Photocatalytic Water Splitting and CO2 Reduction over KCaSrTa5O15 Nanorod Prepared by a Polymerized Complex Method

Single-crystal KCaSrTa5O15 nanorods were successfully synthesized by a polymerized complex method. SEM and TEM observations revealed that the nanorods growing along the c axis of a tungsten bronze structure measured 40-100 mu in diameter and 100-300 urn in length. Tb(0.03 atom %)-doped KCaSrTa5O15 nanorods gave a green luminescence due to the D-5(4) -> F-7(6) and D-5(4) -> F-7(5) transition of Tb3+, when the KCaSrTa5O15 host was excited. The intensity of the luminescence was much higher than that by polycrystalline KCaSrTa5O15 prepared by a solid-state reaction. This indicates that nonradiative deactivation at grain boundaries was suppressed in the KCaSrTa5O15 nanorods compared to the polycrystalline KCaSrTa5O15. NiO cocatalyst-loaded KCaSrTa5O15 nanorods split water into H-2 and O-2 with an apparent quantum yield of 6.6% at 254 nm. The efficiency was three times as high as that of the polycrystalline KCaSrTa5O15. The KCaSrTa5O15 nanorods also showed photocatalytic activity for CO2 reduction, when a Ag-cocatalyst was loaded. Stoichiometric amounts of CO and H-2 as reduction products and O-2 as an oxidation product were obtained. The activity for CO2 reduction was improved by adding NaHCO3 into the reactant solution, giving about 90% CO selectivity (CO/(CO + H-2)).