2D Phthalocyanine-Based MOF for Electrochemical Nitrite Sensing

Abstract

Nitrite (NO2 −) is a common environmental contaminant that appears in the water, soil and other environments, and also serves as a kind of preservative for the food industry.[1] Nitrite-rich contaminants cause terrible impacts on the ecological environment and public health due to the unreasonable utilization/treatment with nitrites in the field of farming, food industry, and environmental protection. Therefore, it is of great importance for the accurate determination of nitrite in the drinking water or pickled foods. Moreover, the World Health Organization (WHO) has established a maximum limit of nitrite dosage of 65.2 μM (3 mg L−1) in drinking water. [2]Two-dimensional (2D) conductive MOFs represent an emerging class of nanomaterials, presenting their exceptional 2D characteristics, enhanced ability of electron transfer and high efficiency of the active sites, as well as the intrinsic merits of conventional MOFs.[3] 2D Cu-TCPP (TCPP, tetrakis(4-carboxyphenyl)porphyrin) modified with gold nanoparticles and polyxanthurenic acid with an exceptional conductivity was demonstrated as an excellent electrochemical sensor towards dopamine with a low detection limit.[4] 2D conductive materials also played an important role in gas analysis owing to their excellent conductivity.[5] Based on the above examples, 2D conductive MOFs present possibilities for achieving a superior electrocatalytic performance for electrochemical sensors.In this work, nickel phthalocyanine (NiPc) was selected as an organic linker to assemble a 2D NiPc-MOF. Three main reasons arise from using this linker for synthesizing a 2D MOF: (i) metal active sites are atomically dispersed on metallophthalocyanines, theoretically; (ii) NiPc-MOFs extend in two-dimension with fully in-plane π delocalization and weak out-of-plane π–π stacking, further promoting electron transfer between electrocatalysts and analytes; (iii) the larger surface area of a 2D NiPc-MOF, the easier absorption on the electrode, keeping its electrochemical stability, and then achieving an excellent sensitivity. Benefiting from excellent conductivity and a large surface area, 2D NiPc-MOF nanosheets present excellent electrocatalytic activity for nitrite sensing, with an ultra-wide linear concentration from 0.01 mM to 11500 mM and a low detection limit of 2.3 μM, better than most reported electrochemical nitrite sensors. Herein, a 2D conductive NiPc-MOF was synthesized through the solvothermal method and used for the electrochemical determination of nitrite for the first time.