Facile Fabrication of MoS2-Modified SnO2 Hybrid Nanocomposite for Ultrasensitive Humidity Sensing.

The exploitation of the interaction between nanostructured matter and small molecules, such as H2O at interfaces via dynamic hydrogen bonding, is essentially the key for smart, responsive nanodevic...

Humidity-sensing performance of layer-by-layer self-assembled tungsten disulfide/tin dioxide nanocomposite

Ultrahigh-performance impedance humidity sensor based on layer-by-layer self-assembled tin disulfide/titanium dioxide nanohybrid film

A comparative study of capacitive humidity sensor based on keratin film, keratin/graphene oxide, and keratin/carbon fibers

A novel functionalized multi-walled carbon nanotube (FMWCNT)/hydroxyethyl cellulose (HEC) composite-based humidity sensor was successfully developed for humidity monitoring applications. FMWCNTs were synthesized by covalently functionalizing multi-walled carbon nanotubes (MWCNTs) in a mixture of sulfuric and nitric acid to enhance their hydrophilicity. The FMWCNTs were characterized using transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and dispersion analysis to verify the presence of functional hydroxyl and carboxyl groups. A FMWCNT/HEC (1 : 6 w/w) composite ink was formulated using the solution blending technique with 2.5 wt% FMWCNTs. A multi-layered humidity sensor was fabricated using additive print manufacturing processes on a flexible polyethylene terephthalate (PET) substrate. Screen printing and gravure printing processes were used to deposit the bottom silver (Ag) electrode and FWMCNT/HEC sensing layers, respectively. The capability of the fabricated humidity sensor was investigated by measuring its resistive response towards relative humidity (RH) varying from 20% RH to 80% RH. As the RH was increased from 20% RH to 80% RH in steps of 10% RH at 25 °C, it was observed that the resistance of the printed sensor increased linearly. The printed sensor demonstrated resistance changes as high as ≈290% at 80% RH, when compared to its base resistance at 20% RH. A sensitivity and a response time of 0.048/%RH and ≈20 s were obtained for the printed sensor, respectively. The results thus demonstrated the feasibility of employing additive print manufacturing processes to develop a highly sensitive sensor for humidity monitoring applications.

In this work, we report the fabrication of a low power, humidity sensor where platinum nanoparticles (NPs) decorated few-layered molybdenum disulphide (MoS2) nanoflakes have been used as the sensing layer. A mixed solvent was used to exfoliate the nanoflakes from the bulk powder. Then the Pt/MoS2 composites were prepared by reducing Pt NPs from chloroplatinic acid hexahydrate using a novel reduction technique using sulphide salt. The successful reduction and composite preparation were confirmed using various material characterization tools like scanning electron microscopy, atomic force microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy and UV–visible spectroscopy. The humidity sensors were prepared by drop-coating the Pt-decorated MoS2 on gold interdigitated electrodes and then exposed to various levels of relative humidity (RH). Composites with different weight ratios of Pt were tested and the best response was shown by the Pt/MoS2 (0.25:1) sample with a record high response of ∼4000 times at 85% RH. The response and recovery times were ∼92 s and ∼154 s respectively with repeatable behaviour. The sensor performance was found to be stable when tested over a few months. The underlying sensing mechanisms along with detailed characterization of the various composites have been discussed.

Facile fabrication of flower-like MoS2/nanodiamond nanocomposite toward high-performance humidity detection

Layer-by-layer self-assembly of tricobalt tetroxide-polymer nanocomposite toward high-performance humidity-sensing

Humidity sensors have wide range of applications. In this paper, an inorganic hybrid thin film of molybdenum disulphide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/zinc oxide (ZnO) was prepared as the sensing layer to develop a resistive humidity sensor containing aluminium electrodes on Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate. The composite was analyzed using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction for their morphology and crystalline information. The sensor was exposed to various levels of relative humidity (RH) at room temperature and the response was found to be far better than pristine MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or ZnO-based humidity sensors with the maximum response being 301 times at 85% RH. The results were reproducible with fast response and recovery, stable over a month with negligible hysteresis. A cost effective prototype was built on printed circuit board, and the data were acquired and transmitted to smartphone wirelessly using a Wi-Fi module (ESP 8266) interfaced to FRDM-KL25Z development platform. The Android application developed for the smartphone had the capability to switch ON/OFF the sensor device over Wi-Fi. Thus, our sensor device holds a great potential to develop an ultrasensitive, low power, low cost, and fast humidity sensor capable of indoor air quality monitoring in home automation systems (smart home).

