Fabrication and Characterization of Polycrystalline WO3 Nanofibers and Their Application for Ammonia Sensing

A Facile Way to Simultaneously Improve Humidity-Immunity and Gas Response in Semiconductor Metal Oxide Sensors

The metal-oxide-based gas sensors show great potential in exhaled breath analysis owing to their simple, fast, and noninvasive characteristics. However, the exhaled breath contains moisture, and the surface-active sites of metal oxides are easily poisoned by water molecules, leading to degradation of the sensor performance, particularly the gas response and selectivity. Therefore, it is essential to develop oxide sensors that can reliably sense target gases over a wide humidity range without sacrificing the gas response. In this study, a facile strategy was proposed to incorporate hydrophobic La into an oxide sensor to simultaneously improve the humidity-stability and sensitivity of NH3 detection for early prediction of kidney failure. WO3 sensors doped with various concentrations of La were successfully synthesized, and their gas-sensing performances under various humid conditions were systematically investigated. Interestingly, a small amount of La doping (1 at. %) effectively prevented water poisoning and improved the gas response simultaneously. This sensor was able to selectively detect NH3 up to 200 ppb with a limit of detection (LOD) of ∼780 ppt over a wide range of humidity. The concurrent enhancement in gas response and humidity-immunity was attributed to the surface hydrophobicity and increased specific surface area caused by the incorporation of La.

Preparation and NH3 gas-sensing properties of Ag/β-AgVO3 nanorods

NH3 gas sensors operating at room temperature, consisting of Ag nanoparticles decorated β-AgVO3 nanorods (Ag/β-AgVO3 NRs), were fabricated via a facile hydrothermal method without the need for a template. The surface characteristics and compositions of Ag/β-AgVO3 NRs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ag nanoparticles, ranging in diameter from approximately 20 to 40 nm, were dispersed on the surface of monoclinic β-AgVO3 NRs with diameters ranging from 50 to 105 nm and lengths from 0.3 to 1.3 μm. The NH3 gas sensing properties of Ag/β-AgVO3 NRs were studied under both dry air and humid conditions at room temperature. Comparative analysis demonstrated that the Ag/β-AgVO3 NRs exhibited a strong response to NH3 gas under 70% relative humidity (RH) at room temperature compared to α-AgVO3 NRs. Specifically, the response of the Ag/β-AgVO3 NRs to 5 ppm NH3 increased by 2.25 times as the RH varied from 20% to 80% at room temperature. This enhanced response was attributed to the effects of formation of nanoheterojunctions, nano-metallic Ag activity and the conductivity of NH4+ and OH- ions induced by the presence of humidity. The room temperature NH3 gas sensors based on Ag/β-AgVO3 NRs demonstrated strong responses to low NH3 concentrations, high selectivity, good reproducibility, and long-term stability, and show promise for the development of low-power and cost-effective NH3 gas sensors for practical applications even under high humidity.

Crafting a powerful shield: Unveiling the potent anti-oxidant magic of ex-situ nanostructured Ag/WO3 composite

The current study focuses the nanocomposites of Ag/WO3 was synthesized via hydrothermal method and extract of Aloe-vera gel was used. Various characterization techniques were used for the analysis of Ag/WO3 nanocomposites which includes SEM (scanning electron microscope), EDX (Energy dispersive spectroscopy), XRD (X-ray diffraction), FTIR (Fourier transform infrared), UV (ultraviolet-visible-spectroscopy) to tell about elemental composition, shape and crystalline structure, band gap, functional group. The presence of composition of elements O, W, Ag in Ag/WO3 nanocomposites was confirmed through EDX spectrum. The hexagonal crystal structure and the border peaks in Ag/WO3 nanocomposites were examined through XRD spectra. The Anti-oxidant activity was synthesized by using (DPPH) free Radical in Ag/WO3 nanocomposites. The outcomes of present study exhibited an excellent anti-oxidant activity and also indicated the reduction of stabilized free radical DPPH analysis using Aloe vera extract. The result revealed that the anti-oxidant activity of Ag/WO3 nanocomposites is essential for biomedical application and various industries.

