Singlet Oxygen and Mobile Hydroxyl Radicals Co-operating on Gas-Solid Catalytic Reaction Interfaces for Deeply Oxidizing NOx

Learning from the important role of porphyrin-based chromophores in natural photosynthesis, a bionic photocatalytic system based on tetrakis (4-carboxyphenyl) porphyrin-coupled TiO2 was designed for photo-induced treating low-concentration NOx indoor gas (550 parts per billion), achieving a high NO removal rate of 91% and a long stability under visible-light (lambda >= 420 nm) irradiation. Besides the great contribution of the conventional O-center dot(2)- reactive species, a synergic effect between a singlet oxygen ((OHf)-O-center dot) and mobile hydroxyl radicals MHO was first illustrated for removing NOx indoor gas (O-1(2) + 2NO -> 2NO(2), NO2 + (OHf)-O-center dot -> HNO3), inhibiting the production of the byproducts of NO2. This work is helpful for understanding the surface mechanism of photocatalytic NOx oxidation and provides a new perspective for the development of highly efficient air purification systems.