and sustainable production technologies is highly urgent. Among many potential options, semiconductor-based photocatalytic H 2 O 2 synthesis from two-electron oxygen reduction at ambient conditions offers a promising strategy, which only uses clean and sustainable solar energy as the energy input. [8][9] The challenge is to explore advanced semiconductor photocatalysts with efficient charge-separation efficiency and favorable surface properties in order to shift the reaction pathway toward the desired H 2 O 2 product. Inorganic semiconductors (such as TiO 2 ) have been investigated for photocatalytic H 2 O 2 production. [10][11][12][13] However, they usually suffer from low H 2 O 2 production rate owing to their narrow light absorption range and undesirable catalytic degradation of H 2 O 2 on transition metals. [14][15] To this end, polymeric photocatalysts, exemplified by graphitic carbon nitride (g-C 3 N 4 ), have attracted increasing attention in recent years because of their tunable chemical structures and metal-free composition. [16][17][18][19] Previous studies revealed that the tri-s-triazine units in g-C 3 N 4 could facilitate the two-electron oxygen reduction by forming a complex with the O 2•− intermediate. [20][21][22] Despite the potential, their demonstrated photocatalytic activities were still unsatisfactory for practical applications.Covalent triazine frameworks (CTFs), as a new class of nitrogen-rich organic photocatalysts, have recently emerged owing to their excellent photocatalytic activities and stability for photocatalytic water splitting, [23][24][25][26] CO 2 reduction, [27][28] N 2 fixation, [29] and organic transformation. [30][31][32] In principle, their chemical and electronic structures can be precisely tuned by varying the corresponding precursors and synthetic routes, making them a versatile platform for designing photocatalysts on demand. [33] Notably, CTFs have intrinsic structural similarity to the polymeric skeletons of g-C 3 N 4 , both of which are constructed from primary triazine units. [34][35][36] This may imply the great potential of CTFs for photocatalytic H 2 O 2 production via the two-electron oxygen reduction. However, their applications in this field have been rarely studied up to now. Recently, Xu and co-workers first reported that the acetylene and diacetylenefunctionalized CTFs could be used as effective photocatalysts for photocatalytic H 2 O 2 production under visible light irradiation. [37] Unfortunately, their photocatalytic efficiency was quite