Interfacial Synthesis And Properties Of Composite Silica Nanotubes

As one-dimensional materials,nanotubes have attracted much attention due to their high length diameter ratio,continuous hollow structure and easily modification of inner and outer surfaces.Janus particles are integration of different shapes or physical properties/chemical components and their shapes,surface groups,functions or structures are clearly divided.In order to find a facile method for preparing asymmetric silica nanotubes,tadpole-like organosilica nanotubes and tadpole-like Janus organosilica nanotubes were prepared by inverse-emulsion interfacial synthesis method,and their morphology and properties were studied.The main research contents are as follows:1.Synthesis and morphology study of tadpole-like nanotubes.A series of tadpole-like nanotubes were synthesized via emulsion interfacial sol-gel method in an inverse-emulsion of water in 1-pentanol stabilized by polyvinylpyrrolidone(PVP),using1,2-bis(triethoxy silyl)ethane(BTEE)as a silica precursor.The structure and morphology were characterized.The effects of reaction time,aqueous phase content,ammonia concentration,hydrochloric acid concentration,reaction temperature,mixing conditions,PVP molecular weight and different silane precursors on the morphology and size of tadpole-like nanotubes were investigated.The formation process of tadpole-like nanotubes was studied.The results show that with the increase of reaction time,the length of the tail increased significantly.With the increase of the water content,the length of the tail increased.The content of the water phase continued to increase until the emulsion droplet changed from nanometer to micron level accompanied by vanishing of tadpole-like nanotubes and forming of hollow silica spheres.With the increase of ammonia concentration,the tail of tadpole-like nanotube became longer,while the diameter of head and tail remained unchanged.Only hollow microspheres were obtained in weak acid medium.With the increase of reaction temperature,tadpole-like nanotubes and many micron sized hollow spheres were produced simultaneously.With the increase of PVP molecular weight(from K17 to K90),the head of tadpole-like nanotube gradually became smaller and finally disappears.Under the same experimental conditions,tadpole-like nanotubes were not obtained using tetraethyl orthosilicate(TEOS),1,6-bis(triethoxysilyl)hexane(BTEH)and 1,8-bis(triethoxysilyl)octane(BTEO)as a silica precursor,respectively,indicating the structure and hydrolysis rate of silane have a certain influence on the formation of tadpole-like nanotubes.2.Synthesis and properties of tadpole-like Janus composite nanotubes.First,In the PVP stabilized inverse-emulsion system of water in 1-pentanol,asymmetric tadpole-like Janus nanotubes with hydrophobic n-octyl(-C₈H₁₇)on the outer surface and hydrophilic silicon hydroxyl(-Si-OH)on the inner surface were prepared through hydrolysis condensation of BTEE and n-octyltriethoxysilane(OTES)precursors by one-step emulsion interface sol-gel method.The structure and morphology were characterized.Secondly,catalytically active tadpole-like Janus/Pd composite nanotubes and photothermal responsive tadpole-like Janus/Pd composite nanotubes were constructed by selectively combination palladium(Pd)and ferroferric oxide(Fe₃O₄)nanoparticles in the cavity of tadpole-like Janus nanotubes.The results show that the tadpole-like Janus/Pd composite nanotubes were driven by the gas released from the catalytic reaction in the presence of hydrogen peroxide(H₂O₂).The tadpole-like Janus/Fe₃O₄composite nanotubes had photothermal response under 808 nm near-infrared light,and also had similar self driving behavior.3.Synthesis and properties of high thermal insulation organosilica nanotubes.Firstly,a series of organosilica nanotubes were synthesized by a sol-gel reaction at the emulsion interface using BTEE as a silica precursor in an inverse-emulsion of water in 1-pentanol stabilized by PVP.The structure and morphology of the structure were characterized.Secondly,the gelation process of organosilica nanotubes was studied by adjusting the concentration of BTEE and ammonia.When the concentration of BTEE and ammonia is increased,it can accelerate the hydrolysis-condensation-nucleation-growth process,thereby accelerating the gelation process,realizing the transformation of the nanotube surface from smooth to rough,and finally forming organosilica nanotube gels.Thirdly,selecting of non-gelatinization organosilica nanotubes,the thermal properties of the nanotubes were studied by measuring thermogravimetry(TG),differential scanning calorimetry(DSC),thermal conductivity and the simulation calculation of the steady-state heat transfer process.The results show that the thermal conductivity of the organosilica nanotubes is small,and the thermal conductivity of some samples is lower than that of the static air at room temperature.The actual measurement temperature on the surface of the nanotubes is consistent with the theoretical simulation results,which proves that organosilica nanotubes have excellent thermal insulation performance.In view of the complexity of the preparation process of asymmetric SiO₂ nanomaterials,the nanomaterials can be prepared at room temperature by means of a mild method of materialization of emulsion interface.The as-prepared tadpole-like nanotubes have porous morphologies,and the characteristics of double asymmetry in shape and surface of internal and external.This novel morphology is expected to be used as nano-motor of smart delivery system and coating materials for thermal insulation protection.