Evaluation of polymeric nanocomposites for the detection of toxic gas analytes

Four different metal oxide nanoparticles, copper oxide (CuO), aluminum oxide (Al₂O₃), nickel oxide (NiO), and titanium dioxide (TiO₂), were added to poly (2,5-dimethyl aniline) (P25DMA) during synthesis to create different polymer nanocomposites. These polymer nanocomposites were evaluated as potential sensing materials for six different gas analytes (acetaldehyde, acetone, benzene, ethanol, formaldehyde, and methanol). It was found that CuO did not incorporate into the P25DMA and only a small percentage of Al₂O₃ was incorporated. However, both NiO and TiO₂ were incorporated into the P25DMA at the same concentration as during the synthesis step. Overall, the type of metal oxide significantly affected the morphology of the sensing material and the amount of each analyte sorbed. For example, P25DMA doped with 5 wt% Al₂O₃ had high selectivity towards ethanol, whereas P25DMA doped with 20 wt% TiO₂ sorbed the most ethanol. However, P25DMA doped with 20 wt% TiO₂ also sorbed a high amount of formaldehyde, making P25DMA doped with 20 wt% TiO₂ less selective than P25DMA doped with 5 wt% Al₂O₃ towards ethanol with respect to formaldehyde.     

Electrospinning preparation of NiO/ZnO composite nanofibers for photodegradation of binary mixture of rhodamine B and methylene blue in aqueous solution: Central composite optimization

One‐dimensional nanofiber of p‐type NiO/n‐type ZnO heterojunctions with various molar ratios of Ni to Zn at different calcination temperatures were successfully synthesized using the electrospinning method, and they were fully characterized. The photocatalysts thus obtained were applied in aqueous solutions for rhodamine B (RDB) and methylene blue (MB) degradation. The p–n heterojunctions built among the cubic structure NiO and hexagonal structure ZnO in the composite nanofiber are responsible for generation of electrons and holes and subsequently superoxide and hydroxyl radical production by carriers which lead to degradation of the dyes in solution. The composite nanofibers (ZnNi1) calcined at 550 °C for 3 h showed the highest photocatalytic activity for degradation of the dyes in aqueous solution. The optimum values were found to be 180 min, 7.0, 1 g l^?1 and 3.0 and 3.0 mg l^?1 for irradiation time, pH, photocatalyst dosage and initial concentration of RDB and MB, respectively. For these optimum conditions, the photocatalytic degradation of RDB and MB was found to be 99.37 and 98.44%, respectively. The maximum photodegradation of RDB and MB using ZnNi1 was 59.41 and 65.43%, respectively. First‐order kinetics based on the Langmuir–Hinshelwood model successfully fitted the experimental data.     

镍基气凝胶催化CH_4-CO_2重整制取合成气反应的研究 Ⅰ.制备方法对NiO-CeO_2-Al_2O_3催化剂物化性质的影响

采用浸渍法、溶胶 凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了具有不同结构特点的NiO CeO2 Al2 O3催化剂 ,分别为浸渍型催化剂 (iNCA)、干凝胶催化剂 (xNCA)和气凝胶催化剂 (aNCA) ,利用BET、TEM、XRD、TPR、NH3 TPD、H2 TPD等方法对各催化剂样品的物化性质进行了考察。研究结果表明 ,经 82 3K焙烧后 ,镍含量为 9%的各催化剂样品中镍物种均分散良好 ;与iNCA相比 ,以溶胶 凝胶法为基础制备的xNCA和aNCA中镍物种与载体的相互作用强并且存在状态均一 ;三种催化剂中 ,气凝胶样品具有比表面积高、堆密度低、表面酸中心数多及表面镍分散度高的特点。     

Electrosynthesis of azopyrazoles via the oxidation of N-alkylaminopyrazoles on a NiO(OH) anode in aqueous alkali – A green method for N-N homocoupling

A nickel oxyhydroxide [NiO(OH)] anode was exploited to develop a new synthetic route for the electrocatalytic N-N homocoupling of N-alkylaminopyrazoles in an alkaline aqueous medium. The advantages of this green electrochemical methodology include low cost, atom economy and high yields.     

Selective Detection of Dopamine in the Presence of Uric Acid Using NiO Nanoparticles Decorated on Graphene Nanosheets Modified Screen‐printed Electrodes

A convenient, low cost, and sensitive electrochemical method, based on a disposable graphene nanosheets (GR) and NiO nanoparticles modified carbon screen printed electrode (NiO/GR/SPE), is described for the simultaneous determination of dopamine (DA) and uric acid (UA). The modified electrode exhibited good electrocatalytic properties toward the oxidation of DA and UA. A peak potential difference of 150 mV between DA and UA was large enough to determine DA and UA individually and simultaneously. The anodic peak currents of DA were found to be linear in the concentration range of 1.0–500.0 μM with the detection limit of 3.14×10^?7 M.     

