Search

Graphical abstract Highlights • A superior QCM humidity sensor with GQDs-CS sensitive film was fabricated. • It was proved that the introduction of GQDs into CS enhanced the mechanical stiffness of the CS film. • The prepared QCM sensor exhibits excellent humidity sensing properties and high Q-factor. Abstract A quartz crystal microbalance (QCM) humidity sensor based on graphene quantum dots-chitosan (GQDs-CS) sensitive film has been successfully fabricated in this work. The composite ratio of sensitive material and the coating quality of the sensitive film were optimized. The morphological and chemical properties of GQDs-CS composites were inspected via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier Transform infrared spectroscopy (FT-IR). The results manifest that prepared QCM sensor exhibits high response sensitivity (a frequency shift of −3291 Hz at 95% RH), short response/recovery time (36 s/3 s), tiny humidity hysteresis (˜1.6% RH), and excellent reproducibility, reversibility and long-term stability. Additionally, the electroacoustic parameters of the QCM sensors were also investigated by means of the impedance analysis method. Based on dynamic and static analysis of the sensor, it is speculated that the introduction of GQDs into CS enhanced the mechanical stiffness of the CS film, which could effectively improve the performance of QCM sensor. [ABSTRACT FROM AUTHOR]

In this work, we have reported a novel NO 2 sensor using molybdenum disulfide nanoparticles (MoS 2 NPs) decorated RGO (MoS 2 -RGO) hybrids as sensing materials, where MoS 2 -RGO hybrids were prepared by a two-step wet-chemical method. Firstly, MoS 2 NPs prepared by modified liquid exfoliation method from bulky MoS 2 powder. Then, MoS 2 -RGO hybrids were obtained by self-assembly of MoS 2 NPs and GO nanosheets, followed by a facile hydrothermal treatment progress. The combined characterizations indicate that MoS 2 NPs with the size of 3–5 nm are uniformly dispersed on RGO nanosheets. Most importantly, the sensor based on MoS 2 -RGO hybrids could detect NO 2 at room temperature. To further improve sensing performances, especially response and recovery rate, sensing properties are further examined by increasing the operation temperature to 160 °C. It is notably seen that MoS 2 -RGO-based NO 2 sensor not only shows improved sensitivity to NO 2 compared to pure RGO-based sensor, but also exhibits fast response and recovery characteristics (response time and recovery time are 8 s and 20 s toward 3 ppm NO 2 ). This work paves a new way for application of MoS 2 and RGO in chemical sensors, providing an effective method for fabrication of NO 2 sensors with high sensitivity and fast response/recovery rate. [ABSTRACT FROM AUTHOR]

The sensing layer composited from the inorganic particles, organic materials, polymers could be regarded as an important and functional component used in electronic devices, such as chemical sensor. Furthermore, it is very important for these materials to own hierarchical and porous structures leading to a large effective specific surface area. Among these, hybrid materials with yolk double-shelled architecture can further realize the required surface chemical reactions. However, it is rarely reported in gas sensors. Herein, a novel SnO 2 -TiO 2 hollow nanostructure consisting of double shells was successfully designed and synthesized. Due to the special multi-shelled structure and abundant hetero-interface, the sensing layer based on SnO 2 -TiO 2 realizes a rapid response rate within 1.7 s to ethanol gas and alluring reproducibility (15 days), which are superior over those for compact structure with similar sensors. The results indicated that the SnO 2 -TiO 2 yolk double-shelled microsphere have the huge potential for designing high performance practical ethanol devices in environmental monitoring and drunk driving. [ABSTRACT FROM AUTHOR]

