Method of preparation of zinc-oxygen-based nanoparticles, zinc peroxide nanoparticles obtained by this method and their use
20230312342 · 2023-10-05
Inventors
- Malgorzata WOLSKA-PIETKIEWICZ (Warsaw, PL)
- Maria JEDRZEJEWSKA (Warsaw, PL)
- Emil BOJARSKI (Warsaw, PL)
- Janusz LEWINSKI (Josefow, PL)
Cpc classification
C01P2002/72
CHEMISTRY; METALLURGY
C01P2004/51
CHEMISTRY; METALLURGY
C01P2004/62
CHEMISTRY; METALLURGY
C01P2004/64
CHEMISTRY; METALLURGY
International classification
Abstract
The subject matter of the invention is a method of preparation of zinc-oxygen-based nanoparticles, in which the organozinc precursor is treated with an oxidizing agent, wherein the organozinc precursor is a compound of the formula (R).sub.n(Zn).sub.m(L).sub.y(X).sub.z, where: R is straight, branched or cyclic C1-C10 alkyl group or straight, branched or cyclic C1-C10 alkenyl group, benzyl group, phenyl group, mesityl group, in which any hydrogen atom may be substituted with fluorine, chlorine, bromine or iodine atom; L is neutral donor organic ligand selected from the group of organic compounds including amine, phosphine, phosphine oxide, sulfoxide, ketone, amide, imine, ether, urea and its organic derivatives, aminosilane or perfluorinated derivatives thereof, or mixtures thereof; X is monoanionic organic ligand derived from the organic compound X-H, where H is a hydrogen atom with acidic properties and the compound X-H is carboxylic acid, amide, amine, imide, alcohol, mono- or diester of phosphoric acid, organic derivatives of phosphinic or phosphonic acid, phenol, mercaptan, hydroxy acid, amino acid, hydroxy amide, amino amide, hydroxy ester, amino ester, hydroxy ketone, amino ketone, urea and its organic derivatives, silanol, aminosilane, mercaptosilane and organic derivatives of alkoxysilane or perfluorinated derivatives thereof, or mixtures thereof; m and n are integers from 1 to 10; y and z are integers from 0 to 10, wherein the oxidizing agent is hydrogen peroxide, peracetic acid or ozone, and the organozinc precursor is treated with the oxidizing agent under an inert gas atmosphere.
The invention also relates to zinc peroxide nanoparticles prepared by the above-defined method and their use as antibacterial and bacteriostatic materials, as a component of pyrotechnic compositions, photocatalyst, and single-source inorganic precursors of nanoparticulate forms of zinc oxide (ZnO).
Claims
1. A method of preparation of zinc-oxygen-based nanoparticles, in which an organozinc precursor is treated with an oxidizing agent, characterized in that the organozinc precursor is a compound of the formula (R).sub.n(Zn).sub.m(L).sub.y(X).sub.z wherein R is at least one subset of a set comprising straight, branched, and cyclic C1-C10 alkyl groups, straight, branched, and cyclic C1-C10 alkenyl groups, a benzyl group, a phenyl group, and a mesityl group, wherein any hydrogen atom can be substituted with at least one subset of a set comprising fluorine, chlorine, bromine and iodine atoms, and wherein L is a neutral donor organic ligand selected from the group of organic compounds including at least one subset of a set comprising amine, phosphine, phosphine oxide, sulfoxide, ketone, amide, imine, ether, urea and related organic derivatives, aminosilane or perfluorinated derivatives thereof, and mixtures thereof, and wherein X is monoanionic organic ligand derived from the organic compound X-H, wherein H is a hydrogen atom with acidic properties and the compound X-H is at least one of a set comprising carboxylic acid, amide, amine, imide, alcohol, mono- or diester of phosphoric acid, organic derivatives of phosphinic or phosphonic acid, phenol, mercaptan, hydroxy acid, amino acid, hydroxy amide, amino amide, hydroxy ester, amino ester, hydroxy ketone, amino ketone, urea and its organic derivatives, silanol, aminosilane, mercaptosilane and organic derivatives of alkoxysilane or perfluorinated derivatives thereof, and a mixtures thereof, and wherein m and n are integers from 1 to 10, and wherein y and z are integers from 0 to 10, and wherein the oxidizing agent is at least one of hydrogen peroxide, peracetic acid, and ozone, and wherein the organozinc precursor is treated with the oxidizing agent under an inert gas atmosphere.
2. The method of claim 1 characterized in that at least one of a set comprising achiral, optically active, and organic compounds with an additional positive charge located at at least one of a set comprising nitrogen (N), phosphorus (P), and sulfur (S) atoms are used as L- and X-type ligands.
3. The method of claim 1 characterized in that at least one of a set comprising zinc peroxide (ZnO.sub.2) nanoparticles and zinc oxide (ZnO) nanoparticles are prepared.
4. The method of claim 1 characterized in that uncoated zinc-oxygen-based nanoparticles are prepared.
5. The method of claim 1 characterized in that zinc-oxygen-based nanoparticles are coated with an organic shell composed of at least one organic ligand selected from X and L, preferably zinc-oxygen-based nanoparticles coated with an organic shell composed of two or more organic ligands selected from X and L.
6. The method of claim 1 characterized in that zinc-oxygen-based nanoparticles with a diameter less than or equal to 5 nm are prepared.
7. The method of claim 1 characterized in that at least one of a set comprising dialkyl- and diarylzinc compound of the formula R.sub.2Zn, wherein R is at least one subset of a set comprising straight, branched, and cyclic C1-C10 alkyl group and straight, branched, and cyclic C1-C10 alkenyl group, a benzyl group, a phenyl group, and a mesityl group, in which any hydrogen atom may be substituted with at least one of a set comprising fluorine, chlorine, bromine, and iodine atoms is used as organozinc precursor.
8. The method of claim 1 characterized in that the organozinc precursor is a compound produced by the reaction between at least one of a set comprising dialkyl- and diarylzinc compound of the formula R.sub.2Zn and an organic L- or X-H-type compound, and a mixture of two or more of these compounds, wherein: R is at least one subset of a set comprising straight, branched, and cyclic C1-C10 alkyl group, straight, branched or cyclic C1-C10 alkenyl group, a benzyl group, a phenyl group, and a mesityl group in which any hydrogen atom may be substituted with at least one of a set comprising fluorine, chlorine, bromine, and iodine atoms; L is at least one of a set comprising amine, phosphine, phosphine oxide, sulfoxide, ketone, amide, imine, ether, urea and its organic derivatives, aminosilane or perfluorinated derivatives thereof, and mixtures thereof; and X-H is a at least one of a set comprising carboxylic acid, amide, amine, imide, alcohol, mono- or diester of phosphoric acid, organic derivatives of phosphinic or phosphonic acid, phenol, mercaptan, hydroxy acid, amino acid, hydroxy amide, amino amide, hydroxy ester, amino ester, hydroxy ketone, amino ketone, urea and its organic derivatives, silanol, aminosilane, mercaptosilane and organic derivatives of alkoxysilane or perfluorinated derivatives thereof, and mixtures thereof.
9. The method of claim 8 characterized in that at least one of a set comprising homoligand precursor or a heteroligand precursor and mixtures thereof is used as organozinc precursor.
10. The method of claim 8 characterized in that at least one of a set comprising diethylzinc, dimethylzinc, di-iso-propylzinc, di-tert-buthylzinc, dicyclopentylzinc, dicyclohexylzinc and dicyclopentadienylzinc are used as dialkylzinc compound.
11. The method of claim 8 characterized in that at least one of a set comprising diphenylzinc and bis (pentafluorophenyl) zinc is used as a diarylzinc compound.
12. The method of claim 1 characterized in that hydrogen peroxide in the form of at least one of a set comprising an aqueous solution and in the form of a solid-state peroxide adduct is used as an oxidizing agent, preferably hydrogen peroxide in the form of the aqueous solution at a concentration in the range from 1 to 75% is used, more preferably hydrogen peroxide in the form of the aqueous solution at a concentration in the range from 3 to 30% is used, most preferably hydrogen peroxide in the form of the aqueous solution at the concentration of 30% is used.
13. The method of claim 12 characterized in that at least one of a set comprising hydrogen peroxide-urea adduct (CO(NH.sub.2).sub.2.Math.H.sub.2O.sub.2) and sodium percarbonate (Na.sub.2CO.sub.3.Math.1.5H.sub.2O.sub.2) is used as a peroxide adduct.
