Jahn-Teller Effect Directed Bandgap Tuning of Birnessite for Pseudocapacitive Application

Birnessite M_(x)MnO_(2)(M=Na^(+),K^(+),etc.)has emerged as a promising alternative to the classical MnO_(2)material owing to its improved pseudocapacitive performance for energy storage.Understanding their structure–property correlation is essential for the development and application of advanced supercapacitors.Herein,we adopt the crystal field theory and density functional simulation to reveal the structural dependence of the pseudocapacitive property of M_(x)MnO_(2).Attributing to the Jahn–Teller effect of Mn^(3+),the bandgap of Kx MnO_(2)can be tuned by changing the x value(i.e.,the Mn(III)/Mn(IV)ratio).Then,we design a narrow-bandgap K 0.25 MnO_(2)(0.84 eV),which affords a high capacitance of 415 F g^(-1)at 1 A g^(-1)and a desirable rate capability of 293 F g^(-1)at 20 A g^(-1).Operando Raman spectroscopy confirms that the Jahn–Teller induced structure evolution of[MnO_(6)]octahedron accounts for the superior pseudocapacitive behavior of K_(0.25)MnO_(2).This finding offers theoretical guidance to the design and application of birnessite materials for pseudocapacitors.

镁离子型Birnessite的合成和表征

采用ＭｎＯ－４和Ｍｎ２＋在强碱性条件下制得层状结构的Ｍｇ＿Ｂｉｒｎｅｓｓｉｔｅ，用ＸＲＤ（Ｘ射线多晶粉末衍射）、ＦＴ－ＩＲ（傅里叶红外光谱）、ＴＧ－ＤＴＧ／ＤＴＡ（热失重－微商热失重／热分析）等方法对它进行了表征。Ｍｇ＿Ｂｉｒｎｅｓｉｔｅ在２００～４００℃时为无定形，在６００℃生成结晶良好的Ｍｎ２Ｏ３相。ＣＣｌ４、ＣＨ３ＯＨ、ｎ＿Ｃ６Ｈ１４的吸附等温线类似于第三种类型的吸附等温线，在接近饱和的情况下都有凝聚现象产生。在６００℃，比表面和吸附数据表明出现层状结构塌陷。吸附吡啶ＦＴ－ＩＲ谱表明在Ｍｇ＿Ｂｉｒｎｅｓｉｔｅ中存在非质子酸（Ｌ酸）和质子酸（Ｂ酸）酸位。

Li-birnessite型层状二氧化锰的合成及电化学性能

采用O2氧化法在碱性条件下氧化Mn2+,制备Li-birnessite型层状MnO2.X射线衍射、扫描电子显微镜、BET、热重等技术表征MnO2样品的性能.以放充电法测试Li-birnessite正极材料性能.结果表明,Li-birnessite结晶良好,层间距约为0.70 nm,呈球状或类球状.以Li-birnessite为正极材料的扣式电池在0.2 C(40 mA/g)条件下放电时容量高达203 mAh/g,且具有良好的倍率性能.

层状Birnessite型锰氧化物国内外研究进展

综述了Birnessite型、负载型层状锰氧化物的结构特点、制备方法、应用现状等,重点介绍了各种制备方法的优缺点,并展望了层状锰氧化物研究的发展趋势。

层状Birnessite型锰氧化物的研究进展

锰氧化物材料具有优越的离子交换性能、吸附性能和氧化性能,在可充锂电池、环保、高级分离技术、催化等领域有重要的潜在应用价值,引起研究者的广泛兴趣。本文概述了锰氧化物中层状Birnessite锰氧化物的结构特点,介绍了其合成方法、应用现状等,总结了层状Birnessite型锰氧化物的优点,并对其研究发展趋势作了展望。

Birnessite型层状MnO_2的制备与剥离

将二维纳米层的制备与表征凝练为材料化学综合实验课题,采用水热法制备了Bir-nessite型层状MnO_2,利用超声辅助离子交换法对层状氧化锰实现了快速剥离。利用X射线衍射表征Birnessite型层状MnO_2在剥离各阶段的结构,利用原子力显微镜表征了氧化锰纳米层的大小和厚度,利用Dyndall现象研究了氧化锰剥离液的胶体性质,探讨了氧化锰纳米层的制备原理。通过该实验可使学生了解二维纳米层制备及表征的基本知识,同时可激发本科阶段学生从事科学研究的兴趣。

