Application of Turbiscan Stability Index for the Preparation of Alumina Photocatalytic Membranes for Dye Removal.

In this work, for the first time, the stability of the TiO2 suspensions used for the photocatalytic membrane preparation was studied by considering the Turbiscan Stability Index (TSI). The use of a stable suspension during the membrane preparation (by the dip-coating method) permitted a better dispersion of the TiO2 nanoparticles into the membrane structure due to a reduction of agglomerates formation. The dip-coating was performed on the macroporous structure (external surface) of the Al2O3 membrane to avoid large reduction of the permeability. In addition, the reduction of the suspension infiltration along the membrane's cross-section allowed us to preserve the separative layer of the modified membrane. The water flux was reduced by about 11% after the dip-coating. The photocatalytic performance of the prepared membranes was evaluated using the methyl orange as a model pollutant. The reusability of the photocatalytic membranes was also demonstrated.

Synthesis and Characterization of Blended Cellulose Acetate Membranes.

The casting and preparation of ultrafiltration ZnO modified cellulose acetate membrane (CA/ZnO) were investigated in this work. CA membranes were fabricated by phase inversion using dimethylformamide (DMF) as a solvent and ZnO as nanostructures materials. Ultrafiltration (UF) performance, mechanical stability, morphology, contact angle, and porosity were evaluated on both CA- and ZnO-modified CA samples. Scanning electron microscopy (SEM) was used to determine the morphology of the membranes, showing different pore sizes either on rough surfaces and cross-sections of the samples, an asymmetric structure and ultra-scale pores with an average pore radius 0.0261 to 0.045 µm. Contact angle measurements showed the highest hydrophobicity values for the samples with no ZnO addition, ranging between 48° and 82.7° on their airside. The permeability values decreased with the increasing CA concentration in the casting solution, as expected; however, ZnO-modified membranes produced lower flux than the pure CA ones. Nevertheless, ZnO modified CA membranes have higher surface pore size, pore density and porosity, and improved surface hydrophilicity compared with pure CA membranes. The results indicated that the incorporated nano-ZnO tends to limit the packing of the polymer chains onto the membrane structure while showing antifouling properties leading to better hydrophilicity and permeation with consistent UF applications.

Tyrosinase immobilized on a hydrophobic membrane.

Polyvinylidene fluoride (PVDF) membrane surfaces were ad hoc functionalized chemically to make them suitable for enzymatic immobilization. The process was performed by grafting the membrane surface with 1,4-diaminobutane and subsequently by activating it with glutarhaldehyde. The chemico-physical properties of the original PVDF membrane and of the modified membranes were studied by infrared spectroscopy, scanning electron microscopy, and static contact angle measurements. The activated membranes were used as a support for covalent immobilization of tyrosinase. The activity of free and immobilized enzyme was studied and compared. The experimental data showing the specific activity of the immobilized enzyme are similar to the value obtained with the free one. This means that the immobilization procedure did not alter the catalytic properties of the tyrosinase. In addition, the surface modification of the PVDF made it a promising material to use in enzyme or biomolecule immobilization processes.

Bio-mimetic sensors based on molecularly imprinted membranes.

An important challenge for scientific research is the production of artificial systems able to mimic the recognition mechanisms occurring at the molecular level in living systems. A valid contribution in this direction resulted from the development of molecular imprinting. By means of this technology, selective molecular recognition sites are introduced in a polymer, thus conferring it bio-mimetic properties. The potential applications of these systems include affinity separations, medical diagnostics, drug delivery, catalysis, etc. Recently, bio-sensing systems using molecularly imprinted membranes, a special form of imprinted polymers, have received the attention of scientists in various fields. In these systems imprinted membranes are used as bio-mimetic recognition elements which are integrated with a transducer component. The direct and rapid determination of an interaction between the recognition element and the target analyte (template) was an encouraging factor for the development of such systems as alternatives to traditional bio-assay methods. Due to their high stability, sensitivity and specificity, bio-mimetic sensors-based membranes are used for environmental, food, and clinical uses. This review deals with the development of molecularly imprinted polymers and their different preparation methods. Referring to the last decades, the application of these membranes as bio-mimetic sensor devices will be also reported.