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

Abstract

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 TiO2–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.