Hybrid ZnO/SWNT Nanostructures Based Gas Sensor

Zinc oxide (ZnO) nanoparticles decorated single walled carbon nanotubes (SWNTs) were electrochemically synthesized where the deposition conditions were systematically explored to tailor the size, density, and microstructure of the ZnO nanoparticles and correlated to the gas sensing performance. Room temperature conductometric detection of various analytes including CO, CO₂, NO₂, NH₃, SO₂, H₂S with ZnO/SWNT hybrid nanostructures demonstrated uncharacteristic selectivity towards H₂S with little to no response for the other analytes examined. Optimal ZnO/SWNTs gas sensor devices showed a significantly increased in H₂S sensitivity over unfunctionalized SWNT networks (i.e. 4.96 % per ppm_V vs. 0.225 % ppm_V) with a lower detection limit in the ppb range. Additionally, the H₂S sensing performance was greatly improved by enhancing the crystallinity of ZnO nanoparticles.     

Ionic Liquid‐based Microchannels for Highly Sensitive and Fast Amperometric Detection of Toxic Gases

Ionic liquid (IL)‐based microchannels sensors have been fabricated and employed for the detection of toxic ammonia (NH₃) and hydrogen chloride (HCl) gases, with enhanced sensitivity and response times compared to conventional electrodes. Electrochemical techniques were employed to understand the behaviour of these highly toxic gases in two ionic liquids, [C₄mpyrr][NTf₂] and [C₂mim][NTf₂], on a gold modified microchannels electrode. The limits of detection (LODs) obtained in [C₄mpyrr][NTf₂] for NH₃ (3.7 ppm) and in [C₂mim][NTf₂] for HCl (3.6 ppm) were lower than the current Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) for the two gases (25 ppm for NH₃ and 5 ppm for HCl). The response time of the sensor is 15 s with a sensitivity of 143 nA ppm^?1 and 14 nA ppm^?1 for HCl and NH₃, respectively. These results demonstrate the superiority of IL‐based microchannels sensors for detecting toxic gases, when compared to commercially available sensors or traditional IL‐based sensor designs, where high sensitivity or fast response time is still a challenge.     

meso‐Tritolylcorrole‐Functionalized Single‐walled Carbon Nanotube Donor?Acceptor Nanocomposites for NO2 Detection

meso‐Tritolylcorrole‐functionalized single‐walled carbon nanotubes (TTC‐SWNT) donor‐acceptor (D–A) heterojunction nanocomposite film was fabricated on a polycarbonate membrane through filtration and non‐covalent functionalization, providing an excellent sensing platform with low‐cost, high flexibility and good gas accessibility. The TTC‐SWNTs nanocomposite displays a fast and sensitive response to nitrogen dioxide with a limit of detection of 10 ppb (S/N=3). The sensing response was significantly amplified compared to the unmodified one, which was ascribed to a D–A heterojunction at the interface between electron donor TTC and electron acceptor SWNTs. This study provides a simple route to fabricate low‐cost and highly sensitive donor‐acceptor nanocomposite‐based gas sensors.     

Self-assembly of TiO2/polypyrrole nanocomposite ultrathin films and application for an NH3 gas sensor

TiO₂/polypyrrole (PPy) nanocomposite ultrathin films for NH₃ gas detection were fabricated by the in situ self-assembly technique. The films were characterized by UV–Vis absorption, FT–IR spectroscopy, and atomic force microscopy (AFM). The electrical properties of TiO₂/PPy ultrathin film NH₃ gas sensors, such as sensitivity, selectivity, reproducibility, and stability were investigated at room temperature in air as well as in N₂. The results showed that the optimum gas-sensing characteristics of TiO₂/PPy ultrathin film were obtained in the presence of 0.1?wt% colloidal TiO₂ for 20-min deposition. Compared with pure PPy thin-film sensors, the TiO₂/PPy film gas sensor has a shorter response/recovery time. It was also found that both humidity and temperature had an effect on the operation of the TiO₂/PPy film gas sensor at low NH₃ concentrations.     

