Antonio Aragón-Piña

Removal of ammonium from aqueous solution by ion exchange on natural and modified chabazite.

The ammonium exchange capacity of a natural chabazite was studied in this work. The XRD analysis of the zeolite sample revealed that the main zeolitic phase was chabazite. The textural properties were determined by the N(2)-BET method and the surface morphology and charge were examined using a scanning electron microscope and a zetameter, respectively. The ion exchange equilibrium data were obtained in a batch adsorber and the Langmuir isotherm fitted plausibly well the equilibrium data. The effects of the temperature and pH on the ammonium exchange capacity of chabazite were investigated and the capacity increased augmenting the temperature from 15 to 35 °C and pH from 3 to 6. The natural chabazite was modified by a hydrothermal treatment using NaCl and KCl solutions and it was found that the modification influenced the ammonium exchange capacity of the chabazite. The ammonium capacity of natural chabazite was compared with that of a natural clinoptilolite and it was concluded that the chabazite capacity was 1.43 times higher than that of clinoptilolite.

Quantification of polycyclic aromatic hydrocarbons based on comprehensive two-dimensional gas chromatography-isotope dilution mass spectrometry

Comprehensive two-dimensional gas chromatography (GCxGC) offers favourable resolution and sensitivity compared with conventional one-dimensional gas chromatography (1D-GC), as reported in many studies. These characteristics are of major interest when analytes are in trace concentration, and are present in complex mixtures, as is the case of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate samples. Whilst GCxGC has been widely applied to identification of different types of analytes in several matrices, less seldom has it been used for quantification of these analytes. Although several quantitative methods have been proposed, they may be tedious and/or require considerable user development. Whereas quantification in 1D-GC is a routine and well-established procedure, in GCxGC, it is not so straightforward, especially where novel or untested procedures have yet to be incorporated into software packages. In the present study, it is proposed that a subset of the modulated peaks generated for each solute may be summed, based on the specific target ion mass of each compound present in a certified standard reference material (SRM) 1649a (urban dust). The ratio between a PAH and its corresponding deuterated (PAH-d) form showed that there is no statistical loss of sensitivity when this ratio is calculated based on whether the total sum of modulated peaks, or if only the two or the three most intense modulated peaks, are employed. Manual integration may be required, and here was found to give more acceptable values than automatic integration. Automated integration has been shown here to underestimate the modulated peak responses when low concentrations of PAHs were analyzed. Although for most PAHs good agreement with the certified values were observed, the analytical method needs to be further optimized for some of the other PAH, as can be see with those PAH with high variability in the range of urban dust analyzed.

Adsorption of Cadmium(II) from an Aqueous Solution onto Activated Carbon Cloth

Abstract The effects of surface properties and solution pH and temperature on the adsorption of cadmium(II) onto activated carbon fiber cloth (ACC) made from polyacrylonitrile (PAN) were investigated in this work. The ACC was oxidized with HNO3 solution and the concentration of acidic sites increased during oxidation whereas that of basic ones diminished. The adsorption capacity of the oxidized ACC was higher than that of ACC without oxidation because the ACC contained greater concentration of acidic sites. It was found that the maximum adsorption took place at pH 8 and the adsorption capacity increased near 22 times, augmenting the pH from 2 to 8. The adsorption capacity diminished on the average twofold, increasing the temperature from 15 to 35°C. Cd(II) adsorbed on ACC at pH 6 can be almost completely desorbed by reducing the solution pH to 2. The adsorption capacity is considerably dependent upon the characteristics of the ACC surface and temperature and pH of the solution.

Interaction of granular maize starch with lysophosphatidylcholine evaluated by calorimetry, mechanical and microscopy analysis

In this study we evaluated the thermo-mechanical properties of maize starch pastes (80% wt/wt) under the effect of exogenous lysophosphatidylcholine (LPC) using differential scanning calorimetry (DSC), dynamic mechanical spectrometry (DMS), and scanning electron microscopy (SEM). Particular attention was paid to the development of the amylose-LPC inclusion complex. Results from SEM and DSC showed that with no exogenous LPC, granular maize starch developed the amylose network structure for starch gelling at 80 – 95 8C. In comparison, at 1.86 and 3.35% of LPC, heating up to 130 8C was needed to develop the three-dimensional network required for starch gelling. Results showed that at these LPC concentrations LPC interacted mainly with amylose within the starch granule. At concentrations

Removal of Toxic Pollutants from Aqueous Solutions by Adsorption onto an Organobentonite

8.26% the LPC interacted with amylose both inside the granule and on the granule’s surface. At such LPC concentrations heating to 130 8C did not fully develop the starch network structure for gelling. These results suggested that a higher thermal stability was achieved by starch granules because of LPC inclusion complex formation. DSC or DMS did not detect the development of this complex, probably because its formation took place below the onset of gelatinization under conditions of limited molecular mobility. Subsequently, a lower level of organization (i.e. complex in form I) was achieved than in the complex developed at high temperature and water excess (i.e. complex in form II). On the other hand, the changes in the starch granule structure observed by SEM as a function of the time – temperature variable were well described by the phase shift angle ðdÞ rheograms for starch pastes with and without addition of LPC. q 2003 Elsevier Ltd. All rights reserved.

