NANOSTRUCTURED IRON/CARBON FOR SCAVENGING OXYGEN

Abstract

The invention is directed to a nanostructured composite material comprising a mixture of at least one metal particle such as iron and a carbon material from biomass such as D-glucose, D-glucosamine hydrochloride or α-cyclodextrin. The invention is also directed to a composition comprising the composite material comprising the composite material and an inorganic salt, and a method for synthesizing the composite material comprising immersing the carbon material into a solution of metal ions, drying the impregnated carbon particle and subjecting the impregnated carbon particle to a carbothermal reduction process. The nanostructured composite material is useful as an oxygen scavenging layer in a multi-layer film which comprises the oxygen scavenging layer and an oxygen barrier layer that retards the permeation of oxygen from an external environment.

Claims

1-27. (canceled)

28. A composite material comprising at least one metal particle and a carbon material, wherein said carbon material is derived from a biomass material selected from a saccharide, wherein the saccharide is selected from a monosaccharide, disaccharide, oligosaccharide or a polysaccharide; wherein the monosaccharide is selected from the group consisting of glucose, fructose and galactose; wherein the oligosaccharide is selected from the group consisting of a sugar or an amino sugar; or wherein the polysaccharide is selected from the group consisting of a cyclodextrin, a cellulose, a glycogen, a chitin and a hemicellulose, and wherein said carbon material is a carbon particle or a sheet-like material having a porous structure with a pore size in the range of 10 to 700 nm.

29. The composite material according to claim 28, wherein the saccharide is selected from the group consisting of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, D-glucosamine hydrochloride, L-glucosamine hydrochloride, α-D-glucose, β-D-glucose, α-L-glucose and β-L-glucose.

30. The composite material according to claim 28, wherein said carbon material has a surface area in the range of 50 m.sup.2/g to 1000 m.sup.2/g.

31. The composite material according to claim 28, wherein said carbon material acts as a support for said metal particle; wherein said metal particle is a transition metal particle.

32. The composite material according to claim 31, wherein the transition metal of said transition metal particle is selected from the group consisting of iron particles, ruthenium particles, osmium particles, cobalt particles, rhodium particles, iridium particles, manganese particles and combinations thereof.

33. The composite material according to claim 28, wherein said metal particle has a particle size of less than 500 nm.

34. The composite material according to claim 28, wherein the concentration of said metal particle in the composite material may be in the range of 1 to 80 wt %, based on the dry weight % of said carbon material.

35. A composition comprising i. a composite material comprising at least one metal particle and a carbon material; ii. an inorganic salt; and iii. optionally an aqueous medium. wherein said carbon material is derived from a biomass material selected from a saccharide, wherein the saccharide is selected from a monosaccharide, disaccharide, oligosaccharide or a polysaccharide; wherein the monosaccharide is selected from the group consisting of glucose, fructose and galactose; wherein the oligosaccharide is selected from the group consisting of a sugar or an amino sugar; or wherein the polysaccharide is selected from the group consisting of a cyclodextrin, a cellulose, a glycogen, a chitin and a hemicellulose, and wherein said carbon material is a carbon particle or a sheet-like material having a porous structure with a pore size in the range of 10 to 700 nm.

36. The composition according to claim 35, wherein the inorganic salt is an electrolyte or an acidifying agent.

37. The composition according to claim 36, wherein the electrolyte is a halide compound selected from the group consisting of an alkali metal halide, an alkaline earth metal halide and a metal halide.

38. The composition according to claim 35, wherein the concentration of said inorganic salt is in the range of 0.1 to 20 wt¾, based on the dry weight of said composite material.

39. The composition according to claim 36, wherein said acidifying agent is a polyacid selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyethylacrylic acid and polymaleic acid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0071] The accompanying drawings illustrate a disclosed embodiment and serves 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.

[0072] FIG. 1 is a series of Transmission Electron Microscope (TEM) images of (a) C1 particles of Example 1, (b) Fe°/C1 particles of Example 4 and (c) Energy Dispersive X-Ray (EDX) mapping analysis of Fe°/C1 particles.

[0073] FIG. 2 is a series of TEM images of (a) C2 particles of Example 2, (b) Fe°/C2 particles of Example 5 and (c) EDX mapping analysis of Fe°/C2 particles.

[0074] FIG. 3 is a series of TEM images of (a) C3 particles of Example 3, (b) Fe°/C3 particles of Example 6 and (c) EDX mapping analysis of Fe°/C3 particles.

