Mesoporous Manganese Oxide Research Articles

Mixed-valence mesoporous manganese oxide spheres from waste manganese nitrate aqueous solution

Abstract The paper presents a novel simple and cost-effective approach to preparation of mixed-valence mesoporous manganese oxide in the form of easy to handle spheres. The synthesis relies on swelling of porous polymer templates (i.e. three selected resins Amberlite® XAD7 HP, XAD4 and XAD16) in a saturated Mn(NO3)2 solution and subsequent removal of the template via calcination in air. The products are porous with the specific surface area ( S B E T ) up to 100 m2 g−1. The detailed characteristic of the materials, thermogravimetric insight into its calcination in air, and the influence of porous polymer (template) on MnOx structure is provided. The final product can be of great significance for electrochemistry, catalysis and is of some importance to the environment protection.

Controllable synthesis of novel nanoporous manganese oxide catalysts for the direct synthesis of imines from alcohols and amines

Abstract A novel template-free oxalate route was applied to synthesize different mesoporous manganese oxides (amorphous manganese oxide (AMO), Mn5O8, Mn3O4, MnO2) in the narrow temperature range from 350 °C to 400 °C by controlling the calcination conditions, which were employed as the efficient catalysts for the oxidative coupling of imines from alcohols and amines. The chemical and structural properties of the manganese oxides were characterized by the methods of thermal analysis and heat flow (TG-DSC), X-ray diffraction (XRD), nitrogen sorption, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), and inductively coupled plasma optical emission spectrometry (ICP-OES) techniques. The structures of different manganese oxides were confirmed by characterization. The M-350 (AMO) presented the maximum surface area, amorphous nature, the lowest reduction temperature, the higher (Mn3+ + Mn4+)/Mn2+ ratio, and the higher adsorbed oxygen species compared to other samples. Among the catalysts, M-350 showed the best catalytic performance using air as an oxidant, and the conversion of benzyl alcohol (BA) and the selectivity of N-benzylideneaniline (NBA) reached as high as 100% and 97.1% respectively at the lower reaction temperature (80 °C) for 1 h. M-350 had also the highest TOF value (0.0100 mmol·mg−1·h−1) compared to the other manganese oxide catalysts. The catalyst was reusable and gave 95.8% conversion after 5 reuse tests, the XRD pattern of the reactivated M-350 did not show any obvious change. Lattice oxygen mobility and (Mn3+ + Mn4+)/Mn2+ ratio were found to play the important roles in the catalytic activity of aerobic reactions.

Controllable synthesis of mesoporous manganese oxide microsphere efficient for photo-Fenton-like removal of fluoroquinolone antibiotics

Controllable synthesis of mesoporous manganese oxide (MnOx) microsphere is successfully achieved using a soft-template P123 assisted method. The as-obtained MnOx materials are highly efficient and versatile to remove the category of fluoroquinolone antibiotics (i.e., ofloxacin, ciprofloxacin, enrofloxacin and levofloxacin) using peroxymonosulfate (PMS) as the oxidant under UV or simulated sunlight irradiation. The mesoporous Mn3O4 microsphere prepared in the presence of 2 g P123 (P2-Mn3O4) exhibits the superior catalytic activity with almost perfect degradation for the fluoroquinolone antibiotics in 10 min under UV irradiation. Moreover, under simulated sunlight irradiation, 74.5% of ofloxacin, 79.4% of ciprofloxacin, 72.3% of enrofloxacin and 81.9% of levofloxacin can be degraded by P2-Mn3O4 in 10 min. Besides, the P2-Mn3O4 catalyst maintains stable without the obvious deactivation of catalytic activity or structural change after several successive runs, and slight leaching of Mn ions is observed. The ESR spectra further document that SO4−, OH, O2− and 1O2 radicals are prominent in the decomposition process of antibiotic molecules. In the end, the reaction kinetic and rational degradation pathway are also investigated and proposed.

