n–p–n Heterojunction Photocatalyst Based on a Polydopamine-Integrated CoFe LDH/Mn ₃ O ₄ Ternary Hybrid

Development of multivalent metal semiconductor-based on heterojunctions with efficient charge separation and electron transfer remains a significant challenge. This study discusses a one-pot, in situ synthetic technique for designing a ternary-hybrid n–p–n heterojunction system. This method utilizes a room-temperature simultaneous polymerization-exfoliation in the aqueous phase, avoiding any rigorous reaction conditions and hazardous discharge to the environment. Here, n-type CoFe LDH nanosheets have been exfoliated with p-type Mn3O4 nanocubes to form a synergistic n–p heterojunction, which subsequently integrated with n-type polydopamine (PDA) microspheres to obtain a robust n–p–n heterojunction interface. The strong chelating ability of PDA ensures engineered interfacial contact and structural integrity during polymerization, thereby promoting efficient charge transfer pathways across the hybrid framework. The resultant polymeric nanocomposite photocatalyst demonstrated 96.3% tetracycline hydrochloride (TC) degradation within 90 min. The enhanced photocatalytic performance can be attributed to efficient charge dynamics at the CoFe LDH/Mn3O4/PDA hybrid interface. A strong synergistic effect arises from the multivalent metal heterojunction that facilitates electron transfer from CoFe LDH nanosheets to the conjugated PDA network via the Mn3O4 mediator. This architecture significantly improves charge carrier separation and reduces recombination. These effects are evidenced by X-ray photoelectron spectroscopy, photoluminescence, time-correlated single-photon counting, electrochemical impedance spectroscopy, chronoamperometry, and transient photocurrent analyses. The developed CoFe LDH/Mn3O4/PDA nanocomposite possesses a large specific surface area of 260.35 m2/g, with an interfacial interaction among LDH nanosheets, Mn3O4 nanocubes, and PDA microspheres. Additionally, the antibacterial activity with a 200 ppm minimum inhibitory concentration and zones of inhibition of 27 and 26 nm against Bacillus pumilus (Gram-positive) and Escherichia coli (Gram-negative) emphasizes CoFe LDH/Mn3O4/PDA as a potent and promising material to be used in real-world environmental remediation.