Surface potentials of metal–gas interfaces compared with analogous electrochemical systems as probed by adsorbate vibrational frequencies

The dependence of adsorbate vibrational frequencies on the surface potential, φ (“Stark-tuning” effect), observed in electrochemical systems is exploited for the same metal surfaces in contact with ambient-pressure gases so to estimate φ values in the latter environment. Saturated CO adlayers on palladium and platinum films are examined along these lines by using surface-enhanced Raman spectroscopy (SERS) to obtain frequencies for both the C–O (ν_CO) and metal–carbon stretching (ν_M--CO) vibrations in CO-containing aqueous electrochemical and gaseous environments. The effective gas-phase surface potentials extracted by matching the vibrational frequencies with the corresponding potential-dependent electrochemical spectra are substantially (ca. 1–1.5 V) lower than the work functions for such interfaces under “clean” (ultrahigh vacuum) conditions. These disparities are ascribed to the occurrence of electrochemical-like redox half-reactions in the ambient-pressure gas-phase environment, leading to surface charging, and, hence, marked alterations in the surface potential as controlled by potential-dependent redox kinetics. The possible implications of these and related findings to ambient-pressure adsorption and catalysis are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of vibrations on interface delamination in metal–polymer composites

The main objective of this work was the study of vibration effects on the viscoelastic coating protecting the steel layer in a metal–polymer composite, with simulated conditions of the transportation of food containers. Mechanical resonance tests in metal–polymer [electrolytic chromium-coated steel–poly(ethylene terephthalate) (PET)] sheets were performed to generate vibration conditions to induce structural modifications in the viscoelastic layer covering the surface of the plates. Consequently, schematic representations of the areas affected by these modifications were made. The modified structures were later analyzed by electron microscopy to detect and evaluate alterations in the morphology of the material. In addition, vibrational Raman spectroscopy analyses were performed to assess the chemical and structural changes on the protective PET at the metal–polymer interface level. The results of this study are expected to provide basic information on the mechanisms and nature of the delamination processes taking place in metal–polymer laminates employed in food-container applications. These damages have previously been detected in some food containers made of PET materials. The study of these damages can lead to the improvement of current composites or the development of higher quality materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

CO adsorption on Ni(100) and Pt(111) studied by infrared–visible sum frequency generation spectroscopy: design and application of an SFG-compatible UHV–high-pressure reaction cell

Infrared–visible sum frequency generation (SFG) surface vibrational spectroscopy was applied to monitor CO stretching vibrations on Ni(100) and Pt(111) in the range from submonolayer coverages up to 200 mbar. Since SFG can operate in a pressure range from ultrahigh vacuum (UHV) to ambient conditions, it is particularly suited for in situ studies of adsorbates at elevated pressure or during a catalytic reaction. At high coverages, a compressed overlayer was formed on Ni(100) at 100 K that can be modeled by a coincidence structure. On Pt(111), terminally bonded (on-top) CO was the only species observed at 230 K, independent of gas pressure. At low pressure the SFG spectra were complemented by LEED, AES and TPD. The experiments were carried out in an SFG-compatible elevated pressure reactor that is attached to a UHV surface analysis chamber. After preparation and characterization in UHV, model catalysts can be transferred in vacuo into the reaction cell. The reactor is separated from the UHV chamber by an arrangement of differentially pumped spring-loaded teflon seals and can be pressurized to 1 bar without degrading the vacuum in the UHV analysis system.     

The Prospects for Using Recirculation–Countercurrent Chromatography for Separating Multicomponent Mixtures

Theoretical Foundations of Chemical Engineering - Computational studies of the separation processes of mixtures of three, four, and six components using the example of lanthanides have shown that,...     

Interaction of diamond grains with nanosized alloying agents in metal–matrix composites as studied by Raman spectroscopy

The effect of added Mo, WC, and ZrO₂ nanopowders on the graphitization of diamond grains in metal–matrix composites was studied by Raman spectroscopy. In the presence of Mo and ZrO₂ nanoadditives, the graphitization process was found to get intensified. But the addition of WC nanopowder was found to suppress the graphitization by 25–30%. This can be expected to improve the adhesion of binder to diamond grains and hence the service life of related cutting tools.     

