The relationship between Sn II fraction and visible light activated photocatalytic activity of SnO x ÁSiO 2 glass studied by Mo¨ssbauer spectroscopy Balazs Kobzi 1 • Erno Kuzmann 2 • Katalin Sinko 2 • Zoltan Homonnay 2 • Mira Ristic 3 • Stjepko Krehula 3 • Tetsuaki Nishida 4 • Shiro Kubuki 1 Received: 4 October 2016 Ó Akade´miai Kiado´, Budapest, Hungary 2017 Abstract The relationship between local structure and visible-light photocatalytic ability of tin silicate glass pre- pared by sol–gel method was investigated. 119 Sn Mo¨ss- bauer spectrum of SnO x ÁSiO 2 glass prepared from SnCl 2 showed a small peak of Sn II component besides the major amount of Sn IV . The smallest bandgap energy of 2.5 ± 0.5 eV was estimated from Tauc plot, and the largest first order rate constant (k) of (13.8 ± 0.1) 10 -3 min -1 was recorded from the methylene blue degradation test under visible-light irradiation. It is concluded that Sn II shows remarkable photocatalytic ability when it is incorporated into silica glass matrix. Keywords Sol–gel method Á Visible-light activated photocatalyst Á Tin silicate glass Á 119 Sn Mo¨ssbauer spectroscopy Introduction Environment friendly and green chemistry have gained more and more attention in our present days. Wastewater cleaning is a major problem worldwide, which is one of the huge challenges in recent years. Application of glasses, ceramics with photocatalytic properties in order to decompose the organic component of the contamination can bring us closer to the solution of these problems. Photocatalytic effect was first discovered by Fujisima and Honda on anatase type TiO 2 which can be activated by UV light [1]. The catalytic activity depends on the energy of the electron–hole pair formation and the extent of their separation. For TiO 2 this band gap energy is relatively high (3.2 eV), therefore only UV light can activate the catalyst. SnO 2 and SnO have attracted considerable interest because of their applications in lithium-ion batteries [2, 3], improving solar cells [4] and photocatalytic activity in the form of nanocrystals [5–7] and composites [8]. Using SnO and heterovalent tin oxides instead of only SnO 2 as pre- cursors results in a drastic decrease in the band gap energy which allows to use visible light to activate the catalysis instead of high energy UV light. The band gap energy of these oxides are around 2.5–2.7 eV [9, 10] for SnO and 3.5 eV for SnO 2 which is rather high. Applying hydrothermal method with various Sn II reagents, Sn 3 O 4 nanostructures were prepared and were used for dye degradation reactions [11, 12], electric conductivity mea- surements [13], and even water splitting [14]. However in these materials the Sn II component can easily oxidised by air or even through the synthesis itself, thus for the structural analysis, it is critical to properly measure the Sn II content in the final product since its visible light acti- vation depends on the amount of Sn II . In order to distinguish Sn II and Sn IV species, Hard X-ray Photoelectron & Shiro Kubuki kubuki@tmu.ac.jp 1 Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami- Osawa, Hachioji, Tokyo 192-0397, Japan 2 Institute of Chemistry, Eo¨tvo¨s Lora´nd University, 1/A Pa´zmany P. s., Budapest 1117, Hungary 3 Division of Materials Chemistry, Rud¯er Bosˇkovic´ Institute, P. O. Box 180, 10002 Zagreb, Croatia 4 Department of Biological and Environmental Chemistry, Faculty of Humanity-Oriented Science and Engineering, Kindai University, Kayanomori 11-6, Iizuka, Fukuoka 820-8555, Japan 123 J Radioanal Nucl Chem DOI 10.1007/s10967-016-5159-9