caa a22 4500 606174036 CHVBK 20210128100736.0 cr unu---uuuuu 210128e20150301xx s 000 0 eng 10.1007/s11244-014-0348-7 doi (NATIONALLICENCE)springer-10.1007/s11244-014-0348-7 Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue [Elektronische Daten] [Wan-Ting Chen, Andrew Chan, Vedran Jovic, Dongxiao Sun-Waterhouse, Kei-ichiro Murai, Hicham Idriss, Geoffrey Waterhouse] This study systematically re-examines the titania-catalysed photo-oxidation of methylene blue (MB) in aqueous solution at 20°C, placing particular emphasis on the effects of TiO2 crystallite size, TiO2 polymorph (anatase, brookite, rutile and combinations thereof) and experimental test conditions on the rate of MB photo-oxidation. For all TiO2 samples tested, the highest rate of MB photo-oxidation was observed at pH 6, slightly above the isoelectric point of TiO2 (~5.8 for P25 TiO2). Increasing the ionic strength at pH 6 induced MB dimer formation in solution, and lowered the rate of MB photo-oxidation by TiO2. For all TiO2 polymorphs, the surface area normalised rate increased with crystallite size reflecting the corresponding reduction in surface and bulk defects (electron-hole pair recombination sites). The optimum crystallite sizes were ~20-25nm for anatase and ~50nm for brookite. The photocatalytic activity of the different TiO2 powders followed the general order P25>anatase>brookite≫rutile, with the high activity of P25 TiO2 providing strong evidence that anatase-rutile heterojunctions act as "hotspots” for MB photo-oxidation. Mixed phase anatase-rutile or brookite-rutile powders, each containing ~5wt% rutile, demonstrated superior area normalized photocatalytic activities for MB photo-oxidation compared to pure phase anatase or brookite powders of comparable crystallite size. Finally, deposition of Pd, Pt or Au nanoparticles decreased the activity of P25 TiO2 for MB photo-oxidation. This paper clarifies long-standing confusion in the scientific literature about the photo-oxidation of aqueous MB over TiO2 and M/TiO2 (M=Pd, Pt and Au) photocatalysts. Springer Science+Business Media New York, 2014 Photocatalysis nationallicence Anatase nationallicence Rutile nationallicence Brookite nationallicence P25 nationallicence Methylene blue nationallicence Chen Wan-Ting School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut Chan Andrew School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut Jovic Vedran School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut Sun-Waterhouse Dongxiao School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut Murai Kei-ichiro Graduate School of Advanced Technology and Science, The University of Tokushima, Tokushima, Japan aut Idriss Hicham SABIC, Corporate Research and Innovation (CRI), KAUST, Thuwal, Saudi Arabia aut Waterhouse Geoffrey School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut Topics in Catalysis Springer US; http://www.springer-ny.com 58/2-3(2015-03-01), 85-102 1022-5528 58:2-3<85 2015 58 11244 https://doi.org/10.1007/s11244-014-0348-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s11244-014-0348-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Chen Wan-Ting School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut NATIONALLICENCE 700 1- Chan Andrew School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut NATIONALLICENCE 700 1- Jovic Vedran School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut NATIONALLICENCE 700 1- Sun-Waterhouse Dongxiao School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut NATIONALLICENCE 700 1- Murai Kei-ichiro Graduate School of Advanced Technology and Science, The University of Tokushima, Tokushima, Japan aut NATIONALLICENCE 700 1- Idriss Hicham SABIC, Corporate Research and Innovation (CRI), KAUST, Thuwal, Saudi Arabia aut NATIONALLICENCE 700 1- Waterhouse Geoffrey School of Chemical Sciences, The University of Auckland, Auckland, New Zealand aut NATIONALLICENCE 773 0- Topics in Catalysis Springer US; http://www.springer-ny.com 58/2-3(2015-03-01), 85-102 1022-5528 58:2-3<85 2015 58 11244