Introduction

Due to the use of various dyes (especially azo) in industries such as textiles, leather, paper, food, and cosmetics, the produced effluents by these industries are contaminated with dyes [1]. With the entry of these effluents into the environment, due to the toxic and destructive effects of dyes, the environmental conditions of surface waters, rivers, and even the soil of the region change. These changes are very dangerous for the health of humans, animals, and plants. Therefore, as much as possible, industrial effluents should be treated before entering the environment and their various pollutants should be reduced as much as possible [2, 3]. Dyes used in various industries, in addition to environmental pollution (water and soil), become very dangerous, carcinogenic, and toxic compounds over time and through various chemical processes [4, 5]. Most dyes are resistant to heat, light, as well as biodegradation and are not easily removed. Therefore, they can stay in the environment for a long time. Methylene blue (MB) is an important aromatic chemical cation dye in the textile industry and is soluble in water [6]. Effluents containing dyes such as MB are hazardous to ecosystems and public health; these substances may affect the light activity of aquatic plants, and increase suspended solids, and water turbidity by reducing light penetration [7]. With the help of conventional purification methods, these compounds cannot be separated from the medium. Various methods such as the use of coagulants, oxidizing agents, optical catalytic processes, and the use of various filters and membranes for the separation of dyes have been used, which have disadvantages such as high cost and continuous need for oxidizing and coagulating agents [8]. In addition, the lack of removal of high-yield dyes is one of their disadvantages. The most efficient and best way to remove the dye is to use different adsorbents that through the adsorption process cause the dye to be transferred to the stationary phase (adsorbent). Features of this method include recycling the adsorbent and reusing it, low cost, simplicity of the method, and its design [9]. So far, many nanomaterials have been used to remove dyes from aquatic environments, including TiO2, ZnO, MgO, and NiO, which have advantages such as a simple preparation method, relatively low cost, separation of the adsorbent from the aqueous medium, and at the same time have a high absorption capacity [3, 10, 11]. On the other hand, surface modification of nanomaterial was given a lot of focus to create biocompatible substances for wastewater treatment, pollutant removal, targeted distribution, antibacterial, and anticancer application [12,13,14,15]. Thus, various researches were informed on the employment of nanomaterials for the treatment of polluted water [16, 17]. Because of their high surface area, nanomaterials can have various applications such as sensors [18], wastewater treatment, antibacterial, and drug carriers [19,20,21,22]. Recently, nanocomposites were identified as one of the most notable materials in biological applications due to their high biocompatibility, economic benefits, and low toxicity, as well as their antibacterial and anticancer attributes [23,24,25,26]. In recent decades, not only the selection of materials that are non-toxic and low cost should be considered, rather the synthesis method plays an essential role in the development of newer materials suitable for health care technology. According to the reports, various research communities have synthesized nanocomposites using the green method and investigated their antimicrobial activity and cytotoxicity. In 2022, Sabouri et al. reported Ag-doped ZnO/MgO NCPs synthesis using green chemistry and also investigated their cytotoxicity effects on Huh-7 cell lines [25]. In 2018, Revathi et al. reported CdO–ZnO–MgO nanocomposites synthesis and studied its antibacterial activity [27]. In 2022, Hosny et al. reported Ag/ZnO@Biohar nanocomposite synthesis and also examined their antibacterial and antioxidant activities [28]. In 2019, Panchal et al. reported ZnO/MgO Nanocomposites synthesis and also examined their photocatalytic and antibacterial activities [20].

