Sensing characteristics of aged zirconia-based hydrogen sensor utilizing Zn–Ta-based oxide sensing-electrode

We report here the enhanced sensing characteristics to H₂ for a potentiometric sensor using an yttria-stabilized zirconia (YSZ) solid electrolyte and a ZnO(+ 84 wt.% Ta₂O₅) sensing electrode (SE) after aging at 500 °C. The emf response toward 400 ppm H₂ was found to gradually increase up to − 800 mV after 40 days operation (aging) and was stabilized at this value until the 90th day. The aged and stabilized sensor exhibited highly sensitive response to H₂, with minor responses toward other examined gases such as NOx and HCs. The 90% response time toward 100 ppm H₂ was approximately 70 s. The H₂ sensitivity of the stabilized sensor was hardly affected by changes in water vapor as well as O₂ concentration, with repeatable and reproducible responses to H₂.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

Non-enzymatic detection of hydrogen peroxide using a functionalized three-dimensional graphene electrode

A novel three-dimensional (3D) electrochemical sensor was developed for highly sensitive detection of hydrogen peroxide (H₂O₂). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Using in-situ polymerized polydopamine as the linker, the 3D electrode was functionalized with thionine molecules which can efficiently mediate the reduction of H₂O₂ at close proximity to the electrode surface. Such stable non-enzymatic sensor is able to detect H₂O₂ with a wide linear range (0.4 to 660 μM), high sensitivity (169.7 μA mM^− 1), low detection limit (80 nM), and fast response (reaching 95% of the steady current within 3 s). Furthermore, this sensor was used for real-time detection of dynamic release of H₂O₂ from live cancer cells in response to a pro-inflammatory stimulant.     

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu₂O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H₂O₂ and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu₂O microcubes exhibited a direct electrocatalytic activity for the reduction of H₂O₂ in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H₂O₂ with detection limit of 1.5 × 10^?6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10^?7 M, a linear detection range up to 500 μM and with a sensitivity of ?70.8 μA/mM.     

Trace gas detection of benzene,toluene, p-, m- and o-xylene with a compact measurement system using cantilever enhanced photoacoustic spectroscopy and optical parametric oscillator

A compact measurement system based on a novel combination of cantilever enhanced photoacoustic spectroscopy (CEPAS) and optical parametric oscillator (OPO) was applied to the gas phase measurement of benzene, toluene, and o-, m- and p-xylene (BTX) traces. The OPO had a band width (FWHM) of 1.3 nm, was tuned from 3237 to 3296 nm in steps of 0.1 nm and so spectra of BTX at different concentrations were recorded. The power emitted by the OPO increased from 88 mW at 3237 nm to 103 mW at 3296 nm. The univariate detection limits (3σ, 0.951 s) for benzene, toluene, p-, m- and o-xylene at 3288 nm were 12.0, 9.8, 13.2, 10.1 and 16.0 ppb, respectively. Multivariate data analysis using science-based calibration was used to resolve the interference of the analytes. The multivariate detection limits (3σ, 3237–3296 nm, 591 spectral points each 0.951 s) for benzene, toluene, p-, m- and o-xylene in the multi-compound sample, where all other analytes and water interfere were 4.3, 7.4, 11.0, 12.5 and 6.2 ppb, respectively. Without interferents, the multivariate detection limits varied between 0.5 and 0.6 ppb. The sum of the cross-selectivities (3237–3296 nm, 591 spectral points, each 0.951 s) per analyte were below 0.05 ppb/ppb, with an average of 0.038 ppb/ppb. The cross-selectivity of water to the analytes was on average 1.22 × 10⁻⁴ ppb/ppb. The OPO is small in size (L × W × H 125 × 70 × 45 mm), commercially available, and easy to operate and integrate to setups. The combination with sensitive CEPAS enables compact measurement systems for industrial as well as environmental trace gas monitoring.     

Microstructure control of WO3 film by adding nano-particles of SnO2 for NO2 detection in ppb level

To fabricate more excellent NO₂ sensor with high sensor response and good linearity between the sensor response and NO₂ concentration, the microstructure of WO₃ lamellae was controlled by adding nano-particles of SnO₂. It was found that the sintering of WO₃ lamellae was inhibited by adding nano-particles of SnO₂. The device using WO₃ lamellae added a small amount of SnO₂ nano-particles had the highest sensor response, exhibiting a high sensor response (S = 60-540) even to dilute NO₂ (100–1000 ppb) in air at 200°C.     

