Sensitization of TiO2 nanoparticles with natural dyes extracts for photocatalytic activity under visible light

Titanium dioxide (TiO2) is the most used semiconductor for heterogeneous photocatalysis. However, TiO2 is activated only by ultraviolet radiation (wavelength less than 390 nm) and only 5% of the sunlight spectrum corresponds to the UV radiation, therefore restricting the efficiency of titania catalysts. Aiming to obtain more efficient photocatalytic TiO2 nanoparticles under visible light, the goal of this study is the sensitization of this semiconductor with natural dye extracts, consequently enabling the absorption of energy in the visible light spectrum. Four natural dyes were used, blackberry and hibiscus (anthocyanins group) and urucum and curcuma (carotenoids group), which were extracted by the solid-liquid extraction method. The Evonik P25 titanium dioxide was used and the sensitization of the nanoparticles was by the liquid route. Samples were characterized by UV–visible spectrophotometry, differential thermal analysis and thermal gravimetric analysis (DTA/TGA), Fourier-transform infrared spectroscopy (FTIR) and pH control. A solution of curcuma was used to determine the photocatalytic activity of the sensitized TiO2 NPs under visible light. As a result, TiO2 without sensitization degraded only 11% of the dye solution, whereas the sensitized catalysts degraded on a range of 51–73%, showing that sensitized TiO2 nanoparticles have a significant increase in the degradability of organic compounds under visible light. The sensitization of TiO2 nanoparticles with natural dye extract has a great potential to increase the photocatalytic efficiency in the visible spectrum, especially in environments without ultraviolet radiation.