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In this paper, a novel Fe 3 O 4 /N/C@MWCNTs composite derived from iron-based metal-organic frameworks (H 2 N-Fe-MIL-88B) with multi-walled carbon nanotubes (MWCNTs) was prepared successfully through a simple calcination process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrochemical measurements were employed to comprehensive characterize the composites. Compare with the physical mixture, in-situ insertion of MWCNTs in the Fe 3 O 4 /N/C formed Fe 3 O 4 /N/C@MWCNTs composite has the higher conductivity, larger BET surface area and more satisfying electrocatalytic properties. Meanwhile, this composite with the reasonable combinations exhibits remarkable electrocatalytic activities for acetaminophen (AP) and metronidazole (MNZ) due to the synergistic interaction between the components. Thus, the Fe 3 O 4 /N/C@MWCNTs-2-600-based electrochemical sensor was established to effectively detect these two medicine molecules, respectively. In the optimized test conditions, the proposed sensor exhibits a wide linear response (0.5-5.0 μM and 5.0-1355.0 μM) for AP and the limit of detection (LOD) was achieved to be 0.14 μM (S/N = 3). Meanwhile, this sensor also shows two linear relationships with the concentration of MNZ in the range of 1.0 μM to 10.0 μM and 10.0 μM to 725.0 μM with the LOD of 0.19 μM (S/N = 3). Moreover, the satisfactory results were also acquired when the proposed sensor was used for the determination of AP and MNZ in the human serum and urine, demonstrating great promising of this electrochemical sensor for clinical applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this work, a novel enzyme-free glucose and hydrogen peroxide (H 2 O 2 ) sensor based on Ni 3 N nanoparticles on conductive 3D graphene aerogels (Ni 3 N/GA) has been successfully synthesized by using hydrothermal reaction, freeze-dried and then calcined under NH 3 atmosphere. The obtained Ni 3 N/GA composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption isotherms and electrochemical methods. The results show the obtained 3D Ni 3 N/GA composites exhibit excellent electrochemical performance toward glucose oxidation and H 2 O 2 reduction with larger catalytic rate constant K cat value of 3.75 × 10 3  M -1  s -1 and 1.24 × 10 3  M -1  s -1 , respectively. As a glucose sensor, the obtained electrode provides a wide detection range of 0.1-7645.3 μM, fast response time within 3 s, high sensitivity of 905.6 μA mM -1  cm -2 and low detection limit of 0.04 μM. For detection of H 2 O 2 , this prepared sensor offers a wide detection range (5 μM-75.13 mM), fast response time (within 5 s), sensitivity (101.9 μA mM -1  cm -2 ) and low detection limit (1.80 μM). This enzyme-free glucose and H 2 O 2 sensor display satisfactory selectivity, reproducibility and long-term storage stability. Additionally, the sensor can also be used for glucose and H 2 O 2 detection in human blood serum. The results demonstrate that 3D GA nanostructures provide an enviable conductive network for efficient charge transfer and avoid Ni 3 N nanoparticles aggregation, which is advantageous for electrocatalytic applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this paper, H 2 N-Fe-MIL-88B@OMC composites were fabricated by the simple hydrothermal method through in-situ growth iron-based metal-organic frameworks (H 2 N-Fe-MIL-88B) on ordered mesoporous carbon (OMC). Compared with pure H 2 N-Fe-MIL-88B crystals, the introduction of OMC can shrink the size of H 2 N-Fe-MIL-88B, increase the specific surface area, decrease the electron transfer resistance and drastically improve the electrochemical performance of H 2 N-Fe-MIL-88B@OMC. The composite exhibits remarkable electrocatalytic activity for p-nitrotoluene (p-NT) reduction and hydrazine (N 2 H 4 ) oxidation. Therefore, a novel electrochemical sensor based on H 2 N-Fe-MIL-88B@OMC was constructed for the efficient detection of these two environmental pollutants, respectively. Under the optimal experimental conditions, the proposed sensor displays a wide linearity range for p-NT that is composed by two line segments (20-225 μM and 225-2600 μM) and the limit of detection (LOD) is 8 μM (S/N = 3). Meanwhile, the sensor also shows a linear response to N 2 H 4 in the range of 0.006-0.061 μM and 0.061-611.111 μM with a high sensitivity of 20.1 μA/μM·cm 2 in low concentration range as well as a very low LOD as 5.3 nM (S/N = 3). And the response time of the sensor for N 2 H 4 detection is about 1 s. In addition, the proposed sensor shows satisfactory electrochemical stability, reproducibility, selectivity and practicability. H 2 N-Fe-MIL-88B@OMC may be a splendid candidate for developing electrochemical sensors to detect environmental pollutants., (Copyright © 2018 Elsevier B.V. All rights reserved.)

