Synthesis And Capacitive Properties Of Pillararene Modified Graphene Composites

As a new supramolecular macrocyclic host compounds,pillar[n]arenes are easy to functionalize,have rigid pillar-shaped structure and can bind various types of guest molecules in a high selectivity.With the rapid development of supramolecular chemistry,a large number of supramolecular materials with specific functions have shown great interest in the inorganic,polymer,biomedical and electrochemical fields.Among them,the emergence of supramolecular host compound functionalized carbon materials provides a new idea for the development of supercapacitor electrode materials,especially the pillar[n]arene functionalized graphene materials.Although graphene-based materials are considered as promising electrode materials,their energy density and specific capacitance are not able to meet the energy storage requirements of actual supercapacitors.Moreover,the strong van der Waals interaction between graphene layers is easy to cause agglomeration or re-stacking,which makes it very difficult to obtain single-layer graphene with larger effective surface area,better electrical conductivity and stability,which greatly limits the improvement of the electrochemical performance of graphene-based electrode materials.In order to alleviate the self-aggregation of graphene and optimize its properties,an effective strategy is to functionalize graphene and combine it with other materials with high theoretical capacity.In this paper,hydrazide-pillar[5]arene(HP5A)with rigid structure and reducibility was used to functionalize graphene for improving capacitive properties.In order to further improve specific capacitance of the composite,HP5A was used to induce the ordered polymerization of conductive polymer monomers on the surface of graphene by host-guest recognition.A variety of nanocomposites with good hydrophilicity and electrochemical properties have been designed and prepared for assembling supercapacitors.The specific work is as follows:1.Synthesis and capacitive properties of pillararene derivatives.HP5A and other pillararene derivatives were successfully synthesized.According to the electrochemical characteristics of HP5A,the contribution of pseudocapacitance could be increased by introducing HP5A into the electrode material of supercapacitor.2.Capacitive properties of graphene composites modified by pillararene.When the graphene composites were prepared with hydrazine hydrate as reducing agent and HP5A as modifying agent,HP5A effectively inhibited the aggregation of graphene sheets and improved the specific capacitance(C_s).Compared with graphene modified with?-cyclodextrin polymer(CDP),sulfonyl calix[6]arene(C6S)and aminated pillar[5]arenes(2CNP5A and 4CNP5A),HP5A modified graphene had the highest C_s.This is mainly due to the rigid structure and redox characteristics of HP5A.Furthermore,the amount of HP5A directly affected the properties of the composites.When the mGO/mHP5A is 1:1,the prepared modified electrode had the highest C_s(182 F·g^-1 at 1 A·g^-1),the minimum charge transfer resistance and excellent rate performance.It provided an important tool for the study of functionalized modification of graphene by pillar[5]arenes,and even the application of supramolecular composites in energy storage.3.Capacitive properties of graphene-based composites modified by pillararene modified gold nanoparticles.In order to enhance the electrochemical reactivity of the composite,gold nanoparticles(HP5A@AuNPs-5.0)prepared by reduction of chlorauric acid with HP5A were used as reducing agent and modifier to react with GO to prepare the ternary composites(RGO-AuHP5A).HP5A@AuNPs-5.0 has good monodispersity and average particle size of 13 nm.RGO-AuHP5A composites used as electrode materials,exhibited high C_s(212 F·g^-1 at 1 A·g^-1)which was much higher than that of RGO alone.Compared with the ternary composite(rGO-HP5A@AuNPs)prepared with hydrazine hydrate as reducing agent,the C_s was increased by 72%.When the current density was 0.5 A·g^-1,the maximum C_s of the composites was 230 F·g^-1,and the C_s retention rate was 79%at 20 A·g^-1,which reflected the good rate performance of the composite.Then,a symmetric supercapacitor(SSC)was assembled,it exhibited high initial C_s,good rate performance and excellent long cycle stability.4.Capacitive properties of pillararene modified graphene supported conductive polymer composites.In order to obtain pillararene modified graphene composites with better electrochemical performance,the RGO-HP5A composites prepared by direct reduction of GO with HP5A as reducing agent was used to induce the ordered polymerization of the conductive polymer monomer.In the absence of the strong reducing agent hydrazine hydrate,HP5A fully utilized its water-solubility and rigid structure,which effectively hindered the aggregation of graphene nanosheets while reducing GO and further improved the C_s of pillar[5]arene modified graphene composites.Compared with pure RGO,H1 modified graphene and the same type of graphene materials reported in the literature,the composite(RGO-HP5A 2:3)showed higher C_s(331 F·g^-1 at 0.5 A·g^-1 and 294 F·g^-1 at 1 A·g^-1)and good rate performance.In addition,the composite could be used as the substrate to induce the orderly polymerization of aniline on the surface of graphene for reducing the capacitance loss caused by polyaniline agglomeration.In order to obtain composites with better capacitance performance,HP5A modified graphene was utilized to induce the ordered polymerization of pyrrole(smaller in size than aniline and easier to enter/exit HP5A cavity)on the surface of the graphene.The maximum C_s of the resulting composites(RGO-HP5A-PPy)was 495 F·g^-1 at the current density of 1 A·g^-1.Compared with pure PPy(319 F·g^-1 at 1 A·g^-1),the C_s was increased by 55%.Both assembled symmetric supercapacitors had a high initial C_s.The C_s retention rates were 86%and 76%after 10,000 cycles at current density of 5 A·g^-1,respectively.The study gave full play to the respective advantages of pillar[5]arene,graphene and conducting polymer,and was expected to promote the development of supramolecular functionalized graphene supported conductive polymers.5.Capacitive properties of bisdemethoxycurcumin doped graphene composites modified by pillararene.Due to the strong supramolecular host-guest interaction between HP5A and bisdemethoxycurcumin(BDMC),the introduction of BDMC could affect the properties of composites.The small organic molecule BDMC matching the size of HP5A was selected as the research object,and the host-guest interaction between HP5A and BDMC was characterized.The binding constant of this interaction was(1.58±0.30)×105 M^-1,and the stoichiometric ratio was 1:1.In addition,the host-guest inclusion complexes formed could be further assembled into fibers.The C_s of RGO-HP5A 2:3 and RGO-HP5A-PANI composites doped with BDMC did not change obviously.After adding BDMC in the process of preparing RGO-HP5A-PPy composite,the C_s of the obtained composite(RHPB)at 1 A·g^-1 was 553 F·g^-1.Compared with RGO-HP5A-PPy 1-4,the C_s was improved by about 20%,and compared with RGO-HP5A-PPy 1-5,the C_s was improved by about 12%.Unlike the first two,PPy in the RHPB composite was a membrane that covered the graphene surface and prevented BDMC from shedding.