14. The method of claim 1 characterized in that a molar ratio of the organozinc precursor to the oxidizing agent ranges from 1:1 to 1:4 is used, preferably the molar ratio of the organozinc precursor to the oxidizing agent equals 1:1 is used.
15. The method of claim 1 characterized in that the organozinc precursor is treated with the oxidizing agent in an aprotic organic solvent or the reaction is carried out by a mechanochemical, i.e., solvent-free approach.
16. The method of claim 15 characterized in that anhydrous or water-containing solvent is used as an aprotic organic solvent, preferably at least one of a set comprising anhydrous and water-containing solvent is used as aprotic organic solvent, wherein with respect to the water-containing solvent, the preferably concentration of water in the solvent is less than 0.5%.
17. The method of claim 16 characterized in that at least one of a set comprising tetrahydrofuran, toluene, xylene, benzene, dimethylsulfoxide, dichloromethane, dioxane, acetonitrile, chloroform, hexane, acetone, diethyl ether, and mixtures thereof are used as aprotic organic solvent.
18. The method of claim 1 characterized in that molar concentration of the organozinc precursor in the reaction mixture ranges from 0.01 mol/L to 0.5 mol/L.
19. The method of claim 1 characterized in that the method is carried out by a mechanochemical, i.e., solvent-free approach.
20. The method of claims 1 wherein zinc peroxide nanoparticles are prepared.
21. The method of claim 20 wherein zinc peroxide nanoparticles are uncoated or coated with an organic shell.
22. The method of claims 21 wherein zinc peroxide nanoparticles are characterized in that the organic shell is composed of at least one organic ligand selected from X and L.
23. The use of zinc peroxide nanoparticles of claims 21 as antibacterial and bacteriostatic materials, or as a component of pyrotechnic compositions, or as photocatalyst, or as single-source inorganic precursors of nanoparticulate forms of zinc oxide (ZnO).
Description
[0071] The results concerning zinc-oxygen-based nanoparticles prepared by the method of the invention are shown in the figure, where:
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[0140] The following examples present the subjects of the invention.
[0141] In all examples, anhydrous solvents pre-dried over molecular sieves, heated with a potassium-sodium alloy and distilled in an atmosphere of dry and oxygen-free inert gas or purified in a solvent purification system (SPS) were used, and depending on the cleaning conditions, they may contain insignificant amounts of water, i.e., less than 0.5%. In all examples, except for Example 4, commercially available dialkyl- or diarylzinc compounds were used with the purity declared by the manufacturer as technical grade (90-99%). The applied in the examples term ambient temperature means a temperature in the range from 10° C. to 30° C., and room temperature means a temperature in the range from 22° C. to 27° C. The resulting materials were characterized by a wide range of analytical techniques, such as transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and dynamic light scattering (DLS).
[0142] The abbreviations ZnO.sub.2 NPs and ZnO NPs used throughout the description refer to nanoparticles of zinc peroxide and nanoparticles of zinc oxide, respectively.
EXAMPLE 1
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et2.Zn and Perhydrol in an Aprotic Organic Solvent
[0143] 10 mL of anhydrous solvent - tetrahydrofuran (THF) was introduced into a Schlenk vessel (V = 100 cm.sup.3) equipped with a magnetic stir bar and cooled to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (30% aqueous solution of H.sub.2O.sub.2, 1 mmol H.sub.2O.sub.2) were then added dropwise via a syringe and under an inert gas atmosphere. Initially the reaction was carried out at -78° C. for ca. 10 minutes. Then the reaction mixture was allowed to gradually warm to room temperature and left at this temperature for additional 30 minutes. After this time, the product in the form of a white precipitate, which is nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(1) NPs), was obtained and characterized. TEM micrographs of the resulting ZnO.sub.2 nanoparticles as well as size distribution of ZnO.sub.2(1) NPs are shown in
EXAMPLE 2
Preparation of ZnO.SUB.2 NPs in a Reaction Between iPr2.Zn and Perhydrol in an Aprotic Organic Solvent
[0144] iPr.sub.2Zn (1 mL of a 1 M solution in toluene, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were successively added dropwise to 10 mL of solvent mixture (5 mL of THF + 5 mL of hexane) placed in a Schlenk vessel, vigorously stirred with a magnetic stir bar and cooled to -10° C. The reaction was carried out at -10° C. for ca. 5 minutes. Then the reaction mixture was allowed to reach room temperature and stirred at this temperature for additional 24 hours. As a result, nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(2) NPs) was obtained and the crystal structure of the resulting product was then confirmed using PXRD (Error! Reference source not found. a; the average size of nanocrystallites is 3.36 ± 0.37 nm). Nanocrystalline ZnO.sub.2(2) decomposes into ZnO at 214° C. (Error! Reference source not found. b). Similar results have been obtained using other dilalkylzinc compounds such as dimethylzinc, di-tert-butylzinc, dicyclopentylzinc, dicyclohexylzinc or dicyclopentadienylzinc.
EXAMPLE 3
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et2.Zn and Perhydrol in an Aprotic Organic Solvent
[0145] Et.sub.2Zn (1 mL of a 1 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were successively added dropwise to 10 mL of hexane placed in a Schlenk vessel, vigorously stirred with a magnetic stir bar and cooled to -78° C. The reaction mixture was left at -78° C. for a few minutes and then warmed to room temperature and stirred for additional 30 minutes. ZnO.sub.2(3) nanoparticles were obtained as a white solid, which was then decanted and dried under vacuum. PXRD analysis confirmed the nanocrystalline cubic crystal structure of ZnO.sub.2(3) (Error! Reference source not found. a; the average size of nanocrystallites is 2.26 ± 0.24 nm). Thermolysis of ZnO.sub.2(3) NPs occurs with a maximum decomposition rate at 158° C. and the decomposition process is finished at ca. 400° C. (
EXAMPLE 4
Preparation of ZnO.SUB.2 NPs in a Reaction Between High Purity Et2.Zn (99.9998%) and Perhydrol
[0146] The reaction between high purity Et.sub.2Zn (99.9998%) and perhydrol was carried out according to the procedure described in Example 3 leads to the formation of nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(4) NPs) with physicochemical properties similar to ZnO.sub.2(1) and ZnO.sub.2(3)NPs. The average size of nanocrystallites calculated from Scherrer’s formula is 3.2 ± 0.21 nm. The lack of additional diffraction peaks proves the high purity of the tested material (Error! Reference source not found. a). FTIR analysis revealed the presence of IR bands characteristic of Zn—O (403 cm.sup.-1) and O—O (1487 and 1376 cm.sup.-1) species that are present in the structure of ZnO.sub.2(4). The thermal stability of the product was determined by thermogravimetric analysis. Decomposition of nanocrystalline ZnO.sub.2(4) occurs with a maximum decomposition rate at 210° C., which indicates the quantitative transformation of ZnO.sub.2 to ZnO (Error! Reference source not found. b).
