Selective and Trace Level Detection of Hydrazine Using Functionalized Single-Walled Carbon Nanotube-Based Microelectronic Devices

Carbon nanotube (CNT) networks are identified as potential substitute and surpass the conventional indium doped tin oxide (ITO) in transparent conducting electrodes, thin-film transistors, solar cells, and chemical sensors. Among them, CNT based gas sensors gained more interest because of its need in environmental monitoring, industrial control, and detection of gases in warfare or for averting security threats. The unique properties of CNT networks such as high surface area, low density, high thermal conductivity and chemical sensitivity making them as a potential candidate for gas sensing applications. Commercial unsorted single walled carbon nanotubes (SWCNT) were purified by thermal oxidation and acid treatment processes and dispersed in organic solvent N-methyl pyrolidone using sonication process in the absence of polymer or surfactant. Optically transparent SWCNT networks are realized on glass substrate by coating the dispersed SWCNT with the help of dynamic spray coating process at 200oC. The SWCNT random network was characterized by scanning electron microscopy and UV-vis-NIR spectroscopy. Gas sensing property of transparent film towards ammonia vapor is studied at room temperature by measuring the resistance change with respect to the concentration in the range 0-1000 ppm. The sensor response is increased logarithmically in the concentration range 0 to 1000 ppm with the detection limit 0.007 ppm. The random networks are able to detect ammonia vapor selectively because of the high electron donating nature of ammonia molecule to the SWCNT. The sensor is reversible and selective to ammonia vapor with response time 70 seconds and recovery time 423 seconds for 62.5 ppm with 90% optical transparency at 550 nm.

Methods to fabricate networks of in-plane aligned single walled carbon nanotubes (SWCNTs) have tremendous potential for improving the properties of various microelectronic devices, including electrodes, transistors, and capacitors. Here, we investigate an SWCNT ink treated with a low-molecular-weight electrolyte, producing a lyotropic liquid crystal (LC) phase in aqueous media. The order parameter and dichroic ratio of the ink were measured by polarized UV–vis–NIR absorption spectra. Well-aligned SWCNT films were obtained by applying mechanical shearing, which was confirmed by polarized optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and polarized UV–vis–NIR absorption spectroscopy.

Abstract. Ambient pine forest air was oxidized by OH, O3, or NO3 radicals using an oxidation flow reactor (OFR) during the BEACHON-RoMBAS (Bio–hydro–atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Biogenic Aerosol Study) campaign to study biogenic secondary organic aerosol (SOA) formation and organic aerosol (OA) aging. A wide range of equivalent atmospheric photochemical ages was sampled, from hours up to days (for O3 and NO3) or weeks (for OH). Ambient air processed by the OFR was typically sampled every 20–30 min, in order to determine how the availability of SOA precursor gases in ambient air changed with diurnal and synoptic conditions, for each of the three oxidants. More SOA was formed during nighttime than daytime for all three oxidants, indicating that SOA precursor concentrations were higher at night. At all times of day, OH oxidation led to approximately 4 times more SOA formation than either O3 or NO3 oxidation. This is likely because O3 and NO3 will only react with gases containing C = C bonds (e.g., terpenes) to form SOA but will not react appreciably with many of their oxidation products or any species in the gas phase that lacks a C = C bond (e.g., pinonic acid, alkanes). In contrast, OH can continue to react with compounds that lack C = C bonds to produce SOA. Closure was achieved between the amount of SOA formed from O3 and NO3 oxidation in the OFR and the SOA predicted to form from measured concentrations of ambient monoterpenes and sesquiterpenes using published chamber yields. This is in contrast to previous work at this site (Palm et al., 2016), which has shown that a source of SOA from semi- and intermediate-volatility organic compounds (S/IVOCs) 3.4 times larger than the source from measured VOCs is needed to explain the measured SOA formation from OH oxidation. This work suggests that those S/IVOCs typically do not contain C = C bonds. O3 and NO3 oxidation produced SOA with elemental O : C and H : C similar to the least-oxidized OA observed in local ambient air, and neither oxidant led to net mass loss at the highest exposures, in contrast to OH oxidation. An OH exposure in the OFR equivalent to several hours of atmospheric aging also produced SOA with O : C and H : C values similar to ambient OA, while higher aging (days–weeks) led to formation of SOA with progressively higher O : C and lower H : C (and net mass loss at the highest exposures). NO3 oxidation led to the production of particulate organic nitrates (pRONO2), while OH and O3 oxidation (under low NO) did not, as expected. These measurements of SOA formation provide the first direct comparison of SOA formation potential and chemical evolution from OH, O3, and NO3 oxidation in the real atmosphere and help to clarify the oxidation processes that lead to SOA formation from biogenic hydrocarbons.

