Bipyridine-silica nanotubes with high bipyridine contents in the framework

Abstract

Abstract Bipyridine-silica nanotubes (BPy-NTs) represent a solid chelate ligand for the formation of efficient heterogeneous metal complex catalysts. BPy-NTs are typically synthesized by the co-condensation of bipyridine (BPy)- and benzene (Ph)-bridged organosilane precursors. However, the amount of BPy in the framework has been limited to a maximum of 1.22 mmol g−1 owing to the difficulty in the formation of the NT structure. In this study, BPy-NTs with a large amount of BPy ligands (2.43 mmol g−1) were prepared from a reaction mixture with a high molar ratio of BPy precursor (up to 80 mol%) via the optimization of synthesis conditions. Stable nanotube structures with inner diameters in the range of 6.1–7.0 nm and lengths of tens to hundreds of nanometers were characterized using scanning transmission electron microscopy, N2 adsorption, and 29Si magic angle spinning nuclear magnetic resonance spectroscopy analyses. A large amount of Pt(bpy)Cl2 complexes were homogeneously immobilized on the NT walls (PtCl2@BPy-NTs), which was confirmed by high-angle annular dark-field scanning transmission electron microscopy, UV–vis absorption, and X-ray photoelectron spectroscopy analyses. PtCl2@BPy-NTs exhibited efficient photocatalysis for H2 evolution under visible light irradiation. The photocatalytic activity increased as the amount of Pt complexes loaded on the BPy-NTs increased. A small amount of Pt metal particles was formed on the BPy-NTs during the photoreaction, which promoted the H2 evolution reaction, as a catalyst with higher activity than only the Pt complex.