The Preparation And Thermal Decomposition Of Silver Nanoparticles Protected With3-Mercaptopropionic Acid

Metal nanoparticles have been used in many fields such as catalyst, biomarker,photonics, optoelectronics and information storage. Different from conventionalmaterials, metal nanoparticles have many individual properties such as small sizeeffect, surface effect, quantum size effect and quantum-tunnel effect. As the key tometal nanoparticles the protective agent influences the nanoparticle’s dispersionability and stability as well as thermal stability, even changes its compostion andstructure during the annealing process. A lot of research studies have been reportedabout the preparation and thermal decomposition of single-function group ligandprotected nanosilvers. However, there is little study on double-function groups ligandprotected nanosilvers. Here we use3-mercaptopropionic acid as protective agent,which possesses double protective function groups, to study the preparation andthermal decomposition of silver nanoparticles.In this paper we prepare nanosilvers via ligand-exchange reaction and chemicalreduction reaction and compare the effects of these two methods on nanosilver’smorphology, size and dispersion. The obtained nanosilvers will turn into the Ag2S-Agcore-shell structure after annealed at200℃. We further investigate its formationmechanism and its conductivity and discuss the dependence of the product structureon its properties. The results show that MPA forms the covalent bond with the Agatom by the interation of the sulfur atom of–SH with the Ag atom and alkyl chainsform the multi-protective agents wrapped layer on the surface of nanosilvers. The sizeof Ag/MPA nanoparticles produced by the ligand-exchange reaction are20to50nmand the thichness of the protective agents on the surface is2to3nm, which, however,are5to20nm and about1nm in the chemical reduction reaction respectively.The study on the thermal decomposition of silver nanoparticles shows that when200℃in air heating sintering, silver nanoparticles first desorbed the physicallyadsorbed MPA and grew up. Then, the chemically adsorbed MPA thermallydecomposed and was accompanied by the formation of Ag2S, SO3–groups. FinallyAg2S-Ag core-shell structure nanoparticles with the average particle size of100nmformed. IR, XPS and TEM are used to deeply discusses the formation mechanism ofAg2S-Ag core-shell structure. The results show that the Ag+of Ag2S may be reducedto metallic silver under the function of-SO3group and S ions, Which made Ag2Smove to the kernel part. Finally, the performance and application of the Ag2S-Ag core-shell nanoparticleswas analyzed. The results showed that the resistivity of the Ag2S-Ag core-shellnanoparticles coating decreased with temperature increasing, which shows goodcharacteristics of negative temperature coefficient thermistor and shows greatpotential for application in temperature control, biomedical and other field.