Method of producing a metal or metal oxide nanoparticle

Abstract

The invention provides a method of producing a metal or metal oxide nanoparticle comprising mixing a metal salt, a metal chelating agent, a whey protein and a reducing saccharide in a solvent; heating and evaporating the solvent from said mixture to form a gel, thereby forming metal or metal oxide nanoparticles within the gel.

Claims

1. A method of producing a metal oxide or metal nanoparticle comprising mixing a metal salt, a metal chelating agent and a whey protein or whey polypeptide in a solvent; heating and evaporating solvent from said mixture to form a gel, thereby forming metal oxide or metal nanoparticles within the gel.

2. The method of claim 1, wherein the whey protein is selected from α-lactalbumin, β-lactoglobulin, serum albumin and immunoglobulins, preferably a lactalbumin; and/or the whey polypeptide is selected from hydrolysates of α-lactalbumin, β-lactoglobulin, serum albumin and immunoglobulins comprising polypeptides with at least 1 kDa.

3. The method of claim 1, further comprising mixing a reducing saccharide with the metal salt, preferably wherein the reducing saccharide is a monosaccharide or disaccharide, preferably lactose.

4. A method of producing a metal or metal oxide nanoparticle comprising mixing a metal salt, a metal chelating agent and whey in a solvent; heating and evaporating solvent from said mixture to form a gel, thereby forming metal or metal oxide nanoparticles within the gel.

5. The method of claim 1, further comprising removal of the gel, preferably by calcination.

6. The method of claim 1, further comprising a reductase enzyme, preferably a reductase enzyme is from whey.

7. The method of claim 1, wherein the chelating agent is a 2-4 valent carboxylic acid, preferably citric acid.

8. The method of claim 1, wherein the metal oxide is of formula MeO, with Me being a metal.

9. The method of claim 1, wherein the metal is zinc.

10. The method of claim 1, wherein the metal oxide is selected from TiO.sub.2, Co.sub.3O.sub.4, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, CeO.sub.2, Ce.sub.2O.sub.3, LiCoO.sub.2, LiMn.sub.2O.sub.4, Li.sub.2Ti.sub.3O.

11. The method of claim 1, any one of claims 1 to 10, wherein the metal salt is water soluble, preferably is a metal chloride or nitrate.

12. A composition comprising a plurality of metal oxide or metal nanoparticles, wherein the nanoparticles have an average size of up to 200 nm in the longest dimension; and wherein less than 0.1% of the nanoparticles deviate in their size by more than 50% from the average size; and/or wherein the nanoparticles comprise 0.2 to 1 mol-% Ca and 0.5 to 4 mol-% K.

13. The composition of claim 12, wherein the average diameter is 15 nm or less, preferably 2 nm to 10 nm.

14. The composition of claim 12, wherein the nanoparticles comprise an organic compound selected from whey pyrolysis products on their surface, preferably wherein the whey pyrolysis products comprise an alkylnitrile, benzyl nitrile, a phenol, a benzenealkyl nitrile, toluene, furfural, 2,5-dimethyl, furan, levoglucosenone, levoglucosan, 3,methyl-pentanoic acid, 5-methyl-2-furancarboxaldehyde, acetamide, picolinamide, 3-pyridinol, indole, thiol groups, sulfur groups.

15. The composition of claim 12, wherein the nanoparticles are grey according to colour code (Hex code) #eeeeee or darker or according to RGB(238, 238, 238) or darker or according to RAL 9003 or darker.

16. The composition of claim 12, obtainable by a method of claim 1.

Description

FIGURES

[0050] FIG. 1 shows a Transmission electronic microscopy (TEM) image of many inventive zinc oxide nanoparticles having a homogenous size of about 20 nm. The nanoparticles were produced by calcination at 600° C. for 1 h. 100 nm scale bar.

[0051] FIG. 2 shows TEM images of zinc oxide nanoparticles having a size of about 20 (left) or 50 nm (right). 20 nm scale bar.