Effect of covalent and non-covalent linking of zinc(II) phthalocyanine functionalised carbon nanomaterials on the sensor response to ammonia

We fabricated a highly stable and sensitive gas sensor based on single-walled carbon nanotubes (SWNTs) protected by metal-oxide coating layer. SWNTs were deliberately decorated with 2–5 nm of oxygen-deficient SiOx and AlOx by pulsed laser deposition, followed by annealing under Ar/H2 ambient. Surpassing the as-grown SWNTs, the metal-oxide coated SWNTs showed an excellent sensing stability with a variation of sensor response less than 7–8%. The obtained sensitivity to NO2 was also improved. Moreover, the relationship between NO2 concentration and sensor response can be described by the Frumkin–Temkin isotherm.

Chemiresistor-based vapour sensors made from network films of single-walledcarbon nanotube (SWNT) bundles on flexible plastic substrates (polyethyleneterephthalate, PET) can be used to detect chemical warfare agent simulants for thenerve agents Sarin (diisopropyl methylphosphonate, DIMP) and Soman (dimethylmethylphosphonate, DMMP). Large, reproducible resistance changes (75–150%),are observed upon exposure to DIMP or DMMP vapours, and concentrations aslow as 25 ppm can be detected. Robust sensor response to simulant vapours isobserved even in the presence of large equilibrium concentrations of interferentvapours commonly found in battle-space environments, such as hexane, xylene andwater (10 000 ppm each), suggesting that both DIMP and DMMP vapours arecapable of selectively displacing other vapours from the walls of the SWNTs.Response to these interferent vapours can be effectively filtered out by using a2 µm thick barrier film of the chemoselective polymer polyisobutylene(PIB) on the SWNT surface. These network films are composed of a1–2 µm thick non-woven mesh of SWNT bundles (15–30 nm diameter), whose sensor response isqualitatively and quantitatively different from previous studies on individualSWNTs, or a network of individual SWNTs, suggesting that vapour sorptionat interbundle sites could be playing an important role. This study also showsthat the line patterning method used in device fabrication to obtain any desiredpattern of films of SWNTs on flexible substrates can be used to rapidly screensimulants at high concentrations before developing more complicated sensor systems.

Vanadium oxide loading on tin dioxide nanoparticles for improving gas detection in a humid atmosphere

Assessing the interaction of alcohol homologs with InAs nanowires in contact with gas-permeable SWCNT electrode: Towards a novel sensing platform

A SERS biosensor with magnetic substrate CoFe2O4@Ag for sensitive detection of Hg2+

Single wall carbon nanotubes (SWCNTs) were synthesized from chemical vapor deposition (CVD) by decomposition of ethanol over a Fe+Co/MgO heterogeneous catalyst. The SWCNTs were treated by fluorine plasma from microwave plasma enhanced chemical vapor deposition (MPECVD) for surface modification, and developed as novel gas sensor materials. In gas-sensing tests, the SWCNT-based gas sensors treated by fluorine plasma have shown a p-type response with resistance enhancement upon exposure to 50-500 ppm ethanol at room temperature. Fluorine plasma modification can enhance the sensor response (100 ppm) from 1.15 to 1.28 on process duration of 60 s due to the apparent elimination of amorphous carbon, as demonstrated by Raman results. The sensitivity (100 ppm) increases two more times (from 0.0009 to 0.0019) and the linear range of measurement can also extend. In addition, the response and recovery time (100 ppm) can decrease apparently from 195 to 69 s and 374 to 202 s due to the existence of numerous fluorine-included functional groups, as demonstrated by the results of x-ray photoelectron spectroscopy and Auger electron spectroscopy. Therefore, the fluorinated SWCNTs can elevate the sensitivity and reactivity for room temperature ethanol sensing.

