CORE-SHELL COMPOSITE AND A PROCESS OF PREPARING THE SAME

Abstract

There is provided a core-shell composite comprising a core which comprises zinc metal and a shell that at least partially encapsulates the core, wherein the shell comprises a salt of the zinc metal as a cation with a sulphur-containing anion. There is also provided a method of forming a core-shell composite comprising the step of heating a mixture of zinc metal particle with elemental sulphur to form the core-shell composite, wherein the zinc metal particle forms the core of the core-shell composite, and wherein the shell of the said core-shell composite at least partially encapsulates the core and comprises a salt of the zinc metal as a cation with a sulphur-containing anion. There is also provided a method of killing or inhibiting the growth of a microbe, comprising the step of subjecting the microbe to the as-disclosed core-shell composite. There is also provided an anti-microbial coating on a substrate surface or an additive in a composition or a formulation comprising the as-disclosed core-shell composite.

Claims

1. A core-shell composite comprising: a core comprising zinc metal; and a shell that at least partially encapsulates said core, said shell comprising a salt of said zinc metal as a cation with a sulphur-containing anion.

2. The core-shell composite of claim 1, wherein said sulphur-containing anion has the formula [S.sub.xO.sub.1-x].sup.y−, where 0<x≤1 and y is 1 or 2.

3. The core-shell composite of claim 1, wherein said shell comprises a plurality of layers, each layer independently comprising said salt of said zinc metal as a cation with a sulphur-containing anion.

4. A method of forming a core-shell composite comprising a step of heating a mixture of a zinc metal particle with elemental sulphur to form said core-shell composite, wherein the zinc metal particle forms the core of said core-shell composite, and wherein the shell of said core-shell composite at least partially encapsulates said core and comprises a salt of said zinc metal as a cation with a sulphur-containing anion.

5. The method of claim 4, further comprising a step of reacting said core-shell composite with an aqueous solution.

6. The method of claim 4, wherein said heating step is undertaken at a temperature in a range of 100° C. to 160° C.

7. The method of claim 4, wherein said heating step is undertaken for a period of time in a range of 1 hour to 10 hours.

8. The method of claim 4, further comprising a step of, before said reacting step, cooling the core-shell composite to a temperature of 100° C.

9. The method of claim 5, wherein said reacting step is undertaken at a temperature in a range of 90° C. to 110° C.

10. The method of claim 5, wherein said reacting step is undertaken for a period of time in a range of 1 hour to 10 hours.

11. The method of claim 5, wherein said aqueous solution is water.

12. A method of killing or inhibiting growth of a microbe, comprising a step of subjecting said microbe to a core-shell composite, wherein said core-shell composite comprises: a core comprising zinc metal; and a shell that at least partially encapsulates said core, said shell comprising a salt of said zinc metal as a cation with a sulphur-containing anion.

13. The method of claim 12, wherein said core-shell composite is present as a coating on a substrate surface.

14. The method of claim 12, wherein said core-shell composite is present as an additive in a composition or a formulation.

15. The method of claim 14, wherein said composition or formulation is non-therapeutic.

16.-17. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0048] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0049] FIG. 1A is a scanning electron microscopy (SEM) image of Zn/ZnS composite (magnification of ×7500, and scale bar of 1 μm) made in accordance to the synthesis process in Example 1.

[0050] FIG. 1B is a scanning electron microscopy-energy dispersive X-ray (SEM-EDX) elemental mapping (Zn) image of Zn/ZnS composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 1.

[0051] FIG. 1C is a SEM-EDX elemental mapping (S) image of Zn/ZnS composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 1.

[0052] FIG. 2A is a SEM image of Zn/ZnS.sub.xO.sub.1-x composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 2.

[0053] FIG. 2B is a SEM-EDX elemental mapping (Zn) image Zn/ZnS.sub.xO.sub.1-x composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 2.

[0054] FIG. 2C is a SEM-EDX elemental mapping (O) image Zn/ZnS.sub.xO.sub.1-x composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 2.

[0055] FIG. 2D is a SEM-EDX elemental mapping (S) image Zn/ZnS.sub.xO.sub.1-x composite (scale bar of 5 μm) made in accordance to the synthesis process in Example 2.

