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 Cr⁶⁺ 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⁺. TiO-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⁺.