Diffusion Path Length Research Articles

Porous self-protonating spiropyran-based NIPAAm gels with improved reswelling kinetics

This study focuses on improving the speed of actuation of poly(N-isopropylacrylamide)-based photoresponsive gels containing copolymerised spiropyran as the photoswitch and acrylic acid as the proton source. The improvement is realised by introducing pores into the material. For this purpose, polyethylene glycol (PEG) of two molecular weights (2000 and 20000 g mol−1) has been used as the porophore in the polymerisation mixture. Upon removal of the PEG porophore post polymerisation, hydrogels of different pore sizes were obtained. This impacts the diffusion of water molecules moving in/out of the hydrogel matrix, thus improving the swelling and shrinking kinetics of the hydrogel due to reduction of the average diffusion pathlength. Most significant improvement was observed in the reswelling step and is demonstrated with optical microscopy combined with kinetic ultraviolet–visible spectroscopy (UV–Vis) analysis. Scanning electron microscopy reveals the PEG-induced pores to be in the range of 0.1–2 μm. Moreover, the mechanical stability of the gels is confirmed with rheometry. Lastly, the presented photoresponsive porous gels exhibit an order of magnitude faster reswelling rate compared to the non-PEG-produced control sample.

Yeast bio-template synthesis of porous anatase TiO2 and potential application as an anode for sodium-ion batteries

ABSTRACT Porous anatase TiO 2 samples have been prepared by a bio-template route using low-cost yeast cells as templates. The structure, morphology and electrochemical performance of the prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, galvanostatic charge/discharge tests and cyclic voltammograms (CV). The results showed that the prepared samples have a hierarchical porous structure replicated from the microstructure of yeast template, which combines macropores (1.5–2.5 μm) and thin pore wall (0.2–0.7 μm) composed by mesopore (9.78 nm) and 10–20 nm active material. The prepared porous TiO 2 delivered a discharge capacity of about 255.98 mAh g −1 and its capacity retention was about 80% after 100 cycles at 1/3C. Remarkably, it still showed a high discharge capacity of 112.93 and 84.65 mAh g −1 even at 5 and 10C, respectively. The good rate performance can be ascribed to the hierarchical porous structure, which provided good access of the electrolyte to the electrode interface, reducing path lengths for ion diffusion and accommodating volume changes during cycling.

Adsorption Kinetics in Nanoscale Porous Coordination Polymers.

Nanoscale porous coordination polymers were synthesized using simple wet chemical method. The effect of various polymer surfactants on colloidal stability and shape selectivity was investigated. Our results suggest that the nanoparticles exhibited significantly improved adsorption kinetics compared to bulk crystals due to decreased diffusion path lengths and preferred crystal plane interaction.

Calendering as a direct shaping tool for the continuous production of fixed-dose combination products via co-extrusion

In this study calendering is used as a downstream technique to shape monolithic co-extruded fixed-dose combination products in a continuous way. Co-extrudates with a metoprolol tartrate-loaded sustained-release core and a hydrochlorothiazide-loaded immediate-release coat were produced and immediately shaped into a monolithic drug delivery system via calendering, using chilled rolls with tablet-shaped cavities. In vitro metoprolol tartrate release from the ethylcellulose core of the calendered tablets was prolonged in comparison with the sustained release of a multiparticulate dosage form, prepared manually by cutting co-extrudates into mini-matrices. Analysis of the dosage forms using X-ray micro-computed tomography only detected small differences between the pore structure of the core of the calendered tablet and the mini-matrices. Diffusion path length was shown to be the main mechanism behind the release kinetics. Terahertz pulsed imaging visualized that adhesion between the core and coat of the calendered tablet was not complete and a gradient in coat thickness (varying from 200 to 600μm) was observed. Modulated differential scanning calorimetry and X-ray diffraction indicated that the solid-state properties of both drugs were not affected by the calendering procedure.

