Investigating and improving the water stability of ZIF-L-Co for electrochemical glucose sensors

More and more studies have shown that zeolitic imidazolate framework (ZIF) materials exhibit very high thermal stability, but poor aqueous stability, that limits their practical application. In this work, leaf-shaped ZIF-67 on the surface of foam nickel (namely as ZIF-L-Co/NF) is selected to deeply investigate the mechanism of water stability. The related reaction process of ZIF-L-Co/NF in water is proposed for the first time and demonstrated based on a series of characterizations. The results show that ZIF-L-Co/NF lost its skeleton after only 1 h in water, and completely converted into cobalt hydroxide (Co(OH)2) after 24 h. The reaction process is proved to be invertible via designed experiments. Considering invertible reaction, two strategies are proposed to improve the water stability of ZIF-L-Co, by (1) introducing second metal center Zn and (2) adding extra 2-methylimidazole (Hmim) to push the reaction process in reverse. Based on the above improving strategies, bimetallic ZIF-L-CoZn/NF(2:1) prepared by introducing the second metal Zn is applied as electrochemical sensor towards glucose, and exhibits high sensing performance with good sensitivity, selectivity, and wide detection range as glucose sensor. Experimental results demonstrate its excellent aqueous stability. This work provides a totally new viewpoint for the application of ZIF materials in aqueous conditions and perfects the characteristics of ZIF family