1 Introduction

Semiconductors based-photocatalysts that have used light radiation energy to remove contaminants have become highly innovative and environmentally beneficial solutions. Removing organic pollutants in sewerage discharge can be a challenging issue. It is crucial to find an appropriate solution to pollutants and promote feasible and eco-friendly techniques [1]. A notable functional photocatalyst has to possess excellent absorption of assisted radiation. Besides, the photo-induced electron–hole pairs caused by exposure to light irradiation should have been isolated to allow the reduction and oxidation reactions adequate time. Even so, photocatalytic degradation is hampered by considerable challenges like the confined area of the absorption of illumination and the limited extraction efficiency of the employed photocatalysts, and this will not be able to address the needs of practical applications [2]. As a result, in current photocatalytic research, the investigation of unique photocatalysts with remarkable efficiency and stability is a modernistic and innovative responsibility [3].

The molybdenum disulfide (MoS2) has shown great promise in many applications [4, 5]. MoS2 is a potential semiconductor photocatalyst as a transition metal dichalcogenide because of its excellent visible-light sensitivity, small bandgap, relatively inexpensive, and lack of toxicity [2, 6,7,8]. MoS2, like a graphene, is a 2D nanomaterial with exceptional breaking tensile strength [9]. Nevertheless, due to its weak intrinsic conductivity and speedy photoinduced electron–hole recombination, MoS2 possesses restricted catalytic activity. Consequently, finding an appropriate modification strategy to boost MoS2’s photocatalytic activity remains a challenge [10].

In this vein, spinel cobaltites MCo2O4 (M = Zn, Ni, Mn,…) as magnetic photocatalysts have revealed outstanding photocatalytic activity by displaying the photo-induced electron/holes to eliminate the organic contaminants [11,12,13]. ZnCo2O4 has been widely used in photodegradation as a p-type semiconductor and binary metal oxide of the spinel cobaltite family. As a result of its wide-range UV–visible ray absorption (200–800 nm), ZnCo2O4 is suitable for organic photodegradation utilizations [14,15,16]. As a result, adding MoS2 to the ZnCo2O4 photocatalyst will improve visible light absorption and reduction reactions in the conduction band while increasing the surface area available for the photocatalytic process. Besides, the ZnCo2O4 possesses magnetic nature and can act as a recyclable magnetic catalyst for ease of separation from the water after treatment [17].

In addition, previous research has displayed that the coating photocatalysts with a host of exciting layers, including such silver Ag and gold Au elements, enhanced the photocatalytic activity due to reducing the rate of the recombination process for induced-charge carriers [18]. Due to “it’s localized surface Plasmon resonance” (LSPR) absorption, silver NPs boost light absorption and work as sinks for photogenerated charge carriers, preventing charge carrier recombination in composites. At the metal/semiconductor interface, noble metals with Fermi levels lower than the semiconductor photocatalyst's conduction band level initiate a Schottky junction. Photoinduced electrons may be successfully trapped by metals, enhancing the separation of electrons and holes as a result [19,20,21]. So, can enhanced the catalysts process by combining Ag nanoparticles to ZnCo2O4/MoS2. So, Ag NPs were decorated on the surface of ZnCo2O4/MoS2, that the electron–hole separation can be enhanced by the improved conductivity of the interface between ZnCo2O4 and MoS2. Yuefa et al. [22] have reported that Au NPs enhanced CoFe2O4–MoS2 photocatalyst to degrade methyl orange by using visible light irradiation. Also, Junwei et al. [23] have improved photocatalytic hydrogen generation of TiO2–Cu2O composite by adding Ag.

An essential biomedical application of NPs is their use as innovative antimicrobial agents, which overcomes the drawbacks of synthetic antimicrobial drugs [24,25,26]. NPs have diverse mechanisms of action to kill pathogenic microorganisms, such as oxidative stress and metal ion release [27]. It has been proven that the smaller the particle size, the better antimicrobial activity [28]. Ag NPs were known as antibacterial and antifungal materials, which depend on their shape and size and after congregation with different active composite to increase their activity at low concentration to avoid the toxicity as reported in recent studies [29,30,31,32]. Baraka et al. [33] synthesized green Ag NPs using natural pigments extracted from Alfalfa leaves. The synthesized Ag NPs possessed a superior antimicrobial activity towards S. aureus ATCC 29213; 24.0 mm ZOI, followed by E. coli ATCC 25922; 17.0 mm ZOI. In addition, Ag NPs were a strong antifungal agent against C. albicans ATCC 10231; 26.0 mm ZOI.

Recently, the utilization of γ-irradiation in the fabrication of metal NPs has been confirmed to have several favorable merits. The regulated reduction for metal ions can be achieved without utilizing an extra reducing factor or assembling any unwanted oxidation by-products. Besides, the rates of reactions begun by radiation are sufficiently defined. Furthermore, the reducing factor is uniformly created in the solution [34].

