Insight into bay-/end-substituted perylene diimide and its S-scheme heterojunction for enhanced photocatalytic H2O2 production under visible-light irradiation

Here, 1D bis(N-carboxymethyl) peryleneimide (H2PDI), 0D 1,6,7,12-tetrachloro- bis(N-carboxymethyl) peryleneimide (4Cl-H2PDI), and 2D 4Cl-H2PDI/graphene quantum dot (4Cl-H2PDI/GQD) nanostructures are synthesized and carefully analyzed. The effect of bay-/end-substitution and S-scheme heterojunction of PDI-based materials as main catalysts on the photocatalytic H2O2 evolution is first studied through the oxygen reduction reaction (ORR). Under the visible-light irradiation (> 420 nm), 4Cl-H2PDI and 4Cl-H2PDI/GQD as photocatalysts exhibit the ∼7 and ∼16 times H2O2 evolution rate than H2PDI (1059.6 vs. 2484.0 vs. 160.0 μM g−1 h−1), respectively. The systematical experiments reveal that 4Cl-H2PDI and 4Cl-H2PDI/GQD should prefer a two-step single-electron ORR process, while H2PDI may involve a 4e‒ water oxidation and one-step 2e‒ ORR process. Further experiments confirm that the bay-substitution and GQD doping of H2PDI can promote the generation, transportation, and separation of photogenerated electrons and holes, and prolong the carrier lifetime. This work provides insight into PDI-based photocatalytic H2O2 production.