The X-ray diffraction data gives us valuable information such as crystalline phase, crystal structure, crystallographic orientation, crystallite size, strain and phase purity, etc. Broader peaks are observed that lead to smaller crystallite sizes. Debye-Scherrer equation is used to determine the crystallite size (D) by ,

with K = 0.9 as the shape factor. λ = 1.54 Å as the CuK wavelength of. β as the full width at half maximum (FWHM). The calculated values are listed in Table 1 .The average crystallite size decreased with the increase in the molybdenum concentration; values are 4.6 nm,4.39 nm, and 4.29 nm, respectively. The D value of VS is 13.81 nm. All calculated values are presented with their corresponding standard deviations, and the detailed calculations are provided in Table S1. The Dislocation density is the number of dislocation lines per unit volume of a crystal as calculated.

In nano-crystalline materials, lattice distortion, characterized by micro-strain and lattice parameter change, is commonly encountered. The fundamental explanation for the lattice distortion is thought to be the internal stress caused by the extra volume at grain boundaries. The micro-strain produced inside the material is given by,

Raman spectra analysis was performed to verify the microstructure and insight into the details of the phonon active mode of VS and VS/MoS nanocomposite. The Raman data was taken in the 50-700 cm range for all the prepared nanocomposites, as presented in Fig. 2. The characteristic pristine VS peaks are located approximately at 192, 219, 271,286.5 and 346 cm, which are arises due to the different rocking and stretching vibration of V-S bond vibrational modes.192 cm and 219 cm peaks are due to the V-S bond stretching. The peak formed at 271 cm and 286 cm is due to the E in-plane phonon mode arises due to the opposite vibration of two S atoms with respect to V atom .

The characteristic peak of VS₂ at 192 cm⁻¹ is observed in the composite sample, while the other peaks are not clearly visible. Both in-plane(E) and out-of-plane (A) vibrational mode peaks of MoS located at 378.9 and 406.9 cm are clearly observed in all three nanocomposite samples. In the nanocomposite the peak appeared at 228 is due to the MoS. The peak intensity gradually increased with higher molybdenum concentration. The presence of both VS and MoS vibrational mode peaks of Raman also confirms the formation of the composite.

The morphology of the nanomaterial is determined by FESEM images. Figure 3.a, b illustrates the FESEM pictures at different magnifications of VS/MoS-1. From the observation, it is found that the VS/MoS-1 sample morphology exhibits a flower-like structure. An essential method for examining the compositional variance in the material is elemental mapping. Figure 3. c-f shows the elemental mapping of VS/MoS-1. The material's homogeneous distribution of V, S, and Mo components confirms the successful completion of a uniform VS/MoS nanocomposite through the elemental mapping. EDX spectra of VS/MoS-1, from Fig. 3.g, confirm the elemental presence of the prepared sample. Figure 4. represents the FESEM pictures of two other compositions, such as VS/MoS-2 and VS/MoS-3, with two different magnifications.

Fig S1a, b represents the FESEM images of VS with different magnifications. Some other reports also show similar morphology. An average thickness of 43 nm is found for the nanosheets. All other EDX spectra are provided in Figure S2a, b, c. Different peaks for the various elements present in the material can be seen in the EDX spectrum. 0.511 keV and 4.952 keV are the energies corresponding to the L and K transitions for the element Vanadium. 2.293 keV is the L transition for molybdenum. The Sulfur peak at 2.307 keV is due to the K transition.

Figure 5 represents the TEM images of VS/MoS-3 with different magnifications, which clearly show the nanosheets stacked together, forming a flower-shaped structure. The other two TEM images are shown in Figure S3. Figure 5c-e shows the HRTEM images with different scales and distinct crystallographic planes. (002) and (103) are the planes corresponding to MoS, with lattice spacing of d = 6.3 Å and d = 2.21 Å, respectively. (101) plane corresponds to VS, which confirms the inter-planar spacing of 2.51 Å. It matches well with the XRD data, conforming to the hexagonal phase of both VS and MoS. Figure 5f is the SAED pattern confirming the presence of both VS and MoS. Each circular ring present demonstrates the (002), (004), (100), and (102) planes corresponding to MoS and VS, respectively. It shows the polycrystalline nature of the prepared sample.