Relation of lead adsorption on birnessites with different average oxidation states of manganese and release of Mn^(2+)/H^+/K^+

The characteristics of Pb^2＋ adsorption on the surface of birnessites with different average oxidation states （AOS） of Mn, synthesized under acidic and alkali conditions, were investigated. The results indicated that the amount of adsorbed Pb^2＋ increased with the increase of Mn AOS in birnessites. The amount of Pb〉 adsorbed positively correlated with the amount of released Mn^2＋, H^＋, and K^＋ （r = 0.9962 〉 0.6614, n = 14, ct = 0.01）. The released Mn^2＋, H^＋, and K^＋ were derived mostly from the corresponding cations adsorbed on the vacant sites. The maximum amount of adsorbed Pb^2＋ increased with the increasing vacant cation sites, leading to an increase of the total amount of released Mn^2＋, H^＋, and K^＋, and the increased likelihood for two Pb^2＋ adsorbed in the region of one side of a vacant site.

Layered Birnessite Cathode with a Displacement/Intercalation Mechanism for High-Performance Aqueous Zinc-Ion Batteries

Mn-based rechargeable aqueous zinc-ion batteries(ZIBs)are highly promising because of their high operating voltages,attractive energy densities,and eco-friendliness.However,the electrochemical performances of Mn-based cathodes usually suffer from their serious structure transformation upon charge/discharge cycling.Herein,we report a layered sodium-ion/crystal water co-intercalated Birnessite cathode with the formula of Na0.55Mn2O4·0.57H2O(NMOH)for high-performance aqueous ZIBs.A displacement/intercalation electrochemical mechanism was confirmed in the Mn-based cathode for the first time.Na+and crystal water enlarge the interlayer distance to enhance the insertion of Zn^2+,and some sodium ions are replaced with Zn^2+ in the first cycle to further stabilize the layered structure for subsequent reversible Zn^2+/H^+ insertion/extraction,resulting in exceptional specific capacities and satisfactory structural stabilities.Additionally,a pseudo-capacitance derived from the surface-adsorbed Na^+ also contributes to the electrochemical performances.The NMOH cathode not only delivers high reversible capacities of 389.8 and 87.1 mA h g^−1 at current densities of 200 and 1500 mA g^−1,respectively,but also maintains a good long-cycling performance of 201.6 mA h g^−1 at a high current density of 500 mA g^−1 after 400 cycles,which makes the NMOH cathode competitive for practical applications.

The Discharge and Charge Behavior of the Pb-Birnessite in LiOH Aqueous Solution

The Pb-birnessite was prepared by ion exchange from K-birnessite, which was synthesized by calcination of KMnO4. Measure methods of SEM (scanning electron microscopy), XRD (X-ray diffraction), TGA (thermogravimetric analyse), AAS (atomic absorption spectrometry), slow-scanning cyclic voltammetry and galvanostatic step discharge/charge are applied. Potentiostatic step method is used for the determination of a chemical diffusion coefficientD is Li+. XRD patterns indicate the Pb-birnessite has layered structure. Slow-scanning voltammograms show the occurrence of a single-phase redox reaction. The galvanostatic discharge/charge curves indicate the Pb-birnessite has better rechargeability at a high discharge/charge rate. Li+ can reversibly intercalate into and de-intercalate from the Pb-birnessite during discharge and charge. Pb between the layers stabilized the layered structure and prevented partially the conversion to spinel-like structures. The average value of the chemical diffusion coefficientD of Li+ intercalated into the Pb-birnessite is 8.24×10?11 cm2·s?1. Key words Birnessite - Pb2+-doped - single-phase redox reaction - Lithium intercalation CLC number O 646.54 Foundation item: Supported by the National Natural Science Foundation of China (20077020)Biography: ZHU Xin-gong (1979-), male, Master, research direction: electrochemistry.

