Electrochemical Synthesis of SnO2/Al2O3 Nanocomposite: Characterization and Antibacterial Activity Study

behavior from the bulk states such as Al₂O₃, and SnO₂. Because of the importance of these materials in multiple applications such as sensors, optoelectronic devices, solar cells, and thin-film transistors, their properties have been extensively studied [1, 2]. Nanometal oxides and their composites are well-known for their structural and high optical transmittance in the UV-Vis region and high IR reflectance [3-6]. The structural and visual properties are improved by relying on composition and size, as well as on the superficial area of nanoparticles. Therefore, the composite of hard nanostructured materials, such as SnO₂ and Al₂O_3. It may be promising to produce excellent nanocomposites, there are many methods for synthesizing NPs, such as chemical vapor deposition [7], solvothermal methods [8], and microemulsion methods [9]. Sol-gel: this wet chemical technique involves converting precursors into a gel, which is then dried and sintered to form the desired nanomaterial. While relatively simple, it can require long processing times and the use of surfactants or stabilizers [10]. Laser ablation: this technique uses a laser to vaporize a target material, creating nanoparticles in a liquid medium. It can produce high-quality nanoparticles, however, the equipment can be expensive, and scaling up production can be challenging [11]. Hydrothermal methods utilizing high-pressure and high-temperature water for chemical reactions can be effective for synthesizing SnO₂/Al₂O₃ materials, often require complex setups and specific conditions. The process depends on the solubility of reactants in water under elevated temperatures and pressures within a closed vessel. Among the most prominent limitations is the difficulty of ensuring a homogeneous nanodistribution of the two different SnO₂-Al₂O₃ phases within the compound, which leads to aggregation of particles or a decrease in the effectiveness of the reaction; the need for high temperatures or pressures or the use of expensive chemicals or harmful solvents; the slow process of synthesis or the inability to effectively expand industrially; weakness in controlling the fine nanostructure and controlling the size of particles and pores, which reduces the antibacterial or photocatalytic effectiveness [12]. The use of electrochemical deposition technology has emerged as a promising option to overcome these limitations due to the better control it provides over the distribution of the nanophase and the formation of a homogeneous film layer on the substrate or in the liquid; the possibility of performing synthesis at lower temperatures and with relatively simple equipment, which reduces the cost and facilitates expansion; greater speed in the formation and growth of particles with the possibility of adjusting the current density, voltage, time, and solvent to obtain a controlled particle size; and the opportunity To obtain more contact interfaces between the SnO₂-Al₂O₃, which may improve the antibacterial properties through greater surface activation or improved charge transfer. Through the data, the need has been to find a way through which effective and low-cost, as well as developmental and environmental, electrodeposition is a process that enables the formation of solid deposits on the surface of the electrically connected materials. It involves coating the surface of an electrode with a thin layer of the desired material. Electroplating employs an electric current to reduce dissolved metal cations in solution, forming a thin coating on the surface of the electrode. These deposits are produced using electrochemical cells, which consist of two conductors or semiconductors [13]. The electrochemical deposition mechanism involves immersing electrodes of the desired metal in a solution containing strong electrolyte ions, then applying an electric voltage or current that causes the ions to move toward the corresponding electrodes, where they undergo reduction and oxidation reactions. The anode electrode undergoing electrolysis is deposited in the middle of the solution by adjusting parameters such as voltage or current, deposition time, and ion concentration, where the size and shape of the particles can be controlled. However, this technique is rarely used in the preparation of SnO₂/Al₂O₃ nanocomposites. And evaluate its antibacterial effectiveness, which constitutes a research gap that this study seeks to fill by preparing the compound by electrochemical deposition, characterizing it, and evaluating its antibacterial activity. This study focuses on the synthesis of SnO₂/Al₂O₃ nanocomposite using an effective and surfactant-free electrodeposition method. The research aims to take advantage of the priority of electrical expression, such as the exact control of the thickness of the film, uniformity, and formation to produce these nanoparticles. The study will investigate the structural and optical properties of the synthesized nanocomposite, with the aim of exploring their potential applications in electronics, optoelectronics and sensor technologies, and antibacterial properties. The advantages of electrodeposition include its low cost, low energy consumption, environmentally friendly nature, reduced material waste, and the ability to produce thin films at low temperatures. The film formation process and fundamental properties can be controlled by adjusting the applied potential [14]. This study aims to prepare SnO₂/Al₂O₃ nanocomposite by electrophoretic deposition technique, describe its compositional, morphological, and surface properties, and then evaluate its antibacterial effectiveness. To achieve this by preparing nanoparticles or SnO₂-Al₂O₃ layers by controlling electrochemical deposition parameters such as voltage, current, time, and ion concentration, and analyzing the crystalline structure, shape, and phase distribution of the compound using techniques such as UV, FTIR, XRD, FESEM, EDX, and HRTEM; evaluating the antibacterial activity of the prepared compound against selected strains; and studying the effect of the concentration of the prepared nanocomposite.

