With a series of widespread applications, resistive gas sensors are considered to be promising candidates for gas detection, benefiting from their small size, ease-of-fabrication, low power consumption and outstanding maintenance properties. One-dimensional (1-D) nanomaterials, which have large specific surface areas, abundant exposed active sites and high length-to-diameter ratios, enable fast charge transfers and gas-sensitive reactions. They can also significantly enhance the sensitivity and response speed of resistive gas sensors. The features and sensing mechanism of current resistive gas sensors and the potential advantages of 1-D nanomaterials in resistive gas sensors are firstly reviewed. This review systematically summarizes the design and optimization strategies of 1-D nanomaterials for high-performance resistive gas sensors, including doping, heterostructures and composites. Based on the monitoring requirements of various characteristic gases, the available applications of this type of gas sensors are also classified and reviewed in the three categories of environment, safety and health. The direction and priorities for the future development of resistive gas sensors are laid out.

One-Dimensional Nanomaterials in Resistive Gas Sensor: From Material Design to Application

Excellent gas-sensitive properties towards acetone of In2O3 nanowires prepared by electrospinning

Polymer blend nanocomposite (PBNC) films consisted of fluoropolymer poly(vinylidene fluoride) (PVDF) and plexiglass polymer poly(methyl methacrylate) (PMMA) blend host matrix (fixed composition blend of PVDF/PMMA = 80/20 wt/wt%) with barium titanate (BaTiO3) ceramic nanofiller of varying concentrations (x = 0, 2.5, 5, 10, and 15 wt%) were prepared via a state-of-the-art solution-cast method. Scanning electron microscope (SEM) images evidenced high homogeneity of these PBNC films and a huge alteration in the spherulite morphology of the PVDF with the increase in dispersed BaTiO3 concentration in the polymer blend matrix. The X-ray diffraction (XRD) patterns identified the presence of electro-active polar β- and γ-phases of the PVDF crystallites in all the composite materials which are supported by the results of Fourier transform infrared (FTIR) spectra. The differential scanning calorimeter (DSC) thermograms explained the high melting temperature of these overlapped PVDF polymorphs and the degree of crystallinity altered anomalously with the variation of nanofiller concentration. The absorbance of ultraviolet-visible (UV-Vis) radiations enhanced while the direct energy band gap of the 80PVDF/20PMMA blend matrix and also the semiconducting BaTiO3 was found to decrease with the increased concentration of nanomaterial in the host polymer matrix. The ambient temperature broadband dielectric spectra covering the frequency range from 20 Hz to 1 GHz explain that the real part of complex dielectric permittivity reduced with a huge dispersion at higher radio frequencies where the dielectric loss tangent and electric modulus spectra exhibited an intense chain segmental relaxation process. The electrical conductivity of these PBNC films increased with frequency augmented and illustrated a small variation for different concentration composites. The experimental results demonstrated that these PVDF/PMMA/BaTiO3 films could be potential candidates for frequency tunable nanodielectric, electromagnetic interference shielders, a flexible dielectric substrate, thermal insulators, and bandgap regulated materials for futuristic microelectronic, capacitive energy storage, and optoelectronic technologies. 

Morphological, structural, optical, broadband frequency range dielectric and electrical properties of PVDF/PMMA/BaTiO3 nanocomposites for futuristic microelectronic and optoelectronic technologies

Design of hierarchical porous carbon nanofibrous membrane for better electrochemical performance in solid-state flexible supercapacitors

In this study, well-designed layer-like WO3 was synthesized by a facile hydrothermal route. Different characterization techniques have been conducted to comprehensively investigate the properties of morphology and structure of WO3-based sensing materials. The resultant consequences demonstrated that the layer-like WO3 with abundant mesoporous structure displayed higher specific surface area with respect to the pristine WO3 nanoplates. For the first time, the excellent gas sensing device based on layer-like WO3 was constructed successfully, which achieved an admirable gas-sensing response of 106 towards 5 ppm nitrogen dioxide gas at the working temperature of 160 ℃, with a favorable selectivity, and the lowest detection limit was reached to 0.243 ppb. Moreover, the layer-like WO3 sensor possessed considerable reproducibility and stability even in aging tests for 30 days. Those results can be ascribed to this promising structure optimization, which not only provides more reaction active sites but also promoted the gas sensing reaction procedure. Undoubtedly, this work is believed to be useful to offer a feasible strategy to enhance NO2 gas response in practical application. 

Superior sensitivity and low detection limit of NO2 sensor based on layered tungsten oxide

Well-ordered polyvinyl alcohol (PVA) parallel nanofiber arrays (PNAs) were fabricated by using electrospinning receiving board with clined gap. A three-dimensional (3D) copper phthalocyanine (CuPc) organic field effect transistor (OFET) sensor was obtained by evaporating CuPc on the PVA PNAs. This 3D structure is conducive to the multi angle adsorption and desorption of the target gas and active layers. The detection limit of the obtained sensors is lower, and the response and recovery time are also shorter. Compared with single CuPc films and CuPc films with disordered PVA nanofibers sensors, the minimum detection concentration is reduced by one third. The CuPc/PVA PNAs sensors have been successfully used in real-time monitoring of NO2 at 0.3 ppm. The response and recovery time of the CuPc/PVA PNAs sensors are both 0.02 min for 25 ppm NO2. The response and recovery time are 350 and 130 times faster than those of CuPc sensors with disordered PVA nanofibers, respectively. Humidity has little effect on the response of the sensor. This convenient and effective method to prepare high performance OFET sensors can be extended to other gas monitoring.

Three-dimensional CuPc films decorated with well-ordered PVA parallel nanofiber arrays for low concentration detecting NO2 sensor

Bilayer polymer dielectric systems for high response NO2 gas sensors

Organic field effect transistors based on blended polymer insulators were fabricated. The effects of polystyrene (PS), poly (vinyldifluoride) (PVDF) and poly (vinylphenyl) (PVP) blended with poly (methylmethacrylate) (PMMA) on the properties of insulating layers were studied. The PMMA:PS films have spherical grains, the PMMA:PVP films exhibit porous pit morphology, and the PMMA:PVDF films still show plane morphology. The morphology of insulating layers can affect the crystallization of organic semiconductors. Meanwhile, the performance of OFET devices indicates that polymer doping decreases the threshold voltage of devices. When the mass ratio of PMMA:PVDF is 10:5, the threshold voltage of OFET devices is about -14.7 V, which is significant lower than that of pure PMMA devices. This is attributed to the larger capacitance and lower roughness of the insulating layers. Therefore, it is a convenient and effective method to optimize the threshold voltage of OFET devices by applying blended polymer insulating layers.

Chang Liu

Papers

Three-dimensional CuPc films decorated with well-ordered PVA parallel nanofiber arrays for low concentration detecting NO2 sensor

Bilayer polymer dielectric systems for high response NO2 gas sensors

Blended polymer as composite insulating layers for organic field effect transistor