The Synthesis and Crystal Structures of New Condensed Phosphates of Manganese

Abstract

This work deals with the synthesis of condensed phosphates of Mn(II), Mn(III), and also their combinations with Na, Cs. The reaction of MnO₂ with molten polyphosphoric acids, partially neutralized with carbonates of Na and Cs is used. In the course of reaction of MnO₂ with molten polyphosphoric acids, Mn(IV) is reduced to Mn(III) or/and Mn(II). The ratio Mn(III)/Mn(II) depends on the conditions of synthesis (temperature, time, presence of oxidants or reductants etc.). By varying these parameters we obtained 7 new manganese phosphates and determined their structures.     

Spectrophotometric Determination of Nitrogen Dioxide <Nitrite>

Abstract

A highly sensitive spectrophotometric method has been developed for the determination of nitrogen dioxide (nitrite as NO_z ^?) by reacting manganese dioxide in 1:20 perchloric acid. An amount of manganese dioxide (MnO_z) equivalent to the concentration of nitrogen dioxide becomes soluble due to the reduction of Mn (IV) to Mn (II) by nitrite in acidic medium. The soluble Mn (II) ion is filtered to remove excess of MnO₂ and is oxidized to permanganate ion by periodic acid in presence of phosphoric acid. The violet colored solution shows maximum absorbance at 525 nm. The sensitivity of the method is 0.08 ppm based on 0.0044 absorbance, and Beer's law is obeyed in the concentration range of 0.2 to 10.0 μg/mL of NO₂ ^?. Molar absorbance is found to be 2442 at 525 nm.

In the present investigation NO₂ ^? was treated with excess of MnO₂ in 1:20 perchloric acid where NO₂ ^? reduces equivalent amount of Mn (IV) to Mn (II) and becomes soluble. The soluble Mn (II) was heated to boiling and 25 mg (approx.) periodic acid is added and cooled. The volume of each solution is made to 50 mL in volumetric flask. Reagent blank is prepared in similar way except sodium nitrite solution. The absorbance is measured at 525 nm against reagent blank.     

Direct Preparation of Metal Ions‐Doped Manganese Oxide by Cyclic Voltammetry

In this work, for the first time, copper ions(II) and cobalt ions(II) were successfully electrodepositioned into manganese oxide by cyclic voltammetry (CV), respectively. The results obtained from energy dispersive X‐ray analysis (EDX) testified that copper ions and cobalt ions were doped into manganese oxide, and the images, taken from scan electron spectroscopy (SEM) also proved that the morphology of the resultant MnO₂ was altered by the doped metal ions to some extent. Interestingly, specific capacitance, obtained by cyclic voltammograms (CVs), for the metal ions‐doped MnO₂ exhibited a higher value compared to the non‐doped MnO₂. Developing a novel and simple method to generate the metal ions‐doped MnO₂ to improve the characteristics of MnO₂ is the main contribution of this work.     

Reactivity of some sulphur- and non-sulphur-containing amino acids towards water soluble colloidal MnO<Subscript>2</Subscript>. A kinetic study

Kinetic data for the oxidation of glutathione (reduced, GSH), cysteine, glycine and glutamic acid by colloidal manganese dioxide, (MnO₂) _n are reported. Colloidal MnO₂, oxidized glutathione to disulphide (glutathione, oxidized), was reduced to manganese (II). Glycine and glutamic acid (structural units of glutathione) are not oxidized by colloidal MnO₂, but the other structural unit, cysteine, is also oxidized by the same oxidant under similar experimental conditions. This is interpreted in terms of the rate-determining colloidal MnO₂-S bonded intermediate. The reactivity of GSH towards colloidal MnO₂ is very much higher than cysteine. Kinetics of oxidation of GSH and cysteine by colloidal MnO₂ were performed spectrophotometrically as a function of [GSH], [cysteine], colloidal [(MnO₂) _n ], [HClO₄], temperature and trapping agents sodium fluoride and manganese (II) (reduction product of colloidal MnO₂). The purpose of this work was to study the role of –NH₂, –COOH, –SH groups present in the carbon chain of the above amino acids. It was found that the reactivity of –SH group is higher than –NH₂ and –COOH groups. The mechanisms, involving a colloidal MnO₂ complex with GSH and cysteine, are proposed. The complexes decompose in a rate-determining step, leading to the formation of free radical and manganese (III), which is also an intermediate. The dimerization of radicals takes place in a subsequent fast step to yield the products.     

