FIELD OF INVENTION

[0001] The present invention is related to the development of a process for nanofabrication of desired material in the clay mineral receptacles for their potential applications as advance nanomaterials to agriculture and could be used in industry in various fields. The process involved breakdown of bulk-form of clay-minerals along with the planes of weakness by physical top-down method to nano-form. This is followed by the transportation of desired ion/ ion pair (especially nutrient ion/ ions/ ion pairs) from solid to liquid phases, which occur through dispersion, and then intercalating them in group or, in sheet form into inter-lattice positions along 001 planes or, on broken bond sites. To avoid coagulation/ aggregate formation, the resultant product must be charged and remain in the dispersed state. The uniqueness of the invention is the use of clay-minerals as receptacle for intercalating desired ions in sheet form.

BACKGROUND OF THE INVENTION

[0002] Nanofabrication involves synthesizing and manufacturing of matter at the scale of 1 to 100 nm. Reference may be made to U.S. Environmental Protection Agency (2007). Nanotechnology White Paper. U.S. Environmental Protection Agency Report EPA 100/B-07/001 , Washington DC 20460, USA, 135 pp wherein nanomaterials exhibit size dependent properties. Therefore, several physical and chemical properties are improved or, greatly manifested and many new properties emerge when bulk materials are converted into their nano-forms. This happens because of increase in the surface area to volume ratio, and quantum confinement. This phenomenon could be exploited for farm, orchard and forest management purposes that involve substances used as inputs in various ecosystems. Singh M V (2009) Micronutrient nutritional problems in soils of India and improvement for human and animal health. Indian J Fert 5: 1 1 -26 discloses the fact that essentially, nanomaterials must improve Input (including Nutrient ) Use Efficiency ( IUE/ NUE), and ensure desired level of uptake and assimilation by plants. The low IUE/ NUE and environmental loads could possibly be countermanded by development of nanofertilizers and nutrients in nano-clay mineral receptacles based products, for which nanofabrication could be a useful technology. The increased Input (including Nutrient) Use Efficiency means reduced financial burden to farmers and reduced cost of environmental clean-up operations.

[0003] Current processes of nanofabrication of materials/ matter involve a variety of physical and chemical techniques such as vapour deposition, laser ablation, arc discharge, lithography or nano-machining, nanoimprinting etc. to generate nanoproducts from bulk counterparts. These processes are complex, energy intensive and require highly sophisticated reactors. Moreover, industrially manufactured nanomaterials may not be compatible to the requirements of plants as nanoproducts of agricultural and managed-forest ecosystems have to address specific sequential functions like adsorption/ encapsulation followed by delivery of payload (fertilizer nutrient/ pesticide active ingredient/ phytohormone) in the order of magnitude of plant-available forms and rate of demands of plant nutrients/ other farm inputs, and also to ensure their uptake happens ionic form(s). The materials nanofabricated by the processes other than ours exist either in oxide form or, in zero-valent form, and hence, they might not be very much sought after in agriculture or managed-forest ecosystems.

[0004] There are more than 34,000 clay-mineral species found in soils/ deep regolith/ clay-mines. Different types of soils are made up of different types of clay- minerals. However, almost all of them behave as receptacles of nutrient ions and also regulate supply of nutrients to plants through ion exchange, and some other reactions. All clay-minerals respond to ecosystem functions. Our novel approach integrates intrinsic properties of clay-minerals with nanotechnology. As surface area and activities of nanomaterials increase manifold compared to their bulk-forms, and they deliver desired functions more efficiently and more rigorously. In other words, clay minerals in nano-form are expected to hold more amounts of plant nutrients, cation/ anion exchange reactions are likely to spruce-up. and there would be superior adsorption and nutrient delivery mechanisms over their bulk counterparts. Our novel process that describes nanofabrication of desired intercalated materials in the clay mineral receptacles would result in numerous useful products in economic and environmental harmonic forms.

OBJECTS OF THE INVENTION

[0005] The principal object of this invention is to design an economic, eco-friendly and unique process for nanofabrication of nutrient ions in plant available forms.

[0006] Another object of the invention is to formulate a process for nanofabrication of nutrient ions on very easily available, naturally occurring groups of clay minerals.