Herein, we have concentrated our efforts on gamma irradiation-assisted synthesis of Ag-decorated ZnCo2O4/MoS2 heterostructure as a novel eco-friendly photocatalyst to degrade methylene blue MB and as effective antimicrobial agents. Ag NPs were decorated on the surface of ZnCo2O4/MoS2; therefore, the segregation of electrons and holes can be improved by enriching the interface's conductivity between ZnCo2O4 and MoS2. As a result, it is essential to consider the unique characteristics of heterostructure Ag-decorated ZnCo2O4–MoS2 photocatalysts for environment water purification.

2 Materials and Methods

2.1 Materials

Molybdenum disulfide (MoS2) is purchased from PubChem CO., cobalt nitrate (Co(NO3)2⋅6H2O), zinc sulfate (ZnSO4⋅7H2O), silver nitrate (AgNO3), citric acid (C6H8O7⋅H2O), ethylene glycol (C2H6O2) were acquired from Sigma Aldrich and employed as raw precursors.

2.2 Synthesis of Ag-Decorated ZnCo2O4–MoS2

Firstly, the spinal ZnCo2O4 was synthesized via the sol–gel technique, as illustrated in Fig. 1 [35]. Secondly, 3 g of the synthesized spinal ZnCo2O4 NPs and 1.5 g of molybdenum disulfide (MoS2) were strongly distributed in the ethanol into the ethanol and deionized water (70/30 v/v). The mixture was homogenized utilizing ultrasonication for 45 min to even get a homogeneous distribution. The product MoS2–ZnCo2O4 was filtered and washed with deionized water several times and dried at 60 °C for 3 h. After that, 3 g of MoS2–ZnCo2O4 NPs and 0.5 g of silver nitrate (AgNO3) were dissolved in 120 ml of deionized water and mixed under magnetic stirring for 45 min. Finally, the solution of the investigated samples was subjected to 50 kGy (dose rate of ~1.1 kGy/h) at ambient conditions. The irradiation was performed by utilizing Co-60 gamma-cell sources. The Ag-decorated ZnCo2O4–MoS2 NPs were filtered and washed via a mixture of ethanol, and water was dried in the air to give Ag-decorated ZnCo2O4–MoS2 NPs. The prepared samples are characterized via X-ray diffractometer, Shimadzu XRD-6000, and scanning electron microscope (SEM), JEOL JSM-5600 LV, Japan). Also, UV diffusion reflectance spectra were measured via Jasco UV–Visible Spectrophotometer (V-670 PC).

Fig. 1
figure 1

Schematic diagram for synthesis of Ag decorated MoS2–ZnCo2O4 NPs

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2.3 Photocatalytic Activity Measurement

All photocatalytic tests were performed at ambient temperature (25 °C ± 2 °C). The Ag-decorated ZnCo2O4–MoS2 nanocomposite was dipped in a methylene blue aqueous environment under vigorous stirring. The MB dye solution and the spinal ZnCo2O4, MoS2, and Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalysts were stirred in the dark for 30 min to specify adsorption–desorption equilibrium. Then, the dye solution having the MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalysts were illuminated by employing a metal halide lamp of 400 W. MB's final concentration (Ct) and the percentage removal of MB were evaluated by utilizing Ref. [36].

2.4 Antimicrobial Activity

The synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples were tested for their antimicrobial potential upon selected pathogens (yeast and bacteria) throughout the agar-disc diffusion method [31, 37].

The activity of the as-synthesized samples had examined against different types of Gram-positive, and Gram-negative bacteria, such as Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Bacillus subtilus, and Proteus vulgaris. The zone of inhibition (ZOI) was displayed after 24 hrs. of incubation and is a suitable parameter regarding the hindrance of microbial growth [38]. Candida albicans and Candida tropicalis were an example of pathogenic unicellular fungi used to evaluate the antifungal potency of the synthesized samples. Before the ZOI testing, the microbial inoculums must be standardized according to 0.5 McFarland (at 600 nm) and fixed from 2–5 × 108 CFU/mL for bacteria and 1–4 × 108 CFU/mL for the tested yeast. Positive standard antibiotics Nystatin (NS) and Amoxicillin (AX) were used to evaluate the ZOI potency [31].

2.5 Potential Antibiofilm Behavior

The synthesized MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag-decorated ZnCo2O4–MoS2 nanocomposite were tested for their potency as antibiofilm agents after conducting biofilm tube method. The anti-biofilm of the synthesized nanocomposites was investigated upon the chosen bacteria and Candida spp. and was persistent and corresponded with the control (non-treated one). A qualitative test about biofilm repression was noted by Christensen et al. [39].