Nanocrystalline yttria stabilized zirconia by metal–PVA complexation

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder was synthesized using polyvinyl alcohol (PVA) as organic precursor and acidic solutions of yttrium oxynitrite and zirconium nitrate. Complex formation was established using Fourier transform infrared (FTIR) spectroscopy and solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Thermal stability of the complex was investigated by thermogravimetric analysis (TGA). X-ray diffractometry (XRD) revealed formation of cubic phase YSZ at a temperature as low as 600 °C. The lattice parameter and average crystallite size were calculated from the XRD data. Particle size of the YSZ powder was investigated through transmission electron microscopy (TEM). The band gap of the sintered YSZ pellet was measured by UV–Vis-diffused reflectance spectroscopy (DRS). AC electrical conductivity was measured in air at 1 kHz frequency using a programmable RCL meter. The activation energy was calculated from the conductivity data at different temperatures using the standard Arrhenius equation.     

Development of self-healing star metallopolymers by metal–ligand crosslinking

The development of artificial materials with reversible and efficient self-healing property is an emerging and challenging task in intelligent materials science. In this article, we have developed a six-arm star copolymer system consisting of terpyridine moieties as end-chain functionality for the formation of self-healing metallopolymer networks. The star was synthesized using the atom transfer radical polymerization technique and subsequent crosslinking by the addition of iron (II) salts with three different counterions. The resulting materials exhibit promising self-healing performance as compared with a linear polymer system within time intervals of 6–8 h at moderate temperatures of 80–120 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48527.     

Alumina–copper joining by the sintered metal powder process

Sintered metal powder process (SMPP) is one of the high technology methods in ceramic–metal joining domain. The present study examines the effect of temperature and time of metalized layer sintering on the thickness and homogeneity of the joining layer, the leakage rate in alumina–copper joining zone, and also identifies the different phases formed during sintering. The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Microstructure studies indicate that sintering the metalized layer with a holding time of 90 min at the temperature of 1530 °C, and with an applied layer thickness of 50 μm with proper plating and brazing stages lead to a completely homogeneous joining zone with an adequate thickness (about 33 μm). The results of leak tests on alumina–copper specimen in this condition was less than 10^?9 Pa l s^?1.     

Dechlorination of 1,2‐dichloroethane catalyzed by Pt–Cu/C: unraveling the role of each metal

The effect of Pt–Cu/C catalyst composition on the activity and selectivity in the reaction of 1,2‐dichloroethane dechlorination in a H₂‐containing atmosphere has been investigated. For monometallic Pt catalysts and those with Cu/Pt atomic ratio ⩽1, the reaction products are almost entirely ethane and monochloroethane. However, increasing the Cu/Pt ratio increases the selectivity towards ethylene. Approximately 90% selectivity towards ethylene is obtained for catalysts with Cu/Pt ratio ⩾9. Monometallic Cu/C produce only ethylene, but the activity is two orders of magnitude lower than that of other catalysts studied. With time on stream during the initial 2–30 h there is a continuous increase in selectivity towards ethylene at the expense of ethane. This behavior was rationalized in terms of equilibration of bimetallic particle surface composition exposed to the reaction mixture. This revised version was published online in July 2006 with corrections to the Cover Date.     

A generalized sample preparation method by incorporation of metal–organic compounds into polymers for electroless metallization

Polymer metallization is important for several applications but triggering of electroless deposition is problematic. A simple and inexpensive method to prepare the polymers for initiating the electroless copper deposition is successfully applied to Liquid Crystal Polymer and Polyethylene Terephthalate. The samples are prepared by incorporation of a small amount (<0.5 wt%) of metal–organic compounds (palladium, nickel, or copper acetates) in the molten polymers. During blending, the polymers are held at sufficiently high temperatures to thermally decompose the acetates, yielding the metallic particles (Pd, Ni, or Cu) which are used as the activators. After surface preparation, copper is deposited on polymers in an electroless bath including formaldehyde as reducer. The influence of bath parameters (temperature, composition) and the nature of activators is investigated. This method can be extended to other polymers by finding an appropriate polymer/metal–organic couple. It is also demonstrated that cheaper Ni or Cu can substitute expensive Pd.     