[0007] Yet another object of this invention is to figure out a process for nanofabrication of nutrient ions on clay minerals, satisfying all the criteria for availability as well as economic feasibility.

[0008] Further object of the invention is to develop a process for nanofabrication of nutrient ions on clay minerals for the agriculture and the environment as a whole. SUMMARY OF INVENTION

[0009] The invention provides a process of retaining desired ions/ sets of ions/ sheets of ions in clay mineral receptacle that eventually yields novel nanomaterial products capable of delivering set of jobs. Clay minerals are acquired from earth, mine, soils and deep regolith. and because of it, they are cheap and thereby affordable to the farmers and other stake-holders. In our experimentations, clay minerals (e.g. kaolin, smectite) were given physical probe sonication treatment in aqueous phase so as to break the bulk-form of clay minerals along the planes of weakness i.e. 001 planes into nano-forms of clay minerals. The desired ions / ion pairs/ sets of ions including nutrient ions / ion pairs/ sets of ions were derived from solid source materials through dissolution and then transported to reaction chamber to facilitate intercalation with the nanoform clay minerals. The dissolution from solid source materials took place in the presence of dilute rhizospheric acid like oxalic acid, formic acid, citric acid, and acetic acid. In our experiments, we extracted phosphate ions from P-rich mineral fractions of Rock Phosphate (sampled from Udaipur mine in Rajasthan, India), and zinc ions from zinc sulphate solution ( 1 mol dm ^"3 ). Then, they were transported to the reaction chamber, where slowly suspension of nano-form clay mineral(s) was added to promote desired intercalation. The mobi lity of desired ions/ sets of ions/ sheets of ions were regulated by creating concentration gradient. In the reaction chamber, ion/ ion pairs were intercalated in the interlattice sites of the nano-clay-mineral, and change of phase occurred as on intercalation with clay minerals neoformed nanoproduct precipitated. Then, the nanoproduct was washed, purified, and dried by lyphilization or in rotary vacuum evaporator, and stored in sterilized container.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings are included to further demonstrate certain properties of the nano-products. Detailed description of specific embodiments presented herein.

[0011 ] Fig. 1 : Electron micrographs of kaolin clay mineral (a) Scanning electron micrograph of kaolinite in bulk, (b) Transmission electron micrograph of nanoform kaolinite at 20.0 K magnification.

[0012] Fig. 2: Electron micrographs of smectite clay mineral (a) Scanning electron micrograph of smectite in bulk, (b) Transmission electron micrograph of nanoform smectite.

[0013] Fig. 3 : Aqueous dispersions prepared 12 cycles each of 5 min sonication and 5 min rest for kaolinite to achieve 190 nni size (by Zeta Potential based Dynamic Light Scattering), and 6-8 cycles each of 5 min sonication and 5 min rest for smectite at 20 kHz.

[0014] Fig. 4: Dynamic Light Scattering results of kaolin aqueous dispersion prepared after (a) twelve cycle and (b) six cycles of probe sonication.

[0015] Fig. 5 : Zeta Potential results obtained for kaolin dispersion prepared after (a) twelve cycle and (b) six cycles of sonication.

[0016] Fig. 6: Three chamber process model for dissolution, transportation. adsorption of the nutrient ion/ ion sets followed by phase separation of the final nanoproduct by precipitation.

[0017] Fig. 7: X-ray mapping of showing distribution pattern of P adsorbed on nano-kaolin in rhizospheric acid environment.

[0018] Fig. 8: Transmission Electron micrograph showing etching of surface and deposition of phosphate on nano-kaolin receptacle. [0019] Fig. 9: Fourier Transform-Infra Red spectra of P adsorbed on nano-kaolinite in rhizospheric acid environment

[0020] Fig. 10: Energy Dispersive Spectroscopy (EDS) spectra-EDS data of nano- form zinc saturated-kaolinite depicting elemental composition that also confirms presence of zinc.

[0021] Fig. 1 1 : Energy Dispersive Spectroscopy (EDS) spectra-EDS data of nano- form zinc saturated-smectite depicting elemental composition that also confirms presence of zinc.

[0022] Fig. 12: (a) Fourier Transform Infra Red (FTIR) comparison spectra of nano- form zinc saturated-smectite and nano-form sodium saturated-smectite showing absorption spectra between wave-numbers 400 and 4000 cm ^{" 1} , (b) Fourier Transform Infra Red (FTIR) comparison spectra of nano-form zinc saturated - kaolin and nano-form sodium saturated-kaolin showing absoiption peaks between wave-numbers 400 and 4000 cm ^{" 1} .

