Interfacial Transfer Rate Research Articles

Two-group drift-flux model for dispersed gas-liquid flow in large-diameter pipes

Interfacial heat and mass transfer are prevalent in industrial processes. The interfacial transfer rate can be obtained by the product of their fluxes and interfacial area concentration (IAC) calculated by the interfacial area transport equation (IATE). Bubbles show different behavior according to their sizes. Hence, bubbles are classified into two groups. Consequently, two-group IATE is required causing to use of two gas momentum equations leading to more complexity. The present study suggests a new reliable two-group drift-flux modeling to reduce the two gas momentum equations to one gas mixture momentum equation for gas-liquid flow in large-diameter pipes. The model is developed based on the drift-flux model concept and experimental data. Group-one and group-two distribution parameters and drift velocities are validated through experimental data. The results show that the proposed two-group drift-flux model can support the concept of drift velocity from the bubbly to beyond the bubbly flow and consistency between the one-group and two-group drift-flux models. Moreover, steam-water data are used to validate the applicability of the model in steam-water flows condition. The developed two-group drift-flux model is indispensable for reducing the two gas momentum equations to one gas mixture momentum equation when two-group IATE is implemented into thermal-hydraulic codes to improve the prediction accuracy of IAC.

2D Ti3C2Tx MXene-Supported Graphitic Carbon-Nitride-Decorated Co3O4 Nanoparticles as Efficient Catalysts for Oxygen Evolution Reaction

Transition metal cobalt oxide (Co3O4) with a typical spinel structure is considered a promising electrocatalyst for oxygen evolution reaction (OER). However, its OER catalytic performance is unsatisfactory owing to its limited activity. In this study, we demonstrate that using graphitic carbon nitride (g-C3N4) loaded Co3O4 nanoparticles and then anchoring them onto 2D Ti3C2Tx MXene with a layered structure can significantly enhance the OER catalytic performance. This performance may be due to the well-layered structure of g-C3N4, thereby enabling it to provide more attachment sites for Co3O4 nanoparticles, reducing their agglomeration properties and exposing more active sites to promote OER catalytic performance. When anchoring Co3O4@g-C3N4 on Ti3C2Tx MXene, solid-state interfacial interactions can adjust the structure of electrons and promote the rate of interfacial charge transfer, which enhances the conductivity of the catalyst and further promotes its OER catalytic performance. The overpotential required for TCN is 247 mV at a current density of 10 mA cm–2, which is significantly lower than that of pure Ti3C2Tx MXene (600 mV) and Co3O4@g-C3N4 (387 mV), in addition to exhibiting excellent electrochemical stability.

Integrating the Z-scheme heterojunction and hot electrons injection into a plasmonic-based Zn2In2S5/W18O49 composite induced improved molecular oxygen activation for photocatalytic degradation and antibacterial performance

The semiconductor-based photocatalysts with local surface plasmon resonance (LSPR) effect can extend light response to near-infrared region (NIR), as well as promote charge-carriers transfer, which provide a novel insight into designing light-driven photocatalyst with excellent photocatalytic performance. Here, we designed cost-effective wide-spectrum Zn2In2S5/W18O49 composite with enhanced photocatalytic performance based on a dual-channel charge transfer pathway. Benefiting from the synergistic effect of Z-scheme heterostructure and unique LSPR effect, the interfacial charge-carriers transfer rate and light-absorbing ability of Zn2In2S5/W18O49 were enhanced significantly under visible and NIR (vis-NIR) light irradiation. More reactive oxygen species (ROS) were formed by efficient molecular oxygen activation, which were the critical factors for both Escherichia coli (E. coli) photoinactivation and tetracycline (TC) photodegradation. The enhancement of molecular oxygen activation (MOA) ability was verified via quantitative analyses, which evaluated the amount of ROS through degrading nitrotetrazolium blue chloride (NBT) and p-phthalic acid (TA). By combining theoretical calculations with diverse experimental results, we proposed a credible photocatalytic reaction mechanism for antibiotic degradation and bacteria inactivation. This study develops a new insight into constructing promising photocatalysts with efficient photocatalytic activity in practical wastewater treatment.

