Method of preparing a carbon hybrid nanomaterial and uses thereof

Abstract

The present disclosure relates broadly to a method of preparing a carbon hybrid nanomaterial. The method may comprise the step of subjecting a base, a carbon source and an acid to a solution combustion reaction to thereby form the carbon hybrid nanomaterial from the base, the carbon source and the acid. The disclosure also relates to a carbon hybrid nanomaterial prepared by the method and use of the carbon hybrid nanomaterial for promoting plant growth.

Description

[0001] Method of Preparing A Carbon Hybrid Nanomaterial and Uses Thereof References to Related Applications

[0002] This application claims priority to Singapore Application No. 10202403554Y filed with the Intellectual Property Office of Singapore on 14 November 2024, the contents of which are incorporated herein by reference.

[0003] Technical Field

[0004] The present invention generally relates to a method of preparing a carbon hybrid nanomaterial. The present invention also relates to a carbon hybrid nanomaterial prepared by the method and use of the carbon hybrid nanomaterial for promoting plant growth.

[0005] Background Art

[0006] Fertilizers are critical for high-yield crop production to meet the increasing global food demand. Current fertilizer practices have caused severe economic and environmental problems due in large part to low uptake efficiencies of the requisite nutrient(s) and, despite this, the demand for fertilizers continues to grow. The environmental impact and economic costs of fertilizers are most significant for sources of nitrogen (N fertilizers) and phosphorus (P fertilizers). This is a result of the sheer scale of N fertilizers required by industry and the typically very low uptake efficiency of P fertilizers due to soil fixation. There is increasing interest and research in the use of nanotechnology for addressing these global agricultural challenges. However, widespread applications of nanotechnology solutions have been limited due to issues such as low uptake efficiency, poor scalability, and high production costs.

[0007] There is thus a need for a method of preparing a nanomaterial fertilizer, such as a carbon hybrid nanomaterial, having one or more advantageous properties, for example, improved nutrient uptake efficiency, ability to scale, and lower production cost.

[0008] Accordingly, there is a need for a method of producing a carbon hybrid nanomaterial for promoting plant growth that overcomes, or at least ameliorates, one or more of the disadvantages mentioned above.

[0009] Summary

[0010] According to a first aspect, there is provided a method of preparing a carbon hybrid nanomaterial, the method comprising the step of subjecting a base, a carbon source and an acid to a solution combustion reaction to thereby form the carbon hybrid nanomaterial from the base, the carbon source and the acid.

[0011] Advantageously, the method as described herein may provide improved scalability and / or lower production costs.

[0012] According to a second aspect, there is provided a carbon hybrid nanomaterial produced by the method as described herein. According to a third aspect, there is provided a use of the carbon hybrid nanomaterial as described herein for promoting plant growth.

[0013] Advantageously, the carbon hybrid nanomaterials as described herein may have improved nutrient uptake efficiency.

[0014] Definitions

[0015] The following words and terms used herein shall have the meaning indicated:

[0016] As used herein, the singular forms “a”, “an”, and “the” designate both the singular and the plural, unless expressly stated to designate the singular only.

[0017] The word “substantially” does not exclude “completely” e g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

[0018] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

[0019] As used herein, the term “about”, in the context of concentrations of components of the formulations, 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. Moreover, “about” may be understood by persons of ordinary skill in the art to allow for small or non-substantial variations reflecting the appropriate level of precision according Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0020] As used herein, the term “about” and the use of ranges in general, whether or not qualified by the term about, means that the number comprehended is not limited to the exact number set forth herein, and is intended to refer to values substantially within the quoted range while not departing from the scope of the invention.

[0021] As used herein, the terms “dopant” and “additive” refer to a substance that is added to the carbon hybrid nanomaterial, and these terms may be used interchangeably.

[0022] As used herein, the term “s.d.” refers to standard deviation.

[0023] Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0024] Detailed Disclosure of Embodiments

[0025] Exemplary, non-limiting embodiments of a method of preparing a carbon hybrid nanomaterial will now be disclosed.

[0026] The method of preparing the carbon hybrid nanomaterial may comprise the step of subjecting a base, a carbon source and an acid to a solution combustion reaction to thereby form the carbon hybrid nanomaterial from the base, the carbon source and the acid.

[0027] The base may be the same as the carbon source such that the base and the carbon source is the same material or compound. This occurs when the base contains organic moieties that can contribute carbon towards the carbon hybrid nanomaterial.

[0028] Alternatively, the base may be different from the carbon source, such as when the base does not contain any organic moieties and therefore the carbon source is needed to provide the carbon atoms for the carbon hybrid nanomaterial. The carbon source may also be added to supplement the base even if the base contains organic moieties if the amount of organic moieties in the base is not sufficient and the carbon source is needed to increase the amount of carbon atoms.

[0029] The subjecting step may comprise the step of mixing the base, the carbon source and the acid. Where the base is the carbon source, the subjecting step may comprise the step of mixing the base and the acid.

[0030] The mixing may be conducted in a reaction vessel such as a reaction flask, stirred tank, jacketed reactor, flow reactor, spray reactor, continuous reactor, batch reactor, mixing drum, or agitated vessel. The choice of the reaction vessel may depend on the scale of the method, which is within the purview of the person skilled in the art to decide on an appropriate reaction vessel depending on whether the method is on a small scale (such as in a laboratory) or on a large scale (such as in a factory or manufacturing plant). The mixing may be conducted using magnetic, mechanical, or ultrasonic means, or a combination thereof.

[0031] The mixing step may comprise the step of adding the base, carbon source, and acid separately or together in any sequence to the reaction vessel. The mixing step may comprise the steps of mixing the base with the carbon source, followed by adding the acid; or the steps of mixing the acid with the carbon source, followed by adding the base. Where the base is the carbon source, the mixing step may comprise the step of adding the base and acid separately or together in any sequence to a reaction vessel. Where the base is the carbon source, the mixing step may comprise the step of mixing the base with the acid: mixing the base, followed by adding the acid; or the step of mixing the acid, followed by adding the base.

[0032] The mixing may be effected by a sprayer, magnetic stirrer, overhead mechanical stirrers, propellertype stirrers, turbine-type stirrers, paddle stirrer, anchor-type stirrers, helical ribbon stirrer, screw agitators, mixers such as high-shear mixer, rotor-stator mixers, static mixer, tumbling mixer, or a combination there of. The mixing speed, duration, and temperature may be varied according to the scale and viscosity of the mixture The acid may be added to the stirred mixture of the base and the carbon source. Where the base is the carbon source, the acid may be added to a stirred base. In the adding step, the acid may be added dropwise or by continuous flow to a stirred mixture comprising the base and the carbon source. The adding step may be dropwise addition via syringe: continuous addition using a peristaltic pump, syringe pump, or metering pump; continuous flow using, for example, a pipe flow; gradual addition through a controlled feed line or drip funnel under pressure or gravity: stepwise or portion-wise addition, in which the acid is added in discrete aliquots at predetermined intervals; simultaneous or co-feeding addition, in which two or more of the base, carbon source and acid are fed concurrently at controlled rates; or automated titration or feedback-controlled dosing, based on monitored parameters such as pH, temperature, or turbidity. The addition may be selected to maintain consistent reaction kinetics, ensure safety, and achieve uniform product quality across differing scales.

[0033] The reaction temperature generated during the solution combustion reaction may be regulated by a heating or cooling means. The reaction may be a solution combustion reaction. The reaction temperature may be initiated at about room temperature and then increased due to the solution combustion reaction which is exothermic. During the exothermic reaction, the reaction temperature may be regulated to a desired temperature by any one or more of the following: a heating or cooling means, regulating the speed and / or frequency of addition of one or more reactants, or by controlling the mixing rate in the reaction vessel.

