Study of chitosan enzymatic gelation kinetics for membrane preparation

Chitosan is a natural biopolymer with excellent sorption properties that can be used to prepare flat-sheet “greener” filtration/sorption membranes without using organic solvent. The first step in chitosan membrane preparation, before drying and cross-linking steps, lies in the formation of a chitosan gel. Generally, chitosan is initially dissolved in acidic water then gelation is induced by basic media intake (usually ammonia) from liquid or vapor phase (Equation 1). However, the gelation process is initiated on one face of the polymer solution, which induces a non-solvent concentration gradient leading to a heterogeneous structure of the gel. An original enzymatic gelation process has been recently proposed (Chenite et al. 2006, Yan et al. 2014), based on the in-situ production of ammonia in the chitosan solution by the enzymatic hydrolysis of urea by urease (Equation 2). Please click Additional Files below to see the full abstract

Polymeric membranes for treatment of produced water on offshore plateform

Introduction Phase separation using non-solvent coagulation of a polymer solution is the most widespread industrial process to manufacture membranes. Large solvent quantity is then use that it complicates the overall process and may lead to environmental and health problems. Knowing that polymer concentration is usually in the range 15-20 % and coagulation and washing baths require to be often renewed, large amounts of aqueous solutions must be treated. For instance 10 m2 of ultrafiltration membrane need about 1 to 1.5 kg of solvent. Our objective in this proposal is to develop a novel process for membrane mass production in agreement with the principles of green chemistry. The main technical and economic output of using water instead organic solvents should consist in a simplification of the manufacturing process by lowering wastes and recycling. Environmental outputs will be a safer process, more economic on atoms, limiting the wastes and applicable to renewable naturally-occurring polymers. Please click Additional Files below to see the full abstract

Dynamic Mechanisms of the Bactericidal Action of an Al2O3-TiO2-Ag Granular Material on an Escherichia coli Strain.

The bactericidal activity of an Al2O3-TiO2-Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al2O3-TiO2-Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (10(5) genomic units·ml(-1)) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced

Elaboration d'hydrogels composites chitosane/charbon actif à visée cicatrisante par procédés d'inversion de phase

Des hydrogels composites de chitosane et de charbon actif ont été préparés par séparation de phase induite par (i) contact de la solution de polymère avec une solution aqueuse de non-solvant (procédé par immersion) et (ii) pénétration de vapeurs de non-solvant dans la solution de polymère (procédé VIPS). La caractérisation multi-échelle (SAXS, WAXS, MEBE, module élastique, tests de diffusion) des gels a montré que le mode de contact n'avait pas d'influence sur les propriétés fonctionnelles des gels. Les structures obtenues sont homogènes, poreuses et amorphes. Elles conviennent pour constituer la couche de pansements cicatrisants en contact avec les plaies de type escarre. Un modèle original de gélification du chitosane, couplant transferts de matière, transferts de chaleur et réactions chimiques, a été élaboré. Il a permis de déterminer les temps caractéristiques de gélification, d'approcher les profils de concentration des espèces, et de corroborer la non-influence du procédé sur la structuration des matrices finales, par l'analyse des transferts mis en oeuvre.Chitosan/Activated carbon composite hydrogels were prepared by phase separation induced by (i) immersing the polymeric solution in a non-solvent solution (wet process) and (ii) exposing the polymeric solution to non-solvent vapors (VIPS process). The multi-scale characterization approach (SAXS, WAXS, MEBE, storage modulus, diffusion tests) did not evidence any influence of the contact mode on the functional properties of the gels. Final structures are homogeneous, porous and amorphous. They are suitable to constitute the wound dressings layer in contact with eschar-like sores. An innovative chitosan gelation model was developed coupling mass transfers, heat transfers and chemical reactions. It permitted to forecast gelation times and concentration profiles. Simulation also corroborated the non-influence of the process on the final structuring of the matrices, analyzing transfers throughout the elaboration.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Se(VI) sorption from aqueous solution using alginate/polyethylenimine membranes: Sorption performance and mechanism

