Spectral Characteristics and Photosensitization of TiO₂ Nanoparticles in Reverse Micelles by Perylenes

Abstract

We report on the photosensitization of titanium dioxide nanoparticles (TiO2 NPs) synthesized inside AOT (bis(2-ethylhexyl) sulfosuccinate sodium salt) reverse micelles following photoexcitation of perylene derivatives with dicarboxylate anchoring groups. The dyes, 1,7-dibromoperylene-3,4,9,10-tetracarboxy dianhydride (1), 1,7-dipyrrolidinylperylene-3,4,9,10-tetracarboxy dianhydride (2), and 1,7-bis(4-tert-butylphenyloxy)perylene-3,4,9,10-tetracarboxy dianhydride (3), have considerably different driving forces for photoinduced electron injection into the TiO2 conduction band, as estimated by electrochemical measurements and quantum mechanical calculations. Fluorescence anisotropy measurements indicate that dyes 1 and 2 are preferentially solubilized in the micellar structure, creating a relatively large local concentration that favors the attachment of the dye to the TiO2 surface. The binding process was followed by monitoring the hypsochromic shift of the dye absorption spectra over time for 1 and 2. Photoinduced electron transfer from the singlet excited state of 1 and 2 to the TiO2 conduction band (CB) is indicated by emission quenching of the TiO2-bound form of the dyes and confirmed by transient absorption measurements of the radical cation of the dyes and free carriers (injected electrons) in the TiO2 semiconductor. Steady state and transient spectroscopy indicate that dye 3 does not bind to the TiO2 NPs and does not photosensitize the semiconductor. This observation was rationalized as a consequence of the bulky t-butylphenyloxy groups which create a strong steric impediment for deep access of the dye within the micelle structure to reach the semiconductor oxide surface.

Recent Advances in Heterogeneous Photocatalytic Decolorization of Synthetic Dyes

“…Meanwhile, other studies have shown that only cationic azo dyes can be adsorbed on the surface of the photocatalyst and simultaneously their photocatalytic degradation was quicker than the degradation of anionic azo dyes like Eriochrome Black T [225, 226]. It has been found that TiO 2 adsorbed almost only cationic azo dyes, except for the anionic Quinizarin with an adsorption efficiency of 21.8% [227, 228]. Apart from photooxidation, the photoreduction of azo dyes is also known as a significant decolorizing or a folding pathway.…”

Controlling Surface Defects and Photophysics in TiO2 Nanoparticles

“…27 The method described in this manuscript presents the possibility of controlling the density of surface defects on the nanoparticles and allows to use TiO 2 nanoparticles without micelles in non-aqueous environments, expanding the available conditions for device optimization and for some applications for which organic solvent is required. 2 Herein, we report a strategy for obtaining small TiO 2 anatase nanoparticles, which offers advantages due to their solubility in a wide range of organic solvents and water.…”

Strategies for designing metal oxide nanostructures

“…0D TiO2 nanoparticles in amorphous or crystalline form in controlled sizes were synthesized from hydrated reverse micelles [56][57][58]. TiO2 nanoparticles with diameters varing from 10 to 20 nm were produced by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of reverse micelles formed in CO2 with the surfactants ammonium carboxylate perfluoropolyether (PFPECOO −+ NH4) (Mw = 587) and poly(dimethyl amino ethyl methacrylate-block-1H, 1H, 2H, 2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA) [57].…”

“…TiO2 nanoparticles with diameters varing from 10 to 20 nm were produced by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of reverse micelles formed in CO2 with the surfactants ammonium carboxylate perfluoropolyether (PFPECOO −+ NH4) (Mw = 587) and poly(dimethyl amino ethyl methacrylate-block-1H, 1H, 2H, 2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA) [57]. Hernandez et al [58] reported the synthesis of TiO2 nanoparticles with a mean diameter of 3.5 ± 0.7 nm inside sodium bis (2-ethylhexyl) [59]. 0D ZnO nanoparticles have been synthesized in reverse micelles or microemulsions, for instance, polystyrene-b-polyacrylic acid (PS(10912)-b-PAA(3638)) copolymer, PEG NP-5/cyclohexane, AOT, non-ionic Pluronic F127, anionic surfactant sodium dodecyl sulfate (SDS), etc.…”