[0034] The reaction temperature may be increased to over about 30 °C, or over about 40 °C, or over about 50 °C, or over about 60 °C, or over about 70 °C, or over about 80 °C, or over about 90 °C, or over about 100 °C, or over about 110 °C, or over about 120 °C, or over about 130 °C, or over about 140 °C, or over about 150 °C, or over about 160 °C, or over about 170 °C, or over about 180 °C, or over about 190 °C, or over about 200 °C, or over about 210 °C, or over about 220 °C from the initiation temperature. The reaction temperature may be increased to be between about 30 °C to about 1000 °C, or between about 40 °C to about 900 °C, or between about 50 °C to about 800 °C, or between about 60 °C to about 750 °C, or between about 70 °C to about 700 °C, or between about 80 °C to about 650 °C, or between about 90 °C to about 600 °C, or between about 100 °C to about 550 °C, or between about 110 °C to about 500 °C, or between about 120 °C to about 450 °C, or between about 130 °C to about 400 °C, or between about 140 °C to about 350 °C, or between about 150 °C to about 300 °C, or between about 160 °C to about 250 °C, or between about 170 °C to about 230 °C, or between about 180 °C to about 220 °C, or between about 190 °C to about 210 °C. The reaction temperature may be increased to be about 200 °C. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0035] The reaction pressure of the method may be atmospheric pressure. The reaction pressure may be regulated to a selected pressure using an external pressure control means. The reaction pressure may be allowed to increase in the reaction vessel at least in part due to gases formed from the reaction between the reagents.

[0036] The reaction time of the method may be between from about 1 minute to about 30 minutes, or from about 3 minutes to about 25 minutes, or from about 5 minutes to about 20 minutes, or from about 7 minutes to about 15 minutes, or from about 8 minutes to about 12 minutes. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). The mole ratio of the acid to the base may be between about 4: 1 to about 1:4, or between about 2: 1 to about 1:2, or between about 3:2 to about 2:3, or between about 4:3 to about 3:4, or between about 5:4 to about 4:5, or between about 6:5 to about 5:6, or between about 7:6 to about 6:7, or between about 8:7 to about 7:8, or between about 9:8 to about 8:9, or between about 10:9 to about 9:10. The mole ratio of acid to the base may be about 1:1. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0037] The base may be one that contains organic moieties such as an amine or one that does not contain organic moieties such as a hydroxide, or a combination thereof. The amine may be selected from the group consisting of ethylenediamine, methylamine, tri ethylamine, tris(2-ethylhexyl)amine, tris(2-aminoethyl)amine, bis(2-hydroxypropyl)amine, 3-(diethylamino)propylamine, ethylamine, propylamine, butylamine, amylamine, hexylamine, polyetherimide, nicotinic acid), N, N, N', N'-tetrakis(2-hydroxypropyl)ethylenediamine, p-phenylenediamine, m-xylylenediamine, triethylenetetramine, 3-(diethylamino)propylamine, hexamethylenediamine, N, N-dimethylethylenediamine, diethylenetriamine, 3, 4 -diaminotoluene, 4-methyl-o-phenylenediamine, bis(3-aminopropyl)amine, triethanolamine, diethylenetriamine, triisopropanolamine, benzylamine, 2-[2-(dimethylamino)ethoxy]ethanol, p-phenylenediamine, 3-(diethylamino)propylamine, N, N, N, N'-tetramethylethylenediamine, 2-(methylamino)ethanol, N-butyldiethanolamine, 2-amino-1-butanol, 2-amino-2-methyl-1,3-propanediol, aminobutanol, bis[2-(N,N-dimethylamino)ethyl] ether, m-xylylenediamine, 2,6-dichloro-4-nitroaniline, 3-(dimethylamino)- 1 -propylamine, N, jV-diethylethylenediamine, aniline, tris(hydroxymethyl)aminomethane, and any combination thereof. The hydroxide may be selected from the group consisting of potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, aluminium hydroxide, ammonium hydroxide, and any combination thereof. The base may be used neat, or may be an aqueous solution from between about 0% to about 100%. It is to be appreciated that this range should be interpreted as including and supporting any subranges or discrete values (which may or may not be a whole number) that are within the stated range.

[0038] The acid may be selected from the group consisting of phosphoric acid, nitric acid, acetic acid, formic acid, sulfuric acid, a derivative thereof, an isomer thereof, and any combination thereof. The concentration of the acid may be from between about 50% to about 100%, or between about 60% to about 99%, or between about 60% to about 98%, or between about 60% to about 70%, or between about 80% to about 90%, or between about 90% to about 99%. The concentration of the acid may be greater than about 95%, or greater than about 98%, or greater than about 99%, or greater than about 99.5%, or greater than about 99.7%. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0039] Where the carbon source is different from the base, the carbon source may be selected from the group consisting of glycerol, ethylene glycol, diethylene glycol, polyethylene glycol, starch, cellulose, chitin, chitosan, carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose, lignin sulfonate, humic acid, fulvic acid, monosaccharide, polysaccharide, biomass, waste biomass, a derivative thereof, an isomer thereof, and any combination thereof. The waste biomass may be agricultural residue, food processing waste, forestry by-product, municipal organic waste, or a combination thereof. The waste biomass may be in the form of a raw, dried, ground, or slurry form of waste. The carbon source may be used neat, or may be an aqueous solution from between about 0% to about 100%. It is to be appreciated that this range should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range.

[0040] The method may further comprise the step of adding an additive. The additive may be pre -added to the base. The additive may be pre-added to the acid. The additive may be added during or after the subjecting step. The additive may be selected from the group consisting of a plant nutrient, an agrochemical, and a combination thereof. The agrochemical may be a pesticide. The plant nutrient may be a secondary macronutrient, a micronutrient, a macronutrient, a plant beneficial element, or any combination thereof. The plant nutrient may be sulfur, calcium, magnesium, iron, zinc, manganese, copper, molybdenum, nitrogen, phosphorus, potassium, silicon, titanium, cerium, selenium, or any combination thereof. The additive may be selected from the group consisting of calcium nitrate, calcium sulfate, calcium hydroxide, calcium oxide, calcium chloride, calcium carbonate, magnesium nitrate, magnesium sulfate, magnesium oxide, magnesium chloride, magnesium carbonate, tetraethyl orthosilicate, silica, 3 -aminopropyltriethoxysilane, silicic acid, iron(II) nitrate, iron(II) sulfate, ethylene diaminetetraacetic acid ferric sodium salt, iron(II) oxide, iron(III)oxide, iron(II) hydroxide, iron(III) nitrate, iron(III) hydroxide, iron(II) chloride, iron(III) chloride, iron(II) acetate, iron(III) hydroxide, potassium chloride, potassium sulfate, potassium nitrate, potassium hydroxide, potassium carbonate, zinc nitrate, zinc sulfate, zinc oxide, zinc chloride, zinc carbonate, zinc hydroxide, manganese(II) oxide, manganese(II) nitrate, manganese(II) sulfate, manganese(II) carbonate, copper(II) chloride, copper(II) oxide, copper(II) hydroxide, copper(II) nitrate, copper(II) sulfate, copper(II) carbonate, boric acid, titanium(IV) chloride, titanium(IV) oxide, titanium(IV) oxide nanoparticle, silver nitrate, silver nanoparticle, a derivate thereof, and any combination thereof. The additive may be used neat, or may be an aqueous solution from between about 0% to about 100%. It is to be appreciated that this range should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range.

[0041] Exemplary, non-limiting embodiments of a carbon hybrid nanomaterial prepared by the method as described herein will now be disclosed.

