacuum oven dried at 50 degrees Celsius for at least 12 hours to obtain 2D Fe-MOF@C@FeO at different compositions depending upon the added quantity of C@FeO. 2D Fe-MOF@C@FeO containing 30% C@FeO by weight was then used for decontamination tests (MP removal). Removal conditions were kept similar as used in Example 4. That is, 1g / L MP and 3g / L 2D Fe MOF@C@FeO were used. Adsorption time was kept for 1 hour. 2D Fe-MOF@C@FeO (with 30% C@FeO) showed 75% MP removal as shown in particle size analysis in Figure 9(A). However, in order to improve MP removal under similar adsorption conditions, similar 2D Fe-MOF were synthesized with 15% C@FeO (wt.%). The resultant material showed 100% removal of MP from water as shown in Figures 9(B) and 9(C). Specifically, Figure 9(B) shows the UV-Vis analysis in which specific MP peak is there for MP. However after adsorption this peak is flattened due to MP removal. Further, particle size analysis in Figure 9(C) shows that in 1000 nm range there is no peak intensity for MP after adsorption. Co-MOF@C@FeO Another MOF-based composition using cobalt for the MOF metal clusters (Co-ZIF) was used to obtain a 2D Co-MOF@C@FeO composition at room temperature. The composition was synthesised using a procedure similar to the one described above for the Fe-MOF correspondent. In particular, iron nonahydrate as MOF metal salt precursor was replaced with cobalt hexahydrate to obtain a corresponding 2D Co-MOF@C@FeO (30%) composition. TEM analysis (not shown) confirmed the intercalation structure of the composition. The structure is made of 2D Co-MOF (Co-ZIF) nanosheets spaced apart by the magnetic C@FeO nanoparticles intercalated between the nanosheets. The composition 2D Co-ZIF MOF@C@FeO was then tested for MP (1g / L) removal from water, using the same adsorption parameters as for 2D Fe MOF@C@FeO. That is, MP concentration of 1g / L, adsorbent dosage of 3g / L, and adsorption time of one hour. The particle size analysis in Figure 10(A) shows that there is 100% MP removal from water. Similarly UV-vis spectroscopy in Figure 10(B) also indicated that in MP region, around 290 nm, there is a flat line after adsorption showing that there are no MPs in the system. 2D Ni-MOF@C@FeO A composition having a MOF based on nickel metal clusters was also synthesised using a different organic ligand relative to the Fe- and Co- correspondents described in this Example. In this instance, the MOF was synthesised at room temperature using a Ni salt using similar weight ratios as above for the Fe and Co correspondents, that is C@FeO : metal salt (30:70), using benzene-1,4-dicarboxylate (BDC) as the organic linker. For the synthesis, in beaker A, 25 mg carbon-encapsulated FeO nanoparticles (C@FeO) were suspended in a mixture of 15 mL dimethylformamide (DMF) + 1 mL distilled water + 1mL ethanol. The particles were suspended and mechanically stirred for 5 minutes. In beaker B, 62 mg benzene-1,4-dicarboxylate (BDC) linker was dissolved in a mixture of 10 mL DMF + 0.5 mL distilled water + 0.5 mL ethanol, and mechanically stirred for 5 minutes. In beaker C, 90 mg Ni chloride hexahydrate was dissolved in 10 mL DMF + 0.5 mL distilled water + 0.5 mL ethanol, and stirred for 5 minutes. Subsequently, the contents of beakers B and C were transferred into beaker A, and the resulting mixture left for at least 6 hours under mechanical stirring. Afterwards, the solution was sonicated to remove solid particles and were vacuum oven dried at 50 degrees for at least 12 hours. The structure is made of 2D Ni-MOF nanosheets spaced apart by the magnetic C@FeO nanoparticles intercalated between the nanosheets. In subsequent adsorption tests, the resulting 2D Ni-MOF@C@FeO composition showed around 22% MP removal in one hour from a 1 g / L MP suspension using 3g / L of the 2D Ni- MOF@C@FeO (30%), as shown in Figure 10(C). EXAMPLE 10 Positively and negatively charged MPs Two types of polystyrene-based microplastics were tested to investigate the adsorption characteristics of the proposed MOF-based compositions. Specifically, amine modified polystyrene microplastics (positively charged MPs of 1000 nm average size) and a carboxylic modified polystyrene microplastic (negatively charged MPs of 500 nm and 30 nm average size). The amine modified MP was completely removed from the water in 30 minutes using 2D MOF@C@FeO (based on MIL-100 MOF as in Example 1) as shown in Figure 11(a). The data also shows removal of 95% of the MP in just 15 minutes exposure to the 2D MOF@C@FeO. Similarly, data of Figure 11(b), relating to removal of carboxylic modified MP 500 nm (negatively charged), show that 14.7% of MPs were removed in an hour when MP concentration was 1g / Kg with adsorbent dosage of 3g / Kg and adsorption time of 1 hour. The data of Figure 11(c) shows approximately 90% removal of carboxylic modified 30 nm MP (1g / L) in an hour. The amount of 2D MOF@C@FeO utilised was 3g / L. The results suggest that the composition of the invention has unique features that affording removal of charged MPs from water. As used herein, the term “about”, in the context of numerical values, typically means + / −5% of the stated value, more typically + / −4% of the stated value, more typically + / −3% of the stated value, more typically, + / −2% of the stated value, even more typically + / −1% of the stated value, and even more typically + / −0.5% of the stated value. Throughout this specification and the claims which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A composition comprising MOF nanosheets spaced apart by magnetic nanoparticles intercalated between the nanosheets.

