Luminescent Chemical Waves in the Cu(II)-Catalyzed Oscillatory Oxidation of SCN^- Ions with Hydrogen Peroxide

Abstract

The oscillatory oxidation of thiocyanate ions with hydrogen peroxide, catalyzed by Cu2+ ions in alkaline media, was so far observed as occurring simultaneously in the entire space of the batch or flow reactor. We performed this reaction for the first time in the thin-layer reactor and observed the spatiotemporal course of the above process, in the presence of luminol as the chemiluminescent indicator. A series of luminescent patterns periodically starting from the random reaction center and spreading throughout the entire solution layer was reported. For a batch-stirred system, the bursts of luminescence were found to correlate with the steep decreases of the oscillating Pt electrode potential. These novel results open possibilities for further experimental and theoretical investigations of those spatiotemporal patterns, including studies of the mechanism of this chemically complex process.

The Model of “Minimal Oscillator” Derived from the Kinetic Mechanism of the H2O2-NaSCN-NaOH-CuSO4Dynamical System

“…Another complex oscillatory and bistable system, discovered and studied by M. Orbán et al as well as later in our group , involved the oxidation of thiocyanate ions with hydrogen peroxide in an alkaline medium (pH ≥ 9), in the presence of CuSO 4 as an initial catalytic species. The original mechanism of Luo et al engaged 26 dynamical variables, from which we extracted simplified nine– and five–variable schemes as the models of the oscillations.…”

Oscillating chemiluminescence systems: state of the art

“…In fact, spatio-temporal patterns were observed in the immobilized (unstirred) thin layer of solution containing this oscillating system (47). The experiment was performed in a thin-layer reactor, assembled from two round glass plates with reacting solution placed between them.…”

“…Hence, considering the CL mechanism of luminol in alkaline medium, the luminescent zones in the thin-layer reactor indicated a relatively high local concentration of oxygen. In this case, luminol may serve as a fast indicator for the local enhancement of oxygen concentration (47).…”

Mechanism of the oscillating chemiluminescence reaction in the luminol‐H2O2‐KSCN‐CuSO4‐NaOH system

“…Gao et al 14 observed the oscillations using a Pt electrode with p-nitrobenzene-azo-naphthol instead of luminol. Orlik et al [15][16][17] observed that the Pt electrode potential peak decreased and the Au electrode potential peak increased at strong oscillating chemiluminescence. They discussed with their simulation that the Au electrode reflected the increase in [Cu(OH) 3 − ]/[Cu(OH) 2 − ] ratio.…”