The sensing layer in electronic device, such as chemical sensor, is an important and functional component consisting of polymer, organic materials, inorganic particles, and other components. These materials are generally hierarchical and porous with a large effective specific surface area to achieve the required surface chemical reactions. Despite the great progress, the synthesis of hollow core-shell nanostructure, especially ternary transition metal with core-in-hollow-shell nanostructure, is rarely reported. Herein, a novel NiFe 2 O 4 core-in-hollow-shell nanosphere with a porous inner and outer surface was prepared by a hydrothermal and co-precipitation method and the acetone sensing properties were reported. The NiFe 2 O 4 sensing layer exhibited high response to 100 ppm acetone gas (10.6) and achieved a rapid response rate and recovery process (within 1 s/7 s) at 280 °C, which are superior over those for nanoparticles of NiFe 2 O 4 and those reported for similar devices. In addition, after 20 days, the response of sensor based on NiFe 2 O 4 decreased ∼4%, indicating an alluring long-term stability. This is attributed to the highly porous but robust core-shell architecture, large utilization ratio of sensing layer and excellent catalytic activity. [ABSTRACT FROM AUTHOR]

The high sensing performance of chemical sensing sensors depends greatly on rational design of nanostructure and smart heterogenization of tailorable nanomaterials. Hybrid materials (HMs) as active sensing layers, are generally used for sensing devices. Here, the heteroassembly of n–type α–Fe 2 O 3 nanoparticles on a p–type LaFeO 3 matrix into a pore-rich hollow nanostructure is reported. The fabrication process uses a hydrothermal and co–precipitation synthesis method and begins from carbon nanospheres as sacrificial templates. The hetero-interfacial area and surface structure can be successfully tailored by changing the composition ratio of α–Fe 2 O 3 to LaFeO 3 . Consequently, as sensing materials in gas sensors, the α–Fe 2 O 3 /LaFeO 3 hetero-materials have a fast response/recovery time of 1 s/5 s after 5 cycles and are able to retain 92.4% of this sensitivity after 15 days, i.e., 10.1, to 100 ppm ethanol gas, which is closely related with the strong hetero–interfacial contact and unique hollow structures. This work offers a new insight into the rational design of chemical sensing devices from the synergetic effect of p–type ternary transition metal oxides as well as n–type nanostructures. [ABSTRACT FROM AUTHOR]

Development of high performance room temperature sensors remains a grand challenge for high demand of practical application. Metal oxide semiconductors (MOSs) have many advantages over others due to their easy functionalization, high surface area, and low cost. However, they typically need a high work temperature during sensing process. Here, p-type sensing layer is reported, consisting of pore-rich dumbbell-like Co 3 O 4 particles (DP-Co 3 O 4 ) with intrinsic high catalytic activity. The gas sensor (GS) based DP-Co 3 O 4 catalyst exhibits ultrahigh NH 3 sensing activity along with excellent stability over other structure based NH 3 GSs in room temperature work environment. In addition, the unique structure of DP-Co 3 O 4 with pore-rich and high catalytic activity endows fast gas diffusion rate and high sensitivity at room temperature. Taken together, the findings in this work highlight the merit of integrating highly active materials in p-type materials, offering a framework to develop high-sensitivity room temperature sensing platforms. [ABSTRACT FROM AUTHOR]

A physical mixing is usually needed in order to load lithium chloride (LiCl) in a matrix. A method of in situ loading LiCl in the cross-linked polymer framework by click reaction is demonstrated in this work. Pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) and divinylbenzene (DVB) were taken as the monomers to construct stable cross-linked polymer matrix, while different contents of LiCl were introduced in the polymerization process for preparing humidity sensitive composites. The cross-linked composites with uniform distribution of LiCl were obtained. Humidity sensors based on the composites were fabricated and their sensing properties were systematically investigated. The optimum mass ratio of LiCl was determined to be 8 wt%, the corresponding sensor owns a variation of impedance modulus beyond two orders of magnitudes from 11% to 95% relative humidity (RH), a maximum humidity hysteresis of ∼1.5% RH, and a short response and recovery time of 3.5 and 63 s, respectively. The humidity sensing mechanism of the obtained sensor was explored by the complex impedance spectroscopy and the equivalent circuit. [ABSTRACT FROM AUTHOR]

