Effect of pH on the morphology and gas sensing properties of ZnO nanostructures

Morphology dependent gas sensing behaviour of zinc oxide has been reported in this paper. Nanostructures of zinc oxide have been synthesized by following a precipitation route at various pH values of the precursor solution. Structural and morphological analyses were carried out by using XRD and FESEM techniques. The XRD pattern confirmed wurtzite hexagonal structure of ZnO. The FESEM study revealed that ZnO synthesized at pH 8 developed nanorod like structure, rods got fused together when synthesized at pH 9 and 10, whereas synthesis at pH 11 resulted in transformation of rods into nanoparticles. The thick films of synthesized samples were deposited on alumina substrate and their sensing response to methanol, ethanol and propanol was investigated at different operating temperatures. It was observed that all the sensors exhibited optimum sensing response at 400 °C. It has also been observed that sample prepared at pH 11, constituting nanoparticles, exhibited high sensing response than an assembly of nanorods prepared at pH 8–10. Sensing response of all the samples tested was significantly higher towards propanol vapour than towards that of methanol and ethanol.