Crystalline-to-Amorphous Phase Transformation in CuO Nanowires for Gaseous Ionization and Sensing Application

Engineered tenorite structure of barium-enriched copper oxide for on-site monitoring of cytotoxic methotrexate in environmental samples

Emerging pharmaceutical pollutants pose a threat to both human and environmental health. The removal and monitoring of such pollutants necessitate the use of practical on-site monitoring devices; however, the designs of such devices are underdeveloped. This study involves the fabrication of a low-cost sensor based on barium-incorporated copper oxide (Ba-CuO) for the on-site monitoring of the cytotoxic drug methotrexate (MTRX) in water and sediment samples. The tenorite structure of CuO was slightly enriched with Ba ions at the td sites, distorting the tetrahedron and enhancing its electrochemical properties. Ba-CuO was obtained from Cu(NO₃)₂ and Ba(OH)₂ by a ligand exchange protocol and was characterized using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray analysis. In addition, the Ba-CuO sensor was tested under various conditions, and it could detect MTRX at concentrations as low as 0.4 nM, with a high sensitivity of 1.3567 µA µM^-1 cm^-2. On-site monitoring yielded recoveries of greater than 93 % from spiked samples, thus exhibiting excellent reproducibility and stability. Therefore, the developed method is practical and has no matrix effect on the MTRX sensor.

Copper Oxide Solution Sensor Formed on a Thin Film Having Nanowires for Detecting Ethanol in Water

Solution sensors are required to detect analytes in liquids with high sensitivity and response speed for environmental and health monitoring. In this study, we introduce the concept of a Cu oxide thin film having nanowires as a solution sensor for detecting ethanol in water. The Cu oxide sensor with grains and nanowires of different shapes was fabricated by a simple method of heating a Cu thin film and dropping an Ag conductive paste. Sensing parameters and mechanisms were evaluated by current-voltage and electrochemical impedance spectroscopy measurements. In the Cu oxide sensor formed on thin film having a large number of nanowires fabricated by heating at 400 °C for 5 h, the sensor sensitivity was 0.96 at 0.1 vol % ethanol concentration, and the response time was 313 s at a voltage of 0.1 V. The Cu oxide sensor detects ethanol by the change in electrical resistance caused by the reaction between ethanol molecules and the lattice oxygen on the Cu oxide surface. Therefore, the large nanowire surface area leads to a higher sensor sensitivity and a faster response time. Furthermore, the grain and nanowire regions on the thin film are represented by equivalent circuits. A high correlation was observed between the sensor sensitivity and the time constant calculated from the equivalent circuit. The proposed Cu oxide solution sensor and detection mechanism offer designs to improve the performance of chemical sensors.