Patent Grant
9704628
The present invention relates to a Ferrofluid-MWCNT (multiwall carbon nano tube) hybrid nanocomposite in liquid state. Particularly, present invention relates to the chemical synthesis of stable dispersions comprising Fe3O4 nanoparticles and functionalized MWCNTs in aqueous phase.
More particularly, present invention relates to nanocomposite in liquid state useful for various applications like MRI, EMI shielding, energy conversion etc.
The stable fluidic dispersions of magnetic nanoparticles especially, ferrofluids have been conscientiously investigated in recent years for their numerous potential applications. Their remarkable magnetoviscous effects have made them highly desirable for scientific and engineering applications e.g. vacuum seals (Journal of Magnetism and Magnetic Materials, 1990, v. 85, no. 1-3, p. 233-245), microelectromechanical systems (MEMS) (Sensors and Actuators A: Physical, 2000, v. 84, no. 1, p. 176-180), magnetic hyperthermia (Journal of physics D: Applied physics, 2003, v. 36, no. 13, p. R167), hearing aids (Indian Journal of Engineering and Materials Sciences, 2004, v. 11, p. 241-252), contrast enhancement in MRI (Journal of Magnetism and Magnetic Materials, 2005, v. 289, p. 328-330), drug delivery and its targeting (Drug Development Research, 2006, v. 67, no. 1, p. 55-60; Nano Today, 2007, v. 2, no. 3, p. 22-32) etc. have been explored. On the other hand, since the historic discovery of carbon nanotubes (CNTs) by Ijima (Nature, 1991, v. 354, p. 56-58), there has been great interests towards its unique electrical, thermal, optical and mechanical properties (Nature, 1996, v. 382, p. 54-56.; Physical Review B, 1998, v. 68, p. 6756-6759; Physical Review B, 1999, v. 59, no. 4, p. 82514; Synthetic Metals, 1999, v. 103, p. 2555-2558; Physical Review Letters, 2000, v. 84, no. 20, p. 4613). Instead, a fewer attempts have been given to enhance their magnetic properties (The Journal of Physical Chemistry B, 2005b, v. 109, no. 41, p. 19060-19063; Nano Letters, 2005, v. 5, no. 5, p. 879-884; Nanotechnology, 2009, v. 20, no. 5, p. 055607; The Journal of Physical Chemistry C, 2010, v. 114, no. 15, p. 6944-6951, Kim, I. T., and R. Tannenbaum, 2011, www.intechopen.com; Magnetic Carbon Nanotubes: Synthesis, Characterization, and Anisotropic Electrical Properties; Carbon, 2011, v. 49, no. 1, p. 54-61).
In U.S. Pat. No. 6,975,063, methods are presented for the metallization of carbon nanotubes for field emission applications. The metallization procedure involves an electrodless plating technique for depositing thin metal layers of few nanometers on SWCNT, MWCNT, etc. Thereafter, dispensing the dispersed mixtures of metallized carbon nanotubes onto any suitable substrate for a thin coating of this material. The presence of magnetic field initiates the alignment of magnetically-active metallized carbon nanotubes. The present invention also directs method for cold cathode field emitting materials comprising metallized carbon nanotubes and using metallized carbon nanotubes as cold cathode field emitters.
In U.S. Pat. No. 8,038,926, the carbon nanotubes with embedded gold, SiC and Fe3O4 nanoparticles are produced. Initially a template of anodized porous aluminum oxide membrane (pore diameter of 20-200 nm) is placed in a solution of desired nanoparticles followed by sonication. The template is separated by treatment to a basic solution and a carbon structure via chemical deposition of carbon on the template is formed.
In U.S. Pat. No. 8,119,021, the nanotubes prepared via chemical vapor deposition on alumina template were loaded with functionally active gold and Fe3O4 nanoparticles. The application of magnetic field therein helps in manipulation of CNTs encapsulated with magnetic particles, drugs or quantum dots.
In U.S. Pat. No. 8,325,079, a radar absorbing (0.1-60 MHz) composite material includes a (CNT)-infused fiber material. The material exhibits radar reflectance as well as dissipation of radar energy in a systematic layer by layer coated form.