[0052] FIG. 3 shows a TEM image of zinc oxide nanoparticles prepared by a comparative example using ethylene glycol as gelling agent. The particles are polydisperse with many larger particles (see upper right). The nanoparticles were produced by calcination at 600° C. for 1 h. 100 nm scale bar.

[0053] FIG. 4 shows thermogravimetric (TGA) and differential thermal analysis (DTA) of ZnO xerogels.

[0054] FIG. 5 shows the XRD patterns (crystalline structure) of the ZnO nanoparticles calcined at different temperatures.

[0055] FIG. 6 presents the Raman spectrum of the ZnO nanoparticles in the spectral range of 200-1000 cm.sup.−1.

[0056] FIG. 7 shows an EDS spectrum of ZnO nanoparticles.

EXAMPLES

Comparative Example

[0057] ZnO nanoparticles were synthesized by using the Pechini method (U.S. Pat. No. 3,330,697; reviewed in Dankes et al., Mater. Horiz.,2016, 3, 91). Zinc citrate was prepared using zinc nitrate hexahydrate (Zn(NO3)2.6H2O) (Sigma-Aldrich), mixed with citric acid (CA) (C6H8O7.Math.H2O) (Sigma-Aldrich) as a chelating agent, previously dissolved in distilled water (0.1 g/ml), in molar ratios of 1:3. Ethylene glycol (E) (Sigma-Aldrich) was then added to the solution, in the mass ratio of CA:E=60:40, to promote gel formation of the citrate. The starting materials are then, mixed, homogenized and kept under magnetic stirring for 1 h at 100° C. until gel formation. A brown colored resin is obtained by heating the sample at 200° C. in an oven to remove the water. Then the resin is calcinated at temperature ranging from 400-800° C. for 1 h to obtain the resultant ZnO nanoparticles.

Example 1: Obtaining, Treatment and Characterization of Whey

[0058] Fresh liquid whey from Minas Frescal (Carvalho et al., Food Control 18(3), 2007: 262-267) cheese production was used in the laboratory. The whey obtained was duly pasteurized, bagged, in 1 l milk bags, and frozen, stored in a freezer until the moment of use. The pasteurized serum was characterized, physically and chemically, by determining, in triplicate, the following analyses:

[0059] 1. Acidity in degrees Dornic (° D)—10 mL of the sample was transferred with a volumetric pipet to a 100 mL beaker, then 5 drops of 1% phenolphthalein solution (brand Neon) was added and titrated with sodium hydroxide solution (Vetec brand) N/9, using a 10 mL buret or Domic acidometer, until a pinkish color appeared. The reading was made and the result given in degrees Domic, and each 0.1 ml of the N/9 sodium hydroxide solution corresponds to 1° D.

[0060] 2. pH, through direct measurement in potentiometer;

[0061] 3. Desiccation loss (humidity)—Direct drying in oven at 105° C.—The samples were evap-orated in a hot plate until the consistency was pasty, then weighed 2 to 10 g of the sample in porcelain capsule, previously tared. This was heated for 3 h in a greenhouse and cooled in a desiccator to room temperature, then weighed, repeating the heating and cooling operation to constant weight. The calculation was carried out using the following formula:

100*N/P=moisture or volatile substances at 105° C. percent m/m

With N=number of humidity grams (loss of mass in g); P=number of grams of the sample.

[0062] 4. Ash, by incineration in muffle furnace at 550° C.;

[0063] 5. Density at 15° C.; Total Protein; Fat; Defoamed dry extract; Lactose; Water added; Freezing point and total solids through the Ultrasonic Milk Analyzer—Lactoscan SLP (manufacturer: Entelbra SA);

[0064] 6. Carbohydrate content was obtained by the difference between the total sample mass (100%) and the contents of humidity, proteins, fat, ash, etc.

