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The NH3 sensor is of great significance in preventing NH3 leakage and ensuring life safety. In this work, the Pd-decorated ZnO hexagonal microdiscs are synthesized using hydrothermal and annealing processes, and the gas sensor is fabricated based on Pd-decorated ZnO hexagonal microdiscs. The gas-sensing test results show that the Pd-ZnO gas sensor has a good response to NH3 gas. Specifically, it has a good linear response within 0.5–50 ppm NH3 at the optimal operating temperature of 230 °C. In addition, the Pd-ZnO gas sensor exhibits good repeatability, short response time (23.2 s) and good humidity resistance (10–90% relative humidity). This work provides a useful reference for developing an NH3 sensor. [ABSTRACT FROM AUTHOR]

Much effort has focussed on enhancing the humidity-sensing performances of humidity sensors, but their fabrication using facile and low-cost methods is also desirable. In this work, a humidity sensor based on a naturally available nanomaterial, sepiolite nanofibers (SNFs), was facilely fabricated without any expensive raw materials or complex processes. Characterization results show that SNFs have a natural slender nanofiber structure (diameter 20–50 nm) and abundant hydrophilic functional groups (–OH). The results of humidity-sensing tests show that the SNF humidity sensor has outstanding humidity-sensing properties (i.e. large response, good linearity and repeatability) within the relative humidity range from 10.9% to 91.5% at room temperature (25 °C). This work presents a moderate and cost-effective strategy for the fabrication of high-performance humidity sensors using the natural SNF nanomaterial. [ABSTRACT FROM AUTHOR]

Combining advanced energy-generation technologies with sensors to develop self-powered sensing shows great potential in intelligent electronics, but sluggish response kinetics and low output are the main obstacles. Herein, we design a hyaluronic acid (HA)-induced crumpling of Nb 2 CT x nanosheet to construct hydrogen bond conduction network, and develop it for fast humidity sensing based on primary battery. The in-situ formation of organic/inorganic hybrid interphase with crumpling structure by electrostatic flocculation is capable to provide abundant adsorption sites and accelerate proton (H+) transport. Benefited from these, the Nb 2 CT x /HA primary battery-based humidity sensor (PBHS) not only exhibits an outstanding response and recovery speed (15.1 s and 3.4 s at 72.0 % relative humidity (RH)), high response (0.7 V), low hysteresis (3.6 % RH), but also can be also used as a nanogenerator with a power of 0.96 μW and sustainable voltage output for 12 h. Furthermore, the multifunctional applications are demonstrated in medical assisted monitoring, health care, intelligent sensing, and green-energy generation. This work offers a new insight into PBHS design and the development of high-performance power-generation humidity sensor. [Display omitted] • An Nb 2 CT x /hyaluronic acid (HA) crumpling structure is designed by electrostatic flocculation. • The crumpling Nb 2 CT x /HA-based primary battery is proposed for fast humidity sensing. • The PBHS shows great potential in intelligent monitoring, health care, and green-energy generation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A neuron-like composite film based on Nb 2 CT x /sodium alginate is developed by electrospinning. • The electrospun film has the dual functions of power generation and humidity sensing. • A prototype of self-powered humidity sensing system is constructed for visual measuring. Existing wearable sensing electronics generally require to connect a battery for the power supply. Despite many years of effort, it still remains a great challenge to develop self-powered sensing systems without external power supplies. Herein, we develop a neuron-like MXene Nb 2 CT x /sodium alginate (Nb 2 CT x /SA) composite films prepared by an electrospinning approach. The Nb 2 CT x /SA composite film not only can be used to fabricate a high-performance electronic humidity sensor, but also to construct a moisture-triggered nanogenerator with a sustainable voltage output. Importantly, the humidity sensor is demonstrated to be portable and compatible for applications in respiration assessment, noncontact monitoring and intelligent alarm. More importantly, by simply integrating the Nb 2 CT x /SA film-based sensor/nanogenerator with a capacitor and light-emitting diode (LED), a prototype of self-powered sensing system capable of indicating different relative humidity (i.e., low, medium or high) through the LED's brightness without external power supplies is demonstrated. This work not only demonstrates the design and fabrication of a smart self-powered humidity sensing system, but also opens a new avenue for development of next-generation intelligent wearable electronics. [ABSTRACT FROM AUTHOR]

Abstract: A supramolecular cryptophane-A-based quartz crystal microbalance (QCM) gas sensor has been developed. Supramolecular cryptophane-A was synthesized from vanillyl alcohol using a double trimerisation method and deposited on a QCM device via electrospray method. The sensor was exposed to various concentrations of CH4 gas and other gases operated at different temperatures. The influence of humidity was also examined. The sensor''s response showed that it is selective to methane gas. A fast response and recovery was observed at room temperature. Detection limit for methane is 0.05% (v/v). The mechanism of the interactions between CH4 gas and cryptophane-A was discussed preliminarily. [Copyright &y& Elsevier]