Influence of the porous support on diffusion in composite membranes

Composite membranes used in gas separation, pervaporation and reverse osmosis applications typically consist of at least one nonporous layer on top of a porous structure. The porous support restricts diffusion in the top layer because molecules can exit the layer only where a pore is present. This not only increases the path length for diffusion, but also increases the concentration gradient of the diffusing molecules as they approach the pore opening. These two effects combine to give the top layer a diffusion resistance that is greater than the intrinsic resistance of the layer, which is calculated as the actual thickness of the top layer, H, divided by the diffusion coefficient, D. In membrane terms, this means that the effective permeance of the composite membrane is smaller than the intrinsic permeance, which is calculated as the permeability coefficient, P, divided by H. The relative reduction in permeance is expressed by the restriction factor, Ψ, and is independent of the solubility and diffusion coefficients.We simulated the diffusion process using computational fluid dynamics (CFD) and determined the restriction factor, Ψ, as a function of the support porosity, ϕ, and a normalized dimension, τ, defined as the top layer thickness divided by the pore radius. By defining a dimensionless Restriction Number, NR, we were able to very accurately correlate the restriction factor data to the following equation:ψ=ϕ+1.6⋅NR1.11+1.6⋅NR1.1withNR=τ⋅ϕ1−ϕThe correlation predicts the restriction factor within 5% for all cases evaluated, which included three different pore distribution patterns and multiple pore size distributions with up to four different pore sizes. Our analysis suggests that the correlation is also applicable to porous supports with more realistic properties, such as random pore location and broader pore size distributions. The correlation is useful to evaluate the influence of the porous support on the permeance of composite membranes and shows that the effect can be significant in high-performance membranes.A limited number of CFD simulations were performed for composite membranes containing a gutter layer and show convincingly that a high permeability gutter layer can significantly improve the permeance of composite membranes while reducing selectivity by only a modest degree.

Enhanced Electrochemical Performance of Electrospun Ag/Hollow Glassy Carbon Nanofibers as Free-standing Li-ion Battery Anode

Silver with a high theoretical capacity for lithium storage is an attractive alloy based anode for Li-ion batteries, but large volume changes associated with AgLix alloy formation leads to electrode cracking, pulverization and rapid capacity fading. A buffer matrix, like the electrospun hollow carbon nanofibers, can reduce this problem to a great extent. Herein, we demonstrate the facile synthesis of a free-standing, binder free Ag-C hybrid electrode through co-axial electrospinning, where well dispersed Ag nanoparticles are embedded in hollow carbon nanofibers. Using this approach, the long cycle life of carbon is complemented with the high lithium storage capacity of Ag, resulting in a high performance anode. The Ag-C composite electrode delivers a capacity of 739mAhg−1 (>conventional graphite anodes) at 50mAg−1, with ∼85% capacity retention after 100 cycles. In addition, the Ag-C composite nanofibers are highly porous and exhibit a large accessible surface area (∼726.9m2g−1) with an average pore diameter of ∼6.07nm. The encapsulation of Ag in the hollow interiors not only provides additional lithium storage sites but also enhances the electronic conductivity, which combined with the reduced lithium diffusion path lengths in the nanofibers result in faster charge-discharge kinetics and hence a high rate performance.

Effect of hierarchical meso–macroporous alumina-supported copper catalyst for methanol synthesis from CO2 hydrogenation

Effects of pore structures of alumina on the catalytic performance of copper catalysts for CO2 hydrogenation were investigated. Copper-loaded hierarchical meso–macroporous alumina (Cu/HAl) catalyst exhibited no significant difference in terms of CO2 conversion with copper-loaded unimodal mesoporous alumina (Cu/UAl) catalyst. However, the selectivity to methanol and dimethyl ether of the Cu/HAl catalyst was much higher than that of the Cu/UAl catalyst. This was attributed to the presence of macropores which diminished the occurrence of side reaction by the shortening the mesopores diffusion path length. The Cu/HAl catalyst also exhibited much higher stability than the Cu/UAl catalyst due to the fast diffusion of water out from the catalyst pellets, alleviating the oxidation of metallic copper to CuO.

