O2(1Δ) Quenching Mechanism in Cl2/Basic Hydrogen Peroxide(Basic Deuterium Peroxide) Gas/Liquid Reaction and the Determination of O2(1Δ)/BHP(BDP) Interface Free Energy

• Published in: Journal of physical chemistry. C Vol. 112; no. 25; pp. 9412 - 9417
• Main Authors: Shi, Wenbo, Deng, Liezheng, Du, Shuyan, Cui, Rongrong, Yang, Heping, Sha, Guohe, Zhang, Cunhao
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.06.2008
• Subjects: C: Surfaces, Interfaces, Catalysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp8005348

In a jet-type singlet oxygen generator, we have studied the generation of O2(1Δ) via the reaction of chlorine gas with aqueous basic hydrogen peroxide (BHP) and with basic deuterium peroxide (BDP). The O2(1Δ) detachment yield with BDP is measured to be 72.5 ± 1.5%, merely 2.5% higher than that with BHP, despite a 10 times longer O2(1Δ) lifetime in BDP than in BHP. By a careful kinetic analysis of the Cl2 + BHP(BDP) reactions, we found that the main resistance that prevents the nascent O2(1Δ) from escaping off the solution into the bulk gas flow does not lie in the liquid or gas phase, but in the gas/liquid interface. Thus, the seemingly weird experimental result can be justified by postulating a higher energy barrier at the O2(1Δ)/BDP interface than that of the O2(1Δ)/BHP so as to detain the O2(1Δ) for a longer time in BDP. In fact, this postulation has been proved as follows: according to the physical model of Copeland and Zagidullin, the O2(1Δ) mass accommodation coefficient is calculated from our experimental solvation detachment yield to be ∼4.0 × 10−6 on the BHP surface and ∼1.7 × 10−6 on the BDP surface. Then, based on the thermodynamics of phase equilibrium in dilute solutions, the corresponding Gibbs energy of O2(1Δ) at the BHP surface is computed as ∼2.65 × 104 J/mol, and the value of O2(1Δ) at the BDP surface is ∼2.86 × 104 J/mol. This higher O2(1Δ)/BDP interface energy barrier may result from both larger D2O molecular mass and stronger hydrogen bonding between D2O molecules in BDP solution. The present methodology can be further improved by using microwave-discharge production of O2(1Δ) so as to make direct measurements of its quenching probability. Hence, more key thermodynamic and kinetic information about the O2/aqueous electrolyte solution interfaces will be made available. Work along this line is now under way.