MnO2 Nanocomposites Research Articles

Enhanced Peroxidase-mimicking Activity of Plasmonic Gold-modified Mn3 O4 Nanocomposites through Photoexcited Hot Electron Transfer.

Enzyme-mimicking artificial nanomaterials often termed nanozymes have broad applications in many fields, including biosensing, pollutant degradation and cancer diagnosis. Herein, we introduce a plasmonic gold nanoparticle-modified Mn3 O4 nanozyme (Mn3 O4 -Au). Visible or near infrared light excitation into the plasmonic absorption band of the surface-bound gold nanoparticles enhances the catalytic oxidation of tetramethylbenzidine (TMB). The mechanism of light-enhanced peroxidase activity is proposed based on the Mn3 O4 conduction band mediated hot electron transfer from photoexcited gold nanoparticles to H2 O2 which undergoes further oxygen-oxygen bond cleavage to yield hydroxyl radical. The surface decoration of plasmonic gold nanoparticles endows Mn3 O4 -Au to be a light-regulated nanozyme.

Facile Synthesis of Reduced Graphene Oxide‐octahedral Mn3O4 Nanocomposites as a Platform for the Electrochemical Determination of Metronidazole and Sulfamonomethoxine

AbstractA facile synthesis strategy of reduced graphene oxide (RGO)‐octahedral Mn3O4 (oct‐Mn3O4) nanocomposites using in situ one‐pot hydrothermal reaction was reported. The RGO‐oct‐Mn3O4 nanocomposites were drop‐casted onto the surface of glassy carbon electrode (GCE) to obtain RGO‐oct‐Mn3O4/GCE. DPV results revealed that the performance of RGO‐oct‐Mn3O4/GCE towards metronidazole displayed a linear ranging from 0.1 to 9.5 μM with a detection limit of 0.037 μM. For sulfamonomethoxine, it exhibited a linear ranging from 1 to 95 μM with a detection limit of 0.27 μM. Moreover, the proposed sensor had good anti‐interference capability, high stability, satisfactory reproducibility, and was successfully applied in real samples.

Hollow N-TiO2/MnO2 nanocomposite based yeast biomass for gaseous formaldehyde degradation under visible light

Synthesis of new hollow nano-composite photocatalysts based yeast biomass has been considered as a future innovation technology to control air pollution. This work demonstrates that a green, environmentally friendly, sustainable, and facile hydrothermal carbonization route of low-cost and renewable yeast biomass used to fabricate natural doping N-colloidal carbon spheres (NCSs) as a hard template for hollow N-TiO2/MnO2. The presence of natural doping nitrogen serves as a stabilizer and reductant. Hence, the yeast provided a solid frame with deposits nitrogen to form the hybrid N/yeast precursor. The resulting NCSs were obtained by hydrothermal method at 180°C for 6h. The characterization was performed using SEM, TEM, XRD, FTIR and N2 adsorption/desorption analysis. It was found that the findings fully retained the morphology of the yeast cells and the size of the hollow spheres was about 1.5–2μm. The results of catalytic test showed that the new hollow nanosphere N-TiO2/MnO2 possessed a higher photodegradation activity for gaseous formaldehyde under visible irradiation than the commercial TiO2, due to their higher surface area (160m2g−1), hollow structure and superior reducibility. Its catalytic efficiency was attained to be more than 90%, which is about 10 times higher than that of the conventional catalyst TiO2–P25.

A multicolor sensing system for simultaneous detection of four foodborne pathogenic bacteria based on Fe3O4/MnO2 nanocomposites and the etching of gold nanorods

