1 Introduction

Infections caused by micro-organisms like bacteria, fungi, viruses, or parasites have impacted public health in many nations and are a significant source of death in the biosphere. Gram-positive and gram-negative bacteria species are reported for fatal diseases such as endocarditic, meningitis, pneumonia in leukemic patients, and septicaemia in those with breast cancer [1]. Bacillus subtilis (MTCC 441) is a multi-drug resistant pathogen, a family of sixty bacteria members, and is also stated as resistant to a range of antibacterial agents. Staphylococcus type of bacteria is usually reported as a significant clinic bacterium, as well as the transporter of methicillin resistance genes (mec A). Different strains of Staphylococcus are mainly opposed to a wide range of prescriptions towards β-lactam medicine such as cephalosporins, penicillin, aminoglycosides, etc. Green synthesis has presently been focused as a new multidisciplinary route based on the preparation of helpful nanocomposite materials from different inorganic metal salts [2, 3]. Several biosynthesized nanocomposites have been revealed to have various remarkable applications including, antibacterial, anti-carcinogenic, anti-parasitic, antidiabetic, and antioxidant properties. Metal oxide nanocomposites can be utilized as an energetic substitute for conventional antibacterial drugs in the antibacterial study [4, 5]. Bimetallic oxide nanocomposite materials are significant nanomaterials that have received a lot of interest owing to their ability to integrate the proper characteristics of several nano-scales that are not present in conventional composites and pure nanoparticles. Furthermore, mixed bimetallic oxide NCs have been known as suitable substitutions to control the drawbacks of clusters of nanoparticles. The most important shortcoming of nanoparticles having a small size is that it prevents them from being used in a varied range of uses because of aggregation, which reduces their surface area along with, their activity and efficacy [6]. According to research findings, green synthesized nanocomposites are known to encourage reactive oxygen species production with their electron-releasing traits [7]. The electrostatic interaction between the positive charges and negative microbial membrane on metal oxide nanocomposites was used to detect bacterial targeting in metal oxide nanocomposites that were considered to kill gram + ve and gram −ve bacteria [1]. The combination of both CuO and NiO as one of the important elements towards the preparation of the nanomaterials might increase not only the resultant nanocomposite features but, also facilitate the additional applications such as photocatalytic, antioxidants, antifungal, anti-inflammatory, and antibacterial agents in food packed manufacturing. It has been illustrated that CuO/NiO nanocomposites are a capable material for antibacterial properties. However, only rare research has been described on the preparation and bactericidal applications of bimetallic CuO/NiO composite nanomaterials [1]. Researchers have developed different mixed metal oxide nanocomposites that act as antioxidants.

