Effect on Optical and Antibacterial Activity of SnO₂ and CuO Blended SnO₂ Nanoparticles

Suresh Gopal¹, Baskaran Iruson^1*, Sathyaseelan Balaraman^2*, Senthilnathan Krishnmoorthy³, Manikandan Elayaperumal⁴

¹Department of Physics, Arignar Anna Govt. Arts College, Cheyyar, India.
²Department of Physics, University College of Engineering Arni (A Constituent College of Anna University Chennai), Arni, India.
³Department of Physics, VIT University, Vellore, India.
⁴Department of Physics, Thiruvalluvar University, TVUCAS Campus, Thennangur, India.

DOI: 10.4236/snl.2023.132001                

Abstract

Nanocrystalline SnO₂ and CuO doped with SnO₂ were prepared by the co-precipitation method and characterized for different physiochemical properties and microbiological activity. The composition and morphological formation were characterized by XRD, HRTEM, Raman, FTIR, and UV-vis spectroscopy. The Powder X-ray analysis reveals that Sn4+ ions have substituted the Cu²⁺ ions without changing the monoclinic structure of SnO₂ but the average particle size of the SnO₂ and CuO doped SnO₂ samples from 11 and 5 nm respectively. However, it exhibits an inhibiting strong bacterial growth against tested bacterial strains.

Keywords

SnO₂, CuO Doped SnO₂, Physiochemical Properties, Microbiological Activity

1. Introduction

Recently, metal oxide nanoparticles received great interest and attention from dynamic researchers in the application of biomedical field technology [1] . Among the Cu doped SnO₂ nanoparticles are considered very interesting materials in chemical and physical studies. As highly efficient catalysis, sensors and biosensors, and photodegradation owing to their potential features and unique properties include semiconductivity and less toxicity [2] [3] [4] [5] . Stannic Oxide is a colorless, odorless, diamagnetic, and amphoteric solid. SnO₂ is an important wide bandgap semiconducting metal oxide (Eg = 3.6 eV, 330 K) that has a wide range of applications, such as in transparent conducting electrodes, gas sensors, Li batteries, and optoelectronic devices [6] [7] [8] [9] . The p-type transition metal oxide with a narrow bandgap CuO nanoparticles, Eg = 1.2 eV shows unique properties, such as super paramagnetism and high magnetic susceptibility at low temperatures [10] [11] [12] [13] . Copper oxide nanomaterials may have the advantage of a lower surface potential barrier than that of the metals, which affects electron field emission properties. Copper-oxide is considered a potential field emitter, an efficient catalytic agent, and a good gas sensing material. An improved understanding of nanoparticles and biological cell interactions can lead to the development of new sensing, diagnostic, and treatment capabilities, such as improved targeted drug delivery, gene therapy, magnetic resonance imaging (MRI) contrast agents, and biological warfare agent detection [14] [15] . Nano-sized metallic copper and its oxides possess the good potential for photo-catalytic, sensing applications [16] [17] [18] .

In recent years, different methods were used to synthesize various metal oxide nanoparticles, such as the mechano chemical method [19] , solvothermal [14] sol-gel method, chemical co-precipitation method [16] [17] . In addition, various attempts were made to enhance the biological activities of metal oxides [20] [21] . The antibacterial/biological activities of pure and doped SnO₂ nanoparticles were recently studied by researchers [22] [23] . Numerous types of doped nanoparticles showed outstanding antibacterial properties against different bacteria such as Escherichia coli, K. neumo, and S. aureus, etc. These nanoparticles can induce membrane stress by direct contact with walls of bacterial cells, damaging and disrupting cell membranes and leading to cell death [24] [25] [26] [27] [28] . Compared to the pure SnO₂ nanoparticles, the Cu doped SnO₂ nanoparticles inhibit more of those bacterial. Therefore, in this study, an attempt was made to synthesize both pure and Cu dope SnO₂ nanoparticles in the absence of reducing agents and their antibacterial activity against three bacterial.

2. Experimental Section

2.1. Co-Precipitation Method

Analytical grade Tin tetrachloride Dehydrate (SnCl₄·2H₂O), Copper(II) nitrate hydrate(Cu(NO₃)₂ xH₂O), and Ammonia solution (NH₄OH) were used as starting materials for Sn, O & Cu, respectively to prepare nanoparticles of SnO₂ compound in the precipitation method. Then the mixture was stirred for 30 min. After mixing, the precipitation of the dissolved chemicals was achieved by the addition of a 4 M NH₄OH solution drop by drop with continuous stirring for about 30 min. In this method, the process of precipitate formation was controlled by pH and temperature change. Precipitates were then filtered, washed away properly with de-ionized water to eliminate any chloride or other impurity. Then these particles were dried at 120˚C for 12 h in an oven. Finally, the synthesized particles are fully dried form were ground to a fine powder in Figure 1.

