Comparison of two procedures for the design of dye-sensitized nanoparticles targeting photocatalytic water purification under solar and visible light

Abstract

In this study, light-sensitive photosensitizers are coupled to titanium dioxide and silicon dioxide nanoparticles in order to develop new kinds of visible light photocatalysts for water treatment applications. The influence of the mode of surface modification of the nanoparticles and the nature of the linked photosensitizer (PS) on the photocatalytic activity under visible and solar light was considered. The TiO2 Degussa P25 core was either coated with a polysiloxane layer formed by two silane reagents (3-aminopropyl tetraethoxysilane (APTES) and tetraethyl orthosilicate (TEOS)) emerging a core-shell nanosystem, or simply modified by APTES alone. In both systems, the APTES mediated the amide covalent linkage between the TiO2 and the PS. Monocarboxylic tetraphenyl porphyrin (P1-COOH) and chlorin e6 (Ce6) were used to sensitize the TiO2 semiconductor. Those photosensitizers serve as visible light antenna, thus modifying the UV-limited photoresponse properties of the hybridized TiO2 nanoparticles. The morphological and structural properties of the synthesized nanosystems were investigated through TEM, XRD, DLS, FTIR, zeta potential and UV–vis absorption. The photophysical properties (fluorescence emission and singlet oxygen formation) were also probed. The photodegradation of two model pollutants, methylene blue and methyl orange, was used to assess the photocatalytic efficiency of the prepared catalysts under simulated solar and pure visible lights. Similar sensitized nanosystems with a SiO2 core were also prepared and characterized in order to assess the contribution of the support in the photocatalytic degradation process. The reactive oxygen species involved in the photodegradation process were also studied.