Cooperative and fully reversible color switching activation in hybrid graphene decorated nanocages and copper-TiO2 nanoparticles


Nanostructured systems showing reversible color switching are envisaged to play a significant role in photo-switches, photo-optical sensors, smart windows, displays, optical storage memories. Most of the materials exhibiting reversible color switching are organic molecules. However, their UV-light activation, low thermal and chemical stability, as well as harmful synthesis methods, limit their extensive use. In this research, we have created an inorganic switchable photochromic material exploiting TiO2 ability of creating an exciton upon excitation, copper as the chromophore, and graphene's extraordinarily high electron mobility. Spatially-resolved electron energy-loss spectroscopy and aberration-corrected transmission electron microscopy imaging highlight the high sp(2) content of the graphene flakes as well as the presence of few-layers nanocage graphene decorating the surface of the flakes. Our material showed itself to be able to work under visible-light, its photochromic property being three times faster than conventional titania based photochromic materials, reaching a stable change in coloration after only 30 min of visible-light irradiation (vs. > 120 min in conventional Cu-TiO2). With the addition of just 1 wt % graphene, the material exhibited a staggeringly stable photochromic switching over repeated cycles. These results relate to the best previously reported values for any form of TiO2-based photochromic material. This is therefore an excellent candidate for smart-windows, light-sensitive information and energy storage devices, and other chromic devices and applications. (C) 2020 Elsevier Ltd. All rights reserved.



subject category

Chemistry; Energy & Fuels; Materials Science


Tobaldi, DM; Lajaunie, L; Dvoranova, D; Brezova, V; Figueiredo, B; Seabra, MP; Calvino, JJ; Labrincha, JA

our authors


This work was partly developed within the scope of the bilateral project between Portugal and the Slovak Republic, FCT/484/January 15, 2019/S and in the frame of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. This study was also partly financially supported by the Scientific Grant Agency of the Slovak Republic (VEGA Project 1/0026/18) and Slovak Research and Development Agency under the contract No. SK-PT-2018-0007. David Maria Tobaldi is very much grateful to FCT and to Portuguese national funds (OE), through FCT, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. This project has also received partial funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 823717 -ESTEEM3. Last but not less important, we are obliged to Miss Dafne Maria Glaglanon for proof-editing the English of the manuscript.

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