AN ANTIMICROBIAL COATING COMPOSITION

Abstract

An antimicrobial coating composition comprising a nanoparticle composite having a core and at least one shell, wherein the core comprises a silver nanoparticle having an antimicrobial action. The at least one shell is formed by a doped semiconductor providing a photocatalytic action and increasing the stability of silver nanoparticle core by controlling the releasing of Ag ions. The nanoparticle composite comprises a nanoparticle of a noble metal providing surface plasmon under the presence of electromagnetic radiation.

Claims

1. An antimicrobial coating composition comprising a nanoparticle composite having a core and at least one shell, wherein the core comprises a silver nanoparticle having an antimicrobial action; the at least one shell is formed by a doped semiconductor providing a photocatalytic action and increasing the stability of silver nanoparticle core by controlling the releasing of Ag ions; the nanoparticle composite comprises a nanoparticle of a noble metal providing surface plasmon under the presence of electromagnetic radiation.

2. The antimicrobial coating composition as claimed in claim 1, wherein the nanoparticle composite is dispersed in a binder material.

3. The antimicrobial coating composition as claimed in claim 1, wherein the silver nanoparticle core has an average diameter from 1 nm to 100 nm.

4. The antimicrobial coating composition as claimed in claim 1, wherein the material of the shell is TiO.sub.2.

5. The antimicrobial coating composition as claimed in claim 1, wherein the shell is doped with a dopant from the group comprising a transition metal, a transition metal oxide, a transition metal hydroxide or a multivalent ion of a transition element.

6. The antimicrobial coating composition as claimed in claim 5, wherein the shell is doped with at least one dopant selected from the group consisting of copper and aluminium.

7. The antimicrobial coating composition as claimed in claim 6, wherein the dopant is a multivalent ion of copper (Cu+2) or aluminium (Au+3).

8. The antimicrobial coating composition as claimed in claim 5, wherein the dopant is 0.1-1% of the shell material.

9. The antimicrobial coating composition as claimed in claim 1, wherein the noble metal nanoparticle is a gold nanoparticle.

10. The antimicrobial coating composition as claimed in claim 9, wherein the diameter of the noble metal nanoparticle is 10-100 nm.

11. The antimicrobial coating composition as claimed in claim 1, wherein the nanoparticle composite is provided in a binder from the group consisting of organosilane, PU, poly vinyl alcohol and acrylic coating.

12. The antimicrobial coating composition as claimed in claim 1 provided in a carrier compound.

13. The antimicrobial coating composition as claimed in claim 12, wherein said carrier compound comprises a solvent that has a lower boiling point than water.

14. The antimicrobial coating composition as claimed in claim 12, wherein said carrier compound comprises isopropanol.

15. A method for producing an antimicrobial coating composition, comprising preparing a silver nanoparticle solution to form a silver nanoparticle core; preparing a titanium isopropoxide (TTIP) solution for a TiO.sub.2 shell of the silver nanoparticle core; preparing a Cu++ dopant solution to provide a surface doping of said TiO.sub.2 shell; preparing a metallic gold nanoparticles solution; generating a sol of doped TiO.sub.2; mixing said silver nanoparticle solution with said gold nanoparticle solution; and adding mixture of said silver nanoparticle solution and said gold nanoparticle solution to sol of doped TiO.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawing, which are incorporated in and constitute a part of this specification, illustrate embodiments and together with the description, serve to explain the principles of the methods and systems.

[0021] FIG. 1 is a schematic view of an antimicrobial coating composition in accordance with the invention.

EXAMPLES

[0022] In one embodiment of the invention, the antimicrobial coating composition is formed by silver-doped TiO.sub.2 in the form core/shell nanoparticles (NPs) with a silver-core and a TiO.sub.2-shell (Ag@TiO.sub.2). The core/shell morphology of such a nanoparticle composite gives several advantages including well-defined and higher stability of silver nanoparticles (due to its encapsulated state inside TiO.sub.2 shell). The mole ratio between TiO.sub.2:Ag is important while preparing an Ag@TiO.sub.2 core-shell nanoparticle. At lower molar ratio an improved core shell particle can be obtained compared to a higher ratio. The silver nanoparticle core has an average diameter from 1 nm to 100 nm, and in some embodiments from 10 nm to 100 nm.

