Synthesis Of Chiral Polyaniline Nanofibers And Amino Acid Molecularly Imprinted Polyaniline

This paper consists of two parts.The first part is to synthesize chiral polyaniline(PANI)using oligomer assisted method and secondary doping method respectively in the water phase,and optimize the synthesis conditions,and obtain the optimal conditions for the synthesis of chiral polyaniline under each method.The morphology,structure and optical activity of the polyaniline nanofibers prepared by the two methods were compared and analyzed.The second part is to synthesize two kinds of amino acid molecularly imprinted polyaniline by chemical oxidation method,and preliminarily investigate their recognition effect on different kinds of amino acid.Objectives:The similarities and differences of chiral polyaniline synthesized by different methods in water system were compared.The recognition ability and selectivity of amino acid molecular imprinted polyaniline were investigated.Methods:(1)Oligomer assisted method:①aniline as monomer,single configuration camphor sulfonic acid(CSA)as dopant,ammonium persulfate(APS)as oxidant,N-phenyl-1,4 p-phenylenediamine as oligomer assisted synthesis of chiral polyaniline.The optimum synthesis conditions of chiral polyaniline were obtained by optimizing the molar ratio of CSA to aniline,CSA concentration,APS addition method,product treatment method,etc.The products were characterized by UV,IR,SEM,CD and XRD.②Using single chiral tartaric acid(TA)as the doping acid,TA doped polyaniline was prepared by the same method,and the similarities and differences of structure,morphology and optical activity between TA doped polyaniline and CSA doped polyaniline were compared.(2)Secondary doping method:first synthesize hydrochloric acid doped polyaniline(HCl-PANI)with aniline as monomer and HCl as dopant.Then,dedoped to get emeraldine(EB),it is synthesized with a single configuration CSA as dopant and chiral inducer to synthesize chiral polyaniline.The structure,morphology and chirality were characterized by UV,IR,SEM,CD and XRD.(3)Chemical oxidation method:aniline as monomer,APS as oxidant,aspartic acid(Asp)and glutamic acid(Glu)as template molecules to synthesize molecularly imprinted polyaniline;Its structure and morphology were characterized by UV and SEM.The recognition effects of two kinds of molecularly imprinted polyaniline on different kinds of amino acids were investigated.Results:(1)Oligomer-assisted method:①The optimal conditions for the synthesis of CSA doped chiral polyaniline are as follows:The concentration of CSA was 2 mol/L,the molar ratio of aniline to CSA was 1:20,APS(molar ratio of aniline to aniline was 1:1)was added once and stirred vigorously for 5 min.At the end of the reaction,the supernatant was directly centrifuged,washed alternately with water and methanol for two times each,and the polyaniline was obtained by vacuum drying.The polyaniline synthesized by this method is a single spiral nanofiber with certain chiral characteristics.②The conditions for the synthesis of TA doped polyaniline are as follows:the molar ratio of TA to aniline is 20:1,APS is used as oxidant,and the doped polyaniline obtained by this method is the inner hollow polyaniline nanofiber tube.(3)The UV and IR results of CSA doped polyaniline and TA doped polyaniline are similar,but they are different in morphology and chirality.(2)The conditions of synthesis of chiral polyaniline fiber by secondary doping method:0.03 mol aniline was dissolved in 300 mL 1 mol/L HCl,APS was added once and stirred vigorously for 5 min,and 3%NH3·H2O was dedoped for 24 h to obtain EB.Doped with D-CSA and L-CSA(mass ratio 1:1.94)in aqueous solvent for 12 h,the supernatant was removed by centrifugation,washed alternately with methanol and water,the supernatant was removed by centrifugation,and the chiral polyaniline was obtained by vacuum drying.The chiral polyaniline synthesized by this method is a spine-like nanofiber with certain chiral characteristics.(3)Synthesis of molecularly imprinted polyaniline by chemical oxidation:0.05 mol aniline was added in 100 mL water,then 1 mol/L hydrochloric acid was dropped to aniline solution.The molar ratio of aspartic acid or glutamate to aniline was 1:20,and APS(molar ratio to aniline was 1:1)was added once and stirred vigorously for 5 min.After the reaction was completed at 0℃,filtration was performed,and 0.2 mol/L hydrochloric acid and water were washed alternately.Molecularly imprinted polyaniline was obtained by vacuum drying.Both kinds of molecularimprinted polyaniline have strong enrichment ability for template molecules.Conclusions:(1)Chiral CSA doped polyaniline nanofibers can be synthesized by both oligomer assisted and secondary doping methods in water system.However,the oligomer assisted product has a single helical structure,while the secondary doping product has a spine-like bulge on the surface.(2)Both of the two amino acids can be used for the separation of amino acids which differ greatly from the template molecular structure.