Capturing of bisphenol A photodecomposition intermediates by composite TiO₂-zeolite sheets

Two types of powders, titanium dioxide (TiO₂) photocatalyst and zeolite adsorbent, were made into a paper-like composite by a papermaking technique using a dual polyelectrolyte system. The photodegradation behavior of bisphenol A (2,2-bis(4-hydroxyphenyl)propane, BPA) in water was investigated under UV irradiation. It was found that TiO₂ sheets could photocatalytically decompose BPA in an aqueous medium. Composite TiO ₂-zeolite sheets, however, demonstrated a higher efficiency for BPA removal from water than did zeolite-free TiO₂ sheets owing to the synergistic effect obtained through the combined use of TiO₂ and zeolite, as reported in our previous study. Furthermore, the total organic carbon (TOC) content of the system was reduced, evidently through the use of composite sheets, rather than a TiO₂ powder suspension or zeolite-free TiO₂ sheets. Trace amounts of intermediates resulting from BPA degradation were detected in the water treated with the composite sheets. In general, various intermediates are formed during the TiO₂ photodecomposition of organic compounds, which can potentially cause a secondary pollution because the degradation products sometimes turn out to be more hazardous than the parent compound. The composite TiO₂-zeolite sheets prepared in the present study helped to overcome this problem by allowing the elimination of BPA without the release of hazardous intermediates into water: most of the intermediates were temporarily captured by the zeolite adsorbent contained in the composite sheets, and eventually decomposed through TiO₂ photocatalysis. Paper-like TiO₂-zeolite composites clearly offer great advantages in efficacy and safety for the aqueous decomposition of BPA.