Manganese cobalt-MOF@carbon nanofiber-based non-enzymatic histamine sensor for the determination of food freshness.

Early detection of histamine in foodstuffs/beverages could be useful in preventing various diseases. In this work, we have prepared a free-standing hybrid mat based on manganese cobalt (2-methylimodazole)-metal organic frameworks (Mn-Co(2-MeIm)MOF) and carbon nanofibers (CNFs) and explored as a non-enzymatic electrochemical sensor for determining the freshness of fish and bananas based on histamine estimation. As-developed hybrid mat possesses high porosity with a large specific surface area and excellent hydrophilicity those allow easy access of analyte molecules to the redox-active metal sites of MOF. Furthermore, the multiple functional groups of the MOF matrix can act as active adsorption sites for catalysis. The Mn-Co(2-MeIm)MOF@CNF mat-modified GC electrode demonstrated excellent electrocatalytic activities toward the oxidation of histamine under acidic conditions (pH = 5.0) with a faster electron transfer kinetics and superior fouling resistance. The Co(2-MeIm)MOF@CNF/GCE sensor exhibited a wide linear range from 10 to 1500 µM with a low limit of detection (LOD) of 89.6 nM and a high sensitivity of 107.3 µA mM-1 cm-2. Importantly, as-developed Nb(BTC)MOF@CNF/GCE sensor is enabled to detect histamine in fish and banana samples stored for different periods of time, which thus indicates its practical viability as analytical histamine detector.

Fabrication of Flexible Poly(m-aminophenol)/Vanadium Pentoxide/Graphene Ternary Nanocomposite Film as a Positive Electrode for Solid-State Asymmetric Supercapacitors.

In this study, poly(m-aminophenol) (PmAP) has been investigated as a multi-functional conductive supercapacitor binder to replace the conventional non-conductive binder, namely, poly(vinylene difluoride) (PVDF). The kye benefits of using PmAP are that it is easily soluble in common organic solvent and has good film-forming properties, and also its chemical functionalities can be involved in pseudocapacitive reactions to boost the capacitance performance of the electrode. A new ternary nanocomposite film based on vanadium pentoxide (V2O5), amino-functionalized graphene (amino-FG) and PmAP was fabricated via hydrothermal growth of V2O5 nanoparticles on graphene surfaces and then blending with PmAP/DMSO and solution casting. The electrochemical performances of V2O5/amino-FG/PmAP nanocomposite were evaluated in two different electrolytes, such as KCl and Li2SO4, and compared with those of V2O5/amino-FG nanocomposite with PVDF binder. The cyclic voltametric (CV) results of the V2O5/amino-FG/PmAP nanocomposite exhibited strong pseudocapacitive responses from the V2O5 and PmAP phases, while the faradaic redox reactions on the V2O5/amino-FG/PVDF electrode were suppressed by the inferior conductivity of the PVDF. The V2O5/amino-FG/PmAP electrode delivered a 5-fold greater specific capacitance than the V2O5/amino-FG/PVDF electrode. Solid-state asymmetric supercapacitors (ASCs) were assembled with V2O5/amino-FG/PmAP film as a positive electrode, and their electrochemical properties were examined in both KCl and Li2SO4 electrolytes. Although the KCl electrolyte-based ASC has greater specific capacitance, the Li2SO4 electrolyte-based ASC delivers a higher energy density of 51.6 Wh/kg and superior cycling stability.

Flexible and freestanding supercapacitor based on nanostructured poly(m-aminophenol)/carbon nanofiber hybrid mats with high energy and power densities.

Nanostructured poly(m-aminophenol) (PmAP) coated freestanding carbon nanofiber (CNF) mats were fabricated through simple in situ rapid-mixing polymerization of m-aminophenol in the presence of a CNF mat for flexible solid-state supercapacitors. The surface compositions, morphology and pore structure of the hybrid mats were characterized by using various techniques, e.g., FTIR, Raman, XRD, FE-SEM, TEM, and N2 absorption. The results show that the PmAP nanoparticles were homogeneously deposited on CNF surfaces and formed a thin flexible hybrid mat, which were directly used to made electrodes for electrochemical analysis without using any binders or conductive additives. The electrochemical performances of the hybrid mats were easily tailored by varying the PmAP loading on a hybrid electrode. The PmAP/CNF-10 hybrid electrode with a relatively low PmAP loading (> 42 wt%) showed a high specific capacitance of 325.8 F g-1 and a volumetric capacitance of 273.6 F cm-3 at a current density of 0.5 A g-1, together with a specific capacitance retention of 196.2 F g-1 at 20 A g-1. The PmAP/CNF-10 hybrid electrode showed good cycling stability with 88.2% capacitance retention after 5000 cycles. A maximum energy density of 45.2 Wh kg-1 and power density of 20.4 kW kg-1 were achieved for the PmAP/CNF-10 hybrid electrode. This facile and cost-effective synthesis of a flexible binder-free PmAP/CNF hybrid mat with excellent capacitive performances encourages its possible commercial exploitation.