[0042] The carbon hybrid nanomaterial prepared by the method as described herein may have a particle size of between about 1 nm to about 1000 nm, or between about 2 nm to about 800 nm, or between about 3 nm to about 600 nm, or between about 4 nm to about 400 nm, or between about 5 nm to about 300 nm, or between about 6 nm to about 200 nm, or between about 7 nm to about 150 nm, or between about 8 nm to about 120 nm, or between about 9 nm to about 110 nm, or between about 10 nm to about 100 nm. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0043] The carbon hybrid nanomaterial (CHN) prepared by the method as described herein may have a surface charge of between about -30 to about +30 mV, or between about -20 to about +20 mV, or between about -10 to about +10 mV. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). The surface charge of the CHN may be tuned by adjusting the pH value of the final solution of CHN. The pH adjustment may be effected by adding a dilute acid or base. The dilute acid may be HC1. The dilute base may be NaOH. The surface charge may also be adjusted by controlling parameters such as elemental composition, for example increasing or decreasing the amount of N in the composition. This change in surface charge, as measured by zeta potential, directly relates to the type and quantity of N-containing functional groups incorporated onto the CHN surface. When N is introduced during synthesis, the zeta potential may shift toward less negative values or may become positive. This could occur because N-containing functional groups alter the surface chemistry. For example, amino groups (-NH2) may be protonated to form ammonium groups ( –NH₃⁺), introducing positive charges. Generally, an increase in the N content in the CHN may increase the zeta potential value and makes it become less negative, and in some extreme cases, may even make the CHN more positively charged. Adjusting the surface charge may also enable modulation of properties such as colloidal stability, surface reactivity, interfacial interactions, dispersibility, selective adsorption, and compatibility with surrounding media such as allowing the charged carbon hybrid nanomaterial to be attracted to roots of a plant to facilitate absorption and uptake.

[0044] The carbon hybrid nanomatcrial prepared by the method as described herein may be a char or a char-like material, such as a biochar. The carbon hybrid nanomaterial maybe produced in the form of a chai', such as a biochar. The carbon hybrid nanomaterial may be produced in the form of a char, or a combination of particles and char. The char, such as the biochar, may have a hierarchical, composite or mixed structure. The hierarchical, composite or mixed structure may comprise any one or more of a nano- scale, micro- scale, and macro-scale structure. The char, such as the biochar, may be partially soluble in water. The char, such as the biochar, may comprise portions with different particle size ranges. The char, such as the biochar, may be subjected to one or more extraction steps. The extraction step may comprise extraction into water.

[0045] The carbon hybrid nanomaterial prepared by the method as described herein may be used without further treatment. The carbon hybrid nanomaterial prepared by the method as described herein may be dissolved in water prior to use. The carbon hybrid nanomaterial prepared by the method as described herein may be subjected to post-treatment. The post-treatment may comprise purification, such as filtration; pH tuning; thermal treatment, such as annealing; chemical treatment such as surface functionalization; solvent treatment; mechanical treatment such as sonication, centrifugation, or ball milling; irradiation, or a combination thereof.

[0046] Exemplary, non-limiting embodiments of a use of the carbon hybrid nanomaterial prepared by the method as described herein will now be disclosed.

[0047] The carbon hybrid nanomaterial prepared by the method as described herein may be used for promoting plant growth The carbon hybrid nanomaterial may be used as a fertilizer. The carbon hybrid nanomaterial may be used for promoting plant reproduction. The carbon hybrid nanomaterial may be used for enhancing nutrient uptake efficiency. The carbon hybrid nanomaterial may be used as a pesticide. The carbon hybrid nanomaterial may be used as an herbicide. The carbon hybrid nanomaterial may be used for increasing disease resistance. The carbon hybrid nanomaterial may be used in environmental remediation, carbon sequestration, or water treatment.

[0048] Brief Description of Drawings

[0049] The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention. Figure 1

[0050] Figure 1 is a schematic diagram showing a method 1 of preparing a carbon hybrid nanomaterial (CHN) 2 according to one embodiment, comprising a step of adding an acid 3 dropwise to a mixture of a base 4 and a carbon source 5 in a reaction vessel 6 to form the CHN.

[0051] Figure 2

[0052] Figure 2 is a schematic diagram showing a method 7 of preparing a CHN 8 according to another embodiment, comprising steps of spray mixing abase 9, acid 10, carbon source 11 and dopant 12 to a reaction vessel 13 to form the CHN and undergoing a continuous reaction, then dissolving the CHN in water.

[0053] Figure 3

[0054] Figure 3 is a schematic diagram showing a method 14 of preparing a CHN 15 according to another embodiment, comprising steps of mixing a base 16 and acid 17, and optionally one or more carbon sources 18 and dopants 19 to a reaction vessel 20 and undergoing a continuous reaction to form the CHN, followed by post -treatment.

[0055] Figure 4

[0056] Figure 4 is a transmission electron microscope (TEM) image, at magnification of 200,000x, of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 16. Figure 5

[0057] Figure 5 is a TEM image, at magnification of 400,000x, of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 9.

[0058] Figure 6

[0059] Figure 6 is a TEM image, at magnification of 20,000x, of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 9.

[0060] Figure 7

[0061] Figure 6 is a TEM image, at magnification of 120,000x, of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 2.

[0062] Figure 8

[0063] Figure 8 is a TEM image, at magnification of 120,000x, of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 11.

[0064] Figure 9

[0065] Figure 9 is an FTIR spectrum of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 16. Figure 10

[0066] Figure 10 is an FTIR spectrum of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 18.

[0067] Figure 11

[0068] Figure 11 is an FTIR spectrum of an example of a CHN made in accordance with Example 1 below and denoted as sample no. 9.

[0069] Figure 12

[0070] Figure 12 is an XPS spectrum for example of two CHNs made in accordance with Example 1 below and denoted as sample no. 16 and sample no. 9.

[0071] Figure 13

[0072] Figure 13 is a photograph of a thin-layer chromatography (TLC) plate with reagents (A) ethylene diamine, (B) phosphoric acid, (C) glycerol and the product (D) spotted from left to right, and eluted with acetate / methanol (1:1), wherein the product is an example of a CHN made in accordance w ith Example 1 below and denoted as sample no. 16.

[0073] Figure 14

[0074] Figure 14 is a photograph of a TLC plate with reagents (A) ethylene diamine, (B) phosphoric acid, (C) FeEDTA, (D) glycerol and the product (E) spotted from left to right, and eluted with acetate / methanol (1:1), wherein the product is an example of a CHN made in accordance with Example 1 below and denoted as sample no. 18.

[0075] Figure 15

[0076] Figure 15 is a graph showing Soil Plant Analysis Development (SPAD) values of spinach leaves grown with different Fe source treatments, including: a control group without any iron; FeEDTA 60 solution comprising FeEDTA at 60 mg / L; FeSO₄ 60 solution comprising FeSO₄ at 60 mg / L; and FeCHN-NA 60 comprising FeCHN-NA at 60 mg / L.

[0077] Figure 16

[0078] Figure 16 is a graph showing SPAD values of spinach leaves grown with different Fe source treatments, including: a control group without any iron; FeEDTA 120 solution comprising FeEDTA at 120 mg / L; FeSO₄ 120 solution comprising FeSO₄ at 120 mg / L; and FeCHN-NA 120 comprising FeCHN-NA at 120 mg / L.

[0079] Figure 17

[0080] Figure 17 is a graph showing chlorophyll content of spinach leaves grown with different Fe source treatments, including: a control group without any iron; FeEDTA 60 solution comprising FeEDTA at 60 mg / L; FeEDTA 120 solution comprising FeEDTA at 120 mg / L; FeSO₄ 60 solution comprising FeSO₄ at 60 mg / L; FeSO₄ 120 solution comprising FeSO₄ at 120 mg / L; FeCHN-NA 60 comprising FeCHN-NA at 60 mg / L; and FeCHN-NA 120 comprising FeCHN-NA at 120 mg / L. Figure 18

[0081] Figure 18 is a graph showing carotenoid content of spinach leaves grown with different Fe source treatments, including: a control group without any iron: FeEDTA 60 solution comprising FeEDTA at 60 mg / L; FeEDTA 120 solution comprising FeEDTA at 120 mg / L; FeSCL 60 solution comprising FeSO4at 60 mg / L; FeSO4120 solution comprising FeSO4at 120 mg / L; FeCHN-NA 60 comprising FeCHN-NA at 60 mg / L; and FeCHN-NA 120 comprising FeCHN-NA at 120 mg / L.

