Fabrication and in-situ fouling mitigation of a supported carbon nanotube/Γ-alumina ultrafiltration membrane

A novel ultrafiltration (UF) membrane with built-in defouling capability was made, characterized and tested for its water purification performance. The asymmetric ultrafiltration membrane with pore size of ~ 8 nm is obtained by coating a carbon nanotube (CNT)/γ-alumina composite layer on a porous PbZr_0.52Ti_0.48O₃ (PZT) piezoelectric support. The PZT support not only serves to provide mechanical strength to the membrane, but can also be used to generate ultrasound by application of an alternating voltage (AV). This ultrasound, in turn, avoids and/or removes any fouling during filtration. The conducting composite layer serves both as a size-selective membrane and an electrode. The optimum membrane composition was a 1:1 CNT to alumina weight ratio at a sintering temperature of 600 °C. PZT-supported membrane structures were poled with a 3 × 10³ kV/m electric field. Filtration of poled and unpoled membranes was carried out with a 2.5 g/L dextran solution to test anti-fouling performance. It was found that a poled membrane with application of a 20 V AV had a stable permeance of 55.6 L m⁻² h⁻¹ bar⁻¹. The permeance of an unpoled membrane without application of a voltage was 31.0 L m⁻² h⁻¹ bar⁻¹. This 79% permeance increase is ascribed to the mitigation of fouling during the filtration of the dextran solution.