The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography

Tungsten trioxide (WO3) is a versatile n-type semiconductor with outstanding chromogenic properties highly used to fabricate sensors and electrochromic devices. We present a comprehensive experimental study related to piezoresponse with piezoelectric coefficient d33 = 35 pmV-1 on WO3 thin films ~200 nm deposited using RF-sputtering onto alumina (Al2O3) substrate with post-deposit annealing treatment of 400 °C in a 3% H2/N2-forming gas environment. X-ray diffraction (XRD) confirms a mixture of orthorhombic and tetragonal phases of WO3 with domains with different polarization orientations and hysteresis behavior as observed by piezoresponse force microscopy (PFM). Furthermore, using atom probe tomography (APT), the microstructure reveals the formation of N2-filled nanovoids that acts as strain centers producing a local deformation of the WO3 lattice into a non-centrosymmetric structure, which is related to piezoresponse observations.

Fabrication of noble metal (Au, Ag, Pt)/polythiophene/reduced graphene oxide ternary nanocomposites for NH3 gas sensing at room temperature

Room temperature NH₃ gas sensors composed of noble metal (Au, Ag or Pt)/polythiophene/reduced graphene oxide (Au, Ag or Pt/PTh/rGO) ternary nanocomposite films were fabricated using a simple one-pot redox reaction. The surface morphology and composition of Au, Ag or Pt/PTh/rGO ternary nanocomposite films were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films, obviously bright Au nanoparticles were observed on the surface of the massive lamination PTh film which wrapped the rGO, and encapsulated Au nanoparticles were observed in the Au/PTh/rGO film. Comparative gas sensing results showed that the Au/PTh/rGO ternary nanocomposite film had the highest response compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films at room temperature, especially when the testing concentration of NH₃ gas was below 5 ppm. The Au/PTh/rGO ternary nanocomposite film also had a fast response time and good reproducibility. The combination of the high catalytic activity of naked Au nanoparticles and the formation of effective carrier transfer channels by encapsulated Au nanoparticles was responsible for the improved response of the Au/PTh/rGO ternary nanocomposite film.

Mechanistic Insights into WO3 Sensing and Related Perspectives

Tungsten trioxide (WO₃) is taking on an increasing level of importance as an active material for chemoresistive sensors. However, many different issues have to be considered when trying to understand the sensing properties of WO₃ in order to rationally design sensing devices. In this review, several key points are critically summarized. After a quick review of the sensing results, showing the most timely trends, the complex system of crystallographic WO₃ phase transitions is considered, with reference to the phases possibly involved in gas sensing. Appropriate attention is given to related investigations of first principles, since they have been shown to be a solid support for understanding the physical properties of crucially important systems. Then, the surface properties of WO₃ are considered from both an experimental and first principles point of view, with reference to the paramount importance of oxygen vacancies. Finally, the few investigations of the sensing mechanisms of WO₃ are discussed, showing a promising convergence between the proposed hypotheses and several experimental and theoretical studies presented in the previous sections.

Acidic and alkaline gas sensitive and self-healing chitosan aerogel based on electrostatic interaction

Gas pollution is a serious problem. More attention has been paid to the detection and monitoring of toxic and harmful gases, and it is urgently needed for a sensor that could simultaneously identify and distinguish between acid and base gases. Based on the electrostatic interaction resulting from amidogen of chitosan (CS) and carboxylic groups of itaconic acid (IA), we successfully prepared a series of biomass aerogels (CS-IA aerogels) that could respond to acidic and alkaline gases with different concentrations. The acidic and alkaline gases could be easily detected and distinguished by changing the content of IA in CS-IA aerogels. Moreover, the electrostatic interactions could also endowed CS-IA aerogels with self-healing ability in the breaks at room temperature. After self-healing, CS-IA aerogels still sensitively answered to acidic and alkaline gases. CS-IA aerogels with sensitivity to acid-base gas and self-healing performance has been suggested to be promising candidates as application of multi-functional aerogels.

