Kinetic parameters obtained from TG and DTG curves of acrylamide-maleic anhydride copolymers

The thermal behaviour of acrylamide-maleic anhydride copolymers was studied by thermogravimetric (TG and DTG) analysis. The obtained data permitted the calculation of activation energies and reaction orders of the decomposition steps by the Coats-Redfern and Freeman-Carroll methods.Thermal analysis shows four distinct peaks in the case of polyacrylamide and AAMA (71) copolymer and only three for AAMA (11) copolymer.In AA:MA (11) copolymers intermolecular imidization occurs only and thermal degradation is influenced more by the anhydride groups which are equal in number with the amide ones.

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Zusammenfassung Das thermische Verhalten von Acrylamid-Maleinsäureanhydrid-Kopolymeren wurde durch thermogravimetrische Analyse (TG und DTG) untersucht. Aus den erhaltenen Daten wurden die Aktivierungsenergien und Reaktionsordnungen der Zersetzungsschritte nach den Methoden von Coats-Redfern und Freeman-Carroll berechnet. Durch thermische Analyse können im Falle von Polyacrylamid und AAMA (71 (-Kopolymeren 4 Peaks und bei AA:MA (11) -Kopolymeren nur 3 Peaks unterschieden werden. Bei AAMA (1 1)-Kopolymeren verläuft nur eine intermolekulare Imidisierung und der thermische Abbau wird mehr durch die in gleicher Zahl wie die Amidgruppen vorliegenden Anhydridgruppen beeinflußt.

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T () — (). , - -, . : ( 71) , : 11 — . : 11 , , .

     

Biosensors designed for environmental and food quality control based on screen-printed graphite electrodes with different configurations

Graphite electrodes fabricated by screen-printing have been used as amperometric detectors in biosensors based on NAD(+)-dependent dehydrogenases, tyrosinase, or genetically modified acetylcholinesterases. The mono-enzyme sensors have been optimized as disposable or reusable devices for detection of a variety of substrates important in the food industry ( D-lactic acid, L-lactic acid, acetaldehyde) or in environmental pollution control (phenols and dithiocarbamate, carbamate and organophosphorus pesticides). The sensors were prepared in four configurations differing in enzyme confinement, enzyme immobilization and location of the immobilization agent in the biosensor assembly. Tests on real samples have been performed with the biosensors; D-lactic acid and acetaldehyde have been detected in wine and phenols in air.     

A Class of Non-associated Materials: n-Monotone Materials—Hooke’s Law of Elasticity Revisited

Generalized Standard Materials are governed by maximal cyclically monotone operators and modeled by convex potentials. Géry de Saxcé’s Implicit Standard Materials are modeled by biconvex bipotentials. We analyze the intermediate class of n-monotone materials governed by maximal n-monotone operators and modeled by Fitzpatrick’s functions. Revisiting the model of elastic materials initiated by Robert Hooke, and insisting on the linearity, coaxiality and monotonicity properties of the constitutive law, we illustrate that Fitzpatrick’s representation of n-monotone operators coming from convex analysis provides a constructive method to discover the best bipotential modeling a n-monotone material. Giving up the symmetry of the linear constitutive laws, we find out that n-monotonicity is a relevant criterion for the materials characterization and classification.     

Mesoporous carbon supported ultrasmall palladium particles as highly active catalyst for Suzuki‐Miyaura reaction

A fast and efficient eco‐friendly two‐step preparation of a palladium‐containing mesoporous carbon catalyst ( C1 ) from green and readily available carbon precursors (phloroglucinol and glyoxal), a porogen template (pluronic F‐127) and PdCl₂ is described. Catalyst C1 contains ultra‐small Pd nanoparticles (1.2 nm) uniformly dispersed in the carbon network and shows an outstanding activity for Suzuki‐Miyaura reactions in pure water: extremely low amounts of palladium (10 μequiv. in most cases) are sufficient to afford almost palladium‐free products (containing <0.25 ppm of precious metal without further purification steps).     

In-syringe magnetic-stirring-assisted liquid–liquid microextraction for the spectrophotometric determination of Cr(VI) in waters

A fully automated method for the determination of chromate is described. It is based on the selective reaction of Cr(VI) with diphenylcarbazide in acidic media to form a colored complex of Cr(III) with the oxidation product diphenylcarbazone. The reaction was performed within the syringe of an automatic burette containing a magnetic stirrer for homogenization of the sample and the required reagents. In-syringe stirring was made possible using a specially designed driving device placed around the syringe barrel to achieve a rotating magnetic field in the syringe, forcing the stirrer to spin. In a second step, the reaction mixture in the syringe was neutralized to allow in-syringe magnetic-stirring-assisted dispersive liquid–liquid microextraction of the complex into 125 μL of n-hexanol. After phase separation by droplet flotation over 30 s, the organic phase was propelled into a coupled spectrophotometric detection cell. The entire multistep procedure including in-system standard preparation was done within 270 s. The method was used for the analysis of natural waters, achieving average analyte recovery of 103 %, a limit of detection of 0.26 μg L^-1, and a repeatability of less than 4 % relative standard deviation.     

