Plasma-enhanced modification of the pore size of ceramic membranes

The aim of this work was to reduce the pore size of inorganic ultrafiltration membranes using cold-plasma techniques. Kerasep tubular multi-channel ceramic membranes (Orelis S.A., France) with a TiO2-ZrO2 selective layer on an Al2O3-TiO2 support and molecular weight cut-offs (MWCO) of 15,000 g/mol were used. Experiments were performed using an originally designed RF-twin chamber plasma reactor, where the tubular membrane is an integrated part of the reaction chamber. It was equipped with a 40 kHz power supply. Membrane surfaces were first cleaned and activated by exposing them to O2 plasmas. To carry out the membrane modification a mixture of TiCl4-O2 was used as plasma-gas. This step was performed under a RF-power of 50 w and for 30 min. Different pressures (50, 100, 150 and 200 mTorr) were considered for the gas-mixture, while the percentage of TiCl4 in the mixture was of 10%. The cold-plasma treatment was able to create TiO2-type structures on the membrane surface. After the treatment water permeability through the membrane decreased, while PEG retention increased. These observations can be related to a decrease of the membrane pore size.