Effects of Al₂O₃contents on the photocatalytic and electrical properties of Al₂O₃–MnO₂nanocomposites prepared by ball milling

Al₂O₃–MnO₂ (Al/MnO) nanocomposites were effectively synthesized in this work using a ball milling approach with different Al₂O₃ contents (0–50 wt%). X-ray diffraction (XRD) examination verified that Al₂O₃ inhibited the growth of MnO₂ grains, demonstrating the formation of nanocrystalline phases with average crystallite sizes ranging from 27.4 to 49.7 nm as the Al₂O₃ content rose. Scanning electron microscopy (SEM) revealed that the Al₂O₃ particles were evenly dispersed throughout the MnO₂. The UV–visible absorption spectra of the Al/MnO nanocomposites showed a notable absorption edge below 400 nm in all samples. The range of the optical band gap (E_g) was 3.27 to 3.56 eV. The sample with the highest Al₂O₃ content, Al/MnO_5, exhibits the most efficient photocatalytic activity towards methylene blue (MB) dye, reaching a maximum degradation of 93 % at 90 min. Due to the high resistivity of Al₂O₃, impedance spectroscopy showed that the complex impedance of the studied samples rose with the addition of Al₂O₃, suggesting an increase in bulk resistance. As the Al₂O₃ content increases, Nyquist plots revealed clear semicircles with growing widths, suggesting a decline in charge mobility where the activation energy for conduction increases from 0.193 eV to 0.234 eV with Al₂O₃ content. According to these results, MnO₂ nanocomposites' photocatalytic electrical and dielectric performance may be greatly influenced by adjusting the Al₂O₃ content, which makes them attractive options for different applications.