Abstract: Propolis or bee glue has very diverse composition and is potentially a source of biologically active compounds. Comprehensive chemical profiling was performed on 22 African propolis samples collected from the sub-Saharan region of Africa by using various hyphenated analytical techniques including Liquid Chromatography (LC)–UltraViolet Detection (UV)–Evaporative Light Scattering Detection (ELSD), LC–High Resolution Mass Spectrometry (HRMS), Gas Chromatography (GC)–MS and LC–Diode Array Detector (DAD)–HRMS/MS. The diversity of the composition of these African propolis samples could be observed by heat mapping the LC–UV and ELSD data. The characteristic chemical components were uncovered by applying Principal Component Analysis (PCA) to the LC–HRMS data and a preliminary dereplication was carried out by searching their accurate masses in the Dictionary of Natural Products (DNP). A further identification was achieved by comparing their GC–MS or LC–DAD–HRMS/MS spectra with previously published data. Generally no clear geographic delineation was observed in the classification of these African propolis samples. Triterpenoids were found as the major chemical components in more than half of the propolis samples analysed in this study and some others were classified as temperate and Eastern Mediterranean type of propolis. Based on the comparative chemical profiling and dereplication studies one uncommon propolis from southern Nigeria stood out from others by presenting prenylated isoflavonoids, which indicated that it was more like Brazilian red propolis, and more significantly a high abundance of stilbenoid compounds which could be novel in propolis. [Copyright &y& Elsevier]

Abstract: KCl-doped ZnO nanofibers are synthesized via an electrospinning method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The humidity sensing properties of these nanofibers are investigated by screen-printing them on a ceramic substrate with a pair of Ag–Pd interdigitated electrodes. The experimental results show that the 5.7wt% KCl-doped ZnO nanofibers hold super-rapid response and recovery, high response value, good reproducibility, linearity, selectivity, and stability at 100Hz. Especially, the response time and recovery time is only about 2 and 1s, respectively. These results demonstrate the potential application of KCl-doped ZnO nanofibers for fabricating high performance humidity sensors. [Copyright &y& Elsevier]

Abstract: A simple method for the large-scale synthesis of SnO2 nanofibers has been demonstrated through an electrospinning method. The as-synthesized fibers are characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and energy dispersive X-ray analysis. The sensor fabricated from these fibers exhibits high response to toluene at 350°C with good selectivity. The response time and recovery time are about 1 and 5s, respectively. The linear dependence of the response value on the toluene concentration is observed in the range of 10–300ppm. The potential application of SnO2 nanofibers for fabricating high performance toluene sensors at industry level has been demonstrated. [Copyright &y& Elsevier]

Abstract: Pure and Cu-doped SnO2 nanofibers are synthesized via a simple electrospinning method, and characterized by transmission electron microscopy and X-ray diffraction. The sensor fabricated from Cu-doped SnO2 nanofibers exhibits improved sensing properties to ethanol at 300°C. The sensitivity is up to 3 when this sensor is exposed to 5ppm ethanol. The response and recovery times are about 1 and 10s, respectively. The linear dependence of the sensitivity on the ethanol concentration is observed in the range of 5–500ppm. Good selectivity is also observed in our studies. The results make Cu-doped SnO2 nanofibers good candidates for fabricating high performance ethanol sensors. [Copyright &y& Elsevier]

Highlights: [•] NiO hollow spheres have been prepared by a one-pot hydrothermal synthesis route. [•] A non-enzymatic glucose sensor based on NiO hollow spheres has been constructed. [•] The glucose sensor exhibits high sensitivity and selectivity for glucose detection. [ABSTRACT FROM AUTHOR]

As the typical toxic and hazardous gases, volatile organic compounds (VOCs) and hydrogen sulfide (H 2 S) pose a threat to the environment and human health. The demand for real-time detection of VOCs and H 2 S gases is growing in many application to protect human health and air quality. Therefore, it is essential to develop advance sensing materials for the construction of effective and reliable gas sensors. Herein, bimetallic spinel ferrites with different metal ions (MFe 2 O 4 , M = Co, Ni, Cu and Zn) were designed by using metal-organic frameworks as templates. The evaluation of cation substitution on crystal structures (inverse/normal spinel structure) and electrical properties (n/p type and band gap) is systematically discussed. The results indicate that p-type NiFe 2 O 4 and n-type CuFe 2 O 4 nanocubes with inverse spinel structure exhibit high response and great selectivity towards acetone (C 3 H 6 O) and H 2 S, respectively. Moreover, the two sensors also display the detection limits as low as 1 ppm (C 3 H 6 O) and 0.5 ppm (H 2 S), which are far below the threshold values of 750 ppm to acetone and 10 ppm to H 2 S for 8 h exposure set by American Conference of Governmental Industrial Hygienists (ACGIH). The finding provides new possibilities for the design of high-performance chemical sensors, which display tremendous potential for practical applications. [Display omitted] • The cation substitution effect was studied for MOF-derived spinel ferrites. • The NiFe 2 O 4 based sensor showed high response to C 3 H 6 O. • The CuFe 2 O 4 based sensor showed the best H 2 S sensing properties. • The sensors were applied in exhaled breath analysis and food quality monitoring. [ABSTRACT FROM AUTHOR]

