Anion impurities in porous alumina membranes: Existence and functionality

We have carried out a detailed investigation on anion impurities in self-organized porous alumina membranes (PAMs) prepared by a two-step electrochemical anodization process in oxalic acid solutions. The employment of the energy dispersive spectroscopy, high resolution transmission electron microscope and infrared absorption spectra has demonstrated the existence and nonuniform distribution of the anions in the PAM sidewalls. The variation of the COO⁻ stretching vibration and CO₂ absorption bands indicates that annealing can lead to the decrease of the concentration in the PAMs due to the decomposition of impurity groups related to . We have further presented clear functionality that the anions have played key roles in the refractive index and absorption coefficient of the PAMs, and the surface morphology and crystallization of the deposited ZnO nanopore arrays.     

Evaporation of methyl- and dimethyl-substituted malonic, succinic, glutaric and adipic acid particles at ambient temperatures

Vapor pressures of five methyl-substituted dicarboxylic acids are inferred from measurements of evaporation rates of sub-micron particles using the TDMA technique at ambient temperatures. Vapor pressures obtained are: , , , , , , . These vapor pressures are compared with available literature data and with vapor pressures of the un-substituted acids. Our results demonstrate that molecular structure is important for solid state vapor pressures of secondary organic aerosol components at ambient conditions.     

Spin design of iron complexes on Fe-ZSM-5 zeolites

The spin state of iron ions in Fe-ZSM-5 zeolites can be purposefully varied by adsorption of gaseous probe molecules. The resulting Fe complexes with half-integer spin (, and ) can be reliably identified by electron paramagnetic resonance (EPR). A good correlation has been found between the concentration of surface sites active in low-temperature nitrous oxide decomposition and the concentration of low-spin () nitrosyl complexes of Fe formed after adsorption of NO molecules. Based on the analysis of the formation of such complexes under varying conditions, we conclude that these active sites contain a binuclear iron complex with S = 0 and three adsorbed NO molecules. An approach to investigate various Fe-containing sites in oxidation catalysts is discussed.     

Synthesis of ultramarine analogs from erionite

Colored products have been obtained by thermal treatment of erionite mixed with elemental sulfur and alkalis (Na₂CO₃ or K₂CO₃). Synthesis at lower temperature (500 °C) resulted in forming colored materials with preserved ERI structure (particularly with potassium cations), whereas the treatment of highly alkaline mixtures at high temperature (800 °C) caused re-crystallization to SOD (when Na was used) or to unknown structures (with K). The ESR spectra of the products with preserved original ERI structure recorded at room temperature show two signals, one with g = 2.030 and another with g tensor value either 2.045 (for sodium containing samples) or 2.005 (for the potassium bearing products). The latter signal could be considered as a reflection of radicals immobilized in small ε-cages, but it is more likely that it presents anisotropic component of the radical spectrum. The spectra measured at 77 K show anisotropy indicating three values of orthorhombic g-tensor, which is typical of radical, although the values vary for particular samples.     

Development of a large sonochemical reactor at a high frequency

The large sonochemical reactor was developed by using 12 PZT transducers. The frequency was 500 kHz and the total effective electric power applied to transducers was 620 W. The sample and volume were aqueous solution of potassium iodide and 112 dm³, respectively. The ultrasonic power dissipated into solutions was measured by a calorimetric method.

The energy conversion efficiency from electricity to ultrasound was 70%. When the liquid height was from 400 to 435 mm, the production rate has a maximum value. The production rate increased with increasing ultrasonic power. In the case of high ultrasonic power, the production rate for transducers located at the side wall was higher than that at the bottom wall. The sonochemical efficiency for a large sonochemical reactor operated at 500 kHz was close in value to those for laboratory scale reactors at 500 kHz.     

The morphology of MoS2, WS2, Co–Mo–S, Ni–Mo–S and Ni–W–S nanoclusters in hydrodesulfurization catalysts revealed by HAADF-STEM

HAADF-STEM studies have provided detailed morphological insight regarding MoS₂, WS₂, Co–Mo–S, Ni–Mo–S and Ni–W–S nanostructures in graphite-supported catalysts. It is found that the technique allows the catalytically active edges to be imaged even for single layer metal sulfide structures. Unpromoted MoS₂ and WS₂ are predominantly present as slightly truncated triangular clusters containing only a single S–M–S layer (M = Mo, W). The addition of promoter atoms results in more heavy truncations consistent with the expected tendency for the Co–Mo–S structures to expose promoted S-type edges at the expense of unpromoted Mo-type edges. However, the HAADF-STEM (High-Angle Annular Dark-field Scanning Transmission Electron Microscopy) results show for the first time that Co–Mo–S and Ni–W–S may also expose extended high index truncations.     

