Preparation Of Nitrogen-doped Carbon Nanotubes And Their Catalytic Performance In Reduction Of Nitroarenes

Carbon nanotubes?CNTs?are a kind of 1-demonsional carbon nanomaterials with unique structure,which have excellent mechanical and electrical properties.Such CNTs have good application prospects in many fields such as composite materials,energy storage,and catalysis.However,the hydrophobicity and chemical inertness of pristine CNTs hamper their applications in chemical catalysis.Both theoretical and experimental studies show that nitrogen and transition metals doping can change the crystal and electronic structures of CNTs and increase the catalytic activity,thereby improving their catalytic performance.However,the large-scale synthesis of nitrogen doped CNTs is still a challenge.In this thesis,two kinds of nitrogen-doped CNTs embedded with cobalt nanoparticles were prepared by the pyrolysis of metal-organic frameworks and melamine precursors,of which their structures were analyzed and characterized in detail.In addition,the catalytic performance of such CNTs the in reduction of nitroarenes was also investigated.The main research results are as follows:?1?Synthesis of N-doped CNTs derived from BIMT-Co-MOF and their catalytic performance in the reduction of nitroarenes.Nitrogen-doped CNTs embedded with the cobalt nanoparticles were prepared by a two-step pyrolysis approach,in which3,6-bis?1-imidazolyl?-1,2,4,5-tetrazine/Co metal organic framework?BIMT-Co-MOF?and melamine were used as the precursor and template,respectively.The obtained N-doped CNTs embedded with cobalt nanoparticles?namely Co-NCNT₁-800?have a bamboo-like morphology with diameter and length in the range of 80?180 nm and3?5?m,respectively.The wrapped cobalt nanoparticles are beneficial to enhance the stability of the Co-NCNT₁-800 in the reduction of nitroarenes.Owing the relatively high content of pyridinic nitrogen?30.57%?,Co-N_x?7.02%?and graphitic nitrogen?45.45%?that all are active in the reduction of nitroarenes,Co-NCNT₁-800 showed good catalytic performance the reduction of nitroarenes.Using Na BH₄as hydrogen source,the apparent rate constant k of the Co-NCNT₁-800 catalyzed 4-nitrophenol reduction reaction was about 0.64 min^-1.In addition,the Co-NCNT₁-800 catalyst can maintain 92%of its catalytic activity after 10th cycles.?2?Synthesis of N-doped CNTs derived from m BIMT-Co-MOF and the catalytic performance in the reduction of nitroarenes.Nitrogen-doped CNTs embedded with the cobalt nanoparticles were prepared by a one-step pyrolysis approach,in which3,6-bis?4-methyl-1H-imidazolyl?-1,2,4,5-tetrazine/Co?II?metal organic framework?m BIMT-Co-MOF?and melamine were used as precursor and template,respectively.The as synthesized N/Co-doped CNTs?namely Co-NCNT₂-800?also have a bamboo-like morphology with diameter and length in the range of 60?80 nm and 2?4?m,respectively.The thin wall of Co-NCNT₂-800?5?10 nm?makes the immobilized cobalt nanoparticles easy to participate in the catalytic reaction.Thanks to the high nitrogen?7.79 at%?and cobalt contents?12.32 wt%?,the Co-NCNT₂-800 catalyst showed excellent catalytic performance in the reduction of nitroarenes.Using Na BH₄as the hydrogen source,the apparent rate constant k of the Co-NCNT₂-800 catalyzed4-nitrophenol reduction reaction was up to 1.66 min^-1,and the apparent activation energy was as low as 32.04 k J mol^-1.In addition,the Co-NCNT₂-800 catalyst also showed excellent selectivity and stability.