Alkanethiolate-Protected PbS Nanoclusters: Synthesis, Spectroscopic and Electrochemical Studies

A series of alkanethiolate-passivated PbS nanoparticles were synthesized with varied feed ratios of the starting reactants, lead acetate and alkanethiols, and characterized by using a variety of spectroscopic and electrochemical techniques. Transmission electron microscopic studies revealed that, of all the samples prepared, the particle size mainly fell into the range of 2−4 nm in diameter, with mostly spherical shape and modest dispersity. In addition, the particles were found to be quite stable where the particle size varied only slightly during particle growth. UV−Vis spectroscopy showed an absorption edge at a wavelength between 700 and 800 nm for the larger particles (>3 nm in diameter), while for the smaller particles (2.5 nm in diameter), the absorption edge was found at 560 nm, which was consistent with the size-dependent quantum confinement effect of PbS nanoparticles. Photoluminescence studies were carried out by measuring the excitation and emission spectra of the PbS nanoparticles in solutions, where the fluorescence was found at around 804 nm and the peak intensity appeared to be depressed greatly by the presence of transition-metal (e.g., Au, Ag, and Pd) nanoparticles, despite the relatively weak absorption of metal particles at the red end. Electrochemical studies of the PbS nanoparticles in solution revealed an analogue to the Coulomb blockade that arose from the particle band gap structure within the potential range of from −0.8 to +0.8 V, and at potentials beyond this range, cathodic reduction as well as anodic dissolution of PbS resulted in a series of voltammetric waves, where rather significant overpotentials were observed as compared to those in aqueous media.