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Monodisperse MFe2O4 (M ) Fe, Co, Mn) Nanoparticles

Monodisperse MFe2O4 (M ) Fe, Co, Mn) Nanoparticles
Monodisperse MFe2O4 (M ) Fe, Co, Mn) Nanoparticles

Monodisperse MFe2O4(M)Fe,Co,Mn)Nanoparticles Shouheng Sun,*,?Hao Zeng,?David B.Robinson,?Simone Raoux,?Philip M.Rice,?

Shan X.Wang,§and Guanxiong Li§

Contribution from the IBM T.J.Watson Research Center,Yorktown Heights,New York10598,

IBM Almaden Research Center,650Harry Road,San Jose,California95120,and Department of Materials Science and Engineering,Stanford Uni V ersity,Stanford,California94305

Received August22,2003;E-mail:ssun@https://www.sodocs.net/doc/6d8550953.html,

Abstract:High-temperature solution phase reaction of iron(III)acetylacetonate,Fe(acac)3,with1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite(Fe3O4) nanoparticles.Similarly,reaction of Fe(acac)3and Co(acac)2or Mn(acac)2with the same diol results in monodisperse CoFe2O4or MnFe2O4nanoparticles.Particle diameter can be tuned from3to20nm by varying reaction conditions or by seed-mediated growth.The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM,SAED,and XRD.Further,Fe3O4can be oxidized to Fe2O3,as evidenced by XRD,NEXAFS spectroscopy,and SQUID magnetometry.The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants,and aqueous nanoparticle dispersion is readily made.These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.

Introduction

Magnetic iron oxide nanoparticles and their dispersions in various media have long been of scientific and technological interest.The cubic spinel structured MFe2O4,or MO?Fe2O3, represents a well-known and important class of iron oxide materials where oxygen forms an fcc close packing,and M2+ and Fe3+occupy either tetrahedral or octahedral interstitial sites.1 By adjusting the chemical identity of M2+,the magnetic configurations of MFe2O4can be molecularly engineered to provide a wide range of magnetic properties.Due in part to this versatility,nanometer-scale MFe2O4materials have been among the most frequently chosen systems for studies of nanomagnetism and have shown great potential for many important technological applications,ranging from information storage and electronic devices to medical diagnostics and drug delivery.Dispersions of magnetic MFe2O4nanoparticles,es-pecially magnetite(Fe3O4)nanoparticles,have been used widely not only as ferrofluids in sealing,oscillation damping,and position sensing2but also as promising candidates for biomol-ecule tagging,imaging,sensing,and separation.3Depending on the chemical identity of M2+,the densely packed solid state form of nanocrystalline MFe2O4-based materials,on the other hand,can have either high magnetic permeability and electrical resistivity(for M representing one or the mixed components from Co,Li,Ni,Zn,etc.)or half-metallicity(for M)Fe),and may be a potential candidate for future high-performance electromagnetic4and spintronic devices.5

To use MFe2O4nanoparticles for future highly sensitive magnetic nanodevice and biomedical applications,a practical route to monodisperse MFe2O4nanoparticles with diameters smaller than20nm and a tight size distribution(less than10% standard deviation)is needed.A commonly used solution phase procedure for making such particles has been the coprecipitation of M2+and Fe3+ions by a base,usually NaOH or NH3?H2O in an aqueous solution6or in a reverse micelle template.7Although this precipitation method is suitable for mass production of

?IBM T.J.Watson Research Center.

?IBM Almaden Research Center.

§Stanford University.

(1)(a)West,A.R.Basic Solid State Chemistry;John Wiley&Sons:New

York,1988;pp356-359.(b)O’Handley,R. C.Modern Magnetic (3)(a)Ha¨feli,U.;Schu¨tt,W.;Teller,J.;Zborowski,M.Scientific and Clinical

Applications of Magnetic Carriers;Plenum Press:New York,1997.(b) Oswald,P.;Clement,O.;Chambon,C.;Schouman-Claeys,E.;Frija,G.

Magn.Reson.Imaging1997,15,1025.(c)Hergt,R.;Andra,W.;d’Ambly,

C.G.;Hilger,I.;Kaiser,W.A.;Richter,U.;Schmidt,H.-G.IEEE Trans.

Mag.1998,34,3745.(d)Jordan,A.;Scholz,R.;Wust,P.;Fa¨hling,H.;

Felix,R.J.Magn.Magn.Mater.1999,201,413.(e)Kim,D.K.;Zhang, Y.;Kehr,J.;Klason,T.;Bjelke,B.;Muhammed.M.J.Magn.Magn.Mater.

2001,225,256.(f)Pankhurst,Q.A.;Connolly,J.;Dobson,J.J.Phys.D: Appl.Phys.2003,36,R167.(g)Tartaj,P.;Morales,M.P.;Veintemillas-Verdaguer,S.;Gonza′lez-Carren?o,T.;Serna,C.J.J.Phys.D:Appl.Phys.

2003,36,R182.(h)Berry,C.C.;Curtis,A.S.G.J.Phys.D:Appl.Phys.

2003,36,R198.

(4)(a)Fannin,P.C.;Charles,S.W.;Vincent,D.;Giannitsis,A.T.J.Magn.

Magn.Mater.2002,252,80.(b)Matsushita,N.;Nakamura,T.;Abe,M.

IEEE Trans.Magn.2002,38,3111.(c)Matsuchita,Chong,C.P.;Mizutani, T.;Abe,M.J.Appl.Phys.2002,91,7376.(d)Nakamura,T.;Miyamoto, T.;Yamada,Y.J.Magn.Magn.Mater.2003,256,340.

(5)(a)Verwey,E.J.W.Nature1939,144,327.(b)Zhang,Z.;Satpathy,S.

Phys.Re V.B1991,44,13319.(c)Anisimov,V.I.;Elfimov,I.S.;Hamada, N.;Terakura,K.Phys.Re V.B1996,54,4387.(d)Gong,G.Q.;Gupta,A.;

Xiao,G.;Qian,W.;Dravid,D.P.Phys.Re V.B1997,56,5096.(e)Coey, J.M.D.;Berkowitz,A.E.;Balcells,L.I.;Putris,F.F.;Parker,F.T.Appl.

Phys.Lett.1998,72,734.(f)Li,X.W.;Gupta,A.;Xiao,G.;Gong,G.Q.

J.Appl.Phys.1998,83,7049.(g)Kiyomura,T.;Maruo,Y.;Gomi M.J.

Appl.Phys.2000,88,4768.(h)Moore,R.G.C.;Evans,S.D.;Shen,T.;

Hodson,C.E.C.Physica E2001,9,253.(i)Versluijs,J.J.;Bari,M.A.;

Coey,J.M.D.Phys.Re V.Lett.2001,87,26601.(j)Soeya,S.;Hayakawa,

Published on Web12/10/2003

magnetic MFe2O4ferrofluids,it does require careful adjustment of the pH value of the solution for particle formation and stabilization,and it is difficult to control sizes and size distributions,particularly for particles smaller than20nm.An alternative approach to monodisperse iron oxide nanoparticles is via high-temperature organic phase decomposition of an iron precursor,for example,decomposition of FeCup3(Cup:N-nitrosophenylhydroxylamine,C6H5N(NO)O-)8or decomposition of Fe(CO)5followed by oxidation to Fe2O3.9The latter process has recently been extended to the synthesis of monodisperse cobalt ferrite(CoFe2O4)nanoparticles.10Although significant progress in making monodisperse Fe2O3and CoFe2O4nano-particles has been made in organic phase reactions,there is still no general process for producing MFe2O4,especially Fe3O4 nanoparticles with the desired size and acceptable size distribu-tion.

