Scientific Seminar / Webinar - by Prof Wojciech Kujawski

PHYSICOCHEMICAL PROPERTIES OF HYDROPHOBIZED CERAMIC MATERIALS (POWDERS AND MEMBRANES)

Keywords: Al2O3, TiO2, ZrO2, ceramic membranes, hydrophobization, vacuum membrane distillation

The fabrication, design and characterization of materials with controlled properties e.g. hydrophobicity, hydrophilicity, wettability or micro-, nano-architecture are extremely interesting and important in material science.

Ceramic materials are characterized by high chemical, thermal and mechanical stability and therefore they are ideal materials for many applications in the chemical, biotechnological and pharmaceutical industries as well as in water and wastewater processing. However, the ceramic materials are hydrophilic by nature. This character of the surface, related to the presence of hydroxyl group, can limit the possible range of applications of the ceramic materials, where the hydrophobic character of the surface is required (e.g. vacuum membrane distillation). For this reason, the hydrophobization process of the ceramic materials must be performed.

The initially hydrophilic micro- and macroporous ceramic powders and membranes were successfully hydrophobized by grafting with fluoroalkylsilane (FAS) molecules. The influence of diverse parameters (e.g. type of molecule, duration of grafting, concentration of FAS solution, type of solvent) on the resulting hydrophobic surface was investigated. The liquid entry pressure of water (LEPw) as a measure of the hydrophobization efficiency of ceramic membranes. The prepared hydrophobic membranes were subsequently investigated in vacuum membrane distillation (VMD) process using pure water and water-organic solvent solutions as feed mixtures. It was found that permeate flux of pure water is strictly correlated with LEPw value. The selectivity of membranes in contact with water-organic mixtures depends strongly on the pore size of the hydrophobized membrane.

It was found that microporous membranes are much less efficient in the separation of organics from water (separation factor of ethyl acetate – EtAc in the range 1.3-30) comparing with macroporous ones (separation factor of EtAc in the range 32-60). The results were also discussed assuming the various mechanism of transports through porous ceramic membranes. These latter results were additionally compared with the results obtained for hydrophobic polymeric membranes (separation factor of EtAc in the range 25-450).