Temporal and spatial dynamics of blocking and ripening effects on bacterial transport through a porous system: a possible explanation for CFT deviation

The studies on transport of particles across porous systems are based on the Colloid Filtration Theory (CFT). According to CFT, the collision efficiency is constant along the system length [J.N. Ryan, M. Elimelech, Colloids Surf. A: Physicochem. Eng. Aspects 107 (1996) 1–56]. Decreasing values of collision efficiency have been reported, a phenomenon that has been interpreted as a deviation from the CFT [X. Li, T.D. Scheibe, W.P. Johnson, Environ. Sci. Technol. 38 (2004) 5616–5625; N. Tufenkji, J.A. Redman, M. Elimelech, Environ. Sci. Technol. 37 (2003) 616–623; N. Tufenkji, M. Elimelech, Langmuir 20 (2004) 10818–10828; N. Tufenkji, M. Elimelech, Langmuir 21 (2005) 841–852]. This paper presents data on transport of Bacillus megaterium spores through quartz sand columns. The occurrence of consecutive phases of increase and decrease of the values of C/C₀, the effluent spore concentration expressed as a fraction of the influent spore concentration, is reported. These patterns of change in C/C₀ were interpreted as the result of the concomitant occurrence of blocking and ripening, the prevalence of these phenomena in different moments of the experiment, and the spatial distribution of the prevalence of blocking and ripening effects along the porous system. It is argued that this spatial distribution in the predominance of blocking and ripening, what leads to the intensification of ripening at the entrance of the porous system, might be a possible explanation for the reported deviation from the CFT for experimental conditions where ripening and blocking take place.     

Thermodynamic quantities relative to solution processes of Naproxen in aqueous media at pH 1.2 and 7.4

Based on van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of naproxen (NAP) in water at pH 1.2 and 7.4, were evaluated from solubility values determined at several temperatures. The solubility at pH 7.4 and 25.0°C was almost 150 times higher with respect to pH 1.2. The enthalpies of solution were positive and greater for pH 1.2, while the entropies of solution were both negative, thereby implying a greater molecular organization at pH 7.4. The results were discussed in terms of solute–solvent interactions.     

Study on gamma-ray-induced degradation of polymer electrolyte by pH titration and solution analysis

Degradation process of polymer electrolyte was investigated by pH titration and solution analysis. Perfluorosulfonic acid, which is generally used for fuel cells and sensors, was irradiated with gamma-ray. Irradiated samples were immersed in distilled water, and the suspensions were titrated with NaCl solution while pH was monitored. Initial pH without any sodium ion decreased as increase in absorbed dose, indicating acid release from polymer electrolyte. To identify the chemical structure of dissolved species, solution analysis was performed by ion chromatography, total organic carbon (TOC) analyzer, and inductively-coupled plasma atomic emission spectrometry (ICP-AES). It was shown that proton, sulfide ion, fluorine ion and organic carbon were detected in the solution, and the ratio among these ions and atoms changed depending on the irradiation conditions. It shows that the solution analysis can identify the scission site by irradiation sensitively, and gives useful information for investigation of polymer degradation process.     

pH fractionation and identification of proteins: comparing column chromatofocusing versus liquid isoelectric focusing techniques

In proteomic investigations, a number of different separation techniques can be applied to fractionate whole cell proteomes into more manageable fractions for subsequent analysis. In this work, utilizing HPLC and mass spectrometry for protein identification, two different fractionation methods were compared and contrasted to determine the potential of each method for the simple and reproducible fractionation of a bacterial proteome. Column-based chromatofocusing and liquid-based isoelectric focusing both utilized pH gradients to produce similar results in terms of the numbers of proteins successfully identified (402 and 378 proteins) and the consistency of proteins identified from one experiment to the next (<10% change). However, there was limited overlap in the protein sets with <50% of the proteins identified as common between the sets of proteins identified by the different systems. In addition to the numbers of proteins identified and consistency of those identified, the reduced monetary costs of experimentation and increased assay flexibility produced by using isoelectric focusing was considered in order to adopt a system best suited for comparative proteomic projects.     

