Microwave-Assisted Synthesis and Properties of Black ZnO

In the present work, zinc oxide (ZnO) was synthesized using two routes: microwave-assisted (480 W) with varying synthesis times, and conventional muffle-furnace heating (600 °C for 2 h). Microwave irradiation produced dark-colored samples, herein referred to as black ZnO. X-ray diffraction (XRD) patterns indicated a hexagonal crystal structure consistent with ICSD 26170. Diffuse reflectance UV Vis spectroscopy (DRS) revealed band gap energies ranging from 2.22 to 3.24 eV. Zeta potential measurements showed a positive value (+12.5 mV) for the conventionally produced material, suggesting low colloidal stability and a greater tendency to aggregate; conversely, microwave-synthesized samples exhibited negative values (–27.4 to –38.0 mV), indicative of good colloidal stability. Scanning electron microscopy (SEM) revealed a morphology composed of ZnO micro-rodlets. The results indicate that microwave-assisted synthesis favors the formation of Black ZnO, with future work involving the development of heterojunctions with persistent luminescent materials for photocatalytic applications.