Morphological evolution of noble metal nanoparticles in chloroform: mechanism of switching on/off by protic species

OSCAR DOUGLAS GALLARDO; CESAR G. GOMEZ; MICAELA MACCHIONE; FERNANDO COMETTO; EDUARDO CORONADO; VICENTE A. MACAGNO; MANUEL PEREZ

RSC Advances

RCS

Año: 2015 vol. 5 p. 100488 - 100497

2046-2069

The morphological stability/morphological reshaping of noble metal nanoparticles are studiedexperimentally in order to unravel the chemical mechanisms lying beneath. Gold and silver nanoparticles(AuNPs and AgNPs, respectively) formed in a chloroformic environment are used, as model syntheticsystems, to study the phenomena of morphological change. The morphological evolution of NPs thatfollows their formation, is characterized by spectroscopy (UV-visible, Raman and FTIR) and TEM(Transmission Electron Microscopy). The change of NP morphology involves the increase of the averageNP size and the broadening of size distribution, in a close resemblance with the effect characteristicallyobtained from the Ostwald ripening. The effect of the poor solvating properties of chloroform instabilizing small charged species (H+, Ag+, Au+) as well as the principle of electroneutrality of matter areanalyzed in order to formulate a feasible reaction scheme consisting of a three-step process: thegeneration of soluble intermediary species by corrosion of nanoparticles, the diffusion of intermediaryspecies from one nanoparticle to another, and the re-deposition process involving the reduction ofintermediary species. This basic reaction scheme is used as a hypothesis to plan and performexperiments, which reveal that molecular oxygen dissolved in the dispersive medium can drive NPcorrosion, however, protic species are also required as co-reactants. The polarity of the hydrogen bondand the ligand properties of the anions produced by de-protonation are features of the protic speciesthat enable/disable corrosion and, in turn, the NP morphological evolution