Generation of alkyl hypochlorites in oxidation of alcohols with carbon tetrachloride catalyzed by vanadium and manganese compounds

Primary alcohols and diols with various structures were subjected to transformations into esters, aldehydes, ketones, and lactones under the action of carbon tetrachloride in the presence of manganese compounds (MnCl₂, MnO₂, Mn(OAc)₂, Mn(acac)₃) and vanadium compounds (VCl₅, V₂O₅, VO(acac)₂) as catalysts. These transformation proceeded with the involvement of alkyl hypochlorites, which were generated in the course of oxidation of alcohols with carbon tetrachloride catalyzed by manganese or vanadium compounds. The optimum molar ratios between the catalyst and reagents were determined, and the reaction conditions for the highly selective synthesis of esters, aldehydes, ketones, and lactones from alcohols were found.     

Electrochemical performances of Li–Mn spinel synthesized from nanosized chemical manganese dioxide

Li–Mn spinel (LiMn₂O₄) is prepared from several chemical manganese dioxides (CMDs) and the electrochemical performances are compared. The CMDs are synthesized via a redox process involving the simultaneous reduction and oxidation reaction of manganese ions in starting materials to converge to MnO₂. KMnO₄ is used as an oxidizing agent and various manganese(II) salts as reducing agents in the redox process. The crystalline phase, particle size and shape, and specific surface area (SSA) of the CMDs and the Li–Mn spinels are examined. The influence of the starting manganese salts on the above properties is also investigated. The CMDs form as aggregates of nanosized particles with different crystalline phase according to the starting manganese salts. Pure Li–Mn spinel phase is obtained from the CMDs irrespective of the different crystalline phases. The charge and discharge profiles of the LiMn₂O₄ are measured and compared.     

Sensitive fluorescent light-up probe for enzymatic determination of glucose using carbon dots modified with MnO<Subscript>2</Subscript> nanosheets

We describe a highly sensitive glucose probe based on carbon dots modified with MnO₂. A strong reduction of the green fluorescence of the carbon dots (CDs) happened due to the surface energy transfer (SET) from CDs to the deposited MnO₂. In the presence of H₂O₂ (formed via enzymatic oxidation of glucose), fluorescence is restored because the MnO₂ nanosheets are reduced to form colorless Mn(II) ions. These findings were used to design a fluorometric glucose assay that has a detection limit as low as 44 nM (at an S/N ratio of 3).

Open image in new window

Graphical Abstract A strong reduction of the green fluorescence of the carbon dots (CDs) occurs due to surface energy transfer (SET) from CDs to the deposited MnO₂. In the presence of H₂O₂ (formed by enzymatic action of glucose oxidase) the MnO₂ nanosheets are reduced to form colorless Mn(II) ions, and glucose can be quantified by the fluorescence restored.

     

锰负载量对活性炭载锰氧化物的结构及催化分解臭氧性能的影响简

将高锰酸钾与活性炭（AC）原位氧化还原制备的活性炭载锰氧化物（MnO_x/AC）用作臭氧分解的催化剂. 采用扫描电镜、X射线光电子能谱、X射线衍射、电子自旋共振波谱、拉曼光谱以及程序升温还原研究了设计Mn负载量对负载锰氧化物性质（形貌、氧化态和晶体结构）的影响. 结果表明,Mn负载量由0.44%增至11%,负载锰氧化物在活性炭表面由疏松的地衣状变为堆叠的纳米球状体,负载层的厚度由~180 nm增加至~710 nm,结构由氧化态+2.9到+3.1的低结晶β-MnOOH生长为由氧化态+3.7到+3.8的δ-MnO₂结晶. MnO_x/AC室温催化分解低浓度臭氧的活性与负载锰氧化物的形貌及含量密切相关. Mn负载量为1.1%的MnO_x/AC具有疏松的地衣状形貌,催化分解臭氧的性能最高,Mn负载量为11%的MnO_x/AC具有紧密的堆积结构,因而表现出最低的催化臭氧分解活性.     

Preparation and characterization of MnO<Subscript>2</Subscript>/MWCNTs-modified graphite electrode and its catalysis for oxygen reduction reaction (ORR)

Manganese dioxides were prepared onto multi-walled carbon nanotubes (MWCNTs) by cyclic voltammetry (CV). The obtained manganese oxide-MWCNTs (MnO₂/MWCNTs) samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and thermogravimetry (TG), respectively. The MnO₂/MWCNTs-modified graphite electrode was utilized in the electrochemical oxygen reduction reaction (ORR) and the enhanced oxygen reduction peak current strongly suggested that MnO₂/MWCNTs has catalysis for ORR when compared to the pure MnO₂ or MWCNTs. The catalysis mechanism of MnO₂/MWCNTs for ORR was also-discussed.     