3.1 X-Ray Diffraction

The XRD patterns of the SnO₂/Al₂O₃ nanocomposites are shown in Figure 1. The miller indices (hkl) of the diffraction peaks of SnO₂/Al₂O₃ and nanocomposites were matched with JCPDS cards No. 71-1123 and No. 41-1445. The crystallite size was calculated using the Scherer formula [15, 16]. where D is the average crystallite size, λ is the used X-ray wavelength and k = 0.94 is a constant, θ is the diffraction angle (in degrees), and β is the full width at half maximum (FWHM, in radians) of the observed diffraction peak [17]. The XRD pattern of SnO₂/Al₂O₃ in Figure 1 shows low peaks at 2θ values of 25.12°, 43.80°, and 57.60°, which correspond Al₂O₃ phase and confirm the presence of Al₂O₃ in the composite. Three intense diffraction peaks at 27.38°, 39.57°, and 49.24° can be attributed to the (110), (200), and (211) planes of SnO₂, respectively. Compared with pure SnO₂, the peaks near 27.38° in the SnO₂/Al₂O₃ composites appear broader, which may be due to the overlap of the SnO₂ (110) and Al₂O₃ (012) peaks [18, 19]. The tabulated X-ray data include: 2-Theta (diffraction angle), d (nm) (interplanar spacing), BG (background), height (peak intensity), I% (relative intensity), area (integrated peak intensity), I%₂ (another relative intensity), full width at half maximum (FWHM), and crystal size (nm). The crystal size, calculated using the Scherrer equation, was approximately 11.13 nm as shown in Table 2.

Figure 1. XRD Pattern of SnO₂/Al₂O₃ nanocomposites (a) Miller Indices (hkl), (b) Two-theta (2θ) represent angles related to the diffraction of X-rays by a crystalline sample

Table 2. The data obtained from X-ray diffraction (XRD)

3.2 UV-Vis spectrum

The UV-Vis spectra were analyzed to investigate the optical properties. The compounds and their absorbance changes are shown in Figure 2(a). The SnO₂/Al₂O₃ nanocomposites exhibit strong absorption at 200 nm, with the absorption decreasing slightly as the wavelength increases. In the UV-visible range, no distinct peak was observed in the long wavelength region. Moreover, the maximum absorption was detected at about 235 nm, after which the absorbance gradually decreased [20]. The UV−Vis diffuse reflectance spectra display the results for the SnO₂/Al₂O₃ samples in the range of 200-700 nm. The results showed that the absorption edge of the SnO₂/Al₂O₃ nanocomposite occurred at 310 nm, which is in good agreement with the value (298 nm) reported by Mishra et al. [5] for SnO₂-Al₂O₃ composites prepared via the sol−gel method. From the reflection spectra, the bandgap energy (Eg), was determined using a Tauc plot. In this method, (αhν)^1/2(eV. cm^–1)^1/2 is plotted against hν, where α is the absorption co-efficient, h is Planck's constant, ν is the photon frequency, and γ depends on the type of electronic transition (e.g., 1/2 for indirect transition, 2 for direct transition). Extrapolating the linear portion of the curve to the x-axis (energy axis) gives the band gap energy, as shown in the inset of Figure 2(b). The bandgap values are found to be 3.65 eV for the SnO₂/Al₂O₃ nanocomposite [21].

Figure 2. (a) UV–Vis Spectra, (b) the plot of (αhν)^1/2 vs. photon energy (hν) for SnO₂/Al₂O₃ nanocomposites

