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Low humidity detection has been a great challenge in the field of humidity sensing. In recent years, polyelectrolytes have been proven to be promising materials for highly sensitive humidity sensors. In this work, cross-linked poly(ionic liquid)s (PILs) were prepared for low humidity detection. The strong hydrophilicity of PILs contributes to humidity sensing while the cross-linked structure guarantees the stability of the sensing film. The optimized sensor shows high response (48.0) in 5–35% RH, with short response/recovery time (1 s/10 s) and a small humidity hysteresis (0.2% RH). The possible sensing mechanism of the sensors was discussed. • Cross-linked poly(ionic liquid)s were used as low humidity sensitive materials. • The optimized sensor shows high response in 5–35% RH. • The optimized sensor has short recovery time and small humidity hysteresis. • The introduction of glycerol could reduce the impedance of the sensor. [ABSTRACT FROM AUTHOR]

Development of room-temperature gas sensors with excellent sensing performances for detection of dimethyl methylphosphonate (DMMP, a simulant of organophosphate) has aroused considerable attention. However, the weak adsorption ability of sensing materials toward DMMP molecules causes poor sensing performances. In this work, a multisite strategy for enhancing sensitivity was proposed by introduction of both N-doped carbon nanoparticles (N-CNPs) and copper ions onto the surface of rGO (designated as GNC). Impressively, optimal GNC-3 exhibits the response value of 10.2% toward 100 ppm DMMP, which is 5.3 times higher than that of pristine rGO. This mechanism for multisite-assisted enhanced DMMP sensing performances was investigated by combined characterizations of Fourier-transform infrared spectra, UV-Vis spectra, photoluminescence spectra and Mott-Schottky curves. Besides the construction of multisite, improvement of hydrogen bonding interactions between DMMP molecules and N-CNPs in hybrids assisted by copper ions, and decrease of conduction band potential by formation of ternary hybrids also contribute to enhance the sensitivity of DMMP sensors. These findings not only provided new insights into designing high-performance room-temperature gas sensors, but also promoted the fundamental research on sensing mechanism for room-temperature gas sensors. • A multisite strategy for enhancing sensitivity was proposed by constructing three kinds of DMMP adsorption active sites. • GNC hybrids demonstrate 5.3-fold improvement in response to 100 ppm DMMP compared to pristine rGO hybrids. • This mechanism for multisite-assisted enhanced DMMP sensing performances was confirmed by the spectroscopy. [ABSTRACT FROM AUTHOR]

The hydrogen bonding interactions are potentially employed to fabricate high-performance room-temperature gas sensors for detection of organophosphorus. Nevertheless, the low response toward target gases of conventional sensing materials hinders their further applications. Herein, an isolated Cu-N 5 sites engineering strategy is reported to improve sensing performances for polypyrrole-reduced graphene oxide hybrids (PPy-rGO)-based room-temperature dimethyl methyl phosphate (DMMP) sensors. The isolated Cu-N 5 sites were simply constructed by adsorption of Cu2+ ions with PPy-rGO hybrids owing to strong metal-support interactions. X-ray absorption fine structure analysis indicates that Cux+ ions with mean chemical valence of + 1.07 nearly atomically distributed on support with coordination structure of Cu-N 5. Benefiting from the structure regulation by Cux+ ions, as-constructed DMMP sensor demonstrated 4.5-fold improvement in response to 100 ppm DMMP and 2.5-fold improvement in limit of detection, compared to PPy-rGO hybrids. The density functional theory, spectroscopic characterizations and quartz crystal microbalance tests prove that the construction of Cu-N 5 sites not only heightens hydrogen bonding interactions between N H bonds and DMMP molecules induced by newly formed coordination interactions between Cux+ ions and N H bonds, but also serves as new active sites for adsorption of DMMP molecules. This work offers a new avenue for developing high-performance room-temperature gas sensors by heightening hydrogen bonding interactions. • Isolated Cu-N 5 sites-assisted heightening hydrogen bonds strategy is proposed to construct room-temperature DMMP sensors. • Cux+-PPy-rGO hybrids demonstrate 4.5-fold improvement in response to 100 ppm DMMP compared to PPy-rGO hybrids. • The limit of detection of the Cux+-PPy-rGO based sensor is 2 ppm. [ABSTRACT FROM AUTHOR]

The development of metal oxides-based gas sensors for DMMP detection simultaneously possessing low operating temperature, low limit of detection and high sensitivity remains formidable challenges. In this work, a facile and efficient colloidal assembly approach is proposed to prepare Au modified SnO 2 hybrids (Au-SnO 2) with perfect metal-semiconductor interface and successfully used in DMMP detection application. After optimization, the best DMMP sensors based on Au-SnO 2 hybrids display outstanding sensing performances, including high response (1.88 to 680 ppb DMMP), low operating temperature (200 °C), extremely low limit of detection (34 ppb), as well as short response/recovery time (25 s/72 s). The sensing mechanism analysis reveals that the excellent sensing performances are mainly attributed to the synergy of chemical oxidation of DMMP catalyzed by Au-SnO 2 hybrids and physical adsorption of DMMP by hydrogen-bonding interactions. The present work not only provides an insight into the DMMP sensing mechanism, but also offers a promising general approach for development of high-performance gas sensors. [Display omitted] • A facile and efficient colloidal assembly approach waa proposed to synthesize Au modified SnO 2 hybrids. • The Au-SnO 2 -based sensor exhibits high response of 1.88 towards 680 ppb DMMP. • The limit of detection of the Au-SnO 2 -based sensor was 34 ppb. • An integrated chemical oxidation and hydrogen-bonding DMMP sensing mechanism model was first proposed. [ABSTRACT FROM AUTHOR]

