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
The layeredδ-MnO_(2)(dMO)is an excellent cathode material for rechargeable aqueous zinc-ion batteries owing to its large interlayer distance(~0.7 nm),high capacity,and low cost;however,such cathodes suffer from struc...The layeredδ-MnO_(2)(dMO)is an excellent cathode material for rechargeable aqueous zinc-ion batteries owing to its large interlayer distance(~0.7 nm),high capacity,and low cost;however,such cathodes suffer from structural degradation during the long-term cycling process,leading to capacity fading.In this study,a Co-doped dMO composite with reduced graphene oxide(GC-dMO)is developed using a simple cost-effective hydrothermal method.The degree of disorderness increases owing to the hetero-atom doping and graphene oxide composites.It is demonstrated that layered dMO and GC-dMO undergo a structural transition from K-birnessite to the Zn-buserite phase upon the first discharge,which enhances the intercalation of Zn^(2+)ions,H_(2)O molecules in the layered structure.The GC-dMO cathode exhibits an excellent capacity of 302 mAh g^(-1)at a current density of 100 mAg^(-1)after 100 cycles as compared with the dMO cathode(159 mAhg^(-1)).The excellent electrochemical performance of the GC-dMO cathode owing to Co-doping and graphene oxide sheets enhances the interlayer gap and disorderness,and maintains structural stability,which facilitates the easy reverse intercalation and de-intercalation of Zn^(2+)ions and H_(2)O molecules.Therefore,GC-dMO is a promising cathode material for large-scale aqueous ZIBs.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
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
Diclofenac(DCF), a widely used non-steroidal anti-inflammatory, reacted readily with birnessite under mild conditions, and the pseudo first order kinetic constants achieved 8.84 × 10^-2 hr^-1. Five products of DC...Diclofenac(DCF), a widely used non-steroidal anti-inflammatory, reacted readily with birnessite under mild conditions, and the pseudo first order kinetic constants achieved 8.84 × 10^-2 hr^-1. Five products of DCF including an iminoquinone product(2,5-iminoquinone-diclofenac) and four dimer products were observed and identified by tandem mass spectrometry during the reaction. Meanwhile, 2,5-iminoquinone-diclofenac was identified to be the major product, accounting for 83.09% of the transformed DCF. According to the results of spectroscopic Mn(III) trapping experiments and X-ray Photoelectron Spectroscopy, Mn(IV) contained in birnessite solid was consumed and mainly converted into Mn(III) during reaction process, which proved that the removal of DCF by birnessite was through oxidation. Based on the identified products of DCF and the changes of Mn valence state in birnessite solid, a tentative transformation pathway of DCF was proposed.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 oxidation of exposed pyrite causes acid mine drainage, soil acidification, and the release of toxic metal ions. As the important abiotic oxidants in supergene environments,oxygen and manganese oxides participate i...The oxidation of exposed pyrite causes acid mine drainage, soil acidification, and the release of toxic metal ions. As the important abiotic oxidants in supergene environments,oxygen and manganese oxides participate in the oxidation of pyrite. In this work, the oxidation processes of natural pyrite by oxygen and birnessite were studied in simulated systems, and the influence of p H, Fe（II） and Cr（III） on the intermediates and redox rate was investigated. SO42-and elemental S were formed as the major and minor products,respectively, during the oxidation processes. Ferric（hydr） oxides including Fe（OH）3and goethite were formed with low degree of crystallinity. Low p H and long-term reaction facilitated the formation of goethite and ferric hydroxide, respectively. The rate of pyrite oxidation by birnessite was enhanced in the presence of air（oxygen）, and Fe（II） ions played a key role in the redox process. The addition of Fe（II） ions to the reaction system significantly enhanced the oxidation rate of pyrite; however, the presence of Cr（III） ions remarkably decreased the pyrite oxidation rate in aqueous systems. The introduction of Fe（II） ions to form a Fe（III）/Fe（II） redox couple facilitated the electron transfer and accelerated the oxidation rate of pyrite. The present work suggests that isolation from air and decreasing the concentration of Fe（II） ions in aqueous solutions might be effective strategies to reduce the oxidation rate of pyrite in mining soils.展开更多
Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The...Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The effects of preparative parameters on thesynthesis of birnessite, such as pretreatment on solutions with N2, reaction temperature, O_2 flowrate, fluxion velocity of the reaction suspension, and dehydration conditions were investigated. Thefluxion velocity of the reactive suspension and O_2 flow rate significantly influenced thesynthesis of birnessite. Vigorous stirring raised the fluxion velocity of the reaction suspensionand easily allowed synthesis of pure crystalline birnessite. However pretreatment of the reactingsolutions with N_2 and the reaction temperature had little effect on the synthesis. Diffusion of O_2was the controlling step during the course of oxidation. The optimum synthetic conditions for purebirnessite were: a NaOH to Mn molar ratio of 13.7, an O_2 flow rate of 2 L min^(-1), and oxidationfor 5 hours with vigorous stirring at normal temperatures. The chemical composition of thesynthesized pure birnessite was Na_(0.25)MnO_(2.07)·0.66H_2O.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 analyse)...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)cm^(2)·s?1.展开更多
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 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
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 Research Foundation of Korea(NRF)grants funded by the Korean Government(NRF-2021R1A4A1030318,NRF-2022R1C1C1011386,NRF-2020M3H4A1A03084258)supported by the"Regional Innovation Strategy(RIS)"through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(MOE)(2021RIS-003)
文摘The layeredδ-MnO_(2)(dMO)is an excellent cathode material for rechargeable aqueous zinc-ion batteries owing to its large interlayer distance(~0.7 nm),high capacity,and low cost;however,such cathodes suffer from structural degradation during the long-term cycling process,leading to capacity fading.In this study,a Co-doped dMO composite with reduced graphene oxide(GC-dMO)is developed using a simple cost-effective hydrothermal method.The degree of disorderness increases owing to the hetero-atom doping and graphene oxide composites.It is demonstrated that layered dMO and GC-dMO undergo a structural transition from K-birnessite to the Zn-buserite phase upon the first discharge,which enhances the intercalation of Zn^(2+)ions,H_(2)O molecules in the layered structure.The GC-dMO cathode exhibits an excellent capacity of 302 mAh g^(-1)at a current density of 100 mAg^(-1)after 100 cycles as compared with the dMO cathode(159 mAhg^(-1)).The excellent electrochemical performance of the GC-dMO cathode owing to Co-doping and graphene oxide sheets enhances the interlayer gap and disorderness,and maintains structural stability,which facilitates the easy reverse intercalation and de-intercalation of Zn^(2+)ions and H_(2)O molecules.Therefore,GC-dMO is a promising cathode material for large-scale aqueous ZIBs.
