Miguel de Icaza

Covalently Bonded Chitosan on Graphene Oxide via Redox Reaction

Carbon nanostructures have played an important role in creating a new field of materials based on carbon. Chemical modification of carbon nanostructures through grafting has been a successful step to improve dispersion and compatibility in solvents, with biomolecules and polymers to form nanocomposites. In this sense carbohydrates such as chitosan are extremely valuable because their functional groups play an important role in diversifying the applications of carbon nanomaterials. This paper reports the covalent attachment of chitosan onto graphene oxide, taking advantage of this carbohydrate at the nanometric level. Grafting is an innovative route to modify properties of graphene, a two-dimensional nanometric arrangement, which is one of the most novel and promising nanostructures. Chitosan grafting was achieved by redox reaction using different temperature conditions that impact on the morphology and features of graphene oxide sheets. Transmission Electron Microscopy, Fourier Transform Infrared, Raman and Energy Dispersive spectroscopies were used to study the surface of chitosan-grafted-graphene oxide. Results show a successful modification indicated by the functional groups found in the grafted material. Dispersions of chitosan-grafted-graphene oxide samples in water and hexane revealed different behavior due to the chemical groups attached to the graphene oxide sheet.

Grafting of methyl methacrylate onto natural keratin

Abstract Keratin fibers from chicken feathers were modified through graft copolymerization with methyl methacrylate in an aqueous medium, using a KMnO4 / malic acid redox system. Original and grafted fibers were characterized by IR and Raman spectroscopy and their thermal behavior was studied by both differential scanning calorimetry and thermogravimetric analysis. The grafted fiber surface was characterized by scanning electron microscopy. The characterization results show that grafting was effectively achieved and this was confirmed by a ninhydrin test after acidic hydrolysis of the grafted keratin.

Photocatalytic Activity in Phenol Removal of Water from Graphite and Graphene Oxides: Effect of Degassing and Chemical Oxidation in the Synthesis Process

Developing new materials or modifying the existing ones is an amply field studied in the world of research. Due to its outstanding physical and chemical properties, graphene is attractive material for new applications. The methodologies for obtaining graphene are diverse and have changed over time. Graphene oxide is a versatile form of graphene, due to the presence of oxygenated functional groups. Chemical oxidation of graphite and exfoliation by ultrasonic waves is one of the preferred methods to obtain graphene oxide; chemical oxidation time and the degassing effect in the ultrasonic bath are parameters that play an important role in the features and properties of graphene oxide. Thus, in this study, the conventional times used for the oxidation of graphite and degassing in an ultrasonic bath to obtain graphene oxide were modified. The structural changes in the carbon materials were evaluated based on their photocatalytic activity in the removal of an organic pollutant in water (removing up to 38% of phenol). The band gaps of the graphitic materials were obtained by UV-vis obtaining a value range of 1.5–4.7 eV and the structure and morphology of the carbon materials were characterized by infrared and Raman spectroscopies and transmission electron microscopy, respectively.

Effect of Keratin Structures from Chicken Feathers on Expansive Soil Remediation

Chicken feathers are composed mainly of avian keratin, a fibrillar protein with a complex structure, and important properties such as durability, hydrophobicity, being chemically unreactive, and depending on the specific function can change its morphological and inner structure. This study takes advantage of these features and for the first time the use of keratin from chicken feathers to modify characteristics on expansive soils is reported. Swelling characteristics of remolded expansive soil specimens were studied through varying the percentage of keratin fiber content using 0.25, 0.50, 1.00 and 3.00 wt%. One-dimensional swell-consolidation tests were conducted on oedometric specimens, specific surface area was determined using methylene blue, and degree of saturation was also analyzed. Finally random distribution and interaction between keratin structures and soil were studied by scanning electron microscopy. The results show that randomly distributed fibers are useful in restraining the swelling tendency of expansive soils. The maximum reduction of pressure (43.99%) due to swelling is achieved by reducing the void ratio, which can be reached with the addition of chicken feather keratin structures to the expansive soil. Finally, the mechanism by which discrete and randomly distributed fibers reduce swelling pressure of expansive soil is explained.

158 Circularity Index of deployed Edwards Sapien aortic valve bioprosthesis

Transcatheter aortic valve replacement is a new alternative to heart surgery in selected patients. The balloon expandable Edwards-Sapien bovine valve is mounted in a stainless-steel stent with a maximal opening diameter of 23 or 26mm. Recent observational, anatomical study suggests that a distorted stent could produce valvular dysfunction impairing the long-term results. The Edwards Sapien bioprosthesis showed to have an optimal deployment and a high radial force in vitro. To further assess its deployment in patients with severe calcified aortic stenosis, we conducted a prospective study to analyze the circularity of the cross-sectional area of the deployed stent. Methods Optimal cross sectional projection of the expanded stent was selected on X-ray after the procedure. Images were analyzed and the corresponding profile of the stent was described by means of a polygon, for each valve, using two computer programs: 1) to measure the coordinates of the points composing this polygon and 2) to compute the corresponding cross-sectional areas. We defined a circularity index to measure the departure of this curve from the (best) theoretical conditions of a circle, the ratio of its area to the squared perimeter as a percent value of the corresponding ratio for a circle (1/4xpi=0.079). Results 23 patients were implanted (23 mm in 9 and 26 mm in 14). Final perimeters from cross-sectional areas of deployed stents were similar to the nominal perimeter in both sizes prosthesis (94–98% from the reference values). Mean circularity index was 0.078 + 0.001, with a mean perceptual difference of 1.6 (98.4% of similarity with a perfect circle). Conclusions Most of the Edwards Sapien valve cross-sectional areas are circular after deployment even within heavily calcified native valves, confirming the high radial force of the stent. The circularity index can be considered a useful parameter to assess the quality of opening of transcatheter aortic valves. Download : Download full-size image