Figure 1. Preparation flowchart of CuO doped SnO₂ nanoparticles.

2.2. Characterization

The prepared CuO-doped SnO₂ nanoparticles underwent analysis to identify their structure, surface morphology, composition, and also to know about optical properties. The structural properties of CuO-doped SnO₂ nanoparticles were studied using an X-ray diffractometer (Philips PW1700) with Cu Kα (λ = 1.5406 Å) radiation in Bragg angle range of “20 - 80”. The Fourier transform infrared (FTIR) spectra of the samples were collected using an AVATAR 360 spectrometer with KBr as compressed slices, in the range of 4000 - 400 cm⁻¹. Absorption spectra and Optical band gap was measured using OPTIMA SP-3000 UV-Vis Spectrometer in the range of 300 - 800 nm. High-resolution transmission electron microscope (HRTEM) was taken with a JEOL-3010 operating at 200 kV and EDX spectra of prepared CuO-doped SnO₂ nanoparticles.

2.3. Antibacterial Activity

Microbiological activities of the SnO₂ nanoparticles are examined against clinically isolated; gram-negative E. coli bacteria by Agar well diffusion method. The SnO₂ nanoparticles are diffused out into the medium and interacted in a plate freshly seeded with the test organisms. The resulting zones of inhibition will be uniformly circular as there will be a confluent lawn of growth. The diameter of the zone of inhibition is measured in centimeters. The medium is prepared by dissolving 28 g of the commercially available Nutrient Agar Medium (Hi-Media) in 1000 mL of distilled water. The dissolved medium is autoclaved at 15 lb pressure at 121˚C for 15 min. The autoclaved medium is mixed well and poured onto 100 mm Petri plates (25 - 30 mL/plate) while still molten. 1 L of nutrient broth is prepared by dissolving 13 g of commercially available nutrient medium (Hi-Media) in 1000 mL distilled water and boiled to dissolve the medium completely. The medium is dispensed as desired and sterilized by autoclaving at 15 lb pressure (121˚C) for 15 min. Gentamycin with a concentration of 20 mg/mL is used as the positive control.

3. Results and Discussion

3.1. X-Ray Diffraction Analysis

The XRD pattern of SnO₂ and CuO doped SnO₂ are illustrated in Figure 1 The growth of nanoparticles reveals along (110), (101), (200), (211), (220), (310), (301) plane at an angle 26.6490, 33.9450, 51.6110, 54.6480, 61.8460, 64.9060, 78.4270 respectively, which is indexed to the tetragonal rutile structure of SnO₂ (JCPDS file no. 71-0652) [29] [30] . Crystallites sizes of nanoparticles were obtained using Debye Scherer’s formula and were found to be in the range 10 - 15 nm. The significant effect of Cu doping on structural parameters of the nanoparticle can be seen in Figure 2 clearly. Diffraction maxima intensity along (110) is reduced while noticeable improvement is observed in diffraction maxima intensity within Cu doping concentration. This confirms the Cu atom successfully replaced the Cu atom from the SnO₂ lattice and developed Cu doping SnO₂ material (Figure 3).

Figure 2. Power XRD pattern of the SnO₂ and CuO-doped SnO₂ nanoparticles.

Figure 3. The XRD pattern of the CuO doped SnO₂ nanoparticles.

3.2. Optical Analysis

Understanding the photosensitive behavior of nanoparticles of SnO₂ and CuO doped SnO₂ to explore electronic structure information of nanoparticles is essential Figure 4, illustrated absorbance spectra of nanoparticles in the UV-vis region. Pure and Cu doped nanoparticles reveal strong absorbance (band edge) at 446 and 566 nm which arises due to the interband transition in SnO₂ material [31] [32] . This confirms the reduction in defects vacancy and photoresponse improved. Tauc’s plots of nanoparticles are illustrated in Figure 5. From Figure 5 to extrapolate linear portion of plots to zero absorption coefficient on the x-axis, these intercept values are the optical band gap of materials.

