The construction of S-scheme heterojunction represents a simple yet effective strategy for enhancing photogenerated charge carrier separation and optimizing the reduction and oxidation capability of the photocatalytic system. However, precise tuning of the internal electric field for optimizing charge carrier migration across the heterojunction remains challenging. Herein, we present a novel defect engineering approach to modulate the potential barrier in S-scheme heterojunctions through strategic oxygen vacancy introduction. Specifically, we first selectively introduce oxygen vacancies on Bi₂WO₆, followed by coupling with g-C₃N₄ to form oxygen-deficient Bi₂WO₆/g-C₃N₄ (OVs-BWO-CN) S-scheme heterojunction. Surprisingly, the selective oxygen vacancy engineering on OVs-BWO cannot only preserve the features of common oxygen vacancies, but also shrink the potential barrier formed between OVs-BWO and CN. This reduction in potential barrier facilitates enhanced charge carrier migration across the heterojunction interface. As a direct consequence of this optimized charge transfer, the CN/OVs-BWO heterojunction demonstrates exceptional photocatalytic CO₂ conversion performance, reaching a CO production rate of 48.65 μmol h⁻¹ g⁻¹. Such a work on selective oxygen vacancy engineering for optimizing potential barrier can provide important guidelines for photocatalysis.

Coupling bulk and interface electric field for enhancing photogenerated charge carrier separation represents an effective strategy toward enhancing photocatalytic performance due to the potential of superposition of electric field. However, the detailed mechanism of synergistic effect of the bulk and interface electric field in facilitating photogenerated charge carrier remains underexplored, limiting its wide applications. Herein, we integrate the bulk electric field of Bi₂MoO₆ (BMO) with interface electric field (IEF) of S-scheme heterojunction formed between BMO and Bi₁₉Br₃S₂₇ (BBS) for enhancing photocatalytic performance. The two electric fields can not only superimpose for amplifying electric field strengths, but also act as the funnel for guiding photogenerated charge carrier migration towards specific regions for redox reactions. Moreover, the Mo–S bonds formed between BMO and BBS act as a channel for charge transfer, accelerating the charge transfer of the S-scheme and achieving effective charge separation. As a proof-of-concept, we employ optimized BMO/BBS S-scheme heterojunction for photocatalytic CO₂ conversion, reaching about 32.4 times and 2.0 times to that of pristine BMO and unmodulated BMO/BBS for CO production. This method of promoting the IEF by coupling bulk and interface electric field provides new insights into the construction of S-scheme heterojunctions for photocatalysis.

Ag surface plasmon resonance promoted step-scheme (S-scheme) SnNb₂O₆/Ag₃PO₄ heterojunctions were constructed via simple chemical deposition and precipitation. The samples were characterized by X-ray diffractometer, field-emission scanning electron microscope, high resolution transmission electron microscope, X-ray photoelectron spectrometer, UV-Vis diffuse reflectance spectrometer and photoluminescence spectrometer. The photocatalytic activities of SnNb₂O₆, Ag₃PO₄ and SnNb₂O₆/Ag₃PO₄ composites can be determined via degradation experiments. The results show that the SnNb₂O₆/Ag₃PO₄ composite possesses an optimum degradation performance in the photocatalytic degradation of methylene blue. Besides, the pseudo–first–order rate constant (K_app) of SnNb₂O₆/Ag₃PO₄ is 0.313 min^–1, which is 13.1 times and 4.8 times greater than that of SnNb₂O₆ and Ag₃PO₄, respectively. Also, Ag surface plasmon resonance–promoted SnNb₂O₆/Ag₃PO₄ S-scheme heterojunction can accelerate the separation of electron-hole pairs, thereby enhancing the redox reaction capability of the whole system.