Visible Light Photo-oxidation of Model Pollutants Using CaCu_3Ti_4O_(12): An Experimental and Theoretical Study of Optical Properties, Electronic Structure, and Selectivity

摘要

Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu_33Ti_4O_(12) has distinct octahedral Ti and square planar Cu sites and is thus a candidate material for this approach. The sol-gel synthesis of high surface area CaCu_3Ti_4O_(12) and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO_4 units within the structure of CaCu_3Ti_4O_(12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu_3Ti_4O_(12) which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.