Carbonate Radical Formation in Radiolysis of Sodium Carbonate and Bicarbonate Solutions up to 250 °C and the Mechanism of its Second Order Decay

Abstract

Pulse radiolysis experiments published several years ago (J. Phys. Chem. A, 2002, 106, 2430) raised the possibility that the carbonate radical formed from reaction of *OH radicals with either HCO(3)(-) or CO(3)(2-) might actually exist predominantly as a dimer form, for example, *(CO(3))(2)(3-). In this work we re-examine the data upon which this suggestion was based and find that the original data analysis is flawed. A major omission of the original analysis is the recombination reaction *OH + *CO(3)(-) --> HOOCO(2)(-). Upon reanalysis of the published data for sodium bicarbonate solutions and analysis of new transient absorption data we are able to establish the rate constant for this reaction up to 250 degrees C. The mechanism for the second-order self-recombination of the carbonate radical has never been convincingly demonstrated. From a combination of literature data and new transient absorption experiments in the 1-400 ms regime, we are able to show that the mechanism involves pre-equilibrium formation of a C(2)O(6)(2-) dimer, which dissociates to CO(2) and peroxymonocarbonate anion: *CO3(-)+*CO3(-)<-->C2O6(2-)-->CO2+O2COO(2-) *CO3(-) reacts with the product peroxymonocarbonate anion, producing a peroxymonocarbonate radical *O2COO(-), which can also recombine with the carbonate radical: *CO3(-)+CO4(2-)-->*CO4(-)+CO3(2-) *CO3(-)+CO4(-)-->C2O7(2-).

Mechanistic Studies on the Role of [CuII(CO3)n]2−2n as a Water Oxidation Catalyst: Carbonate as a Non‐Innocent Ligand

“…The formation of C 2 O 6 2− is followed by the reactions given in Equations …”

“…The mechanism of C 2 O 6 2À formation at pH 11 is summarised in Scheme 1. The formation of C 2 O 6 2À is followed by the reactions given in Equations (40)- (42). [42]…”

Controlled leaching with prolonged activity for Co–LDH supported catalyst during treatment of organic dyes using bicarbonate activation of hydrogen peroxide

“…4C, it is clear that CoMgAl-4 catalyst showed the lowest catalytic activity both with H 2 O 2 and bicarbonate alone, but its activity significantly increased by the addition of H 2 O 2 together with bicarbonate. This enhanced activity of catalyst together with H 2 O 2 and bicarbonate suggested hydrogen peroxide activation produces different reactive oxygen species, such as • OH, singlet oxygen, superoxide, carbonate anion radical, and a prominent peroxymonocarbonate [14][15][16][17][18][29][30][31]. From Fig.…”

“…The carbonate radical anion is produced by the scavenging of • OH as shown in Eqs. (1) and (2), exists for a long time and producing various ROS directly or indirectly [17,18,[29][30][31].…”

Reactive Inorganic Oxy‐Species of C, N, S, and P

“…The self-recombination of CO 3 •− is second order [38,39]. The kinetics of the reaction was studied with temperatures of up to 250°C to understand the mechanism, which suggests oxygen transfer reactions [38].…”