• A facile applicable approach to synthesize different one–dimensional (1D) Mn 3 O 4 /Zn 2 SnO 4 heterostructures is reported. • The Mn 3 O 4 nanowires decorated with Zn 2 SnO 4 achieved high response and rapid response time within 3 s to C 3 H 6 O. • Loading Zn 2 SnO 4 onto Mn 3 O 4 nanowires can generate more adsorbed oxygen and facilitate gas sensing reaction effectively. One–dimensional (1D) heterostructures are promising for the fascinating physical/chemical properties. However, the selective deposition of innovative materials as efficient active sites on the backbone material is still challenging and meaningful. Herein, a universal strategy is presented to synthesize the novel 1D heterostructure, which is constituted of Mn 3 O 4 nanowires (Mn 3 O 4 NWs) and nano–sized Zn 2 SnO 4 subunits with controllable morphologies including Zn 2 SnO 4 nanorods (Zn 2 SnO 4 NRs), Zn 2 SnO 4 nanocubes (Zn 2 SnO 4 NCs) and Zn 2 SnO 4 nanooctahedrons (Zn 2 SnO 4 NOs). The 1D Mn 3 O 4 /Zn 2 SnO 4 heterostructure is proved to generate abundant surface adsorbed oxygen molecules to modulate the sensing activity in chemical sensors (CSs) for application in the acetone vapor detection. The developed gas sensor shows enhanced responses, ultrafast response time and great stability. The selective deposition method and interface engineering will open up an avenue to design the heterostructured nanomaterials for high–performance CSs and other potential applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MOF–derived 1D α–Fe 2 O 3 /NiFe 2 O 4 nanomaterials provide the high specific surface area and a mass of active sites. • The α–Fe 2 O 3 /NiFe 2 O 4 -based sensors exhibit the enhanced acetone sensing performances compared to α–Fe 2 O 3 and NiFe 2 O 4. • The α–Fe 2 O 3 /NiFe 2 O 4 sensing layer achieves a high acetone response and fast response process. Abstract The key challenge to develop gas sensors with high performances lies in the novel design of superior functional materials for effective reactions between target gases and sensing layers. Metal–organic frameworks (MOFs) have emerged as versatile candidates for preparation of ideal nanostructured materials with controllable composition, various structures and tunable pore size. Herein, a series of Fe–based and Fe/Ni–based one–dimensional (1D) nanostructures using MOFs as templates were prepared systematically. As a result of the hollow structure and nanohybrid features, the optimized α–Fe 2 O 3 /NiFe 2 O 4 nanotubes can exhibit high specific surface area (118.03 m2 g−1) and provide a mass of active sites compared to individual components (α–Fe 2 O 3 nanowires and NiFe 2 O 4 nanowires), which is beneficial to improve the response (R a /R g = 23) to acetone vapors. In addition, the smart design also endows the sensor based on α–Fe 2 O 3 /NiFe 2 O 4 nanotubes with good selectivity, fast response time (4 s) and long–term stability (30 days). In this work, the advantages of 1D hollow heterogeneous materials will provide a new perspective of MOF–derived nanostructures for the particular application in acetone gas sensors. [ABSTRACT FROM AUTHOR]

