Triphasic Conditions Research Articles

Electroanalytical Probing of Triphasic Hydrogen Storage and Transport in Films of Nanoparticulate Polymer of Intrinsic Microporosity (PIM-1)

AbstractPreliminary experiments are reported to show quantitatively that hydrogen gas can be stored under triphasic conditions in wet nanoparticulate polymer of intrinsic microporosity (PIM-1) applied as a film to a platinum disk electrode surface. Based on chronoamperometric data, it is shown that the resulting triphasic interface is able to store hydrogen gas at apparent concentrations higher (3 orders of magnitude increase for an approx. 15 μm thick film with typically capp,hydrogen = 80 mM; Dapp,hydrogen = 1.2 × 10–11 m2s−1) than the known solubility of hydrogen gas in aqueous electrolyte (chydrogen = 0.08 mM; Dhydrogen = 5.0 × 10–9 m2s−1) at room temperature. Due to film roughness/heterogeneity, the apparent hydrogen concentration can only be estimated, but it increases with film thickness. At the same time the apparent diffusion coefficient is lowered considerably due to the molecularly rigid/glassy polymer host. The resulting modified electrode is investigated/proposed for energy storage applications with different amounts of PIM-1 nanoparticle deposits attached to the platinum surface. Graphical Abstract

Molecular Insights into the Wettability and Adsorption of Acid Gas-Water Mixture.

Sequestration of acid gas in geological formations is a disposal method with potential economic and environmental benefits. The process is governed by variables such as gas-water interfacial tension, wetting transition, and gas adsorption into water, among other things. However, the influence of the pressure and temperature on these parameters is poorly understood. This study investigates these parameters using coarse-grained molecular dynamics (CG-MD) simulations and density gradient theory (DGT). Simulations were carried out at 313.15 K and a pressure range of 0-15 MPa. A comparison was made against H2S-water systems to clarify the effects of adsorption on interfacial tension due to vapor-liquid-liquid equilibrium. The predicted H2S-water interfacial tension and phase densities by CG-MD and DGT matched the experimental values well. The adsorption can be quantified via the Gibbs Adsorption function Γ12, which correlated well with the three-phase transition. On the one hand, pressure increments below the three-phase transition revealed a significant adsorption of H2S. On the other hand, above the three-phase transition, the Gibbs Adsorption capacity remained constant, which indicated a saturation of H2S at the water surface due to liquid-liquid equilibrium. Finally, H2S behaves markedly differently in wetting transition, rather than the involved for CO2 to different molecular layers beneath the surface of aqueous solutions. In this respect, H2S is represented by a first-order wetting transition while CO2 presents a critical wetting. Finally, it has also been found that the preferential adsorption of H2S over the H2O interface is greater if compared to that of CO2, due to its strong interaction with water. In fact, we have also demonstrated that CO2 under triphasic conditions strongly influences the wetting of the ternary system.

Polymer of intrinsic microporosity (PIM-1) enhances hydrogen peroxide production at Gii-Sens graphene foam electrodes

3D-graphene foam electrodes (Gii-Sens) immersed in a phosphate buffer solution of pH 7 are shown to generate hydrogen peroxide at a significantly faster rate in the presence of a nanoparticulate polymer of intrinsic microporosity (PIM-1). The effect is demonstrated to be associated at least in part with oxygen binding into PIM-1 under triphasic conditions. The release of the oxygen at the electrode|solution interface quadruples H2O2 production. Generator–collector experiments are performed with a graphene foam disk generator and a platinum disk electrode collector to allow in situ detection of hydrogen peroxide and oxygen.

