Ultrasound-assisted process intensification for the synthesis of nitrogen-doped ZnO photocatalyst and its application to malachite green degradation

Abstract

This research study illustrates that synthesizing nitrogen-doped ZnO (N–ZnO) nanoparticles using ultrasound is a viable alternative method for improving photocatalytic performance. Acoustic cavitation during ultrasonication leads to improved incorporation of nitrogen atoms, a decrease in crystallite size, and alteration of the electronic structure of the N–ZnO nanoparticles, which ultimately improves their catalytic properties. The N–ZnO nanoparticles synthesized using this method have been extensively characterized using XRD, FESEM, EDS, XPS, and UV-visible spectroscopy. XRD analysis confirmed the hexagonal wurtzite structure of ZnO with successful nitrogen incorporation, which induced lattice distortions and reduced crystallite size. FESEM analysis revealed irregular and non-uniform morphology of the N–ZnO crystallites. Moreover, the successful and uniform incorporation of nitrogen ions into the crystal lattice of the ZnO particles is confirmed by both EDS and XPS analysis. Additionally, UV-Visible spectroscopy indicated a significant red shift in the absorption edge and a reduction in the bandgap from 3.21 eV (ZnO) to 2.59 eV (N-ZnO), enhancing visible-light absorption. Furthermore, the photocatalytic activity of N-ZnO has been evaluated for malachite green (MG) dye degradation under various operating conditions. Among the samples, 3% N-ZnO exhibited a maximum degradation efficiency of 96.43% at a photocatalyst loading of 0.15 g/100 mL of dye solution, an initial dye concentration of 20 ppm, and pH 12. Kinetic analysis demonstrated that MG degradation followed pseudo-first-order reaction kinetics. Thus, the results of this study support the use of ultrasound-assisted synthesis as an effective method for the preparation of N-ZnO nanoparticles.