MnO2 Nanocomposites Research Articles

Fe3O4 and MnO2 assembled on halloysite nanotubes: A highly efficient solid-phase extractant for electrochemical detection of mercury(II) ions

In this study, a novel and simple magnetic electrochemical sensing protocol for the sensitive detection of Hg(II) in aqueous media was demonstrated. For this purpose, the halloysite nanotubes-iron oxide–manganese oxide nanocomposite (HNTs-Fe3O4–MnO2) was successfully synthesized for the first time. The synthesis process involves the deposition of Fe3O4 nanoparticles on the surface of HNTs using a simple chemical precipitation method, subsequent formation of wire-like MnO2 nanoparticles on the surface of HNTs-Fe3O4 composites by hydrothermal method with potassium permanganate (KMnO4) and ammonium persulfate ((NH4)2S2O8). The resulting HNTs-Fe3O4–MnO2 nanocomposite was suspended in mercury solution and then brought on the surface of a magnetic carbon paste electrode (MCPE). The amount of analyte was detected electrochemically by applying differential pulse voltammetry (DPV). The conditions of extraction and voltammetric determination were studied and optimized. The proposed method exhibited a linear relationship towards Hg(II) concentrations ranging from 0.5 to 150μgL−1. The detection limit achieved was 0.2μgL−1 (3Sb/m), which is lower than the US Environmental Protection Agency (EPA) standard (2μgL−1 for drinkable water). The proposed methodology was applied for quantification of Hg(II) in real water samples and good recoveries were obtained from 96.0 to 102.7%.

Novel method for preparation of the hybrid metal (I)-metal (II) oxide nanoparticles

Metal-based core–shell nanoparticles (NPs) as a research topic has attracted attention owing to their unique catalytic, biomedical, magnetic and electric properties compared to their bulk counter parts. Surface functionalisation of free-standing metal NPs by coupling with another metal oxide provides means to prepare a hybrid nanomaterial with target properties. A novel bottom-up strategy has been developed to synthesise metal (I)–metal (II) oxide hybrid NPs, which involves electrochemical formation of metal (I) nanoparticles spatially stabilised by organic shell molecules and coupling with a metal (II) oxide formed via oxide-precursor reduction by organic shell. This paper describes application of a novel strategy to synthesise Ag–MnO2 nanocomposites with improved catalytic properties. Kinetic study indicates relatively fast three-step reduction of a permanganate ion (MnO2 precursor) by an oleic acid (shell material) catalysed by a silver core. Surface analytical (SEM, TEM and EDX), spectroscopic (UV–VIS, FT-IR and XRD) and thermal stability (TGA and DTA) studies of Ag–MnO2 nanocomposites reveal strong chemical bonding of the components in a bi-composite. The catalytic properties of supported Ag–MnO2 nanocomposites were tested for oxidation of carbon monoxide. The improvement of a CO conversion rate compared to a single AgNP nanocatalyst was demonstrated.

Accelerated synthesis of MnO2 nanocomposites by acid-free hydrothermal route for catalytic soot combustion

MnO2 nanocomposites with porous structure were successfully synthesized by a facile hydrothermal route from KMnO4 without the addition of any acid.

Fe3O4–Mn3O4 nanocomposites with moderate magnetism for in vitro cytotoxicity studies on macrophages

Reduced magnetism of Fe3O4–Mn3O4 nanocomposites synthesised by alkaline hydrolysis has been explored for in vitro cytotoxicity studies on splenic macrophages.

Enhancing alkaline hydrogen evolution reaction activity through Ni-Mn3O4 nanocomposites.

Developing efficient, stable and cost-effective electrocatalysts towards hydrogen production in alkaline environments is vital to improve energy efficiency for water splitting. In this work, we prepared Ni-Mn3O4 nanocomposites on Ni foam which exhibit an excellent hydrogen evolution reaction catalytic activity with a current density (j) of 10 mA cm(-2) at an overpotential (η) of 91 mV and show good stability in an alkaline medium.

