(160u) Formation Kinetics and Characteristics of Lead Sulfate Nanocrystals in Reverse Microemulsion

Formation kinetics and characteristics of lead sulfate nanocrystals, PbSO4, in the nonionic W/O reverse microemulsion were studied mainly with the UV/Visible light spectroscopy, the TEM with electron diffraction, and the dynamic light scattering. The average size of reverse microemulsion droplets measured by the DLS is around 30 nm. However, the TEM micrograph of the harvested lead sulfate crystals at 48 hours after two reverse microemulsions respectively containing Pb+2 and SO4-2 brought into contact exhibits a larger dimension, circa 120~200 nm, than that of the reverse microemulsion (Figure 1). Moreover, long narrow rods of PbSO4 extended to about 10 microns could be occasionally observed. The electron diffraction patterns of these PbSO4 nanocrystals shown in Figure 1 indicate orthorhombic lattices as their preferred structure. The Beer-Lambert's law was successfully employed to observe the formation kinetics of PbSO4 in reverse microemulsion by monitoring the change of their absorbance at 248 nm. It was found that the apparent reaction order of the formation reaction was one in both Pb+2 and SO4-2 concentrations. In this presentation, we will discuss the growth mechanism of lead sulfate crystals, and the advantages and difficulties of using the UV/Visible light spectroscopy as an on-line tool to observe the reaction of the nan0particle formation in reverse microemulsion.

Figure 1: TEM micrograph of harvested PbSO4 crystal in reverse microemulsion.