Synthesis, Characterization and Antimicrobial Activity of Copper Oxide Nanoparticles Using Sol-Gel Method

This study investigates a novel way for producing copper oxide (CuO) nanoparticles using the sol-gel process and citric acid as a surfactant. In this technique, water is used as a potent solvent. Because of its low cost, ease of preparation, and commercial practicality, the synthetic approach is environmentally beneficial. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive X-ray spectroscopy (EDX), Fourier Transform Infra-Red spectroscopy (FTIR), and Ultra-Violet visible spectroscopy (UV-Vis) were used to examine the antimicrobial activity of bacterial, fungal, as well as Pneumonia activity. Copper oxide NPs synthesized demonstrates highly scattered characterization and application findings. The green method is a practical, eco-friendly, simple, and valuable method for producing copper oxide nanoparticles

The unique properties of nanomaterials, as well as their high surface-to-volume ratio, have made them a viable and new tool in many scientific disciplines. This flexible material has numerous applications, including antimicrobial activities, photovoltaics, sensors, storage devices, medicine administration, photocatalytic training, and so on. Copper oxide nanoparticles most used because they are cheap, common, have low toxicity, and are easy to manufacture. Because of their high catalytic activity and durability, photo-catalysts constructed of single metal oxides are becoming increasingly popular [1-2].

A multitude of procedures can be used to create single metal oxide nanoparticles. Solid-state synthesis, the hydrothermal method, the electrochemical approach, the sol-gel technique, co-precipitation, microwave-assisted synthesis, the thermal decomposition method, and others are examples[3-4]. We choose the sol-gel process due to worries about overheating and hazardous solvents in other procedures. The sol-gel method is the most environmentally friendly and cutting-edge of these techniques because it does not require high pressure or high temperature, is inexpensive, and allows for easy monitoring of the crystalline size and structure of the nanomaterial through pH modification of the medium while preparing a large amount of sample. This paper describes a simple sol-gel method for producing copper oxide (CuO) nanoparticles with citric acid as a suitable surfactant. Synthesized Copper oxide nanoparticles were screened for biological activity of antibacterial, antifungal, and antimalarial activity which showed better to excellent results.

The unique properties of nanomaterials, as well as their high surface-to-volume ratio, have made them a viable and new tool in many scientific disciplines. This flexible material has numerous applications, including antimicrobial activities, photovoltaics, sensors, storage devices, medicine administration, photocatalytic training, and so on. Copper oxide nanoparticles most used because they are cheap, common, have low toxicity, and are easy to manufacture. Because of their high catalytic activity and durability, photo-catalysts constructed of single metal oxides are becoming increasingly popular [1-2].

A multitude of procedures can be used to create single metal oxide nanoparticles. Solid-state synthesis, the hydrothermal method, the electrochemical approach, the sol-gel technique, co-precipitation, microwave-assisted synthesis, the thermal decomposition method, and others are examples[3-4]. We choose the sol-gel process due to worries about overheating and hazardous solvents in other procedures. The sol-gel method is the most environmentally friendly and cutting-edge of these techniques because it does not require high pressure or high temperature, is inexpensive, and allows for easy monitoring of the crystalline size and structure of the nanomaterial through pH modification of the medium while preparing a large amount of sample. This paper describes a simple sol-gel method for producing copper oxide (CuO) nanoparticles with citric acid as a suitable surfactant. Synthesized Copper oxide nanoparticles were screened for biological activity of antibacterial, antifungal, and antimalarial activity which showed better to excellent results.

Characterization

Copper chloride, citric acid, hydrochloric acid, and ammonium hydroxide were purchased from SD-Fine Chemical Company and used without further purification. The X-ray diffraction (XRD) pattern was recorded by the Rigaku X-ray Diffractometer with a Cu K-α radiation source (λ=1.5406 A°) operated at 40 kV. Field emission scanning electron microscopy (FE-SEM) images were obtained on JEOL 6390LA, Japanand the energy dispersive spectrometry (EDS) analysis was studied by JEOL/JEM 2100, Japan, with an acceleration voltage of 200 kV. Fourier transform infrared (FT-IR) spectra were recorded on Shimadzu IR spectrophotometer. Ultraviolet visible (UV-Vis) spectra were recorded on Thermo Scientific UV-Vis’s spectrophotometer.

