Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Nanostructured Materials for Room-Temperature Gas Sensors

Energy and environment will head the list of top global issues facing society for the next 50 years. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. The route toward these nano-objects is based primarily on electrospinning: a highly versatile method that allows the fabrication of continuous fibers with diameters down to a few nanometers. The mechanism responsible for the fiber formation mainly includes the Taylor Cone theory and flight-instability theory, which can be predicted theoretically and controlled experimentally. Moreover, the electrospinning has been applied to natural polymers, synthetic polymers, ceramics, and carbon. Fibers with complex architectures, such as ribbon fiber, porous fiber, core-shell fiber, or hollow fiber, can be produced by special electrospinning methods. It is also possible to produce nanofibrous membranes with designed aggregate structure including alignment, patterning, and two-dimensional nanonets. Finally, the brief analysis of nanofibers used for advanced energy and environmental applications in the past decade indicates that their impact has been realized well and is encouraging, and will continually represent a key technology to ensure sustainable energy and preserve our environment for the future.

Electrospun Nanofibers: Solving Global Issues

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

/pdf/humidity-sensors-principle-mechanism-and-fabrication-q8mq7scozc.pdf

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

This Review provides an overview of the synthesis of one-dimensional (1D) composite nanomaterials by electrospinning and their applications. After a brief description of the development of the electrospinning technique, the transformation of an inorganic nanocomponent or polymer into another kind of polymer or inorganic matrix is discussed in terms of the electrospinning process, including the direct-dispersed method, gas-solid reaction, in situ photoreduction, sol-gel method, emulsion electrospinning method, solvent evaporation, and coaxial electrospinning. In addition, various applications of such 1D composite nanomaterials are highlighted in terms of electronic and optical nanodevices, chemical and biological sensors, catalysis and electrocatalysis, superhydrophobic surfaces, environment, energy, and biomedical fields. An increasing number of investigations show that electrospinning has been not only a focus of academic study in the laboratory but is also being applied in a great many technological fields.

One-Dimensional Composite Nanomaterials: Synthesis by Electrospinning and Their Applications

Detection of hazardous volatile organic compounds (VOCs) by metal oxide nanostructures-based gas sensors: A review

Pd0-loaded SnO2 nanofibers have been successfully synthesized with different loaded levels via electrospinning process, sintering technology, and in situ reduction. This simple strategy could be ex...

Ultrasensitive Hydrogen Sensor Based on Pd0-Loaded SnO2 Electrospun Nanofibers at Room Temperature

A facile and versatile method for the large-scale synthesis of sensitive mesoporous ZnO–SnO2 (m-Z–S) nanofibers through a combination of surfactant-directed assembly and an electrospinning approach is reported. The morphology and the structure were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and nitrogen adsorption–desorption isotherm analysis. The results showed that the diameters of fibers ranged from 100 to 150 nm with mixed structures of wurtzite (ZnO) and rutile (SnO2), and a mesoporous structure was observed in the m-Z–S nanofibers. The sensor performance of the prepared m-Z–S nanofibers was measured for ethanol. It is found that the mesoporous fiber film obtained exhibited excellent ethanol sensing properties, such as high sensitivity, quick response and recovery, good reproducibility, and linearity in the range 3–500 ppm.

/pdf/a-highly-sensitive-ethanol-sensor-based-on-mesoporous-zno-1i9to3hs6i.pdf

A highly sensitive ethanol sensor based on mesoporous ZnO-SnO2 nanofibers.

In 2 O 3 nanofibers with diameters of around 60 nm have been fabricated by electrospinning with a solution containing both poly (vinyl pyrrolidone) (PVP) and indium nitrate, followed by calcination in air at 700 °C. Without further adding catalysts or doping other metal oxides, the sensor based on the as-prepared indium oxide (In 2 O 3 ) nanofibers showed high response and selectivity, fast response and recovery time towards ethanol gas. The simple preparation and excellent properties significantly advance the viability of electrospun gas sensors.

A highly sensitive and fast-responding sensor based on electrospun In2O3 nanofibers

Here we demonstrate the preparation and improved hydrogen monitoring properties based on p-NiO/n-SnO2 heterojunction composite nanofibers via the electrospinning technique and calcination procedure. NiO/SnO2 heterojuction composite nanofibers were spin-coated on the ceramic tube with a pair of Au electrodes for the detection of hydrogen. Extremely fast response−recovery behavior (∼3s) has been obtained at the operable temperature of 320 °C, based on our gas sensor, with the detection limit of approximate 5 ppm H2. The role of the addition of NiO into the SnO2 nanofibers and the sensing mechanism has also been discussed in this work.

Improved Hydrogen Monitoring Properties Based on p-NiO/n-SnO2 Heterojunction Composite Nanofibers

A nano-gas sensor based on Pd–SnO2 composite nanofibers is fabricated by electrospinning technique and calcination procedure. The morphology, structure and composition of the as-prepared nanofibers are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), respectively. The nano-gas sensor shows excellent hydrogen sensing properties such as high sensitivity and extremely fast response–recovery behavior (∼9 s) at a lower operation temperature (280 °C). The detection limit of approximately 4.5 ppm H2 is demonstrated. The function of adding Pd into the SnO2 nanofibers and the sensing mechanism have also been discussed in this work.

Zhaojie Wang

Papers

Ultrasensitive Hydrogen Sensor Based on Pd0-Loaded SnO2 Electrospun Nanofibers at Room Temperature

A highly sensitive ethanol sensor based on mesoporous ZnO-SnO2 nanofibers.

A highly sensitive and fast-responding sensor based on electrospun In2O3 nanofibers

Improved Hydrogen Monitoring Properties Based on p-NiO/n-SnO2 Heterojunction Composite Nanofibers

Enhancement of hydrogen monitoring properties based on Pd-SnO2 composite nanofibers