ABSTRACT
Polysulfone (PSU) membranes with poly(vinyl pyrrolidone) (PVP) as a pore-forming and hydrophilic additive were prepared using the non-solvent-induced phase separation (NIPS) technique. PVP immobilization by radical-initiated crosslinking using potassium persulfate (KPS) was studied in view of obtaining membranes with high and long-lasting surface hydrophilicity. A method based on the ATR-FTIR technique was developed to discriminate crosslinked PVP from unreacted PVP in the membrane. The crosslinking progress was investigated as a function of temperature, KPS concentration, and reaction time. The results showed that temperature was the main factor influencing the crosslinking reaction since radical formation is temperature-dependent. Increasing the concentration of KPS and the reaction time led to an increase in the crosslinking rate. The effect of the degree of PVP crosslinking on the structure and properties of the prepared membranes was examined by studying mechanical properties, morphology by SEM, surface hydrophilicity by contact angle measurements, and water permeability.
ABSTRACT
In the context of designing a photocatalytic self-cleaning/low-fouling membrane, the stability of PVDF-PVP-TiO2 hollow-fiber membranes under UV irradiation has been studied. The effect of irradiation power, aqueous environment composition and fouling state on the properties of the membranes has been investigated. With this aim, SEM observations, chemical analysis and tensile strength measurements have been conducted. The results indicate that pristine membranes that undergo UV irradiation in ultra-pure water are significantly degraded due to attacks of OH° radicals. However, when methylene blue, used as a model pollutant, is introduced in the aqueous environment, OH° radicals preferentially react with this molecule rather than the membranes, successfully preserving the original properties of the latter. The presence of an adsorbed BSA layer (pre-fouling by immersion) on the surface of the membrane delays membrane aging, as the BSA layer is degraded by radicals instead of the membrane material. The degradation of the BSA layer also validates the self-cleaning properties of the membrane. However, when membranes are pre-fouled by filtration of a 2 g/L BSA solution, delay to aging is less. This is because OH° radicals do not reach BSA molecules that are trapped inside the membrane pores, and therefore react with the membrane material.
ABSTRACT
Radial freezing experiments on wastewater models were conducted in the presence of imposed stirring in order to remove impurities. The studied samples (dilute Na-montmorillonite suspensions charged with nitrates and with zinc or lead) were placed inside a cylindrical annulus, cooled at a controlled temperature around -7 degrees C at its inner wall which rotated around a vertical axis. The freezing front propagated toward the still outer wall which was maintained at a constant temperature around +1 degrees C. Thanks to stirring, considerable purification rates up to 99.97% were attained. It was also demonstrated that combining radial freezing and stirring ended in residual concentrations which agreed with drinking water standards.