The general drawbacks of hitherto known ferrofluid-CNT composites is that they are all in solid state. The manipulation of such homogenized composite in a well dispersed liquid state can give more flexibility in its magnetic and electrical response as mentioned below.
In U.S. Pat. No. 6,975,063, inventors have utilized the carbon nanotubes metallized with magnetically active, in thin coated form for cathode field emitters. A thin metallic coating induces the magnetic response in the prepared composite.
In U.S. Pat. No. 8,038,926, a composite material comprising carbon nanotubes with embedded with magnetic nanoparticles, is prepared in dried state. The size selection of nanoparticles ranges from 20-200 nm, depending on porosity of template.
In U.S. Pat. No. 8,119,021, empty carbon nanotubes have been loaded with functionalized magnetic nanoparticles for carrying out desired magnetic manipulation.
In U.S. Pat. No. 8,325,079, a CNT-infused fiber material is used in coated form for radar absorbing applications.
Our invention provides a new method to prepare a stable new hybrid nanofluid comprising a composite of ferrofluid and functionalized MWCNT. In each of these earlier inventions, the preparation of this magnetic composite has been described in dried state. This limits the control orientation of CNTs loaded with nano-magnetic particles. A homogeneous distribution of CNTs is not achievable in dried state. Further, the uniform coating of CNTs loaded with magnetic particles is not attainable in dried state. None of the inventors has prepared the ferrofluid-MWCNT composite in liquid state. The present method is successful in synthesis of this composite and its stable dispersion in water. Therefore, the preparation method resulting in aqueous dispersion of ferrofluid-MWCNT composite is unique and opens door for several other possible applications.
The main object of the present invention is to provide a stable a Ferrofluid-MWCNT (multiwall carbon nano tube) hybrid nanocomposite in liquid state.
Another object of the present invention is to provide two different processes for the preparation of stable aqueous dispersions of MWCNTs and magnetite nanoparticles separately.
Still another object of the present invention is to provide a process wherein we can efficiently functionalize MWCNTs without much damaging graphene layer organization for compatibility with ferrofluid dispersion.
Yet another object of the present invention is to use nitric acid as the only source for functionalization of outer nanotube layer.
Yet another object of the present invention is to stabilize magnetite nanoparticles in aqueous medium.
Yet another object of the present invention is to synthesize double surfactant coated magnetite nanoparticles.
Still another object of the present invention is to provide a process wherein we can have both MWCNTs and magnetite nanoparticles in same system.
Yet another object of the present invention is to provide a fluid which has constituents having both electrical and magnetic properties.
Accordingly, present invention provides a Fe3O4-MWCNT hybrid nanocomposite in liquid state comprising water based ferrofluid in fixed volume concentration and MWCNT in the ratio ranging between 1 to 30.
In an embodiment, present invention provides a process for the preparation of Fe3O4-MWCNT hybrid nanofluid comprising the steps of:
In another embodiment of the present invention, emulsifier used is acetone.
In yet another embodiment of the present invention, primary surfactant used is oleic acid.
In yet another embodiment of the present invention, secondary surfactant used is sodium oleate.
In yet another embodiment of the present invention, ion-dipole interaction between Fe3O4-MWCNTs leads to stable suspension.
Present invention provides a stable hybrid nanofluid of Fe3O4 and MWCNTs, which comprises the preparation of aqueous dispersions of Fe3O4 nanoparticles and MWCNTs separately and thereafter, mixing of both components using mechanical stirring.
The synthesis of Fe3O4 nanoparticles was performed using reverse micelles of primary surfactant oleic acid in aqueous medium.
The prepared coated nanoparticles were coated with sodium oleate as secondary surfactant for dispersibility in water.
The mild acidic conditions created via nitric acid in a stepwise manner yields purified and functionalized MWCNTs and finally its stable aqueous dispersion.
