LAUSR

Abstract NO x liberated into atmosphere from automobile exhausts and fossil fuel combustion, comprise the major air pollutants. They are responsible for serious environmental problems such as acid rain, ozone accumulation, haze and photochemical smog. Besides they contribute to the deterioration of human health by causing decrease of the lung function and respiratory problems. The application of photocatalytic methods in order to mitigate the presence of NO x in the atmosphere is preferable as they are environmentally friendly, mild and low cost. Therefore, in this review, the photocatalytic activity of g-C 3 N 4 and graphene based composites towards NO x removal was discussed. NO x oxidation to non volatile nitrates on the surface of graphene and g-C 3 N 4 based photocatalysts has attracted much interest during the last years due to their structures with unique features such as large specific surface area, thermal and chemical stability and enhanced visible light utilization. The formation of 2D-2D intimate heterojunctions between graphene or g-C 3 N 4 and other components ensures the enhanced charge transfer, lifetime of electron/hole pairs and thus photocatalytic activity. The increased visible light harvesting also contributes to their usefulness as effective photocatalytic materials. In the present work, the advantages of these novel photocatalysts and the differences/similarities between them were exhaustively highlighted. The role of graphene as catalyst promoter, electron reservoir, support and photosensitizer in its photocatalytic composites was emphasized. The effect of g-C 3 N 4 doping and copolymerization with metals/semiconductors on its photocatalytic activity towards NO x oxidation was thoroughly discussed. Besides, the preparation methods, photocatalytic efficiencies, type of irradiation, utilization of appropriate cocatalysts, and reaction mechanisms during the photocatalytic NO x removal by graphene and g-C 3 N 4 composies, were summarized. It was demonstrated that in the vast majority of graphene and g-C 3 N 4 based photocatalysts, the dominant reactive species on their surface during photocatalytic NO x removal, are O 2 − radicals.