MnO2 nanorods grown NGNF nanocomposites for the application of highly sensitive and selective electrochemical detection of hydrogen peroxide

Regulating the nitrogen content in graphene to modify manganese dioxide for the sensitive detection of dopamine in biological samples

A 3D neural network-shaped nitrogen-doped graphene-coated MnO2 composite (N@Gr-MnO2) was successfully prepared by hydrothermal method. The nitrogen content in graphene is effectively regulated by changing the amount of urea added. Upon achieving a graphene oxide (GO) to urea mass proportion of 1/200, the resultant N@Gr exhibited maximal nitrogen concentration. Moreover, XPS analyses confirmed that this configuration led to an apex in the total abundance of both pyridinic nitrogen and graphitic nitrogen, elements pivotal for catalytic proficiency. The N@Gr-MnO2 was prepared by the combination of N@Gr (at the mass ratio of 1/200) and manganese dioxide and was used to construct an electrochemical sensor (N@Gr/α-MnO2/GCE) to detect dopamine. There are two linear relationships between the current response of the sensor to DA concentration: the first section is 0.01 to 8.79 μmol·L-1, the corresponding linear equation and correlation coefficient (R2) are I (μA) = 7439.5 C (mmol·L-1) + 2.27 and 0.986, respectively, and the sensitivity is 16,907.9 μA (mmol·L-1) -1 cm-2. The second section of concentration is 11-104 μmol·L-1, and the corresponding linear equation and correlation coefficient (R2) are I (μA) = 2883.9 C (mmol·L-1) + 45.5 and 0.995. The detection limit (S/N) of DA by N@Gr/α-MnO2/GCE is 1.7 nmol·L-1. The sensor can be applied to the quantification detection of dopamine in human serum and urine, with a recovery percentage of 92%, confirming its significant potential for real-world implementation.

A review on the origin of nanofibers/nanorods structures and applications

In this review work, we highlight the origin of morphological structures such as nanofibers/nanorods in case of various materials in nano as well as bulk form. In addition, a discussion on different cations of different ionic radii and other intrinsic factors is provided. The materials (ceramic titanates, ferrites, hexaferrites, oxides, organic/inorganic composites, etc.,) exhibiting the nanofibers/nanorods like morphological structures are tabulated. Furthermore, the significance of nanofibers/nanorods obtained from distinct materials is elucidated in multiple scientific and technological fields. At the end, the device applications of these morphological species are also described in the current technology. The nucleation and growth mechanism of α-MnO₂ nanorods using natural extracts from Malus domestica and Vitis vinifera [3].

Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H₂O₂ reduction and excellent sensing performance for the electrochemical detection of H₂O₂. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 μM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H₂O₂ in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

Design and fabrication of cost-effective and sensitive non-enzymatic hydrogen peroxide sensor using Co-doped δ-MnO2 flowers as electrode modifier

The development of a cost-effective and highly sensitive hydrogen peroxide sensor is of great importance. Electrochemical sensing is considered the most sensitive technique for hydrogen peroxide detection. Herein, we reported a cost-effective and highly sensitive hydrogen peroxide sensor using Co-doped δ-MnO₂ (Co@δ-MnO₂) flower-modified screen-printed carbon electrode. The δ-MnO₂ and Co@δ-MnO₂ flowers were synthesized by employing a hydrothermal approach. Advanced techniques such as PXRD, SEM, FTIR, Raman, UV, EDX, BET, and TEM were utilized to confirm the formation of δ-MnO₂ and Co-doped δ-MnO₂ flowers. The fabricated sensor exhibited an excellent detection limit (0.12 μM) and sensitivity of 5.3 μAμM^-1 cm^-2.Graphical abstract.