Recently,we reported a convenient organic phase process for making monodisperse Fe3O4nanoparticles through the reaction of Fe(acac)3and a long-chain alcohol.11Our further experiments indicated that this reaction could be readily extended to the synthesis of MFe2O4nanoparticles(with M) Co,Ni,Mn,Mg,etc.)by simply adding a different metal acetylacetonate precursor to the mixture of Fe(acac)3and1,2-hexadecanediol.Here we present detailed syntheses and char-acterization of Fe3O4and related MFe2O4nanoparticles(with M)Co and Mn as two examples)with sizes tunable from3to 20nm in diameter.The process involves high-temperature(up to305°C)reaction of metal acetylacetonate with1,2-hexade-canediol,oleic acid,and oleylamine.The size of the oxide nanoparticles can be controlled by varying the reaction tem-perature or changing metal precursors.Alternatively,with the smaller nanoparticles as seeds,larger monodisperse nanopar-ticles up to20nm in diameter can be synthesized by seed-mediated growth.The process does not require a low-yield fractionation procedure to achieve the desired size distribution and is readily scaled up for mass production.The nanoparticles can be dispersed into nonpolar or weakly polar hydrocarbon solvent,such as hexane or toluene.The hydrophobic nanopar-ticles can be transformed into hydrophilic ones by mixing with a bipolar surfactant,tetramethylammonium11-aminounde-canoate,allowing preparation of aqueous nanoparticle disper-sions.These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.Experimental Section

The synthesis was carried out using standard airless procedures and commercially available reagents.Absolute ethanol,hexane,and dichlo-romethane(99%)were used as received.Phenyl ether(99%),benzyl ether(99%),1,2-hexadecanediol(97%),oleic acid(90%),oleylamine (>70%),cobalt(II)acetylacetonate,Mn(II)acetylacetonate,and poly-ethylenimine(water-free,average M w ca.25000)were purchased from Aldrich Chemical Co.Iron(III)acetylacetonate was from Strem Chemicals,Inc.Tetramethylammonium11-aminoundecanoate was prepared by titrating a methanolic suspension of11-aminoundecanoic acid with methanolic tetramethylammonium hydroxide(both from Aldrich),evaporating the solvent under reduced pressure,and recrystal-lizing in tetrahydrofuran.

Synthesis of4nm Fe3O4Nanoparticle Seeds.Fe(acac)3(2mmol), 1,2-hexadecanediol(10mmol),oleic acid(6mmol),oleylamine(6 mmol),and phenyl ether(20mL)were mixed and magnetically stirred under a flow of nitrogen.The mixture was heated to200°C for30 min and then,under a blanket of nitrogen,heated to reflux(265°C) for another30min.The black-brown mixture was cooled to room temperature by removing the heat source.Under ambient conditions, ethanol(40mL)was added to the mixture,and a black material was precipitated and separated via centrifugation.The black product was dissolved in hexane in the presence of oleic acid(~0.05mL)and oleylamine(~0.05mL).Centrifugation(6000rpm,10min)was applied to remove any undispersed residue.The product,4nm Fe3O4nano-particles,was then precipitated with ethanol,centrifuged(6000rpm, 10min)to remove the solvent,and redispersed into hexane.

Under identical conditions,reaction of Co(acac)2(1mmol)with Fe-(acac)3led to3nm CoFe2O4nanoparticles that could be readily dispersed into hexane,giving a dark red-brown hexane dispersion.

Synthesis of6nm Fe3O4Nanoparticle Seeds.Fe(acac)3(2mmol), 1,2-hexadecanediol(10mmol),oleic acid(6mmol),oleylamine(6 mmol),and benzyl ether(20mL)were mixed and magnetically stirred under a flow of nitrogen.The mixture was heated to200°C for2h and then,under a blanket of nitrogen,heated to reflux(~300°C)for 1h.The black-colored mixture was cooled to room temperature by removing the heat source.Following the workup procedures described in the synthesis of4nm particles,a black-brown hexane dispersion of 6nm Fe3O4nanoparticles was produced.

Similarly,by adding Co(acac)2or Mn(acac)2,10nm CoFe2O4or7 nm MnFe2O4nanoparticle seeds can be made.

Synthesis of8nm Fe3O4Nanoparticles via6nm Fe3O4Seeds. Fe(acac)3(2mmol),1,2-hexadecanediol(10mmol),benzyl ether(20 mL),oleic acid(2mmol),and oleylamine(2mmol)were mixed and magnetically stirred under a flow of N2.A84mg sample of6nm Fe3O4nanoparticles dispersed in hexane(4mL)was added.The mixture was first heated to100°C for30min to remove hexane,then to200°C for1h.Under a blanket of nitrogen,the mixture was further heated to reflux(~300°C)for30min.The black-colored mixture was cooled to room temperature by removing the heat source.Following the workup procedures described in the synthesis of4nm particles,a black-brown hexane dispersion of8nm Fe3O4nanoparticles was produced.

Similarly,80mg of8nm Fe3O4seeds reacted with Fe(acac)3(2 mmol)and the diol(10mmol)led to10nm https://www.sodocs.net/doc/6d8550953.html,ing this seed-mediated growth,bigger nanoparticles of Fe3O4up to20nm, CoFe2O4up to20nm,or MnFe2O4up to18nm have been made.

Synthesis of Hydrophilic Fe3O4Nanoparticles.Under ambient conditions,a hexane dispersion of hydrophobic Fe3O4nanoparticles (about20mg in0.2mL)was added to a suspension of tetramethy-lammonium11-aminoundecanoate(about20mg in2mL)in dichlo-romethane.The mixture was shaken for about20min,during which time the particles precipitated and separated using a magnet.The solvent

(6)See for example:(a)Kang,Y.S.;Risbud,S.;Rabolt,J.F.;Stroeve,P.

Chem.Mater.1996,8,2209.(b)Hong,C.-Y.;Jang,I.J.;Horng,H.E.;

Hsu,C.J.;Yao,Y.D.;Yang,H.C.J.Appl.Phys.1997,81,4275.(c)

Fried,T.;Shemer,G.;Markovich,G.Ad V.Mater.2001,13,1158.(d)Tang,

Z.X.;Sorensen,C.M.;Klabunde,K.J.;Hadjipanayis,G.C.J.Colloid

Interface Sci.1991,146,38.(e)Zhang,Z.J.;Wang,Z.L.;Chakoumakos,

B.C.;Yin,J.S.J.Am.Chem.Soc.1998,120,1800.(f)Neveu,S.;Bec,

A.;Robineau,M.;Talbol,D.J.Colloid Interface Sci.2002,255,293.

(7)See for example:(a)Pileni,M.P.;Moumen,N.J.Phys.Chem.B1996,

100,1867.(b)Liu,C.;Zou,B.;Rondinone,A.J.;Zhang,Z.J.J.Phys.

Chem.B2000,104,1141.

(8)Rockenberger,J.;Scher,E.C.;Alivisatos,P.A.J.Am.Chem.Soc.1999,

121,11595.

(9)(a)Bentzon,M.D.;van Wonterghem,J.;M?rup,S.;Tho¨le′n,A.;Koch,C.

J.Philos.Mag.B1989,60,169.(b)Hyeon,T.;Lee,S.S.;Park,J.;Chung,

Y.;Na,H.B.J.Am.Chem.Soc.2001,123,12798.(c)Guo,Q.;Teng,X.;

Rahman,S.;Yang,H.J.Am.Chem.Soc.2003,125,630.(d)Redl,F.X.;

Cho,K.-S.;Murray,C.B.;O’Brien,S.Nature2003,423,968.

A R T I C L E S Sun et al.

to remove excess surfactants before drying under N 2.The product was then dispersed in deionized water (18M ?)or 1mM phosphate buffer at neutral pH.

Nanoparticle Characterization.Fe,Co,Mn,and S elemental analyses of the as-synthesized nanoparticle powders were performed on inductively coupled plasma -optic emission spectrometry (ICP-OES)at Galbraith Laboratories (Knoxville,TN).To prepare samples for elemental analysis,the particles were precipitated from their hexane dispersion by ethanol,centrifuged,washed with ethanol,and dried.Samples for transmission electron microscopy (TEM)analysis were prepared by drying a dispersion of the particles on amorphous carbon-coated copper grids.Particles were imaged using a Philips CM 12TEM (120kV).The structure of the particles was characterized using HRTEM and selected area electron diffraction (SAED)on a JEOL TEM (400kV).X-ray powder diffraction patterns of the particle assemblies were collected on a Siemens D-500diffractometer under Co K R radiation (λ)1.788965?).Near-edge X-ray absorption fine structure (NEXAFS)spectroscopy was performed at the Advanced Light Source at beamline 7.3.1.1,which was equipped with a spherical grating monochromator and had an energy resolution of E /?E )1800.Magnetic studies were carried out using a MPMS2Quantum Design SQUID magnetometer with fields up to 7T and temperatures from 5to 350K.Infrared spectra of dried particles pressed into KBr pellets were obtained on a Nicolet Nexus 670FTIR spectrometer.A homemade spin valve sensor 12was used to detect a single layer of 16nm Fe 3O 4nanoparticles.