Novel poly (neutral red) nanowires as a sensitive electrochemical biosensing platform for hydrogen peroxide determination

Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H₂O₂ and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H₂O₂ at −0.1 V with a linear response range of 1 μM to 8 mM with a correlation coefficient of 0.996. The detection limit (S/N = 3) and the response time were determined to be 1 μM and <5 s and the high sensitivity is up to 318 μA mM⁻¹ cm⁻².     

Solubility of hydrogen in toluene for the ternary system H2 + CO2 + toluene from 305 to 343 K and 1.2 to 10.5 MPa

The solubility of hydrogen in toluene in the presence of the compressed CO₂ at the temperatures from 305 to 343 K and the pressures from 1.2 to 10.5 MPa was measured by using a continuous flow technique. The obtained data indicate that more hydrogen could be dissolved in toluene at the pressures higher than a certain value depending on temperature and the molar ratio of H₂ to CO₂ in gas. The Peng–Robinson equation of state associated with the van der Waals mixing rule were found to correlate the VLE data of the ternary system H₂ + CO₂ + toluene satisfactorily. From the volume expansion resulted from the dissolution of CO₂ in toluene calculated by the proposed model, it was found that hydrogen solubility was generally increased with increasing volume expansion. A large volume expansion was required to enhance hydrogen solubility when the mole fraction of hydrogen in gas was low.     

A sensitivity-controlled hydrogen peroxide sensor based on self-assembled Prussian Blue modified electrode

In this communication, a hydrogen peroxide (H₂O₂) sensor based on self-assembled Prussian Blue (PB) modified electrode was reported. Thin film of PB was deposited on the electrode by self-assembly process including multiple sequential adsorption of ferric ions and hexacyanoferrate ions. The as-prepared PB modified electrode displayed sufficient stability for practical sensing application. At an applied potential of ?0.05 V vs. Ag/AgCl (sat. KCl), PB modified electrode with 30 layers exhibited a linear dependence on H₂O₂ concentration in the range of 1 × 10^?6–4 × 10^?4 M (r = 0.9998) with a sensitivity of 625 mA M^?1 cm^?2. It was found that the sensitivity of H₂O₂ sensors could be well controlled by adjusting the number of deposition cycles for PB preparation. This work demonstrates the feasibility of self-assembled PB modified electrode in sensing application, and provides an effective approach to control the sensitivity of PB-based amperometric biosensors.     

Determination of hydrogen sulfide in gasoline by Au nanoclusters modified glassy carbon electrode

A promising hydrogen sulfide (H₂S) sensor was prepared by electrodeposition of Au nanoclusters on glassy carbon electrode (GCE) and the surface structure was characterized by SEM and EDAX. These flower-like form Au nanoclusters, which were made up of highly dense clustering Au nanorods with an average diameter of 20 nm and length up to 80 nm, had an average size about 600 nm and uniformly distributed on the GCE surface. The electrocatalytic oxidation of H₂S in gasoline was performed on this modified electrode, which had a satisfactory liner response to H₂S in the range of 1–80 ppm and a detection limit of 0.45 ppm (s/n = 3). This sensor was sensitive, selective and stable.     

Thermodynamics of organic mixtures containing amines. X. Phase equilibria for binary systems formed by imidazoles and hydrocarbons: Experimental data and modelling using DISQUAC