Pt-loaded In 2 O 3 mesoporous nanofibers (NFs) have been prepared by electrospinning, followed by a facile reduction method. The sample obtained by adding tea saponin into the spinning solution, sample In-TS, displays a more than 4 times higher specific surface area, value of 86.9 m 2  g −1 , than that of conventionally prepared samples. The loading with small-sized Pt nanoparticles (NPs) determines excellent gas sensing performance towards NO 2 down to ppb level (R g /R a  = 2.8 to 10 ppb and 23.9–1 ppm) at room temperature (RT), by that significantly lowering the power consumption. The reason is that the open pores and channels on the mesoporous NFs generated by the foaming agent not only promote the adsorption and desorption of NO 2 molecules on the sensing layers, but also improves the transduction function of the sensors by ensuring that there are no parts of the fiber that are not accessible to the gases. The introduction of Pt to the mesoporous NFs could accelerate the dissociation of absorbed oxygen and the active surface reactions in NO 2 owing to the catalytic property and chemical sensitization of well-dispersed Pt NPs. Due to the unique gas sensing performance, sample In-TS-Pt has a prospect for applications in low-concentration NO 2 detection at RT. [ABSTRACT FROM AUTHOR]

Horseshoe-shaped SnO 2 with annulus-like mesoporous was successfully synthesized by self-assembly method in this work. The obtained materials were characterized by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results revealed that the horseshoe-shaped samples were composed of amounts of annulus-like mesoporous with an average diameter about 2 nm and high specific surface area. Moreover, gas sensor based on the as-prepared samples was fabricated and its sensing performances were investigated. It was revealed that the sensitivity towards 100 ppm of ethanol enhanced to 17.3 under the operation temperature 225 °C for the sensor based on SnO 2 calcined at 400 °C. And the sensor based on SnO 2 calcined at 400 °C presented a higher response towards 10–200 ppm ethanol. In addition, the relationship between morphology and sensing property of synthesized materials towards ethanol has been investigated. The results above indicate the potential of the annulus-like mesoporous SnO 2 as ethanol gas sensor material. [ABSTRACT FROM AUTHOR]

Mesoporous ZnFe 2 O 4 with ordered tunnel and large specific surface area has been successfully prepared through hard template (mesoporous silica KIT-6). The necessary characterizations such as X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been carried out to investigate the obtained material. ZnFe 2 O 4 with mesoporous structure presents excellent crystallinity and periodic mesostructure. The sensing properties of gas sensor based on ZnFe 2 O 4 mesoporous material towards acetone has been investigated. The sensor presents outstanding sensitivity, selectivity and longtime stability. This indicates that the obtained mesostructured ZnFe 2 O 4 through hard template method is a potential acetone gas sensor material. [ABSTRACT FROM AUTHOR]

The stability of sensitive materials is of great importance to humidity sensors. A novel method is used to synthesize cross-linked polymers by a free radical polymerization while introducing the pyridine salt unit with a click reaction by a one-pot reaction. The obtained polymers were used for humidity sensors and the humidity sensitive properties were researched systematically. By introducing polar units to the side chain of the polymer, the humidity sensitive properties were improved greatly. The optimum sensor shows good sensing properties during the whole relative humidity range. In addition, the polymer sensor shows very quick response to humidity, with a response time of 6 s and a recovery time of 17 s. This method is also applicable for developing other functional materials. [ABSTRACT FROM AUTHOR]

A facile and effective strategy has been successfully developed to synthesize reduced graphene oxide-multiwalled carbon nanotubes-tin oxide nanoparticles (rGO-CNT-SnO 2 ) hybrids by hydrothermal method. The combined characterizations of X-ray diffraction, Raman spectrum and Transmission electron microscopy were used to characterize the samples thus obtained, indicating the successful preparation of rGO-CNT-SnO 2 hybrids. A room temperature NO 2 sensor was fabricated by dropping the dispersion of rGO-CNT-SnO 2 hybrids on the surface of ceramic substrate previously printed Au electrodes. Most importantly, the sensor based on rGO-CNT-SnO 2 hybrids shows high response, fast response and recovery rate, high selectivity and good stability, which are much better than NO 2 sensors based on pure rGO and rGO-SnO 2 hybrids. [ABSTRACT FROM AUTHOR]

