Fabrication Of Porous Hierarchical AlOOH Via Template-free Hydrothermal Method And Its Adsorption Properties

In this paper, hierarchical γ-AlOOH materials were prepared by a template-free hydrothermal method using inorganic salts as precipitating agent. In addtition, the adsorption properties towards organic dyes were also investigated. The main researches are as followed:Using NaHCO3 as the precipitating agent and Al(NO3)3 as the aluminium sources, the influence of concentration of NaHCO3 and Al(NO3)3 on products’ morphology was discussed. Monodispersed, uniform ellipsoid-like hierarchical γ-AlOOH were parpared when adding amounts of Al(NO3)3 and NaHCO3 were 10 mmol at 190℃ for 24 h. It find that the samples have an average length of 1.4 μm and width of 0.7μm. Using Na2C2O3 as the precipitating agent and Al(NO3)3 as the aluminium sources, the influence of addtion amount of Na2C2O3 on products’ morphology was discussed. Hollow ellipsoid-like hierarchical γ-AlOOH were parpared when adding amounts of Na2C2O3 was 2mmol at 190℃ for 24 h. It find that the samples have an average length of 1.7-2.2μm and width of 0.8-1.0μm. Using Na2HPO4 as the precipitating agent and Al(NO3)3 as the aluminium sources, the influence of addtion amount of Na2HPO4 on products’ morphology was discussed. Monodispersed,uniform,bundle-like hierarchical AlOOH were parpared when adding amount of Na2HPO4 was 1mmol at 190℃ for 24 h. It find that the samples have an length of 3.3-4.0μm, end width of 2.0μm, middle width of 1.1μm. Using Na3PO4 and Al(NO3)3 as raw material, the influence of addtion amount of Na3PO4 was investigated. Bundle-like hierarchical γ-AlOOH were parpared when adding amount of Na3PO4 was 1mmol at 190℃ for 24 h. It find that the samples have an length of 2.5-3.3μm, width of 0.9-1.6μm.The formation mechanism of hierarchical boehmite is as follow: in the hydrothermal process, inorganic salts will hydrolyze and gives rise to OH- ions and then colloids Al(OH)3 would be formed, with subsequent increase in reaction time, AlOOH is obtained from the early formed Al(OH)3 colloids in Ostwald ripening process. The surface energy is changed and the growth direction is changed due to the inorganic anion is adsorbed to boehmite surface. At the same time, inorganic anion can reduce the repulsion between the particles of boehmites, the boehmite are assembled together under the action of van der Waals forces to form a hierarchical structure.The adsorption experiments tawords organic dye were conducted using the obtained boehmite as adsorbent. The results indicated that the obtained γ-AlOOH showed good adsorption properties towards congo red. For NaHCO3, the maximum adsorption capacity of ellipsoid-like γ-AlOOH was 97.9mg/g. For Na2C2O3, the hollow elliosoid–like γ-AlOOH prepared by adding 2mmol Na2C2O3 showed a maximum adsorption capacity of 99mg/g. For Na2HPO4, the bundle-like hierarchical γ-AlOOH with 2mmol Na2HPO4 adding showed a maximum adsorption capacity of 98.6mg/g. For Na3PO4, the bundle-like hierarchical AlOOH with 1mmol Na3PO4 adding showed a maximum adsorption capacity of 99.4mg/g. For other dyes, the obtained boehmite showed a certain adsorption capacity towards acid chrome blue K, and no adsorption capacity for methylene blue.