(Solid + liquid) equilibrium (SLE) temperatures have been determined using a dynamic method for the systems (1H-imidazole, + benzene, + toluene, + hexane, or + cyclohexane; 1-methylimidazole + benzene, or + toluene, 2-methyl-1H-imidazole + benzene, + toluene, or + cyclohexane, and benzimidazole + benzene). In addition (liquid + liquid) equilibrium (LLE) temperatures have been obtained using a cloud point method for (1H-imidazole, + hexane, or + cyclohexane; 1-methylimidazole + toluene, and 2-methyl-1H-imidazole + cyclohexane). The measured systems show positive deviations from the Raoult’s law, due to strong dipolar interactions between amine molecules related to the high dipole moment of imidazoles. On the other hand, DISQUAC interaction parameters for the contacts present in these solutions and for the amine/hydroxyl contacts in (1H-imidazole + 1-alkanol) mixtures have been determined. The model correctly represents the available data for the examined systems. Deviations between experimental and calculated SLE temperatures are similar to those obtained using the Wilson or NRTL equations, or the UNIQUAC association solution model. The quasichemical interaction parameters are the same for mixtures containing 1H-imidazole, 1-methylimidazole, or 2-methyl-1H-imidazole and hydrocarbons. This may be interpreted assuming that they are members of a homologous series. Benzimidazole behaves differently.     

(Liquid + liquid) equilibria of ternary and quaternary systems containing n-hexane,toluene, m-xylene,propanol, sulfolane,and water at T = 303.15 K

(Liquid + liquid) equilibrium data for ternary and quaternary systems containing n-hexane (C₆H₁₄), toluene (C₇H₈), m-xylene (C₈H₁₀), propanol (C₃H₈O), sulfolane (C₄H₈SO₂), and water (H₂O) were measured at T = 303.15 K. Phase diagrams of {w₁C₄H₈SO₂ + w₂C₇H₈ + (1 − w₁ − w₂)C₆H₁₄}, {w₁C₄H₈SO₂ + w₂C₈H₁₀ + (1 − w₁ − w₂)C₆H₁₄}, {w₁C₄H₈SO₂ + w₂C₃H₈O + w₃C₇H₈ + (1 − w₁ − w₂ − w₃)C₆H₁₄} and also systems containing water: {w₁C₄H₈SO₂ + w₂H₂O + w₃C₇H₈ + (1 − w₁ − w₂ − w₃)C₆H₁₄} and {w₁C₄H₈SO₂ + w₂H₂O + w₃C₈H₁₀ + (1 − w₁ − w₂ − w₃)C₆H₁₄} (w = mass fraction) were obtained at T = 303.15 K. The (liquid + liquid) equilibrium data of the systems were used to obtain interaction parameters in non-random two-liquid (NRTL) and universal quasi-chemical theory (UNIQUAC) activity coefficient models. These parameters can be used to predict equilibrium data of ternary and quaternary systems. The root mean square deviations (RMSDs) using these models were calculated and reported. The partition coefficients and the selectivity factors of solvents for extraction of toluene or m-xylene from n-hexane at T = 303.15 K are calculated and presented. The experimental selectivity factors of sulfolane for the system {w₁C₄H₈SO₂ + w₂C₇H₈ + (1 − w₁ − w₂)C₆H₁₄} at T = 298.15 K and T = 323.15 K were taken from the literature and the influence of temperature on the extraction of toluene was also investigated. The phase diagrams for the ternary and quaternary systems including both the experimental and correlated tie lines are presented. The tie-line data of the studied systems were also correlated using the Hand equation and the correlation parameters are calculated and reported.     

Advanced oxidation of aromatic VOCs using a pilot system with electron beam–catalyst coupling

The decomposition of volatile organic compounds (VOCs) using a pilot system of electron beam (EB)–catalyst coupling was investigated. Two aromatic VOCs, toluene (1800 ppmC) and o-xylene (1500 ppmC), were irradiated with a dose range of 0–10 kGy at room temperature. The removal efficiencies for toluene and o-xylene were 92.4% and 94.5%, respectively, under a 10 kGy absorbed dose condition, which were higher than the results of 45.7% and 52.3% when EB-only was used, respectively. The CO₂ selectivity approached 100% for both toluene and o-xylene using the EB-catalyst coupling system, while the concentrations of O₃ formed were 0.02 ppm (toluene) and 0.003 ppm (o-xylene) at 10 kGy. The aerosol concentration was also measured as 43.2 μg/m³ (toluene) and 53.4 μg/m³ (o-xylene) at 10 kGy absorbed dose.     