Hollow Carbon Nanosphere/Germanium Nanoparticle Composite Li-Ion Anode

Since their introduction, lithium ion batteries have become ubiquitous for powering portable electronic devices. However, the charging rate of graphite (by far the most common anode material) is relatively slow due to long lithium diffusion pathlengths. Highly graphitic hollow carbon nanospheres (HCNS) have a tremendous advantage over micron-sized graphite particles as the diffusion path length is on the nanoscale, 3 orders of magnitude shorter than graphite’s, facilitating rapid charging within a few minutes, rather than many hours. In addition, HCNS anodes cycle stably in inexpensive low melting point electrolytes, cycling with excellent capacity retention and high rate at temperatures as low as -50 ˚C. Unfortunately, HCNS anodes have lower specific capacity compared to those made with graphite (~220 mAh/g vs. 372 mAh/g).(1) However, the high surface area, good electrical conductivity and excellent electrochemical stability of HCNS make it a promising support material for other high capacity lithium alloying materials, suggesting the possibility of significantly higher specific capacities, much better low temperature performance and charging rates than graphite-based anodes. Here we present our studies to date on the incorporation of germanium metal, second only to Si in gravimetric capacity as a Li alloying material (1385 mAh/g) and nearly equal to it in volumetric capacity (7372 mAh/mL), into HCNS anodes. Syntheses were performed at room temperature by solution phase reduction of germanium precursors in the presence of the HCNS to produce conductive composites of Ge nanoparticles supported on HCNS. When cycling from 1.5 to 0.02 V vs. Li, a stable capacity of ~600 mAh/g electrode ( ~1200 mAh/g Ge) was obtained with average capacity fade of 0.03% per cycle. Long-term coulombic efficiency values were 99.9 and 99.6% for 20 and 40% Ge/HCNS, respectively. Owing to the high volumetric capacity of Ge and porous structure of the HCNS, areal capacities of ~2.5 mAh/cm2 could be obtained by slurry casted techniques. Performance comparisons of multiple Ge/HCNS compositions with differing cycling environments will be presented. (1) Michael J. Wagner, J. Thomas McKinnon, J. Cox and K. Gneshin, “Hollow Carbon Naonsphere Based Secondary Cell Electrodes”, United States Patent 8,262,942, September 11, 2012. Figure 1

C-Doped TiO2-B Nanowires Derived from TiC As an Anode Materials for Lithium Ion Batteries with High Rate Performance

In the recent past nanostructured materials have been attracting much interest owing to their physical and chemical characteristics, which make them extremely suitable for a number of applications. In particular, one of the most promising applications is their use as electrode materials for rechargeable lithium ion batteries (LIB)1-2. Among the anode materials, Titanium dioxide (TiO2) has been deeply investigated for lithium intercalation/de-intercalation due to high rate capability, very good reversible capacity, low volume expansion ( <2% ) upon cycling and furthermore lost cost, high abundant and very safe lithium reaction potential ~ 1.5 V vs Li/Li+, owing to these characteristics, TiO2 anodes have been considered to target in EVs and HEVs application1-3. Recently, the various polymorphs of TiO2 (anatase, rutle, brookite and bronze) have been explored as efficient anodes for LIB3. In particular, TiO2-Bronze (TiO2-B) has been receiving significant interest due to its theoretical capacity of 335 mAh g-1. Importantly, TiO2-B manifests the major advantages of fast charging-discharging through a pseudo-capacitive mechanism in addition to the bulk diffusion, whereas other polymorphs of TiO2 mostly show intercalation of Li-ion through bulk diffusion controlled mechanism3. However, the low electronic conductivity and low rate of Li-ion diffusivity of TiO2 are key issues for a high rate capable anode. To overcome these issues, we report synthesis of carbon-doped TiO2-B nanowires by facile and inexpensive method without using external carbon source. The carbon doping was verified by UV–visible and X-ray photoelectron spectroscopy and further structure and morphology was investigated with X-ray diffraction, Raman spectroscopy and Scanning and Transmission microscopies. The electrochemical performances of the C doped and undoped TiO2-B nanowires were tested by galvanostatic charge/discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. This novel C-doped materials presented high capacities and higher rate capability in electrochemical cycling experiments with respective to undoped material. This is attributed to the reduction of Li-ion diffusion path lengths along with improving electrical conductivity of TiO2-B nanowires. The electrochemical experiments demonstrated that C-TiO2-B nanowires electrodes exhibited superior lithium storage capacity of ~306 mAh g-1 at current rate of 0.1C as well as excellent rate ability of ~160 mAh g-1even at high current rate of 10C after 1000 cycle in lithium-ion batteries.