Abstract: A quartz crystal microbalance (QCM) modified with poly(vinylidene fluoride) (PVDF) was fabricated and used for detection of dimethyl methylphosphonate (DMMP) vapor, a simulant of nerve agents using a drop-coating method. Measurements were based on the frequency shifts due to the adsorption of DMMP vapor on the surface of the modified electrodes. It was found that frequency shifts were linear to the concentrations of analyte in the range of 5–60ppm with a correlation coefficient of above 0.997. The influences of temperature and humidity on the sensors were also examined. Results showed that the sensitivity to DMMP vapor was almost identical in various humidity circumstances, and the sensitivity was higher in a lower temperature range. [Copyright &y& Elsevier]

[Display omitted] • The humidity sensor based on daily writing carbon ink is firstly fabricated. • The humidity sensor has a wide detection range (2–95 % RH). • The humidity senor has a low detection limit (2% RH). • The humidity senor has a high detection resolution (1% RH) • The positive humidity sensing property of the humidity sensor is analyzed. For a long time, the application of the daily writing carbon ink is mainly reflected on writing and painting, and rarely used in electronic field. Herein, we analyzed the physical and chemical properties of the daily writing carbon ink. Characterization results show that the daily writing carbon ink is mainly composed of carbon nanoparticles, and has good hydrophilicity and very stable dispersion. Further, the humidity sensor was fabricated using daily writing carbon ink and its humidity sensing performances were investigated at room temperature (20 °C). The testing results show that the resistance of the humidity sensor increases with the increase of relative humidity (RH), showing a positive humidity sensitive characteristic. Compared with most of the reported humidity sensors, the carbon ink humidity sensor has better humidity sensing performances on wide detection range (2 − 95 % RH), low detection limit (2% RH) and high detection resolution (1% RH). Finally, the positive humidity sensitive characteristic of the humidity sensor is analyzed using electron tunneling effect (blocking of water molecular membrane). This work not only demonstrates a facile and low-cost way to realize high performance humidity sensor, but also provides a pathway for the research of humidity sensor with positive response characteristic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The power generation humidity sensor based on primary battery structure is developed. • The humidity sensor can spontaneously output voltage at 41.1–91.5% RH. • The humidity sensor can output 0.58 V at 91.5% RH. • The humidity sensor has potential applications in respiratory rate and diaper monitoring. The power generation humidity sensors based on the principles of triboelectricity, piezoelectricity and ion diffusion have been proposed in recent years. However, these power generation humidity sensors usually have complex preparation process and application limitation. Here we develop a simple Cu/NaCl paper/Al power generation (CPG) humidity sensor based on primary battery structure. Combined with the hydrophilicity of paper and the chemical reactions of primary battery, the CPG humidity sensor can spontaneously output voltage and shows good humidity sensing properties at 41.1–91.5% relative humidity (RH). Specifically, a single CPG humidity sensor can output 0.58 V at 91.5% RH with a power of 1.33 μW. Benefiting from good humidity sensing performance and material safety, the CPG humidity sensor has been proved to have potential applications in respiratory rate, diaper monitoring and non-contact switch. Through the series integration of 8 CPG humidity sensors, it can realize an output voltage of 4.21 V and charge the capacitor, proving the potential self-powered characteristic of the CPG humidity sensor. This research not only proposes a simple, low-cost and eco-friendly power generation humidity sensor, but also opens a new pathway for power generation humidity sensor. [ABSTRACT FROM AUTHOR]

Abstract: A new polysiloxane material, polymethyl[3-(2-hydroxy)phenyl] siloxane (PMPS), was synthesized. The PMPS is a linear polysiloxane polymer functionalized with o-allyl phenol group. The chemoselective polymer was spin-coated on a 434MHz surface acoustic wave (SAW) device for detection of dimethyl methylphosphonate (DMMP) vapor ranging from 5 to 40ppm. It was found that the frequency shifts were linear to the vapor concentrations with a high sensitivity of 3kHz/ppm. Fast response of 30s and good reproducibility were achieved as well. The influence of humidity on the sensor response was also examined. The results showed that the sensitivity decreased about 1/2 when tested in 70% RH wet air than in dry nitrogen. [Copyright &y& Elsevier]

