Metal (OXY)hydroxide nanoparticles, methods for manufacturing same and uses thereof

Abstract

The present disclosure reports compositions of matter, methods of synthesis, and methods of catalyzing chemical reactions - all relating to metal (oxy)hydroxide nanoparticles having all size dimensions less than about 20 nm. Unlike conventional approaches, the methods of the present disclosure utilize a stoichiometry-controlled base- addition protocol, optionally in the presence of an ambidentate ligand. By: (i) selecting a suitable base and optionally a suitable ambidentate ligand; and (ii) tuning the reaction stoichiometry appropriately, the methods of the present disclosure may provide sufficient control over the nucleation and growth processes to encourage the formation of metal (oxy)hydroxide nanoparticles at the low end of the nanoparticle size spectrum.

Description

METAL (OXY)HYDROXIDE NANOPARTICLES, METHODS FOR MANUFACTURING SAME AND USES THEREOFRELATED APPLICATION

[0001] This application claims priority under applicable laws to United States provisional application No. 63 / 583.070 filed on September 15, 2023, the content of which is incorporated herein by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present disclosure generally relates to metal nanoparticles, their methods of production and their use in catalytic chemical reactions. More specifically, the present disclosure relates to metal (oxy) hydroxide nanoparticles, their methods of production and their use in catalytic chemical reactions.BACKGROUND

[0003] Metal clusters and metal nanoparticles are expected to have widespread utility in chemistry, particularly in catalysis applications. However, commercializable technologies utilizing metal clusters and / or metal nanoparticles are still largely in their infancy. Metal clusters typically comprise metal atoms coordinated by ligands, forming discrete units having well-defined chemical compositions and structures, and having particle sizes of less than about 2 nm. Metal nanoparticles are often larger ( / .e., between about 1 nm and about 100 nm) and their structures are usually less well defined. Researchers tend to define narrower size classifications within this range, as metal nanoparticles often exhibit size-dependent properties. For example, the term “nanodot” has been proposed to characterize nanoparticles with dimensions between about 2 nm and about 20 nm (Park, H., et al. "Categorization of quantum dots, clusters, nanoclusters, and nanodots." Journal of Chemical Education 98.3 (2021): 703-709). The upper and lower ends of this size range may be associated with electronic mean free path where size-dependent surface plasmonic resonance absorption properties occur (Pelton, M., and G. Bryant. "Introduction to Metal-Nanoparticle Plasmonics John Wiley and Sons." (2013): 6-8; and Lin, Cheng-An J., et al. "Synthesis of fluorescent metallic nanoclusters toward biomedical application:recent progress and present challenges." Journal of Medical and Biological Engineering29.6 (2009): 276-283), and particles within this size range may have unique properties.

[0004] Controlling nanoparticle size is an important aspect of metal nanoparticle synthesis. The LaMer model of particle formation is illustrative in this respect, and it links nanoparticles size to two synthetic phases: nucleation and growth. In the nucleation phase, a supersaturated solution of a metal precursor is generated, nucleation is induced when the concentration exceeds a critical level of supersaturation where nucleation is energetically favorable, and a dispersion of nuclei forms rapidly. In most cases, the rate of nucleation quickly surpasses the rate of precursor addition, which attenuates further nucleation. In the growth phase, slow addition of additional precursor leads to particle size increases through accretion.

[0005] Controlling the size of nanoparticles synthesized via the LaMer method remains challenging. As will be appreciated by those skilled in the art, balancing nucleation and growth rates requires precise control over reaction conditions. Small variations in reagent purity, temperature, concentration, rates of addition, and the like often lead to larger than desired particle sizes and / or size distributions. This is particularly problematic for those pursuing metal nanoparticles having specific size-dependent properties.

[0006] Transition metal (oxy) hydroxides are a class of metal nanoparticles likely to exhibit useful size dependent properties. Conventional methods for synthesizing transition metal (oxy)hydroxides typically involve the reaction of a transition metal salt with a suitable base - generally under hydrothermal or solvothermal conditions. These conditions are believed to promote the formation of metal-oxygen-metal bridges, which are integral to the structure of transition metal (oxy)hydroxides. However, a common drawback of such conventional synthetic approaches is that they tend to yield particles at the upper end of the nanoparticle range and / or larger aggregates. The large size of conventionally synthesized metal (oxy)hydroxides often presents a challenge for catalytic applications, where surface phenomena are of primary importance.

[0007] Accordingly, there is a need for improved synthetic approaches to produce a metal (oxy)hydroxide nanoparticle that overcome one or more of the disadvantages encountered with conventional synthetic approaches. More particularly, there is a need for syntheticapproaches that yield in metal (oxy)hydroxide nanoparticles at the low end of the nanoparticle-size scale. In particular, there is a need for metal (oxy) hydroxide nanodots, methods of synthesizing metal (oxy) hydroxide nanodots, and methods of catalyzing chemical reactions with metal (oxy)hydroxide nanodots.SUMMARY

[0008] The present disclosure reports methods of synthesizing metal (oxy) hydroxi de nanoparticles having all size dimensions less than about 20 nm. Unlike conventional approaches, the methods of the present disclosure utilize a stoichiometry-controlled baseaddition protocol, optionally in the presence of an ambidentate ligand. By: (i) selecting a suitable base and optionally a suitable ambidentate ligand; and (ii) tuning the reaction stoichiometry appropriately, the methods of the present disclosure may provide sufficient control over the nucleation and growth processes to encourage the formation of metal (oxy)hydroxide nanoparticles at the low end of the nanoparticle size spectrum. Without being bound to any particular theory, it appears that precise stoichiometric control of the base-addition protocol not only promotes nucleation, but it also attenuates particle growth, thereby enabling reliable synthesis of metal (oxy)hydroxide nanoparticles having all size dimensions of less than about 20 nm. The metal (oxy)hydroxide nanodots of the present disclosure are characterized by a suite of analytical techniques, including: Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDX) mapping, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD). The metal(oxy)hydroxide nanodots of the present disclosure may catalyze chemical reactions as evidenced, by way of example, in the experiments detailed herein.