However, nanocomposite combinations engrossed the focus of many because of their unique attributes containing low toxicity and high stability. Different procedures were applied for the synthesis of these nanomaterials, such as sol–gel [29], microwave [30], hydrothermal [31], and co-precipitation [32] which contain chemical solvents and great costs. For this reason, currently researchers are working on green approaches that are wholly vital for the synthesis of NCPs. Green methods can exhibit many advantages such as being more economical and avoiding the use of organic substances and easy control of the processes. In summary, the successful synthesis of nanocomposites using a green manner has been described from several natural sources, such as Sambucus nigra L. [33], Diospyros kaki [34], Eichhornia Crassipes [35] and the attained produces are suitable for photocatalytic investigations in wastewater treatment. The abundant use of zinc and calcium oxides in medical science and the removal of pollutants led to the synthesis of NCPs using Caccinia macranthera extract through a green chemistry approach for the first time. In this research, the aim is to prepare Ag-doped ZnO/CaO nanocomposites by the green method to investigate their photocatalytic properties, cytotoxicity effects, and antibacterial applications. Our new effort involves the application of C. macranthera seed extract as a stabilizing and capping agent to control the size and shape of NCPs through the manufacturing process. The structural attributes and morphology of NCPs were studied through the XRD, FTIR, and FESEM/PSA/EDX techniques. Also, the biocompatibility and cytotoxicity of synthesized NCPs were evaluated on Huh-7 cancer cell lines with an MTT test. Furthermore, the photocatalytic activity of NCPs towards the degradation of MB dye under UVA-light was also investigated. Additionally, the outcomes of the broth microdilution method were examined to perceive the antibacterial functionality of NCPs towards gram-positive bacteria and gram-negative bacteria.

Experimental

Merck Co. provided Ca(NO3)2∙4H2O, Zn(NO3)2∙6H2O, and AgNO3 salts (99%). The aqueous extract was prepared using collected fresh C. macranthera plant from the Razavi Khorasan province of Iran. The materials needed for the cytotoxicity, antibacterial, and photocatalyst tests were purchased from Merck and Sigma. The Huh-7 cancer cell line was achieved by the Pasteur institute of Iran. Throughout the experiments, the solvent was distilled water.

Caccinia macranthera seed extract preparation

Caccinia macranthera extract was prepared by adding 1 g of completely washed C. macranthera seeds to 100 mL of distilled water and stirring for 2 h at 60 °C. The gained extract was filtered with Whatman paper and stored at 4 °C for future use.

Fabrication of Ag-doped ZnO/CaO nanocomposites

The NCPs were manufactured using a green procedure that included zinc, calcium, and silver nitrates as the suppliers of salts and C. macranthera seed extract as the capping agent. The first, 20 mL Zn(NO3)2∙6H2O solution (A, 0.50 M) was added to 20 mL Ca(NO3)2∙6H2O solution (0.50 M) (Zn to Ca, 1:1). The obtained solution (A) was stirred at 25 °C for 30 min. After, 10 mL AgNO3 solution (10%) was extra to the A solution. In the result, the attained solution (B) was stirred for 40 min. In the continue, 20 mL of C. macranthera extract was extra to the B solution and the resulting solution was stirred at 80 °C for 6 h. This method led to the attainment M(OH)2 el, which was dried at 100 °C for 6 h. Then, a calcination routine was performed for 2 h at 700 ºC to achieve the gray-colored NCPs. The biosynthesis plan of NCPs is exhibited in Fig. 1.

Fig. 1
figure 1

The green synthesis plan of NCPs

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Characterization

To validate the synthesized NCP, the samples were characterized using various approaches such as UV–Vis, FTIR, XRD, and FESEM/PSA/EDX. The chemical structure of the compound was checked using FTIR analysis (Shimadzu, model UV-1800). UV–Vis spectrophotometry (Shimadzu, model UV-1800) was used to evaluate the optical properties of NCPs. Furthermore, the crystal structure of NCPs was investigated using the XRD pattern (model, D8-Advance Bruker). Following the estimation of particle size, the morphology and elemental analysis of NCPs were checked using FESEM/EDX/PSA images (Model TESCAN BRNO-Mira3), Afterward, various applications of synthesized NCPs such as antibacterial, anticancer, and photocatalytic activity were investigated.