• Novel SrGe 4 O 9 nanowires were combined with PANI (PSN) for NH 3 detection at 25 °C. • The sensitivity of the PSN sensor was twice that of PANI sensor at 0.2–10 ppm NH 3. • The response time of the PSN sensor was reduced to 0.38 of the PANI sensor at most. • The sensor possessed ultra-low detection limit of 250 ppt toward NH 3. Detection limit as an important parameter of gas sensors, much effort has been devoted to developing high-performance gas sensors with low detection limit. However, the development of gas sensors with ppt-level detection limit still faces enormous challenges. In this work, a flexible and ultra-highly sensitive ammonia (NH 3) sensor based on polyaniline/SrGe 4 O 9 nanocomposites (PSN) was successfully fabricated via a facile in situ chemical oxidation polymerization method. When exposed to 0.2–10 ppm NH 3 at 25 °C in 60% relative humidity (RH), the PSN sensor showed larger sensitivity (20.59% ppm−1) than that of PANI sensor (9.82% ppm−1). The response of the PSN sensor (16%) was two-fold higher than that of the PANI one (8%) to 0.2 ppm NH 3 at room temperature. Meanwhile, the response time of the PSN sensor (24 s) was reduced to up to a third of that of the PANI sensor (64 s) for 800 ppb NH 3. Additionally, the flexible PSN sensor exhibited good reproducibility, satisfactory long-term stability, excellent selectivity and outstanding flexibility to NH 3 at room temperature. Significantly, the PSN sensor presented the ultra-low detection limit of 250 ppt toward NH 3. Such outstanding gas-sensing properties were attributed to the unique hierarchical architecture with abundant mesoporous and the formation of p-n heterojunction at the interface between p-type PANI and n-type SrGe 4 O 9. This research provides new strategies for developing high-performance NH 3 sensors with supersensitive and ultra-low detection limit. [ABSTRACT FROM AUTHOR]

• PANI/Ti 3 C 2 T x hybrid films is firstly designed toward agricultural application. • High-performance NH 3 -sensing properties are achieved. • Synergistic effects and improved protonation degree in the hybrids are discussed. The monitoring of ammonia (NH 3) produced in agricultural fields is of great importance due to its huge threat to ecological environment and human health, yet routine monitoring technologies rely on manual completion and complex agricultural environment brings great challenges to the application feasibility of gas sensors. Herein, a flexible chemiresistive gas sensor based on polyaniline (PANI)/Ti 3 C 2 T x hybrid sensitive films is developed toward agricultural NH 3 volatilization monitoring. The hybrid film was deposited on the flexible polyimide substrate by an in-situ self-assembly method. The sensor shows high sensitivity, low detection limit, excellent repeatability, high selectivity and good air stability, which could be attributed to the gas-sensing enhancement effects of PANI/Ti 3 C 2 T x Schottky junction and improved protonation degree of PANI in the hybrids. Especially, the sensor exhibits excellent NH 3 -sensing properties to 20–80 % relative humidity (RH) environments at a temperature range of 10–40 ℃, making it promising for practical agricultural applications. Furthermore, the application feasibility of the sensor to ammonia volatilization monitoring is verified through agricultural simulation experiments. This work provides a fast and accurate gas sensor methodology toward unattended agricultural application, which is an important supplement to the existing technical methods and may greatly pushes forward the development of modernized intelligent agriculture. [ABSTRACT FROM AUTHOR]

The electrochemical power generation humidity sensor has received widespread attention due to its zero-power consumption. In this work, we propose an electrochemical power generation humidity sensor using WS 2 nanoflakes as the humidity sensing material, without adding additional alkali metal salts (such as LiCl and NaCl) or other added materials or functional group treatments. The results show that the humidity sensor exhibits wide humidity detection range (18.7%−91.5% relative humidity (RH)), fast response/recovery speeds (8.4/5.2 s), good repeatability (20 cycles) and small humidity hysteresis (∼3.4% RH) at room temperature of 25 °C. The output voltage of the humidity sensor is 0.47 V at 91.5% RH. Combined with good water molecule adsorption and proton conductivity of the WS 2 nanoflakes, the humidity sensing and power generation mechanism of the WS 2 electrochemical power generation humidity sensor can be explained by the redox reactions occurring at the positive and negative electrodes (Cu and Al). Finally, we demonstrate the application of the humidity sensor in respiratory detection. This work provides a useful approach for fabricating electrochemical power generation humidity sensor with a simple single humidity sensing material. [Display omitted] • The electrochemical power generation humidity sensor is fabricated based on WS 2 nanoflakes. • The WS 2 electrochemical power generation humidity sensor has short response/recovery times of 8.4/5.2 s. • The WS 2 electrochemical power generation humidity sensor can be used for respiratory detection. [ABSTRACT FROM AUTHOR]