Lithium promoted mesoporous manganese oxide catalyzed oxidation of allyl ethers

Herein we report the first example of the catalytic aerobic partial oxidation of allyl ether to its acrylate ester derivative. Many partial oxidations often need an expensive oxidant such as peroxides or other species to drive such reactions. In addition, selective generation of esters using porous catalysts has been elusive. This reaction is catalyzed by a Li ion promoted mesoporous manganese oxide (meso-Mn2O3) under mild conditions with no precious metals, a reusable heterogeneous catalyst, and easy isolation. This process is very attractive for the oxidation of allyl ethers. We report on the catalytic activity, selectivity, and scope of the reaction. In the best cases presented, almost complete conversion of allyl ether with near complete chemo-selectivity towards acrylate ester derivatives is observed. Based on results from controlled experiments, we propose a possible reaction mechanism for the case in which N-hydroxyphthalimide (NHPI) is used in combination with trichloroacetonitrile (CCl3CN).

Synthesis of MoS2 nanoparticle deposited graphene/mesoporous MnOx nanocomposite for high performance super capacitor application

The present study deal with the fabrication of low cost nanocomposite based electrodes based on Nickel foam binder free substrate for supercapacitor applications. The composition of nanocomposite is molybdenum sulphide nanoparticle/graphene coated on mesoporous manganese oxide. The first step is to involve the preparation of mesoporous manganese oxide by non-ionic surfactant assisted method. In the second stage is to deposit the reduced graphene on mesoporous manganese oxide in the presence of ultrasonic irradiation followed by addition of known quantity of commercial MoS2 nanopowder (particle size below 90 nm). The manganese oxide based nanocomposite is showing porous architecture with graphene sheet formation together with MoS2 nanoparticle deposition. N2 adsorption-desorption Isotherm curves for MoS2 nanoparticle (NP) modified graphene oxide/meso-MnO2 and pure meso-MnO2 displayed type IV isotherm with improved surface area values. The reduced graphene oxide (graphene) and MoS2 exist in the form of glassy flaky morphology as well as tubular/needle shapes are obtained after the deposition process in the final nanocomposite. The orderly arranged and anchored nano-sized mesoporous manganese oxide nanocomposites are showed increased specific capacitance (up to 527, 727 and 1160 F/g) and continuous cyclic stability.

PtxCo/meso-MnOy: Highly efficient catalysts for low-temperature methanol combustion

The KIT-6-templating and polyvinyl alcohol-protected NaBH4 reduction methods were adopted to prepare the mesoporous manganese oxide (meso-MnOy) and its supported Co, Pt, and PtxCo catalysts, respectively. Numerous techniques were used to characterize the physicochemical properties of the materials. Catalytic performance of the samples was evaluated for methanol combustion. All of the samples possessed a three-dimensionally ordered mesoporous structure and a surface area of 94–110 m2/g. The Co, Pt, and PtxCo nanoparticles (NPs) with an average size of 2.2–3.0 nm were uniformly dispersed on the surface of meso-MnOy. The 0.70 wt% Pt2.42Co/meso-MnOy sample performed the best: the T50% and T90% (temperatures required for achieving methanol conversions of 50 and 90%, respectively) were 50 and 86 °C at a space velocity of 80,000 mL/(g h). The partial deactivation of the 0.70Pt2.42Co/meso-MnOy sample due to water vapor or carbon dioxide introduction was reversible. It is concluded that the excellent catalytic activity of 0.70 wt% Pt2.42Co/meso-MnOy was associated with its highly dispersed Pt2.42Co alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pt2.42Co alloy NPs and meso-MnOy.

Capacitor behavior in neutral electrolytes of ordered mesoporous manganese oxide obtained from oxidation of perfluorinated alkenes by soft template CTAMnO4

Ordered mesoporous manganese oxides were produced as a by-product of the oxidation of perfluorinated alkenes by soft template CTAMnO4 (CTA = cetyltrimethylammonium). Pores diameter was in the 2.4–6.0 nm range and pore walls were made of birnessite nanocrystallites. Alkene dimensions influenced the oxides morphological and textural properties, including pore ordering. For a particular alkene (1H, 1H, 2H Perfluoro-1-Decene), the surface specific area (SSA) of the manganese oxide was as high as 265 m2 g−1. Mesoporosity, combined with large SSA, guarantee rapid diffusion and access of the electrolyte to the electrochemical capacitor electrode surfaces. Composites of mesoporous oxides, black carbon and Teflon in a 75/12.5/12.5 wt ratio provided capacitances in the 150–175 F g−1 range in neutral aqueous 1 M K2SO4 electrolyte. Asymmetric AC||MnO2 devices, cycled reversibly in a 0–1.7 V voltage window, had a pore-depending activation time during which capacitance increases upon cycling. Ragone plot for these MnO2-based electrodes shows suitable gravimetric energy retention with increasing power, comparable or higher than most of the literature results concerning composite electrodes (except for microsupercapacitors). For instance, energy provided by such devices, at power close to 0.2 kW kg−1, approaches 20 Wh.kg−1. From this point of view, our devices can compete with others containing a very high amount of low density and expensive conductive additive in the positive electrode formulation, which penalizes the volume and cost of the final device.

Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior

Magnetic behavior of nanostructured mesoporous manganese oxide materials, designated UCT-1 and UCT-18, were studied using a combination of superconducting quantum interference device (SQUID) magnetometry and 55Mn zero-field spin–echo nuclear magnetic resonance (NMR). Curie–Weiss fits to the magnetic susceptibility for the UCT-1 and UCT-18 samples calcined at 550 °C yielded paramagnetic moment values consistent with spin-only Mn3+ ions in the α-Mn2O3 phase (S = 2, 4.90 μB). However, the magnetization and NMR results reported here clearly identify a small amount of the Mn3O4 second phase (ferrimagnetic with TC ≈ 43 K) that does not appear in X-ray diffraction (XRD). The study resulted in the observation of fascinating magnetic behavior: (1) exchange bias, which occurs in cases where a ferromagnetic (or ferrimagnetic) phase forms a boundary with an antiferromagnetic phase and (2) a magnetic contribution attributed to uncompensated spins on the surfaces of the α-Mn2O3 nanoparticles. The presence of Mn3O4 and ...

Facile synthesis of amorphous mesoporous manganese oxides for efficient catalytic decomposition of ozone

Amorphous mesoporous manganese oxides (MnOx) with different microstructures were synthesized via a facile redox method between manganese acetate and potassium permanganate by modulating the addition sequence of the precursors and directly used for catalytic decomposition of ozone.

Mesoporous cobalt/manganese oxide: a highly selective bifunctional catalyst for amine–imine transformations

Cobalt doped mesoporous manganese oxide: an excellent oxidative catalyst (for producing asymmetric imines with >98% selectivity) with significant reductive properties.

Theoretical and Practical Approach of Soft Template Synthesis for the Preparation of MnO2 Supercapacitor Electrode

Mesoporous manganese dioxide was successfully synthesized by alkene oxidation with permanganate in soft template medium. Four linear and three cyclic alkenes have been used as reactants to show their impact on the MnO2 particles microstructure (specially the pore volume), on their agglomeration, and hence on their electrochemical performances as positive electrode materials in supercapacitors. The reaction proceeds via an intermediate product step, a manganate(V) cyclic diester, capable of producing aggregates. Aggregate macromolecular characteristics, such as intrinsic viscosity [η], molecular weight M, aggregation number N, and radius R, depend on the alkene employed. The role of CTAP as phase-transfer agent and as templating agent for MnO2 synthesis when associated with alkene is also confirmed. This first study allowed the proposition of a structure for the aggregates (called model B in the text). The electrochemical performances of the manganese oxides were subsequently determined with aqueous, environmentally friendly K2SO4 electrolyte. Suitable performances, in terms of high specific capacitances (>150 F·g–1) are provided by oxides prepared by employing bulky cyclic or long-chain linear alkenes. Asymmetric devices AC∥MnO2 with one of the mesoporous manganese oxide as the positive electrode, obtained from the oxidation of 1-octadecene, and activated carbon (AC) as the negative electrode yield suitable energy density of 18.2 Wh·kg–1 and a power density of 0.2 kW·kg–1 for electrochemical capacitor purposes. Finally, this particular device, cycled under galvanostatic regimes, shows a high-capacitance retention (81.2% after 10000 cycles). Therefore, this particular soft template method is suitable for the preparation of supercapacitor electrodes.

