Oxygen vacancy-rich BiOCl/Fe-MOF-NH2 S-scheme heterojunction: High-efficiency tetracycline photodegradation and relieved ecotoxicity

In this work, an S-scheme heterojunction photocatalyst composed of Fe-MOF-NH 2 -modified BiOCl (denoted as BFN) was successfully prepared via a one-step hydrothermal technique for the efficient photocatalytic (PC) decomposition of tetracycline hydrochloride (TC-HCl). The morphology, crystal structure, composition, specific surface area, and photoelectric characteristics of BFN were systematically characterized using multiple techniques. XRD patterns confirm the successful fabrication of Fe-MOF-NH 2 /BiOCl (BFN) heterostructures. Introducing Fe-MOF-NH 2 shrinks BiOCl lattices via partial replacement of Bi 3+ with smaller Fe 3+ , which further exposes more active BiOCl (110) facets. SEM images display BiOCl nanosheets evenly grown on spindle hexagonal Fe-MOF-NH 2 to create compact heterointerfaces. This structure optimizes pore configuration and light capture. Owing to its elaborate heterojunction and regulated crystal texture, BET data confirm the optimal BFN possesses a high specific surface area of 116.2 m 2 ‧g −1 . UV–vis DRS further verifies a 420 nm red shift in its light absorption edge. XPS and EPR analyses reveal that the oxygen vacancy concentration in the heterojunction is significantly increased, 3 and 8 times higher compared to those of Fe-MOF-NH 2 and BiOCl, respectively. The compact S-scheme heterojunction constructs a directional charge-carrier transfer pathway. This structure strongly suppresses photocarrier recombination while preserving robust redox potentials. Higher photocurrent density and lower EIS impedance jointly confirm accelerated charge separation. PC experiments demonstrate that the 70% BFN sample achieves markedly higher degradation efficiency for TC-HCl under Light-emitting diode (LED) lamp irradiation compared with the individual components, and the degradation process involves multiple reactive species, including h + , ·O 2 − , and ·OH. LC-MS analysis revealed three possible degradation pathways, and hydroponic toxicity tests using mung bean as the model plant confirmed that the TC-HCl degradation products exhibit substantially reduced biotoxicity and even exert a certain growth-promoting effect. This study unveils the quadruple synergism of extended light absorption, S-scheme carrier migration, abundant oxygen vacancies and enhanced surface adsorption, offering experimental and theoretical support for bismuth/MOF photocatalysts in antibiotic wastewater remediation and agricultural ecological protection.