Determination of real-time oxygen transfer rate based on an electrochemical method

The interfacial oxygen transfer rate is one of the main factors to control the composition of alloys. The commonly employed method of studying the interfacial oxygen transfer rate is the chemical composition analysis; however, it is difficult to be studied in situ. Here, a new method of measuring the oxygen transfer rate at the gas–slag and slag–metal interfaces was reported based on electrochemical analyses. The interfacial oxygen transfer rate in the smelting process of Inconel 718 superalloy was investigated at 1723, 1773, 1823, and 1873 K. The experimental results show that the electrochemical method can measure the real-time oxygen content; hence, this method is promising in controlling the oxygen content in alloys. As the temperature increased, both the equilibrium oxygen content and the rate of oxygen absorption increased significantly, and the increase was the most obvious when the temperature was 1873 K. The possible reason is that the increase in temperature weakens the mass transfer resistance of the electric double layer at the interface, thus accelerating the oxygen transfer rate.

Evolution of Surface Oxidation on Ta3N5 as Probed by a Photoelectrochemical Method.

In this work, we present an in situ method to probe the evolution of photoelectrochemically driven surface oxidation on photoanodes during active operation in aqueous solutions. A standard solution of K4Fe(CN)6-KPi was utilized to benchmark the photocurrent and assess progressive surface oxidation on Ta3N5 in various oxidizing solutions. In this manner, a proportional increase in the surface oxygen concentration was detected with respect to oxidation time and further correlated with a continuous decline in the photocurrent. To discern how surface oxidation alters the photocurrent, we experimentally and theoretically explored its impact on the surface carrier recombination and the interfacial hole transfer rates. Our results indicate that the sluggish photocurrent demonstrated by oxidized Ta3N5 arises because of changes in both rates. In particular, the results suggest that the N-O replacement present on the Ta3N5 surface primarily increases the carrier recombination rate near the surface and to a lesser degree reduces the interfacial hole transfer rate. More generally, this methodology is expected to further our understanding of surface oxidation atop other nonoxide semiconductor photoelectrodes and its impact on their operation.

Emulsifiers of Pickering-like characteristics at fluid interfaces: Impact on oil-in-water emulsion stability and interfacial transfer rate kinetics for the release of a hydrophobic model active

The influence of interfacial layer composition on the release kinetics of a model hydrophobic active (dimethyl phthalate, DMP) from oil-in-water (o/w) emulsions relevant to foods is reported. The present study considers various food-relevant emulsifiers known to form colloidal particles in aqueous solutions. These range from a low molecular weight surfactant and protein polyelectrolytes, to biopolymer complexes and solid particles: sodium stearoyl lactylate (SSL); bovine serum albumin (BSA); sodium caseinate (NaCAS), chitosan (Ch); BSA/Ch or NaCAS/Ch complexes; and silica (Pickering) nanoparticles (A200), were all investigated. In all cases, DMP release from the oil droplets of the o/w emulsions was controlled by the interfacial transport of the active rather than by its diffusion through the globules’ interior. Release data followed first-order kinetics, where emulsions stabilised by soft (protein/polysaccharide complexes) colloidal structures were shown to provide similar (528 nm2 s−1) or even lower interfacial rate constants (241 nm2 s−1) to harder (silica) particulate entities (625 nm2 s−1). SSL (a lamellar-phase forming surfactant that has been previously suggested to stabilise o/w emulsions via a mechanism closely resembling that of Pickering particles) exhibited the lowest interfacial release rate (17 nm2 s−1). Overall, the present study contributes to current understanding on how emulsion interfacial architecture can be controlled to provide desirable molecular release performances.

