Two-dimensional interface engineering of g-C3N4/g-C3N4 nanohybrid: Synergy between isotype and p-n heterojunctions for highly efficient photocatalytic CO2 reduction

The creation of an isotype phase junction has been recognized as an effective means of improving the spatial charge separation and migration in g-C3N4 materials. Nevertheless, due to a lack of electrostatic control in the internal electric field, isotype heterojunction alone is incapable of providing a sufficient driving force to maximize charge carrier transfer. Herein, we present an interface engineering strategy for co-integrating isotype and p-n heterojunctions to fabricate g-C3N4/g-C3N4 nanohybrids using a facile ultrasonic-assisted self-assembly method. The coherent boundary between the two distinct phases of g-C3N4 demonstrates that an intimate 2D interfacial contact can be easily established by π-π stacking interactions because of their high structural similarities and low lattice strain. Furthermore, their compatible and well-matched electronic band structures led to a staggered type II alignment in the lateral heterojunction, which confers the resulting composite with strong redox ability, efficient exciton dissociation, and desirable optoelectronic characteristics beyond those of the two constituents. Essentially, the isotype and p-n heterojunctions work in tandem to create a robust built-in electric field, allowing for effective interfacial charge steering for directional electron migration from BCN to CNx. Benefiting from these merits, the BCN/CNx nanohybrid manifested remarkable CH4 generation from photocatalytic CO2 reduction, outperforming its CNx and BCN counterparts by 1.91 and 6.88-fold, respectively. The midgap states induced by nitrogen defects in CNx also pose a positive effect on the improved photoactivity of the binary composite by acting as an electron reservoir to mediate electron transfer and further impede charge carrier recombination. This proof-of-concept study highlights the significance of interface engineering in charge flow manipulation and utilization for photocatalytic enhancement.