Capturing of bisphenol A photodecomposition intermediates by composite TiO_2-zeolite sheets

摘要

Two types of powders,titanium dioxide (TiO_2) photocatalyst and zeolite adsorbent,were made into a poaper-like composite by a papermaking technique using a dual polyelectroyte system.The photodegradation behavior of bisphenol A (2,2-bis(4-hydroxy9phenyl)propane,BPA) in water ws investigated under UV irradiation.It was found that TiO_2 sheets could photocatalytically decompose BPA in an aqueous medium.Composite TiO_2-zeolite sheets,however,demnstrated ahigher efficiency for BPA removal from water than did zeolite-free TiO_2 sheets owing to the synergistic effect obtained through the co9mbined use of TiO_2 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 TiO_2 powder suspension or zeolite-free TiO_2 sheets.Trace amounts of intermediates resulting from BPA degradation were detected in the water treated with the composite sheets.In general,various intermediates are formedduring the TiO_2 photodecomposition of organic compounds,which can poitentially cause a secondary pollution because the degradation products sometimes turn out to be more hazardous than the parent compound.The composite TiO_2-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 th intermediates were temporarily captured by the zeolite adsorbent contained in the composite sheets,and eventually decomposed through TiO_2 p0hotocatalysis.Paper-like TiO_2-zeolite composites clearly offer great advantages in efficacy and safety for the aqueous decomposition of BPA.