Competence Center for Micro- and Nanotechnologies

A novel route to synthesize large area ZnO/Zn(OH)2 origami thin films at air/liquid interface is reported. ZnO materials derived from this route show the largest blue-shifted band-to-band emission at 3.85 eV (3.37 eV in bulk ZnO) so far, resulting from the quantum confinement in the ultrathin ZnO/Zn(OH)2 nanosheets. Interband defect levels (IDLs) related broadband photoluminescence is observed from UV to red region by excitation wavelength dependent photoluminescence measurements. The ZnO origami structures show photocatalytic methylene blue degradation (MB-degradation) activity even under sub-bandgap visible light illumination from 405 nm to green region at 505 nm, measured by low power monochromatic light emitting diode light sources. From the consistent light absorption, luminescence, and MB-degradation activity, it can be concluded that the broadband visible light MB-degradation activity is attributed to photogenerated carriers via IDLs. The 2D ZnO-nanosheets in the origami structure better solve the dilemma of the IDLs in bulk materials, i.e., they are beneficial for light absorption in visible range but detrimental for enhanced recombination loss of carriers, and they can be quickly extracted to the surface without substantial recombination. This finding makes the ZnO origami a promising candidate for efficient photocatalyst that harvesting the sunlight and for indoor applications.