Cadmium(II) Ion-Selective Electrodes Based on Nanocadmium Sulfide Particles Prepared from Sparingly Soluble Cadmium(II) Salts
Nano CdS particles have been prepared by a novel homogeneous precipitation method. In a solution of thioacetamide, whereby S2- ions are supplied through hydrolysis, one of the sparingly soluble salts CdCO3, CdC2O4, and CdS was brought into contact with the solution to release Cd(II) ion in infinitesimal doses. The size of the formed particles has been confined by capping the nuclei with cetyltrimethylammonium bromide (CTAB). The produced particles were characterized using UV-Visible spectrophotometry, FTIR and X-ray diffraction spectroscopy, as well as transmission electron microscopy (TEM). The results showed that the particles are capped with CTAB, have face centered cubic and hexagonal structures, and characterized by energy gaps far less than that of bulk CdS. The prepared CdS nanoparticles were used as the active ingredient in a PVC polymeric Cd(II)-ion selective electrode. The investigation of the performance characteristics of the electrode showed that it has working concentration range of 1.0 x 10-6 - 1.0 x 10-2 M, a pH range of 2.2 – 5.8, a response time of about 10 s, a life-span extending to 70 days, average detection limit of 8.65 x 10-7M average calibration graph slope of 28.56mV/concentration decade, and high selectivity towards many inorganic cations.
To determine the cause of limitation regarding the life span of the electrodes, the surfaces of exhausted and fresh electrodes have been analyzed with depth profiling X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results showed that the electrode has lost its activity as a result of leaching of the active ingredients as a result of extending use over a long time.