Tailoring the electronic structure of polymeric carbon nitrides is key to advancing sustainable photocatalysis. Nitrogen-rich graphitic carbon nitride (g-C3N5) exhibits a narrower band gap, higher electron density, and stronger basicity than conventional g-C3N4, yet its photocatalytic activity remains limited by inefficient charge separation and fast recombination. Here, a 0D/2D heterojunction of amino-rich carbon quantum dots (AR-CQDs) anchored onto triazole-based g-C3N5 is reported via an ultrasound assisted hydrothermal strategy. The AR-CQDs induce N2C vacancies and generate shallow interfacial states, enhancing charge separation and surface reactivity. The AR-CQDs/g-C3N5 heterojunction achieves a CO2 reduction rate of 2653 ± 0.5 µmol h−1 g−1, outperforming g-C3N5 and g-C3N4 by factors of 7 and 48, respectively. It exhibits a 3.4-fold increase (91 ± 2 µmol g−1) in H2 evolution over g-C3N5, with excellent stability across multiple cycles. Femtosecond transient absorption spectroscopy reveals an interfacial electron transfer on the picosecond timescale from photoexcited AR-CQDs to g-C3N5. This oxidative quenching process provides mechanistic evidence that ultrafast charge transfer underpins the enhanced photocatalytic performance. The combined structural engineering and spectroscopic insights establish AR-CQDs/g-C3N5 heterojunctions as a robust and metal-free platform, coupling defect/interface design with ultrafast charge dynamics for improved solar-to-fuel energy conversion systems.