[0075] FIG. 4 demonstrates a X-Ray Diffraction (XRD) pattern of Fe°/C1 particles (a) before and (b) after exposure to air at 100% room humidity (RH) for 24 hours.

[0076] FIG. 5 shows the XRD pattern of (a) Fe°/C1 particles and (b) Fe°/C1 with addition of NaCl after exposure to air at 100% RH for 24 hours.

EXAMPLES

[0077] 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.

Example 1

[0078] Preparation of Carbon Particles Derived from α-Cyclodextrin Templated by F-127 Block Copolymers (C1)

[0079] 22.5 mg of F-127 block copolymers obtained from Sigma Aldrich (of St. Louis, Mo. of the United States of America) was dissolved in 15 ml of deionised water and stirred at room temperature overnight. A total of 45 mg of α-cyclodextrin (TCI-GR, obtained from Tokyo Chemical Industry Co Ltd of Japan) was dissolved in 15 ml of deionised water and stirred at room temperature overnight. The prepared α-Cyclodextrin solution was then injected into the solution of F-127 under stirring at 700 rpm. The F-127 block copolymers functions to control the carbon particle size and 2) create pores in the carbon particle.

[0080] The mixed solution was stirred overnight and then transferred into a Teflon-lined stainless-steel autoclave (125 ml in capacity). The autoclave was heated at 200° C. for 6 hours, and then allowed to cool to room temperature. The Cl particles were obtained by centrifugation at 9000 rpm for 30 minutes. The particles were then washed with deionised water for 3 times, by centrifugation at 9000 rpm for 15 minutes each. C1 particles obtained were air dried and then vacuum dried at room temperature for further use.

Example 2

Preparation of Carbon Particles Derived from D-(+)-Glucosamine Hydrochloride (C2)

[0081] 160 mg of D-(+)-glucosamine hydrochloride (≥99%, Sigma Aldrich) was dissolved in 30 ml of deionised water to form a clear solution. Then, the solution was transferred into a Teflon-lined stainless-steel autoclave (125 ml in capacity). The autoclave was heated at 200° C. for 12 hours, and then allowed to cool to room temperature. The C2 particles were obtained by centrifugation at 9000 rpm for 30 minutes. The particles were then washed with deionised water for 3 times, by centrifugation at 9000 rpm for 15 minutes each. C2 particles obtained were air dried and then vacuum dried at room temperature for further use.

Example 3

[0082] Preparation of Carbon Particles Derived from D-(+)-Glucose (C3)

[0083] 3.0-4.5 g of D-(+)-glucose (>99.5%, Tokyo Chemical Industry Co., Ltd, Japan) was dissolved in 30 ml of deionised water to form a clear solution. Then, the solution was transferred into a Teflon-lined stainless-steel autoclave (125 ml in capacity). The autoclave was heated at 180° C. for 3 hours, and then allowed to cool to room temperature. The C3 particles were obtained by centrifugation at 9000 rpm for 30 minutes. The particles were then washed with deionised water for 3 times, by centrifugation at 9000 rpm for 15 minutes each. C3 particles obtained were air dried and then vacuum dried at room temperature for further use.

Example 4

[0084] Preparation of Nanostructured Fe°/C1 Particles (Fe°/C1)

[0085] 0.15 g of C1 particles obtained from Example 1 was dispersed in deionised water. An appropriate amount of iron (III) nitrate nonahydrate (≥98%, Sigma Aldrich) (˜50 wt % of Fe to carbon) was dissolved in deionised water. Iron (III) nitrate nonahydrate solution was then added into C1 solution, sonicated for 10 minutes and vibrated intermittently for a few hours. The C1 particles were immersed in iron (III) solution overnight. The water was evaporated and dried in the vacuum oven at room temperature. The C1 particles powder collected was then placed in a quartz tube inside a tube furnace and heated to 800° C. with ramp rate of 5° C./min, under argon flow rate of 200 sccm. The sample was kept at 800° C. for 3 hours. After that, the sample was allowed to cool to ambient temperature under argon before removing from the tube furnace. The as synthesized nanostructured Fe°/C1 particles were ready for characterization.