Kinetics and Mechanism of the Autocatalytic Oxidation of Mn(II) by Bromine

The oxidation of Mn(II) by bromine is an autocatalytic reaction, which seems to be important for a detailed elucidation of chemical oscillators, based on manganese chemistry. With regard to the mechanism proposed previously, an alternative reaction mechanism is proposed, based on a micro-heterogeneous oxidation of Mn(II) ion, adsorbed on a surface of the MnO₂ colloid. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigations of the catalytic properties of manganese oxides for the oxygen reduction reaction in alkaline media

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on different manganese oxides, dispersed on a carbon powder (MnO_x/C). The oxides were prepared by different methods, for producing MnO, Mn₃O₄ and MnO₂ as major phases dispersed on the Vulcan XC-72 carbon. The oxides were characterized by XRD (X-ray diffraction) and in situ XANES (X-ray absorption near edge structure). The electrochemical measurements were made using cyclic voltammetry and steady state polarization curves carried out in an ultra-thin layer rotating ring/disk electrode. The results have shown lower activity for the ORR on the MnO_x/C species compared to that on Pt/C, but higher activity compared to that of pure Vulcan carbon. Formation of involving 2e⁻ per O₂ molecule is the main path of the ORR in the studied MnO_x/C catalysts but, at low overpotentials and rotation rates the number of electrons is raised to 4 due to the occurrence of a disproportionation reaction. Large differences of electrocatalytic activity were seen for the different oxide species, and these were related to the presence of a Mn(IV) phase and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen.     

Three-dimensional manganese dioxide-functionalized carbon nanotube electrodes for electrochemical supercapacitors

Three-dimensional manganese dioxide (MnO₂)-functionalized multiwalled carbon nanotube (MWCNT) electrodes have been produced by a simple and scalable thermal decomposition process. The electrodes are prepared by treating planar MWCNT sheets with manganese(II) nitrate (Mn(NO₃)₂) solution and annealing at low temperature (200–300 °C) and ambient pressure. The morphology, chemical composition, and structure of the resulting matrices have been investigated with scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. Supercapacitors assembled with three-dimensional electrodes exhibit a 14-fold increase in specific capacitance (C _sp) in comparison to those containing pristine, two-dimensional MWCNT electrodes. C _sp varies linearly with Mn(NO₃)₂ thermal decomposition temperature (from 100 to 61 F/g at 0.2 A/g), a trend that is discussed in the context of nitrate reaction chemistry and MWCNT structure. This efficient and promising approach allows for simultaneous enhancement of electrode–electrolyte contact area and incorporation of redox-based charge storage within electrochemical capacitors.     

Shape-controlled Synthesis of Nanostructure Ramsdellite-type Manganese Oxide at Atmospheric Pressure

Ramsdellite (R‐MnO₂) was prepared by oxidizing bivalent manganese salts, such as MnCl₂, MnSO₄ and Mn(NO₃)₂, with NaClO solution using a refluxing process at atmospheric pressure. The products were characterized by X‐ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and flame photometry. R‐MnO₂ microstructure and morphology were controlled by adjusting reaction temperature, the amount of hydrochloric acid (HCl) and anions of bivalent manganese salts. Ramsdellite grain was formed with three different bivalent manganese salts oxidized by NaClO solution at 60°C, and increased with the increase of reflux temperature. R‐MnO₂ nanorod and nanowire crystals were obtained when MnCl₂ and MnSO₄ were used as bivalent manganese salts at 100°C respectively. Nanosized flake of R‐MnO₂ came into being when Mn(NO₃)₂ was applied at 80°C. When 30 mmol MnCl₂ was oxidized by 60 mmol NaClO solution with adding 20 mmol HCl in refluxing solution, specific surface area of R‐MnO₂ grain obtained at 60°C was greater than 140 m²/g, and the self‐assembly of nanorod bundles into interesting flowerlike architectures was achieved at 100°C. The process of dissolution‐precipitation equilibrium might be the primary cause for the morphology transformation.     

Al and/or Ni-doped nanomanganese dioxide with anisotropic expansion and their electrochemical characterisation in primary Li–MnO2 batteries

A variety of MnO₂ nanorods containing one or two transition metals (M) (with M?=?Al and/or Ni) have been successfully synthesised via a facile hydrothermal synthesis route. The physical–chemical properties and electrochemical performance of manganese oxide were analysed by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-OES), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller method (BET), galvanostatic discharge and cyclic voltammetry (CV). The result indicated that α-type MnO₂ was obtained, and a small quantity of Al and/or Ni were embedded into the crystal lattice of manganese oxide instead of the partial Mn ion, which resulted in anisotropic expansion of the MnO₂ unit cell. The doping of Al can strengthen Mn–O bonds in the [MnO₆] octahedral and increases the specific surface area of the modified material (i.e., Al–MnO₂ is 119 m² g^?1). Interestingly, MnO₂ electrode co-doped with equimolar Al and Ni exhibited the highest specific capacity of 169 mAh g^?1 at 0.05 mA cm^?2. The substantial enhancement of the electrochemical lithium storage capacity was due to the ameliorating of integrative factors, such as high specific surface area, excellent lattice parameters and lower electrical resistance, as well as short Li⁺ and electron transport length. In addition, a more stable host skeleton also guaranteed an endurable Li⁺ intercalation behaviour during the discharge process.     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

