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–...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.展开更多
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 th...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.展开更多
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...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.展开更多
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 a...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.展开更多
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 micro...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+.展开更多
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...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.展开更多
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...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.展开更多
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 f...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.展开更多
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 condition...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.展开更多
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 (...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.展开更多
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 conver...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.展开更多
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 spe...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.展开更多
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, scan...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.展开更多
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 perf...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.展开更多
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 m...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.展开更多
基金supported by Ministry of Science and Technology of China(2016YFA0201904)National Natural Science Foundation of China(21631002,52172219,51872192)+3 种基金Projects of International Cooperation and Exchanges NSFC(22120102004)Beijing National Laboratory for Molecular Sciences(BNLMS-CXTD-202001)the Jiangsu Natural Science Foundation(No.BK20180002)Fundamental Research Program of Shanxi Province(202103021223019).
文摘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.
基金supported by the National Natural Science Foundation of China (No. 40471070)the National Excellent Doctoral Dissertation of China(No. 200767)
文摘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.
基金Financial support from the National Natural Science Foundation of China (51972016, 51533001)the National Key Research and Development Program of China (2016YFC0801302)State Key Laboratory of Organic-Inorganic Composites (oic-201801002)
文摘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.
文摘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.
基金This work was supported by the National Natural Science Foundation of China (No. 20671092)the Fund of Fujian Key Lab. of Nanomaterials (No. 20062005)the Natural Science Foundation of Fujian Province (No. 2006J0178)
文摘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+.
基金Sponsored by the China Postdoctoral Science Foundation(Grant No.2016M592746).
文摘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.
基金the National Natural Science Foundation of China(Grant No.51908092)Projects(No.2020CDJXZ001,2020CDCGJ006 and 2020CDCGCL004)supported by the Fundamental Research Funds for the Central Universities,the Joint Funds of the National Natural Science Foundation of China-Guangdong(Grant No.U1801254)+5 种基金the project funded by Chongqing Special Postdoctoral Science Foundation(XmT2018043)the Chongqing Research Program of Basic Research and Frontier Technology(cstc2017jcyjBX0080)Natural Science Foundation Project of Chongqing for Post-doctor(cstc2019jcyjbsh0079,cstc2019jcyjbshX0085)Technological projects of Chongqing Municipal Education Commission(KJZDK201800801)the Innovative Research Team of Chongqing(CXTDG201602014)the Innovative technology of New materials and metallurgy(2019CDXYCL0031).
文摘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.
文摘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.
基金supported by the National Natural Science Foundation of China(Nos.51974379,52274414)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.52121004)+2 种基金the Project of National Science Fund for Excellent Young Scholars of China(No.52022111)the National Key R&D Program of China(No.2022YFD1700101)the Huxiang Youth Talent Support Program(No.2020RC3012)。
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.40403009 and 40101017)by Research Fund for the Doctoral Program of Higher Education(Grant No.2002050411).
文摘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.
基金Yiying Wu acknowledges support from the U.S.Department of Energy under Award No.DE-FG02-07ER46427 and a Research Corporation Cottrell Scholar Award.
文摘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.
基金supported by the National Natural Science Foundation of China (No. 20871118,21007076)the Knowledge Innovation Program of the Chinese Academy of Sciences (CAS) (No. KSCX2-YW-G-059)+1 种基金the National Basic Research Program (973) of China (No.2010CB934103)the "Hundred Talents Program" of CAS
文摘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.
基金supported by the National Basic Research Program(973)of China(No.2014CB846001)the NationalNatural Science Foundation of China(Nos.41230103,41402032&41402301)
文摘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.
基金supported by the National Natural Science Foundation of China(No.51278409)the Education Department of Shaanxi Province(No.15JS046)
文摘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.
基金supported by the National Natural Science Foundation of China (Nos. 41301246, 41271253, 41401250)
文摘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.