Synthesis of CuMn2O4 nanoparticles

Synthesis of Copper oxide (CuO) nanoparticles was carried out by the sol-gel method. Initially, 0.25 M of copper chloride were dissolved in 100 ml of distilled water. 0.1 N hydrochloric acid improves the solubility of copper chloride in water. Both the solutions were mixed with constant stirring. After mixingthe solutions, 1 gm of the citric acid solution was added as a surfactant. The pH of the above solution was adjusted at 8-8.5 (basic) using 3 to 3.5 ml NH4OH solution. Precipitation was formed, which stirred with constant stirring for an hour at room temperature. The mixture was filtered using Whatman filter paper No. 42 and washed with deionized water 2-3 times. The obtained product was dried in an oven at 100˚C for 2 hours. Finally, the dried material was calcinated for 3 hours at 500˚C in the furnace. The black-colored precipitate was obtained as a final product and was stored for further study (Figure 1).

Figure 1: Flow Chart for Synthesis Method of CuO NPs

UV-Visible Analysis of CuO oxide Nanoparticle

The UV-Visible diffused reflectance spectra of nanostructured equimolar concentration of copper oxide NPs are shown in Figure. It has a wide range of absorption at 260 to 300 nm [5]. This proves that equimolar concentrations of copper oxide NPs result in lower reflectance. These findings suggest that synthesized copper oxide NPs metal to shift the absorption of the resulting nanoparticles from the infrared to the visible. This indicates that transition metal oxides that have been optically active.

The copper oxide NPs effect on the band gaps of CuO semiconductors is the more immediate cause of the change in reflectance. The increased photogeneration rate of charge-transfer between Cu2+ electrons valence band greatly improves the photo reactivity, catalytic activity of copper oxide NPs (Figure 2).

Figure 2: Uv-Vis’s data of CuO NPs

FTIR analysis of CuO oxide nanomaterial

Fourier transform infrared spectrometer confirms the formation of metal oxide bonds in the CuO nanoparticles as shown in Figure 2. Investigation of nanomaterial is observed at the wavelength range from 397 cm-1 to 3980 cm-1. The low-frequency vibrations of the M-O bond appear below 1000 cm-1. In Figure 1the firm peaks at position 403.12cm-1   and 462.92 cm-1 represent Cu–O stretching of CuO stretching vibrational modes, respectively and the band that appeared in the range of 800–1300 cm-1 is recognized as the stretching vibration of –OH (Figure 3). These results as approximately match with another study [6-7].

Figure 3: FTIR data of CuO NPs

XRD characterization of CuMn2O4 oxide nanomaterial

The X-ray diffraction technique investigated the chemical, structural, and spectroscopic properties of CuO nanomaterial. All X-ray diffraction peaks were indexed according to the standard data for CuO as shown in Figure 2. The significant peaks are obtained for 2θ at 32.5°,35.49°, 38.71°, 47.42°, 56.29°, 61.59°, 66.32068.11°and 75.17°, corresponding to the planes (110), (111), (111), (220), (020), (113), (022) (220) and (004) respectively (Figure 4). In addition, the Fd-3m space group and Monoclinic Crystal system of CuO nanomaterial are recognized in the X-ray diffraction pattern and correctly matched with the standard JCPDs card no. 05-0661[8-9]. The average crystallite size (D) of CuO nanomaterial was calculated by using the Scherer formula [5, 10].

Where, K is a shape factor, D is the size of the nanomaterial, λ is the incident X-ray beam’s wave length, θ is Bragg’s diffraction angle, and β is the Full width half maximum. The average particle size of the investigating nanomaterial was 15.5 nm.

Figure 4: XRD data of CuO NPs

SEM and EDX studies of CuO oxide nanomaterial

The morphology and complete structures of CuO nanomaterial were contributed by scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) spectroscopy. SEM images of CuO nanomaterial synthesized by sol-gel method from chloride precursors strengthening the precursors at 500°C are shown in as shown in (Figure 6 and Figure 7). Scanning electron microscope (SEM) instrument in the range of scale taken between 500 nm and 1μm. 

The elemental compositional investigation of CuO nanomaterial is shown in as shown in (Figure 8 and Table 1). The presence of Cu and O and the Cu/O ratio were determined by EDX investigation, which matches perfectly with CuO. This confirms the availability of copper and oxygen with a weight percentage of 94 %, 6 %, and atomic percentages of 79.9% and 20.1% respectively.

