Improved photocatalytic H2O2 production of boron doped g-C3N4 by controllably co-modifying nanosized PDI and Ag

•Nanosized PDI and Ag co-modified boron doped g-C3N4 is successfully designed and synthesized.•The optimal heterojunction exhibits high H2O2 production rate under visible light irradiation.•Improved photoactivity is due to the enhanced charge separation and promoted oxygen activation.•There is a dual channel for H2O2 production on as-fabricated heterojunctions.