As a novel single-atom-thick sheet of sp 2 hybridized carbon atoms, graphene (GR) has attracted extensive attention in recent years because of its unique and remarkable properties, such as excellent electrical conductivity, large theoretical specific surface area, and strong mechanical strength. However, due to the π-π interaction, GR sheets are inclined to stack together, which may seriously degrade the performance of GR with the unique single-atom layer. In recent years, an increasing number of GR-based electrochemical sensors and biosensors are reported, which may reflect that GR has been considered as a kind of hot and promising electrode material for electrochemical sensor and biosensor construction. However, the active sites on GR surface induced by the irreversible GR aggregations would be deeply secluded inside the stacked GR sheets and therefore are not available for the electrocatalysis. So the alleviation or the minimization of the aggregation level for GR sheets would facilitate the exposure of active sites on GR and effectively upgrade the performance of GR-based electrochemical sensors and biosensors. Less aggregated GR with low aggregation and high dispersed structure can be used in improving the electrochemical activity of GR-based electrochemical sensors or biosensors. In this review, we summarize recent advances and new progress for the development of electrochemical sensors based on less aggregated GR. To achieve such goal, many strategies (such as the intercalation of carbon materials, surface modification, and structural engineering) have been applied to alleviate the aggregation level of GR in order to enhance the performance of GR-based electrochemical sensors and biosensors. Finally, the challenges associated with less aggregated GR-based electrochemical sensors and biosensors as well as related future research directions are discussed., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Designing and preparing porous transition metal ferrites without using any template, shape-directing agent, and surfactant is a challenge. Herein, heterojunction MFe2O4 (M = Co, Ni, Cu, Mn) nanofiber (NF) based films with three-dimensional configurations were synthesized by electrospinning and the subsequent thermal treatment processes. Characterization results indeed show the 3D net-like textural structures of the electrospun spinel-type MFe2O4 NFs. In particular, the resulting MFe2O4 NFs have lengths up to several dozens of micrometers with an average diameter size of about 150 nm and possess abundant micro/meso/macropores on both the surface and within the films. The hierarchically porous structures and high surface areas of these MFe2O4 NFs (for example, the CoFe2O4 NFs possess a larger BET specific surface area (61.48 m(2) g(-1)) than those of the CoFe2O4 NPs (5.93 m(2) g(-1))) can afford accessible transport channels for effectively decreasing the mass transport resistances, enhancing the electrical conductivity, and increasing the density and reactivity of the exposed catalytic active sites. All these advantages will be responsible for the better electrocatalytic performances of these MFe2O4 NFs compared with their structural isomers (i.e. the MFe2O4 NPs) for the oxygen evolution reaction (OER) and H2O2 reduction in alkaline solution. Meanwhile, both the OER and H2O2 reduction catalytic activities for these MFe2O4 NFs obey the order of CoFe2O4 NFs > CuFe2O4 NFs > NiFe2O4 NFs > MnFe2O4 NFs > Fe2O3 NFs. The CoFe2O4 NFs represent a new class of highly efficient non-noble-metal catalysts for both OER and H2O2 reduction/detection in alkaline media.

The thermal, water and electrochemical stability of Cu-based metal organic frameworks (Cu-MOFs) confined in macroporous carbon (MPC) hybrids has been investigated. Thermogravimetric analyses, X-Ray diffraction, scanning electron microscopy, and cyclic voltammetry were employed to confirm the stability of pure Cu-MOFs, MPC, and Cu-MOFs-MPC. As compared to pure Cu-MOFs, the porous composite materials of MPC and Cu-MOFs interact and seem to form new materials having homogenous structure and chemistry, which show structural stability in aqueous media and electrochemical stability in phosphate buffer solution (PBS pH 7.4). The detection of ascorbic acid and hemoglobin is performed as an electrochemical probe, indicating Cu-MOFs-MPC holds great promise for the design of electrochemical sensors., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Two-dimensional ordered mesoporous carbon nitride (OMCN) has been successfully prepared for the first time using SBA-15 mesoporous silica and melamine as template and precursor respectively, by a nano hard-templating approach. A series of OMCN-x samples with different pyrolysis temperatures have been reported. The formation of these composite materials was verified by detailed characterization (e.g., Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2 adsorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy). The results showed that the materials were structurally well ordered with two-dimensional porous structure, high surface area and large pore volume. The influence of BET surface area and different amounts of N-bonding configurations formed at different pyrolysis temperatures of OMCN-x for the electrocatalysis towards hydrogen peroxide, nitrobenzene, and nicotinamide adenine dinucleotide were investigated in detail. Results indicated that OMCN treated at 800°C with largest BET surface area and highest amounts of pyrindinic N showed improved electrocatalytic activity for H2O2, nitrobenzene, and NADH in neutral solution., (© 2013 Published by Elsevier B.V.)