Interfacial transfer and phase evolution between Cu and Sn solder doped with minor Cu, Ag and Ni: experimental and theoretical investigations

The effects of minor Cu (0.7%), Ag (3.5%) and Ni (0.1%) additions in Sn solder on the interfacial transfer and phase evolution were clarified in Sn/Cu solder joints. (Cu,M)6Sn5 and (Cu,M)3Sn (M = Cu, Ni) layers were observed at the Sn/Cu interface during thermal aging at 150 °C. The additions of Cu, Ag and Ni alloy elements were found to change the growth of the Cn–Sn intermetallic compounds (IMCs). The results showed that Cu, Ag and Ni additions were able to suppress the growth of (Cu,M)3Sn (M = Cu, Ni) layers, but promoted the (Cu,M)6Sn5 growth. This was because the reactions on the (Cu,M)6Sn5 side were promoted by the refined IMCs grain size, whose growth was at the expense of (Cu,M)3Sn. In addition, the interfacial transfer rate (thickness ratio, y) of (Cu,M)3Sn/(Cu,M)6Sn5 versus the thermal aging time (t) was found to be close to parabola relationship, the y increased gradually with the alloy elements from Ni, Cu to Ag. The phase evolution (η′-Cu6Sn5, η-Cu6Sn5, e-Cu3Sn, Ag3Sn, η′-(Cu,Ni)6Sn5, η-(Cu,Ni)6Sn5 and e-(Cu,Ni)3Sn) at the interface between Cu and Sn solder doped with minor Cu, Ag and Ni was also elucidated.

B/Co/Fe tridoped TiO2/SiO2 composite films for improved photocatalytic degradation of organic pollutants under visible light

In order to effectively overcome the inherent defects of TiO2 in practical applications including low quantum efficiency and wide band gap, the B/Co/Fe tridoped TiO2/SiO2 composite films with high photocatalytic properties were prepared by the sol-gel method. The physicochemical properties of catalysts were characterized by XRD, FE-SEM, EDS, DTA-TG, BET, DRS and PL. The results shown that the compositing of SiO2 and doping of B/Co/Fe ions in TiO2 could effectively inhibit the phase transformation of anatase to rutile and the growing of crystal grains at high annealing temperatures. The compositing of SiO2 could enhance the specific surface area (82.6 increased to 335.8 m2/g) of samples and provide more adsorption sites. The doping of B/Co/Fe tridoping could form impurity levels in the band gap of TiO2 to shorten the band gap energy (2.54 ev). And the B/Co/Fe tridoped TiO2/SiO2 films could increase the interfacial transfer rate and decrease recombination rate of electrons and holes. The photocatalytic activities of the B/Co/Fe tridoped TiO2/SiO2 films were evaluated under UV or visible light irradiation with two pollutants as target for photodegradation. The results indicated that the films exhibited more excellent photocatalytic activities compared to pure TiO2. The plausible photocatalytic degradation mechanism had been proposed.

Engineering donor-acceptor conjugated organic polymers with boron nitride to enhance photocatalytic performance towards visible-light-driven metal-free selective oxidation of sulfides

In this work, a novel heterojunction photocatalyst (BN@TTCOP) was designed and fabricated by a facile in situ growth of boron nitride (BN) on donor-acceptor type thiophene-triazine based conjugated organic polymer (TTCOP). Results revealed that the incorporation of BN could simultaneously boost light harvesting and narrow bandgap structure. More importantly, the separation efficiency and interfacial transfer rate of photogenerated charge carriers of the TTCOP were greatly promoted since negatively charged BN might exceptionally attract photogenerated holes from the surface of TTCOP by electrostatic interaction between them. Benefiting from these features, BN@TTCOP heterojunctions exhibited superior photocatalytic activity under visible-light illumination for metal-free selective oxidation of sulfides; the highest activity reached to >99 % of conversion, which was nearly 2 times higher than that of pristine TTCOP. Further analyses unveiled that the mechanism for the photooxidation is probably triggered by photogenerated superoxide radical. This study highlights a promising strategy for enhancing photocatalytic performance.