The microbial inoculums had been adjusted according to 0.5 McFarland and fixed from 1–3 × 108 CFU/mL, and were incubated for 1 day at 37.0 ± 0.5 °C. A 5.0 mL nutrient broth medium was mixed with the tested samples inside distinct test tubes. After the incubation time, all the media components in the treated and control (cell-free supernatant) were discarded. All tubes were washed with phosphate buffer saline (PBS; pH 7.0), and after that, all tubes were cleaned with deionized water [40]. The resulted cells inside tube walls were fixed with 5.0 mL (3.5%) sodium acetate for 20 min, and finally, they were washed with de-ionized water. If the result is positive, the created biofilm was stained with (0.15%) crystal violet (CV) and, after the staining process, washed with de-ionized water to remove the excess CV. At the end of the experiment, about 5.0 mL of absolute ethanol was added to measure the semi-quantitative analysis of the anti-biofilm potential. UV–Vis. examined the stained microbial biofilms with a CV applying UV–Vis. spectrophotometer at 570.0 nm. The microbial biofilms repression percentage was calculated by using the following Eq. (1) [39].

$${\text{Percentage\, of\, bacterial\, and\, yeast\, biofilm\, inhibition}} \left( \% \right) = \frac{{\text{O.D.\,of\,the\,control\,sample}} - {\text{O.D.\,of\,the\,treated\,sample}}}{\text{O.D.\,of\,the\,control\,sample}} \times 100$$
(1)

2.6 Growth Curve Assay

The influence of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite on the growth of S. aureus (the most sensitive microbes) was determined by the growth curve assay according to Huang et al. [41]. The microbial suspension was adapted to 0.5 McFarland (1 × 108 CFU/mL) in 5.0 ml of nutrient broth tubes. MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite were included separately in the examined tubes. The absorbance of the microbial growth following treatment was evaluated each 2 hrs. intervals up to 24 hrs. (Wavelength of 600 nm). The relationship had been conducted between the average of duplicate readings and a time to obtain the typical growth curve.

2.7 Potential Effect of UV Illumination

Two hours incubated, bacterial cultures were established to standard 0.5 McFarland (1 × 108 CFU/mL). MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite were incorporated into the estimated tubes. After illumination with UV, the antimicrobial potency of the synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite was tested towards S. aureus operating the optical density method in comparison with the control non-UV irradiation [31].

The tubes were categorized as two states, tubes containing non-UV irradiated MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite and tubes with MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite and UV-irradiated which was exhibited to different periods as 0, 15, 30, 45, 60, and 75 min and the intensity was determined as 6.9 mW cm−2 disturbance on the samples at 37 °C, and the sample turbidity was assessed at 600 nm. The inhibition % was defined by Eq. (1), according to Abd Elkodous et al. [42].

2.8 Effect of the Synthesized Nanocomposites on Bacterial Protein Leakage

Fresh 18 hrs. bacterial culture (S. aureus) was fixed at 1 × 108 CFU/mL, and the synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite were combined with 10 mL of the nutrient broth. MoS2-, the spinal ZnCo2O4-, and Ag-decorated ZnCo2O4–MoS2 nanocomposite-free broth mixed with culture were utilized as the control. The treated samples were incubated for 5 hrs. (37 °C) and then centrifuged at 5500 rpm for 15 min [43]. The resulted supernatant (100 μL) for the examined samples was combined with Bradford reagent (1 mL). Optical density was assessed after 10 min of dark incubation (at 595 nm) [43].

2.9 Reaction Mechanism Determination by SEM

The tested S. aureus was washed with PBS and fixed with 3.5% glutaraldehyde. After that, the fixed S. aureus was washed repeatedly with PBS and rinsed with ethanol at 27 °C for 20 min before dehydration. Finally, S. aureus was fixed and set over the aluminum stump to start the SEM imaging. The treated and untreated S. aureus morphological and surface features with the examined Ag-decorated ZnCo2O4–MoS2 nanocomposite was tested using SEM imaging.

2.10 Statistical Determination

The ONE WAY ANOVA (at P < 0.05) was conducted to determine the statistical investigation of the obtained results and arranged as a Duncan's multiple sequence analyses [44]. The results were examined and studied via SPSS software version 15.

3 Results and Discussions

3.1 Characterization of the Investigated Photocatalysts

The XRD patterns of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples are shown in Fig. 2. Figure 2 exhibited the XRD pattern of ZnCo2O4 NPs. The detected peaks at \(2\theta\) \(=\) 19.19° (111), 31.44° (220), 36.97° (311), 44.86° (400), 55.76° (422), 59.58° (511), and 65.42° (440) are in good matching with the standard cards of JCPDS No. 23-1390. These peaks have belonged to the Fd3m space group of those of spinel ZnCo2O4 NPs [45]. Further, the peaks that have been seen of bulk MoS2 were unique for 2H-MoS2 with a distinctive peak detected at \(2\theta\) = 14.42° (002) which are in good matching with the phase of the hexagonal MoS2 (JCPDS: 37-1492). Also, the appearance of the distinctive peak with the plane (002) proved that the exfoliated MoS2 nanosheets have existed [46,47,48,49,50]. At the same time, the Ag-decorated ZnCo2O4–MoS2 nanocomposite sample showed characteristic peaks of Ag NPs at \(2\theta =\) 38.15° (111), 44.27° (200), 64.68° (220), and 77.66° (311) (JCPDS 4-0783) [51, 52]. Also, the crystallite size of Ag-decorated ZnCo2O4–MoS2 nanocomposite is found of 47.25 nm via using the Debye–Scherer formula [53]. The XRD results for MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples confirmed the successful preparation and purity of the studied samples [31].

