MOF‐Derived Spinel NiCo2O4 Hollow Nanocages for the Construction of Non‐enzymatic Electrochemical Glucose Sensor

Non‐enzymatic glucose sensor is greatly expected to take over its enzymatic counterpart in the future. In this paper, we reported on a facile strategy to construct a non‐enzymatic glucose sensor by use of NiCo₂O₄ hollow nanocages (NiCo₂O₄ HNCs) as catalyst, which was derived from Co‐based zeolite imidazole frame (ZIF‐67). The NiCo₂O₄ HNCs modified glassy carbon electrode (NiCo₂O₄ HNCs/GCE), the key component of the glucose sensor, showed highly electrochemical catalytic activity towards the oxidation of glucose in alkaline media. As a result, the proposed non‐enzymatic glucose sensor afforded excellent analytical performances assessed with the aid of cyclic voltammetry and amperometry (i–t). A wide linear range spanning from 0.18 μΜ to 5.1 mM was achieved at the NiCo₂O₄ HNCs/GCE with a high sensitivity of 1306 μA mM^?1 cm^?2 and a fast response time of 1 s. The calculated limit of detection (LOD) of the sensor was as low as 27 nM (S/N=3). Furthermore, it was demonstrated that the non‐enzymatic glucose sensor showed considerable anti‐interference ability and excellent stability. The practical application of the sensor was also evaluated by determination of glucose levels in real serum samples.     

Facile Green Synthesis of NiO/NiCo2O4 Nanocomposite as an Efficient Electrochemical Platform for Determination of Dopamine

The synthesis of NiO/NiCo₂O₄ nanoparticles by an eco-friendly, fast, simple and cost-effective approach employing Urtica extract is reported in this study. The NiO/NiCo₂O₄ nanocomposite were characterized using VSM, FTIR, XRD, and SEM techniques. Moreover, to construct a modified carbon paste electrode, NiO/NiCo₂O₄ were employed and this sensor was used for dopamine (DA) detection. Using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques, the electrochemical behavior of dopamine at the NiO/NiCo₂O₄/CPE was investigated. Analysis of dopamine, with a limit of detection (LOD) equal to 0.04 μM, in the concentration range of 0.1–100.0 μM, was facilitated by NiO/NiCo₂O₄/CPE. Moreover, the satisfactory selectivity for DA determination in the presence of uric acid (UA) and ascorbic acid (AA), was obtained. The suggested new sensor displayed a good reproducibility, sensitivity, and stability for determination of DA in drug and biological samples.     

Cauliflower‐like NiCo2O4−Zn/Al Layered Double Hydroxide Nanocomposite as an Efficient Electrochemical Sensing Platform for Selective Pyridoxine Detection

In the present study, a cauliflower‐like NiCo₂O₄?Zn/Al layered double hydroxide (NiCo₂O₄?Zn/Al LDH) nanocomposite was used as a novel electrode material for the sensitive and selective determination of pyridoxine (vitamin B₆). The structure and morphology of the as‐prepared nanocomposite were characterized by X‐ray diffraction (XRD), FT‐IR, field emission scanning electron microscopy (FESEM) and energy dispersive X‐ray spectroscopy (EDX). The NiCo₂O₄?Zn/Al LDH nanocomposite exhibited excellent electrocatalytic ability in the oxidation of pyridoxine, which could result from the synergistic effect of the two components. The developed sensor also provided a selective determination of pyridoxine in the presence of other species such as vitamins (B₁, B₂, B₁₂ and ascorbic acid), inorganic ions and biomolecules. The fabricated sensor showed a good linear response for pyridoxine over the concentration ranges 2×10^?7–2.0×10^?4 mol L^?1 with a low detection limit of 8.6×10^?8 mol L^?1. Finally, the proposed method was successfully applied for the determination of pyridoxine in commercial tablets and plasma samples with satisfactory results. Furthermore, this novel sensor displayed superior benefits in terms of stability, sensitivity, repeatability and cost. The present work aims to expand NiCo₂O₄ based nanocomposites to sensor fields and promote the development of pyridoxine sensors.     

