Presence Of MnO2 Research Articles

Effects of manganese(VI) oxide on polyacrylonitrile-based activated carbon nanofibers (ACNFs) and its preliminary study for adsorption of lead(II) ions

In this work, the effect of adding manganese oxide towards polyacrylonitrile-based activated carbon nanofibers (ACNFs) was evaluated. The properties of PAN-based ACNFs/MnO2 were analyzed by using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and Fourier transform infrared (FTIR). The sorption study of the electrospun ACNFs/MnO2 in comparison to neat ACNFs and commercial granular AC towards lead (Pb) was also conducted. SEM micrograph analysis displays more compact nanofibers with dispersion of beads that were observed in the ACNF/MnO2 with the diameter of 437.2 nm while aligned nanofibers with the diameter of 575.5 nm were observed in the neat ACNFs. The FTIR analysis showed the peak of Mn–O, which indicates the presence of MnO2 in the ACNFs/MnO2. In comparison to the neat ACNFs, surface area of the prepared ACNFs/MnO2 is lower. It was found out that the removal of Pb(II) using ACNFs and ACNFs/MnO2 is higher than commercial granular activated carbon with a removal rate of 100% at initial concentration of 3.5 ppm. The promising results of ACNFs/MnO2 contributed by their satisfactory specific surface area and vast presence of surface functional groups.

Degradation kinetics and transformation products of chlorophene by aqueous permanganate

This paper evaluates the oxidation of an antibacterial agent, chlorophene (4-chloro-2-(phenylmethyl)phenol, CP), by permanganate (Mn(VII)) in water. Second-order rate constant (k) for the reaction between Mn(VII) and CP was measured as (2.05 ± 0.05) × 101 M−1 s−1 at pH 7.0 for an initial CP concentration of 20.0 μM and Mn(VII) concentration of 60.0 μM. The value of k decreased with increasing pH in the pH range of 5.0–7.0, and then increased with an increase in solution pH from 7.0 to 10.0. The presence of MnO2 and Fe3+ in water generally enhanced the removal of CP, while the effect of humic acid was not obvious. Fourteen oxidation products of CP were identified by an electrospray time-of-flight mass spectrometer, and direct oxidation, ring-opening, and decarboxylation were mainly observed in the reaction process. The initial reaction sites of CP by Mn(VII) oxidation were rationalized by density functional theory calculations. Toxicity changes of the reaction solutions were assessed by the luminescent bacteria P. phosphoreum, and the intermediate products posed a relatively low ecological risk during the degradation process. The efficient removal of CP in secondary clarifier effluent and river water demonstrated the potential application of this Mn(VII) oxidation method in water treatment.

