The structure was determined by X-ray diffraction (XRD) using
a bruker D8 diffractometer operating with Cu Kα radiation
(λ=1.54056 A). The surface area was measured by BET method using ˚
ASAP 2020 volumetric adsorption analyzer (from Micromeritcs).
Prior to the adsorption measurements, each sample was degassed
at 300 °C for 2 h. The total porosity, APS or diameter and pore
size distribution (PSD) have been determined by mercury intrusion
porosimetry (Micromeritics, Model Autopore 9220) for samples
sintered at different temperatures. The morphology, surface quality
and thickness of intermediate and top-layer membranes were previously
metalized with platinum and examined by using scanning
electron microscope (SEM, Hitachi S4500). The tangential filtration
experiments were performed using a home-made pilot plant working
at room temperature. The transmembrane water pressure was
controlled by an adjustable valve that lets in pressurized air