International audienceNew high percolating alginate membranes are designed without using sophisticated drying methods: negatively charged alginate reacts with positively charged polyethylenimine (PEI), prior to be crosslinked with glutaraldehyde and air-dried. This is sufficient to obtain a highly macroporous structured membrane. Highly percolating properties of these new A-PEI membranes make the material applicable in natural drainage systems. The high density of amine groups in composite membranes explain their high affinity for anions in acidic solutions. FTIR, SEM-EDX and XPS analysis are used to explore the sorption mechanism. Se(VI) is sorbed through electrostatic attraction between positive amine groups and negative selenium anions; in a second step, bound Se(VI) is reduced by amine and hydroxyl groups in acidic conditions. A-PEI membranes are successfully used for recovering Se(VI) anions at pH 2. The maximum sorption capacity is close to 83 mg Se g−1; the sorption isotherm is described by the Sips and Langmuir equations. The membranes are poorly sensitive to flow rate in the range 15–50 mL min−1. The kinetic profiles are fitted by the pseudo-first order rate equation. Solute desorption is operated using NaOH solutions; the sorbent shows a remarkable stability in sorption and desorption properties for a minimum of 4 cycles

Selective adsorption on fibrous activated carbon of organics from aqueous solution: correlation between adsorption and molecular structure

International audienceIn industrial processes, granular activated carbon (GAC) is generally used to remove pollutants from wastewater. Recently, a new adsorbant has been explored, fibrous activated carbon (FAC). Experiments were carried out with two FACs having different specific surface areas (1500 and 1300 m2.g−1) and pore-size distributions to study adsorption of various organic compounds from aqueous solution. Results were compared with adsorption onto one GAC with a specific surface area of about 1000 m2.g−1. Classic models were applied and kinetic constants were computed. In most cases, FAC with the higher specific surface area (named CS 1501) showed better adsorption capacities and kinetics than the two other FACs. For example, adsorption velocity of benzaldehyde was 7.2 ξ 10−5 1.mg−1·min−1 with CS 1501 and about 3 ξ 10−5 1.mg−1.min−1 with other FACs. Furthermore, adsorption onto CS 1501 of a great number of organic compounds (aliphatic and aromatic) depended on solute molecular characteristics. For instance, solute molecular size seemed to play an important role: adsorption capacity of high molecular weight compounds (humic substances) was about 3 mg.g−1, a value much lower than those of low molecular weight compounds, which were respectively 200 mg.g−1 and 400 mg.g−1 for phenol and benzoic acid. From experimental results, a correlation of QSAR (Quantitative Structure-Activity Relationship) type has been set up. This relationship predicts the adsorbability of organics compounds onto fibrous activated carbon from the molecular properties of these compounds

Adsorption of dyes onto activated carbon cloth: Using QSPRs as tools to approach adsorption mechanisms

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Adsorption onto Fibrous Activated Carbon: Applications to Water Treatment

International audienceThe adsorption of polluted waters is performed by activated carbon fibers (ACF). This new material is characterized by scanning electronic microscopy. BET surface areas and pore volumes are determined. Adsorption of natural organics (humic substances) and micropollutants (aromatic compounds such as benzene and toluene) is carried out in a batch or dynamic reactor. Classical models are applied and kinetic constants calculated. The results show that the performance of ACF is significantly higher than that of granular activated carbon (GAC) in terms of adsorption velocity and selectivity for micropollutants. These higher performances are due to some ACF physical properties, such as their high BET surface area and micropore volume. Moreover, the micropores are directly connected on the external surface area of fibers, which allows smaller mass transfer resistance. In a dynamic reactor, the breakthrough curves obtained with ACF beds are particularly steep, suggesting a smaller mass transfer resistance than that of GAC. The adsorption zone in an ACF bed is about 3.5 mm and is not really dependent on the water flow rate within the studied range