Oxidation of diclofenac by permanganate: Kinetics,products and effect of inorganic reductants

The large consumption and discharge of diclofenac (DCF) lead to its frequent detection in surface water and groundwater, posing great threats to humans and ecosystems. This study explored the oxidation kinetics of DCF by permanganate (Mn(VII)), and expounded the underlying reason for the unusual pH-dependency that was unclear in previous studies. The kinetics of DCF analogues (i.e., aromatic secondary amines) by Mn(VII) oxidation were comparatively investigated. Then, a tentative kinetic model involving the formation of an intermediate between Mn(VII) and DCF or its analogues was proposed to fit the pH-rate profile. Since DCF contained two chloro groups, and a carboxyl group which could be ionized by negative electrospray ionization, a precursor ionization scanning approach was used for the first time for detection of N-containing chlorinated oxidation products. New degradation pathways of DCF containing ring opening, carboxylation, carbonylation, electrophilic addition, hydroxylation and dehydrogenation were proposed based on the identified oxidation products. Moreover, it was demonstrated that the introduction of various reducing agents such as Mn(II), Fe(II) and bisulfite significantly improved the oxidation kinetics of DCF by Mn(VII). The positive effects of Mn(II) and Fe(II) were mainly attributed to the accelerated formation of MnO₂ that acted as a catalyst or co-oxidizer contributing to DCF degradation. The presence of bisulfite caused two-stage kinetics, where a sharp drop of DCF concentration followed by a slowdown of DCF removal. In the first stage, potent reactive manganese species (e.g., Mn(III), Mn(V), and Mn(VI)) and sulfate radical were generated during reaction of bisulfite with Mn(VII), whereas bisulfite was depleted fast due to excess Mn(VII) concentrations and the system became the Mn(VII)/MnO₂ system in the second stage. These results provide new insight into reaction mechanism of DCF with Mn(VII) as well as propose a feasible strategy for enhancing the treatment of DCF contaminated water by Mn(VII).     

Synthesis, characterization and catalytic oxyfunctionalization of cyclohexene with tert-butylhydroperoxide over a manganese(II) complex covalently anchored to multi-wall carbon nanotubes (MWNTs)

The chemical modification of multi-wall carbon nanotubes (MWNTs) is an emerging area in material science. In the present study, an hydroxyl functionalized manganese(II) Schiff-base has been covalently anchored on modified MWNTs. The new modified MWNTs have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron (XPS), thermal analysis, UV–Vis, diffuse reflectance (DRS), FT-IR spectroscopy and elemental analysis. The results suggest that the symmetrical Schiff-base; N,N-bis(4-hydroxysalicylidene)-ethylene-1,2-diamine; H₂[(OH)₂-salen]; is a bivalent anion with tetradentate N₂O₂ donors derived from the phenolic oxygens and azomethine nitrogens. The formulae was found to be [Mn((OH)₂-salen)] for the 1:1 non-electrolytic complex. The multi-wall carbon nanotubes covalently anchored manganese(II) complex ([Mn((OH)₂-salen)]@MWNTs) catalyze the oxidation of cyclohexene with TBHP. Oxidation of cyclohexene catalyzed by this complex gave 2-cyclohexene-1-ol, 2-cyclohexene-1-one and 1-(tert-butylperoxy)-2-cyclohexene as the major products. The manganese(II) complex covalently anchored on MWNTs shows significantly higher catalytic activity than [Mn((OH)₂-salen)]. The activity of the immobilized catalyst remains nearly the same after three cycles, suggesting the true heterogeneous nature of the catalyst. This catalyst is more selective towards 2-cyclohexene-1-one.     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

活性炭表面担载氧化锰复合电极的电化学电容性能

通过在两种商品活性炭XC-72(比表面250m2·g-1)和YEC-8(比表面1726m·2g-1)电极表面涂刷Mn(NO3)2,并在200℃进行热分解得到表面担载氧化锰的复合材料电极.采用扫描电子显微镜(SEM)和X射线衍射(XRD)表征电极的形貌和氧化锰的晶体结构,采用循环伏安、恒流充放电和交流阻抗考察了不同电极的电化学电容性能.结果表明,Mn(NO3)2在200℃的热解产物是α-Mn2O3和α-Mn3O4的混合物.当C和MnOx的质量比为2∶1和9∶1时,XC-72/MnOx中氧化锰的比电容分别达到499和435F·g-1,YEC-8/MnOx中氧化锰的比电容分别达到554和606F·g-1,表明氧化锰的赝电容对电极比电容的贡献十分显著.