[0082] Figure 19

[0083] Figure 19 is a graph showing wet biomass of spinach leaves grown with different Fe source treatments, including: a control group without any iron; FeEDTA 60 solution comprising FeEDTA at 60 mg / L; FeEDTA 120 solution comprising FeEDTA at 120 mg / L; FeSO460 solution comprising FeSO4at 60 mg / L; FeSO4120 solution comprising FeSO4at 120 mg / L; FeCHN-NA 60 comprising FeCHN-NA at 60 mg / L; and FeCHN-NA 120 comprising FeCHN-NA at 120 mg / L.

[0084] Figure 20

[0085] Figure 20 is a number of photographs of kailan plant phenotypes at harvest, wherein the kailan was grown with different P sources at 1.24 mg / plant, 1.86 mg / plant, 2.48 mg / plant using NPCHN (sample no. 16) in the top row (labelled CHN) and KH2PO4 in the bottom row (labelled CT). Figure 21

[0086] Figure 21 is a graph showing kailan wet biomass, wherein kailan was grown with different P sources at 1.24 mg / plant, 1.86 mg / plant, 2.48 mg / plant using NPCHN (labelled CHN) and KH2PO4 (labelled CT).

[0087] Figure 22

[0088] Figure 22 is a graph showing kailan dry biomass, wherein the kailan was grown with different P sources at 1.24 mg / plant, 1.86 mg / plant, 2.48 mg / plant using NPCHN (labelled CHN) and KH2PO4 (labelled CT).

[0089] Figure 23

[0090] Figure 23 is a number of photographs of soybean plant phenotypes at harvest, wherein the soybean was grown with different P sources at 2.07 mg / plant, 3.1 mg / plant, 4.13 mg / plant using NPCHN (sample no. 16) on the right (labelled CHN) and KH2PO4 on the left (labelled CT).

[0091] Figure 24

[0092] Figure 24 is a graph showing the height of soybean plants at harvest, wherein the soybean was grown with different P sources at 2.07 mg / plant, 3.1 mg / plant, 4.13 mg / plant using NPCHN (labelled CHN) and KH2PO4 (labelled CT).

[0093] Figure 25

[0094] Figure 25 is a graph showing the wet and dry biomasses of soybean plants at harvest, wherein the soybean was grown with different P sources at 2.07 mg / plant, 3.1 mg / plant, 4.13 mg / plant using NPCHN (labelled CHN) and KH2PO4(labelled CT). Figure 26

[0095] Figure 26 is a graph showing alfalfa tissue P content upon treatment with 0.2 mL of different P sources - control group (labelled as Control); group 1: KH2PO4, Ca(NC>3)2, FeCL, urea (labelled as KH2PO4); and group 2: NPCHN (sample no. 16), Ca(NOs)2, FeCL (labelled as NPCHN). Figure 27

[0096] Figure 27 is a graph showing Fe content in alfalfa tissue upon treatment with 0.2 mL of FeSO₄ and NPFeCHN solutions at 135 pg / mL of Fe.

[0097] Figure 28

[0098] Figure 28 is a schematic diagram showing a process 21 of preparing a partially soluble char-like material 22 having hierarchical, composite or mixed structure, comprising the steps of subjecting carbon-containing waste 23 to a solution combustion condition 24 to form the char-like material 22, followed by repeated extractions with water 25 to obtain extracted solutions 26 which comprise the char-like material progressively dissolved in solution.

[0099] Examples

[0100] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

[0101] Example 1 - Preparation and characterisation of carbon hybrid nanomaterials Materials and equipment

[0102] Ethylenediamine, glycerol, phosphoric acid, nitric acid, ethylenediaminetetraacetic acid ferric sodium salt, potassium hydroxide, FeCE, FeSO₄. potassium dihydrogen phosphate, calcium nitrate tetrahydrate, magnesium sulfate, manganese(ii) chloride tetrahydrate, calcium chloride, zinc sulfate, SiC>2 nanoparticles were purchased from Sigma-Aldrich (from Missouri, USA) and were used without further purification. Spectra / Por 6 Standard Regenerated Cellulose (RC) Dialysis Tubing with cutoff molecular weight of 2 kDa was purchased from VWR International GmbH (from Darmstadt, Germany) and w as used in purification of produced carbon hybrid nanomaterials where required. Potassium nitrate, calcium nitrate, magnesium sulfate, urea, boric acid, zinc sulphate, copper sulphate, manganese (ii) chloride and sodium molybdate were included in the preparation of Hoagland solution for plant growth. The amount and resultant concentration of compounds used to prepare the Hoagland solution is shown in Table 1.

[0103] Table 1: Hoagland solution components.

[0104] Compound Amount of Compound Volume of stock solution Final concentration of compound used for concentration (mL) used to prepare 1 L compound in stock solution (g / L) (stock solution) of Hoagland solution Hoagland solution " KNOI “1 7 " TinM

[0105] KH₂PO₄ 136 09. TM. i. TmM.

[0106] MgSO₄ 246 4§ IM 1 1 t»M

[0107] Ca(NO₃)₂ 164 15 1 M 5 5 mM

[0108]

[0109] H₃BO₃ 0.1175 19×10⁻³ M 2 38 μM

[0110] MnCh. 1**6*4656. r3*7*xi6’-rM*. "2. ry.riiM.

[0111] FeNaEDTA 1.9660 5.372×10⁻³ M 2 10.7 μM

[0112] ZnSO₄ 0.05167 0.32×10⁻³ M 2 0.64 μM

[0113] CuSO₄ 0.02075 0.13×10⁻³ M 2 0.26 μM Na₂MoO₄ 0.00824 0.04×10⁻³ M 2 0.08 μM

[0114]

[0115] X-ray Photoelectron Spectroscopy (XPS) spectrum was measured using a KRATOS Axis ultra-DLD X-ray photoelectron spectrometer (from Manchester, UK) with Mg Kα X-ray (hv = 1283.3 eV). Transmission electron microscopy (TEM) images were obtained using a Jeol 2010 UHR (200 kV) transmission electron microscope (from Tokyo, Japan). The particle size of the carbon hybrid nanomaterials was determined using a Malvern ZEN3690 Zetasizer (from Worcestershire, England). Metal and phosphorus content in carbon hybrid nanomaterials and dried plant tissue were quantified with Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) determined using a PerkinElmer Avio 550 Max ICP-OES (from Waltham, USA). Method A - Preparing a carbon hybrid nanomaterial with base, acid and carbon source

[0116] As shown in the schematic diagram of Figure 1, a carbon hybrid nanomaterial (2 such as nitrogen-, phosphorus-doped carbon hybrid nanomaterial or NPCHN; which is termed herein as “sample no. 16”) was prepared according to the following steps. Base (4 such as ethylenediamine (6 mL)) was mixed with carbon source (5 such as glycerol (2 mL)) with magnetic stirring. Acid (3 such as concentrated phosphoric acid (85% w / w; 4 L)) was added dropwise to the mixture of ethylene diamine and glycerol. The resulting solution combustion reaction produced the NPCHN in the form of a brown solid with a yield of 84.5%. For further use and characterization, the NPCHN was dissolved in deionized water. The particle size of the NPCHN was found to be 76.1 nm and the zeta potential was found to be -2.43 mV.

[0117] Method B - Preparing a carbon hybrid nanomaterial with base, acid and carbon source, wherein the base is the carbon source

[0118] As shown in the schematic diagram of Figure 1, a carbon hybrid nanomaterial (2 such as CHN-NA / NC; which is termed herein as “Sample No. 1”) was prepared according to the following steps. To base (4 such as ethylenediamine (5 mL) wherein the base is the same as the carbon source 5) stirred with a magnetic stirrer was added acid (3 such as concentrated nitric acid (69% w / w; 9.8 mL)) dropwise. The resulting solution combustion reaction produced the CHN-NA / NC in the form of a brown solid at a yield of 96.8%. For further use and characterization, the CHN-NA / NC was dissolved in deionized water. The particle size of the CHN-NA / NC was found to be 26.5 nm, and the zeta potential was found to be -4.8 mV.

