The Mechanism Of Photocatalytic Synthesis Of Azotetrazolate Energetic Salts

Azotetrazolate are C-N heterocyclic compound with a high nitrogen content and high enthalpy of formation,which can be used as potential high energy density material in military and civil fields.The most critical step in the synthesis of azotetrazolate salts is the dehydrogenation and oxidative-coupling of amino groups on 5-amino-1H-tetrazole.At present,chemical oxidation is the most commonly way to realize the oxidative-coupling of 5-amino-1H-tetrazole,but it has the problems of waste of raw materials and auxiliary materials,complicated separation of products,high energy consumption,and insufficient reaction safety.Semiconductor photocatalysts can absorb sunlight and generate highly oxidizing active species such as photogenerated holes and·OH,which have a high possibility of driving 5-amino-1H-tetrazole to achieve oxidative-coupling reactions.On the basis of the above background,the feasibility and related mechanism of Fe₂O₃ photoelectrocatalytic and g-C₃N₄photocatalysis for the oxidative-coupling of 5-amino-1H-tetrazole to azotetrazolate salts were systematically studied.The main research contents and conclusions are as follows:?1?In 0.1 M NaOH-0.05 M 5-amino-1H-tetrazole electrolyte,the Fe₂O₃ film photoanode could absorb and utilize sunlight to drive the 5-amino-1H-tetrazole oxidative-coupling to sodium azotetrazolate directly at room temperature and atmospheric pressure,this reaction was kinetically more likely to occur than water oxidation.The Faradaic efficiency of 65%for the oxidative-coupling into sodium azotetrazolate was achieved on the Fe₂O₃ film photoanode at 1.23 V vs.RHE.In addition,in the Fe₂O₃ film photoanode-based electrolytic cell,the Faraday efficiency of the reduction of hydrogen ions to hydrogen on the Pt wire cathode was99%.Further studies had found that the activity of sodium azotetrazolate synthesis reaction and hydrogen evolution reaction would be further improved after the 0.5 T magnetic field was applied to the Fe₂O₃ film photoanode-base electrolytic cell.The main reason was that the presence of magnetic field inhibits the non-radiative recombination of photogenerated electrons and holes on the Fe₂O₃ film photoanode.Long-term tests showed that the Fe₂O₃ film photoanode had a relatively stable oxidative-coupling activity of 5-amino-1H-tetrazole.The experiments of hole trapping agent confirmed that the Fe₂O₃ film photoanode driven the 5-amino-1H-tetrazole oxidative-coupling to sodium azotetrazolate was a typical photogenerated hole-driven reaction.?2?In 0.2 M NaOH/0.1 M 5-amino-1H-tetrazole/g-C₃N₄ photocatalytic reaction system,5-amino-1H-tetrazole could be oxidatively coupled to sodium azotetrazolate compound at room temperature and atmospheric pressure,and the reaction selectivity was close to 100%.Since g-C₃N₄ had good stability in alkaline solutions,repeated experimental studies had found that the photocatalytic activity of g-C₃N₄ photocatalyst had basically not changed before and after 6 reactions.The mechanism study found that photogenerated holes were the main active materials during the oxidative-coupling of 5-amino-1H-tetrazole to azotetrazolate with g-C₃N₄.Moreover,·OH and·O₂^-in the reaction system also played an important role in the formation of azotetrazolate,which could promote the dehydrogenation of amino group on 5-amino-1H-tetrazole,and facilitate its oxidative-coupling.Based on the experimental results under the simulated sunlight,we further found that g-C₃N₄ could absorb and utilize the natural sunlight to synthesize a level of 20 g sodium azotetrazolate,the yield was close to 71.7%.The research findings in this thesis could not only provide a method reference for the green synthesis of azotetrazolate compounds,but also provide ideas and reference of research methods for semiconductor photocatalytic synthesis of azo organic compounds.