An optimization of MnO2 amount in CNT-MnO2 nanocomposite as a high rate cathode catalyst for the rechargeable Li-O2 batteries

A series of CNT⿿MnO2 nanocomposites containing different values of MnO2 were prepared and applied as the cathode materials in the Li-O2 batteries to obtain the optimum rate. The optimum theoretical ratio of MnO2 to the CNT used in synthesis was 60% (w/wcarbon) but the TGA analysis confirmed that the exact MnO2/CNT ratio in the optimum catalyst was 41% (w/wtotal). The CNT⿿60% MnO2 nanocomposite was characterized by FE-SEM, TEM, XRD, EDS, TGA, FT-IR, and N2 adsorption-desorption analyses. The Electrochemical Impedance Spectroscopy (EIS) and discharge⿿charge cycles were also studied for all the cathodes fabricated using various CNT⿿MnO2 nanocomposites. The N2 physisorption analysis showed a lower surface area for the produced composite compared to that of the pristine CNT but it did not negatively affect the battery rate. The synthesized CNT⿿60% MnO2 compound had a capacity of about 4600mAh/gtotalcathode at a current density of 1000mA/gtotalcathode. The battery fabricated using the optimum nanocatalyst revealed over-voltages equal to 0.20V and 0.87V for discharge and charge, respectively, having a cycleability using the current density of 100mA/gtotalcathode.

Reduced graphene oxide (RGO)/Mn3O4 nanocomposites for dielectric loss properties and electromagnetic interference shielding effectiveness at high frequency

Reduced graphene oxide (RGO)/Mn3O4 nanocomposites are prepared by a one-step hydrothermal approach and the performance of electromagnetic interference (EMI) shielding was studied. Based on an enhanced electrical conductivity through micro-current network induced by unique 2D nanostructures of RGO, the electron hopping between Mn2+ and Mn3+ is discussed. Benefiting from the enhanced effect of Debye dipolar relaxation and Maxwell-Wagner-Sillars (MWS) polarization on dielectric properties, electromagnetic wave propagating and microwave attenuation performance, the maximum EMI shielding effectiveness of 29dB is achieved.

Solvothermal synthesis of graphene–MnO2 nanocomposites and their electrochemical behavior

Well-crystallized Manganese Dioxide (MnO2) nanorods anchored on graphene sheets have been successfully synthesis via a facile, effective and scalable solvothermal process as electrode material for electrochemical capacitors. Highly pristine graphene synthesized from mild treatment of raw highly pyrolytic graphite in a proper ratio of ethanol and water was integrated with MnO2 resulting in a strong synergistic effect between the two materials which produced hybrid nanocomposites with better electrochemical properties. The results from X-ray diffraction (XRD) and Raman analysis revealed the formation of tetragonal α-MnO2 structure from the MnO2 precursors. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM) revealed the nanorods structure of MnO2 anchored on the graphene sheet. The electrochemical properties of graphene–MnO2 nanocomposites were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. Electrochemical measurements showed an improved specific capacitance of 380F/g at a scan rate of 5mV/s, an average energy density of 53Wh/kg and excellent cyclic performance. This enhanced energy storage ability and high rate capability can be attributed to the excellent pseudo-capacitance of MnO2 coupled with the high electrical conductivity of the synthesized graphene suggesting its potential as an electrode material for electrochemical capacitors.

Solid-State Reaction Assisted Synthesis of Co-Doped MnO2 Nano-Composite Materials for Supercapacitor