DETAILED DESCRIPTION OF THE INVENTION

[0023] Nanotec l no logy (NT) is defined by the US Environmental Protection Agency (US EPA, 2007) as a science of understanding and control of matter at dimensions of roughly 1 - 100 nm, where unique physical properties make novel applications possible. Conceptually, nanotechnology could be illustrated as the science of designing and building of machines in which every atom and chemical bond is specified precisely. At the nanoscale, matter shows extraordinary properties that are not exhibited by bulk materials. Due to these extra-ordinary properties, nanoparticles have become significant in recent years and nano-products are entering in the market at rapid pace. Because of smal l size of the nano clay minerals, and because of existence of nutrient ion potential gradients towards rhizosphere, nutrient ion adsorbed on/ in clay-mineral receptacles would move to rhizosphere spontaneously when applied in nanoforms to soils. The nutrient ion is perceived to be held on the surfaces of the bulk-form clay minerals by van-der Waals forces. The force could possibly be increased by increasing retention potential by nanosizing the clay mineral . [0024] The present invention discloses a nanofabrication process involving clay minerals as receptacles for manufacturing advanced nanomate rials including novel fertilizers comprises the steps of extraction of desired material from the natural source, dispersion state of nutrient ions in dispersion media and coordination thereof, opening up of the clay mineral along the cleavage plane, and subsequent intercalation and/ or adsorption of the ions in their hydration state on the reactive faces or sites of the clay mineral.

[0025] In an embodiment of the present invention the nanomaterials composed mainly of two materials viz. (i) sourcing of plant-nutrient ions, and (ii) desired clay- minerals, and comprising of application of biodegradable polymer for encapsulation.

[0026] In yet another embodiment of the present invention the step of extraction comprises of dissolution of solid phase, dissociation and transport of plant nutrient ions, retention of nutrient ions and formation of coordinate group(s) or coordinate sheet(s) thereof in aqueous suspension.

[0027] In an embodiment of the present invention the dissolution of solid phase was achieved through the use of rhizospheric acids.

[0028] In another embodiment of the present invention the concentration of rhizospheric acid was in the range of 0.005 - 2.0 Mole.

[0029] In still yet another embodiment of the present invention the dispersion state of nutrient ions in dispersion media and coordination was achieved through immediate transportation to the reaction chamber.

[0030] In another embodiment of the present invention the step of opening up of the clay mineral along the cleavage plane was achieved through breaking down of bulk materials to nano-materials or nano-crystals in aqueous suspension by probe sonication.

[0031 ] In yet another embodiment of the present invention the step of intercalation and/ or adsorption included drop wise addition of clay suspension to the reaction chamber containing plant nutrient ions.

[0032] In an embodiment of the present invention the desired material was plant nutrient which included cationic group consisting of Zir ⁺ , Cu ²⁺ and anionic group consisting of B0 S0 ~ ^" , P0 ^" and clay mineral as receptacles, preferably Zn ^" in cationic group and P0 ^3' in anionic group.

[0033] In another embodiment of the present invention the desired material was plant nutrient in which the cationic group is Zn ²⁺ and the anionic group is P0 ^3' .

[0034] In an embodiment firstly, a homogenous dilute suspension of clay mineral in bulk-form was prepared in proper solvent. The proper solvent can also be defined as an aqueous suspension. Secondly, the bulk-form of clay mineral (kaolin and smectite) was converted into nano-form using physical probe sonication method. The nano clay minerals thus obtained were then characterized (i) by SEM to check the morphology, (ii) by TEM to specify the size of nanoproducts (iii) by SEM-EDS to check the elemental composition, and (iv) by FT-IR to check the structural groups. Later the nano-form of the clay mineral was reacted with rock phosphate dissolved in 2 to 10 percent rhizospheric acid (oxalic acid, formic acid, citric acid, and acetic acid) solution to undergo chemical surface etching to develop nano kaolin clay mineral based phosphate fertilizers. While sodium saturation of smectite clay mineral was performed for replacement by zinc ion using 1 molar zinc sulphate solution.

