Metal phosphate nanotubes with multiple and abundant elements of the inorganic frameworks have a wide range of applications in catalysis, photoelectronics, and electromagnetics. These unique properties are not found in carbon nanotubes and others inorganic nanotubes materials. Due to its structure peculiarities, it's very difficult to synthesize by means of the conventional template-assisted method. This thesis is aimed to research and develop the new method of synthesis the nickel phosphate nanotubes (NiPO-NTs) with an open skeleton structure by an organic template free method.In this thesis, NiPO-NTs with uniform pore structures were obtained via a simple urea-assisted hydrothermal route in the absence of organic surfactant as the structure-directing agent. The structure and apparent performance are studied by means of SEM, TEM, XRD, N2adsorption-desorption et al.. A possible mechanism of nanotube formation was proposed based on the time and temperature-dependent experimental evidence. The resulting NiPO-NTs were used to catalysis of epoxidation of cyclohexene. The main points can be summarized as follows:(1) Nickel phosphate nanotubes (NiPO-NTs), with outer diameter of6.5-7.0nm, inner diameter of3.4-4.0nm, and length of around0.75μm, were obtained via a simple urea-assisted hydrothermal route in the absence of organic surfactant as the structure-directing agent. The effects of reaction temperature, urea/Ni2+molar ratio, and pH value on the stucture of NiPO-NTs were investigated. It is indicated that increase of reaction temperature can increase the hydrolysis rate of urea in aqueous solution, and then there have a fast pH variation and fast precipitation of NiPO. The compactly packed tubes were obtained at high reaction temperature (120℃) and the loose tubes were obtained at low temperature (90℃).(2) Based on the time and temperature-dependent experimental evidence, a mechanism for the formation of NiPO-NTs is proposed. During the heating process of the mixture, urea undergoes hydrolysis to release NH4+and OH-, which leads to the rise of the pH in the solution. The increased pH leads to the initially fast formation of porous spheres structures. After the formation of porous sphere structures, urea will concentrate on the outer surface of the NiPO spheres due to the urea molecule with abundant nitrogen and oxygen atoms, easily form hydrogen bonding with metal atoms. The urea molecule on the outer surface of the NiPO spheres will continuously hydrolyze, resulting in increased local pH on the outer surface of the sphere. Therefore, nickel phosphates will precipitate around the outer surface of the NiPO sphere. The rate of the urea hydrolysis decreased in the basic environment. The slight variation of the pH value lead to the slowly precipitate of NiPO, and the precipitation may give rise to the formation of short nanotubes by a self-assembly mechanism. Meanwhile, the Ni2+and PO43-or HPO42-would sequentially precipitate on the tips of the NTs, because the tip of the NTs usually possesses a larger free enthalpy due to the small surface. The gradual depositions of NiPO around the tip of the tubes lead to the growth of the NiPO-NTs. The driving force of the total free enthalpy may be responsible for the morphology development.(3) NiPO-NTs were used to catalyze the epoxidation of cyclohexene using hydrogen peroxide as the oxidant. The effect of reaction conditions on epoxidation reaction of cyclohexene was reviewed. High cyclohexene conversion (50.6%) and selectivity for epoxycyclohexane (72.1%) were obtained at60℃,6h, and H2O2/cyclohexene of3.(4) Bulk Ni2P catalysts with high surface area were prepared by NiPO-NTs as precursor. The Ni2P catalysts show high activity in the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions. The investigation of the effect of the final reduction temperature of catalysts on the HDS performance indicates that the highly active nickel phosphides catalysts can be obtained when final reduction temperature was in range of500-550℃.(5) Binary metallophosphate nanotubes (CoNiPO, FeNiPO and TiNiPO NTs) have been synthesized by the addition of urea under hydrothermal conditions. Structure and morphology of the NTs were investigated by XRD, TEM, UV-Visible, and N2adsorption-desorption. It is confirmed that cobalt or ion atom incorporated into the nickel phosphate nanotubes (NiPO-NTs) framework. |