[0056] FIG. 3 is a X-ray powder diffraction (XRD) spectra of elemental sulphur, Zn/ZnS.sub.xO.sub.1-x (II), Zn/ZnS, ZnO, Zn and Zn/ZnS.sub.xO.sub.1-x (I) particles as characterized in Example 3.

[0057] FIG. 4 is a UV-vis spectra of Zn/ZnS.sub.xO.sub.1-x (I), Zn/ZnS.sub.xO.sub.1-x (II) and Zn/ZnS particles as characterized in Example 3.

[0058] FIG. 5 is a bar graph showing absorbance values at wavelength 470 nm for the soluble reduced product formazan of the tetrazolium dye XTT corresponding to the superoxide radical released for the various synthesized core-shell composites and the blank sample which is a control composed of XTT solution only. All data is expressed as mean (±standard deviation) of three replicates.

EXAMPLES

[0059] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Materials and Methods

[0060] All the reagents were obtained from commercial suppliers and used without further purification. Commercially available Zn powder of 1 μm to 10 μm particle size and sulphur were purchased from Sigma-Aldrich (of St Louis, Mo. of the United States of America). Samples such as the various synthesized core-shell composites were subjected to imaging using the scanning electron microscope-energy dispersive X-ray (SEM-EDX) (model JEOL JSM-7400F) at an accelerating voltage of 5 keV. Prior to SEM imaging, the samples were sputter-coated with platinum using the Auto Fine Coater (model JEOL JFC-1600). Further characterizations of the samples were done using the X-ray powder diffraction (XRD) and UV-vis spectroscopy. Samples were pressed onto a sample holder and powder XRD analysis was performed using a Bruker D8 Advance system equipped with Cu Kα radiation (λ=1.5406 Á̊). UV-vis spectra were collected using a Shimadzu UV-Vis-NIR spectrophotometer (model UV-3600), equipped with an integrating sphere attachment.

Example 1: Synthesis of Zn/ZnS Core-Shell Composite

[0061] Zn/ZnS core-shell composite was prepared by direct reaction between zinc powder and elemental sulphur. Fresh zinc powder was mixed with sulphur (0.01 to 20% by weight) and grounded by hand for 10 minutes. The mixture was subsequently heated at a constant temperature between 100 to 160° C. for 1 to 10 hours. Zn/ZnS composite was obtained after cooling to room temperature (which is about 25° C.). From FIG. 1A, a deposited layer of ZnS forming the shell of the resultant Zn/ZnS core-shell composite was clearly observed on the surface of zinc particles (the zinc particle(s) forming the core of the core-shell composite). The presence of sulphur in the shell was further confirmed by SEM-EDX elemental mapping analysis as depicted in FIG. 1B and FIG. 1C. The ZnS shell layer was observed to be thin and mainly amorphous.

Example 2: Synthesis of Zn/ZnS.SUB.x.O.SUB.1-x .Core-Shell Composite

[0062] Zn/ZnS.sub.xO.sub.1-x core-shell composites were prepared by direct reaction between zinc powder and elemental sulphur and water. Fresh zinc powder was mixed with sulphur (0.01 to 20% by weight) and grounded by hand for 10 minutes. The mixture was subsequently heated at a constant temperature between 100 to 160° C. for 1 to 10 hours. After cooling to about 100° C., water was added to the system and temperature was kept at 90 to 110° C. for 1 to 10 hours to produce the Zn/ZnS.sub.xO.sub.1-x composites. From FIG. 2A, a layer of ZnS.sub.xO.sub.1-x was clearly observed on the surface of zinc particles (the zinc particle(s) forming the core of the core-shell composite). The presence of S and O in the shell was further confirmed by SEM-EDX elemental mapping analysis as depicted in FIG. 2B, FIG. 2C and FIG. 2D. The ZnS.sub.xO.sub.1-x shell layer was observed to be mainly amorphous.

