Mechanism Study On Aggregation And Dissolution Processes Ofγ-AlOOH Nanoparticles Due To The Effect Of Inorganic Acid

Identification of the key factors of morphology control in nanomaterial synthesis is important for mechanistic understanding of the reactivity-structure relationship and rational design of crystals with desired morphology. Among others, the inorganic ions in solution were found to be important in controlling the final morphology of metal oxide or metal hydroxide. The investigation of metal oxide or metal hydroxide and inorganic ion interface at the atomic level represents a fundamental issue for the understanding of chemical and physical processes involved in several fields such as catalysis, adsorption, directed synthesis and mechanism study of crystal growth. In this paper, a combined hydrothermal synthesis and computational approach based on DFT theory are adopted to investigate the aggregation and dissolution process of y-AlOOH nanoparticles under the effect of inorganic ions. Morphologies predicted by DFT calculations are consistent with the experimental results, which not only explains the formation process of y-AlOOH nanocrystals with different morphologies, but also provides a thought to research on the interactions between metal oxide or metal hydroxide and inorganic ion.1. Study of the formation mechanism of boehmite with different morphology upon surface hydroxyls and adsorption of chloride ionsThe y-AlOOH nanocrystals with different morphologies were prepared using y-AlOOH nanoparticles, NaCl and HCl as raw materials. Experimental results revealed that nanoplanes and nanorods were obtained under neutral and acidic environment, respectively. To reveal the effect of inorganic ions, the boehmite with different morphologies influenced by chloride ions was studied by a combined experimental and computational approach. The quantum mechanical calculations reveal that the chloride ions interact with crystal planes through surface hydroxyls and act as morphology-directing agent by planes protection. The HR-TEM images reveal the growth directions and exposed planes of the boehmite, indicating an oriented-aggregation process which is consistent with the DFT calculations. It is envisaged that the defects caused by excessive hydrochloric acid is due to its dissolving property combined with the reduction of adsorption energies. Overall, all the morphologies of boehmite suggested by the calculations are confirmed by experimental results.2. Synthesis of y-AlOOH nanocrystals with different morphologies under sulfate ion and corresponding formation mechanism studyIn this paper, a combined hydrothermal synthesis and computational approach based on DFT theory are adopted to investigate the effects of sulfate ions on the final morphologies of y-AlOOH. The quantum mechanical calculations reveal that the sulfate ions interact with y-AlOOH facets through surface hydroxyls and act as morphology-directing agent. The adsorption type and chemical bonds between sulfate ion and y-AlOOH are discussed. Through the time-dependent experimental TEM analysis, the formation of nanosheet and nanorod of y-AlOOH are controlled by thermodynamic factors. Moreover, The HR-TEM images reveal the growth directions and exposed planes of the boehmite, indicating an oriented-aggregation process which is consistent with the DFT calculations. Overall, all the morphologies of boehmite suggested by the calculations are confirmed by experimental results.3. Large-scale synthesis and formation mechanism study of basic aluminium sulfate microcubic crystalsCubic-like basic aluminium sulfate crystals were prepared by a facile template-free hydrothermal strategy. The microstructures, morphologies and textual properties of as-synthesized material were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy. X-ray crystallography reveals cubic basic aluminium sulfate possesses single crystal nature. Chemical formation mechanism studies of sulfuric acid with y-AlOOH were performed using a combined experimental and computational approach. Time dependent experiments reveal formation of basic aluminium sulfate is based on dissolution-recrystallization process, and source of Al3+is only dissolved from y-AlOOH in high H+concentration. Moreover, the quantum mechanical calculations reveals that dramatic structural changes occurred in (100) plane under high H+concentration which is inferred to be the initiation for source of Al3+. Meanwhile, surface energy calculations can well explain the exposed plane of basic aluminium sulfate microcubes which is consistent with the XRD result. Besides, equations to quantitative describe the relationship of the molar amount of H+and final phase is proposed which has been confirmed by experimental results.4. A facile strategy to fabricate large-scale uniform mesoporous γ-Al2O3microcubes with high thermal stability and good adsorption performance towards Cr2O72-A facile route is initiated to fabricate uniform mesoporous γ-Al2O3, with a three-dimensional micro/nanostructure, based on a combination of template-free hydrothermal and sequential calcination strategy. The as-synthesized γ-Al2O3is cubic-like in morphology with an average size of ca.6(μm and formation mechanism is attributed to the in situ transformation process. Mesoporous γ-Al2O3synthesized by this method is highly thermal stable, indicating it could be used in high-temperature catalysis. Furthermore, such γ-Al2O3microcubes exhibited superior adsorption performance (maximum adsorption capacity9.93mg/g) with good recycling efficiency (more than76%of its original adsorption capacity after4cycles) as an adsorbent to remove the heavy metal ions Cr(VI) as a result of its unique structure, which made it to be a promising material for environmental remediation.