Controllable Synthesis And Properties Of Hierarchical Micro-/Nanostructures Of Iron-containing Compounds

In recent years, hierarchical micro-/nanostructures with peculiar morphologies andstructures, constructed by the self-assembly of these low-dimensional building blocks,have received more and more attention. These hierarchical micro-/nano structures notonly show the properties of nano-structured unit, but also show the properties generat-ed by the coupling effects and synergies effects. As a result, they exhibit distinguisha-ble electric, magnetic, optical, thenrmodynamic and mechanical properties. The synth-esisand self-organization of micro-and nanoscale inorganic materials with special mor-phology, size, and hierarchy become the foundamental for design and investigation no-vel nanodevices.Various synthetic methods have been devoted to the controlled synthesis of hierar-chical micro-/nanostructures with specific sizes and morphologies. Among them,solution-phase synthetic methods have many advantages, including relatively low reaction tem-peratures, convenience in handling, inexpensive reaction instruments, and ease in proc-edural control, making them very promising for the large scale synthesis of materials.In this thesis, several facile,cost-efficient and environmentally-friendly aqueous solutionroutes were developed for the synthesis of flower-like hierarchical micro-/nanostructure-s.under mild conditions. The main contents are as follows:1. In this article, flower-like hierarchical ferrihydrite microstructures were preparedby the simple oxidation and hydrolysis of ferric sulphate heptahydrate (FeSO47H2O)inthe presence of the citrate ion as a shape-directing/capping agent at room temperature.Owing to the less expensive and nontoxic raw reaction materials, especially water asthe solvent, our method represents an economic and green approach for the controlle-d synthesis of flower-like hierarchical ferrihydrite. Flower-like hierarchical ferrihydritemicrostructures exhibit enhanced photocatalytic activity, due to its novel hierarchical p-orous structure,higher surface area and citrate modification,possess better adsorption andphotocatalytic abilities.2. β-FeOOH microstructures with flower-like morphologies were successfully syn-thesized by a facile5-sulfosalicylic acid dihydrate (SSA)-assisted hydrothermal process.All chemicals used were low-cost compounds and environmentally benign. The resultsshowed that the chelating ligand SSA played important roles in the morphological con trol of the β-FeOOH microstructures. A possible formation mechanism was describedbased on the experimental results. The obtained flower-like β-FeOOH exhibited an ex-cellent adsorption capacity for Cr(VI) ions because of their high surface area and a g-ood ability to preserve the accessible surface. The effect of various parameters such ascontact time, adsorbent dosage, initial Cr(VI) concentration and pH has been studied.The Cr(VI) adsorption followed both the Langmuir and Freundlich’s equation isother-ms.3. Novel hierarchical Fe5(PO4)4(OH)32H2O hollow spheres were synthesized by afacile one-pot template-free hydrothermal method. All chemicals used were low-costcompounds and environmentally benign. The asprepared samples were characterized byFESEM, FT-IR spectroscopy, TEM, HRTEM, XRD and BET gas sorptometry. A poss-ible formation mechanism was described based on the experimental results.The obtaine-d Fe5(PO4)4(OH)32H2O hollow spheres exhibited an excellent adsorption capacity forCr(VI) ions because of their high surface area and a good ability to preserve the acc-essible surface.The effect of various parameters such as contact time, adsorbent dosage,initial Cr(VI) concentration and pH has been studied. The chromium (VI) adsorptionfollowed both the Langmuir and Freundlich’s equation isotherms.