Microgel-based etalon coated quartz crystal microbalances for detecting solution pH: The effect of Au overlayer thickness

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels were “painted” on the Au electrode of a quartz crystal microbalance (QCM). Another Au layer (overlayer) was subsequently deposited on the microgel layer. This structure is known as a microgel-based etalon. These devices have been shown to exhibit optical properties (i.e., color) that depend on solution pH and temperature, among other things. Previously, we measured QCM frequency shifts that are a result of solution pH changes; the frequency shifts are a direct result of the pH dependent solvation state of the microgels that make up the etalon. In fact, the shifts observed for the etalons were much greater in magnitude than just a microgel layer immobilized on the QCM crystal without the Au overlayer. We reasoned that the Au overlayer lead to an enhancement of the observed frequency change due to its mass. In this submission we investigate how the Au overlayer thickness (mass) affects the observed sensitivity to solution pH. We found that the change in QCM resonant frequency depended dramatically on the mass of the Au overlayer.     

Prediction of soluble solids content, firmness and pH of pear by signals of electronic nose sensors

The objective of this study was to investigate the predictability of an electronic nose for fruit quality indices. Responses signal of sensor array in electronic nose were employed to establish quality indices model for “xueqing” pear. The relationships were established between signal of electronic nose and the quality indices of fruit (firmness, soluble solids content (SSC) and pH) by multiple linear regressions (MLR) and artificial neural network (ANN). The prediction models for firmness and soluble solids content indicated a good prediction performance. The SSC model by ANN had a standard error of prediction (SEP) of 0.41 and correlation coefficient 0.93 between predicted and measured values, the model by ANN for the penetrating force (CF) had a 3.12 SEP and 0.94 coefficient, respectively. The results imply that it is possible to predict “xueqing” pear quality characteristics from signal of E-nose.     

Tripodal lipophilic ionophores: synthesis, cation binding and transport through liquid membranes

New C₃-symmetric lipophilic tripodal ionophores, Et(CH₂OCH₂COR)₃; R=NMePh (1), R=NEtPh (2), R=piperidyl (3), have been prepared and their binding abilities for alkali and alkaline earth metal cations evaluated by extraction equilibrium and cation transport through bulk liquid membranes. Experiments show that these ionophores have considerable potential for transporting lithium, sodium and calcium ions relative to potassium and magnesium ions. The cation transport rates by ionophores 1 and 2 decrease in the order Li⁺>Na⁺>Ca²⁺>Ba²⁺>K⁺>Mg²⁺, and the selectivities of Li⁺/K⁺, Na⁺/K⁺ and Ca²⁺/Mg²⁺ are 6.47–7.24, 6.05–6.19 and 9.39–16.13, respectively. The extraction selectivity sequences of the ionophores 1 and 2 are in agreement with the descending order of the cation transport rate, and the complexation constants in chloroform phase were estimated.     

Comparison of calibrations for the determination of soluble solids content and pH of rice vinegars using visible and short-wave near infrared spectroscopy

Visible and short-wave near infrared (Vis/SWNIR) spectroscopy combined with chemometrics was investigated for the fast determination of soluble solids content (SSC) and pH values of rice vinegars. Two hundred and twenty-five samples (45 for each variety) were selected randomly for the calibration set, whereas, 75 samples (15 for each variety) for the validation set, and the remaining 25 samples for the independent set. After some preprocessing, partial least squares (PLS) analysis was implemented for calibration models with different wavelength bands including visible, SWNIR and Vis/SWNIR regions. The best PLS models were achieved with Vis/SWNIR (550–1000 nm) region. Furthermore, different latent variables (5, 6, 7, 8 LVs) were used as inputs of least squares-support vector machine (LS-SVM) to develop the LV-LS-SVM models with grid search technique and RBF kernel. The optimal models were obtained with 6 LVs and they outperformed PLS models. Moreover, effective wavelengths (EWs) were selected according to regression coefficients. The EW-LS-SVM models were developed and an excellent prediction precision was achieved, and the effectiveness of the EWs was also validated. The correlation coefficient (r), root mean square error of prediction (RMSEP) and bias for the best prediction by EW-LS-SVM were 0.999, 0.189 and 0.051 for SSC, whereas 0.999, 0.008 and −1.7 × 10⁻³ for pH, respectively. The overall results indicated that Vis/SWNIR spectroscopy combined with LS-SVM could be applied as a high precision and fast way for the determination of SSC and pH values of rice vinegars.     