Photochromic Polyamide 6 Based on Spiropyran Synthesized via Hydrolyzed Ring-Opening Polymerization

We report photochromic polyamide 6 (PA6) which was synthesized by hydrolyzed ring-opening polymerization of ε-caprolactam with spiropyran (SP) embedded in the polymer chains. It indicated that crystallinity degree of the resulting copolymers was decreased since only PA6 segments can crystallize with increasing content of SP modifier. Meanwhile, toughness of photochromic PA6 was decreased. The photochromic property analysis indicated that the sample with more flexibility and more content of SP was more sensitive to UV light at the beginning of irradiation than other samples and its color after being irradiated for 1 min tended to reddish. Investigation revealed that the UV-vis absorbance of SP-PA6-3 had negligible decay after 10 cycles, which indicated SP-modified PA6 possessed excellent photoresponse reversibility and fatigue resistance.

Electrospun Metal Oxide Nanofibers and Their Conductometric Gas Sensor Application. Part 2: Gas Sensors and Their Advantages and Limitations

Electrospun metal oxide nanofibers, due to their unique structural and electrical properties, are now being considered as materials with great potential for gas sensor applications. This critical review attempts to assess the feasibility of these perspectives. This article discusses approaches to the manufacture of nanofiber-based gas sensors, as well as the results of analysis of the performances of these sensors. A detailed analysis of the disadvantages that can limit the use of electrospinning technology in the development of gas sensors is also presented in this article. It also proposes some approaches to solving problems that limit the use of nanofiber-based gas sensors. Finally, the summary provides an insight into the future prospects of electrospinning technology for the development of gas sensors aimed for the gas sensor market.

Electrospun Metal Oxide Nanofibers and Their Conductometric Gas Sensor Application. Part 1: Nanofibers and Features of Their Forming

Electrospun metal oxide nanofibers, due to their unique structural and electrical properties, are now being considered as materials with great potential for gas sensor applications. This critical review attempts to assess the feasibility of these perspectives. The article in Part 1 discusses the basic principles of electrospinning and the features of the formation of metal oxide nanofibers using this method. Approaches to optimization of nanofibers’ parameters important for gas sensor application are also considered.

Metal-incorporated mesoporous oxides: Synthesis and applications

Mesoporous oxides are outstanding metal nanoparticle catalyst supports owing to their well-defined porous structures. Such mesoporous architectures not only prevent the aggregation of metal nanoparticles but also enhance their catalytic performance. Metal/metal oxide heterojunctions exhibit unique chemical and physical properties because of the surface reconstruction around the junction and electron transfer/interaction across the interface. This article reviews the methods used for synthesizing metal-supported hybrid nanostructures and their applications as catalysts for environmental remediation and sensors for detecting hazardous materials.

Facile Preparation of WO3 Nanowires by Bubble-Electrospinning and their Photocatalytic Properties

BACKGROUND

As a relatively novel and promising method, the bubble electrospinning is to fabricate continuous and uniform nanowires using an aerated polymer solution in an electric field. A large number of oxidized docking nanowires were established on a silicon substrate using the bubble electrospinning, and then using Tungsten Oxide Ammonium (AMT) as an appropriate calcined air with the WO3 sources. WO3 production can enhance its catalytic activity, stability, and can raise its rhodamine B degradation rate as well; the prospect of its wide application.

METHODS

The high aspect ratio of WO3 nanowires is successfully prepared by a lightweight bubble electrospinning technique using Polyoxyethylene (PEO) and Ammonium-Tungstate (AMT) as the WO3 precursor after annealing in air at 400, 450 and 500°C, respectively. The products were characterized by SEM, FTIR, XRD, and TG analysis. This Paper reviews the related patents on bubble electrospinning and WO3 nanowires.