Catalytic evaluation of mesoporous metal oxides for liquid phase oxidation of styrene

Mesoporous manganese oxide, cobalt oxide, and hybrid Mn-Co oxide were synthesized using an inverse surfactant micelle method. The synthesized materials were monodispersed nanoparticle aggregates with connected and well defined intra-particle voids. An increase in the pore and crystallite size with increase in calcination temperature was observed with TEM, SEM, p-XRD, and N2-sorption. These mesoporous metal oxides were employed in the selective oxidation of styrene using tert-butyl hydrogen peroxide as an oxidant. Higher selectivity towards styrene oxide was achieved using manganese oxide followed by cobalt oxide while the hybrid oxide showed the lowest selectivity towards styrene oxide. The catalytic activities of the compared catalysts were decreasing in the order of Mn-Co_350 (66.6 h−1) > MnO2_350 (47.4 h−1) > Co3O4_350 (35.6 h−1). The catalytic activities and selectivity profiles under various reaction conditions such as solvent type, catalyst amount, styrene to TBHP ratio and temperature are discussed. The catalytic recyclability of metal oxides showed that they are stable, and the structure of the catalyst was retained.

Isothermic adsorption of morin onto the reducible mesoporous manganese oxide materials surface

A series of mesoporous manganese oxide materials were synthesized following the inverse micelle sol-gel method and categorized by the heat treatment. The tunable features and crystallinity of the mesoporous materials were analyzed by BET and XRD analyses. The HR-TEM and TRP analyses were conducted to analyze the meso-ordered structure and reducibility of the mesoporous manganese oxide materials. The catalytic activity of the mesoporous materials was investigated in aerobic oxidation of morin as a model reaction. The experimental data were interpreted according to the Mars-van Krevelen and Langmuir-Hinshelwood approach. The heat treatment influenced the crystallite size and the activity of the mesoporous manganese oxide materials. The activity of the lattice oxygen was a critical factor in the aerobic process. MnO2–350°C exhibited the largest lattice oxygen activity ((64.3±5.6)×kJmol−1m−2).

Electrochemical Deposition of Mesoporous Manganese Oxide Films Using Mixed Surfactants as Templating Agents

Electrochemical Deposition of Mesoporous Manganese Oxide Films Using Mixed Surfactants as Templating Agents

Ullmann Reaction Catalyzed by Heterogeneous Mesoporous Copper/Manganese Oxide: A Kinetic and Mechanistic Analysis.

A heterogeneous copper oxide supported on mesoporous manganese oxide (meso Cu/MnOx) was explored for Ullmann-type cross-coupling reactions. An inverse micelle-templated evaporation-induced self-assembly method with in situ addition of copper was adopted to synthesize the mesoporous catalyst. Broad substrate scope and excellent functional group tolerability in C-O, C-N, and C-S bond formation reactions were observed using the optimized reaction conditions. The catalytic protocol was ligand free, and the catalyst was reusable without any significant loss of activity. The kinetic and Hammett analyses provided evidence for oxidative addition to a Cu(I) reaction center followed by nucleophilic addition and reductive elimination at the active copper oxide surface. Rate acceleration was observed for aryl halides with electron-withdrawing groups. The Hammett analysis determined ρ = +1.0, indicative of an oxidative addition, whereas the electronic effect in the phenol ring (ρ = -2.9) was indicative of coordination to a metal ion. Theoretically, the oxidative addition of the aryl halides is assisted by the ligand environment of the copper center. Relevant mechanistic implications are discussed on the basis of the experimental and computational results.

Silver nanoparticle/r-graphene oxide deposited mesoporous-manganese oxide nanocomposite for pollutant removal and supercapacitor applications

Mesoporous manganese oxide was prepared by a non-ionic surfactant route using Triton X-100, followed by Ag nanoparticle (NP) and graphene oxide incorporation by an ultra-sonication-assisted process. Fine Ag NPs were incorporated into the tubular texture of mesoporous manganese oxide. The crystalline phase, particle size, and morphology of the prepared materials were characterized by X-ray diffraction (XRD), Barrett–Joyner–Halenda–Brunauer–Emmett–Teller analysis, scanning electron microscopy–energy dispersive X-ray analysis, and high-resolution transmission electron microscopy (HR-TEM). The XRD results confirmed the formation of the Mn2O3 phase for the as-prepared mesoporous manganese oxide and its nanocomposite. Very fine Ag NPs (<5–10 nm) were obtained. The mesoporous MnO2 and graphene-incorporated Ag NPs/meso-MnO2 had a tubular structure and “flaky pastry”-type morphology for the synthesized nanocomposites. HR-TEM images further confirmed the beautiful structural formation upon graphene addition and spherical/dot-shaped NP incorporation into the matrix of MnO2. Improved surface area was obtained for the Ag NPs and graphene-incorporated mesoporous MnO2 as compared to bulk MnO2. The Cr(VI) removal analysis was performed using a batch technique, and enhanced removal of Cr(VI) was achieved (>98% removal of Cr(VI) within 1–2 h of reaction time) for Ag NP-incorporated mesoporous MnO2. Efficient activity was observed because of the fine Ag NPs present in mesoporous manganese oxide, as opposed to the case of graphene oxide-doped meso-MnO2 and pristine mesoporous meso-MnO2.

