Synthesis, Characterization of ZnO Nanoparticles and the Impact of Changing the Proportion of Precursor on Their Morphology, Average Formation, and its Antimicrobial Activity

Introduction

Nanostructures of different metal oxide have already proved their revitalization importance for the production of energy saving and harvesting devices, viz fuel cells, light emitting devices, solar cells, transistors, humidity, lithium batteries, and temperature sensor, UV-screening,  photoelectrodes etc. Nevertheless, they have fabulous applications in biological and medical sciences like cancer treatment, drug delivery, bio tagging, bio labelling,  fluorescent imaging etc. Transition metals like Zn doped metal oxide (ZnO) called as diluted magnetic semiconductors (DMS). Nowadays ZnO nanomaterials have garnered significant research  attention for potential applications as it is cheap replacement for Si and GaN, and hence recommended as “Future promising material”. Crystalline ZnO possess wurtzite crystal structure at normal temperature and pressure and has a hexagonal unit cell Fig.1. Zinc oxide as it has polar nature exhibits variety of unique properties.  ZnO change its physical properties with the dimension of nanostructures. ZnO nanoparticles reported vital important metal oxides as popularly employed in different field promising its vast useful properties like physical and chemical. The direct band gap 3.37 eV showing the transparency in visible region.^1-6 As it has shown distinctive optical and electrical properties, ZnS Co-doped with Cd and Fe showed magnetic properties⁷, hybrid Fe₂O₃–ZnO/PS-PEG Nanocomposites showed optomagnetic properties⁸ it is considered as important material in the field of optoelectronics applications for visible and very near to ultraviolet spectral regions. ZnO nanoparticles are vastly used in various industries as UV-visible light emitting devices and also in different pharmaceuticals and cosmetic industries. It further includes non-toxic and compatible property with skin, antimicrobial and dermatologic associate degreed are dynamically used in sunscreen.^9-11 Zinc oxide (ZnO) nanoparticles have been fabricated by using numerous methods like laser ablation, hydrothermal synthesis, electrochemical deposition, Sonochemical method, thermal evaporation, electrophoretic deposition, sol-gel, anodization.¹² Moreover, development of inorganic/polymer hybrid material on nanoscale obtains more consideration for their potential applications in optoelectronics field. A doped ZnO variants for the development of latent finger print.^13-14 Earlier investigation between inorganic fillers and organic polymer reveals the changes in mechanical properties due to addition of inorganic filler in polymer matrix, and functional properties like antibacterial activities and UV -protection are largely explored.¹⁵ PANI@ZnO hybrid materials in Adsorption of Congo Red and Methylene Blue Dyes have good adsorption property.¹⁶ Zinc Oxide Nanoparticles, for dye-sensitive solar cells.¹⁷. Novel green synthesis of Zinc Oxide nanoparticles using orange waste also showed Antibacterial Activity.¹⁸ ZnO nanoparticles induced by surface stabilization due to positive aging effect¹⁹

In our previous work, we presented the research work for the synthesis of ZnO nanoparticles in polymer matrix by using zinc nitrate as an inorganic salt and polyphynelene sulphide (PPS) as a polymer. In this research we observed typical 1:1 molar ratio only (zinc nitrate: PPS) to produce ZnO nanoparticles²⁰. This study investigates cost effective, eco-friendly, synthesis and  real-world  applications of ZnO nanoparticles in polymer matrix by changing the molar ratio of inorganic salt zinc nitrate to PPS as 1:5,1:10.1:15, and 1:20. For the present work we kept the fixed ratio of zinc nitrate and variable ratio of PPS. Polyphenylene sulphide has been broadly used polymeric material for nonwoven bag filter as it has good mechanical and high resistance property to high temperature, also this is high-performance thermoplastic tremendously strong, tough, and  rigid and does not change these properties above the temperature 200 ˚C. Melting range of PPS ranges from 280 ˚C to 290˚C has good resistance to chemicals, fluids and oils. Furthermore, it has fabulous property to change upon heating in the presence of ambient oxygen.²¹

Figure 1: Tetrahedral structure of ZnO Click here to View table

Experimental

Materials

Analytical grade reagents Poly-phenylene sulphide (C₆H₄S)_n, zinc nitrate (ZnNO₃)₂ and acetone (CH₃COCH₃) from Sigma Aldrich (99% purity) were directly used for the synthesis for ZnO nanoparticles.

Synthesis procedure

ZnO nanoparticles were synthesized by using one step, very simple, ecofriendly solid-state method. In this procedure zinc nitrate to variable ratio of PPS were admixed physically in agate mortar pastel for minimum 20 minutes with acetone. Further admixed sample was dried under IR lamp and then subjected to melting temperature of PPS at 285˚C in muffle furnace for five hours under normal atmosphere condition in alumina crucible. After 5 hours the synthesized product was cooled at room temperature. The received shady brown coloured product was then crushed to fine powder to study the different properties of ZnO nanoparticles.

