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.     

Electrochemical Properties of a Boron‐Doped Diamond Electrode Modified with Gold/Polyelectrolyte Hollow Spheres

Oppositely charged polyelectrolyte (poly(allyamine hydrochloride) (PAH) and poly(sodium 4‐styrene‐sulfonate) (PSS)), and negatively charged gold nanoparticles (Au) were assembled alternately on polystyrene (PS) spheres via layer‐by‐layer technique, and the different PAH/(PSS/PAH)_n/(Au/PAH)_m/Au composite hollow spheres were derived by dissolving PS core. These hollow spheres were used to modify boron‐doped diamond (BDD) electrodes for electrochemical sensors. The cyclic voltammetric results for dopamine (DA) detection demonstrated that hollow‐sphere‐modified BDD exhibited better electrocatalytic activity than did bare BDD. Influence of the wall thickness and composition of hollow spheres on electrochemical properties were investigated. The results showed that the oxidative peak potential of DA and the peak current varied with different PSS/PAH and Au/PAH layers. The optimized wall structure of hollows spheres was PAH/(PSS/PAH)₇/(Au/PAH)₅/Au.     

Influence of Calcination Temperature on Properties of Au/Fe2O3 Catalysts for Low Temperature Water Gas Shift Reaction

A series of Au/Fe₂O₃ catalysts for the water gas shift (WGS) reaction were prepared by modified deposition-precipitation method. The sample calcined at 300 °C showed higher catalytic activity and better stability than other samples. Using N₂ physisorption, in situ XRD, H₂-TPR, and XPS techniques, the influence of calcination temperature on properties of Au/Fe₂O₃ catalyst was explored, and the cause of deactivation was analyzed as well. The results showed that the catalytic behaviors were related to the interaction between Au and Fe₂O₃, and the reductive property of support, both of which were significantly affected by calcination temperature. Furthermore, according to the results of XPS, although stable carbonate and carbonyl surface species were found on the spent catalysts, the semiquantitative analysis of these species indicated that they were not the main cause of the deactivation. In fact, the deactivation of Au/Fe₂O₃ was sensitive to the structure change of support. During the water gas shift reaction, Fe₃O₄ particle would aggregate and crystallize leading to increase in the crystallinity of support and a significant reduction in the surface area of the catalysts, which resulted in the deactivation of Au/Fe₂O₃.     

In situ AFM study of electrochemical synthesis of polypyrrole/Au nanocomposite

In this work, in situ AFM measurements with simultaneously electrochemical characterization were developed to study the mechanisms of both polypyrrole (PPy) and PPy/Au composite deposition. The nanoscale information derived from the in situ AFM images associated with theoretical simulation from the measured current–time transient (i–t) reveals that Au nanoparticles with negatively charged carboxylic groups can be the nuclei by both adsorption on the electrode surface and doping on PPy for the polymerization, and thus has faster nucleation and growth rate than Py alone at the early polymerization stage. The PPy/Au deposition shows parallel nucleation processes of Au nanoparticle and Py, and an instantaneous 3D nucleation mode. The work not only provides fundamental insights for PPy/Au nanocomposite deposition process, but also optimization approaches to fabricate a superior PPy/Au film with favorable features for greater potential applications.     

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%。     

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%。     

Sensitively electrochemical detection of the DNA damage in situ by electro-Fenton reaction based on Fe@Fe2O3 core-shell nanonecklace and multi-walled carbon nanotube composite

An electrochemical biosensor for mimicking the metal-mediated DNA damage pathway in situ was presented. The Fenton reagents (H₂O₂ and iron ion) for the DNA damage were generated in situ with a constant rate from the sensing film. H₂O₂ and iron ion reacted further together to yield hydroxyl radical, which attacked DNA in the film. These courses of DNA damage were just like those happened in organism. The DNA damage was detected by monitoring the differential pulse voltammetric response of an electrochemical indicator, Co(phen)₃³⁺. Another electrochemical indicator, Ru(NH₃)₆³⁺, was also used for monitoring the DNA damage as a complementary means and the minimal detectable amount of DNA damage was 0.16 μg. The biosensor had good reproducibility. After this biosensor was used for 11 times, 90% of the first detection signal was obtained.     

A facile one-pot interfacial synthesis of Pt nanoparticles/polypyrrole composites and their application for non-enzymatic sensing hydrogen peroxide

Pt nanoparticles (PtNPs)/polypyrole (PPy) composites were successfully prepared through a facile one-pot interfacial polymerization of pyrrole by using H₂PtCl₆ as the oxidant for the first time. The as-prepared PPy was granular particles with particle size within a few hundred nanometers, on which PtNPs (1.7–3.5) nm were homogeneously dispersed. The PtNPs/PPy composites displayed excellent electrocatalytic activity toward redox of H₂O₂. The non-enzyme sensor constructed with PtNPs/PPy composites displayed good sensing ability toward H₂O₂ at ?0.1 V with a significantly high sensitivity of 6056 μAmM^?1cm^?2 and a low detection limit of 1.8 μM (S/N = 3).     