Synthesis and Magnetic Properties of a Novel Birnessite Oxide Cs_(0.24)MnO_2

The synthesis of a novel birnessite structure manganese oxide, Cs0.24MnO2, via a modified sol-gel route is reported in this work. The product was characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, thermogravimetric analysis （TGA）, and magnetic susceptibility. It is found that Cs0.24MnO2 crystallizes in a monoclinic phase with a nanosheet morphology. With lowering the temperature, Cs0.24MnO2 shows an antiferromagnetic transition at about 43.8 K, which is different from its paramagnetic K-counterpart. The effective moment of Mn ions in Cs0.24MnO2 is determined to be 4.2 μB, indicating a mixed valence of Mng＋/Mn3＋.

Delamination of Birnessite MnO_(2) into Nanosheets as Anode Materials for Lithium Ion Batteries

The delamination of birnessite MnO_(2) into nanosheets by freezing and thawing method was reported here.The proton⁃type birnessite manganese oxide(H⁃birnessite)was added to tetramethylammonium hydroxide(TMAOH)solution in a polypropylene tube which was then sealed.Fifty cycles consisting of fast freezing(in liquid nitrogen for 30 s)and thawing(in 70℃ water for 30 min)were operated.The as⁃prepared slurry was characterized by X⁃ray diffraction(XRD)and transmission electron microscope(TEM).The XRD result showed the layered structural H⁃birnessite was delaminated.The TEM result revealed the product had a nanosheet⁃like morphology.Employed as an anode material for lithium⁃ion batteries,MnO_(2) nanosheets as⁃prepared delivered a specific charging capacity of 1040.6 mAh/g after 100 cycles at 100 mA/g.

Compulsive malposition of birnessite slab in 2D-Parallel birnessite on β-MnO_(2) networks for enhanced pseudocapacitance performances

High electrochemically active bimessite is always desirable pseudocapacitive material for supercapacitor.Here,two-dimensional(2D)compulsive malposition parallel bimessite standing on β-MnO_(2) interconnected networks have been designed.Due to the retrition of β-MnO_(2),compulsi ve malposition,slippage of MnO6 slab,occured in bimessite resulting in weaken bi nding force between bimessi te slab and interlayer cations,which enhanced their electrochemical performances.Additionally,the electrical conductivity of the structure was largely promoted by the 2D charge transfer route and double-exchange mechanism in bimessite,also leading to desirable electro-chemical properties.Based on the fraction of as-prepared nanostructure,the par all bimessite exhibited good pseudocapacitance performance(660 F g^(-1))with high rate capability.In addition,the asymmetrice supercapacitor assembled by reduced graphene oxide(RGO)and as-prepared nanostructure,which respectively served as the negative and positive eletrode,delivered an energy density of 33.1 Wh kg^(-1) and a mad mum power density of 64.0 kW kg^(-1) with excellent cyeling stability(95.8% after 10000 cycles).Finally,the study opens new avenwes for synthesizing high eletrochemically actiwe bimessite structure for high-performance energy storage devices.

Humid Air Plasma Treatment of Birnessite Surface: Application to the Removal of Cochineal Red

The thin layers of birnessite (Mn7O13?5H2O) are exposed to reactive species gliding arc plasma in humid air, which induces the treatment of the thin layers surface. Plasma treatment thin layer of birnessite was used for the degradation of Cochineal Red. The experimental results showed that 95% of the CR solution was completely decolorized by thin layer of birnessite treated by plasma compared to 80% of the same solution after interaction of thin layer of birnessite untreated. The decay kinetics always follows a pseudo-first order reaction. The application of the humid air plasma for the surface treatment of thin layers of birnessite improves the efficiency of treatment for Cochineal Red degradation.