Electrochemical behavior in simulated body fluid of TiO2 nanotubes on TiAlNb alloy elaborated in various anodizing electrolyte

The present study is focused on tailoring the morphology of TiO₂ nanotubes obtained on Ti6Al7Nb alloy and evaluating their electrochemical behavior in simulated body fluid. The presence of the α and β phases on the Ti6Al7Nb alloy leads to a two‐scale organization of the nanotubes on the samples – which in turn affects the electrochemical stability. Furthermore, five different types of TiO₂ nanotubes were obtained in various electrolytes (e.g. Generation I, a mixture of Generation II and Generation III, Generation III). Electrochemical behavior analysis of all obtained nanotubes morphologies was composed of Tafel plots, cyclic voltammetry and electrochemical impedance spectroscopy and was correlated with morphology data obtained from SEM (nanotubes diameters from top‐view and nanotube length from cross‐section view). The electrochemical results showed that morphological modifications of the Ti6Al7Nb alloy's surface by electrochemical anodizing have induced changes to the electrochemical behavior of the material, evident in the corrosion rates. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis,characterization and controlled toxicity of a novel hybrid material based on cisplatin and docetaxel

This paper is focused on the synthesis and characterization of a novel hybrid material based on cisplatin and docetaxel-loaded functionalized simultanously carbon nanotubes able to be used in cancer therapy as drug delivery system with controlled toxicity. This material was physico-chemically investigated by determining the structure, as evidenced by Fourier transform infrared (FTIR) spectroscopy, transmission electronmicroscopy (TEM) and its stability was studied with the aid of thermogravimetric analysis (TGA). The amount of platinum ions released into the solution of simulated body fluid (SBF) was highlighted by coupled plasma mass spectrometry (ICP-MS). Toxicology experiments were performed with MDA-MB 231 breast cancer epithelial cells. The performance of the new drug delivery hybrid material was compared with functionalised carbon nanotubes with therapeutic agents functionalized with a single therapeutic agent.      

Influence of surface chemistry on the adsorption of oxygenated hydrocarbons on activated carbons

The objective of this work was to study the adsorption of different oxygenated hydrocarbons (methanol, ethanol, 1 and 2-butanol, methyl acetate) on activated carbons from organic mixtures with cyclohexane. Three activated carbons prepared by thermal and chemical treatments of a commercial carbon were employed for this purpose. Their textural properties were found to be similar, whereas their surface chemistries were modified, as shown by temperature-programmed desorption coupled to mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms were obtained by depletion method, and the analysis of adsorbed species was evaluated by TPD-MS to obtain new insight into the interactions between the different hydrocarbons and the carbon surface. Ethanol leads to a high-energy interaction between its hydroxyl function and the oxygenated surface groups and also to a lower energy interaction between the aliphatic part of the molecule and the carbon material. The desorption activation energy for this hydrophilic interaction is high (50 to 105 kJ/mol), and it is related to the nature of the carbon surface groups. The relative importance of these two interactions depend on the size of the alcohol/methanol is similar to ethanol, whereas butanols lead to more dispersive interactions. Methyl-acetate cannot undergo this kind of strong interaction and behaves like cyclohexane, having desorption activation energies ranging between 25 and 45 kJ/mol no matter the molecule and the carbon surface chemistry.     

Morphology,structure, and photoactivity of two types of graphene oxide-TiO<Subscript>2</Subscript> composites

Two types of graphene oxide-TiO₂ composites were prepared: one by including graphene oxide flakes in the TiO₂ sol, followed by thermal treatment (GI composite) at 300°C, and the second by including graphene oxide flakes in the calcined (at 500°C) TiO₂ xerogel (GII composite). The composites were characterized by SEM, TEM-EDS, TEM-SADP, STEM-HAADF, HRTEM coupled with FT, XRD, and XPS. Photocatalysis results were fitted to different kinetic models (pseudo-first and pseudo-second kinetics, intraparticle Weber-Morris diffusion, film diffusion, and external mass transfer). The results showed that by introducing graphene oxide flakes in the TiO₂ sol, followed by thermal treatment at 300°C (GI composite), an efficient graphene oxide-TiO₂ catalyst with high specific surface area, heterogeneity, and many graphitized areas can be obtained. Complete crystallization of the composite is not the key issue for the best photoactivity achievement. The rate limiting step in the photocatalytic process is the photooxidation of SA molecules on the TiO₂ surface.