Organic solvent free in situ growth of flower like Co-ZIF microstructures on nickel foam for glucose sensing and supercapacitor applications

Flower like microstructures of cobalt zeolitic imidazolate framework (FLCo-ZIF) was grown on flexible nickel foam (NF) when water was used as a solvent using Co-salt and imidazole as precursors. No such flower like microstructures was formed when ethanol or methanol was used as a solvent. Interestingly, no microstructures were grown on NF in the presence of DMF or DMSO. The microstructure growth was optimized with respect to the mole ratio of 2-methylimidazole (2-MI) and Co salt, solvent and immersion time. The scanning electron microscopy (SEM) images confirmed the formation of FLCo-ZIF on NF with an average framework size of 5 mu m from 1: 2 mole ratio in water at an immersion time of 3 h. Here, water acted as a green solvent and structure-directing agent to favour Co2+ nuclei to interact with the smaller building units of 2-MI to form FLCo-ZIF microstructures on NF. The cyclic voltammogram of FLCo-ZIF showed two redox waves corresponding to Co and Ni. Further, the FLCo-ZIF fabricated on NF was directly used as a binder free electrocatalyst for glucose oxidation and supercapacitor electrode. When the concentration of glucose increases the amperometric current was increased linearly from 2 mu M to 1 mM in 0.1 M NaOH and the limit of detection (LOD) was found to be 0.42 mu M(S/N = 3) with a sensitivity of 2.981 mA/(mM cm(2)). The clinical application of the present method was evaluated by determining glucose in human blood serum samples and the results were validated with the commercial glucometer. Besides, NF modified with FLCo-ZIF was also used for supercapacitor application. It showed a specific capacitance (C) of 87 F g(-1) at the current density of 0.5 A g(-1) and good stability for 2000 cycles. Thus, the FLCo-ZIF formed on NF from a green solvent shown here is a potential candidate for not only nonenzymatic sensing of glucose but also supercapacitor application. (c) 2019 Elsevier Ltd. All rights reserved.