Green synthesis of zinc oxide nanoparticles using Terminalia arjuna bark extract: structural, optical and photocatalytic study

Zinc oxide (ZnO) nanoparticles have been successfully synthesized by using Terminalia arjuna bark extract via a green route. Structural analysis using X-ray diffraction confirmed the prepared samples are crystalline having hexagonal wurtzite structure with space group P63mc and average crystallite size is found to be 8.93 nm. Rietveld refinement of the data was carried out using Material Analysis Using Diffraction (MAUD) software and reliability parameters of the refinement have been obtained. Optical properties of the sample investigated by ultraviolet - visible diffuse reflectance spectroscopy reveal an absorption peak to lie at 348 nm and the direct optical band gap energy using Kubelka-Munk function is found to be 3.20 eV. Morphological investigation using scanning electron microscopy revealed that ZnO nanoparticles are nearly spherical and agglomerated. Energy-dispersive X-ray spectrometry analysis showed the presence of Zn and O only. Transmission electron microscopy imaging confirmed the predominant hexagonal structure of the prepared nanoparticles having average particles size of 9.66 nm, which is in agreement with the X-ray diffraction result. Fourier transform infrared spectroscopy was used to identify the functional groups and different vibrational modes present in the sample. The photocatalytic activity of the prepared ZnO nanoparticles was studied using methylene blue (MB) dye under a single wavelength UV light source (lambda = 254 nm). The degree of degradation of MB solution was about 56 % within 120 min of illumination to UV light and the degradation reaction follows first order kinetics with rate constant 0.00434 min(-1).