Induced Hydrothermal Synthesis Of WO₃ And Investigation Of Their Applications

Tungsten trioxide (WO₃) is a kind of semiconductor with great importance. It has attracted broad attention due to its wide-ranging applications in electrochromic devices, photocatalysts, gas sensors et al. Researches have demonstrated that the property of materials is profoundly dependent on their morphologies. Properties can be endued or enhanced when nanostructures are introduced into the materials. Therefore, it is valuable synthesizing nanostructured WO₃ and investigating their properties. The main contents of our work can be summarized as follows:1. WO₃ with numerous morphologies like nanowire/rod, flake, network, pompon and square were synthesized by an induced hydrothermal method. Experiment showed that the effect of diverse salt on the morphology of the product was gigantic different. The as-synthesized products were characterized by XRD and SEM to analyze their phase and structure. According to the experiment results, a possible inducing mechanism concerning electrostatic adsorption was proposed. In addition, novel WO₃ network squares were synthesized by controlling pH value of the reaction system with the assistance of Na₂SO₄. Besides the ionic inducement, analysis indicated that the etching effect of HNO3 also contributed a lot in the growth process of the network squares.2. The work was then focused on the as-synthesized tungsten trioxide network squares, aiming to study its photosensitive and humidity-sensing properties. A micro-device was fabricated based on a single piece of WO₃ network square. The nonlinear I-V curve implied the existence of Schottky barriers. The I-V characteristic of the device was greatly changed when the device was placed under the stimulated sunlight. Further investigation revealed ultrafast photoelectric response, high repeatability and excellent stability of the device. Humidity-sensing measurement showed when the relative humidity changed periodically between 20% and 60%, the sensor responded much faster (²s) than that of the previous reports. Analysis indicated that the protonic conductivity played a leading role in the sensing process of the humidity sensor.