Increasing the optical response of TiO2 and extending it into the visible region through surface activation with highly stable Cu5 clusters
12 pags., 6 figs. -- Open Access funded by Creative Commons Atribution Licence 3.0 ; The decoration of semiconductors with subnanometer-sized clusters of metal atoms can have a strong impact on the optical properties of the support. The changes induced differ greatly from effects known for their well-studied, metallic counterparts in the nanometer range. In this work, we study the deposition of Cu5 clusters on a TiO2 surface and investigate their influence on the photon-absorption properties of TiO2 nanoparticles via the computational modeling of a decorated rutile TiO2 (110) surface. Our findings are further supported by selected experiments using diffuse reflectance and X-ray absorption spectroscopy. The Cu5 cluster donates an electron to TiO2, leading to the formation of a small polaron Ti3+ 3d1 state and depopulation of Cu(3d) orbitals, successfully explaining the absorption spectroscopy measurements at the K-edge of copper. A monolayer of highly stable and well fixated Cu5 clusters is formed, which not only enhances the overall absorption, but also extends the absorption profile into the visible region of the solar spectrum via direct photo-induced electron transfer and formation of a charge-separated state. ; This work has been partly supported by the Spanish Agencia Estatal de Investigacion (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grant No. MAT2016- 75354-P, the Austrian Science Fund (FWF) under Grant P29893-N36, the COST Action CM1405 "Molecules in Motion" (MOLIM), La Caixa Foundation (LCF/PR/PR12/11070003), the Ramon Areces Foundation (Project CIVP18A3940), European Union's Horizon 2020 Research and Innovation Programme (Grant Agreement No. Bac-To-Fuel 825999), the MINECO, Spain (MAT2015-67458-P – conanced with FEDER Funds – and CTQ2013-44762-R), the Xunta de Galicia, Spain (GRC ED431C2017/22), and the ANPCyT (PICT 2015-2285) and UNLP (Project 11/X790), Argentina. The CESGA Supercomputing Center (Spain) is acknowledged for having provided the computational resources used in this work. The partial support by the Laboratorio Nacional de Luz Sıncrotron (LNLS) under proposals 20170352 and 20180123 is also acknowledged. D. B. expresses gratitude for a postdoctoral grant from the Xunta de Galicia, Spain (ED481D 2017/021). ; Peer reviewed