• PPy/N-MWCNT gas sensor after annealing treatment was synthesized for NO 2 sensing. • The response of optimal hybrids exhibited 44.12 times than that of unannealed one. • The effect of annealing treatment on NO 2 sensing was discussed. A flexible NO 2 gas sensor based on a polypyrrole/nitrogen-doped multi-walled carbon nanotube (PPy/N-MWCNT) composite film was successfully prepared on PI substrates using a combined in situ self-assembly and annealing treatment method. After annealing at 350 °C, the gas sensor exhibited a high response of 24.82% ((R g −R a)/R a ×100%) under 5 ppm of NO 2 , which is 44.12 times greater than that of the unannealed sensor. The PPy/N-MWCNT gas sensor exhibited excellent repeatability, remarkable selectivity, good long-term stability, and acceptable flexibility. Furthermore, the effect of the relative humidity on the gas sensing properties was examined. The excellent gas sensing performances of the sensor were attributed to the enriched adsorption sites due to degradation of the amount of stacked PPy structures on the surface of the N-MWCNTs after the annealing treatment. The results demonstrated that PPy/N-MWCNT composite films are highly promising for potential applications in the field of NO 2 gas sensing. [ABSTRACT FROM AUTHOR]

Highlights • Carbon nanotubes modified by poly- l -lysine is proposed to develop humidity sensor. • The response is improved 600 times by poly- l -lysine modification at 91.5% RH. • The composite film based humidity sensor is of multi-applications in human activity. Abstract Multi-walled carbon nanotubes (MWCNTs) as one of excellent conductive and poor-hydrophilicity materials are difficult to be directly used in humidity sensing field. In order to obtain MWCNTs with both good semiconducting characteristic and improved humidity sensing performances, MWCNTs composite film via poly- l -lysine (PLL) modification was developed for humidity detection. The humidity sensing properties of the as-fabricated sensor were investigated at room temperature (25 °C) within the relative humidity (RH) range from 0 to 91.5% RH. Due to abundant hydrophilic functional groups and conduction-blocking effect of PLL, the resistive-type humidity sensor based on MWCNTs/PLL film exhibits a good humidity sensing response of 659.97% at 91.5% RH. Especially, the resistance of the humidity sensor displays a clear positive humidity coefficient (PHC) that caused by the swelling effect of PLL. Finally, various potential applications of the humidity sensor were further performed for the real-time monitoring of skin humidity, baby diaper wetting, spatial humidity distribution and human exhaled breath, which provide an ingenious strategy for the practicability of the humidity sensor. [ABSTRACT FROM AUTHOR]

Humidity sensing material is a key component of humidity sensor. In this short communication, we synthesized zirconium phosphate (ZrP) nanoplates and investigated their capacitive humidity sensing performance. The results show that the ZrP humidity sensor exhibits a wide response range (10.9–91.5 % relative humidity (RH)), high response (2409 at 91.5 % RH), short recovery time (9 s), and good repeatability at the optimal working frequency of 100 Hz and room temperature of 25 °C. In addition, the humidity sensing mechanism of the ZrP humidity sensor is analyzed by combining the characterization, dielectric constant and impedance testing results. [Display omitted] • The zirconium phosphate (ZrP) nanoplates are synthesized using a simple hydrothermal method. • The ZrP humidity sensor shows a wide humidity sensing response range (10.9–91.5 % RH). • The ZrP humidity sensor shows high response (2409 at 91.5 % RH) and short recovery time (9 s). [ABSTRACT FROM AUTHOR]

In this work, a fundamental new approach for humidity detection was proposed. By coupling triboelectric nanogenerator (TENG) with resistive humidity sensor, the degree of ambient moisture can be actively detected at room temperature, where the voltage drops across the interdigital electrodes (IDEs) has a reversely proportional relationship with relative humidity. The prepared self-powered triboelectric humidity sensor (THS) holds high humidity response of ∼7, fast response/recovery time of 2.8 s and 3.5 s, stable repeatability and excellent long term stability. With respect to selectivity, the response of THS to gaseous water was at least 2-fold higher than those for other gases. Furthermore, through a signal processing circuit, a self-powered humidity alert system was developed for real-time monitoring the ambient humidity. Finally, the underlying working principle of the proposed sensor was discussed in detail. This research not only provides a simple, low-cost and efficient means in humidity sensing but also greatly broadens the applicability of TENGs as self-powered active sensors. [ABSTRACT FROM AUTHOR]

