Sol–gel synthesized MgO nanoparticles: Versatile applications in photocatalytic dye degradation, heavy metal removal, CO2 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 CO₂ 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, CO₂ conversion, and hydrogen production, demonstrating their high effectiveness for environmental and energy applications.