Examples

[0035] The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of present disclosure. It is to be understood that both the foregoing general description and the fol lowing detailed description are exemplary and explanatory only and are intended to provide further explanation of the claimed subject matter.

Example 1 :

Extraction of clay minerals:

[0036] Clay minerals could be extracted/ procured from soil, deep regolith and mine, by following simple physical and chemical methods.

[0037] Source of the clay minerals:

Two phyllosilicate clay-minerals viz. kaolin and smectite were selected for the study. They were used as receptacles for nanofabricating with zinc. Kaol in was obtained from a mine in Kerala (India) and smectite was extracted from a soil sample obtained from Vertisols in Nagpur (India).

[0038] It is to be understood that this disclosure is not limited to particular source, and experimental conditions described, as such source and conditions may vary and the method can be applied to the clay mineral obtained from other sources also.

[0039] Extraction of Kaolin: Impurities of kaolin procured from Kerala was removed by repeated washing with distilled water.

[0040] Extraction of Smectite: Soil sample was collected from a Vertisol. Clays were extracted from the sample following the procedure described by Jackson ( 1973). Two pretreatments were given, to remove: (i) soluble salts and fractions of inorganic cementing agents and (ii) organic matter. Soluble salts and carbonates were removed by using sodium acetate -acetic acid buffer at pH 5.0. Clays were extracted by following gravity sedimentation technique using mild alkali for activating surface (functionalization). Separated Clays thus were analyzed by FT-IR, and illite and smectites were found. Therefore, clays were further separated in the coarse clay ( 1 -2 μηι), and fine clay (<1 μηι) fractions by centrifugation, for which time for sedimentation was calculated by the use of Stokes' law.

Example 2:

Preparation and purification of homoionic forms of kaolin and smectite:

[0041] Sodium salts were used throughout the process of the present invention. Further, for rapid flocculation of the solution obtained after extraction, excess of sodium chloride salt was added. After the so obtained was completely flocculated, supernatant solution was decanted and discarded. Excess of salt was removed by washing once with distilled water and then with 99% methanol till suspension became free from CI ^" . Clays were retained as Na ⁺ -clay.

Example 3:

Nano formulation of kaol in and smectite from their bulk forms:

[0042] Kaolin and smectite were made to nanoform by top down approach using probe sonicator (Ultrasonic Processor, model PR- 1 000 MP). Stable dispersions of clay minerals were prepared by dispersing 0.5 gm of clay-mineral in 700 ml of distilled water. Cycles of sonication and pulse rates were standardized to achieve complete and steady state of dispersion of the clay minerals.

Example 4:

Basic properties of the bulk-form and nano-fonn clay minerals:

[0043] The bulk-form and nano-form clay minerals were analysed for the following physical and chemical parameters:

pH:

[0044] The pH was determined in 1 : 10 clay-water suspensions by using Elico Glass Electrode pH meter by following the procedure described by Jackson ( 1973).

Electrical conductivity:

[0045] The electrical conductivity of clay minerals at 1 : 10 clay-water ratio was measured at the suspension depth after equilibrated for 24 hr by using a Conductivity Bridge.

[0046] The observed pH and Electrical Conductivity for the sample clay minerals was six cycles of sonication resulted conductivity 0.104 mS cm- 1 and (ζ) of -25.9 mV, which increased to 0.201 mS cm- 1 along with zeta potential to -26.3 mV on twelve cycles of sonication for kaolin. The pH of the nano-form Na+- smectitite (pH = 7.20) was higher than the pH of nano-form Na+- kaolin (pH = 6.2). The Electrical conductivity measured at the suspension depth after 24 hrs equilibriation was 0.73 dS m- 1 for nano-form Na+-smectitite, 0.58 dS m- 1 for nano-form kaolin.

Cation exchange capacity:

[0047] The cation exchange capacity of the bulk-form and nano-form clay minerals was determined by saturating clay minerals with Na ⁺ (using NaOAc salt) and subsequently replacing it by NH (using NH ₄ OAc salt) as described by Jackson ( 1973 ). The Na ^{^} was determined by flame photometer.

[0048] The observed cation exchange capacity (CEC) for the sample clay minerals was 24 cmol kg- 1 for nano-form kaolin and 83 cmol kg- 1 for nano-form smectite.