Characterization

The ZnO nanoparticles were characterised by various physicochemical techniques. To obtain the UV-visible analysis sample were dispersed in methanol and sonicated for about 20 minutes. The solution then transferred in a quartz cuvette. The optical spectrum then recorded within the range of 200-800 nm.

The structural analysis was accomplished via X-ray diffraction analysis. The Rigaku Miniflex X-ray diffractometer armed with copper target (CuKα1, λ=1.5406Å) nickel filter. The sample was placed on stub and diffraction pattern 2θ recorded ranging from 20˚- 80 ˚ angle.

The morphology of ZnO nanoparticles were studied through scanning electron microscopy (SEM) (FEI Nova SEM450).  For this analysis the sample was prepared as given below; the product was dispersed in acetone and sonicated for about 20 minutes.

Antimicrobial activity test was performed by the commonly used Agar diffusion method which is designed to determine the smallest amount of the antibiotic needed to inhibit the growth of micro-organism. Antimicrobial activity was tested using Kirby-Bauer Method. Plates were incubated at 37˚C for 24-48 hrs. in an incubator and the diameter of zone of inhibition in mm  was measured using a ruler on the underside of the plate

FTIR spectrum of ZnONP solid sample was performed in the spectral range from 500-4000cm^-1. The IR Affinity- 1 Shimadzu interferometer with High-energy ceramic light source was used for the analysis of product.

Result and Discussion

Synthesis

ZnO-pps nanoparticles were synthesised by mixing zinc nitrate with various proportions of PPS. Poly-phenylene sulphide has glass transition temperature ( T_g) approximately 85° C and melting temperature 285˚C (approximately) (average molecular weight 10,000). The reaction temperature of 285˚C was selected because PPS thermally decomposition at ~ 450 ˚C and melting temperature of polymer is 285˚C. The loosely bound sulphur in PPS reacts with Zn to produce ZnO in polymer matrix which gives desired product. The synthesised nanoparticle was characterised by various physicochemical techniques. The chemical and electrolysis route for the synthesis is shown in fig.2.

Figure 2: Procedure for the synthesis of ZnO nanoparticles Click here to View Figure

XRD

To get insight into crystalline nature and size of synthesised X-ray diffraction studies were carried out. X-ray Diffraction patterns of ZnO nanoparticles in polymer matrix with different molar ratio as 1:5, 1:10, 1:15, and 1:20 were recorded and shown in Fig.3. The peaks at 31.7, 34.4, 36.2, 47.5, 56.6, 62.8, 66.3, 67.9, 69.09 are attributed to the presence of Hexagonal  ZnO nanoparticle corresponding to zincite mineral according to JCPDS: 36-1451. The very strong and peak broadening at 36.2 derive the good crystallinity of the nanoparticles.

The average crystallite size of nanoparticles was calculated from Scherrer equation

D=(Kλ/βcosθ)              (1)

Where D -Crystallite size, K is shape factor,   λ is wavelength, β is full width at half maximum (FWHM) and θ is angle of diffraction (Bragg’s angle).

The crystallite sizes obtained from above equation are tabulated in Table 1.

It has been observed that the crystallite size varies from 12-22 nm as proportion of Zn nitrate to PPS is changed.

Figure 3: XRD pattern of ZnO nanoparticles at different molar ratios (1:5, 1:10, 1:15, 1:20). Click here to View Figure

Table 1: Crystallite size of nanoparticles prepared

Proportion	Particle size nm
1:5	12.27
1:10	14.74
1:15	14.08
1:20	22.38

 FTIR

The nanoparticles of ZnO in polymer matrix was examined via FTIR for different molar ratios of ZnO in  PPS i.e. 1:1, 1:5, 1:10, 1:15 & 1:20  can be seen in Fig 4. In the Fig 4, for the molar ratio 1:1 (ZnO:PPS) the absorption peak at 547.78 represents the ZnO stretching frequency, the peaks at 640.36, 740.66 and 1002.9 represents C=C bending and 1465.9 and 1566.1 represents C-H bending frequencies of polymer.

Figure 4: IR spectrum of PPS and zinc nitrate mixture heated at different molar ratio. Click here to View Figure

SEM

The synthesised nanoparticles were analysed by SEM for further characterisation and to get the information of morphology of ZnO nanoparticles. The photomicrographs of SEM [recorded with secondary electron (SE) mode] of the stated molar ratios sample product are presented in Fig.5. All the images of SEM of all ratios depict the formation of globular morphology of size between 10-25 nm. These values are also in accordance with particle size calculated from powder XRD using Scherrer formula. Further, SEM study revealed globular morphology in molar ratio 1:5 with intense unequal dispersion of globular particles in polymer matrix. Whereas, less distribution of globular particles observed as the molar ratio increases can be attributed to less percentage of availability of zinc compare to PPS. In addition, chunk like morphology is observed for all samples, such features appeared to be characteristics property of PPS. The average particle size distribution (histogram) from SEM image is shown in figure Fig.6.