Photoelectrochemistry of immobilised Pt@g-C3N4 mediated by hydrogen and enhanced by a polymer of intrinsic microporosity PIM-1

Graphitic carbon nitride with photo-attached platinum nanoparticles of typically 2.5 nm diameter, Pt@g-C3N4, is known for photo-generation of hydrogen in aqueous environments and in the presence of hole quenchers. Here, the generation of photocurrents from photo‑hydrogen production is observed at a platinum electrode, driven by oxalate or glucose hole quenchers, and enhanced with a polymer of intrinsic microporosity PIM-1 coated over the Pt@g-C3N4 deposit. The ability of PIM-1 to create triphasic conditions and to capture hydrogen leads to enhanced photocurrent responses, even in the presence of ambient oxygen. Effects are discussed in terms of triphasic solid|liquid|hydrogen gas-based electrode processes. A glucose-concentration-dependent (super-Langmuirian) photo-response is observed. Possible applications are proposed in glucose sensing and in hydrogen-mediated photovoltaics.

Polymer of Intrinsic Microporosity (PIM‐7) Coating Affects Triphasic Palladium Electrocatalysis

AbstractA film of the polymer of intrinsic microporosity PIM‐7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water‐insoluble microcrystalline anthraquinone is immobilised directly into the PIM‐7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM‐7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano‐palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM‐7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM‐7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial “gas management” layer.

A micromechanical [formula omitted]UNSAT effective stress expression for stress-strain behaviour of wet granular materials

The definition of an effective stress variable for idealized triphasic granular media as the contact stress arising from interparticle forces is examined through discrete element modelling computations in concert with appropriately derived analytical stress expressions based on homogenization. The latter take a more practical importance, in that they also circumvent the need for direct measurements of interparticle contact forces. Considering dry or pendular-regime conditions for slightly polydisperse dense and loose packings, the contact stress–strain behaviours in dry or wet conditions are compared along a variety of loading paths, depending on the level of plastic dissipation involved. The contact stress indeed emerges as an effective stress variable with a remarkable stress-strain character along contractant loading paths and for dense solid packings where the behaviour is close to be non-dissipative. Along more dilatant loading paths or for looser packings, plastic dissipation increases and the coincidence of the constitutive behaviour in both dry and triphasic conditions is restricted to the initial stages of the loading paths, limiting the applicability of the contact stress to the estimation of initial stiffnesses. The stark constitutive differences between the proposed effective stress and Bishop’s stress are also highlighted.

One-step preparation of microporous Pd@cPIM composite catalyst film for triphasic electrocatalysis

Triphasic microporous materials (containing solid, liquid, and gas) are of interest in electrocatalysis. In this exploratory study, a polymer of intrinsic microporosity (PIM-EA-TB) is impregnated with PdCl42− metal precursor and vacuum‑carbonised to give an electrically conductive microporous heterocarbon with embedded Pd nanoparticles of typically 10–30nm diameter. This microporous composite catalyst is formed (via spin-coating) as “flakes” of typically 100nm thickness and 1 to 20μm diameter that are readily re-deposited onto glassy carbon electrode substrates. Due to the triphasic conditions, Pd@cPIM electrocatalytic reactivity is high but only for gases (H2 oxidation or O2 reduction). This selectivity is observed even in the presence of excess formic acid fuel in the aqueous/liquid phase. The potential for application in membrane-less micro-fuel cells is discussed.

Effect of Cosolvent in a Nucleophilic Substitution Reaction Using Organoclay in Triphase Catalytic System

A remarkable rate enhancement technique has been devised for a typical nucleophilic displacement reaction by using triphase catalytic materials based on tetraoctylammonium exchange forms of hectorite clay. Pseudo-first order rate constants (kobs) for the conversion of 1-bromobutane to the corresponding chloride under triphase conditions using the clay catalyst in the presence of various polar cosolvents have been observed. The results here have shown that the addition of a cosolvent increases the catalytic activity of the triphase system by several fold. In addition, the results have demonstrated that each cosolvent has a unique concentration for achieving an optimum reaction rate.