Results and Discussion

Fe 3O 4Synthesis.As illustrated in Scheme 1,reaction of Fe-(acac)3with surfactants at high temperature leads to monodis-perse Fe 3O 4nanoparticles,which can be easily isolated from reaction byproducts and the high boiling point ether solvent.If phenyl ether was used as solvent,4nm Fe 3O 4nanoparticles were separated,while the use of benzyl ether led to 6nm Fe 3O 4.As the boiling point of benzyl ether (298°C)is higher than that of phenyl ether (259°C),the larger sized Fe 3O 4particle obtained from benzyl ether solution seems to indicate that high reaction temperature will yield larger particles.However,regardless of the size of the particles,the key to the success of making monodisperse nanoparticles is to heat the mixture to 200°C first and remain at that temperature for some time before it is heated to reflux at 265°C in phenyl ether or at ~300°C in benzyl ether.Directly heating the mixture to reflux from room temperature would result in Fe 3O 4nanoparticles with wide size distribution from 4to 15nm,indicating that the nucleation of Fe 3O 4and the growth of the nuclei under these reaction conditions is not a fast process.

The low cost of Fe(acac)3and the high yields it produces makes it an ideal precursor for Fe 3O 4nanoparticle synthesis.The more expensive Fe(acac)2or Fe(II)acetate can also be used but yields no better result than Fe(acac)3.Fe(II)(D -gluconate)is another good precursor for Fe 3O 4synthesis.In benzyl ether,the reaction of Fe(II)(D -gluconate)with a 3-fold excess of each of oleic acid and oleylamine and a 5-fold excess of 1,2-hexadecanediol led to nearly monodisperse 8nm Fe 3O 4nano-particles.

Several different alcohols and polyalcohols have been tested for their reactions with Fe(acac)3.It was found that 1,2-hydrocarbon diols,including 1,2-hexadecanediol and 1,2-dodecanediol,react well with Fe(acac)3to yield Fe 3O 4nano-particles.Long-chain monoalcohols,such as stearyl alcohol and oleyl alcohol,can also be used,but particle quality is worse and product yield is poorer than those with diols in the synthesis of Fe 3O 4nanoparticle seeds.However,in the seed-mediated growth process,these monoalcohols can be used to form larger Fe 3O 4nanoparticles.11

Oleic acid and oleylamine are necessary for the formation of particles.Sole use of oleic acid during the reaction resulted in a viscous red-brown product that was difficult to purify and characterize.On the other hand,the use of oleylamine alone produced iron oxide nanoparticles in a much lower yield than the reaction in the presence of both oleic acid and oleylamine.When the 4nm particles were oxidized by bubbling oxygen through the dispersion at room temperature,they precipitated from hexane as a red-brown powder (the characterization of a similar product is discussed below).Adding more oleic acid did not cause re-dispersion of this powder into hexane.However,adding oleylamine did,leading to an orange-brown hexane dispersion.This is consistent with the previous observation that γ-Fe 2O 3nanoparticles can be stabilized by alkylamine surfac-tants,13suggesting that -NH 2coordinates with Fe(III)on the surface of the particles.

The larger Fe 3O 4nanoparticles can also be made by seed-mediated growth.This method has been recently applied to larger metallic nanoparticle and nanocomposite synthesis 14and is believed to be an alternative way of making monodisperse nanoparticles along with LaMer’s method through fast super-saturated-burst nucleation 15and Finke’s method via slow,continuous nucleation and fast,autocatalytic surface growth.16In our synthesis,the small Fe 3O 4nanoparticles,the seeds,are mixed with more materials as shown in Scheme 1and heated,and particle diameters can be increased by ~2nm or more in each seed-mediated reaction,allowing diameter to be tuned up to about 20nm.

TEM analysis shows that Fe 3O 4nanoparticles prepared according to Scheme 1or the seed-mediated growth method are monodisperse.Figure 1shows typical TEM images from representative 6,10,and 12nm Fe 3O 4nanoparticles deposited from their hexane (or octane)dispersions and dried under ambient conditions.It can be seen that the particles have a

(13)(a)Rajamathi,M.;Ghosh,M.;Seshadri,https://www.sodocs.net/doc/6d8550953.html,m .2002,1152.(b)

Boal,A.K.;Das,K.;Gray,M.;Rotello,V.M.Chem.Mater .2002,14,2628.

(14)(a)Brown,K.R.;Natan,https://www.sodocs.net/doc/6d8550953.html,ngmuir 1998,14,726.(b)Jana,N.R.;

Gearheart,L.;Murphy,C.J.Chem.Mater .2001,13,2313.(c)Yu,H.;Gibbons,P.C.;Kelton,K.F.;Buhro,W.E.J.Am.Chem.Soc .2001,123,Scheme

1

MFe 2O 4(M )Fe,Co,Mn)Nanoparticles

A R T I C L E S

narrow size distribution and can form a self-ordered Fe3O4 superlattice(Figure1C)if solvent is made to evaporate slowly. Fe3O4Structural Characterization.Structural information from a single Fe3O4nanoparticle was obtained using high-resolution TEM(HRTEM).Figure2A is the HRTEM image of an isolated6nm Fe3O4nanoparticle.The lattice fringes in the image correspond to a group of atomic planes within the particle,indicating that the particle is a single crystal.The distance between two adjacent planes is measured to be2.98?,corresponding to(220)planes in the spinel-structured Fe3O4.17

Structural information from an assembly of Fe3O4nanopar-ticles was obtained from both electron and X-ray diffraction. Figure2B is a selected area electron diffraction(SAED)pattern acquired from a6nm nanoparticle assembly.Table1displays the measured lattice spacing based on the rings in the diffraction pattern and compares them to the known lattice spacing for bulk Fe3O4along with their respective hkl indexes from the PDF

database.Figure3is a group of representative size-dependent XRD patterns of Fe3O4nanoparticles.The position and relative intensity of all diffraction rings/peaks match well with standard Fe3O4powder diffraction data.17The average particle diameter estimated from Scherrer’s formula18is consistent with that determined by statistical analysis of the TEM images,indicating that each individual particle is a single crystal.

Figure1.TEM bright field images of(A)6nm and(B)12nm Fe3O4 nanoparticles deposited from their hexane dispersion on an amorphous carbon-coated copper grid and dried at room temperature,and(C)a3D superlattice of10nm Fe3O4nanoparticles deposited from their octane dispersion on an amorphous carbon surface and dried at room

temperature.Figure2.Structural characterization of Fe3O4nanoparticles:(A)High-Resolution TEM image of a single6nm Fe3O4nanoparticle;and(B)selected area electron diffraction(SAED)pattern acquired from a6nm Fe3O4 nanoparticle

assembly.

Figure3.X-ray diffraction patterns of(A)4nm,(B)8nm,(C)12nm, and(D)16nm Fe3O4nanoparticle assemblies.All samples were deposited on glass substrates from their hexane dispersions.Diffraction patterns were collected on a Siemens D-500diffractometer under Co K R radiation(λ) 1.788965?).

Table1.Measured Lattice Spacing,d(?),Based on the Rings in Figure2B and Standard Atomic Spacing for Fe3O4along with Their Respective hkl Indexes from the PDF Database

ring

12345678910 d 4.86 2.98 2.54 2.12 1.73 1.63 1.5 1.34 1.29 1.22 Fe3O4 4.86 2.97 2.53 2.1 1.71 1.62 1.48 1.33 1.28 1.21 hkl111220311400422511440620533444

A R T I C L E S Sun et al.

