Volume 8, June 2020, pages 1-13

Synthesis, optimization, optical and structural characterization properties of Zinc oxide nanoparticles

Sandeep sirohi1, Kalu Singh Chundawat2, Pankaj K. Tyagi3,4

1 Research scholar, Department of Biotechnology, Mewar University, Gangrar, Chittorgarh, Rajasthan, India

2 Professor, Department of Life Sciences, Mewar University, Gangrar, Chittorgarh, Rajasthan, India

3 Professor, Department of Biotechnology, Noida Institute of Engineering and Technology,      Greater Noida, Uttar Pradesh, India 

Guest Faculty, Department of Biotechnology, Mewar University, Gangrar, Chittorgarh, Rajasthan, India


* Corresponding Author Email: sandeep.sirohi@miet.ac.in  | Tel: +919756547418

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Zinc oxide nanoparticles (ZnO NPs) are known as a multifunctional material because of its unique physical and chemical properties. Synthesis conditions of ZnO NPs were optimized in to different parameters, e.g. metal ion concentrations (0.1M to 0.8M), contact time variations (0.5hr to 4hr), effect of pH (4 to 9), and effect of temperatures (55 to 850C). The resultant zinc nano powder further characterized by analytical techniques, such as UV-Vis spectroscopy, Fourier Transform Infra-Red (FTIR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) patterns. Synthesized zinc nano powder was stored in dried form in the room temperature for further study. Best sharp and stable plasmon peak were monitored at 390nm, 393nm, 395nm and 390nm in the analysis of optimizing parameters metal ion concentrations, contact time variations, effect of pH and effect of temperatures respectably. Results of XRD clearly indicate that the zinc nitrite acted both as reducing and capping agents in ZnO NPs. Under optimum conditions the size of ZnO NPs range of 20-24nm as reported by TEM and shape  as reported by SEM. The crystalline nature of the ZnO NPs was confirmed by XRD.


zinc oxide optimization, Debye–Scherrer equation, FTIR, SAM, TAM, XRD pattern



The concept of nanotechnology was introduced by Richard Feynman in 1959. Nanobiotechnology thus becomes a combination of biotechnology and nanotechnology to create bio-synthetic, natural and eco-friendly technology for the production of nano scale based products. In present scenario, the nano sized material have emerged as novel antimicrobial properties to kill microbes. These properties enhance due to their high surface area to volume ratio1.

Nano scale particles have emerged as novel antimicrobial agents owing to the high surface area to volume ratio, which is coming up as the current interest in the researchers due to the growing microbial resistances against metal ions, antibiotics and the development of resistance strains2. The recent growth in the field of porous and nanometric materials prepared by non-conventional processes has stimulated the search of new application of ZnO nanoparticles3&11.

 Nanoscale sciences and technology have emerged over the past- decade as the forefront of science and technologies. The interesting fields of the study that create that domain of science and engineering perfectly typified as rapid, multidisciplinary advancement of contemporary science and technology. Metal nanoparticles have received considerable attention in recent years because of their unique properties and potential application in catalysis4, plasmonics, optoelectronics, biosensor5 and pharmaceutical applications.

Materials and Methods

All chemical were used for the highest purity and procured from Merck and Sigma. Analytical grade (AR) Zinc nitrate, soluble starch and sodium hydroxide were used for chemical synthesis of zinc oxide nanoparticles. Deionized double distilled water was used throughout the experimental work. 
Optimization and synthesis of synthesis parameters for ZnO NPs
ZnO NPs were synthesized using zinc nitrate6. A solution of 0.1M of zinc nitrate with 1% soluble starch and 300 ml (0.2M) sodium hydroxide were taken. The pH of the mixture was maintained at 8 and the solution was stirred continuously for 2 hours. White precipitates were obtained and then dry at 800C for 24 hours. Prior to drying, the precipitate was centrifuged at 10,000 rpm for 10 min and washed thrice with deionized water. During the drying process the precipitate completely converted to ZnO NPs. However, varying various parameters involved in the optimized synthesis conditions. Different concentrations of zinc nitrate, from 0.1M to 0.8M, were used as substrates (Figure 2a-h). The temperature was maintained at 55, 65, 75 and 850C. After synthesis of ZnO NPs the mixture were proceed under UV-Vis spectrophotometer for different times intervals 0.5, 1, 2 ,3 and 4 hours.

