Non-degradable triazine substrates of atrazine and cyanuric acid hydrothermally and in supercritical water under the UV-illuminated photocatalytic cooperation

Strong oxidation by titanium dioxide photocatalysis can occur by photodegradation of organic contaminants in air and water. Some endocrine disruptors such as 2,4-dichlorophenoxy acetic acid (Chamarro and Esplugas, 1993; Pichat et al., 1993; Muller et al., 1998; Modestov and Lev, 1998), 2,4-dichlorophenol (Al-Ekabi and Serpone, 1988; D'Oliveira et al., 1990, 1993; Lee et al., 1992; Ku and Hsieh, 1992), nonylphenol (Hidaka et al., 1990; Horikoshi et al., 2000), bisphenol A (Barbeni et al., 1987), diethyl phthalate (Sundstrom et al., 1989; Watanabe et al., 2003), etc. which can be neither biodegraded by bacteria nor degraded thermally can be degraded by TiO(2) photocatalytic treatment. However, incomplete photomineralization partly occurred, when TiO(2) photocatalytic degradation is employed for the treatment of certain endocrine disruptors. For example, no atrazine pesticide having triazine skeleton can be completely mineralized even by a photocatalytic procedure; the photodegradation of atrazine ultimately stops at the intermediate step of cyanuric acid, which cannot be photodegraded even after long illumination times (Pelizzetti et al., 1990). In this study, the decomposition of atrazine and cyanuric acid was carried out with a device combining photocatalytic degradation in supercritical water (scH(2)O) or hydrothermal water (hyH(2)O). Atrazine and cyanuric acid can be degraded by the cooperation of either scH(2)O or hyH(2)O and UV illuminated TiO(2)-photocatalytic dispersed system under the fixed pressure of 23 MPa at 623 K or 683 K in a 120-ml Hastelloy batch reactor. The photocatalytic degradation method under high temperature and pressure has found appropriate for the photocatalytic oxidation of acetic acid and 2-chlorobiphenyl under continuous flow conditions at 160 degreesC and 20 atm. (Duffy et al., 2000a). In addition, the wet peroxide oxidation of PCBs by high temperature and pressure has been reported (Duffy et al., 2000b). The main aims of this research are following. (i): the degradation of atrazine and cyanuric acid within the scH(2)O or hyH(2)O, (ii) the decomposition of atrazine and cyanuric acid catalyzed by TiO(2) particles under scH(2)O or hyH(2)O, and the synergistic effect for several reactions with TiO(2) and scH(2)O or hyH(2)O, and (iii) the mineralization yield of nitrogen and chlorine atoms concerning the chemical structures of atrazine or cyanuric acid (only nitrogen). (C) 2003 Elsevier Science Ltd. All rights reserved.