Figure 3. FTIR spectrum of the SnO₂/Al₂O₃ nanocomposites

3.3 FTIR analysis of 1:1 SnO₂/Al₂O₃ nanocomposites

For important information about functional groups in SnO₂/Al₂O₃, FTIR spectra are recorded in transmission mode. FTIR spectra are shown in Figure 3. The broad peak at around 3200 cm^-1 can be attributed to the O-H. It is noted that the lowest is in SnO₂/Al₂O₃. Moreover, the bending vibrations of the O-H stretching vibration. It is noted that this peak is less intense in SNO₂/Al₂O₃. Moreover, the bending vibrations of the O-H group are responsible for the peaks at about 1630 cm^-1 in SnO₂/Al₂O₃ nanocomposites [22]. The peak at about 500 cm^-1 in SnO₂/Al₂O₃ nanocomposites can be assigned to Sn-O or O-Sn-O vibrations [23]. The intensity of this peak decreases significantly for SnO₂/Al₂O₃ nanocomposites, as shown in Figure 3. This decrease in metal-oxygen vibrations can be attributed to Sn or O vacancies in SnO₂/Al₂O₃ powder. Similarly, the peaks at about 650 cm^-1, 1100 cm^-1, and 1450 cm^-1 in SnO₂/Al₂O₃ nanocomposites are mostly due to Al-O and O-Al-O vibrations as in Table 3 [24]. The disappearance or reduction of Al or O atom can lead to a decrease in the strength of these peaks. The absence of Sn, Al or O may result in weaker metal-oxygen stretching in the SnO₂/Al₂O₃ bonding. The broadening of these peaks in the SnO₂/Al₂O₃ powder suggests the presence of multiple weak vibrations instead of one strong vibration [22, 23]. From the FTIR spectrum, it is evident that the SnO₂/Al₂O₃ powder contains a significant number of Sn, Al or O vacancies. However, these vacancies are relatively few compared to what might be expected, likely due to the absence of severe metal-oxygen loss during high-temperature calcination. Since the powder was dried in a hot air oven at 200℃ in an oxygen-adequate environment, the possibility of O vacancies is minimized. Furthermore, in SnO₂/Al₂O₃ powder, the reduction of peak intensities related to metal-oxygen vibrations supports the presence of such lattice defects.

Table 3. FTIR vibration bands and their corresponding bond assignments for the SnO₂/Al₂O₃ nanocomposite

3.4 FESEM, RHTEM, and EDX

Figure 4 shows the field emission scanning electron microscopy (FESEM) image of SnO₂/Al₂O₃ nanocomposite particles in various size ranges up to 500 nm. The microscopic image reveals that the nanocomposites tend to aggregate on the surface, confirming the presence of pores, which can be useful in sensing applications. The particle size is approximately 21-37 nm, which is larger than that calculated from XRD analysis [31]. Figure 5 shows high-resolution transmission electron microscopy (HR-TEM) images of the SnO₂/Al₂O₃ nanocomposite. HRTIM analysis is among the most effective methods to investigate nanoparticle size. The practical size in this work was found to be around 20 nm. The images also show that the grain size distribution is not uniform. During sample preparation, agglomeration of particles may occur. Energy dispersive X-ray (EDX) spectroscopy of the SnO₂/Al₂O₃ nanocomposite confirms the presence of its constituent elements. Energy‑Dispersive For the 1:1 sample (Experiment 5), the mass composition was O = 43.01%, Al = 28.67% and Sn = 28.32%. Also, maps with a resolution of 768 × 512 were obtained to ensure racial distribution. These results confirm the expected chemical structure of the SnO₂/Al₂O₃ compound, and show good agreement with X-Ray Diffraction (XRD) data, as in Figure 6 [32, 33].

Figure 4. FESEM micrograph of SnO₂/Al₂O₃ nanocomposite

Figure 5. HRTEM micrograph of SnO₂/Al₂O₃ nanocomposite

The average particle size of SnO₂/Al₂O₃ nanoparticles, as determined by XRD, FE-SEM, and HRTEM analyses, showed a good agreement through the three characterization techniques, with minor differences attributed to the related differences in the principles of measurement. The XRD-derived size, calculated using the Scherrer equation, reflects the average size of crystals, and that may be a little smaller than the size of the particles observed in the FESEM and HRTEM images due to the potential assembly and the polycrystal nature of the particle. FESEM analysis presented a direct visualization of particle morphology. This reveals a structure with agglomeration and uniform particles with a small mass. HRTEM has provided high-resolution images, allowing an accurate measurement of individual molecules and confirming the crystallinity of the lattice corresponding to SnO₂ and Al₂O₃, when compared to the values mentioned in the literature shown in the Table 4, the sizes of the particles obtained within the expected range of XRD were within the expected range of 11.13 nm, in line with pre-reported studies [5, 34-37]. Slight deviations from literature data may result from differences in the terms of synthesis, base materials, calcination temperatures, and SnO₂ to Al₂O₃ ratios. This indicates that the approved synthesis method produces effectively from nanoparticles of similar particles, or smaller than those that have been previously reported, which can enhance the surface area and catalytic activity.

Figure 6. Energy dispersive X-ray (EDX) spectroscopic analysis of SnO₂/Al₂O₃ nanocomposite showing Al=28.67 atomic%, Sn =28.32 atomic%, O = 43.01 atomic%

Table 4. Comparing the average particle size of the SnO₂/Al₂O₃ nanoparticles calculated by XRD, FESEM, and HR-TEM techniques with reported literature values