High dielectric constant PrYxOy sensing films electrolyte-insulator-semiconductor pH-sensor for the detection of urea

In this paper, we describe the structural and sensing properties of high-k PrY_xO_y sensing films deposited on Si substrates through reactive co-sputtering. Secondary ion mass spectrometry and atomic force microscopy were employed to analyze the compositional and morphological features of these films after annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device incorporating a PrY_xO_y sensing membrane that had been annealed at 800 °C exhibited good sensing characteristics, including a high sensitivity (59.07 mV pH⁻¹ in solutions from pH 2 to 12), a low hysteresis voltage (2.4 mV in the pH loop 7 → 4 → 7 → 10 → 7), and a small drift rate (0.62 mV h⁻¹ in the buffer solution at pH 7). The PrY_xO_y EIS device also showed a high selective response towards H⁺. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based urea biosensor incorporating a high-k PrY_xO_y sensing film annealed at 800 °C allowed the potentiometric analysis of urea, at concentrations ranging from 1 to 16 mM, with a sensitivity of 9.59 mV mM⁻¹.     

Wafer-Level Fabrication and Gas Sensing Properties of miniaturized gas sensors based on Inductively Coupled Plasma Deposited Tin Oxide Nanorods

SnO₂ nanorods were successfully deposited on 3” Si/SiO₂ wafers by inductively coupled plasma-enhanced chemical vapor deposition (PECVD) and a wafer-level patterning of nanorods layer for miniaturized solid state gas sensor fabrication were performed. Uniform needle-shape SnO₂ nanorods in situ grown were obtained under catalyst- and high temperature treatment-free growth condition. These nanorods have an average diameter between 5 and 15 nm and a length of 160 to 300 nm. The SnO₂-nanords based gas sensors were tested towards NH₃ and CH₃OH and gas sensing tests show remarkable response, showing promising and repeatable results compared with the SnO₂ thin films gas sensors.     

On the ammonolysis of Ga2O3: An XRD, neutron diffraction and XAS investigation of the oxygen-rich part of the system Ga2O3-GaN

We investigated the ammonolysis of β-Ga₂O₃ at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction and in situ X-ray absorption spectroscopy. Within the detection limits of these methods, we can rule out the existence of a crystalline or amorphous oxynitride phase that is not derived from wurtzite-type GaN. No evidence for a β-Ga₂O₃ related oxynitride phase was found, and the nitrogen solubility in β-Ga₂O₃ was found to be below the detection limit of about 2-3 at% in the anionic sublattice. These findings were obtained by monitoring the anionic occupancy factors and the lattice parameters of the β-Ga₂O₃ phase obtained from total diffraction pattern refinement with the Rietveld method and by linear combination fitting of the X-ray absorption spectra that were recorded during the ammonolysis.     

Polyelectrolyte membranes prepared by dynamic self-assembly of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) for nanofiltration (I)

In recent years, the layer-by-layer (LBL) self-assembly of polyelectrolyte has attracted much attention for the preparation of nanofiltration (NF) membranes. However, most researchers focused on the homopolymers, few studied on the copolymers for the preparation of NF membranes. In the present work, a series of nanofiltration membranes were prepared by dynamic self-assembly of a copolymer polyelectrolyte containing both weakly and strongly ionized groups, poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA), with poly (allylamine hydrochloride) (PAH) and poly (styrenesulfonic acid sodium salt) (PSS) on the modified polyacrylonitrile (PAN) ultra-filtration membranes. The effects of substrate, deposition pH, SS/MA ratio in PSSMA, concentration of the PSSMA and bilayer number on the properties of the NF membranes were investigated. The results indicated that the performances of the NF membranes prepared by dynamic self-assembly process were superior to those prepared by the static self-assembly process. The membranes terminated with PSSMA were negatively charged. Due to the changes of charge density and conformation of PSSMA in different pH conditions, the [PAH/PSS]₁PAH/PSSMA membrane prepared at pH 2.5 showed higher Na₂SO₄ rejection and larger flux than those of the membrane prepared at pH 5.7. The NF membrane [PAH/PSS]₁PAH/PSSMA composed of only two bilayers exhibited 91.4% Na₂SO₄ rejection and allowed solution flux of 28.6 L/m² h at 0.2 MPa. The solution flux increased to 106.6 L/m² h at 0.8 MPa, meanwhile, no obvious decrease in Na₂SO₄ rejection was observed.     

Efficient synthesis of mono- and disubstituted 2,3-dihydroquinazolin-4(1H)-ones using KAl(SO4)2·12H2O as a reusable catalyst in water and ethanol

KAl(SO₄)₂·12H₂O was found to catalyze efficiently a one-pot three-component cyclocondensation of isatoic anhydride and primary amines or ammonia sources such as (NH₄)₂CO₃, NH₄OAc and NH₄Cl with aromatic aldehydes under mild conditions to afford the corresponding mono- and disubstituted 2,3-dihydroquinazolin-4(1H)-ones in good yields.     

