Organometallic Iridium(III) Complex Sensitized Ternary Hybrid Photocatalyst for CO2 to CO Conversion

Abstract

A series of heteroleptic iridium(III) complexes functionalized with two phosphonic acid (-PO3H2) groups ((IrP)-Ir-dfppy, (IrP)-Ir-ppy, (IrP)-Ir-btp, and (IrP)-Ir-piq) were prepared and anchored onto rhenium(I) catalyst (ReP)-loaded TiO2 particles (TiO2/ReP) to build up a new IrP-sensitized TiO2 photocatalyst system (IrP/TiO2/ReP). The photosensitizing behavior of the IrP series was examined within the IrP/TiO2/ReP platform for the photocatalytic conversion of CO2 into CO. The four IrP-based ternary hybrids showed increased conversion activity and durability than that of the corresponding homo- (IrP+ReP) and heterogeneous (IrP+TiO2/ReP) mixed systems. Among the four IrP/TiO2/ReP photocatalysts, the low-energy-light (>500 nm) activated (IrP)-Ir-piq immobilized ternary system ((IrP)-Ir-piq/TiO2/ReP) exhibited the most durable conversion activity, giving a turnover number of >= 730 for 170 h. A similar kinetic feature observed through time-resolved photoluminescence measurements of both (IrP)-Ir-btp/TiO2 and TiO2-free (IrP)-Ir-btp films suggests that the net electron flow in the ternary hybrid proceeds dominantly through a reductive quenching mechanism, unlike the oxidative quenching route of typical dye/TiO2-based photolysis.