EXAMPLE 5
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et.SUB.2.Zn and CO(NH.SUB.2.).SUB.2..Math.H.SUB.2.O2 in a Molar Ratio of 1:3
[0147] 282 mg (3 mmol) of hydrogen peroxide-urea adduct (CO(NH.sub.2).sub.2.Math.H.sub.2O.sub.2) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) was then added dropwise via a syringe and under an inert gas atmosphere. The reaction was carried out at -78° C. for ca. 20 minutes. Then the reaction mixture was allowed to spontaneously warm to ambient temperature and stirred at this temperature for additional 24 hours. Hereby, the product was obtained as a yellow precipitate, which was then decanted, purified by washing the resulting product two times with a small portions of ethanol and centrifugated (9000 rpm, 10 minutes). Nanocrystalline zinc peroxide (ZnO.sub.2(5) NPs) with a mean core size of 1.71 ± 0.21 nm was identified by PXRD (Error! Reference source not found. a). The lack of additional peaks on the diffraction pattern proves the high purity of the tested sample. Slight changes in the intensity and the bands’ position corresponding to C═O and N—H moieties, respectively, demonstrate the possible coordination of both the carbonyl and the amine groups on the surface of the resulting ZnO.sub.2 NPs (Error! Reference source not found. b). Thermogravimetric analysis of ZnO.sub.2(5) NPs indicates more complex nature of the decomposition profile of the tested system compared to those presented in the previous examples. Thermal decomposition of urea (which is a compound with a low melting point, i.e., ~133° C., and quickly decomposes at higher temperatures) occurs at 149° C., while the transformation of ZnO.sub.2 to ZnO begins at higher temperatures with a maximum decomposition rate at 214° C. (
EXAMPLE 6
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of Butyric Acid - One-Step Approach
[0148] 88 mg (1 mmol) of butyric acid (C.sub.3H.sub.7COOH) or 214 mg (1 mmol) of heptafluorobutyric acid (C.sub.3F.sub.7COOH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. After a while, the cooling bath was removed and the reaction mixture was allowed to spontaneously warm to ambient temperature and stirred at this temperature for additional 24 hours. A clear stable colloidal solution of ZnO.sub.2 nanoparticles (ZnO.sub.2(6) NPs) was obtained. The reaction product was precipitated from the post-reaction system using hexane (ca. 5 mL) and isolated by centrifugation (9000 rpm, 10 minutes). The resulting sediment was then washed with a small portion of hexane (2 mL), re-centrifuged and dried under vacuum. PXRD analysis (Error! Reference source not found.) confirmed the nanocrystalline cubic crystal structure of ZnO.sub.2(6) NPs and the average core size was determined to be 2.29 ± 0.31 nm. The lack of additional peaks on the diffraction pattern proves the high purity of the tested sample. Similar results have been obtained using glycine and 2-hydroxypropanoic acid. DLS analysis showed that the average solvodynamic diameter of the ZnO.sub.2(6) nanoparticles is 4.63 nm. Moreover, a low degree of polydispersity index (PdI = 0.157) indicated a narrow size distribution and high colloidal stability of ZnO.sub.2(6) NPs (Error! Reference source not found.). FTIR analysis confirmed the presence of an organic shell composed of deprotonated butyric acid molecules on the surface of nanocrystalline ZnO.sub.2 (Error! Reference source not found. a). Absence of a band characteristic for C═O stretching vibrations in the butyric acid molecule (1712 cm.sup.-1) and the appearance of the asymmetric v.sub.as(COO.sup.-) and the symmetric v.sub.s(COO.sup.-) stretches at 1569 and 1406 cm.sup.-1 (Δv = 163 cm.sup.-1), respectively, indicates that monoanionic carboxylate moieties bound to the ZnO.sub.2(6) NPs surface and act as bridging bidentate .Math..sub.2-type ligands. The decomposition temperature of ZnO.sub.2 into ZnO is 204° C. We also noted that at higher temperatures (i.e., above 250° C.) the organic shell of ZnO.sub.2(6) NPs decomposes (Error! Reference source not found. b).
EXAMPLE 7
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of Butyric Acid - Two-Step Approach
[0149] In the first step, 88 mg (1 mmol) of butyric acid in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (0.34 mL of a 3 M solution in hexane, 1 mmol) was then added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at a reduced temperature and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 3 hours. After this time, the molecular structure of the resulting product in the form of an ethylzinc derivative of butyric acid was confirmed by spectroscopic methods. In the next step, 0.1 mL of 30% aqueous solution of H.sub.2O.sub.2 (1 mmol) was added dropwise to the as-prepared organozinc precursor solution cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. The reaction mixture was allowed to gradually warm to room temperature and stirred at this temperature for additional 12 hours. Then a clear stable solution was obtained. Product in the form of nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(7) NPs) was isolated from the post-reaction mixture and purified according to the method described in Example 6. TEM micrographs of the resulting ZnO.sub.2 nanoparticles as well as the size distribution of ZnO.sub.2(7) NPs are shown in Error! Reference source not found.. The micrographs show quasi-spherical ZnO.sub.2 nanocrystallites with a core size of a few nanometers (ca. 2 - 5.5 nm) and a mean core diameter of 3.66 ± 0.79 nm (Error! Reference source not found. f). The average core size of ZnO.sub.2(7) determined by PXRD (Error! Reference source not found.) is 2.11 ± 0.19 nm. Similar results have been obtained using glycine and 2-hydroxypropanoic acid.
EXAMPLE 8
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Phenylacetate Ligands
[0150] 136 mg (1 mmol) of phenylacetic acid (C.sub.7H.sub.7COOH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice -isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. The reaction was carried out at -78° C. for ca. 10 minutes. Then the reaction mixture was allowed to spontaneously warm to ambient temperature and stirred at this temperature for additional 24 hours. A clear, stable solution was obtained. The reaction product was isolated and purified according to the method described in Example 6 as well as identified as nanocrystalline zinc peroxide (from now on termed (ZnO.sub.2(8) NPs) (Error! Reference source not found.). The average core size of ZnO.sub.2 is 2.24 ± 0.23 nm. DLS analysis in THF confirmed the monodispersity of the tested system (PdI = 0.168) and the solvodynamic diameter equal to 5.55 nm (Error! Reference source not found.). FTIR analysis revealed the presence of an organic shell composed of deprotonated phenylacetic acid molecules attached to the surface of the nanocrystalline ZnO.sub.2 core (Error! Reference source not found. a). The thermal decomposition of this material shown in
EXAMPLE 9
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of 2-(2-methoxyethoxy)acetic Acid or Monoanionic Derivatives of Betaine
[0151] 134 mg (1 mmol) 2-methoxyethoxy)acetic acid (CH.sub.3OCH.sub.2CH.sub.2OCH.sub.2COOH) or 117 mg (1 mmol) of betaine (i.e., zwitterion compound with an positively charged cationic functional quaternary ammonium group - (CH.sub.3).sub.3N.sup.+CH.sub.2CO.sub.2-) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled to 0° C. and Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. The reaction was carried out at 0° C. for ca. 1 hour. Then the reaction mixture was allowed to reach ambient temperature and stirred at this temperature for additional 24 hours. After this time, a stable slightly turbid colloid was obtained and nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(9) NPs) was precipitated after the addition of 5 mL of ethanol and isolated from the resulting mixture by centrifugation (9000 rpm, 10 minutes). The resulting sediment was washed with a small portion of ethanol (2 mL), re-centrifuged and dried under vacuum. PXRD analysis confirmed the nanocrystalline, cubic crystal structure of the resulting ZnO.sub.2 and the average core size of crystallites is 1.96 ± 0.17 nm (Error! Reference source not found.). Solvodynamic diameter of ZnO.sub.2(9) NPs is 4.83 nm (PdI = 0.082) (Error! Reference source not found.). The presence of a stable and strongly bound protective layer on the surface of ZnO.sub.2 composed of carboxylate ligands was confirmed by FTIR method. ZnO.sub.2(9) NPs form stable colloidal solutions or stable suspensions in organic solvents such as THF, toluene, hexane, methanol, ethanol, DMSO, dichloromethane, ethyl acetate, diethyl ether and acetone as well as in water (Error! Reference source not found.). Likewise, betaine-coated ZnO.sub.2 NPs form stable dispersions in a wide range of organic solvents and water.
EXAMPLE 10
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of S-(+)-2-amino-1-phenylethanol
[0152] In the first step, 137 mg (1 mmol) of S-(+)-2-amino-1-phenylethanol (C.sub.6H.sub.5CH(OH)CH.sub.2(NH.sub.2) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. Then the resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at -78° C. for ca. 10 minutes and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. After this time, the molecular structure of the resulting product in the form of an ethyl zinc derivative of S-(+)-2-amino-1-phenylethanol was confirmed by spectroscopic methods. In the next step, 0.1 mL of 30% aqueous solution of H.sub.2O.sub.2 (1 mmol) was added dropwise to the as-prepared organozinc precursor solution cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. Then the reaction mixture was allowed to gradually warm to room temperature and stirred at ambient temperature for additional 24 hours (note that the reaction time can be shortened by heating the reaction mixture at reflux temperature, i.e., 65° C. - 70° C. for 3 - 4 hours). After that, a stable slightly turbid colloid was obtained. The product in the form of nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(10) NPs) was isolated from the post-reaction mixture and purified according to the method described in Example 6. The average core size of ZnO.sub.2(10) determined by PXRD (Error! Reference source not found.) is 2.55 ± 0.33 nm and the solvodynamic diameter of the associates present in the solution is 25.54 nm (PdI = 0.169) (Error! Reference source not found.). TGA profile shown in Error! Reference source not found. exhibits two main decomposition steps with maximum decomposition rates at 214° C. and 439° C., respectively, and the thermolysis is finished at ~ 450° C. with a total weight loss of 44.24%.
