Enhancement of electron transfer kinetics on a polyaniline-modified electrode in the presence of anionic dopants

The electrocatalytic redox behavior of 1,4-naphthoquinone (NQ) has been studied on a polyaniline-modified platinum electrode (PANI) using cyclic voltammetry and rotating disc electrode (RDE) as diagnostic techniques. The modified electrode was prepared by electropolymerization of aniline in different acidic solutions. The PANI showed electrocatalytic activity toward the redox behavior of NQ. This process includes the participation of PANI to the redox reaction of NQ via the surface catalysis phenomena. The cyclic voltammograms of NQ in HCl on the PANI-Cl-modified electrode showed an overlapped oxidation peak, the peak potential of which did not change with increasing scan rate. The influence of other anions including and as dopant was also studied and compared with Cl⁻. The use of HClO₄ as a supporting electrolyte resulted in well-separated redox peaks. The RDE voltammogram was used to obtain a quantitative assessment of reaction rate at the PANI-modified electrode. It was found that PANI acts as an electrocatalyst for NQ reduction with decreasing ΔE _p and increasing k°.     

Viscosity of Ionic Liquids: Application of the Eyring’s Theory and a Committee Machine Intelligent System

Accurate determination of the physicochemical characteristics of ionic liquids (ILs), especially viscosity, at widespread operating conditions is of a vital role for various fields. In this study, the viscosity of pure ILs is modeled using three approaches: (I) a simple group contribution method based on temperature, pressure, boiling temperature, acentric factor, molecular weight, critical temperature, critical pressure, and critical volume; (II) a model based on thermodynamic properties, pressure, and temperature; and (III) a model based on chemical structure, pressure, and temperature. Furthermore, Eyring’s absolute rate theory is used to predict viscosity based on boiling temperature and temperature. To develop Model (I), a simple correlation was applied, while for Models (II) and (III), smart approaches such as multilayer perceptron networks optimized by a Levenberg–Marquardt algorithm (MLP-LMA) and Bayesian Regularization (MLP-BR), decision tree (DT), and least square support vector machine optimized by bat algorithm (BAT-LSSVM) were utilized to establish robust and accurate predictive paradigms. These approaches were implemented using a large database consisting of 2813 experimental viscosity points from 45 different ILs under an extensive range of pressure and temperature. Afterward, the four most accurate models were selected to construct a committee machine intelligent system (CMIS). Eyring’s theory’s results to predict the viscosity demonstrated that although the theory is not precise, its simplicity is still beneficial. The proposed CMIS model provides the most precise responses with an absolute average relative deviation (AARD) of less than 4% for predicting the viscosity of ILs based on Model (II) and (III). Lastly, the applicability domain of the CMIS model and the quality of experimental data were assessed through the Leverage statistical method. It is concluded that intelligent-based predictive models are powerful alternatives for time-consuming and expensive experimental processes of the ILs viscosity measurement.     

Preparation of polyphenylsulfone/graphene nanocomposite membrane for the pervaporation separation of cumene from water

Polyphenylsulfone (PPSU) was applied for the first time in the hydrophobic PV process. Nanocomposite membranes of PPSU/graphene (Gr) nanosheets were prepared and used to separate isopropyl benzene (cumene) from water via pervaporation (PV). Analysis of the mechanical properties of the membranes showed that the tensile strength and Young's modulus had an increasing trend with the incorporation of Gr into PPSU. The water contact angle of the membranes had a rising trend with the addition of Gr, confirming the improved hydrophobicity of membranes. In the PV experiments, the membrane containing 3.5 wt% Gr provided the highest separation factor, which was 4.5-fold as much as that of the neat PPSU membrane. Cumene separation from water by the PPSU/3.5 wt% Gr membrane was associated with the total flux of 132.73 gMH, the separation factor of 1566.36, and the PSI of 208,124.8 gMH.     

A wide potential window aqueous supercapacitor based on LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>–rGO nanocomposite

Aqueous supercapacitors based on neutral solutions have the advantages of high-ionic conductivity, being environmentally friendly, safe, and low cost. However, the operating potential window for most aqueous electrolytes is far lower than that of organic electrolytes that are commonly used in commercial supercapacitors. In this work, we report on the fabrication of a wide potential window, high-energy aqueous asymmetric supercapacitor, without sacrificing power, by using a nanostructured LiMn₂O₄/reduced graphene oxide (LMO–rGO) nanocomposite. We synthesized the uniformly distributed LMO in the LMO–rGO nanocomposite using a co-precipitation route followed by a low-temperature hydrothermal treatment. In a three-electrode cell setup, the specific capacitance of the LMO–rGO nanocomposite electrode at 1 A/g (1.2 mA/cm²) is 268.75 F/g (258 mF/cm²), which shows a dramatic improvement over the sum of the specific capacitances of pristine LMO (162.5 F/g) and pure rGO (29.94 F/g) electrodes in their relative ratios, when used alone. This finding suggests a synergistic coupling of LMO and rGO in the nanocomposite. We also assembled the LMO–rGO nanocomposite, as the positive electrode, with activated carbon, as the negative electrode, into an asymmetric cell configuration. The device shows an ultra-wide potential window of 2.0 V in a neutral aqueous Li₂SO₄ electrolyte, with a maximum energy density of 29.6 Wh/kg (which approaches the commercial lead-acid batteries), power density of up to 7408 W/kg, and an excellent cycle life (5% loss after 6000 cycles). These findings confirm that an LMO–rGO nanocomposite is a promising material to meet the demands of real world energy storage.     