Copper and nickel oxide nanoparticles have been studied for their antioxidant activity due to their potential to mitigate oxidative stress, a key factor in various diseases and aging. These nanoparticles possess unique properties that can scavenge harmful free radicals and reduce oxidative damage in biological systems. They are known for their ability to catalyze the decomposition of reactive oxygen species (ROS) and exhibit free radical scavenging properties. Additionally, their high surface area and small size allow them to interact effectively with biomolecules, making them promising candidates for various biomedical applications, including drug delivery and therapeutic interventions. Nonetheless, it's essential to conduct further research to understand their long-term safety and effectiveness before widespread clinical use [8]. Antioxidants are substances that can shield live cells against free radicals, which are essential in the development of heart disease, cancer, and other health issues [8]. For antibacterial and antioxidant applications, it is important to synthesize the Cu/NiO composite nanomaterials. Metal oxide nanocomposites have been prepared using a number of fabrication approaches, including physical, chemical, and green techniques. The chemical and physical approaches have been found to be non-cost effective, toxic and have adverse effects on human beings and earth as well. Some important physical, chemical and green routes for the fabrication of different nanocomposites (NCs) are microwave assisted, hydrothermal, sol–gel and mechanical alloying [9, 10]. One of them, green microwave assisted is one of the fastest routes for the production of metal oxide nanomaterials. This approach with plant extract is cost effective, eco-friendly and non-toxic for synthesis of different nanocomposites. The different nanostructures including CuO, ZnO, NiO, Co3O4, Fe2O3 are fabricate through microwave assisted approach [11]. Nickel oxide and copper oxide are two metal oxides that have received scientific interest for the multifunctional applications. Nickel oxide nanoparticles exhibited super paramagnetic as well as ferromagnetic behaviour with multifunctional applications in different fields such as gas sensors, catalyst, battery, cathode materials in supercapacitors, antibacterial and electro chromic films [12]. In contrast, p-type semiconductor copper oxide has monoclinic crystal and low band gap (~ 1.2 eV), having outstanding chemical reliability, ecological friendly, anticancer, antifungal, anti-inflammatory, and anti-bacterial applications [13]. Few studies have been conducted on the microwave synthesized Cu/NiO nanocomposites. Copper–Nickel Oxide nanocomposites (Cu–NiO) were used for photocatalytic degradation of volatile organic compounds and photo electrochemical hydrogen evolution [14]. In the present work, Cu/NiO nanocomposites using Ipomoea carnea leaf extract were prepared by microwave assisted green approach and the irradiation of time, the power of irradiation and morphology of the nanocomposites were investigated. And the antioxidant and bactericidal potential of the synthesized Cu/NiO nanocomposite materials was systematically investigated against DPPH and human pathogens. Improvement in the antibacterial activity was exhibited by Cu/NiO nanocomposite materials. Ipomoea carnea plant species is also known as the pink morning glory and is sometimes referred to as the besharam or behaya plant because of its endless spreading. The various plant components, including the stem, flowers, and leaves, are widely utilised for their anti-oxidant, bactericidal, anti-carcinogenic, anti-fungal, anti-inflammatory, and wound-healing properties. Alkaloids and polyphenols found in Ipomoea carnea can be employed as reducing and stabilizing agents for synthesizing nanoparticles [15]. Ipomoea carnea derived nanoparticles have well-proven antibacterial capabilities, and numerous researchers have suggested an inhibitory mechanism [16]. Using precursors [Cu(CH3COO)2.H2O] and [Ni(NO3)2.6H2O], the Ipomoea carnea leaf extract was employed in the current investigation to produce CuO/Cu2O-NiO NCs under microwave. Moreover, the microwave green method will demonstrate the fastest technique to investigate the antibacterial and antioxidant properties of as-produced CuO/Cu2O-NiO NCs. This present research is totally based on the evaluation of the antibacterial potential of NCs synthesized from leaf extract of Ipomoea carnea against the bacteria viz. two Gram + ve and one Gram -ve pathogens. The ability of biosynthesized 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs to suppress human infections was assessed. The primary goal of this research is to examine and use the capacity of 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs to treat several kinds of bacterial diseases.

2 Materials and methods

2.1 Materials

Cu(CH3COO)2.H2O, 99.9% Merck, Ipomoea carnea dried leaves, Ni(NO3)2.6H2O, 99.9% Merck, distilled water, sodium hydroxide pellets (NaOH, 99.9%), Mueller Hinton broth (MHB), Nutrient agar, ciprofloxacin, DPPH, Agar–agar Type I, ascorbic acid (C6H8O6), and C2H5OH were used for the synthesis of 90:10, 80:20 and 70:30 CuO/Cu2O-NiO NCs. Pathogen colonies which include Gram-negative (MTCC 739) and Gram-positive (MTCC 441 & MTCC 737) were acquired from the CSIR-IMTECH, Chandigarh.

2.2 Methods

2.2.1 Extraction of leaf extract

The green Ipomoea carnea leaves were gathered from the nearby campus of the university. The collected green leaves were thoroughly cleaned using normal tap water around 2–3 times, and then it was rinsed with deionized water (DW) and dehydrated at ambient temperature for about 5–6 days. The dehydrated leaves were grinded into powder form through a mortar pestle. Then, 100 ml of deionized water (DW) was mixed with 5 g of the dried powdered leaves, and the mixture was refluxed at 85 °\({\text{C}}\) for 45–50 min. The prepared extract was clean and further utilized for the fabrication of different 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs after being stored at 4 \(^\circ {\text{C}}\) in a refrigerator to prevent thermal damage.