Example 5

[0086] Preparation of Nanostructured Fe°/C2 Particles (Fe°/C2)

[0087] 0.15 g of C2 particles obtained from Example 2 was dispersed in deionised water. An appropriate amount of iron (III) nitrate nonahydrate (≥98%, Sigma Aldrich) (˜50 wt % of Fe to carbon) was dissolved in deionised water. Iron (III) nitrate nonahydrate solution was then added into C2 solution, sonicated for 10 minutes and vibrated intermittently for a few hours. The C2 particles were immersed in iron (III) solution overnight. The water was evaporated and dried in the vacuum oven at room temperature. The C2 particles powder collected was then placed in a quartz tube inside a tube furnace and heated to 800° C. with ramp rate of 5° C./min, under argon flow rate of 200 sccm. The sample was kept at 800° C. for 3 hours. After that, the sample was allowed to cool to ambient temperature under argon before removing from the tube furnace. The as synthesized nanostructured Fe°/C2 particles were ready for characterization.

Example 6

[0088] Preparation of Nanostructured Fe°/C3 Particles (Fe°/C3)

[0089] 0.15 g of C3 particles obtained from Example 3 was dispersed in deionised water. An appropriate amount of iron (III) nitrate nonahydrate (≥98%, Sigma Aldrich) (˜50 wt % of Fe to carbon) was dissolved in deionised water. Iron (III) nitrate nonahydrate solution was then added into C3 solution, sonicated for 10 minutes and vibrated intermittently for a few hours. The C3 particles were immersed in iron (III) solution overnight. The water was evaporated and dried in the vacuum oven at room temperature. The C3 particles powder collected was then placed in a quartz tube inside a tube furnace and heated to 800° C. with ramp rate of 5° C./min, under argon flow rate of 200 sccm. The sample was kept at 800° C. for 3 hours. After that, the sample was allowed to cool to ambient temperature under argon before removing from the tube furnace. The as synthesized nanostructured Fe°/C3 particles were ready for characterization.

[0090] Test Methods

[0091] Transmission Electron Microscope (TEM) and Energy Dispersive X-Ray (EDX)

[0092] TEM and EDX analyses were performed with a transmission electron microscope (JEOL 2100 TEM) under an acceleration voltage of 200 kV. All the samples were first dispersed and diluted with ethanol and then dropped on a 200-mesh carbon coated copper grid and dried at room temperature before observation.

[0093] FIG. 1(a) and FIG. 1(b) show the TEM images of C1 particles and Fe/C1 particles respectively while FIG. 1(c) shows the EDX mapping analysis of Fe/C1 particles. FIG. 2(a) and FIG. 2(b) show the TEM images of C2 particles and Fe/C2 particles respectively while FIG. 2(c) shows the EDX mapping analysis of Fe°/C2 particles. FIG. 3(a) and FIG. 3(b) show the TEM images of C3 particles and Fe/C3 particles respectively while FIG. 3(c) shows the EDX mapping analysis of Fe/C3 particles.

[0094] From FIG. 1(a), FIG. 2(a) and FIG. 3(a), it can be seem that the synthesized carbon particles derived from biomass have a particle size ranging from 150 nm to 800 nm, depending on the types of carbon source and its concentrations. The size of carbon particles can be easily fine-tuned by changing the carbon source concentrations. For the C1 carbon particles, the carbon particles are hollow with a size of about 700 nm after the hydrothermal treatment process. The spherical hollow carbon particles were ruptured after the iron impregnation and carbothermal reduction process (FIG. 1(b)). The carbon particle is now present as a porous sheet-like carbon structure. The inventors postulate that the C1 hybrid structure with hydrophilic property was strongly bonded with iron ions during the impregnation process. Such a strong interaction may lead to C1 shrinkage or rupture during the carbothermal reduction process due to the decomposition of the F127.

[0095] As for the C2 and C3 carbon particles, spherical carbon particles with a size of about 600 nm and about 250 nm were obtained respectively. The spherical carbon structures (see FIG. 2(b) and FIG. 3(b) respectively) remained stable and unchanged after the surface functionalization processes. The zero-valent iron particles that grew on the carbon supports had an average particle size of less than 500 nm.

[0096] The iron particles were uniformly distributed on the carbon supported, as confirmed by the TEM images and EDX mapping analyses (see additionally FIG. 1(c), FIG. 2(c) and FIG. 3(c)). These iron particles strongly interacted with and adhered to the surfaces of the C1, C2 and C3 carbon particles.

