Martha Cobo

The Effect of NaOH on the Liquid-Phase Hydrodechlorination of Dioxins over Pd/γ-Al2O3

The effect of sodium hydroxide on the-liquid phase hydrodechlorination (LPHDC) of polychlorinated dibenzo- p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) over 2% Pd/gamma-Al 2O 3 was evaluated. Reactions were carried out using 2-propanol both as a hydrogen donor and as a solvent. Fresh and used catalyst samples were characterized by BET, hydrogen chemisorption, TEM/EDS, XPS, and TPR. When the reaction mixture contained no NaOH, active-phase leaching and Pd-C formation were observed even after 10 min of reaction. Therefore, sodium hydroxide appears to be required to maintain surface metal clusters on the support and avoid binding of carbon species to the active metal. On the other hand, excess NaOH in the reaction mixture led to deposition of organic and inorganic solid residues on the catalyst surface, blocking the active sites. Under the conditions of this study, the addition of 30 mg of NaOH maintained the basicity of the system and diminished deposition of solid residues on the catalyst samples, and almost 100% detoxification was reached after a 3 h reaction.

Environmental variation of PCDD/Fs and dl-PCBs in two tropical Andean Colombian cities using passive samplers

Passive air-sampling data of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) taken in Manizales (a medium-sized city) and Bogotá (a megacity), Colombia, were analyzed in order to identify potential sources of pollution and the possible influence of meteorological variables like temperature and precipitation. The results indicate important differences in levels of PCDD/Fs and dl-PCBs between Bogotá and Manizales, attributed to differences in site characteristics and potential local/regional sources. Higher PCDD/Fs concentrations were observed in Bogotá (373fg/m(3)) compared to those observed in Manizales, with mean levels ranging from 64fg/m(3) in a residential zone to 151fg/m(3) around a vehicular-influenced area. Higher dl-PCBs concentrations were observed in the industrial area of Manizales compared to those observed in Bogotá, with mean levels of 6668fg/m(3) and 4388fg/m(3) respectively. In terms of PCDD/Fs congener distribution, there was a predominance of octachlorodibenzodioxin (OCDD) followed by 1,2,3,4,6,7.8-heptachlorodibenzofuran (HpCDF) congeners, with both cities showing higher levels in zones of high vehicular activity. Industrial influence was most evident in dl-PCB levels. In comparison to the mean levels of dl-PCB congeners obtained in the vehicular zones of Bogotá and Manizales, the industrially influenced sampling stations showed higher concentrations of dl-PCB congeners. Passive sampling results suggested that congener concentration profiles are characteristic of their different emission sources, and can be used to distinguish between their industrial or vehicular origins.

Microbial degradation, cytotoxicity and antibacterial activity of polyurethanes based on modified castor oil and polycaprolactone

Abstract The objective of this study was to assess the effects of type of polyol and concentration of polycaprolactone (PCL) in polyurethanes (PUs) on microbial degradability, cytotoxicity, biological properties and antibacterial activity to establish whether these materials may have biomedical applications. Chemically modified and unmodified castor oil, PCL and isophorone diisocyanate in a 1:1 ratio of NCO/OH were used. PUs were characterized by stress/strain fracture tests and hardness (ASTM D 676-59). Hydrophilic character was determined by contact angle trials and morphology was evaluated by scanning electron microscopy. Degradability with Escherichia coli and Pseudomonas aeruginosa was evaluated by measuring variations in the weight of the polymers. Cytotoxicity was evaluated using the ISO 10993-5 (MTT) method with mouse embryonic fibroblasts L-929 (ATCC® CCL-1) in direct contact with the PUs and with NIH/3T3 cells (ATCC® CRL-1658) in indirect contact with the PUs. Antimicrobial activity against E. coli and P. aeruginosa was determined. PUs derived from castor oil modified (P0 and P1) have higher mechanical properties than PUs obtained from castor oil unmodified (CO). The viability of L-929 mouse fibroblasts in contact with polymers was greater than 70%. An assessment of NIH/3T3 cells in indirect contact with PUs revealed no-toxic degradation products. Finally, the antibacterial effect of the PUs decreased by 77% for E. coli and 56% for P. aeruginosa after 24 h. These results indicate that PUs synthesized with PCL have biocidal activity against Gram-negative bacteria and do not induce cytotoxic responses, indicating the potential use of these materials in the biomedical field.

Effect of the incorporation of chitosan on the physico-chemical, mechanical properties and biological activity on a mixture of polycaprolactone and polyurethanes obtained from castor oil.

In the present study, polyurethane materials were obtained from castor oil, polycaprolactone and isophorone diisocyanate by incorporating different concentrations of chitosan (0.5, 1.0 and 2.0% w/w) as an additive to improve the mechanical properties and the biological activity of polyurethanes. The polyurethanes were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, stress/strain fracture tests and swelling analysis, and the hydrophilic character of the surface was determined by contact angle trials. The objectives of the study were to evaluate the effect of the incorporation of chitosan on the changes of the physico-chemical and mechanical properties and the in vitro biological activity of the polyurethanes. It was found that the incorporation of chitosan enhances the ultimate tensile strength of the polyurethanes and does not affect the strain at fracture in polyurethanes with 5% w/w of polycaprolactone and concentrations of chitosan ranging from 0 to 2% w/w. In addition, PCL5-Q-PU formulations and their degradation products did not affect cell viability of L929 mouse fibroblast and 3T3, respectively. Polyurethane formulations showed antibacterial activities against Staphylococcus aureus and Escherichia coli bacteria. The results of this study have highlighted the potential biomedical application of this polyurethanes related to soft and cardiovascular tissues.

Advances in ethanol reforming for the production of hydrogen

Catalytic steam reforming of ethanol (SRE) is a promising route for the production of renewable hydrogen (H2). This article reviews the influence of doping supported-catalysts used in SRE on the conversion of ethanol, selectivity for H2, and stability during long reaction periods. In addition, promising new technologies such as membrane reactors and electrochemical reforming for performing SRE are presented.