Synthesis of minimal-size ZnO nanoparticles through sol–gel method: Taguchi design optimisation

Abstract

Abstract Zinc oxide (ZnO) has excellent potential to be used in water and wastewater treatment, either as a photocatalyst or in membrane incorporation. In this work, the synthesis of smaller ZnO NPs through a sol–gel approach was enhanced by applying Taguchi design. Recent work on the synthesis of ZnO NPs was optimised to ensure relatively smaller sized particles were obtained. Several parameters of the synthesis process, such as molar ratio of starting materials, molar concentration and calcination temperature, were selected as they have the dominant effects on the particle size of ZnO NPs. Each of these factors was studied at three levels. Various analyses such as ANOVA, model adequacy check and numerical optimisation were performed to validate the predicted optimal model. As a result, the optimum conditions were estimated at a molar ratio of 50:50, an oxalic acid molar concentration of 0.1 M and a calcination temperature of 400 °C. Experiments were performed to validate the model at the selected conditions and the particle size was around 20 ± 2 nm according to XRD analysis, which was in good agreement with the predicted size of 19.8 nm. In addition, the actual size of the synthesised NPs was confirmed by TEM analysis, with the average size of 13 ± 5 nm. Hence, the Taguchi design was an essential tool in the optimisation of ZnO NP synthesis process with fewer experimental runs and relatively low cost approach.