Re(bpy)(CO)3Cl Immobilized on Bipyridine Organosilica Nanotubes for Photocatalytic CO2 Reduction

Organosilica nanotubes were synthesized via the co-condensation of 1,4-bis(triethoxysilyl)benzene and 5,5'-bis(triisopropoxysilyl)-2,2'-bipyridine in the presence of a surfactant micelle template under acidic conditions. These materials are termed BPy(X)-NTs, where X represents the BPy loading in the framework. The surface BPy moieties in these materials acted as chelating ligands to immobilize metal complexes in the nanotube pores, such that rhenium complexes [Re(bpy)(CO)(3)Cl] were successfully formed on the pore surfaces. The resulting Re-BPy(X)-NTs exhibited efficient photocatalytic CO2 reduction in the presence of a sacrificial reductant under visible light. Re-BPy(X)-NTs with higher BPy contents showed higher turnover numbers (TONs) and quantum yields than those previously obtained from periodic mesoporous organosilica systems. The photocatalytic activity of these materials was improved by the surface co-immobilization of tris(2,2'-bipyridine)ruthenium, [Ru(bpy)(3)](2+), on the Re-BPy(X)-NTs as a photosensitizer, giving a quantum yield of 15 % in response to visible light (>385 nm). The value exceeds those previously reported for heterogeneous systems.