New approach in effective and reproducible green synthesis of pure ZnO nanoparticles using lemon juice with less solvent and without strong base chemical precursor

In this research ZnO nanoparticles obtained through green colloidal route using lemon juice as solvent and precursor while the Zn precursor concentration was varied from 0.1, 0.2, 0.3 and 0.4 M respectively. The particles with and without annealing treatment, were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS), photoluminescence (PL) and Ultraviolet–Visible (UV–Vis) techniques. From the unannealed samples, the wurtzite ZnO structure was identified, a crystallite average size of ⁓32–34 nm and the dislocation density and micro strain value were calculated noticing a decrease from L1 to L4, albeit rectangle like microparticles and the presence of several byproducts such as carbon, potassium, Phosphorous and calcium were identified from EDS. Furthermore, the PL showed the Zni, V Zn and Vo intrinsic defects presence, at last the optical band gap (Eg) was calculated which goes from 3.7 to 3.42 eV. In contrast from the annealed samples at 500 °C, show a clear ZnO wurtzite pattern, an average crystallite size of ⁓ 26–32 nm, and flower like particles, with a small amount concentration of ions like Na, C, Ca, and P. Finally, from the PL spectra, was identified the presence of intrinsic defects transitions such as V Zn , Zni, Vo and Oi respectively with an Eg value from 3.63 to 3.47 eV. These results highlight the green process as highly effective on ZnO successful synthesis, with well characteristics without chemical strong base use, reducing the byproducts content making this route greener than those reported in the literature.