A MnOOH‐Polyaniline Nanocomposite Modified Gold Electrode for Electrochemical Sensing of Nitrite

A novel non‐enzymatic nitrite sensor was fabricated by immobilizing MnOOH‐PANI nanocomposites on a gold electrode (Au electrode). The morphology and composition of the nanocomposites were investigated by transmission electron microscopy (TEM ) and Fourier transform infrared spectrum (FTIR ). The electrochemical results showed that the sensor possessed excellent electrocatalytic ability for NO₂⁻ oxidation. The sensor displayed a linear range from 3.0 μmol•L⁻¹ to 76.0 mmol•L⁻¹ with a detection limit of 0.9 μmol•L⁻¹ (S/N = 3), a sensitivity of 132.2 μA •L•mol⁻¹•cm⁻² and a response time of 3 s. Furthermore, the sensor showed good reproducibility and long‐term stability. It is expected that the MnOOH‐PANI nanocomposites could be applied for more active sensors and used in practice for nitrite sensing.     

Ammonia Gas Sensor Using Polypyrrole‐Coated TiO2/ZnO Nanofibers

Highly porous polypyrrole (PPy)‐coated TiO₂/ZnO nanofibrous mat has been successfully synthesized. The core TiO₂/ZnO nanofibers have an average diameter of ca. 100 nm and the shell of ultrathin PPy layer has a thickness of ca. 7 nm. The NH₃ gas sensor using the as‐prepared material exhibited a fast response over a wide dynamic range and high sensitivity with a detection limit of 60 ppb (S/N=3). Compared to conventional pristine PPy film, the improved performance in NH₃ detection can be attributed to the free access of NH₃ to PPy and a minimized gas diffusion resistance through the ultrathin PPy layer.     

Analysis of gasoline contaminated water samples by means of dopant-assisted atmospheric pressure photoionization differential ion mobility spectrometry

In this study the influence of aromatic dopant benzene on the sensitivity of GC-APPI-DMS to gasoline related aromatic compounds was investigated. This influence was investigated on example of four gasolin related fingerprints (toluene, ethylbenzene, o-xylene, and 1,2,4-trimethylbenzene), which were found in high relative abundance in the water-soluble gasoline fraction. The analysis of calibration curves slopes demonstrats that the GC-APPI-DMS sensitivity to gasoline fingerprints can be improved by up to seven times when benzene concentration in nitrogen carrier gas is less than 10 ppm_v/v. The estimated detection limits (S/N?=?3) for the analyzed in this study compounds were found to be within the range of 33–105 μg L^?1 at benzene concentration in the carrier gas of 2.27 ppm_v/v (10 μL injection volume). These limits of detection may be reduced (at the cost of lower resolution) using the larger injection volumes. For example, increase of injection volume to 100 μL at benzene concentration in the carrier gas of 2.27 ppm_v/v leads to reduction of LOD values for toluene, ethylbenzene, and o-xylene to 11.1, 13.3, and 5.3 μg L^?1, respectively.     

Porous reduced graphene oxide for ultrasensitive detection of nitrogen dioxide

The defect engineering in graphene plays a significant role for the application of gas sensors. In this work, we proposed an efficient method to prepare ultrasensitive gas sensors based on the porous reduced graphene oxide (PRGO). Photo-Fenton etching was carried out on GO nanosheets in a controlled manner to enrich their vacancy defects. The resulting porous graphene oxide (PGO) was then drop-coated on interdigital electrodes and hydrothermal reduced at 180 °C. Controllable reduction was achieved by varying the water amount. The gas sensor based on PRGO-5 min-6 h exhibited superior sensing and selective performance toward nitrogen dioxide (NO₂), with an exceptional high sensitivity up to 12 ppm^?1. The theoretical limit of detection is down to 0.66 ppb. The excellent performance could be mainly attributed to the typical vacancy defects of PRGO. Some residue carboxylic groups on the edges could also facilitate the adsorption of polar molecules. The process has a great potential for scalable fabrication of high-performance NO₂ gas sensors.     

