Multifunctional Ni-MOF (3D) with N-rich structures for self-generated reactive oxygen species and enhanced electron transfer for synergistic degradation of organic pollutants and removal of Hg(II)

Metal–organic frameworks (MOFs) can effectively adsorb or remove pollutants; however, their application to water treatment remains limited. Herein, we report the preparation of two novel multifunctional Ni-based MOFs (2D and 3D), via the design and synthesis of multi-nitrogen-like ligands. The introduction of polynitrogen-containing organic macrocyclic ligands improved the structure and electron transfer capability of the MOF, and its adsorption and synergistic degradation performance were further enhanced via coordination with Ni. The 3D MOF (MOF-2) had a maximum adsorption capacity of 948 mg/g for Hg(II). The adsorption and synergistic degradation capacities of MOF-2 for tetracycline (TC, 18 mg/L), 17α-ethynylestradiol (EE2, 3 mg/L), rhodamine B (RhB, 6 mg/L), and methylene blue (MB, 6 mg/L) were 98.54%, 97.32%, 91.08%, and 85.02%, respectively. The addition of KHSO5 (PMS, 0.01 g/L) resulted in nearly 100% degradation of the organic pollutants within 100 min. MOF-2 alone simultaneously degraded more than 90.73% (360 min Hg(II) adsorption equilibrium) of five pollutants in ultrapure water, tap water, and lake water. MOF-2+PMS degraded 99.13% of TC within 60 min, and the remaining four pollutants were completely adsorbed and degraded. DFT calculations and experiments indicated that the efficient adsorption of Hg(II) and efficient degradation of the organic pollutants by MOF-2 were mainly attributed to its abundant N atoms, which provide active sites for Hg(II) capture; and the structure itself has strong electron transfer ability and self-produced reactive oxygen species (ROS), which can effectively degrade organic pollutants and activate PMS to enhance the degradation efficiency. MOF-2 also exhibited 100% antibacterial activity against Escherichia coli and Staphylococcus aureus. This work provides a basis for designing synthesis pathways for MOFs and elucidates the electron-transfer mechanism underlying the enhanced synergistic removal of complex pollutants from water. Schematic diagram of Ni-based MOF(3D) enhanced synergistic degradation of pollutants through adsorption and electron transfer. [Display omitted] •N-rich ligand (Pyrazole derivatives) was designed and synthesized.•The Ni-MOF adsorbs heavy metal ions and degrades organic pollutants synergistically.•The Ni MOF has maximum adsorption capacity of 948 mg/g for Hg(II).•The addition of KHSO5 degraded nearly 100% of the organic pollutants(TC and EE2) within 100 min.•Synergistic degradation was activ