On the remarkable resistance to coke formation of nanometer-sized and hierarchical MFI zeolites during ethanol to hydrocarbons transformation

The impact of the textural properties of H-ZSM-5 zeolites in the conversion of ethanol to hydrocarbons at 623K and under 3.0MPa pressure is investigated. We highlight that the lifetime of the catalysts is not correlated to the coking rate but to the number of pore mouths. The addition of macropores (fluoride leaching) or mesopores (alkaline leaching) to micron-sized zeolites is a simple approach to increase the number of pore mouths and reduce the diffusion path length of molecules in the micropores. However, the most efficient way is to reduce the zeolite crystal size to nanometers. The longest catalyst lifetime (>100h) is obtained with a hierarchical nanometer-sized zeolite even though most of its acid sites are poisoned. The important impact of the nature of coke on the catalysts regeneration is also highlighted.

Radiation-stimulated surface diffusion of adatoms on a tungsten {321} face

The surface erosion of tungsten bombarded with accelerated 5-keV helium atoms has been studied by the method of field-ion microscopy. Radiation-stimulated appearance of adatoms localized in the central region of terraces on the {321} W face has been observed. The distribution of W adatoms on {321} terraces is characterized by the presence of zones free of adatoms in the vicinity of atomic steps. The existence of “empty” zones upon irradiation is evidence of transient surface diffusion. The diffusion path lengths of adatoms on the {321} W face reach six interatomic distances and reveal anisotropy of the radiation-stimulated transient surface diffusion.

Mass transfer considerations in solid-liquid two-phase partitioning bioreactors: a polymer selection guide

BACKGROUND Selection of polymers for two-phase partitioning bioreactors (TPPBs) has been focused primarily on predicting a polymer's affinity for the target molecule. Although the extent to which a polymer absorbs a solute is important, the rate of uptake/release must be sufficiently rapid such that a TPPB is not mass transfer limited. This work focused on developing a guide to identify combinations of polymer diffusivities and diffusional path lengths that will ensure a TPPB is not limited by substrate delivery. RESULTS TPPB systems limited by substrate delivery yielded linear growth, while biologically limited systems exhibited exponential growth. Release rates of phenol from various polymer phases increased as polymer diffusivity increased, or as diffusional path length (polymer bead size) decreased. A polymer selection guide was developed identifying combinations of polymer diffusivity and bead size that will ensure a TPPB is not mass transfer limited, for a desired maximum substrate consumption rate. CONCLUSION In selecting polymers for TPPB applications, solute affinity (extent of uptake) has been relatively well characterized using first principles methods, and the present work has now ‘completed the picture’ by providing a description of polymer transport properties (diffusivity and diffusional path length) to be able to generate a guide for selecting polymers. © 2015 Society of Chemical Industry

ChemInform Abstract: Transformers: The Changing Phases of Low‐Dimensional Vanadium Oxide Bronzes

AbstractReview: 140 refs.

Hollow Carbon Nanosphere/Germanium Nanoparticle Composite Li-Ion Anode

Since their introduction, lithium ion batteries have become ubiquitous for powering portable electronic devices. However, the charging rate of graphite (by far the most common anode material) is relatively slow due to long lithium diffusion pathlengths. Highly graphitic hollow carbon nanospheres (HCNS) have a tremendous advantage over micron-sized graphite particles as the diffusion path length is on the nanoscale, 3 orders of magnitude shorter than graphite’s, facilitating rapid charging within a few minutes, rather than many hours. In addition, HCNS anodes cycle stably in inexpensive low melting point electrolytes, cycling with excellent capacity retention and high rate at temperatures as low as -50 ˚C. Unfortunately, HCNS anodes have lower specific capacity compared to those made with graphite (~220 mAh/g vs. 372 mAh/g).(1) However, the high surface area, good electrical conductivity and excellent electrochemical stability of HCNS make it a promising support material for other high capacity lithium alloying materials, suggesting the possibility of significantly higher specific capacities, much better low temperature performance and charging rates than graphite-based anodes. Here we present our studies to date on the incorporation of germanium metal, second only to Si in gravimetric capacity as a Li alloying material (1385 mAh/g) and nearly equal to it in volumetric capacity (7372 mAh/mL), into HCNS anodes. Syntheses were performed at room temperature by solution phase reduction of germanium precursors in the presence of the HCNS to produce conductive composites of Ge nanoparticles supported on HCNS. When cycling from 1.5 to 0.02 V vs. Li, a stable capacity of ~600 mAh/g electrode ( ~1200 mAh/g Ge) was obtained with average capacity fade of 0.03% per cycle. Long-term coulombic efficiency values were 99.9 and 99.6% for 20 and 40% Ge/HCNS, respectively. Owing to the high volumetric capacity of Ge and porous structure of the HCNS, areal capacities of ~2.5 mAh/cm2 could be obtained by slurry casted techniques. Performance comparisons of multiple Ge/HCNS compositions with differing cycling environments will be presented. (1) Michael J. Wagner, J. Thomas McKinnon, J. Cox and K. Gneshin, “Hollow Carbon Naonsphere Based Secondary Cell Electrodes”, United States Patent 8,262,942, September 11, 2012. Figure 1