ЕЛЕКТРОДИ НА ОСНОВІ ОКСИДІВ ІНДІЮ ТА СТАНУМУ, ЩО МОДИФІКОВАНІ MnO2, ДЛЯ ВИЗНАЧЕННЯ ГІДРОГЕН ПЕРОКСИДУ

Nanostructured transition metal oxide nanoparticles possess a catalytic activity to hydrogen peroxide. Manganese dioxide particles are one of the promising and available modificators of the electrode surface. Nanostructured MnO2 deposited onto the surface of the electrode enhances the electron transport from the H2O2 molecule to the surface. Thus selectivity and sensitivity of H2O2 detection can be improved. There are a lot of different methods of the impregnation of manganese dioxide particles onto electrode surface. An electrophoretic deposition is one of the most simple and rapid. By adjusting the electrodeposition parameters, particles of different sizes or films can be obtained. A simple and novel hydrogen peroxide sensor based on layer-by-layer assembly of MnO2 nanoparticles and SiO2 film on the ITO electrode was developed. For this purpose MnO2 nanoparticles were electrodeposited on the surface of ITO electrode from MnSO4/CH3COOK solution. The electrochemical characteristics of the modified electrodes were investigated by cyclic voltammetry.The presence of MnO2 on the surface of modified electrode was indicated by the appearance of clear oxidation-reduction peaks of Mn(IV)/Mn(III,II) at E=0.65 V in the electrolyte solution in contrast to unmodified electrode. Optimization of measurement parameters such as the amount of MnO2, applied potential and pH value were studied in details. Under the optimum conditions, the calibration curve for H2O2 determination using modified electrode was linear in the range from 1×10−4 to 1×10−3 mol/dm3 with a detection limit of 0.09×10−4 mol/dm3 (S/N = 3). The linear rang for non-modified electrode was from 1×10−3 to 1×10−2 mol/dm3 with a detection limit of 1.8×10−4 mol/dm3 (S/N = 3). The modified ITO electrode was characterized by higher current than non modified ITO as a result of increasing of electroactive surface area and catalytic effect of electrodeposited MnO2.For the stabilization of MnO2 particles and protection of the electrode surface from impurities, the ITO/MnO2 was covered by thin silica film. The selectivity of H2O2 determination at ITO modified with MnO2/SiO2 was better than at ITO especially in the presence of ascorbic acid which is oxidized at the same potential as H2O2. The oxidation current of ascorbic acid was much higher than H2O2 at nonmodified ITO in contrast to ITO modified with MnO2/SiO2. The developed ITO electrode modified with MnO2/SiO2 is a perspective element of amperometric sensor for the detection of hydrogen peroxide.

Characterizing the Impacts of Deposition Techniques on the Performance of MnO2 Cathodes for Sodium Electrosorption in Hybrid Capacitive Deionization.

Capacitive deionization (CDI) is currently limited by poor ion-selectivity and low salt adsorption capacity of porous carbon electrodes. To enhance selectivity and capacity via sodium insertion reactions, carbon aerogel electrodes were modified by depositing amorphous manganese dioxide layers via cyclic voltammetry (CV) and electroless deposition (ED). MnO2-coated electrodes were evaluated in a hybrid capacitive deionization system to understand the relationship between oxide coating morphology, electrode capacitance, and sodium removal efficacy. Both deposition techniques increased electrode capacitance, but only ED electrodes improved desalination performance over bare aerogels. SEM imaging revealed ED deposition distributed MnO2 throughout the aerogel, while CV deposition created a discrete crust, indicating that CV electrodes were limited by diffusion. Sodium adsorption capacity of ED electrodes increased with MnO2 mass deposition, reaching a maximum of 0.77 mmol-Na+ per gram of cathode (2.29 mmol-Na+ g-MnO2-1), and peak charge efficiency of 0.95. The presence of MnO2 also positively shifted the electrode potential window of sodium removal, reducing parasitic oxygen reduction and inverting the desalination cycle so that energy discharge coincides with salt removal (1.96 kg-NaCl kWh-1). These results highlight the importance of deposition technique in improving desalination with MnO2-coated electrodes.

Synthesis of MnO2 nanosheets on montmorillonite for oxidative degradation and adsorption of methylene blue

In this research, MnO2 nanosheets on montmorillonite (MnO2 nanosheets@MMt) was synthesized by one-pot hydrothermal method and characterized by X-ray diffraction, Fourier transform infrared spectra, nitrogen adsorption and scanning electron microscopy. It was found that honeycomb-like MnO2 nanosheets vertically grew on the surface of montmorillonite. MnO2 nanosheets@MMt exhibited high methylene blue (MB) removal rate, which reached 97.7% within 5min under the condition of pH 2, MnO2 nanosheets dosage of 0.1gL−1 and initial dye concentration of 10mgL−1. Additionally, the influencing factors such as pH value, amount of MnO2 nanosheets@MMt, and MB concentration were also investigated in this paper. Results showed the MB degradation process was correlated with pH value, and the MnO2 nanosheets@MMt achieved MB removal rate of 92.8% within 5min under pH 11 because of its absorption capacity of MB. The kinetics of the adsorption process complied with the Pseudo-second-order model. The Langmuir model was found to be the most suitable for describing the experimental equilibrium data of MnO2 nanosheets@MMt. The MnO2 nanosheets@MMt showed high adsorption capacity of 363.63mgg−1 for MB dye. The oxidative decomposition of MB was conducted in the presence of MnO2 nanosheets@MMt in the low pH, finding that the lower the pH was, the faster the degradation rate was. This research demonstrates that MnO2 nanosheets@MMt has potential applications in wastewater treatment.