[0009] According to some aspects, embodiments of the technology as described herein include the following items:1 . A metal (oxy)hydroxide nanoparticle having all particle-size dimensions less than about 20 nm.2. The metal (oxy)hydroxide nanoparticle of item 1 , wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 15 nm.3. The metal (oxy) hydroxi de nanoparticle of item 1 or 2, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 10 nm.4. The metal (oxy) hydroxi de nanoparticle of any one of items 1 to 3, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 5 nm.5. The metal (oxy) hydroxi de nanoparticle of any one of items 1 to 4, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are greater than about 2 nm.6. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 5, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of between about 3.0 nm and about 5.0 nm.7. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 6, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of between about 3.5 nm and about 4.0 nm.8. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 7, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of about 3.9 nm and a particle size standard deviation of less than about 0.5 nm.9. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a vanadium (oxy)hydroxide nanoparticle, a chromium (oxy)hydroxide nanoparticle, a manganese (oxy) hydroxi de nanoparticle, an iron (oxy)hydroxide nanoparticle, a cobalt (oxy)hydroxide nanoparticle, a nickel (oxy) hydroxide nanoparticle, a ruthenium (oxy)hydroxide nanoparticle, or an aluminum (oxy) hydroxide nanoparticle.10. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising at least two metals selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, and aluminum.11. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising iron and at least one metal selected from the group consisting of vanadium, chromium, manganese, cobalt, nickel, ruthenium, and aluminum.12. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed valence metal (oxy) hydroxi de nanoparticle comprising at least one metal selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, and aluminum, wherein the metal is present in more than one oxidation state.13. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is an iron (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 17.8 (13.5) 20, 21.2 (100) 20, 33.2 (43.9) 20, 36.6 (73.3) 20, 41.2 (18.3) 20, 53.2 (39.0) 20, 59.0 (25.8) 20 and 63.9 (12.9) 20.14. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is a cobalt (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 20.3 (100) 20, 36.5 (14.0) 20, 38.4 (72.1) 20, 50.3 (45.5) 20, 61.7 (17.9) 20 and 64.4 (19.2) 20.15. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is a nickel (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 12.9 (100) 20, 25.9 (8.2) 20, 37.8 (9.7), 43.0 (13.0) and 51.5 (8.4) 20.16. The metal (oxy)hydroxide nanoparticle of any one of items 1 to 15, which comprises an ambidentate ligand.17. The metal (oxy)hydroxide nanoparticle of item 16, wherein the ambidentate ligand is selected from the group consisting of acetylacetonate, acetylacetonate derivatives, acetate, acetate derivatives, ethylene diamine, ethylene diamine derivatives, triethanolamine, triethanolamine derivatives, and a combination of at least two thereof.18. A method of synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(A1) contacting an aqueous solution comprising a metal cation with an ambidentate ligand to form an aqueous composition; and(A2) contacting the aqueous composition with a base, wherein the ratio of the base to the metal cation is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.19. The method of item 18, wherein the ratio of the base to the metal cation is between about 6.0 : 1.0 and about 2.0 : 1.0.20. The method of item 19, wherein the ratio of the base to the metal cation is between about 5.0 : 1.0 and about 3.0 : 1.0.21. The method of any one of items 18 to 20, wherein step (A2) is performed until a pH of less than about 10.0 is reached at completion.22. The method of any one of items 18 to 20, wherein step (A2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.23. The method of any one of items 18 to 22, wherein the metal cation is a vanadium (III) cation, a chromium (III) cation, a manganese (III) cation, an iron (III) cation, a cobalt (III) cation, a nickel (III) cation, a ruthenium (III) cation, an aluminum (III) cation, or a combination of at least two thereof.24. The method of any one of items 18 to 23, wherein the metal cation and the ambidentate ligand are contacted as a salt.25. The method of any one of items 18 to 24, wherein at least one of step (A1) and step (A2) is carried out at a reaction temperature of less than about 50°C.26. The method of item 25, wherein both steps (A1) and (A2) are carried out at a reaction temperature of less than about 50°C.27. The method of item 25 or 26, wherein the reaction temperature is between about 0°C and about 30°C.28. A method for synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(B1) adding a base to an aqueous solution comprising a metal (II) cation, wherein the ratio of the base to the metal (II) cation is less than about 6.0 : 1.0; and(B2) oxidizing the metal (II) cation.29. The method of item 28, wherein step (B2) comprises contacting the metal (II) cation with an oxidizing agent.30. The method of item 29, wherein the oxidizing agent is sodium hypochlorite.31. The method of item 28, wherein step (B2) comprises heating the metal (II) cation in the presence of oxygen or air.32. The method of item 28, wherein step (B2) comprises an electrochemical oxidation.33. The method of any one of items 28 to 32, wherein the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0.34. The method item 33, wherein the ratio of the base to the metal is between about 5.0 : 1.0 and about 3.0 : 1.0.35. The method of any one of items 28 to 34, wherein step (B1) is performed until a pH of less than about 10.0 is reached at completion.36. The method of any one of items 28 to 34, wherein step (B1) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.37. The method of any one of items 28 to 36, wherein the transition metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.38. The method of any one of items 28 to 37, further comprising a step of contacting the aqueous solution comprising the metal (II) cation with an ambidentate ligand.39. The method of item 38, wherein the metal (II) cation and the ambidentate ligand are provided as salts.40. The method of any one of items 28 to 39, wherein step (B1) is carried out at a reaction temperature of less than about 50°C.41. The method of item 40, wherein the reaction temperature is between about 0°C and about 30°C.42. A method for synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(C1) oxidizing a metal (II) cation to form an oxidized metal composition; and(C2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the oxidized metal composition is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.43. The method of item 42, wherein step (C1) comprises heating the metal (II) cation in the presence of oxygen or air.44. The method of item 42, wherein step (C1) comprises contacting the metal (II) cation with an oxidizing agent.45. The method of item 42, wherein step (C1) comprises an electrochemical oxidation.46. The method of any one of items 42 to 45, wherein the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0.47. The method of item 46, wherein the ratio of the base to the metal is between about 5.0 : 1.0 and about 3.0 : 1.0.48. The method of any one of items 42 to 47, wherein step (C2) is performed until a pH of less than about 10.0 is reached at completion.49. The method of any one of items 42 to 47, wherein step (C2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.50. The method of any one of items 42 to 49, wherein the metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.51. The method of any one of items 42 to 50, wherein step (C1) is carried out in the presence of an ambidentate ligand.52. The method of item 51, wherein the metal (II) cation and the ambidentate ligand are provided as salts.53. The method of any one of items 42 to 52, wherein step (C2) is carried out at a reaction temperature of less than about 50°C.54. The method of item 53, wherein the reaction temperature is between about 0°C and about 30°C.55. A method for synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(D1) partially oxidizing a metal (II) cation to form a mixed valence metal composition; and(D2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the mixed valence metal composition is less than about 6.0 : 1.0 to form the metal (oxy) hydroxi de nanoparticle.56. The method of item 55, wherein step (D1) comprises heating the metal (II) cation in the presence of oxygen or air.57. The method of item 55, wherein step (D1) comprises contacting the metal (II) cation with an oxidizing agent.58. The method of item 55, wherein step (D1) comprises an electrochemical oxidation.59. The method of any one of items 55 to 58, wherein the ratio of the base to the metal is between about 6.0 : 1 .0 and about 2.0 : 1.0.60. The method of item 59, wherein the ratio of the base to the metal is between about 5.0 : 1 .0 and about 3.0 : 1.0.61. The method of any one of items 55 to 60, wherein step (D2) is performed until a pH of less than about 10.0 is reached at completion.62. The method of any one of items 55 to 60, wherein step (D2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.63. The method of any one of items 55 to 62, wherein the metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.64. The method of any one of items 55 to 63, wherein step (D1) is carried out in the presence of an ambidentate ligand.65. The method of item 64, wherein the metal (II) cation and the ambidentate ligand are provided as salts.66. The method of any one of items 55 to 65, wherein step (D2) is carried out at a reaction temperature of less than about 50°C.67. The method of item 66, wherein the reaction temperature is between about 0°C and about 30°C.68. A method of catalyzing a chemical reaction, the method comprising contacting reactants in the presence of a catalyst to form a product, wherein the catalyst comprises metal (oxy)hydroxide nanoparticles having all particle-size dimensions less than about 20 nm.- IQ -BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various objects, features and advantages of the disclosure will be apparent from the following description of particular embodiments, as illustrated in the accompanying drawings.

[0011] Figure 1 is a T ransmission Electron Microscopy (TEM) image of a plurality of iron (oxy)hydroxide nanoparticles prepared in accordance with a method of the present disclosure. The scale bar represents 20 nm.

[0012] Figure 2 shows an X-ray Diffraction (XRD) diffractogram of a plurality of iron (oxy)hydroxide nanoparticles prepared in accordance with a method of the present disclosure.DETAILED DESCRIPTION

[0013] The following detailed description and examples are illustrative and should not be interpreted as further limiting the scope of the invention. On the contrary, it is intended to cover all alternatives, modifications and equivalents that can be included as defined by the present description. The objects, advantages and other features of the metal (oxy)hydroxide nanoparticles, their synthesis methods, as well as methods of catalyzing a chemical reaction using them will be more apparent and better understood upon reading the following non-restrictive description and references made to the accompanying drawings.

[0014] All technical and scientific terms and expressions used herein have the same definitions as those generally understood by the person skilled in the art when relating to the present technology. The definition of some terms and expressions used herein is nevertheless provided below for clarity purposes.