[0119] Preparation and characterization of carbon hybrid nanomaterial samples nos. 1 to 27

[0120] The following samples nos. 1 to 27, as shown in Table 2, were obtained by adapting the protocol of Method A or Method B as described herein to obtain the corresponding carbon hybrid nanomaterials. The yield, particle size, and zeta potential of each carbon hybrid nanomaterial w ere determined. Where an additive was added, the additive was added to the mixture of base and carbon source (Method A) or to the base (Method B) before adding the acid. The weight percentage (wt%) of the active species (eg, P in phosphoric acid: Fe in Fe₂SO₄) in the carbon hybrid nanomaterial was also calculated and compared to the expected wt% of the active species in the reagents. The actual wt% of active species was calculated based on [the weight amount of active species found in the CHN] / [the total weight of the CHN synthesized]. The expected wt% amount of active species was calculated based on [the weight amount of active species present in the reagents] / [the total weight amount of reagents] and expressed as ‘"expected wt% of active species”.

[0121] Table 2: Carbon hybrid nanomaterials (CHN) sample nos. 1 to 27 produced according to the invention showing the reagents used for forming each CHN, as well as the yield, particle size, and zeta potential of each CHN and, the actual wt% of active species compared to the expected wt% of active species in the CHN.

[0122]

[0123] 1> MnCI:

[0124] li®

[0125] 16

[0126] r P. H.01

[0127] K 9 3 | I I I Xl | 18

[0128] PA

[0129] 20

[0130] 21

[0131] 22 CHN-AA

[0132] 23 FCSO4

[0133] ■■1 24 / nSO

[0134] 25

[0135] w 26

[0136]

[0137] The surface charge of the carbon hybrid nanomaterial (CHN) may be tuned by adjusting the pH value of the final solution of CHN using diluted HC1 or NaOH solution. The surface charge change s (Zeta potential value change) are shown below in Table 3 using CHN-NA (sample no. 2) as an example.

[0138] Table 3: Tuning surface charge by adjusting the pH value of the final solution of CHN using diluted HC1 or NaOH solution.

[0139] pH 3 pH 4 pH 5 pH 6 pH 7 pH 8 pH 9 pH 10 10.5 mV i 7.0 mV 10.42 mV -8.5 mV 'TfH'rnV

[0140]

[0141]

[0142] Transmission electron microscope (TEM) imaging

[0143] A TEM image of NPCHN (sample no. 16) is shown in Figure 4. Dynamic Light Scattering (DLS) indicated an average particle size of 76.1 nm.

[0144] TEM images of FeCHN-NA (sample no. 9) are shown in Figure 5 and Figure 6. DLS indicated an average particle size of 26.3 nm.

[0145] A TEM image of CHN-NA (sample no. 2) is shown in Figure 7. DLS indicated an average particle size of 38.8 nm.

[0146] A TEM image of SiCHN-NA (sample no. 11) is shown in Figure 8. DLS indicated an average particle size of 132 nm.

[0147] FTIR and XPS spectra

[0148] The chemical composition and surface groups of NPCHN (sample no. 16), NPFeCHN (sample no.

[0149] 18) and FeCHN-NA (sample no. 9) were characterized by FTIR and XPS spectra, as shown in Figures 9 to 12. The stretch vibration peaks of C=C from alkene / conjugated alkene groups (at about 1645 cm ') shown in Figures 9, 10 and 11 indicated the successful generation of aromatic structures in NPCHN, NPFeCHN and FeCHN-NA, respectively. Characteristic absorption peaks of P-OH bending vibration from 2500 cm-1to 2750 cm-1as well as the sharp strong absorption of PO₄³⁻ stretching vibration at 539 cm⁻¹ implied the successful incorporation of phosphorus in the carbon hybrid nanomaterials. As shown in Figure 12, the existence of phosphate in the product was confirmed by XPS spectra with characteristic peak of P 2p observed at about 132 eV for NPCHN and NPFeCHN. In addition, the characteristic Fe 2p peak observed at about 709 eV suggested successful incorporation of Fe for NPFeCHN.

[0150] Thin-layer chromatography (TLC) analysis

[0151] Complete conversion of respective reagents to NPCHN (sample no. 16) and NPFeCHN (sample no. 18) was also indicated by thin-layer chromatography (TLC) results.

[0152] As shown in Figure 13, wherein the reagents (A) ethylene diamine, (B) phosphoric acid, (C) glycerol and the product (D) NPCHN were spotted from left to right, and eluted with acetate / methanol (1: 1), the TLC plate indicates that all the reagents were consumed and not present in the NPCHN product without any post-synthesis treatment. As shown in Figure 14, wherein the reagents (A) ethylene diamine, (B) phosphoric acid, (C) FeEDTA, (D) glycerol and the product (E) NPFeCHN were spotted from left to right, and eluted with acetate / methanol (1:1), the TLC plate indicates that all the reagents were consumed and not present in the NPFeCHN product without any post-synthesis treatment.

[0153] Example 3 - Spinach models for iron (Fe) uptake

[0154] Iron-doped carbon hybrid nanomaterials (FeCHN-NA; sample no. 9) were investigated for Fe uptake using spinach.

[0155] Growth and treatment methods

[0156] Fourteen-day-old baby spinach seedlings (Spinacia oleracea Platypus RZ), all of similar size, were sourced from Sustenir Pte Ltd. These seedlings were then transplanted into individual pots (measuring 10x10x10 cm) filled with 150 g of moist vermiculite. The pots were subsequently placed in a growth chamber (Aralab, FITOCLIMA D1200, from Sintra, Portugal) set at 19 / 17°C, with a 12 / 12-hour light cycle (4 LED tubes, PT 600 mm 11W / 1780 Im, 75% intensity) and a relative humidity of 60%. The spinach seedlings were divided into seven groups, each including six replicates in one tray. The seven experiment groups included (1) a control group without any iron; (2) FeEDTA 60 solution comprising FeEDTA at 60 mg / L; (3) FeEDTA 120 solution comprising FeEDTA at 120 mg / L: (4) FeSCL 60 solution comprising FeSCL at 60 mg / L; (5) FeSCft 120 solution comprising FeSOi at 120 mg / L; (6) FeCHN-NA 60 comprising FeCHN-NA at 60 mg / L; and (7) FeCHN-NA 120 comprising FeCHN-NA at 120 mg / L. Each concentration specified was based on the concentration of Fe in each solution (in mg / mL).

[0157] The day of transplantation into the pots and commencement of growth in the growth chamber was designated as DAY 14. From DAY 14 to DAY 21, a half-strength Hoagland solution without Fe content was added to each spinach seedling at one-day intervals, at 5 mL per seedling.

[0158] Different treatments were applied to facilitate spinach growth beginning from DAY 21. From DAY 21, the treatments were mixed with half-strength Hoagland solution and added to the spinach twice a week, with 5 mL per seedling per dosing. Each day, 250 mL of deionized water was used to irrigate the spinach plants by pouring directly into tray instead of the pots.

[0159] SPAD measurement values

[0160] The “SPAD value” refers to a quantitative measure of the relative chlorophyll content or leaf greenness index of a plant, obtained using a SPAD (Soil Plant Analysis Development) meter. The SPAD meter operates by measuring the transmission of light at two wavelengths, typically around 650 nm (red) and 940 nm (near -infrared), through a leaf sample, and calculating a unitless SPAD value corresponding to chlorophyll concentration. A higher SPAD value may indicate greater chlorophyll content and enhanced photosynthetic activity, while a lower SPAD value may indicate nutrient deficiency or stress.