Thermal degradation and viscoelastic properties of Kevlar/Cocos nucifera sheath reinforced epoxy hybrid composites

The aim of this research work is to develop high performance structural composites using Kevlar 29 (K) and Cocos nucifera sheath (CNS). The Kevlar and CNS laminates were fabricated by using hand lay-up method followed by hot pressing. The weight ratios of Kevlar/CNS are as follows 100/0 (S1), 75/25 (S2), 50/50 (S3), 25/75 (S4), 0/100 (S5). Thermal and viscoelastic properties of laminated composites were investigated as a function of temperature using thermogravimetric (TGA) and dynamic mechanical analyzer (DMA). The obtained results revealed that the thermal stability, char residue of S2 laminate was higher compared S3, S4 and S5 laminates. Moreover, S2 laminates showed comparable thermal stability with Kevlar/epoxy composites (S1). Differential scanning calorimetry (DSC) results revealed that hybrid composite (S2) offers a virtuous resistance or stability towards heat in the epoxy composites. Viscoelastic analysis results showed that the storage modulus (E′) and loss modulus (E″) of S2 composites were higher among the laminates due to improved interfacial interactions and effective stress transfer rate. Moreover, the damping of hybrid laminates (S2) almost closer to Kevlar/epoxy laminates (S1). Hence, it was observed that hybrid Kevlar/CNS composites (S2) can be efficiently utilized for advanced structural applications where rigidity, thermal stability along with renewability are prime requirements.

Electron transfer and cascade relaxation dynamics of graphene quantum dots/MoS2 monolayer mixed-dimensional van der Waals heterostructures

We realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs) and find that the cascaded relaxation of hot electrons in GQDs that originate from the quantum confinement effect is the ultimate reason. With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve the interfacial dynamics. Van der Waals (VdW) heterostructures have emerged as promising materials for atomically thin optoelectronic and photovoltaic applications, where the efficient charge separation after photo-excitation is significant to enhance device performances. However, modulating the interfacial charge transfer is still challenging due to the weak interlayer VdW interaction. Revealing electron transfer and relaxation processes in heterostructures lays foundation to tune the interfacial dynamics and optoelectronic properties. Here, we realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs). With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve interfacial transfer rates of mixed-dimensional VdW heterostructures. We find that the cascaded relaxation of hot electrons in GQDs that originates from the quantum confinement effect can intensively affect the interfacial dynamics. Our established model is instructive to optimize performances of future photon-harvesting devices based on mixed low-dimensional heterostructures.

Synthesis of TiO2-loaded Co0.85Se thin films with heterostructure and their enhanced catalytic activity for p-nitrophenol reduction and hydrazine hydrate decomposition

P-nitrophenol (4-NP) and hydrazine hydrate are considered to be highly toxic pollutants in wastewater, and it is of great importance to remove them. Herein, TiO2-loaded Co0.85Se thin films with heterostructure were successfully synthesized by a hydrothermal route. The as-synthesized samples were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy and selective-area electron diffraction. The results demonstrate that TiO2 nanoparticles with a size of about 10 nm are easily loaded on the surface of graphene-like Co0.85Se nanofilms, and the NH3 · H2O plays an important role in the generation and crystallization of TiO2 nanoparticles. Brunauer–Emmett–Teller measurement shows that the obtained nanocomposites have a larger specific surface area (199.3 m2 g−1) than that of Co0.85Se nanofilms (55.17 m2 g−1) and TiO2 nanoparticles (19.49 m2 g−1). The catalytic tests indicate Co0.85Se–TiO2 nanofilms have the highest activity for 4-NP reduction and hydrazine hydrate decomposition within 10 min and 8 min, respectively, compared with the corresponding precursor Co0.85Se nanofilms and TiO2 nanoparticles. The enhanced catalytic performance can be attributed to the larger specific surface area and higher rate of interfacial charge transfer in the heterojunction than that of the single components. In addition, recycling tests show that the as-synthesized sample presents stable conversion efficiency for 4-NP reduction.

Rate of Molecular Transfer of Allyl Alcohol across an AOT Surfactant Layer Using Muon Spin Spectroscopy.