According to the present invention, a stable hybrid was prepared after the preparation of dispersions of magnetite nanoparticles and MWCNTs in water. The water based ferrofluid was synthesized by taking Fe2+ and Fe3+ ions (1:2 molar ratio) in aqueous phase in presence of surfactant and emulsifier. The MWCNTs were purified and functionalized by mild acid treatment and dispersed in deionized water. The present invention describes a simple preparation of hybrid nanofluid of Fe3O4 nanoparticles and MWCNTs in aqueous medium. The simultaneous use of oleic acid and acetone as primary surfactant and emulsifier for the preparation of single layer coated magnetite nanoparticles. Thereafter, sodium oleate is coated as secondary surfactant. On the other side, a mild acid treatment to MWCNTs by HNO3 leads to efficient functionalization of sidewalls. This step is very important in obtaining a stable dispersion of MWNCTs. Thereafter, both dispersions were mixed in different volume ratios for desired nanoparticle to MWCNTs content in the hybrid fluid.
The process of the invention involves i) reaction of ferrous sulphate heptahydrate and ferric chloride with a mixture of 25% (v/v) ammonia, ii) heating of reaction mixture at 70° C., iii) magnetic decantation followed by washing by deionized water (2 L), iv) 3.85 g of sodium oleate dissolved in 20 mL deionized water at 50° C., v) the slurry was added to above mixture, vi) the final mixture is centrifuged at 13000 rpm and supernatant separated.
The process of the invention also involves i) treatment of 0.03 g of MWCNTs with 150 mL of 69% HNO3 and heated at 50° C. for 180 min. ii) The MWCNTs were filtered and washed with deionized water iii) The as obtained dried MWCNTs were treated with 200 mL of 69% HNO3 and sonicated at 35 kHz iv) The mixture is heated 90° C. for 65 hours and allowed to cooled down on its own. v) the obtained solution is filtered and washed using deionized water, vi) the filtered product was dispersed in 300 mL of deionized water.
Thereafter, both dispersions obtained by these two process were mixed in different volume ratios for desired nanoparticle to MWCNTs content in the hybrid fluid.
The Inventive Steps Involved in the Present Invention are
Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.
Initially 0.03 g of as obtained MWCNTs were treated with 150 mL of 69% HNO3 and sonicated at 35 kHz for half an hour. Then it was followed by 180 min. magnetic stirring at room temperature i.e. 25° C. The mixture was filtered and washed with MILLI-Q® purified water till pH reaches 6. The slurry was dried at 70° C. for 24 hours and labeled as PCNT. For chemical oxidation on side walls, some part of PCNT was taken in 200 mL of 69% HNO3 followed by sonication and then heating at 90° C. for 65 hours under constant stirring. After this second stage of acid treatment, the acid mixture containing functionalized carbon nanotubes (FCNTs) was allowed to cool down to room temperature and washed carefully by MILLI-Q® purified water using two layers of Whatman filter paper (grade no. 42). The washing was continued with 3 liters of water till it pH reaches 6. The slurry was transferred to 350 mL of distilled water. It was found that the MWCNTs readily disperse in water without any further treatment. The dispersion was labelled as WCNT.
In the other synthesis procedure, 15.9 g FeCl3 and 14.0 g FeSO4.7H2O were dissolved in 100 mL 100 mL MILLI-Q® purified water along with 4 mL oleic acid as primary surfactant and 1 mL acetone as emulsifier to form oil-in-water emulsion. The mixture was then heated from 30° C. to 60° C. at 2° C./min heating rate under rigorous stirring. During heating, 22 mL of 25% aq. NH3 was added dropwise. The precipitate was separated magnetically from mixture and washed with 700 mL hot MILLI-Q® purified water (200° C.) to remove unwanted ions. The slurry was then dried at 100° C. Simultaneously on the other side, a 20 mL aqueous solution of sodium oleate (3.47 g) as secondary surfactant was prepared by heating at 50° C. for 10 min. The dried slurry of previously obtained nanoparticles was transferred to above solution and heated for further 10 min. Then this mixture was allowed to cool down to room temperature and later on centrifuged at 13500 rpm for 20 min. The filtrate was separated carefully via pipette and labeled as WFF. The dispersions WCNT and WFF were mixed in v/v ratio 1:1 to obtain desired MWCNT-Fe3O4 hybrid composites in well a dispersed liquid state.
