Gamma-Rays Induced Synthesis of Ag-Decorated ZnCo2O4–MoS2 Heterostructure as Novel Photocatalyst and Effective Antimicrobial Agent for Wastewater Treatment Application

The development of novel semiconductors-based-photocatalysts is a promising strategy for addressing environmental pollution. In the present study, gamma irradiation was utilized to induce the synthesis of the exceptionally efficient Ag-decorated ZnCo2O4–MoS2 heterostructure. XRD and EDX analyses were verified the successful synthesis of Ag-decorated ZnCo2O4–MoS2 heterostructure. Also, SEM and HR-TEM images were illustrated the heterostructure nature of the synthesized photocatalyst in the nanoscale regime. The obtained optical bandgap values verified that photocatalyst possesses a narrow semiconductor bandgap. Further, the Ag-decorated ZnCo2O4–MoS2 heterostructure exhibited superior photodegradation potential towards MB (95.4% removal of the MB). The antimicrobial potency of the synthesized samples had been investigated through ZOI, MIC, growth curve assay, and the effect of UV illumination. Also, the antibiofilm behaviour has been studied. The antibacterial reaction mechanism had been estimated by membrane leakage assay and SEM imaging. The tested samples displayed a positive potency to a broad spectrum of bacteria like Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. In particular, Ag–MoS2–ZnCo2O4 nanocomposite possessed the highest impact, followed by the spinal ZnCo2O4 NPs towards all the tested pathogenic microbes. In this assessment, the Ag-decorated ZnCo2O4–MoS2 heterostructure has been shown to be a promising candidate for wastewater treatment application.


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 ecofriendly 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 M. I. A. Abdel Maksoud and Gharieb S. El-Sayyad have equal contribution. of unique photocatalysts with remarkable efficiency and stability is a modernistic and innovative responsibility [3].
The molybdenum disulfide (MoS 2 ) has shown great promise in many applications [4,5]. MoS 2 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]. MoS 2 , 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, MoS 2 possesses restricted catalytic activity. Consequently, finding an appropriate modification strategy to boost MoS 2 's photocatalytic activity remains a challenge [10].
In this vein, spinel cobaltites MCo 2 O 4 (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]. ZnCo 2 O 4 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), ZnCo 2 O 4 is suitable for organic photodegradation utilizations [14][15][16]. As a result, adding MoS 2 to the ZnCo 2 O 4 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 ZnCo 2 O 4 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 ZnCo 2 O 4 /MoS 2 . So, Ag NPs were decorated on the surface of ZnCo 2 O 4 /MoS 2 , that the electron-hole separation can be enhanced by the improved conductivity of the interface between ZnCo 2 O 4 and MoS 2 . Yuefa et al. [22] have reported that Au NPs enhanced CoFe 2 O 4 -MoS 2 photocatalyst to degrade methyl orange by using visible light irradiation. Also, Junwei et al. [23] have improved photocatalytic hydrogen generation of TiO 2 -Cu 2 O 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 ZnCo 2 O 4 / MoS 2 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 ZnCo 2 O 4 / MoS 2 ; therefore, the segregation of electrons and holes can be improved by enriching the interface's conductivity between ZnCo 2 O 4 and MoS 2 . As a result, it is essential to consider the unique characteristics of heterostructure Agdecorated ZnCo 2 O 4 -MoS 2 photocatalysts for environment water purification.

Synthesis of Ag-Decorated ZnCo 2 O 4 -MoS 2
Firstly, the spinal ZnCo 2 O 4 was synthesized via the sol-gel technique, as illustrated in Fig. 1 [35]. Secondly, 3 g of the synthesized spinal ZnCo 2 O 4 NPs and 1.5 g of molybdenum disulfide (MoS 2 ) 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 MoS 2 -ZnCo 2 O 4 was filtered and washed with deionized water several times and dried at 60 °C for 3 h. After that, 3 g of MoS 2 -ZnCo 2 O 4 NPs and 0.5 g of silver nitrate (AgNO 3 ) 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 Agdecorated ZnCo 2 O 4 -MoS 2 NPs were filtered and washed via a mixture of ethanol, and water was dried in the air to give Ag-decorated ZnCo 2 O 4 -MoS 2 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).

Photocatalytic Activity Measurement
All photocatalytic tests were performed at ambient temperature (

Antimicrobial Activity
The synthesized MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 × 10 8 CFU/ mL for bacteria and 1-4 × 10 8 CFU/mL for the tested yeast. Positive standard antibiotics Nystatin (NS) and Amoxicillin (AX) were used to evaluate the ZOI potency [31].

Potential Antibiofilm Behavior
The synthesized MoS 2 NPs, the spinal ZnCo 2 O 4 NPs, and Ag-decorated ZnCo 2 O 4 -MoS 2 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 × 10 8 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].

Growth Curve Assay
The influence of MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 × 10 8 CFU/mL) in 5.0 ml of nutrient broth tubes. MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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.

Potential Effect of UV Illumination
Two hours incubated, bacterial cultures were established to standard 0.5 McFarland (1 × 10 8 CFU/mL). MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite were incorporated into the estimated tubes. After illumination with UV, the antimicrobial potency of the synthesized MoS 2 , the spinal ZnCo 2 O 4 , and Agdecorated ZnCo 2 O 4 -MoS 2 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 MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite and tubes with MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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].

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 ZnCo 2 O 4 -MoS 2 nanocomposite was tested using SEM imaging.

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.