Fig. 2
figure 2

XRD patterns of MoS2, the spinal ZnCo2O4, and Ag decorated MoS2–ZnCo2O4 nanocomposite samples

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Figure 3 showed the surface morphology of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples. Figure 3A revealed that the Ag-decorated ZnCo2O4–MoS2 nanocomposite sample possesses a heterogeneous structure. Where SEM image of MoS2 exhibited a disordered array of nanoflakes shape for exfoliated MoS2 sample (Fig. 3B) [54]. Also, Fig. 3C revealed the spherical shape nature of the spinal ZnCo2O4 NPs. Similar observed surface morphology is seen in previous work [29].

Fig. 3
figure 3

SEM images of A Ag decorated MoS2–ZnCo2O4 nanocomposite, B MoS2, and C the spinal ZnCo2O4 NPs

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EDX spectra and elemental mapping images were addressed to present the elemental composition and distribution of the sample. Figure S1 showes the EDX spectra of the Ag-decorated ZnCo2O4–MoS2 nanocomposite. Every one of the elements in the Ag-decorated ZnCo2O4–MoS2 nanocomposite can be viewed (such as Ag, Zn, Co, O, C, Mo, and S) with stoichiometric ratios. At the same time, the appearance of the carbon (C) peak is attributable to the citric acid used in the preparation of the spinal ZnCo2O4 NPs. Furthermore, the elemental mapping images Ag-decorated ZnCo2O4–MoS2 nanocomposite proved all fundamental elements are homogeneously distributed (Fig. 4). Also, HR-TEM images confirmed the conjugation of Ag NPs with MoS2–ZnCo2O4 NPs (composite external layer), as shown in Fig. 5. Further, the TEM images confirmed that the particles of Ag-decorated ZnCo2O4–MoS2 nanocomposite possessed nearly spherical shapes, with an average diameter in nanoscale.

Fig. 4
figure 4

The elemental mapping images Ag decorated MoS2–ZnCo2O4 nanocomposite

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Fig. 5
figure 5

TEM images of Ag decorated MoS2–ZnCo2O4 nanocomposite

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Figure S2 shows the typical diffuse reflectance spectra (DRS) of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples. The wavelength at maximum reflection (λmax) for MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples was found to be within 200 and 300 nm, as can be seen in the figure. Besides, the optical band gap for MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples can be evaluated via the reflectance results via Kubelka–Munk theory and Tauc’s equation [55, 56]. The observed optical bandgap (Eg) for MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples is 2.31, 2.68, and 2.52 eV, respectively, as illustrated in Fig. S3. When compared to ZnCo2O4 and MoS2 NPs, the absorption band edge of Ag-decorated ZnCo2O4–MoS2 nanocomposite deposited with Ag was red-shifted i.e. decrease of optical bandgap. This may be interpreted by the LSPR effect of loaded Ag NPs, which enhanced the photocatalytic performance by broadening visible light's absorption range and speeding up the separation rate of photoexcitation charging [19,20,21].

4 Photocatalytic Activity of the Investigated Samples

4.1 Effect of Initial pH Value

Due to various reaction mechanisms that can affect dye degradation, determining the effect of pH on photodegradation rate is a complicated process [57]. Contribution depends on the photocatalyst's characteristics and pH value [58,59,60]. The influence of solution pH on the rate of MB removal in the presence of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalysts is illustrated via using 10 mg of the photocatalysts for 1 × 10–5 M of MB (Fig. 6a–j). The absorbance spectrum of MB, which displayed a noticeable absorption wavelength around 665 nm (λmax = 600–700 nm), was well-matched with early-declared investigations [61,62,63]. In alkaline solution (pH 12), the investigated photocatalysts showed an exceptional reduction of the MB concentration compared to the neutral and acidic conditions as well as MB dye removal due to adsorption in the dark. It was evident that the adsorption in the dark declined about 43%, 23.6%, and 6.3% of the dye at 30 min by using the MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalysts, respectively. It is observed that both MoS2 and ZnCo2O4 exehibted 89%, 90.5% degradation efficiency of the MB at pH 12, respectively, as illustrated in Fig. 6a and c. In the same context, the Ag-decorated ZnCo2O4–MoS2 nanocomposite exhibited high efficiency of MB dye decolorization; about 95.4% removal of the dye at pH 12 was achieved after 180 min under light, as presented in Fig. 6b. In comparison, MB degradation simultaneously reached about 66% and 69% from its original concentration using Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst in the neutral (i.e., pH 7) and acidic (i.e., pH 4) environments, respectively. The degradation of MB is significantly rapid in alkaline environments than in neutral or acidic ones. The electrostatic interaction between the MB molecules and the Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst is responsible for this outcome leading to the enhancement of redox reactions [64]. This indicates the significance of Ag NPs in boosting charge transfer between the ZnCo2O4–MoS2 interface.

