Humidity sensing properties of Pd-doped ZnO nanotetrapods

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).