Oxidation Fe 3O 4to Fe 2O 3.It is well known that Fe 3O 4can be oxidized to γ-Fe 2O 3,which can be further transformed into R -Fe 2O 3at higher temperature.19Observation of these trans-formations can further help to confirm the formation of Fe 3O 4nanoparticles from the synthesis based on Scheme 1.Figure 4A is the XRD pattern from the as-synthesized,black 16nm Fe 3O 4nanoparticle assembly.After oxidation under O 2at 250°C for 6h,the black assembly is transformed to a red-brown one.Figure 4B shows that all XRD peak positions and relative intensities of this red-brown material match well with those of commercial γ-Fe 2O 3powder materials (Aldrich catalog No.48,-066-5),indicating that the oxidation of Fe 3O 4under O 2leads to γ-Fe 2O https://www.sodocs.net/doc/6d8550953.html,pared to Figure 4A,the large-angle peaks in Figure 4B shift slightly to higher angles,whereas at lower angles there exist additional weak diffraction peaks of (110),(113),(210),and (213)that are characteristic of γ-Fe 2O 3.17Figure 4C shows the XRD of the dark red-brown materials obtained after 500°C annealing of γ-Fe 2O 3in Figure 4B under Ar for 1h.The diffraction pattern matches with that from known R -Fe 2O 3materials,17indicating the transformation of γ-Fe 2O 3to R -Fe 2O 3at high temperature.However the as-synthesized Fe 3O 4nano-particles do not go through such a change if annealed under inert atmosphere.Even at 650°C,the Fe 3O 4structure is still retained,as evidenced by both XRD and HRTEM.This confirms the valence state of the iron cations in the as-synthesized sample closely matches that of Fe 3O 4rather than similarly structured γ-Fe 2O 3.20

The transformations of Fe 3O 4to Fe 2O 3can be further characterized by near-edge X-ray absorption fine structure (NEXAFS)spectroscopy in total electron yield mode.Figure 5shows the NEXAFS spectra at the Fe L absorption edges of the as-synthesized 8nm Fe 3O 4nanoparticles and γ-Fe 2O 3and R -Fe 2O 3nanoparticles derived from the oxidation of the Fe 3O 4particles.For comparison,reference spectra of Fe 3O 4,γ-Fe 2O 3,

and R -Fe 2O 3films grown on MgO (001)21are also inserted into the figure as dotted lines.The increased splitting of the L 3peak in the region of 705-710eV and the varying ratio of the two peaks at the L 2edge (719-725eV)are indicative of the transformation of the as-synthesized Fe 3O 4nanoparticles into γ-Fe 2O 3and to R -Fe 2O 3under different annealing conditions.Magnetic Properties of the Fe 3O 4Nanoparticle Assem-blies.Magnetic measurements on all Fe 3O 4nanoparticles indicate that the particles are superparamagnetic at room temperature,meaning that the thermal energy can overcome the anisotropy energy barrier of a single particle,and the net magnetization of the particle assemblies in the absence of an external field is zero.Figure 6shows the hysteresis loops of 16nm Fe 3O 4nanoparticles measured at both 10K and room temperature.It can be seen that the particles are ferromagnetic at 10K with a coercivity of 450Oe (Figure 6A).At room temperature there is no hysteresis (Figure 6B).Under a large external field,the magnetization of the particles aligns with the field direction and reaches its saturation value (saturation magnetization,σs ).For Fe 3O 4nanoparticles,we noticed that the

(19)Bate,G.In Magnetic Oxides Part 2;Craik,D.J.,Ed.;John Wiley &Sons:

New York,1975;pp 705-707.

(20)Although the evidence presented so far suggests that Fe 3O 4is obtained

Figure 4.X-ray diffraction patterns of (A)a 16nm Fe 3O 4nanoparticle assembly,(B)a γ-Fe 2O 3nanoparticle assembly obtained from the oxidation of (A)under oxygen at 250°C for 6h,(C)an R -Fe 2O 3nanoparticle assembly obtained from the further annealing of (B)under Ar at 500°C for 1

h.

Figure 5.NEXAFS spectra at the Fe L edge of Fe 3O 4,γ-Fe 2O 3,and R -Fe 2O 3nanoparticle assemblies,with the dotted lines representing reference spectra of thin film oxide samples of Fe 3O 4,γ-Fe 2O 3,and R -Fe 2O 3

.

Figure 6.Hysteresis loops of the 16nm Fe 3O 4nanoparticle assembly measured at (A)10K and (B)300K.

MFe 2O 4(M )Fe,Co,Mn)Nanoparticles A R T I C L E S

σs was dependent on the size of the particles.For example,σs for16nm Fe3O4nanoparticles is83emu/g,close to the value of84.5emu/g measured from the commercial magnetite fine powder.For particles smaller than10nm,however,σs is smaller, most likely due to the surface spin canting of the small magnetic nanoparticles.22However,if annealed under Ar at high tem-perature(600°C),even4nm Fe3O4nanoparticles show aσs close to82emu/g due to the average size increase caused by particle aggregation.After the16nm Fe3O4nanoparticles were oxidized under oxygen at250°C for6h,theirσs is reduced to 70emu/g,close to74emu/g from commercialγ-Fe2O3powder, suggesting the transformation of Fe3O4to Fe2O3.

Possible Mechanism for the Formation of Fe3O4.The mechanism leading to Fe3O4in the reactions presented is not yet clear.However,evidence suggests that reduction of the Fe(III)salt to an Fe(II)intermediate occurs,followed by the decomposition of the intermediate at high temperature.The formation of an Fe(II)intermediate was indicated by the fact that product separated after a short refluxing time(5min)instead of30min showed no magnetic response and contained FeO,as evidenced by XRD.Furthermore,in the presence of a slight excess of1-hexadecanethiol,a black powder corresponding to FeS(as characterized by ICP-OES analysis and XRD)could be separated.If Fe(II)(D-gluconate)or Fe(II)acetyl-acetonate was used,the same product was obtained.No metallic Fe was detected in the final product.

MFe2O4(M)Co,Mn)Nanoparticles.The process described in Scheme1can be readily extended to the synthesis of other types of MFe2O4nanoparticles.For example,when Co-(acac)2was partially substituted for Fe(acac)3in a1:2ratio in the same reaction conditions as in the synthesis of Fe3O4, CoFe2O4nanoparticles were formed.When Mn(acac)2was used, MnFe2O4nanoparticles were made.ICP-OES elemental analysis indicated that the ratio of Co/Fe and Mn/Fe in both cobalt ferrite and manganese ferrite was retained from the ratio of initial metal precursors,and the final Co/Fe and Mn/Fe compositions could be readily controlled.Figure7shows the TEM images of14 nm CoFe2O4nanoparticles and14nm MnFe2O4nanoparticles made from seed-mediated growth.XRD for both samples are very similar to that of Fe3O4,indicating the cubic spinel structure of the particles.At temperatures up to300K,16nm CoFe2O4 nanoparticles are ferromagnetic.Figure8shows the hysteresis loops of16nm CoFe2O4nanoparticles measured at both10and 300K.The coercivity of the assembly is about400Oe at300 K,but reaches20kOe at10K,much larger than that of the16 nm Fe3O4nanoparticles(450Oe at10K),indicating that the incorporation of the Co cation in the Fe-O matrix greatly increases the magnetic anisotropy of the materials.Such

anisotropy enhancement of CoFe2O4vs Fe3O4has also been observed in films deposited from aqueous solution.23To the contrary,the incorporation of Mn cation in the Fe-O matrix reduces the magnetic anisotropy of the materials,1a as the14 nm MnFe2O4nanoparticles shows a coercivity of only140Oe at10K.

Possible Applications of MFe2O4Nanoparticles.The MFe2O4nanoparticles presented above may have numerous applications in magnetic nanodevices and biomedicine,but additional requirements may arise from particular applications. For example,in biomagnetic applications,the superparamagnetic nanoparticles often need to be water-soluble.3,24Here we demonstrate briefly that superparamagnetic Fe3O4nanoparticles can be made water-soluble and yield a good magnetic signal that is suitable for spin valve sensor detection.

To make water-soluble iron oxide nanoparticles,we mix hydrophobic nanoparticles with a bipolar molecule,tetramethyl-ammonium11-aminoundecanoate.Shaking the hexane disper-

(22)Morales,M.P.;Veintemillas-Verdaguer,S.;Montero,M.I.;Serna,C.J.;

Roig,A.;Casas,L.;Martinez,B.;Sandiumenge,F.Chem.Mater.1999,

Figure7.TEM bright field images of(A)14nm CoFe2O4nanoparticles and(B)14nm MnFe2O4nanoparticles made from seed-mediated growth and deposited from their hexane dispersion on amorphous carbon-coated copper grid at room

temperature.

Figure8.Hysteresis loops of the16nm CoFe2O4nanoparticle assembly measured at(A)10K and(B)300K.