Algal Foams Applied in Fixed-Bed Process for Lead(II) Removal Using Recirculation or One-Pass Modes

International audienceThe incorporation of brown algae into biopolymer beads or foams for metal sorption has been previously reported. However, the direct use of these biomasses for preparing foams is a new approach. In this study, two kinds of porous foams were prepared by ionotropic gelation using algal biomass (AB, Laminaria digitata) or alginate (as the reference) and applied for Pb(II) sorption. These foams (manufactured as macroporous discs) were packed in filtration holders (simulating fixed-bed column) and the system was operated in either a recirculation or a one-pass mode. Sorption isotherms, uptake kinetics and sorbent reuse were studied in the recirculation mode (analogous to batch system). In the one-pass mode (continuous fixed-bed system), the influence of parameters such as flow rate, feed metal concentration and bed height were investigated on both sorption and desorption. In addition, the effect of Cu(II) on Pb(II) recovery from binary solutions was also studied in terms of both sorption and desorption. Sorption isotherms are well fitted by the Langmuir equation while the pseudo-second order rate equation described well both sorption and desorption kinetic profiles. The study of material regeneration confirms that the reuse of the foams was feasible with a small mass loss, even after 9 cycles. In the one-pass mode, for alginate foams, a slower flow rate led to a smaller saturation volume, while the effect of flow rate was less marked for AB foams. Competitive study suggests that the foams have a preference for Pb(II) over Cu(II) but cannot selectively remove Pb(II) from the binary solution

Quantitative Structure Property Relationships (QSPR) for the adsorption of organic compounds onto activated carbon cloths. Comparison between multiple linear regression and neural network

International audienceQuantitative structure-property relationship (QSPR) for the adsorption of organic compounds onto activated carbon cloth: Comparison between multiple linear regression and neural network By: Brasquet, C; Bourges, B; Le Cloirec, P ENVIRONMENTAL SCIENCE & TECHNOLOGY Volume: 33 Issue: 23 Pages: 4226-4231 Published: DEC 1 1999 Context Sensitive Links Close AbstractClose Abstract The adsorption of 55 organic compounds is carried out onto a recently discovered adsorbent, activated carbon cloth. Isotherms are modeled using the Freundlich classical model, and the large database generated allows qualitative assumptions about the adsorption mechanism. However, to confirm these assumptions, a quantitative structure-property relationship methodology is used to assess the correlation between an adsorbability parameter (expressed using the Freundlich parameter K) and topological indices related to the compounds molecular structure (molecular connectivity indices, MCI). This correlation is set up by mean of two different statistical tools, multiple linear regression (MLR) and neural network (NN). A principal component analysis is carried out to generate new and uncorrelated variables. It enables the relations between the MCI to be analyzed, but the multiple linear regression assessed using the principal components (PCs) has a poor statistical quality and introduces high order PCs, too inaccurate for an explanation of the adsorption mechanism. The correlations are thus set up using the original variables (MCI), and both statistical teals, multiple linear regression and neural network, are compared from a descriptive and predictive point of view. To compare the predictive ability of both methods, a test database of 10 organic compounds is used. Results show the good descriptive ability of NN compared with that of MLR, with more than 68% variance explained by NN, whereas MLR allows only 44% variance explanation. However, the predictive ability of NN seems to be low, especially when the structure of the test compounds is not well described in the training database. The good descriptive ability of NN is then exploited to carry out a variable analysis using the Garson weight partitioning method and to give information about the adsorption process. This study shows that fiat molecules seem to be better adsorbed onto activated carbon fibers than bulky molecules, because of an adsorption which is located between the micrographitic planes of fibers. The adsorption process occurs via an electron donor-acceptor interaction between the surface of the activated carbon fiber(donor) and the solute (acceptor). Consequently, the aromatic compounds with electron-withdrawing substituents seem to be favored. Furthermore, the lower the solute affinity for the aqueous media, the greater seems to be the adsorption