The transfer rate of a probe molecule across the interfacial layer of a water-in-oil (w/o) microemulsion was investigated using a combination of transverse field muon spin rotation (TF-μSR), avoided level crossing muon spin resonance (ALC-μSR), and Monte Carlo simulations. Reverse microemulsions consist of nanometer-sized water droplets dispersed in an apolar solvent separated by a surfactant monolayer. Although the thermodynamic, static model of these systems has been well described, our understanding of their dynamics is currently incomplete. For example, what is the rate of solute transfer between the aqueous and apolar solvents, and how this is influenced by the structure of the interface? With an appropriate choice of system and probe molecule, μSR offers a unique opportunity to directly probe these interfacial transfer dynamics. Here, we have employed a well characterized w/o microemulsion stabilized by bis(2-ethylhexyl) sodium sulfosuccinate (Aerosol OT), with allyl alcohol (CH2═CH-CH2-OH, AA) as the probe. Resonances due to both muoniated radicals, CMuH2-C*H-CH2-OH and C*H2-CHMu-CH2-OH, were observed with the former being the dominant species. All resonances displayed solvent dependence, with those in the microemulsion observed as a single resonance located at intermediate magnetic fields to those present in either of the pure solvents. Observation of a single resonance is strong evidence for interfacial transfer being in the fast exchange limit. Monte Carlo calculations of the ΔM = 0 ALC resonances are consistent with the experimental data, indicating exchange rates greater than 10(9) s(-1), placing the rate of interfacial transfer at the diffusion limit.

Electrochemical Measurement of Hydrogen and Nitrogen Nanobubble Lifetimes at Pt Nanoelectrodes

The lifetimes of individual H2 and N2 nanobubbles, electrochemically generated at Pt nanoelectrodes (7–85 nm-radius), have been measured using a fast-scan electrochemical technique. To measure lifetime, a stable single H2 or N2 bubble is first generated by reducing protons or oxidizing hydrazine, respectively, at the Pt nanoelectrode. The electrode potential is then rapidly stepped (<100 μs) to a value where the bubble is unstable and begins to dissolve by gas molecule transfer across the gas/water interface and diffusion. The electrode potential is immediately scanned back to values where the bubble was initially stable. Depending on the rate of this second voltammetric scan, the initial bubble may or may not have time to dissolve, as is readily determined by the characteristic voltammetric signature corresponding to the nucleation of a new bubble. The transition between these regimes is used to determine the bubble's lifetime. The results indicate that dissolution of a H2 or N2 nanobubble is, in part, limited by the transfer of molecules across the gas/water interface. A theoretical expression describing mixed diffusion/kinetic control is presented and fit to the experimental data to obtain an interfacial gas transfer rate of ∼10−9 mol N−1 s−1.

ChemInform Abstract: B‐Site Metal (Pd, Pt, Ag, Cu, Zn, Ni) Promoted La1‐xSrxCo1‐yFeyO3‐ δ Perovskite Oxides as Cathodes for IT‐SOFCs

AbstractReview: 77 refs.

Microscopic Barrier Mechanism of Ion Transport through Liquid-Liquid Interface.

Microscopic mechanism of ion transport through water-oil interface was investigated with molecular dynamics simulation. The formation/breaking of a water finger during the ion passage was explicitly formulated in the free energy surface. The calculated 2D free energy surface clearly revealed a hidden barrier of ion passage accompanied by the water finger. This barrier elucidates the retarded rate of interfacial ion transfer.