Comprehensive Characterization of Interfacial Behavior for the Mixture CO2 + H2O + CH4: Comparison between Atomistic and Coarse Grained Molecular Simulation Models and Density Gradient Theory

The accurate description of the phase equilibria and interfacial behavior of the ternary mixture H2O + CO2 + CH4 is of fundamental importance in processes related with enhanced natural gas recovery, CO2 storage, and gas-oil miscibility analysis. For this reason, the physical understanding and theoretical modeling of this remarkably complex mixture, in a wide range of thermodynamic conditions, constitutes a challenging task both for scientists and engineers. This work focuses on the description of the interfacial behavior of this mixture, with special emphasis on several regions that yield different scenarios (vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria) and in pressure and temperature ranges related with the practical applications previously mentioned. A comparison between three alternative approaches has been performed: atomistic Monte Carlo simulations (MC), coarse grained molecular dynamics (CG-MD) simulations, and density gradient theory (DGT) have been used to characterize the interfacial region, describing in detail complex phenomena, including preferential adsorption and wetting phenomena even in the ternary triphasic region. Agreement between the results obtained from different methods indicate that the three alternative approaches are fully equivalent to analyze the interfacial behavior. It has been also found that the preferential adsorption of CO2 over H2O interface is greater if compared to CH4 in all conditions characterized. In fact, we have also demonstrated that CH4 under triphasic conditions has very limited influence on the complete wetting of the binary system H2O + CO2.

Triphase Catalysis Using Silica Gel as Support

Abstract The oxidation reaction of 2-ethyl-1-hexanol with potassium permanganate in the presence and absence of silica-gel-supported phase-transfer catalyst (PTC) in triphasic conditions was studied. In a batch reactor, the performance of the solid-supported catalysts was compared with unsupported catalyst and without the catalyst. The effect of speed of agitation, catalyst concentration, potassium permanganate concentration and temperature on reaction rate was studied. The reaction is found to be in the kinetic regime. The rate of reaction with the catalyst immobilised on the silica gel was less compared to the catalyst without immobilisation. Triphase catalysis with supported PTCs has potential applications in the continuous quest for greener industrial practices.

Gypsum-carbonate speleothems from Cueva de las Espadas (Naica mine, Mexico): mineralogy and palaeohydrogeological implications

Some of the most outstanding hypogenic gypsum speleothems worldwide have been recently discovered in the Naica mines. The Cueva de las Espadas (Swords Cave), which lies at 120 m depth, hosts a rare type of speleothem called “espada” (“sword”). This study contributes to the understanding of the mineralogical composition of these singular speleothems, by means of their examination using micro-Raman spectroscopy, FT-IR spectroscopy and EDX microprobe. Our data revealed a complex mineralogy comprising a high-purity selenite core covered by several layers of calcite, aragonite and gypsum. Solid inclusions of polymetallic oxides (Mn-Pb-Zn) and graphite were also detected. The position of the water table during the genesis of the “espada” speleothems (over the past 60 kyr) was deduced from their mineralogy. Water level fluctuations at around -120 m depth led to environmental changes within the Cueva de las Espadas. The selenite core and gypsum layers were precipitated under biphasic (water-rock) conditions when the cave was submerged under hydrothermal water. The aragonite precipitation required triphasic (air-water-rock) conditions and occurred when the water table intercepted the cave, allowing the CO2 exchange necessary for carbonate precipitation. Solid inclusions were trapped in an aerobic environment when the gypsum-aragonite boundary condition occurred. A thin calcite layer was precipitated under vadose conditions after the water table definitively moved out of the cave.

Inhibition of activated sludge respiration by sodium azide addition: Effect on rheology and oxygen transfer

Although microorganism respiration inhibition by sodium azide (NaN 3) is used in some studies to identify activated sludge adsorption capacity, little is known about the effect of this compound on the suspension properties. In this study we have investigated the effect of NaN 3 addition on both volumetric oxygen mass transfer coefficient and rheology of activated sludge (AS) suspensions in a 1.9 L bioreactor. The rheological properties (shear thinning one) of AS suspensions with and without NaN 3 addition are measured in situ (triphasic conditions). It appears that NaN 3 addition leads to a deflocculation of AS suspensions and thus a decrease in apparent viscosity. A small amount of suspended solids was added in order to obtain identical apparent viscosities (under 1.2 or 46.3 s −1) for AS suspensions with and without NaN 3 addition. K L a values were then measured in both respiring and non-respiring suspensions for different air flow rates (2, 3 or 4 L/min) and under low or high mechanical shear rate (1.2 or 46.3 s −1). Results show that under high mechanical shear rate, the respiration state for a given air flow rate does not impact the K L a values. On the contrary, under low mechanical shear rate, NaN 3 addition induces an increase of K L a values in comparison with those obtained with the respiring biomass. This effect, for a same apparent viscosity, is attributed to the deflocculation observed in the presence of NaN 3. Indeed, AS with and without NaN 3 addition used for the K L a measurements induce a modification of the floc internal structure, corresponding to smaller floc size in the case of NaN 3 addition.