Optical Characterization 
The ZnO NPs was primarily optically characterized by UV-Vis spectrophotometer (JASCO-V-530), and Fourier Transform Infra-Red spectroscopy (FTIR), the scanning range for UV-Vis samples was 280-700 nm at a scan speed of 400nm/min. The absorption spectra of ZnO NPs of the samples were recorded. Further FTIR carried out in order to ascertain the purity and nature of the metal nanoparticles wavelength range of 4000-500 cm-1 clearly shows that the absorption band of ZnO NPs. 
Structural Characterization 
Scanning Electron Microscopy (SEM) analysis   of ZnO NPs were obtained using FE-SEM at IIT, Roorkee focused on electron beam which is scanned the surface of the sample to produce high quality images of the surface topography. SEM essentially offers a very high magnification with very high resolution capabilities and a large depth of focus. TEM analysis of the sample was done at National Physical Laboratory (NPL) New Delhi. TEM examination can yield the information like morphology, topography, composition as well as crystallographic information. Crystallinity of the zinc oxide nanoparticles was studied using an X-ray diffractometer. XRD patterns of the powdered samples were recorded using a advanced X-ray diffractometer with CuKa radiation (? = 1.54 Å, rated as 1.6 kW).

Results and Discussions

The impact of different metal ion concentrations (0.1M to 0.8M), contact time variations (0.5hr to 4hr), effect of pH (4 to 9), effect of temperatures (55 to 850C) solutions of zinc nitrate on the formation of ZnO NPs were monitored by using UV-Vis spectroscopy, FTIR, TEM, SEM and XRD patterns. After the optimization process the best plasmon peak and results of FTIR, TEM, SEM and XRD patterns of ZnO NPs were observed on 0.3M concentrated zinc nitrate solution derived; ZnO NPs, absorption spectrum was observed at 390nm (Figure 2c). The impact of different concentrations (0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M and 0.8M) of zinc nitrate on the formation of ZnO NPs were monitored by using UV spectroscopy (Figure 1a-c) and FTIR. The ZnO NPs synthesized at optimum concentration exhibit the plasmon peak of variations at 390 nm (Figure 1d) was stored in dry from in centrifuge tube (Figure 1b).  
Increasing concentrations of zinc nitrate were used in optimization of metal ion concentration. It clearly seen from the present work that concentration of zinc nitrate from 0.1M to 0.3M exhibited upward formation of peaks however at concentration 0.3M the peak was highest subsequently concentration of zinc nitrate from 0.4M to 0.8M, there was hump formation in the peaks indicating poor absorption of zinc nitrate. Hence, it was concluded on the basses of present results that increasing concentration of metal ions beyond the limit leeds to decreasing the formation of ZnO NPs (Figure 2a-h). The impact of pH in the nanoparticles was influence under various pH, at low pH small with broadening band was produced indicates synthesis of large size of nanoparticles. The effect of pH on the production of zinc oxide nanoparticles was analysed by using UV spectroscopy, FTIR and TEM. Formation of ZnO NPs mostly determined on the pH of the reaction medium and the results are shown in figures 3b. In the present work, it was reported that increasing in pH from 4 to 9 led to increase gradually which indicates the rate of production of ZnO NPs enhanced acidic medium to basic medium (Figure 3b ). An almost straight line of absorption with no peak was observed at pH 4, spectrum at pH 8 and 9 showed characteristic absorption peak.  However, the best absorption and sharp peak was obtained at pH 9 in case of ZnO NPs. 
Temperature plays one of the most significant physical parameter on the production of Zinc nanoparticles, different figure of UV visible spectroscopy indicate the effect of temperature in the nanoparticles production. The elevated rate of reduction was arising at higher temperature due the expenditure of zinc ions in the configuration of nuclei whereas the secondary reduction was stopped up on the surface preformed nuclei. The optimization of the suitable temperature for the reduction of ZnO NPs in the reaction process was optimized between 250C to 950C. No spectra were observed between 250C to 450C. Spectra between 550C to 650C showed similar pattern with low and extremely broad absorption peak, while absorption peak increased considerable from 750C. A sharp and stable peak was observed at 850C with the absorption 390 nm (Figure 3c). No prominent peak was observed at 950C. No major peak shifted during optimization process in the synthesis of ZnO NPs. However it was noticed that high temperature (850C) was most favorable for ZnO NPs synthesis.
The contact or incubation period also influence the synthesis of ZnO NPs.  For contact hours we were recorded spectra up to 0.5hr to 4hr. The sharpest absorption peak was observed in 393 nm (after 2 hr) which remain stable after 3 to 4hr. While in 0.5 and 1hr no peak were observed (Figure 3a) 
Zn  nitride (control)  and  ZnO NPs  in the form of nano powder obtained  upon optimization was characterized through FTIR spectroscopy and various peaks were found at 3169,3119, 2939, 2429, 2339, 2074, 1919, 1764, 1634, 1509, 1384, 1154, 1104, 1019, 934, 834 cm-1 in Zn nitride samples as control (Figure 4a ). The IR spectrum of Zn oxide showed sharp absorption bands at 3169 and 3119 cm-1 are may be due to O-H stretching vibrations N-H stretch7. Peaks at 2429 to 1919 correspondence to stretching vibrations of C = C stretch of alkynes8. The 1764 to 1509 peaks result from the stretching bands of function group C = O9. The peak at 1384 to 1104 results from aromatic amines and the peak 1019 and 934 indicates the C-N stretching. The peaks of below 834 and above 614 indicate alkanes and C-H bend. Further, the FTIR spectrum of ZnO NPs showed peaks at 3444, 3384, 3342, 3288, 3225, 3201, 2973, 2946, 2898, 2745, 2343, 1767, 1638,1590, 1591, 1497, 1383, 1236, 1152, 1077, 1020, 924, 831, 759, 738 cm-1 due to symmetric stretching vibration of surface bounded zinc nitride molecules (Figure 4b). Therefore, these results clearly demonstrated that Zn nitride acted both as reducing and capping agents in ZnO NPs formation.
The XRD patterns of the zinc oxide nanoparticles show well defined peaks located at Bragg angles (2? = 20–80 degrees) The zinc oxide nanoparticles showed good crystalline nature and pure with value of 31.75O (100), 34.440 O (002), 36.252 O (101), 47.543 O  (102), 56.555 O (110), 62.870 O (103), 67.917 O (112) and 76.95 O (202). No peaks corresponding to impurities were detected (Figure 5a and 5b). The average crystallite sizes (s) were calculated using Debye–Scherrer equation as below10. The preferred orientation corresponding to the plane (101) is observed in the samples. 

