Unravelling the role of dual quantum dots cocatalyst in 0D/2D heterojunction photocatalyst for promoting photocatalytic organic pollutant degradation.

• FeOOH QDs/CQDs/g-C 3 N 4 0D/2D heterojunction has been first prepared. • 0D/2D heterojunction can realize H 2 O 2 generation and in-situ decomposition. • The composite has excellent charge carrier transfer and separation efficiency. • The introduction of CQDs can improve the photoconversion efficiency. • The generated Fe2+ in FeOOH QDs can promote H 2 O 2 in-situ decomposition. Hydrogen peroxide (H 2 O 2) was generally considered as an ideal energy carrier and environment-friendly oxidant to process environmental modification. Here, FeOOH QDs and CQDs was interspersed on g-C 3 N 4 ultrathin nanosheet to promote H 2 O 2 generation and in-situ decomposition. FeOOH QDs/CQDs/g-C 3 N 4 composite (FCCN) exhibited excellent photoactivity for degrading oxytetracycline (OTC) under visible light illumination. The accelerated photoactivity is ascribed to the following merits: 1) the exciton dissociation interface and carrier transfer channel are fabricated to facilitate photoexcited electron transfer; 2) the photoexcited electron can be rapidly utilized by molecular oxygen to generate H 2 O 2 , resulting in facilitated molecular oxygen activation; 3) Fe3+ in FeOOH QDs is reduced to Fe2+ by photoexcited electron, and then reacts with generated H 2 O 2 to produce OH, thereby promoting photodegradation efficiency. The H 2 O 2 generation yield of FCCN-2 composite was 224.24 µmol h−1 g−1, which was higher than that of pure g-C 3 N 4. 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation and O 2 − quantitative determination displayed outstanding molecular oxygen activation capacity of hybrid composite. Moreover, 0D/2D heterojunction photocatalyst displayed weakened charge carrier recombination efficiency (0.0015 s−1) and expedited surface carrier transfer efficiency (41.01%) compared to g-C 3 N 4 and CQDs/g-C 3 N 4 photocatalyst. Finally, the photodegradation mechanism were rationally evaluated based on the experiment results. [ABSTRACT FROM AUTHOR]