[0015] When the term "about" is used herein, it means approximately, in the region of, or around. For example, when the term "about" is used in relation to a numerical value, it modifies it above and below by a variation of 10% from its nominal value. This term may also take into account rounding of a number or the probability of random errors in experimental measurements; for instance, due to equipment limitations.

[0016] When a range of values is mentioned herein, the lower and upper limits of the range are, unless otherwise indicated, always included in the definition. When a range of values is mentioned in the present disclosure, then all intermediate ranges and subranges, as well as the individual values included in the ranges of values, are included in the definition.

[0017] It is worth mentioning that throughout the following description when the article "a" is used to introduce an element, it does not have the meaning of "only one", but rather of "one or more". It is to be understood that where the specification states that a step, component, feature, or characteristic “may”, “might”, “can” or “could” be included, that particular step, component, feature or characteristic is not required to be included in all alternatives. When the term “comprising" or its equivalent terms “including” or “having” are used herein, it does not exclude other elements. If a group is defined hereinafter to include at least a certain number of embodiments, it is also to be understood to disclose a group, which preferably consists only of these embodiments.

[0018] The term "metal (oxy)hydroxide nanoparticle" as used herein refers to a class of nanoscale particles that comprises metal ions, hydroxide (OH-) ions, and / or oxide (O2ions. The metal (oxy) hydroxide nanoparticles of the present disclosure are characterized by dimensions less than about 20 nm and, in particular, by dimensions between about 2 nm and about 20 nm.

[0019] The term "all particle-size dimensions" as used herein pertains to the linear measurements encompassing the greatest extents of the nanoparticle, regardless of its geometrical form. These dimensions are inherently determined by the shape of the nanoparticle, which can vary and includes, but is not limited to, spherical, cuboidal, cylindrical, discoidal, rod-shaped, and irregular forms among others. For a spherical nanoparticle, the dimension is represented by the diameter. For a cuboidal or cubic nanoparticle, the dimensions refer to the length, width, and height. For cylindrical or rodshaped nanoparticles, the dimensions refer to the height and diameter. Similarly, for irregular shapes, the dimensions correspond to the maximum linear extents along different directions. Notably, these definitions apply to the primary structure of the nanoparticles, excluding any associated ligands, coatings, or surface modifications, unless explicitly stated.

[0020] The term "aqueous solvent" as used herein refers to a solvent including water. The aqueous solvent can be water or a mixture including water an additional solvent miscible with water. For example, the additional solvent can be an alcohol such as methanol, ethanol, and propanol.

[0021] The term "base" as used herein refers to a substance that can accept a proton (H+) or donate a pair of nonbonding electrons in a chemical reaction. Non-limiting examples of bases include lithium hydroxide (LiOH), potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium hydroxide (NH4OH), sodium carbonate (Na2COs), potassium carbonate (K2CO3), and a mixture of at least two thereof, when compatible. In one variant of interest, the base is NaOH.

[0022] The terms "oxidizing agent" and "oxidant" as used herein refer to a chemical substance having the ability to accept electrons in a redox reaction, thereby facilitating the oxidation of other species. Oxidizing agents are integral to various chemical processes and any compatible oxidizing agent is contemplated. Non-limiting examples of oxidizing agents include air, elemental oxygen (O2), hydrogen peroxide (H2O2), ozone (O3), sodium hypochlorite (NaCIO), and various inorganic ions such as permanganate (MnO4‘), dichromate (C^O?2-), and ferric ion (Fe3+). In one variant of interest, the oxidizing agent is NaCIO.

[0023] The term "electrochemical oxidation" as used herein refers to a process wherein an oxidation reaction is driven by the application of an electric potential or current. During electrochemical oxidation, a species loses electrons at the anode (the positively charged electrode in an electrochemical cell), resulting in an increase in its oxidation state. The specifics of the electrochemical oxidation process, including the applied potential and the duration, can be finely tuned to control the degree and selectivity of oxidation. This method may provide an environmentally friendly and controllable way to induce oxidation reactions and may be particularly pertinent to the synthesis and modification of metal (oxy) hydroxide nanoparticles.

[0024] The term "ambidentate ligand" as used herein refers to a chemical species capable of binding to a central atom or ion through two different atoms in its structure simultaneously. This ability to bind via multiple sites may allow the ligand to exhibitversatile binding behavior, potentially forming distinct complexes with different coordination geometries. Ambidentate ligands can be neutral, wherein they do not carry any net charge, or anionic, wherein they carry a net negative charge. The neutral or anionic nature of the ligand can significantly influence its coordination behavior and the properties of the resultant complex. Any compatible ambidentate ligand is contemplated. Non-limiting examples of ambidentate ligands can include amino acids (such as glycine), acetylacetonate, acetylacetonate derivatives, acetate, acetate derivatives, ethylene diamine, ethylene diamine derivative, triethanolamine, triethanolamine derivatives, and a combination of at least two thereof. In one variant of interest, the ambidentate ligand is acetylacetonate. In the context of the present disclosure, ambidentate ligands may play a key role in modulating the nucleation and growth of metal (oxy)hydroxide nanoparticles during their synthesis.

[0025] The term "catalyst" as used herein refers to a substance that accelerates the rate of a chemical reaction without being consumed or changed by the reaction.

[0026] The term "alkane" as used herein refers to saturated hydrocarbons having between twenty and thirty carbon atoms. Non-limiting examples of alkanes may include eicosane, heneicosane, tetracosane, pentacosane, hexacosane, heptacosane, and so on. The term "Cm-Cnalkane" refers to an alkane having from the indicated number "m" to the indicated number "n" of carbon atoms.

[0027] In view of the unmet need for metal (oxy) hydroxi de nanoparticles at the low end of the nanoparticle-size scale (for example, nanodots) the present disclosure details: (i) compositions of matter; (ii) methods of synthesis; and (iii) methods of catalyzing chemical reactions - each relating to metal (oxy)hydroxide nanoparticles having at least one physical dimension less than about 20 nm, and preferably all size dimensions of the nanoparticles are less than about 20 nm. The utility of metal (oxy)hydroxide nanodots in catalysis may arise from the unique physicochemical properties these materials often exhibit, which may be amplified by their high surface area to volume ratios, their unique coordination environments, their high active site densities, their unique electronic configurations, and / or their redox activity.

[0028] An aspect of the present disclosure relates to a metal (oxy) hydroxide nanoparticle having all particle-size dimensions less than about 20 nm.

[0029] In some embodiments, the metal (oxy) hydroxide nanoparticle is a transition metal (oxy)hydroxide nanoparticle selected from a vanadium (oxy)hydroxide nanoparticle, a chromium (oxy)hydroxide nanoparticle, a manganese (oxy) hydroxide nanoparticle, an iron (oxy)hydroxide nanoparticle, a cobalt (oxy)hydroxide nanoparticle, a nickel (oxy) hydroxide nanoparticle, and a ruthenium (oxy)hydroxide nanoparticle. Other metal (oxy)hydroxide nanoparticles having properties similar to those of the transition metal (oxy) hydroxide nanoparticles listed above are also contemplated. For example, aluminum oxy(hydroxide) nanoparticles can be prepared by the methods of the present disclosure and have shown promise in some catalytic reactions.

[0030] In some embodiments, all the particle-size dimensions of the metal (oxy) hydroxi de nanoparticle may be less than about 15 nm, less than about 10 nm, or less than about 5 nm. In some embodiments, all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are greater than about 2 nm. Without being bound to any particular theory, the implicit spatial constraints associated nanoparticles in the nanodot size range ( / .e., between about 2 nm and about 20 nm) may favor the adoption of syn orientations for metal-oxo moieties. In the syn conformation, oxygen atoms in the metal-oxo moieties may be oriented in close proximity to each other. This may impact stereo-electronic effects, for example, by facilitating electron transfer and / or impacting reactivity and selectivity in catalytic reactions as generally described by Zhang et al. (Zhang, Hong-Tao, et al. "Iron- Catalyzed Water Oxidation: 0-0 Bond Formation via Intramolecular Oxo-Oxo Interaction." Angewandte Chemie 133.22 (2021): 12575-12582).