The power generation humidity sensor has received great attention, however, how to improve its humidity sensing performance (e.g., detection range and response speed) is still facing many challenges. Herein, we propose a simple power generation humidity sensor using NaCl as electrolyte and halloysite nanotubes (HNT) as humidity sensing material. The results show that the introduction of HNT can significantly improve the humidity sensing performance of the humidity sensor based on bare NaCl electrolyte. Specifically, the NaCl/HNT humidity sensor has a wide detection range (10.9 −91.5% relative humidity (RH)), short response time (11.3 s), and good repeatability (20 cycles). The output voltage of the NaCl/HNT humidity sensor reaches 0.537 V at 91.5% RH, and the corresponding maximum power is 1.56 μW. In addition, the NaCl/HNT humidity sensors with series integration can charge the capacitor at high humidity, and the NaCl/HNT humidity sensor can be used for monitoring respiratory patterns. This work provides a useful strategy for fabricating high-performance power generation humidity sensor. [Display omitted] • The power generation humidity sensor based on NaCl/halloysite nanotubes is developed. • The humidity sensor has a wide humidity detection range of 10.9−91.5% RH. • The humidity sensor can output 0.537 V at 91.5% RH. • The humidity sensor has a short response time of 11.3 s • The humidity sensor can be used for monitoring respiratory patterns. [ABSTRACT FROM AUTHOR]

Gas sensors have made great progress in gas sensing performances (such as response, sensitivity, detection limit and response speed), but they are generally affected by temperature and humidity. Here, we proposed a local Gaussian process regression with small samples for temperature and humidity compensation of gas sensors. Specifically, the above method is used to compensate the temperature and humidity influence of the polyaniline-cerium dioxide (PANI-CeO 2) ammonia (NH 3) sensor (10–50 °C, 20%−70% relative humidity (RH); It should be noted that the law of humidity influence is messy when the RH is greater than 70%.). The adaptive matching results show that the optimal number of K-neighbor points is 15, which greatly reduces the amount of computation. The temperature and humidity compensation results show that the predicted concentration achieved high accuracy (the mean absolute error is 0.19 ppm, and the mean relative error is 0.65%), and the absolute error showed a good normal distribution (N∼(0.00047, 0.3772)). This work provides an effective compensation strategy with small samples, high precision and low computational cost for the temperature and humidity influences of gas sensor. • The compensation method of temperature and humidity effect on gas sensor is systematically studied. • The optimal number of samples for Gaussian process regression is 15, and concentration prediction time is 0.06 s. • Predicted concentration after temperature and humidity compensation achieves high accuracy. [ABSTRACT FROM AUTHOR]

In this work, a novel graphene oxide (GO)/Poly(ethyleneimine) (PEI) layered film was designed and prepared on quartz crystal microbalance (QCM) for humidity detection through a feasible spray process at room temperature. The morphological and chemical properties of GO/PEI layered film were examined by means of field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR), and Raman spectroscopy. The effect of GO solution concentration on humidity-sensing characteristics was investigated and an optimized QCM humidity sensor was obtained. An intriguing phenomenon was observed that a three-dimension structure of GO sheets was formed due to the redissolution effect at the interface between PEI and GO layers. Results showed that a layered film QCM sensor exhibited superior humidity sensing properties than a pure GO film or a PEI one including high response, short response/recovery time, small humidity hysteresis (less than 1%RH), excellent repeatability, selectivity and long-term stability. Moreover, the humidity features of sensors were also researched via the method of impedance analysis. Lastly, a convincing sensing mechanism model was established to interpret the enhanced humidity-sensing performance of layered film sensors. The results demonstrated the potential application of GO/PEI layered films to humidity sensors. [ABSTRACT FROM AUTHOR]

Metal phosphide has been widely exploited in the field of energy storage and catalysis instead of chemical sensors. In this work, Ni-Co-P hollow nanobricks (HNBs) was developed via template synthesis method followed by etching and phosphating treatments. The hierarchical morphology and composition of the Ni-Co-P HNBs were respectively characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen sorption analysis and transmission electron microscopy (TEM). High sensitivity (~ 3.6 kΩ / % RH), low hysteresis (~ 3% RH) and good repeatability were achieved in a wide moisture range from 0% RH to 97.5% RH. By adjusting the ratio of Ni and Co, humidity sensing performance can be efficiently modulated. The optimal humidity sensing properties were attained at a ratio of Ni and Co of 1:5. Finally, the as-prepared sensor demonstrates great capability in respiratory analysis and noncontact human-machine interfacing. This work opens up a new paradigm for developing high-performance wearable sensing devices. [Display omitted] • Metal phosphides Ni-Co-P are employed to fabricate humidity sensor. • The hierarchical hollow nanobricks endows a large surface area and abundant adsorption sites to interact with water molecules. • The optimal humidity sensing properties are attained at a ratio of Ni and Co of 1:5. • The sensor enables non-contact monitoring of breath and limb motions. [ABSTRACT FROM AUTHOR]

