Mn3O4多面体纳米晶体的制备及其电化学性能

Mn3O4多面体纳米晶体的制备及其电化学性能

杨陆峰;高闯;郑明涛;胡超凡;崔江虎;刘应亮

【摘 要】通过对未加添加剂的醋酸锰-乙醇体系的一种简易的水基热解过程,制备了

Mn3O4多面体纳米晶体.借助X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射

电子显微镜(TEM)、傅里叶变换红外光谱法(FTIR)、拉曼光谱和X-射线光电子能谱

(XPS)等对Mn3O4的结构和形貌进行了表征.提出了Mn3O4多面体纳米晶体的形

成机理.循环伏安法(CV)测试结果表明,所制得的Mn3O4电极呈现良好的赝电容性

能.在扫描速率为5 mVs-1时,得到了Mn3O4的最大比电容值173 Fg-

1.%Hausmannite Mn3O4 polyhedral nanocrystals have been fabricated

through a simple solution-bad thermolysis process in the mangane

acetate-alcohol ural and morphological characterizations of

the as-obtained product have been carried out using XRD,FTIR,Raman

spectraoscopy,XPS,SEM and formation mechanism of polyhedral

nanocrystals was cyclic voltammetry (CV) result show that

the as prepared Mn3O4 electrode exhibits a good pudo-capacitance

behavior.A maximum specic capacitance of 173 Fg-1 is obtained for the

nanocrystals at a sweep rate of 5 mVs-1.

【期刊名称】《无机化学学报》

【年(卷),期】2013(029)002

【总页数】8页(P381-388)

【关键词】纳米结构;氧化物;水热法;电化学性能

【作 者】杨陆峰;高闯;郑明涛;胡超凡;崔江虎;刘应亮

【作者单位】暨南大学化学系纳米化学研究所,广州 510632;暨南大学化学系纳米

化学研究所,广州 510632;华南农业大学理学院,广州 510642;暨南大学化学系纳米

化学研究所,广州 510632;暨南大学化学系纳米化学研究所,广州 510632;华南农业

大学理学院,广州 510642

【正文语种】中 文

【中图分类】O614.7+1

The development of mangane oxides nanocrystals has been intensively

pursued due to their uful applications in the areas of catalysis,energy

storage,chemicalnsing devices,magneticdata storage and ferro-uids[1-

4].Among them,hausmannite Mn3O4prents particular interest becau

of its application as an effective catalyst for the decomposition of waste

gas and waste solution[5-6].Recent studies have shown that nanostructural

Mn3O4 posss interesting electrochemical

instance,Zhang et al.[7]prepared Mn3O4polyhedron nanocrystal via

thermolysis of a hydrogen-bonded polymer,which exhibitsa

betterelectrochemical capacitance performance than spinel Mn3O4layered

nanostructure[8].The performance of the metal oxides is dependent on the

structure and morphology including crystallite size,stacking

manner,orientation and aspect ratio,which are nsitive to the synthesis

route of their preparation[9].

Owing to the unique shape and size-dependent properties,Mn3O4has

been prepared with various methods such as solvothermal treatment of

manganite(MnOOH)[10-12],solvothermal treatment of mangane

acetate(Mn(CH3COO)24H2O)with a hydrogen-bonded

polymer[7300字作文写景 ],sonochemical method to prepare sphere-like nanocrystals

[13],calcination of nitrate (Mn(NO3)2),carbonate (MnCO3),mangane

oxides(MnO2,Mn2O3,etc.)and oxyhydroxide(g-MnOOH)at high

temperature(1 000℃)[14-16],precipitation method from mangane nitrate

(Mn(NO3)2)at moderate temperature[17],sol-gel process with a post-

treatment at higher temperature[18-19],chemical bath deposition to

prepare thin lms[20],electro spinning technique[21],gas condensation[22].

However,synthetic methods that take advantage of costly organic

surfactants and templates often require subquent purification

procedures which markedly increa manufacture costs[23-24].The

preparation of Mn3O4by using the precursor mangane oxides with the

sophisticated instrument could not be afforded by the average

laboratories in the practical the meanwhile,owing to the

complex inuence of pH value,temperature,ion concentration,and so

forth,limited breakthrough has been achieved for the morphology and

size-controlled synthesis ofnanostructured Mn3O4 through the solution

bad approach without any ore,it is of great significance

to develop an environmentally friendly,low-cost and template-free

synthetic method for the synthesis of Mn3O4nanostructures.