Characterization of the Investigated Photocatalysts
The XRD patterns of MoS 2 , the spinal ZnCo 2 O 4 , and Agdecorated ZnCo 2 O 4 -MoS 2 nanocomposite samples are shown in Fig. 2. Figure 2 [51,52]. Also, the crystallite size of Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite is found of 47.25 nm via using the Debye-Scherer formula [53]. The XRD results for MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite samples confirmed the successful preparation and purity of the studied samples [31]. Figure 3 showed the surface morphology of MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite samples. Figure 3A revealed that the Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite sample possesses a heterogeneous structure. Where SEM image of MoS 2 exhibited a disordered array of nanoflakes shape for exfoliated MoS 2 sample (Fig. 3B) [54]. Also, Fig. 3C revealed the spherical shape nature of the spinal ZnCo 2 O 4 NPs. Similar observed surface morphology is seen in previous work [29].
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 ZnCo 2 O 4 -MoS 2 nanocomposite. Every one of the elements in the Ag-decorated ZnCo 2 O 4 -MoS 2 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 ZnCo 2 O 4 NPs. Furthermore, the elemental mapping images Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite proved all fundamental elements are homogeneously distributed (Fig. 4). Also,  Figure S2 shows the typical diffuse reflectance spectra

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 MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 (λ max = 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

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. 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 ZnCo 2 O 4 -MoS 2 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 [66-68].

Reaction Kinetics and Apparent Rate Constant
This can be seen in Fig. 9, the reaction kinetics of MB degradation under light irradiation through synthesized Agdecorated ZnCo 2 O 4 -MoS 2 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].
Based on the given findings, we provide a suggestion to the MB photodegradation mechanism via the Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite photocatalyst using Fig. 10. Generally, the free radicals (h + , . O 2 , . OH) possess predominant roles in the photodegradation of organic dye residuals. Likewise, Z-scheme-based on Au decorated CoFe 2 O 4 /MoS 2 photocatalyst was previously reported [22]; it will be more proper to assume that the presence of Ag NPs at the surface of ZnCo 2 O 4 and MoS 2 can enrich the interface conductivity. This leads to the recombination inducing for the electrons from the conduction band (CB) of ZnCo 2 O 4 with the holes in the valence band (VB) of MoS 2 . 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 ZnCo 2 O 4 -MoS 2 nanocomposite photocatalyst.

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 MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 ZnCo 2 O 4 -MoS 2 nanocomposite possessed the highest impact, followed by the spinal ZnCo 2 O 4 NPs towards all the tested pathogenic microbes, as mentioned in Table 1 and Fig. 11.
The synthesized samples was effective against Grampositive bacteria more than Gram-negative ones. The Gramnegative 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   [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 H 2 O 2 . Reactive oxygen species (ROS) diffusion was a superoxide anion (O 2 − ) 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].

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 MoS 2 NPs, the spinal ZnCo 2 O 4 NPs, and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite was assessed operating the tube method [31].
Results described the stage of tube method for the antibiofilm potential of MoS 2 , the spinal ZnCo 2 O 4 , and Agdecorated ZnCo 2 O 4 -MoS 2 nanocomposite upon S. aureus, which inoculated without MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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 Table 2, and Fig. 12.
The synthesized MoS 2 , the spinal ZnCo 2 O 4 , and Agdecorated ZnCo 2 O 4 -MoS 2 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 MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 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].

Growth Curve Method
The influence of MoS 2 , the spinal ZnCo 2 O 4 , and Agdecorated ZnCo 2 O 4 -MoS 2 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 (OD 600 ) value having arrived at about 2.78 nm. After adding MoS 2 NPs, slight changes were detected, and OD 600 was calculated to be 1.87 nm. Indifference, the OD 600 value of ZnCo 2 O 4 NPs (0.596 nm) was Table 2 Semi-quantitative inhibition % of the biofilm production for non-treated and treated bacterial and yeast pathogens with MoS 2 , the spinal ZnCo 2 O 4 , and Ag-decorated ZnCo 2 O 4 -MoS 2 nanocomposite Nil means that no ZOI had been measured. a AX Amoxicillin (antibacterial standard), NS Nystatin (antifungal standard), ZOI Zone of Inhibition, MIC Mininum Inhibitory Concentration.
Data within the groups are analyzed using one-way analysis of variance (ANOVA) followed by a, b, c, d, e, f, g, h Duncan's multiple range test (DMRT).  [29][30][31][32]. Typically, on the NPs surface, the photo-generation of reactive oxygen species (ROS) has been characterized by earlier reports [76]. Silver-loaded MoS 2 -ZnCo 2 O 4 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 MoS 2 -ZnCo 2 O 4 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 MoS 2 -ZnCo 2 O 4 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]. 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  [78]. Microbial disinfection can be illustrated as ROS (H 2 O 2 ) 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].

Bacterial Protein Leakage Investigation
In the treated S. aureus suspension, the amounts of proteins discharged were determined by the Bradford method. From The presented results indicated that the synthesized Agdecorated ZnCo 2 O 4 -MoS 2 nanocomposite enhanced the dissolving of S. aureus membrane and altering its permeability more than MoS 2 NPs, the spinal ZnCo 2 O 4 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.

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 ZnCo 2 O 4 -MoS 2 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.
After Ag-decorated ZnCo 2 O 4 -MoS 2 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 MoS 2 -ZnCo 2 O 4 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 ZnCo 2 O 4 -MoS 2 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 ZnCo 2 O 4 -MoS 2 nanocomposite. It is recommended that; the synthesized Ag-decorated ZnCo 2 O 4 -MoS 2 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 ZnCo 2 O 4 -MoS 2 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

Conflict of interest
The authors declare that they have no conflict of interest.
Ethical Approval Not required.
Consent to Participate Not applicable.

Consent to Publish Not applicable.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.