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Pd2+-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd2+-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl2 was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd2+-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl2. Linear regression algorithm was used for evincing the highly linear behavior of the Pd2+-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd2+-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity (R2 = −0.98834), short response and recovery time (less than 5 s).

Zinc oxide (ZnO) products with the morphologies of balls, nunchakus and belts have been synthesized from aqueous solutions by adjusting the reagent concentration and reaction time. The X-ray diffraction (XRD) peaks of the products were indexed to ZnO materials, but exhibited different relative intensities for the (0 0 2) diffraction peak. Field emission (FE) measurements showed that the turn-on and threshold field for the ZnO nanonunchakus were 3.01 ± 0.005 and 5.47 ± 0.005, 3.71 ± 0.005 and 6.43 ± 0.005 V/μm, respectively, for the ZnO nanobelts, revealing that the products have comparable FE properties with those of the reported ZnO nanowires and carbon nanotubes (CNTs).