EXAMPLE 11
Preparation of ZnO.SUB.2 NPs Coated With Diphenyl Phosphate Ligands
[0153] 250 mg (1 mmol) of diphenyl phosphate ((C.sub.6H.sub.5O).sub.2P(O)OH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Similar results can be obtained using a crystalline organozinc precursor of the formula [tBuZn(O.sub.2P(OPh).sub.2].sub.4. Initially the reaction was carried out at -78° C. for ca. 10 minutes and then it was allowed to gradually warm to ambient temperature and stirred at this temperature for additional 4 hours. After this time, a colorless solution was obtained. The reaction product was then isolated and purified according to the method described in Example 6 and identified as nanocrystalline zinc peroxide (from now on termed ZnOz(11) NPs) with a small core size equal to 1.60 ± 0.10 nm (Error! Reference source not found.). Similar results have been obtained using other organophosphorous compounds such as phenyl dihydrogen phosphate, diphenylphosphinic acid or phenylphosphonic acid.
EXAMPLE 12
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of Myristic Acid
[0154] In the first step, 228 mg (1 mmol) of myristic acid (CH.sub.3(CH.sub.2).sub.12COOH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) was then added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at the temperature of the cooling bath and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 5 hours. After this time, the molecular structure of the resulting product in the form of an ethyl zinc derivative of myristic acid was confirmed by spectroscopic methods. In the next step, 0.2 mL of 15% aqueous solution of H.sub.2O.sub.2 (1 mmol) was added dropwise to the as-prepared organozinc precursor cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. Then the reaction mixture was allowed to gradually warm to room temperature and stirred at ambient temperature for one day. After this time, a clear solution was obtained. Product in the form of nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(12) NPs) was isolated from the post-reaction mixture and purified according to the method described in Example 6. PXRD analysis (Error! Reference source not found.) confirmed the nanocrystalline structure of the resulting nanoparticles and the average core size was determined to be 2.01 ± 0.13 nm. The solvodynamic diameter of ZnO.sub.2(12) NPs in THF is 5.98 nm and the resulting solution is characterized by high colloidal stability and monodispersity (PdI = 0.122) (Error! Reference source not found.). Absence of a band characteristic for C=O stretching vibrations in the myristic acid molecule (~ 1700 cm.sup.-1) and the appearance of the asymmetric v.sub.as(COO.sup.-) and the symmetric v.sub.s(COO.sup.-) stretches at 1581 and 1416 cm.sup.-1 (Δv = 165 cm.sup.- .sup.1), respectively, indicates the presence of monoanionic carboxylate ligand bound to the surface of ZnO.sub.2(12) NPs.
EXAMPLE 13
Preparation of ZnO.SUB.2 NPs Using Ethylzinc Derivative of Propionamide as a Precursor
[0155] In the first step, 73 mg (1 mmol) of propionamide (CH.sub.3CH.sub.2CONH.sub.2) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C., and Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) was then added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at a reduced temperature and then it was allowed to gradually warm to ambient temperature and stirred at this temperature for additional 3 hours. After this time, the molecular structure of the resulting [EtZn—X]—type precursor (where X - monoanionic propionamide ligand) was confirmed by spectroscopic methods. In the next step, 1 mL of a 3% aqueous solution of H.sub.2O.sub.2 (1 mmol) was added dropwise to the in situ generated organozinc precursor cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. Then the reaction mixture was allowed to gradually warm to room temperature and stirred at ambient temperature for one day. After this time, nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(13) NPs) was obtained in the form of a precipitate, which was isolated from the post-reaction mixture by centrifugation (9000 rpm, 10 minutes). Similar ZnO.sub.2 NPs have been obtained using phthalimide, dicyclohexylurea and cysteine. The resulting sediment was then washed two times with a small portion of hexane (2 mL), re-centrifuged and dried under reduced pressure. The average core size of ZnO.sub.2(13) NPs determined by PXRD (Error! Reference source not found.) is 2.48 ± 0.29 nm. Thermolysis of nanocrystalline ZnO.sub.2(13) is a complex and multi-stage process. TGA profile shown in
EXAMPLE 14
Preparation of ZnO.SUB.2 NPs Coated With an Organic Shell Composed of Monoanionic Derivatives of 2,2-dimethyl-1-propanol
[0156] In the first step, 88 mg (1 mmol) of 2,2-dimethyl-1-propanol ((CH.sub.3).sub.3CCH.sub.2OH) or 182 mg (0.25 mmol) of [EtZn(OCH.sub.2C(CH.sub.3).sub.3)].sub.4 in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar and cooled in a dry ice - isopropyl alcohol bath. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at out at the temperature of the cooling bath for ca. 15 minutes and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. After this time, product as a precipitate falling to the vessel’s bottom was obtained and then purified according to the procedure described in Example 6. Based on PXRD, the reaction product was identified as nanocrystalline zinc peroxide (from now on termed ZnO.sub.2(14) NPs) with a relatively small core size equal to 3.03 ± 0.10 nm (Error! Reference source not found.) and coated with organic shell (Error! Reference source not found.). DLS measurements for the colloidal solution of ZnO.sub.2(14) NPs in DMSO confirmed the presence of associates with an average size of 133.6 nm and the polydispersity index equal to 0.161 (Error! Reference source not found.). The presence of IR band located in the area of 3300 cm.sup.-1 corresponds to O—H stretching vibrations, which indicates the adsorption of water molecules and the parent alcohol on the surface of nanoparticles. Thermal decomposition shown in
EXAMPLE 15
Preparation of ZnO.SUB.2 NPs Coated with Triethylene Glycol Monomethyl Ether
[0157] 164 mg (1 mmol) of triethylene glycol monomethyl ether (CH.sub.3O(CH.sub.2CH.sub.2O).sub.3CH.sub.2CH.sub.2OH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at a reduced temperature and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. Nanocrystalline zinc peroxide (ZnO.sub.2(15) NPs) was obtained as a precipitate falling to the vessel’s bottom and then purified according to the procedure described in Example 6. The average size of nanocrystallites calculated from Scherrer’s formula is 2.29 ± 0.16 nm, and the lack of additional peaks on the diffraction pattern proves the high purity of the tested material (Error! Reference source not found.). DLS measurements confirmed that the solvodynamic diameter of ZnO.sub.2 NPs dispersed in DMSO is 68.2 nm, which indicates the presence of small soft-type associates. The colloidal solution of ZnO.sub.2(15) NPs is characterized by monodispersity (PdI ═ 0.095) and high stability both in organic solvents and in water (Error! Reference source not found.).
EXAMPLE 16
Preparation of ZnO.SUB.2 NPs Coated With N-(2-aminoethyl)-3-aminopropyltrimethoxysilane
[0158] 222 mg (1 mmol) of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (C.sub.8H.sub.22N.sub.2O.sub.3Si.sub.2) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Immediately after mixing the reactants (i.e., after ca. 5 seconds) the reaction mixture was allowed to gradually warm to ambient temperature and stirred for additional hour. The reaction product was obtained as a precipitate falling to the vessel’s bottom, which was then purified according to the procedure described in Example 6 and identified as nanocrystalline zinc peroxide (ZnO.sub.2(16) NPs) (Error! Reference source not found.). Broadening of diffraction peaks indicates the relatively small size of the resulting nanocrystallites (d < 1 nm). Example 17.
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et2.Zn (99.9998%) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and Perhydrol in a Molar Ratio of 1:2:2
[0159] 167 mg (1 mmol) of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (C.sub.8H.sub.22N.sub.2O.sub.3Si.sub.2) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.75 mL of a 2 M solution in hexane, 1.5 mmol) and 0.15 mL of perhydrol (1.5 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at -78° C. and then it was allowed to gradually warm to room temperature and stirred at this temperature for an additional one hour. The reaction product was obtained as a precipitate falling to the vessel’s bottom, which was then purified according to the procedure described in Example 6 and identified as nanocrystalline zinc peroxide (ZnO.sub.2(17) NPs) (Error! Reference source not found. a) with a mean core size equal to 1.56 ± 0.24 nm. FTIR analysis revealed the presence of IR bands corresponding to the Si—O vibrations (1044, 1013 cm.sup.-1) and thus confirmed the presence of the ligand shell on the surface of nanocrystalline ZnO.sub.2 (Error! Reference source not found. b).
