Band Edge Reorganization via Symmetry Constraints in Covalent Bonding Heterojunctions Boosts Photocatalytic Metronidazole Degradation

ABSTRACT The covalent bonds at heterojunction interfaces enable more efficient charge carrier separation than traditional weakly coupled heterojunctions, with enhanced photocatalytic performance for organic wastewater purification. The interfacial covalent bonds drive energy band reorganization, rendering the conventional independent band edge mechanism inadequate for explaining the photocatalytic behavior of covalent bonding heterojunctions, thereby impeding the rational design of high‐performance covalent bonding heterojunction photocatalysts. This study constructs a covalent bonding ZnIn 2 S 4 /MgO (ZIS/MgO) heterojunction, which exhibits a 1.86‐fold increase in the apparent kinetic constant for photocatalytic degradation of metronidazole (MNZ) compared to pristine ZIS. Comprehensive experimental characterization, density functional theory (DFT) calculations, and group theory analysis demonstrate that the orbital symmetry drives the merging and crossing of band edges in the ZIS/MgO. DFT calculations reveal a delocalized band edge distribution in the ZIS/MgO caused by band edge reorganization. The valence band maximum (VBM) is co‐localized on both MgO and ZIS components, whereas the conduction band minimum (CBM) resides exclusively on ZIS. Photoelectrochemical measurements and time‐dependent DFT (TDDFT) analyses prove that the ZIS/MgO heterojunction owns enhanced carrier spatial delocalization due to the delocalized band edge distribution, which, in turn, boosts the photocatalytic activity. This work provides novel insights into the band edge reorganization mechanism to guide the design and synthesis of high‐performance covalent bonding heterojunction photocatalysts.