[0031] The particle size dimensions of the metal (oxy)hydroxide nanoparticle of the present disclosure may be readily characterized by a variety of analytical techniques familiar to those skilled in the art, including but not limited to, Dynamic Light Scattering (DLS), microscopy techniques such as Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), and X-ray Diffraction (XRD) by way of the Scherrer equation or the modified Scherrer equation as described with reference to Equation 1 and Equation 2 below.

[0032] A TEM image of a plurality of metal (oxy)hydroxide nanoparticles prepared in accordance with a method of the present disclosure is shown in Figure 1. The TEM image of Figure 1 shows an array of nanoparticles, all of which exhibit dimensions: (i) less than about 20 nm; (ii) less than about 15 nm; (iii) less than about 10 nm; (iv) less than about 5 nm; and / or (v) greater than about 2 nm. At this scale, individual particles can be discerned by visual inspection and / or by using a particle analysis software {e.g., Imaged software), and the average particle size was calculated to be about 3.9 nm with a standard deviation of about 0.4 nm. Accordingly, the TEM image of Figure 1 also evidences a metal (oxy)hydroxide nanoparticle that is one of a plurality of metal (oxy)hydroxide nanoparticles having an average particle size of: (i) between about 3.0 nm and about 5.0 nm; (ii) between about 3.5 nm and about 4.5 nm; and / or (iii) about 3.9 nm and having a particle size standard deviation of less than about 0.5 nm. This small particle size and narrow size distribution illustrate the utility of the synthetic methods set out below. The TEM image of Figure 1 was recorded after routine sample preparation consisting of casting and airdrying an aqueous suspension of the metal (oxy) hydroxi de nanoparticles on a TEM support grid to obtain a substantially thin and uniform layer of metal (oxy) hydroxi de nanoparticles on the TEM support grid.

[0033] An XRD diffractogram obtained for a plurality of metal (oxy)hydroxide nanoparticles prepared in accordance with a method of the present disclosure is shown in Figure 2. Such a diffractogram may be analyzed with the Scherrer equation to calculate average nanoparticle size. The principle behind the Scherrer equation is that the broadening of an XRD peak is inversely proportional to the size of the crystallites causing the diffraction (assuming that other sources of line broadening have been accounted for). The basic form of the Scherrer equation is set out in Equation 1 :_ KA.U = - Equation 1 ft cos 6 wherein:D is the mean size of the crystalline domains, which is usually less than or equal to the particle size;K is the Scherrer constant, a dimensionless geometrical factor with a value close to unity (usually assumed to be in the range of from 0.62 to 2.08, depending on the crystallite geometry);X is the X-ray wavelength;P is the peak broadening at half the maximum intensity ( / .e. full width at half maximum, FWHM) when deconvolved from instrumental broadening, in radians; and0 is the Bragg angle.

[0034] Equation 1 assumes that particle size is the only source of peak broadening, which is not always accurate, especially in real-world samples. As such, the modified Scherrer equation as expressed in Equation 2 is often used to calculate particle size while accounting for auxiliary factors impacting microstrains within lattice structures: ? Equation 2wherein:P, K, A, D, and 0 are as defined in Equation 1 ; and e is the microstrain factor.

[0035] The modified Scherrer equation (Equation 2) was applied to the XRD diffractogram of Figure 2 and to a second XRD diffractogram (also obtained from a plurality of metal (oxy)hydroxide nanoparticles prepared in accordance with a method of the present disclosure) and the average particle sizes were determined to be about 6.2 nm and about 8.73 nm, respectively. The geometrical factor (K), typically varies between 0.64 and 0.9, depending on the crystal symmetry and shape of the peak being analyzed. A geometrical factor of 0.64 best described the shape of the peak ( / .e., a tall peak with narrow tails, otherwise known as a Cauchy distribution) (Langford, J. II, and A. J.C. Wilson. "Scherrer after sixty years: a survey and some new results in the determination of crystallite size." Journal of applied crystallography 11.2 (1978): 102-113).

[0036] The base stoichiometry-controlled methods of the present disclosure may not be limited to any particular metal. In some embodiments, the metal (oxy) hydroxide nanoparticle is a vanadium (oxy)hydroxide nanoparticle, a chromium (oxy)hydroxide nanoparticle, a manganese (oxy)hydroxide nanoparticle, an iron (oxy)hydroxide nanoparticle, a cobalt (oxy) hydroxi de nanoparticle, a nickel (oxy)hydroxide nanoparticle, a ruthenium (oxy) hydroxi de nanoparticle, or an aluminum (oxy)hydroxide nanoparticle. For the synthesis of nickel and cobalt (oxy) hydroxi des, an additional oxidant may be required due to the intrinsic redox properties of these transition metals. Under basic conditions, nickel and cobalt ions in solution may be in lower oxidation states. The addition of an oxidant may induce oxidation of these metal ions, leading to the formation of metal (oxy)hydroxide complexes. Subsequent hydrolysis and condensation reactions under controlled stoichiometry of the base may promote the nucleation and growth of the metal (oxy)hydroxide nanoparticles. For manganese, the stoichiometry-controlled base addition method may be applied without any additional oxidant, owing to the different oxidation states exhibited by manganese. Under basic conditions, manganese ions in solution may readily hydrolyze to form manganese (oxy)hydroxide complexes. Adjusting the stoichiometry of the base may then allow for the controlled nucleation and growth of the manganese (oxy)hydroxide nanoparticles.

[0037] The base stoichiometry-controlled synthesis methods of the present disclosure may also be adapted for the preparation of mixed metal (oxy) hydroxi des. This may involve the simultaneous introduction of multiple metal precursors into the reaction system, followed by controlled base addition to direct the nucleation and growth of the mixed metal (oxy)hydroxide nanoparticles. The relative proportions of the precursors may dictate the final metal stoichiometry in the mixed metal (oxy)hydroxides. In some embodiments, the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising at least two metals selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, and aluminum. In some embodiments, the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising iron and a metal selected from the group consisting of vanadium, chromium, manganese, cobalt, nickel, ruthenium, and aluminum. For certain metal combinations, an additional oxidant may be required. This may be particularly relevant when one of themetal constituents in the mixed metal (oxy)hydroxides is in a lower oxidation state and needs to be oxidized to form the mixed metal (oxy)hydroxide complex.

[0038] The base stoichiometry-controlled synthesis methods of the present disclosure may also be adapted for the preparation of mixed valence metal (oxy) hydroxi des containing a metal which is present in more than one oxidation state. This may involve the partial oxidation of the metal cations, for example, via the addition of an oxidant to induce oxidation of the metal cations, leading to the formation of mixed valence metal (oxy)hydroxide complexes. Subsequent hydrolysis and condensation reactions under controlled stoichiometry of the base may promote the nucleation and growth of the mixed valence metal (oxy)hydroxide nanoparticles. In some embodiments, the mixed valence metal (oxy) hydroxide nanoparticles can be mixed valence iron (oxy) hydroxi de nanoparticles. For example, the mixed valence iron (oxy) hydroxi de nanoparticles can be obtained via the partial oxidation of iron(ll) ( / .e., iron in its +2 oxidation state) to iron(lll) ( / .e., iron in its +3 oxidation state), leading to the formation of mixed valence (Fe(l l) / Fe(l 11)) (oxy)hydroxide complexes. Subsequent hydrolysis and condensation reactions under controlled stoichiometry of the base may promote the nucleation and growth of the mixed valence (Fe(l l) / Fe(l 11)) (oxy)hydroxide nanoparticles. It is to be noted that when the mixed valence metal (oxy)hydroxide nanoparticles are mixed valence iron (oxy)hydroxide nanoparticles, the partial oxidation of Fe(ll) to Fe(lll) preferably does not lead to the formation of magnetite (iron(l 1 , 111) oxide). In some embodiments, the metal (oxy)hydroxide nanoparticles are mixed metal (oxy) hydroxi de nanoparticles comprising at least two metals, wherein at least one metal is present in more than one oxidation state. In some embodiments, the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising iron present in more than one oxidation state and a metal selected from the group consisting of vanadium, chromium, manganese, cobalt, nickel, ruthenium, and aluminum. The mixed valence metal (oxy)hydroxide nanoparticles, when used as a catalyst in a catalytic reaction, may substantially accelerate the initiation phase and / or increased reaction rate compared to metal (oxy)hydroxide nanoparticles in which the metal is present in a single oxidation state. Without being bound to any particular theory, this can be achieved through optimizing the ratios of oxidation states in the metal components of the catalyst.