XPS is widely recognized as a powerful tool for surface analysis. It enables the identification of a material's surface elemental composition, oxidation states, and bonding environments, offering precise insights into the outermost layers, generally within the top ~ 10 nm of the sample. This data further confirms the presence of S, V, and Mo in the prepared sample. The comparison between pure VS spectra and VS/MoS spectra will give proof of nanocomposite formation. The XPS spectra of pristine VS and VS/MoS nanocomposite are presented in Fig. 6.a. The characteristic core levels for VS are located at 524.7 eV and 517.4 eV. The V-2p and V- 2p atomic orbitals correspond to the V state. V oxidation state is also present, confirmed by the peak located at 514 eV (Fig.S4(a)). Due to the overexposure of the sample to air, another characteristic peak located at 530.1 eV is present due to O1s atomic orbital. The 162.8 eV and 163. 9 eV peaks are for S-2p and S-2p atomic orbitals, respectively, with the state S Fig. S4(b).

Figure 6a. presents the comparison between the XPS survey spectra of VS₂ and the VS₂/MoS₂-3 nanocomposite, while Fig. 6b and c display the high-resolution spectra of the V 2p and S 2p orbitals, respectively. In nanocomposite, the peaks for V-2p are slightly shifted towards the lower binding energy value as 524.5 and 517.04 eV that correspond to V-2p and V-2p with the same oxidation state V. The peak for state V is not present here. The sulfur peak for 2p atomic orbital also shifted towards the lower binding energy value. S-2p and S-2p atomic orbitals correspond to binding energy values 163.22 and 162.08 eV, respectively, for S state. Figure 6. d confirms the presence of Mo with the characteristic peak at 232.4 eV and 229.29 eV with the emission of electrons from the 3d and 3d atomic orbitals, and the Oxidation state is Mo. A small peak at 226.45 eV is for the S-2s orbital. The peak at 235.75 eV indicates the formation of the Mo state. The BE of nanocomposite is also less than that of pure MoS. This peak shift is due to the transfer of electrons from the VS to the MoS. The shift amount for both v-2p and S-2p is shown in Fig. 6b and c, respectively. This is the effect of the low work function of VS, the observed peak shifts indicate electron transfer from VS₂ to MoS₂, in conjunction with the strong interfacial coupling between the two materials. There is no need for carbon correction because the peak for C-C is exactly at 284.6 eV, fig. S5(C). Individual XPS spectra and high-resolution XPS spectra are shown in Fig. S4 and Fig. S5.

The atomic percentage can be calculated for the area under different oxidation states of the different elements present in a sample. The S-2p area is more in the VS/MoS-3 composite as compared to VS. Same for the S-2p oxidation states. The atomic percentage for each oxidation state is provided in the supporting information Table S2 and Table S3 for VS and VS/MoS-3 composite. The oxidation states identified by XPS directly correlate with the antibacterial performance, indicating that the surface oxidation states govern the generation of reactive species responsible for bacterial inhibition. It is reported in a journal that Vanadium serves as the primary catalytic site for peroxymonosulfate (PMS) activation, where the generation of reactive oxygen species(ROS) originates from the redox transition among V, V, and V.XPS analysis confirmed the V/V redox cycling, which plays a decisive role in radical generation and thereby enables efficient degradation of organic pollutants in the VS/PMS system.Nano-VO films have been shown to display strong antibacterial activity, particularly against S.aureus, with the effect intensifying at higher vanadium oxidation states due to enhanced intracellular ROS generation.Upon ultrasound stimulation, VS generated abundant electrons that were efficiently captured by Mxene, resulting in enhanced electron-hole separation. This process promoted the production of multiple ROS species and imparted strong antibacterial activity, particularly through the POD-like catalytic generation of -OH by VS.Mo@ZIF-8 nanozymes, synthesized by refluxing Na₂MoO₄ with ZIF-8 and pyrolyzing at 600 °C, exhibited peroxidase-like *OH generation with broad antibacterial activity against E. coli and S. aureus, demonstrating strong potential as biocompatible antibacterial agents. Thus, the oxidation states V and Mo identified by XPS play a crucial role in generating reactive species, which in turn enhance the inhibition of bacterial growth against E.coli, and S.aureus.