Rapid Ultrasound‐Assisted Synthesis of Mesoporous Manganese Oxides for Low‐Concentration NO Elimination with Superior Water‐Resistance

Through a room‐temperature ultrasound‐assisted redox process, mesoporous manganese oxides were synthesized in short reaction times of 3–9 h. At room temperature, the resultant materials showed superior performance for the elimination of low‐concentration NO (10 ppm). Specifically, under humid conditions (50–90 % relative humidity), 97 % NO removal efficiency was obtained over 110 h without deactivation. Synergetic effects between Mn2+, Mn3+, and Mn4+ ions were proposed to explain the oxidation of NO to NO2 on the surface of the catalyst. Density functional theory (DFT) calculations indicated that water molecules strengthen the chemisorption of NO2 on manganese oxide (001) owing to a much higher adsorption energy. As a result, the probability of the reaction between NO2 and H2O increases, and the formation of volatile nitric acid ensures that the catalytically active sites are always available.

Mesoporous manganese oxide with large specific surface area for high-performance asymmetric supercapacitor with enhanced cycling stability

Boosting the energy density of supercapacitors without sacrificing their power capability and cyclability is highly desired. Herein, we reported high-performance asymmetric supercapacitor device with high cycling stability using mesoporous manganese oxide nanococoons (MONCs) as positive electrode, and activated carbon (AC) as negative electrode. The mesoporous manganese oxide nanococoons exhibit excellent electrochemical performances because of their large surface area. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0–1.7V in aqueous electrolyte, which exhibits a maximum energy density of 32Whkg−1 at a power density of 185Wkg−1 and still remains 21Whkg−1 at a power density of 1630Wkg−1. Importantly, such asymmetric supercapacitor exhibits superior long cycle life with ∼100% specific capacitance retained after ∼2700 cycles and ∼98% after 5000 cycles.

Fabrication of Three-Dimensional Ordered Mesoporous Manganese Oxides Used as High-Efficient Catalysts for Removal of Toluene and Carbon Monoxide

Fabrication of Three-Dimensional Ordered Mesoporous Manganese Oxides Used as High-Efficient Catalysts for Removal of Toluene and Carbon Monoxide

Sorption of strontium ions onto mesoporous manganese oxide of OMS-2 type

Sorption of stable and radioactive strontium ions onto mesoporous manganese oxide of OMS-2 type, prepared by the sol–gel method via reduction of potassium permanganate with polyvinyl alcohol in aqueous medium, was studied. The influence exerted by the pore structure parameters and by the phase and chemical composition of manganese oxide on its sorption properties and selectivity to Sr ions was examined. Manganese oxide samples prepared using a 0.1 wt % KMnO4 solution exhibit the highest values of the sorption capacity for Sr, about 100–150 mg g–1, and of the Sr distribution coefficient, K d = (11.5–19.5) × 103 cm3 g–1. Introduction of 0.1 M NaCl into this solution considerably decreases the sorption of stable Sr ions, and for all the samples the sorption capacity is 25–35 mg g–1. On the other hand, for the most active sorbents the distribution coefficient in the presence of 0.1 M NaCl increases by a factor of approximately 8–10 relative to distilled water and reaches (91–208) × 103 cm3 g–1. Introduction of 0.05 M CaCl2 also decreases the Sr uptake, and the sorption capacity of the most active sorbents for stable Sr ions is 25–35 mg g–1 at K d (85Sr) equal to (0.14–0.35) × 103 cm3 g–1.