Molecular transport of aromatic hydrocarbons through nylon‐6/ethylene propylene rubber blends: Relationship between phase morphology and transport characteristics

Molecular transport of aromatic hydrocarbons through nylon/ethylene propylene rubber (EPR) blend has been investigated in the temperature range of 25 to 65 °C. The effect of blend ratio on the transport behavior was studied in detail. Nylon/EPR‐50/50 blend shows the lowest uptake among all the systems studied. This behavior is related to blend morphology, density, and crystallinity of the blend composition. The transport property was correlated with the extent of interfacial adhesion in the blends. The effects of temperature and penetrant size on the sorption behavior were examined. Thermodynamic and Arrhenius parameters were evaluated from the diffusion data. Theoretical and experimental diffusion results were compared. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2136–2153, 2000     

Ion transport regulation through triblock copolymer/PET asymmetric nanochannel membrane:Model system establishment and rectification mapping

Controlling ions transport across the membrane at different pH environments is essential for the physiological process and artificial systems.Many efforts have been devoted to pH-responsive ion gating,while rarely systems can maintain the rectification in pH-changing environments.Here,a composite nanochannel system is fabricated,which shows unidirectional rectification with high performance in a wide pH range.In the system,block copolymer(BCP) and polyethylene te rephthalate(PET) are employed for the amphoteric nanochannels fabrication.Based on the composite system,a model is built for the theoretical simulation.Thereafter,rectification mapping is conducted on the system,which can provide abundant info rmation about the relations between charge distribution and ions transport prope rties.The proposed rectification mapping can definitely help to design new materials with special ion transport properties,such as high-performance membranes used in the salinity gradient power generation field.     

Pyrolysis of carbonaceous foundry sand additives: Seacoal and gilsonite

Seacoal and gilsonite are used by the foundry industry as carbonaceous additives in green molding sands. In this study, pyrolysis was used to simulate the heating conditions that the carbonaceous additives would experience during metal casting. Gas chromatography–mass spectrometry was used to tentatively identify major organic products generated during their pyrolysis at 500, 750, and 1000 °C. A number of compounds of environmental concern were identified during the pyrolysis of seacoal and gilsonite, including substituted benzenes, phenolics, and polycyclic aromatic hydrocarbons (PAHs). These thermal decomposition products, and especially PAHs, were generated at each pyrolysis temperature in all foundry sands containing seacoal. In gilsonite-amended sand, however, mainly alkanes and alkenes were identified at 500 and 750 °C and PAHs at 1000 °C. Compared to seacoal, the most intense peaks occurred during the pyrolysis of sand containing gilsonite. The greatest loss of pyrolyzable material also occurred during heating of gilsonite-amended sand from ambient temperature to 1000 °C in a thermogravimetric analyzer. The results obtained from this study will be useful to green sand foundries looking to reduce volatile hydrocarbon emissions.     

Combined effect of solvent content,temperature and pH on the chromatographic behaviour of ionisable compounds. III: Considerations about robustness

We previously reported a model able to predict the retention time of ionisable compounds as a function of the solvent content, temperature and pH [J. Chromatogr. A 1163 (2007) 49]. The model was applied further, developing an optimisation of the resolution based on the peak purity concept [J. Chromatogr. A 1193 (2008) 117]. However, we left aside an important issue: we did not consider incidental overlaps caused by shifts in the predicted peak positions, owing either to uncertainties in the source data, modelling errors, or the practical implementation in the chromatograph of the optimal mobile phase (or any other). These shifts can ruin the predicted separation, since they can easily amount several peak-width units at pH values close to the logarithm of the solutes’ acid–base constants. A probabilistic optimisation is proposed here, which is able to evaluate the uncertainties associated with the model and the consequences when the optimal mobile phase is implemented in the chromatograph. This approach assumes peak fluctuations in replicated assays obtained through Monte Carlo simulations, which gives rise to a distribution of elementary peak purities. The results yielded by the conventional (i.e. non-robust), derivative-penalised, and probabilistic optimisations were compared, checking the predicted and experimental chromatograms at several critical experimental conditions. Among the three approaches, only the probabilistic one was able to appraise properly the practical difficulties of the separation problem.     

Kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode: effects of pore length distribution and solution resistance

The effects of pore length distribution (PLD) and solution resistance, R_sol, on the kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode (ACFCE) were investigated in a 30 wt% H₂SO₄ solution using nitrogen gas adsorption, a.c. impedance spectroscopy, the current transient technique, and cyclic voltammetry. The impedance spectra of the ACFCE were theoretically calculated based upon the transmission line model in consideration of the pore size distribution (PSD) and the PLD. From comparison of both the experimental and theoretical impedance spectra of the ACFCE, it is suggested that the deviation from the ideal impedance behavior of a cylindrical pore in the experimental impedance spectrum of the ACFCE is mainly ascribed to PLD, rather than to PSD. The cathodic current transients and cyclic voltammograms were theoretically calculated based upon the transmission line model as functions of the standard deviation of the PLD and R_sol. From the results, it is concluded that ion penetration into the pores is closely related to both and R_sol during double-layer charging/discharging of the ACFCE, that is, the larger and R_sol, the lower is the rate capability, thus causing higher retardation of ion penetration into the pores.     

Response mechanism of novel polyaniline composite conductimetric pH sensors and the effects of polymer binder, surfactant and film thickness on sensor sensitivity

This paper reports on investigations into the response mechanism of novel polyaniline composition conductimetric pH sensors and the effects of polymer binder, surfactant and film thickness on this response. It was revealed through X-ray photoelectron spectroscopy, focussed ion beam milling and impedance spectroscopy that the response mechanism was due to the deprotonation of the polymer backbone nitrogen atoms located on the uppermost surface level of the functional material particles. The equivalent circuits for the sensing layer were modelled using the Cole-Cole model for a range of pH environments. The optimum sensing layer composition was determined to contain less than 50 wt.% polymer binder with 5 wt.% surfactant. This composition was determined by examining the effects of both binder and surfactant on the electrical characteristics and sensor response of the composite films. The thickness of the sensing layer was found to have no discernable response on the sensing characteristics of the conductimetric pH sensors.     

The effect of phosphorus content on the thermal and the burning properties of cotton fabric coated with an ultrathin film of a phosphorus-containing polymer

The effect of phosphorus content on thermal degradation and burning behavior of poly(acryloyloxyethyl diethyl phosphate) or PADEP-coated cotton was studied. The results showed that PADEP-coated cotton prepared by admicellar polymerization using hexadecyltrimethylammonium bromide (HTAB) as a surfactant has higher amounts of phosphorus than that prepared using dodecyltrimethylammonium bromide (DTAB). Higher phosphorus content led to lower decomposition temperatures and greater amounts of char formation after thermal degradation. The effectiveness of the amount of phosphorus on the burning behavior of the treated cotton was investigated by an ASTM flammabilty test. In the case of PADEP-coated cotton prepared with DTAB, the flame spread slowly and extinguished with char formation on the fabric. For untreated cotton however, the flame spread quickly and burned the fabric entirely without char formation. Cotton coated with PADEP using HTAB exhibited self-extinguishing behavior after removing the ignition source. Decrease in decomposition temperature, increase in char formation and the burning behavior of PADEP-coated cotton are all consistent with phosphorus content on the treated fabric.     

Extraction and carrier mediated transport of urea using noncyclic receptors through liquid membrane systems

Extraction and carrier mediated transport through bulk liquid membrane and supported liquid membrane systems have wide applications in separation technology. This paper highlights the use of six noncyclic receptors (podands) having variations in chain length and end group for the removal of urea using liquid membrane system. These receptors R_1, R_2, R_3, R_4, R_5, R₆ are diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol dibenzoate, diethylene glycol, triethylene glycol and tetraethylene glycol respectively. The sequence of extraction and transport of urea by BLM system using various receptors is R₂ > R₃ > R₁ > R₄ > R₅ > R₆ and R₆ ≈ R₃ > R₅ > R₄ > R₁ > R₂ respectively. Receptor R₂ containing butyl end group is best extractant while receptor R₆ with flexible backbone is best carrier and this carrier efficiency is used to remove urea using BLM system from the feed phase by recyclization process up to 88.16%. The experimental results influenced by concentration of receptors and urea. Effect of time was also studied.     

