Role Of Interfacial Reactions Research Articles

The role of interfacial reactions in controlling the distribution of Cd within goethite−humic acid−bacteria composites

Mineral-organic interfacial reactions strongly influence the adsorption, distribution and bioavailability of metal cations in soil systems. The molecular binding mechanisms and distribution of Cd onto goethite, humic acid, Pseudomonas putida cells, and their composites at different mass ratios were studied through the combination of bulk adsorption coupled with EXAFS, ITC and SCM. In binary and ternary composites, the energetics of the overall adsorption of Cd was dominated by the entropy of Cd adsorption onto the organic fraction. The formation of a type-B HA bridging complex >FeOH−HACOOCdOH enhanced Cd adsorption by 10−30% at low Cd concentrations, and more than 93.5% of the adsorbed Cd was bound onto HA fraction. In ternary systems, the component additivity over-estimated Cd adsorption onto bacteria by ~21.8%, likely due to site blocking effects. Models involving the masking of phosphoryl sites and HA bridging reactions can simulate the distribution of Cd in the composites. Our modelling suggests that HA is the main scavenger of Cd under a range of environmental conditions, and that bacteria become important in affecting the distribution of Cd under lower pH settings. This study demonstrates the impact of iron oxide−HA−bacteria interactions on the fate and distribution of Cd in soils and associated environments.

Role of interfacial reactions in biodegradation: A case study in a montmorillonite, Pseudomonas sp. Z1 and methyl parathion ternary system.

Organophosphate pesticides are currently the most commonly used pesticides, but the mechanisms of biodegradation of these compounds are often unknown. In this study, we constructed a ternary biodegradation system containing methyl parathion (MP), a bacterial strain of Pseudomonas sp. Z1 with capability of degrading MP and montmorillonite, which is a common clay mineral in soils. The role of interfacial reactions between montmorillonite and the MP degrader on the biodegradation of MP was investigated by batch adsorption as well as through semi-permeable membrane experiments. The contact between degrader and montmorillonite in biodegradation was also dynamically examined using in situ attenuated total reflectance Fourier transform infrared spectroscopy. The metabolic activity of the degrading bacteria was also assessed using an isothermal microcalorimetric technique. The results indicate that sorption of bacterial cells onto montmorillonite enhances the metabolic activity of the bacteria and hence the biodegradation of MP by the bacteria, and that an amide group on a bacterial surface protein is responsible for the bacterial adhesion onto the montmorillonite. This stimulated effect ceased when the bacteria were physically separated from the surface of the clay by a membrane, demonstrating the importance of sorption of both the bacteria and the MP in the biodegradation process.

Role of interfacial reaction on the mechanical performance of Al/steel dissimilar refill friction stir spot welds

ABSTRACTAl/steel welds were successfully fabricated by refill friction stir spot welding. The welding parameters were optimised based on the clamping ring temperature and weld strength. 85.7% of welds achieve a strength which exceeds the American Welding Society requirement when the clamping ring temperature ranges from 230 to 265°C. Cracks are formed under the pin and sleeve in the Al substrate at the Al/steel interface, which are associated with the tool sleeve plunging period and attributed to the α-Al + Al–Zn eutectic structure. The interdiffusion between Al and Zn at the steel surface produced an Al–Zn eutectic structure layer at the Al/steel interface, while part of the zinc coating materials is squeezed out of the sleeve periphery, leading to a brazing effect which contributes to weld strength. Nanoscale discontinuous Fe4Al13 and FeAl intermetallics form as a layer localised at the Al–Zn layer/steel substrate interface.

The Role of Interfacial Reactions in Determining Plasma–Liquid Chemistry

In this work, we investigate the production of highly oxidative species in solutions exposed to a self-pulsed corona discharge in air. We examine how the properties of the target solution (pH, conductivity) and the discharge power affect the discharge stability and the production of H2O2. Indigo carmine, a common organic dye, is used as an indicator of oxidative strength and in particular, hydroxyl radical (OH·) production. The observed rate of indigo oxidation in contact with the discharge far exceeds that predicted from reactions based on concentrations of species measured in the bulk solution. The generation of H2O2 and the oxidation of indigo carmine indicate a high concentration of highly oxidizing species such as OH· at the plasma–liquid interface. These results indicate that reactions at the air plasma–liquid interface play a dominant role in species oxidation during direct non-equilibrium atmospheric pressure plasma treatment.

Wetting by Liquid Metals—Application in Materials Processing: The Contribution of the Grenoble Group

The wettability of ceramics by liquid metals is discussed from both the fundamental point of view and the point of view of applications. The role of interfacial reactions (simple dissolution of the solid in the liquid or formation of a layer of a new compound) is illustrated and analysed. Several results are presented in order to illustrate the role of wettability in materials processing, namely infiltration processing, joining dissimilar materials by brazing and selecting crucibles for crystallising liquid metals and semiconductors. The review includes results obtained during the last 15 years mainly, but not only, by the Grenoble group.

Role of Interfacial Reaction in Heterogeneous Aromatic Nitration

The previously established mechanism of two-phase nitration has been revised by proposing an additional mode of reaction, viz., interfacial nitration. The interfacial mechanism involves adsorption of the nitronium ion at the interface, followed by its reaction with the aromatic substrate present in the interfacial monolayer. The evidence for the proposed mechanism is provided by the results of the experiments, conducted in this work, on nitration of nitrobenzene. Relative magnitudes of the bulk and the interfacial rates during the nitration of nitrobenzene have been determined. The effects of interfacial area, concentrations of sulfuric and nitric acids, and addition of surfactant and inert diluent in the organic phase on the rate of interfacial nitration are studied. On the basis of the proposed mechanism, plausible explanations have been provided to the anomalies in the rates of nitration, observed under the industrially relevant operating conditions.

The role of interfacial reactions in Pt/CdTe contact formation

The reactions at the interface between CdTe and the contact metal platinum have been studied using various approaches including theoretical and experimental ternary phase diagram determination, bulk and thin film diffusion couples and electrical characterization of elemental and compound contacts on p- and n-Cd0.95Zn0.05Te (CZT). At the interface of Pt/CdTe diffusion couples a non-planar reaction layer of the intermetallics PtCd and PtTe is formed. This is consistent with the studied ternary phase diagram. Additional compounds which are stable in direct contact to CdTe can also be identified using these data. The contact barrier heights of pure Pt and of alloys with Cd or Te on CZT substrates and their variation after various annealing procedures were determined both on etched (Te-rich) and on virtually stoichiometric CZT surfaces. All the Pt-based contacts on the etched CZT surface showed a similar behaviour, determined by the Te excess and the ensuing formation of PtTe in direct contact to CZT. In contrast to that, a wide range of electrical properties can be achieved on the stoichiometric surface by deposition of Pt with or without additional Cd or Te interlayers due to the variety of phases forming in direct contact to CZT after deposition and annealing.