Electrochemical Ammonia Gas Sensing in Nonaqueous Systems: A Comparison of Propylene Carbonate with Room Temperature Ionic Liquids

First, the direct and indirect electrochemical oxidation of ammonia has been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. In the case of the indirect oxidation of ammonia, its analytical utility of indirect for ammonia sensing was examined in the range from 10 and 100 ppm by measuring the peak current of new wave resulting from reaction between ammonia and hydroquinone, as function of ammonia concentration, giving a sensitivity 1.29×10^?7 A ppm^?1 (r²=0.999) and limit‐of‐detection 5 ppm ammonia. Further, the direct oxidation of ammonia has been investigated in several room temperature ionic liquids (RTILs), namely 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C₄mim] [BF₄]), 1‐butyl‐3‐methylimidazolium trifluoromethylsulfonate ([C₄mim] [OTf]), 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₂mim] [NTf₂]), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim] [NTf₂]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim] [PF₆]) on a 10 μm diameter Pt microdisk electrode. In four of the RTILs studied, the cyclic voltammetric analysis suggests that ammonia is initially oxidized to nitrogen, N₂, and protons, which are transferred to an ammonia molecule, forming NH via the protonation of the anion(s) (A^?). However, in [C₄mim] [PF₆], the protonated anion was formed first, followed by NH . In all five RTILs, both HA and NH are reduced at the electrode surface, forming hydrogen gas, which is then oxidized. The analytical ability of this work has also been explored further, giving a limit‐of‐detection close to 50 ppm in [C₂mim] [NTf₂], [C₄mim] [OTf], [C₄mim] [BF₄], with a sensitivity of ca. 6×10^?7 A ppm^?1 (r²=0.999) for all three ionic liquids, showing that the limit of detection was ca. ten times larger than that in propylene carbonate since ammonia in propylene carbonate might be more soluble in comparison with RTILs when considering the higher viscosity of RTILs.     

Individual and Simultaneous Voltammetric Determination of Cd(II), Cu(II) and Pb(II) Applying Amino Functionalized Fe3O4@Carbon Microspheres Modified Electrode

Amino‐functionalized Fe₃O₄@carbon microspheres (NH₂?Fe₃O₄@C) were prepared and the electrochemical sensor was constructed using NH₂?Fe₃O₄@C modified glassy carbon electrodes (GCE) to determine toxic heavy metals in aqueous solution. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure and phase of NH₂?Fe₃O₄@C. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results indicate that NH₂?Fe₃O₄@C modified GCE possesses large active area and excellent electron transfer. Under optimized electrochemical condition, Cd(II), Pb(II) and Cu(II) were determined using NH₂?Fe₃O₄@C modified GCE. The electrode through amino functionalization exhibits higher sensitivity and lower detection limit toward Cd(II) and Cu(II) due to the acid‐base pairing interaction between the electron‐rich ?NH₂ ligand and the electron‐deficient heavy metal ions. Compared with other similar results reported in the literature, the NH₂?Fe₃O₄@C modified electrode exhibits wider linear response range while with comparable lower detection limit. It also exhibits excellent stability, reproducibility and anti‐interference ability.     

Polyaniline Sheathed Black Phosphorous: A Novel,Advanced Platform for Electrochemical Sensing Applications

Despite its excellent properties, the inherent unstable nature of black phosphorus (BP) in ambient atmosphere has severely restricted its use in electrochemical sensing applications. In this work, polyaniline (PANI) sheathed BP was prepared via the electrochemical polymerisation of aniline on BP coated screen printed carbon electrode (i. e., SPCE/BP) which resulted in an efficient, stable electrochemical platform (i. e., SPCE/BP@PANI) with improved properties which was evaluated for electrochemical detection of two model bioanalytes namely, ascorbic acid (AA) and Hydrazine (Hy). The formation of PANI on the SPCE/BP exhibited a pair of stable and well‐defined redox peaks indicating the better adsorption energy and fast electron transfer nature of BP as compared to other 2D materials like graphene and transitional metal dichalcogenides. FESEM and XPS studies revealed the formation and uniform growth of PANI on BP surface without any aggregation. Electrochemical impedance spectroscopy analyses revealed that SPCE/BP@PANI can act as a suitable electrocatalyst material for the sensing of AA and Hy. Thus, SPCE/BP@PANI electrode exhibited low limit of detection (D_L; 1.69 μM), excellent reproducibility and better selectivity towards AA oxidation over glucose, sucrose, urea, citric acid, sodium, nitrate, nitrite and magnesium with a sensitivity of 3.38 A M^?1 cm^?2 (R²=0.98) in the dynamic range of 10–1100 μM. The excellent analytical performance of the BP@PANI is plausible due to better adsorption energy and fast electron transfer of BP. Further, SPCE/BP@PANI was also used for successful detection of AA in processed fruit juice with good recovery. Under the optimal DPV conditions, the modified electrode was extended for detection of Hy in a linear range of 100–1500 μM with sensitivity of 0.09 A M^?1 cm^?2 (R²=0.99) and D_L=89 μM validating the potential of BP based composites in wide range of electrochemical applications.     