Synthesis of Spinel-Structured Core-Shell Nanocrystals for Lithium Ion Batteries

High power density and excellent cycling stability in lithium ion battery (LIBs) are required to meet the criteria for the power source such as electric vehicles. Higher power density is generally hindered by sluggish diffusion of Li ions in micrometric materials commonly adopted in LIBs.[1] Size reduction of active materials can significantly improve the rate of lithium ions because of the shortened length of diffusion path. In the meantime, high surface area enables facile access of charges via large contact area with the electrolyte or electronic conducting additives. In this perspective, much effort have been devoted to the nanosized particles, which report the high power density that cannot be achieved from the micrometric counterparts. However, in return, increased surface area of particles can lead to the vigorous unfavorable interfacial reaction that mainly occurs through the energetically unstable surface such as dissolution of active materials and decomposition of electrolyte.[2] Reducing the active transition metal in the vicinity of the surface by partially replacing inactive ions can improve the interfacial stability, but must be prepared as the form of thin passivating barriers to preserve storage capacity. Post-synthetic coating procedure with stable phases such as Al2O3 and MgO, has been performed on the surface of particles as the most common approach,[3] however, it is difficult for coating phases to access buried interfaces because of agglomerated feature of the particles. Herein, Mn3O4 nanocrystals (NCs) were synthesized by thermal decomposition of manganese acetate in oleylamine and an ultra-thin shell layers that are enriched in aluminum were introduced, finally leading to the formation of core-shell (C-S) NCs. The particle size of Mn3O4 and C-S NCs were approximately 21 nm and 24 nm, respectively, as shown in Figure 1. The atomic ratio of Al/Mn in C-S NCs was found to be ~0.2 by energy dispersive X-ray spectroscopy (EDX). The crystal structures of Mn3O4 and C-S NCs were studied using X-ray diffraction (XRD) in Figure 2, both of which matched with a tetragonal spinel structures (I41amd, JCPDS card # 55492) without any peaks related to Al2O3. In order to study composition and microstructure of the shell layer, the scanning transmission electron microscopy (STEM) will be carried out. C-S LiMn2O4 NCs are prepared by mixing precursor C-S NCs and Li sources followed by thermal treatment. The electrochemical properties will be evaluated in Li metal half cells compared to the counterpart without shell layer. The effect of the shell layer on the electrochemical stability will be discussed. Fig. 1. TEM images of (a) Mn3O4 and (b) C-S NCs. Magnified images are shown in the insets (Scale bars of (a) and (b) are 5 nm and 10 nm, respectively). Fig. 2. XRD patterns of (a) Mn3O4 and (b) C-S NCs, which match well with a tetragonal phase Reference: Isaac D. Scott, Yoon Seok Jung, Andrew S. Cavanagh, Yanfa Yan, Anne C. Dillon, Steven M. George, and Se-Hee Lee, Nano Letters, 414–418, 11 (2011). Peter G. Bruce, Bruno Scrosati, and Jean-Marie Tarascon, Angew. Chem. Int. Ed, 2930-2946, 47 (2008). Jun Liu and Arumugam Manthiram, Chem. Mater. 1695-1707, 21 (2009). Figure 1

