In Situ Loading Transition Metal Oxide Clusters on TiO2 Nanosheets As Co-catalysts for Exceptional High Photoactivity

In this work, transition metal oxide clusters (MnOx, FeOx, CoOx, NiOx, and CuOx, denoted as TM-TiO2) are in situ loaded on TiO2 nanosheets through one-pot reaction. Structural and pore structural characterizations prove that metal ions do not dope into the frameworks of TiO2 nanosheets. Through TEM and STEM, we can determine that clusters with similar to 2 nm size are finely dispersed on TiO2 nanosheets. PL spectra and photoelectrochemical measurements suggest that these metal oxide clusters can serve as hole traps. Time-resolved PL spectra demonstrate that the charge-transfer process in TM-TiO2 is significantly accelerated, leading to higher charge separation efficiency. Metal oxide clusters show significant promotion effect in photocatalytic water oxidation to 02 compared to RuO2/TiO2 and IrO2/TiO2 nanosheets (denoted as Ru-TiO2(IM) and Ir-TiO2(IM)) prepared through conventional impregnation method. We also prepared RuO2/TiO2 and Ir/TiO2 nanosheets (denoted as Ru-TiO2(HT) and IrTiO2(HT)) through the in situ loading method. Ru-TiO2(HT) and Ir-TiO2(HT) show O-2 evolution rates much better than those of Ru-TiO2(IM) and Ir-TiO2(IM) due to the smaller sizes of RuO2 and IrO2. However, Mn-TiO2 and Co-TiO2 still display better photoactivities compared to those of Ru-TiO2(HT) and Ir-TiO2(HT). These results indicate that transition metal oxides with small sizes can also work as co-catalysts in photocatalysis to substitute noble metal oxides.