EXAMPLE 18
Preparation of ZnO.SUB.2 NPs Coated With Neutral Donor Ligands From the Group of Sulfoxides, Ketones and Ethers
[0160] 78 mg (1 mmol) of dimethylsulfoxide ((CH.sub.3).sub.2SO) in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) was then added dropwise using a syringe and under an inert gas atmosphere and the resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Then 0.1 mL of 30% aqueous solution of H.sub.2O.sub.2 (1 mmol H.sub.2O.sub.2) was added dropwise to the system. Initially the reaction was carried out at the temperature of the cooling bath, which was removed after ca. 20 minutes, and then the reaction mixture was allowed to reach ambient temperature and stirred at this temperature for additional 24 hours. After this time, a stable suspension was obtained. In order to isolate ZnO.sub.2, 5 mL of acetone was added to the post-reaction mixture and centrifugated (9000 rpm, 10 minutes). Then the resulting precipitate was washed with a small portion of acetone (2 mL), re-centrifuged and dried. Nanocrystalline zinc peroxide (ZnO.sub.2(18) NPs) with a core size of 2.39 ± 0.22 nm was identified usig PXRD (Error! Reference source not found. a). The lack of additional peaks on the diffraction pattern proves the high purity of the tested product. FTIR analysis indicated the presence of —OH groups/water molecules and DMSO molecules coordinated to the surface of ZnO.sub.2(18) NPs. The quantitative thermal decomposition of ZnO.sub.2 into ZnO is at 196° C. (Error! Reference source not found. b). Similar results can be obtained using 1 mmol of acetone, fluoroacetone or diethyl ether, which also act as L-type stabilizing ligands, insted of dimethylsulfoxide.
EXAMPLE 19
Preparation of ZnO.SUB.2 NPs Coated With Triphenylphosphine or Triphenylphosphine Oxide Ligands
[0161] 262 mg (1 mmol) of triphenylphosphine ((C.sub.6H.sub.5).sub.3P) or 278 mg (1 mmol) of triphenylphosphine oxide ((C.sub.6H.sub.5O).sub.3P) in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol (1 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe at room temperature (ca. 22 - 27° C.) and under an inert gas atmosphere. The reaction mixture was stirred for one day. Then product was isolated from the post-reaction mixture and purified according to the procedure described in Example 6. PXRD data confirmed that nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(19) NPs) with a cubic crystal structure was obtained (Error! Reference source not found. a). Broadening of diffraction peaks indicates the relatively small size of the resulting nanocrystallites (d < 1 nm). FTIR analysis confirmed the presence of an organic shell composed of triphenylphosphine molecules as well as water molecules adsorbed of the surface of ZnO.sub.2(19) NPs (Error! Reference source not found. b).
EXAMPLE 20
Preparation of ZnO.SUB.2 NPs Coated with N-[3-(trimethoxysilyl)propyl]ethylenediamine
[0162] In the first step, 222 mg (1 mmol) of N-[3-(trimethoxysilyl)propyl]ethylenediamine ((CH.sub.3O).sub.3Si(CH.sub.2).sub.3NHCH.sub.2CH.sub.2NH.sub.2) in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. Then the resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) was then added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at a reduced temperature and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. After this time, the structure of the as-prepared product was confirmed by spectroscopic methods. In the next step, 0.1 mL of 30% aqueous solution of H.sub.2O.sub.2 (1 mmol) was added dropwise to the solution of the organozinc precursor cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. Immediately after adding the oxidizing agent, the reaction mixture was warmed to room temperature and stirred at this temperature for additional 24 hours. Nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(20) NPs) in the form of a precipitate was isolated using centrifugation (9000 rpm, 10 minutes) and then washed with a small portion of hexane (2 mL), re-centrifugated and dried. The inorganic core of ZnO.sub.2(20) NPs is characterized by a relatively small size of ca. 1 nm. (
EXAMPLE 21
Preparation of ZnO.SUB.2 NPs Coated With Octylamine Ligands
[0163] 129 mg (1 mmol) of octylamine (CH.sub.3(CH.sub.2).sub.7NH.sub.2) in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 0.1 mL of perhydrol were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at a reduced temperature and then it was allowed to gradually warm to room temperature and stirred at this temperature for 1 hour. The reaction product was isolated and purified according to the procedure described in Example 6 and then identified as nanocrystalline ZnO.sub.2 (ZnO.sub.2(21) NPs) using PXRD (Error! Reference source not found.). The average core size of ZnO.sub.2(21) nanoparticles is 2.15 ± 0.17 nm (Error! Reference source not found.) and the solvodynamic diameter measured in DMSO is 81.3 nm (PdI = 0.150) (Error! Reference source not found.). FTIR analysis (Error! Reference source not found.) confirmed the presence of an organic shell on the surface of nanocrystalline ZnO.sub.2(21) NPs.
EXAMPLE 22
Preparation of ZnO.SUB.2 NPs Coated With a Two-Component Ligand Shell Composed of Monoanionic Derivatives of Phenylacetic Acid and 2,2-dimethyl-1-propanol
[0164] 136 mg (1 mmol) of phenylacetic acid (C.sub.7H.sub.7COOH) and 88 mg (1 mmol) of 2,2-dimethyl-1-propanol in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled to -78° C. and Et.sub.2Zn (1 mL of a 2 M solution in hexane, 2 mmol) and 0.2 mL of perhydrol (2 mmol of H.sub.2O.sub.2) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at -78° C. for several minutes and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. After this time, a colorless solution was obtained and nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(22) NPs) was precipitated using 5 mL of hexane and isolated from the post-reaction mixture by centrifugation (9000 rpm, 10 minutes). The resulting precipitate was washed with a small portion of hexane (2 mL), re-centrifuged and dried. PXRD analysis confirmed the nanocrystalline, cubic crystal structure of the resulting ZnO.sub.2 with a crystallite size of 2.10 ± 0.15 nm (
EXAMPLE 23
Preparation of ZnO.SUB.2 NPs Coated With a Two-Component Ligand Shell Composed of Monoanionic Derivatives of Phenylacetic Acid and 2,2-dimethyl-1-propanol From Two Homoligand Organozinc Precursors
[0165] In the first step, organometallic precursors were prepared according to the following procedure. 136 mg (1 mmol) of phenylacetic acid (C.sub.7H.sub.7COOH) and 88 mg (1 mmol) of 2,2-dimethyl-1-propanol in 10 mL of anhydrous THF were placed in a separate Schlenk vessels (100 cm.sup.3) equipped with a magnetic stir bars. Reagents were cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (1 mL of a 2 M solution in hexane, 2 mmol) was then added dropwise to each vessel. Initially the reaction was carried out at out at the temperature of the cooling bath and then it was allowed to gradually warm to room temperature and stirred at this temperature for additional 2 hours. After this time, the entire volume of the reaction mixture containing the ethylzinc derivative of phenylacetic acid was transferred to the reaction mixture containing the ethylzinc derivative of 2,2-dimethyl-1-propanol using a disposable syringe and under inert conditions. Similar results could be obtained by using the appropriate amounts of the respective crystalline organozinc precursors, i.e., [EtZn(O.sub.2H.sub.7C.sub.8)].sub.n and [EtZn(OCH.sub.2C(CH.sub.3).sub.3)].sub.4 dissolved in the appropriate amount of an organic solvent (THF or toluene). The mixture with a final volume of 10 mL was stored at room temperature for additional 24 h. After this time, 0.2 mL of perhydrol (2 mmol of H.sub.2O.sub.2) was added to the reaction mixture cooled to -78° C. Then the reaction system was allowed to gradually warm to room temperature and left at this temperature for 24 hours (in the case of toluene, the reaction were carried out at 40° C. for 8 hours). The as-prepared ZnO.sub.2 nanoparticles are similar to ZnO.sub.2(22) NPs.