Counting and particle transmission efficiency of the aerodynamic particle sizer

The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8–), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8-μm drops to 25% for 10-μm drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument's inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations.     

About randomness of aerosol size distributions

All aerosol formation and evolution processes, such as nucleation, condensation, fragmentation, etc., are understood and rationalized via fundamental probabilistic concepts such as probabilities of collision, coagulation, dispersion, etc. Therefore all theoretical size distribution functions (lognormal, modified gamma distribution, self-preserving particle size distribution for Brownian coagulation, etc.) are in fact size probability density functions pdf(r). Any (e.g., measured) size distribution f(r) of an aerosol system is some random realization of its pertinent size probability density function pdf(r). When pdf(r) is viewed as a continuous function, the corresponding size distribution vanishes almost everywhere excluding some randomly set of sizes where f(r)=1. We investigate proximity between f(r) and pdf(r) in finite size intervals and derive expressions for estimation of the standard deviations of several aerosol size-dependent properties arising from randomness of f(r).     

Changes in large particle size distribution due to dry deposition processes

A dry deposition model is described that can simulate variations in the size-resolved mass size distribution of large ( diameter) atmospheric particles due to dry deposition processes. The model is unique because it is based on both gravitational and inertial effects in turbulent flow and includes deposition and suspension velocities for large, airborne particles. The model allows the integration of a large number of variables, covering a wide range of conditions (height of particle injection, meteorological conditions, and removal time). Changes in the size distributions that result from model simulations of deposition show the expected decrease in concentration with size since the deposition is greater for the larger particles. However, the size distribution does not decrease with size in a uniform manner as would be suggested by Stokes settling velocity due to the effect of inertial forces acting on the particles. Application of the model reveals a number of patterns, including the development of two peaks in the large particle mass size distribution, a persistent peak in the 1– size range, and a second peak in the 10– range that is strongly affected by meteorological conditions.     

Microcalorimetry for characterization of film formation and cure of coatings and adhesives

A new microcalorimeter with eight parallel channels using robust, low cost sensors for characterization of coatings and adhesives is described and first experiments on coatings and adhesives are presented. The calorimetric sensors are based on thin glass plates (20 mm × 20 mm, thickness 150 μm) with heater and thermocouple sputtered on the surfaces (calorimetric active area of about 9 mm²). The setup allows heating and cooling experiments as well as isothermal measurements in the temperature-modulated mode with up to eight sensors in parallel. The measured quantities are the real (C^′_p) and imaginary part (C^″_p) of the complex heat capacity (), the related absolute value of the heat capacity () and the heat flow . An industrial computer (NI PXI system) with specific software for calibration and data recording controls the electronic components. Sensors can be embedded in a temperature controlled oven (heating and cooling by Peltier elements) or alternatively in a climatic cabinet with controlled temperature and humidity.

The method has been applied successfully to monitoring of film formation of aqueous polymer dispersions (styrene-acrylate copolymer) and curing of coatings.     

Nature of cadmium cationic sites in cadmium-modified ZSM-5 zeolite according to the DRIFT studies of molecular hydrogen adsorption

The samples of CdZSM-5 prepared by ion-exchange, incipient wetness impregnation, and the interaction of HZSM-5 with cadmium vapor were studied by DRIFT spectroscopy using molecular hydrogen as a probe adsorbed at 77 K. Three different cadmium cationic species were detected. Dicadmium ions most weakly perturb adsorbed hydrogen molecules. They are characterized by a band at 4102 cm⁻¹. Two other kinds of isolated Cd²⁺ sites are characterized by bands at 3982 and 3940 cm⁻¹. The former band was ascribed to isolated Cd²⁺ cations which compensated the negative charges of neighboring aluminum–oxygen tetrahedra. The latter band corresponds to isolated Cd²⁺ cations which compensate the negative charges of distantly separated aluminum–oxygen tetrahedra. The calcination of samples containing species in oxygen converts these species into cadmium oxocations [Cd₂O_x]²⁺. Hydrogen molecules dissociate at room temperature on the isolated Cd²⁺ cations which most strongly perturb adsorbed hydrogen molecules at 77 K.     

Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger

Recently, Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420–430] have introduced a methodology for performing simple and fast measurements of submicron aerosol particles having a log-normal size distribution, using a unipolar diffusion charger, an electrometer, and a condensation particle counter (CPC). The methodology can be applied to particles of 30–700 nm and requires an assumption of their geometric standard deviation in size. In this paper we propose a much cheaper but faster method which involves substituting a unipolar field charger and another electrometer for the CPC. With the data obtained using this dual-charger system, we developed a data inversion algorithm and estimated the particle size distribution by minimizing the differences between the measured aerosol currents and the calculated values. To compare the size distribution with the data measured using a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles smaller than in diameter, and dioctyl sebacate (DOS) particles with a diameter of 0.1–, were used. The estimated results for the NaCl and DOS particles were within 10% of the data measured with the SMPS, while a 33% deviation from the SMPS results was obtained in Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420–430]. Furthermore, the detection time obtained with the use of our dual-charger system was faster () than the 5 s obtained by Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420–430].     

Cl electrosorption on Ag(1 0 0): Lateral interactions and electrosorption valency from comparison of Monte Carlo simulations with chronocoulometry experiments

We present Monte Carlo simulations using an equilibrium lattice-gas model for the electrosorption of Cl on Ag(1 0 0) single-crystal surfaces. Fitting the simulated isotherms to chronocoulometry experiments, we extract parameters such as the electrosorption valency γ and the next-nearest-neighbor lateral interaction energy ϕ_nnn. Both coverage-dependent and coverage-independent γ were previously studied, assuming a constant ϕ_nnn [I. Abou Hamad, Th. Wandlowski, G. Brown, P.A. Rikvold, J. Electroanal. Chem. 554–555 (2003) 211]. Here, a self-consistent, entirely electrostatic picture of the lateral interactions with a coverage-dependent ϕ_nnn is developed, and a relationship between ϕ_nnn and γ is investigated for Cl on Ag(1 0 0).     

Separation of weak and strong acids by electro-electrodialysis—Experiment and theory

The experimental results of the separation of acetic acid (HA) from the sulfuric acid by the electro-electrodialysis (EED) method and the modeling of process have been presented. The Neosepta membranes CMX and ACM have been used. It has been found that the efficiency of retention of HA is high (>0.9) when the process is conducted below the limiting current density with respect to HSO₄⁻ or SO₄²⁻ anions. The observed current efficiency of the H₂SO₄ removal was rather low (CE_S = ca. 0.7, when the initial concentration of H₂SO₄ in the mixture was 1 or 2 M) which was caused by the nonideal selectivity of the anion-exchange membrane. The experimental results have been described by the model based on the extended Nernst-Planck equation and the Donnan equilibrium. Since the efficiency of the process depended mainly on the selectivity of anion-exchange membrane (ACM), the concentration of fixed charges of that membrane, , and the ratio of volume fraction of pores to their squared tortuosity, V_p/θ², have been chosen as the main fitting parameters. It has been found that the fitting of the EED data depends mainly on , whereas in the modeling of diffusion experiment (or an EED experiment conducted at low current density) both parameters are important. The best fit has been obtained for , i.e. ca. one order smaller than that determined experimentally. The obtained optimal value of V_p/θ², equal to 0.013, is consistent with those previously obtained for other Neosepta anion-exchange membrane.     

Effect of spacers on the electrostatic charge properties of metered dose inhaler aerosols

The electrostatic charge properties of commercial metered dose inhaler (MDI) aerosols, including Ventolin^®, Flixotide^®, Tilade^® and QVAR^®, sampled through new and detergent-coated AeroChamber^® Plus spacers were studied using a modified 13-stage electrical low pressure impactor (ELPI) with aerodynamic cutoff diameters ranging from 0.028 to . Aerosol particles deposited on the impactor stages according to their aerodynamic diameters and their charges were simultaneously measured by the electrometers. The deposited drug mass was assayed chemically using HPLC. The surface potential on the inner spacer wall was measured with an electrostatic probe before and after aerosol actuation. High surface potentials were found on the new spacers whereas the detergent-coated spacers had minimal charges due to the conductive coating. MDI aerosol charges were decreased when spacers were used but the charge profiles of the aerosols were not altered qualitatively. New spacers had the lowest throat deposition, fine particle dose, and net aerosol and fine particle charges as a result of high spacer retention. These trends were partially reversed by the detergent-coated spacers. In general, the charge per mass of drug (charge-to-mass ratio) for particles from detergent-coated spacers was higher than those from new spacers. This was thought to be due to the reduction of electrostatic deposition inside the spacer thus leading to particles carrying higher charges being sampled. The calculated number of elementary charges per drug particle ranged from zero to several hundred, which is sufficiently high to potentially affect lung deposition. The ELPI provided high resolution charge profiles on MDI aerosols delivered through spacers.     

