Development and characterisation of functionalised ceramic microtubes for bacteria filtration

A very challenging objective of todayʹs research in the membrane technology for microfiltration applications is the development and processing of ceramic microtubes which are especially attractive due to their excellent chemical, thermal and mechanical properties compared to polymeric membranes. Another challenge is the fabrication of self-cleaning membranes to avoid blockage of filtering pores and to ensure a long service life. In this study we present the fabrication of zirconia microtubes featuring a specific surface functionalisation for bacteria filtration and digestion, using a sequence of slurry preparation, extrusion process, final sintering and subsequent surface modification. Tubular zirconia membranes with 1.6 and 1.0 mm outer and inner diameters, respectively, were extruded and sintered at temperatures between 950 °C and 1250 °C after a debinding step. The ceramic microtubes were characterised by microstructural analysis including Hg intrusion porosimetry, BET analysis, strength tests and profilometer measurements. A sintering temperature of 1050 °C was found to provide membrane properties featuring an open porosity of 51.3% with pore sizes ≤0.2 μm, a BET surface area of 7.85 m2/g and an average bending strength of 57.0 MPa, being suitable for bacteria filtration. In addition, a straightforward procedure for heterogeneous membrane functionalisation using an acid hydroxylation pre-treatment, followed by utilisation of 3-aminopropyltriethoxysilane (APTES) and finally immobilisation of the antibacterial model enzyme lysozyme was successfully realised.