Efficient photoelectrochemical (PEC) water splitting requires rapid separation and transport of photogenerated carriers. These processes can be enhanced by engineering a built-in electric field (BIEF) and tuning the electronic structure of the photoanode. In this study, we introduce a Ni-based metal–organic framework (Ni-MOF) as a surface cocatalyst on hematite (α-Fe₂O₃) to form an interfacial heterojunction that generates a strong BIEF. Incorporation of Fe into the Ni-MOF creates Ni–O–Fe bonds, while –OH functional groups in the MOF ligands donate electrons and modulate the electronic structure of α-Fe₂O₃/NiFe-MOF(2OH). The resulting photoanode achieves a photocurrent density of 3.48 mA·cm⁻² at 1.23 V vs. reversible hydrogen electrode (V_RHE), approximately four times that of pristine α-Fe₂O₃ (0.88 mA·cm⁻²). Mechanistic studies reveal that the strong BIEF, vigorous Ni–O–Fe coupling, and electron-donating –OH groups synergistically facilitate electron delocalization, suppress charge recombination, prolong hole lifetime, and improve adsorption of oxygen evolution intermediates. These effects significantly enhance carrier separation and transfer efficiency, leading to superior PEC water-splitting performance.

Metal–organic framework-based compounds have recently gained great attention because of their unique porous structure, ordered porosity, and high specific surface area. Benefiting from these superior properties, metal–organic framework-based compounds have been proven to be one of the most potential candidates for environmental governance and remediation. In this review, the different types of metal–organic framework-based compounds are first summarized. Further, the various environmental applications of metal–organic framework-based compounds including organic pollutant removal, toxic and hazardous gas capture, heavy metal ion detection, gas separation, water harvesting, air purification, and carbon dioxide reduction reactions are discussed in detail. In the end, the opportunities and challenges for the future development of metal–organic framework-based compounds for environmental applications are highlighted.