A room-temperature high-performance ammonia (NH3) gas sensor based on hydroxyapatite (HAp) film with three-dimensional network structure was reported in this paper. The gas sensor was fabricated on the indium tin oxide glass (ITO) interdigital electrode via simple electrochemical deposition technique. The HAp film gas sensor shows good sensitivity, high reproducibility and excellent selectivity to NH3 gas under dry and relative humidity (RH) conditions at room temperature. The response and recovery time of the HAp film gas sensor to 1000 ppm NH3 gas are 23 s and 14 s under N2 (dry) condition, and are 4 s and 11 s under air (RH≈30) condition, respectively. The HAp film gas sensor has no considerable deviation in the 1000 ppm NH3 gas for 3 cycles under N2 (dry), and so is air (RH≈30) conditions. The HAp film gas sensor shows excellent selectivity to methanol, acetone and ethanol under N2 (dry) and air (RH≈30) conditions. Above all, two sensing mechanisms of the HAp film gas sensor to NH3 gas have been also researched in this work.
A novel non‐enzymatic carbohydrates sensor which was an indium tin oxide (ITO) glass electrode modified by nickel and copper nanoparticles (Cu/Ni/ITO) was developed by an electrochemical method. The crystallinity, morphology, electrochemical measurements and amperometric response of the as‐prepared ITO modified electrode were examined by the X‐ray diffraction (XRD), scanning electron microscopic (SEM), cyclic voltammetry (CV) and chronoamperometry, respectively. The Cu/Ni/ITO electrode had better electroactivity for glucose oxidation than that obtained using Cu/ITO, Ni/ITO, and Ni/Cu/ITO. The logistic regression equation, Ipa = (A1 – A2)/[1 + (Cglucose/x0)p] + A2, was used to fit the calibration curves of glucose aqueous solution concentrations and responsive current intensity. In research of other saccharides, such as fructose, lactose, sucrose, and maltose, which were detected by the Cu/Ni/ITO electrode, it was obvious that the Cu/Ni/ITO electrode was more sensitive to monosaccharides than disaccharides. Monosaccharides and disaccharides can be detected because the saccharides themselves had aldehyde group or be isomerized to an isomer having an aldehyde group in alkaline environment, and then aldehyde group produced carboxylic acid in the catalytic oxidation of the electrode, which lead to the change of electrode surface conductivity and the appearance of oxidation peak, and the alkaline environment further promotes the above reaction.
A rapid response/recovery ribbon‐like hydroxyapatite (HAp) humidity sensor with loose spatial structure has been fabricated in this work. The HAp film was prepared on polyethylene terephthalate‐indium tin oxide (PET‐ITO) interdigital substrate by electrochemical deposition method. The HAp film was characterized by XRD, SEM, FTIR techniques. Electrochemically deposited HAp has a preferred orientation in a‐plane, which exposes a great many of hydroxyl groups. The HAp has a flat ribbon‐like microstructure that effectively captures and detects water molecules. The gap of the interdigital electrode was filled with long ribbon‐like HAp to form a loose spatial structure which facilitates water molecules adsorption and desorption. The HAp humidity sensor showed high sensitivity, low hysteresis and good linearity. In particular, HAp sensor has a short response time of 0.9 s and recovery time of 5.6 s. Besides, the humidity sensing mechanism of HAp sensor was also investigated in detail.
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