γ-Irradiation induced preparation of pyrazolate-based metal–organic framework for efficient uranium adsorption

Pyrazolate-based materials are an important category of MOFs with robust coordinative bonds and high porosity, which possess potential advantages for uranium adsorption. However, the preparation still faces the challenges of low energy-consuming and scalable synthesis. Herein, for the first time, we demonstrated the rapid synthesis of pyrazolate-based MOFs (NiBDP-γ) by γ-irradiation induced preparation strategy and applied them to uranium adsorption. The NiBDP-γ samples can be achieved at decagram scale within minutes at room temperature and even in open-air condition. It is revealed that the high-energy γ-rays can also induce structure defects during the irradiation process, resulting in the generation of additional –NH- and –OH sites. At the optimally irradiation dose, the defective NiBDP-γ accompanied with –NH- and –OH sites show a faster removal rate and enhanced adsorption capability for U(VI). The maximum adsorption capacity for the uranium of NiBDP-γ can reach 430.8 mg/g at pH = 5 and 298 K. Kinetic adsorption results demonstrate that the introduction of defects leads to a transformation from physical adsorption to being primarily dominated by chemical adsorption. DFT calculations reveals a thermodynamically favorable binding of –NH- and –OH ligands with uranyl ions. This work offers a general approach for scalable synthesis of the pyrazolate-based MOFs and presents a novel attempt for the future application of pyrazolate-based MOFs in the treatment of uranium-containing wastewater.