Template-free solvothermal synthesis of hierarchical boehmite hollow microspheres with strong affinity toward organic pollutants in water

Three-dimensional hierarchical boehmite hollow microspheres with a very high yield at low cost were successfully synthesized via a one-pot template-free solvothermal route using aluminum chloride hexahydrate as precursor in a mixed ethanol–water solution with assistance of trisodium citrate. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption/desorption techniques. The results show that Cl− and addition amount of trisodium citrate have significant effect on the morphologies of the resultant products, and 6–8 mmol of trisodium citrate is optimal for the synthesis of boehmite hollow microspheres assembled from randomly interconnecting and aligned nanorods with solvothermal time no less than 15 h. A synergistic mediation mechanism of citrate ions and Cl− to form boehmite hollow spheres via self-assembly morphology evolution was proposed based on the experimental results. Interestingly, the typical boehmite hollow microspheres with a surface area of 102 m2 g−1, pore volume of 0.37 cm3 g−1, and the average pore size of 14.6 nm show superb adsorption properties for Congo red with maximum capacity of 114.7 mg g−1 which is higher than that of a commercial boehmite. This simple synthetic route is a very promising way for the design and synthesis of new functional hierarchical nanostructured materials with desired adsorptive properties.

Boehmite hollow microspheres with strong affinity toward organic pollutants were successfully synthesized via a one-pot template-free solvothermal route using AlCl3·6H2O as aluminum precursor in a mixed ethanol–water solution with assistance of trisodium citrate, and its adsorption performance toward Congo red is much higher than that of the commercial boehmite powder due to its unique hollow structure. Figure optionsDownload as PowerPoint slideHighlights
► Boehmite hollow microspheres were solvothermally synthesized from AlCl3·6H2O.
► Diameter of the boehmite microspheres assembled from nanorods varies between 3 and 6 μm.
► The surface nanorods aligned in an ordered fashion show mean thick of 60 nm.
► Morphology changes of boehmite are dependent on the trisodium citrate concentration.
► The boehmite microspheres show good adsorption performance toward Congo red.