Sol–gel synthesized <scp>MgO</scp> nanoparticles: Versatile applications in photocatalytic dye degradation, heavy metal removal, <scp> CO ₂ </scp> conversion, hydrogen production, and photoelectrochemical performance

Abstract This study investigates the synthesis and applications of magnesium oxide nanoparticles (MgO NPs) using the sol–gel method. X‐ray diffraction (XRD) confirmed a cubic crystalline structure with an average crystallite size of 22.53 ± 3.42 nm. Scanning electron microscopy (SEM) showed spherical nanoparticles with sizes ranging from 40 to 60 nm, with a mean diameter of 56.52 nm. Optical analysis showed a direct bandgap of 3.12 eV and a UV absorption peak at 308 nm. Fluorescence spectra revealed emission peaks at 408, 445, and 478 nm, attributed to oxygen vacancies. The MgO NPs demonstrated excellent photocatalytic activity, degrading 99.82% of Malachite Green dye in 120 min under sunlight (k = 0.02763 min −1 ). They also removed 98.75% of cadmium ions in 120 min (k = 0.01695 min −1 ) and exhibited stable adsorption for copper and lead over five cycles. In CO 2 conversion, the NPs produced 63 μmol/g methane and 58 μmol/g hydrogen in 4 h, with a hydrogen production rate of 1034 μmol·g −1 ·h −1 . Photoelectrochemical tests showed stable photocurrent response. These findings highlight MgO NPs' potential for wastewater treatment, heavy metal removal, CO 2 conversion, and hydrogen production, demonstrating their high effectiveness for environmental and energy applications.