Kinetics and thermodynamics of adsorption of red dye 40 from acidic aqueous solutions onto a novel chitosan sulfate

The kinetic and thermodynamics of adsorption of Red Dye 40 from acidic aqueous solutions onto a partially sulfated chitosan (ChS) was studied. The partially sulfated ChS was water insoluble in the pH range of 2-12. Experiments were carried out batch wise to determine the effect of pH, dye concentration, and temperature on the adsorption capacity of ChStowards Red Dye 40. It was found that the equilibrium dye-binding capacity of ChS (qe) increased with increasing initial dye concentration; however, the percentage of dye removal decreased. Dye adsorption capacity of ChS increased when the solution pH was reduced. The Langmuir model was better fitted the experimental adsorption equilibrium data, and therate of dye adsorption onto ChS follows the pseudosecond order kinetic model. The adsorption capacity of ChS was enhanced by increasing the temperature.The thermodynamic adsorption parameters, enthalpy(ΔH°), entropy (ΔS°), and Gibbs energy (ΔG°) were evaluated. The adsorption process was endothermic, and the Gibbs energy negative indicating that it occurred spontaneously

Removal of Cd (II) from aqueous solutions by batch and continuous process using chitosan sulfate dispersed in a calcium alginate hydrogel

A novel chitosan sulfate (ChS) which is insoluble at acidic pHs was synthesized and then dispersed in calcium alginate hydrogel beads to be used to remove Cd(II) from aqueous solutions at acidic pHs using a batch process and a continuous process. By batch wise experiments, it was found that the equilibrium adsorption capacity of the Alg-ChS beads increase with the increase in the initial concentration of Cd; however, the percentage of Cd removal decreased.The Freundlich model had the best fit to the experimental adsorption equilibrium data. The adsorption rate of Cd onto Alg-ChS beads followed the kinetic model of pseudo-second order and the time to reach equilibrium increased slightly with increasing initial concentration of Cd(II). The removal of Cd using a fixed bed column (continuous process) packed with the Alg-ChS beads had a much higher efficiencythan the Batch process. An adsorption mechanism of Cd(II) onto the Alg-ChS beads was proposed using the FTIR, and XPS spectra of samples of Cd(II) adsorbed onto ChS and the mechanisms of adsorption of metals by alginate and chitosan proposed by other authors

Evaluation of water properties in HEA–HEMA hydrogels swollen in aqueous-PEG solutions using thermoanalytical techniques

Hydrogels are polymeric materials used in many pharmaceutical and biomedical applications due to their ability to form 3D hydrophilic polymeric networks, which can absorb large amounts of water. In the present work, polyethylene glycols (PEG) were introduced into the hydrogel liquid phase in order to improve the mechanical properties of hydrogels composed of 2-hydroxyethylacrylate and 2-hydroxyethylmethacrylate (HEA–HEMA) synthesized with different co-monomer compositions and equilibrated in water or in 20 % water–PEG 400 and 600 solutions. The thermoanalytical techniques [differential scanning calorimetry (DSC) and thermogravimetry (TG)] were used to evaluate the amount and properties of free and bound water in HEA–HEMA hydrogels. The internal structure and the mechanical properties of hydrogels were studied using scanning electron microscopy and friability assay. TG “loss-on-drying” experiments were applied to study the water-retention properties of hydrogels, whereas the combination of TG and DSC allowed estimating the total amount of freezable and non-freezing water in hydrogels. The results show that the addition of viscous co-solvent (PEG) to the liquid medium results in significant improvement of the mechanical properties of HEA–HEMA hydrogels and also slightly retards the water loss from the hydrogels. A redistribution of free and bound water in the hydrogels equilibrated in mixed solutions containing 20 vol% of PEGs takes place

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

pH-sensitive polyvinylpyrrolidone-acrylic acid hydrogels: Impact of material parameters on swelling and drug release

In this study, we fabricated pH-sensitive polyvinylpyrrolidone/acrylic acid (PVP/AA) hydrogels by a free-radical polymerisation method with variation in the content of monomer, polymer and cross-linking agent. Swelling was performed in USP phosphate buffer solutions of pH 1.2, 5.5, 6.5 and 7.5 with constant ionic strength. Network structure was evaluated by different parameters and FTIR confirmed the formation of cross-linked hydrogels. X-ray crystallography showed molecular dispersion of tramadol HCl. A drug release study was carried out in phosphate buffer solutions of pH 1.2, 5.5 and 7.5 for selected samples. It was observed that swelling and drug release from hydrogels can be modified by changing composition and degree of cross-linking of the hydrogels under investigation. Swelling coefficient was high at higher pH values except for the one containing high PVP content. Drug release increased by increasing the pH of the medium and AA contents in hydrogels while increasing the concentration of cross-linking agent had the opposite effect. Analysis of the drug release mechanism revealed non-Fickian transport of tramadol from the hydrogels

MICELIZACIÓN EN SISTEMAS COPOLÍMEROS DE BLOQUE/LÍQUIDOS-ORGANICOS. DIFUSIÓN DE LUZ Y VISCOSIMETRÍA

RESUMEN   La forma de las micelas de poliestireno-b-poli(etileno/propileno) y poliestireno-b-poli(etileno/butileno)-b-poliestireno en las cetonas ha sido investigada mediante difusión de luz y viscosimetría. Las micelas de los diferentes sistemas estudiados presentan una dependencia cúbica entre el peso molecular promedio en peso y su radio de giro (aparente). Para los mismos sistemas se ha encontrado que la relación entre el radio hidrodinámico y el radio de giro, posee un valor próximo a 1,3. Estos dos comportamientos, sugieren que las micelas formadas por los copolímeros estudiados (dibloque y tribloque) en las cetonas son de forma esférica. Por otra parte se ha encontrado que una fuerte variación en el gradiente de la concentración de unimeros con la temperatura influye sobre el llamado comportamiento anómalo en las soluciones micelares. Se relaciona la variación de la concentración de unimeros con la temperatura mediante parámetros termodinámicos.  ABSTRACT The shape of the micelles of polystyrene-b-poly(ethylene/propylene) and polystyrene-b-poly(ethylene/butylene)-b-polystyrene in ketones has been investigated by means of light scattering and viscosimetry. The micelles of the different systems studied show a cubic dependence between the weight-average molar mass and their (apparent) radius of gyration. For the same systems it has been found that the relationship between the hydrodynamic radius and the radius of gyration has a value close to 1,3. These two previous behaviors suggest that the micelles formed by the copolymers studied (diblock and triblock) in ketones are sphere-shaped. On the other hand, it has been found that one strong variation of the concentration of frees-chains in a little interval of the temperature has an influence upon the so-called anomalous behavior in the micellar solutions