A review on the transformation of birnessite in the environment:Implication for the stabilization of heavy metals

Birnessite is ubiquitous in the natural environment where heavy metals are retained and easily transformed.The surface properties and structure of birnessite change with the changes in external environmental conditions,which also affects the fate of heavy metals.Clarifying the effect and mechanism of the birnessite phase transition process on heavy metals is the key to taking effective measures to prevent and control heavy metal pollution.Therefore,the four transformation pathways of birnessite are summarized first in this review.Second,the relationship between transformation pathways and environmental conditions is proposed.These relevant environmental conditions include abiotic(e.g.,co-existing ions,pH,oxygen pressure,temperature,electric field,light,aging,pressure)and biotic factors(e.g.,microorganisms,biomolecules).The phase transformation is achieved by the key intermediate of Mn(Ⅲ)through interlayer-condensation,folding,neutralizationdisproportionation,and dissolution-recrystallization mechanisms.The AOS(average oxidation state)of Mn and interlayer spacing are closely correlated with the phase transformation of birnessite.Last but not least,the mechanisms of heavy metals immobilization in the transformation process of birnessite are summed up.They involve isomorphous substitution,redox,complexation,hydration/dehydration,etc.The transformation of birnessite and its implication on heavy metals will be helpful for understanding and predicting the behavior of heavy metals and the crucial phase of manganese oxides/hydroxides in natural and engineered environments.

Pathways of birnessite formation in alkali medium

Birnessite is a common weathering and oxidation product of manganese-bearing rocks. An O2 oxidation procedure of Mn(OH)2 in the alkali medium has been used to synthesize birnessite. Fast and powder X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), energy dispersed X-ray analysis (EDAX), infrared spectroscopy (IR) techniques and chemical composition analysis, Eh-pH equilibrium diagram approaches were employed to investigate the reaction process and pathways of birnessite formation. Results showed that the process of the birnessite formation could be divided into four stages: (1) forma- tion stage for hausmannite and feitknechtite, (2) stage of transformation of hausmannite and feitknechtite to buserite, (3) buserite crystal growing stage, and (4) stage of conversion of buser- ite into birnessite. Mn(OH)2 was mainly present as amorphous state only for a short initial time of oxidation reaction. In the oxidation process, buserite formed following two pathways by recrys- tallization after dissolution of the intermediates, and the transformations of the minerals de- pended on the Eh determined by the dissolved O2 concentration on their surfaces. The results are fundamental in further exploration on the mechanism of birnessite formation in the alkali medium. A great practical significance would also be expected with respect to the areas of mate- rial sciences.

Formation of Na_(0.44)MnO_(2) Nanowires via Stress-Induced Splitting of Birnessite Nanosheets

High aspect ratio Na0.44MnO2 nanowires with a complex one-dimensional(1 D)tunnel structure have been synthesized.We found that the reaction went through layered birnessite nanosheet intermediates,and that their conversion to the final product involved splitting of the nanosheets into nanowires.Based on our observations,a stress-induced splitting mechanism for conversion of birnessite nanosheets to Na0.44MnO2 nanowires is proposed.The final and intermediate phases show topotaxy with〈001〉f//〈020〉b or〈110〉b where frepresents the final Na_(0.44)MnO_(2)phase and b the intermediate birnessite phase.As a result of their high surface areas,the nanowires are efficient catalysts for the oxidation of pinacyanol chloride dye.

Preparation of birnessite-supported Pt nanoparticles and their application in catalytic oxidation of formaldehyde

Flaky and nanospherical birnessite and birnessite-supported Pt catalysts were successfully prepared and characterized by means of Xray diffraction （XRD）,transmission electron microscopy （TEM）,energy dispersive spectroscopy （EDS） and N2 adsorption-desorption.Effects of the birnessite morphology and Pt reduction method on the catalytic activity for the complete oxidation of formaldehyde （HCHO） were investigated.It was found that flaky birnessite exhibited higher catalytic activity than nanospherical birnessite.The promoting effect of Pt on the birnessite catalyst indicated that the reduction method of the Pt precursor greatly influenced the catalytic performance.Flaky birnessite-supported Pt nanoparticles reduced by KBH 4 showed the highest catalytic activity and could completely oxidize HCHO into CO2 and H2O at 50℃,whereas the sample reduced using H2-plasma showed lower activity for HCHO oxidation.The differences in catalytic activity of these materials were jointly attributed to the effects of pore structure,surface active sites exposed to HCHO and the dispersion of Pt nanoparticles.