Structural characterization of TiO2–P2O5–CaO glasses by spectroscopy

The structure of glasses with composition x TiO₂·(65 ? x) P₂O₅·35 CaO (x = 0–30 mol%) has been studied and their glass transition temperature, Raman and NMR spectra have been analysed.For TiO₂-free glass two phosphate species have been identified as Q² and Q³. Increasing TiO₂ content in glass compositions results in the disappearance of the Q³ and Q² species and in the formation of, mainly, pyrophosphate structure, Q¹.In calcium titanophosphate glass with higher TiO₂ content the structure consists of a distorted Ti octahedral linked to pyrophosphate unit through P–O–Ti bonds. In these glass series the structural cohesion increases with TiO₂, although a depolymerization in the original P–O–P network occurs.The study of these glasses and the understanding of their structural characteristics can give a valuable contribution for the clarification of their degradation behaviour namely in biological environments.     

In-situ generation of metal–metal oxide catalysts for the growth of highly oriented graphitic nanowiggles

In this work we demonstrate an in situ generated growth catalyst that produces highly oriented graphitic nanowiggles (GNWs). GNWs are a new form of disordered nanocarbons with graphite domains stacked perpendicular to the filament axis. They had been prepared by acetylene decomposition at ∼525 °C on Al–Mg mesh coated with iron-based nanoparticles. During CVD, inter-diffusion of Mg, Fe, and O between the electrodeposited Fe particles and the mesh generate flakes which become the active site for nanowiggle growth. The properties of this unique form of carbon were evaluated by TEM, HRTEM, SEM, Raman spectroscopy, XPS and cyclic voltammetry.     

Aluminum metal–organic framework as a new host for preparation of encapsulated metal complex catalysts

A facile strategy for encapsulation of metal complex guests into MOFs was proposed. This strategy involves pre-adsorbing metal salt on MOF, and then coordinating the metal ions with the organic ligand, as exemplified by encapsulation of tris(1,10-phenanthroline) Cu(II) complexes (CuPhen) in MIL-100(Al) (denoted as CuPhen/MIL). CuPhen encapsulated in MIL-100(Al) showed higher catalytic activity than the neat CuPhen and CuPhen encapsulated in zeolite-Y. The prepared CuPhen/MIL catalyst was stable and could be reused at least three times without significant loss in activity. This work is beneficial for the host–guest chemistry study and the development of new heterogeneous catalysts.     

Rapid construction of hierarchically porous metal–organic frameworks by a spray-drying strategy for enhanced tannic acid adsorption

Metal–organic frameworks (MOFs) have attracted much attention owing to their tailored pore environment and surface functionality. However, most of the currently reported MOFs are confined to small pore sizes (<5 nm), limiting their practical applications. Here, a facile and versatile strategy for rapid construction of hierarchically porous MOFs (HP-MOFs) by spray-drying is reported, in which presynthesized nanosized MOFs (N-MOFs) can be assembled to form MOF microspheres with meso/macropores resulting from the interspace among closely arranged N-MOFs. This strategy enables the construction of multicomponent HP-MOFs with various functions. As a proof of concept, we show that the adsorption for tannic acid (TA) can be significantly enhanced using HP-MIL-101(Cr). Particularly, HP-MIL-101-30 (30 represents the primary nanoparticle size) exhibits a record-high adsorption capacity (1175 mg g⁻¹), and the adsorption rate of HP-MIL-101-30 is increased by 50% compared to that of N-MIL-101-30. These findings have important implications for the rapid construction of HP-MOFs, which is beneficial for the adsorption of large molecules.     

