Optimum Pore Diameter Research Articles

A Next Generation Label-Free PoC Sensing Platform

Current Point-of-Care Testing (PoCTs) or biomarkers are affinity based and require immobilisation on the substrate for sensitive detection. This not only increases the production and overall costs but also introduce measurement error leading to false interpretations. The PoCT devices are well established for protein and cell based assays but challenges remain for label-free, inexpensive and multiplex protein screening tools. Nanopore sensing allows detection of biomolecular interactions and intramolecular structural alterations. It monitors ionic currents changes when a charged molecule translocates through the pore with external electric potential. The ultimate advantage is removing the clouding of ensemble averaging. There are two types of nanopores, biological and solid-state which both efficiently probe analytes at the single molecule level but they either have limitation on pore diameter or required very expensive equipment to fabricate the pore. Here we employ a conical solid-state nanopore - nanopipettes (sub-nanometer size) to screen through different targets. They are quicker and cheaper to fabricate and can select the optimum pore diameter. The material of nanopipette (quartz) have low electrical noise which would be ideal to differentiate the binding signal with the complex. Traditional assays use antibodies because of high specificity and selectivity however they are difficult to implement onto the nanopipette due to relatively large size and hydrodynamic complexity in the nanochannels. Distinguishing between binding and transient blockade remains unresolved. Aptamers are single-stranded oligonucleotides which bind to relevant target molecules with high affinities similar to antibodies but are more robust, smaller in size and cost effective. Due to the specificity of the aptamers, integrating with nanopipette will allow single protein molecules to be detected to in a low cost, label-free manner and able to screen targets in a high-throughput format leading to next generation PoC electrochemical sensing platforms for screening proteins.

Heat transfer performance of lotus-type porous copper heat sink with liquid GaInSn coolant

Lotus-type porous copper is a new kind of micro-channel structure with long cylindrical pores (channels) aligned in one direction. It can be used as a heat sink for cooling of high-power electronic components. Through experiments and Fluent-3D numerical simulations, the heat transfer performance of a lotus-type porous copper heat sink with a liquid GaInSn coolant was systematically studied under different struc- tural and hydrodynamic parameters conditions. The experimental results showed that this kind of heat sink has an excellent heat transfer coefficient, as high as 9.6 W/cm 2 K, only under a fixed pressure drop as low as 17.5 kPa. The simulation showed that optimal porosity and pore diameter existed for the heat sink to conduct a maximal equivalent heat transfer coefficient. For the GaInSn coolant, the optimal porosity and pore diameter were about 45-55% and 0.7-0.9 mm, respectively. However, at the same pressure drop conditions the optimal pore diameter for the water coolant was smaller (0.1-0.2 mm) and the optimal porosity was the same as that for the GaInSn coolant. Overall, the simulated heat transfer coefficients and structural parameters window agreed well with the experimental results.

Design of Anodic Aluminum Oxide Rear Surface Plasmonic Heterostructures for Light Trapping in Thin Silicon Solar Cells

A metal-dielectric heterostructure that provides the combined capability of light trapping and surface passivation is reported. The light-trapping layer employs a porous aluminum anodic oxide (AAO) with metal nanoparticles formed in the pores on the rear surface of a thin crystalline silicon solar cell. Numerical finite-difference time domain (FDTD) simulations were performed to determine the pore diameter and spacing that would result in optimal light trapping for this metal-dielectric heterostructure. For a 2.5-μm-thick crystalline silicon device, the optimal pore diameter and spacing were determined to be ~250 and ~450 nm, respectively. These conditions resulted in an enhancement of the simulated photocurrent by ~12.6% compared with a device in which the heterostructure was replaced with a homogenous aluminum oxide layer. Simulations also confirmed that the thickness of an underlying dielectric layer should be minimized to 10-20 nm, with the AAO barrier layer being maintained as thin as possible. Finally, it was shown that replacement of silver by aluminum in the pores resulted in a reduction in the photocurrent of 6.3% and would necessitate much larger pore spacing that is difficult to achieve experimentally and would result in thicker AAO barrier layers, which are undesirable.

Ordered mesoporous mixed metal oxides: remarkable effect of pore size on catalytic activity.

