Synthesis, Characterization, and Oxygen Sensing Properties of Functionalized Mesoporous SBA-15 and MCM-41 with a Covalently Linked Ruthenium(II) Complex

Abstract

Novel oxygen sensing materials consisting of the [Ru(dpp) 2 Phen] 2+ (dpp = 4, 7-diphenyl-1,10-phenanthroline, Phen = 1,10-phenanthroline) portion covalently grafted to the ordered functionalized mesoporous SBA-15 and MCM-41 backbones are prepared by co-condensation of tetraethoxysilane (TEOS) and the functionalized Ru(II) complex [Ru(dpp) 2 Phen-Si] 2+ (Phen-Si = 2-[4‘-{3-(Triethoxysilyl)propyl}phenyl]imidazo [4,5-f]-1,10-phenanthroline) in the presence of Pluronic P123 or cetyltrimethylammoniumbromide (CTAB) surfactant as template, respectively. 1,10-Phenanthroline covalently grafted to 3-(triethoxysilyl)propyl isocyanate is used not only as the precursors but also as the second ligand of the Ru(dpp) 2 Cl 2 ·2H 2 O complex to prepare the functionalized mesoporous materials for oxygen sensors. For comparative purposes, two different synthesis procedures, including the one-pot synthesis and the postsynthetic treatment methods, are used to prepare the covalently grafted samples. Furthermore, the oxygen sensing materials in which [Ru(dpp) 2 Phen] 2+ is conventionally physically incorporated into the matrix are also prepared. The derivative mesoporous oxygen sensing materials are characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), small-angle X-ray diffraction, luminescence intensity quenching Stern−Volmer plots, nitrogen adsorption/desorption, elemental analysis, and excited-state decay analysis. The functionalized mesoporous sensing materials appear to be highly sensitive to the O 2 concentration in N 2 . In addition, these mesoporous sensing materials exhibit short response times and can be restored within seconds. The oxygen quenching result shows that the homogeneity and the sensitivity of the covalently assembled samples are superior to those of the physically incorporated ones. Furthermore, a greatly minimized leaching effect of the sensing molecules could be observed in the covalently grafted systems. In addition, the Ru(II)Phen-MCM-41 oxygen sensing materials show an overall increase in luminescent lifetime compared with the Ru(II)Phen-SBA-15 oxygen sensing materials, which is explained in detail by the difference of Ru(II) content and pore structure between the two kinds of mesoporous oxygen sensing materials.