[0039] XRD may also be used to differentiate the compositions of the present disclosure from other materials. For example, goethite is an iron (oxy) hydroxi de composition, and it can be prepared as a nanoparticle having all size dimensions less than about 20 nm using a method of the present disclosure. In contrast, other iron nanoparticles may have all size dimensions less than about 20 nm, but they may not be metal (oxy)hydroxide nanoparticles. For example, iron oxide and / or iron nitride nanoparticles are readily differentiated from goethite by comparison to goethite’s XRD standard (JCPDS card No. 17-0536). Those skilled in the art who have benefitted from the teachings of the present disclosure will appreciate that additional analytical techniques may be complement such differentiations {e.g., Fourier Transform Infrared Spectroscopy (FTIR)).

[0040] In one embodiment, the metal (oxy) hydroxide nanoparticle is an iron (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 17.8 (13.5) 20, 21.2 (100) 20, 33.2 (43.9) 20, 36.6 (73.3) 20, 41.2 (18.3) 20, 53.2 (39.0) 20, 59.0 (25.8) 20 and 63.9 (12.9) 20.

[0041] In another embodiment, the metal (oxy)hydroxide nanoparticle is a cobalt (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 20.3 (100) 20, 36.5 (14.0) 20, 38.4 (72.1) 20, 50.3 (45.5) 20, 61.7 (17.9) 20 and 64.4 (19.2) 20.

[0042] In another embodiment, the metal (oxy) hydroxide nanoparticle is a nickel (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 12.9 (100) 20, 25.9 (8.2) 20, 37.8 (9.7), 43.0 (13.0) and 51.5 (8.4) 20.

[0043] In another embodiment, the metal (oxy) hydroxide nanoparticle is a manganese (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 21.2 (100) 20, 31.9 (45.0) 20, 38.0 (58.9), 54.1 (36.5) and 61.3 (14.8) 20.

[0044] The base stoichiometry-controlled synthesis methods of the present disclosure may also be suitable for incorporating various ambidentate ligands into metal (oxy)hydroxide nanoparticles. As the names suggest, ambidentate ligands have multiple binding sites, and they may interact simultaneously with a single metal ion or multiple metal ions. This multi-point binding strategy may confer greater stability to metal-ligandcomplexes compared to monodentate ligands that bind at only one point. For example, the iron (oxy)hydroxide nanoparticles recorded in the TEM image of Figure 1 comprise acetylacetonate (acac) ligands. Without being bound to any particular theory, ambidentate ligands may promote nucleation by forming stable complexes with the metal ions, thereby reducing their tendency to aggregate in solution. Moreover, the interaction between ambidentate ligands and metal ions may influence the local coordination environment of the metal ions, potentially inducing the formation of nucleation sites that serve as seeds for nanoparticles growth. On the other hand, ambidentate ligands may inhibit the growth of nanoparticles, for example, through the steric hindrance that discourages further attachment of metal ions or (oxy) hydroxide moieties, effectively capping the size of the nanoparticles. Overall, the use of ambidentate ligands in the base stoichiometry-controlled synthesis methods of the present disclosure may provide an effective means to control the size, morphology, and structure of metal (oxy)hydroxide nanoparticles.Synthesis of metal (oxy)hydroxide nanoparticles

[0045] Various methods as described below may be used to synthesize the metal (oxy)hydroxide nanoparticles of the present disclosure.

[0046] Another aspect of the present disclosure relates to a method of synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising adding a base to a solution comprising a metal cation.

[0047] The metal cation in the solution may be selected from the group consisting of vanadium cations, chromium cations, manganese cations, iron cations, cobalt cations, nickel cations, ruthenium cations, aluminum cations, and a combination of at least two thereof. For example, the concentration of metal cation in the solution can be between about 0.01 M and about 10 M.

[0048] In some embodiments, the solution including a metal cation is an aqueous solution. The aqueous solution can be obtained by adding an aqueous solvent to a source of the metal cation. For example, the source of metal cation may be selected from the group consisting of metal salts, metal oxides, metal hydroxides, metal sulfates, metal nitrates, metal chlorides, metal bromides, metal iodides, metal acetates, metal citrates, metaltartrates, metal lactates, metal-ethylenediaminetetraacetic acid (EDTA) complexes, metal alkoxides, metal hydrides, metal oxalates, and a combination of at least two thereof. In one variant of interest, the source of metal cation is a metal salt.

[0049] In some embodiments, the ratio of the base to the metal cation is between about 6.0 : 1.0 and about 2.0 : 1.0. For example, the ratio of the base to the metal cation can be between about 5.0 : 1.0 and about 3.0 : 1.0.

[0050] In some embodiments, the base is added until a pH of less than about 10.0 is reached at completion. For example, the alkaline solution can be added until a pH of between about 7.0 and about 9.0 is reached at completion.Synthesis of metal (oxy) hydroxide nanoparticles as defined herein (with an ambidentate ligand)

[0051] Another aspect of the present disclosure relates to a method of synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(A1) contacting an aqueous solution comprising a metal cation with an ambidentate ligand to form an aqueous composition; and(A2) contacting the aqueous composition with a base, wherein the ratio of the base to the metal cation is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.

[0052] In some embodiments, the aqueous composition formed in step (A1) comprises a coordination complex consisting of the ambidentate ligand and the metal cation.

[0053] In some embodiments, the metal cation is a transition metal (III) cation. One such example is the synthesis of the iron (oxy)hydroxide nanoparticles recorded in the TEM image of Figure 1. The synthesis of the iron (oxy)hydroxide nanoparticles is further described in Example 1(a).

[0054] In some embodiments, the ratio of the base to the metal cation is between about 6.0 : 1.0 and about 2.0 : 1.0. For example, the ratio of the base to the metal cation can be between about 5.0 : 1.0 and about 3.0 : 1.0.

[0055] In some embodiments, step (A2) is performed until a pH of less than about 10.0 is reached at completion. For example, step (A2) can be performed until a pH of between about 7.0 and about 9.0 is reached at completion.

[0056] In some embodiments, the metal cation is a vanadium (III) cation, a chromium (III) cation, a manganese (III) cation, an iron (III) cation, a cobalt (III) cation, a nickel (III) cation, a ruthenium (III) cation, an aluminum (III) cation, or a combination of at least two thereof.

[0057] In some embodiments, the metal cation and the ambidentate ligand are provided as salts.

[0058] In some embodiments, step (A1), step (A2), or both steps (A1) and (A2) are carried out at a reaction temperature of less than about 50°C. For example, the reaction temperature can be between about 0°C and about 30°C.Synthesis of a metal (oxy) hydroxide nanoparticles (with oxidation)

[0059] Another aspect of the present disclosure relates to a method for synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(B1) adding a base to an aqueous solution comprising a metal (II) cation, wherein the ratio of the base to the metal (II) cation is less than about 6.0 : 1.0; and(B2) oxidizing the metal (II) cation.

[0060] One such example is the synthesis of the manganese (oxy) hydroxide nanoparticles prepared in Example 1(b) and described in Table 1 (below) with respect to their XRD pattern.

