Au- ZnFe2O4 hollow microspheres based gas sensor for detecting the mustard gas simulant 2-chloroethyl ethyl sulfide.

Mustard gas, a representative of blister agents, poses a severe threat to human health. Although the structure of 2-chloroethyl ethyl sulfide (2-CEES) is similar to mustard gas, 2-CEES is non-toxic, rendering it a commonly employed simulant in related research. ZnFe2O4-based semiconductor gas sensors exhibit numerous advantages, including structural stability, high sensitivities, and easy miniaturization. However, they exhibit insufficient sensitivity at low concentrations and require high operating temperatures. Owing to the effect of electronic and chemical sensitization, the gas-sensing performance of a sensor may be remarkably enhanced via the sensitization method of noble metal loading. In this study, based on the morphologies of ZnFe2O4 hollow microspheres, a solvothermal method was adopted to realize different levels of Au loading. Toward 1 ppm of 2-CEES, the gas sensor based on 2 wt.% Au-loaded ZnFe2O4 hollow microspheres exhibited a response sensitivity twice that of the gas sensor based on pure ZnFe2O4; furthermore, the response/recovery times decreased. Additionally, the sensor displayed excellent linear response to low concentrations of 2-CEES, outstanding selectivity in the presence of several common volatile organic compounds, and good repeatability, as well as long-term stability. The Au-loaded ZnFe2O4-based sensor has considerable potential for use in detecting toxic chemical agents and their simulants.

Recent Progress in Flexible Surface Acoustic Wave Sensing Technologies.

In this work, the major methods for implementing flexible sensing technology-flexible surface acoustic wave (SAW) sensors-are summarized; the working principles and device characteristics of the flexible SAW sensors are introduced; and the latest achievements of the flexible SAW sensors in the selection of the substrate materials, the development of the piezoelectric thin films, and the structural design of the interdigital transducers are discussed. This paper focuses on analyzing the research status of physical flexible SAW sensors such as temperature, humidity, and ultraviolet radiation, including the sensing mechanism, bending strain performance, device performance parameters, advantages and disadvantages, etc. It also looks forward to the development of future chemical flexible SAW sensors for gases, the optimization of the direction of the overall device design, and systematic research on acoustic sensing theory under strain. This will enable the manufacturing of multifunctional and diverse sensors that better meet human needs.

Synthesis and Application of Polymer SXFA in the Detection of Organophosphine Agents with a SAW Sensor.

The effective detection of isopropyl methylfluorophosphonate (GB, sarin), a type of organophosphine poisoning agent, is an urgent issue to address to maintain public safety. In this research, a gas-sensitive film material, poly (4-hydroxy-4,4-bis trifluoromethyl)-butyl-1-enyl)-siloxane (SXFA), with a structure of hexafluoroisopropyl (HFIP) functional group was synthesized by using methyl vinylpropyl dichlorosilane and hexafluoroacetone trihydrate as initial materials. The synthesis process products were characterized using FTIR. SXFA was prepared on a 200 MHz shear surface wave delay line using the spin-coating method for GB detection. A detection limit of <0.1 mg/m3 was achieved through conditional experiments. Meanwhile, we also obtained a maximum response of 2.168 mV at a 0.1 mg/m3 concentration, indicating the much lower detection limit of the SAW-SXFA sensor. Additionally, a maximum response standard deviation of 0.11 mV with a coefficient of variation of 0.01 and a maximum recovery standard deviation of 0.22 mV with a coefficient of variation of 0.02 were also obtained through five repeated experiments. The results show that the SAW-SXFA sensor has strong selectivity and reproducibility, good selectivity, positive detection ability, high sensitivity, and fast alarm performance for sarin detection.

Sensitive Materials Used in Surface Acoustic Wave Gas Sensors for Detecting Sulfur-Containing Compounds.