Results and discussion

Photocatalytic activity

One of the chief purposes of this project is to examine the photocatalytic properties of synthesized NCPs in the removal of azo organic contaminants. Therefore, MB dye was selected as an organic contaminant, and the photocatalytic properties of synthesized NCPs were investigated in the degradation process. To evaluate the efficiency of synthesized NCPs in optical degradation of MB dye changes the absorption spectra of the reaction mixture were investigated several times. To obtain the absorption spectrum, the first 100 mL of MB dye solution with a concentration of 1 × 10–5 M was prepared. After making the MB solution and adjusting the pH ~ 10, a certain amount of NCPs (30 mg) was added to it and sonicated for 10 min. Then, the mixture solution was stirred in dark conditions for 45 min to reach the absorption and desorption equilibriums. The resulting solution was then exposed under UV light. During the photocatalytic degradation test of MB dye, about 2 mL of the solution was removed at specified intervals (20 min). In continue, the absorbance of the samples was determined after centrifugation (12,000 rpm) using UV–Vis spectrophotometry at 663 nm. The amount of dye degradation before and after the addition of NCPs was measured and the maximum dye degradation efficiency was calculated using Eq. 1. As can be seen from Fig. 2a, the destruction efficiency decreased with increasing time, so that after 100 min, the degradation efficiency reached about 90%.

Fig. 2
figure 2

Photocatalytic diagram of MB dye a and kinetic curve b of NCPs

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$$\mathrm{Degradation} \left(\%\right)=\frac{{C}_{0}-{C}_{t}}{{C}_{0}}\times 100$$
(1)

C0 = Initial concentrations of the MB dye solution.

Ct = Final concentrations of the MB dye solution.

The reaction kinetics of MB dye degradation was investigated using Eq. 2. The plot of Ln (Ct/C0) vs time is displayed in Fig. 2b. The result shows reaction kinetic is first-order.

$$\mathrm{Ln}\left(\frac{{C}_{\mathrm{t}}}{{C}_{0}}\right)={K}_{\mathrm{obs}}t$$
(2)

where C0 and Ct are the initial and the final concentration of the dye solution after the passage of time t and k is the kinetic constant of the reaction respectively. The rate constant (Kobs) value was obtained to be 0.024 min−1.

The mechanism of photocatalytic reactions is presented in Fig. 3. In the following, H2O molecules react via the holes (h+) of VB and creation OH° radicals, while the reaction of O2 with CB electrons leads to the production of \(^\circ {\mathrm{O}}_{2}^{-}\) and the active radicals (H2O2, \(^\circ {\mathrm{O}}_{2}^{-}\), OH°) that able to destroy the MB dye in the course of serial chain reactions. The applicability of this method for degrading the MB dye is dependent on the capability of radicals in altering the organic materials into CO2, H2O, etc. [17, 36]. The reactions of the photocatalytic test are depicted below (3–7).

Fig. 3
figure 3

Mechanism of photocatalytic degradation

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$$\mathrm{hv} \left(\mathrm{UV}\right)+\mathrm{NCPs}\to {\mathrm{h}}^{+}+{\mathrm{e}}^{-}$$
(3)
$${\mathrm{H}}_{2}\mathrm{O}+{\mathrm{h}}^{+}\to {\mathrm{H}}^{+}+{\mathrm{OH}}^{^\circ }$$
(4)
$${\mathrm{O}}_{2}+{\mathrm{e}}^{-}\to {\mathrm{O}}_{2}^{^\circ -}$$
(5)
$$\mathrm{Dye}+{\mathrm{h}}^{+}\to \mathrm{Oxidated products}$$
(6)
$$\mathrm{Dye}+{\mathrm{e}}^{-}\to \mathrm{Reducted products }$$
(7)

Catalyst recovery

A catalyst is a substance that, by participating in a chemical reaction, accelerates it without undergoing chemical changes. That is why catalysts can be used many times, which is economical. At this stage of the project, to evaluate the performance of the prepared photocatalyst, the used photocatalyst in the dye degradation process was collected by centrifugation and washed times several with distilled water and ethanol. The collected sediment was dried at room temperature and applied for reuse in the degradation reaction. Evaluating the efficiency of the collected photocatalyst in the degradation reaction was performed similarly to Photocatalytic activity. The results of dye degradation indicated that the photocatalyst efficiency remained constant in three reuses and reduced in the fourth recovery. The results are reported in Fig. 4.