A R T I C L E S Sun et al.

sion of 6nm Fe 3O 4nanoparticles with a suspension of tetramethylammonium 11-aminoundecanoate in dicholoromethane rendered Fe 3O 4nanoparticles hydrophilic and water-soluble.Figure 9shows the IR spectra of both the hydrophobic nanoparticles (Figure 9A)and the hydrophilic ones (Figure 9B).The absorptions around 1565and 1478cm -1in Figure 9B from the hydrophilic nanoparticles match with the one from free tetramethylammonium 11-aminoundecanoate (1566,1487cm -1),indicating the existence of the free -COO -group in the hydrophilic nanoparticles.25Figure 9C is the TEM image of 6nm Fe 3O 4nanoparticles from aqueous dispersion.It indicates that nanoparticles in water are well dispersed without any noticeable agglomeration.

Magnetic nanoparticles dispersed in water are superparamag-netic and under a tickling field can yield good magnetic signals that are readily sensed by a spin valve sensor.Such a sensor has been patterned as rectangular strips with a submicron width and a magnetoresistance (MR)ratio of 10%and has shown great potential as a sensitive and efficient detector for biomolecules

labeled by magnetic nanoparticles.12,26We have performed several experiments on a monolayer of 16nm Fe 3O 4nanopar-ticles deposited on the 0.3μm wide spin valve sensors via poly-(ethylenimine)-mediated self-assembly.27These submicron spin valve sensors produced signals on the order of 10μV due to the presence of a layer of Fe 3O 4nanoparticles.This suggests that these magnetic nanoparticles,if functionalized with single-strand DNA and immobilized on a similarly functionalized spin valve surface via DNA hybridization,could be used as labels for highly sensitive and quantitative DNA detection.

Conclusions

We have reported a convenient organic phase process of making monodisperse MFe 2O 4nanoparticles through the reac-tion of metal acetylacetonate and 1,2-hexadecanediol.The diameter of the particles is tunable from 3to 20nm by varying reaction conditions or by seed-mediated growth.The process does not require a low-yield fractionation procedure to achieve the desired size distribution and is readily scaled up for mass production.The hydrophobic nanoparticles can be transformed into hydrophilic ones by mixing with bipolar surfactants,allowing preparation of aqueous nanoparticle dispersions.These iron oxide nanoparticles and their aqueous dispersions have great potential in magnetic nanodevice and biomagnetic applications.

Acknowledgment.The work is supported in part by DARPA

through ONR under grant nos.N00014-01-1-0885.H.Z.and D.B.R.thank the support from DARPA through Stanford University.

Supporting Information Available:Figure S1:Thermal

gravimetric analysis (TGA)results for hydrophilic Fe 3O 4and hydrophobic Fe 3O 4nanoparticles.This material is available free of charge via the Internet at https://www.sodocs.net/doc/6d8550953.html,.

JA0380852

(25)If the -COO -attaches to the surface of Fe 3O 4particles,the IR spectrum

will show absorptions in different region and intensity,as the IR spectrum of a model compound ferric stearate exhibits four broad,asymmetric peaks at 1466,1534,1589,1613cm -1.It should also be noted that whether or not the -NH 2in the 11-aminoundecanoate unit is bound to the particle surface has not been determined.From the IR data,we cannot exclude the presence of the oleate and oleylamine species in the hydrophilic particles.Thermal gravimetric analysis (TGA)(see Supporting Information)of this material shows a sharp mass loss at relatively low temperature (200°C),but above 300°C the curve seems similar to that of hydrophobic particles,losing mass between 380and 440°C.This seems to suggest that the bipolar surfactant does not displace a significant amount of the original ligands and is loosely bound,forming a bilayer or intercalated layer.

(26)(a)Baselt,D.R.;Lee,G.U.;Natesan,M,;Metzger,S.W.;Sheehan,P.E.;

Colton,R.J.Biosens.Bioelectron.1998,13,731.(b)Edelstein,R.L.;Tamanaha,C.R.;Sheehan,P.E.;Miller,M.M.;Baselt,D.R.;Whitman,L.J.;Colton,R.J.Biosens.Bioelectron.2000,14,805.(c)Miller,M.M.;Sheehan,P.E.;Edelstein,R.L.;Tamanaha,C.R.;Zhong,L.;Bounnak,S.;Whitman,L.J.;Colton,R.J.J.Magn.Magn.Mater .2001,225,138.(27)(a)Sun,S.;Anders,S.;Hamann,H.F.;Thiele,J.-U.;Baglin,J.E.E.;

Thomson,T.;Fullerton,E.E.;Murray,C.B.;Terris,B.D.J.Am.Chem.Soc.2002,124,2884.(b)Sun,S.;Anders,S.;Thomson,T.;Baglin,J.E.E.;Toney,M.F.;Hamann,H.F.;Murray,C.B.;Terris,B.D.J.Phys.Chem.B 2003,107,

5419.

Figure 9.(A)Infrared spectrum of the as-synthesized hydrophobic 6nm Fe 3O 4nanoparticles,(B)infrared spectrum of tetramethylammonium 11-aminoundecanoate-coated 6nm Fe 3O 4nanoparticles,and (C)TEM bright field image of the 6nm Fe 3O 4nanoparticles in (B)deposited from water dispersion on amorphous carbon-coated copper grid.

MFe 2O 4(M )Fe,Co,Mn)Nanoparticles A R T I C L E S

混合气体平均式量的几种计算方法

混合气体平均式量的几种计算方法 ⑴标准状态密度法:M=22.4(L·mol-1)×p(g·L-1); ⑵相对密度法:D=ρ1/ρ2= M1/M2; ⑶摩尔质量定义法:M=m(总)/n(总) ⑷物质的量或体积含量法M=MA·a%+Mb·b%+……(a%、b%等为各组分气体的体积分数或物质的量分数)。 二、2007年高考试题评析 【例1】(07年广东化学卷,第3题)下列叙述正确的是() A.48 g O3气体含有6.02×1023个O3分子 B.常温常压下,4.6g NO2气体含有1.81×1023个NO2分子 C.0.5mol/LCuCl2溶液中含有3.01×1023个Cu2+ D.标准状况下,33.6L 水含有9.03×1023个H2O分子 【解析】48 g O3的物质的量为1 mol,含O3分子6.02×1023个,A正确;由于存在2NO2N2O4这一隐含条件,故4.6g NO2气体中含有的NO2分子数应界于0.1NA 和0.05NA之间,B错误;由于不知道CuCl2溶液的体积,故无法确定Cu2+离子的数目,C错误;标准状况下,水为固态,不能用22.4L/mol进行计算。故本题应选A。 【例2】(07年四川理综卷,第7题)用NA代表阿伏加德罗常数,下列说法正确的是 A.标准状况下,22.4LCHCl3中含有的氯原子数目为3NA B.7gCnH2n中含有的氢原子数目为NA C.18gD2O中含有的质子数目为10NA D.1L 0.5 mol/L Na2CO3溶液中含有的CO32-数目为0.5NA 【解析】标准状况下,CHCl3为液态,不能用22.4L/mol进行计算,A项错误;B项中CnH2n 的最简式为CH2,其最简式的物质的量为7g/14g·mol-1=0.5mol,故其氢原子数为NA,B 正确;由于D2O的摩尔质量为20g/mol,则18gD2O的物质的量小于1 mol,C错误;由于在水溶液中CO32-要水解,故CO32-数目应小于0.5NA,D错误。故本题应选B。 【例3】(07年上海化学卷,第20题)设NA为阿伏加德罗常数,下列叙述中正确的是A.常温下,11.2L甲烷气体含有甲烷分子数为0.5NA B.14g乙烯和丙烯的混合物中总原子数为3NA C.0.1mol/L的氢氧化钠溶液含钠离子数为0.1NA个 D.5.6g 铁与足量稀硫酸失去电子数为0.3NA 【解析】A项中所给的条件并不是标准状况下,故甲烷的物质的量不是0.5 mol,故A项错误;B项中乙烯和丙烯的最简式为CH2,其最简式的物质的量为14g/14g·mol-1=1mol,故其总原子数为3NA,B项正确;由于不知道氢氧化钠溶液的体积,故无法确定钠离子的数目,C项错误;Fe与稀硫酸反应生成的是Fe2+,D项错误。故本题应选B。 【例8】(07年全国理综卷I,第9题)在三个密闭容器中分别充入Ne、H2、O2三种气体,当它们的温度和密度都相同时,这三种气体的压强(p)从大到小的顺序是() A.P(Ne)>P(H2)>P(O2) B.P(O2)>P(Ne)>P(H2) C.P(H2) >P(O2)>P(Ne) D.P(H2)>P(Ne)>P(O2) 【解析】根据上述阿伏加德罗定律推论“三反比”结论③“在相同温度下,同密度的任何气体的压强与其摩尔质量成反比”,得摩尔质量越小压强越大。由于三种气体的摩尔质量从小到大顺序为M(H2)<M(Ne)<M(O2),故其气体压强从大到小的顺序为P(H2)>P(Ne)>P(O2)。【综合点评】以上是考查阿伏加德罗常数及阿伏加德罗定律命题时的一些常见角度。阿伏加德罗常数试题是高考常见题型之一,尽管题型不变,但考查的知识却都千变万化。主要考查了对阿伏加德罗常数、物质的量、气体摩尔体积等概念的理解及简单计算,还经常涉及弱电