Preparation of manganese-impregnated alumina-pillared bentonite, characterization and catalytic oxidation of CO

Al-pillared clays from local available bentonite were synthesized via two methods by the application of conventional and ultrasonic treatments during the intercalation stage. The results of XRD and N2 adsorption indicated an increase in the basal spacing, the specific BET surface area, and porosity subsequent to pillaring by both methods with a considerable shortening of the intercalation process for the ultrasonic method. Al-pillared bentonites were used as supports to prepare manganese oxide catalysts by the wet impregnation of 2 and 10 wt% of Mn. The presence of MnO2 and Mn2O3 were detected by X-ray diffraction and confirmed by temperature-programmed reduction for the higher loading catalyst with 10 wt% of Mn. The catalytic activity of our catalysts was evaluated in the CO oxidation reaction. According to our results, the concentration of the Mn seems to be the factor that decisively affects the catalytic activity at the expense of the preparation method.

Effect of carbon black to facilitate galvanic leaching of copper from chalcopyrite in the presence of manganese(IV) oxide

It is well known that galvanic interactions between sphalerite or pyrite and manganese (IV) oxide(MnO2) accelerate the leaching of these minerals. Because MnO2 is nobler than chalcopyrite, chalcopyrite acts as cathode to be oxidized in contact with MnO2. We investigated the feasibility of galvanic leaching of chalcopyrite concentrate using chemical reagent MnO2. Leaching experiments were performed in an erlenmeyer flask containing a sulfuric medium agitated on a magnetic stirrer at room temperature. Although the addition of MnO2 improved the leaching rate of chalcopyrite, its effect was limited. Adding carbon black significantly accelerated the kinetics of chalcopyrite leaching in the presence of MnO2, and the Cu extraction yield was 81% at MnO2/carbon black/chalcopyrite ratios of 4:1:1 in 29h. In the absence of carbon black, the extraction was 7%. The extraction rate of Mn from MnO2 also increased. Carbon black did not affect the sulfuric acid or ferric sulfate leaching of chalcopyrite without MnO2, indicating that it could play an important role in the galvanic interaction between chalcopyrite and MnO2. The effects of several variables such as pH, dosage of MnO2 and carbon black, and temperature on the kinetics of chalcopyrite leaching were examined.

MnO2-induced synthesis of fluorescent polydopamine nanoparticles for reduced glutathione sensing in human whole blood.

Polydopamine (PDA) nanoparticles, as a kind of popular polymer material, have attracted a great deal of attention from various areas including materials science, biomedicine, energy, environmental science and so on owing to their striking physicochemical properties. Herein, we reported for the first time the synthesis of intrinsic fluorescent PDA nanoparticles using MnO2 as an oxidant. In the presence of MnO2, dopamine was quickly oxidized into its quinone derivative, and autopolymerized into fluorescent PDA nanoparticles. Using fluorescent PDA nanoparticles as a fluorescence signal indicator, we further established a cost-effective sensor for rapid, sensitive and selective sensing of reduced glutathione (GSH) based on the redox reaction between MnO2 and GSH, and the key role of MnO2 in the formation of fluorescent PDA nanoparticles. GSH has the capability of reducing MnO2 into Mn(2+), which inhibited the formation of the fluorescent PDA nanoparticles. Thus, the concentration of GSH was directly related to the decreased fluorescence signal intensity of the PDA nanoparticles. The sensor showed good sensing performance for GSH detection with high sensitivity and desirable selectivity over other potential interfering species. Additionally, the sensor exhibited excellent practical applications for GSH detection in human whole blood samples, which presents potential applications in biological detection and clinical diagnosis.