2. The composition of claim 1, wherein the MOF nanosheets are made of MOF comprising at least one of iron, cobalt, nickel, zirconium, manganese, and copper.

3. The composition of claim 1 or 2, wherein the magnetic nanoparticles comprise carbon-encapsulated magnetic nanoparticles.

4. The composition of any one of claims 1-3, wherein the magnetic nanoparticles comprise a core made of a magnetic metal or a magnetic metal oxide.

5. The composition of claim 4, wherein the magnetic metal comprises one or more of iron, nickel, cobalt, lead, platinum, neodymium, and an alloy thereof.

6. The composition of claim 4, wherein the magnetic metal oxide is selected from FeO, Fe2O3 , Fe3O4, and a mixture thereof.

7. The composition of any one of claims 1-6, wherein the MOF nanosheets are spaced apart to a spacing from about 0.1 nm to about 1,200 nm.

8. The composition of any one of claims 1-7, wherein the magnetic nanoparticles have a largest dimension of from about 0.1 nm to about 1,200 nm.

9. The composition of any one of claims 1-8, having a surface area between 10% and 50% larger than the surface area of the MOF nanosheets absent the magnetic nanoparticles.

10. The composition of any one of claims 1-9, having a surface area of at least 8 m2 / g.

11. The composition of claim 10, having a surface area of about 750 m2 / g.

12. A method of synthesis of a composition according to any one of claims 1-11, the method comprising: dissolving MOF precursors in a liquid medium, dispersing the magnetic nanoparticles in the liquid medium, and promoting formation of MOF nanosheets.

13. The method of claim 12, wherein formation of the MOF nanosheets is promoted in an autoclave.

14. The method of claim 12 or 13, wherein formation of the MOF nanosheets is promoted at a temperature of from about 5 to about 250°C.

15. The method of any one of claims 12-14, wherein formation of the MOF nanosheets is promoted for a duration of from about 1 second to about 24 hours.

16. The method of any one of claims 12-15, wherein the MOF nanosheets precursors comprise a metal ion precursor and a multi-dentate organic ligand having at least two chemical moieties capable of coordinating a metal ion.

17. The method of claim 16, wherein the metal ion precursor comprises a salt selected from a metal-chloride, -nitrate, -acetate, -sulphate, -hydrogen sulphate, -bromide, - carbonate, -phosphate, and derivatives thereof, and the organic ligand has at least two chemical moieties comprising a carboxylate, a phosphonate, a sulphonate, a N-heterocyclic group, and a combination thereof.

18. The method of any one of claims 12-17, wherein the magnetic nanoparticles are dispersed in the liquid medium in the form of a liquid dispersion.

19. The method of any one of claims 12-18, wherein the magnetic nanoparticles are used in weight amount of from about 5% to about 75% relative to the weight of the MOF nanosheets precursors.

20. A method of removing contaminants from a liquid medium, the method comprising: contacting a composition according to any one of claims 1-11 with a liquid medium containing contaminants, whereby at least a portion of the contaminants adsorbs on the composition, and isolating composition having contaminants adsorbed thereto from the liquid medium by magnetic separation, thereby removing contaminants from the liquid medium.

21. The method of claim 20, wherein the contaminants comprise at least one of a micro- plastic and a molecular contaminant.

22. The method of claim 20 or 21, wherein the liquid medium is water.

23. The method of any one of claims 20-22, wherein the composition is added to the liquid medium to a concentration of 5 g / kg or less.

24. The method of any one of claims 20-23, wherein the composition is left in the liquid medium for 120 minutes or less before extraction.

25. The method of any one of claims 20-24, wherein at least 90% of the contaminants adsorb on the composition after 60 minutes from the addition of the composition to the liquid medium.

26. The method of any one of claims 20-25, wherein following extraction, the magnetic extractant is regenerated for further removal of contaminant from the liquid medium.

27. The method of claim 26, wherein regeneration of the composition comprises at least one washing cycle with water and ethanol, followed by drying.

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