[0161] The SPAD measurement values of the spinach plants are shown in Figures 15 and 16. When the Fe concentration was at 60 mg / L, FeCHN-NA showed a more notable change in value compared to the FeEDTA and FeSO₄ fertilizers. However, when FeSO₄ was added to the spinach, the SPAD value changes were limited and showed no significant difference compared to the control treatment. When the Fe concentration was at 120 mg / L, there w ere limited changes in SPAD values for each of FeEDTA, FeSO₄, and FeCHN-NA, possibly due to an overall overdosing of iron. Chlorophyll and carotenoid content

[0162] The addition of Fe fertilizers helped to increase the chlorophyll content compared to the control treatment. As shown in Figure 17, the use of FeEDTA and FeSCL at 60 mg / L increased the chlorophyll content by 64.8 to 76.7% compared to the control treatment. When FeCHN-NA was added to the spinach at 60 mg / L concentration, the chlorophyll content further increased to 1.835 mg / g fresh leaf, which was a 97.5% increase compared to the control treatment. Comparing to the commercial FeEDTA fertilizer, the chlorophyll content was further increased by 19.9%. These results indicated that FeCHN-NA may be more effective in enhancing chlorophyll content in the spinach leaf compared to the commercial Fe fertilizer, and thus, enhanced the fresh leaf weight. However, as shown in Figure 18 and Table 4, there was a decrease in chlorophyll content when the Fe content increased to 120 mg / L and added to the spinach in FeEDTA, FeSO₄ and FeCHN-NA treatments, possibly due to an overall overdosing of Fe and cytotoxicity.

[0163] Table 4: Chlorophyll and carotenoid content of spinach leaves grown with different Fe source treatments

[0164] Chlorophyll (mg / g) i s.d.; Carotenoid (mg / g) i s.d.

[0165] ''FeEDTA

[0166] FeEDTA 120.1 '1.47. [ (i'TT. P(>.34. [ o'i>5.

[0167] “FeSoTfiO pL64 fojl() ["0'35““ To'o7

[0168] I i 1

[0169] FeCilN-NA 60 1.84 OJK, i 0.36 Lo.06

[0170] ''FcCilN-NA 1.20 |" U9

[0171]

[0172] With the addition of Fe fertilizers to the plant, the carotenoid content increased significantly compared to the control treatment, however, no significant difference was observed between FeEDTA, FeSO₄. and FeCHN-NA treatment.

[0173] Biomass analysis

[0174] The progressive spinach leaf cutting was conducted from DAY 35 with a seven -day interval. The complete growth cycle for spinach spanned 49 days, with the plants being harvested on DAY 63. After 45 days’ growth, the spinach leaf was cut twice, and the accumulated weight was measured and shown in Figure 19 and Table 5. The control treatment without Fe addition to the spinach showed the lowest fresh leaf biomass of 2.62 g, while with the addition of different types of iron-containing fertilizers, including FeEDTA, FeSO₄. and FeCHN-NA, it was observed that fresh leaf biomass significantly increased compared to the control treatment. The FeEDTA treatments increased the fresh leaf biomass by 53.4-58.0% compared to the control treatment, and the FeSCL treatments increased the fresh leaf biomass by 11.1 -27.1% compared to the control treatment. The results indicate that the commercial FeEDTA could be used as a more efficient Fe fertilizer compared to FeSCL. However, the addition of FeCHN-NA to the spinach further enhanced the leaf fresh biomass compared to the FeEDTA treatments. FeCHN-NA increased the leaf fresh biomass by 77.5-83.2% compared to the control treatment, and 12.3-19.4% even compared to the FeEDTA treatment. These results were consistent with the chlorophyll content results described above. As also noted above, the addition of Fe fertilizer at 120 mg / L may result in overdosing of Fe and cytotoxicity, as observed by reduced leave weight.

[0175] Table 5: Wet biomass of spinach first & second cutting at DAY 45 wherein the spinach was grown with different Fe source treatments

[0176] i Leaf Weight (g) i s.d.

[0177] S Control; 2.62 > 045

[0178] FeEDTA 60 i 4,02 i () 6X

[0179] FeEDTA 12(i. p---.

[0180] FeSO.60 [ 3.33 1'6'44

[0181] FeSOi 120. 2.91. [ 133

[0182] pFeciTN-NA'oO...

[0183]

[0184] On the basis of these results, FeCHN-NA produced in accordance with the method disclosed herein may significantly enhance spinach plant growth and provide nutrients more efficiently compared to commercial Fe fertilizers such as FeEDTA and FeSO4.

[0185] Example 4 - Kailan model for phosphorus (P) uptake

[0186] Due to good availability of kailan seedlings and its easy plantation, kailan was selected as a plant model to test the effectiveness ofNPCHN (sample no. 16) in P delivery. A conventional P fertilizer, KH2PO4, was incorporated as control. Locally purchased soil was used as growth media to mimic the practical plant growth. Locally purchased kailan seedlings with nearly equal sizes were transplanted into growth pots (size of 15cm l5cmxl5cm) and filled with soil. There were five replicates for each treatment and fertilization started 2 days after the seedling transplantation. Hoagland solutions were applied weekly at 100 mL per pot. Three P dosages of 1.24 mg / plant, 1.86 mg / plant, 2.48 mg / plant were employed in the growth study. The pH value of the Hoagland solution was adjusted to 5.9-6.0 before application. By harvest time, the fertilization solution had been applied 4 times, and the cumulative phosphorus dosages were 4.96 mg / plant, 7.44 mg / plant and 9.92 mg / plant, respectively. Deionized water was applied as irrigation water when needed. In using NPCHN, there was an assumption that there was no loss in nitrogen (N) and P from producing NPCHN from phosphoric acid, ethylenediamine (EDA) and glycerol. le, it was assumed that there was a complete conversion. The conventional P source in the form of KH2PO4 as a control included the same P dosage as the NPCHN solution. All other nutrients were also maintained.

[0187] The phenotypes of the kailan at harvest are shown in Figure 20. The kailan was harvested four weeks after transplantation with the growing medium washed off from the roots. Their roots were separated from above ground part (stem and leaves), and their corresponding mass was recorded as the wet biomass. After drying in an oven at 60 °C for 7 days, their corresponding mass was recorded as the dry biomass.

[0188] The wet and dry biomass of kailan at harvest are shown in Figure 21 and Figure 22, respectively. As shown in Figure 21, the above-ground wet biomass of kailan seedlings treated with NPCHN was inversely proportional to the amount of P that was provided with the least supplemented (1.24 mg / plant) plant producing the highest biomass, which suggests over-dosage of P at other dosages. However, in the conventional P fertilizer, the biomass yield was highest at the medium dosage of 1.86 mg / plant. At the same dosage of P at 1.24 mg / plant per week, the biomass of kailan treated with NPCHN was 60% higher than that treated with conventional P fertilizer.

[0189] The results for above-ground dry biomass showed the same trend. As shown in Figure 22, to achieve their corresponding optimum productions, the P amount required for conventional P fertilizer was 50% (1.86 mg / plant) more than that required for NPCHN (1.24 mg / plant). Even though the P input for conventional P fertilizer was 50% higher, wet and dry biomasses of kailan were 5% and 13% less than those produced with NPCHN as P fertilizer. The production of wet and dry above ground biomass of kailan suggested more efficient uptake of P with the carbon hybrid nanomaterial as delivery vehicle as contrasted to the conventional P source.

