Oxygen — Catalysed and heat treatment effect on ZnO nanoparticles properties synthesized via precipitation techniques

In this study, we diffuse O₂ gas in parallel to the solution to serve as catalyst and promote the oxidation of ZnO nuclei. We also deployed DEA as capping agent and introduce fast pyrolysis treatment at 550, 700 and 850°C to produce uniformly spherical particles and improve the crystallinity of ZnO. The effect of heat treatment on ZnO morphology, structural and optical properties was characterized using Scanning electron microscope (SEM), X-ray powder diffractometer (XRD) and room temperature Photoluminescence (PL) spectroscopy. The SEM results demonstrate relatively small and dense particles for all the samples prepared with excess of O₂ compared to without O₂ which display less dense and uneven surface. Based on PL results, samples prepared with excess of O₂ shows better crystallinity and approach pure ZnO as implied by peak shifting to higher energy whereas without excess of O₂, the peak were shifted to lower energy indicating poor crystallinity and reducing of energy band gap with respect to increment of calcination temperatures. The ZnO samples prepared with excess of O₂ calcined at 550°C exhibit single violet emission with energy 2.90 eV while without O₂ displaying violet and green emission with energy at 3.02 eV and 2.27 eV respectively. The average crystallite size calculated using Scherer equation for sample prepared with excess of O₂ calcined at 550°C is about 21 nm, whereas without excess of O₂, is approximately 31 nm in size. Likewise, crystallite size calculated via effective mass approximation is within the range as calculated by Scherrer equation.