Construction Of Microspherical Nitrogen-Doped Carbon Nanotube Assembly And Their Catalytic Applications

The complex architectures with macroscopic assembly of nano-building blocks have attracted great attention in both academia and industry,since the advantages of nanostructures and microstructures can be synergistically combined which are less-pronounced in their individual building blocks.To achieve the construction of such materials,several synthetic methods have been developed,including MOFs derived method,spray drying technology,microfluidic method,emulsion templated method et al.Although these methods are efficient,they also suffer from some drawbacks,such as the necessity for specific instruments and complicated processes,making them less accessible for practical utilization.Moreover,finely engineering of the interior structure are usually difficult in these methods.Therefore,it is still highly desired to find a simpler and interior-controllable method for pushing forward the development micro-or macroscopic assemblies.In this thesis,for the first time,we present a novel and simple microconfined-annealing approach,in which a Pickering microdroplet patterned method and unique pyrolysis-stimulated-transformation processes are coupled unprecedentedly,for the fabrication of spherical nitrogen-doped carbon nanotube assemblies(NCNTA).Such a material is applied in catalysis applications.The main results are summarized as follows:(1)The preparation of microspherical nitrogen-doped carbon nanotube assemblies.Solid emulsifier stabilized Pickering droplets were utilized concomitantly as a microconfined reaction locus and an‘architecture-directing agent' for the formation of a polymer precursor,melamine formaldehyde(MF)resin,which would be totally gasified during the subsequent pyrolysis process(>800 o C,N2)and transformed into carbon nanotubes under the assistance of cobalt catalyst.With such architecture-directing processes,this method enables the formation of a NCNT superstructure with micrometer dimension and spherical morphology.While the polymerization situations happened in the droplet interior and at the boundary are independent and different,the finally obtained microscopic assembly possesses a complex pomegranate-like structure,which is made up with numerous interconnected NCNT particles and a carbon crust.(2)Achieving the controlled evolution of interior structures through tuning the synthesis parameters.It was found that the dosage of MF precursors,cobalt amount and annealing temperature influence the interior structure of the yielded superstructures significantly.With suitable MF content and annealing temperature(>800 o C)were utilized,NCNT superstructure could be got.Interestingly,we also found that the interior structure of NCNT particles is highly dependent on the dosage of cobalt.(3)The catalytic performance of microspherical nitrogen-doped carbon nanotube assemblies.With abundant Co-N-C species,the yielded NCNTA exhibited excellent activity in the hydrogenation of nitrobenzene and the cross-esterified oxidative reaction between diverse benzyl alcohols and methanol.And featuring with unique micro-/nano-complex structure,the solid catalyst could be easily separated from the reaction solution by an external magnet within only 10 s.Moreover,after supporting with uniform Ru NPs,the produced solid catalyst also showed good catalytic performance and recyclability in the hydrogenation of aromatic compounds.