Food safety problems attributed to foodborne pathogenic bacteria seriously endanger human health and cause substantial economic losses. Novel assays for rapid and sensitive identification of foodborne pathogenic bacteria are highly desired. In this study, a multicolor sensing system has been established for simultaneous determination of four foodborne bacteria by exploiting oxidase mimicking activity of aptamer-functionalized manganese dioxide-coated ferriferrous oxide (apt-Fe3O4/MnO2) nanocomposites and oxTMB etching of gold nanorods (AuNRs). Apt-Fe3O4/MnO2 nanocomposites were used as capture probes to recognize and capture specific bacteria. The captured bacteria blocked the catalytic sites of the magnetic conjugate, which inhibited the catalyzation of oxTMB and further reduced the etching of AuNRs. Consequently, the longitudinal shift of AuNRs decreased linearly with the increase of the concentration of bacteria ranging from 10 to 106 CFU mL−1. Instrumental detection limits for S. aureus, L. monocytogenes, E. coli O157:H7 and V. parahaemolyticus reached down to 1.3 CFU mL−1, 1.2 CFU mL−1, 1.3 CFU mL−1 and 1.4 CFU mL−1, respectively. And their visual detection limit was as low as 10 CFU mL−1. The whole detection process only needs 40 min, suggesting that this method is promising in on-site detection of bacteria.

Bipolar resistive switching and non-volatile memory properties of MnO2-polyaniline (PANI) nanocomposite

Organic materials are becoming a promising candidate for non-volatile memory especially resistive switching memories. The present work reports bipolar resistive switching and memristive properties of polyaniline coated MnO2 nanocomposite. The hybrid nanocomposite was synthesized by oxidative polymerization of aniline in the presence of the MnO2 nanostructures. The XRD analysis confirms the α-MnO2 phase and the TEM micrograph reveals the formation of nanorods of the material. The results of Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) and Thermogravimetric analysis (TGA) confirmed the presence of the polymer in the composite. The developed device shows bipolar resistive switching behavior with a memory window ~7 × 102, switches efficiently over 103 cycles, and can retain the data over 104 seconds. Space charge limited current conduction model along with the possible filamentary route of operation describes conduction and resistive switching mechanisms of the device.

Structure and activity of lysozyme on binding to lithium-manganese oxide nanocomposites prepared from seabed nodule

In this work, synthesis of lithium-manganese dioxide from natural manganese (Mn) bearing resources is described. The purified nodule leach solution is taken as the potential source for the fabrication of Li–MnO2 nanocomposite (NC). Herein, we reported a simple room temperature chemical precipitation route for the synthesis of lithium-manganese dioxide NC in absence of surface directing reagent/template. Also, we investigated the molecular interactions of the prepared NCs with lysozyme (Lyz) to understand the biocompatibility of these NCs. A systematic study of the interactions between NC and biomolecule plays a key role in understanding the fate of NCs in biological applications like biosensing, imaging, and drug delivery etc. The conformational changes of Lyz in NC solutions are characterized by using circular dichroism and FTIR which revealed that the secondary structure of Lyz remains stable in presence of NCs. Moreover, we studied the activity of Lyz using Micrococcus lysodeikticus cells. The results indicate that the NC prepared at 1 M LiOH concentration showed better lysis activity as compared to NC prepared at low LiOH concentration. This work provides a simple preparation route for the synthesis of NCs from natural Mn resources and recommends the use of different NCs for further biological studies.

Fluorescence Detection of Glutathione Using N-Doped Graphene Quantum Dots–MnO2 Nanoarchitecture

We build a novel fluorescence resonance energy transfer (FRET) method based on N-doped graphene quantum dots (NGQDs)–MnO2 nanocomposite for rapid, sensitive detection of glutathione (G SH) levels in human serum. In this strategy, MnO2 nanosheets on the NGQDs surface serve as a quencher. NGQDs fluorescence can make a recovery by the addition of GSH, which can reduce MnO2 to Mn2+, and thus the GSH can be monitored. The MnO2 platform affords minimal background and high sensitivity for detecting GSH in this proposed scheme. Meanwhile, relevant fluorescence on–off–on processes were monitored, and the sensing mechanism was explored.

