From bulk metal Bi to two-dimensional well-crystallized BiOX (X = Cl, Br) micro- and nanostructures: Synthesis and characterization

In this article, for the first time, two-dimensional (2D) single-crystalline bismuth oxyhalides (BiOX, X = Cl, Br) micro- and nanostructures, such as nanoplates, nanosheets, and microsheets, were synthesized in a large scale by a simple wet chemistry approach of hydrogen peroxide (H(2)O(2)) direct oxidation of bulk metal bismuth (Bi) particles in a mixed solution followed by a hydrothermal treatment, instead of previous coprecipitation of Bi salts route. The in-plane size and thickness of the 2D products can be conveniently tailored by varying the temperature and the concentrations of the Bi precursor. The products were characterized by a range of methods, such as X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction, thermogravimetric analysis, Fourier transform infrared spectra, and UV-vis diffuse reflectance spectra. The BiOBr nanoplates, nanosheets, and microsheets have also been selectively synthesized via a similar route. The formation process investigation revealed that under hydrothermal treatment the spherical Bi oxhydrohalide nanopariticles could be side-by-side self-assembled to form Bi oxyhalide nanoplates by increasing the in-plane size, and nanosheets could be piled up to form Bi oxyhalide thick microsheets by increasing the thickness. The UV-vis diffuse reflectance spectra revealed that the estimated band gap energies were about 3.5, 3.3, 2.3, and 2.1 eV for BiOCl nanoplates, BiOCl micro- and nanosheets, BiOBr nanoplates, and BiOBr micro- and nanosheets, respectively. It is expected that the present study could be extended to facile, large-scale synthesis of various multicomponent 2D inorganic micro- and nanostructures, which would have better performances than the corresponding spherical nanoparticles and would be the new members in the family of advanced functional inorganic materials well-applied in industry.