Syntheses of fluorous quaternary ammonium salts and their application as phase transfer catalysts for halide substitution reactions in extremely nonpolar fluorous solvents

Perfluoromethyldecalin solutions of the fluorous alkyl halides R f 8(CH 2) m X ( m=2, 3; X=Cl, I) are inert toward aqueous NaCl, KI, KCN, and NaOAc. However, substitution occurs at 100 °C in the presence of 10 mol % of the fluorous ammonium salts ( R f 8(CH 2) 2)(R f8 (CH 2) 5) 3N + I − ( 1) or ( R f 8(CH 2) 3) 4N + Br − ( 2) (10 mol %), which are fully or partially soluble in perfluoromethyldecalin under these conditions. Stoichiometric reactions of (a) 1 and R f 8(CH 2) 3Br, and (b) 2 and R f 8(CH 2) 2I are conducted in perfluoromethyldecalin at 100 °C, and yield the same R f 8(CH 2) m I/ R f 8(CH 2) m Br equilibrium ratio (60–65:40–35). This shows that ionic displacements can take place in extremely nonpolar fluorous phases, and suggests a classical phase transfer mechanism for the catalyzed reactions. Interestingly, the non-fluorous ammonium salt mixture CH 3(CH 3(CH 2) m ) 3N + Cl − ( 3, Aliquat ® 336; m=2:1 7/9) also catalyzes halide substitutions, but under triphasic conditions with 3 suspended between the lower fluorous and upper aqueous layers. NMR experiments establish very low solubilities in both phases, suggesting interfacial catalysis.

Studying PW-Amberlite catalyst deactivation in limonene epoxidation by hydrogen peroxide

The PW-Amberlite catalyst is active for limonene epoxidation in triphasic conditions; it becomes deactivated in reaction conditions. Catalyst stability during the reaction and recovery of catalyst activity when it was treated with several solvents were evaluated. It was found that the catalyst recovered 99% of its initial activity when it was washed with toluene and that the recovery was 95% and 97% when ethanol or acetone were used as washing solvents, respectively. Leaching tests showed that the reaction did not continue when the catalyst was removed from the reaction mixture, confirming the absence of leaching during the catalyst's active phase. FTIR analysis revealed that the characteristic species of the phosphotungstate complex did not vary with successive reusing of the catalyst.

Kinetic Modeling of Limonene Epoxidation over PW-Amberlite

The kinetics of limonene epoxidation catalyzed by PW-Amberlite under triphasic conditions is described. A mechanistic pathway was postulated, and a heterogeneous kinetic model was derived following...

Nucleophilic substitution reactions using Polyacrylamide-Based phase transfer catalyst in organic and aqueous media

Poly [N-(2-aminoethyl) acrylamido] trimemethyl ammonium chloride was prepared and used as an effective heterogeneous phase-transfer catalyst. This modified polyacrylamide catalyzed nucleophilic displacement of alkyl halides for easy preparation of alkyl thiocyanates, alkyl cyanides, alkyl azides, and alkyl aryl ethers in high yields and short reaction times in organic and aqueous media under two-phase and triphase conditions. The catalyst can be recovered and reused several times.

