Hydrophilic Zinc Metal-Organic Frameworks with Optimized Lewis Acid Centers for Enhanced Photocatalytic Performance

Abstract

Water-stable metal–organic frameworks (MOFs) have emerged as promising porous materials for addressing water pollution challenges, owing to their tailorable structures and unique active sites. However, the regulatory role of metal centers with fully or partially filled d orbitals in interfacial behaviors during advanced oxidation processes remains insufficiently understood, posing a critical barrier to the development of efficient decontamination systems. In this study, we rationally designed and fabricated a series of MOF materials featuring ordered π-conjugated skeletons. These MOFs were constructed using 2-aminoterephthalic acid as the ligand, incorporating diverse metal nodes (Zn, Ti, and Co), and engineering hydrophilic or hydrophobic channels. The tetracycline (TC) degradation efficiencies of these MOFs under visible-light irradiation were systematically compared. By correlating the degradation results with structural characteristics elucidated via X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS), combined with photoelectrochemical measurements, the influence of different metal centers on charge separation efficiency was comprehensively evaluated. The findings reveal that the Zn-MOF exhibits exceptional photocatalytic performance, which originates from the closed-shell d10 electronic configuration of Zn2+. This unique electronic structure confines electrons within the organic linker, effectively suppressing the recombination of photogenerated electron–hole pairs. Furthermore, the incorporation of Zn2+ centers prolongs the lifetime of photoexcited electrons and optimizes the ligand-to-metal charge transfer (LMCT) process, thereby significantly enhancing photocatalytic activity. Radical trapping experiments identified superoxide radicals (•O2−), photogenerated electrons (e−), and holes (h+) as the dominant reactive species involved in the TC degradation process. This work highlights the potential of water-stable MOFs with suppressed charge recombination for applications in various photochemical processes beyond water treatment.