Mediatorless Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Immobilized on 4‐Carboxyphenyl Film Electrografted on Gold Electrode

A novel method to fabricate a third‐generation hydrogen peroxide biosensor was reported. The electrode was first derivatized by electrochemical reduction of in situ generated 4‐carboxyphenyl diazonium salt (4‐CPDS) in acidic aqueous solution yielded stable 4‐carboxyphenyl (4‐CP) layer. The horseradish peroxidase (HRP) enzyme was then covalently immobilized by amidation between NH₂ terminus of enzyme and COOH terminus of 4‐CP film making use of the carbodiimide chemistry. Electrodeposition conditions used to control electrode functionalization density and film electron transfer kinetics were assessed by chronoamperometry and electrochemical impedance spectroscopy. The immobilized HRP displayed excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H₂O₂) without any mediators. The effect of various operational parameters was explored for optimum analytical performance. The reported biosensor exhibited fast amperometric response (within 5 s) to H₂O₂. The detection limit of the biosensor was 5 μM, and linear range was from 20 μM to 20 mM. Furthermore, the biosensor exhibited high sensitivity, good reproducibility, and long‐term stability.     

Reversed‐phase liquid chromatographic determination of enantiomers of atenolol in rat plasma using derivatization with Marfey's reagent

An HPLC method was established for enantioseparation of (R,S)‐atenolol (ATE) and determination of enantiomers in rat plasma. Marfey's reagent (1‐fluoro‐2,4‐dinitrophenyl‐5‐L‐alanine amide, FDNP‐L‐Ala‐NH₂, MR) was used as chiral derivatizing reagent with detection of diastereomers at 340 nm. It was shown that the R‐isomer eluted before the S‐isomer. The method was validated for linearity, repeatability, limits of detection and limit of quantification (LOQ). Recovery of ATE at LOQ was 92.8% for (R)‐ATE and 92.6% for (S)‐ATE. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel low humidity sensor made of TiO(2) nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (TiO₂ NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50 wt.% of TiO₂ NWs/PAMPS composite material films showed excellent sensitivity (2.63 −ΔHz/Δppm_v) at 31.5 ppm_v), linearity (R² = 0.9959) and acceptable response time (64 s at 34.6 ppm_v). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50 wt.% TiO₂ NWs into PAMPS in the increased sensitivity of low humidity sensing.     

Fabrication of New Magnetic Nanoparticles (Fe3O4) Grafted Multiwall Carbon Nanotubes and Heterocyclic Compound Modified Electrode for Electrochemical Sensor

Magnetic Fe₃O₄ nanoparticles functionalized multiwalled carbon nanotubes (nano‐Fe₃O₄ MWNTs) were prepared for electrochemical sensors. 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole was used as a connecter to form a network that connected nano‐Fe₃O₄ MWNTs to the Au electrode surface. Modified process of the electrode was studied with SEM, TEM and cyclic voltammetry. Cyclic voltammetry and amperometric i‐t curve were used to investigate characteristics of the obtained electrode. The sensor has been successfully used on the direct detection of catechol and showed excellent performances. The linear regression equation was I_pa(μA)=0.07763+0.16739 C (μmol/L); R=0.9993 and the detection limit was 5.38×10^?8 mol/L. The modified electrode showed good reproducibility and stability.     