怎样计算混合物的密度

怎样计算混合物的密度 江苏丰县广宇中英文学校刘庆贺 两种物质混合,有如下的基本关系:混合物的总质量等于原来两种物质质量之和,即:m总=m1+m2;混合物的总体积等于原来两种物质体积之和,即:V总=V1+V2;混合物 的密度等于总质量与总体积之比,即:。解题时,需要根据具体情况,对上述公式灵活地选用。 【例1】某冶炼厂,用密度为ρ1金属和密度为ρ2的另一种金属以不同的配方(不同的比例搭配)炼成合金材料。若取等体积的这两种金属进行配方,炼出的金属材料密 度为ρ;若取等质量的这两种金属进行配方,炼出的金属材料密度为,请你通过数学运算,说明ρ与的大小关系。 解析:题目为两种固体的混合。取等体积混合时,设取相等体积为V,则密度为ρ1金属的质量为ρ1V,密度为ρ2的另一种金属的质量为ρ2V,炼出的金属材料密度为: 取等质量混合时,设取相等质量为m,则密度为ρ1金属的体积为m/ρ1,密度为ρ2的另一种金属的体积为m/ρ2,炼出的金属材料密度为: 要比较ρ与的大小关系,可用比值法或比差法。即因ρ与ρ均大于零,若ρ/ 大于1,则ρ>;若ρ/小于1,则ρ<.或若ρ-大于0,则ρ>;若ρ- 小于0,则ρ<。 答案:取等体积混合时,炼出的金属材料密度为:

取等质量混合时,炼出的金属材料密度为: 若用比差法,同学们可试着证明。 【例2】有密度分别为ρ1和ρ2的两种液体各m千克,只用这两种液体,最多可配制密度为ρ=1/2(ρ1+ρ2)的溶液多少千克?(已知ρ1>ρ2,不计混合过程中的体积变化) 解析:题目为两种液体的混合,由例1可知,要配制密度为ρ=1/2(ρ1+ρ2)的溶液,两种液体的体积必然要相等。再根据要配制的溶液最多,必然要有一种液体用完。而且是体积较小者,即密度为ρ1的液体要用完。这样,只须计算出另一种液体用多少质量即可。 答案:要配制密度为ρ=1/2(ρ1+ρ2)的溶液,两种液体的体积必然要相等。再根据题意可知,密度为ρ1的液体要用完。则 跟踪练习:从2005年12月起,我市开始推广使用乙醇汽油。乙醇汽油是一种由乙醇和普通汽油按一定比例混配形成的替代能源,其中普通汽油体积占90%,乙醇(即酒精)体积占10%。乙醇汽油能有效改善油品的性能和质量。它不影响汽车的行驶性能,还能减少有害气体的排放量。乙醇汽油的推广及使用,可以缓解因石油资源短缺而造成的经济压力,乙醇汽油作为一种新型清洁燃料,是目前世界上可再生能源的发展重点。 (1)请写出使用乙醇汽油的两点好处? ①;

多元混合气体在煤表面的竞争吸附分析

多元混合气体在煤表面的竞争吸附分析 摘要:煤的吸附与煤的氧化风化、燃烧与自燃、矿井瓦斯含量等有直接关系,而在工业实践中气体分离和净化所处理的对象又都是混合物,多组分气体吸附平衡理论成为吸附领域内的一个重点研究课题。针对我国煤矿自燃发严重以及与煤吸附多元混合气体相关实验缺乏的问题,本文从吸附数学模型、吸附影响因素对多元气体在煤表面的竞争吸附进行总结分析,找出当前我国煤吸附理论研究和技术应用中存在的问题和不足,对煤吸附研究的发展趋势和需要解决的问题作进一步的探讨。 关键词:煤;混合气体;吸附机理;吸附模型 1煤对气体的吸附机理研究现状近年来对于混合气体吸附理论的研究兴趣在增长,其动机在于利用平衡理论和数学模型,基于单组分气体的等温吸附线获得的信息来预测给定温度和压力下混合气中每一组分的吸附量。目前国内对这方面的研究较少,而且主要集中在液相吸附平衡。国外研究人员对于临界温度以下的多组分气体吸附平衡理论已做了大量的工作,在假设吸附相为饱和液体的基础上,从不同的角度出发,提出了许多预测多组分吸附平衡的模型和方法。 Moffat [3]、Ruthven[4]和Yang[5] 在各自的专著中均对多组分吸附平衡理论作了简要的介绍。 Stevenson[6] 等使用干煤样进行了CH4-N2-CO2 的二元和三元混

合气体的吸附测试。Greaves[7] 等在研究了混合气的吸附解吸后,发现吸附和解吸过程中压力与吸附量的关系存在显著差异,并将这种行为描述为滞后效应。唐书恒等[8] 研究认为煤中多元气体吸附时,各组分间相互影响为竞争吸附关系而且吸附一解吸应是一种动态平衡。王继仁和邓存宝[9][10][11] 等人应用量子化学密度泛函理论对矿井采空区各种混合气体进行研究,,研究得出煤表面与各种气体发生吸附的亲和顺序为: O2>H2O>CO2>N2>CO>CH4 。 现在普遍认为多元气体吸附时,每种气体不是独立吸附的,之间存在着吸附位的竞争。而煤的吸附研究现集中在对气体分子如 CH4 、CO2、N2、O2 和重金属离子上,对单组分和多组分气体的吸附建立了不同的模型,这些模型尚不能完全模拟煤对气体的吸附过程,对其进行完善将成为未来研究的重要课题之一。 2煤表面对多种气体吸附模型目前,吸附领域针对不同的吸附系统和基于不同的假设,研究者提出了许多等温吸附理论模型。如Langmuir 单分子层定位吸附模型、BET 多分子层吸附模型、基于吸附势理论的各类等温吸附模型以及毛细管填充理论等在煤的吸附研究中都有一定的应用[12] 。吸附等温线是反应吸附量和平衡压力的曲线,是对吸附现象以及吸附剂表面结构进行研究的基础数。IUPAC 将吸附等温线分为六种类型[13] :图1 IUPAC 的六种等温吸附曲线 I型适用于无孔均一表面的单分子层吸附或微孔吸附

物质的量计算专题-混合气体

1.(2018海南卷) NA代表阿伏加德罗常数的值,下列说法正确的是( ) A.12 g金刚石中含有化学键的数目为4N A B. 18 g的D2O中含有的质子数为10N A C. 28 g的乙烯和环己烷混合气体中所含原子总数为6 N A D. 1L 1 mol.L-1,的NH4Cl溶液中NH4+和Cl-的数目均为1N A 2. (2018年全国卷II) N A代表阿伏加德罗常数的值。下列说法正确的是() A. 常温常压下,124 g P4中所含P—P键数目为4N A B. 100 mL 1mol·L?1FeCl3溶液中所含Fe3+的数目为0.1N A C. 标准状况下,11.2 L甲烷和乙烯混合物中含氢原子数目为2N A D. 密闭容器中,2 mol SO2和1 mol O2催化反应后分子总数为2N A 3. 题组训练二:正误判断,正确的划“√”,错误的划“×” (1) 在相同条件下,相同物质的量CO、N2的混合气体与O2的分子个数相同,原子个数也相同() (2) 在同温同压下,体积相同的任何气体或混合气的物质的量相同( ) (3)分子总数为N A的NO2和CO2混合气体中含有的氧原子数为2N A () (4)常温常压下,14 g由N2与CO组成的混合气体含有的原子数目为N A() (5)28 g乙烯和环丁烷(C4H8)的混合气体中含有的碳原子数为2N A() (6)常温常压下,92 g的NO2和N2O4混合气体含有的原子数为6N A() (7)120g 由NaHSO4和KHSO3组成的混合物含有N A硫原子中() (8)常温常压下,22.4 L的NO2和CO2混合气体含有2n A个O原子()(9)常温常压下,2.24LCO和CO2混合气体中含有的碳原子数目为0.1N A() 4.在下列条件下,两种气体的分子数一定相等的是() A.同密度、同压强的N2和C2H4 B.同温度、同体积的O2和N2 C.同体积、同密度的C2H4和CO D.同压强、同体积的O2和N2 5.下列两种气体的分子数一定相等的是()。 A.质量相等、密度不同的N2和C2H4 B.体积相等的CO和N2 C.等温、等体积的O2和N2 D.等压、等体积的N2和CH4 6. 3.用N A表示阿伏加德罗常数的值,下列说法正确的是()。 A.100 mL 0.1 mol·L-1 Na2SO4溶液中,粒子总数是0.03N A B.1 mol Al3+完全水解生成氢氧化铝胶体粒子的数目为N A C.常温常压下,32 g O-2中所含电子的数目为17N A D.标准状况下,分子数为N A的N2、C2H4混合气体的质量无法确定