RESULTS

The results were shown that the diameter of WO3 nanowires ranges from 2μm to 450nm, which varies with the calcination temperature. XRD diffraction and infrared spectroscopy showed that monoclinic crystals were prepared at different calcination temperatures (400, 450 and 500°C).

CONCLUSION

In addition, the UV-vis diffuse reflectance spectroscopy showed that the fiber had a bandgap energy of 2.63 eV after calcination at 450oC, showing excellent photocatalytic activity in the degradation of Rh B at 245 nm. The preparation of WO3 nanowires by bubble electrospinning method is a feasible patented technology.

Synthesis of Graphene Oxide Interspersed in Hexagonal WO3 Nanorods for High-Efficiency Visible-Light Driven Photocatalysis and NH3 Gas Sensing

WO₃ nanorods and GO (at 1 wt% loading) doped WO₃ were synthesized using a template free deposition-hydrothermal route and thoroughly characterized by various techniques including XRD, FTIR, Raman, TEM-SAED, PL, UV-Vis, XPS, and N₂ adsorption. The nano-materials performance was investigated toward photocatalytic degradation of methylene blue dye (20 ppm) under visible light illumination (160 W, λ> 420) and gas sensing ability for ammonia gas (10–100 ppm) at 200°C. HRTEM investigation of the 1%GO.WO₃ composite revealed WO₃ nanorods of a major d-spacing value of 0.16 nm indexed to the crystal plane (221). That relevant plane was absent in pure WO₃ establishing the intercalation with GO. The MB degradation activity was considerably enhanced over the 1%GO.WO₃ catalyst with a rate constant of 0.0154 min⁻¹ exceeding that of WO₃ by 15 times. The reaction mechanism was justified dependent on electrons, holes and •OH reactive species as determined via scavenger examination tests and characterization techniques. The drop in both band gap (2.49 eV) and PL intensity was the main reason responsible for enhancing the photo-degradation activity of the 1%GO.WO₃ catalyst. The later catalyst initiated the two electron O₂ reduction forming H₂O₂, that contributed in the photoactivity improvement via forming •OH moieties. The hexagonal structure of 1%GO.WO₃ showed a better gas sensing performance for ammonia gas at 100 ppm (R_a-R_g/R_g = 17.6) exceeding that of pure WO₃ nanorods (1.27). The superiority of the gas-sensing property of the 1%GO.WO₃ catalyst was mainly ascribed to the high dispersity of GO onto WO₃ surfaces by which different carbon species served as mediators to hinder the recombination rate of photo-generated electron-hole pairs and therefore facilitated the electron transition. The dominancy of the lattice plane (221) in 1%GO.WO₃ formed between GO and WO₃ improved the electron transport in the gas-sensing process.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Electrospinning of Ultrafine Conducting Polymer Composite Nanofibers with Diameter Less than 70 nm as High Sensitive Gas Sensor

Polyvinyl alcohol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PVA/PEDOT:PSS) composite ultrafine fibers were successfully fabricated by high pressure airflow assisted electrospinning. The electrical properties of PVA/PEDOT:PSS nanofibers with different diameters were characterized. The average diameter of the nanofibers can be down to 68 nm. Due to its large specific surface area, ammonia sensing of the ultrafine nanofibers is more sensitive than the traditional electrospun fibers (average fiber diameter of 263 nm). The ammonia sensing properties of the samples were tested by impedance analysis. The results show that ultrafine PVA/PEDOT:PSS nanofibers are more suitable for detecting low concentrations of ammonia with higher sensitivity.

