Fabrication of orderly changed ZnO hierarchical structures by calcining different zinc precursors and morphology-depended photocatalytic property

Different zinc precursors, Zn-5(OH)(6)(CO3)(2) (S1), the mixture of Zn-5(OH)(6)(CO3)(2) and ZnCO3 (S-2), and ZnCO3 (S3) were formed by simple hydrothermal method using different amount of reagents, and then these zinc precursors were calcined to produce various hierarchical morphologies of ZnO: nanosheets, nanospheres and/or microrods in an orderly way. In other words, different zinc precursors correspond to various morphologies. The addition of NH4F inhibits the formation of OH-, and increases the concentration of CO32-, which leads to the presence of zinc precursor of ZnCO3 and novel microrod-based ZnO structure after calcination. Comparing to S1 and S-2, the H-2 evolution rate of the microd-based S-3 is significantly enhanced, which value is 223.43 mu mol.g(-1) after 4 h. According to the discussion of the structure, morphology, composition, and surface area, optical and photocatalytic properties of ZnO particles, it is obvious that the charge transfer efficiency and specific surface area are not the key effect factors in photocatalytic process, and the orderly changed morphologies lead to the transformation of active planes from (002) to (100) and the improvement of electron excitation ability, which may be favourable for the enhancement of photocatalytic H2 evolution. The photocatalytic mechanism of ZnO was proposed.

Automated summary

By adjusting the reagent dosage and adding NH4F, different zinc precursors were synthesized by hydrothermal method, resulting in various ordered morphologies of ZnO. It was found that ZnO with microrod morphology exhibited enhanced photocatalytic hydrogen evolution activity.