THIOL-DERIVATIZED AGI NANOPARTICLES - SYNTHESIS, CHARACTERIZATION, AND OPTICAL-PROPERTIES

Thiol-passivated AgI nanoparticles of 7-15 nm were synthesized in larg e quantities by changing the initial molar ratio of iodide to 1-thiogl ycerol, and thus their competitive reaction rates with silver ions was adjusted, leading to a precise control of the final particle size. Po wder X-ray diffraction and transmission electron microscopy showed tha t these particles crystallized as a mixture of beta- and gamma-AgI, wi th the content of the gamma-phase increasing from 26% for 7 nm to 60% for 15 nm. Elemental analysis, thermogravimetric analysis, and Fourier transform infrared spectroscopy indicated that thiolate anions are at tached to the AgI surface through mercapto groups, and furthermore, th e silver thiolate molecular complex exists as a result of the competit ive reactions. The percentage of the initial thiolate used for capping AgI particles increased linearly with the increase in [I-]/[1-thiogly cerol], showing that almost pure thiol-covered AgI particles of 15 nm can be obtained. Optical spectroscopic studies in diluted solution con firmed the above competitive mechanism of AgI formation. The smallest AgI particles stabilized by 1-thioglycerol and surviving several days in water, observed in a solution of 3.33 x 10(-4) M Ag+, 6.67 x 10(-4) M I-, and 6.67 x 10(-3) M 1-thioglycerol at room temperature, had an absorption peak at 331 nm.