Photosynthetic membranes. Part 74. Solar energy driven photocatalytic membrane modules for water reuse in agricultural and food industries. Pre-industrial experience using s-triazines as model molecules

A membrane module, utilizing photocatalytic membranes, has been employed in a pilot plant, in conditions of solar irradn., to investigate photomineralization of atrazine, propazine, terbutylazine, symazine, prometryn, and ametryn, as model mols. of s-triazine herbicides, at a std. concn. (1.0 ppm) simulating those of contaminated aquifers, by using ozone as oxygen supplier. Photocatalytic composite membranes immobilized 30 ? 3 wt.% of TiO2 and 6 wt.% of a synergic mixt. of tri-(t-butyl)- and tri-(i-propyl)vanadate(V). Photomineralization was followed by anal. of substrate disappearance, as such, and by total org. carbon (TOC) anal. A four parameters kinetic model was employed, as set up in previous studies of this series, to interpret the whole photomineralization curve. Quantum yields, as indicative of catalytic and photocatalytic mechanisms, were evaluated satisfactorily: they are discussed, and compared with those of previous studies on the same substrates, carried out in the same module, but in conditions of practically monochromatic irradn. (254 nm) within the range of optical absorption of semiconductor. Finally, in order to compare effectiveness of composite photocatalytic membranes, described above, prepd. by photografting, either in the presence or in the absence of an added photopromoter, as well as that of metallic membranes, onto which the semiconductor without any photopromoter was present as a 3-4 ?m thick surface layer, directly produced on the nanotechnol. treated surface, with those of other com. materials, parallel expts. were carried out, by using com. sheets in which the semiconductor was immobilized, by a method based substantially on gluing by colloidal silica. All of these comparison expts. were carried out at a lab. scale, by using, in these expts., dioxygen of air, or ozone as oxygen donors.