In this work, the two-dimensional MoS 2 film was prepared by sulfuring the molybdenum atomic layer on SiO 2 /Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS 2 film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 °C/min, reaction temperature of 750 °C, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS 2 gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH 3 ) and oxidizing gas (NO 2 ) at room temperature. The sensitivity to 100 ppm of NO 2 was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO 2 sensors.
Jing Bo Zhang,Xiao Ning Li,Shou Li Bai,Rui Xian Luo,Ai Fan Chen,Yuan Lin
Well-crystallized one-dimensional (1D) SnO 2 nanobelts were in situ prepared using a simple water-assisted chemical vapor deposition (CVD) method. The small Sn particles with Au-modifications were used as source materials instead of big size Sn grains to ensure the high yield of SnO 2 belts. The Au layer was modified on the small Sn particles by treating Sn powders in HAuCl 4 solution combined with the UV irradiation. The as-prepared SnO 2 nanobelts were characterized by SEM, HRTEM, XRD, EDS and XPS. These results indicate that the growth temperature plays an important role in controlling the length-to-width ratio of nanobelts. The length-to-width ratio decreases with the growth temperature from 850 °C to 1000 °C. The nanobelts prepared at 850 °C shows a single-crystalline tetragonal rutile phase with a high length-to-width ratio (approximately tens of microns in length and 40–70 nm in width). However, below 850 °C, nanobelts cannot be formed. The as-prepared nanobelts exhibited excellent sensing properties compared with SnO 2 nanoparticles and high sensing selectivity towards NO 2 . The high sensing selectivity to NO 2 is attributed to the oxygen vacancies presenting in the as-prepared nanobelts.
Metal oxide based gas sensors should mostly work at high temperatures; the high working temperature is associated with safety concerns and high energy consumption, which makes portable and wearable devices almost impossible, and the inhomogeneous temperature distribution over a sensor also has a detrimental effect on the device performance. However, all the above problems can be effectively resolved by using visible light-excited sensors working at room temperature. By depositing an array of well-aligned In2O3 nanowires on polyimide (PI) substrates, we fabricate flexible and transparent sensors that achieve room temperature gas sensing using visible light as the excitation source. The detection limit to NO2 is as low as 10 ppb under illumination using both monochromatic (blue) and polychromatic (white) light sources. The sensing performance remains consistent after repetitive bending and long-term operation. Remarkably, the sensor exhibits recoverable response to 500 ppb NO2 even under the illumination of an iPhone screen with a low irradiance of 0.56 W m−2. Through a systematic study of the interaction between the photoelectric and gas sensing properties of the materials, we also explore the mechanism of photo-induced gas sensing reactions at room temperature. This work will lay the foundation for gas sensors that can be used in portable and wearable devices.
A novel gas-sensing material and photocatalyst was successfully obtained by decorating Ag/AgCl nanoparticles on the W 18 O 49 nanorods through a clean photochemical route. The as-prepared samples were characterized using combined techniques of X-ray diffractometry, electron microscopy , energy dispersive X-ray spectrometry , and X-ray photoelectron spectroscopy. Gas-sensing measurements indicate that the Ag/AgCl/W 18 O 49 NRs sensors exhibit superior reducing gas-sensing properties to those of bare W 18 O 49 NRs, and they are highly selective and sensitive to NH 3 , acetone, and H 2 S with short response and recovery times. The Ag/AgCl/W 18 O 49 NRs photocatlysts also possess higher photocatalytic performance than bare W 18 O 49 NRs for degradation of methyl orange under simulated sunlight irradiation. Possible mechanisms concerning the enhancement of gas-sensing and photocatalytic activities of the Ag/AgCl/W 18 O 49 NRs composite were proposed.
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