Eur. Phys. J. Special Topics 224, 1849-1859 (2015)
https://doi.org/10.1140/epjst/e2015-02504-x

Regular Article

A fatal damage of the water dissociation equilibrium on a photocatalyst surface in situ: A real or an imaginary danger?

¹ Ecole des Mines d'Alès, Centre des Matériaux des Mines d'Alès (C2MA), 6 avenue de Clavières, 30319 Alès Cedex, France
² Ecole des Mines d'Alès, Innov'Up, 6 avenue de Clavières, 30319 Alès Cedex, France

^a e-mail: alexis.evstratov@mines-ales.fr

Received: 5 January 2015
Revised: 21 May 2015
Published online: 30 July 2015

Abstract

The surfaces of photocatalytic materials are extremely hydrophilic and so always overcharged, in standard and near standard conditions, in adsorbed water. As shown in the present study, the water adsorbed on the surface of a photocatalyst in operation is deeply dissociated. Its released cationic part, namely the hydronium ions H⁺, stays not involved in the photocatalytic oxidation process. If no compensatory mechanism exists allowing efficient elimination of the H⁺ions from the adsorbed water, a strongly concentrated acid solution may be formed (pH_surf → 0) during a few seconds after the photocatalytic process starts. The current study highlights a particular role of the adsorbed molecular oxygen (AMO) permanently occurring on the photocatalyst surface. Besides of its frequently referred free electron scavenging ability, the AMO ensures a continuous maintenance of the surface acid-base equilibrium at a near-neutral pH thus protecting a photocatalyst in operation against an inevitable and rapid acid destruction.