TABLE-US-00001 TABLE 1 Results of the characterization of whey: Teixeira and Fonseca Brasil Parameter measurement (2008) (2013) pH 6.12 ± 0.02 6.3 6.0-6.8 Acidity (º D) 11.66 ± 0.02  12.49  8-14 Density (g/mL) 1025 ± 0.15  1.024 — Humidity (g/100 g) 90.69 ± 0.84  93.72 — Fat (g/100 g) 0.92 ± 0.03 0.68 — Proteins (g/100 g) 2.38 0.84 — Ash (g/100 g) 0.71 ± 0.11 0.49 — Carbohydrates (g/100 g) 5.28 — — Lactose (g/100 g) 3.58 4.12 — ESD (g/100 g) 6.52 ± 0.01 — — Cryoscopy (º H) −0.39 −0.55 —

[0065] References: Teixeira and Fonseca, Arquivo Brasileiro de Medicina Veterinária e Zootecnia 60(1), 2008: 243-250; Ministério da Agricultura Pecuária e Abasteci-mento, BRASIL, “Regulamento Técnico de Identidade e Qualidade de Soro de Leite,” Diário Oficial da União, Brasilia, DF, pp. Portaria n° 53, 10 Apr. 2013. The values of acidity and pH found for whey in normal ranges. The values of acidity and pH are related directly to the total bacterial count, since these bacteria ferment lactose present in the milk, forming lactic acid, which increases the acidity and consequently decreases the pH. The composition of the whey can vary with the following aspects: type of cheese to be manufactured, type of coagulation used, composition of milk, cattle feed and others.

[0066] Whey is a product resulting from precipitation of milk fats and casein during cheese fabrication and accounts for 85 to 90% of milk volume, but also retains most of the nutrients of milk.

Example 2: Experimental Synthesis to Obtain 10 g Nanoparticles

[0067] Zinc oxide (ZnO) nanoparticles were synthesized using a whey assisted sol-gel method. In a modified protein sol-gel method, whey was successfully used as a size-limiting gelling agent to obtain nanostructured ZnO. The synthesized nanoparticles were characterized by Transmission electronic microscopy (TEM). The diameters of the particles were measured and the size was in the range of 20-50 nm.

[0068] The material used for synthesis:

[0069] 73 g zinc nitrate (Zn(NO3)2.6H2O)

[0070] 75 mL deionized water (H2O)

[0071] 80 g citric acid (C6H8O7.Math.H2O)

[0072] 150 mL whey

[0073] The sol-gel method was chosen to prepare the nanoparticles, since it allows mixing the initial reagent at an atomic level and has good reproducibility. This method also allows control of chemical composition and homogeneous materials in its composition reducing the possibility of having impurities that are difficult to detect. The sol-gel method has certain advantages over other chemical forms of preparation of metal oxide nanoparticles, providing faster nucleation and growth and can be used for large-scale industrial production of nano-powders. In addition, the use of whey in this process is advantageous over other high cost methods of the precursors for obtaining metal nanomaterials. Nanoparticles of ZnO were synthesized by a sol-gel route using whey as a polymerization agent. Zinc citrate was prepared using zinc nitrate hexahydrate, mixed with citric acid (CA) as a chelating agent, previously dissolved in distilled water (0.1 g/ml), in the molar ratio of approximately 1:1.5. The whey was then added to this solution, in the mass ratio of approximately CA: whey=1:2, to promote the polymerization of citrate. The starting materials were mixed and homogenized and kept under magnetic stirring for 1 h at 80° C. until gelatinization, a stable resin with a brown color and transparent appearance was then obtained (xerogel) and heated to 100° C. to eliminate excess of water. Thereafter, the xerogel was calcined at temperatures of 200° C., 400° C., 800° C. and 1000° C. for 1 h to obtain the resulting ZnO nanoparticles.

[0074] It is important to emphasize that the whey:

[0075] 1.) Provides a polymer matrix that confines the metal ions. As the solution is dehydrated it polymerizes (Puff formation), forming a resin of a chemical environment of biological origin that changes the surface of the particles.

[0076] 2.) acts as a thickening and gelling agent, which improves the stability of the puff.

[0077] The size of the zinc oxide nanoparticles obtained according to the method of the present invention is controlled by the temperature. FIG. 2 shows nanoparticles of 20 nm or 50 nm as determined by Transmission Electron Microscopy (TEM). According to the present invention, it is possible to produce highly uniform and stable metal oxide nanoparticles using an environmentally friendly synthesis. Due to using whey, the stability is improved.

