Understanding the Effect Models of Ionic Liquids in the Synthesis of NH4-Dw and γ-AlOOH Nanostructures and Their Conversion into Porous γ-Al2O3

Well-dispersed ammonium aluminum carbonate hydroxide (NH4-Dw) and gamma-AlOOH nanostructures with controlled morphologies have been synthesized by employing an ionic-liquid-assisted hydrothermal process. The basic strategies that were used in this work were: 1) A controllable phase transition from NH4-Dw to gamma-AlOOH could be realized by increasing the reaction temperature and 2) the morphological evolution of NH4-Dw and gamma-AlOOH nanostructures could be influenced by the concentration of the ionic liquid. Based on these experimental results, the main objective of this work was to clarify the effect models of the ionic liquids on the synthesis of NH4-Dw and gamma-AlOOH nanostructures, which could be divided into cationic- or anionic-dominant effect models, as determined by the different surface structures of the targets. Specifically, under the cationic-dominant regime, the ionic liquids mainly showed dispersion effects for the NH4-Dw nanostructures, whereas the anionic-dominant model could induce the self-assembly of the gamma-AlOOH particles to form hierarchical structures. Under the guidance of the proposed models, the effect of the ionic liquids would be optimized by an appropriate choice of cations or anions, as well as by considering the different effect models with the substrate surface. We expect that such effect models between ionic liquids and the target products will be helpful for understanding and designing rational ionic liquids that contain specific functional groups, thus open up new opportunities for the synthesis of inorganic nanomaterials with new morphologies and improved properties. In addition, these as-prepared NH4-Dw and gamma-AlOOH nanostructures were converted into porous gamma-Al2O3 nanostructures by thermal decomposition, whilst preserving the same morphology. By using HRTEM and nitrogen-adsorption analysis, the obtained gamma-Al2O3 samples were found to have excellent porous properties and, hence, may have applications in catalysis and adsorption.