[0097] X-Ray Diffraction (XRD)

[0098] The structure characteristic and crystalline phase of sample was evaluated by XRD analysis. The XRD analysis was performed by using a Bruker D8 General Area Detector Diffraction System (GADDS) XRD using Cuka radiation (k=0.154 nm) with a scanning angle ranging from 20-86°. The sample Fe°/C1 particles were analysed here and the XRD pattern of the tested Fe°/C1 particles at different conditions are shown in FIG. 4 and FIG. 5.

[0099] As shown in FIG. 4, iron particles supported on the C1 carbon showed predominantly bode centered cubic α-Fe at 2θ of 44, 65 and 85°, which indicated the formation of zero-valent iron particles (FIG. 4(a)). Similar XRD patterns were obtained for Fe°/C2 and Fe°/C3 (results not shown). It is to be noted that the carbon material stabilized the zero-valent iron from further oxidation, even after exposure to ambient conditions for long hours. The stability of carbon supported iron particles was verified after exposure of the sample to air at 100% relative humidity for 24 hours (see FIG. 4(b)). This is further supported by oxygen scavenging results (see section and Table 1 to 3 below). Negligible oxidation process was observed, as none of the Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4 peak was detected from the XRD pattern. This criterion is important to ensure high stability and lifetime of the oxygen scavenger during storage. The Fe°/C products of this application may be easily handled in air since there is no significant reduction of Fe°/C with air at ambient conditions. In contrast, iron particles prepared by chemical reduction process using an excess of reducing agent such as sodium borohydride are easily oxidized and will react with air. This is due to the lack of the protective carbon, leading to the fast oxidization of iron particles made in this manner even when the oxygen is dissolved in water. Once the iron particles are oxidized, the iron particles change from black color to brown color.

[0100] As shown by the XRD pattern in FIG. 5, addition of 10 wt % sodium chloride with Fe°/C powder had significantly reacted with oxygen under 100% relative humidity condition, proving that oxidation process had occurred, forming the Fe.sub.3O.sub.4 structure. The XRD peaks of Fe° were diminished, and replaced with Fe.sub.3O.sub.4 peaks at 2θ of 30°, 35.5°, 43°, 53.6°, 57.2° and 62.8°. The sodium chloride crystalline phase was also detected from the XRD pattern at 2θ os 31.7° and 45.5°. In this manner, inorganic salts were used as an accelerator to control the absorption rate of oxygen in the scavenging system.

[0101] Oxygen Scavenging Analysis Test

[0102] 25 ml of glass conical flasks were used as sample containers (model packaging) to characterise the O.sub.2 scavenging property of the samples. The full capacity of flask initially was filled with air (20.90% O.sub.2) at ambient condition. One 2 ml vial containing 1 ml of water was placed inside the flask to adjust the room humidity (RH) to 100%. Approximately 0.03-0.05 g of sample (Fe°/C1, Fe°/C2 and Fe°/C3) with or without sodium chloride (dry or 50 μl solution) was placed inside the flask. Then, the flask was sealed by a gas-tight rubber septum stopper (Suba-Seal, W. Freeman & Co. Ltd, UK) and placed at room temperature for the duration of the oxygen scavenging experiment. The oxygen content in the flask headspace (% O.sub.2) was analysed by a headspace oxygen/carbon dioxide analyser (model GS3, Systec Illinois, USA; accuracy to 0.005% O.sub.2) in a procedure in which an aliquot of the headspace gas was taken out and analysed using a zirconium-based sensor. A sampling needle with a 0.45 μm PTFE filter was inserted and ˜0.875 ml headspace gases were sampled through the stopper. Calibration of headspace analyser was done using ambient air after each sample measurement. Oxygen uptake (mass of oxygen consumed/mass of sample) was calculated indirectly from the decrease in the oxygen content in the headspace of the flasks over time (of about 96 hours).

[0103] The oxygen scavenging ability of Fe°/C1, Fe°/C2 and Fe°/C3 are shown in the following Table 1, Table 2 and Table 3 respectively. All the samples were tested in 100% relative humidity. As expected, Fe°/C samples were quite stable with a very slow rate of uptake and low capacity of oxygen absorption at 100% relative humidity. The presence of a trace amount of sodium chloride (about 10 wt % based on the dry weight of Fe°/C), either added as a solid or dissolved in a minimum amount of water (about 30 to 50 μl) had abruptly increased the rate of oxygen uptake. The products had removed most of the oxygen from the model packaging after 4 days, and the highest scavenging rate took place in the first day.

