Defect-induced Polymerization Of Pyrrole To Construct Nanocomposites For Electromagnetic Wave Absorption

Nowadays,with the rapid development of electronic information technology,the human survival environment is filled with various electromagnetic wave signals,which adversely affects the equipment operation,information security,and human health.The key to solve this problem lies in the development of new high-performance electromagnetic wave absorption（EWA）materials.Polypyrrole（PPy）has a broad prospect for the EWA materials due to its unique physical and chemical properties.However,single PPy EWA material suffers from the poor stability,narrow absorption bandwidth,and single absorption mechanism,which severely affects its practical application.The nanocomposite method is considered an important way to regulate and improve the performance of single polypyrrole,which not only combines the unique advantages of various components but also can realizes multiple electromagnetic loss effects.In this dissertation,we propose a defect-induced composite strategy to design and synthesize two PPy-based EWA nanocomposites using sulfonic acid-doped polyphenylene and oxygen vacancy-containing molybdenum trioxide as the revulsive,respectively,and systematically study their composite microstructure,chemical compositions,EWA properties and corresponding operation mechanism on electromagnetic waves.This dissertation provides new ideas for the design and development of new EMA nanocomposites.The main contents are as follows:（1）Sulfonic acid doping-induced polypyrrole/microporous polyphenylene nanocomposites for electromagnetic wave absorptionWe firstly prepared conjugated microporous polyphenylene（MPP）,and then sulfonic acid-doped microporous polyphenylene（SMPP）was obtained via sulfonation treatment.Next,we used SMPP as revulsive to construct polypyrrole/sulfonic acid doped microporous polyphenylene（PPy/SMPP）composites through the induction polymerization of pyrrole by sulfonic acid groups.The results show that the sulfonic acid groups are uniformly doped into the MPP framework,and then the pyrrole is successfully guided to polymerize and grow in the pore channels of SMPP,constructing a unique architecture in which SMPP nanoparticles are connected by PPy.The PPy/SMPP composite shows excellent EWA properties,its minimum reflection loss(RL_min)can reach-56.3 d B with only 10 wt%filling,far outperforming pure PPy（-17.85 d B）.The efficient EMA performance of composite benefits from the improved impedance matching by SMPP,while the presence of abundant interfaces and functional groups enables multiple dissipation for electromagnetic waves.This work points out the direction on the design of EWA composites based on the doped groups,and paves the way for expanding the functions of conjugated microporous polymers.（2）Oxygenvacancy-inducedpolypyrrole/molybdenumtrioxide nanocomposites for electromagnetic wave absorptionFirstly,the oxygen vacancy-containing molybdenum trioxide（o-MoO₃）was prepared via a sodium borohydride treatment process using molybdenum trioxide（MoO₃）as the raw material.The as-prepared o-MoO₃ was then used as revulsive to guide the polymerization of pyrrole on its surface to construct polypyrrole/oxygen vacancy-containing molybdenum trioxide（PPy/o-MoO₃）composites.The results show that the oxygen vacancies in o-MoO₃ induce the pyrrole to polymerize on the surface of o-MoO3,forming a composite structure of PPy wrapped with o-MoO₃.The RL_min of composite is-31.8 d B at 30 wt%filling,and its maximum effective absorption bandwidth can cover11.56-17.82 GHz,while the single polypyrrole shows no effective absorption.The oxygen vacancies and pyrrole units can act as active sites,providing abundant polarization loss and significantly increasing conductivity（7.5 times that of single PPy）.This work provides new ideas for the construction of EMA composites and promotes the application of transition metal oxides in the field of EMA.