[0190] Example 5 - Soybean model for phosphorus (P) uptake

[0191] Soybean was also selected as the plant model to test the effectiveness of NPCHN (sample no. 16) in P delivery, using KH2PO4 as a conventional P fertilizer as control. Soybean seeds with nearequal sizes were soaked in deionized water overnight after which three soybean seeds were each sowed in a 10 L plastic growth pot filled with soil, as described in Example 4. The seeds were covered with a thin layer (around 3 cm) of soil and watered as necessary to promote soybean germination. There were three replicates for each treatment and only single seedlings of similar size were kept for each pot after germination. Fertilization started when the seedling was around 3-5 cm in height. Hoagland solutions were applied weekly at 250 mL solution per pot. The pH value of the Hoagland solution was adjusted to 5.9-6.0 before application. The Hoagland solutions were applied twice weekly from the bloom stage onward (about 4 weeks after seed sowing) and continued until 50% of all soybean pods turned yellow. Three P dosages of 2.07 mg / plant, 3.1 mg / plant, 4.13 mg / plant were employed in the growth study. Upon harvest, the fertilization solution had been applied 20 times, and the cumulative phosphorus dosages were 40.14 mg / plant, 62.00 mg / plant and 80.26 mg / plant, respectively. Tap water was applied as irrigation water as needed. The heights of soybean plants were measured with a ruler upon harvest.

[0192] The soybean was harvested by cutting from the soil surface when approximately 80% of the pods turned brown. The seeds were separated from the pod shell. The seeds, pod shell and the aboveground biomass (excluding seeds and pod shell) were weighed and dried in an oven at 60 °C for 7 days and their corresponding dry biomass were recorded. The growing medium was washed off from the roots and wet weight of the roots was measured and recorded after which the roots were dried following the same protocol. The dry weights of the roots were recorded 7 days later as the dry below-ground biomass.

[0193] As indicated in Example 4, any loss of N and P sources during formation of NPCHN from its precursors were ignored - a complete conversion was assumed. The conventional P source in the form of KH2PO4 was used as the control and the P dosages of the NPCHN Hoagland solution were the same as those of the conventional P source while the amount of all other nutrients was kept the same.

[0194] All the soybean plants matured in about 12 weeks. The plant phenotypes are shown in Figure 23. The height of the soybean plants was measured with a ruler upon harvest, as shown in Figure 24. On average, the plant heights were 58.0 cm, 72.2 cm, and 84.4 cm upon treatment with conventional P fertilizer (control) at dosages of 2.07 mg / plant, 3.1 mg / plant and 4.13 mg / plant, respectively. For the plants treated with NPCHN, the average soybean heights were 62.2 cm, 70.2 cm and 77.6 cm, respectively, for dosages of 2.07 mg / plant, 3.1 mg / plant and 4.13 mg / plant. At the P dosage of 2.07 mg / plant, the height of the soybean treated with NPCHN was about 7.2% higher than the height of the soybeans treated with conventional P sources at the same dosage. In contrast, the heights of soybeans treated with NPCHN at dosage of 3.1 mg / plant and 4.13 mg / plant were 2.8% and 8.1% lower than those treated with conventional phosphorus fertilizer at the same dosage. Based on these results, it is clear that for both P sources, the plant height corresponded with increasing P dosage.

[0195] The wet biomass of soybean seeds treated with NPCHN were 7.5%, 21.7%, and 2.8% higher, respectively, than those treated with the conventional P fertilizer at the same dosage. The increase in the dry biomass of soybean seeds treated with NPCHN was 15.3%, 12.1% and 13.9% higher, respectively, than those treated with the conventional P fertilizer at the same dosage. These results are shown in Figure 25.

[0196] The seed yield results strongly suggested that NPCHN was more efficient in P delivery when compared to the conventional P fertilizer, as a higher seed yield was observed for soybean treated with NPCHN across all tested dosages. Another observation was that above the optimum dosage of 3.1 mg / plant / week, there was a decreased yield with increased P dosage for both P sources, which suggested over-dosage of P.

[0197] Example 6 - Alfalfa model

[0198] P uptake and translocation with NPFeCHN using alfalfa as plant model

[0199] Alfalfa was used as plant model to study P uptake and translocation and to verify the efficiency of NPCHN (sample no. 16) over a conventional P fertilizer such as KH2PO4.

[0200] In order to mimic the soil conditions, KH2PO4, Ca(NO₃)₂·4H₂O, FeCl₃·6H₂O were intentionally included and their dosages were adjusted so that the concentrations of the main species were P: 0.2 M, Ca: 1 M, Fc: 0.025 M, N: 2.6 M, and K: 0.2 M.

[0201] Two groups of fertilizers were employed. The first group comprised KH₂PO₄, Ca(NO-,)2. FcCh and urea with final concentrations of P: 0.2 M, Ca: 1 M, Fe: 0.025 M, N: 2.6 M, and K: 0.2 M. The second group comprised NPCHN (sample no. 16), Ca(NO₃)₂, FeCl₃ with final concentrations of P: 0.2 M, Ca: 1 M, Fe: 0.025 M, and N: 2.6 M. Urea was included in order to balance the N dosage while the effect of 0.2 M of K in the group of conventional P fertilizer was ignored.

[0202] Alfalfa seeds with nearly equal sizes were soaked in deionized water overnight. The soaked seeds were drained before treatment. For each treatment, 30 seeds were put in a 20 mL glass sample vial, and the seeds were allowed to germinate for 3 days before a fertilizer solution was introduced. The sample vials were placed on a laboratory bench at ambient temperature of ~25 °C. Alfalfa seedlings were harvested 6 hours after 0.2 mL of fertilizer solution was added.

[0203] The root of harvested alfalfa was washed with 0.01 M EDTA disodium salt solution and carefully dried with soft tissue. Alfalfa seedlings were cut and separated into root, stem and leaves. All plant tissues were dried in an oven at 60 °C until the materials reached a constant weight.

[0204] The dry tissues (root, stem and leaf) of alfalfa were weighed and ground into a powder to measure the content of total Fe or P. Digestion of ground samples (10 mg) was conducted in 20 mL glass digestion tubes with a mixture of 1 mL of concentrated nitric acid and 1 mL of 36% hydrogen peroxide at 105 °C for 2 hours using a hot block (DigiPREP System; SCP Science, Champlain, NY). The total Fe or P content in plant tissue was quantified by ICP-OES; element content was expressed as iron or phosphorus wt% dry weight plant tissue. The tissue P content of alfalfa upon treatment with different P sources is shown in Figure 26.

[0205] The results indicated that P content in root, stem and leaf of alfalfa treated with NPCHN are 4.6%, 13.5% and 29.7% higher than those treated with KH₂PO₄, respectively. The increase of P content in the plant root is not obvious, which may be because of the existence of leftover residue of nutrient solution on plant root. Nevertheless, the increase of P content in plant tissue is most significant in plant leaf, followed by stem and root. This strongly suggested that P translocation was much faster with NPCHN as a P carrier.

[0206] The P translocation factors, as shown in Table 6, of alfalfa upon different P sources treatment were calculated as [P]stem / [P]root. These results indicated that P translocation with NPCHN as the P source is more efficient than its translocation with KH₂PO₄ as the P source.

[0207] Table 6: P translocation factors of alfalfa upon treatment different P sources Stcm / Root

[0208] CT

[0209] KH₂PO₄ | 0.655

[0210] NPCHN | 0.711

[0211]

[0212] Delivery of Fe with NPFeCHN with alfalfa as plant model

[0213] The uptake and translocation of Fe with NPFeCHN was investigated with alfalfa as plant model. FeSO₄ was included as a control.

[0214] The alfalfa seeds were pre-treated as described above. Fertilizers employed included NPFeCHN and FeSO₄ solutions, both with Fe concentration at 135 pg / mL. The sample vials were put on the bench of laboratory at ambient temperature of ~25 °C. The alfalfa seedlings were harvested 6 hours after 0.2 mL of fertilizer solution was added.

[0215] The tissue iron content of alfalfa treated with FeSO₄ and NPFeCHN is shown in Figure 27. The results indicated that root iron content is 30% higher with FeSO₄ treatment while the leaf iron content is 14% higher in alfalfa treated with NPFeCHN. These results suggest that the presence of phosphate ions did not hinder the plant uptake and translocation of Fe. In contrast, NPFeCHN appeared to promote the uptake and translocation of Fe, even though co-existence of iron and phosphate ion may have resulted in the generation of insoluble FePO₄. The translocation factors are shown in Table 7.