[0023] The silver nanoparticle was prepared in the presence of 13-D-Glucose as reducing agent and PEG (polyethylene glycol) as a dispersion agent and water as a solvent. After the dispersion of silver ions in a PEG aqueous solution matrix, PEG reacted with the Ag to form a PEG complex [Ag(PEG)]+, which reacted with β-D-glucose to form [Ag(PEG)] due to the reduction of silver ions through the oxidation of glucose to gluconic acid. There is an increase of NPs size depending on reaction time. The Ag NPs size could vary substantially, from about 10 nm at a 3 h reaction time to about 25 nm at 48 h reaction time.

[0024] After preparation of nanoparticles, these particles were added to TiO.sub.2 sol in different proportions 2.5%, 5%, 7.5%, 10%, 20%, molar ratio. Hydrothermal treatment at 120° C. for 4 hours helped in forming proper crystallized form. The nanoparticle was added to a solvent having gold particle equivalent to silver molar ratio. The different proportions initially resulted in nearly equal efficiency, except using 20%. With time this efficiency is reduced in the case of the lower percentage of 2.5% while a percentage between 5% and 10% gives better result in antimicrobial action.

[0025] A drawback of using TiO.sub.2 as a photocatalyst is that its band gap lies in the near-UV range of the electromagnetic spectrum: 3.2 eV for the anatase phase. As a result, only UV light can create electron-hole pairs and initiate the photocatalytic process.

[0026] Doping is the common strategy used to improve the photocatalytic activity by introducing impurities into the TiO.sub.2 matrix. The surface-doped ions play a key role in the kinetics of interfacial charge transfer. They are able to interact with both charge carriers and reactant to mediate charge transfer.

[0027] Various transitional element multivalent ions can be used as dopant i.e. Cu++, Al+++, Fe+++, Mn+7, Ni++. All these ions are very well-known electric conductors. They can accept an electron due to its ionic charge present on it. Using Cu++ as dopant resulted in a very favourable for antimicrobial action. Various Cu++ molar concentration was used. Source of Cu++ used is at 1%, 0.5%, 0.25%, 0.1% mole with Titanium. CuO at 0.25% provided very good photocatalytic action based on methylthioninium chloride degradation test.

[0028] A gold nanoparticle absorbs visible light and will improve photocatalysis response in a broader light spectrum. This is a result of the gold nanoparticle showing good surface plasmon under the presence of electromagnetic rays. Conduction electrons will oscillate in the phase with the electric field of electromagnetic rays.

Preparation Methods

[0029] Step 1, Synthesis of Nano Silver [0030] Solution A: 1.0 M Silver (1) nitrate (AgNO.sub.3) were prepared in double distilled water. [0031] Solution B: 1% Polyethylene Glycol (PEG) solution in double distilled water [0032] Solution C: 1.0 M D glucose in Double distilled water [0033] 10 mL of solution A was mixed with 200 mL of solution B and stirred for 20 min at high speed. A transparent solution is generated. In this mixture, 20 mL of solution C was added and stirred for another 20 minutes. This mixture is heated at 80° C. under stirring condition until pale yellow colour appears. [0034] Stop the reaction immediately by lowing temperature below 15° C. [0035] Store colloidal suspension in dark bottle to avoid any photoactivity.

[0036] Step 2, Synthesis of Core-Shell Particle [0037] Solution D: Colloidal Nano silver particle generated in step 1 (used for generating Ag@ TiO.sub.2 core shell) [0038] Solution E: 1.0 M titanium isopropoxide (TTIP) in 2-propanol [0039] Solution D was stirred for 10 min at high speed. [0040] Solution E was added dropwise to solution D. [0041] Lactic acid was added to make pH 2-3. [0042] The yellow-white precipitate was generated. Stirred for more 4 hours at 60° C. Transparent sol was generated. This sol was treated under hydrothermal environment, 120° C. for 4 hours. This particle suspension can be used directly or dry it out at 80° C. under vacuum condition.

