Structural, Optical, and Antibacterial Properties of PEO/PANI Nanocomposites Doped with WO₃, Cr₂O₃, and NiO Nanoparticles

INTRODUCTION
The need to develop new and effective materials with antibacterial properties has become urgent, given the continuous increase in bacterial resistance to traditional antibiotics. Therefore, polymers have received significant attention in research circles due to the possibility of modifying their properties. They can be employed as matrices support and maintain active nanoparticles, as active chemicals, or as carriers of antibacterial agents. For instance, two of the most popular polymers in this sector are polyaniline (PANI) and polyethylene oxide (PEO)[1].Since adding nanoscale oxides to polymers increases their capacity to produce reactive oxygen species (ROS), cause proteins and DNA within cells to oxidize, they can be utilized as active chemicals [2].Oxides such as tungsten oxide (WO3), chromium oxide (Cr2O3), and nickel oxide (NiO), are commonly used to change the thermal stability, electrical conductivity, and antibacterial activity of polymers [3]. Due to its large energy gap, tungsten oxide can absorb light and react with it to generate reactive oxygen species [4]. Free radicals are produced as a result of this electrical excitation, which breaks down the bacterial cell wall [5]. Chromium trioxide’s antibacterial action, however, is ascribed to its capacity to modify the polymer’s surface characteristics, which lessens bacterial adhesion to the material’s surface [6]. Additionally, it interferes with the bacterial cell membrane’s permeability, which stops the bacteria from preserving their ionic equilibrium. [7]. These species attach to the bacterial cell wall due to their positive surface charge, which also facilitates their ability to break down proteins and cellular membranes. Furthermore, doping the polymers with it helps to boost the polymer material’s efficiency [8]. Two common forms of pathogenic bacteria have been identified, and bacteria are among the most prevalent and significant microbes impacting human health. Escherichia coli (E⋅ coli) is a gram-negative bacterium [9]. The most common E. coli infection is a urinary tract infection, but individuals can also contract intestinal infections by consuming contaminated food (such as undercooked ground beef), coming into contact with infected animals, or drinking contaminated water.[10]. However, Staphylococcus aureus S.aureus) is a gram-positive bacterium that can cause post-operative wound infections and mild skin diseases [11]. Polymers are employed in the production of antimicrobial dressings that aid in wound healing and infection prevention, as well as in the coating of medical devices, such as catheters [12], needles [13], and other [14]. They are also used in food packaging to prevent bacterial growth on food, as well as in drug delivery systems [15], for treating fabrics [16], and in the production of medical clothing [17], masks [18], and bedding [19]. In addition, they are used in air and water filters found in laboratories and hospitals [20]. Antibacterial polymers are therefore crucial in the fight against bacteria’s growing resistance to conventional antibiotics [21].

MATERIALS AND METHODS
Materials 
Polyethylene oxide (PEO, Mw ≈ 3,000,000), polyaniline (PANI, emeraldine salt), tungsten trioxide (WO3), chromium (III) oxide (Cr2O3), and nickel (II) oxide (NiO) nanopowders were purchased from commercial suppliers with purity ≥99%. Every chemical was used exactly as it was delivered, requiring no additional purification. The solvent utilised was distilled water (DW).

Preparation of a blend of PEO/PANI Solution
The polymer blend was prepared by dissolving 1.5gm of PEO in 450 mL of DW under magnetic stirring at ~20 °C until complete dissolution (~20h). Separately, 1.0 g of PANI (emeraldine base) was ultrasonically dispersed in 100 mL of DW for 2 h. The two solutions were then combined and stirred for an additional 2 h to form a homogeneous PEO/PANI blend.

Preparation of Nanocomposites
Metal oxide nanopowders (WO3, Cr2O3, and NiO) were dispersed individually in 50 mL of distilled water by ultrasonication (40 kHz, 60 min). Each dispersion containing 0.05 g of oxide was gradually added to the PEO/PANI blend under continuous stirring for 3 h, followed by ultrasonication for 15 min to ensure uniform nanoparticle dispersion mixtures. These were cast into clean Petri dishes and dried slowly at ~20 °C for 10 days to obtain uniform thin films, as shown in Fig. 1 and Table 1 summarizes the mass of each component used to prepare PEO/PANI nanocomposite samples doped with WO3, Cr2O3, and NiO oxides while the compositions are shown in Table 2.

RESULTS AND DISCUSSION
X-Ray Diffraction
The pure blend polymer (B) exhibits broad and weak diffraction peaks, indicating its predominantly amorphous or semi-crystalline nature. This is typical for polymeric systems such as PEO and PANI, where the degree of crystallinity is limited by chain entanglement and structural disorder. Upon incorporation of metal oxide nanoparticles, the XRD patterns of the nanocomposites (NC1, NC2, and NC3) exhibit a series of sharp and intense diffraction peaks, confirming the presence of crystalline phases corresponding to the added oxides. The emergence of these peaks is indication of the successful embedding of the oxide [22]. The increased intensity and sharpness of the diffraction peaks with the progression from NC1 to NC3 suggest enhanced crystallinity, which can be attributed to the nucleating effect of the nanoparticles, which promotes local ordering of polymer chains. incorporated oxides’ intrinsic crystalline nature dominates the XRD response. The incorporation of nanostructured oxides not only improves the crystallinity of the system but also is expected to enhance its functional properties, including electrical conductivity, thermal stability, and gas sensing performance, as shown in Fig. 2 [23]. In Table 3, calculations showed that the crystalline size of samples loaded with nanocomposites NC1, NC2, and NC3and blend.