[0216] Table 7: Fe translocation factors of alfalfa upon treatment with different Fe sources

[0217] I Stem / Root

[0218] FeSO₄ | 0.639

[0219] NPFeCHN | 1.049

[0220]

[0221] Example 7 - Biomass carbon hybrid nanomaterials

[0222] The solution combustion method as described herein may be used to produce composite or hierarchical structured materials containing CHNs and char mixture using waste materials, such as biomass waste.

[0223] In one example, biomass waste (in the form of plant waste), a base (in the form of ethylenediamine), and an acid (such as in the form of nitric acid, sulfuric acid, phosphoric acid, acetic acid, or a combination thereof) were added in a suitable ratio into a reactor. The biomass waste foamed significantly initially during the reaction and eventually formed a dark-colored solid char-like substance.

[0224] The char was ground into powder and was found to be partially soluble. 1 g of the ground char was dispersed in 50 mL of deionized water, and the mixture was centrifuged at 10000 rpm for 10 mins. The extracted supernatant was examined and found to contain soluble material or a low-dimension suspension of materials. This extraction procedure was repeated.

[0225] The initial extract solution obtained was transparent with orange / brown color. The color of the extraction solution became lighter in color in subsequent repeated extractions, providing a yellow-colored solution at the third extraction. Significant fluorescence was observed when the UV light was applied to all three extracted solutions, and the fluorescence intensity decreased with the increasing number of times the extraction was performed. These results indicated that the char may comprise a hierarchical, mixed or composite structure which comprises a nano-, micro- and macroscale structure. These steps are shown in Figure 28.

[0226] These results indicated that partially soluble char-like materials with hierarchical, composite or mixed structure may be produced using a solution combustion method. The materials may contain portions with different particle size ranges. The extraction solutions contain nanosized particles and give the highest fluorescence intensity. The char-like solid residual after extraction was essentially a biochar, which may have different applications including those in agriculture and environmental remediation, carbon sequestration, and water treatments. The char -like materials (including both soluble and insoluble portions) obtained from this method may be applied directly without going through an extraction process, although the extraction process indicates (i) the possibility of different or the same applications for the soluble and insoluble portions, and also (ii) the possibility of progressive release of the soluble portion. Industrial Applicability

[0227] The method of preparing the carbon hybrid nanomaterial as defined herein may be used to produce carbon hybrid nanomaterials that can be used in agriculture. The carbon hybrid nanomaterials may be used as fertilizers to promote plant growth, improve plant health and reproduction, enhance nutrient uptake efficiency, and increase resistance of the plant to diseases.

[0228] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

Claims1. A method of preparing a carbon hybrid nanomaterial, the method comprising the step of subjecting a base, a carbon source and an acid to a solution combustion reaction to thereby form the carbon hybrid nanomaterial from the base, the carbon source and the acid.

2. The method of claim 1, wherein the base is the same as the carbon source.

3. The method of claim 1 or 2, wherein the subjecting step comprises the step of mixing the base, the carbon source and the acid or mixing the base and the acid.

4. The method of claim 3, wherein the mixing step comprises the steps of mixing the base with the carbon source followed by adding the acid, or mixing the base followed by adding the acid.

5. The method of claim 4, wherein in the adding step, the acid is added dropwise or by continuous flow to a stirred mixture comprising the base and the carbon source, or a stirred base.

6. The method of any one of claims 1 and 3 to 5, wherein the carbon source is selected from the group consisting of glycerol, ethylene glycol, diethylene glycol, polyethylene glycol, starch, cellulose, chitin, chitosan, carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose, lignin sulfonate, humic acid, fulvic acid, monosaccharide, polysaccharide, biomass, waste biomass, a derivative thereof, an isomer thereof, and any combination thereof.

7. The method of any one of claims 1 to 6, wherein the base is selected from the group consisting of an amine, a hydroxide, and a combination thereof.

8. The method of any one of claims 1 to 7, wherein the base is an amine.

9. The method of claim 7 or 8, wherein the amine is selected from the group consisting of ethylenediamine, methylamine, triethylamine, tris(2-ethylhexyl)amine, tris(2-aminoethyl)amine, bis(2-hydroxypropyl)amine, 3-(diethylamino)propylamine, ethylamine, propylamine, butylamine, amylamine, hexylamine, polyetherimide, nicotinic acid), N, N, N', 7V'-tetrakis(2 -hydroxypropyl)ethylenediamine, p-phenylenediamine, m-xylylenediamine, triethylenetetramine, 3-(diethylamino)propylamine, hexamethylenediamine, N, A-dimethylethylenediamine,diethylenetriamine, 3,4-diaminotoluene, 4-methyl-o-phenylenediamine, bis(3-aminopropyl)amine, triethanolamine, diethylenetriamine, triisopropanolamine, benzylamine, 2-[2-(dimethylamino)ethoxy]ethanol, p-phenylenediamine, 3-(diethylamino)propylamine, N, N, N', N’-tetramethylethylenediamine, 2-(methylamino)ethanol, N-butyldiethanolamine, 2-amino-l-butanol, 2-amino-2 -methyl- 1,3-propanediol, aminobutanol, bis[2-(N,N-dimethylamino)ethyl] ether, m-xylylene diamine, 2,6-dichloro-4-nitroaniline, 3-(dimethylamino)-l-propylamine, N, N-diethylethylenediamine, aniline, tris(hydroxymethyl)aminomethane, and any combination thereof.

10. The method of claim 7, wherein the hydroxide is selected from the group consisting of potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, aluminium hydroxide, ammonium hydroxide, and any combination thereof.

11. The method of any one of claims 1 to 10, wherein the acid is selected from the group consisting of phosphoric acid, nitric acid, acetic acid, formic acid, sulfuric acid, a derivative thereof, an isomer thereof, and any combination thereof.

12. The method of any one of claims 1 to 11, further comprising the step of adding an additive.

13. The method of claim 12, wherein the additive is pre -added to the base or to the acid.

14. The method of claim 12, wherein the additive is added during or after the subjecting step.

15. The method of any one of claims 12 to 14, wherein the additive is selected from the group consisting of a plant nutrient, an agrochemical, and a combination thereof.

16. The method of any one of claims 12 to 15, wherein the additive is selected from the group consisting of calcium nitrate, calcium sulfate, calcium hydroxide, calcium oxide, calcium chloride, calcium carbonate, magnesium nitrate, magnesium sulfate, magnesium oxide, magnesium chloride, magnesium carbonate, tetraethyl orthosilicate, silica, 3-aminopropyltriethoxysilane, silicic acid, iron(II) nitrate, iron(II) sulfate, ethylenediaminetetraacetic acid ferric sodium salt, iron(II) oxide, iron(III)oxide, iron(II) hydroxide, iron(III) nitrate, iron(III) hydroxide, iron(II) chloride, iron(III) chloride, iron(II) acetate, iron(III) hydroxide, potassium chloride, potassium sulfate, potassium nitrate, potassium hydroxide, potassium carbonate, zinc nitrate, zinc sulfate, zinc oxide, zinc chloride, zinc carbonate, zinc hydroxide, manganese(II) oxide, manganese(II) nitrate, manganese(II) sulfate, manganese(II) carbonate, copper(II) chloride, copper(II) oxide, copper(II) hydroxide, copper(II) nitrate, copper(II) sulfate, copper(II) carbonate, boric acid, titanium(IV) chloride, titanium(IV) oxide, titanium(IV) oxide nanoparticle, silver nitrate, silver nanoparticle, a derivate thereof, and any combination thereof.

17. A carbon hybrid nanomaterial produced by the method of any one of claims 1 to 16.

18. The carbon hybrid nanomaterial of claim 17. having a particle size of between about 10 nm to about 100 nm.

19. The carbon hybrid nanomaterial of claim 17 or 18, produced in the form of a char, or a combination of particles and char.

20. Use of the carbon hybrid nanomaterial of any one of claims 17 to 19 for promoting plant growth.

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