engleski

Voltammetry of chalcogenide nanoparticles ; The preconcentration mechanism at Hg0 surfaces

Methods for detecting synthetic chalcogenide (MeX, X = S, Se, Te) nanoparticles at trace levels in the environment are of interest in view of possible large-scale comercialization of nanotechnology. Natural aquatic metal sulfide nanoparticles already have been observed. Nanoparticles composed of several metal sulfides sorb strongly at Hg0 electrodes , where cumulative deposits can be quantified by cathodic scans (MeS&#61664; Me0 amalgam). Thus Hg0 electrodes can serve both for preconcentration and for determination of chalcogenide nanoparticles. Detection at <10-6 M (as MeT) has been demonstrated and lower limits are probably feasible. Understanding the preconcentration mechanism is the key to optimizing detection of chalcogenide nanoparticles. In a detailed study of semi-spherical, copper sulfide (CuxS) aggregate particles having mean diameters of 5-20 nm, a threestep mechanism is required to explain preconcentration. The first step involves Brownian diffusion of particles to the Hg0 surface. When both the electrode and particles have negative surface potentials, this process resembles charge-impeded coagulation, obeying the Schulze-Hardy rule in various electrolytes. The second step involves atomic reordering of CuxS, probably to CuxS adlayers. A very significant (~0.3 V) negative shift in the CuxS reduction potential results, owing to a free energy decrease from release of the nanoparticles. surface energy and from favorable chemical interactions between CuxS adlayers and Hg0. The third step, which competes with the second, involves size-dependent, reductive loss of electroactive CuxS prior to the cathodic scan. This loss is greatest for the smallest particles with greatest surface free energy.

voltammetry; calcogenide nanoparticles

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