2.2.2 Synthesis of nanocomposites

The preparation of three 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites using the leaf extract of Ipomoea carnea in a microwave oven. The aqueous solution of 0.01 M (10 mM) [Cu(CH3COO)2.H2O] along with [Ni (NO3)2.6H2O] were magnetically stirred at different amounts such as 90:10, 80:20, and 70:30 to make a complete volume of 200 mL and also, 15–20 mL of leaf extract was used. The pH was then maintained at 12 by mixing 1 M (2 gm: 50 ml DW) NaOH through a burette and irradiating it in a simple microwave for 20 min. Colloidal solutions of different colours including green, dirty green, and dark brown precipitates were formed that indicates complete production of the different 90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposites. The precipitates were produced, cooled to ambient temperature, washed three to four times with C2H5OH and deionized water (DW), then further dried for 24 h in the oven at 90 °C. Figure 1 depicts a schematic depiction of a synthesized nanocomposite.

Fig. 1
figure 1

The fabrication approach of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs

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2.3 Characterization techniques

Utilizing different spectroscopic techniques, the prepared CuO/Cu2O-NiO NCs were characterized.

2.3.1 XRD

XRD, or X-ray diffraction (XRD, Rigaku Japan smart lab 9 kW rotating anode X-ray diffractometer Philips, 2θ = 5–90◦, CuK radiation with wavelength = 1.5418 Å), is a technique used for analyzing the crystal structure and crystalline size of a material by measuring the diffraction pattern produced when X-rays are scattered by the crystal lattice.

The following equations (Eqs. 1–4) were used to evaluate the full width at half maximum (FWHM), dislocation density (\(\delta\)), crystallite size (D), interplanar space (d), micro-strain (\(\varepsilon\)), and stacking fault (SF) of the synthesized CuO/Cu2O-NiO NCs.

$$D= \frac{0.9 \lambda }{\beta COS \theta }$$
(1)
$$\delta =\frac{1}{{D}^{2}}$$
(2)
$$\varepsilon =\frac{\beta COS \theta }{4}$$
(3)
$$\frac{2{\pi }^{2}}{45{\left(3tan\theta \right)}_{2}^{1/}}* \beta$$
(4)

where θ represents diffraction angle; β denotes FWHM; k denotes Scherrer constant; λ signifies wavelength.

2.3.2 SEM and EDS

Scanning Electron Microscopy and energy dispersive X-ray (model: SEM + EDX- Carl Zeiss model supra-55) is a technique that uses electron beams to create high-resolution, three-dimensional images of the surface of a sample and elemental composition of the samples.

2.3.3 TEM

Transmission electron microscopy (TEM-FP 5022/22-Tecnai G2 20 S-TWIN) is a technique that uses electrons to create detailed images of the internal structure of specimens at a nanoscale level.

2.3.4 UV–visible spectroscopy

UV–visible spectroscopy (UV-LABINDIA Analytical UV3092 UV–vis spectrophotometer) is a technique that measures the absorption of ultraviolet and visible light by a substance to determine its electronic structure and concentration. The direct energy band gap was approximated by using Eq. 5.

$${\text{E}}_{{\text{g}}} = \frac{{{\text{hc}}}}{\lambda }$$
(5)

Here c is the velocity of radiation; h is the plank constant.

2.3.5 FTIR

FTIR or Fourier Transform Infrared Spectroscopy (Perkin Elmer—Spectrum RX-IFTIR) is a technique used to analyze the infrared absorption or emission spectrum of a sample, providing information about its molecular composition.

