α-zirconium phosphate (α-ZrP) crystals with high-crystallinity were synthesized via hydrothermal method and exfoliated with tetrabutylammonium hydroxide (TBAOH) in aqueous dispersion maintained at 0℃ in an ice bath. The exfoliated α-ZrP nano-sheets were then transferred into selected organic solvents, such as acetone, via centrifugal precipitation and re-dispersion process. This process was repeated 3 to 5 times to replace the water with the desired organic solvents. During the solvent-replacing process, most of the free TBAOH in α-ZrP/H₂O dispersion was also removed, which was confirmed by characterizing the organic contents via thermo-gravimetric analysis for the solids obtained from both the water dispersion and the resulted acetone dispersion. Serendipitously, the dispersions of α-ZrP/organic solvent with structural colors could be easily obtained using this solvent-replacement method. After the solvent-replacing process was repeated for 5 times, the resulted α-ZrP/acetone dispersions could reflect visible light in the range of 426 nm to 635 nm when the mass fraction of α-ZrP was between 0.76% and 1.86%, thus showing the corresponding structural colors. Increasing the concentration of TBA⁺ ions in α-ZrP/acetone dispersion (α-ZrP mass fraction 0.87%), its UV-Vis reflection spectrum showed a blue-shift, indicating that the formation of periodic structures mainly depended on the electrostatic repulsion between α-ZrP nano-sheets. The formation of structural color also showed a size-dependence on the exfoliated α-ZrP nano-sheets. The nano-sheets with large-size was more likely to form the long-range ordered structure showing structural color compared with the relatively small ones (1.10 μm vs. 0.48 μm). The dispersions with acetonitrile or butyronitrile as solvent, which exhibited obvious structural colors, could also be obtained using this solvent-replacement method. At present, many plate-like inorganic particles used in the research have intrinsic charges on their gallery faces that similar to the microstructure of α-ZrP crystals, so the method reported here can give general guidance for the preparation of the dispersions with long-range periodic structures for these particles.

Key words: α-zirconium phosphate, nano-sheets, dispersion, liquid crystal phase, structural color