Modification of Oxygen/(Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ Interfaces Derived by Metal-Organic Deposition

Mixed ionic-electronic conducting (MIEC) perovskite oxides ABO3-δ have attracted great interest as materials for a variety of high-temperature applications, e.g., ceramic oxygen transport membranes (OTM) for oxy­­gen separation with a high permea­bility and selectivity for O2/N2 separation. Several MIEC materials, namely members of the com­position AxSr1-xCoyFe1-yO3-δ (A = La, Ba), are known to exhibit ex­cellent oxygen-ionic and electronic trans­port pro­per­ties at tem­peratures of 700…1000 °C [1]. Among these Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), in par­ticular, has been reported to exhibit unmatched permeation properties to-date [2,3]. Permeation mainly depends on both the chemical oxygen bulk diffusion and the surface transfer of oxygen between gas phase and oxide. The former can be accelerated by limiting the diffusion path length, i.e., thinning the OTM. With the help of thin-film technology, microscale thicknesses are readily achievable. However, the oxygen flux cannot be significantly increased by fabricating membranes with a thickness below a certain material-specific value (“characteristic length”) because surface transfer limitations dominate. In order to further increase the oxygen permeation one must therefore improve the oxygen surface exchange. Recently, an enhancement of O2 flux through a BSCF membrane was achieved with a microscale functional layer [4]. Furthermore, it was reported that metal-organic deposition (MOD)-derived nanoscale thin-film SOFC cathodes made from La0.6Sr0.4CoO3-δ exhibit ex­tre­mely low polarization losses [5]. These results suggest that the oxygen flux through a thin BSCF OTM can be significantly enhanced by nanoscale surface mo­di­fications leading to a geometric in­crease of the gas/ solid interface. Recent MIEC performance-modelling ac­ti­vities [6] also addressed the influence of microstructure on oxygen-transport kinetics. In this work, nanoscaled BSCF thin films (thicknesses below 100 nm) have been successfully deposited onto NdGaO3 single crystal substrates from a homogeneous BSCF starting solution using an MOD method. The films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. In contrast to physical vapor deposition techniques, e.g. PLD or magnetron sputtering, BSCF thin films formed by an MOD method provide the possibility to custom-tailor the surface morphology by subsequent annealing treatments. Fig. 1 shows the surface morpho­logy variation of BSCF. Depending on the annealing process, different surface morphologies could be observed, e.g., oriented grain growth with a textured surface as shown in Fig. 1(i) or a smooth, stepped surface as shown in Fig. 1(ii). Changes of surface area or phase composition (cu­bic, hexagonal BSCF, others) are expected to affect the catalytic activity of OTM membranes. A systematic study of surface morphologies achie­ved by a parameter variation in the annealing process is presented. The samples were characterized electrically and elec­tro­chemically (conductivity σ(T,pO2), chemical oxy­­gen sur­face exchange coefficient k δ(T)) and results compared to those obtained on epitaxial BSCF thin films and other MIEC compositions.

The effects of leaf size and microroughness on the branch‐scale collection efficiency of ultrafine particles

AbstractWind tunnel experiments were performed to explore how leaf size and leaf microroughness impact the collection efficiency of ultrafine particles (UFP) at the branch scale. A porous media model previously used to characterize UFP deposition onto conifers (Pinus taeda and Juniperus chinensis) was employed to interpret these wind tunnel measurements for four different broadleaf species (Ilex cornuta, Quercus alba, Magnolia grandiflora, and Lonicera fragrantissima) and three wind speed (0.3–0.9 ms−1) conditions. Among the four broadleaf species considered, Ilex cornuta with its partially folded shape and sharp edges was the most efficient at collecting UFP followed by the other three flat‐shaped broadleaf species. The findings here suggest that a connection must exist between UFP collection and leaf dimension and roughness. This connection is shown to be primarily due to the thickness of a quasi‐laminar boundary layer pinned to the leaf surface assuming the flow over a leaf resembles that of a flat plate. A scaling analysis that utilizes a three‐sublayer depositional model for a flat plate of finite size and roughness embedded within the quasi‐laminar boundary layer illustrates these connections. The analysis shows that a longer leaf dimension allows for thicker quasi‐laminar boundary layers to develop. A thicker quasi‐laminar boundary layer depth in turn increases the overall resistance to UFP deposition due to an increase in the diffusional path length thereby reducing the leaf‐scale UFP collection efficiency. It is suggested that the effects of leaf microroughness are less relevant to the UFP collection efficiency than are the leaf dimensions for the four broadleaf species explored here.