Debye–Scherrer equation            0.89?
  D =   -----------------
           ß cos ?/Q

Where D, 0.89 is the scherre’s constant, ? is the x-ray structure (1.54 Å), ß is full width at half maximum (FWHM) of the selected diffraction peak corresponding to 101 plane the peak located at 2 ? = 36.25O and ? is the Bragg’s angle of diffraction.   The crystallite size of ZnO NPs obtained using this formula is 24.84 nm which is under fall of the range of 20-26nm. TEM image and selected area diffraction pattern of ZnO nanoparticles are shown in Figure 6 selected area diffraction patterns of the nanoparticles indicates that the ZnO nanoparticles prepared via solid state reaction method are crystalline in nature. Nanoparticles obtained in this case are adhering to one another. Agglomeration of nanoparticles is more in these images. The average particle size is 20- 26 nm which is in agreement with the crystallite size obtained from XRD. The SAED pattern of TEM images clearly indicates the crystalline (bright sports) or poly-nano crystalline (small sports mainly up to a ring, each spot arising from Bragg refection from an individual crystallite).  The SAED pattern shows diffraction rings of the synthesized ZnO NPs at (1?0?0), (0?0?2), (1?0?2), (1?1?0) and (1?0?3) lattice planes, indicating that ZnO NPs presented in the TEM images are nano-crystalline as shown in figure 6 d. The particle size determined from the TEM analysis is in good agreement with that of the XRD analysis. An average particle size of 20-26 nm is found in agreement with tunneling electron microscopy analysis results. A high-resolution transmission electron microscope (HRTEM) indicates that ZnO nanoparticles are highly crystallized, with a size of 26 nm and hexagonal wurtzite structure (Figure 6a and 6b).  Other images further provided the much evident in high resolution images (Figure 6c). It may be possible due to van der Waals interactions between the surface molecules of the nanocrystallites forms that driving force for self assembly and ten colloidal nanocrystal can be assembled to form of solids. In addition, due to the capping ability of starch, the solvent may behave as a microemulsion system, causing individual ZnO subcrystal to grow up separately and finally assemble to from secondary ZnO nanoparticles. 
SEM images have a peculiar 3D appearance and helps in the interpretation of the surface morphology of nano compounds. The resolution power is almost similar to that of TEM. Figure 7 shows SEM results of ZnO nanoparticles. The SEM images it was observed that the particles were well shaped. Most of the particles were hexagonal in shape.  The average crystallite size of Zn O nanoparticles were observed at 200nm (Figure 7a to 7d).   
The SEM micrograph (Figure 7a) clearly showed nano structural homogeneities and remarkably different morphologies of the ZnO nanoparticles. The SEM result showed the presence of agglomerated nanoparticles with an average diameter of 20-26 nm. Therefore, from this observation only the rough morphology was found. Nevertheless, the accurate sizes and morphology of the nanoparticles can be estimated from the TEM analysis. 


Authors are highly thankful to Chairman and Director for providing necessary facility of Biotechnology Department of this Institute. Authors are highly acknowledged Department of Science and Technology, Uttar Pradesh (CSTUP) for financial support vide reference no CST/1586 to carry to this work.