Example 5:

Preparation of polymer for the encapsulation of nanofabricated clay mineral receptacles: [0049] Microcapsules containing nano-particles were prepared using green- synthesized sodium alginate (SA) polymer. Sodium alginate (1%) was dispersed in distilled water with agitation to obtain homogeneous gels. Clay mineral suspensions were then added to the SA gel. The composite gels were adjusted to their final weight. The solution thus formed was sprayed on the CaCl ₂ ( 1 0 %) solution resulting into the formation of beads.

Example 6:

Characterization of nano-form clay minerals, polymer and nanoproducts:

X-ray Diffraction (XRD)

[0050] X-ray Diffraction was done on oriented (along the 001 plane) powder samples of the clay minerals (in both bulk-forms and nanoforms) and also zinc saturated clay minerals (in both bulk-forms and nanoforms) in order to analyze changes in the d-spacing due to interlayer occupancy of Zn ²⁺ coordinated with OH ₂ . Clay minerals in suspension form were mounted on glass slides and air dried. A Bruker D8 Advance X-ray diffractometer installed at Inter University Accelerated Centre (IUAC), New Delhi was used to characterize the samples. Diffractograms were obtained with Ni filtered Cu tube with wavelength (λ) of 0.1 54058 nm. Samples were scanned at 40 mA current at 40 kV voltage at scanning speed of 1 ° 20 min ^{" 1} . Data were recorded from 2°-50° 2Θ with step size of 0.02° 2Θ.

FT-IR

[0051 ] Clay minerals, polymer and nanoproducts were analyzed by Infra-Red Spectroscopy between 400 to 4000 cm ^{" 1} wavelength using Thermo Nicolet 6700 Fourier Transform Infrared Spectrometer installed at the Electron Microscopy and Nanoscience Lab, PAU, Ludhiana.

Scanning Electron Microscopy ( SEM), and SEM -Energy Dispersive Spectroscopy ( SEM-EDS )

[0052] Clay minerals, clay mineral based nanoproducts and encapsulated materials were viewed under Scanning Electron Microscope (Model : Hitachi S-3400 N) installed at the Electron Microscopy and Nanoscience Lab, PAU. Ludhiana and viewed under the microscope at 1 5 to 30 kV accelerated voltage at the working distance of 10 mm so as to get best possible image. Secondary electron images were captured.

Electron Dispersive Spectroscopy (EDS)

[0053] Elemental occurrence of the samples was determined by Electron Dispersive Spectroscopy (EDS) attached with SEM at 30 kV accelerated voltage. Spectra was obtained keeping all elements switched on.

Transmission Electron Microscopy (TEM)

[0054] The clay minerals were sonicated to get stable dispersions. Thoroughly dispersed clay mineral samples with a defined or set concentration was used for this purpose. Droplet of stable and dispersed sample was deposited on Formvar coated copper grid and dried before viewing under TEM.

Example 7:

Preparation of nanoproducts

Reaction of clay minerals with Z11SO ₄ .7H ₂ 0

[0055] The reaction between zinc source and clay minerals were carried out in a way that phase separation occurred. Suspensions of clay minerals were added drop by drop into the heptahydrate zinc sulphate solution. The product thus formed was allovved to flocculate and supernatant was discarded. This process was repeated thrice to achieve complete saturation of kaolin and smectite with Zn ²⁺ . To ensure that there no excessive salts. Zn ²⁺ saturated clay minerals were washed three times with methanol.

Addition of polymer into the zinc saturated clay minerals

[0056] Zinc saturated clay minerals were added to 1 % solution of sodium alginate, and mixed thoroughly to form smooth viscous dispersion. It was then sprayed into 1 0 percent calcium chloride solution by means of a sprayer. The droplets were retained in calcium chloride for 1 5 minutes. The microcapsules were obtained by decantation and repeated washing with iso-propyl alcohol followed by drying at 45 °C for 12 hours.

Characterization of nanoproducts [0057] Altogether four products, i.e. , Zn ²⁺ -smectite, Zn ²⁺ -kaolin, Zn ²⁺ -smectite composite and Zn ²⁺ -kaolin composite were properly dispersed by sonication and characterized through XRD, FT-IR, SEM and TEM.