EXAMPLE 24
Preparation of ZnO.SUB.2 NPs Coated With a Two-Component Ligand Shell Composed of Monoanionic Derivatives of Phenylacetic Acid and 2,2-dimethyl-1-propanol From Two Heteroligand Organozinc Precursors
[0166] 136 mg (1 mmol) of phenylacetic acid (C.sub.7H.sub.7COOH) and 88 mg (1 mmol) of 2,2-dimethyl-1-propanol in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. Reagents were cooled in a dry ice - isopropyl alcohol bath to -78° C. and Et.sub.2Zn (1 mL of a 2 M solution in hexane, 2 mmol) was then added dropwise. Initially the reaction was carried out at the temperature of the cooling bath for ca. 1 hour and then the reaction mixture was allowed to gradually warm to room temperature and stirred at this temperature for additional 2 hours. After this time, the molecular structure of the resulting product in the form of heteroligand organozinc compound was confirmed by spectroscopic methods. In the next step, 0.1 mL of 30% aqueous solution of H.sub.2O.sub.2 (2 mmol) was added dropwise to the as-prepared organozinc precursor solution cooled to the temperature of a dry ice - isopropyl alcohol cooling bath. Then the reaction mixture was allowed to gradually warm to room temperature (ca. 3 h) and stirred at ambient temperature for additional 24 hours. In the above reaction, a product similar to ZnO.sub.2(22) NPs was obtained.
EXAMPLE 25
Preparation of ZnO.SUB.2 NPs Coated with a Two-Component Ligand Shell Composed Of Monoanionic Derivatives of Phenylacetic Acid and Octylamine
[0167] 136 mg (1 mmol) of phenylacetic acid (C.sub.7H.sub.7COOH) and 129 mg (1 mmol) of octylamine in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 2 mmol) and 0.1 mL of 75% aqueus solution of H.sub.2O.sub.2 (2 mmol) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Initially the reaction was carried out at -78° C. for ca. 10 minutes and then it was allowed to gradually warm to ambient temperature and stirred at this temperature for additional 24 hours. After this time, a colorless solution was obtained. The reaction product was purified according to the method described in Example 6 and identified as nanocrystalline zinc peroxide (from now on termed ZnO.sub.2(23) NPs) wit a core size equal to 2.06 ± 0.17 nm (Error! Reference source not found.) and solvodynamic diameter equal to 4.79 nm (PdI = 0.123) (Error! Reference source not found.). FTIR analysis shown in
EXAMPLE 26
Preparation of ZnO.SUB.2 NPs coated with a Two-Component Ligand Shell Composed of Octylamine and Triphenylphosphine
[0168] 129 mg (1 mmol) of octyalmine and 262 mg (1 mmol) of triphenylphosphine in 10 mL of anhydrous THF (the usage of water-containing solvent does not affect the properties of the resulting) was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 2 mmol) and 0.2 mL of 30% aqueous solution of H.sub.2O.sub.2 (2 mmol) were then sequentially added dropwise using a syringe and under an inert gas atmosphere. Then the reaction mixture was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. The reaction product was isolated and then purified according to the method described in Example 6. The presence of nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(24) NPs) with a mean core size equal to 1.97 ± 0.22 nm was confirmed using PXRD. The composition of the organic shell was determined on the basis of the IR spectrum shown in
EXAMPLE 27
Preparation of ZnO.SUB.2 NPs in a Reaction Between R2.Zn (R = Et, Cy) and Peracetic Acid
[0169] 0.2 mL (1 mmol) of peracetic acid solution (concentration = 40%; CH.sub.3COOOH) in 10 mL of THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 2 mmol) or Cy.sub.2Zn (1 mL of a 1 M solution in toluene, 1 mmol) was then added dropwise using a syringe and under an inert gas atmosphere. The reaction was carried out at -78° C. for ca. 40 minutes and then the reaction mixture was allowed to gradually warm to room temperature and stirred at this temperature for additional 1 hour. The resulting product in the form of sediment was purified according to the method described in Example 6. As a result, nanocrystalline ZnO.sub.2 (from now on termed ZnO.sub.2(25) NPs) was obtained and then the crystal structure of the resulting product was confirmed using PXRD (Error! Reference source not found. a). The average core size of ZnO.sub.2(25) is equal to 2.20 ± 0.15 nm, and FTIR analysis indicates the presence of acetate ligands bound to the surface of the as-prepared nanoparticles (Error! Reference source not found. b). Nanocrystalline ZnO.sub.2(25) decomposes into ZnO at 210° C. (with a total weight loss of ca. 15.4%), which is shown in Error! Reference source not found..
EXAMPLE 28
Annealing of ZnO.SUB.2.(3) NPs and its Transformation Into Nanocrystalline ZnO
[0170] 20 mg of ZnO.sub.2 NPs prepared according to the procedure described in Example 3 was placed in a glass vial and introduced into an oven pre-heated to a temperature of 200° C. The material was annealed at this temperature for 30 minutes. This process can be carried out both under anaerobic and aerobic conditions, without affecting the properties of the final product. The resulting material was allowed to gradually cool down to ambient temperature and characterized using PXRD. PXRD analysis revealed the presence of nanocrystalline ZnO with a wurtzite-type crystal structure and a crystallite size of 7.57 ± 0.94 nm (Error! Reference source not found.). The as-prepared ZnO NPs exhibit fluorescent properties both in the solid state as well as dispersed in a selected organic solvent. TEM micrographs of the resulting ZnO nanoparticles as well as their size distribution are shown in Error! Reference source not found.. The micrographs show single quasi-spherical ZnO nanocrystallites with a core size of a few nanometers (ca. 3.5 - 12 nm) as well as their bigger aggregates. Both the time and the temperature of annealing are parameters that should be adjusted to the starting ZnO.sub.2-type material and the values presented in this example are optimal for a larger group of nanocrystalline forms of ZnO.sub.2 (note that the annealing temperature should be in the range from 100° C. to 1000° C. and the time in the range from 1 minutes to 48 hours).
EXAMPLE 29
Grinding of ZnO.SUB.2.(3) NPs in a Ball Mill
[0171] 100 mg of ZnO.sub.2 NPs and steel ball with a diameter of 1 cm, acting as the grinding element, were placed in a steel ball mill with a capacity of 15 cm.sup.3. The mechanochemical transformation was carried out at a frequency of 30 Hz for 30 minutes (the mechanosynthesis process can be carried out both under anaerobic and aerobic conditions, since it does not affect the properties of the final product). Then the as-prepared product in the form of a white solid exhibiting luminescent under UV light irradation was characterized using PXRD. PXRD analysis confirmed the presence of both nanocrystalline ZnO with a wurtzite-type crystal structure and the residual phase of nanocrystalline zinc peroxide (
EXAMPLE 30
Annealing of ZnO.SUB.2.(5) NPs and its Transformation Into Nanocrystalline ZnO
[0172] 20 mg of ZnO.sub.2 NPs prepared according to the procedure described in Example 5 was placed in a glass vial and introduced into an oven pre-heated to a temperature of 200° C. The material was annealed at this temperature for 1 hour. As a result of high temperature treatment, the powder changed its color from light yellow to brown, which evidences, among others, partial degradation or the condensation reaction of the ligand on the NPs surface. The resulting material was gradually cool down to ambient temperature and characterized using PXRD (Error! Reference source not found. a). The resulting ZnO NPs exhibit fluorescence both in the solid state as well as dispersed in a selected organic solvent. Despite the partial decomposition of the organic layer, FTIR analysis (Error! Reference source not found. b) confirmed the presence of urea or its deriveatised in the tetsted material.
EXAMPLE 31
Annealing of ZnO.SUB.2.(6) NPs and its Transformation Into Nanocrystalline ZnO
[0173] 20 mg of ZnO.sub.2 NPs prepared according to the procedure described in Example 6 was placed in a glass vial and introduced into an oven pre-heated to a temperature of 180° C. The material was annealed at this temperature for 30 minutes and then allowed to reach ambient temperature. As a result of high temperature treatment, the powder changed its color from white to dark gray, which evidences, among others, partial degradation of the ligand on the NPs surface. The resulting product was cheracterized using PXRD. Diffractogram analysis indicated the presence of the nanocrystalline, wurtzite-type ZnO structure with a crystallite size of 7.31 ± 0.3 nm (Error! Reference source not found. a). The lack of diffraction pattern characteristic for the ZnO.sub.2 phase proves the complete decomposition of ZnO.sub.2 NPs into ZnO. Despite the partial decomposition of the organic layer, FTIR analysis confirmed the presence of an organic shell composed of deprotonated butyric acid molecules on the surface of nanocrystalline ZnO core (Error! Reference source not found. b), which is evidenced by the presence of relatively weak IR bands characteristic for the carboxylate ligands bound to the nanoparticles surface (1557 cm.sup.-.sup.1 and 1410 cm.sup.-1).
