Desorption mechanism of gold adsorbed into sub-nanopores of activated carbon in ETAAS

Complete text of publication follows. Thermal desorption of gold from a graphite furnace occurs from microdroplets of various sizes or adsorbed atoms (adatoms), depending on the analyte mass of gold in the conventional pyrolytic graphite (PG) furnace. When the mechanical roughened PG, the tendency of the microdroplets to disperse on the PG was lowered and the decrease in activation energy (Ea) for gold atomization with the decrease in the analyte mass was reported. The Ea with the first order reaction was reached to a lower constant value to be adatom desorption on the roughened PG. On the conventional PG, the appearance and peak temperatures were decreased with decreasing the analyte mass. The first order reaction was observed at the lowest mass. This phenomenon was resulted in the interaction between gold atom and active site on PG surface (surface fractal dimension D2).When the gold was absorbed into powdered activated carbon, the first order reaction process with a great increase of Ea was observed. This increased Ea value means an increase in the interaction between carbon surface and gold atom. Activated carbon (D=3) includes the sub-nanopores, whose diameter is less than 1nm. It was found a correlation ship between the Ea values observed and the capacity of CH4 adsorption at relatively lower pressure. Experimental: A Hitachi model Z-5000 GFAAS equipped with a Zeeman-effect background corrector was used. The output data from a Konica-Minolta TR-600 radiation thermometer was restored in a PC. The thermometer was calibrated with a Pt-Rh thermocouple. Kinetic analysis(S. Imai et al., J. A. A. S., 16 (2001) 398-403.): Kinetic analysis was carried out by the following equation Ln[g(a)T-2]=-Ea R-1 T-1 + Ln[QR(dT/dt)-1 Ea-1] where g(a) is a function for a controlled reaction on the reaction solid phase.