Synthesis of Boehmite Hollow Core/Shell and Hollow Microspheres via Sodium Tartrate-Mediated Phase Transformation and Their Enhanced Adsorption Performance in Water Treatment

Abstract

A variety of boehmite hollow core/shell and hollow microspheres with high adsorption affinity toward organic pollutants in water were prepared via a facile one-pot hydrothermal method using aluminum sulfate as a precursor and urea and sodium tartrate as precipitating and mediating agents, respectively. These microspheres were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption. In addition, the aforementioned microspheres were examined as potential adsorbents for Congo red and phenol from aqueous solutions. This study shows that the crystallinity, specific surface area, and pore structure of the resulting microspheres can be controlled by varying the concentration of sodium tartrate and reaction time. The reported experiments allowed us to propose the mechanism of formation of hollow core/shell and hollow microspheres, which involves sodium tartrate-mediated phase transformation, followed by a subsequent self-assembly process. Adsorption performance of the boehmite microspheres studied is gradually enhanced with increasing concentration of sodium tartrate. This enhancement is substantial in comparison to the performance of the microspheres prepared without sodium tartrate and commercial boehmite powders, and it is probably due to several factors, such as high specific surface area, large pore volume, proper crystallite size, and unique core/shell morphology and structure of the aforementioned microspheres. Especially, the hollow core/shell microspheres prepared at 0.01 M concentration of sodium tartrate exhibited the best adsorption performance, which can be easily regenerated without any great loss in the adsorption capacity. This study suggests that the degree of chemical self-transformation of amorphous particles into crystalline shells, followed by their self-assembly into complex higher-order architectures with desirable functionality, can be mediated by simple organic anions.