Visible light active self-cleaning materials based on porphyrin-sensitised titanium dioxide

Abstract

Starting from second half of last century, nanostructured semiconductors have had a crucial function in the material science because of their wide application field going from renewable energy to organic/hybrid electronics up to photocatalysis. Among those materials, titanium dioxide is probably the most used because of some important characteristics like the chemical/mechanical stability, environmental sustainability, its low cost and versatility. Indeed, it has been successfully employed as photo- and electro-active component in electronic devices as well as photocatalytic agent1 in water de-pollution application. Interestingly and importantly together, titanium dioxide may also be applied in the protection of cultural heritages2 by using its photocatalytic properties to prepare self-cleaning materials able to passivate the manufact surfaces and degrade organic pollution, in this way limiting blackening and reducing maintenance costs. Unluckily, the photoactivity of TiO2 under the natural sunlight exposition or artificial illumination is greatly reduced because its low absorption in the Vis range. Hence, in order to improve the material performance under the environmental illumination conditions, the extension of the absorption range in the visible region is crucial.3 To this end, we prepared novel TiO2-based photocatalysts functionalized in-bulk with meso-tetra(carboxyphenyl)-porphyrin (TCPP) and its metal complex (Me-TCPP) working as visible-light antennas. The peculiar sol-gel synthesis used for the preparation allows porphyrin dye to be bonded inside the TiO2 structure rather than being easily adsorbed onto the outer surface due to the in situ incorporation of the dye during the synthesis of the TiO2.3,4 The material structure, composition and electronic properties were investigated by Raman, diffuse reflectance spectroscopy and photoelectron spectroscopy while photocatalytic properties were studied by following the degradation kinetic of carminic acid by UV-Vis spectrophotometry under both UV and visible light. The sensitised materials showed an enhanced photocatalytic activity in the visible range compared to commercial titanium dioxide under different illumination conditions, indicating that in-bulk dye sensitisation is a valuable strategy for effective visible-light TiO2 photocatalysts. References: 1. Q. Guo, C. Zhou, Z. Ma, Z. Ren, H. Fan, X. Yang; Chem Soc Rev, 2016, 45, 3701. 2. P. Munafò, G.B. Goffredo, E. Quagliarini; Constr Build Mater, 2015, 84, 201. 3. M. Rico-Santacruz, A.E. Sepúlveda, E. Serrano, E. Lalinde, J.R. Berenguer, J. García-Martínez; J Mater Chem C, 2014, 2, 9497. 4. M. Rico-Santacruz, A.E. Sepúlveda, C. Ezquerro, E. Serrano, E. Lalinde, J.R. Berenguer, J. García-Martínez; Appl. Catal. B: Environm. 2017, 200, 93