Coconut shell derived activated biochar–manganese dioxide nanocomposites for high performance capacitive deionization

In this study, a Faradaic/electric double-layer hybrid capacitor using coconut shell derived activated biochar (AB) and MnO2 nanocomposite was fabricated for capacitive deionization (CDI) applications. Three different co-precipitation methods including indirect, direct, and acid-assisted grafting oxidation methods were explored to produce the AB-MnO2 nanocomposites. The α-MnO2 with an excellent ion intercalation ability was successfully deposited onto the AB, making the AB-MnO2 an excellent electrode material for CDI application in the presence of neutral Na2SO4 electrolytes. Notably, the AB-MnO2 nanocomposites prepared by indirect co-precipitation method (AB-MnO2-indirect) has shown a high specific surface area of 304 m2 g−1 with high mesopore volume ratio, high capacitance retention, good hydrophilicity and suitable pore texture to shorten the diffusion distance of ions. Cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) spectra showed that the AB-MnO2 yields a quasi-rectangular and symmetric CV plot, and specific capacitances of 410–523 F g−1 at 5 mV s−1 were observed. Moreover, the AB-MnO2-indirect exhibits excellent CDI performance at 1.2 V, and the specific electrosorption capacity of 33.9–68.4 mg g−1 was obtained. Results of this study demonstrate that AB-MnO2 nanocomposites are superior electrochemical materials for CDI application, which can serve as alternative materials for designing an innovative electrochemical technology for water purification, desalination, and energy storage.

Synthesis, characterization and photocatalytic activity of visible-light-driven Mn3O4 and reduced graphene oxide- Mn3O4 nanocomposite

Synthesis, characterization and photocatalytic activity of visible-light-driven Mn3O4 and reduced graphene oxide- Mn3O4 nanocomposite

Enhanced lithium storage performance of binary cooperative complementary CuO–Mn3O4 nanocomposites directly synthesized by hydrothermally controlled method

In this work, Mn3O4 nano-octahedrons and quasi-octahedron shaped CuO–Mn3O4 nanocomposites were prepared by hydrothermal reduction method. A “dissolution-recrystallization-cocrystallization” mechanism was applied to elucidate the growth process of quasi-octahedron shaped CuO–Mn3O4 nanocomposites. The obtained two Mn3O4 samples for their use in lithium-ion batteries were investigated. During cycling, the phase stability and charge-transfer behavior of Mn3O4 can be enhanced by introducing another cooperative complementary transition metal oxide. After 350 cycles, the formed CuO–Mn3O4 nanocomposites exhibit an essentially constant capacity of 1100 mA h g−1. It suggests the synergetic effects of binary cooperative complementary metal oxides can accelerate electron transfer that occurs between active material and substrate. At the same time, the formation of nano-bulges and nano-crevices on the surface of quasi-octahedron shaped nanostructure enhances the contact area, shortens the lithium diffusion pathway, facilitates the electrolyte to access into the electrode material and effectively reduces volume change during Li+ insertion/extraction process. This work presents a new strategy of Mn3O4 nanostructure doping with transition-metal ions and demonstrating its application feasibility for the preparation of high performance lithium ion batteries.

Graphene quantum dots wrapped square-plate-like MnO2 nanocomposite as a fluorescent turn-on sensor for glutathione

Benefiting from their excellent optical absorption and electron transfer properties, manganese dioxide nanomaterials have been widely applied for fluorescence-based nanosensors. In this work, graphene quantum dots (GQDs) wrapped square-plate-like MnO2 nanocomposite was synthesized from potassium permanganate via an in situ redox procedure under ultrasonication with poly(allylamine hydrochloride) (PAH) being involved. Through an effective fluorescence resonance energy transfer (FRET) process and inner filter effect (IFE) between GQDs and MnO2, the fluorescence of GQDs was quenched. Furthermore, the introduction of glutathione (GSH) decomposed MnO2 and caused fluorescence recovery of GQDs. Therefore, a MnO2 mediated nanosensor was established for fluorescent turn-on sensing of GSH. A satisfactory linear range was found to be 0.07–70 μM and the detection limit was as low as 48 nM. Besides, the fluorescent recognition of cancer cells using GQDs-MnO2 nanocomposite was achieved because of the obviously higher GSH content in cancer microenvironment than normal cells. This nanosensor was constructed directly in GQDs solution in the presence of PAH without the complicated modifications or connections, making it a facile and novel nanosensor for GSH.