Photoelectrochemical performance of birnessite films and photoelectrocatalytic activity toward oxidation of phenol

Birnessite films on fluorine-doped tin oxide（FTO） coated glass were prepared by cathodic reduction of aqueous KMnO4. The deposited birnessite films were characterized with X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy.The photoelectrochemical activity of birnessite films was investigated and a remarkable photocurrent in response to visible light was observed in the presence of phenol, resulting from localized manganese d–d transitions. Based on this result, the photoelectrocatalytic oxidation of phenol was investigated. Compared with phenol degradation by the electrochemical oxidation process or photocatalysis separately, a synergetic photoelectrocatalytic degradation effect was observed in the presence of the birnessite film coated FTO electrode.Photoelectrocatalytic degradation ratios were influenced by film thickness and initial phenol concentrations. Phenol degradation with the thinnest birnessite film and initial phenol concentration of 10 mg/L showed the highest efficiency of 91.4% after 8 hr. Meanwhile, the kinetics of phenol removal was fit well by the pseudofirst-order kinetic model.

Removal of ammonium ion from water by Na-rich birnessite:Performance and mechanisms

Na-rich birnessite（NRB） was synthesized by a simple synthesis method and used as a high-efficiency adsorbent for the removal of ammonium ion（NH＋4） from aqueous solution.In order to demonstrate the adsorption performance of the synthesized material,the effects of contact time,pH,initial ammonium ion concentration,and temperature were investigated.Adsorption kinetics showed that the adsorption behavior followed the pseudo second-order kinetic model.The equilibrium adsorption data were fitted to Langmuir and Freundlich adsorption models and the model parameters were evaluated.The monolayer adsorption capacity of the adsorbent,as obtained from the Langmuir isotherm,was 22.61 mg NH＋4-N/g at283 K.Thermodynamic analyses showed that the adsorption was spontaneous and that it was also a physisorption process.Our data revealed that the higher NH＋4adsorption capacity could be primarily attributed to the water absorption process and electrostatic interaction.Particularly,the high surface hydroxyl-content of NRB enables strong interactions with ammonium ion.The results obtained in this study illustrate that the NRB is expected to be an effective and economically viable adsorbent for ammonium ion removal from aqueous system.

Coordination geometry of Zn^(2+) on hexagonal turbostratic birnessites with different Mn average oxidation states and its stability under acid dissolution

Hexagonal turbostratic birnessite,with the characteristics of high contents of vacancies,varying amounts of structural and adsorbed Mn^（3＋）,and small particle size,undergoes strong adsorption reactions with trace metal（TM）contaminants.While the interactions of TM,i.e.,Zn^（2＋）,with birnessite are well understood,the effect of birnessite structural characteristics on the coordination and stability of Zn^（2＋）on the mineral surfaces under proton attack is as yet unclear.In the present study,the effects of a series of synthesized hexagonal turbostratic birnessites with different Mn average oxide states（AOSs）on the coordination geometry of adsorbed Zn^（2＋）and its stability under acidic conditions were investigated.With decreasing Mn AOS,birnessite exhibits smaller particle sizes and thus larger specific surface area,higher amounts of layer Mn^（3＋）and thus longer distances for the first Mn／O and Mn／Mn shells,but a low quantity of available vacancies and thus low adsorption capacity for Zn^（2＋）.Zn K-edge EXAFS spectroscopy demonstrates that birnessite with low Mn AOS has smaller adsorption capacity but more tetrahedral Zn（^（IV）Zn）complexes on vacancies than octahedral（^（VI）Zn）complexes,and Zn^（2＋）is more unstable under acidic conditions than that adsorbed on birnessite with high Mn AOS.High Zn^（2＋）loading favors the formation of^（VI）Zn complexes over^（IV）Zn complexes,and the release of Zn^（2＋）is faster than at low loading.These results will deepen our understanding of the interaction mechanisms of various TMs with natural birnessites,and the stability and thus the potential toxicity of heavy metal pollutants sequestered by engineered nano-sized metal oxide materials.