Ni/NiCo2O4电极的制备及其析氧反应性能

采用溶胶-凝胶法制备NiCo₂O₄尖晶石粉体, 然后以多孔Ni 为基体, 通过复合溶胶涂覆结合烧结制备Ni/NiCo₂O₄ 涂层电极. 运用扫描电子显微镜(SEM)、能量色散谱(EDS)和X 射线衍射(XRD)表征粉体以及Ni/NiCo₂O₄涂层电极的组成和结构. 采用循环伏安(CV), 稳态极化(LSV), 电化学阻抗谱(EIS), 恒电位阶跃以及恒电位长时间电解研究涂层电极在5 mol·L^-1 KOH溶液中的电催化析氧反应(OER). 结果表明: Ni/NiCo₂O₄涂层电极与多孔Ni 电极对比, 具有低的析氧过电位、高的比表面积和高的稳定性能; 其中比表面积增大了28.69倍,表观活化能在不同过电位分别降低了166.78和162.15 kJ·mol^-1.     

A Facile Chemical Synthesis of Cu2O Nanocubes Covered with Co3O4 Nanohexagons for the Sensitive Detection of Glucose

Copper (I) oxide nanocubes (Cu₂O NCs) covered with cobalt oxide nanohexagons (Co₃O₄ NHs) were prepared through simple chemical method. Here, ascorbic acid is used as reducing and capping agent for the synthesis of nanocubes and nanohexagons. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy‐dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction spectroscopy (XRD) were employed to confirm the prepared nanocomposite. Cu₂O NCs?Co₃O₄ NHs nanocomposite is drop cast on the glassy carbon electrode (GCE) for the fabrication of glucose sensor. The fabricated Cu₂O NCs?Co₃O₄ NHs/GCE exhibited a better electrocatalytic activity towards the determination of glucose than that of individually fabricated Cu₂O NCs and Co₃O₄ NHs modified GCE. Our finding exhibited a wide linear range from 1 μM to 5330 μM with LOD of 0.63 towards glucose. In addition, the sensor attained appreciable stability, repeatability and reproducibility. Practicality of the sensor was demonstrated in human serum samples. The main advantages of the fabricated sensor are simple, biocompatible, cost effective, fast response and highly stable electrode surface.     

A Highly Sensitive and Selective Non-enzymatic Hydrogen Peroxide Sensor Based on Nanostructured Co3O4 Thin Films Using the Sol-gel Method

In this work we report an easy and efficient way to fabricate nanostructured cobalt oxide (Co₃O₄) thin films as a non-enzymatic sensor for H₂O₂ detection. Co₃O₄ thin films were grown on ITO glass substrates via the sol-gel method and characterized with several techniques including X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorbance. The Co₃O₄ thin films’ performance regarding hydrogen peroxide detection was studied in a 0.1 M NaOH solution using two techniques, cyclic voltammetry (CV) and amperometry. The films exhibited a high sensitivity of 1450 μA.mM⁻¹.cm⁻², a wide linear range from 0.05 μM to 1.1 mM, and a very low detection limit of 18 nM. Likewise, the Co₃O₄ thin films produced showed an exceptional stability and a high selectivity.     

Facile Preparation of Snowflake-Like MnO2@NiCo2O4 Composites for Highly Efficient Electromagnetic Wave Absorption

Snowflake-like MnO₂@NiCo₂O₄ composites were successfully fabricated by employing crossed snowflake-like MnO₂ nanorods as cores and one-dimensional (1D) NiCo₂O₄ nanoneedles as shells. Impressively, the MnO₂@NiCo₂O₄ composites exhibited a highly efficient electromagnetic wave (EMW) absorbing capability, and the minimum reflection loss (RL) value reached −58.4 dB at 6.8 GHz for a thickness of 4.0 mm. The reasons for the improved EMW absorption capability of snowflake-like MnO₂@NiCo₂O₄ composites were analyzed. The unique core–shell structure, good impedance matching, and high dielectric loss were all found to be important contributors. Moreover, the interfacial polarization mainly stemmed from the heterostructure, a microcurrent generated from the 1D MnO₂ nanorods and NiCo₂O₄ nanoneedles under alternating electromagnetic fields, and the synergistic effect from the different components were all beneficial to improve the EMW absorption performance. These results demonstrated that snowflake-like MnO₂@NiCo₂O₄ composites could be utilized as promising materials for practical EMW absorbing applications.     