In our previous work,we have reported a simple method for the controlled

synthesis of uniform shaped carbon hollow structures by an ethanol-

assisted thermolysis of zinc acetate[25],which us the generated zinc

oxide nanostructures as in-situ ,we report a one-step

synthesis of Mn3O4polyhedral nanocrystals through a facile solution-

bad thermolysis route in the mangane acetate-alcohol system without

any addition,the formation mechanism of the products has

also been electrochemical properties of the optimized

products of Mn3O4nanocrystals were examined by cyclic voltam

metry(CV)measurements.

1 Experimental

1.1 Synthesis of Mn3O4polyhedral nanocrystals

All chemicals ud were of analytical grade and purchad from the

commercial market without further synthesis of

Mn3O4nanostructures was carried out via a solvothermal a

typical procedure,2.5 mmol Mn(CH3COO)24H2O(Mn(Ac)2)were dissolved

in 30 mL of absolute the mixture was stirred to give a clear

solution and transferred into a 45 mL Teflon-lined stainless steel

autoclave was maintained at 200 ℃ for 1～24 h,with a

heating rate of 10℃min-1in an electronic furnace,and then cooled

naturally to room resulting precipitate was centrifuged

and thoroughly washed with deionized water and ethanol veral times

before drying in air at 60℃ for 24 h.

1.2 Characterization

Crystallographic phas of the products were examinedbyXRD

usingaMSALXD2X-ray diffractometer with Cu K radiation(36 kV,20

mA,=0.154 18 nm).FTIR spectra were measured by an Equinox 55

(Bruker)spectrometer with the KBr pellet technique from 400 to 4 000 cm-

spectra of sampleswere measured using a Renishaw Via

microspectrometer using an excitation wavelength of 514 nm generated

by an Ar+lar.A 100 objective was ud to focus the lar beam and to

collect the Raman al state analysis was carried out by X-ray

photoelectron spectroscopy (XPS)using a Shimadzu AXIS侍候 Ultra X-ray

photoelectron XPS spectra were corrected using the C1s

line at 284.6 XPS Version 2.3.13 software and Origin Pro 8.0 were

ud to analyze the experimental data and morphologies of

the samples were characterized with scanning electron microscopy

(SEM,PhilipsXL-30s),transmission electron microscopy (TEM,Philips Tecnai-

10)and high-resolution TEM (HR-TEM,GEOL-2010).The typical components

of the liquid fractions after the reaction were detected by the gas

chromatography and mass spectrometry(GC-MS) conditions

for GC-MS are given in the supporting information.

1.3 ElectrochemicalmeasurementofMn3O4 electr唯物辩证法认为 ode

The electrochemical electrode was tested on a CHI 660B electrochemical

workstation in a three-electrode working electrode was

fabricated by pressing the mixture of Mn3O4,carbon black and 5%-

PTFE(Polytetrafluoroethylene)(75∶15∶10,W/W/W)into foam nickel

electrode.A Pt slice was ud as auxiliary electrode and a Ag/AgCl as

reference the studies,all measurements were performed in a

0.5 molL-1Na2SO4aqueous electrolyte solution and all electrochemical

experiments were carried out at room temperature.

2 Results and discussion

2.1 Characterization of materials

The crystalline structure and pha purity of the product were investigated

by XRD as shown in 3O4are synthesized with 2.5 mmol

Mn(Ac)2under the prent condition,which can be easily indexed to pure

tetragonal pha of -Mn3O4(PDF No.89-4837)with lattice constants a of

0.576 3 nm and c of 0.945 6 atively,with the coexistence of -

Mn3O4,the sample prepared with 7.5 mmol Mn(Ac)2exhibits strong

diffraction peak of MnO (PDF No.89-4835)(Fig.1b),indicating that the

reaction dosage of Mn(Ac)2has vital influence on the crystals structure of

the product.

The FTIR spectrum in Fig.2 provides more convincing evidence of pure

Mn3O4fabricated with 2.5 mmol Mn(Ac)2,which displays three

characteristic peaks at 638,532 and 416 cm-1[26-27].Besides,strong

absorptions at 3 442 cm-1and weak absorptions around 2 800～3 000 cm-

1respectively reveal the stretching vibrations of O-H and

absorptions at 1 635,1 384 and 1 112 cm-1correspond to the vibrations of

CO,C-H ore,the FTIR spectrum suggests that the surface of

the nanoparticles is coated by a layer of ethanol molecules.