Fig. 6
figure 6

Degradation of MB 1 × 10–5 M, and 10 mg from a ZnCo2O4, b composite and c MoS2 at pH 12, d ZnCo2O4, e composite and f MoS2 at pH 8 and h ZnCo2O4, i composite and j MoS2 at pH 4

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4.2 Effect of Photocatalysts Dose and Initial MB Concentration

As shown in Fig. 7, the effect of the photocatalysts dose on photocatalytic performance was investigated. The effect of the photocatalysts dose on MB degradation under light illumination was examined by changing the amount of the utilized photocatalysts (5 and 20 mg) at pH 12. Whenever the dosage of nanocomposite photocatalyst in aqueous MB solution was varied from 5 to 20 mg, the percentage of MB removal increased from 83.6 to 94.5% after 150 min of irradiation for light. It is ascribing that the enhancement of the amount of photocatalyst leads to the enrichment of the number of active sites obtainable for MB reduction [65]. In other terms, having a lot of active sites on the surface of the photocatalyst used will increase the number of absorbed photons, resulting in more electrochemical reactions and improved performance [65]. As a result, numerous charge carriers and free radicals will most obviously be produced.

Fig. 7
figure 7

Degradation of MB 1 × 10–5 M at pH 12 using a 5 mg and b 20 mg from Ag decorated MoS2–ZnCo2O4 nanocomposite

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Furthermore, a specified amount of adsorbent can only absorb a certain amount of adsorbate molecules. As a result, the appropriate amount of the initial concentration of the adsorbate solution must be evaluated. Variable initial MB concentrations (5 × 10–6 and 5 × 10–5 M) are being used to explore the effects of MB initial concentration on the photodegradation efficiency of Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst (Fig. 8). The amount of MB eliminated over time dropped as the MB initial concentration was increased. The percentage amount of MB elimination dropped from 93.07% to 51.07% at 120 min as the initial MB concentration was increased from 5 × 10–6 to 5 × 10–5 M [66,67,68].

Fig. 8
figure 8

Degradation of MB using 10 mg of Ag decorated MoS2–ZnCo2O4 nanocomposite at pH 12 for a 5 × 10–6 M and b 5 × 10–5 M of MB

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4.3 Reaction Kinetics and Apparent Rate Constant

This can be seen in Fig. 9, the reaction kinetics of MB degradation under light irradiation through synthesized Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst followed very well the pseudo-first-order model. In addition, it was observed that the value of reaction rate constant k decreased with increasing the initial concentration of MB. In contrast, it increases with enriching the nanocomposite photocatalyst dose, consistent with the degradation performance [69].

Fig. 9
figure 9

Pseudo first-order kinetics plots for MB degradation by using Ag decorated MoS2–ZnCo2O4 photocatalyst

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Based on the given findings, we provide a suggestion to the MB photodegradation mechanism via the Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst using Fig. 10. Generally, the free radicals (h+,.O2,.OH) possess predominant roles in the photodegradation of organic dye residuals. Likewise, Z-scheme-based on Au decorated CoFe2O4/MoS2 photocatalyst was previously reported [22]; it will be more proper to assume that the presence of Ag NPs at the surface of ZnCo2O4 and MoS2 can enrich the interface conductivity. This leads to the recombination inducing for the electrons from the conduction band (CB) of ZnCo2O4 with the holes in the valence band (VB) of MoS2. Consequently, incorporating Ag NPs can provide the most acceptable pathway for electron transfer, which is the principal explanation for the excellent photocatalytic potential for Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst.

Fig. 10
figure 10

Reaction mechanism for MB degradation by using Ag decorated MoS2–ZnCo2O4 photocatalyst

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Thus, the photodegradation of MB utilizing Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst may be described as follows:

$${\text{MoS}}_{{2}} + h\upsilon \mathop{\longrightarrow}\limits^{radiation}{\text{MoS}}_{{2}} ({\text{e}}^{ - } + {\text{h}}^{ + } )$$
(2)
$${\text{ZnCo}}_{{2}} {\text{O}}_{{4}} + h\upsilon \mathop{\longrightarrow}\limits^{radiation}{\text{ZnCo}}_{{2}} {\text{O}}_{{4}} ({\text{e}}^{ - } + {\text{h}}^{ + } )$$
(3)
$$e^{ - } \left( {ZnCo_{2} O_{4} } \right) + h^{ + } \left( {MoS_{2} } \right) \to heat$$
(4)
$$O_{2} + e^{ - } \left( {MoS_{2} } \right) \to ^{ \cdot } {\text{O}}_{{2}}^{ - }$$
(5)
$$h^{ + } \left( {ZnCo_{2} O_{4} } \right), O_{2}^{ - } + MB \to Dye^{ \cdot + } \left( {Degradation\, products\, of\, the\, dye} \right)$$
(6)

4.4 Antimicrobial Activity

It was determined that some antibiocidal agents were operated to prevent microbial diseases, and with time the microbe received a resistance [31]. New methods and materials were used to create unexplored antimicrobial agents, particularly those used to manage spreading diseases [70].

The antimicrobial action of all the synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite is concerned at a selected concentration (10 µg/mL) by a disc agar diffusion assay [30]. The tested samples display a positive potency to a wide spectrum of bacteria like P. mirabilis, S. aureus, P. aeruginosa, and C. albicans. In particular, Ag-decorated ZnCo2O4–MoS2 nanocomposite possessed the highest impact, followed by the spinal ZnCo2O4 NPs towards all the tested pathogenic microbes, as mentioned in Table 1 and Fig. 11.

