Cu(II) nanocluster-grafted, Nb-doped TiO2 as an efficient visible-light-sensitive photocatalyst based on energy-level matching between surface and bulk states

Although visible-light-sensitive photocatalysis has been reported for cupreous ion (Cu(II)) nanocluster-grafted titanium dioxide (TiO2), the visible-light absorption (alpha) of this system is relatively low because of its limited interfacial excitation. In the present study, we synthesized niobium, (Nb)-doped TiO2 grafted with Cu(II) nanoclusters and examined its capacity for visible-light absorption and photocatalytic activity for decomposing organic molecules. We speculated that the matching of energy levels between the surface Cu(II) nanoclusters and bulk-doped Nb ions would markedly increase the visible-light activity of TiO2. The doped Nb ions produced partially occupied energy levels below the conduction band of TiO2 that closely matched the potential of the Cu2+/Cu+ redox couple in the surface-grafted Cu(II) nanoclusters. The well-matched energy levels induced the effective transfer of photogenerated electrons from the doped Nb states to the surface-grafted Cu(II) nanoclusters, which mediated the efficient multi-electron reduction of oxygen molecules. The prepared Cu(II)-NbxTi1-xO2 nanocomposites exhibited a high photocatalytic reaction rate for the decomposition of 2-propanol into CO2 under visible light. Our results demonstrate that efficient photocatalysts can be generated by matching the energy levels of bulk-doped ions and surface nanoclusters, which represents a strategic approach for the rational design and development of high-performance photocatalysts.