Al-MFI Nanosheets as Highly Active and Stable Catalysts for the Conversion of Propanal to Hydrocarbons

The conversion of propanal to hydrocarbons is investigated over mesoporous aluminosilicate MFI nanosheets (Al-MFI-ns) of single-unit-cell thickness and conventional aluminum MFI zeolite (Al-MFI) at 673 K and atmospheric pressure. Al-MFI-ns exhibits a fivefold in- crease in stability attributed to the shorter diffusion path lengths and open architecture of the nanosheets, which minimizes pore blocking from fouling. The overall ratio of olefin to aromatic products is similar for Al-MFI-ns and Al-MFI at all conversion levels. However, the product distribution within each group shows that the Al-MFI-ns generate a fivefold increase in selectivity to C6-8 olefins and a twofold increase in selectivity to C9-10 aromatics compared to Al-MFI. The very high selectivity to C9- aromatic trimethylbenzene supports an aromatization mechanism involving sequential aldol condensation and dehydration sequences. The very short diffusion paths in the single-unit-cell thick nanosheets allows for the C9 aromatics to diffuse out of the pores before they can be converted to lighter aromatics or olefins. Al-MFI-ns shows no indication of irreversible deactivation, fully recovering its original activity after regeneration by calcination, and retaining similar deactivation rates and product selectivities as the fresh catalyst. Al-FMI-ns improves the production of aromatics from light oxygenates at mild conditions, a key feature for bio-oil upgrading.

A Study of Calcareous Deposits on Cathodically Protected Mild Steel in Artificial Seawater

Calcareous deposits were formed on steel under conditions of cathodic protection in artificial seawater at applied constant current densities ranging from 50 to 400 mA·m−2. The calcareous layers were characterized using a Field Emission Gun Scanning Electron Microscope (FEG SEM) in conjunction with Energy Dispersive X-Ray Analysis (EDX), and Electrochemical Impedance Spectroscopy (EIS). At cathodic current densities of 50–100 mA·m−2 where corrosion was still occurring, a clear correlation existed between the iron containing corrosion product and the overlying magnesium hydroxide layer. This revealed that the mapping of magnesium rich areas on a steel surface can be used in the identification of local corrosion sites. At current densities of 150–200 mA·m−2, a layered deposit was shown to occur consisting of an inner magnesium-containing layer and an outer calcium-containing layer. At current densities of 300–400 mA·m−2, intense hydrogen bubbling through macroscopic pores in the deposits gave rise to cracking of the deposited film. Under such conditions deposits do not have a well-defined double layer structure. There is also preferential formation of magnesium-rich compounds near the steel surface at the early stages of polarisation and within the developing pores and cracks of calcareous deposits later on. Based on SEM/EDX investigation of calcareous depositions the impedance model was proposed and used to monitor in situ variations in steel corrosion resistance, and to calculate the thickness of formed deposits using the length of oxygen diffusion paths.

A dye-sensitized solar cell having polyaniline species in each component with 3.1%-efficiency

Pursuit of technological implementation with no sacrifice of photovoltaic performances has been a persistent objective for dye-sensitized solar cells (DSSCs). We launch here the experimental realization of a class of DSSCs consisting of polyaniline (PANi) incorporated TiO2 anodes, PANi counter electrodes (CEs), and iodide doped PANi solid-state electrolytes. The PANi filled in photoanode can inject electrons for dye recovery, whereas the PANi CE fulfills the function of reducing triiodide into iodide ions. In particular, the solid PANi electrolyte has an ability of catalyzing triiodide species, shortening charge diffusion path length, and recovering dye molecules at anode/electrolyte interface. The photovoltaic performances are optimized by adjusting assembly process and lithium iodide dosage, yielding a maximum efficiency as high as 3.1% in the resultant DSSC device accompanied with fast start-up, multiple start/stop cycling, and good stability under persistent irradiation.