3.3. FT-IR Analysis

Figure 6 shows the FTIR spectra showing absorption regions and their functional groups of SnO₂ and CuO doped SnO₂ nanoparticles. The broadband around the 3392 cm⁻¹ and band at 1626 cm⁻¹ can be attributed to the O-H vibration of absorbed water on the sample surface. Intense broadband around 661 cm⁻¹ was observed the samples are assigned to the O-Sn-O bridge functional groups of SnO₂ which confirms the presence of SnO₂ as a crystalline phase [33] [34] .

3.4. HRTEM Analysis

The morphology of SnO₂ and CuO doped SnO₂ composite was investigated by TEM techniques (Figure 7 and Figure 8). Figure 7 and Figure 8 display the HRTEM images of SnO₂ and CuO doped SnO₂ nanoparticles and reveal the aggregated. Hence, HRTEM analyses also indicate the successful formation of spherical shapes. The selected area diffraction (SAED) pattern of SnO₂ and CuO doped SnO₂ shows the ring patterns, which is a characteristic feature of polycrystalline. As is evident, an interplanar distance of 0.333 nm is close to the d-spacing of the (110) planes of the tetragonal rutile SnO₂. On the other hand, an interplanar distance of 0.252 nm is in good agreement with the d-spacing of the (002) planes of the monoclinic structure CuO [35] . From these results, CuO-SnO₂ nanocomposite structure has been possibly facilitating the creation of the p-n junctions compared with large-grained CuO-SnO₂ normal composite materials.

Figure 4. The UV pattern of the SnO₂ and CuO doped SnO₂ nanoparticles.

Figure 5. The Band gap energy of the SnO₂ and CuO doped SnO₂ nanoparticles.

Figure 6. FTIR spectrum of the SnO₂ and CuO doped SnO₂ nanoparticles.

Figure 7. The HRTEM of the SnO₂ nanoparticles.

Figure 8. The HRTEM of the CuO doped SnO₂ nanoparticles.

3.5. EDX Analysis

The surface electronic state and composition of SnO₂ and CuO doped SnO₂ were assessed by EDX analysis (Figure 9). The survey EDX spectrum shows the clear signals of Copper (Cu), oxygen, (O) and tin (Sn), Nickel (Ni), Calcium (Ca), and Chlorine (Cl) elements, which are consistent with the EDX reports. It is clear from Figure 9 that Cu ions are successfully incorporated in the host SnO₂ material. The consistent and sharp peaks with tin oxide and cupric-tin oxide demonstrated that both synthesized nanoparticles were crystalline. Hence, synthesized nanoparticles were obtained in their pure forms.

3.6. Antibacterial Activity Analysis

CuO doped SnO₂ a nanoparticle were investigated to evaluate antibacterial activity against bacterial strains. As K. neumo, S. aureus and E. coli by Agar-well diffusion method. Evaluation of the antibacterials activity of these varieties recorded in Table 1 and illustrated in Figure 10. The results revealed that higher inhibition zone was recorded in E. coli 10 mm in 0.005 moles of CuO doped SnO₂, a gram +ve bacterial strain whereas gram +ve K. neumo showed inhibition of 9 mm in 0.01 mole CuO doped SnO₂ (Figure 10). Both the bacterial strains were tested against 1 mg SnO₂ nanoparticles. S. aureus is a major hospital-acquired pathogen thus the prevention of microbial surfaces is of utmost concern in the health care system similar results were reported [36] [37] [38] [39] [40] . Metal oxide nanoparticles possess a high surface area which is responsible for their increased chemical and biological activity. It is assumed that nanoparticles interact with the cell wall of the bacteria and disturbs the membrane permeability and respiration system of the bacteria and consequently, leading to their death. That created by nanoparticles depends on their bacterial potential.

Figure 9. EDX of the CuO doped SnO₂ nanoparticles.

Table 1. Antibacterial Activity of the CuO doped SnO₂ nanoparticles.

Figure 10. Antibacterial Activity of the CuO doped SnO₂ nanoparticles.

4. Conclusion

In summary, SnO₂ and CuO doped with SnO₂ were prepared by the co-precipitation method. As grown nanoparticle structural and optical properties were studied in detail in correlation with the Cu doping concentration. Structural studies of nanoparticles found that the crystallinity of the particles becomes improved on Cu doping in the SnO₂ matrix. The current study showed a significant level of antibacterial activity in all tested bacterial strains. Further, re-engineering offers interesting and immense future impact with unexplored biological activities.

Acknowledgements

This research has been funded by Tamilnadu State Council for Science and Technology under grant number, C. No. TNSCST/STP-PRG/AR/2018-2019/9333.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

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