In-situ construction of Bi₃O₄Br onto Ni-MOF-74 heterojunction with interfacial charge separation for photocatalytic degradation of organic pollutants

The tandem combination of Two-dimensional heterostructures (2D/2D) has gained significant attention for environmental remediation, due to their improved mass transfer and enhanced photocatalytic activities. Herein, Bi₃O₄Br, a 2D semiconductor photocatalyst with a narrow band gap for the remediation of organic pollutants, suffers from the rapid recombination of photogenerated charge carriers. To address this challenge, the Bi₃O₄Br photocatalyst was loaded onto Ni-MOF-74 (a 2D structure) via an in situ hydrothermal synthesis to enhance its photocatalytic activity for the degradation of tetracycline (TC) and Methyl Orange (MO). The introduction of Bi₃O₄Br forms an intimate interfacial contact with the aggregated nanosheet structure of the Ni-MOF-74 framework. Characterization analyses (SEM, TEM, PL, and XPS) evidenced that the optimized Bi₃O₄Br@Ni-MOF-74 heterojunction (B/N-11%) significantly shortened the transport distance of photogenerated charge carriers and reduced carrier recombination. The degradation rates of B/N-11% for MO and TC (initial concentration of 20 mg/L) under UV irradiation (90 mW·cm⁻²) at 80 and 24 min achieved 90.4% and 98.7%, respectively. In addition, the B/N-11% exhibited an excellent pseudo-first-order rate constant of 0.135 min^-1 for TC compared to the MO (0.032 min^-1), largely attributed to its strong affinity for the photocatalyst interface. Radical trapping experiments identified superoxide radicals (·O₂⁻) as the dominant reactive species. Moreover, the intermediate products and degradation pathways of TC were identified. Overall, intercalating the 2D Ni-MOF-74 framework imparted the heterostructure with better adsorption capacity and superior photodegradation performance.