Effects of deposited ions on the photocatalytic activity of TiO2-Au nanospheres

Photocatalytic TiO2-Au nanospheres (TiO2-Au NSs, 206 +/- 23.7 nm) have been prepared and used as catalysts for the photo degradation of methylene blue (MB) and for the reduction of C-r6+ to Cr3+. TiO2 NSs are firstly prepared from titanium isopropoxide (TIP) via a solvothermal method. The TiO2 NSs are then sequentially modified with poly-(sodium-4-styreneulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), which then interact with Au NPs (15 +/- 1.3 nm) as seeds. Through reduction of HAuCl4 by ascorbic acid, core-shell structures of TiO2-Au NSs are prepared. Under UV irradiation, TiO2-Au NSs provide highly catalytic activity for the degradation of MB and reduction of Cr6+ within 15 and 60 min, respectively. The TiO2-Au NSs relative to commercial TiO2 (P25) and TiO2 NSs provide 1.8 and 1.2-fold activity higher for the photo degradation of MB, and 4.3 and 1.8-fold higher for the reduction of Cr6+. TiO2-Au/Hg and TiO2-Au/Ag NSs that are prepared from the deposition of Hg2+ and Ag+ onto TiO2-Au NSs, respectively, allow degradation of MB within 10 min, with activities 4.2- and 3.3-fold greater than that of the TiO2-Au NSs. The present study reveals that TiO2-Au/Hg and TiO2-Au/Ag NSs are effective for removal of organic pollutants, while TiO2-Au NSs are useful for the reduction of Cr6+.