We report a hydrothermal method for synthesis of nickel‐doped tin oxide (Ni–SnO2) nanoparticles. The samples are characterized by different analysis techniques to understand their structural, morphological, and optical properties. The synthesized nanomaterials are characterized by X‐ray diffraction, it is crystallized in a tetragonal rutile crystal structure and the crystallite size increases from ∼5 to ∼23 nm with the increasing nickel (Ni) doping concentration. The field emission electron microscopy demonstrates that in case of doping the addition of polyethylene glycol is responsible for the development of densely packed flower like bunches. Further, the synthesized n‐type SnO2 materials are systematically investigated for humidity sensing toward atmospheric moisture. The results indicate that nickel doping improves the performance of SnO2 sensor and is highly sensitive over a wide relative humidity (%RH) range from 10% to 100% at room temperature than pure SnO2. It is found that the resistance of the films decreases with increasing RH as the multilayer stacking of water molecules occurred on the surface of synthesized nanomaterials. Also, the fast response time of 15 s and recovery time of 4 s are observed for the 5% nickel‐doped SnO2 sensor. This improved sensing performance is attributed to nickel doping as doping developed the proportions of oxygen vacancy and improves the large surface to volume ratio as well as exhibited high conductivity. Thus, the doping of SnO2 nanoparticles with Ni should be a promising approach for designing and fabricating the high‐performance humidity sensor.

Real time humidity monitoring is crucial in several fields such as pharmaceuticals, electronic device manufacturing, in agricultural irrigation system due to drastic changing climates and so forth. In this work, we studied humidity sensing behavior of molybdenum trioxide (MoO3) in composition with conductive polyaniline (PAni). The conductive PAni used in the present study was in the emeraldine salt (ES) form and was doped with amino tris‐methylene phosphonic acid (PAni‐ATMPA) as a potential candidate for humidity sensors. PAni‐ATMPA is synthesized by oxidative polymerization of aniline monomers and ATMPA in the ratio of 1:1. Thus synthesized PAni and hydrothermally synthesized MoO3 were mixed together to form nanocomposites. The synthesized composites were then used to fabricate planar sensors on alumina substrate with pre‐deposited silver electrodes. XRD analysis of synthesized MoO3 shows an orthorhombic crystal structure whereas synthesized PAni shows amorphous nature. FESEM analysis of synthesized MoO3 shows sheet‐type morphology. Different compositions of MoO3:PAni were prepared by varying MoO3 and PAni wt%. The fabricated sensors were then tested over the range of 20%–90% RH and concluded that the sensitivity of the composite is seen to be higher for the composite with 20% PANi and 80% MoO3 with response time, recovery time and the linearity 7 s, 4 s, 13–62 RH% respectively. The above mentioned parameters are found to be improved in the composites as a result of PAni addition to MoO3 than the pristine MoO3. The experimental knowledge demonstrates that the films showed good repeatability (with ±4%uncertainty)and reproducibility (with ±3% uncertainty). Altogether, these results indicate that it is possible to tune the humidity sensing characteristics by optimizing the amount of MoO3 and PAni in MoO3:PAni composite.

Nitrogen dioxide (NO 2 ) has been identified as a serious air pollutant that threats to our environment, human life and world ecosystems. Therefore, detection of this air pollutant is crucial. Metal oxide semiconductor is one of the best approaches frequently used to detect NO 2 at relatively low temperatures. Hydrated tungsten trioxide (WO 3 · H 2 O), an n-type semiconductor, is regarded to be a promising material for fabricating gas sensors, which are widely used in environmental and safety monitoring. In this work, WO 3 · nH 2 O nanoparticles have been synthesized using a polyfunctional surfactant-mediated hydrothermal approach in the addition of H 2 C 2 O 4 and K 2 SO 4 at a molar ratio of 1 : 1. This paper has also reported the effect of reaction temperature (120°C to 200°C) on morphological changes and gas-sensing performance. The characterization of these synthesized nanostructures was carried out by UV–Vis absorption spectroscopy, X-ray diffraction and field-emission scanning electron microscopy (FESEM). The UV absorption peak was obtained around 300 nm. FESEM analysis showed sheet-like structures come together to form flower-type morphology. The synthesized WO 3 · nH 2 O flower-like structures was then used for NO 2 gas-sensing application. The prepared sensors showed considerably better sensor response ( R g / R a = 17.48) at 185°C for 25 ppm NO 2 .