Biomolecule-free,selective detection of clenbuterol based on disposable screen-printed carbon electrode

We report here the development of a selective clenbuterol sensor made of disposable screen-printed carbon electrode (SPCE) without the need of adding any biorecognition element. Good analytical performance was achieved through the proper function of both the oxygen functionalities and edge plane sites on the “preanodized” SPCE (SPCE*). It is the amino group of clenbuterol to effectively form hydrogen bond with the SPCE* to induce the adsorption of clenbuterol. The edge plane sites enhance the electron transfer process and further help the dimer formation of clenbuterol to generate electroactivity for analysis. Square wave voltammetry was applied to increase the detection sensitivity with a linear response in the range of 7–1000 ppb and a detection limit of 0.51 ppb (S/N = 3). In the real sample analysis, results observed were satisfactory with meat, human blood, and human urine. High reproducibility in sensor fabrication further favors the disposable purpose of applications.     

Amperometric enzyme biosensor for hydrogen peroxide via Ugi multicomponent reaction

A novel strategy based on the Ugi multicomponent reaction was employed for immobilizing horseradish peroxidase on sodium alginate-coated gold electrode. The electrode was employed for constructing an amperometric biosensor device using 1 mM hydroquinone as electrochemical mediator. The electrode showed linear response (poised at −300 mV vs Ag/AgCl) toward H₂O₂ concentration between 70 μM and 8.8 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 12 s and its sensitivity was 33.8 mA/M cm². The electrode retained full initial activity after 30 days of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0.     

Selective and rapid detection of triacetone triperoxide by double-step chronoamperometry

A selective detector for the improvised explosive, triacetone triperoxide is proposed. This is based on the rapid redox reaction of peroxides (hexamethylene triperoxide diamine, benzoyl peroxide, t-butyl peroxide, triacetone triperoxide and H₂O₂) with bromide at 55 °C. Consumption of bromide is indicative of the reduction of the R–O–O–R moiety, the appearance of Br₂ was found for all except for triacetone triperoxide. The latter was found to breakdown to acetone which rapidly reacts with Br₂ producing bromoacetones. The lack of Br₂ production is unique to triacetone triperoxide. Double step chronoamperometry (E₁ = 700 mV, E₂ = 960 mV (vs. Ag/AgCl)) allows for the quantitation of bromine (Br₂ + 2e^? ? 2Br^?) and bromide (2Br^? ? Br₂ + 2e^?) respectively. The results yielded a detection limit of 8.5 µM for triacetone triperoxide with a sensitivity of 0.026 µA µM^? 1. The detection limits of 16.3 µM and 14.9 µM were found respectively for HMTD and H₂O₂ based on the appearance of Bromine. These results indicate a possibility to develop a handheld sensor for TATP dermination.     

New analysis of clopidogrel bisulfate in plavix tablet and human biological fluids utilizing chemically modified carbon paste sensor

The fabrication and the performance response characteristics of a sensitive, selective, simple, and rapid sensor for the determination of clopidogrel bisulfate (CLO-H₂SO₄) were described. The constructed carbon paste sensor comprised of an ion-pair based on clopidogrel with silicotungstate (CLO-ST) where this study included: composition, usable pH range, response time and temperature. The sensor exhibited a wide linear dynamic concentration ranging from 1.00 × 10⁻⁷ to 1.00 × 10⁻² and the usable pH ranges from 1.2 to 4.8 with the response time ranging from 5 to 8 s which is much faster compared to liquid ISEs with a detection limit equalling 0.34 nM. The selectivity of the sensor (CLO-H₂SO₄) was applied with respect to many of organic and inorganic cations, amino acids and sugars. The sensor had applications in bulk powder, tablets, humans (serum-urine) and in monitoring Plavix tablets’ dissolution rates. The obtained results were statistically analyzed for both accuracy and precision and were compared using the US pharmacopeial method where no significant difference was observed.     

One-step fabrication of chitosan–hematite nanotubes composite film and its biosensing for hydrogen peroxide

This work reports on a novel chitosan–hematite nanotubes composite film on a gold foil by a simple one-step electrodeposition method. The hybrid chitosan–hematite nanotubes (Chi–HeNTs) film exhibits strong electrocatalytic reduction activity for H₂O₂. Interestingly, two electrocatalytic reduction peaks are observed at −0.24 and −0.56 V (vs SCE), respectively, one controlled by surface wave and the other controlled by diffusion process. The Chi–HeNTs/Au electrode shows a linear response to H₂O₂ concentration ranging from 1 × 10⁻⁶ to 1.6 × 10⁻⁵ mol L⁻¹ with a detection limit of 5 × 10⁻⁸ mol L⁻¹ and a sensitivity as high as 1859 μA μM⁻¹ cm⁻².     

