Monodispersed hollow aluminosilica microsphere@hierarchical γ-AlOOH deposited with or without Fe(OH)₃ nanoparticles for efficient adsorption of organic pollutants

Some conventional micro- or nano-structured adsorbents are subject to the problem that they can hardly show most of their adsorption sites for adsorbing pollutants in solution because of serious aggregation of adsorbents. Here, monodispersed hollow aluminosilica microsphere (HAM)hierarchical γ-AlOOH nanomaterials have been first synthesized via a simple one-step template method. Positively charged Fe(OH)₃ colloid nanoparticles with a diameter of about 4 nm have been effectively deposited onto the negatively charged surfaces of the hierarchical γ-AlOOH nanosheets to form HAMγ-AlOOH/Fe(OH)₃ with hierarchical structure via electrostatic attraction without forming large aggregates. Both the HAMγ-AlOOH and HAMγ-AlOOH/Fe(OH)₃ with hierarchical structure have high specific surface areas and large pore volumes. The HAMγ-AlOOH with the electronegative surface and the HAMγ-AlOOH/Fe(OH)₃ with the electropositive surface are used as adsorbents to remove methylene blue (MB) (cationic dye) and congo red (CR) (anionic dye) from aqueous solution, respectively. The maximum capacities of the monodispersed HAMγ-AlOOH and HAMγ-AlOOH/Fe(OH)₃ with hierarchical structure for MB and CR are determined to be 87.80 mg g^-1 and 252.53 mg g^-1, respectively, which are higher than those of other metal oxide nanostructures reported to date. In addition, the adsorption rates of MB and CR onto the monodispersed HAMγ-AlOOH and HAMγ-AlOOH/Fe(OH)₃ with hierarchical structure are rather fast. This study also shows that efficient adsorbents for organic pollutant removal can be designed by depositing nanoparticles with high adsorption capacity on mesoporous supports with abundant surface hydroxyl groups and a large surface area.