Table 1 Antibacterial and antifungal potential of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag-decorated ZnCo2O4–MoS2 nanocomposite as ZOI (mm), and MIC (µg/mL)
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Fig. 11
figure 11

Antibacterial and antifungal potential of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag decorated MoS2–ZnCo2O4 nanocomposite as ZOI (mm)

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The synthesized samples was effective against Gram-positive bacteria more than Gram-negative ones. The Gram-negative cell wall consisted mainly of lipopolysaccharide (protective layer) and thin peptidoglycan. The antimicrobial potency of the synthesized samples had been compared with the standard antibiotics (AX & NS), which are more influential than all. At the same time, Gram-positive possesses a thick peptidoglycan building coating [30]. It should be mentioned that basic formatting (the purity), sample configuration, and conjugated metal NPs should be evaluated to comprehend the antimicrobial characteristics [31].

It should be stated that there is applicability between the features of the prepared sample and the results monitored. They maintained appropriate physical and chemical effects over synthetic organic and manufactured antimicrobial agents, such as more formal interaction relationships, allowing for more helpful relations with more microbial cells, thus, improving their antimicrobial activity [71]. The dimensions and chemical configuration of the prepared samples was not the most significant parameter controlling their antimicrobial effects; different factors as purity, conjugation with active metal NPs, and strength should be evaluated [72].

The antimicrobial reaction means of samples is still not detected. The prepared models alter the bacterial morphology and its coating network, change the microbial membrane permeability and construct the existence of oxidative pressure response genes inside the microbial cell due to the creation of H2O2. Reactive oxygen species (ROS) diffusion was a superoxide anion (O2−) and were suggested as an effective mechanism [73], the connection between the prepared samples with the microbial cell, following depleting the pathogenic microbes. Another antimicrobial activity mechanism had been investigated, like an alkaline attraction [30].

4.5 Antibiofilm Activity

Biofilm formation was specified in different exo-polysaccharide-producing pathogenic microbes [40]. Biofilm produced by the pathogenic bacteria in the lack and presence of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag-decorated ZnCo2O4–MoS2 nanocomposite was assessed operating the tube method [31].

Results described the stage of tube method for the antibiofilm potential of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite upon S. aureus, which inoculated without MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite, created the air–liquid interface compact whitish-yellow matt, and adhered to the tube walls and appeared the blue color of the adhered microbial cells after CV staining. A deep blue solution was formed after softening CV by absolute ethanol. In addition, no blue color was constructed following ethanol treatment, and the adhesive bacterial cells color was faint (Figures not shown). Otherwise, the treated tubes inoculated by S. aureus in the presence of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite detected a negative result bacterial ring growth was restricted.

A spectrophotometer (set at 570.0 nm) is functioned. UV–Vis. spectrophotometer represents the inhibition % of biofilm produced by the pathogens. Stained CV-biofilm had been dissolved by ethanol, and the optical density was assessed to calculate the creation of microbial biofilm. The inhibition % had been tabulated in Table 2 and calculated the biofilm hindrance created by the synthesized samples. The highest inhibition of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite percentage was noted for S. aureus (61.85%, 73.94%, and 97.06%), followed by C. albicans (76.67%, 84.15% and 94.08%), and P. aureginosa (59.84%, 66.79%, and 92.40%), respectively as illustrated in Table 2, and Fig. 12.

Table 2 Semi-quantitative inhibition % of the biofilm production for non-treated and treated bacterial and yeast pathogens with MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite
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Fig. 12
figure 12

Antibiofilm potential of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag decorated MoS2–ZnCo2O4 nanocomposite

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The synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite hinder biofilm construction at its irreversible bonding step (also understood as the initial step) [74]. Nevertheless, the mechanical movement of the synthesized samples against biofilm construction has yet to be confirmed. The interpretation in the inhibitory percentage might be defined by many aspects, including antimicrobial action, bio-sorption, physical possessions, penetration capabilities and different chemical effects concerning the relationship, metal NPs conjugation and interchange of the synthesized samples with biofilms [75]. It was seen that the synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite hindered microbial development by more than 98%. It must be noted that the microbial cells cannot produce biofilm due to the control of exopolysaccharide, and microbial capsule formations [40].

4.6 Growth Curve Method

The influence of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite on S. aureus growth had presented in Fig. 13. S. aureus growth in the control sample happened quickly, with the most potent optical density at λ = 600 nm (OD600) value having arrived at about 2.78 nm. After adding MoS2 NPs, slight changes were detected, and OD600 was calculated to be 1.87 nm. Indifference, the OD600 value of ZnCo2O4 NPs (0.596 nm) was lower than the control and MoS2 NPs, while the value of Ag-decorated ZnCo2O4–MoS2 nanocomposite showed the weakest results (0.125 nm), showing the repression impact on the growth of S. aureus. Silver-loaded MoS2–ZnCo2O4 nanocomposite display further suppressing power rather than ZnCo2O4 NPs, and MoS2 NPs that the unique synergistic effects may define, and the antibacterial activity of Ag NPs that described by various previous studies [29,30,31,32].