Chemiresistive Graphene Sensors for Ammonia Detection

The primary objective of this work is to demonstrate a novel sensor system as a convenient vehicle for scaled-up repeatability and the kinetic analysis of a pixelated testbed. This work presents a sensor system capable of measuring hundreds of functionalized graphene sensors in a rapid and convenient fashion. The sensor system makes use of a novel array architecture requiring only one sensor per pixel and no selector transistor. The sensor system is employed specifically for the evaluation of Co(tpfpp)ClO₄ functionalization of graphene sensors for the detection of ammonia as an extension of previous work. Co(tpfpp)ClO₄ treated graphene sensors were found to provide 4-fold increased ammonia sensitivity over pristine graphene sensors. Sensors were also found to exhibit excellent selectivity over interfering compounds such as water and common organic solvents. The ability to monitor a large sensor array with 160 pixels provides insights into performance variations and reproducibility-critical factors in the development of practical sensor systems. All sensors exhibit the same linearly related responses with variations in response exhibiting Gaussian distributions, a key finding for variation modeling and quality engineering purposes. The mean correlation coefficient between sensor responses was found to be 0.999 indicating highly consistent sensor responses and excellent reproducibility of Co(tpfpp)ClO₄ functionalization. A detailed kinetic model is developed to describe sensor response profiles. The model consists of two adsorption mechanisms-one reversible and one irreversible-and is shown capable of fitting experimental data with a mean percent error of 0.01%.

Flexible Graphene-Based Wearable Gas and Chemical Sensors

Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO₂), ammonia (NH₃), hydrogen (H₂), hydrogen sulfide (H₂S), carbon dioxide (CO₂), sulfur dioxide (SO₂), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.

Electrospun metal–organic framework polymer composites for the catalytic degradation of methyl paraoxon

Electrospun polymer fibers containing poly(methyl methacrylate) (PMMA), Ti(OH)₄, and UiO-66 convert a chemical warfare agent simulant to non-toxic product via catalytic hydrolysis.

Selective conversion of fructose to 5-hydroxymethylfurfural over WO3/SnO2 catalysts

The effective solid acid catalyst WO₃/SnO₂ has been synthesized and applied to the dehydration of fructose to HMF.

Simple One-Pot Syntheses and Characterizations of Free Fluoride- and Bifluoride-Containing Polymers Soluble in Non-Aqueous Solvents

One of the problems that arise with bifluoride- or fluoride-containing compounds is their poor solubility in non-aqueous solvents. We report herein a facile one-pot synthesis and the chemical analysis of fluoride/bifluoride-containing polymers, which are soluble in MeCN. Different polymers, such as Polyvinylacetate or Polyethylene imine and saccharides, such as maltodextrin, were complexed with ammonium (bi)fluoride using hydrogen bonds to form the desired (bi)fluoride-containing compounds. The newly formed hydrogen bonding (bi)fluoride-doped polymer matrices were analyzed using infrared and nuclear magnetic resonance spectroscopies, and X-ray diffraction. The promising materials also underwent impedance spectroscopy, conductivity measurements and preliminary tests as electrolytes for room temperature fluoride ion batteries along with an analysis of their performance.

Polyaniline nanofibers and their self-assembly into a film to be used as ammonia sensor

In this research, polyaniline nanofibers were synthesized by the HCl assisted interfacial polymerization method, where the morphologies and electrical properties of the nanofibers were controlled by the concentration of the HCl solution.

Facile and controllable synthesis of hydroxyapatite/graphene hybrid materials with enhanced sensing performance towards ammonia

In this work, needle-like and micro-spherical agglomerates of nanocrystalline hydroxyapatite (HA) were successfully assembled on the surface of graphene sheets with the aid of dopamine having two roles, as a template and a reductant for graphite oxide during the process of self-polymerization. The crystalline structure and micromorphology of HA can be conveniently regulated by controlling the mineralization route either with a precipitation (cHA/GR) or biomimetic methodology (bHA/GR). Both the composites exhibit improvements of ∼150% and ∼250% in sensitivity towards the sensing of ammonia at room temperature, compared with that of bare graphene. The combination of the multi-adsorption capability of HA and the electric conductivity of graphene is proposed to be the major reason for the observed enhancements. Gas sensing tests demonstrated that the HA/GR composites exhibit excellent selectivity, high sensitivity and repeatable stability towards the analytical sensing of ammonia.

