Synergistic photocatalytic treatment of aromatic hydrocarbons/NOx mixtures over TiO2: The activation and replenishment of lattice oxygen

The photocatalytic oxidation (PCO) mechanisms of single aromatic hydrocarbons/NO x gases and the synergistic photocatalytic treatment of their mixtures over TiO 2 (anatase) are proposed by analyzing the evolution of adsorbed and gas-phase intermediates through in-situ FTIR and mass-spectroscopy. Photo-activated surface lattice oxygen of TiO 2 (TiO 2 (·O L )) is found to be a strong oxidant for the PCO of both o-xylene and NO x and their consumption led to the deactivation of photocatalysts. As an important coexist air pollutant, NO is firstly discovered as a helper for the persistent ring-opening and degradation of aromatics including o-xylene, toluene, styrene and benzene. NO 2 , a PCO intermediate of NO, acts as a powerful oxidant for replenishing lattice oxygen of TiO 2 , which guarantees the continuous generation of active TiO 2 (·O L ) and prevents the deactivation of photocatalyst. With the introduction of NO, the PCO efficiency of o-xylene increases from ∼65% to 100% and no performance decay of TiO 2 happens in 6 h. The existence of aromatics prevents the escape of toxic NO 2 into air and promotes the harmless transformation of NO into nitrite/nitrate ions and N 2 . This work outlines the essential role of activation and replenishment of lattice oxygen in the PCO process by analyzing the synergistic and stable photocatalytic treatment of aromatic hydrocarbon/NO x mixtures, which explores the practical potentiality of photocatalysis in air purification.