[0104] In this regard, it is feasible to control the oxygen scavenging rate and oxygen scavenging capacity in a package (known volume) by monitoring the Fe°/C, sodium chloride and moisture conditions. Moreover, different types of biomass derived carbon particles revealed different oxygen scavenging capabilities. Here, oxygen scavenging capacities in a range of 147 to 208 cm.sup.3/g Fe was achieved with the highest oxygen absorption performance at 208 cm.sup.3/g Fe. The oxygen scavenging ability of the various iron/carbon particles may depend on the surface areas of the carbon material/particles and the types of saccharide chains that surround the carbon material/particles, which control the dispersion of the iron particles on the carbon supports. Hence, the higher the surface area and/or the greater the amount of saccharide chains, this may lead to an increase in the oxygen scavenging property.

TABLE-US-00001 TABLE 1 Oxygen Scavenging Property of Fe°/C1 Test Oxygen concentration (%) time 50 mg 50 mg Fe°/C1 + 50 mg Fe°/C1 + 5 mg (hour) Fe°/C1 5 mg NaCl NaCl + 50 μl H.sub.2O 0 20.9 20.9 20.9 1 20.9 18.6 13.4 2 20.9 17.4 10.2 3 20.9 15.6 7.72 4 20.9 13.8 5.85 5 20.9 12.1 4.6 6 19.8 10.4 3.58 7 19.4 8.69 2.61 8 19.3 7.14 1.92 24 18.8 1.43 0.174 48 17.8 1.33 0.112 72 17.4 1.75 0.099 96 17.4 1.51 0.071

TABLE-US-00002 TABLE 2 Oxygen Scavenging Property of Fe°/C2 Test Oxygen concentration (%) time 50 mg 50 mg Fe°/C2 + 50 mg Fe°/C2 + 5 mg (hour) Fe°/C2 5 mg NaCl NaCl + 50 μl H.sub.2O 0 20.9 20.9 20.9 1 20.9 16.8 8.42 2 20.9 14.2 5.14 3 20.9 11.6 3.8 4 20.9 9.01 3.08 5 20.9 6.55 1.82 6 20.7 4.65 1.25 7 20.8 3.07 1.18 8 20.6 1.96 1.19 24 20.8 1.83 1.58 48 19.2 1.58 1.58 72 19.4 1.09 1.38 96 19.4 1.17 1.31

TABLE-US-00003 TABLE 3 Oxygen Scavenging Property of Fe°/C3 Test Oxygen concentration (%) time 50 mg 50 mg Fe°/C1 + 50 mg Fe°/C1 + 5 mg (hour) Fe°/C1 5 mg NaCl NaCl + 50 μl H.sub.2O 0 20.9 20.9 20.9 1 20.9 19.4 19.4 2 20.9 18.6 17.8 3 20.9 17.2 15.6 4 20.2 16.4 14 5 20 15.7 12.9 6 19.5 15.2 12.2 7 19.3 14.7 11.8 8 19.1 14.6 11.7 24 19.2 14.3 11.7 48 19.1 14.1 11.8 72 19.4 14.4 12.1 96 19.3 14.4 12.1

INDUSTRIAL APPLICABILITY

[0105] The composite material may be used as an oxygen scavenging nanostructured composite. The oxygen scavenging nanostructured composite may be used in food packaging and may be placed in a variety of containers such as sachets, permeable bags, sheet-like mat and laminated sheets to protect the contents of such containers from degradation or reaction with oxygen.

[0106] The composite material may be mixed with a polymer and applied onto a plastic film to form a coating layer. The coating layer may be flexible to contour according to a variety of packaged materials and applications. This polymer may be a matrix material such as a hydrogel with controlled release water ability or a high oxygen permeable polymer. It is to be appreciated that the polymer matrix is highly permeable to oxygen molecules, so that the headspace oxygen molecules could freely penetrate through the polymer and for reaction with the nanostructured composite.

[0107] The composite material may be applied together with an external oxygen barrier layer to form a multilayer film having (1) an oxygen barrier layer and (2) the composite material as an oxygen scavenging layer as a packaging agent. The oxygen barrier layer could be clay/polymer composites to retard the permeation of oxygen from an external environment to penetrate into the packages. Meanwhile, the headspace oxygen from the packages may be removed by the composite material.

[0108] The composite material may be mixed with a biomass derived polymer to form a sheet-like mat via electrospinning method. Such a sheet-like mat oxygen scavenger may be easily fixed or applicable to a variety shape of packages.

[0109] 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.