Fig. 4
figure 4

Recoverability curve of NCPs

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Cytotoxicity

The MTT [3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT)] test is a colorimetric process for measuring the vital capacity of a cell. It is based on the reduction of tetrazolium yellow crystals by mitochondrial succinate dehydrogenase and the formation of purple crystals of formazan, which are insoluble in water. First, Huh-7 cancer cells were cultured in a DMEM medium containing 10% FBS and 1% antibiotic (100.0 μg/mL streptomycin/penicillin) and were incubated at 37 °C and 5% CO2. Then 1 × 104 cells were poured into each of the 96-well plate wells (100 μL). After 24 h, the cells were treated with NCPs at different concentrations (0–500 ppm) for 48 h. Then, the cytotoxicity of nanocomposite on cancer cells was investigated in such a way that after the treatment period, 60 μL of MTT was added to each well and incubated for 4 h. In continue, the MTT was removed and 50 μL of DMSO was extra to each well. The absorbance was scanned at 570 nm by a spectrophotometer. All experimental steps were repeated three times and the viability of cells at each concentration was measured according to the following equation (Eq. 8).

$$\mathrm{Viability} \left(\mathrm{\%}\right)= \frac{{A}_{\mathrm{t}}}{{A}_{\mathrm{C}}}\times 100$$
(8)

At = Absorption of the treated sample, Ac = Absorption of the control sample.

The results of the MTT test showed that the synthesized NCPs were able to inhibit the proliferation of cancer Huh-7 cells and in a dose-dependent manner induce cytotoxicity in cancer cells. As shown in Fig. 5, NCPs at concentrations of 0–500 ppm reduce the survival of cancer cells and exert a cytotoxic effect. An examination from the MTT test showed IC50 value is about 250 ppm. According to the results of cytotoxicity, these NCPs can be effective on Huh-7 cell lines at high concentrations, which can be suggested as a suitable candidate for biomedical applications.

Fig. 5
figure 5

Evaluation of cell viability by MTT method after 48 h of treatment of NCPs

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Antibacterial activity of NCPs

This section implicated the usage of the broth microdilution method to assess the antibacterial functionality of NCPs against gram-positive bacteria Enterococcus faecalis (ATCC 29212) and Staphylococcus aureus (ATCC 29213), and gram-negative bacteria Escherichia coli (ATCC 25922) and Salmonella enterica (ATCC 14028). Once the growth of strains as the target organisms was completed in the nutrient broth at 37 °C for 24 h, the microbial suspension was arranged by microbial colonies and normal saline while being adjusted to 0.5 McFarland turbidity standard [37]. Subsequently, 100 µL of Mueller Hinton Broth media culture was decanted into every well. The first well of each row was considered a positive control that consisted of a culture medium, chlorhexidine 2% (100 µL), and bacteria (5 µL), whereas the last well of each row was considered a negative control that contained a culture medium and bacteria. In the continuation, next to adding 100 µL of NCPs solution (1000 ppm) to the second well of each row, serial dilution was performed up to the 11th well, which was continued by the addition of 5 µL of diluted microbial suspension equivalent to 0.5 McFarland; the substances were incubated at 37 °C for 24 h. The last well, which was identified with turbidity, was the Minimum Inhibition Concentration (MIC) as the lowest concentration of an antimicrobial with the ability to prevent the visible expansion of a microorganism through an overnight incubation. To better observe the turbidity, 50 µL of resazurin was applied to every well and incubation at 37 °C for 5 h. The antibacterial influence of NCPs (1000 ppm) can be studied by determining the state of turbidity or non-turbidity of the wells to be compared with the control wells. The last well sensed with turbidity was labeled as MIC. The results of investigative the antibacterial activity of NCPs against the bacterial strains are exhibited in Fig. 6. The gathered data indicated that the case of gram-positive bacteria displayed the highest sensitivity to NCPs when compared to the gram-negative bacteria. The MIC values of E. faecalis and S. aureus are about 0.97 ppm, and E. coli and S. enterica are about 125 ppm.