B-Site Metal (Pd, Pt, Ag, Cu, Zn, Ni) Promoted La1−xSrxCo1−yFeyO3–δ Perovskite Oxides as Cathodes for IT-SOFCs

Perovskite oxides La1−xSrxCo1−yFeyO3–δ (LSCF) have been extensively investigated and developed as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to mixed ionic–electronic conductivity and high electrooxygen reduction activity for oxygen reduction. Recent literature investigations show that cathode performances can be improved by metal surface modification or B-site substitution on LSCF. Although the specific reaction mechanism needs to be further investigated, the promoting effect of metal species in enhancing oxygen surface exchange and oxygen bulk diffusion is well recognized. To our knowledge, no previous reviews dealing with the effect of metal promotion on the cathodic performances of LSCF materials have been reported. In the present review, recent progresses on metal (Pd, Pt, Ag, Cu, Zn, Ni) promotion of LSCF are discussed focusing on two main aspects, the different synthesis approaches used (infiltration, deposition, solid state reaction, one pot citrate method) and the effects of metal promotion on structural properties, oxygen vacancies content and cathodic performances. The novelty of the work lies in the fact that the metal promotion at the B-site is discussed in detail, pointing at the effects produced by two different approaches, the LSCF surface modification by the metal or the metal ion substitution at the B-site of the perovskite. Moreover, for the first time in a review article, the importance of the combined effects of oxygen dissociation rate and interfacial oxygen transfer rate between the metal phase and the cathode phase is addressed for metal-promoted LSCF and compared with the un-promoted oxides. Perspectives on new research directions are shortly given in the conclusion.

Synergetic effect enhanced photoelectrocatalysis.

We report synergetic effect enhanced photoelectrocatalysis, in which Fe(3+) and Br(-) are used as the acceptors of photogenerated charges on TiO2 nanoparticles. The kinetic rate of interfacial charge transfer is promoted from (4.0 ± 0.5) × 10(-4) cm s(-1) (TiO2/(O2, Br(-))) to (1.5 ± 0.5) × 10(-3) cm s(-1) (TiO2/(Fe(3+), Br(-))). The synergetic effect provides a valuable approach to the design of photoelectrocatalytic systems.

Mass‐transfer enhancement by a reversible chemical reaction across the interface of a bubble rising under Stokes flow

Mass transfer around a bubble rising in a liquid under Stokes regime is investigated when a reversible chemical reaction, , is taken into account. Four dimensionless parameters control the interfacial transfer rate: the Péclet and Damköhler numbers, the ratio of the diffusion coefficient of both species, and the reaction equilibrium constant. The mass‐transfer equations are solved numerically with a finite element technique. A boundary layer approach is also proposed and solved with a coupled technique of finite difference and Chebyshev‐spectral method. The equilibrium constant and the ratio of diffusion coefficients have a strong influence on the coupling between the chemical reaction and mass transfer leading to an increase of the Sherwood number. The interaction between the chemical reaction and advection is clearly established by the simulations. Conditions corresponding to Péclet number larger than the Damköhler number reduces the effect of the chemical reaction. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3376–3388, 2014

Stranski–Krastanov Shell Growth in ZnTe/CdSe Core/Shell Nanocrystals

ZnTe/CdSe core/shell nanoparticles are synthesized in noncoordinating solvents at different temperatures. The experimental results show that CdSe shell deposition at 215 °C on spherical ZnTe core particles is analogous to Stranski-Kranstanov growth of 2D epitaxial films. The shell thickness inhomogeneity is determined by measuring the inhomogeneity in interfacial hole transfer rates to an adsorbed hole acceptor, phenothiazine. We find that the first approximately three layers of CdSe are deposited uniformly and that subsequent layers produce a rough shell surface. The origin of the shell thickness inhomogeneity is investigated. ZnTe and CdSe have very close to the same lattice constants, and the interface therefore has very little lattice strain. However, cation interdiffusion changes the radial composition profile of the ZnTe-CdSe interface, leading to a large amount of lattice strain. The extent of cation interdiffusion and hence the surface morphology can be controlled by varying the deposition temperature and the subsequent annealing time and temperature. The particle spectroscopy and the shell thickness inhomogeneity are consistent with calculations based on an elastic continuum model with a cation interdiffusion constant of 1.3 × 10–2 nm2 min–1 in the ZnTe/CdSe particles at 250 °C. The comparison of the energetics involved in S–K growth of thin films and nanocrystal shells is discussed.