2.4 Antibacterial and antioxidant activities of the CuO/Cu2O-NiO nanocomposites

2.4.1 Antibacterial activity

Gram-negative (MTCC 739) and Gram-positive (MTCC 441 & MTCC 737) pathogens were employed to assess antibacterial efficacy. Using a well diffusion method to explain microbial inhibition potential of prepared CuO/Cu2O-NiO nanocomposites [17, 18]. Media (MHB) and glass plates were disinfected by autoclaving at 15 psi (121 \(^\circ C\)) for 15 min. Under uninfected environments (laminar airflow about 25 ml of the media was filled into a separate plate. After solidification of the media, the different bacterial inoculum NaCl solutions were washed on the outside of agar plates. Cork-borer was used to form wells, and then 10, 25, and 50 mg/mL of 30 µL methanolic solution of each synthesized nanocomposites to different wells with methanol as −ve control and ciprofloxacin as + ve control. Afterward, MIC and MBC are followed. The 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs filled plates were placed in the incubator for 24 h at 37 \(^\circ C\) to analyze zones of inhibition, MIC and MBC of the synthesized CuO/Cu2O-NiO nanocomposites.

2.4.2 Antioxidant activity

The efficacy of the synthesized CuO/Cu2O-NiO nanocomposites to scavenge free radicals at different dosages such as 25, 50, 100, 200, 400, and 800 µg/mL, was assessed against the DPPH (0.1 mM) by serial dilution. Following dilution, the different prepared materials in the test tubes were kept at room temperature for about 30 min in the dark. By using the UV–visible spectrophotometer, the 1,1-diphenyl-2-picryl hydroxyl scavenger by different synthesized nanocomposites was measured at 517 nm when the color was shifted from deep violet to bright yellow [14]. The determination of % age scavenging activity using Eq. 6 at various dilutions.

$$\mathrm{\%Scavenging}=\frac{\mathrm{Absorbance \, of \, Ascorbic \, acid}-\mathrm{Absorbance \, of \, test samples}}{\mathrm{Absorbance \, of \, Ascorbic \, acids}}\times 100$$
(6)

3 Results and discussion

3.1 XRD analysis

Pure CuO, NiO, 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs XRDs were noted in 2θ values ranging from 20 \(^\circ\) to 80 \(^\circ\). The different 2θ diffraction peaks located at 29.56, 38.44, 43.86, 48.84, 61.89, 73.53, 48.07, and 36.31 represents (110), (111), (200), (202), (220), (311), (202), and (111) directions of cubic and monoclinic phases for CuO/Cu2O respectively, equivalent to the XRD diffraction patterns of JCPDS card No.: 80–1268 and 05–0667 [14]. The XRD peaks at 27.34, 37.26, 43.63, 62.92, and 75.54 attributed to (110), (111), (200), (220), and (311) peaks of cubic NiO, equivalent to the XRD data of JCPDS card No. 65–2901 & 04–0835 [19]. The diffraction patterns of three different synthesized NCs revealed that the diffraction patterns of CuO/Cu2O overlapped with the diffraction peaks of NiO i.e., (110), (111), (200), (220), (311), and (222). It is clear that as the concentration of CuO/Cu2O content in the nanocomposites rises (Cu: Ni 90:10, 80:20, and 70:30), the peaks of CuO/Cu2O become more intense. The full width at half maximum (FWHM), dislocation density (\(\delta\)), crystallite size (D), interplanar space (d), micro-strain (\(\varepsilon\)), and stacking fault (SF) of the synthesized CuO/Cu2O-NiO NCs reported in Table 1 [20].

Table 1 Different XRD parameters D, d, \(\updelta\), \(\upvarepsilon\) and SF of pure (CuO and NiO) and 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs
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Figure 2 shows that the (NCs A1) 90:10 CuO/Cu2O-NiO NCs exhibited small crystal size 23.14 nm which is less than those of (NCs B1) 80:20 (42.28 nm) and (NCs C1) 70:30 (29.80 nm) CuO/Cu2O-NiO nanocomposites. Due to the small crystalline size, 90:10 (NCs A1) is very active against pathogens.