A Simple Method of Electrospun Tungsten Trioxide Nanofibers with Enhanced Visible-Light Photocatalytic Activity

The present study involves the fabrication of tungsten trioxide (WO3) nanofibers by an electrospinning technique using polyvinyl pyrrolidone (PVP)/citric acid/tungstic acid as precursor solution. It was found that the PVP concentration was one of the most crucial processing parameters determining the final properties of WO3 nanofibers. The optimum concentration of PVP was from 75 to 94 g L-1. The average diameter of the nanofibers increases with increasing the PVP concentration, whereas it is decreased after sintering and orthorhombic structure were formed at 500 °C. The photocatalytic properties of the as-synthesized nanofibers were also investigated by degrading methylene blue and twofold efficiency was obtained compared with that of commercial WO3 microparticles.

Tailored Electrospinning of WO₃ Nanobelts as Efficient Ultraviolet Photodetectors with Photo-Dark Current Ratios up to 1000

In this work, polycrystalline WO3 nanobelts were fabricated via an electrospinning process combined with subsequent air calcination. The resultant products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy in regard to the structures. It has been found that the applied voltage during the electrospinning process played the determined role in the formation of the WO3 nanobelts, allowing the controlled growth of the nanobelts. The ultraviolet (UV) photodetector assembled by an individual WO3 nanobelt exhibits a high sensitivity and a precise selectivity to the different wavelength lights, with a very low dark current and typical photo-dark current ratio up to 1000, which was the highest for any WO3 photodectectors ever reported. This work could not only push forward the facile preparation of WO3 nanobelts but also represent, for the first time, the possibility that the polycrystalline WO3 nanobelts could be a promising building block for the highly efficient UV photodetectors.

N-type SnO2nanosheets standing on p-type carbon nanofibers: a novel hierarchical nanostructures based hydrogen sensor

The synergistic relationship of n-type SnO₂nanosheets and p-type CNFs offers an exciting pathway to enhanced sensors.

Ribbon-like and spontaneously folded structures of tungsten oxide nanofibers fabricated via electrospinning

Electrospinning of sub-100 nm thick WO₃ ribbon-like nanofibers and their periodically folded patterns is reported for the first time.

Nanocrystalline tin oxide nanofibers deposited by a novel focused electrospinning method. Application to the detection of TATP precursors

A new method of depositing tin dioxide nanofibers in order to develop chemical sensors is presented. It involves an electrospinning process with in-plane electrostatic focusing over micromechanized substrates. It is a fast and reproducible method. After an annealing process, which can be performed by the substrate heaters, it is observed that the fibers are intertwined forming porous networks that are randomly distributed on the substrate. The fiber diameters oscillate from 100 nm to 200 nm and fiber lengths reach several tens of microns. Each fiber has a polycrystalline structure with multiple nano-grains. The sensors have been tested for the detection of acetone and hydrogen peroxide (precursors of the explosive triacetone triperoxide, TATP) in air in the ppm range. High and fast responses to these gases have been obtained.

WO₃ nanolamella gas sensor: porosity control using SnO₂ nanoparticles for enhanced NO₂ sensing