We report the synthesis of ordered mesoporous NiAl mixed metal oxides (MMOs) from NiAl-layered double hydroxides (LDHs) through a soft template method using pluronic-F127 as the structure-directing agent. Ordered mesopores were obtained by the thermal decomposition of as-synthesized LDHs at different temperatures. The effects of the pluronic-F127 amount and the calcination temperature on the pore size distribution of the MMO were investigated. NiAl MMOs exhibited excellent catalytic activity in the Knoevenagel condensation of benzaldehyde with acidic methylene group-containing malononitrile. Finally, the dependence of the catalytic activity on the surface properties of NiAl MMOs was investigated. The pore diameter and the pore volume of NiAl MMOs were well correlated with the performance of the catalysts. MMO obtained from the calcination of NiAl-F127(3%)LDH at 750 °C for 5 h gave the highest conversion (>99%) in the Knoevenagel condensation in 30 min. The optimum pore diameter for the model reaction described here was 7.7 nm, which gave rise to more than 99% conversion with 100% selectivity. Ethanol gave the best conversion at 60 °C. The regenerated catalyst showed 93.0 and 89.0% of the initial catalytic activity after the first and the second regeneration cycles, respectively.

Fast pyrolysis of cellulose with solid acid catalysts for levoglucosenone

Various metal oxides, such as zirconia, titania, and alumina, were screened as solid acid catalysts in the fast pyrolysis of cellulose for levoglucosenone production. The liquid yields were affected by the properties of the catalyst, and an increase in levoglucosenone was observed with the addition of mesoporous metal oxides. Good catalytic properties were observed for anatase titanium oxide with an optimum surface area and pore diameter resulting in a levoglucosenone yield that was as much as 4.98%. The activities of calcined sulfated zirconia increased substantially compared to zirconia-impregnated sulfuric acid without calcination. In the presence of solid super-acid SO42−/ZrO2, cellulose produced levoglucosenone in a 7.25% yield.

Pore-Size Dependent Protein Adsorption and Protection from Proteolytic Hydrolysis in Tailored Mesoporous Silica Particles

Protein adsorption and interactions with mesoporous silica are of interest for a broad range of applications including drug delivery, chemical synthesis, biosensors, and bioseparations. A major challenge in designing mesoporous silica supports for tailored protein interaction is the differentiation of protein interactions at the surface of the particle from interactions within the pore, important features when considering mesoporous silica as a protective support for active proteins. In this investigation, the location of Enhanced Green Fluorescent Proteins (EGFPs) adsorbed on tailored mesoporous silica particles is examined as a function of pore diameter using proteolytic hydrolysis to distinguish between accessible and inaccessible proteins. Pore size control is achieved by tuning the hydrothermal aging temperature (60-110 °C) during synthesis, where the synthesis results in 5-15 μm diameter spherical particles appropriate for imaging by confocal scanning laser microscopy (CSLM). In low pH environments, EGFP unfolds within pores and on the surface of particles, rendering it susceptible to proteolytic hydrolysis by the protease Pepsin A. Upon return to neutral pH, un-hydrolyzed EGFP regains its fluorescence and can be visualized within the mesoporous particles. The pore-size dependent loading and protection of EGFP (2.4 nm diameter×4.2 nm) from proteolytic attack by Pepsin A (7.3 nm×3.6 nm×5.4 nm) is demonstrated by the retention of fluorescence in 7.3 nm pores. Larger-pored materials (>9 nm) provide diminishing protection for EGFP, and the protection is greatly reduced with increasing pore size and pore size distribution breadth. Proteolytic hydrolysis is used to delineate the activity of pore-loaded versus surface-bound proteins and to establish that there is an optimal pore diameter for loading EGFP while protecting it from attack by a larger proteolytic enzyme.

Optimal Design of a Silicon Carbide Ceramic Foam Solar Volumetric Receiver

A simple procedure for an optimal designing of a silicon carbide ceramic foam volumetric solar receiver has been proposed by utilizing a local thermal non-equilibrium model of porous media and the Rosseland radiation model. Heat received from a large number of heliostats to the receiver frontal part is carried by the air as it passes through the silicon carbide ceramic foam volumetric solar receiver. Thus, complex combined heat transfer takes place within the receiver, associated radiation, convection and conduction. Sano et al. recently applied the Rosseland approximation to account for the radiative heat transfer through the solar receiver. They exploited the low Mach approximation to investigate the compressible flow through the receiver. Analytic solutions reveal that an optimal pore diameter exists for given porosity, receiver length and pumping power. The pore diameter must be larger than its critical value to reduce pressure drop and pumping power to achieve high receiver efficiency. At the same time, it must be sufficiently small to acquire a large interstitial heat transfer surface. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency. In this paper, useful expressions are sought for shooting an optimal set of the pore diameter, and receiver length for given porosity and pumping power.

