Efficient Photocatalytic Production of H2O2 over ZnO/D-A Conjugated Polymer S-Scheme Heterojunction and Charge Transfer Dynamics Investigation

Abstract

Photocatalytic technology harnesses clean, non-polluting solar energy to synthesize hydrogen peroxide (H₂O₂). In this study, ZnO/PBD S-scheme heterojunction composites, featuring ZnO nanoparticles on a donor-acceptor conjugated polymer substrate (PBD), were synthesized via the Suzuki-Miyaura reaction and hydrothermal method. The optimal ZnO/PBD composite achieved an H₂O₂ production efficiency of 4.07 mmol·g⁻¹·h⁻¹, which is 5.4 times higher than that of pristine ZnO. This significant enhancement is attributed to the formation of S-scheme heterojunctions. The successful construction of S-scheme heterojunctions was confirmed through UV-visible absorption spectroscopy and in situ irradiated X-ray photoelectron spectroscopy. Steady-state photoluminescence and femtosecond transient absorption (fs-TA) spectroscopies identified and verified the presence of defect states in ZnO. These defect states trap photogenerated electrons, adversely affecting the photocatalytic reaction. However, the S-scheme heterojunction effectively promotes the separation and transfer of electrons, mitigating this issue. The measured lifetimes of photogenerated electrons in these defect states, as determined by fitted fs-TA decay kinetics, provided further evidence of the carrier transfer mechanism in S-scheme heterojunctions. This work introduces a novel approach for studying organic/inorganic S-scheme heterojunctions using fs-TA spectroscopy.

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