Initially 0.03 g of as obtained MWCNTs were treated with 150 mL of 69% HNO3 and sonicated at 35 kHz for half an hour. Then it was followed by 180 min. magnetic stirring at room temperature i.e. 27° C. The mixture was filtered and washed with MILLI-Q® purified water till pH reaches 6. The slurry was dried at 70° C. for 24 hours and labeled as PCNT. For chemical oxidation on side walls, some part of PCNT was taken in 200 mL of 69% HNO3 followed by sonication and then heating at 90° C. for 65 hours under constant stirring. After this second stage of acid treatment, the acid mixture containing functionalized nanotubes (FCNTs) was allowed to cool down to room temperature and washed carefully by MILLI-Q® purified water using two layers of Whatman filter paper (grade no. 42). The washing was continued with 3 liters of water till it pH reaches 6. The slurry was transferred to 350 mL of distilled water. It was found that the MWCNTs readily disperse in water without any further treatment. The dispersion was labelled as WCNT.
In the other synthesis procedure, 15.9 g FeCl3 and 14.0 g FeSO4.7H2O were dissolved in 100 mL 100 mL MILLI-Q® purified water along with 4 mL oleic acid as primary surfactant and 1 mL acetone as emulsifier to form oil-in-water emulsion. The mixture was then heated from 30° C. to 60° C. at 2° C./min heating rate under rigorous stirring. During heating, 22 mL of 25% aq. NH3 was added dropwise. The precipitate was separated magnetically from mixture and washed with 700 mL hot MILLI-Q® purified water (200° C.) to remove unwanted ions. The slurry was then dried at 100° C. Simultaneously on the other side, a 20 mL aqueous solution of sodium oleate (3.47 g) as secondary surfactant was prepared by heating at 50° C. for 10 min. The dried slurry of previously obtained nanoparticles was transferred to above solution and heated for further 10 min. Then this mixture was allowed to cool down to room temperature i.e. 25° C. and later on centrifuged at 13500 rpm for 20 min. The filtrate was separated carefully via pipette and labeled as WFF. The dispersions WCNT and WFF were mixed in v/v ratio 1:2 to obtain desired MWCNT-Fe3O4 hybrid composites in well a dispersed liquid state.
Initially 0.03 g of as obtained MWCNTs were treated with 150 mL of 69% HNO3 and sonicated at 35 kHz for half an hour. Then it was followed by 180 min. magnetic stirring at room temperature i.e. 30° C. The mixture was filtered and washed with MILLI-Q® purified water till pH reaches 6. The slurry was dried at 70° C. for 24 hours and labeled as PCNT. For chemical oxidation on side walls, some part of PCNT was taken in 200 mL of 69% HNO3 followed by sonication and then heating at 90° C. for 65 hours under constant stirring. After this second stage of acid treatment, the acid mixture containing functionalized nanotubes (FCNTs) was allowed to cool down to room temperature and washed carefully by MILLI-Q® purified water using two layers of Whatman filter paper (grade no. 42). The washing was continued with 3 liters of water till it pH reaches 6. The slurry was transferred to 350 mL of distilled water. It was found that the MWCNTs readily disperse in water without any further treatment. The dispersion was labelled as WCNT.
In the other synthesis procedure, 15.9 g FeCl3 and 14.0 g FeSO4.7H2O were dissolved in 100 mL 100 mL MILLI-Q® purified water along with 4 mL oleic acid as primary surfactant and 1 mL acetone as emulsifier to form oil-in-water emulsion. The mixture was then heated from 30° C. to 60° C. at 2° C./min heating rate under rigorous stirring. During heating, 22 mL of 25% aq. NH3 was added dropwise. The precipitate was separated magnetically from mixture and washed with 700 mL hot MILLI-Q® purified water (200° C.) to remove unwanted ions. The slurry was then dried at 100° C. Simultaneously on the other side, a 20 mL aqueous solution of sodium oleate (3.47 g) as secondary surfactant was prepared by heating at 50° C. for 10 min. The dried slurry of previously obtained nanoparticles was transferred to above solution and heated for further 10 min. Then this mixture was allowed to cool down to room temperature and later on centrifuged at 13500 rpm for 20 min. The filtrate was separated carefully via pipette and labeled as WFF. The dispersions WCNT and WFF were mixed in v/v ratio 1:10 to obtain desired MWCNT-Fe3O4 hybrid composites in well a dispersed liquid state.