EXAMPLE 32
Annealing of ZnO.SUB.2.(8) NPs and its transformation into nanocrystalline ZnO
[0174] 20 mg of ZnO.sub.2 NPs prepared according to the procedure described in Example 8 was placed in a glass vial and introduced into an oven pre-heated to a temperature of 200° C. The material was annealed at this temperature for 30 minutes and then allowed to reach ambient temperature. The resulting product was cheracterized using PXRD (Error! Reference source not found. a). Diffractogram analysis indicated the presence of the nanocrystalline, wurtzite-type ZnO structure with a crystallite size of 3.35 ± 0.58 nm as well as the lack of diffraction pattern characteristic for the ZnO.sub.2. FTIR analysis confirmed the presence of an organic shell composed of deprotonated phenylacetate acid molecules on the surface of nanocrystalline ZnO core (Error! Reference source not found. b), which is evidenced by the presence of two bands characteristic for COO.sup.- group (1544 cm.sup.-1 and 1398 cm.sup.-1).
EXAMPLE 33
Annealing of ZnO.SUB.2.(25) NPs and its Transformation Into Nanocrystalline ZnO
[0175] 20 mg of ZnO.sub.2(25) NPs prepared according to the procedure described in Example 27 was placed in a glass vial and introduced into an oven pre-heated to a temperature of 400° C. The material was annealed at this temperature for 20 minutes (similar results can be obtained by changing both the time and the temperature of annealing, while the annealing temperature should not be lower than 100° C.). Then the resulting material was allowed to gradually reach ambient temperature and was cheracterized using PXRD. Diffractogram analysis (Error! Reference source not found. a) indicated the presence of the nanocrystalline, wurtzite-type ZnO structure with a crystallite size of 7.03 ± 1.06 nm. The lack of diffraction pattern characteristic for the ZnO.sub.2 phase proves the complete decomposition of ZnO.sub.2 NPs into ZnO. The resulting ZnO NPs exhibit fluorescence properties both in solid state and dispersed in selected organic solvent. Absorption and emission spectra of the dispersion of ZnO NPs in DMSO are shown in Error! Reference source not found. b. ZnO NPs reveald a broad absorption with a maximum located at λ = 343 nm and characteristic for ZnO emission centered at λ = 567 nm (Error! Reference source not found. b). FTIR analysis confirmed the presence of an organic shell composed of deprotonated acetic acid molecules on the surface of nanocrystalline ZnO core.
EXAMPLE 34
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et.SUB.2.Zn and H.SUB.2.O2 in in a Solvent with Coordinating Properties
[0176] 5 mL of dimethylsulfoxide (water-containing commercially available DMSO was used as received, i.e, without purification) was placed in a Schlenk vessel equipped with a magnetic stir bar. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) and 3 mL of 1% aqueus solution of H.sub.2O.sub.2 (1 mmol) were then sequentially added dropwise via a syringe at ambient temperature and under an inert gas atmosphere. The oxidizing agent was added in small portions for about an hour. Then the reaction mixture was stirred at ambient temperature for 24 hours. After this time, a fluorescent suspension was obtained. Afterwards 5 mL of acetone was added to the reaction mixture and the resulting precipitate was separated by centrifugation (9000 rpm, 10 minutes), washed with acetone (2 mL), re-centrifuged and dried. PXRD analysis (Error! Reference source not found. a) confirmed the nanocrystalline wurtzite-type structure of ZnO NPs. The average size of nanocrystallites is 9.23 ± 1.6 nm, and the lack of additional peaks on the diffraction pattern proves the high purity of the tested sample. Absorption and emission spectra of the dispersion of ZnO NPs in DMSO are shown in Error! Reference source not found.. FTIR analysis confirmed the presence of an organic layer composed of DMSO and/or water molecules on the surface of nanocrystalline ZnO (Error! Reference source not found. b).
EXAMPLE 35
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et.SUB.2.Zn and Na.SUB.2.CO.SUB.3..Math.1.5H.SUB.2.O.SUB.2 in a Molar Ratio of 0.75:1 (the Molar Ratio of the Organozinc Precursor to H.SUB.2.O2 is 1:2)
[0177] 157 mg (1 mmol) of sodium percarbonate (Na.sub.2CO.sub.3.Math.1.5H.sub.2O.sub.2) in 10 mL of anhydrous THF or in THF/hexane mixture was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.75 mL of a 2 M solution in hexane, 1 mmol) was then added dropwise via a syringe at ambient temperature and under an inert gas atmosphere. The reaction was carried out at -78° C. for several minutes and then the reaction mixture was allowed to spontaneously warm to ambient temperature and stirred at this temperature for additional 24 hours. The resulting sediment showed luminescent properties immediately after air exposure and under UV light irradiation. The resulting product was purified by washing two times with small portions of ethanol and then isolated from the reaction mixture by centrifugation (9000 rpm, 10 minutes). The product in form of white solid (Error! Reference source not found. a) was identified as the nanocrystalline wurtzite-type crystal structure of ZnO NPs with a core size equal to 6.16 ± 0.60 nm using PXRD. The lack of additional peaks on the diffraction pattern proves the acceptable purity of the tested sample. The as-prepared NPs revealed a broad and well-formed absorption band with a maximum at λ = 337 nm and relatively broad emission band with a maximum in the visible light range λ.sub.em = 540 nm (Error! Reference source not found. b).
EXAMPLE 36
Preparation of ZnO.SUB.2 NPs in a Reaction Between R.SUB.2.Zn (R = Et, Me) and Na.SUB.2.CO.SUB.3..Math.1.5H.SUB.2.O.SUB.2 in a Molar Ratio of 1:2 (the Molar Ratio of the Organozinc Precursor to H.SUB.2.O2 is 1:3)
[0178] 315 mg (2 mmol) of sodium percarbonate (Na.sub.2CO.sub.3.Math.1.5H.sub.2O.sub.2) in 10 mL of anhydrous THF was placed in a Schlenk vessel equipped with a magnetic stir bar. The resulting solution was cooled in a dry ice - isopropyl alcohol bath to -78° C. Et.sub.2Zn (0.5 mL of a 2 M solution in hexane, 1 mmol) or Me.sub.2Zn (1 mL of 1 M solution in toluene, 1 mmol) was then added dropwise via a syringe and under an inert gas atmosphere. The reaction was carried out at -78° C. for several minutes and then the reaction mixture was allowed to spontaneously warm to ambient temperature and stirred at this temperature for additional 24 hours. The resulting precipitate was separated from the post-reaction mixture and purified according to the procedure described in Example 35 and it was identified as nanocrystalline ZnO with a wurtzite-type crystal structure (
EXAMPLE 37
Testing the Stability of ZnO.SUB.2.(3) NPs in Solutions With Different pH Values - a Method of Preparation of ZnO by ZnO.SUB.2 Dispersing in a Solution With a Reduced pH
[0179] Nanocrystalline zinc peroxide - ZnO.sub.2(3) NPs — prepared according to the procedure described in Example 3 was placed in 5 glass vials (50 mg each) with a capacity of 25 mL and equipped with magnetic stir bars. Then 10 mL of deionized water (MilliQ) with different pH values (i.e., 6; 6.5; 7; 7.5; 8) was added to each vial and the resulting mixtures were stirred for additional 24 h. After this time, all samples were centrifugated (9000 rpm, 5 min), and the resulting sediments were dried. The as-prepared materials were characterized using PXRD (
EXAMPLE 38
Preparation of ZnO.SUB.2 NPs in a Reaction Between Et2.Zn and Ozone
[0180] Et.sub.2Zn (1 mL of a 1 M solution in hexane, 1 mmol) was added dropwise to 10 mL of THF placed in a Schlenk vessel, vigorously stirred with a magnetic stir bar and cooled to -20° C. (an ice bath with a sodium chloride was used). Subsequently, the reaction vessel was connected to an ozone generator (ozone production was 3.5 g/h) and exposed to ozone for 3 minutes. Then the reaction mixture was allowed to gradually warm to room temperature and stirred at this temperature for additional 24 hours. The resulting product in the form of a precipitate was washed two times with small portions of hexane (2 mL), isolated using centrifugation (9000 rpm, 10 minutes) and dried. Nanocrystalline ZnO was obtained and the crystal structure of the resulting product was confirmed using PXRD (Error! Reference source not found.). The average size of ZnO nanocrystallites is 3.70 ± 0.48 nm. Similar results have been obtained using dimethylzinc or by dissolving 220 mg of Ph.sub.2Zn (1 mmol) in 20 mL of toluene or THF.