Fig. 6
figure 6

Assessment of the antibacterial activity of NCPs

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FT-IR

The FT-IR was used to determine the functional groups that exist in the compound. The FT-IR diagram of synthesized NCPs is shown in Fig. 7. The identified bands at 470 and 530 cm−1 can be ratioed to metal–oxygen (M–O) stretching vibrations, confirming the synthesis of NCPs [38]. Moreover, the stretching and bending vibrations of the O–H group were detected at 3430 and 1410 cm−1, respectively. The detected peak at 1530 cm−1 can be attributed to the residual nitrates, indicating the potential of phytoconstituents in increasing NCP stabilization. [39]. The gathered outcomes conformed to the research of Anand et al. [19] and Wang et al [40].

Fig. 7
figure 7

The FTIR spectrum of NCPs

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UV–Vis spectrophotometry

UV–Vis spectrophotometry was used to examine the optical studies of NCPs. The UV–Vis diagram (Fig. 8a) revealed a band at 280 nm, corresponding to the UV zone. Furthermore, the small size and high surface area of NCPs resulted in their powerful ability for photon receiving. The bandgap energy of NCPs was calculated to be around 3.5 eV using the Tauc equation (Eq. 9) [41].

$$(\alpha h\nu {)}^{n}=A\left(h\nu -{E}_{g}\right)$$
(9)

which A is constant, hυ equivalent photon energy (eV), n = 2 for direct transition and 0.5 for indirect transition. The Eg of NCPs was obtained via extrapolating the linear region of the diagram (αhυ)2 vs. hυ (eV) (Fig. 8b).

Fig. 8
figure 8

UV–Vis curve a and Bandgap b of NCPs

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XRD

The crystallinity of manufactured NCPs was investigated using the XRD spectrum (Fig. 9). All observed bands were associated with the NCPs and confirmed their face-centered cubic (fcc) structure via the Fm3m space group. The absence of any other bands approved that these nanoparticles successfully were synthesized [42]. These findings were consistent with standard pattern data. The crystallite size of NCPs was obtained using the Scherrer equation (Eq. 10) which was approximately 29 nm.

$$D\left(\mathrm{nm}\right)=\frac{k\lambda }{\beta \mathrm{cos}\theta }$$
(10)

which k = 0.90, λ is 0.154 nm, β corresponds to FWHM (Full width at half-maximum), and θ is the angle.

Fig. 9
figure 9

XRD pattern of NCPs

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FESEM/EDX/PSA

Corresponding to the FESEM/PSA/EDX images of manufactured NCPs in Fig. 10a–g, the nanocomposites had spherical morphology (Fig. 10a ,c), and their average size was approximately 23–49 nm (Fig. 10d, f). Furthermore, the lack of agglomerated nanocomposites in the FESEM images confirmed the high porosity of our product [12, 20, 43, 44]. The EDX analysis (Fig. 10g) also confirmed the existence of Zn, Ag, Ca, and O elements in the synthesized NCPs. The obtained results agreed with the findings of Arana et al. [45]. Size and morphology are important factors in cytotoxicity, antibacterial, and photocatalytic activity studies [9].

Fig. 10
figure 10

FESEM (a–c), PSA (d–f), and EDX (g) of NCPs

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Conclusions

For the first time, the present paper used a green method to synthesize of NCPs using C. macranthera seed extract. The results of FESEM, EDX, and XRD studies confirmed the synthesis of NCPs. Furthermore, FT-IR and UV–Vis techniques were applied for examining the optical attributes and determining the functional groups of NCPs. In comparison to previous studies, silver ion doping significantly increased the photocatalytic activity of NCPs to degradation of MB dye. The broth microdilution technique was done to assess the antibacterial effects of NCPs on gram-positive bacteria including E. faecalis (ATCC 29212) and S. aureus (ATCC 29213), and gram-negative bacteria including E. coli (ATCC 25,922) and S. enterica (ATCC 14028). The MIC values of E. faecalis and S. aureus are about 0.97 ppm, and E. coli and S. enterica are about 125 ppm. Furthermore, the cytotoxicity of NCPs was assessed on Huh-7 cell lines using an MTT test, that revealed concentration-dependent cytotoxicity, and the IC50 amount was reported at approximately 250 ppm.