In the present work, it is very surprising to find that the precursors mass, a long overlooked factor for synthesis of 2D g-C₃N₄, exerts unexpected impact on g-C₃N₄ fabrication. The nanoarchitecture and photocatalytic capability of g-C₃N₄ can be well-tailored only by altering the precursors mass. As thiourea mass decreases, thin g-C₃N₄ nanosheets with higher surface area, elevated conduction band position and enhanced photocatalytic capability was triumphantly achieved. The optimized 2D g-C₃N₄ (CN-2T) exhibited exceptional high photocatalytic performance with a NO removal ratio of 48.3%, superior to that of BiOBr (21.3%), (BiO) ₂CO₃ (18.6%) and Au/(BiO)₂CO₃ (33.8%). The excellent activity of CN-2T can be ascribed to the co-contribution of enlarged surface areas, strengthened electron-hole separation efficiency, enhanced electrons reduction capability and prolonged charge carriers lifetime. The DMPO ESR-spin trapping and hole trapping results demonstrate that the superoxide radicals (•O₂−) and photogenerated holes are the main reactive species, while hydroxyl radicals (•OH) play a minor role in photocatalysis reaction. By monitoring the reaction intermediate and active species, the reaction mechanism for photocatalytic oxidation of NO by g-C₃N₄ was proposed. This strategy is novel and facile, which could stimulate numerous attentions in development of high-performance g-C₃N₄ based functional nanomaterials. Copyright © 2015 Nature Publishing Group, a division of Macmillan Publishers Limited.