气体吸附分析技术知识讲解

目前,气体吸附分析技术作为多孔材料比表面和孔径分布分析的不可或缺的手段,得到了广泛应用。物理吸附分析不仅应用于传统的催化领域,而且渗透到新能源材料、环境工程等诸多领域。 本专题分为基础篇,实验篇和应用篇,旨在以实用为目的,力求避免冗余和数学公式,按实验的思维顺序逐步理清物理吸附相关的疑难点。当然,对于一些比较复杂的问题,我们将会专门出专题文章进行介绍。 1. 什么是表面和表面积? 表面是固体与周围环境, 特别是液体和气体相互影响的部分;表面的大小即表面积。表面积可以通过颗粒分割(减小粒度)和生成孔隙而增加,也可以通过烧结、熔融和生长而减小。 2. 什么是比表面积? 为什么表面积如此重要? 比表面积英文为specific surface area,指的是单位质量物质所具有的总面积。分外表面积、内表面积两类。国际标准单位为㎡/g。表面积是固体与周围环境,特别是液体和气体相互作用的手段和途径。一般有下列三种作用:1) 固体-固体之间的作用:表现为自动粘结,流动性(流沙),压塑性等。2) 固体-液体之间的作用:表现为浸润,非浸润,吸附能力等。3) 固体-气体之间的作用:表现为吸附,催化能力等。 3. 什么是孔? 根据ISO15901 中的定义,不同的孔(微孔、介孔和大孔)可视作固体内的孔、通道或空腔,或者是形成床层、压制体以及团聚体的固体颗粒间的空间(如裂缝或空隙) 4. 什么是开孔和闭孔? 多孔固体中与外界连通的空腔和孔道称为开孔(open pore),包括交联孔、通孔和盲孔。这些孔道的表面积可以通过气体吸附法进行分析。除了可测定孔外,固体中可能还有一些孔,这些孔与外表面不相通,且流体不能渗入,因此不在气体吸附法或压汞法的测定范围内。不与外界连通的孔称为闭孔(close pore)。开孔与闭孔大多为在多孔固体材料制备过程中形成的,有时也可在后处理过程中形成,如高温烧结可使开孔变为闭孔。 5. 什么是孔隙度? 孔隙度是指深度大于宽度的表面特征,一般用孔径及其分布和总孔体积表征。 6. 什么是多孔材料? 多孔材料是一种由相互贯通或封闭的孔洞构成网络结构的材料,孔洞的边界或表面由支柱或平板构成。多孔材料可表现为细或粗的粉体、压制体、挤出体、片体或块体等形式。其表征通常包括孔径分布和总孔体积或孔隙度的测定。在某些场合,也需要考察其孔隙形状和流通性,并测定内表面和外表面面积。

燃气基本性质计算公式

计算公式 探公式分类宀燃气基本性质| 来源:《燃气燃烧与应 -华白数计算 中 用》 公式说明: 公式: 参数说明:W ——华白数,或称热负荷指数; H ――燃气热值(KJ/Nm 3),按照各国习惯,有些取用高热值,有些取用低热值; S ――燃气相对密度(设空气的S=1)o 公式说明: 含有氧气的混合气体 爆 炸极限 来源:《燃气输配》 中 国建筑工业岀版社 2003-6-30 2003-11-12

公式: 参数说明:L T――包含有空气的混合气体的整体爆炸极限(体积%); L nA――该混合气体的无空气基爆炸极限(体积%); y AiR -------- 空气在该混合气体中的容积成分(%)。 含有惰性气体的混合来源:《燃气输配》中 2003-6-30 气体的爆炸极限国建筑工业岀版社 公式说明: 公式: 参数说明:L——含有惰性气体的可燃气体的爆炸极限(体积%); L c――该燃气的可燃基(扣除了惰性气体含量后、重新调整计算岀的各燃气容积成分)的爆炸极限值(体积%); yN——含有惰性气体的燃气中,惰性气体的容积成分(% )。

公式说明: 公式: 参数说明:L ――混合气体的爆炸(下上)限(体积 %); L 1、L 2……L n ——混合气体中各可燃气体的爆炸下(上)限(体积 %); 屮、y ……y n ——混合气体中各可燃气体的容积成分( %) 液态碳氢化合物的容 来源:《燃气输配》 中 积膨胀 国建筑工业岀版社 公式说明: 只含有可燃气体的混 合气体的爆炸极限 来源:《燃气输配》 中 国建筑工业岀版社 2003-6-30 2003-6-30

冷凝及吸附特点介绍

江苏中川通大环保设备制造有限公司 冷凝法冷凝法、、冷凝+吸附吸附法法的介绍 1 油气回收方法简介 1.1冷凝法 冷凝法油气回收工艺是依据汽油油气组分的基本热力学性质参数,采用烃类物质在不同温度下的蒸汽压差异,通过降温使油气中一些烃类蒸汽压达到过饱和状态,过饱和油气组分产生相变,从气态变为液态,得到液态汽油。冷凝法是一次性工艺就完成对油气的回收利用的唯一方法,而且能够见到可以计量的回收汽油。对于苯类蒸气,由于其沸点都比较高、熔点也都不是很低,容易实现冷凝回收的处理。 近二十余年,传统行业与新兴产业得到有效结合,制冷技术实现了系统化、信息化、绿色化。美国机械工程师协会ASME 评选出的20世纪十大工程成就中,制冷技术名列第七。低温制冷技术、新型制冷压缩机产品得到长足发展,技术成熟、质量稳定、体积缩小、能耗减少。促进了油气回收冷凝工艺技术的进步。 1.2 吸附法 将收集的汽油油气送进吸附罐内,以活性炭或分子筛沸石或硅胶等有丰富孔容的吸附剂,将油气先储存起来,让空气排放。待油气吸附量达到一定程度,再脱附取出油气成分。脱附油气的方法有高温水蒸汽冲刷或抽真空的方式。如果以水蒸汽脱附,脱附的油气混入凝结水中,需要进行油水分离处理。如果抽真空脱附,脱附出来的只是气态富集油气,要使其转变为液态,还需要采用冷凝或喷淋冷汽油的方法作二次处理。 2 回收方法之于油气回收适用性分析 2.1 冷凝法的适用性分析

(1)冷凝法先将汽油油气回收为液态。回收的液态烃可以一定的稳定性单独储存。如果洁净度等指标达不到成品油标准,处理至达标的总量很小;或者将回收的油定性为污油一次性回收。 (2)冷凝法冷后仍有一定的残余浓度,根据冷凝至冷温度的饱和蒸汽压数据可以测算出冷后的残余浓度。一般油气在-50℃时的残余浓度为80g/m3左。 (3)冷凝法处理较轻组分的油气(如C2、C3等)、需要深低温(-110℃),具体可根据具体油气的组分数据确定合适而经济的深冷冷温度。 (4)与吸附法组合实现优势强化,缺陷互补。 2.2 吸附法适用性分析 (1)对控制尾气达标排放具有一定优势。 (2)其入口浓度宜低不宜高。活性炭直接吸附高浓度油气,工况恶劣,容易产生吸附热而增加不安全因素和降低活性炭的寿命。对于大处理量、较高浓度的油气处理单元不适合。 (3)与冷凝法组合时,与冷凝法较低的油气残余浓度相适应和互补,可以作为冷凝法的尾气达标控制单元。 3 冷凝+吸附组合工艺优点 综上几种油气回收方法之于本案的介绍,根据冷凝法可使处理气体的浓度有效降低和吸附法适合于处理低浓度油气混合气的特点,结合汽油油气排放的特点,综合相关技术的发展现状,认为冷凝+吸附的组合处理工艺是冷凝法基础上进行优化的一种油气处理方法,为汽油油气回收工艺路线之优选。 冷凝+吸附的组合工艺优点总结如下: (1)冷凝可以在浅冷将油气浓度降低到很低的浓度,但大流量下达到国家排放标准(25g/m3)时需要功率较大;吸附法只适合于低浓度油气吸、脱附。两者结合,优势互补。

