Role of hydrogen bonding interactions in directing one-dimensional thiol-assisted growth of silver-based nanofibers

We present evidence, based on scanning and transmission electron microscopy measurements, for the formation of nanofibers from silver-thiol materials treated with water. Mercapto acetic acid, a thiol with a carboxylic acid group at one end, was employed for the experiments presented here. Nanoparticles, with diameters as large as 1 nm, fill the nanofibers and are responsible for absorption bands between 2 and 5.5 eV in UV-visible absorption spectroscopy measurements. The nanofibers disappear at pH values larger than the first pK(a) of the acid, while rods are observed for pH values between 3.6 and 7. This result is interpreted in the context of hydrogen bonding interactions playing an important role in driving the one-dimensional growth of the fibers, a proposal that is supported by the vibrational frequency of the carbonyl stretching mode in surface reflection Fourier transform infrared measurements on dry deposits of aqueous dispersions of the thiol-silver material.