Gold-doped nano-perovskite-decorated carbon nanotubes for electrochemical sensing of hazardous hydrazine with application in wastewater sample

Detection of volatile organic compounds by an interferometric sensor

Striking colorimetric probe (CynH) for abrupt detection of hydrazine under complete aqueous solution was achieved. The water soluble probe was designed with electron "push-pull" strategy by coupling of 4-hydroxy benzaldehyde and 2, 3, 3-trimethylindolinine. The positively charged N-propylated indolinine make the probe completely soluble in water. The probe yields eye catching selective detection of hydrazine over other competing analytes with high sensitivity. Obvious colour change was observed from colourless to appearance of bright pink colour with hydrazine. It reacts quickly with hydrazine within 2min and makes the probe an effective candidate for practical application. The real time application was demonstrated using paper strip to detect hydrazine vapour. This probe is superior to earlier reported probes because of its effective sensing of hydrazine displayed with various applications including real-time strip based sensing, spray test and soil analysis. In all the examinations, the probe yields distinct response with rapid naked eye colour change which overcomes the drawbacks of previous reports.

The tunable synaptic plasticity of biological sensory systems plays a pivotal role in efficient information processing and adaptation. Bio‐mimetic sensory synaptic devices, particularly those for tactile synapses, usually lack effective sensory gating control and thus exhibit limited adaptability to external stimuli. Here, an artificial tactile synaptic sensor is introduced that mimics the features of biological systems. The monolithic device utilizes an iongel‐gated single‐walled carbon nanotube (SWCNT) network transistor with slow but reversible electrochemical doping characteristics. Utilizing an iongel with a mechanosensitive 3D structure, the device demonstrates pressure sensing ability and nonvolatile changes to the p‐doping of the SWCNT network that depend on pressure amplitude and duration and enable long‐term memory of pressure signals for up to ≈22 h. The device can work in excitatory or inhibitory mode. In both cases, the synaptic plasticity can be adjusted independently from the tactile stimulus by varying the gate voltage, which emulates the intrinsic plasticity of biological systems. Furthermore, the time‐dependent and spatially nonuniform doping of the SWCNT channel during and after pressure loading is corroborated through in situ photoluminescence imaging. This visualization of the doping process in SWCNT networks provides direct insights into the operation mechanism underlying the nonvolatile pressure response in these artificial tactile synaptic sensors.

<p>Comprehensive measurements were conducted to simultaneously monitor the trace gases (HCl, HONO, HNO<sub>3</sub>, SO<sub>2</sub>, and NH<sub>3</sub>) and inorganic chemical constituents (Cl<sup>-</sup>, NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, Na<sup>+</sup>, NH<sub>4</sub><sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, and Mg<sup>2+</sup>) of fine particulates (PM<sub>1</sub> and PM<sub>2.5</sub>) at hourly resolution during the Winter Fog Experiment (WIFEX) field campaign, Delhi, India, for the winter period of 2017-2018. The measurements were performed using the instrument called Monitor for AeRosols and Gases in Ambient air (MARGA-2S) to study the role of chemical composition and gas-particle interplay chemistry in the life cycle of fog, i.e., formation, development, and dissipation phase. In the past, the variation of fine particle acidity (pH) and its impact on fog has not been studied explicitly and quantitatively over Delhi. The pH is a fundamental property of aerosol that plays a significant role in the chemical behavior and composition of particles, but it is very challenging and difficult to measure directly. Particulate water is also a significant component of aerosol and can serve as a medium for aqueous-phase reactions under foggy conditions. The pH depends on the particle water amount, as pH represents the concentration of H<sup>+</sup> per liquid water volume (i.e., particulate water). Whereas, H<sup>+</sup> concentration per unit volume of air is defined as the particulate proton loading.</p><p>Using the measured gas-phase and particle-phase concentrations and meteorological observations (T, RH), the particulate water and pH were estimated from the thermodynamic model ISORROPIA-II. In this study, the gas phase NH<sub>3</sub>, HNO<sub>3</sub>, and HCl and particle-phase NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>-</sup>, Cl<sup>-</sup>, and SO<sub>4</sub><sup>2-</sup> species were estimated using ISORROPIA-II, and model predictions of these species were validated by using the measured gas and particle-phase species. The predictions were confirmed by a good agreement between predicted and measured ammonia concentrations (r=0.94) and aerosol species concentrations ammonium (r=0.97) chloride (r=0.61), nitrate (r=0.61), and sulfate (r=0.74). The predicted PM<sub>2.5</sub> pH ranged from 2.55 to 6.54, with mean pH of 4.55 ± 0.51. This was consistent with the findings of previous studies. It is concluded that high particle water content, higher acidic pH, and abundant ammonia concentrations can promote the gas-particle partitioning and formation of more secondary particles under foggy conditions. The scattering cross-section of these secondary fine hygroscopic particles increases under high humidity conditions due to water uptake, resulting in visibility degradation.</p>