Au-loading SnO 2 hollow microtubes (Au-SnO 2 -MTs) have been successfully prepared by the coaxial electrospinning method, where the sol solution containing poly-vinylpyrrolidone and metal salts were used as outer solution and paraffin was used as inner solution, respectively. The combined characterizations of scanning electron microscopy and X-ray diffraction indicating the successful preparation of Au-SnO 2 -MTs with the diameter of MTs about 500-600 nm, and the thickness of the hollow MTs about 70-80 nm. It is also found that the Au-SnO 2 -MTs exhibit catalytic activity for electrochemical reduction of H 2 O 2 , leading to a non-enzymatic H 2 O 2 sensor. The H 2 O 2 sensor thus obtained shows the linear detection range from 10 μM to 1 mM ( r = 0 . 997), and the detection limit about 0.60 μM at a signal-to-noise ratio of 3. Furthermore, the H 2 O 2 sensor also exhibits excellent selectivity for H 2 O 2 in comparison to other normally co-existing electroactive species (such as dopamine, ascorbic acid, uric acid and glucose) and inorganic anions. [ABSTRACT FROM AUTHOR]

Highly sensitive and selective toluene sensors based on ordered mesoporous Co3O4 have been successfully developed. The combined characterizations of X-ray diffraction (XRD) patterns, nitrogen adsorption–desorption isothermal, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicate that mesoporous Co3O4 with ordered mesoporous structure and high surface area has been successfully prepared by the nanocasting method using mesoporous silica (SBA-15) as hard template and Co(NO3)2·6H2O as cobalt source. It is also found that mesoporous Co3O4 thus obtained shows good response toward toluene with the concentrations ranging from 1ppm to 1000ppm. Furthermore, mesoporous Co3O4 also exhibits high selectivity for detection of toluene, compared to other interferences, such as ethanol, formaldehyde, ethanol, acetone, methanol and ammonia. Most importantly, mesoporous Co3O4 exhibits better sensing performance than that of non-porous Co3O4 obtained by direct calcination of Co(NO3)2·6H2O in the absence of any templates, which can be attributed to unique properties of mesopotous Co3O4, such as high surface area, open mesoporous structure as well as relatively small crystal size. [ABSTRACT FROM AUTHOR]

Abstract: Polyvinylpyrrolidone-grafted carbon black (CB-PVP) was prepared by a free radical polymerization reaction. The resultant CB-PVP could disperse well in water. Dew sensors based on CB/PVA (polyvinyl alcohol) and CB-PVP/PVA were obtained respectively, and their humidity switching properties were researched. Thermal annealing was used to improve the stability of the sensitive films effectively. Both CB/PVA and CB-PVP/PVA sensors showed obvious humidity switching properties, and CB-PVP/PVA sensor performed properties better than CB/PVA sensor. In the case of the 6wt% CB-PVP/PVA film, the resistance was about 10kΩ below 80% relative humidity (RH) and increased sharply over 85% RH, with a resistance of 170kΩ at 100% RH. The conductive mechanism of the CB-PVP/PVA materials was discussed through direct current reverse polarity method. The CB-PVP/PVA composite is a promising dew sensing material. [Copyright &y& Elsevier]

Abstract: Hollow ZnO microspheres with tunable interior architecture are successfully synthesized by a simple green chemistry routes at low temperature. This process is environmentally friendly processing, which based on without using solvents, employing carbon microspheres as template and reaction at low temperature. The layer-control of hollow ZnO microspheres can be easily adjusted by varying the concentration of the zinc precursor added. To demonstrate the usage of such hollow ZnO microspheres, gas sensors have been fabricated from the as-synthesized hollow ZnO microspheres with different shelled and investigated for formaldehyde (HCHO) detection. Interestingly, the response of hollow ZnO microspheres increased with increasing the number of shell structures. These results indicate that three-shelled ZnO sensor displays about 1.5 and 3–4 fold enhancement in response compared to double and single-shelled one, respectively. The mechanism of enhanced sensor performances is also proposed. [Copyright &y& Elsevier]