Microwave‐Assisted Synthesis of Arylated Pyrrolo[2,1‐a]Isoquinoline Derivatives via Sequential [3 + 2] Cycloadditions and Suzuki‐Miyaura Cross‐Couplings in Aqueous Medium

Treatment of 5‐bromo‐2‐(bromoacetyl)thiophene (1) with isoquinoline gave the isoquinolinium bromide 2. Reaction of 2 with acrylic acid derivatives, in the presence of MnO2, afforded the 3‐[(5‐bromothiophen‐2‐ylcarbonyl]pyrrolo[2,1‐a]‐isoquinolines 3a, 3b. Suzuki–Miyaura cross‐coupling reactions of the bromides 3a, 3b in aqueous solvent with several activated and deactivated aryl(hetaryl)boronic acids 4a, 4b, 4c, 4d, 4e, 4f using a Pd(II)‐complex under thermal heating as well as microwave‐irradiating conditions afforded the corresponding new arylated pyrrolo[2,1‐a]isoquinoline derivatives 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 in high to excellent isolated yields.

The Effect of Precipitants on MnOx-Ni/TiO2 SCR Catalysts Prepared by Titanium Slag as Raw Material

Mn-Ni/TiO2 catalysts were prepared using a joint precipitation method with acid-dissolved titanium slag as raw material for selective catalytic reduction of nitrogen oxide. The joint precipitation method was accomplished with different precipitants, such as sodium hydroxide, carbamide, ammonia, or hydrogen peroxide. The deNOx activities of the catalysts prepared by different precipitants were investigated with SCR activity reactor within temperatures of 90–350°C. It is evident that the Mn-Ni/TiO2 catalyst with carbamide-ammonia-hydrogen peroxide as precipitant has superior catalytic activity, which the NO conversion can reach 90% at 120°C, with a wider temperature window (120–300°C) for the NH3-SCR reaction. H2-TPR results showed that the reduction potential of MnOx species on Mn-Ni/TiO2 catalysts is increased compared to that of Mn/TiO2 catalysts. Oxygen mobility is enhanced by interaction between Ni and Mn atoms due to use of carbamide-ammonia peroxide as precipitant. XPS results suggest that the presence of MnO2 is the major phase in nickel-doped Mn/TiO2 catalysts. Our NH3-TPD results illustrated that the catalysts have a lot of acid-active sites, which lead to attracting more ammonia to participate in the catalytic reaction.

Development of a carbon–manganese dioxide nanomaterial as a glucose fuel-cell electrode

The development of a non-platinum (Pt)-based inexpensive material, as fuel-cell electrode, is the most needful to produce clean electrical renewable energy. A nanocomposite material of manganese dioxide–carbon (MnO2–C) was synthesised by an electrodeposition technique, at optimum parameters of current, potential and chemistry of the electrolyte. The performance of the synthesised material compared to that of Pt was tested by cyclic voltammetry, chronoamperometry and potentiodynamic polarisation. It was found that the MnO2–C material was superior to Pt for glucose oxidation in fuel cells. It delivered a much higher current and a lower polarisation resistance. The X-ray diffraction (XRD) graph reflected the presence of MnO2 and C. The particle size estimated from XRD data using the Scherrer formula came out in the nano range. The morphology of deposits from field-emission scanning electron microscopy (FESEM) images indicated that the nano-carbon particles are randomly distributed within the MnO2 matrix. The carbon particles not only act as a high-energetic electrocatalytic surface but also act as a nano grain refiner of MnO2. The real substrate area in three dimension is much more than the geometrical substrate area in two dimension, giving rise to an increase in current.

ChemInform Abstract: 6‐Azabicyclo[3.2.1]octanes via Copper‐Catalyzed Enantioselective Alkene Carboamination.

