Internal Interactions within the Complex Type-II Heterojunction of a Graphitic Carbon Nitride/Black Phosphorus Hybrid Decorated with Graphene Quantum Dots: Implications for Photooxidation Performance

Abstract

In this study, Fermi levels of graphitic carbon nitride (CN), black phosphorus (BP), and graphene quantum dots (GQDs) were rationally combined and tuned through a band engineering approach. The structure–activity relationship of the resulting heterojunction was characterized by using a combination of X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance techniques. The results revealed that CN and BP were in contact through the formed P–N bridges, while the polar functional groups of GQDs interacted with BP and CN via P–O and N–O interactions, respectively. The superior degradation efficiency is attributed to the synergistic effect of the strong coupling at the interfaces where GQDs@CNBP was tested in removal of organic pollutants [methyl orange (MO) and tetracycline (TC)]. The degradation intermediates in both cases were enlightened by NMR experiments showing no trace of either pollutant or photocatalyst in wastewater. The photogenerated charge migration mechanism was experimentally elucidated as a complex-type-II, which is based on the usage of the farthest charges on the band edges. Scavenger experiments and photooxidation of glucose confirmed the in situ generation of oxidative species of •O2–, H2O2, and •OH, which played a vital role in the photooxidation reactions. A GQDs@CNBP heterojunction with the kinetic rate constants of 0.1415 min–1 (30 min) for MO and 0.0371 min–1 (120 min) for TC is one of the highest kinetics that has been reported in the literature so far.