[0043] Step 3, Addition of Dopant (Surface Doping) [0044] Solution F: 30% hydrogen peroxide (H.sub.2O.sub.2) solution [0045] Solution G: 1 mM Copper oxide (CuO) in 1:1 double distilled water: 2 Propanol [0046] Ag@TiO2 core-shell synthesised in step 2 is doped with Cu++ dopant. [0047] 1 mM of powder of step 3 is prepared in 100 mL solution G. [0048] 1 mL of Solution F was added. [0049] Well-dispersed under ultrasonication of the solution. [0050] Light stirred for an hour. [0051] High speed stirred for an hour. [0052] Calcination process for 600° C. for 2 hours. [0053] Nanoparticle 1 (surface doped core-shell particle) [0054] Step 4, Synthesis of Nano Gold Particle [0055] Solution H: Aqua regia (1:3 solution of concentration HNO.sub.3:HCl) [0056] Solution I: 38 mM solution of Tri-sodium citrate in solution B [0057] Solution J: 100 mM Hydrogen tetrachloroaurate trihydrate [0058] 1. 1.0 g of gold was put in 500 mL flask and slowly added 100 mL of solution H. [0059] 2. Allowed it to stand for 60 min at room temperature. When the dissolution of gold slows down, the temperature was gradually increased up to boiling. [0060] 3. Once metallic gold is completely dissolved, the solution is continuously heated until it was concentrated to 50 mL [0061] 4. HCl was slowly added to the hot solution, until brown vapours were completely eliminated. [0062] 5. The final solution was in 100 mM in strength. 20 mL of 1 mM solution J was added to 100 mL flask. [0063] The solution was heated to boiling and then add 2 mL of solution I (1:3.8 molar ratio). [0064] After some time, deep wine-red sol was obtained. [0065] No further change of colour upon prolonged boiling was observed. [0066] The solution was cooled down to room temperature. [0067] Nano gold colloidal suspension is ready. [0068] Store it in dark bottle to avoid photo reaction. [0069] Nanoparticle 2 (Plasmonic Nanoparticle)

[0070] Step 5, Synthesis of TiO.sub.2 Sol [0071] 88 g of TTIP was added dropped wise in 2-Propanol under starring condition. Starred for 60 min at high speed temperature should not increase beyond 50° C. Lactic acid was added up to pH was drop to 2. [0072] Starred for another 60 min at high speed. [0073] Stand for 6-8 hours until clear sol is generated. [0074] Transparent sol is generated.

[0075] Final Solution [0076] Nanoparticle 1 and Nanoparticle 2 was mixed 1:2 proportion. [0077] Sonicated this mixture. [0078] 500 mL of this mixture is added to 500 mL of TiO.sub.2 sol.

[0079] In a process for the preparation of the coating composition a solvent used for preparing the solution or suspension will preferably be removed again after the shell has been applied. The coating material obtainable by the process of the invention can, be further processed and used in a variety of ways: for example, by spraying, dipping or spin coating. Depending on the base (binder) used for the composition the finishing of the coating is accomplished in different ways. The binder can be organ silane, PU, poly vinyl alcohol, acrylic coating or other material with corresponding properties.

[0080] The coating composition can be provided in a carrier compound that can be water and/or solvent which has a lower boiling point than water. It will then easily evaporate at room temperature. Examples of a carrier compound can be methanol, ethanol, n-propanol or isopropanol alone or mixtures thereof.

[0081] Depending on the mode of application the resulting thicknesses of the coatings may differ in magnitude, the aim in principle being for coat thicknesses which are as low as possible. Thus, it is preferred for the coat thicknesses of the coating ultimately obtained to be between 0.0005 mm and 0.05 mm, in particular between 0.001 mm and 0.01 mm. As an example, 1 liter of final solution will be applied to 25 m.sup.2 area. In this case the thickness d=1000/2500*2500=0.0016 mm.

[0082] The invention combines well known oligodynamic properties of silver nanoparticles with a photocatalytic action from a shell of TiO.sub.2 doped with a metal. The shell increases the stability of the silver nanoparticles and prolongs the oligodynamic effect. The photocatalytic action is further improved by adding a gold nanoparticle to the nanoparticle composite. The gold nanoparticle will provide surface plasmon under the presence of electromagnetic radiation where conduction electrons oscillate in phase with the electric field of the electromagnetic radiation.

[0083] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the inventive concept. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, and that the claims be construed as encompassing all equivalents of the present invention which are apparent to those skilled in the art to which the invention pertains.