Photocatalytic Oxygen Evolution from Cobalt-Modified Nanocrystalline BiFeO3 Films Grown via Low-Pressure Chemical Vapor Deposition from beta-Diketonate Precursors
BiFeO3 is an interesting multifunctional narrow band gap semiconductor that exhibits simultaneous multiferroic, photovoltaic, and photocatalytic behavior. Hence there is much interest in the growth of thin films of BiFeO3 via chemical vapor deposition (CVD); however, the number of suitable bismuth precursors is severely limited. A series of homoleptic bismuth(III) β-diketonate complexes were synthesized via simple room temperature ligand-exchange reactions from [Bi(N(SiMe3)2)3] and free diketonate ligands, which yielded the crystal structure of [Bi(acac)3] as a 1-D polymer. We attempted to use these complexes for low pressure CVD (LPCVD) growth of BiFeO3 films with [Fe(acac)3]; however, all bismuth complexes exhibited poor volatilities and decomposition characteristics, and as a result film growth was unsuccessful. Subsequently, the volatile alkoxide [Bi(OtBu)3], with [Fe(acac)3], was used to grow dense BiFeO3 films via low pressure CVD. The BiFeO3 films possessed multiferroic properties at room temperature and exhibited activity for visible light-driven water oxidation in the presence of a Ag+ electron scavenger, which improved significantly when modified with a cobalt surface cocatalyst. The increase in activity, probed by time-resolved photoluminescence spectroscopy, was attributed to improved charge carrier separation arising from the in-built internal electric field of BiFeO3 in addition to the presence of an efficient cobalt oxygen evolution catalyst
