In this research, a single-aligned nanofiber of pure TiO and gold nanoparticle (GNP)-TiO were fabricated using a novel electro-spinning procedure equipped with secondary electrostatic fields on highly sharp triangular and rectangular electrodes provided for gas sensing applications. The sol used for spinning nanofiber consisted of titanium tetraisopropoxide (CHOTi), acetic acid (CHCOOH), ethanol (CHOH), polyvinylpyrrolidone (PVP), and gold nanoparticle solution. FE-SEM, TEM, and XRD were used to characterize the single nanofiber. In triangular electrodes, the electrostatic voltage for aligning single nanofiber between electrodes depends on the angle tip of the electrode, which was around 1.4-2.1, 2-2.9, and 3.2-4.1 kV for 30°, 45°, and 60°, respectively. However, by changing the shape of the electrodes to rectangular samples and by increasing distance between electrodes from 100 to 200 μm, electro-spinning applied voltage decreased. Response of pure TiO single nanofiber sensor was measured for 30-200 ppb carbon monoxide gas. The triangular sample revealed better response and lower threshold than the rectangular sample. Adding appropriate amounts of GNP decreased the operating temperature and increased the responses. CO concentration threshold for the pure TiO and GNP-TiO triangular samples was about 5 ppb and 700 ppt, respectively.
The supercapacitive behavior of polypyrrole/reduced graphene oxide/Au nanoparticles as a ternary composite electrode was studied by CV, galvanostatic charge/discharge, EIS and fast Fourier transform continuous cyclic voltammetry techniques.
In this research, a Pd-TiO 2 nanofiber structure with photo-activation capability for H 2 gas sensing is made using the electro-spinning procedure. The solution which was stacked into the syringe for electro-spinning Pd-TiO 2 nanofibers consisted of titanium tetraisopropoxide, acetic acid, ethanol, polyvinyl pyrrolidone (PVP), and different amounts of Pd solution. The XRD, FESEM, TEM, and spectrophotometry techniques were employed to analyze the crystalline structure and surface morphology of the nanofibers. Moreover, Fe 2 O 3 and HNO 3 were also used as additional additives and the effect of additives in the absorption spectrum shift towards the visible light spectrum was investigated. About 95 nm red shift towards visible light from 370 nm to 465 nm for TiO 2 /Pd/N/Fe 2 O 3 was observed in comparison with the pure TiO 2 nanofibers. By using additives and visible light irradiation, the operating temperature lowered from 290°C to 130°C and the response increased from 11 to 368. At an operating temperature of 150°C, the response time also reduced from 25s to 0.9 s and recovery times reduced from 40 s to 2 s. The response dropped only by about 30%, 12%, and 5% after nine months for the TiO 2 , TiO 2 /Pd, TiO 2 /Pd/N/Fe 2 O 3 samples, respectively.Index Terms -Pd-TiO 2 nanofiber, hydrogen sensor, electrospinning, sensing mechanism, UV-Vis irradiation.
A three-dimensional heterostructure using selective growth of ZnO nanowires on TiO 2 /ZnO nanocomposite nanofiber by a novel combination of a postseeding method in an electrospinning process and a hydrothermal technique is presented in this work. A hierarchical dense array of ZnO nanowires with a diameter of 70−120 nm and an aspect ratio of about 10 on TiO 2 /ZnO composite nanofibers (ZnO@TiO 2 /ZnO) was fabricated. XRD, UV−vis, FESEM, HRTEM, TEM, EDX, and XPS analyses were used for characterization of nanofibers. The results demonstrate about 4 times enhancement in UV spectrum absorption in the range of 240−300 nm compared to the nonhierarchical structures. It was found that the optimized operating temperatures for TiO 2 /ZnO nanofibers were 260 and 240 °C in the dark and under UV illumination. Results showed that ZnO@TiO 2 /ZnO exhibit about 3 times improvement in gas sensitivity with UV irradiation for 10−200 ppm of ethanol gas with reduced response and recovery times. UV-illuminated ZnO@TiO 2 /ZnO had about 3.81 and 4.30 times selectivity on ethanol with respect to acetone and toluene.
Detection of volatile organic compounds (VOCs) is one of the most challenging tasks in modelling breath analyzers because of their low concentrations (parts-per-billion (ppb) to parts-per-million (ppm)) in breath and the high humidity levels in exhaled breaths. The refractive index is one of the crucial optical properties of metal-organic frameworks (MOFs), which is changeable via the variation of gas species and concentrations that can be utilized as gas detectors. Herein, for the first time, we used Lorentz–Lorentz, Maxwell–Ga, and Bruggeman effective medium approximation (EMA) equations to compute the percentage change in the index of refraction (Δn%) of ZIF-7, ZIF-8, ZIF-90, MIL-101(Cr) and HKUST-1 upon exposure to ethanol at various partial pressures. We also determined the enhancement factors of the mentioned MOFs to assess the storage capability of MOFs and the biosensors’ selectivity through guest-host interactions, especially, at low guest concentrations.
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