A sensitive non-enzymatic electrochemical sensor based on acicular manganese dioxide modified graphene nanosheets composite for hydrogen peroxide detection

In this work, a novel manganese dioxide-graphene nanosheets (MnO₂-GNSs) composite was synthesized by a facile one-step hydrothermal method, in which manganese dioxide (MnO₂) was fabricated by hydrothermal reduction of KMnO₄ with GNSs. The structure and morphology of MnO₂-GNSs composite were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS). A sensitive non-enzymatic electrochemical sensor based on MnO₂-GNSs composite for the detection of low concentration hydrogen peroxide (H₂O₂) was fabricated. The electrochemical properties of MnO₂-GNSs composite modified glassy carbon electrode (MnO₂-GNSs/GCE) were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometry. The observations confirmed that the fabricated sensor exhibited high electrocatalytic activity for oxidation of H₂O₂ owing to the catalytic ability of MnO₂ particles and the conductivity of GNSs. Under the optimum conditions, the calibration curve was linear for the amperometric response versus H₂O₂ concentration over the range 0.5-350 μM with a low detection limit of 0.19 μM (S/N = 3) and high sensitivity of 422.10 μA mM^-1 cm^-2. The determination and quantitative analysis of H₂O₂ in antiseptic solution on MnO₂-GNSs/GCE exhibited percent recovery of 96.50%-101.22% with relative standard deviation (RSD) of 1.48%-4.47%. The developed MnO₂-GNSs/GCE might be a promising platform for the practical detection of H₂O₂ due to its prominent properties including excellent reproducibility, good anti-interference and repeatability.

A novel non-enzymatic H2O2 sensor using ZnMn2O4 microspheres modified glassy carbon electrode

With a facile solvothermal technique, ZnMn₂O₄ microspheres were synthesized in this work, which were used as enzyme mimics for the electrocatalytic reduction of H₂O₂. The morphology, crystal phase and structure of the ZnMn₂O₄ microspheres underwent characterization under X-ray diffraction spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy. The synthesized ZnMn₂O₄ microspheres showed an average diameter of 2 μm with great crystallinity, and exhibited excellent catalytical activity towards H₂O₂ electroreduction in alkaline media. The glassy carbon electrode modified by ZnMn₂O₄ microspheres showed a linear amperometric response for H₂O₂ in a wide concentration range of 0.02 ˜ 15 mM with detection limit of 0.13 μM under the optimized conditions. Besides, the sensor proposed here was successfully used to determine H₂O₂ in milk, suggesting that ZnMn₂O₄ microspheres can be used for non-enzymatic electrochemical sensor applications.

Effect of carbonate on U(VI) sorption by nano-crystalline α-MnO2

U(VI) sorption on nano-crystalline α-MnO2was studied in NaClO4medium as a function of pH by batch sorption method in presence and absence of carbonate and subsequently employing surface complexation modeling (SCM) to predict species responsible for U(VI) sorption. The kinetic study of U(VI) sorption on nano-crystalline α-MnO2was carried out to fix the time of equilibration. In presence of carbonate, U(VI) sorption on nano-crystalline α-MnO2increases with pH of the suspension, leveling off in the pH range 5–8.5 thereafter decreasing at higher pH. However, in absence of carbonate, U(VI) sorption on nano-crystalline α-MnO2remains close to 100% at pH>5. The difference in sorption behavior of uranium in the presence and absence of carbonate can be explained in terms of uranium speciation in the two systems. The dissolution of nano-crystalline α-MnO2was studied in presence and absence of carbonate to ascertain its role in sorption. Surface complexation modeling was satisfactorily able to explain the sorption phenomena in all the systems. In addition, U(VI) sorption on nano-crystalline α-MnO2was compared with literature data on U(VI) sorption by δ-MnO2.

An environmentally benign one pot green synthesis of reduced graphene oxide based composites for the enzyme free electrochemical detection of hydrogen peroxide

An rGO/Ag–Pd nanocomposite prepared by using Arachis hypogaea scrap extract was exploited as an enzyme-free electrochemical probe for the detection of H₂O₂.

One-pot synthesis and first-principles elasticity analysis of polymorphic MnO2 nanorods for tribological assessment as friction modifiers

XRD analysis of hydrothermally synthesized polymorphic MnO₂ nanorods and their frictional torque when added with palm oil as against pure palm oil.