Indirect reversed‐phase high‐performance liquid chromatographic and direct thin‐layer chromatographic enantioresolution of (R,S)‐Cinacalcet

Enantioresolution of the calcimimetic drug (R,S)‐Cinacalcet was achieved using both indirect and direct approaches. Six chiral variants of Marfey's reagent having l ‐Ala‐NH₂, l ‐Phe‐NH₂, l ‐Val‐NH₂, l ‐Leu‐NH₂, l ‐Met‐NH₂ and d ‐Phg‐NH₂ as chiral auxiliaries were used as derivatizing reagents under microwave irradiation. Derivatization conditions were optimized. Reversed‐phase high‐performance liquid chromatography was successful using binary mixtures of aqueous trifluoroacetic acid and acetonitrile for separation of diastereomeric pairs with detection at 340 nm. Thin silica gel layers impregnated with optically pure l ‐histidine and l ‐arginine were used for direct resolution of enantiomers. The limit of detection was found to be 60 pmol in HPLC while in TLC it was found to be in the range of 0.26–0.28 µg for each enantiomers. Copyright © 2010 John Wiley & Sons, Ltd.     

聚甲基丙烯酸甲酯包覆(CH3NH3)PbBr3纳米晶静电纺丝膜的制备及对氨气的荧光传感

采用原位合成法制备了聚甲基丙烯酸甲酯包覆MAPbBr₃纳米晶(MAPbBr₃@PMMA,MA=甲铵离子)静电纺丝膜。当氨气(NH₃)通入MAPbBr₃@PMMA纤维膜时与MAPbBr₃中的MA发生取代,能显著降低MAPbBr₃@PMMA纤维的荧光强度,以此构建了基于MAPbBr₃@PMMA纤维荧光猝灭的NH₃传感器。通过扫描电镜、透射电镜、粉末X射线衍射和红外对静电纺丝膜的形貌和结构进行表征,通过紫外可见光谱、荧光光谱对其光学特性进行表征。结果表明,传感器的荧光强度与NH₃浓度在8~90 mg·L^-1之间呈现出良好的线性关系(r=0.995 9),NH₃的检出限低(3 mg·L^-1),且具有良好的重现性和选择性。在实际样品气体的测定中,加标回收率为92.2%~102.1%,相对标准偏差(RSD)为1.8%~3.2%。     

Thinner is Better: An Ultrathin Conducting Oligoaniline Film for Gas Microsensors with Ultralow Detection Limits

An ultralow‐limit gas microsensor based on an ultrathin conducting oligoaniline film integrated with microscale gold electrodes is developed. A nanoscale oligoaniline film is fabricated on a poly(dimethylsiloxane) (PDMS) substrate using graft polymerization using FeCl₃, a mild oxidant, rather than conventional (NH₄)₂S₂O₈. The as‐fabricated film is around 14 nm in thickness and above 85% transmittance on a PDMS substrate with a smooth surface morphology and high conductivity. Taking NH₃ as a protocol, the nanoscale oligoaniline film microsensor shows an ultralow detection limit to the ppb level with more rapid response and high sensitivity to NH₃ compared to the thicker PANI film using conventional methods.

     

Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12 min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n = 20). Reproducibility of area counts at two levels, namely 100 ppm_v and 1000 ppm_v over a period of two days were found to be less than 5.5% (n = 20). Oxygen and nitrogen were found to be linear over a range from 20 ppm_v to 10,000 ppm_v with correlation coefficients of at least 0.998 and detection limits of less than 10 ppm_v. Hydrocarbons of interest were found to be linear over a range from 200 ppb_v to 1000 ppm_v with correlation coefficients of greater than 0.999 and detection limits of less than 100 ppb_v.     

Humidity Sensing Properties of Flower‐Like VO2(B) and VO2(M) Nanostructures

VO₂(B) nanoflowers were synthesized via hydrothermal method, and VO₂(M) nanoflowers were obtained through heat‐transformation. Two sensors based on VO₂(B) and VO₂(M) nanoflowers were fabricated and their humidity characteristics were studied. It was found that these sensors exhibited fast response and recovery, perfect reproducibility and good stability. The VO₂(M) type sensor is more sensitive at high RH and can be used for high humidity detection. On the contrary, the VO₂(B) type sensor has a higher sensitivity at low RH, and can be used for low humidity detection, which is difficult for humidity sensors based on many other semiconductor oxides.