Example 8:

Germination test

[0058] To test the germination and Zn ²⁺ uptake in the plants, maize (Zea mays, cv. PMH 1 ) seeds were sown in the culture tubes. For this, seeds were sterilized by mercuric chloride and soaked in water overnight. The experiment was conducted with 18 treatments containing double control (distilled water, and nutrient solution; pH 5.2) and 3 doses of each of 4 products with 3 replications in Completely Randomized Design at the room temperature. Nutrient solution (Table 3.2) was prepared by following the nutrient concentrations prescribed in the Hoagland' s solution (pH 5.2) except that Zn was fully eliminated. The details of the treatments are described in the Table 3.3.

Table 3.2 Concentration of the Plant Nutrient Solution

Component Stock Solution Stock

(g L ') Solution (ml

L ')

2M KN0 ₃ 202 2.5

2M Ca(N0 ₃ ) ₂ .4H ₂ 0 236 2.5

Iron (Sprint 138 iron 15 1.5

chelate)

2M MgS0 ₄ .7H ₂ 0 493 1

Ι Μ ΝΚ,ΝΟ;, 80 1

Minors:

H ₃ BO3 2.86 1

MnCl ₂ .4H ₂ 0 1 .81 1

Table 3.3 Treatment details

[0059] Three doses viz. 0.04, 0.05 and 0.06 mg Zn ²⁺ L ^{" 1} seed ^{" 1} were used in the experiment (Table 3.3). Plants were harvested 15 days after germination, and roots and shoots were separated. Then, washed with distilled water and excess water was removed by placing them in the tissue paper, followed by air-drying for an hour and then placed in a forced-air oven at 70° C till materials reached to a constant weight. The oven-dry samples were then grounded and digested in diacid mixture (HN0 ₃ -.HC10 ₄ at 3: 1 ). The Zn ²⁺ was estimated using Atomic Absorption Spectrophotometer (Model:) by following the method described by Jackson M L, 1973, Soil Chemical Analysis. Prentice-Hall, New Delhi, pp. 204. (Jackson ( 1 973)).

[0060] Observations: Germination test confirmed that nano-Zn and nano-P products were safe. Zinc nanoproducts in smectite receptacles showed better results than Zn-nanoproducts in kaolin receptacles. The shoot length of maize plant varied from 33.7 to 44.7 cm, while root length varied from 22.5 to 27.6 cm. The highest shoot and root lengths occurred when nano Zn2+-smectite was applied at the concentration of 0.06 mg L- l . The shoot dry weight varied from 5 1 .9 to 77.3 mg, while root dry weight varied from 16.5 to 32.9 mg. Similarly, highest shoot and root dry weights were observed when nano Zn2+-smectite was applied at the concentration of 0.06 mg L- l . The shoot and root dry weights were lowest when plants were grown in nutrient solution. There was significant effect of Zn application in nano-form on zinc contents and zinc uptake in shoot and root in maize plant. The shoot zinc content varied from 6.45 to 10.76 ng g- 1 , while, root zinc content varied from 8.60 to 1 3.38 μ« g- 1 . The highest zinc contents in shoot and root were when nano-Zn2+-smectite was applied at the concentration of 0.06 mg L- 1 . whi le they were lowest when nutrient solution was used. The zinc uptake in shoot and root varied from 0.334 to 0.83 1 ig plant- 1 and 0. 1 42 to 0.440 ig plant- 1 , respectively. Overall, nano-products proved non-toxic, and capable of supplying Zn2+ to plants. The results specifically demonstrated significant impact of nano- Zn2+-smectite and its composite on growth parameters of young corn saplings, and its superiority over nano-kaolin and its composite.

[0061] Advantages/ Industrial capabilities of the invention:

Advantages of the products claimed in the present invention are:

(i) The clay minerals in nanoform are easy to make through simple and economic methods.

(ii) Clay minerals in nanoform could invariably be used as vehicles to capture nutrient ions in plant-available form, and would deliver nutrients ions effectively, when applied to soils or sprayed on plants.

(iii) There could be demand for clay-minerals based nanoproducts for their possible use in paints, drugs, ceramics, enhancing mechanical, flammability, and gas barrier properties.

(iv) The nanofabricated clay mineral based fertilizers are easy to apply through fertigation or. as polymer encapsulated product/ hydrogel to soil through placement / broadcasting.