Synthesis of Na-doped ZnO hollow spheres with improved photocatalytic activity for hydrogen production.

The fabrication of p-type doped ZnO nanostructures is key in opening up substantial opportunities for the application of ZnO nanostructures. Owing to their stable p-type property, Na ions are the best candidates for ZnO p-type doping. However, Na-doped ZnO nanostructures had never been prepared until now. For the first time, we successfully synthesized Na-doped ZnO ultrathin hollow spheres using an ion adsorption and templating method. The obtained hollow spheres have ultrathin shells, uniform Na elemental distribution and a controllable concentration of doped Na. The energy position of the Fermi level decreased with continuously increasing Na doping concentration, revealing the p-type conductivity of Na-doped ZnO. We demonstrate that the photocatalytic hydrogen generation efficiency (with methanol) using ZnO ultrathin hollow spheres can be enhanced by more than 50 times after Na-doping and that the quantum efficiency can be as high as 13.5%.