There have been many studies on surface acoustic wave (SAW) sensors for detecting sulfur-containing toxic or harmful gases. This paper aims to give an overview of the current state of polymer films used in SAW sensors for detecting deleterious gases. By covering most of the important polymer materials, the structures and types of polymers are summarized, and a variety of devices with different frequencies, such as delay lines and array sensors for detecting mustard gas, hydrogen sulfide, and sulfur dioxide, are introduced. The preparation method of polymer films, the sensitivity of the SAW gas sensor, the limit of detection, the influence of temperature and humidity, and the anti-interference ability are discussed in detail. The advantages and disadvantages of the films are analyzed, and the potential application of polymer films in the future is also forecasted.

A passive wireless surface acoustic wave (SAW) sensor system for detecting warfare agents based on fluoroalcohol polysiloxane film.

Long-term monitoring of environmental warfare agengts is a challenge for chemical gas sensors. To address this issue, we developed a 433 MHz passive wireless surface acoustic wave (WSAW) gas sensor for dimethyl methylphosphonate (DMMP) detection. This WSAW gas sensor includes a YZ lithium niobate (LiNbO3) substrate with metallic interdigital transducers (IDTs) etched on it, and an antenna was placed near the IDT. A DMMP-sensitive viscoelastic polymer fluoroalcoholpolysiloxane (SXFA) film was prepared on a LiNbO3 substrate, and mode modeling coupling was used to optimize the design parameters. The sensor can function properly in an environments between -30 °C and 100 °C with humidity less than 60% RH. When the wireless transmission distance was within the range of 0-90 cm, the sensor noise increased with distance, and the stability was less than 32°/h. While optimizing the film thickness of SXFA, a relationship was observed between sensor sensitivity and film thickness. When the film thickness of SXFA reached 450 nm, the optimal value was reached. At a distance of 20 cm between the transmitting and receiving antennas, DMMP was detected at different concentrations with the developed WSAW gas sensor. The lower detection limit of DMMP was 0.48 mg/m3, the sensitivity of the sensor was 4.63°/(mg/m3), and repeatable performance of the sensor was confirmed.

Study on Porosity Defect Detection in Narrow Gap Laser Welding Based on Spectral Diagnosis.

As an advanced connection technology for large thick-walled components, narrow gap laser welding has the advantages of small heat input and high efficiency and quality. However, porosity defects are prone to occur inside the weld due to the complex welding environment. In this study, the influence of the process parameters and pollutants such as water and oil on the porosity defect were explored. The action mechanism of water on the electron temperature and spectral intensity of the laser-induced plasma was analyzed. The results showed that the spectral intensity during narrow gap laser welding was weaker than that of flat plate butt welding. Under the optimal welding process conditions, the electron temperature during narrow gap laser self-fusion welding was calculated as 7413.3 K by the Boltzmann plot method. The electron density was 5.6714 × 1015 cm-3, conforming to the thermodynamic equilibrium state. With six groups of self-fusion welding parameters, only sporadic porosity defects were observed according to the X-ray detection. When there was water on the base metal surface, a large number of dense pores were observed on the weld surface and in the weld through X-ray inspection. Compared with the spectral data obtained under the normal process, the relative light intensity of the spectrometer in the whole band was reduced. The electron temperature decreased to the range of 6900 to 7200 K, while the electron density increased. The spectrum variation during narrow gap laser wire filling welding was basically the same as that of laser self-fusion welding. The porosity defects caused by water and oil pollutants in the laser welding could be effectively identified based on the intensity of the Fe I spectral lines.

High-performance metal-oxide gas sensors based on hierarchical core-shell ZnFe2O4 microspheres for detecting 2-chloroethyl ethyl sulfide.