Fig. 13
figure 13

The effect of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag decorated MoS2–ZnCo2O4 nanocomposite on the growth curve of S. aureus

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Typically, on the NPs surface, the photo-generation of reactive oxygen species (ROS) has been characterized by earlier reports [76]. Silver-loaded MoS2–ZnCo2O4 nanocomposite creates ROS, inducing protein oxidation, DNA injury, and lipid peroxidation that can eliminate the bacteria without damaging the other cells. Moreover, S. aureus membrane maintains a negative charge, while the metal ion released from silver-loaded MoS2–ZnCo2O4 nanocomposite (Ag+) possess a positive charge. So, they evolve in direct connection to crop to DNA replication, protein denaturation, and collapse of bacterial cells. The more increased hypersensitivity of the Gram-positive bacteria to the Ag NPs may be described due to the more inferior immobility of the bacterial cell membrane. A different probable causality can be the size, appearance, and surface charge of silver-loaded MoS2–ZnCo2O4 nanocomposite, which could afford them more beneficial to connect with Gram-positive bacteria. Xu et al. [77], reported that NPs, behind UV-irradiation for 80 min, broke the E. coli membrane, suggesting that disinfection was completed. Different reports demonstrated that, most NPs, possessed antibacterial prospects toward other bacterial strains, like S. aureus and E. coli [29, 31].

4.7 UV Potential

Figure 14 shows that UV light is a promising deactivation of S. aureus, and the sensitivity is proportional to the exposure period. The positive influences regarding the attachment and growth of S. aureus had been noted across the display time (0 to 90 min with 15 min time intervals). The development of S. aureus was significantly hindered behind the treatment with silver-loaded MoS2–ZnCo2O4 nanocomposite compared with the untreated control sample, MoS2 NPs, and ZnCo2O4 NPs.

Fig. 14
figure 14

a The UV effect on the antibacterial activity of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag decorated MoS2–ZnCo2O4 nanocomposite against S. aureus, and b zooming area of UV effect

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In UV experiment, the bacterial growth finished at the lowest growth because of the deactivation after UV illumination. UV rays was decided to increase the potential for photo-activation of silver-loaded MoS2–ZnCo2O4 nanocomposite, and the prospect of silver-loaded MoS2–ZnCo2O4 nanocomposite was more elevated than silver-free MoS2 NPs, and ZnCo2O4 NPs. Silver-loaded MoS2–ZnCo2O4 nanocomposite is an excellent disinfectant once it had excited by UV rays. NPs acquire photons, contribution in the formation of new ROS (O2−, and H2O2), and active hydroxyl radical (.OH) in the existence of O2 and H2O (in air and/or water states) [78]. Microbial disinfection can be illustrated as ROS (H2O2) interacting with the membranes. After the penetration inside the microbes, active oxidative hydroxyl free radical was stable, and the effectual hindrance had been noted [76].

4.8 Bacterial Protein Leakage Investigation

In the treated S. aureus suspension, the amounts of proteins discharged were determined by the Bradford method. From Fig. 15, the amount of bacterial protein removed is directly proportional after increasing the concentration of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite (at different concentrations) and counted to be 89.20, 112.90, and 259.25 µg/mL following the treatment with MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite (1.0 mg/mL), respectively which demonstrates the antibacterial features of the Ag-decorated ZnCo2O4–MoS2 nanocomposite and describes the appearance of holes in the S. aureus membrane, which help in making the proteins bleed out from the S. aureus cytoplasm.

Fig. 15
figure 15

The effect of MoS2 NPs, the spinal ZnCo2O4 NPs, and Ag decorated MoS2–ZnCo2O4 nanocomposite on the protein leakage from S. aureus cell membranes

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The presented results indicated that the synthesized Ag-decorated ZnCo2O4–MoS2 nanocomposite enhanced the dissolving of S. aureus membrane and altering its permeability more than MoS2 NPs, the spinal ZnCo2O4 NPs. The main cause for the repression of the bacterial growth is the positive effect of the metal against the bacterial membrane permeability which finally caused the protein leakage. Similar articles such as [79] and [80] define the same results after the treating with NPs, which showed concentration-dependence for the dislodgement in the bacterial membrane and suggested leakage of bacterial intracellular organelles into the extracellular cell structure.

Paul et al. [81] demonstrated that the dissimilarity in membrane permeability of the bacteria was established in rate dissimilarity in connected electric conductivity. To determine the integrity of any microbes, the protein leakage assay is a critical method used for the determination. The leakage developed over time as standard microbial damage, and the leakage of cell constituents caused cell collapse.

4.9 SEM Reaction Mechanism

SEM analysis was directed to indicate the potential antimicrobial mechanism against S. aureus, as noted in Fig. 16. The SEM study regarding the control bacterial cells in the absence of Ag-decorated ZnCo2O4–MoS2 nanocomposite (the most potent sample) presented bacterial groups typically prolonged and grown with a standard shape and count with the whole regular surface, as displayed in Fig. 16a and b.