[0061] In some embodiments, step (B2) comprises contacting the metal (II) cation with an oxidizing agent. In one variant of interest, the oxidizing agent is NaCIO. In another variant of interest, step (B2) comprises contacting the metal (II) cation with oxygen or air. For example, this could be performed by adding oxygen or air to a suspension comprising the metal (oxy) hydroxide in a solvent or by pulling oxygen or air through a damp solid comprising the metal (oxy)hydroxide, but not immersed in a solvent.

[0062] In some other embodiments, step (B2) comprises heating the metal (II) cation in the presence of oxygen or air.

[0063] In some other embodiments, step (B2) comprises an electrochemical oxidation of the metal (II) cation.

[0064] In some embodiments, the ratio of the base to the metal (II) cation is between about 6.0 : 1.0 and about 2.0 : 1.0. For example, the ratio of the base to the metal (II) cation can be between about 5.0 : 1.0 and about 3.0 : 1.0.

[0065] In some embodiments, step (B1) is performed until a pH of less than about 10.0 is reached at completion. For example, step (B1) can be performed until a pH of between about 7.0 and about 9.0 is reached at completion.

[0066] In some embodiments, the metal (II) cation is a vanadium (II) cation, a chromium (II) cation, a manganese (II) cation, an iron (II) cation, a cobalt (II) cation, a nickel (II) cation, a ruthenium (II) cation, an aluminum (II) cation, or a combination of at least two thereof.

[0067] In some embodiments, the method further comprises a step of contacting the aqueous solution comprising the metal (II) cation with an ambidentate ligand. For example, the metal (II) cation and the ambidentate ligand can be provided as salts.

[0068] In some embodiments, step (B1) is carried out at a reaction temperature of less than about 50°C. For example, the reaction temperature can be between about 0°C and about 30°C.

[0069] Another aspect of the present disclosure relates to a method for synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(C1) oxidizing a metal (II) cation to form an oxidized metal composition; and(C2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the oxidized metal composition is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.

[0070] In some embodiments, step (C1) comprises heating the metal (II) cation in the presence of oxygen or air.

[0071] In some other embodiments, step (C1) comprises contacting the metal (II) cation with an oxidizing agent. In another variant of interest, step (C1) comprises contacting the metal (II) cation with oxygen or air. For example, this could be performed by adding oxygen or air to a suspension comprising the metal (II) cation in a solvent or by pulling oxygen or air through a damp solid comprising the metal (II) cation, but not immersed in a solvent.

[0072] In some other embodiments, step (C1) comprises an electrochemical oxidation.

[0073] In some embodiments, the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0. For example, the ratio of the base to the metal can be between about 5.0 : 1 .0 and about 3.0 : 1.0.

[0074] In some embodiments, step (C2) is performed until a pH of less than about 10.0 is reached at completion. For example, step (C2) can be performed until a pH of between about 7.0 and about 9.0 is reached at completion.

[0075] In some embodiments, the metal (II) cation is a vanadium (II) cation, a chromium (II) cation, a manganese (II) cation, an iron (II) cation, a cobalt (II) cation, a nickel (II) cation, a ruthenium (II) cation, an aluminum (II) cation, or a combination of at least two thereof.

[0076] In some embodiments, step (C1) is carried out in the presence of an ambidentate ligand. For example, the metal (II) cation and the ambidentate ligand can be provided as salts.

[0077] In some embodiments, step (C2) is carried out at a reaction temperature of less than about 50°C. For example, the reaction temperature can be between about 0°C and about 30°C.

[0078] Another aspect of the present disclosure relates to a method for synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(D1) partially oxidizing a metal (II) cation to form a mixed valence metal composition; and(D2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the mixed valence metal composition is less than about 6.0 : 1.0 to form the metal (oxy) hydroxi de nanoparticle.

[0079] In some embodiments, step (D1) comprises heating the metal (II) cation in the presence of oxygen or air.

[0080] In some other embodiments, step (D1) comprises contacting the metal (II) cation with an oxidizing agent. In another variant of interest, step (D1) comprises contacting the metal (II) cation with oxygen or air. For example, this could be performed by adding oxygen or air to a suspension comprising the metal (II) cation in a solvent or by pulling oxygen or air through a damp solid comprising the metal (II) cation, but not immersed in a solvent.

[0081] In some other embodiments, step (D1) comprises an electrochemical oxidation.

[0082] In some embodiments, the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0. For example, the ratio of the base to the metal can be between about 5.0 : 1 .0 and about 3.0 : 1.0.

[0083] In some embodiments, step (D2) is performed until a pH of less than about 10.0 is reached at completion. For example, step (D2) can be performed until a pH of between about 7.0 and about 9.0 is reached at completion.

[0084] In some embodiments, the metal (II) cation is a vanadium (II) cation, a chromium (II) cation, a manganese (II) cation, an iron(ll) cation, a cobalt (II) cation, a nickel (II) cation, a ruthenium (II) cation, an aluminum (II) cation, or a combination of at least two thereof.

[0085] In some embodiments, step (D1) is carried out in the presence of an ambidentate ligand. For example, the metal (II) cation and the ambidentate ligand can be provided as salts.

[0086] In some embodiments, step (D2) is carried out at a reaction temperature of less than about 50°C. For example, the reaction temperature can be between about 0°C and about 30°C.

[0087] It is to be understood that oxidation of the metal (II) cation in step (D1) is carried out partially to obtain a mixed valence metal composition in which the metal is present in more than one oxidation state.

[0088] In some methods of the present disclosure, the addition rate of the base to the metal precursor(s) may influence the size of the resulting nanoparticles. In reactions where the metal precursor(s) is / are soluble in the reaction medium, the droplet size of the basic solution may be a controlling variable, as the metal oxy(hydroxide) particles appear to form instantly at the point where the base drips into the reaction medium. In some methods of the present disclosure, the solubility of metal precursor(s) may influence the size of the resulting nanoparticles.

[0089] The methods of the present disclosure employ bases that are sufficiently basic to counter the acid generated by the ligands on the metal precursor(s) as they are protonated. Based on the present work, the preferred tested base is an aqueous NaOH solution, however, any compatible base is contemplated. Non-limiting examples of suitable bases can include lithium hydroxide (LiOH), potassium hydroxide (KOH), NaOH, ammonium hydroxide (NH4OH), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and a mixture of at least two thereof, when compatible. In the methods of the present disclosure: (i) the rate of base addition may be about 5 mL / min on average, and (ii) the concentration of the base may be about 1 M for hydroxides and about 0.5 M for carbonates.

[0090] The metal oxy( hydroxi de) nanoparticles of the present disclosure may further be purified (or isolated) in a variety of ways. Based on the present work, the preferred tested purification method is filtration, however, any compatible purification method is contemplated. For example, the metal oxy(hydroxide) nanoparticles of the present disclosure may be isolated by centrifugation and / or filtration. The methods of the present disclosure may further include a washing step (for example, with deionized water) to substantially remove any residual base and / or free ligand salts. Exposure to acidicconditions may be avoided, as it may degrade the metal oxy(hydroxide) nanoparticles of the present disclosure.

[0091] The metal (oxy)hydroxide nanoparticles of the present disclosure may have unique electronic, chemical, and / or physical properties conferred by the small size, high surface area to volume ratios, and / or the specific electronic characteristics of their metal ions. Their applications may extend to diverse fields, with catalysis being a domain of particular interest. These nanoparticles can serve as highly efficient catalysts for a variety of chemical reactions, underpinning their importance in industrial, environmental, and energy-related contexts.

[0092] Another aspect of the present disclosure thus relates to a method of catalyzing a chemical reaction, the method comprising contacting a reactant with a catalyst to form a product, wherein the catalyst comprises a metal (oxy) hydroxide nanoparticle as defined herein.

[0093] Another aspect of the present disclosure relates to a method of catalyzing a chemical reaction, the method comprising contacting reactants in the presence of a catalyst to form a product, wherein the catalyst comprises a metal (oxy)hydroxide nanoparticle having all particle-size dimensions less than about 20 nm.

