Novel hybrid self-assembly of an ultralarge ZnO macroflower and defect intensity-induced photocurrent and photocatalytic properties by facile hydrothermal synthesis using CO(NH2)2-N2H4 as alkali sources

Different flower-like ZnO nanoarchitectures were synthesized by a facile hydrothermal method using CO(NH2)2 and N2H4 as alkali sources simultaneously. A novel ultralarge ZnO macroflower was constructed by the ultrathin leaf-like nanobelts, hollow semisphere-like, sphere-like and apple-shaped nanoparticles simultaneously. The diameter of an individual flower can reach 90 µm. Meanwhile, three or five flower-like ZnO nanostructures with different diameters, lengths and tips (Planar, semi-pyramid, and/ or pyramid tips) were formed simultaneously under the same reaction condition. XRD shows that all the ZnO crystals possess the hexagonal wurtzite structure. When the samples range from S1 to S5, the crystallinity is improved. EDX shows that the Zn/ O atom ratio of S1-S5 is close to the 1:1 stoichiometric ratio, and that of S3 is almost equal to 1:1. FTIR indicates that S4 and S5 are pure. However, the surface of S1, S2 and S3 adsorbs the CO32− group. The reflectance of S1-S4 in the range of 300-370 nm is inversely proportional to that in visible region. Meanwhile, when the grain size of S1-S4 decreases, their band gap increases. The Raman results of S1 and S5 are different from those of S4 and exhibit the higher crystal quality, which are favorable for the improvement of photocatalytic performance. S1 and S5 exhibit the highest photocatalytic performance and decompose 65% and 70% of MB within 50 min respectively. The photocatalytic activity and photocurrent strongly depend on the defect intensity of the ZnO crystals. The ZnO photocatalyst of S5 is still stable and efficient after three cycles. However, the photocatalytic activity of S1 decreases continuously, due to its unique morphology and the adsorption of intermediates. In addition, A hybrid self-assembly process of the ultralarge ZnO macroflower was proposed.