Preparation of ZnO hollow spheres with different surface roughness and their enhanced gas sensing property

ZnO hollow spherical samples with different surface roughness have been synthesized using a one-step, template-free hydrothermal method. Materials characterization has included XRD, SEM, TEM, XPS and XRF. It was found that the surface roughness of the ZnO hollow spheres can be tuned from rough to smooth via regulating trisodium citrate concentration during the synthesis. When 2 mM of trisodium citrate was used, ZnO hollow spheres showed the roughest surface morphology. With increasing the citrate concentration from 2 to 6 mM, the resultant ZnO hollow sphere morphology became increasingly denser and smoother. When the citrate concentration was further increased to 8 mM, however, the morphology became rough again. Sensors fabricated using the ZnO hollow spheres were characterized by the response to alcohol vapor. The roughest sample gave the best sensor response toward 10–500 ppm alcohol vapor, about 11–16 times higher than the reference one prepared without citrate. This corresponds to a remarkable sensor response as high as 402 and an extrapolated detection limit 0.5 ppm. The reasons behind the improvements in sensor performance are discussed.