Papers by Author: Jun Boo Yu

Abstract: A novel and simple approach has been developed for a large-scale synthesis of ZnO nanorods using ultrasound radiation. Double-pod-like ZnO nanorods were directly grown from the starting precursors of zinc nitrate hydrate [Zn(NO3)26H2O] and hexamethylene tetramine (HMT) in deionized water without any templates or seeds. The obtained double-pod-like product had a diameter ranging from 80 to 150 nm and length ranging from 1 to 5 um. Scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that these products are of high purity, hexagonal and of single-crystalline structure. The ZnO nanorods synthesized were utilized for gas sensing application. Alumina plate consists of Pt interdigitated electrode was used as sensor substrate. The as-prepared products were transferred to the surface of substrate by screen printing method to fabricate the gas sensor. The sensing properties of the sensor were investigated toward methyl mercaptan (CH3SH). The sensor shows good and fast response towards methyl mercaptan at a fixed operating temperature. The high sensitivity may be ascribed to the high surface area and aspect ration of the double-pod-like nanomaterial.

Abstract: The influence of oxidant on surface morphology and sensing property of polypyrrole (PPy) – poly (vinyl alcohol) (PVA) double layer sensors was investigated. PPy–PVA double layer sensors were prepared by vapor polymerization using FeCl3 as oxidizing agent and PVA as adhesive agent. The surface of PPy–PVA layer was observed on a scanning electron microscope (SEM). The surface morphology of sensor showed homogeneous layer and thickness of 1µm. And the sensing properties were investigated using a flow measuring system. The maximum sensitivity to methanol 1000ppm was proportional to increasing 12wt % FeCl3 concentration at 25°C. The response time was not affected by FeCl3 concentration, but the recovery time increased according to the amount of FeCl3. The best amount of FeCl3 was observed at 12wt%.

Abstract: The polyaniline (PAn) polymer was synthesized by a chemical method using aniline (AN) as monomer, ammonium persulfate (APS) as initiator, and dodecylbenzene sulfonic acid (DBSA) as dopant at 0ı. Conducting polymer films were prepared on the alumina substrate with an interdigitated electrode by using the dip coating method. These films were soaked in methanol solvent for 1h at room temperature to remove excessive DBSA and then were heated at 70ı for 4h in N2. The detecting materials having a liquid phase at one atmospheric were precisely controlled by the system having a mass flow controller (MFC), temperature controller and measuring chamber. The sensitivity was estimated by heating from 70ı. The sensitivity observed in PAn sensor was lower than PAn-DBSA sensor at 1000 ppm methanol vapors under N2. because the additional thermal doping effect was resulted from increasing molecular motion in polymer chain to 70ı but DBSA used as dopant was decomposed by heating over 120ı. It caused the melting point of DBSA to be lower than 120ı. So the thermal properties of PAn and PAn-DBSA were investigated by DSC (differential scanning calorimetry). The DSC was scanned with a heating rate of 10ı/min. The PAn sample did not show the melting peak but PAn-DBSA sample showed the melting peak at 190ı. From this result, the new crystalline-region was evaluated in PAn-DBSA and increased of crystallinity of PAn polymer. And FE-SEM studies showed that the presence of the dopant strongly influenced the morphology of the polymer.