Detection of nitrogen dioxide using mixed tungsten oxide-based thick film semiconductor sensor

The thick film semiconductor sensor for NO₂ gas detection was fabricated by screen-printing method using a mixed WO₃-based as sensing material. The sensing characteristics, such as response time, response linearity, sensitivity, working range, cross sensitivity, and long-term stability were further studied by using a WO₃-based mixed with different metal oxides (SnO₂, TiO₂ and In₂O₃) and doped with noble metals (Au, Pd and Pt) as sensing materials was observed. The highest sensitivity for low concentrations (<16 mg l⁻¹) was observed using WO₃-based mixed with In₂O₃ or TiO₂. The NO₂ gas sensor showing the fastest response and recovery time (both within 2 min), good linearity (Y=0.606X+0.788 R²=0.991) for gas concentrations from 3 to 310 mg l⁻¹, low resistance (3 MΩ), high sensitivity, undesirable cross sensitivity effect and good long-term stability (at least 120 days) using WO₃-SnO₂-Au as sensing material.     

Gas Sensing Ability of a Nanostructured Conducting Polypyrrole Film Prepared by Catalytic Electropolymerization on Cu/Au Interdigital Electrodes

Nanostructured conductive polypyrrole has been prepared electrochemically on the surfaces of Cu/Au interdigital electrodes in the presence of Fe(II) as catalyst and ClO₄^? as anion dopant by using constant potential amperometry and cyclic voltammetry. The morphology of the conducting films was examined by field emission scanning electron microscopy, indicating a dependence from the processing technique. The synthesized polymer was used to investigate the properties of the gas sensing ability. The effect of the catalyst concentration on the oxidation mechanism of pyrrole was discussed. The PPy‐ClO₄ gas sensors had demonstrated fast response time and high sensitivity to VOCs.     

Excess enthalpies of alkane-1-amines {CnH2n+1NH2, n = 3-8} + methyl methylthiomethyl sulfoxide and +dimethyl sulfoxide at 298.15 K

Excess enthalpies of binary mixtures between each of alkane-1-amines {C_nH_2n+1NH₂, n=3-8} and methyl methylthiomethyl sulfoxide (MMTSO) or dimethyl sulfoxide (DMSO) have been determined at 298.15 K. All mixtures showed positive enthalpy changes over the whole range of mole fractions.The limiting excess partial molar enthalpies of the aliphatic amines, H₁^E,∞, of all the mixtures with MMTSO or DMSO studied were smaller than those of MMTSO or DMSO, H₂^E,∞, respectively. Linear relations are obtained between limiting excess partial molar enthalpies and number of methylene groups.     

Synthesis of layered cathode material Li[CoxMn1−x]O2 from layered double hydroxides precursors

Cathode materials Li[Co_xMn_1−x]O₂ for lithium secondary batteries have been prepared by a new route—precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass spectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH·H₂O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li⁺ into the lattice, resulting in the formation of layered Li[Co_xMn_1−x]O₂ with α-NaFeO₂ structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[Co_xMn_1−x]O₂, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[Co_xMn_1−x]O₂ have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAh g⁻¹ for the layered material Li[Co_0.80Mn_0.20]O₂.     

Ionothermal synthesis of β-NH4AlF4 and the determination by single crystal X-ray diffraction of its room temperature and low temperature phases

β-NH₄AlF₄ has been synthesised ionothermally using 1-ethyl-3-methylimidazolium hexafluorophosphate as solvent and template provider. β-NH₄AlF₄ crystals were produced which were suitable for single crystal X-ray diffraction analysis. A phase transition occurs between room temperature (298 K) and low temperature (93 K) data collections. At 298 K the space group=I4/mcm (no. 140), α=11.642(5), c=12.661(5) Å, Z=2 (10NH₄AlF₄), wR(F²)=0.1278, R(F)=0.0453. At 93 K the space group=P4₂/ncm (no. 138), α=11.616(3), c=12.677(3) Å, Z=2 (10NH₄AlF₄), wR(F²)=0.1387, R(F)=0.0443. The single crystal X-ray diffraction study of β-NH₄AlF₄ shows the presence of two different polymorphs at low and room temperature, indicative of a phase transition. The [AlF_4/2F₂]⁻ layers are undisturbed except for a small tilting of the AlF₆ octahedra in the c-axis direction.     

Application of principal component analysis to gas sensing characteristics of Cr0.8Fe0.2NbO4 thick film array

The transient changes in resistances of Cr_0.8Fe_0.2NbO₄ thick film sensors towards specified concentrations of H₂, NH₃, acetonitrile, acetone, alcohol, cyclohexane and petroleum gas at different operating temperatures were recorded. The analyte-specific characteristics such as slopes of the response and retrace curves, area under the curve and sensitivity deduced from the transient curve of the respective analyte gas have been used to construct a data matrix. Principal component analysis (PCA) was applied to this data and the score plot was obtained. Distinguishing one reducing gas from the other is demonstrated based on this approach, which otherwise is not possible by measuring relative changes in conductivity. This methodology is extended for three Cr_0.8Fe_0.2NbO₄ thick film sensor array operated at different temperatures.