The effects of sintering atmosphere on the properties of symmetric TiO

2

membranes are studied with regard to sintering behavior

porosity

mean pore size

surface composition

and surface charge properties.The experimental results show that the symmetric TiO

2

membranes display better sintering activity in the air than in argon

and the mean pore diameters and porosities of the membrane sintered in argon are higher than those of the membrane sintered in the air at the same temperature.The surface compositions of the symmetric TiO

2

membrane sintered in the air and in argon at different temperatures

as studied by X-ray photoelectron spectroscopy

are discussed in terms of their chemical composition

with particular emphasis on the valence state of the titanium ions.The correlation between the valence state of the titanium ions at the surface and the surface charge properties is examined.It is found that the presence of Ti

3+

introduced at the surface of the symmetric TiO

2

membranes by sintering in a lower partial pressure of oxygen

is related to a significant decrease in the isoelectric point.TiO

2

with Ti

4+

at the interface has an isoelectric point of 5.1

but the non-stoichiometric TiO

2-x

with Ti

3+

at the interface has a lower isoelectric point of 3.6.