Humidity sensors have broad applications in health monitoring, environmental protection and human-machine interface, and robotics. Here, we developed a humidity sensor using alkali oxidation method to grow in situ TiO2 nanowires on two-dimensional Ti3C2 MXene. With an order of magnitude larger surface area compared to pure Ti3C2 or TiO2 materials, the urchin-like Ti3C2/TiO2 composite demonstrates a record high sensitivity in a low relative humidity (RH) environment (∼280 pF/% RH from 7% RH to 33% RH). Complex impedance spectroscopy and Schottky junction theory were employed to understand the underlying sensing mechanisms of the Ti3C2/TiO2 composite under various humidity conditions. We demonstrate the application of humidity sensors made with the Ti3C2/TiO2 composite for noncontact detection of the presence of various liquids as well as human fingers.

This study reports the humidity sensing characteristics of aluminum (Al) and fluorine (F) co-doped zinc oxide (ZnO) nanostructured thin films with different Al concentrations. Sol–gel method was used in the synthesis of Al and F doped ZnO nanoparticles. The Al concentration was changed to 0.5 mol%, 1 mol% and 1.5 mol% while F concentration was kept constant at 2 mol%. Al and F co-doped ZnO (AFZO) nanostructured thin films for manufacturing relative humidity (RH) sensors were fabricated on glass substrates with a dip coating technique and then annealed at 500 °C for 1 h. The scanning electron microscopy (SEM) micrographs indicated that all AFZO films had uniform and homogeneous surfaces. The X-ray diffraction (XRD) patterns revealed that AFZO films were polycrystalline and have a hexagonal wurtzite structure with a preferential orientation along the (002) plane. The RH sensing characteristics of AFZO sensors was determined by electrical resistance measurements in the range of 40–90% RH at room temperature (RT). Both the electrical resistivity and RH sensing characteristics of AFZO sensors were found to be highly dependent on the Al concentration. All AFZO sensors exhibited high sensitivity, excellent stability, fast response and recovery times and a repeatable characteristic. The lowest electrical resistivity and best humidity sensor characteristics were obtained for AFZO sensor containing 1 mol% Al (AFZO–010). The sensitivity ratio between 40 and 90% RH is approximately 247 × for AFZO–010. This study showed that AFZO nanostructured thin films are promising for high performance humidity sensor applications.

In this study, a high-performance humidity sensor based on KCl-doped CuO/SnO2 p-n heterostructures was fabricated by a ball milling-roasting method. The morphology and nanostructure of the fabricated KCl-CuO/SnO2 composite were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption analysis. The results showed that the humidity sensor had a high sensitivity of 194 kΩ/%RH, short response and recovery times of 1.0 and 1.5 s, a low hysteresis value, and good repeatability. The energy band structure and complex impedance spectrum of the KCl-CuO/SnO2 composite indicated that the excellent humidity sensing performance originated from the ionic conductivity of KCl, the formation of heterojunctions, the change in the Schottky barrier height, and the depletion of electronic depletion layers. The KCl-CuO/SnO2 sensor has great potential in respiratory monitoring, noncontact sensing of finger moisture, and environmental monitoring.