Figure 5: SEM photomicrographs (SE mode) corresponding to zinc nitrate and PPS heated admixture of (a) 1:5, (b)1:10, (c)1:15, (d) 1:20  molar ratios. Click here to View Figure

Figure 6: Average particle size distribution (histogram) from SEM image by Image J software for Zinc nitrate and PPS heated admixture of (f) 1:5, (g)1:10, (h)1:15, (i) 1:20 molar ratios. Click here to View Figure

Antimicrobial activity

Since ZnO has been found to exhibit antimicrobial activity, we have tested the antimicrobial activity of ZnO enforced polymer matrix against E. Coli and S. aureus Fig.7. It has been found that the ZnO enforced polymer matrix with 1:5 proportion exhibited efficient antimicrobial activity or inhibitory action. Antimicrobial activity for ratios 1:5 and 1:20 reveals the similar trends as we increase the proportion of PPS activity report is supressed as less availability of ZnO nanoparticles and more entrapment in polymer matrix.

Figure: 7:  Zone of inhibition of ZnO enforced in polymer matrix against (A) S. aureus and (B) E. Coli for (a) 1:5 and (b) 1:20 respectively. Click here to View Figure

Table 2 shows zone of inhibition of these compounds against E. Coli and S. Aureus. This result indicates the antimicrobial potential of ZnO enforced polymer matrix. These results are also compared with streptomycin and gentamycin as reference drug. The graph of antimicrobial activity of ZnO enforced polymer matrix against E. Coli and S. Aureus is presented in Fig.8. 

Table 2: Antimicrobial activity of ZnO enforced polymer matrix against E. Coli and S. aureus.

Sr. No.	Compound	Zone of inhibition (mm)
		E. Coli	S. Aureus
1	ZnO:PPS (1:5)	11	13
	DMSO	9	—
	Streptomycin	31.6	29.6
	Gentamycin	36	33.5
2	ZnO:PPS (1:20)	10.6	11.6
	DMSO	9	–
	Streptomycin	31.6	29.6
	Gentamycin	36	33.5

*  Ec* – Escherichia  coli (NCIM2065)* Sa* :- Staphylococcus aureus (NCIM2178)           

Figure 8: Graph of Zone of inhibition of ZnO nanoparticles enforced in polymer matrix against E. Coli and S. aureus Click here to View Figure

Conclusion

To the extent that, Zno nanoparticle can be produced by chemical methods with the evolution of many hazardous and environment polluting gases but recently more standards are focused on eco-friendly production of such nanoparticles. In this research we have demonstrated, cost effective, single step, eco-friendly formation of ZnO nanoparticle in PPS matrix at various proportions of zinc nitrate and PPS with real-world applications.   As proportion of PPS was increased, formation of ZnO nanoparticles was found to be decreased due to less availability of Zn. The prominent diffraction peaks revealed, and confirmed the formation of ZnO nanoparticles which are strongly supported by SEM images. Flower like morphology in molar ratio 1:1 with intense unequal dispersion of globular particles in polymer matrix. Whereas, as the percentage of PPS increases less distribution of globular particles observed which can be attributed to less percentage of availability of zinc compare to PPS. The 1:5 ratio showed optimal properties due  to ZnO availability in higher PPS ratios.  The representative investigation of antimicrobial activity for ZnO enforced polymer matrix with 1:5 and 1:20 proportion exhibited efficient antimicrobial activity or inhibitory action. This result indicates the antimicrobial potential of  ZnO enforced polymer matrix. These ZnO nanoparticles may be useful as UV absorber in different cosmetics as sunscreen lotion, catalysis in various organic reaction to produce bioactive compounds, optics and in electrical engineering.

Future Prospects

Based on easy, simple and cheap generation of ZnO nanoparticles, continuing generation of ZnO nanoparticle by using alternative polymer is highly interested because of its important applications in biology, medical, and engineering field. For this study more antibacterial strains may add other important properties.

Acknowledgement

This research did not receive any specific grant form any funding agencies in the public, commercial or not-for-profit sector.

We wish to acknowledge constant encouragement from the Principal of MES Abasaheb Garware College, Karve Road, Pune, and Principal N.V.P. Mandal’s Lasalgaon, Nashik

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest

The author(s) do not have any conflict of interest.

Data Availability Statement

This statement does not apply to this article.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval.