[0078] The whey sol-gel method proved to be highly efficient for the synthesis of crystalline ZnO nanoparticles. The present investigations confirm that whey is a useful chelating agent to prepare ZnO nanoparticles with good crystallinity, high purity, control of crystallite size, and an ecologically friendly synthesis, substituting ethylene glycol. The nanoparticle composition had a grey appearance, i.e. color of code #e0e0e0 (RGB: 224, 224, 224).

Example 3: Effect of Whey in Comparison with Other Reagents

[0079] Table 2 presents the average particle sizes for the ZnO samples, comparing different reagents. Whey is more efficient than ethylene glycol (EG) in obtaining smaller particles.

TABLE-US-00002 TABLE 2 Estimated particle size of the ZnO powder after calcination as a result of different temperatures with ethylene glycol, whey and citrate only. Temperature of 1 hour With Ethylene- With Without agents, calcination process glycol (EG) Whey with citrate only 400° C. 18 nm  6 nm Polydispers*) 600° C. 26 nm 15 nm Polydispers*) 800° C. 34 nm 30 nm Polydispers*) 1000° C.  200 nm  120 nm  Polydispers*) *)Size and form are not controlled, dispersity is large, NPs are formed from very small (few nm) to very large (few 100 nm) at the same time in the same process.

[0080] With whey, smaller nanoparticles are possible, compared to EG-manufactured ones (see Table 2). A larger range of different sizes of ZnO NPs can be produced in a reproducible manner using whey. The size of the ZnO nanoparticles is a function of the temperature, pH and concentration of the whey. Consequently, a larger variation of the bandgap is possible as compared to EG produced ZnO NPs. This manifests itself in a variation of the optical absorption spectrum.

[0081] Ethylene glycol is a petroleum-based material, while whey is a renewable, sustainable product as well as a side product from cheese production. Using whey allows recycling of waste from the dairy industry. Whey is rich in protein and sucrose. The sol-gel method is the method chosen for the synthesis of nanoparticles.

Example 4: Characterization of ZnO Nanoparticles

[0082] Table 3 presents the average crystallite sizes and lattice parameters for ZnO samples produced by calcination at different temperatures. TEM: Transmission electronic microscopy, XRF: X-ray fluorescence spectroscopy, XRD: X-ray diffraction.

TABLE-US-00003 TABLE 3 Grain size- TEM Crystallite size - Lattice constants (nm) Unit cell Nomenclature T (° C.) (nm) XRD (nm) a = b c volume (nm.sup.3) ZnO-1 400 20.5 18.3 3.2511(8) 5.2110(8) 47.702 ZnO-2 600 36.1 33.7 3.2497(9) 5.2102(7) 47.654 ZnO-3 800 72.0 75.1 3.2531(4) 5.2108(9) 47.758 ZnO-4 1000 120.1 88.6 3.2500(7) 5.2101(8) 47.661

TABLE-US-00004 ZnO-1 ZnO-2 ZnO-3 Mg 0.07 0.12 0.07 Al 0.03 0.05 0.03 Si 0.04 0.09 0.06 P 0.39 0.61 0.37 S 0.05 0.10 0.06 K 1.76 1.45 0.89 Ca 0.52 0.69 0.54 Fe Nd 0.01 Nd Ti 0.01 Nd Nd Ni Tr 0.01 0.01 Zn 97.13 96.87 97.91 Ag Nd Nd 0.06 Mo Nd 0.01 Nd Total 100.00 100.00 100.00

[0083] Table 4 shows XRF data of the ZnO nanoparticles calcined at different temperatures. Nd stands for not detectable and Tr stands for traces.

[0084] Thermogravimetric (TGA) and differential thermal analysis (DTA) of the ZnO xerogels are shown in FIG. 4.

[0085] FIG. 5 shows the XRD patterns (crystalline structure) of the ZnO nanoparticles calcined at different temperatures. FIG. 6 presents the Raman spectra of the ZnO nanoparticles in the spectral range of 200-1000 cm.sup.−1. FIG. 7 shows an EDS spectrum.