Power generation humidity sensor has attracted attention in recent years due to its great potential in self-powered electronics. Herein, combining with the working mechanisms of primary battery and humidity sensor, we propose a facile primary battery-based device (PBD) with dual functions of humidity sensing and power generation, which is fabricated by copper adhesive tape (as positive electrode), lithium chloride (LiCl) active layer (for adsorption and conduction), and aluminum adhesive tape (as negative electrode) on the ceramic substrate. By regulating the concentration of the LiCl, 1.0 mol/L LiCl-based PBD can be developed as a humidity sensor, which exhibits a sensitivity of 4.86 mV/RH and good linearity in a wide detection range (10.9%−91.5% relative humidity) at room temperature (25 °C). Moreover, 2.0 mol/L LiCl-based PBD can be developed as a power generator due to its high output of 0.55 V. Finally, multifunctional applications (such as respiratory monitoring, non-contact switch, lighting light-emitting diode (LED)) of the PBDs are demonstrated. This work not only provides a facile avenue to develop dual-function devices, but also exhibits a great potential in self-powered humidity sensors. [Display omitted] • A primary battery-based device (PBD) is proposed with low cost and simple process. • The PBD exhibits dual functions of humidity sensing and power generation. • As a sensor, the PBD shows a wide detection range, good linearity and repeatability. • The primary battery-based sensor shows potential in multifunctional applications. [ABSTRACT FROM AUTHOR]

The synthesis of polyaniline (PANI) composites is an effective method to improve the ammonia (NH 3) gas sensing performance of PANI, and it is of great significance to develop a simple method to prepare PANI composites. Herein, the PANI/halloysite nanotubes (PANI/HNTs) composite was prepared via a simple in-situ polymerization method. Morphology characterization results show that the HNTs are covered by PANI to form a porous three-dimensional structure. Especially, the specific surface areas of the PANI and PANI/HNTs are 15.892 and 25.899 m2/g, respectively, and the specific surface area of PANI has been greatly improved (1.63 times). Gas sensing properties test results show that the PANI/HNTs sensor exhibits larger response (1.60 times) and shorter response/recovery times (0.93/0.6 times) than that of the PANI sensor to 10 ppm NH 3 (25 °C, 50% relative humidity). In addition, the PANI/HNTs sensor exhibits low detection limit of 10 ppb NH 3 and excellent selectivity. The enhanced NH 3 sensing performance of PANI can be attributed to the unique hollow structure and large specific surface area of HNTs. In this work, a simple method is proposed to improve the NH 3 sensing performance of PANI only by morphology modification. Meanwhile, it provides an idea for the application of HNTs in the field of gas sensors. • The NH 3 sensing performance of PANI is improved by a facile morphology modification strategy. • PANI/HNTs sensor was prepared by the in-situ polymerization method. • PANI/HNTs sensor exhibits higher NH 3 sensing response than the PANI sensor. • PANI/HNTs sensor has an ultra-low detection limit of 10 ppb NH 3. [ABSTRACT FROM AUTHOR]

As one of the obstinate problems for gas sensors, humidity interference has troubled researchers for decades. In this short communication, an n-type semiconductor Ag 2 Te is selected as the NO 2 gas sensing material. Through the hydrothermal method, Ag 2 Te nanowires are synthesized and then spin-coated on an integrated electrode to fabricate gas sensor. The sensing properties of the Ag 2 Te sensor are investigated at room temperature (~25 °C) and 50% relative humidity (RH), revealing its good sensing characteristics towards NO 2 with a rapid response (10.2 s towards 5 ppm NO 2), low limit of detection (ppb-level), and repeatable detection. It is worth noting that the Ag 2 Te sensor is humidity resistible. The resistance of Ag 2 Te sensor in air and 1 ppm NO 2 are both stable in humidity range from 10% to 90% RH with resistance variation of 1.84%and 0.95% respectively, demonstrating the humidity-resistant property of the Ag 2 Te sensor. This work is expected to provide a new pathway for the development of room temperature humidity-resistant gas sensors. [Display omitted] • The room temperature NO 2 gas sensor based on Ag 2 Te nanowires is firstly reported. • The Ag 2 Te gas sensor has a ppb-level NO 2 detection ability. • The Ag 2 Te gas sensor has fast response speed and complete recovery feature. • The Ag 2 Te gas sensor has an excellent humidity resistance (10–90% RH). [ABSTRACT FROM AUTHOR]