Quantum cryo-sieving for hydrogen isotope separation in microporous frameworks: an experimental study on the correlation between effective quantum sieving and pore size

Different microporous frameworks have been experimentally investigated by cryogenic (below 77 K) hydrogen and deuterium adsorption measurements. The D2/H2 molar ratio is strongly dependent on pore size, pressure and temperature. The experiments clearly indicate that the optimum pore diameter for quantum sieving lies between 3.0 A and 3.4 A.

Single file and normal dual mode diffusion in highly confined hard sphere mixtures under flow

We use Monte Carlo simulations to study the dual-mode diffusion regime of binary and tertiary mixtures of hard spheres confined in narrow cylindrical pores under the influence of an imposed flow. The flow is introduced to the dynamics by adding a small bias directed along the long axis of the pore to the random displacement of each Monte Carlo move. As a result, the motion of the particles in all the components is dominated by a drift velocity that causes the mean squared displacements to increase quadratically in the long time limit. However, an analysis of the mean squared displacements at intermediate time scales shows that components of the mixture above and below their passing thresholds still exhibit behaviors consistent with normal and single-file diffusion, respectively. The difference between the mean squared displacements of the various components is shown to go though a maximum, suggesting there may be an optimal pore diameter for the separation of mixtures exhibiting dual-mode diffusion.

A Local Thermal Nonequilibrium Analysis of Silicon Carbide Ceramic Foam as a Solar Volumetric Receiver

A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Heat transfer takes place from the receiver solid phase to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, associated radiation, convection and conduction, are investigated using a local thermal nonequilibrium model. The Rosseland approximation is applied to account for the radiative heat transfer through the solar receiver, while the low Mach approximation is exploited to investigate the compressible flow through the receiver. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. The results show that the pore diameter must be larger than its critical value to achieve high receiver efficiency. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency under the equal pumping power. The solutions serve as a useful tool for designing a novel volumetric solar receiver of silicon carbide ceramic foam.

Properties of fibrous polypropylene materials obtained by the aerodynamic method for use in capturing petroleum products

Studies are made of the ability of fibrous materials obtained by the aerodynamic method (FMAF) to sorb different petroleum products. The oil capacity of materials differing in their main structural indices is determined along with the extent to which they retain petroleum products over time. It is found that these structural indices affect the static sorptivity of FMAFs, and it is shown that an FMAF with a minimum fiber diameter of 3.2 μm and an optimum pore diameter has the greatest capacity to sorb oil.

F111 太陽光受熱SiCボリューメトリックレシーバーの熱解析(OS-6:多孔質の最近の進展(1))

A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Heat transfer takes place from the receiver solid phase to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, associated radiation, convection and conduction, are investigated using a local thermal non-equilibrium model. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. The results show that the pore diameter must be larger than its critical value to achieve high receiver efficiency. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency under the equal pumping power.

Efficiency of filtration technique for isolation of leptospires from surface waters: Role of different membranes with different pore size and materials

The objective of this research focused on evaluation of membrane filters application for isolation of Leptospira from surface water samples. The filter materials evaluated included nitrocellulose (0.22 and 0.45 µm pore diameters), polyvinylidene fluoride (Durapore 0.22 and 0.40 μm pore diameters), nylon mesh (37 μm), and glass fiber (1.0 µm). Millipore polyvinylidene fluoride filter (0.22 μm) was examined by scanning electron microscopy to verify that leptospires were present following filtration. Our results suggest for isolate nearly 100% ofLeptospira from water samples, the optimal pore diameter should be less than 0.45 µm (a standard pore size used to detect indicator microorganisms in 100 ml of water). Although filtration method can be used to isolation leptospires from surface water samples, it is unclear whether this is a useful method for detection of all leptospires exist within surface water samples. Accordingly, a large proportion of leptospires can be retained by membrane filter with a pore diameter commonly used to isolate leptospires from surface water samples (0.45 µm pore size). Key words: Leptospira, filtration technique, leptospirosis.