Considering the C-OH and C-H vibration,and Ac-/C2H5OH ud in

hydrothermal conditions,the Raman spectra have been provided to

investigate the surface microstructure of the pure Mn3O4nanocrystals,as

shown in the Raman spectrum,the Raman peaks at 652.3 cm-

1corresponding to crystalline hausmannite structure are clearly

found,which are in good agreement with the microstructure information of

as-prepared Mn3O4[28-29].In addition,there are no diffraction peaks

around～1 360 cm-1and 1 580 cm-1,suggesting the abnce of carbon

layer on the Mn3O4 prepared under the hydrothermal conditions at 200℃.

Chemical state information for the as-prepared Mn3O4was studied using

shown in Fig.4a,the survey spectrum shows no significant prence

of impurities,except for the contaminant levels of

Mn3s,O1s,Mn2p and Mn3p are obtained in the exact energy locations as

reported earlier[30-31].In Fig.4b,the binding energy value of Mn2p3/2is

641.6 eV,and the spin orbit splitting between the Mn2p3/2and

Mn2p1/2level is 11.7 eV,which perfectly matches the previously reported

values for hausmannite[32].The oxidation state of the mangane atom is

further analyzed by deconvoluted for relative intensities of the component

peaks of 3p3/2XPS binding energy of the Mn2p3/2peak

components (640.9 and 642.6 eV)is in good agreement with the literature

report,respectively,for the occurrence of Mn2+and Mn4+[31,33]for the

formation of atomic concentration of the total oxygen

and the mangane from the results of XPS is 64.5% and

35.5%, atomic ratio of O to Mn in the Mn3O4 is 1.82,which

is greater than the theoretical value of excess O may come from

the ethanol molecules coated on the surface ofMn3O4as demonstrated by

the FTIR spectrum.

In order to study the inuence of the reaction time on the morphology

ofthe products,ries of experiments were carried images in Fig.5a

shows a low-magnication of the sample obtained after solvothermal

reaction at 200℃for 2 h,which exhibit large-scale formation of uniform

nanoparticles with diameters about 10 ～20 nanometer-sized

particles are obrved with diameter of 创新的故事 40～60 nm aggregative attached

together in increasing the reaction time to 24 h,many

polyhedral Mn3O4 nanocrystals with mean diameter of 250 nm are

prented in ore,the SEM images of the samples reveal that

the reaction time plays vital role in the shape evolution of

the reaction time is extended,the size of Mn3O4sample grows bigger and

exhibits distinct polyhedral nanocrystals.

For the reason that the poor resolution of SEM images can not throw light

on the formation process of Mn3O4,the morphology and microstructures

of the asprepared Mn3O4were further investigated with TEM and

shown in Fig.6a,a mass of uniform tiny nanoparticles with

average diameter of 8 nm are obrved after reaction of 1 the

reaction time is incread to 2 h,it can be clearly obrved that the initial

nanocrystals grow into uniform hexagonal flakelike morphology with

widths of 10～15 nm as shown in the reaction time is further

incread to 12 h,many polyhedral nanocrystals with rough surface are

obrved,which project to regular tetragonal shape with edge lengths of

40～60 nm(Fig.6c).

The uniform polyhedral nanocrystals with smooth surface are produced

when the reaction time is extended to 18 h (Fig.7a).In the same time,the

corresponding XRD pattern exhibits sharp and strong diffraction peaks of

-Mn3O4(Fig.1a).More details of the structure are investigated by HRTEM

neous octahedral like nanocrystals with edge lengths

about 120 nm are clearly en in shown in Fig.7c,the

corresponding lattice fringes exhibit distinct ts of lattice spacing of

about 0.306 nm,consistent with(112)crystal planes of a tetragonal

ore,the Mn3O4nanostructure can be well controlled by

tuning the reaction time at 200℃with 2.5 mmol Mn(Ac) time-

dependent experiments reveal that the formation of Mn3O4nanocrystals

experience an Ostwald ripening dominated process,which is well

consistent with the SEM investigation.