醇水法制备纳米氧化镍电极的结构与电化学性能

采用醇水法制备了纳米氧化镍粉体材料并分析了其粉体形成过程,重点研究了热处理温度对氧化镍粉体的相组成、形态以及氧化镍电极电化学性能的影响。结果表明,氧化镍粉体由前驱体Ni2(OH)2CO3·xH2O在270℃附近分解产生;热处理温度对合成粉体的结晶度和比表面积具有显著影响,而粉体的结晶度和比表面积又是影响氧化镍电极电化学性能的重要因素,其中,粉体结晶度的作用占主导地位。当氧化镍粉体热处理温度为250℃时,所制氧化镍电极具有优异的电化学性能,在测试电流密度为5mA/cm2的条件下,其比电容达到1180F/g。     

Temperature and set field dependence of exchange bias training effects in Co/NiO/[Co/Pt] heterostructures with orthogonal easy axes

Training effects in a new class of exchange biased ferromagnet/antiferromagnet/ferromagnet trilayers (Co/NiO/[Co/Pt]₃) with mutually orthogonal easy axes have been measured and successfully modeled. Previous experiments have demonstrated an enhanced blocking temperature as well as the ability to isothermally field tune the magnitude of the room temperature in-plane exchange bias. These effects have been attributed to the presence of the [Co/Pt] multilayer with perpendicular magnetic anisotropy, which variably pins the backside NiO domains. Here we show that the tuning of the exchange bias and the blocking temperature enhancement are highly dependent on both the temperature and the in-plane remanence of the normally out-of-plane [Co/Pt] multilayer, achieved using modest in-plane set fields. Training effects and their dependence on temperature and in-plane remanence are modeled using a thermodynamic approach. The in-plane remanence of the [Co/Pt] acts only to set the equilibrium exchange bias value and sets the scale for the blocking temperature; it has no effect on the training. We conclude that training effects occur only at the Co/NiO interface and that the relaxation towards equilibrium is confined to this interface. The field enhanced blocking temperature and isothermal tuning of exchange bias in these magnetic heterostructures with mutually orthogonal easy axes could play a role in the enhancement of exchange bias effects in future spin-valve devices. A thorough knowledge of the training effects is essential to account for the fundamental relaxation mechanisms that occur with repeated field cycling.     

Interpretation of the Ni K-edge EXAFS in nanocrystalline nickel oxide using molecular dynamics simulations

Analysis of atomic structure at the nanoscale is a challenging task, complicated by relaxation phenomena and thermal disorder. In this work, the x-ray absorption spectroscopy at the Ni K-edge was used to address this problem in nanocrystalline NiO (nano-NiO) at 300 K. The analysis of the first two coordination shells using conventional two-shell single-scattering approximation allowed us to determine the expansion of the average lattice but contraction of the Ni―O bonds in the first coordination shell in nano-NiO in comparison with the bulk nickel oxide. The EXAFS signal generated within the first six coordination shells (up to ~ 6.5 Å) was successfully interpreted using classical molecular dynamics and ab initio multiple-scattering EXAFS theory. We found that simple rigid-ion force-field model is able to describe the structure relaxation and dynamics in both bulk and nano-NiO. Such approach requires less parameters than conventional EXAFS analysis and allows accounting explicitly for thermal effects and many-atom distribution functions. Finally, we showed that the EXAFS signal is rather sensitive to small variations of the force-field model and, thus, the agreement between the experimental and calculated EXAFS signals can be used for the force-field model optimization.     

High‐performance gas‐sensing properties of octahedral NiO crystals prepared via one‐step controllable synthesis route

Octahedrally shaped NiO powders have been synthesized via a one‐step composite‐hydroxide‐mediated method without any surfactant. The synthesized materials are characterized by XRD, EDS, TEM and FESEM techniques. Each particle exhibited a nearly perfect octahedron shape with sharp edges and corners as well as smooth surfaces. The octahedral NiO particles performed better gas‐sensitivity toward ethanol than that of NiO nanopowders, which was attributed to the exposed ｛111｝ facets of octahedron. The result was confirmed by the first‐principle calculation which indicated that the (111) facet was more active than (100) and (110) facet.