A straightforward technique for determining the optical characteristics of the powdered crystalline materials is demonstrated using diffuse reflectance spectra (DRS). The energy gap between the valence band and the conduction band, where electrons can move, is referred to as the band gap. Diffuse reflection is the phenomenon that arises from the reflection, refraction, diffraction, and absorption of particles oriented in all directions. Kubelka-Munk theory is valid at the condition where the particle size is equivalent to or lower than the wavelength of the incident ray. Figure 7(a) represents the reflectance plot of the samples. The sample's thickness does not affect reflectance when it falls within the appropriate range. The Kubelka-Munk is written for any wavelength as.

Here, R is the diffuse reflectance, and f(R) is the Kubelka-Munk function. K as the absorption coefficient and S as the scattering coefficient. Absorption coefficient (α) and band gap (E) are related by the famous Tauc relation. given by

Here, the value of C is significantly influenced by transition probability. At the same time, 'ν' is the frequency of the incident light, and 'h' represents the Planck constant. Here, 'm' is related to the transition mode power factor. The 'd' value is different for various types of electronic transition, like d= ½ or 2 for direct and indirect allowed transitions. The absorption coefficient becomes twice for the perfect diffuse scattering of incident radiation. At this condition, scattering coefficient "s" remains constant with wavelength. Applying Eq. (5) for direct allowed transition, it can be written as

Now E calculation was done by plotting [F(R)hν] vs. hν. The evaluated values are listed in Table 2.

Figure 7.b confirms that the band gap of the prepared sample is increasing with an increased amount of molybdenum concentration. The energy gap and refractive index are two key parameters that determine semiconductors' optical and electrical behavior. The photon absorption threshold of the energy gap is determined by a semiconductor, while the transparency of the incident photon is measured by the refractive index. The refractive index of materials can be evaluated through different approaches, including spectroscopic ellipsometry, prism coupling, refractometry, and UV-is spectroscopy. Among these, spectroscopic ellipsometry is generally regarded as the most precise and widely accepted method for thin films and smooth bulk substrates, as it yields both the real and imaginary components of the refractive index with high accuracy. Nevertheless, this technique cannot be applied to powdered samples, since their surface irregularities and intense diffuse scattering hinder reliable polarization-based measurements.

For the hydrothermally synthesized VS/MoS nanocomposite obtained in powder form, UV-Vis diffuse reflectance spectroscopy(DRS) serves as the most appropriate technique. The reflectance spectra can be converted into the Kubelka-Munk function, and in combination with Tauc analysis, the optical bandgap can be estimated. Using this bandgap, the refractive index may be approximated through an empirical relation such as the Dimitrov-Sakka or Herve-Vandamme models. Although these estimates are indirect and less accurate compared to ellipsometry, they remain suitable for nanocomposite powders, where DRS provides the most dependable means of optical characterization. Therefore, while ellipsometry stands as the reference method for flat films and bulk samples, DRS-based evaluation offers the most credible pathway for refractive index determination in the present composite system. There are many theories for calculating the refractive index; some of the methods are listed below. According to the Moss relation, the refractive index (n) and energy gap (E) are related by the Eq.

