Construction of Stable 2D Cationic Breathing Ni-MOF for Cr(VI) Trapping and Electrochemical Sensing.

Pollution of surface water by heavy metal hexavalent chromium ions poses a serious threat to human health; herein, a two-dimensional (2D) cationic breathing Ni-MOF with free nitrate ions between the layers was designed and synthesized according to the characteristics of hexavalent chromium ions, {[Ni(L) ₂ ](NO ₃ ) ₂ ·5H ₂ O} _n (L = 1,3,5-tris[4-(imidazol-1-yl)phenyl]benzene). The flexible layer spacing of the 2D breathing Ni-MOF allows the exchange of NO ₃ ^- by CrO ₄ ^2- without destroying the original structure. Electrostatic and hydrogen bonding interactions between CrO ₄ ^2- and Ni-MOF facilitate its exchange with NO ₃ ^- . Moreover, CrO ₄ ^2- exhibits a higher binding energy with Ni-MOF compared to NO ₃ ^- , and the hydrophobic channels of Ni-MOF favor CrO ₄ ^2- trapping due to its lower hydration energy. Consequently, Ni-MOF demonstrates both effective sorption and electrochemical sensing of Cr(VI), achieving a sensitivity of 2.091 μA μM ^-1 and a detection limit of 0.07 μM.