One-step synthesis and stabilization of Au, Ag and Au-Ag nanoparticles with an ion-exchange polymer contained amide and carboxylic acid functional groups

The synthesis and characterization of ion exchange polymer poly(4-acryloylaminobenzoic acid) (poly(4-AABA)), which contains amide and carboxylic acid functional groups on each repeating unit are reported. The polymer was used as reducing and stabilizing agent in the synthesis of gold nanoparticles, silver nanoparticles, and gold-silver nanoparticles at room temperature and 75 °C. The poly(4-AABA)-stabilized metallic nanoparticles were characterized by ultraviolet-visible spectroscopy, transmission electron microscopy, X-ray diffraction, and infrared spectroscopy. It was found that the amide group of the repeating unit of poly(4-AABA) confers the ability to reduce gold and silver ions by transferring the free electrons from the N atom. UV-Vis results showed that the process of reduction of the metallic ions by poly(4-AABA) at room temperature occurs slowly, and the obtention of the nanoparticles take place after several days. On increasing the temperature to 75 °C, the reduction rate increases considerably, and the formation of nanoparticles occurs over a few minutes. Conformational arrangement of poly(4-AABA) play an important role in controlling the size and shape of the nanoparticles. The composition of the Au-Ag nanoparticles strongly depends on the reaction temperature, changing from an Au-rich alloy when the temperature is 25 °C to an Ag-rich alloy at 75 °C. The poly(4-AABA) stabilizing to the nanoparticles in aqueous solution through the electro-steric stabilization mechanism, since through the carboxylic acid groups it interacts electrostatically with the surface of the particles and due to the long length of the polymeric chains, the poly(4-AABA) also envelops to particles controlling their growth and preventing agglomeration. Probable mechanism for formation of colloidal metallic nanoparticles in aqueous solution of poly(4-AABA) is proposed is discussed.