Adsorption of Heavy Metal Ions from Aqueous Solution onto Sepiolite

An organobentonite was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) onto the surface of a calcium bentonite. The adsorption capacity of the organobentonite towards 2,4-dichlorophenoxyacetic acid (2,4-D), phenol and the dichromate ion (HCrO−4) from aqueous solutions was investigated. The Langmuir isotherm gave a reasonable fit to the experimental data for the sorption of 2,4-D, phenol and the HCrO−4 ion onto the organobentonite. The adsorption equilibrium data for 2,4-D demonstrated bimodal adsorption for equilibrium concentrations of 2,4-D greater than 650 mg/l. The capacity of the organobentonite for sorbing 2,4-D, phenol and the HCrO−4 ion was considerably higher than that of the bentonite. This capacity was compared to that of a commercial activated carbon (F-400), from which it was concluded that modification of the bentonite substantially enhanced its adsorption capacity whereas the capacity of the organobentonite was lower than that of the F-400 carbon.

Dispersion of atmospheric coarse particulate matter in the San Luis Potosí, Mexico, urban area

The adsorption capacity of sepiolite towards the removal of heavy metal ions from aqueous solution was studied in this work, with adsorption equilibrium data being obtained with a bath adsorber. The sepiolite sample was chemically stable over the pH range 2–12, but dissolved in acidic solutions with pH values less than 2. The Langmuir isotherm gave a better fit of the experimental adsorption equilibrium data, since the average absolute percentage deviation of the Langmuir isotherm was lower than that of the Freundlich isotherm. The adsorption capacity of sepiolite towards metal ions decreased in the following order: Cr(III) > Cd(II) > Cu(II) > Zn(II) > Ni(II) > Ag(I). Increasing the temperature from 15 °C to 35 °C led to an increase in the adsorption capacity. The capacity of sepiolite towards the adsorption of Cd(II) ions was diminished considerably on reducing the solution pH from 7 to 3. The effect of the solution pH was attributed to electrostatic interaction between the negatively charged sepiolite surface and the positively charged Cd(II) ions in the aqueous solution. The surface charge of sepiolite became less negative when Cd(II) ions were adsorbed onto the sepiolite surface. This result indicates that electrostatic interaction between the sepiolite surface and the Cd(II) ions in the aqueous solution played a very important role in determining the adsorption capacity of sepiolite. The adsorption of Cd(II) ions onto sepiolite at pH 7 was reversible when desorption was undertaken at pH 3, but not when desorption was undertaken at pH 7.

Risk factors and biofilm detection on central venous catheters of patients attended at tertiary hospital

Atmospheric pollution in urban areas of Mexico has become a serious problem. The study of spatio-temporal evolution of concentrations of particulate matter is an important issue. A total of 188 samples were randomly collected at 24-hour running time within the period from May 2003 to April 2004 for the San Luis Potosi urban area, located in the central-north part of Mexico, using quartz fiber filters. A series of numerical modeling experiments were conducted for the same period of measurements to investigate particulate matter (PM) concentrations in the above-mentioned urban area. Although there is a considerable annual variability in the atmospheric circulation, the analysis of results indicates preferential seasonal circulation patterns: southwesterly winds during winter and southeasterly during summer. High concentration values of particulate matter were closely associated to local characteristics of the atmospheric circulation. A net transport from the industrial zone into the urban area is one of most important outcomes of the investigation.

Continuous Drip Flow System to Develop Biofilm of E. faecalis under Anaerobic Conditions

AIM To determinate the significance of risk factors with the presence of biofilm on catheters of patients attended at tertiary hospital cares. MATERIAL AND METHODS A total of 126 patients were included, data collection by observing the handling of the CVC, clinical history and microbiological isolation methods of CVCs tips (Roll-plate, sonication and scanning electron microscopy) were evaluated. RESULTS Certain factors, such as the lack of proper hand washing, the use of primary barriers and preparing medications in the same hospital service, showed an important relationship between biofilm formation in CVCs. The sonication method presented that most of the samples had isolation of multispecies 29 samples (64%); in contrast with the roll-plate method, just one sample (3%) was isolated. CONCLUSIONS The importance of the strict aseptic techniques of insertion and of the handlings of CVC was highlighted, the failure of both techniques was related to the biofilm formation and was evidenced using the scanning electron microscopy. Since this tool is not available in most hospitals, we present the correlation of those evidences with other standard microbiological methods and risk factors, which are necessary for the sensible detection of the different steps of the biofilm formation on CVC and their correct interpretation with clinical evidences.

Antagonistic, synergistic and non-interactive competitive sorption of sulfamethoxazole-trimethoprim and sulfamethoxazole‑cadmium (ii) on a hybrid clay nanosorbent

Purpose. To evaluate a structurally mature E. faecalis biofilm developed under anaerobic/dynamic conditions in an in vitro system. Methods. An experimental device was developed using a continuous drip flow system designed to develop biofilm under anaerobic conditions. The inoculum was replaced every 24 hours with a fresh growth medium for up to 10 days to feed the system. Gram staining was done every 24 hours to control the microorganism purity. Biofilms developed under the system were evaluated under the scanning electron microscope (SEM). Results. SEM micrographs demonstrated mushroom-shaped structures, corresponding to a mature E. faecalis biofilm. In the mature biofilm bacterial cells are totally encased in a polymeric extracellular matrix. Conclusions. The proposed in vitro system model provides an additional useful tool to study the biofilm concept in endodontic microbiology, allowing for a better understanding of persistent root canal infections.