Initial steps in the reduction of selenium dioxide in aqueous solution and subsequent colloid formation

Abstract

The reduction of selenium(IV) in aqueous solution at pH 6.1 is described employing optical and conductometric pulse radiolysis methods. The reduction of selenium dioxide by hydrated electrons yields SeO−2 with a rate constant of 1.7 × 109 dm3 mol−1 s−1. On the 1 ms time-scale, this reduction is followed by a number of processes yielding Se2O2−4, HSe2O3−5 and H2Se4O6−10 as intermediates with the rate constants 2k2 = 2 × 109 , k3 = 1 × 109 and 2k4 = 1.6 × 108 dm3 mol−1 s−1. The extinction coefficients of the intermediates have been determined by simulating the kinetic traces at different wavelengths, and based on those values the respective absorption spectra were constructed. If the solution is irradiated by several pulses of high-energy electrons or with 60Co γ-rays, small selenium clusters are produced exhibiting a broad absorption with a maximum at 270 nm. These results suggest that the final product of the reduction of Se(IV) by hydrated electron is the selenium aggregate. The selenium clusters are stable for some months in the presence of air and are characterized using transmission electron microscope with a diameter ranging between 50 and 120 nm.