Abstract: SBA-15, SBA-16 and crystal like-SBA-16 were synthesized by a simple chemical method, and the copolymer template was removed by calcination or microwave digestion (MWD) method. They were investigated as humidity sensing materials at room temperature within the relative humidity range of 11–95%RH. It was found that after MWD treatment, the humidity sensitive property of mesoporous silica have been greatly improved, and the impedance of MWD-crystal like SBA-16 changed by more than three orders of magnitude over the whole humidity range. Further testing proved that it is a promising humidity sensing material and can be widely used. A possible mechanism was also proposed to explain the correlation between material and property. [Copyright &y& Elsevier]

Abstract: We report the synthesis of flowerlike ZnO nanostructure using a facile hydrothermal process, and the investigation on the ammonia (NH3)-sensing properties of the pure and palladium (Pd)-sensitized flowerlike ZnO nanostructure. The phase purity, morphology, and structure of the pure and Pd-sensitized ZnO nanostructure are investigated. The characterized results reveal that the flowerlike ZnO has a wurtzite structure and is composed of numerous aggregated single-crystalline ZnO nanorods with a diameter of about 60nm. Having fabricated gas sensors based on the pure and Pd-sensitized flowerlike ZnO, we find that the Pd-sensitized sensor exhibits a response of 45.7–50ppm NH3 at 210°C, which is about 8 times higher than that of pure ZnO at the optimal operating temperature of 350°C. The enhanced NH3-sensing performance demonstrates that the significant decrease in optimal operating temperature and the distinct increase in response are attributed to the sensitization effect of Pd. [Copyright &y& Elsevier]

Abstract: A simple chemical method was employed to form Fe2+ doped polypyrrole (PPY) by the introduction of hydrated ferric chloride (FeCl3·6H2O) during the polymerization of pyrrole, where FeCl3·6H2O played a role of oxidant for the polymerization and the in situ forming reduced product (FeCl2·2H2O) was well doped in PPY. The resultant Fe2+ doped PPY species were characterized by using various techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electronic microscope (FE-SEM). Humidity-sensitive properties of the samples were also examined. The Fe2+ doped PPY exhibited a fast response to humidity change (about 20s), in which great changes of more than three orders (nearly four) of magnitude in impedance was observed when relative humidity was varied over the whole range. The improved properties may be related to the presence of the hydrophilic Fe2+, and a possible mechanism was also provided. [Copyright &y& Elsevier]

Abstract: Li-doped 3D periodic mesoporous silica SBA-16 has been successfully prepared and investigated as humidity sensor material. After doping of 10% (wt) lithium chloride, mesoporous silica SBA-16 showed significant change in impedance of more than three orders of magnitude over almost the whole humidity range (11–95%RH), with fast response time (about 25s), and relatively low hysteresis (about 4%). The comprehensive affections of the 3D mesoporous structure, highly dispersed uniform morphology, hydrophilic behavior of triblock copolymer surfactant F108, and the doped Li+ maybe make a great contribution to the improvement in the humidity sensitive property. A possible mechanism was also provided to explain the humidity sensitive properties. [Copyright &y& Elsevier]

Crystalline phase regulation could optimize the band gap, which has a great impact on the amount of chemisorbed gas molecules on the gas sensing materials. Herein, a facile route of hydrothermal method followed by calcination treatment was used to synthesize cubic bixbyite-type (C-In 2 O 3), rhombohedral corundum-type (Rh-In 2 O 3) and the mixed phase In 2 O 3 (Rh+C-In 2 O 3). The band gap of C-In 2 O 3 was narrowed to a suitable value (2.38 eV) and the relative percentage of chemisorbed oxygen was enhanced (31.8%). The sensing results to ozone (O 3) indicated that the C-type structure stood out. The gas sensor based on C-In 2 O 3 exhibited extraordinary O 3 sensing performances with a response of 5.7 (100 ppb) and an ultralow limit of detection of 30 ppb. The amazing results could be attributed to the narrow band gap and the enrichment of chemisorbed oxygen. This work inspires a new perspective to design highly sensitive and reliable O 3 sensors. [Display omitted] • Crystalline phase regulation was used to design In 2 O 3 with different phases. • Cubic bixbyite-type In 2 O 3 based sensor showed the best sensing properties. • The response of the optimal sensor was 5.7 towards 100 ppb ozone. • The limit of detection of the optimal sensor was 30 ppb. [ABSTRACT FROM AUTHOR]