Abstract
A bottom-up-then-up-down route was proposed to construct multi-level Bi2S3 hierarchical architectures assembled by two-dimensional (2D) Bi2S3 sheet-like networks. BiOCOOH hollow spheres and flower-like structures, which are both assembled by 2D BiOCOOH nanosheets, were prepared first by a “bottom-up” route through a “quasi-emulsion” mechanism. Then the BiOCOOH hierarchical structures were transferred to hierarchical Bi2S3 architectures through an “up-down” route by an ion exchange method. The obtained Bi2S3 nanostructures remain hollow-spherical and flower-like structures of the precursors but the constructing blocks are changed to 2D sheet-like networks interweaving by Bi2S3 nanowires. The close matching of crystal lattices between Bi2S3 and BiOCOOH was believed to be the key reason for the topotactic transformation from BiOCOOH nanosheets to 2D Bi2S3 sheet-like nanowire networks. Magnetism studies reveal that unlike diamagnetism of comparative Bi2S3 nanostructures, the obtained multi-level Bi2S3 structures display S-type hysteresis and ferromagnetism at low field which might result from ordered structure of 2D networks.
Highlights
A bottom-up--up-down route was proposed to construct multi-level Bi2S3 hierarchical architectures assembled by two-dimensional (2D) Bi2S3 sheet-like networks
Hollow spherical and flower-like BiOCOOH structures assembled by BiOCOOH nanosheets were first prepared by a “bottom-up” route through a “quasi-emulsion” mechanism
The morphology of the sample was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)
Summary
The BiOCOOH structure were prepared by solvothermally treating Bi(NO3)[3] in glycerol, H2O and DMF mixture. Without the addition of glycerol, no hierarchical BiOCOOH hollow spheres but flower-like BiOCOOH structures assembled by sheet-like BiOCOOH (XRD pattern is shown in Fig. 1b) were obtained as SEM images in Fig. 2e and f display. Novel multi-level Bi2S3 superstructures, hollow spheres and flower-like structures constructed by 2D sheet-like networks, have been successfully synthesized using BiOCOOH as the precursors through a “bottom-up--up-down” topotactic transformation process. The glycerol in the reaction system plays an important role for the formation of hierarchical BiOCOOH hollow structures and the crystal lattice matching is demonstrated to be responsible for the topotactic transformation from BiOCOOH to Bi2S3 to construct the multi-level hierarchical structures. Unlike diamagnetism of comparative Bi2S3 nanostructures, the obtained multi-level Bi2S3 structures display ferromagnetism at low field
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