Structural, spectroscopic and morphology studies on green synthesized ZnO nanoparticles

Abstract

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.

Dielectric Property, AC Conductivity, and Electric Modulus Studies of Pristine and Green‐Synthesized ZnO Nanoparticles

“…[ 10 ] In contrast, surface modification of the conducting grains by poorly conducting extract molecules, i.e., modification of the grain boundary surfaces will change the dielectric constant of the modified ZnO NPs which depends on the polarizable bonds on the surface manifested through their shape and size. [ 58 ] These may explain why the dielectric constant values at steady temperatures in the low‐frequency range change with the changing particle size as observed in the present case (at 50 Hz and 24 °C, ZnO0: = 1040, D = 17.5 nm; [ 71 ] ZnO10: = 55, D = 20.8 nm [ 71 ] )…”

“…As porosity decreases when effective pressure on the material is increased and as samples were pelletized under high pressure for the dielectric measurements, the amount of void is naturally reduced in the pelletized samples while compared to that present in powdery as‐grown samples. From morphology study on these two samples reported earlier, [ 71 ] no apparent difference in the surface texture could be distinguished which may be due to small difference in the porosity levels in ZnO0 and ZnO10 samples.…”

“…[ 98 ] T. divaricate contains a wide range (at least sixty six types) of phytochemicals including of alkaloids and nonalkaloids such as terpenoids, steroids, flavonoids, phenyl propanoids, phenolic acids, and enzymes. [ 99 ] As significant effect of presence of the extract molecules during the synthesis of ZnO NP on their size, strain and other important physical properties has been confirmed, [ 71 ] obviously these phytochemicals present in TFE act as reducing/stabilizing/capping agents during the green synthesis process of these NPs. Figure illustrates a schematic illustration of the growth procedure of the TFE‐capped ZnO NPs.…”

“…The NPs of ZnO synthesized using varying amounts of aqueous extract of Pinwheel ( Tabernaemontana divaricata ) flower as reducing/capping agent used for the present study are from the same batch of the samples as described earlier. [ 71 ] Four ZnO samples used here are obtained by varying the volume of TFE: 0 mL for ZnO0, 5 mL for ZnO5, 10 mL for ZnO10, and 15 mL for ZnO15. Fine powders of these ZnO materials were isostatically pressed under ≈7 MPa to get circular pellets for dielectric studies.…”

“…Recently, we reported green‐synthesized ZnO NPs (17.5–23.3 nm) [ 71 ] using Tabernaemontana divaricata flower extract (TFE), where the extract efficiently modifies the structure, optical property, and defect levels of the NPs. For these ZnO NPs, with increase in the TFE content, the average size of the particles increased whereas the microstrain decreased.…”