Electrochemical supercapacitors are charge–storage devices that have greater power density and longer cycle life than batteries, and they possess higher energy density compared with conventional capacitors. Based on the different operation mechanisms, supercapacitors can be classified into two different categories: double-layer capacitors and pseudocapacitors [1,2]. Recently, relatively cheap oxide alternatives with similar characteristics have been developed to replace ruthenium oxide as electrode materials for use in pseudo-capacitors due to their low cost and no-toxicity. MnO2 has been used as one of the promising electrode materials for supercapacitor mainly because of its abundance in nature, low price, environment friendliness, wide charge/discharge potential range and large specific area [3]. In this work, a mechanically assisted solid-state reaction method was employed to prepare Co-doped MnO2 nanocomposites for supercapacitor electrode materials. It was found that the specific capacitance of 2.3 wt% Co doped MnO2 composite electrode was up to 340.1 F g-1 in 1.0 M KCl solution (Figure 1). Additionally, as prepared Co doped MnO2 composite electrode showed other desirable electrochemical properties, including good stable electrochemical properties, excellent reversibility and the long cycle life (Figure 2), demonstrating that it had potential advantages for the fabrication of electrochemical capacitor.

Turn-on fluorescence sensor for glutathione in aqueous solutions using carbon dots–MnO2 nanocomposites

A novel fluorescence sensor based on carbon dots–MnO2 nanocomposites was fabricated successfully, which can detect glutathione (GSH) in aqueous solutions succinctly, rapidly and selectively. The carbon dots (CDs), which were synthesized by using organosilane as a coordinating solvent, had a highly luminescent quantum yield. The nanoflower-like MnO2 had an enormous specific surface area, which could react with more CDs. Subsequently, CDs–MnO2 nanocomposites were synthesized through a facile one-step method. As a result of fluorescence resonance energy transfer (FRET) from CDs to the MnO2, the fluorescence of CDs can be quenched by MnO2. However, when GSH was introduced into the system, the quenched fluorescence could be restored because MnO2 was reduced to Mn2+ by GSH, which led to the elimination of FRET. Compared with other electrolytes and biomolecules, we find that the chemical response of the CDs–MnO2 nanocomposites exhibited good selectivity toward GSH. Under the optimal conditions, the proposed immunosensor was successfully performed with a linear range of 0.03–974.1μmolL−1, with a detection limit of 0.015μmolL−1. In addition, the proposed fluorescence sensor has several merits, such as low cost, good selectivity, great biocompatibility and chemical turn-on fluorescence response.

Effect of cetyltrimethylammonium bromide on the morphology of self assembled water soluble MnO2 nano-composites

Self-assembled water soluble MnO2 nano-composites have been synthesized by a facile one-step chemical reduction method at room temperature for the first time. MnO4−, tri-ethyl amine (TEA) and cetyltrimethylammonium bromide (CTAB) were acted as a reducing-, oxidizing-, and shape directing-agents, respectively. Stoichiometry, kinetics, and morphology of resulting colloidal particles were determined by using UV–visible spectrophotometric and transmission electron microscopic techniques. TEM images show that the MnO2 nanoparticles are self aggregated and/or adsorbed in an un-symmetric manner with a horizontal axis of 108nm and longitudinal axis of 126nm. CTAB increases the absorbance of MnO4− solution, alters the morphology of MnO2 particles from nano-composites to nano-sheets and inhibits the TEA oxidation rates. The lamellar δ-MnO2 nano-sheets are single crystals and formed from two types of building blocks, i.e., nano-wires and nano-particles. The role of inorganic salts (NaCl, NaNO3 and Na2SO4) on the formation kinetics of MnO2 has also been studied and discussed.

POMANI-Mn3O4 based thin film NTC thermistor and its linearization for overheating protection sensor

Hydrochloric acid doped thin film of poly-o-methyl aniline (POMANI)-Mn3O4 nanocomposites have been fabricated on glass substrate. The nanocomposite films showed RT-NTC characteristics in the temperature range of 35–185 °C with repeatability in the temperature range of 75–185 °C. The cut off temperature of the thermistor fabricated from the nanocomposite material was found to be between 165 and 170 °C. Synthesised nanocomposite material has been characterized using FT-IR, XRD, TEM for structure, morphology and TGA/DTC for thermal stability. Thermistor constant (β) observed from RT characteristics are in the range of 7363 K–10,188 K and activation energy (ΔE) was calculated which was in the range 0.634 eV–0.878 eV. Further linearization of thin film based NTC thermistors was carried out using an low cost analog circuit by adding parallel (RP), series resistance (RS) and operational amplifier (OP-AMP). It has been observed that these thin film based temperature sensors have repeatable temperature sensing behavior on linearization with high sensitivity and low power dissipation (Pdiss).