The accuracy and reliability of gas sensor are directly by temperature and humidity. In this study, an improved deep Back Propagation (BP) neural network was designed to lower the impact of environmental factors on NO 2 gas sensor based on PbS nanoparticles sensitive film. The contradiction between high performance and low time complexity was usually faced by current compensation methods of gas sensor. Moreover, poor self-learning ability always resulted in more recognition errors. To solve the above problems, a 14-layer deep BP neural network model was constructed after hyperparameter searching. Stochastic Gradient Descent (SGD) algorithm with Mini-batch algorithm was adopted to well balance the model performance and the training time complexity, resulting in 76.68% performance improvement and nearly 6 times training time reduction after 1000 epochs, respectively. Softplus activation function was combined with Adam optimizer to further improve the model performance with a good recognition accuracy (1.37% relative error, corresponding to 0.0087 Mean Square Error (MSE)). The self-learning and self-adaptability of the improved deep BP neural network made it an excellent compensation method for the gas sensor applied in complex environments. • An improved deep BP neural network was designed to lower the environmental factors' impact on PbS based NO 2 gas sensor. • SGD algorithm with mini-batch was chosen to balance the model performance and the training time complexity. • Softplus activation function combined with Adam optimizer were selected to obtain accurate prediction of NO 2 concentrations. • Self-adaptation and self-learning capabilities of the model helped to achieve good recognition accuracy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The humidity sensor based on 3D mesoporous Co 3 O 4 hollow polyhedron is prepared. • The Co 3 O 4 humidity sensor exhibits an ultrafast response time of 1.0 s. • The Co 3 O 4 humidity senor has high detection resolution of 1% RH. • The Co 3 O 4 humidity sensor is of multi-applications in human activities. In this work, the three-dimensional (3D) hollow mesoporous Co 3 O 4 was successfully prepared by calcining the Co-based zeolitic imidazolate framework-67 (ZIF-67). As-obtained Co 3 O 4 inherited the rhombohedral framework structure of ZIF-67 and possessed mesoporous and hollow structure. Further, the humidity sensor based on Co 3 O 4 was fabricated, and its humidity sensing properties were investigated at room temperature (25 °C). The results indicated that the Co 3 O 4 humidity sensor exhibited high humidity sensing performance with a wide linear detection range (10%−95% relative humidity (RH)), small humidity hysteresis (2.6% RH), and fast response/recovery times (1.0/13.5 s). In particular, the Co 3 O 4 humidity sensor was of high detection resolution (1% RH). The excellent performance was attributed to the strong hydrophilicity and the unique 3D porous structure of Co 3 O 4. In addition, the potential applications of the fabricated Co 3 O 4 humidity sensor in skin humidity, simulated diaper, human breathing, and non-contact switch were demonstrated. This work provides a promising humidity sensing material for fabricating high-performance humidity sensors. [ABSTRACT FROM AUTHOR]

• A novel Nb 2 CT x /PANI-based NH 3 sensor directly driven by a facile TENG is proposed. • The Nb 2 CT x /PANI-2 sensor exhibits a superior sensitivity (2.87 % ppm−1) toward a wide sensing range of 1–100 ppm NH 3. • High RH influence on sensing response of the Nb 2 CT x /PANI-2 sensor is 8.94 times lower than that of PANI one. As a new member of the MXene family, two dimensional (2D) niobium carbide MXene (Nb 2 CT x) holds a promising potential in gas detection due to the abundant surface terminated groups and large specific surface area. In this work, a selective NH 3 sensor based on polyaniline (PANI) nanofibers-supported Nb 2 CT x nanosheets (Nb 2 CT x /PANI) directly driven by a facile triboelectric nanogenerator (TENG) is proposed to provide a possible method for enhancing the NH 3 -sensing response. In addition, the gas sensing properties have been optimized by regulating different spray volumes of Nb 2 CT x nanosheets. Test results demonstrate that the NH 3 -sensing response and the response speed of the Nb 2 CT x /PANI-2 sensor have been evidently improved, indicating a good linear response toward a wide sensing range of 1–100 ppm NH 3 at room temperature (∼25℃) under 87.1 % relative humidity (RH). Moreover, the influence of high humidity on gas sensing response of the Nb 2 CT x /PANI-2 sensor has been efficiently reduced due to the occupied active sites for water adsorption caused by intermolecular hydrogen bonds between PANI and Nb 2 CT x. Finally, mechanism of the enhanced gas sensing properties has been further investigated, which should be mainly attributed to the gas sensing improvement effect of p-n junction. This work is expected to offer a useful reference for the development of high-performance Nb 2 CT x /polymer-based gas sensors. [ABSTRACT FROM AUTHOR]

Breath analysis is an attractive strategy that holds tremendous potential to achieve non-implantable physical health management enabled by flexible humidity sensors for breathing behaviors (e.g., continuity, frequency) related to disease monitoring and chemiresistive gas sensors related early disease diagnosis. Compared to other techniques for breath component detection, non-invasive breathing diagnostics based on chemical sensors can offer several advantages like miniaturization, low power consumption, simple structure and cost-saving, which is helpful to enhance the portability of practical tests. Although extensive research has been carried out over the past two decades to improve sensing performances of breath gas sensors, many problems need to be further addressed when it comes to clinical disease diagnosis. Developing integrated gas sensor arrays have become one of the efficient solutions to improve detection accuracy. To get rid of external power supply, various novel sensors combining with self-powered technology are designed to exhibit a desirable development prospect in breath analysis. Thus, this review aims to summarize the latest research advances on wearable humidity-enabled breathing behaviors monitoring and typical biomarker gases-based disease screening, and also provides the prospects of future development from individual sensors to integrated devices and self-powered health monitoring systems. [ABSTRACT FROM AUTHOR]

