Nanocomposite of polypyrrol and silica rods-gold nanoparticles core-shell as an ammonia sensor

Highly sensitive, room temperature operated gold nanowire-based humidity sensor: adoptable for breath sensing

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing. Both humidity and breath sensors are widely needed. Despite a lot of research on humidity and breath sensors, there is a need for simple, inexpensive, reliable, sensitive and selective sensors, which will operate at room temperature. Here we have synthesized gold nanowires by a simple, wet chemical route. The nanowires synthesized by us are 4–7 nm in diameter and a few micrometers long. The nanowires are amine functionalized. The sensor was prepared by drop casting gold nanowires on an alumina substrate to form a AuNW layer with different thicknesses (10, 20, 30 μm). The AuNW sensor is highly selective towards humidity and shows minimum cross sensitivity towards other gases and organic vapors. At an optimum thickness of 20 μm, the humidity sensing performance of the AuNW sensor over 11% to 92% RH was found to be superior to that of 10 and 30 μm thick layers. The response time of the sensor is found to be 0.2 s and the recovery time is 0.3 s. The response of the AuNW sensor was 3.3 MΩ/% RH. Further, the AuNW sensor was tested for sensing human breathing patterns.

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing.

Ruthenium-decorated vanadium pentoxide for room temperature ammonia sensing

Layer structured vanadium pentoxide (V₂O₅) microparticles were synthesized hydrothermally and successfully decorated by a facile wet chemical route, with ∼10–20 nm sized ruthenium nanoparticles. Both V₂O₅ and ruthenium nanoparticle decorated V₂O₅ (1%Ru@V₂O₅) were investigated for their suitability as resistive gas sensors. It was found that the 1%Ru@V₂O₅ sample showed very high selectivity and sensitivity towards ammonia vapors. The sensitivity measurements were carried out at 30 °C (room temperature), 50 °C and 100 °C. The best results were obtained at room temperature for 1%Ru@V₂O₅. Remarkably as short a response time as 0.52 s @ 130 ppm and as low as 9.39 s @ 10 ppm recovery time at room temperature along with high selectivity towards many gases and vapors have been noted in the 10 to 130 ppm ammonia concentration range. Short response and recovery time, high reproducibility, selectivity and room temperature operation are the main attributes of the 1%Ru@V₂O₅ sensor. Higher sensitivity of 1%Ru@V₂O₅ compared to V₂O₅ has been explained and is due to dissociation of atmospheric water molecules on 1%Ru@V₂O₅ as compared to bare V₂O₅ which makes hydrogen atoms available on Brønsted sites for ammonia adsorption and sensing. The presence of ruthenium with a thin layer of oxide is clear from X-ray photoelectron spectroscopy and that of water molecules from Fourier transform infrared spectroscopy.

Layer structured vanadium pentoxide (V₂O₅) microparticles were synthesized hydrothermally and successfully decorated by a facile wet chemical route, with ∼10–20 nm sized ruthenium nanoparticles.