Photocatalytic treatment of water for the preparation of ultra pure water

DETAILED DESCRIPTION OF THE INVENTION This invention is widely applicable for the purpose of removing a small amount, particularly a last trace amount, of organic impurities included in TOC content of water to be purified for the purpose of preparation of ultra pure water from a source of water as specified above by various known multi-step processes.
Thus, the source of water, i.
e.
the raw water, to be utilized for the preparation of ultra pure water may be selected from city water, well water, industrial water and washings removed from rinsing steps of semiconductor wafers in integrated circuit manufacturing processes.
The catalytic photolysis step, the characteristic step, according to this invention may be incorporated at any point, as desired, in the course of the stage (b) as specified above, that is after the finish of the stage (a), the pretreatment stage, as hereinafter explained in detail.
The inorganic semiconductor in fine particulate form which may be used as the first component of the photocatalyst according to this invention is selected from TiO.
sub.
2, SrTiO.
sub.
3 and CdS, amond which TiO.
sub.
2, particularly in anatase form, is most preferred, in view of the energy gap of valence band and conduction band and of the position in respect of standard hydrogen electrode potential.
The particle diameter of the fine particulate inorganic semiconductor to be used according to this invention is generally about 30 m.
mu.
to 100 .
mu.
and preferably about 100 m.
mu.
to 10 .
mu.
.
The noble metals and/or an oxide thereof which may be used in this invention in deposited form on the fine particles of the inorganic semiconductor are Pt, Pd, Rh, Ru and RuO.
sub.
2, separately or in combination.
The amount of noble metal and/or oxide thereof deposited on the semiconductor particles may vary dependent upon the nature of said noble metal and/or oxide thereof used, the nature of said semiconductor material used, the purpose of the use of said photocatalyst and other factors, but is usually about 0.
1 to 15% by weight based on the weight of the semiconductor used