2.2 Formation mechanism of polyhedral nanocrystals

X-ray crystallography analysis shows that Mn3O4is ob社会实践的目的和意义 tained with 2.5 mmol

Mn(Ac)2through the solvothermal stingly,the synthesized

product exhibits the crystalline pha of MnO when increasing the do of

Mn(Ac)2to 7.5 mmol at 200 ℃ (Fig.1b).Therefore,it can be deduced that

there is an oxidizing process of MnⅡto MnⅢ with O2both in the autoclave

and the ethanol the limited amount of O2in the reaction

system is not enough to have 7.5 mmol MnⅡall oxidized into

MnⅢ.Meanwhile,an inten odor of ester is noticed from the solution after

the shed light on the formation process of Mn3O4,the reaction

by-product has been investigated via GC/MS /MS analysis

conducted on the extract of the post-reaction solution clearly reveals the

existence of ethyl acetate (Fig.S1，S2,Supporting Information),indicating

the formation of butyl acetate during the synthetic procedure,which is

similar to the previous report[34].Thus,On the basis of the experimental

results,a formation mechanism of Mn3O4 polyhedral nanocrystals is

believe that the reaction process of the mangane acetate-

alcohol solution may be as follows:

In the current solvothermal synthesis at 200℃,the reaction between

mangane acetate and alcohol firstly results in the coordination of

C2H5OH to mangane centers,to form unstable alcohol acetate

complexes(CH3COO)2-xMn(OC2H5)xby ligand

exchange/substitution,concomitant with the relea of

CH3COOH(eq.1).The produced acetic acid could then react with the

solvent alcohol to form water by a slow esterification

reaction(eq.2).Subquently,(CH3COO)2-xMn(OC2H5)x would hydrolyze

and generate MnO under the lfgenerated pressure

(eq.3).Finally,Mn3O4nanostructures are achieved after the oxidation

reaction of the active MnO with the O2both in the reaction container and

ethanol solution (eq.4).In this current situation,many newly formed

Mn3O4colloids aggregate together andform

ile,thenascentMn3O4 nanocrystals with high surface

energies might be temporarily stabilized by ethanol ,the

dissolution recrystallization and lf-asmbly process

uently,an Ostwald ripening process

propod pathway is supported by our time-dependent experiments,as

shown in Fig.6a～c.

2.3 Electrochemical properties of Mn3O4 polyhedral nanocrystals

The electrochemical performance of Mn3O4 polyhedral nanocrystals

synthesized at 200℃for 18 h were evaluated as a supercapacitor electrode

in view of their intrinsic properties and unique structural .8

shows the cyclic voltammetry (CV)analysis at various scan rates in 0.5

molL-1Na2SO4electrolyte with a potential range of 0.1 to 0.9

V.(/AgCl).The CV curves at slow scan rate prent an ideal capacitive

behavior with ne rectangular deviation from rectangularity of

the CV becomes distinct with the increa of scan obvious redox

peaks are prent in the CV curves,revealing that the measured electrode

is charged and discharged at a pudo-constant rate over the complete

voltammetric cycle[35].

The MnO2bad electrode[36]reveal maybe the charge storage mechanism

in slower scan rate,almost all available pores both on

the surface and inside of Mn3O4electrode can be filled with Na+from

electrolyte,resulting in a better effective utilization of Mn3O4for redox

reaction and a better r,the effective interaction

between the ions and the electrode is greatly decread when increasing

the scan ,the effective redox reaction of Mn3O4is confined only

to the outer surface of Mn3O4electrode,resulting in decread

specic capacitance of the electrode at different current

densities can be calculated from the following equation[37]

where C is the specific capacitance of the electrode bad on the mass of

active materials(Fg-1),Q is the sum of anodic and cathodic voltammetric

charges on positive and negative sweeps(C),I is the sample current(A),W is

the weight of active materials(g),and V is the total potential deviation of

the voltage window(V).v is the scanning rate(Vs-1)and is the mass of

active electrode materials (g).According to formula(1),specic capacitance

ranging from 173 to 84 Fg-1can be delivered at the various scan rates of

2～50 mVs-1,as shown in Fig.8,which is a little lower than that of

Mn3O4nano-octahedrons[38].Thus,the superior crystal structure should be

provided for a better functional properties of Mn3O4。

3 Conclusions

In summary,Mn3O4nanocrystals with wellcontrolled polyhedral shape have

been synthesized via Ethanol-assisted thermolysis of 2.5 mol mangane

acetate at 200℃ for 18 the basis of the results,a formation

mechanism of Mn3O4polyhedral nanocrystals is is valuable to

study the shape evolution of -Mn3O4in the prent reaction system for

the understan天麻粉的正确吃法 ding of the formation process of polyhedron

voltammetry measurement shows that the as prepared

Mn3O4electrode exhibits a good pudo capacitance behavior with a

discharge specific capacitance of 173 Fg-1at a sweep rate of 5 mVs-

results suggest that Mn3O4 polyhedral nanocrystals materials may

have potential applications in electrochemical capacitor.

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