A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo₂O₄ nanosheets as electrode materials for lithium‐ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller methods. Owing to the porous nanosheet structure, the NiCo₂O₄ electrodes exhibited a high reversible capacity of 891 mA h g^?1 at a current density of 100 mA g^?1, good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo₂O₄ nanosheets demonstrated a specific capacitance of 400 F g^?1 at a current density of 20 A g^?1 and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode–electrolyte contact area and facilitate rapid ion transport.     

静电纺丝法制备的钴酸镍微米带的磁性以及电化学性能

通过直接退火静电纺丝前驱样品以及调节升温速率最终得到了钴酸镍(NiCo₂O₄)微米带. 通过X射线衍射、扫描电镜、振动样品磁强计以及电化学工作站等分析手段对钴酸镍微米带的晶体结构、形貌、磁学性能以及电化学性能进行了研究. 结果显示, 以1℃·min^-1的升温速率得到的NiCo₂O₄微米带属于立方尖晶石结构, 高温处理后仍能保持一维结构. 室温磁化结果显示制备的NiCo₂O₄微米带具有超顺磁性, 在10 kOe时磁化强度为6.35 emu·g^-1. 此外, 电化学测试结果显示, NiCo₂O₄微米带的电容特性是典型的赝电容, 并且比电容随着放电电流密度的增加而减小.     

Effects of CNT‐film Pretreatment on the Characteristics of NiCo2O4/CNT Core‐shell Hybrids as Electrode Material for Electrochemistry Capacitor

NiCo₂O₄/CNT nanocomposite films were fabricated by in‐situ growing ultrafine NiCo₂O₄ nanoparticles on acid‐modified carbon nanotube (CNT) films. The effects of CNT‐film pretreatment were investigated thoroughly by various characterization outfits including Fourier Transform Infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, RTS‐9 four‐point probes resistivity measurement system, X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and CHI660D electrochemical workstation. These results suggested that carbon nanotubes were uniformly wrapped by NiCo₂O₄ nanoparticles forming a hierarchical core‐shell structure. And the crystallinity, conductivity of the CNTs and detail structure (both morphology and size) of the NiCo₂O₄ nanoparticles varied with prolonged acid treatment time which resulted in increased functional groups and defects on CNT films and further affected the electrochemical properties. The composite film composed of the CNT film pretreated by mixed acid for 12 h exhibited excellent electrochemical properties: 828 F/g at 1 A/g and 656 F/g at 20 A/g, and maintained over 99 % of its capacitance after 3000 cycles of charge/discharge at 5 A/g. Acid treatment for either too long or too short is detrimental to the electrochemical properties of the composite films. Such work should be of fundamental importance for tailoring electrochemical properties by elaborate design of acid treatment on CNTs.     

脊椎状NiCo2O4纳米棒的制备及其析氧和氧还原性能研究

以水热法并进一步焙烧合成脊椎状NiCo₂O₄纳米棒,通过透射电子显微镜（TEM）、X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）和热重分析仪（TG）等来表征其结构形态及热稳定性.采用线性扫描法（LSV）、循环伏安（CV）研究所制备催化剂的在玻碳和旋转圆盘电极上的电催化活性：在0.1 mol·L^-1 KOH溶液中的电催化析氧反应（OER）和电催化氧还原反应（ORR）.研究结果表明,所制备的脊椎状NiCo₂O₄纳米棒有大量的不饱和态,200℃焙烧制备的脊椎状NiCo₂O₄纳米棒析氧过电位最小可达309 mV,Tafel斜率145.6 mV/dec,其氧还原极限电流密度在1600 rmp可达到5.095 mA·cm^-2,电子转移数在3.2~3.8之间,接近四电子转移机理,其优良电化学性能可能是由于暴露了更多的边缘缺陷的缘故.     

Detection of acetaminophen using cyclic voltammetry on MnFe2O4/polyaniline

A novel sensing material, MnFe₂O₄/polyaniline (PANI), was fabricated by doping PANI to MnFe₂O₄ on a modified glassy carbon electrode (GCE). This sensing material was characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and high‐resolution transmission electron microscopy (HR‐TEM). Using a cyclic voltammetry electrochemical‐sensing method, we tested MnFe₂O₄/PANI, and an acetaminophen concentration of 0.0625–5 mM was recorded. Furthermore, the sensor responses were 2.05–22.44. The detection limit was 2.23 × 10^?7 M. Strong selectivity was observed for MnFe₂O₄/PANI, which is a possible sensing mechanism.     

Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting

Bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo₂O₄) has been considered a promising electrode material for the OER. However, NiCo₂O₄ that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self‐assembled hierarchical NiCo₂O₄ hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo₂O₄ electrode shows excellent activity toward overall water splitting, with 10 mA cm^?2 water‐splitting current reached by applying just 1.65 V and 20 mA cm^?2 by applying just 1.74 V across the two electrodes. The synthesis of NiCo₂O₄ microflowers confirms the importance of structural features for high‐performance overall water splitting.     

Ionic liquid-assisted electrochemical determination of pyrimethanil using reduced graphene oxide conjugated to flower-like NiCo2O4

The novel hierarchical flower-like superstructure NiCo₂O₄/reduced graphene oxide (rGO) hybrids have been successfully synthesized with a facile one-step hydrothermal process for the determination of fungicide pyrimethanil (PMT). For comparison, various structures of NiCo₂O₄/rGO including hexagonal nanoplates and nanorods were also synthesized. Among them, three-dimensional (3D) flower-like NiCo₂O₄/rGO exhibited the highest electrocatalytic activity for the oxidation of PMT. With the synergistic effect of [OMIM]PF₆ ionic liquid (IL), the electrochemical sensor film (NiCo₂O₄/rGO/IL) further facilitated interfacial electron transfer and enhanced electrocatalytic activity for the oxidation of PMT. Under the optimum conditions, the electrochemical sensor exhibited two linear ranges of 0.1–10.0 μmol/L and 20.0–140 μmol/L for PMT with a low detection concentration of 11.0 nmol/L. Besides, the interference, repeatability, reproducibility and stability measurements were also evaluated. The proposed method was successfully applied to the detection of PMT in water, seawater, fruits and vegetables with good recovery ranging from 93% to 105%, and possessed potential applications in the analysis of real samples.     

MnO_2/NiCo_2O_4的静电自组装合成及其电化学性能

通过带负电荷的MnO2纳米片与带正电荷的Co-Ni层状双氢氧化物(LDHs)纳米片的静电自组装外加后续热处理合成了异质层状结构的MnO2/NiCo2O4复合物.采用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、拉曼光谱、原子吸收光谱(AAS)、场发射扫描电镜(FESEM)和透射电子显微镜(TEM)对其结构和形貌进行了表征.用循环伏安(CV)、恒流充放电和电化学交流阻抗技术对其电化学性能进行了测试.研究结果表明,该方法制得的异质复合物具有多孔层状堆垛结构,这种特殊的结构不仅增大了电解液离子的接触面积,而且还为其嵌入-脱出提供了有效途径.该复合物在1 A·g-1电流密度时,-0.6-0.45 V电位窗口内的比电容达482 F·g-1,优于纯组分MnO2和NiCo2O4的电容性能.     

Hierarchical ZnCo2O4@NiCo2O4 Core–Sheath Nanowires: Bifunctionality towards High‐Performance Supercapacitors and the Oxygen‐Reduction Reaction

Increasing energy demands and worsening environmental issues have stimulated intense research on alternative energy storage and conversion systems including supercapacitors and fuel cells. Here, a rationally designed hierarchical structure of ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires synthesized through facile electrospinning combined with a simple co‐precipitation method is proposed. The obtained core–sheath nanostructures consisting of mesoporous ZnCo₂O₄ nanowires as the core and uniformly distributed ultrathin NiCo₂O₄ nanosheets as the sheath, exhibit excellent electrochemical activity as bifunctional materials for supercapacitor electrodes and oxygen reduction reaction (ORR) catalysts. Compared with the single component of either ZnCo₂O₄ nanowires or NiCo₂O₄ nanosheets, the hierarchical ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires demonstrate higher specific capacitance of 1476 F g^?1 (1 A g^?1) and better rate capability of 942 F g^?1 (20 A g^?1), while maintaining 98.9 % capacity after 2000 cycles at 10 A g^?1. Meanwhile, the ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires reveal comparable catalytic activity but superior stability and methanol tolerance over Pt/C as ORR catalyst. The impressive performance may originate from the unique hierarchical core–sheath structures that greatly facilitate enhanced reactivity, and faster ion and electron transfer.     