Fig. 2
figure 2

The XRD patterns for pure CuO and NiO (a) as well as CuO/Cu2O-NiO NCs with varying Cu:Ni ratios 90:10 (NC1), 80:20 (NCs B1) and 70:30 (NCs C1) (b)

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3.2 Morphology and elementary analysis

Morphological structures of 90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposites synthesized by green microwave-assisted method are revealed in Fig. 3a, c, e). Figure 3 exhibits the formation of aggregated [21] particles of the synthesized nanocomposites. The morphological features have a strong impact on the antibacterial potential of the synthesized 90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposites. EDX study exhibits the elemental compositions of 90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposites in Fig. 3b, d, f. The EDX established the existence of Ni, Cu, and O in NCs. It is clear from EDAX and elemental % age that the nanocomposites are easily prepared. The compatible and spire peaks with CuO and NiO illustrate that the synthesized nanocomposites are polycrystalline in nature with no impurity phases. Hence, nanocomposites are obtained in pure form. Hassanpour et al. [22] have synthesized CuO/NiO nanocomposites via the microwave method. SEM results show the aggregation type of particles at different times of irradiation in a microwave. Sedighi et al. [23] have synthesized CuWO4 nanoparticles and CuWO4/NiO nanocomposite by using the co-precipitation method. These nanocomposites showed simply aggregated types of particles via SEM analysis.

Fig. 3
figure 3

Morphological characteristics of nanocomposite by scanning electron microscopy (a) 90:10 CuO/Cu2O NC at 100.00 KX; (b) EDXS spectra of 90:10 CuO/Cu2O; (c) 80:20 CuO/Cu2O NC at 50.00 KX; (d) EDXS spectra of 80:20 CuO/Cu2O and (e) 70:30 CuO/Cu2O Nc at 100.00 KX and (f) EDXS spectra of 70:30 CuO/Cu2O

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3.3 TEM analysis

TEM investigations of the synthesized CuO/Cu2O-NiO NCs showed aggregated small spherical particles with typical uniform quantum sizes of 4.078, 4.74, and 4.928 nm for the prepared 90:10 (NCs A1), 80:20 (NCs B1) and 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites (Fig. 4a–c). The NiO and CuO/Cu2O NPs were polydispersed which shows changeability in particle size while on the other hand; the CuO/Cu2O-NiO NCs were monodispersed.

Fig. 4
figure 4

SAED and TEM micrographs of (a) 90:10 (NCs A1), (b) 80:20 (NCs B1), and (c) 70:30 (NCs C1) of the synthesized CuO/Cu2O-NiO NCs and their particles size distribution

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The nature of developed nanoparticles here are comparable to previous results [5]. To understand the capping impact of the extract biomolecules, the synthesised nanocomposites were dry in an oven at under 100 \(^\circ C\) for 24 h instead of being subjected to high temperatures. Although this approach saves energy, it may be the reason why CuO/Cu2O and NiO NPs are agglomerative in nature. Contrarily, it is highly intriguing that the NCs were able to achieve consistent quantum sizes, which may have been made possible by the use of microwave synthesis and higher Cu solution concentrations in the fabrication of the nanocomposites with ratios of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO. The ring-like SAED (Selected Area Electron Diffraction) patterns of the 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs were shown in Fig. 4a–c. These findings suggest that all three synthesized CuO/Cu2O-NiO NCs are polycrystalline in nature. Similar outcomes were also reported by Mohammadi-Aloucheh et al. [9], whose findings can be analogized with those of the current investigation of the smaller average particle size of nanocomposites. However, copper oxide and zinc oxide nanoparticles having average particle size between 6 to 18 nm and ~ 65 and 60 to 180 nm, correspondingly, were produced using a green synthesis method [17, 18]. At present, copper and nickel are combined in various ratios such as 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) to synthesize polycrystalline materials with particle sizes of 4.078, 4.74 and 4.928 nm.