Ionic Transformations in Extremely Nonpolar Fluorous Media: Easily Recoverable Phase-Transfer Catalysts for Halide-Substitution Reactions

Solutions of the fluorous alkyl halides R(f8)(CH(2))(m)X (R(fn)=(CF(2))(n-1)CF(3); m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (R(f8)(CH(2))(2))(R(f6)(CH(2))(2))(3)P(+)X(-) (X=I (1), Br (3)) and (R(f8)(CH(2))(2))(4)P(+)I(-) (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76-100 degrees C). Stoichiometric reactions of a) 1 with R(f8)(CH(2))(2)Br and b) 3 with R(f8)(CH(2))(2)I were conducted under homogenous conditions in perfluoromethyldecalin at 100 degrees C and yielded the same R(f8)(CH(2))(2)I/R(f8)(CH(2))(2)Br equilibrium ratio ( approximately 60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase-transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH(3)(CH(2))(11))(CH(3)(CH(2))(7))(3)P(+)I(-) (4) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape.

Eco-friendly, Selective Hydroxylation of C-7 Aromatic Compounds Catalyzed by TS-1/H2O2System under Solvent-free Solid−Liquid−Liquid-Type Triphase Conditions

Direct ring hydroxylation of aromatics, namely, anisole, toluene, and benzylchloride, using TS-1 catalyst, a MFI-type titanium silicate molecular sieve, dilute H2O2 as oxidizing agent, and water as reaction medium, was investigated under solid−liquid−liquid (SLL)-type triphase conditions. The aim was to study the relative influence of commonly used organic solvents, under solid−liquid (SL)-type biphase reaction conditions, as compared to that of water, on the conversion and product selectivity. Under solvent-free triphase conditions, the ring hydroxylation of anisole, toluene, and benzylchloride leads to significant enhancement in the conversion, turn-over frequency, and para-selectivity. However, in the case of benzyl chloride, no ring hydroxylation took place under biphase conditions (using acetone as solvent) contrary to significant ring hydroxylation (ca. 60% H2O2 efficiency) under triphase aqueous medium conditions. The simple product recovery (phase separation of organic and aqueous layers) and use ...

Highly Efficient C−C Bond-Forming Reactions in Aqueous Media Catalyzed by Monomeric Vanadate Species in an Apatite Framework

A calcium vanadate apatite (VAp), in which PO4(3-) of hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is completely substituted by VO4(3-) in the apatite framework, was synthesized. Physicochemical analysis of the VAp reveals the presence of isolated VO4 tetrahedron units with a pentavalent oxidation state. The VAp acts as a high-performance heterogeneous base catalyst for various carbon-carbon bond-forming reactions such as Michael and aldol reactions in aqueous media and the H-D exchange reactions using deuterium oxide. For example, a 200-mmol-scale Michael reaction under triphasic conditions proceeded rapidly, with an extremely high turnover number of up to 260 400 and an excellent turnover frequency of 48 s(-1). No vanadium leaching was detected during the above reactions, and the catalyst was readily recycled with no loss of activity.

Phase Behavior and Phase-Transfer Catalysis of Tetrabutylammonium Salts. Interface-Mediated Catalysis

The phase behavior and component composition of the coexisting phases in the tetrabutylammonium bromide (TBABr)/benzene/water/NaBr four-component system were strongly influenced by the temperature, TBABr content, and NaBr concentration. The phase-transfer catalytic activity of TBABr for the reaction of decyl methanesulfonate with sodium bromide was closely related to the phase behavior. Under O (oil-rich phase) + L (TBABr-rich liquid phase) + W (aqueous phase) triphase conditions, the influences of temperature and stirring speed on the phase-transfer catalytic activity were small compared with those under O + W biphase conditions. The addition of other quaternary salts that were able to form w/o aggregates in the O phase enhanced the TBABr catalytic activity even under O + W conditions. The relationship between phase behavior and catalytic activity of tetrabutylammonium chloride or iodide (TBACl or TBAI) was also examined. The results strongly suggested that the catalysis of TBAX was attributable to the interfacial reactions of TBAX with the substrate. The interface includes the water-oil microinterface formed in the microemulsion-like L phase as well as the bulk water-oil interface.