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

• Published in: Chemistry : a European journal 2019-10, Vol.25 (59), p.13609-13623
• Main Authors: Kim, Pil Soo, Choi, Sunghan, Kim, So‐Yoen, Jo, Ju Hyoung, Lee, Yoon Seo, Kim, Bupmo, Kim, Wooyul, Choi, Wonyong, Kim, Chul Hoon, Son, Ho‐Jin, Pac, Chyongjin, Kang, Sang Ook
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbon monoxide; Catalysts; Chemistry; Conversion; Durability; heterogeneous catalysis; Hybrids; Iridium; Iridium compounds; Phosphonic acids; Photocatalysis; Photocatalysts; photochemistry; Photoluminescence; Photolysis; Photons; Photosensitization; Quenching; Rhenium; sensitizers; supported catalysts; Ternary systems; Titanium dioxide
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201903136

A series of heteroleptic iridium(III) complexes functionalized with two phosphonic acid (−PO3H2) groups (dfppyIrP, ppyIrP, btpIrP, and piqIrP) 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 piqIrP immobilized ternary system (piqIrP/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 btpIrP/TiO2 and TiO2‐free btpIrP 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. Electron transfer: An organometallic IrIII dye‐sensitized TiO2 hybrid exhibited efficient and steady photocatalytic activity, as a result of efficient photoelectron collection/transportation from the IrIII photosensitizer to the ReI catalytic site through the TiO2 semiconductor (see figure).