3.4 UV–Visible investigation

The UV–Visible assessment was considered for the evaluation of the optical behaviours of the synthesized nanocomposites. The absorption peak values are affected by various parameters, including synthesis process, surface effects, precursor type and concentration, oxygen vacancies, morphology, pH, particle size, micro-strain, and temperature [18]. The synthesized nanocomposites spectra revealed different peaks at 465.23, 476, and 515.37 nm indicating the formation of 90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposite by the use of Ipomoea carnea leaf extract, respectively as shown in Fig. 5. The 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs UV–visible spectra showed a wider peak, which might be attributed to surface defects caused by metal oxide coupling. In the present study, the direct energy band gap (Eg) values are larger as related to pure synthesized copper oxide NPs (1.2–1.7 eV) and also, the absorbance of NiO NPs (280–320 nm). Sedighi et al., 2018 [23] reported similar findings, observing absorbance bands between 400–500 nm. The results they reported indicated band gap values of 2.8 and 3.2 eV for the synthesized Cu(WO4)/NiO and Cu(WO4). The direct energy band gap was approximated by using Eq. 5 and listed in Table 2.

Fig. 5
figure 5

UV–vis spectrum for 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs

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Table 2 Calculated Direct energy band gaps (Eg) and λmax values for CuO/Cu2O-NiO NCs synthesized at various ratios of [Cu(CH3COO)2.H2O] and [Ni (NO3)2. 6H2O] solutions
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3.5 FTIR analysis

The FTIR analysis of the 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs and pure CuO and NiO was performed in the 4000–400 cm−1 range to estimate the structural bond formation in prepared bi-metallic CuO/Cu2O-NiO nanocomposites (Fig. 6). The absorption spectrum of CuO NPs reveals distinctive bands at 615.01, 530.64, and 489.23 cm−1, indicating the presence of Cu(II)-O bonds. The prominent peak at 615.01 cm−1 is a characteristic feature of Cu–O bond formation. In addition, there are observable peaks at 453.75 and 653.56 cm−1, which can be attributed to Ni–O bond stretching vibrations. The broadening of these peaks suggests that both CuO and NiO nanoparticles possess a crystalline structure. Furthermore, two absorption bands at 2385.80 and 2321.14 cm−1 can be attributed to the symmetric and asymmetric stretching vibrations of CO2 molecules that have been absorbed from the surrounding air. Additionally, a broad band is evident at 3419.60 cm−1, along with another at 1616.87 cm−1, signifying the presence of stretching and bending vibrations originating from –OH groups that have been absorbed onto the catalyst's surface from the atmosphere during FTIR analysis.

Fig. 6
figure 6

FTIR spectrum of three different (a) 90:10 (NCs A1), (b) 80:20 (NCs B1), and (c) 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites and pure CuO and NiO NPs (d)

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All the observed absorption bands (\(\overline{{\varvec{\nu}}}\)) of NCs are given in Table 3. The transmittance at 3400–3500 cm-1 in Table 3 was caused by the presence of –OH stretching and C–H stretching in the produced nanocomposites [19]. The transmittance appeared at ~ 1600–1700 cm−1exist because of N–H group bending via the presence of alkaloids grasp the amino group [24, 25]. Other peak displayed at ~ 1080–1039.60 cm−1 designates the C–O–C devoted to bi-metallic 90:10, 80:20 and 70:30 CuO/Cu2O-NiO nanocomposites, whereas the peaks appearing at ~ 600–700 cm−1 are probably connected with metal–carbon association [26].

Table 3 Absorption peaks and associated organic groups for different synthesized 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs
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3.6 Antibacterial activity

Since 90:10, 80:20 and 70:30 CuO/Cu2O-NiO nanocomposites are likely to be used as an antibacterial agent due to their low toxicity and thermal resistance, antibacterial activity of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites was scientifically demonstrated using the well diffusion technique with Mueller Hinton Agar media (MHA).

Bacteria like S. aureus, E. coli, and B. subtilis, were used to investigate bactericidal (antibacterial) activity. Negative control (methanol) showed the absence of any zone of inhibition (ZOI) against all three pathogens. ZOI (mm) of 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs and negative controls against, B. subtilis, S. aureus, and E. coli are given in Fig. 7 and Table 4.