One-pot synthesis of a Ni–Mn3O4 nanocomposite for supercapacitors

Ni–Mn3O4 nanocomposite has been prepared successfully by chemical oxidation in an alkaline solution of Mn2+ on the surface of Ni nanoparticles with OH functional groups using one-pot method. The obtained Ni–Mn3O4 nanocomposite was characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM), X-ray diffraction (XRD) analysis and various electrochemical techniques, such as cyclic voltammetry (CV), galvanostatic charge/discharge (GC/D) and electrochemical impedance spectroscopy (EIS). The average crystal sizes of Mn3O4 were found to decrease linearly with increasing Ni content in the Ni–Mn3O4 composite. The Ni–Mn3O4 nanocomposite could be easily conditioned and inverted to birnessite-type MnO2. A specific capacitance of 230Fg−1 (based on pure Mn3O4) was obtained for the Ni (17.3%)–Mn3O4 nanocomposite at a current rate of 0.25Ag−1, and 94% of the initial capacitance was retained after 1000 GC/D cycles at a current rate of 1Ag−1. It is concluded that the Ni–Mn3O4 nanocomposite is a promising electrode materials for supercapacitors.

Synthesis of Ag–HNTs–MnO2 nanocomposites and their application for nonenzymatic hydrogen peroxide electrochemical sensing

Flower-like Ag–HNTs–MnO2 nanocomposites have been synthesized successfully and they were used for fabricating a non-enzymatic hydrogen peroxide (H2O2) sensor.

Hierarchically Porous Carbon/MnO<sub>2</sub> Nanocomposites as High-Performance Electrode for Asymmetric Supercapacitors

Hierarchically porous carbon (HPC)/MnO2 nanocomposites were fabricated for asymmetric supercapacitor applications. The microstructures of HPC/MnO2 nanocomposites were characterized by X-ray diffraction and scanning electron microscopy. The asymmetric supercapacitor consisting of a HPC/MnO2 cathode and a HPC anode shows an excellent performance with energy density and power density of 23.8 Wh kg-1 and 12.5 kW kg-1, respectively. In addition, the asymmetric supercapacitor exhibits an excellent cycle life with 91% retention of capacitance after 1000 cycles.

Activation of peroxymonosulfate with magnetic Fe3O4–MnO2 core–shell nanocomposites for 4-chlorophenol degradation

Heterogeneous catalysts with low cost, little hazardous, high effective and facile separation from aqueous solution are highly desirable. In this study, magnetic Fe3O4–MnO2 core–shell nanocomposites with various Fe/Mn weight ratios were synthesized through a facile one pot method and then characterized. These as-synthesized solids were applied to activate the peroxymonosulfate (PMS) for 4-chlorophenol degradation. The sample 3 with a Fe/Mn molar ratio of 4:1, which can be separated conveniently through external magnetic field, exhibited higher activity than other Fe3O4–MnO2 nanocomposites, pure MnO2 and physical mixture of Fe3O4 and MnO2. The effects of operational parameters on the catalytic activity of sample 3, including initial Oxone and pollutant dosage, pH and catalyst dosage, were assessed. The catalyst had high stability and good reusability according to five successive repeated reaction. The reactive radicals generated in the PMS/Fe3O4–MnO2 nanocomposites system were sulfate radical (SO4−) and hydroxyl radical (OH). The enhancement of the nanocomposites may be attributed to the interaction of Fe3O4 with MnO2 on the basis of the in situ ATR-FTIR analysis and XPS spectrum.