Author Contributions

All authors contributed to the study conceptualization, design and work on materials. Material preparation, data collection, analysis and characterization, draft writing were performed by Ajinkya Thorat, Sujata M. Kasabe  and Anup Kate,  draft writing, design, editing of the review, and manuscript preparation by Bajirao B. Ahire. Dinesh Amalnerkar supervised and discussed the results.

References

1. S.C. Sing, D.P. Sing, J. Sing, P.K. Dubey, R.S. Tiwari and O.N. Srivastava, 2010. https://www.researchgate.net/publication/20203228
2. Sabir, M. Arshad, and S. K. Chaudhari, (Hindavi Publishing Corporation, Scientific World Journal Volume 2014. http://dx.doi.org/10.1155/2014/925494
   CrossRef
3. G Smijs, S. Pavel, Nanotechnology Science and Applications, 2011.DOI: 10.2147//NSA.S19419
4. A Joanna, Ruszkiewicza, A. Pinkasa, B. Ferrera, T. V. Peresa, A. Tsatsakisb, M. Aschnera,, Toxicology Reports 4, 2017, 245-259.http://dx.doi.org/10.1016/j.toxrep.2017.05.006
   CrossRef
5. S. Sivkumar, P. Venkateswarlu, V. R. Rao, and G. N. Rao, , International Nano Letters, 2013. http://www.inl-journal.com/content/3/1/30
   CrossRef
6. C. Pushpalatha, J. Suresh, V. Gayathri, S. Sowmya, D. Augustine, A. Alamoudi, B. Zidane, N. H. Mohammad and S. Patil, , Frontiers in Bioengineering and Biotechnology, 2022. doi:10.3389/fbioe.2022.917990.
   CrossRef
7. 7 K. Heiba, M. B. Mohamed,. J Inorg Organomet Polym 2020, 30, 879–888. https://doi.org/10.1007/s10904-019-01226-9
   CrossRef
8. A. Hammad, A.B. Mansour, A.M. Elhelali,. J Inorg Organomet Polym 2023, 33. https://doi.org/10.1007/s10904-022-02519-2
   CrossRef
9. R. P. Singh, V. K. Shukla, R. Yadav, P. Sharma, P. Singh, A.  Pandey, , Advanced Material Letters, 2011, 2, 4, 313-317. DOI: 10.5185/amlett.indias.204
   CrossRef
10. H. Mirzaeia, M. Darroudic, Ceramic international, 2017, 43, 907-914.
    CrossRef
11. V. Srivastava, D. Gusain, Y. Sharman, Ceramic International 2013, 39, 9803-9808.DOI 1016/j.ceramint.2013.04.110
    CrossRef
12. M. Ana, D.Pascual, and L. Angel. D.Vicente, Applied Materials & Interfaces, 2014, 6, 3729-3741. doi.org/10.1021/am500171x
    CrossRef
13. M. Chougule, S, Sen, V. Patil, Journal of Applied Polymer, 2012, 125, 541-547
    CrossRef
14. M. Zargham, M. F. Khan, R. A. Rehman, A. Rakha, R. Nazir, M. Salman, S. Akhtar, S. Nazir, I. Zareef, A. Munawar, ,Inorganic Chemistry Communications, 2024,162. https://doi.org/10.1016/ j.inoche.2024.112269
    CrossRef
15. S. Chandramouleeswaran, S. Mhaske, A. Kathe, P. Varadarajan, V. Prasad and N. Vigneshwaran, Nanotechnology, 2007,18. doi:10.1088/0957-4484/18/38/385702.
    CrossRef
16. I.Toumi, H.Djelad, F.Chouli, J Inorg Organomet Polym. 2022,32, 112–121. https://doi.org/10.1007/s10904-021-02084-0
    CrossRef
17. A. Degefa, B.Bekele, L.Jule ,B. Fikadu , S.Ramaswamy ,L. Dwarampudi , N. Nagaprasad ,and K.Ramaswamy,  , Journal of Nanomaterials. 2021, 9. https://doi.org/10.1155/2021/3941923.
    CrossRef
18. A Menazea, A.M.Ismail, & A.Samy, J Inorg Organomet Polym. 2021, 31, 4250–4259. https://doi.org/10.1007/s10904-021-02074-2
    CrossRef
19. W. Zhang , X.Chen , Y.Ma , Z.Xu , L.Wu , Y.Yang , S.W.Tsang , and S.Chen , The Journal of Physical Chemistry Letters, 2020, 11,15, 5863-5870.doi: 10.1021/acs.jpclett.0c01640
    CrossRef
20. S. Kasabe, P. Adhyapak, U. Mulik, D. Amalnerkar, C. Bhongale, International Journal of Innovative Trends in Engineering (IJITE), 2015, 9,1.https://doi.org/10.1021/acs.jpclett.0c01640,32618473.
    CrossRef
21. A. Rahate, K.Nemade and S. Waghule, Rev Chem Eng, 2013, 29,6, 471-489
    CrossRef

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