Improving mixing in microbioreactors

This paper describes a possible active mixing method for a microbioreactor that was designed, simulated and tested. Pressure based recycle flow was investigated in a cylindrical microreactor for mixing efficiency. Based on the computational fluid dynamics (CFD) simulation results and the requirements of the application, the recycle flow mixing method proved to be suitable as a method to induce sufficient mixing in the microbioreactor. This was verified experimentally using image analysis of dye distribution behavior.     

The performance of composite supported polymeric liquid membranes in the Membrane Aromatic Recovery System (MARS)

This study investigates the possibility of using a composite-supported polymeric liquid membrane (CSPLM) configuration for the Membrane Aromatic Recovery System (MARS). The membrane was prepared by impregnating the liquid membrane phase into the pores of a composite flat sheet membrane consisting of a microporous support and a thin non-porous layer. A polyvinylidenfluoride (PVDF) microporous support coated with a thin non-porous polydimethylsiloxane (PDMS) layer was chosen as a composite membrane due to its superior combination of mass transfer rates and chemical resistance among the membranes tested and polypropylene glycol (PPG) was used as a liquid membrane phase due to its high affinity for phenol. The resulting membrane showed uniform selectivity and operational stability under the continuous MARS operating conditions for more than two months. The mass transfer rates () were 5 times higher than those of the silicone rubber tubing () which is used in commercial scale MARS technology. The CSPLM also exhibited reduced water flux and low sodium ion transfer. The partition coefficient of phenol between PPG/water was measured as 84. A marked effect of ionic strength on partition coefficient of phenol was observed with partition coefficient increase to 134 when measured in the presence of 20 wt% KCl in phenol aqueous solution.     

Synthesis of ceria nanoparticles by flame electrospray pyrolysis

A flame electrospray pyrolysis is presented for synthesizing CeO₂ nanoparticles with a dense morphology, high crystallinity and nanometer size. Hydrated cerium nitrate precursor dissolved in an ethanol/diethylene glycol butyl ether mixture was injected into a CH₄/air premixed flame using an electrospray method. The number size distributions of the as-prepared particles were trimodal. It is suggested that the particles for the fine mode were formed by a Rayleigh disintegration of the charged precursor droplets during the droplet evaporation. The particles for the coarse and middle modes are surmised to come from primary and secondary droplets, respectively, which were formed simultaneously during the atomization processes. The CeO₂ nanoparticles for the coarse mode were nonspherical and composed of few crystallites. The nanoparticles for the fine and middle modes were nearly spherical and nonagglomerated. The as-prepared CeO₂ nanoparticles showed highly crystallinity.     

Inverting cascade impactor data for size-resolved characterization of fine particulate source emissions

In this paper, the inversion processing of cascade impactor data to construe continuous size distributions within fine particulate matter (PM_2.5) is examined for residential oil furnace and fireplace appliance emissions. Impactor data from tests with these emissions sources are selected for the challenges they pose to comprehending the size distributions of aerosol mass and chemical species. In specific, the oil furnace aerosol offers an opportunity to apply data inversion to study a bimodal lognormal distribution in which much of the aerosol mass is impactor-penetrating nanoparticles . The fireplace emissions on the other hand cover the issue of a chemical size distribution, which is subject to particle loss and characterized by a single lognormal, accumulation mode peak. Computational steps relevant to the application of the data inversion are illustrated in detail. Evaluation of correlation coefficients (0.992) indicates that the inversion model predictions fit the impactor data well. Simulations of systematic measurement error (±10%) at each impactor stage are shown to have a negligible impact on the inversion results for test data. It is concluded that data inversion can be effective when (i) source emissions contain a portion of particles that falls outside the measurement range of cascade impactors, (ii) a mass size distribution of an individual species is determined without the knowledge of the total mass concentration for that species, or when (iii) losses in the particle charger system are significant.     

Comparison of parameters calculated from the BET and Freundlich isotherms obtained by nitrogen adsorption on activated carbons: A new method for calculating the specific surface area

The empirical linear relationship between the BET surface area S_BET and the Freundlich constant K_F, calculated from nitrogen adsorption isotherms of activated carbons, S_BET = a₀K_F is mathematically demonstrated. This correlation exists in the relative pressure domain in which the BET equation is valid, whatever the value of c for the BET equation and for values of the Freundlich exponent, , between 0 and 0.2. This study allows to determine the correlation factor a₀ = 1/a with . From this result, a new expression, depending of and K_F, can be deduced for calculating the specific surface area.