Steric effects of pH switchable,substituted (2-pyridinium)urea organocatalysts: a solution and solid phase study

The study of hydrogen bonding organocatalysis is rapidly expanding. Much research has been directed at making catalysts more active and selective, with less attention on fundamental design strategies. This study systematically increases steric hindrance at the active site of pH switchable urea organocatalysts. Incorporating strong intramolecular hydrogen bonds from protonated pyridines to oxygen stabilizes the active conformation of these ureas thus reducing the entropic penalty that results from substrate binding. The effect of increasing steric hindrance was studied by single crystal X-ray diffraction and by kinetics experiments of a benchmark reaction.     

Removal of arsenic from aqueous solution: A study of the effects of pH and interfering ions using iron oxide nanomaterials

Nanophase Fe₃O₄ and Fe₂O₃ were synthesized through a precipitation method and were utilized for the removal of either arsenic (III) or (V) from aqueous solution as a possible method for drinking water treatment. The synthesized nanoparticles were characterized using X-ray diffraction, which showed that the Fe₃O₄ and the Fe₂O₃ nanoparticles had crystal structures of magnetite and hematite, respectively. In addition, Secherrer's equation was used to determine that the grain size nanoparticles were 12 ± 1.0 nm and 17 ± 0.5 nm for the Fe₂O₃ and Fe₃O₄, respectively. Under a 1 h contact time, batch pH experiments were performed to determine the optimum pH for binding using 300 ppb of either As(III) or (V) and 10 mg of either Fe₃O₄ or Fe₂O₃. The binding was observed to be pH independent from pH 6 through pH 9 and a significant drop in the binding was observed at pH 10. Furthermore, batch isotherm studies were performed using the Fe₂O₃ and Fe₃O₄ to determine the binding capacity of As(III) and As(V) to the iron oxide nanomaterials. The binding was found to follow the Langmuir isotherm and the capacities (mg/kg) of 1250 (Fe₂O₃) and 8196 (Fe₃O₄) for As(III) as well as 20,000 (Fe₂O₃) and 5680 (Fe₃O₄) for As(III), at 1 and 24 h of contact time, respectively. The As(V) capacities were determined to be 4600 (Fe₂O₃), 6711(Fe₃O₄), 4904 (Fe₂O₃), and 4780 (Fe₃O₄) mg/kg for nanomaterials at contact times of 1 and 24 h respectively.     

Synthesis of HgSe quantum dots through templates controlling and gas–liquid transport with emulsion liquid membrane system

A new synthetic method of HgSe quantum dots has been investigated through template controlling with emulsion liquid membrane system. The membrane system consists of kerosene as solvent, span80 as surfactant, N7301 as carrier, and HgCl₂ solution as internal-aqueous phase containing template of different concentrations, and uses gas–liquid transport on interface of external phase. Its optimum condition is as follows, kerosene:span80:N7301 = 74:6:20, Roi=1:1. While using inorganic KI as the template and adjusting HgCl₂ concentrations (keeping KI/HgCl₂ = 10), transmission electron microscope shows that HgSe quantum dots of different sizes can be obtained respectively, X-ray diffraction (XRD) reveals that the products have a cubic structure. The research has shown that quantum confinement effect of these HgSe quantum dots (2–3 nm) have inverted band structure (HgSe bulk) increase their effective bandgap giving rise to infrared (IR) luminescence. Its forming process is also inferred.     

Influence of adsorption orientation of methyl orange on silver colloids by Raman and fluorescence spectroscopy: pH effect

This work seeks to characterize the UV–Vis absorption, SRES and fluorescence of methyl orange (MO) on silver colloids at different pH. The gradual changes of SERS signals indicate differing adsorption orientations of dyes on silver surface when pH changed and thus, results in different energy transfer efficiencies, i.e., the fluorescence quenching at 428 nm and synchronous enhancement at 560 nm changed gradually with pH increased by step-up. Both experimental evidence and theoretic analysis indicate that, different molecular structures and differing adsorption orientations of dyes on silver surface were existence when pH changed, and thereat caused the diverse spectral phenomena.