Biosynthesis of ZnO photocatalyst and its application in photo catalytic degradation of methylene blue dyestuff

Abstract

In this research, biosynthesis of zinc oxide nanoparticles (ZnO-NPs) was performed using aqueous extract of the leaves of Cynara scolymus L (CsL, artichoke) plant. The synthesized CsLZnO-NPs were characterized by Ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD) and Energy dispersive x-ray spectroscopy (EDS). Production of CsLZnO-NPs was approved by surface plasmon resonance (SPR) peak localized at 366 nm and the band seen at 417 cm−1 (Zn-O stretching) in the FTIR spectrum. EDS spectrum also confirmed formation of CsLZnO-NPs. The percentage composition by mass of the synthesized CsLZnO-NPs is close to the theoretical mass percentage composition (Zn: 80%, O: 20%) of the ZnO molecule. TEM analysis showed that the particles are of sub-micron size and have no sharp boundaries or morphologies. CsLZnO-NPs with wurtzite structure were characterized by XRD analysis. The average size of CsLZnO-NPs was measured to be 332.5 nm. The band gap energy value of CsLZnO-NPs was found to be 2.9 eV which is lower than the band gap of bulk ZnO (3.37 eV). Produced CsLZnO-NPs were utilized as a photocatalyst for decolorization of Methylene Blue (MB) dyestuff. Under UV-light, 80% decolorization efficiency was achieved in 240 min. In the present study, correct results were obtained by taking first derivative spectra in the presence of turbidity in centrifuged and filtered samples or in samples with high background absorbance in the spectrophotometric measurements of photocatalysis reactions. Decolorization of MB dyestuff follows the pseudo-first order kinetic.