Fig. 7
figure 7

Zones of inhibition (ZOI) of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs versus (a, d & g) B. subtilis, S. aureus (b, e & h) and (c, f & i) E. coli

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Table 4 Zones of inhibition (ZOI) by various amounts (10, 25, and 50 mg.ml−1) of the three prepared CuO/Cu2O-NiO nanocomposites against the three bacteria
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Within the bacterial species, CuO/Cu2O-NiO NCs revealed highest antibacterial results at dosage of 10, 25 and 50 mg/mL of 90:10 (NCs A1), 80:20 (NCs B1) and 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites against bacteria. The results of antibacterial activity were analysed due to the production of reactive oxygen species (ROS) from nanocomposites that bacterial species to die [22,23,24,25]. Specific surface area as well as oxygen vacancies contained by CuO/Cu2O-NiO nanocomposites, diffusion potential of reactant molecules and discharge of Ni2+, Cu2+ and Cu1+ ions facilitate the formation of ROS [26, 27]. The hydrogen peroxide (H2O2), hydroxyl radical (OH), and superoxide (O2−) existing in ROS have the ability to break cellular and DNA coverings, resulting in significant pathogen cell damage. This increases the antibacterial potential showed by CuO/Cu2O-NiO nanocomposites and therefore, it can be determined that comparatively more production of ROS to execute the death of bacterial strains. Usually, the physiochemical features of CuO/Cu2O-NiO NCs such as large surface area, perfect crystalline size, uniform quantum size, and small band gap are responsible for this greater ROS formation. Among the CuO/Cu2O-NiO nanocomposites, 90:10 (NCs A1) CuO/Cu2O-NiO nanocomposite with relatively uniform quantum size, higher oxygen vacancies, simply aggregated particles, and small crystalline size enables the highest antibacterial potential against all three bacterial species when compared to 80:20 (NCs B1) and 70:30 (NCs C1) CuO/Cu2O-NiO nanocomposites. This can be justified based on the specific structures like aggregated particles of the 90:10 (NCs A1), 80:20 (NCs B1) and 70:30 CuO/Cu2O-NiO nanocomposites. Increased antibacterial activity by 90:10 (NCs A1) CuO/Cu2O-NiO nanocomposites when compared to 80:20 (NCs B1) and 70:30 (NCs C1) CuO/Cu2O-NiO NCs can be interrelated to its structural features dependent antibacterial potential as it has comparatively small NCs particles. Hence, the antibacterial performance determination of synthesized nanocomposites suggests that surface area, and particle size of prepared nanocomposites plays an important role when compared to crystalline size and oxygen vacancies.

The mechanism of the bactericidal property for the prepared nanocomposites is illustrated in Fig. 8. Using a 96-well microtiter plate, the minimal inhibitory along minimal bacterial concentration have been evaluated. The MIC and MBC values were observed between 195.31–1562.5 μg/ml and 390.62–12,500 μg/ml, respectively (Table 5). In Fig. 10 shows the ZOI of B. subtilis, S. aureus and E. coli (a, b and c) having 10, 25 and 50 mg ml−1 doses of ciprofloxacin drug. Figure 10 shows the total inhibition of bacterial growth in the plates.

Fig. 8
figure 8

Bactericidal activity mechanism of CuO/Cu2O-NiO NCs

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Table 5 MIC and MBC values of the 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs and ciprofloxacin for three bacteria
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Electrostatic interactions occur between the bacterial cell wall and CuO/Cu2O-NiO nanocomposite particles, which can cause oxidative stress and break the pathogenic cell wall. The bactericidal mechanism completed in 3 steps: (i) the production of ROS, (ii) rupture of microbial cell wall (iii) discharge of ions [28]. The smaller particles size of 90:10 (NCs A1) CuO/Cu2O-NiO NCs can simply rupture the microbial cell wall, leading to the discharge of cytoplasm and finally, the cell destroyed. The maximum and minimum ZOI against the bacterial species are shown in Fig. 9. However, the bactericidal results of the nanocomposites are compared with presently synthesized CuO/Cu2O-NiO NCs against the gram + ve and gram −ve pathogens (Table 6). The results of ciprofloxacin drug, MIC and MBC against the bacteria are given in Figs. 10, 11 and Table 5.

