Page 476 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanocomposite membrane for environmental remediation 429

magnitude of the interactions between the membrane and the substances to be
processed. Best example is the effect of surface electrochemical properties on the
adsorption of proteins [175]. Nowadays, ceramic technology is used to generate inor-
ganic membranes having a more complex pore structure. Furthermore, some ceramic
membranes are formed using a combination of oxides and the resulting membranes
called mixed oxide ceramic membranes (Rappore). Their surface electrochemical
properties have been analyzed as a result of computerized measurements of rates
of electroosmosis as a function of pH (reported as zeta 0 potentials) and computerized
pH surface titration. The membranes have different values of zeta potential and high
titratable surface charge. The membranes have a negative zeta potential above the
entire pH range 10–3 for an inorganic oxide material. Both the zeta potential-pH
and surface charge-pH profiles at two ionic strengths might be effectively modeled
by considering the surface of the membrane composed of a three-dimensional array
(“gel”) of charged groups, both protons and counter ions being able to penetrate the
“gel” layer. Especially, at the lower pH values, counter ion penetration was found to
be significant, where the surface charge of the membrane was positive but the zeta
potential was negative. To the surface chemistry, such a model permits estimation
of the “gel” thickness and the relative contribution of the component oxides. Based
on the bulk composition, it was found that aluminum oxide groups played the supreme
role in determining surface-related properties although zirconium dioxide was defi-
nitely the largest component of the membrane. Results demonstrated that the surface
electrochemistry of such membranes is complex and that in characterizing such
membranes, it is important to create measurements directly on the membrane rather
than on the component oxides [176].
Ceramic membranes have drawn much interest in many industrial applications
[177] and offer many potential advantages over commercial organic membranes
because of stability at high temperatures and pressure resistance and stability toward
chemicals and exhibit high strength, high mechanical resistance, long life, and excel-
lent defouling properties.
Among various ceramic oxide membranes, alumina membranes have been exten-
sively used worldwide. Many other porous membrane materials including ZrO 2 ,
titania, and SiO 2 were also most studied membranes. For inorganic membranes,
among all these, ZrO 2 is the most promising and effective material.
ZrO 2 membranes exhibit high chemical resistance that allows steam sterilization
and cleaning procedures in the pH range 0–14 [177], decent pure water permeability
and high membrane flux in separation and filtration [178,179], and high thermal
stability [178], which is very attractive for catalytic membrane reactors at high
temperature.
In the early 1970s, the first profitable ZrO 2 membrane prepared of a layer of
nonsintered ZrO 2 deposited on a porous carbon was the Ucarsep1 membrane (4 nm).
Many porous ZrO 2 membranes are formerly developed by several companies
worldwide; most of them are ultrafiltration membranes prepared mainly using sol-
gel method. Although on the preparation and characterization of ZrO 2 or YSZ ultra-
filtration membranes, several studies have been reported [178], but few efforts have
been made directly to the synthesis of ZrO 2 microfiltration membranes. In comparison