Chemical Oxidative Synthesis And Multifunctionality Of 2-Amino-1,3,4-Thiadiazole And 2-Mercapto-1,3,4-Thiadiazole Polymer

2-amino-1,3,4-thiadiazole and 2-mercapto-1,3,4-thiadiazole polymers are both five-membered heterocyclic aromatic polymers with a high content of N and S atoms,while their main chains contain alternating single and double bond structure and delocalized π-electron structure with high negative charge density.Besides,they also have similar chemical and electronic structures to polyaniline,polypyrrole and polythiophene.These special structures endow them with promising multifunctions.In this study,poly-2-amino-1,3,4-thiadiazole and poly-2-mercapto-1,3,4-thiadiazole were successfully synthesized by using a facile and efficient chemical oxidative polymerization method,and their structures and multifunctions were studied systematically.Firstly,2-amino-1,3,4-thiadiazole(AT)and 2-mercapto-1,3,4-thiadiazole(TT)were polymerized by a simple chemical oxidative polymerization to obtain poly-2amino-1,3,4-thiadiazole(PAT)and poly-2-mercapto-1,3,4-thiadiazole(PTT).In this case,the optimization of polymerization conditions includes the selection of oxidation system and optimization of reaction parameters.On the one hand,the oxidant and reaction medium were investigated to find the appropriate oxidation system for the polymerization of AT and TT.On the other hand,the reaction parameters including monomer concentration,molar ratio of oxidant to monomer,and temperature were optimized systematically to increasethe yield of the polymer.It is found that if using NaClO as the oxidant,N,N-dimethylformamide(DMF)or 0.05mol L-1 HCl as the reaction medium without adding any additional stabilizer and surfactant,the yields of PAT could reachup to 70.5%and 75.4%,respectively.When the anhydrous CuCl2 and DMF were used as the oxidant and reaction medium,respectively,the highest yield of 71.6%for PTT was obtained.Then,the molecular structure,particle size distribution,micro-morphology and properties of the two polymers wereanalyzed in detailby UV-Vis,IR,and fluorescence spectroscopies,X-ray photoelectron spectroscopy,X-ray diffraction,MADI-TOF mass spectrometry,element analyses,gel permeation chromatography,field emission scanning and transmission electron microscopies.Finally,the potential of application of these two polymers in the fields of heavy metal ion adsorption,fluorescence detection and antimicrobial was exploited.PAT demonstrated strong and very fast adsorbability toward Pb2+ and Ag+.The adsorptivity and adsorption capacity reached up to 86%and 172 mg g-1 for Pb2+,and 99.9%and 199 mg g-1 for Ag+,respectively.The adsorption equilibrium could be achieved within 5 min.By contrast,PTT showed strong affinity toward Hg2+and Ag+,and the adsorptivity and adsorption capacitywere 94.82%and 186.9 mg g-1 for Hg2+,and 96.80%and 193.1 mg g-1 for Ag+,respectively.The adsorption equilibrium was achieved within 20 min.Compared with other adsorbents,PAT and PTT have the advantages of large adsorption capacity and rapid adsorptionrate.The main chains of these polymers contain large conjugated structures with alternating single and double bonds.This special structure facilitates the emission of strong fluorescence.The addition of trace of Co2+,Ag+ or Cr3+ caued significant enhancements of the fluorescence intensities of PAT,whereas the addition of Zn2+,Cu2+,Pb2+or Mg2+ led toa fluorescence quenchingof PAT.Similarly,Cu2+caused a fluorescence enhancement of PTT,where as Pb2+led to a fluorescence quenching of PTT.At the same time,nitrogen and sulfur atoms may play a key role in destructing the formation of hydrogen bonds between the DNA basesof bacteriaprotein,thusshowing good antibacterial effect When both the concentration of Escherichia coli and that of Staphylococcus aureus were 10-7 CFU g-1,the minimum inhibitory concentrations of PAT were 8×10-4 and 4×10-3 g L-1,respectively,whilst the minimum inhibitory concentrations of PTT were 2.4×10-3 and 4×10-3 g L-1,respectively.