Figure 5: FESEM data of CuO NPs

Figure 6: FESEM data of CuO NPs 

Figure 7: EDX data of CuO NPs

Table 1: EDX data of CuO NPs

In recent years, nanomaterial has a broader range of applications and uses in various fields. Some researchers have studied the use of nanomaterials for catalytic activity for oxidation [11], photo-catalytic activity [12], a high-performance electrode for supercapacitors [13], solid oxide fuel cells [14]and catalytic ozonation membrane reactor [15]. These example sconfirm that CuO oxide nanomaterial is environmentally supportive for living organisms and extremely useful in different fields.

Biological Activity

Synthesized copper oxide nanoparticles were tested for their antimicrobial efficacy against four different bacteria. - S. aureus (MTCC 96), E. coli (MTCC 443), P. aeruginosa (MTCC 1688), S. pyogenus (MTCC442), and three fungi-C. Albicans (MTCC 227), A.  clavatus (MTCC1323)and A. niger (MTCC282 )using broth dilution method[16-17]. Gentamycin, Ampicillin chloramphenicol, ciprofloxacin and norfloxacin were used as the standards for antibacterial activity, whereas griseofulvin and nystatin were used as the standards for antifungal activity. Minimum Inhibitory Concentration (MIC) values were used to describe the outcomes. The MIC of a drug is the smallest concentration of the sample that clearly stunts the growth of the microbe. Minimum Inhibitory Concentration (MIC) values were used to describe the outcomes. The MIC of a drug is the smallest concentration of the sample that clearly stunts the growth of the microbe[18-19].

The efficiency of synthesized copper oxide nanoparticles to act as antimalarial hits was studied in-vitro against Plasmodium falciparum in 96-well microtitre plate according to the different reported method [20-21].chloroquine was used as the standard, and the results were reported in terms of IC50 values. All the screening was performed at Microcare Laboratory, Surat, Gujarat, India. 

Antibacterial activity

Antibacterial activity was tested on the synthesized copper oxide nanoparticles compounds[22-23]. The broth dilution technique was used to demonstrate antibacterial activity against E. coli (MTCC443), P. aeruginosa (MTCC1688), S. aureus (MTCC96), S. pyogenus (MTCC442) bacterial strains using Gentamycin, Ampicillin, chloramphenicol, ciprofloxacin and norfloxacin as the standard drugs. Copper oxide nanoparticles showing a strong and excellent antibacterial activity against S. aureus. The standard chloramphenicol (50µg/mL) other had weaker antibacterial activity against E. coli, P. aeruginosa and S. pyogenus as compared to the standard chloramphenicol show in (Table1). copper oxide nanoparticles showing a weak antibacterial activity against E. coli, P. aeruginosa, S. aureus and S. pyogenus the standard Gentamycin, Ampicillin, ciprofloxacin and norfloxacin show in (Table 2).

Table 2: Antibacterial activity data of CuO NPs

Antifungal Activity

Antifungal Activity was studied against C. albicans (MTCC227), A. niger (MTCC282), A. clavatus (MTCC1323) fungal strains. The results of antifungal activity reveal that the copper oxide nanoparticles synthesized compounds showed lower antifungal activity as compared to the standard Nystatin and Greseofulvin. The compounds were less active against the C. albicans, A. niger and A. clavatus fungal strains in comparison with both the standards (Table 3).

Table 3: Antifungal activity data of CuO NPs

Antimalarial Activity

Copper oxide nanoparticles synthesized compounds showed the antimalarial activity was carried against Plasmodium falciparum. The compound copper oxide nanoparticles showed less antimalarial activity.  The results of antimalarial activity revealed that copper oxide nano particles compounds were moderately active but less potent than the standard chloroquine, which is show in (Table 4).

Table 4: Antimalarial activity data of CuO NPs

In summary, we report the synthesis, characterization, antibacterial, antifungal and antimalarial activity of copper oxide nano particles antibacterial activity against E. coli as they had lower MIC values in comparison with the standard ampicillin. Copper oxide nanoparticles compounds the compounds were less active against the C. albicans, A. niger and A. clavatus fungal strains in comparison with both the standards. The compounds exhibited moderate antimalarial activity but less than the standard chloroquine. Antibacterial and antimalarial entities are thus revealed by the current studies, highlighting their potential future significance in medicinal chemistry. A CuO oxide nanomaterial was successfully prepared using a sol-gel, an environmentally supportive method. In the synthesis of CuO nanomaterial, copper chloride with using citric acid as a surfactant.  This method is eco-friendly, cheap, easy handling, non-hazardous, and harmless aqueous solvent systems.

Funding

This research received no external funding.

Acknowledgments

This research has no acknowledgment.

Conflicts of Interest

The authors declare no conflict of interest.