Self-supported polymer films were fabricated by the thiol-ene click cross-linking reaction in this work. The cross-linked frameworks were used to guarantee the stability the films. The hydrophilic monomer with different contents were introduced into the self-supported thick films and uniformly dispersed in the polymer frameworks. The interdigitated electrodes were screen printed with silver paste on the self-supported films to obtain humidity sensors. Herein, the self-supported film acts as both the sensor substrate and the humidity-sensing material. The humidity sensing performances of the obtained sensors were systematically researched. By optimizing the ratio of hydrophilic monomer in the polymer films, the sensitivities of the sensors were enhanced from 1.58 to 103.75 (in the humidity from 11% RH to 95% RH), the response under low RH environment was significantly improved with good linearity. The response/recovery times of the sensor within the humidity range are measured to be 12.5 s and hundreds of seconds. The prepared flexible sensors possess certain mechanical properties, and exhibit good stability under bending and long-term tests up to 60 days. The applications of the as-prepared sensor in the detection of non-contact human skin humidity, human respiration and relative humidity of green plant were explored. The sensor shows excellent sensing performance in various applications and indicates the potential application in wearable and multifunctional devices. [Display omitted] • Self-supported polymer films were fabricated by the thiol-ene click cross-linking reaction. • Flexible and stable humidity sensors were fabricated by screen printing electrodes on the self-supported films. • The roles of the self-supported film are the substrate of the sensor, as both the humidity-sensing material. • The humidity sensing properties and the multifunctional applications of the obtained sensors were systematically researched. [ABSTRACT FROM AUTHOR]

Low humidity detection has always been a challenge in the field of humidity detection. Humidity sensors base on ionic liquid modified metal organic frameworks (MOFs) derived polymer films were prepared in this work. The ionic liquid ligand was uniformly introduced in the frameworks of UIO-66 to enhance the hydrophilicity of sensing materials, the caused defects sites are beneficial for adsorption and desorption, and the MOFs based functional films were easily obtained by in situ photoinduced thiol-ene click reaction. The obtained humidity sensor exhibits a linear response in low relative humidity (RH) range (5% RH - 30% RH) with a tiny humidity hysteresis (~0.2% RH) and short response time to humidity change (response/recovery time is 0.6 s/1.7 s, respectively). ● Humidity sensors based on ionic liquid modified UIO-66 derived polyelectrolyte films were prepared. ● The sensors were prepared facilely in situ on the electrodes by thiol-ene click polymerization in batches. ● The sensor presents linear response under low humidity (5% RH - 30% RH) with a small hysteresis and fast response speed. ● The introduction of ILs and the resulting defect sites are the reasons for effective low humidity detection. [ABSTRACT FROM AUTHOR]

• Polypyrrole decorated-reduced graphene oxide (PPy-rGO) hybrids were successfully synthesized by a self-redox strategy. • The PPy-rGO-3-based sensor exhibits a higher response and fast response and recovery behavior to DMMP than pristine rGO. • The enhanced DMMP sensing properties were attributed to formation of hydrogen bonds between DMMP and PPy. The development of fast-response, high sensitivity and selectivity gas sensors for monitoring of organophosphorus is essential, where two dimensional graphene-based materials possessing exceptionsal carrier mobility are considered as promising candidates for room-temperature organophosphorus detection. However, it is challenging to fabrication of graphene-based gas sensors for detection of organophosphorus with excellent sensing performances. Herein, we develope a self-redox strategy to synthesize polypyrrole decorated-reduced graphene oxide hybrids (PPy-rGO) by redox reactions between pyrrole and GO during hydrothermal treatment process. This self-redox strategy results in the formation of perfact interfical strucutre between PPy and rGO through the π-π interactions without the impurity from the conventional oxidation/reducing agents. Most importantly, such PPy-rGO hybrids can be used as novel sensing materials for detection of dimethyl methylphosphonate (DMMP) at room temperature. Specially, the response of PPy-rGO-based sensor towards 100 ppm DMMP can reach 12.9 %, which is 3-fold higher than that pristine rGO-based sensor. Meanwhile, PPy-rGO-based sensor exhibits short response time/recovery time (43 s/75 s), low detection limit (5 ppm), excellent repeatability, and high selectivity. By combination of FT-IR and N 2 sorption isotherms, the enhanced DMMP sensing performances of PPy-rGO hybrids are concluded as following two aspects. Firstly, the formation of hydrogen bonds between PPy-rGO hybrids and DMMP molecules regulates the adsorption/desorption of DMMP. Secondly, increasing BET surface area by introduction of PPy into rGO matrix is beneficial to DMMP diffusion among the sensing materials. Our work would offer a new strategy for rational development of graphene-based materials for detection of organophosphorus at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated. • The paper is used for the purpose of the humidity sensing material and the sensor substrate. • The as-fabricated paper-based humidity sensor is provided with outstanding humidity sensing properties and good stability. • The humidity sensor was applied to multifunctional applications including human breath rate, non-contact switch and skin humidity. It is of great significance to exploit a simple, cost-effective and environmentally friendly preparation method of multifunctional humidity sensors. However, most humidity sensors need complex manufacturing processes, high cost and narrow usage range. Herein, humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated, among which the paper is used for the purpose of the humidity sensing material and the sensor substrate. The sensitivity of the obtained sensor was improved by the modification of EPTAC, the response time was decreased to 25 s, which is equivalent to the first-rate paper-based humidity sensors. In addition, the paper-based humidity sensor is provided with well flexibility and biocompatibility, and it exhibits multifunctional applications in respiratory monitoring, non-contact switch and skin humidity monitoring. The low cost and facile preparation technique in this work could provide a useful strategy for developing multifunctional humidity sensor. [ABSTRACT FROM AUTHOR]