Elaboration et mise en oeuvre de membranes alginate, polyethylenimine à haut pouvoir de percolation : application en tant que matériaux adsorbants ou catalyseurs supportés

Alginate is a hydrophilic and biocompatible polymer with abundant free carboxyl and hydroxyl groups. This work developed and optimized the process for the fabrication of highly-percolating membranes based on alginate. The simple process has been designed by mixing alginate and polyethyleneimine (PEI) to obtain a structured hydrogel and subsequently improved stability by crosslinking between glutaraldehyde (GA) and amine groups of PEI. This double interaction (PEI/alginate, PEI/GA) makes it possible to produce macroporous membranes, after air-drying (without energy-consuming and sophisticated drying procedure), allowing natural drainage. The prepared membranes have been used for two applications: (a) sorption of metal ions (cationic and anionic), and (b) hydrogenation of nitrophenolic compounds by heterogeneous catalysis. The membranes and their interactions with metal ions were analyzed by FTIR, SEM, and XPS. The adsorbent was characterized by the presence of carboxylic groups and amino functions, which offers numerous possibilities for interacting with metal ions by complexation (i.e., carboxylates, free amines) and ion exchange/electrostatic attraction (i.e., protonated amine groups) depending on the pH of solution and metal speciation. These different possibilities have been illustrated by a series of experiments on metal ions such as Hg(II), Cu(II), Se(VI), Cr(VI), As(V). These various studies illustrate the particular affinity of membranes for metal anions (preferentially to cations) due in particular to the greater availability of protonated amino functions. Furthermore, an additional study was conducted on PEI crosslinked with GA (as a powder) for exploring the effect of the crosslinking of PEI on the binding of metal ions. The study demonstrated that the crosslinking rate has a moderate effect on the sorption of Se(VI) ions. At last, after briefly studying the sorption of Pd(II) on the membranes, a reduction was made of Pd(II) loaded on the support (partially converted to Pd(0)) in order to synthesize catalysis for the hydrogenation of 3-NP to 3-AP. This demonstrates the feasibility of applying these supports for heterogeneous catalysis.