The Effects of Surface and Pore Characteristics of Natural Fiber on Interfacial Adhesion of Henequen Fiber/PP Biocomposites

The pore characteristics and morphological changes of henequen fiber after electron beam (EB) irradiation were studied, and their effects on interfacial adhesion between henequen fiber and polypropylene (PP) matrix of biocomposites were investigated. The surface morphologies of the fibers exposed to various EB irradiation doses were observed with an atomic force microscope (AFM). The porosity and pore distribution of fibers were characterized by mercury porosimetry and nonfreezing bound water (NFW) was measured by differential scanning calorimeter (DSC). Henequen fiber-reinforced polypropylene biocomposites were manufactured by the compression molding method and interlaminar shear strength (ILSS) was analyzed to examine the interfacial adhesion between henequen fiber and the PP matrix of the biocomposites. The AFM images indicated that pectin, waxy materials and impurities were removed from the surfaces of the henequen fibers during EB irradiation, resulting in changes of the surface morphology and characteristics of the fibers. When pectin, waxy compounds and impurities were removed, small pores of 1–0.01 μm were produced, and total surface area and porosity were increased. The increase in total surface area and porosity induced better adhesion between fiber and polymer which was confirmed by ILSS tests. However, the excessive creation of small pore size gives a negative effect on the tensile strength of henequen fiber. The best interfacial adhesion between henequen fiber and PP was obtained for the biocomposite reinforced with the henequen fiber treated with 10 kGy, which has the highest surface area and optimum pore diameter for interlocking between henequen fiber and polypropylene.

Optimization of the MnCeOx system for the catalytic wet oxidation of phenol with oxygen (CWAO)

A class of MnCeOx catalysts has been synthesized via the new redox-precipitation route in alternative to the conventional co-precipitation technique. The effects of preparation method, composition and calcination temperature on catalyst texture, dispersion and reduction pattern properties have been addressed. Redox-precipitated systems exhibit high surface area (SA, 120–170m2/g), large pore volume (PV, 0.4–0.5cm3/g) and a “narrow” pore size distribution (PSD) in a wide range of the Mn/Ce ratio (1/3–3/1). A quasi-molecular dispersion markedly improves oxide-support interactions and reducibility of the active phase. Redox-precipitated systems show a superior performance in the catalytic wet oxidation of phenol with oxygen (CWAO) at 373K in terms of substrate and total organic carbon (TOC) elimination and mineralization (i.e., CO2 formation) selectivity. Carbon mass-balance from TG-DSC data of used catalysts and CO2 selectivity values signal that the CWAO of phenol proceeds via a L–H reaction path, the oxidation of C-containing species being the rate limiting step (r.l.s.). Then, an optimum average pore diameter (APD, 10–15nm) enhances the rate of the adsorption step, while a straight relation between CO2 selectivity and reducibility prove that dispersion and redox properties of the active phase control the mineralization activity of the MnCeOx system.

Enhancement of the light extraction efficiency in organic light emitting diodes utilizing a porous alumina film

The light extraction efficiencies of organic light emitting diodes (OLEDs) utilizing various kinds of porous alumina films with different pore diameters were investigated. The OLEDs with the porous alumina film deposited on the glass surface were fabricated to improve their light extraction efficiency. The porous alumina film was fabricated by using a two step anodizing electrochemical procedure. The current densities as functions of the applied voltage do not significantly change, regardless of the existence and the magnitude of the pore diameter in the porous alumina film. The luminance efficiency of the OLEDs increased with increasing pore diameter. The luminance efficiency of the OLEDs utilizing the porous alumina film with a pore diameter of 70 nm was enhanced approximately 9% in comparison with that of the OLEDs without the porous alumina film. These results indicate that highly efficient OLEDs can be fabricated using a porous alumina film with an optimum pore diameter.

Key aspects of individual layers in solid-state dye-sensitized solar cells and novel concepts to improve their performance