Enhancement of activity for NO removal of MFI‐type H‐Co‐silicate by high‐temperature pretreatment

The effect of high‐temperature pretreatment in the presence of steam on NO conversion of protonated cobalt‐incorporated silicate having MFI structure (H‐Co‐silicate) and copper‐ion‐exchanged MFI‐type zeolite (Cu/H‐ZSM‐5) was studied. The activity of Cu/H‐ZSM‐5 decreased with an increase of pretreatment temperature. In contrast with Cu/H‐ZSM‐5, the activity of H‐Co‐silicate for NO removal increased with the pretreatment temperature. As for H‐Co‐silicate, the pretreatment at 1000^°C was the optimum condition to enhance the conversion that was four times higher than that without pretreatment. The destruction of framework and loss of cobalt species were not observed after the pretreatment. Some parts of cobalt species migrated from the framework and became active sites that enhance the activity for NO removal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solvent-free route for metal–organic framework membranes growth aiming for efficient gas separation

Industrial applications of membranes based on metal–organic frameworks (MOFs) are challenged by their complex fabrication procedures and poor processability, despite their huge potential for efficient gas separation. Especially, the consumption of a large amount of toxic, expensive solvent, and harsh operation by conventional solvothermal growth also make it less attractive for industrial production. Herein, a solvent-free method is proposed to fabricate continuous defect-free MOF membranes on commercial porous stainless steel substrates, where the metal precursors are electrodeposited on the support followed by a heat treatment with the ligand powder via solid-state reaction without using any solvent. This strategy is proven to be applicable for various MOF membranes and it is expected to be a facile, cheap, and environmental friendly way for future large-scale production. © 2018 American Institute of Chemical Engineers AIChE J, 65: 712–722, 2019     

Partial oxidation of ethane to syngas over nickel‐based catalysts modified by alkali metal oxide and rare earth metal oxide

The catalytic activity, thermal stability and carbon deposition of various modified NiO/γ‐Al₂O₃ and unmodified NiO/γ‐Al₂O₃ catalysts were investigated with a flow reactor, XRD, TG and UVRRS analysis. The activity and selectivity of the NiO/γ‐Al₂O₃ catalyst showed little difference from those of the modified nickel‐based catalysts. However, modification with alkali metal oxide (Li, Na, K) and rare earth metal oxide (La, Ce, Y, Sm) can improve the thermal stability of the NiO/γ‐Al₂O₃ and enhance its ability to suppress carbon deposition during the partial oxidation of ethane (POE). The carbon deposition contains graphite‐like species that were detected by UVRRS. The nickel‐based catalysts modified by alkali metal oxide and rare earth metal oxide have excellent catalytic activities (C₂H₆ conversion of ~100%, CO selectivity of ~94%, 7 × 10⁴ l/(kg h), 1123 K), good thermal stability and carbon‐deposition resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sol–gel derived PMN–PT thick films for high frequency ultrasound linear array applications

A 12-µm PMN–PT [0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃] thick film was produced by alternate spin-coating of a ceramic powder/sol–gel composite and infiltration of the sol–gel. Using this technique, a high quality PMN–PT thick film was obtained, showing a permittivity ε_r of ~3300 and dielectric loss factor of ~0.02 at 1 kHz. Photolithographic and wet etching techniques were used to fabricate a 32-element linear array from the film. The completed array showed a center frequency of approximately 110 MHz and a bandwidth of 60% at ?6 dB without a matching layer. The performance of the kerfless array was studied and compared to a kerfed array simulated with finite element analysis.     

Self-assembled cerium-based metal–organic tetrahedrons for selective recognition of natural saccharides

By incorporating the amide groups into building blocks, two M₄L₄ molecular tetrahedrons were designed and synthesized for selective recognition of natural saccharides. Tetrahedron Ce–TBSB showed fluorescent enhancement in the presence of natural monosaccharides, whereas the larger analogy Ce–TBAB having twelve additional free amide groups exhibited fantastically selective luminescent enhancement toward sucrose over other natural mono- and di-saccharides. The selective responses of the tetrahedrons thus should be attributed to both the size-fitting of the cavities and the potential hydrogen bond interaction of the amide groups.