Mustard gas, an erosive chemical agent, is primarily used as a chemical weapon, which seriously threatens human life and health. Therefore, detecting mustard gas and its simulant, 2-chloroethyl ethyl sulfide (2-CEES), is a very important task. As a binary metal oxide with a spinel structure, ZnFe2O4 is widely used for fabricating gas sensors because of its stable chemical structure and abundant oxygen vacancies. In this study, gas-sensing ZnFe2O4 microspheres with a hierarchical core-shell nanosheet structure were prepared via a simple one-step solvothermal method. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and N2 adsorption analyses were performed to characterize the morphology, structure, and chemical composition of these microspheres. A gas sensor was fabricated from the as-synthesized material, and its gas sensing performance was evaluated, using 2-CEES as a target gas. The obtained ZnFe2O4-based sensor exhibited a high sensitivity of 9.07 to 1 ppm 2-CEES at the optimal working temperature of 250 °C. The sensor response and recovery times were 18 and 546 s, respectively, and its detection sensitivity of 2.87 achieved at a 2-CEES concentration of 0.01 ppm was within an acceptable range. Additionally, the sensor demonstrated sufficiently high 2-CEES selectivity, repeatability, and long-term stability.

Development of a SAW poly(epichlorohydrin) gas sensor for detection of harmful chemicals.

The uniformity and compactness of the surface of a viscoelastic sensitive film are among the most important factors that influence the characteristics of a surface acoustic wave (SAW) gas sensor, directly affecting the detection sensitivity of a SAW sensor on a target gas. In this paper, poly(epichlorohydrin) (PECH) with viscoelastic properties was used as sensitive film for the detection of 2-chloroethyl ethyl sulfide (CEES), a common simulant of the chemical agent mustard gas. Nanoscale films were prepared using a spin coating technology on a SAW delay line of 200 MHz. Films were evaluated using polarizing microscopy and atomic force microscopy and observed with uniform surface states and particle diameter in the cluster region of 4.52-5.22 µm. The interface parameters, including contact angle, surface tension, Gibbs free energy, work of adhesion, work of immersion, and spreading coefficient values were 9.31° to 39.63°, 22.475 to 29.945 mN m-1, -85.70 to -78.08 J m-2, 78.08 to 85.70 J m-2, -42.62 to -35.00 J m-2, and 0.46 to 8.08 J m-1, respectively. These values were obtained by experiments combined with the Young T equation and Gibbs adsorption isotherm, and the surface analysis was carried out theoretically. The glass transition temperature (-22.4 °C), viscosity, pyrolysis, and other physical characteristics of the prepared PECH were discussed. Five SAW sensors prepared at the same time were used to test the repeatability of CEES measurements at one concentration, where the consistency of the sensor preparation was confirmed. At a concentration of 13.6 mg m-3 for CEES, 10 consecutive detection results showed good repeatability (i.e., standard deviation = 0.295, coefficient of variance = 0.021, and population mean deviation = 0.364). At room temperature (20 °C ± 5 °C), different concentrations of CEES were detected using the developed sensor, which showed good linearity in the concentration range of 1.9-19.6 mg m-3 (y = 0.0309 + 1.13x, r = 0.99478). The limit of detection was 0.85 mg m-3, the limit of quantitation was 1.91 mg m-3, and the sensitivity of the SAW sensor was 1.13 mV (mg m-3). The adsorption mechanism related to PECH in the detection of CEES was also discussed.

Interface and Sensitive Characteristics of the Viscoelastic Film Used in a Surface Acoustic Wave Gas Sensor.

