One-step synthesis of visible light CO₂ reduction photocatalyst from carbon nanotubes encapsulating iodine molecules

We describe the synthesis and visible-light CO₂ photoreduction catalytic properties of a three-component composite consisting of AgI, AgIO₃, and single-walled carbon nanotubes (SWCNTs). The catalyst is synthesized by immersing SWCNTs encapsulating iodine molecules in AgNO₃ aqueous solution, during which neutral iodine (I₂) molecules encapsulated in SWCNTs transform disproportionately to I⁵⁺ (AgIO₃) and I^- (AgI), as revealed from the characterization of the composite by Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In addition, photoirradiation experiments using a solar-simulator (AM1.5G) showed that the obtained three-component composite works as a CO₂ photoreduction catalyst under visible light despite the wide band gap of AgIO₃, suggesting possible transfer of the visible light-excited electron from AgI via SWCNTs.