Synergistic effects of alkali metals in the alkylation of naphthalene and toluene with ethene in the ArH–alkali metal systems in THF (ArH – naphthalene,phenanthrene)

The use of mixtures of metallic lithium and sodium in the naphthalene–alkali metal systems in THF leads to a synergistic acceleration of the naphthalene alkylation with ethene at room temperature and atmospheric pressure. The greatest synergistic effect is observed at a Li:Na molar ratio of 2:1. Under these conditions, the overall conversion of naphthalene into alkylation products (linear 1-alkylnaphthalenes and their dihydro derivatives) attains 88% after 24 h (a (Li + Na):C₁₀H₈ ratio is 2:1). The use of mixtures of metallic lithium and potassium in such systems results, however, in a synergistic retardation of the alkylation process. The strongest retarding effect is observed at a Li:K molar ratio of 1:1. The efficiency of the toluene alkylation with ethene in the naphthalene–alkali metal systems in THF is also increased on the replacement of lithium or sodium by their mixtures. The best results are obtained at a Li:Na molar ratio of 1:3. With this Li:Na ratio, toluene is almost quantitatively converted into linear and α-branched higher monoalkylbenzenes (24 h, (Li + Na):C₁₀H₈ = 2:1). The rate of the naphthalene alkylation with ethene in the presence of toluene is enhanced as well on an introduction of mixtures of lithium and sodium into the system. However the maximum of the activity is shifted here towards higher lithium content (Li:Na = 1:1). A similar synergistic effect of lithium and sodium was found on studying the toluene alkylation with ethene in the phenanthrene–Li–Na systems in THF (a (Li + Na):phenanthrene ratio is 3:1). An addition of potassium to sodium also considerably increases the efficiency of the toluene and naphthalene alkylation with ethene in the naphthalene-based systems. The possible mechanism of the alkali metal synergism in the above-mentioned alkylation reactions is discussed.     

Activation of C–H bonds of hydrocarbons by the ArH–alkali metal systems in THF (ArH – naphthalene,biphenyl, anthracene,phenanthrene, trans-stilbene,pyrene). Alkylation of naphthalene and toluene with ethene

Systems based on naphthalene and alkali metals (Li, Na, K) in THF are able to induce the alkylation of naphthalene with ethene at room temperature and atmospheric pressure. The highest activity in this reaction is exhibited by the naphthalene–potassium system which converts naphthalene into 1-ethylnaphthalene (1) and small amounts of two isomeric dihydro derivatives of 1 in a yield of 85% (24 h, K:C₁₀H₈ = 2:1). The same alkylation products are formed when metallic sodium is used instead of potassium. The interaction of ethene with the naphthalene–lithium system (24 h, Li:C₁₀H₈ = 2:1) affords 1 together with 1-n-butylnaphthalene (4), 1-n-hexylnaphthalene (5), 1-n-oktylnaphthalene (6) and dihydro derivatives of 5 and 6 in a total yield of 60%. Alkylation of toluene with ethene in the naphthalene–alkali metal systems leads to the formation of higher monoalkylbenzenes. The greatest toluene conversion (48%, 24 h) is observed on using the lithium-containing system (Li:C₁₀H₈ = 2:1), in the presence of which a mixture of n-propylbenzene (11), n-pentylbenzene (12), 3-phenylpentane (13) and 3-phenylheptane (14) is produced from ethene and toluene. On the replacement of lithium by sodium or potassium, only 11 and 13 are obtained. A treatment of biphenyl, phenanthrene, trans-stilbene, pyrene and anthracene with alkali metals in THF also gives systems capable of catalyzing the alkylation of toluene with ethene at 22 °C. Of particularly active is the stilbene–lithium system (Li:stilbene = 3:1) which converts toluene into a mixture of 11–14, n-heptylbenzene and 5-phenylnonane in a yield of 58%. In all cases, the rate of the alkylation considerably increases in the presence of the solid phase of alkali metal. The mechanism of the reactions found is discussed.