Noble-metal-free Z-Scheme MoS2–CdS/WO3–MnO2 nanocomposites for photocatalytic overall water splitting under visible light

To fabricate an efficient two-component Z-scheme system for visible light induced overall water splitting, CdS/WO3 nanocomposites, with cubic CdS nanoparticles grown on the surface of hexagonal WO3 nanorods, were prepared via a facile precipitation of Cd2+ with S2− in the presence of pre-obtained hexagonal WO3 nanorods. MnO2 and MoS2, the co-catalysts for O2 and H2 generation respectively, were selectively deposited on WO3 and CdS in the CdS/WO3 nanocomposites. The resultant MoS2–CdS/WO3–MnO2 composites show photocatalytic activity for overall water splitting under visible light, with an optimized performance observed over 2.0%MoS2-0.2 CdS/WO3-1.0%MnO2. The visible light induced overall water splitting over MoS2–CdS/WO3–MnO2 nanocomposites can be attributed to the presence of a Z-scheme charge transfer pathway in the CdS/WO3 nanocomposites, ie, the transfer of the photo-generated electrons from the CB of WO3 to the VB of CdS to recombine with the photo-generated holes through an efficient interface between cubic CdS and hexagonal WO3. The left photo-generated holes in VB of WO3 and the photo-generated electrons in CB of CdS therefore can accomplish the water oxidation and water reduction simultaneously, with the assistance of the surface deposited cocatalysts (MnO2 and MoS2). This work demonstrated the great potential of fabricating the two-component direct Z-scheme photocatalytic systems for overall water splitting from two semiconductors with a staggered band structure.

Carbon supported manganese(IV)–cobalt(II/III) oxides nanoparticles for high-performance electrochemical supercapacitors

The carbon supported manganese(IV)–cobalt (II/III) oxides nanoparticles labelled as MnO2–Co3O4/C nanocomposites have been prepared by a simple one-step microwave-assisted heating method using different precursor materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) have been used for the characterization of morphology, structure and composition of the synthesized nanocomposites, whereas the electrochemical performance of the prepared nanocomposites has been evaluated by using cyclic voltammetry (CV). It was determined that the use of different precursor materials for the synthesis of the carbon supported MnO2 and Co3O4 nanocomposites results in a different morphology of the prepared substances. A high specific capacitance (Cs) of 658.8 F g−1 at a scan rate of 10 mV s−1 in a 1 M Na2SO4 solution has been obtained for the MnO2–Co3O4/C-2 nanocomposite that has a spherical shape of nanoparticles. Moreover, it significantly outperforms the MnO2–Co3O4/C-1 nanocomposite that has a lamellar shape of nanoparticles.

MnO2 and TiO2 based Nanocomposites for Macroscopic and Individual Nanodevices in Sensing, Energy Storage and Photocatalysis Applications

The present nanotechnological trend is promising for the devices based on nanocomposites. We focus on three application areas, biosensing, energy storage and photocatalyst. A newer frontier trend is related to individual nano-devices based on individual nano-objects giving the exciting advantages. In the present work, the MnO2 and TiO2 nanocomposites were developed by simple and economical means. The MnO2 and Cu/MnO2 were potentiodynamically deposited on stainless steel sheets and ITO coated glass substrates for energy storage and sensing applications. The electrochemically anodized TiO2 nanotubes and Ag nanoparticles decorated TiO2 nanotubes were fabricated on Ti base for photocatalysis. The MnO2 film electrode, Cu/MnO2 film electrode, Ag/TiO2 nanotubes were preliminarily demonstrated as macroscopic devices in capacitors, glucose sensors and photocatalysis water treatments. The specific capacitance of MnO2 film electrode is as high as 135 Fg−1and the Cu/MnO2 sensor has the low detection limit of 0.986. For the water purification, the photodegradation efficiency of Ag/TiO2 nanotubes is as high as 95% under UV irradiation.