Initially 0.03 g of as obtained MWCNTs were treated with 150 mL of 69% HNO3 and sonicated at 35 kHz for half an hour. Then it was followed by 180 min. magnetic stirring at room temperature i.e. 25° C. The mixture was filtered and washed with MILLI-Q® purified water till pH reaches 6. The slurry was dried at 70° C. for 24 hours and labeled as PCNT. For chemical oxidation on side walls, some part of PCNT was taken in 200 mL of 69% HNO3 followed by sonication and then heating at 90° C. for 65 hours under constant stirring. After this second stage of acid treatment, the acid mixture containing functionalized nanotubes (FCNTs) was allowed to cool down to room temperature and washed carefully by MILLI-Q® purified water using two layers of Whatman filter paper (grade no. 42). The washing was continued with 3 liters of water till it pH reaches 6. The slurry was transferred to 350 mL of distilled water. It was found that the MWCNTs readily disperse in water without any further treatment. The dispersion was labelled as WCNT.
In the other synthesis procedure, 15.9 g FeCl3 and 14.0 g FeSO4.7H2O were dissolved in 100 mL 100 mL MILLI-Q® purified water along with 4 mL oleic acid as primary surfactant and 1 mL acetone as emulsifier to form oil-in-water emulsion. The mixture was then heated from 30° C. to 60° C. at 2° C./min heating rate under rigorous stirring. During heating, 22 mL of 25% aq. NH3 was added dropwise. The precipitate was separated magnetically from mixture and washed with 700 mL hot MILLI-Q® purified water (200° C.) to remove unwanted ions. The slurry was then dried at 100° C. Simultaneously on the other side, a 20 mL aqueous solution of sodium oleate (3.47 g) as secondary surfactant was prepared by heating at 50° C. for 10 min. The dried slurry of previously obtained nanoparticles was transferred to above solution and heated for further 10 min. Then this mixture was allowed to cool down to room temperature and later on centrifuged at 13500 rpm for 20 min. The filtrate was separated carefully via pipette and labeled as WFF. The dispersions WCNT and WFF were mixed in v/v ratio 1:30 to obtain desired MWCNT-Fe3O4 hybrid composites in well a dispersed liquid state.
Characterization
The structural characterization was performed by Rigaku powder X-ray diffractometer with Cu-Kα radiation (λ=1.54059 Å), 40 kV & 30 mA with step size 0.002°, scan rate 2°/min, scan range (2θ) from 15°-80°. For these measurements, the oleic acid coated NPs prepared in synthesis were separated and dispersed in kerosene. The supernatant of the suspension was allowed to evaporate on a 1×1 cm2 glass slide at room temperature. The XRD pattern of dispersed MWCNT in WCNT sample was recorded by drying its few drops on glass slides in ambient conditions. On the other hand, as obtained MWCNT and purified MWCNT were used in powder form for recording their XRD pattern. The surface morphology of nanoparticles, nanotubes and nanocomposite was examined with a SEM model LEO 440 PC based.
The specimens were prepared by leaving few drops of required dispersions on 1×1 cm2 surgical glass slides and allowed to dry in an experimental setup with specified magnetic field at room temperature. The closer morphological details of samples were recorded via M/s Tecnai F30 HRTEM. The specimens for HRTEM characterization were prepared by leaving few drops of the desired dispersions on carbon-coated Cu-TEM grid (400 meshes). The wet TEM grid was allowed to evaporate at room temperature. After drying, the specimen was transferred into microscope for imaging.
The XRD patterns of as such obtained, purified and functionalized MWCNTs are shown in
The λ, β and θ corresponds to X-ray wavelength and FWHM in radians and Bragg's angle respectively.
The calculated value of N comes out to be 9.7, 9.4 and 9.0 for pristine, purified and functionalized MWCNTs. These results indicates that the reaction procedure involves damage to the graphene layer organization, but to a lesser extent. The intensity of (002) peak was found to be reduced in functionalized MWCNTs, when compared with as such and purified MWCNTs. This gives an indication of lower packing fraction caused by introduction of carboxylic group and simultaneous defragmentation and debundling of side walls in the former sample.
