Structural, spectroscopic and morphology studies on green synthesized ZnO nanoparticles

Zinc oxide nanoparticles (ZnO NPs) were synthesised using Tabernaemontana divaricata flower extract (TFE) in different weight percentages by facile, eco-friendly and cost-effective green synthesis method. Formation and structure of the ZnO NPs were studied by powder XRD, FT-IR, Raman and TEM studies. The crystals formed are of hexagonal wurtzite structure with biological functional groups attached. Average crystallite size of the ZnO NPs (17.5-23.3 nm) was obtained from the analysis of powder XRD data which increased with increase of TFE amount while the estimated values of dislocation density and micro-strain exhibited an opposite behaviour. The optical (direct and indirect) energy band gap values estimated using UV-vis DRS spectral data decreased with increasing amount of TFE. The photoluminescence spectra for the ZnO NPs exhibited multiple peaks spread over the visible region with one peak in the NIR region indicating the existence of various defect levels of Zn and O. Position of these defect levels within the band gap was assigned which is significantly modulated by TFE. TFE amount-dependent peak shift and/or peak broadening were observed in the Raman spectra of the ZnO NPs which were correlated with the growing disorder in the crystals induced by the extract molecules. FESEM study showed the agglomerated NPs with quasi-spherical morphology. Particle size of the ZnO NPs was estimated from FESEM images. EDX study indicated that increased presence of TFE in ZnO decreased the oxygen content in the synthesised material. HRTEM study revealed the agglomeration of nanoparticles with single crystalline nature. Present study convincingly established that flower extract used for the green synthesis efficiently modified the structure and optical property, defect levels and morphology of the potentially useful ZnO nanoparticles.