Determination of hydroxylamine using a carbon paste electrode modified with graphene oxide nano sheets

A carbon paste electrode that was chemically modified with 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid (3,4-AA) was used as a selective electrochemical sensor for the detection of hydroxylamine. Cyclic voltammetry (CV), choronoamperometry (CHA) and square wave voltammetry (SWV) were used to investigate oxidation of hydroxylamine in aqueous solution. Under optimized concentration the electrocatalytic oxidation current peak for hydroxylamine increased linearly with concentration in the range of 0.025–10.0 μM. The detection limits for hydroxylamine was 0.012 μM. Finally, the modified electrode was applied to detection hydroxylamine in water samples.     

Simple design of an aligned transparent biofilm by magnetic particles and its cellular study

The aim of this study was to produce aligned biodegradable films. In this study, we used magnetic microparticles and strong magnetic field for orientation of gelatin gels. The samples were evaluated by microscopic analyses and cell culture assays with Schwann cells. Results of structural analyses showed a good arrangement and orientation of films under strong magnetic field with movement of magnetite particles. Cellular experiments showed a good cell adhesion and orientation on the designed films compared with those on unmodified ones. This aligned guide appears to have the right organization for testing in vivo nerve tissue engineering studies. Copyright © 2016 John Wiley & Sons, Ltd.     

Connectivity of Pore Space as a Control on Two-Phase Flow Properties of Tight-Gas Sandstones

We predict capillary-pressure (drainage) curves in tight-gas sandstones which have little matrix or microporosity using a quantitative grain-scale model. The model accounts for the geometric results of some depositional and diagenetic processes important for porosity and permeability reduction in tight-gas sandstones, such as deformation of ductile grains during burial and quartz cementation. The model represents the original sediment as a dense, disordered packing of spheres. We simulated the evolution of this model sediment into a low-porosity sandstone by applying different amounts of ductile grains and quartz precipitation. A substantial fraction of original pore throats in the sediment is closed by the simulated diagenetic alteration. Because the percolation threshold corresponds to closure of half of the pore throats, the pore space in this type of tight-gas sandstone is poorly connected and is often close to being completely disconnected. The drainage curve for different model rocks was computed using invasion percolation in a network taken directly from the grain-scale geometry and topology of the model. Some general trends follow classical expectations and were confirmed by experimental measurements: increasing the amount of cement shifts the drainage curve to larger pressures. This is related to reduction of the connectivity of pore space resulting from closure of throats. Existence of ductile grains in the ductile grain model also reduces the connectivity of pore space but it treats the throats distribution differently causing the drainage curves to be shifted to larger irreducible water saturation when cement is added to the model. The range of porosities in which these connectivity effects are important corresponds to the range of porosities common for tight gas sandstones. Consequently these rocks can exhibit small effective permeability to gas even at large gas saturations. This problem occurs at larger porosities in rocks with significant content of ductile grains because ductile deformation blocks a significant fraction of pore throats even before cementation begins. Predicted drainage curves agree with measurements on two samples with little microporosity, one dominated by rigid grains, the other containing a significant fraction of ductile grains. We conclude that connectivity of the matrix pore space is an important factor for an understanding of flow properties of tight-gas sandstones.     

Analytical solution for bending problem of moderately thick composite annular sector plates with general boundary conditions and loadings using multi-term extended Kantorovich method

An analytical solution for bending of composite sector plates is presented using multi-term extended Kantorovich method (MTEKM). The governing equations are derived using the displacement field of the first-order shear deformation theory and converted into two sets of coupled ordinary differential equations (ODEs) utilizing MTEKM. Next, an analytical iterative procedure is presented for solving the derived sets of ODEs based on state-space method. Numerous examples are studied by the present method, and as special cases, solid sector and rectangular plates are also investigated. Next, the results obtained by the present method are compared to those of finite element method and other results available in the literature. It is found that the present method has a high convergence rate as well as good accuracy in all cases.     

Analysis of cracked functionally graded piezoelectric strip

The fracture behavior of a cracked strip under antiplane mechanical and inplane electrical loading is studied. A functionally graded piezoelectric strip with exponential material gradation is under consideration. The mechanical and electrical loading is combined via loading coupling factor. The problem of a graded piezoelectric strip containing a screw dislocation is solved. This solution results in stress and electric displacement components with Cauchy singularity. Based on the solution achieved for the dislocation, the distributed dislocation technique (DDT) is utilized to form any geometry of multiple cracks and analyze the behavior of a cracked strip under antiplane mechanical and inplane electrical loading. This technique is capable of the analysis of a strip with a system of interacting cracks. Several examples including strips with single crack, two straight cracks and two curved cracks are presented.