• The humidity sensor based on halloysite nanotubes (HNTs) is firstly fabricated. • The HNTs humidity sensor has a large response of five orders of magnitude. • The response time of the HNTs humidity senor is only about 0.7 s. • The HNTs humidity senor has wide humidity detection range of 0–91.5% RH. • The HNTs humidity senor has an obvious response to very low RH of 7.2%. Benefiting from the development of nanomaterials synthesis technology, the performance of many electronic devices, including humidity sensors, has been improved greatly. However, the synthesis of nanomaterials usually involves complex processes, expensive raw materials and even toxic reagents. Herein, the natural nanomaterials of halloysite nanotubes (HNTs) are deliberately selected for the fabrication of high-performance humidity sensor. Characterization results show that the HNTs have good hydrophilicity, hollow tubular nanostructure and large specific surface area, which contribute to humidity sensing performance of the humidity sensor. Further, the humidity sensor based on HNTs is fabricated and its humidity sensing properties are tested at the room temperature (25 °C). The results show that the impedance variation of the HNTs humidity sensor is five orders of magnitude within the humidity range from 0% to 91.5% relative humidity (RH) at the optimum working frequency (100 Hz), and its response time is only about 0.7 s. Notably, the HNTs humidity sensor exhibits wide humidity detection range of 0–91.5% RH, very low RH (7.2%) response characteristic and good linear responses at 0–28.8% and 28.8–91.5% RH. This work provides a simple, low-cost and environmental-friendly strategy for fabricating high-performance humidity sensor by exploring the natural nanomaterials like HNTs. [ABSTRACT FROM AUTHOR]

• The high performance humidity sensor based on attapulgite is firstly fabricated. • The impedance change of the sensor is more than five orders of magnitude. • The response time of the attapulgite humidity senor is only 3 s. • The attapulgite humidity senor can respond to relative humidity as low as 7.2 %. Attapulgite, as a natural mineral with excellent physicochemical properties, abundant reserves, and low price, has been widely used in industry and agriculture. With the advancement of research, novel applications of attapulgite are still emerging. In this work, a low-cost humidity sensor based on attapulgite is firstly fabricated. The results show that the attapulgite humidity sensor exhibits excellent humidity sensing performance at room temperature (25 °C). The impedance variation of the sensor is more than five orders of magnitude within the humidity range from 0 % to 91.5 % relative humidity (RH) at the excitation frequency of 100 Hz and the response time (adsorption process) of the senor is only 3 s. Especially, the sensor not only has a good linear response to high RH (28.8 %–91.5 %), but also to low RH (0 %–28.8 %). Moreover, the sensor exhibits small humidity hysteresis (∼3.4 % RH), good repeatability and long-term stability. This work expands the novel application of attapulgite on humidity sensors, and also brings opportunities for the development of high performance and low-cost humidity sensors. [ABSTRACT FROM AUTHOR]

• The gas sensor based on based on TiO2/Ti3C2Tx bilayer film is firstly fabricated. • The TiO2/Ti3C2Tx gas sensor can respond to 0.5 ppm NH3 at room temperature. • Enhanced NH 3 sensing response mechanism of the TiO 2 /Ti 3 C 2 T x is discussed. As a novel 2D material, Ti 3 C 2 T x has been proved to be promising in the field of room temperature ammonia (NH 3) sensors by theoretical calculation and experimental testing. However, its NH 3 sensing properties still need to be enhanced. In this short communication, the gas sensor based on TiO 2 /Ti 3 C 2 T x bilayer film is fabricated for enhancing the NH 3 sensing properties of pure Ti 3 C 2 T x. The results show that the TiO 2 /Ti 3 C 2 T x sensor exhibits larger response value (1.63 times) and shorter response/recovery times (0.65/0.52 times) that of pure Ti 3 C 2 T x sensor to 10 ppm NH 3 at room temperature of 25 °C (60.8% relative humidity). Meanwhile, the TiO 2 /Ti 3 C 2 T x sensor is of good linear response (R2 = 0.95596) at 2–10 ppm NH 3 and can respond to NH 3 as low as 0.5 ppm. This work is expected to provide useful reference for the development of high performance Ti 3 C 2 T x -based NH 3 sensors. [ABSTRACT FROM AUTHOR]