Structure Directing Amine Mediated Hydrothermal Synthesis of Mn Doped ZnO Microrods for Hazardous Methylene Blue Dye Degradation

Abstract

The controlled synthesis of Mn-doped ZnO nanospheres using an amine-mediated hydrothermal method was systematically investigated. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure and phase purity of the synthesized samples, with crystallite sizes reducing significantly from 58 nm to 18 nm upon Mn doping, as calculated using the Williamson-Hall (W-H) plot method. Secondary XRD peaks indicated the successful incorporation of Mn ions on the ZnO surface. Fourier transform infrared (FTIR) spectroscopy further confirmed the presence of ZnO vibrations along with Mn-O bonding. UV-Vis diffuse reflectance spectroscopy (UV-DRS) analysis revealed a reduction in bandgap from 3.07 eV (pure ZnO) to 2.62 eV (Mn-doped ZnO), enhancing visible-light absorption. High-resolution scanning electron microscopy (HRSEM) and high-resolution transmission electron microscopy (HRTEM) confirmed the transformation of nanospheres into a microrod morphology and provided insights into particle size distribution, showing an average size of 32 nm for pure ZnO and 16.6 nm for Mn (5%)-doped ZnO. BET surface area analysis revealed a significant increase to 90 m2/g, which enhances light-harvesting efficiency and provides more active sites for catalytic applications. The photocatalytic performance was evaluated through methylene blue dye degradation under visible light, achieving an impressive 90.8% degradation efficiency. This study highlights the potential of Mn-doped ZnO nanospheres as an efficient photocatalyst for environmental remediation.