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)2 or related catalysts in the presence of MnO2 as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization.

Understanding the role of manganese dioxide in the oxidation of phenolic compounds by aqueous permanganate.

Recent studies have shown that manganese dioxide (MnO2) can significantly accelerate the oxidation kinetics of phenolic compounds such as triclosan and chlorophenols by potassium permanganate (Mn(VII)) in slightly acidic solutions. However, the role of MnO2 (i.e., as an oxidant vs catalyst) is still unclear. In this work, it was demonstrated that Mn(VII) oxidized triclosan (i.e., trichloro-2-phenoxyphenol) and its analogue 2-phenoxyphenol, mainly generating ether bond cleavage products (i.e., 2,4-dichlorophenol and phenol, respectively), while MnO2 reacted with them producing appreciable dimers as well as hydroxylated and quinone-like products. Using these two phenoxyphenols as mechanistic probes, it was interestingly found that MnO2 formed in situ or prepared ex situ greatly accelerated the kinetics but negligibly affected the pathways of their oxidation by Mn(VII) at acidic pH 5. The yields (R) of indicative products 2,4-dichlorophenol and phenol from their respective probes (i.e., molar ratios of product formed to probe lost) under various experimental conditions were quantified. Comparable R values were obtained during the treatment by Mn(VII) in the absence vs presence of MnO2. Meanwhile, it was confirmed that MnO2 could accelerate the kinetics of Mn(VII) oxidation of refractory nitrophenols (i.e., 2-nitrophenol and 4-nitrophenol), which otherwise showed negligible reactivity toward Mn(VII) and MnO2 individually, and the effect of MnO2 was strongly dependent upon its concentration as well as solution pH. These results clearly rule out the role of MnO2 as a mild co-oxidant and suggest a potential catalytic effect on Mn(VII) oxidation of phenolic compounds regardless of their susceptibility to oxidation by MnO2.

Characterizing the impact of sand addition on the efficiency of granular iron for contaminant removal in batch systems

The impact of sand on the efficiency of metallic iron (Fe0) at discoloring a methylene blue (MB) solution in the presence of MnO2 was characterized. The MB initial concentration was 10mgL−1. 22.0mL of this solution was used for each test. Investigated systems were: (i) Fe0 alone, (ii) MnO2 alone, (iii) sand alone, (iv) a sand/MnO2 mixture, and (v) Fe0/sand/MnO2 mixtures with three different natural MnO2-bearing minerals. Tested material loadings varied from 0.0 to 45.0gL−1. A commercial Fe0 and three natural MnO2 materials (Manganite, Psilomelane and X-MnO2) were tested in shaken experiments at 75rpm for 14days. The documented delay of MB discoloration by Fe0 in the presence of MnO2 was the evaluation criterion. This characteristic discoloration delay was observed for all tested materials at MnO2 loadings <6gL−1. For higher MnO2 loadings, the Fe0/Manganite/sand system was more efficient than the Fe0/sand system. The largest extend of the delay of MB discoloration was observed in the Fe0/X-MnO2/sand system. This observation delineated the crucial importance of characterizing the intrinsic reactivity of tested MnO2 materials for comparable results. This study highlighted the crucial importance of experimental conditions as major source of confusing/conflicting reports.

Catalysed thermal decomposition of KClO3 and carbon gasification

The catalytic decomposition of KClO3 is studied in the presence of MnO2, activated carbons and sodium sulphide. This investigation describes the use of thermogravimetry as a convenient technique to investigate catalytic activity of a simple chemical reaction. It is observed that the MnO2 catalyst decreases the decomposition temperature from 480 to 350 °C while the activated carbons cause its decomposition at 320–325 °C. At the same time the carbons undergo facile gasification. Presence of Na2S was the most effective as it induced the carbon-catalysed decomposition of KClO3 at a temperature as low as 220 °C, a temperature at which the carbons were stable and no gasification was observed.