[0094] One such example is the catalytic conversion of waste polyethylene {e.g., conventional garbage bags) into high-value fuel components ( / .e., diesel and C20-C30 alkane fractions) as set out in Example 3 below.EXAMPLES

[0095] The following non-limiting examples are illustrative embodiments and should not be construed as further limiting the scope of the present invention. These examples will be better understood in combination with the accompanying Figures.Example 1: Synthesis of metal (oxy) hydroxide nanoparticles

[0096] Vanadium (oxy) hydroxide nanoparticles, chromium (oxy)hydroxide nanoparticles, manganese (oxy) hydroxi de nanoparticles, iron (oxy)hydroxidenanoparticles, cobalt (oxy)hydroxide nanoparticles, nickel (oxy)hydroxide nanoparticles, ruthenium (oxy)hydroxide nanoparticles, and aluminum (oxy) hydroxi de nanoparticles as well as mixed metal (oxy)hydroxide nanoparticles and mixed valence metal (oxy) hydroxide nanoparticles were prepared in accordance with methods of the present disclosure. The synthesis of iron (oxy)hydroxide nanoparticles and manganese (oxy)hydroxide nanoparticles are presented below. It is to be understood that metal precursors, bases, oxidants, solvents, quantities thereof as well as synthesis methods and reaction conditions can be adapted to obtain the desired metal (oxy) hydroxi de nanoparticles.(a) Synthesis of iron (oxy) hydroxide nanoparticles (with an ambidentate ligand)

[0097] Iron (oxy) hydroxi de nanoparticles were prepared in accordance with methods of the present disclosure. The first step involved the preparation of an aqueous suspension of a ferric coordination complex featuring acetylacetonate ligands. More particularly, an aqueous suspension of Fe(acac)3 was obtained by the reaction of iron trichloride with acetylacetone in water. The second step involved the preparation iron (oxy) hydroxide nanoparticles by the base-addition protocol of the present disclosure. More particularly, 3.6 equivalents of NaOH(aq) were added to the aqueous suspension of Fe(acac)3 at room temperature to form a reaction mixture. The iron (oxy) hydroxi de nanoparticles precipitated from the reaction mixture. The resulting precipitated iron (oxy) hydroxide nanoparticles were subsequently isolated by filtration.

[0098] In the present example, the reaction rate may have been controlled by the poor solubility of Fe(acac)3 in water, as slow addition of the base was not necessary. In related methods where the metal (III) salt was soluble, slow addition of the aqueous NaOH solution was used.(b) Synthesis of manganese (oxy) hydroxide nanoparticles

[0099] Manganese (oxy) hydroxide nanoparticles were prepared in accordance with methods of the present disclosure. To do so, 3.5 equivalents of an aqueous NaOH solution was added dropwise to a solution of manganese(ll) chloride tetrahydrate (MnCl2*4H2O) at room temperature to form a reaction mixture. After the addition of the base was complete, a solution of bleach (sodium hypochlorite; NaCIO) was added dropwise to the reactionmixture in order to ensure substantially complete oxidation. The manganese (oxy)hydroxide nanoparticles precipitated from the reaction mixture and were subsequently isolated by filtration.

[0100] Nickel (oxy)hydroxide nanoparticles and cobalt (oxy)hydroxide nanoparticles were prepared by the synthesis of the present example using nickel(ll) chloride (NiCh) and cobalt(ll) chloride (C0CI2) as metal precursors.Example 2: Characterization of the metal (oxy)hydroxide nanoparticles

[0101] The metal (oxy) hydroxide nanoparticles prepared in Example 1 were characterized by TEM and XRD.(a) Characterization of the metal (oxy) hydroxide nanoparticles by TEM

[0102] The metal (oxy) hydroxide nanoparticles prepared in Example 1 were characterized by TEM.

[0103] Figure 1 is a TEM image of the iron (oxy)hydroxide nanoparticles prepared in Example 1(a). The TEM image was recorded after routine sample preparation. The iron (oxy)hydroxide nanoparticles prepared in Example 1(a) were dispersed in water to form a suspension. The suspension thus obtained was then casted onto a copper TEM support grid. Finally, the suspension was air-dried at room temperature overnight. This TEM sample preparation allowed to obtain a substantially thin and uniform layer of iron (oxy)hydroxide nanoparticles on the copper TEM support grid.

[0104] As can be observed in Figure 1 , the iron (oxy)hydroxide nanoparticles prepared in Example 1(a) exhibit dimensions of less than about 20 nm.(b) Characterization of the metal (oxy) hydroxide nanoparticles by XRD

[0105] The metal (oxy) hydroxide nanoparticles prepared in Example 1 were also characterized by XRD.

[0106] Figure 2 is an XRD diffractogram obtained for the iron (oxy) hydroxide nanoparticles prepared in Example 1(a).

[0107] XRD data for select metal (oxy)hydroxide nanoparticles prepared in accordance with methods of the present disclosure are set out in Table 1.Table 1 : XRD data for select metal (oxy)hydroxide nanoparticles prepared in accordance with methods of the present disclosureExample 3: Catalytic conversion of waste polyethylene using metal (oxy)hydroxide nanoparticles

[0108] The catalytic conversion of waste polyethylene into high-value fuel components was carried out in accordance with a method of the present disclosure. In this example, a Parr™ reactor containing 1.04 g of an iron (oxy) hydroxide nanoparticle composition of thepresent disclosure and 10.33 g of polyethylene was heated to a temperature of about 300°C and stirred overnight. The reaction mixture was cooled down to room temperature, dissolved in ethyl acetate, filtered on Celite™ , and the mother liquor was analyzed by gas chromatography-mass spectrometry (GC-MS) to provide the product distribution set out in Table 2.Table 2 Product distribution as determined by GC-MS.

[0109] The product distribution showed about 62% of (C10-C19) diesel fraction and about 20% of higher molecular weight acyclic saturate alkanes {e.g., C20-C27 alkanes).

[0110] Although the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof, it is not to be so limited sincemodifications and changes can be made therein which are within the full, intended scope of the invention as understood by those skilled in the art.

Claims

CLAIMS1 . A metal (oxy)hydroxide nanoparticle having all particle-size dimensions less than about 20 nm.

2. The metal (oxy)hydroxide nanoparticle of claim 1 , wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 15 nm.

3. The metal (oxy)hydroxide nanoparticle of claim 1 or 2, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 10 nm.

4. The metal (oxy)hydroxide nanoparticle of any one of claims 1 to 3, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are less than about 5 nm.

5. The metal (oxy)hydroxide nanoparticle of any one of claims 1 to 4, wherein all the particle-size dimensions of the metal (oxy)hydroxide nanoparticle are greater than about 2 nm.

6. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 5, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of between about 3.0 nm and about 5.0 nm.

7. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 6, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of between about 3.5 nm and about 4.0 nm.

8. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 7, wherein the metal (oxy) hydroxi de nanoparticle is one of a plurality of metal (oxy) hydroxide nanoparticles having an average particle size of about 3.9 nm and a particle size standard deviation of less than about 0.5 nm.

9. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a vanadium (oxy)hydroxide nanoparticle, a chromium (oxy)hydroxide nanoparticle, a manganese (oxy) hydroxi de nanoparticle, an iron(oxy)hydroxide nanoparticle, a cobalt (oxy)hydroxide nanoparticle, a nickel (oxy) hydroxide nanoparticle, a ruthenium (oxy)hydroxide nanoparticle, or an aluminum (oxy) hydroxide nanoparticle.

10. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising at least two metals selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, and aluminum.

11. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed metal (oxy)hydroxide nanoparticle comprising iron and at least one metal selected from the group consisting of vanadium, chromium, manganese, cobalt, nickel, ruthenium, and aluminum.

12. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy)hydroxide nanoparticle is a mixed valence metal (oxy) hydroxi de nanoparticle comprising at least one metal selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, and aluminum, wherein the metal is present in more than one oxidation state.

13. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is an iron (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 17.8 (13.5) 20, 21.2 (100) 20, 33.2 (43.9) 20, 36.6 (73.3) 20, 41.2 (18.3) 20, 53.2 (39.0) 20, 59.0 (25.8) 20 and 63.9 (12.9) 20.

14. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is a cobalt (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 20.3 (100) 20, 36.5 (14.0) 20, 38.4 (72.1) 20, 50.3 (45.5) 20, 61.7 (17.9) 20 and 64.4 (19.2) 20.

15. The metal (oxy) hydroxi de nanoparticle of any one of claims 1 to 8, wherein the metal (oxy) hydroxide nanoparticle is a nickel (oxy)hydroxide nanoparticle having an X-ray diffraction pattern comprising reflectance peaks at 12.9 (100) 20, 25.9 (8.2) 20, 37.8 (9.7), 43.0 (13.0) and 51.5 (8.4) 20.

16. The metal (oxy)hydroxide nanoparticle of any one of claims 1 to 15, which comprises an ambidentate ligand.

17. The metal (oxy)hydroxide nanoparticle of claim 16, wherein the ambidentate ligand is selected from the group consisting of acetylacetonate, acetylacetonate derivatives, acetate, acetate derivatives, ethylene diamine, ethylene diamine derivatives, triethanolamine, triethanolamine derivatives, and a combination of at least two thereof.

18. A method of synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(A1) contacting an aqueous solution comprising a metal cation with an ambidentate ligand to form an aqueous composition; and(A2) contacting the aqueous composition with a base, wherein the ratio of the base to the metal cation is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.

19. The method of claim 18, wherein the ratio of the base to the metal cation is between about 6.0 : 1.0 and about 2.0 : 1.0.

20. The method of claim 19, wherein the ratio of the base to the metal cation is between about 5.0 : 1.0 and about 3.0 : 1.0.

21. The method of any one of claims 18 to 20, wherein step (A2) is performed until a pH of less than about 10.0 is reached at completion.

22. The method of any one of claims 18 to 20, wherein step (A2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.

23. The method of any one of claims 18 to 22, wherein the metal cation is a vanadium (III) cation, a chromium (III) cation, a manganese (III) cation, an iron (III) cation, a cobalt (III) cation, a nickel (III) cation, a ruthenium (III) cation, an aluminum (III) cation, or a combination of at least two thereof.

24. The method of any one of claims 18 to 23, wherein the metal cation and the ambidentate ligand are contacted as a salt.

25. The method of any one of claims 18 to 24, wherein at least one of step (A1) and step (A2) is carried out at a reaction temperature of less than about 50°C.

26. The method of claim 25, wherein both steps (A1) and (A2) are carried out at a reaction temperature of less than about 50°C.

27. The method of claim 25 or 26, wherein the reaction temperature is between about 0°C and about 30°C.

28. A method for synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(B1) adding a base to an aqueous solution comprising a metal (II) cation, wherein the ratio of the base to the metal (II) cation is less than about 6.0 : 1.0; and(B2) oxidizing the metal (II) cation.

29. The method of claim 28, wherein step (B2) comprises contacting the metal (II) cation with an oxidizing agent.

30. The method of claim 29, wherein the oxidizing agent is sodium hypochlorite.

31. The method of claim 28, wherein step (B2) comprises heating the metal (II) cation in the presence of oxygen or air.

32. The method of claim 28, wherein step (B2) comprises an electrochemical oxidation.

33. The method of any one of claims 28 to 32, wherein the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0.

34. The method claim 33, wherein the ratio of the base to the metal is between about 5.0 : 1.0 and about 3.0 : 1.0.

35. The method of any one of claims 28 to 34, wherein step (B1) is performed until a pH of less than about 10.0 is reached at completion.

36. The method of any one of claims 28 to 34, wherein step (B1) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.

37. The method of any one of claims 28 to 36, wherein the transition metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.

38. The method of any one of claims 28 to 37, further comprising a step of contacting the aqueous solution comprising the metal (II) cation with an ambidentate ligand.

39. The method of claim 38, wherein the metal (II) cation and the ambidentate ligand are provided as salts.

40. The method of any one of claims 28 to 39, wherein step (B1) is carried out at a reaction temperature of less than about 50°C.

41. The method of claim 40, wherein the reaction temperature is between about 0°C and about 30°C.

42. A method for synthesizing a metal (oxy)hydroxide nanoparticle having all particlesize dimensions less than about 20 nm, the method comprising:(C1) oxidizing a metal (II) cation to form an oxidized metal composition; and(C2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the oxidized metal composition is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.

43. The method of claim 42, wherein step (C1) comprises heating the metal (II) cation in the presence of oxygen or air.

44. The method of claim 42, wherein step (C1) comprises contacting the metal (II) cation with an oxidizing agent.

45. The method of claim 42, wherein step (C1) comprises an electrochemical oxidation.

46. The method of any one of claims 42 to 45, wherein the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0.

47. The method of claim 46, wherein the ratio of the base to the metal is between about 5.0 : 1.0 and about 3.0 : 1.0.

48. The method of any one of claims 42 to 47, wherein step (C2) is performed until a pH of less than about 10.0 is reached at completion.

49. The method of any one of claims 42 to 47, wherein step (C2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.

50. The method of any one of claims 42 to 49, wherein the metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.

51. The method of any one of claims 42 to 50, wherein step (C1) is carried out in the presence of an ambidentate ligand.

52. The method of claim 51, wherein the metal (II) cation and the ambidentate ligand are provided as salts.

53. The method of any one of claims 42 to 52, wherein step (C2) is carried out at a reaction temperature of less than about 50°C.

54. The method of claim 53, wherein the reaction temperature is between about 0°C and about 30°C.

55. A method for synthesizing a metal (oxy)hydroxide nanoparticle as defined herein, the method comprising:(D1) partially oxidizing a metal (II) cation to form a mixed valence metal composition; and(D2) contacting the oxidized metal composition with a base, wherein the ratio of the base to the metal of the mixed valence metal composition is less than about 6.0 : 1.0 to form the metal (oxy)hydroxide nanoparticle.

56. The method of claim 55, wherein step (D1) comprises heating the metal (II) cation in the presence of oxygen or air.

57. The method of claim 55, wherein step (D1) comprises contacting the metal (II) cation with an oxidizing agent.

58. The method of claim 55, wherein step (D1) comprises an electrochemical oxidation.

59. The method of any one of claims 55 to 58, wherein the ratio of the base to the metal is between about 6.0 : 1.0 and about 2.0 : 1.0.

60. The method of claim 59, wherein the ratio of the base to the metal is between about 5.0 : 1.0 and about 3.0 : 1.0.

61. The method of any one of claims 55 to 60, wherein step (D2) is performed until a pH of less than about 10.0 is reached at completion.

62. The method of any one of claims 55 to 60, wherein step (D2) is performed until a pH of between about 7.0 and about 9.0 is reached at completion.

63. The method of any one of claims 55 to 62, wherein the metal is vanadium, chromium, manganese, iron, cobalt, nickel, ruthenium, aluminum, or a combination of at least two thereof.

64. The method of any one of claims 55 to 63, wherein step (D1) is carried out in the presence of an ambidentate ligand.

65. The method of claim 64, wherein the metal (II) cation and the ambidentate ligand are provided as salts.

66. The method of any one of claims 55 to 65, wherein step (D2) is carried out at a reaction temperature of less than about 50°C.

67. The method of claim 66, wherein the reaction temperature is between about 0°C and about 30°C.

68. A method of catalyzing a chemical reaction, the method comprising contacting reactants in the presence of a catalyst to form a product, wherein the catalyst comprises metal (oxy)hydroxide nanoparticles having all particle-size dimensions less than about 20 nm.

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