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

Reusable photocatalytic optical fibers for underground, deep-sea, and turbid water remediation

An approach for underground, deep, and turbid water remediation is presented based on optical fibers with a photocatalytic coating. Thus, photocatalytic TiO2 P25 nanoparticles immobilized in a poly(vinylidene difluoride) (PVDF) matrix are coated on polymeric optical fibers (POFs) and the photocatalytic performance of the system is assessed under artificial sunlight. To the best of our knowledge, poly(methyl methacrylate)-POF coated with TiO2/PVDF and the reusability of any type of POF for photocatalytic applications are not previously reported. The photocatalytic efficiency of the hybrid material in the degradation of ciprofloxacin (CIP) and its reusability are evaluated here. It is shown that 50 w/w% of TiO2 P25 achieves a degradation of 95% after 72 h under artificial sunlight and a reusability of three times leads to a loss of activity inferior to 11%. The efficient removal of ciprofloxacin and the stability of the POF coated with TiO2 P25 successfully demonstrate its suitability in the degradation of pollutants with potential application in regions with low light illumination, as in underground and deep water.Peer ReviewedPostprint (published version

High performance PVDF-TiO2 membranes for water treatment

International audienc

Diffusion of polymers in concentrated solutions for applications to phase separation

International audienceFor modeling phase separation (PS) of concentrated polymer solutions, such as for describing the fabrication of membranes by introduction of a non-solvent or by inducing a temperature change, one needs an adequate description of polymer mobility, or equivalently collective diffusion. However several theoretical models were proposed in literature in the last 40 years without always reaching a clear consensus. Here we report on a test of such different models in the framework of 2D phase-field calculations of PS without hydrodynamics for polymer solutions. It is concluded that the dependence of mobility with concentration is crucial but that the choice of the model is not so critical as far as PS is concerned. This situation could change when hydrodynamics is taken into account

Anti-fouling nanocomposite PVDF-TiO2 membranes for improved water treatment

International audienc

Elaboration of "green" chitosan membranes by an original enzymatic gelation process

International audienc

Process intensification by coupling the Joule effect with pervaporation and sweeping gas membrane distillation

This work concerns the intensification of membrane processes by coupling the Joule effect with two membrane processes: pervaporation and sweeping gas membrane distillation. For this purpose, conducting metallic hollow fibers impregnated or coated with polydimethyl siloxane were simultaneously used as membrane and heating electric resistance. The application of an electrical potential resulted in an enhancement of 40% of the water vapor permeate flux in sweep gas membrane distillation. However, the flux enhancement is the result not only of the heating on the membrane vicinity but also on the enhancement of the feed temperature. In the case of pervaporation of aqueous ethanol solutions (20%), the direct heating of fibers allowed improving by 100% the ethanol permeate flux while increasing the process selectivity.status: publishe

Performance of PVDF-TiO₂ Membranes during Photo-Filtration in the Presence of Inorganic and Organic Components

In this study, the anti-fouling performance of PVDF-TiO2 composite membranes, indicated by their permeate flux, was studied with different types of synthetic feed solutions. Photo-filtration (filtration under continuous UV irradiation) of solutions containing inorganic and organic components, which are ubiquitous in drinking/natural water, was performed to evaluate their influence on the photo-induced properties and performance of the membranes. The results indicated that inorganic fouling was unlikely to occur on PVDF-TiO2 membranes, and the presence of common inorganic ions in drinking water did not hinder their performance. However, in the particular case where a small amount of Cu2+ coexisted alongside HCO3− in the feed solution, inorganic fouling occurred, causing severe flux decline and prohibiting the photo-induced properties of the membranes. On the other hand, when used to filter organic fouling solutions, the membranes showed strong resistance to sodium alginate fouling, and less so for humic acids. In terms of separation efficiency, the membranes showed no advantages when operated in photo-filtration mode, as the rejection rate of both foulants under photo-filtration was not higher than that under normal filtration. In the case of humic acids, the photodegradation of humic substances into smaller compounds that were able to enter the permeate stream led to a lower rejection rate. Nevertheless, photo-filtration of these organic foulants still offered a higher permeate flux than normal filtration, up to a certain concentration level (5 mg/L for humic acids and 50 mg/L for sodium alginate)

Process intensification by coupling the Joule effect with pervaporation and sweeping gas membrane distillation

This work concerns the intensification of membrane processes by coupling the Joule effect with two membrane processes: pervaporation and sweeping gas membrane distillation. For this purpose, conducting metallic hollow fibers impregnated or coated with polydimethyl siloxane were simultaneously used as membrane and heating electric resistance. The application of an electrical potential resulted in an enhancement of 40% of the water vapor permeate flux in sweep gas membrane distillation. However, the flux enhancement is the result not only of the heating on the membrane vicinity but also on the enhancement of the feed temperature. In the case of pervaporation of aqueous ethanol solutions (20%), the direct heating of fibers allowed improving by 100% the ethanol permeate flux while increasing the process selectivity