6-Azabicyclo[3.2.1]octanes Via Copper-Catalyzed Enantioselective Alkene Carboamination.

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)2 or related catalysts in the presence of MnO2 as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization.

Recovery of noble metals from refractory sulfide black-shale ores

The processing of refractory sulfide black-shale ores and concentrates from the Sukhoy Log deposit containing gold, silver and platinum group metals (palladium and platinum) was investigated. The noble metals were leached both under atmospheric pressure and at 700kPa at 200°C in an autoclave. It was found that the preferred leaching method is the chlorination of the ore in HCl/NaCL solutions in the presence of MnO2. The sorption recovery of noble metals on Purolite anion exchangers and carbon adsorbent Calgon GRC-22 was carried out from solution with the following initial concentrations of noble metals (in mg/L): Au — 25; Pt — 5; Pd — 5; and Ag — 10 in the presence of 1M FeCl3, 0.1 М CuCl2, 1M NaCl and 1М HCl. It was shown that the chloride complexes of noble metals can be effectively adsorbed from this solution. Then, the selective elution of noble metals from anion exchangers Purolite A170 and Purolite S992 by means of different complex-forming reagents was studied. The best elution results were obtained with Na2SO3+NaNO2 and thiourea solutions.

ChemInform Abstract: Copper‐Catalyzed Oxidative Amination and Allylic Amination of Alkenes.

Enamines and enamides are useful synthetic intermediates and common components of bioactive compounds. A new protocol for their direct synthesis by a net alkene C-H amination and allylic amination by using catalytic Cu(II) in the presence of MnO2 is reported. Reactions between N-aryl sulfonamides and vinyl arenes furnish enamides, allylic amines, indoles, benzothiazine dioxides, and dibenzazepines directly and efficiently. Control experiments further showed that MnO2 alone can promote the reaction in the absence of a copper salt, albeit with lower efficiency. Mechanistic probes support the involvement of nitrogen-radical intermediates. This method is ideal for the synthesis of enamides from 1,1-disubstituted vinyl arenes, which are uncommon substrates in existing oxidative amination protocols.

MnO2 decorated graphene nanoribbons with superior permittivity and excellent microwave shielding properties

Microwave shielding properties of chemically synthesized MnO2 decorated graphene nanoribbons (GNRs) are reported for the first time. The nature of MnO2 decoration on the GNRs has been investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. The electromagnetic interference (EMI) shielding effectiveness of this material was investigated in the microwave region (Ku-band, 12.4–18 GHz). The presence of MnO2 on GNR enhances the interfacial polarization, multiple scattering, natural resonances and the effective anisotropy energy, which leads to absorption dominated high shielding effectiveness of −57 dB (blocking >99.9999% radiation) by a 3 mm thick sample. Dielectric attributes (ε′ and ε′′) were evaluated to understand the mechanism of the excellent shielding effectiveness. The material will be an excellent choice for radar absorbing applications.

Systematic and consistent ferromagnetism in InMnP:Zn bilayers for various Mn concentrations and annealing temperatures

The p-type InP:Zn epilayers were prepared by using metal-organic chemical vapor deposition, and Mn was subsequently deposited onto the epilayer by using molecular beam epitaxy. The p-type InMnP:Zn epilayers were annealed at relatively low temperatures of 200–350 °C and contained no secondary phases such as InMn, MnP, and MnO2, as verified by x-ray diffraction. However, minute presence of MnO2 was confirmed using transmission electron microscopy, which agreed with the magnetic properties measured by using a superconducting quantum interference device (SQUID). From the SQUID measurements, consistent and systematic ferromagnetic properties with clear ferromagnetic hysteresis loops were observed. The Curie temperature, TC, which persisted up to ∼ 180 K, was recorded depending on the Mn concentrations and annealing temperature. These results indicate that the ferromagnetic semiconductor InMnP:Zn can be fabricated at a very low annealing temperature without forming ferromagnetic precipitates except for MnO2.