Example 3: Characterization of the Synthesized Core-Shell Composites

[0063] In addition to SEM and SEM-EDX analysis, the synthesized core-shell composites were characterized by XRD and UV-vis spectroscopy. From FIG. 3, the XRD diffraction patterns of the synthesized Zn/ZnS and Zn/ZnS.sub.xO.sub.1-x composites exhibit strong diffraction peaks related to zinc with very weak ZnO, ZnS and S peaks. In contrast, the UV-vis spectra from FIG. 4 demonstrated different absorption patterns of different core-shell composites. Based on FIG. 3 and FIG. 4, the synthesized core-shell composites possess different compositional and absorption characteristics from other known core-shell materials.

Example 4: Reactive Oxygen Species Release and Antimicrobial Properties

[0064] Reactive oxygen species release, like the superoxide radicals (O.sub.2.sup.−) level, was studied by using XTT (2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide) as probe. 10 mg of the synthesized core-shell composites were weighed out and transferred to micro-centrifuge tubes. 1 mL of 0.1 mM XTT solution was then added to the tubes containing the composites, vortexed and left in the dark at 35° C. for 24 hours. The tubes were then centrifuged, and a 100 μL aliquot was subsequently transferred to a 96-well plate, where absorbance readings at 470 nm were measured. Experiments were performed in triplicates. The results as shown in FIG. 5, clearly demonstrate that Zn/ZnS and Zn/ZnS.sub.xO.sub.1-x core-shell composites can release higher level of superoxide radicals as compared to the blank which is a control composed of XTT solution only.]

[0065] To test the antibacterial properties of these composites, 0.02 g synthesized core-shell composite was dispersed in ethanol, and coated onto a glass slides with a dimension of 2.5 cm×2.5 cm. A blank glass slide used as a control. The antimicrobial properties of the surfaces were evaluated by the JIS Z 2801/ISO 22196 method against E. coli (gram-negative, ATCC 8739) and S. aureus (gram-positive, ATCC 6538P) and C. albicans (fungi). Briefly, 20 mg of core-shell composites were dispersed on pre-cleaned glass slides and an aliquot of microbe (gram positive or gram negative bacteria at concentration of 10.sup.5 CFU mL.sup.−1 or fungi at concentration of 10.sup.4 CFU mL.sup.−1) was introduced onto the slides. Untreated and Zn-coated glass slides were used as negative controls. The slides were incubated for 18 hours at 37° C. and the resultant colony growth on the glass was then washed off with phosphate buffered solution (PBS, 1× concentration), diluted using standard microdilution techniques and counted using standard plate count techniques. The number of colony forming units per mL was calculated and compared against the negative controls, to determine the log reduction and the effective killing efficiency of the core-shell composites. Experiments were done in triplicates. After the 18 hours incubation period, microbial growth was observed on the untreated glass slides such that there was an increase of 2 log units from 10.sup.5 to 10.sup.7 CFU mL.sup.−1 while for Zn-coated glass slides, there was a minimal reduction of microbial growth at less than 1 log unit from 10.sup.5 to >10.sup.4 CFU mL.sup.−1. Based on log reduction data (Table 1), surfaces treated with Zn/ZnS, Zn/ZnS.sub.xO.sub.1-x core-shell composites all showed excellent antimicrobial properties. All tested microbes that were exposed to surfaces with Zn/ZnS, Zn/ZnS.sub.xO.sub.1-x core-shell composites were killed after an 18 hours incubation period and no colony was observed even at a dilution factor of 10.sup.2. A 5-log reduction of microbe population was observed for E. coli, S. aureus and C. albicans respectively, exhibiting the excellent antimicrobial properties of Zn/ZnS, Zn/ZnS.sub.xO.sub.1-x core-shell composites.

TABLE-US-00001 TABLE 1 Antimicrobial Properties of Glass Slides Coated with Different Synthesized Core-Shell Composites log reduction Materials E. coli S. aureus C. albicans Glass control 0 0 0 Zn <1 <1 <1 Zn/ZnS >5 >5 >5 Zn/ZnS.sub.xO.sub.1−x(I) >5 >5 >5 Zn/ZnS.sub.xO.sub.1−x(II) >5 >5 >5

INDUSTRIAL APPLICABILITY

[0066] The core-shell composite may be used as additives that can be incorporated into liquid, gel, emulsion or cream antimicrobial systems. The core-shell material may also be applied as surface coatings to create long-term, self-disinfecting surfaces, inclusive of hard surfaces, fabrics or textiles.

[0067] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.