EXAMPLE 39
Preparation of ZnO.SUB.2 NPs Using Solvent-Free Approach (the Molar Ratio of the Organozinc Precursor to H.SUB.2.O2 is 1:2)
[0181] 220 mg of Ph.sub.2Zn (1 mmol) or 400 mg of (C.sub.6F.sub.5).sub.2Zn (1 mmol) and 282 mg of hydrogen peroxide-urea adduct (CO(NH.sub.2).sub.2.Math.H.sub.2O.sub.2) and steel ball with a diameter of 1 cm, acting as the grinding element, were placed in a steel ball mill with a capacity of 15 cm.sup.3 under an inert gas atmosphere. The mechanochemical transformation was carried out at a frequency of 30 Hz for 30 minutes. Thus product as a black solid was obtained. PXRD analysis confirmed the presence of a nanocrystalline zinc peroxide phase stabilized with urea resulting from the hydrogen peroxide-urea adduct decomposition (
EXAMPLE 40
Bacteriostatic Properties of ZnO.SUB.2 NPs
[0182] Magnetic stir bars and 10 mg of selected nanocrystalline zinc peroxide - i.e., ZnO.sub.2(3) NPs (sample marked as 1), ZnO.sub.2(9) NPs (sample marked as 10) and ZnO.sub.2(15) NPs (sample marked as 19), which were prepared according to the procedures described in Example 3, Example 9 and Example 15, respectively - were placed in glass vials of the capacity of 25 mL. Then 10 mL of deionized water (MilliQ) with different pH values (i.e., 6 and 7) was added to each vial and the resulting mixtures were stirred for additional 24 h. Additional solutions with concentrations ranges from 5 .Math.g/mL to 100 .Math.g/L were prepared by the method of successive dilutions. Microbiological tests were performed using the disc diffusion method. In order to determine the bacteriostatic/bactericidal properties of ZnO.sub.2 NPs against gram(+) - Staphylococcus aureus and gram(-) - Pseudomonas aeruginosa bacteria, the materials selected for tests in the form of an aqueous solution with a specific pH were spotted on a filter paper (350 .Math.l) and then the as-obtained disc was placed on a plate inoculated with bacterial isolate. Tests were performed for the nanomaterial concentration from 5 .Math.g/mL to 100 .Math.g/L in solutions with a pH of 6 and 7. The representative results are shown in
EXAMPLE 41
Antibacterial Properties of Surfaces Coated by ZnO.SUB.2 NPs
[0183] Magnetic stir bars and 10 mg of selected nanocrystalline zinc peroxide - ZnO.sub.2(1) NPs and ZnO.sub.2(16) NPs, which were prepared according to the procedures described in Example 1 and Example 16, respectively - were placed in glass vials of the capacity of 25 mL. Then 10 mL of deionized water (MilliQ) was added for each vial and sonicated for 10 minutes. Additional solutions with concentrations of 1 mg/mL (for ZnO.sub.2(16) NPs) and 10 mg/mL (for ZnO.sub.2(1) NPs and for ZnO.sub.2(16) NPs) were prepared by the method of successive dilutions. The antibacterial properties of the tested nanomaterials were determined in accordance with the ISO 22196:2011/JIS Z 2801:2010 test method. ZnO.sub.2 NPs in the form of aqueous solutions with a specific concentration were evenly applied in the form of a thin layer on the entire surface of a sterile glass square plates (5 cm x 5 cm). Then as-prepared plates were dried at 40° C. The whole process was repeated three times, and the total volume of material suspension applied on each glass plate was 1 mL. For each bacterial strain (i.e., gram(+) - Staphylococcus aureus, gram(-) -Pseudomonas aeruginosa and gram(-) - Escherichia coli) the inoculum was prepared as described in the test method. Inoculum concentration ranged between 2.5 × 10.sup.5 and 1.0 × 10.sup.6 CFU/mL. Each test sample (both control samples that are not covered with any material and those that contain a tested nanomaterial layer) was inoculated with 0.4 mL of the inoculum. Then the as-prepared samples were covered with sterile plastic in order to ensure direct contact between viable bacteria and tested nanomaterial. Control sample, immediately after inoculation, was washed using neutralizing solution (broth SCDLP) in a volume of 10 mL per sample and then plated on the propagation medium at serial dilutions from 10.sup.0 do 10.sup.-4. Thest samples were incubated for 24 h at 35° C. and a relative humidity of not lover than 90%. After this time, samples were washed with a neutralizing solution and plated on the propagation medium at dilutions from from 10.sup.0 do 10.sup.-4. The study was carried out in triplicate, separately for each of the mentioned bacterial strains. After 72 h of incubation, bacterial colonies were counted for each test sample and the survival of bacterial cells on each of the test samples was calculated according to the formulas described in ISO 22196/JIS Z 2801 test method. The value of antibacterial activity (R) was calculated according to the formulaR = B.sub.t — C.sub.t (where: B.sub.t— average of logarithm numbers of viable bacteria from control sample at time = 24 hour; C.sub.t— average of logarithm numbers of viable bacteria from treated sample at time = 24 hour). According to the ISO 22196/JIS Z 2801 standard sufficient antibacterial effectiveness is reached when the antibacterial activity (R) is rated 2 or more. Both ZnO.sub.2(1) NPs and ZnO.sub.2(16) NPs show a very good antibacterial effectiveness against selected bacterial strains (i.e., R is equal to 6.04 (S. aureus), 6.20 (E. coli) and 6.49 (P. aeruginosa) and R is equal to 7.84 (S. aureus), 7.53 (E . coli) and 6.43 (P. aeruginosa) for ZnO.sub.2(1) and ZnO.sub.2(16) NPs) concentration of 10 mg/mL, respectively). In addition, ZnO.sub.2(16) NPs at concentration of 1 mg/mL is also characterized by a very good antibacterial effectiveness against P. aeruginosa (R = 8.93) and S. aureus (R = 3.39).
EXAMPLE 42
Biocidal Properties of ZnO.SUB.2.(16) NPs According to the Modified Koch Sedimentation Test
[0184] ZnO.sub.2 nanoparticles were prepared according to the procedure described in Example 16 and prepared for testing according to the method described in Example 41. The biocidal properties of ZnO.sub.2 were determined by comparing the number of viable bacterial/fungal cells deposited from the air on the surface of sterile glass square plates (5 cm x 5 cm) protected with a thin layer of ZnO.sub.2(16) NPs and on a control (uncovered) plates. Material was applied to the glass square plates according to the procedure described in Example 41. The as-prepared test samples (both control samples and those that contain a tested nanomaterial layer) were placed in sterile Petri dishes and left in the room for the specified time (in this study, three different exposure times of 5, 30 and 60 minutes, respectively, were carried out). Immediately after exposure, the samples were washed with a neutralizing solution (SCDLP broth) in a volume of 10 mL per sample and plated on bacterial and fungal media at serial dilutions from 10.sup.0 to 10.sup.-4. After 72 h of incubation, bacterial/fungal colonies were counted for each test sample and the number of microbial cells was calculated per 1 m.sup.3 of air. The value of the antibacterial efectiveness was determined according to the formula: L = a × 1000 / B × k (where: L: average number of bacterial/fungal cells deposited on the plate per 1 m.sup.3 of air; R: number of microorganisms in 1 m.sup.3 of air; a: number of colonies microorganisms grown on appropriate media; B: area of the tested material sample [cm.sup.2]; k: exposure time factor of the tested material; k = t (exposure time in minutes) × ⅕. Results (L < 10 for all tested cases, where L - the average number of bacterial/fungal cells deposited on the plate per 1 m.sup.3 of air; data averaged for three different exposure times) confirm that ZnO.sub.2(16) NPs show strong antimicrobial effect on the surface exposed to free deposition of bacteria and fungi from the air.
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