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NH 3 gas sensors operating at room temperature, consisting of Ag nanoparticles decorated β-AgVO 3 nanorods (Ag/β-AgVO 3 NRs), were fabricated via a facile hydrothermal method without the need for a template. The surface characteristics and compositions of Ag/β-AgVO 3 NRs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ag nanoparticles, ranging in diameter from approximately 20 to 40 nm, were dispersed on the surface of monoclinic β-AgVO 3 NRs with diameters ranging from 50 to 105 nm and lengths from 0.3 to 1.3 μm. The NH 3 gas sensing properties of Ag/β-AgVO 3 NRs were studied under both dry air and humid conditions at room temperature. Comparative analysis demonstrated that the Ag/β-AgVO 3 NRs exhibited a strong response to NH 3 gas under 70% relative humidity (RH) at room temperature compared to α-AgVO 3 NRs. Specifically, the response of the Ag/β-AgVO 3 NRs to 5 ppm NH 3 increased by 2.25 times as the RH varied from 20% to 80% at room temperature. This enhanced response was attributed to the effects of formation of nanoheterojunctions, nano-metallic Ag activity and the conductivity of NH 4 + and OH - ions induced by the presence of humidity. The room temperature NH 3 gas sensors based on Ag/β-AgVO 3 NRs demonstrated strong responses to low NH 3 concentrations, high selectivity, good reproducibility, and long-term stability, and show promise for the development of low-power and cost-effective NH 3 gas sensors for practical applications even under high humidity.

Conifer-like TiSnO 2 nanorods mixed metal oxide was synthesized via the one-pot polyol method utilizing ethylene glycol (EG), poly(diallyldimethylammonium chloride) (PDDA), tin(II) chloride dihydrate (SnCl 2 ·2H 2 O), and titanium(IV)-ethylhexanoate (TE) as precursor materials, aimed at room temperature H 2 S gas sensing. The effects of polyol duration time and capping agent concentration (PDDA) were examined to explore the morphological, structural, and gas-sensing characteristics, as well as to propose potential growth mechanisms of conifer-like TiSnO 2 nanorods mixed metal oxide. The morphology and composition of the synthesized TiSnO 2 mixed metal oxide were carried out employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD). The experimental findings demonstrated a significant influence of polyol duration time and PDDA concentration on the morphological evolution of the synthesized TiSnO 2 mixed metal oxide structures. Comparative gas-sensing analysis indicated that the conifer-like TiSnO 2 nanorods mixed metal oxide exhibited the highest response (2.45%) towards H 2 S gas at a concentration of 1 ppm, along with a low detection limit (0.20 ppm) and good linearity ( R 2 = 0.9865) within the range of 1-15 ppm of H 2 S gas at room temperature.

Room temperature NH 3 gas sensors composed of noble metal (Au, Ag or Pt)/polythiophene/reduced graphene oxide (Au, Ag or Pt/PTh/rGO) ternary nanocomposite films were fabricated using a simple one-pot redox reaction. The surface morphology and composition of Au, Ag or Pt/PTh/rGO ternary nanocomposite films were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films, obviously bright Au nanoparticles were observed on the surface of the massive lamination PTh film which wrapped the rGO, and encapsulated Au nanoparticles were observed in the Au/PTh/rGO film. Comparative gas sensing results showed that the Au/PTh/rGO ternary nanocomposite film had the highest response compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films at room temperature, especially when the testing concentration of NH 3 gas was below 5 ppm. The Au/PTh/rGO ternary nanocomposite film also had a fast response time and good reproducibility. The combination of the high catalytic activity of naked Au nanoparticles and the formation of effective carrier transfer channels by encapsulated Au nanoparticles was responsible for the improved response of the Au/PTh/rGO ternary nanocomposite film.

Novel QCM NH 3 gas sensors made of reduced graphene oxide-SnO 2 (rGO-SnO 2 ) composite films were fabricated using a one-pot technique, which is a fast and easy fabrication route that is useful for practical applications. The surface morphology and composition of the rGO-SnO 2 composite films were analyzed using Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy coupled with energy-dispersive X-ray elemental mapping and transmission electron microscopy. On the basis of the microstructural observations, SnO 2 connected to rGO sheets and naked rGO sheets were observed on the surface of the rGO-SnO 2 composite films. The effects of the amount of added rGO sheets on the enhancement of the NH 3 gas sensing properties of the rGO-SnO 2 composite films were studied. The analysis of the adsorption dynamics (association constant) confirmed the higher sensitivity of the QCM NH 3 gas sensor based on the rGO-SnO 2 composite film than that of the sensor with the pristine SnO 2 film.

ppb-level SO 2 gas sensors for use at room temperature were fabricated using an in situ one-pot polyol method combined with metal organic decomposition (MOD) of nanocomposite films of multi-walled carbon nanotubes/WO 3 (MWCNTs/WO 3 ) and reduced graphene oxide/WO 3 (RGO/WO 3 ) on an alumina substrate. Comparative gas sensing results showed that the SO 2 gas sensor based on the RGO/WO 3 nanocomposite film exhibited a higher response compared with the MWCNTs/WO 3 nanocomposite film and pristine WO 3 film, sensing SO 2 gas at very low (ppb-level) concentrations at room temperature. The SO 2 gas sensor based on the RGO/WO 3 nanocomposite film also had fast response and recovery times, good reproducibility, and the lowest detection limit. The formation of new conducting pathways and the spread of the depletion layers at the interface of the doped MWCNTs or RGO and the WO 3 matrix upon interaction with SO 2 gas were responsible for the enhanced response.

A single-yarn H2-gas sensor was fabricated by self-assembling poly(allylamine hydrochloride) (PAH), poly(styrenesulfonic acid) sodium salt (PSS), graphene oxide (GO) and Pd-based complex thin films layer-by-layer on a single-yarn and then in situ reducing the Pd-based complex to a Pd/GO/PAH/PSS/PAH multilayered thin film. The H2-gas sensing properties, effect of bending and humidity influence on this sensor were investigated. The sensor exhibited a high response and good linearity over the range of 1000 to 10 000 ppm of H2 gas. The response of the sensor decreased under both conditions of a bending angle up to 20° and ambient humidity above 50% RH. A fast Fourier transform (FFT) analyzer was employed to disperse the signals of the sensor under the conditions of bending and ambient humidity influence in the presence of H2 gas. Differentiation of the amplitude of FFT from the first-order to second-order frequency spectra effectively increased the discrimination capability of the sensor under the conditions of bending and humidity influence.