For MWCNT-ferrofluid composite dried in 1:1 v/v ratio, the recorded diffraction pattern did not show any signature of (002) due to CNTs in the pattern. While intense peaks due to Fe3O4 nanoparticles is observed only (
FTIR spectra of pristine MWCNTs, PCNTs and FCNTs, WFF and Fe3O4/MWCNTs hybrid fluid were recorded at 298 K and are shown in
It is due to the similarity of hydrocarbon fragments and functional groups in these systems. The intensity of C—H vibrations (2850-3000 cm−1) and CO vibrations (2340-2360 cm−1) is quite enhanced in the latter samples due to contribution by oleic acid and sodium oleate surfactants. The C═O vibrations, characterized by peak at ˜1730 cm−1 is sharper in Fe3O4/MWCNTs as compared to WFF. This behavior can be explained as the result interactions between MWCNTs and Fe3O4 nanoparticles.
To see the manipulation of nanotubes caused by magnetic field, the hybrid fluids were prepared in different ratios viz., 1:2, 1:10 and 1:30 and dried on the glass substrate in two different sets of experimental setup i.e., in the absence (H=0 G) and presence of magnetic field (H=3 kG). The WCNT dispersions were sonicated at 35 kHz frequency for 15 min prior to the mixing with WFF dispersion. This step is followed to avoid any kind of entanglement between FCNTs. The required field was applied by placing the samples in between two rectangular NdFeB permanent magnets. The setup provides a coplanar magnetic field to the sample on glass surface. The other advantage is that the strength of field remains constant over the period of drying. The carrier medium i.e. water, was evaporated off at room temperature. Images (i), (j), (k), (l), (m) and (n) shown in
In the absence of field, a random network of Fe3O4/FCNTs heterostructure is obtained. It is observed since magnetic moments of Fe3O4 nanoparticles are randomly oriented in different directions resulting in zero net magnetization. The homogeneity of nanosized constituents in dried composites seems to remain unaffected with respect to v/v ratio of mixed WFF and WCNT dispersions (images i and k).
In the presence of field, a long and orderly dried linear fibrous structure of FCNTs was observed (images j, l and n). This structural transformation of the composites in presence of field occurs due to the alignment of magnetic moments of nanoparticles, which are concomitantly interacting with functional groups of nanotubes (The Journal of Physical Chemistry B, 2005b, v. 109, no. 41, p. 19060-19063). Thus, a combined movement of the chemically interacting system in compliance with applied field results in oriented nanostructures. The thickness of these fibrous heterostructures in the composite form varied from 0.15 μm, 0.5 μm to 5 μm for 1:2, 1:10 and 1:30 WFF/WCNT ratios. A notable increase in thickness is observed as the content of FCNTs increase in the fluid. The role of interparticle magnetic interactions between nanoparticles attached to the side walls of CNT, can be easily discarded as another way of thickening. Since such an arrangement have been reported with instability imparted by anisotropic dipolar interactions among particles in chain-like structures (Journal of Physics: Condensed Matter, 2003, v. 15, no. 15, p. S1451; The Journal of Physical Chemistry B, 2005b, v. 109, no. 41, p. 19060-19063). So the thickening can be attributed to the dominating intertube interactions resulting by the consequent weakening of interactions between nanotubes and nanoparticles. This kind of intertube interactions are similar to the ones present in dried WCNT dispersion (images c-h). Moreover, a controlled slow evaporation favors the orderly formation of Fe3O4/FCNTs heterostructure in all the samples.
After second stage of acid treatment as mentioned in section 6.2, the as obtained WCNT dispersion were dried on Cu-TEM grid to record TEM micrographs.
The TEM images of dried MWCNT-Fe3O4 hybrid fluid is shown in
Outer surface groups interact weakly via ion-dipole interaction with functional groups of FCNTs. Since only a fraction of particles are attached to FCNTs, the density of nanotubes is increased only slightly and fluid shows good magnetic stability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1673/DEL/2014 | Jun 2014 | IN | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6975063 | Mao et al. | Dec 2005 | B2 |
| 8038926 | Gogotsi et al. | Oct 2011 | B2 |
| 8119021 | Gogotsi et al. | Feb 2012 | B2 |
| 8325079 | Shah et al. | Dec 2012 | B2 |
| 9129732 | Rwei | Sep 2015 | B2 |
| 20130112911 | Mazyar | May 2013 | A1 |
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| Number | Date | Country | |
|---|---|---|---|
| 20150371776 A1 | Dec 2015 | US |
