Recent progress in the studies of electrochemical interfaces by surface plasmon resonance spectroscopy and microscopy

Surface plasmon resonance (SPR) is a label-free spectroscopic technique that is highly sensitive to various surface reactions. Incorporating SPR into electrochemical measurements has emerged as a powerful method to study both faradaic and non-faradaic processes. SPR microscopy (SPRM) integrates an optical microscope into SPR detection, which further offers high throughput detection and spatially resolved information at an electrode surface and thus, has attracted attention especially in single entity electrochemical studies. In this review, the progress in the studies of electrochemical interfaces by SPR and SPRM during the past two years will be discussed.     

Elucidation of Gram-Positive Bacterial Iron(III) Reduction for Kaolinite Clay Refinement

Recently, microbial-based iron reduction has been considered as a viable alternative to typical chemical-based treatments. The iron reduction is an important process in kaolin refining, where iron-bearing impurities in kaolin clay affects the whiteness, refractory properties, and its commercial value. In recent years, Gram-negative bacteria has been in the center stage of iron reduction research, whereas little is known about the potential use of Gram-positive bacteria to refine kaolin clay. In this study, we investigated the ferric reducing capabilities of five microbes by manipulating the microbial growth conditions. Out of the five, we discovered that Bacillus cereus and Staphylococcus aureus outperformed the other microbes under nitrogen-rich media. Through the biochemical changes and the microbial behavior, we mapped the hypothetical pathway leading to the iron reduction cellular properties, and found that the iron reduction properties of these Gram-positive bacteria rely heavily on the media composition. The media composition results in increased basification of the media that is a prerequisite for the cellular reduction of ferric ions. Further, these changes impact the formation of biofilm, suggesting that the cellular interaction for the iron(III)oxide reduction is not solely reliant on the formation of biofilms. This article reveals the potential development of Gram-positive microbes in facilitating the microbial-based removal of metal contaminants from clays or ores. Further studies to elucidate the corresponding pathways would be crucial for the further development of the field.     

Effect of graphene nanoplatelets as nanofiller in plasticized poly(lactic acid) nanocomposites

Plasticized PLA-based nanocomposites were prepared by melt blending of the matrix with 5 mass% of epoxidized palm oils (EPO) and different amount of graphene nanoplatelets (xGnP). Plasticized PLA (p-PLA) reinforced with 0.3 mass% xGnP resulted in an increase of up to 26.5 and 60.6 % in the tensile strength and elongation at break of the nanocomposites, respectively. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were performed to study the thermal behavior of the prepared nanocomposites. p-PLA reinforced with xGnP shows that increasing the xGnP content triggers a substantial increase in thermal stability. Crystallinity of the nanocomposites as well as cold crystallization and melting temperature did not show any significant changes upon addition of xGnP. However, there is a significant decrease of glass transition temperature up to 0.3 mass% of xGnP incorporation.     

Constructing a force interaction model for thermal conductivity computation using molecular dynamics simulation: ethylene glycol as an example

This study aims to construct a force interaction model for thermal conductivity computation and to analyze the liquid properties in atomic level for liquid ethylene glycol (EG) using molecular dynamic simulation. The microscopic details of the molecular system and the macroscopic properties of experimental interest are connected by Green-Kubo relations. In addition, the major contributions of heat transfer modes for thermal conductivity due to convection, interaction, and torque are obtained quantitatively. This study reveals that the intramolecular interaction force fields result in different conformations of the EG in the liquid and thus the molecular shapes. The trans∕gauche ratio for EG's O-Me-Me-O torsional angle and the number of intermolecular∕intramolecular H-bonds are found to be important parameters affecting the thermal conductivity.     

Improved Catalytic Performance of Pt Supported on Multi‐Wall Carbon Nanotubes as Cathode for Direct Methanol Fuel Cell Applications Prepared by Dual‐Stepped Surface Thiolation Processes

This study develops a simple surface modification process for modifying the MWCNT surface by thiolation reaction after the conventional nitric acid treatment for strong interface attachment of Pt NPs and improved dispersion onto MWCNTs. The thiolated MWCNTs (Pt/MWCNTs) showed significant improvement of methanol electro‐oxidation activity compared with that treated only by nitric acid solution. The prepared electrode with thiolated MWCNTs was used as the cathode for assembling MEA for DMFC single‐cell applications. Testing results indicate that the thiolated MWCNT cathode can improve the power density of MEA by more than 300% (from 4.6 to 20.6 mW cm^?2) compared with that treated only by conventional nitric acid reactions. The dual‐step modification process for MWCNT surface treatment showed significant improvement over the convention nitric acid treatment and can be successfully used in DMFC applications.     

