ABSTRACT
To in situ and noninvasively monitor the biofilm development process by low-field nuclear magnetic resonance (NMR), experiments should be made to determine the mechanisms responsible for the T2 signals of biofilm growth. In this paper, biofilms were cultivated in both fluid media and saturated porous media. T2 relaxation for each sample was measured to investigate the contribution of the related processes to T2 relaxation signals. In addition, OD values of bacterial cell suspensions were measured to provide the relative number of bacterial cells. We also obtained SEM photos of the biofilms after vacuum freeze-drying the pure sand and the sand with biofilm formation to confirm the space within the biofilm matrix and identify the existence of biofilm formation. The T2 relaxation distribution is strongly dependent on the density of the bacterial cells suspended in the fluid and the stage of biofilm development. The peak time and the peak percentage can be used as indicators of the biofilm growth states.
ABSTRACT
Volatile organic compounds (VOCs), which originate from painting, oil refining and vehicle exhaust emissions, are hazardous gases that have significant effects on air quality and human health. The detection of VOCs is of special importance to environmental safety. Among the various detection methods, chemoresistive semiconductor metal oxide gas sensors are considered to be the most promising technique due to their easy production, low cost and good portability. Sensitivity is an important parameter of gas sensors and is greatly affected by the microstructure, defects, catalyst, heterojunction and humidity. By adjusting the aforementioned factors, the sensitivity of gas sensors can be improved further. In this review, attention will be focused on how to improve the sensitivity of chemoresistive gas sensors towards certain common VOCs with respect to the five factors mentioned above.
ABSTRACT
In this paper, In2O3 nanotubes were prepared by an electrospinning method combined with an oriented-contract calcinations scheme, and characterized by differential thermal and thermal gravimetric analyzer (DTA-TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Ethanol sensing properties of the as-prepared nanotubes were investigated. The results showed that the In2O3 nanotubes were obtained at a fast heating rate of 100 degrees C/min. Ethanol sensing properties indicated that the nanotubes exhibit a high response of 87.5 to 500 ppm ethanol, fast response (20 s) and recovery (18 s) rate at the optimal operating temperature of 260 degrees C. Moreover, the nanotubes also exhibit good selectivity.
ABSTRACT
A Zr(0.04)Ti(0.96)O(2) solid solution nanowire (NW) array was prepared and characterized in detail. Zr doping effectively changed Zr(x)Ti(1-x)O(2)'s bandgap and led to better photoelectric properties, which indicated the possibility for deep UV detector fabrication. Based on the NW array, high-performance Schottky diode UV detector with Ag electrode was fabricated. At -3 V bias, the dark current of the detector is only 5 nA, and a high photoresponse of 5.6 A/W was achieved because of the internal gain. The ratio of photocurrent to dark current is more than three orders of magnitude. The device is promising for large-area UV detector applications.
ABSTRACT
High-responsivity metal-semiconductor-metal TiO(2) UV photodetectors with Ni and Au electrodes were fabricated identically. Their Schottky barrier heights and photocurrent gain mechanism were studied. The effective barrier height Φ and ideality factor n were evaluated according to the thermionic emission theory. The result that Φ(Ni) was lower than Φ(Au) may be attributed to the electron transfer from Ni to the TiO(2) substrate, which would lead to a dipole layer and, accordingly, decrease the barrier height. In addition, the I-V characteristics of the Ni/TiO(2)/Ni and Au/TiO(2)/Au photodetectors were observed. A significant internal gain was obtained, and the mechanism of the internal gain was studied by the phototransistor model in detail.
ABSTRACT
Acidic sols of TiO2, ZrO2 and Ti-Zr mixed oxide precursors were prepared. The sols were then smeared on quartz substrate and annealed at 650 degrees C for 2 hour to form polycrystalline oxide films. XRD, SEM, UV-visible absorption spectra and XPS were carried out to characterize the films. It was found that the crystalline phase of pure titania is an anatase and pure zirconia is a tetragonal. The binary oxides show the anatase phase at the molar ratio of Ti:Zr = 2.73:1, which means that solid solution was formed. The absorption edge of the TiO2-ZrO2 binary oxides showed obvious blue shift as the Zr ratio increased. The results obtained indicate that the band gap of the binary oxides could be adjusted from 3.2 eV (TiO2) to 7.8 eV (ZrO2) by varying the molar ratio of Ti and Zr. Au interdigitated electrodes were produced by planar technology and MSM (metal-semiconductor-metal) structure UV detector based on TiO2-ZrO2 binary oxides was fabricated. Obvious photoelectric response was observed.
ABSTRACT
In the search for efficient photocatalysts working under visible light, we have investigated the effect of metal ions (Bi/Co, Fe/Co) codoping on the photocatalytic activity of TiO(2) prepared by stearic acid gel method. UV-vis spectra revealed that doped Co enhanced the absorbency of TiO(2) under visible light, and Bi/Co codoped TiO(2) showed higher absorbance than Fe/Co codoped TiO(2). The photoreaction based on the prepared samples for photodegradation of 20mg/l rhodamine B solution was examined. The results showed that Fe(0.1%)/Co(0.4%) codoped TiO(2) had the highest photoactivity among all as-prepared samples under visible light, though less absorbency of visible light, indicating that the photoactivity not only benefits from absorbency but also relates to the cooperative effect of the two dopants.