Surfactant-assisted microwave synthesis of carbon supported MnO2 nanocomposites and their application for electrochemical supercapacitors

MnO2/C nanocomposites have been prepared using a simple onestep microwave heating method by applying different concentrations of cationic surfactant – cetyl trimethylammonium bromide (CTAB). The morphology and composition of the prepared MnO2/C nanocomposites have been investigated using X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The electrochemical performance of the prepared nanocomposites has been analysed using cyclic voltammetry. It was found that a high specific capacitance (Cs) of 742 F g−1 at a scan rate of 10 mV s−1 in a 1 M Na2SO4 solution has been obtained for the MnO2/C nanocomposite that has the mass loading of 0.140 mg cm−2 and has been synthesized in the absence of CTAB. Meanwhile, the application of CTAB allowed the increase in the mass loading of MnO2 in the nanocomposites. In the presence of CTAB, the highest value of 654 F g−1 at a scan rate of 10 mV s−1 has been obtained for MnO2/C that has the mass loading of 0.570 mg cm−2. This result confirmed a good performance of the prepared MnO2/C nanocomposites as the electrode material for supercapacitors.

Quasi-1D MnO2 nanocomposites as gas sensors for hazardous chemicals

Quasi-1D MnO2 nanocomposite materials (A/MnO2 with A = CuO, SnO2) were developed by a two-step plasma-assisted process, involving the plasma enhanced-chemical vapor deposition (PE-CVD) of MnO2 nanomaterials and their functionalization with copper or tin oxides by radio frequency (RF)-sputtering. A thorough characterization by means of specific surface analytical techniques highlighted the formation of high purity nanocomposites, endowed with a controlled morphology and a tailored spatial dispersion of the functionalizing agents. The target materials were tested as gas sensors for the recognition of hazardous gases [H2 and di(propyleneglycol) monomethyl ether (DPGME) / dimethyl methyl phosphonate (DMMP), the latter used as simulants for chemical warfare agents]. Functional data evidenced the obtainment of low detection limits and promising gas responses, whose improvement with respect to the pristine MnO2 was traced back to the formation of built-in p-n and n-n junctions for CuO/MnO2 and SnO2/MnO2 systems, respectively. The possibility of discriminating between the target analytes depending on the functionalizing species already at moderate working temperatures demonstrates the potential of the developed materials for eventual gas sensing applications under real-world conditions.

Synthesis and Characterization of Fe3O4/Carbon Dot Supported MnO2 Nanoparticles for the Controlled Oxidation of Benzyl Alcohols

AbstractIn recent past, magnetic catalyst has gained much attention because it can be easily separated from the reaction mixture. Herein we report a facile synthesis of magnetic carbon dot supported MnO2 nanoparticles for the oxidative transformation of organic compounds. In the actual synthesis, initially Fe3O4 nanoparticles were prepared by microwave assisted method and carbon dots were prepared instantaneously from glucose by simple incineration under closed condition. The synthesized carbon dots were coated over iron oxide nanoparticles via sonochemical deposition method. Further, magnetic carbon dot supported MnO2 nanocomposite was synthesized by conventional homogeneous precipitation using potassium permanganate. The synthesized nanocomposite material was characterized using FT‐IR, SEM, TEM, XRD and VSM techniques. The catalytic efficiency of the nanomaterial was successfully demonstrated for the oxidation of benzyl alcohols to benzaldehydes. The advantages of this method include, controlled oxidation of alcohols to aldehydes with broad substrate scope, the use of molecular oxygen as a green oxidant and beyond that a facile magnetic separation of the catalyst material. Moreover, the catalyst can be recycled for 5 times without much loss in its efficiency.

Recovery of strontium (Sr2+) from seawater using a hierarchically structured MnO2/C/Fe3O4 magnetic nanocomposite

