Dang Thi Thanh Le

A comparative study on the NH3 gas-sensing properties of ZnO, SnO2, and WO3 nanowires

In this work, a large quantity of ZnO, SnO2 and WO3 nanowires (NWs) was successfully synthesised by simple and efficient methods. Their morphology and microstructure were characterised by FE-SEM, TEM, XRD, PL, and Raman. The NH3 gas-sensing properties of these NWs were investigated and compared. It was found that the responses and response-recovery time of SnO2 and WO3 NWs sensors to NH3 gas are relatively comparable, and they have a better NH3 gas-sensing performance than that of ZnO NWs sensor. In addition, the SnO2 NWs sensor has the lowest operating temperature.

C2H5OH and NO2 sensing properties of ZnO nanostructures: correlation between crystal size, defect level and sensing performance

ZnO nanostructures can be synthesized using different techniques for gas sensor applications, but different synthesis methods produce different morphologies, specific surface areas, crystal sizes, and physical properties, which consequently influence the gas-sensing properties of materials. Many parameters such as morphology, specific surface areas, crystal sizes, and defect level can influence the gas-sensing properties of ZnO nanostructures. However, it is not clear which parameter dominates the gas-sensing performance. This study clarified the correlation between crystal size, defect level, and gas-sensing properties of ZnO nanostructures prepared from hydrozincite counterparts by means of field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and photoluminescence spectra. Results showed that the average crystal size of the ZnO nanoparticles increased with thermal decomposition temperatures from 500 °C to 700 °C. However, the sample treated at 600 °C, which has the lowest visible-to-ultraviolet band intensity ratio showed the highest response to ethanol and NO2. These results suggested that defect level but not size is the main parameter dominating the sensor performance. The gas sensing mechanism was also elucidated on the basis of the correlation among decomposition temperatures, crystal size, defect level, and gas sensitivity.

A comparative study on the electrochemical properties of nanoporous nickel oxide nanowires and nanosheets prepared by a hydrothermal method

Metal oxide nanostructures have been extensively used in electrochemical devices due to their advantages, including high active surface area and chemical stability. However, the electrochemical properties of metal oxides are strongly dependent on their structural characteristics. We performed a comparative study on the electrochemical performance of nanoporous nickel oxide (NiO) nanosheets and nanowires. The advanced nanoporous NiO nanomaterials were synthesized by a facile hydrothermal method followed by thermal calcination. The synthesized nanomaterials, as characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and nitrogen adsorption/desorption isotherms, demonstrated the nanoporosity and high crystallinity of the NiO nanosheets and nanowires. Cyclic voltammetry measurement was performed using a three-electrode system to evaluate the electrochemical properties of the synthesized materials. Results showed that the nanoporous NiO nanosheets possessed a higher current density than that of the nanowires by approximately ten times. Moreover, the nanoporous NiO nanosheets showed exceptionally high stability of almost 100%, after three cycles in strong alkaline environments, thereby suggesting possible application in electrochemical devices.

Fabrication of Electrochemical Electrodes Based on Platinum and \(\text{ZnO}\) Nanofibers for Biosensing Applications

Platinum (Pt) electrodes were designed in imitation of screen-printed electrodes, and prepared by microelectronic techniques. These electrodes were then modified with zinc oxide (ZnO) nanofibers for biosensing applications. ZnO nanofibers with average length ∼20-30 μm and diameter ∼150 nm in hexagonal crystalline structure are prepared using electrospinning method. Their surface characteristics were analyzed by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Electrochemical properties of modified Pt electrodes were investigated in comparison with commercial carbon screen-printed electrodes. The results showed that the cyclic voltammogram of modified Pt electrodes was stable, but has much lower resistance compared to that of carbon screen-printed electrodes.