Fig. 9
figure 9

ZOI of B. subtilis, S. aureus and E. coli having 10, 25 and 50 mg ml−1 doses of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs

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Table 6 Evaluation of antibacterial activities of the fabricated 90:10 (NCs A1), 80:20 (NCs B1) and 70:30 (NCs C1) CuO/Cu2O-NiO NCs with previously studied nanocomposites towards the bacterial species
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Fig. 10
figure 10

ZOI of B. subtilis, S. aureus and E. coli (a, b, c) having 10, 25 and 50 mg ml−1 doses of ciprofloxacin drug

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Fig. 11
figure 11

The calculations of (a) MIC and (b) MBC values of the synthesized 90:10, 80:20 and 70:30 CuO/Cu2O-NiO NCs

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3.7 Antioxidant activity

To examine the potential of the synthesized NCs samples to scavenge (DPPH) was used [31,32,33]. One of the greatest important uses of composite nanomaterials is their antioxidant activity, which plays an important role to all living systems. According to the outcomes of the present study, the microwave-assisted prepared 90:10, 80:20, and 70:30 CuO/Cu2O-NiO NCs exhibit high antioxidant activity at various doses, because of the existence of capping/stabilizing agents from the leaf extract. In free radical scavenging processes, capping agents/stabilizing are said to be extremely important. As can be seen in Fig. 12, the ascorbic acid utilized as a standard is used to compare the radical scavenging ability of various 90:10, 80:20 and 70:30 CuO/Cu2O-NiO NCs samples. Table 7 represents the outcomes of the determination of the % age scavenging activity. Figure 10 demonstrates that, in comparison to other NCs, the prepared 70:30 (NCs C1) CuO/Cu2O-NiO NCs exhibit greater scavenging action at several concentrations of 25, 50, 100, 200, 400, and 800 µg/mL of DPPH solutions. It is interesting to observe that scavenging occurs at a rate of around 96.40% (Fig. 12), whereas ascorbic acid reported scavenging at a rate of about 98.63% at 800 µg/ml DPPH solutions (Fig. 12).

Fig. 12
figure 12

% Radical Scavenging activity of 90:10 (NCs A1), 80:20 (NCs B1), and 70:30 (NCs C1) CuO/Cu2O-NiO NCs in comparison with the ascorbic acid used as standard

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Table 7 The percentage free radical scavenging activity of 90:10, 80:20 and 70:30 CuO/Cu2O-NiO nanocomposites at various dilutions
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Maximum radical scavenging activity of 96.40% was recorded at 800 µg/mL and increased with Ni concentration. Increased antioxidant activity may be due to the increase in the amount of Ni with phytochemicals presents in the Ipomoea carnea leaf extract. In the literature, related antioxidant studies for ZnO NPs mediated by plant extracts were published [8].

4 Conclusions

90:10, 80:20, and 70:30 CuO/Cu2O-NiO nanocomposites were synthesized using a microwave-assisted green method. XRD analysis confirmed their polycrystalline nature with monoclinic and cubic phases. SEM micrographs revealed different nanocomposite shapes. From the TEM and SAED images, the average uniform quantum sizes of 4.078, 4.74, and 4.928 nm and ring-like patterns in SAED images were confirmed which reveals the polycrystallinity for the prepared nanocomposites. EDX analysis confirmed the presence of Ni, O, and Cu in the nanocomposites. UV–visible spectral analysis showed visible range absorption peaks. The energy band gaps decreased with higher Ni2+ ion concentrations. These nanocomposites demonstrated antibacterial activity, with 90:10 (NCs A1) being the most effective against gram-positive bacteria (S. aureus and B. subtilis) compared to gram-negative (E. coli). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranged from 195.31 to 1562.5 µg/mL and 390.62 to 12,500 µg/mL. The prepared CuO/Cu2O-NiO nanocomposites outperformed other green-synthesized nanocomposites as antibacterial agents, highlighting their potential as alternatives to current antibacterial agents for drug-resistant pathogens in humans.