Photocatalytic treatment of water for the preparation of ultra pure water

Claim 1

In a process for the preparation of ultra pure water from a source of water selected from the group consisting of city water, well water, industrial water and washings removed from rinsing steps of semiconductor wafers in integrated circuit manufacturing processes, which process comprises two basic stages (a) and (b), the former stage (a) comprising treating the raw water in one or more mechanical filtration steps to remove solid particulate contaminants suspended therein and the latter stage (b) comprising producing ultra pure water from the pretreated water by subjecting said pretreated water to one or more purification treatments selected from the group consisting of reverse osmosis, adsorption on ion exchange resins, adsorption on activated carbon ultrafiltration, UV sterilization and microfiltration, whereby the removal of residual solid particulate contaminants, of ionic contaminants, of organic contaminants included in total organic carbon (TOC) contents and of microorganisms from the pretreated water to produce ultra pure water is effected, the improvement which comprises incorporating into the stage (b) a catalytic photolysis step for decreasing the TOC content of the water being treated to a level lower than about 0.05 mg C/l, the said step comprising irradiating the water to be so treated in the presence of a catalytic amount of a photocatalyst comprising an inorganic semiconductor in fine particulate form selected from TiO 2 , SrTiO 3 and CdS and a noble metal and/or oxide thereof selected from Pt, Pd, Ru, RuO 2 and Rh deposited on said semiconductor particles, said irradiation being with a light of a wave length corresponding to an energy higher than the band gap of said semiconductor and for a period of time sufficient to oxidatively decompose the organic contaminants so as to give said low level of the TOC content in the treated water.