Morphology modulation of SnO photocatalyst: from microplate to hierarchical architectures self-assembled with thickness controllable nanosheets

Shape-controllable SnO microstructures were successfully synthesized via a facile inorganic alkali-assisted hydrothermal method. The morphologies of the prepared samples could be simply modulated from plate-like blocks to hierarchical architectures assembled using nanosheets with tuned thicknesses, including flowers, bird nests and microspheres, through varying the alkali used in the synthesis process. Based on the experimental results, the origins and detailed formation mechanisms of the plate-like and hierarchical SnO architectures were comprehensively proposed. It was found that the formation of SnO was governed by dissolution-recrystallization and an oriented attachment process; the different dissociation rates of various alkalis played an important role in the final SnO morphology. The thicknesses of the assembling nanosheets greatly decreased with an increase in the dissociation rates of the alkalis. Furthermore, it was proved experimentally that all the hierarchical SnO structures exhibited better photocatalytic activities than those of the plate-like structures in the photodegradation of MB under fluorescent and UV light irradiation. The microspheres, with decreased size and assembling nanosheets of decreased thickness, showed the highest activity for MB dye degradation owing to an increased specific surface area and the reduced recombination of photogenerated electron-hole pairs. The mechanism for the photocatalytic degradation of MB over SnO was discussed in detail.