The recovery of strontium ions (Sr2+) from seawater has attracted much attention as an approach to securing Sr resources to meet increasing industrial demand. In this study, we synthesized a magnetic MnO2 nanocomposite (MnO2/C/Fe3O4) using a simple redox reaction under ambient conditions and applied this nanocomposite to the extraction of Sr2+ from natural seawater. The synthesized nanocomposite exhibited a hierarchical structure of MnO2, carbon, and Fe3O4 with a saturation magnetization of 25 emu/g that enabled effective separation under an external magnetic force. Regardless of the initial Sr2+ concentration, the adsorption of Sr2+ onto MnO2/C/Fe3O4 proceeded rapidly (within <10 min) following a pseudo-second-order kinetic model and agreed well with the Langmuir isotherm model, indicating a maximum adsorption capacity of 42 mg/g. Among the competitive ions, Mg2+ and Ca2+ significantly hindered Sr2+ adsorption onto MnO2/C/Fe3O4, whereas Na+ and K+ had little effect on Sr2+ adsorption. A detailed study of the distribution coefficient (Kd) revealed 11.2-fold and 1.8-fold higher selectivities toward Sr2+ than toward Mg2+ and Ca2+, respectively. The Sr2+ ions adsorbed onto MnO2/C/Fe3O4 were completely recovered through desorption in 0.1 M HCl eluent. Finally, a Sr2+-enriched solution with a concentration of 501 mg/L could be obtained via seawater adsorption and subsequent acid desorption over 8 iterative cycles, demonstrating its effectiveness for practical applications of Sr2+ recovery from seawater.

Hydrothermal synthesis and characterization studies of α-Fe2O3/MnO2 nanocomposites for energy storage supercapacitor application

In this present study, semiconductor magnetic α-Fe2O3/MnO2 nanocomposites (NCs) were prepared by a facile hydrothermal (HT) method. The crystallographic structure, morphology, chemical configuration and magnetic features were analysed by X-ray powder diffraction (XRD), high resolution scanning electron microscope (HR-SEM), energy dispersive X-ray analysis (EDX), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analyses. The as-prepared NCs were used as an electrode in energy storing supercapacitor was systematically examined. The electrochemical deeds of α-Fe2O3/MnO2 NCs was analysed by cyclic voltammetry (C–V) and galvanostatic charge–discharge (GCD) tests. The CV analysis of the NCs electrode showed a distinctive pseudocapacitive behaviour in 1 M KOH solution. The NCs electrode reveals enhanced specific capacitance compared to plain α-Fe2O3 and MnO2 nanoparticles (NPs) and generates high specific capacitance of 216.35 Fg−1. Pseudocapacitor obtains of energy density 135.42 Wh kg−1 at power density of 6.399 kW kg−1, indicating the as-prepared α-Fe2O3/MnO2 NCs shows noteworthy high-energy, specific capacitance, power densities and long-standing cyclic stability with 89.2% of preliminary capacitance reserved at 1A g−1 after 10000 cycles in judgement with the pure α-Fe2O3 and MnO2 NPs electrode. The α-Fe2O3/MnO2 NCs electrode having noteworthy electrochemical characteristics performance renders promising applications in energy storing systems.

Role of GAC-MnO2 catalyst for triggering the extracellular electron transfer and boosting CH4 production in syntrophic methanogenesis

The addition of conductive materials or metal oxide nanoparticles (NPs) to anaerobic systems is an attractive strategy to enhance the anaerobic digestion and the production of CH4. This study proposed a strategy to boost the CH4 production by adding granular activated carbon (GAC)-MnO2 nanocomposites into an anaerobic methanogenic system. The associated mechanisms and the microbial community structure during anaerobic digestion were investigated systematically. Compared with a control with GAC only, after adding GAC-MnO2 composite the chemical oxygen demand (COD) removal efficiency and CH4 yield were increased by 77% and 36%, respectively. The addition of GAC-MnO2 stimulated the secretion of extracellular polymeric substance (EPS), while the secretion of humic substances was inhibited. The spatial distribution of EPS in the anaerobic sludge affects the extracellular electron transfer efficiency as well. Manganese ions concentrated in the EPS layer facilitated the electron flow and, thus, accelerated the extracellular electron transfer. The enhancement of anaerobic methanogenesis can be mainly attributed to the reduction/oxidation cycle of Mn4+/Mn2+. Electron transfer system activity and Cytochrome C content reached up to 341 and 38 nmol/L, respectively, under optimal conditions. 16S rRNA gene sequencing analysis indicated that Spirochaetaceae, Cloacibacterium, and Treponema were the dominant bacteria. The abundance of the methanogenic archaea Methanobacterium and Methanosaeta were increased with the addition of GAC-MnO2.