A green strategy for the synthesis of graphene supported Mn3O4 nanocomposites from graphitized coal and their supercapacitor application

A by-product free strategy based on modified Hummers method was proposed to synthesize graphene/Mn3O4 composites without any additional manganese source. Coal-derived graphite (CDG) was used as carbon source instead of conventional natural graphite flakes and MnSO4 produced from the modified Hummers was in situ transformed into Mn3O4 by precipitation in air. After reduction with hydrazine, the reduced coal-derived graphene oxide/Mn3O4 (RCDGO/Mn3O4) was obtained and employed as the electrode material for the supercapacitors. In addition, K2SO4 produced from the modified Hummers was used as electrolyte, as a result, residual-free was achieved during the whole process, and the atom utilization was calculated as high as about 97%. A maximum specific capacitance of 260Fg−1 was achieved for RCDGO/Mn3O4 composite with 86% Mn3O4 in saturated K2SO4 electrolyte solution based on the synergetic effects between coal-derived graphene and attached Mn3O4 nanoparticles. Its specific energy density reached 8.7Whkg−1 at a current density of 50mAg−1 when used as a symmetrical supercapacitor. The good capacitance retention (92–94%) was also observed after 1000 continuous cycles of galvanostatic charge–discharge.

Mn3O4/Carbon Nanotube Nanocomposites as Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Solution

AbstractElectrodes based on helical carbon nanotubes (CNTs) and Mn3O4 nanocomposites are investigated for catalysis of the oxygen reduction reaction (ORR) in alkaline solutions. Modification of Mn3O4 with helical CNTs allows these nanocomposite materials to exhibit high catalytic activity for the ORR, in which a four‐electron pathway dominates, and also remarkable stability in air‐saturated alkaline solutions. These properties are attributed to a combination of fast electron transport by the helical CNTs and high catalytic activity of Mn3O4 in the ORR.

Synthesis and Characterization of Polyaniline–Mn3O4 Nanocomposite: Electrical Conductivity and Magnetic Studies

Polyaniline (PANI)–Mn3O4 nanocomposites (NCs) have been synthesized by in situ chemical oxidative polymerization of aniline with different molar ratios of aniline:Mn3O4 (3.3:1 and 2.5:1) using ammonium per sulfate as an oxidant in an aqueous solution of sodium dodecyl benzene sulfonic acid, as surfactant and dopant at 5 °C under N2 atmosphere. The structural components and the crystalline phase of the Mn3O4 nanoparticles (NPs) and PANI–Mn3O4 NCs were identified from Fourier transform infrared spectroscopy and X-ray diffraction. The result of FTIR and TGA shows that the interaction between Mn3O4 particles and PANI matrix could improve the thermal stability of NCs. The room temperature electrical conductivity of the synthesized PANI, PANI-Mn3O4 NCs (3.3:1) and (2.5:1) was found to be 3.26 × 10−4, 8.11 × 10−7 and 3.93 × 10−7 S/cm respectively, indicating the decrease of conductivity with an increase of Mn3O4 content in PANI. The magnetic behavior of composite was studied at 5 K. The coercive force (Hc) and remnant magnetization (Mr) increases with increase in addition of Mn3O4 NPs in PANI matrix.

Rational design of manganese dioxide decorated skeleton of colloidal mesoporous carbon nanocomposites for supercapacitors

Colloidal mesoporous carbon (MC) supported MnO2 nanocomposites have been synthesized via a facile and cost-effective strategy at room temperature. The structure and morphology of as-prepared nanocomposites are characterized by X-ray diffraction (XRD), Thermogravimetric analyzer (TGA), nitrogen adsorption, focused ion beam scanning electron microscopy (FIB/SEM) and high-resolution transmission electron microscopy (HRTEM). The as-obtained three-dimensional architecture can be well controlled by tailoring preparative parameters (e.g., the ratio of KMnO4 and MC) and applied as supercapacitor electrodes. Cycle voltammetric (CV) and galvanostatic charge–discharge (GC) measurements present MC–MnO2 composites exhibit the optimized pseudocapacitance performance (270.5Fg−1) with newfangled cycling stability, and ideal rate capability owning to rational design of the novel nanostructures. In principle, these findings exhibit potential in developing long cycling and quick-charge/slow-discharge supercapacitors for practical applications.