Here, the K value is 95 eV. The Moss relation is valid within the 0.5 to 3.67 eV energy range. Another well-known relation is Ravindra's relation

where the 'n' and 'E are linearly connected. This model deals with the band gap energy 1.50 eV < E<3.50 eV. Using oscillator theory, Herve and Vandamme developed a relation between band gap and UV resonance energy, which gives the materials a low optical energy gap. The model works between the energy range 2.00 eV < E<4.00 eV. It is the redefined Moss rule that is suitable for low optical energy gap materials. It is expressed as:

The value of A = 13.6 eV and B = 3.74 eV, with A representing the hydrogen ionization energy. This equation is expressed by:

Tripathy also put forth a different 'n' and 'E' relationship, where he showed that the 'n' and 'E' are exponentially related

Another way of calculating the band gap is the Dimitrov and Sakka relation, given by the Eq.

The calculated values of the refractive index are listed in Table 2. The refractive index value in the higher wavelength region is higher than in the lower wavelength region, as seen in Fig. 7 c. The blue shift in the absorption spectra increases the band gap of the material from VS to higher concentrations of molybdenum gradually. This is due to the quantum confinement effect. This is also confirmed from the XRD data that the crystallite size of the prepared material gradually decreases with a higher amount of molybdenum concentration. The prepared material can be used in solar cells, photodetectors, and waveguides, as it has a lower band gap calculated from DRS data due to the high refractive index.

The procured result showed that there is a sequential reduction in turbidity of both gram-negative and gram-positive bacterial strains with an increase in the concentration of the test material, which is shown in the Figs. 8 and 9 respectively. There is a visible turbidity bacterial culture incubated along with DMF, which suggests that DMF is not meddlesome in bacterial growth. This implies that the test material can significantly inhibit the growth of both gram-positive and gram-negative bacteria.

The result obtained from the disk diffusion method showed that the material has a significant antibacterial property against both gram-negative (E. coli) and gram-positive (S. aureus) bacteria. The inhibition zone diameter obtained against E. coli and S. aureus is 12 mm and 11 mm, respectively. It shows that the inhibition zone against E. coli is more prominent than S. aureus, which implies that the material has better antibacterial efficacy against gram-negative bacteria than gram-positive bacteria. The disk diffusion method also shows that the material is easily diffused over the agar plate to inhibit the growth of bacteria. Figure 10. illustrates the evaluation of antimicrobial properties of the material in both gram-negative and gram-positive strains, the related inhibition zone against (a) S. aureus, (ATCC 25923), (b) E. coli, (ATCC 25922), whereas 1 & 3 are positive control impregnated disks with DMF, and 2, 4 are disks impregnated with material dissolved in DMF.

In this manuscript, the primary method selected was the broth dilution method to evaluate the antibacterial efficacy of the material against both gram-negative (ATCC-25922, E. coli) and gram-positive (ATCC-25923, S. aureus) bacteria. In this particular method, three different concentrations of material were taken to evaluate which concentration has better efficacy against both, where all the concentrations that were taken are effective, significantly inhibiting the growth. For further confirmation of the antibacterial activity of the synthesized MoS/VS nanocomposite, the disk diffusion method was adopted. In this process, a sterile disk was impregnated with material and then applied to a bacterial culture to observe the sensitivity of the bacteria towards the nanocomposite.

There are several methods being used for the antibacterial assay, such as flow cytometry, ATP bioluminescence assay, and time kill assay, which is better for real-time monitoring, but here we selected the broth dilution and disk diffusion method for their broad acceptability. These are conventional antibacterial assays for initial screening of antibacterial efficacy in a microbiology laboratory. The diffusion capacity of MoS/VS-3 nanocomposite and its sensitivity towards bacteria were well observed in the disk diffusion method. In this study, MoS/VS-3 nanocomposite has been used as the sole material for antibacterial assay; therefore, the comparison focused on the effect of the material on gram-negative and gram-positive bacteria rather than different samples.