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

Abstract

Different zinc precursors, Zn 5 (OH) 6 (CO 3 ) 2 (S1), the mixture of Zn 5 (OH) 6 (CO 3 ) 2 and ZnCO 3 (S2), and ZnCO 3 (S3) can be formed by simple hydrothermal method using different amount of reagents, and then these different zinc precursors were calcined to produce orderly changed morphologies of hierarchical ZnO: nanosheets, nanospheres and/or microrods. The addition of NH 4 F inhibits the formation of OH – , and increases the concentration of CO 3 2– , which leads to the presence of zinc precursor of ZnCO 3 and the formation of novel microrod-based ZnO after calcination. To our best knowledge that when HMT or CO(NH 2 ) 2 was added to the reaction solution, the presence of the precursor of ZnCO 3 and/or the microd-based ZnO was not reported under these solution environment. Comparing to S1 and S2, the H 2 evolution rate of the microd-based S3 is significantly enhanced, which value is 223.43 μmol*g −1 after 4h. The orderly changed morphologies lead to the transformation of active planes from (0 0 2) to (1 0 0) and the improvement of electron excitation ability, which may be favourable for the improvement of photocatalytic H 2 evolution. Different zinc precursors, Zn 5 (OH) 6 (CO 3 ) 2 (S1), the mixture of Zn 5 (OH) 6 (CO 3 ) 2 and ZnCO 3 (S2), and ZnCO 3 (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 NH 4 F inhibits the formation of OH – , and increases the concentration of CO 3 2– , which leads to the presence of zinc precursor of ZnCO 3 and novel microrod-based ZnO structure after calcination. Comparing to S1 and S2, the H 2 evolution rate of the microd-based S3 is significantly enhanced, which value is 223.43 μmol·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 (0 0 2) to (1 0 0) and the improvement of electron excitation ability, which may be favourable for the enhancement of photocatalytic H 2 evolution. The photocatalytic mechanism of ZnO was proposed.