Inorganic–Organic Bi4Nb1–xTaxO8Cl/rGO/SA-PTA Z-Scheme Heterojunction with a Third-Order Polarized Electric Field and a Fast Electron Transfer Channel for Photocatalytic Overall Water Splitting

The effective separation and rapid transfer of photogenerated charges in the hydrogen evolution photocatalyst (HEP) and oxygen evolution photocatalyst (OEP) are crucial for achieving overall water splitting. Here, a third-order polarization electric field composed of an internal electric field (InEF1), an internal electric field (InEF2), and a Z-scheme interface electric field (IfEF3) was formed by the flowable π electrons of rGO to couple the enhanced interlayer polarization in Bi₄Nb_1–xTa_xO₈Cl and the increased molecular dipole moment in perylene tetracarboxylic acid (SA-PTA). This third-order polarized electric field with full space coverage provided a continuous driving force for the effective separation of photogenerated charges from the interior to the surface of the OEP (Bi₄Nb_1–xTa_xO₈Cl) and then to the HEP (SA-PTA), resulting in a 3.6-fold increase in charge separation efficiency. Furthermore, in the inorganic–organic Bi₄Nb_1–xTa_xO₈Cl/rGO/SA-PTA Z-scheme heterojunction, SA-PTA was selectively anchored to rGO through hydrogen bonding and π–π stacking, thereby establishing a fast electron transfer channel between Bi₄Nb_1–xTa_xO₈Cl and SA-PTA, achieving flow of interface charges from the OEP to HEP, and shortening of the interface charge transfer time from 54.8 to 38.2 ps. Benefiting from the accelerated charge transfer kinetics and strong oxidation–reduction ability, Bi₄Nb_1–xTa_xO₈Cl/rGO/SA-PTA exhibited a high activity of water oxidation and overall water splitting. In water oxidation, the evolution rate of O₂ was 31.6 μmol h^–1, which was 18.6 times that of Bi₄NbO₈Cl. In the overall water splitting, the evolution rates of H₂ and O₂ were 3.7 and 1.9 μmol h^–1, respectively, which were 5.2 times that of Bi₄Nb_1–xTa_xO₈Cl/SA-PTA. In conclusion, this work provides a guideline for regulating interface interactions and accelerating charge transfer kinetics.