The surface morphology of viscoelastic-sensitive films significantly affects sensing characteristics of surface acoustic wave (SAW) sensors. Uniformity and compactness of the film surface directly influences detectability of the SAW sensor toward target gases. Viscoelastic fluoroalcoholpolysiloxane (SXFA) was prepared in this work using spin coating technology on an SAW delay line of 200 MHz and then used as coating for detection of dimethyl methylphosphonate (DMMP). Polarizing, atomic force, and scanning electron microscopies confirmed the uniformity of the SXFA surface. The particle diameter in the cluster region was 10-15 µm. The contact angle (5.72-26.69°), surface tension (21.053-29.155 mN/m), Gibbs free energy (-160.68 to -153.45 J/m2), and spreading coefficient (0.3028-6.9453 J/m2) of different concentrations of SXFA were obtained through experiments, and their relation was analyzed using the Young T equation and Gibbs adsorption isotherm. The glass transition temperature (-19.7 °C) and elasticity of SXFA were also discussed. The consistency of sensor preparation was confirmed by detecting DMMP with five SAW sensors prepared simultaneously. Seven consecutive tests showed that the SAW sensor presents satisfactory repeatability (standard deviation, s, 1.134; coefficient of variance, v, 0.065; and population mean deviation, δ, 0.913) at a concentration of 1.71 mg/m3 and acceptable linear relationship at a concentration range of 0.058-1.92 mg/m3, with a sensitivity of around 1.21 mv/(mg/m3). The sensor exhibited outstanding sensitivity and satisfactory linearity and repeatability to DMMP. Meanwhile, the sensing mechanism in gas adsorption was also discussed in terms of LSER formulation and hydrogen bonding formation between SXFA and DMMP.

Electron-acceptor-dependent light absorption, excited-state relaxation, and charge generation in triphenylamine dye-sensitized solar cells.

By choosing a simple triphenylamine electron donor, we herein compare the influence of electron acceptors benzothiadiazole benzoic acid (BTBA) and cyanoacrylic acid (CA), on energy levels, light absorption, and dynamics of excited-state evolution and electron injection. DFT and time-dependent DFT calculations disclosed remarkable intramolecular conformational changes for the excited states of these two donor-acceptor dyes. Photoinduced dihedral angle variation occurs to the triphenylamine unit in the CA dye and backbone planarization happens to conjugated aromatic blocks in the BTBA dye. Femtosecond spectroscopic measurements suggested the crucial role of having a long excited-state lifetime in maintaining a high electron-injection yield because a reduced driving force for a low energy-gap dye can result in slower electron-injection dynamics.

Efficient triarylamine-perylene dye-sensitized solar cells: influence of triple-bond insertion on charge recombination.

We synthesize two new metal-free donor-acceptor organic dyes (C266 and C267) featuring a N-annulated perylene block. Owing to the improved coplanarity of conjugated units as well as the prolonged conjugation upon inserting a triple bond between the triarylamine and perylene segments, the C267 dye exhibits a slightly red-shifted absorption peak and an enhanced maximum molar absorption coefficient with respect to its reference dye C266, leading to an improved photocurrent output in dye-sensitized solar cells. However, the triple-bond introduction also brings forth an over 100 mV reduced open-circuit photovoltage owing to faster interfacial charge recombination, which presents a clear correlation with a reduced mean thickness of self-assembled dye layer on titania as revealed by X-ray reflectivity measurements. The C266 dye, albeit with a relatively weaker light-harvesting capacity, displays a higher power conversion efficiency of 9.0% under the 100 mW cm(-2), simulated AM1.5G sunlight.

Multiple-state interfacial electron injection competes with excited state relaxation and de-excitation to determine external quantum efficiencies of organic dye-sensitized solar cells.

A comprehensive description of the complicated dynamics of excited state evolution and charge transfer at the photochemical interface in dye-sensitized solar cells is crucial to understand the mechanism of converting solar photons to clean electricity, providing an informative basis for the future development of advanced organic materials. By selecting two triarylamine-based organic donor-acceptor dyes characteristic of the respective benzoic acid and cyanoacrylic acid anchors, in this paper we reveal stepwise excited state relaxations and multiple-state electron injections at a realistic titania/dye/electrolyte interface based upon ultrafast spectroscopic measurements and theoretical simulations. Density functional theory (DFT) and time-dependent DFT calculations show that the optically generated "hot" excited state of the dye molecules can undergo a significant conformational relaxation via multistage torsional motions, and thereby transform into an equilibrium quinonoid structure characteristic of a more planar conjugated backbone. A set of kinetic parameters derived from the target analysis of femtosecond transient absorption spectra have been utilized to estimate the electron injection yield, which is in good accord with the maximum of external quantum efficiencies.