High-performance humidity sensors have received widespread attention for their wide use in healthcare, archaeology, electronic device manufacturing, etc., thus developing humidity sensors with wide sensing range, high response, narrow humidity hysteresis, fast response/recovery, and excellent stability are urgently needed. Humidity-sensitive materials are the core of humidity sensors. To obtain high-performance humidity sensors, humidity-sensitive materials should have high hydrophilicity, conductivity, and stability. Metal organic frameworks (MOFs) are promising humidity-sensitive materials due to their special characteristics, but often limited by the poor conductivity and hydrophilicity. Herein, a proton conduction enhanced CMC-Na/MOF-801/PPY (CMP) humidity-sensitive material was prepared through in-situ polymerization, and the corresponding humidity sensor was fabricated via drop-casting. The structure, functional groups, specific surface area, and element distribution of the CMP material were investigated by powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N&lt;sub&gt;2&lt;/sub&gt; sorption isotherm, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The abundant hydrophilic groups and continuous hydrogen bond network lead to tight dependence of the proton conductivity and impedance of the sensing material on the humidity. The results show that the optimized CMP sensor is highly sensitive to humidity change with high response of 516.7 at 43% RH and 1.24×10&lt;sup&gt;5&lt;/sup&gt; at 85% RH, narrow hysteresis of 1.9% RH, and short response/recovery time of 2.8 s and 1.2 s in the humidity range of 7–85% RH. Compared to reported MOFs-based humidity sensors, the CMP sensor exhibits unique technical characteristics. Further, the humidity sensing mechanism of the CMP sensor was investigated through a combination of material characterization, water adsorption kinetics, carrier concentration, complex impedance spectroscopy (CIS) plot, and equivalent circuit (EC). As proof of concept, by monitoring the humidity on the finger surface, we evaluated the potential applications of the CMP sensor in noncontact sensing. Moreover, a palmar hyperhidrosis diagnosis system based on the CMP sensor was assembled, realizing quick, intuitive, and accurate diagnosis the severity of palmar hyperhidrosis. It is believed that this work provides a reasonable strategy for constructing high-performance humidity sensors.

The present study focuses the development and the evaluation of humidity sensors based on reduced graphene oxide—tin oxide (rGO-SnO2) nanocomposites, synthesized by a simple redox reaction between GO and SnCl2. The physico-chemical characteristics of the nanocomposites were analyzed by XRD, TEM, FTIR, and Raman spectroscopy. The formation of SnO2 crystal phase was observed through XRD. The SnO2 crystal phase anchoring to the graphene sheet was confirmed through TEM images. For the preparation of the sensors, tantalum substrates were coated with the sensing material. The sensitivity of the fabricated sensor was studied by varying the relative humidity (RH) from 11% to 95% over a period of 30 days. The dependence of the impedance and of the capacitance with RH of the sensor was measured with varying frequency ranging from 1 kHz to 100 Hz. The long-term stability of the sensor was measured at 95% RH over a period of 30 days. The results proved that rGO-SnO2 nanocomposites are an ideal conducting material for humidity sensors due to their high sensitivity, rapid response and recovery times, as well as their good long-term stability.

Capacitive humidity sensor is designed on interdigitage electrodes (IDEs) by lithography process for nice humidity absorption and desorption. This paper proposed the IDEs humidity sensor base on bilayers sensing of graphene oxide (GO) structure by dip coating method. Each GO layer is held by covalent-bond forces from adhesive layer. It demonstrates durable of sensing layer material. Raman spectroscopy analysis is exhibited on GO presence and scanning electron microscope (SEM) explored on the GO bilayers structure. The IDEs/GO bilayers humidity sensor demonstrated ultrahigh sensitivity (up to 2014.61%) and linear responses at relative humidity (RH) ranges 10 to 70% while IDEs/GO single layer showed exponential responses. Moreover, it significantly improved on response (12 sec) and recovery times (18sec), a little hysteresis (up to 46.77%) and stable repeatability. Finally, the durable of IDEs/GO bilayers humidity sensor is exhibited by long-term ability measurement (time period 35 days). Therefore, these characteristics of GO bilayers structure base on adhesive layer are clearly demonstrated high performances for alternatively used with humidity sensor applications.