In this feature article, we discuss the key aspects of solid-state dye-sensitized solar cells (SDSC) and propose different concepts based on extensive studies carried out in our group to improve their performance. The influence of compact TiO 2 layer, novel donor-antenna sensitizing dyes, nature of nanocrystalline-TiO 2 layers and solid-state organic hole conductors on the performance of SDSC is discussed in this article. Both preparation and thickness of the compact TiO 2 layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 120–150 nm of compact TiO 2 yielded the best rectifying behavior and SDSC performance. The influence of three different mesoporous titania films, obtained from three different titania nanocrystals, prepared by sol–gel, thermal, and colloidal-microwave process, was also studied and discussed here. The TiO 2 layer with the optimum pore volume and pore diameter (∼44 nm) displayed the highest efficiency and IPCE in SDSC. The importance of pore size rather than high surface area for filling the mesoporous layer with solid-state hole conductor became evident from this study. A series of heteroleptic Ru(II) complexes carrying donor antenna moieties, namely, triphenylamine (TPA) or N, N′-bis(phenyl)- N, N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), were synthesized and applied in SDSC. These novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies in the range 1.5–3.4%, as measured under AM 1.5 spectral conditions. This was attributed to highly efficient light harvesting of these novel dyes and the improved charge-transfer dynamics at TiO 2-dye and dye-hole conductor interfaces. Different low molecular weight and polymeric triphenyldiamines were synthesized and utilized as hole-transporting layers (HTL) in SDSC. Different studies showed that low molecular TPDs displayed better efficiency than polymeric counterparts due to their improved filling into the pores of nc-TiO 2 layer. Another interesting study revealed that an optimum driving force in terms of HOMO-level difference between the dye and HTL decides charge carrier generation efficiency. Recently, novel hole conductors with spiro-bifluorene-triphenylamine core for transporting holes and tetraethylene glycol side chains for binding lithium ions were synthesized and applied in SDSC. This work clearly emphasizes that Li +-salt is required at the TiO 2/dye interface as well as in the bulk of HTL. It was also found that the addition of about 5–20% of these Li +-binding hole conductors and higher Li-salt ( N-lithiotrifluoromethane sulfonamide) concentrations improved the SDSC performance. An improvement of about 120% in the solar cell efficiency as compared to the reference cells was achieved with an optimum composition of Li +-binding hole conductor and Li-salt.

Different mesoporous titania films for solid-state dye sensitised solar cells

The nature and morphology of titanium dioxide films play a significant role in determining the overall efficiency of the dye sensitised solar cell (DSSC). The influence of three different nanocrystalline titania films, prepared from three different routes, namely sol–gel (FMF), thermal (P-25), and colloidal-microwave process (CMP), on the performance of solid-state dye sensitised solar cells was studied and discussed here. The difference in the preparation of nanotitania leads to different surface area, pore size and morphology of the mesoporous films. FMF–TiO 2 displayed the highest efficiency and IPCE in DSSC among the other two because it possessed pure anatase phase, optimum surface area, pore volume and pore diameter; and well-connected network of individual nanoparticles. P-25 films exhibited pore structural and morphological features similar to FMF films but it displayed lower efficiency than FMF–TiO 2 due to the presence of small percentage of rutile phase besides major anatase phase. Although, CMP films had high surface area, it possessed smaller pore diameter and pore volume besides agglomerates and macropores leading to lower efficiency. The work clearly demonstrates the optimal pore and morphological structures required for efficient functioning of solid-state dye sensitised solar cell.

Study to improve the quality of a Mexican straight run gasoil over NiMo/γ-Al 2O 3 catalysts

Four NiMo catalyst supported on Al 2O 3 with different textural properties have been studied in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) of a Mexican straight run gasoil (SRGO). All reactions were carried out at three different temperatures 613, 633, and 653 K. Alumina supports were analysed by pyridine FTIR-TPD and nitrogen physisorption in order to determine their surface acidity and textural properties, respectively. TPR studies of the NiMo catalysts were analysed to correlate their hydrogenating properties. Metallic particles were characterized (after sulfidation) using transmission electron microscopy (TEM). Catalytic activities are discussed in relation to the physicochemical properties of NiMo catalysts. The importance of textural properties on coke deposition has been emphasized. The results of catalytic activity of these materials varied depending on dispersed MoS particles and pore distribution in final catalysts. The optimum pore diameter was found around 80 Å for HDS and HDN.

Hydrogen adsorption properties of activated carbons with modified surfaces

The hydrogen adsorption isotherms of activated carbon fibers loaded with platinum (Pt-ACF) and palladium (Pd-ACF) were accurately measured at ambient temperature over the hydrogen pressure range 0–3.5MPa by using a high-pressure adsorption apparatus. The amounts of hydrogen adsorbed on the Pt-ACF and Pd-ACF samples were larger than the amount adsorbed on the unmodified ACF sample. Detailed measurement of the hydrogen adsorption isotherms of Pt-ACF and Pd-ACF at a hydrogen pressure up to 0.1MPa indicated that the increase in adsorption was due to chemisorption of hydrogen on the metal. The hydrogen adsorption properties of ACF oxidized with (NH4)S2O8 or reduced in a hydrogen flow at 1073K were evaluated at 77 and 303K over the hydrogen pressure range 0–3.5MPa. The amount of adsorbed hydrogen was decreased by oxidation and increased by reduction. This result is attributable to a change in the pore structure: that is, oxygen functional groups introduced on the carbon surface inhibited hydrogen adsorption into the micropore with an optimum pore diameter.