Solar-Driven Photodegradation of Methylene Blue Dye Using Al-Doped ZnO Nanoparticles

ZnO semiconductor-based photocatalysts are mainly studied for the elimination of toxic textile dyes. Metal-doped ZnO displays better performance for this purpose. Herein, Al-doped ZnO (Al–ZnO) was prepared using the mechanochemical calcination method with varying aluminum concentrations for the degradation of the persistent methylene blue (MB) dye. Various characterization techniques, including XRD, FTIR, FESEM, TEM, UV-DRS, and XPS, revealed the improved properties of 3% Al–ZnO in degrading the MB dye. It exhibits 96.56% degradation of 25 mg/L MB dye under 60 min of natural sunlight irradiation with a catalyst dose of 0.5 g/L at a natural pH of 6.4. A smaller particle size, a lower band gap energy of 3.264 eV, and the presence of oxygen vacancies and defect states all facilitate photocatalytic degradation. Radical scavenger experiments using ascorbic acid (for •O2−), 2-propanol (for •OH), and diammonium oxalate (for h+) confirmed the crucial role of superoxide (•O2−) and hydroxyl (•OH) radicals in the degradation mechanism. The achievement of 82.80% MB degradation efficiency at the 4th cycle validates the notable stability and excellent reusability of Al–ZnO.