Tungsten trioxide (WO3) is one of the important multifunctional materials used for photocatalytic, photoelectrochemical, battery, and gas sensor applications. Nanostructured WO3 holds great potential for enhancing the performance of these applications. Here, we report highly sensitive NO2 sensors using WO3 nanolamellae and their sensitivity improvement by morphology control using SnO2 nanoparticles. WO3 nanolamellae were synthesized by an acidification method starting from Na2WO4 and H2SO4 and subsequent calcination at 300 °C. The lamellae were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), which clearly showed the formation of single-crystalline nanolamellae with a c-axis orientation. The stacking of each nanolamella to form larger lamellae that were 50-250 nm in lateral size and 15-25 nm in thickness was also revealed. From pore size distribution measurements, we found that introducing monodisperse SnO2 nanoparticles (ca. 4 nm) into WO3 lamella-based films improved their porosity, most likely because of effective insertion of nanoparticles into lamella stacks or in between assemblies of lamella stacks. In contrast, the crystallite size was not significantly changed, even by introducing SnO2. Because of the improvement in porosity, the composites of WO3 nanolamellae and SnO2 nanoparticles displayed enhanced sensitivity (sensor response) to NO2 at dilute concentrations of 20-1000 ppb in air, demonstrating the effectiveness of microstructure control of WO3 lamella-based films for highly sensitive NO2 detection. Electrical sensitization by SnO2 nanoparticles was also considered.

On the origin of the spontaneous formation of nanocavities in hexagonal bronzes (W,V)O3

The synthesis route followed to prepare h-WO₃ type oxides results in the production of nanostructured crystals by the spontaneous formation of self-assembled and regular nano-cavities on their surface.

TiO2(B) nanoparticle-functionalized WO3nanorods with enhanced gas sensing properties

TiO₂(B)–WO₃nanorods exhibited fast response–recovery speeds, good reproducibility and good stability to several organic gases, indicating promising applications in gas sensing.

Simple patterned nanofiber scaffolds and its enhanced performance in immunoassay

Cancer has become the leading cause of death worldwide; early diagnosis and treatment of cancers is critical for the survival of the patients. The concentration of cancer markers in easy-to-access biological fluids can provide great assistance in screening for occult primary cancers, distinguishing malignant from benign findings, determining prognosis and prediction for cancer patients. The multiplex detection technology of a panel of cancer markers can greatly increase the accuracy of disease diagnosis. Herein, we briefly fabricate a high-throughput micro-immunoassay based on the electrospun polystyrene (PS) substrates to improve detection sensitivity. The immunoassay was evaluated by analyzing three different cancer biomarkers (AFP, CEA, VEGF). For AFP, CEA, VEGF immunofluorescence assay, the LOD of assay conducted on electrospun PS substrates before or after plasma and the conventional PS substrates were 0.42, 0.10, 1.12 ng/mL, 0.57, 0.09, 1.24 ng/mL, and 159.75, 26.19, 385.59 pg/mL, respectively (P < 0.05). Due to the high porosity and large surface area-to-volume ratio which is the foremost merit of nanostructures, and the plasma treatment which make the hydrophobic PS nanofibers hydropholic, the nanofibers substrates showed sufficient retention of immunoassay functionality and high potential for capture molecules immobilization. Consequently, the immunofluorescence assay conducted on electrospun PS substrates could significantly enhance the sensitivity and limits of detection.

CO and NO₂ Selective Monitoring by ZnO-Based Sensors

ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO₂ in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, respectively. CO and NO₂ sensing tests have demonstrated that the annealing temperature and shape of zinc oxide nanomaterials are the key factors in modulating the electrical and sensing properties. Specifically, ZnO NPs annealed at high temperature (700 °C) have been found sensitive to CO, while they displayed negligible response to NO₂. The opposite behavior has been registered for the one-dimensional ZnO NFs annealed at medium temperature (400 °C). Due to their adaptable sensitivity/selectivity characteristics, the developed sensors show promising applications in dual air quality control systems for closed ambient such as automotive cabin, parking garage and tunnels.

High performance field-effect ammonia sensors based on a structured ultrathin organic semiconductor film

High performance organic field-effect transistor (OFET)-based ammonia sensors are demonstrated with ultrathin (4-6 molecular layers) dendritic microstripes of an organic semiconductor prepared via dip-coating. These sensors exhibit high sensitivity, fast response/recovery rate, good selectivity, low concentration detection ability, and reliable reversibility, as well as stability. Such a performance represents great progress in the field of OFET-based sensors.