Construction of a Switchable g-C3N4/BiVO4 Heterojunction from the Z-Scheme to the Type II by Incorporation of Pyromellitic Diimide

g-C3N4/BiVO4 is considered to be a preeminent composite photocatalyst owing to its suitable band position, intrinsic Z-scheme heterostructure, and high photostability. However, its application is limited owing to the short lifetime of photoexcited charges and weak photooxidation capability. In this work, the g-C3N4 structure is tailored using pyromellitic diimide (PI) then hybridized with BiVO4 to construct the g-C3N4/PI/BiVO4 (CPB) photocatalyst. The morphology analysis shows that coral-like nanorod BiVO4 is coated on the stacked lamellar g-C3N4/PI surface. Addition of g-C3N4/PI enhances the solar efficiency as well as promotes interfacial charge separation and migration, thus lengthening the charge carriers' life span. Photocatalytic activity is detected via photooxidation of the organic dye methylene blue (MB) and phenolic antibiotics bisphenol A (BPA) and norfloxacin (NFC). A significantly boosted photocatalytic activity is achieved by the CPB photocatalyst, the CPB-2 photocatalyst with a 30% mass fraction of g-C3N4/PI displays the best visible-light catalytic activity, and 89.9% MB is mineralized within 100 min, which is significantly enhanced in composition with g-C3N4/BiVO4 (74%) and mix(g-C3N4/PI, BiVO4) (56%). An improved activity results in a higher light absorption capacity, a lower transfer resistance of electron-hole pairs, and a stronger photooxidation power. Importantly, the Z-scheme g-C3N4/BiVO4 composite with an inherent built-in electric field (E) switches to a type-II heterojunction after incorporating PI with g-C3N4 but without compromising the photocatalytic performance. The result may be due to the fact that the van der Waals force of BiVO4 and g-C3N4 is destroyed after incorporating PI into g-C3N4, giving rise to the disappearance of the built-in electric field. The study provides a paradigm for designing efficient photocatalysts by tailoring organic frameworks for specific photocatalytic reactions or photoreactions.