화학공학소재연구정보센터
Chemical Reviews, Vol.117, No.17, 11302-11336, 2017
Generation and Detection of Reactive Oxygen Species in Photocatalysis
The detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS), i.e., superoxide anion radical (O-center dot(2)-), hydrogen peroxide (H2O2), singlet oxygen (O-1(2)), and hydroxyl radical ((OH)-O-center dot) in photocatalysis, were surveyed comprehensively. Consequently, the major photocatalyst used in heterogeneous photocatalytic systems was found to be TiO2. However, besides TiO2 some representative photocatalysts were also involved in the discussion. Among the various issues we focused on the detection methods and generation reactions of ROS in the aqueous suspensions of photocatalysts. On the careful account of the experimental results presented so far, we proposed the following apprehension: adsorbed (OH)-O-center dot could be regarded as trapped holes, which are involved in a rapid adsorption desorption-equilibrium at the TiO2-solution interface. Because the equilibrium shifts to the adsorption side, trapped holes must be actually the dominant oxidation species whereas (OH)-O-center dot in solution would exert the reactivity mainly for nonadsorbed reactants. The most probable routes of generating intrinsic ROS at the surfaces of two polymorphs of TiO2, anatase and rutile, were discussed along with some plausible rational reaction processes. In addition to the four major ROS, three ROS, that is organic peroxides, ozone, and nitric oxide, which are less common in photocatalysis are also briefly reviewed.