jorge ibañez - Academia.edu (original) (raw)

Papers by jorge ibañez

Environmental Science & Technology, 2005

The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with... more The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with reticulated vitreous carbon (RVC) electrodes; this reduction can be accomplished by the application of relatively small potentials. Treatment of synthetic samples and field samples (from an electrodeposition plant) results in final Cr(VI) concentrations of 0.1 mg/L (i.e., the detection limit of the UV-vis characterization technique used here) in 25 and 43 min, respectively. Such concentrations comply with typical environmental legislation for wastewaters that regulate industrial effluents (at present time ) 0.5 mg/L for discharges). The results show the influence of the applied potential, pH, electrode porosity, volumetric flow, and solution concentration on the Cr(VI) reduction percentage and on the required electrolysis time. Values for the mass transfer coefficient and current efficiencies are also obtained. Although current efficiencies are not high, the fast kinetics observed make this proposed treatment an appealing alternative. The lower current efficiency obtained in the case of a field sample is attributed to electrochemical activation of impurities. The required times for the reduction of Cr(VI) are significantly lower than those reported elsewhere.

Polymer Degradation and Stability, 2008

Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) ... more Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8e9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl 2 gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given.

Environmental Science & Technology, 2000

Studies of pollution due to hexavalent chromium are important because it represents a risk to hum... more Studies of pollution due to hexavalent chromium are important because it represents a risk to human health and the environment. Hexavalent chromium is a toxic substance and has been found to be carcinogenic. Fortunately, its reduced form, Cr(III), is much less toxic. This paper discusses the remediation Cr(VI) by its reduction in aqueous media by polypyrrole (PPy)-coated reticulated vitreous carbon substrates (RVC). The study is focused on the effect of PPy-film electropolymerization conditions and its efficiency toward the reduction of toxic chromate. We have studied parameters such as the influence of the polymerization electrolyte, the scan rate, the potential limits, and the polymerization cycles concerning the reduction capability of the film. Key results obtained in the present study show that in the presence of different anions during formation of the PPy film, the efficiency of chromate reduction depends on the nature of the anion. We found that the films prepared and treated in the presence of KI performed much better and lasted much longer than those prepared in the presence of KF. Films synthesized at lower scan rates, and higher positive potential limits showed higher chromate reduction efficiencies. Some of our results show reduction of ca. 100% of Cr(VI) from a 10 mg/L solution, even after using the film in 20 contacts with the chromium solution, with films synthesized in KBr and KI electrolytes, at a scan rate of 20 mV/s, between -0.3 and 0.9 V and 40 polymerization cycles. Our study shows that remediation of Cr(VI) by reduction with PPy-coated substrates could be developed into an effective method toward the solution of this problem.

Annals of Surgery, 2010

There are reports with conflicting results on the expression of toll-like receptors (TLRs) in tra... more There are reports with conflicting results on the expression of toll-like receptors (TLRs) in trauma patients. In addition, these studies analyzed TLR expression only at patients&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; hospital admission but not later when complications usually arise. To analyze the surface expression of TLR2 and TLR4 on circulating monocytes from trauma patients during the hospitalization period and to correlate this with cytokine production after stimulation with TLR2 and TLR4 agonists. The phagocytic capacity of monocytes was analyzed at the same time points of TLR expression analysis; to correlate these molecular findings with the presence or absence of infections. Prospective and observational study from June 2005 to June 2007. In all analysis, a control group composed of healthy subjects was included. We studied 70 trauma patients admitted to the intensive care unit (ICU) of a tertiary hospital, and 30 healthy volunteers. Blood samples were collected at hospital admission, on day 7 and 14. Forty-four patients (63%) developed at least one episode of infection. Monocytes from trauma patients expressed higher levels of TLR2 and TLR4 than monocytes from control subjects at all time points. Expression of TLR2 and TLR4 in monocytes from those patients who developed any infection was significantly lower than in those patients without infection but still significantly higher than in control subjects. Cellular responses to TLR4 agonist were impaired. Monocytes from traumatic patients phagocytosized less efficiently than monocytes from control subjects. These results indicate that trauma patients present a dysregulation of the innate immune system that persists during the first 14 days after hospital admission.

Critical Care Medicine, 1982

An indirect method for measuring the increment of functional residual capacity (FRC) produced by ... more An indirect method for measuring the increment of functional residual capacity (FRC) produced by positive end-expiratory pressure (PEEP) during controlled mechanical ventilation was evaluated in 13 patients with acute respiratory failure. The actual FRC with and without PEEP was measured with a computerized nitrogen washout method. The results obtained did not show significant differences between the measured and the calculated increment of FRC. This indirect method accurately measures how much alveolar recruitment (estimated as increment of FRC) is produced by PEEP.

Critical Care Medicine, 1981

Wolters Kluwer Health may email you for journal alerts and information, but is committed to maint... more Wolters Kluwer Health may email you for journal alerts and information, but is committed to maintaining your privacy and will not share your personal information without your express consent. For more information, please refer to our Privacy Policy. ... Skip Navigation Links Home > March ...