FTIR Fourier transform infrared spectroscopy 
In Fig. 3, FTIR spectra of the synthetic polymers with or without the respective NCs after doping nanomaterials in the ternary blended polymers have been shown. Infrared spectrum analysis of polymer (B) (ternary blended) showed noticeable peaks of functional groups 3414,2883,1103,1467,960,842,617 and 470 cm−1. The formation of robust hydrogen bonds due to the existence of numerous hydroxyl and carboxyl groups was indicated by the stretching vibration of –OH bands derived from PEO [22]. Table 4 shows FTIR spectra results. 

Optical properties
Absorption (A)
Absorbance values rise as a function of wavelengths, as seen in Fig. 4. In the infrared range (200-1100 nm) and near to it, the absorbance rises with increasing doping of nanocomposites for all of the produced films. According to the results in Fig. 4. Thin film absorbance declines with increasing wavelengths, which is why PEO/PANI were found to have the lowest absorbance spectrum. The best results were obtained by adding nanocomposite films. PEO/PANI blend shows a primary absorption peak that redshifts, or shifts toward higher wavelengths, in the doped samples. This change implies that oxide incorporation is responsible for the creation of localized electronic states within the bandgap. All the samples show a significant increase in absorption intensity, indicating an intense light–matter interaction and improved optical activity.

Transition (T)
At a wavelength of roughly 200–1100 nm, the blend’s transmittance spectra and those of its nanocomposites doped with WO3, Cr2O3 and NiO, were measured. According to the results, the addition of metal oxide nanoparticles appears to reduce transmittance, suggesting improved light-matter interaction in the composite materials. The highest transmittance, indicating lower optical absorption, was shown by the pure PEO/PANI blend but adding nanocomposites showed the lowest transmittance throughout the spectrum, suggesting increased absorption and/or scattering effects. Oxide doping, which creates localized energy levels inside the bandgap to encourage photon absorption, explains this effect. Since the observed decrease in transmittance suggests enhanced optical activity and possibly a reduced optical bandgap, the doped composite is a viable option for use in optoelectronic devices, and antibacterial surfaces exposed to light.

The Coefficient of Absorption (A)
The optical absorption coefficient is shown Fig. 6 All thin films with values α>104 cm-1 in the visible range have a direct optical energy gap [30]. The optical absorption coefficient (α) was calculated using the relation α=2.303 A/t Where A is the absorbance and t is the film thickness [31]. The film thickness measured using a digital micrometer was approximately 100 ± 10 μm.

Energy gap (Eg) 
 The optical bandgap 𝘌𝘨 was determined using Tauc plots Fig. 7. Doping reduced Eg due to the formation of localized energy levels, facilitating low-energy electronic transitions. The Eg values are presented in Table 5, confirming improved photo-responsiveness in doped samples.

Antibacterial activity
The bacteria were cultured in a Mueller-Hinton (MH) agar (20 mL) with an inoculation loop [32] was used at a temperature of 37°C [33]. A small amount is placed in a Petri dish and holes are made with a diameter of six mm [34]. Several concentrations were taken, and the diameter of the inhibition zone was calculated for each concentration. The antibacterial efficiency of the PEO/PANI and its nanocomposites was evaluated against Escherichia coli (𝗀ram-negative) and Staphylococcus aureus (𝗀ram-positive) [35]. Using the agar diffusion method (Figs. 8 and 9). The inhibition zones are summarized in Table 6. The PEO/PANI blend exhibited moderate antibacterial activity. Upon doping with metal oxides, a significant improvement was observed. The enhanced antibacterial performance can be attributed to several factors: Transition nano oxides that generate reactive oxygen species (ROS) [36], electrostatic interaction between positively charged polyaniline (PANI) and negatively charged bacterial membranes, resulting in the disruption of cell wall [37] and the surface area and porosity of doped samples led to the better interaction of bacteria with the nanoparticles [38].

CONCLUSION
The ternary blend polymers (PEO/PANI) and their nanocomposites (WO₃, Cr₂O₃, NiO) were successfully prepared by casting. FESEM showed rough, irregular, and agglomerated surfaces with granular structures. FTIR confirmed strong crosslinking in both polymers and nanocomposites. UV spectra showed enhanced absorbance with strong peaks from 320 to 400 nm. Antibacterial tests revealed notable inhibition against S. aureus and E. coli. These results indicate that oxide-doped PEO/PANI blends have promising structural, optical, and biological properties for optoelectronic and antimicrobial applications.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.