Precursor Dependent Morphologies of Microwave Assisted ZnO Nanostructures and their VOC Detection Properties

Abstract In the present work, Zinc Oxide (ZnO) nanostructures have been prepared by microwave assisted synthesis method. ZnO powders from four different precursor solutions were synthesized followed by calcination at 600°C to form polycrystalline ZnO nanostructures. The wurzite crystal structure of ZnO powders were determined by X-ray diffraction (XRD). Surface morphology of the prepared four ZnO powders were studied using Field Emission Scanning Electron Microscopy (FESEM) and showed four different types of surface alignments. Gas sensing characteristics for four Volatile Organic Compounds (VOCs), namely, acetone, formaldehyde, isopropanol and toluene in their vapor forms, were studied to investigate the response behavior of the prepared ZnO powders. ZnO synthesized from the zinc nitrate precursor showed the highest sensitivity compared with the rest three powders synthesized from acetate, chloride and sulphate precursors of zinc. The sensitivity of the ZnO (nitrate) sensor was found to exhibit the highest response [%S = 50.54% & 66.21%] for 10 and 20 ppm formaldehyde, respectively at room temperature, in presence of the other three VOCs and thus, it can be inferred that the synthesized ZnO is selective to formaldehyde. The mechanism of sensing has been explained according to the ionosorption model. The influence of the precursor on the morphology of derived ZnO samples and the effect of the morphologies on the gas sensing activities has been discussed.