Comparative Studies of the Synthesis and Physical Characterization of ZnO Nanoparticles Using Nerium oleander Flower Extract and Chemical Methods

Abstract

This contribution reports on the comparative synthesis and the main physical properties of ZnO NPs using green and chemical methods. A green approach was applied for synthesis of zinc oxide NPs for the first time using Nerium oleander flower extract as capping and reducing agent (ZnO–G). The chemical method was applied using sodium borohydride as reducing agent (ZnO–C). The green chemistry plant-based ZnO NPs are safer, energy efficient, eco-friendly, and less toxic than chemically synthesized counterparts. The characterization of ZnO–G and ZnO–C NPs was ascertained through Fourier Transform-Infrared (FT-IR), UV–Vis spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), Thermal gravimetric and differential thermal analysis (TG–DTA). From the FT-IR spectra of ZnO NPs, the characteristic absorption peak of Zn–O bond was observed at 478 and 466 cm−1 for ZnO–G and ZnO–C respectively. The shifted of Zn–O band due to the difference of bio-functional groups of N. oleander extract. Formation of nanoparticles was monitored using UV–Vis spectroscopy and a characteristic absorption peak for ZnO–G and ZnO–C was observed at 271 and 323 nm respectively. The XRD result for the ZnO shows the tendency of the three most intense diffraction peaks with crystalline structure of ZnO–C more than ZnO–G. The average crystallite size of ZnO–G and ZnO–C at scattering angle (2θ) 23.96 and 33.10 was 37.10 and 27.03 nm respectively. The EDX gave strong signals for zinc and oxygen indicating the occurrence of the nanoparticles in their oxide form rather than the pure zinc form. The SEM image shows the surface morphology of ZnO–G and ZnO–C displays a drastic modification of the surface morphology with the change of the synthesis method. Kinetic analyses of the ZnO thermal decomposition was calculated using Broido equation. This new eco-friendly synthesis of ZnONPs is a convenient technique for large scale commercial manufacture of ZnO NPs.