The Adsorption,Thermal Desorption and Photochemistry of Methyl Iodide on an Ag‐Covered TiO2(110) Surface

The thermal reactions and photochemistry of monolayer methyl iodide (CH₃I) on a silver covered TiO₂(110) surface have been studied using combinative techniques of temperature programmed desorption (TPD) and x‐ray photoelectron spectroscopy (XPS). About ? 60% of CH₃I at monolayer coverage on Ag/TiO₂(110) dissociates between 130 and 200 K yield adsorbed CH₃ and I, with the rest desorbing molecularly at a peak temperature of 200 K in a TPD study. Photochemistry of CH₃I on Ag/TiO₂(110) is wavelength dependent. Irradiation of monolayer CH₃I by 404 nm photon causes C‐I bond dissociation and CH₃ desorption. Upon 290 nm, UV irradiation, the depletion of CH₃I_(a) is dominated by photodesorption of molecular CH₃I.     

Antibacterial activity of silver bionanocomposites synthesized by chemical reduction route

ABSTRACT: BACKGROUND: The aim of this study is to investigate the functions of polymers and size of nanoparticles on the antibacterial activity of silver bionanocomposites (Ag BNCs). In this research, silver nanoparticles (Ag NPs) were incorporated into biodegradable polymers that are chitosan, gelatin and both polymers via chemical reduction method in solvent in order to produce Ag BNCs. Silver nitrate and sodium borohydride were employed as a metal precursor and reducing agent respectively. On the other hand, chitosan and gelatin were added as a polymeric matrix and stabilizer. The antibacterial activity of different sizes of silver nanoparticles was investigated against Gram-positive and Gram-negative bacteria by the disk diffusion method using Mueller-Hinton Agar. RESULTS: The properties of Ag BNCs were studied as a function of the polymer weight ratio in relation to the use of chitosan and gelatin. The morphology of the Ag BNCs films and the distribution of the Ag NPs were also characterized. The diameters of the Ag NPs were measured and their size is less than 20 nm. The antibacterial trait of silver/chitosan/gelatin bionanocomposites was investigated. The silver ions released from the Ag BNCs and their antibacterial activities were scrutinized. The antibacterial activities of the Ag BNC films were examined against Gram-negative bacteria (E. coli and P. aeruginosa) and Gram-positive (S. aureus and M. luteus) by diffusion method using Muller-Hinton agar. CONCLUSIONS: The antibacterial activity of Ag NPs with size less than 20 nm was demonstrated and showed positive results against Gram-negative and Gram-positive bacteria. The Ag NPs stabilized well in the polymers matrix.     

Computations using the preconditioning BI-CGSTAB algorithm in chemical non-equilibrium problems

A robust method for solving the chemical non-equilibrium Navier–Stokes equations, including all of the species conservation and energy production equations, is developed. The algorithm is embodied in a fully coupled, implicit, large block structure. Van Leer flux splitting for inviscid terms and central differencing for viscous terms in the explicit operators are applied in the numerical algorithm. The fully-coupled system is solved implicitly and the bi-conjugate gradient stable (Bi-CGSTAB) method with a preconditioner of incomplete lower–upper (LU)-factorization (ILU) is used for solving large block structure and diagonal dominate matrix equations. The computations are performed for the hypersonic inflow over blunt bodies including half cylinder, double ellipse and blunt nose. The adaptive grid constructed by moving grid method is employed to capture the shock location. Computational results in the present study are compared with other calculated data and exhibit good agreement. Convergence histories of the mean flow variables and species equations demonstrate that the fast convergent rate can be achieved by the preconditioned Bi-CGSTAB method. © 1998 John Wiley & Sons, Ltd.     

Microporous polymeric materials by microemulsion terpolymerization

Transparent microstructural solid polymers have been prepared by polymerization of methyl methacrylate, 2-hydroxyethyl methacrylate and reactive sodium 11-(N-ethylacrylamido) undecanoate in microemulsions. The transparent polymeric solids could be formed from fluid microemulsions within 10 minutes by photoinitiated polymerization. SEM micrographs of the polymerized samples reveal the existence of microporous structures. The results seem to indicate that the open-cell porous structures of transparent polymers could be obtained from those precursor microemulsions with water content higher than 20% or the closed-cell structures from those with less than 20%.