钴酸镍纳米花/活性炭纤维复合物的制备和表征及其超级电容器性能

利用简单的水热法以及后续热处理, 将钴酸镍纳米花成功生长在活性炭纤维支架上. 场发射扫描电镜(FESEM)及透射电镜(TEM)结果表明, 纳米花是由纳米针自组装而成, 而纳米针呈多孔结构. 这种三维复合多级结构非常有利于电解质离子的渗透和电子的传输. 将该多孔钴酸镍纳米花/活性炭纤维布作为工作电极, 表现出优良的电容性能. 在1 A·g^-1时, 比电容高达1626 F·g^-1; 在10 A·g^-1时, 电容保持率为65%, 具有超高的电容值和优异的倍率特性.     

Facile large scale synthesis of CuCr2O4/CuO nanocomposite using MOF route for photocatalytic degradation of methylene blue and tetracycline under visible light

MIL-101(Cr) template method has been employed successfully to synthesize CuCr₂O₄/CuO composite. The synthesized sample was characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, N₂ adsorption–desorption isotherm (BET) analysis, and UV vis- diffuse reflectance spectroscopy (UV-DRS). The photocatalytic efficiency of the nanocomposite was evaluated towards the degradation of methylene blue (MB) dye and antibiotic tetracycline (TC) solution. The morphological studies confirmed that the CuO was uniformly dispersed on the CuCr₂O₄ matrix. The CuCr₂O₄/CuO nanocomposite showed high degradation efficiency of about 90% in the presence of H₂O₂ where the MB degradation reaction got completed in a mere 35 min and ~95% TC got degraded within 120 min.     

Construction of three-dimensional crumpled Ni-Co TMOs for electrochemical energy storage

Due to excellent electrochemical performances, mixed transition metal oxides (TMOs) as electrode materials have attracted scholarly attention. However, the issues of volume expansion, unstable structure, and low electrical conductivity have limited their development for lithium battery (LIB). Drawing on the strategy of MOFs derivation synthesis combined with low temperature hydrothermal method, this study successfully synthesized the three-dimensional (3D) NiCo₂O₄@Fe₂O₃ with a flower-like crossing channel and a surface crumpled structure. As anode for LIBs, NiCo₂O₄@Fe₂O₃ exhibits more reliable performance than Ni−Co oxides. Our experiments verified that the Ni−Co composite electrical conductivity and cycling stability were both improved by the Fe₂O₃ coating. Under the high current density of 1000 mA g⁻¹, the capacity decay rate of NiCo₂O₄@Fe₂O₃ tends to be stable after 60 cycles, and the capacity remains at 945 mAh g⁻¹ after 400 cycles. Besides, the specific crossing porous-channel structure mode improved the composite's carrier transport efficiency, and coulombic efficiency reached 100 % after 400 cycles. Noteworthy is the fact that the crumpled surface structure formed by the 2D Ni−Co nanosheets promotes the construction of heterostructures, further enhances the interface capacitance effect, and strengthens the rating capacity.     

Synthesis and characterization of a novel and green rod-like magnetic ZnS/CuFe2O4/agar organometallic hybrid catalyst for the synthesis of biologically-active 2-amino-tetrahydro-4H-chromene-3-carbonitrile derivatives

The magnetic biocompatible rod-like ZnS/CuFe₂O₄/agar organometallic hybrid catalyst was designed and prepared based on a natural macromolecule (agar) through a green and convenient method using inexpensive, nontoxic, and easily available substances. Then, the as-prepared catalyst was characterized by several techniques such as Fourier transform-infrared spectroscopy, energy-dispersive X-ray analysis, scanning electron microscopy image, transmission electron microscopy, vibrating sample magnetometry curve, X-ray diffraction pattern, and thermogravimetric analysis. Eventually, the catalytic application of the ZnS/CuFe₂O₄/agar nanobiocomposite was assessed in sequential Knoevenagel condensation–Michael addition reaction of dimedone, malononitrile, and different substituted aromatic aldehydes for the synthesis of 2-amino-tetrahydro-4H-chromene-3-carbonitrile derivatives. Some notable strengths of this environmentally benign catalyst include simplicity of catalyst preparation and separation, affording desired products with satisfactory yields (81%–97%) in very short reaction times (3–18 min), and with no need for complicated work-up processes. Experimental tests showed that the catalyst can be successfully reused after five sequential runs without significant reduction in its catalytic efficiency.