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.
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.
基金supported by the National Program of Control and Treatment of Water Pollution (No. 2018ZX07109-004)the project from the China Geological Survey (No. DD20190323)the Agricultural Science and Technology Innovation Program of China。
文摘Diclofenac(DCF), a widely used non-steroidal anti-inflammatory, reacted readily with birnessite under mild conditions, and the pseudo first order kinetic constants achieved 8.84 × 10^-2 hr^-1. Five products of DCF including an iminoquinone product(2,5-iminoquinone-diclofenac) and four dimer products were observed and identified by tandem mass spectrometry during the reaction. Meanwhile, 2,5-iminoquinone-diclofenac was identified to be the major product, accounting for 83.09% of the transformed DCF. According to the results of spectroscopic Mn(III) trapping experiments and X-ray Photoelectron Spectroscopy, Mn(IV) contained in birnessite solid was consumed and mainly converted into Mn(III) during reaction process, which proved that the removal of DCF by birnessite was through oxidation. Based on the identified products of DCF and the changes of Mn valence state in birnessite solid, a tentative transformation pathway of DCF was proposed.
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.
基金supported by the National Natural Science Foundation of China (Nos: 41171375, 41171364 and 41571228)the Program for New Century Excellent Talents in University of China (No. NCET-12-0862)+2 种基金the Fok Ying-Tong Education Foundation (No. 141024)the Natural Science Foundation of Hubei Province of China (No: 2012FFA031, 2014CFA016)the Fundamental Research Funds for the Central Universities (Nos.: 2662015JQ002, 2013PY029, 2013PY030)
文摘The oxidation of exposed pyrite causes acid mine drainage, soil acidification, and the release of toxic metal ions. As the important abiotic oxidants in supergene environments,oxygen and manganese oxides participate in the oxidation of pyrite. In this work, the oxidation processes of natural pyrite by oxygen and birnessite were studied in simulated systems, and the influence of p H, Fe（II） and Cr（III） on the intermediates and redox rate was investigated. SO42-and elemental S were formed as the major and minor products,respectively, during the oxidation processes. Ferric（hydr） oxides including Fe（OH）3and goethite were formed with low degree of crystallinity. Low p H and long-term reaction facilitated the formation of goethite and ferric hydroxide, respectively. The rate of pyrite oxidation by birnessite was enhanced in the presence of air（oxygen）, and Fe（II） ions played a key role in the redox process. The addition of Fe（II） ions to the reaction system significantly enhanced the oxidation rate of pyrite; however, the presence of Cr（III） ions remarkably decreased the pyrite oxidation rate in aqueous systems. The introduction of Fe（II） ions to form a Fe（III）/Fe（II） redox couple facilitated the electron transfer and accelerated the oxidation rate of pyrite. The present work suggests that isolation from air and decreasing the concentration of Fe（II） ions in aqueous solutions might be effective strategies to reduce the oxidation rate of pyrite in mining soils.
基金Project supported by the National Natural Science Foundation of China (Nos. 40101017 and 40071048) the Senior Visitor Foundation of Chinese Educational Ministry.
文摘Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The effects of preparative parameters on thesynthesis of birnessite, such as pretreatment on solutions with N2, reaction temperature, O_2 flowrate, fluxion velocity of the reaction suspension, and dehydration conditions were investigated. Thefluxion velocity of the reactive suspension and O_2 flow rate significantly influenced thesynthesis of birnessite. Vigorous stirring raised the fluxion velocity of the reaction suspensionand easily allowed synthesis of pure crystalline birnessite. However pretreatment of the reactingsolutions with N_2 and the reaction temperature had little effect on the synthesis. Diffusion of O_2was the controlling step during the course of oxidation. The optimum synthetic conditions for purebirnessite were: a NaOH to Mn molar ratio of 13.7, an O_2 flow rate of 2 L min^(-1), and oxidationfor 5 hours with vigorous stirring at normal temperatures. The chemical composition of thesynthesized pure birnessite was Na_(0.25)MnO_(2.07)·0.66H_2O.
基金Supported by the NationalNatural Science Foun-dation of China(20077020)
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)cm^(2)·s?1.
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＋.
