In this work, we report the effect of a capping agent on the structural and optical properties of nanocrystalline ZnS particles, which have been synthesized by co-precipitation method. The structural properties of ZnS nanoparticles have been characterized by X-ray diffraction (XRD) analysis. The XRD patterns show a hexagonal structure in the nanoparticles. The mean crystallite size calculated from the XRD patterns has been found to be in the range of 1.80 to 2.45 nm with the increase in molar concentration of the capping agent. Absorption spectra have been obtained using a UV-vis spectrophotometer to find the optical direct band gap. We also found that optical band gap (Eg) increases with the increase in molar concentration of the capping agent. This behavior is related to size quantization effect due to the small size of the particles.

ZnS phosphorescent nanocrystal of a size ~ (50±7A°) has been synthesized which exhibit quantum effects. The phosphorescent nanocrystal compound is linked to an affinity molecule (e.g. Mercaptoethanol or mercap toacetic acid) to form an organo phosphorescent nanocrystal probe capable of bonding with a detectable substance in a material being analyzed (biological target e.g. biotin) and capable of emitting electromagnetic radiation in a narrow wavelength band. The products were analyzed by the x-ray diffraction (XRD), photoluminescence (PL) transmission electron microscopy (TEM).

A carbon-paste electrode modified with iron (II) phthalocyanine (FePc) was used as a sensitive potentiometric sensor for determination of 2-pyridinethiol (2PT), 2-Mercaptoethanol (2ME) and sulfide ion in aqueous solutions. The modified electrode acts as an electrocatalyst for oxidation of these compounds, and lowers the overpotential for oxidation reactions by more than 400 mV, compared to the unmodified electrode. The process was dependent on the pH of the supporting electrolyte. The fast rate of electron transfer results in a near-Nernstian behavior of the modified electrode, and makes it a suitable potentiometric sensor for measurement of these compounds. Calibration studies were performed using potentiometry in oxygen or air saturated stirred solutions; linear responses were obtained over the range of about 1x10-6 to 5x10-3 M (correlation coefficients, r, of similar 0.999, n=8). The modified electrode exhibited a fast response time (< 20 s), good stability, and had an extended lifetime; the standard deviation of slopes, during a period of two months, was 1.7-2.4% (n=10). Appropriate electrochemical and analytical data are presented.