Solution-Based Chemical Synthesis, Growth Mechanism And Catalytic Property Of Nanomaterial

Based on the development of the solution methodology to synthesize nanomaterials with catalytic properties nowadays,we have synthesized the newly emerging microporous molecular sieve of VSB-5 and TiO₂ nanostructures with distinctive photocatalytic properties.The distinctive growth and transformation process of TiO₂ crystal includes the classical crystal growth mechanism and the nonclassical one of mesocrystal formation and oriented attachment.It is found that the transformation of TiO₂ mesocrystals to single crystal proceeds based on the mechanism of oriented attachment.Considering the significance of VSB-5 and TiO₂ in the area of catalytic materials,we chose them as the model system in this dissertation.The main results can be summarized as follows:1.By using hexamethylenetetramine(HMT) as a structure-directing agent, NaH₂PO₂ as a reducing agent and phosphor source,VSB-5 microspheres assembled by wires and rods with different ranges of diameters and aspect ratios can be obtained hydrothermally via adjusting the pH value of the reaction solution with control of the precipitation rate ofα-Ni(OH)₂ and redox rate of HPO₂^- to PO₄^3-.It is demonstrated that the pH value,reaction time as well as the ratio of HMT to NaHPO₂·H₂O have crucial influence on the morphology and quality of the final products.In addition,the catalytic property of VSB-5 in selective hydrogenation of several unsaturated organic compounds such as trans-cinnamaldehyde(CAL), 3-methylcrotonaldehyde(MCA),nitrobenzene(NB) and 2-chloronitrobenzene (2-CNB) has been tested.The results demonstrated that Ni(â…¡) in VSB-5 have the catalytic activity in the process of selective catalytic hydrogenation,showing that a new kind of catalyst has sprout out and the VSB-5 would have potential applications in developing dyes,agrochemicals,and pharmaceuticals perfume industries.2.Novel TiO₂ microboxes and tree-like structures assembled by hollow cubes via conversion from the rectangular particulates with cracks and a composition of (TiO₂)₂·C₄H₆O₅·6H₂O can be synthesized in large scales by a simple hydrothermal method.It is demonstrated that the boxes grow with double-layer walls and in the inner part there may exist inserted layers or several separate room.The influences of the reaction time,temperature and molar ratio between D,L-malic acid and TiCl₄ on the formation of this distinctive structure have been investigated in detail.The results demonstrate that a larger molar ratio of D,L-malic acid and TiCl₄ would benefit for the formation of TiO₂ hollow boxes with larger aspect ratios.Moreover, these distinctive structures show excellent photocatalytic properties,which would find potential applications in photocatalytic fields.3.Using N,N'-dicyclohexylcarbodiimide(DCC) and L-serine as biologic additives,rutile TiO₂ hollow spheres assembled by nanorods can be synthesized by a simple hydrothermal reaction route.A distinctive crystallization and transformation routte of the rutile TiO₂ hollow spheres has been proposed,which includes emergence of polycrystalline,mesoscale transformation to mesocrystals with morphologies of sectors,transformation of mesocrystals to bundles of rods based on oriented attachment,the simultaneous assembled process of sectors to solid spheres,and a cavitating process of solid spheres through the Ostwald ripening mechanism.Two ways of oriented attachment,side-by-side and end-to-end,were observed during the assembly process.It has been found that the presence of DCC and L-serine and their synergistic effects are essential for the formation of rutile TiO₂ hollow spheres.The stability of the rutile TiO₂ mesocrystals has been studied.The results revealed that the mesocrystals could be maintained longer at lower temperature,while proper choice of organic additives can also enhance the stability of mesocrystals at higher temperature under solution conditions.