Fig. 16
figure 16

Reaction mechanism determination using SEM analysis where a, b Control untreated S. aureus, and c, d Treated S. aureus with the most active synthesized sample (Ag decorated MoS2–ZnCo2O4 nanocomposite)

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After Ag-decorated ZnCo2O4–MoS2 nanocomposite treatment, unusual morphological irregularities are identified in S. aureus (Fig. 16c), including the semi-lysis of the outer surface in some bacterial cells established by deformations of the S. aureus cells. On the other hand, the synthesized Ag decorated MoS2–ZnCo2O4 nanocomposite performed the complete lysis of the bacterial cell and cell malformation, decreasing the total viable number (Fig. 16d) and creating holes on the surface of bacterial cells, and white layers are formed over the bacterial cells due to the chemisorption attractions between the active Ag-decorated ZnCo2O4–MoS2 nanocomposite and the bacterial cell wall, which confirmed by the membrane leakage assay (Fig. 15).

The schematic diagram in Fig. 17 shows the possible antimicrobial mechanism. There were important and excellent potential actions such as reactive oxygen species (ROS) production due to the Ag loaded in the synthesized Ag-decorated ZnCo2O4–MoS2 nanocomposite.

Fig. 17
figure 17

Schematic indication about the four significant forms of the antibacterial possibility of Ag decorated MoS2–ZnCo2O4 nanocomposite, where: 1. Ag decorated MoS2–ZnCo2O4 nanocomposite attaches to the bacterial cell surface and results in membrane injury and limited transport movement. 2. Ag decorated MoS2–ZnCo2O4 nanocomposite stop the ions transportation to and from the bacterial cell. 3. Ag decorated MoS2–ZnCo2O4 nanocomposite develop and improve the ROS directing to bacterial cell wall crack. 4. Ag NPs liberated from Ag decorated MoS2–ZnCo2O4 nanocomposite penetrate inside the bacterial cells and interact with cellular organelles, thereby influencing individual cellular machinery and modulating the cellular signal design and inducing cell end. Ag decorated MoS2–ZnCo2O4 nanocomposite may serve as a vehicle to effectively deliver Ag+, Co2+, Zn2+, and Mo2+ ions to the bacterial cytoplasm and membrane, where proton motive force would reduce the pH to be less than 3.5 and enhance the liberation of ions

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It is recommended that; the synthesized Ag-decorated ZnCo2O4–MoS2 nanocomposite adhere to the microbial cells by chemisorption, and ROS will be developed, which could change the microbial morphology, reduce the microbial membrane permeability and provide the occupancy of oxidative stress genes about their replies because of the ROS production. We realize that Ag-decorated ZnCo2O4–MoS2 nanocomposite begin their movement by bonding at the surface of the microbes, permitting membrane damage (as discussed in Fig. 17), construction of pits, and switching off the ions transportation activity. Then, the formation of ROS inside the microbial cells moved to the corresponding ions in the microbial cell, damaging all intracellular structures like DNA, plasmid, and various critical bacterial organelles. Now, cellular toxicity happens because of the oxidative stress created by ROS production [29, 30].

5 Conclusion

A Facile process was applied to synthesize Ag-decorated ZnCo2O4–MoS2 nanocomposite photocatalyst via gamma irradiation. The XRD and EDX results indicated the efficient fabrication and purity of the studied samples. Also, HR-TEM images confirmed the conjugation of Ag NPs with MoS2–ZnCo2O4 NPs. The photocatalyst shows enhanced, stable, and outstanding photocatalytic degradation towards MB 95.4% degradation of the dye at pH 12 was achieved after 180 min under light irradiation. The synthesized MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite samples had been tested for their antimicrobial potential upon selected pathogens (yeast and bacteria) throughout the agar-disc diffusion method. The tested samples display a positive potency to a wide spectrum of bacteria like P. mirabilis, S. aureus, P. aeruginosa, and C. albicans. In particular, Ag-decorated ZnCo2O4–MoS2 nanocomposite possessed the highest impact, followed by the spinal ZnCo2O4 NPs towards all the tested pathogenic microbes. In antibiofilm assay, the highest inhibition % of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite percentage was documented for S. aureus (61.85%, 73.94%, and 97.06%), followed by C. albicans (76.67%, 84.15% and 94.08%), and P. aureginosa (59.84%, 66.79%, and 92.40%), respectively. In growth curve assay, S. aureus growth in the control sample happened quickly, with the most potent optical density at λ = 600 nm (OD600) value having arrived at about 2.78 nm, while the value of Ag-decorated ZnCo2O4–MoS2 nanocomposite showed the weakest results (0.125 nm), showing the repression impact on the growth of S. aureus. In UV experiment, the bacterial growth finished at the lowest growth because of the deactivation after UV illumination. In protein leakage assy, the amount of bacterial protein removed is directly proportional after increasing the concentration of MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite (at different concentrations) and counted to be 89.20, 112.90, and 259.25 µg/ml following the treatment with MoS2, the spinal ZnCo2O4, and Ag-decorated ZnCo2O4–MoS2 nanocomposite, respectively (1.0 mg/mL). SEM imaging reaction mechanism illustrated that, after Ag-decorated ZnCo2O4–MoS2 treatment, unusual morphological irregularities are identified in S. aureus, including the semi-lysis of the outer surface in some bacterial cells established by deformations of the S. aureus cells.