混合气体平均摩尔质量的求算

混合气体摩尔质量(或相对分子质量)的计算 (一)平均摩尔质量的概念 (1)已知标况下密度,求相对分子质量. 相对分子质量在数值上等于气体的摩尔质量,若已知气体在标准状况下的密度ρ,则Mr 在数值上等于M =ρ·22.4L/mol (2)已知相对密度,求相对分子质量 若有两种气体A 、B 将)()(B A ρρ与的比值称为A 对B 的相对密度,记作D B ,即 D B =)()(B A ρρ,由推论三,)()()()(B A B Mr A Mr ρρ==D B ? Mr(A)=D B ·Mr(B) 以气体B (Mr 已知)作基准,测出气体A 对它的相对密度,就可计算出气体A 的相对分子质量,这也是测定气体相对分子质量的一种方法.基准气体一般选H 2或空气. (3)已知混和气体中各组分的物质的量分数(或体积分数),求混和气体的平均相对分子质量. 例 等物质的量的CO 、H 2的混和气,气体的平均相对分子质量Mr. 单位物质的量的混合物所具有的质量叫做平均摩尔质量。 符号: 单位:g·mol -1 例如:空气的平均摩尔质量为29g·mol -1 平均摩尔质量不仅适用于气体,对固体和液体也同样适用, 常用于混合物的计算

解:平均相对分子质量在数值上等于平均摩尔质量,按照摩尔质量的定义 设CO 、H 2的物质的量均为1mol M = mol g mol mol g mol mol g mol n m /152/21/281==总总 ?+? 由此例推广可得到求M 的一般公式: 设有A 、B 、C …诸种气体 M = ++++=总总)()()()()()(B n A n B n B M A n A M n m ?? [推论一] M =M(A)·n(A)%+M(B)n(B)%+…… [推论二] M =M(A)·V(A)%+M(B)·V(B)%+…… 例:1.空气的成分N 2约占总体积的79%,O 2约占21%,求空气的平均相对分子质量. 2.由CO 2、H 2和CO 组成的混合气在同温同压下与氮气的密度相同,则该混合气体中CO 2、H 2和CO 的体积比为 A.29:8:13 B.22:1:14 C.13:8:29 D.26:16:57

天然气流量计算公式

(1)差压式流量计 差压式流量计是以伯努利方程和流体连续性方程为依据,根据节流原理,当流体流经节流件时(如标准孔板、标准喷嘴、长径喷嘴、经典文丘利嘴、文丘利喷嘴等),在其前后产生压差,此差压值与该流量的平方成正比。在差压式流量计中,因标准孔板节流装置差压流量计结构简单、制造成本低、研究最充分、已标准化而得到最广泛的应用。孔板流量计理论流量计算公式为: 式中, qf 为工况下的体积流量, m3/s ; c 为流出系数, 无量钢; β =d/D , 无量钢; d 为工况下孔板径, mm

D 为工况下上游管道径, mm ; ε 为可膨胀系数,无 量钢; Δ p 为孔板前后的差压值, Pa ; ρ 1 为工况下流体的密度, kg/m3 。 对于天然气而言,在标准状态下天然气积流量的实用计算公式为: 式中, qn 为标准状态下天然气体积流量, m3/s

As 为秒计量系数,视采用计量单位而定, 此式 As=3.1794×10 -6 ; c 为流出系数; E 为渐近速度系数; d 为工况 下孔板径, mm ; FG 为相对密度系数, ε 为可膨胀系数; FZ 为超压缩因子; FT 为流动湿度系数;

为孔板上游侧取压孔气流绝对静压, MPa ; Δ p 为气流流经 孔板时产生的差压, Pa 。 差压式流量计一般由节流装置(节流件、测量管、直管段、流动调整器、取压管 路) 和差压计组成, 对工况变化、 准确度要求高的场合则需配置压力计 (传感器 或变送器)、温度计(传感器或变送器)流量计算机,组分不稳定时还需要配置 在线密度计(或色谱仪)等。 ( 2 )速度式流量计

吸附剂一般有以下特点

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2、几种常见吸附剂的特性 (1)活性氧化铝是由铝的水合物加热脱水制成,它的性质取决于最初氢氧化物的结构状态,一般都不是纯粹的Al2O3,而是部分水合无定形的多孔结构物质,其中不仅有无定形的凝胶,还有氢氧化物的晶体。由于它的毛细孔通道表面具有较高的活性,故又称活性氧化铝。它对水有较强的亲和力,是一种对微量水深度干燥用的吸附剂。在一定操作条件下,它的干燥深度可达露点‐70℃以下。市售的层析用氧化铝有碱性、中性和酸性三种类型,粒度规格大多为100~150目。 碱性氧化铝(pH9—10):适用于碱性物质(如胺、生物碱)和对酸敏感的样品(如缩醛、糖苷等),也适用于烃类、甾体化合物等中性物质的分离。但这种吸附剂能引起被吸附的醛、酮的缩合。酯和内酯的水解、醇羟基的脱水、乙酰糖的去乙酰化、维生素A和K等的破坏等不良副反应。所以,这些化合物不宜用碱性氧化铝分离。 酸性氧化铝(pH3.5—4.5):适用于酸性物质如有机酸、氨基酸等以及色素和醛类化合物的分离。 中性氧化铝(pH7—7.5):适用于醛、酮、醌、苷和硝基化合物以及在碱性介质中不稳定的物质如酯、内酯等的分离,也可以用来分离弱的有机酸和碱等。 (2)硅胶:硅胶是硅酸的部分脱水后的产物,其成分是SiO2·xH2O,又叫缩水硅酸。是一种坚硬、无定形链状和网状结构的硅酸聚合物颗粒,为一种亲水性的极性吸附剂。它是用硫酸处理硅酸钠的水溶液,生成凝胶,并将其水洗除去硫酸钠后经干燥,便得到玻璃状的硅胶,它主要用于干燥、气体混合物及石油组分的分离等。工业上用的硅胶分成粗孔和细孔两种。粗孔硅胶在相对湿度饱和的条件下,吸附量可达吸附剂重量的80%以上,而在低湿度条件下,吸附量大大低于细孔硅胶。

理想状态下气体的密度公式

理想状态下气体的密度公式 PV=Nrt ① ρ=M/V ② 由①②得: ρ=PM/nRT 对1摩尔气体,有: ρ=PM/RT 式中ρ为密度,P为压强,M为质量,V为体积,n为物质的量,R为常数。 记得普通物理讲的理想气体公式: PV = nRT (P:气压,V:体积,n:物质的量,R:常数,T:温度)。 刚刚看书,却有这样的公式, ________________ Q2 = Q1*√(P1*T2)/(P2*T1) Q是流量,立方米/秒。 我的问题是那个平方根从那里来的? 气体流量测量的温度与压力补偿 汤良焕 摘要综述了干、湿气体及水蒸气流量测量中的温度、压力补偿方案,还介绍了其它类型流量计的温度、压力补偿,指出几点应注意的问题。 关键词:流量测量气体流量温度补偿压力补偿 The Temperature and Pressure Compensations for Gas Flow Measurement Abstract The strategies of the temperature and pressure compensations for flow measurements of dry gas,wet gas and steam are described.The temperature and pressure compensations for other types of flow meters are also introduced.Some cautions are pointed out. Key words:Flow measurement Gas flow Temperature compensation Pressure compensation 由于气体的可压缩性,决定了它的流量测量比液体复杂,仪表的输出信号除了与输入信号有关,还与气体密度有关,而气体的密度又是温度和压力(简称温压)的函数。所以,气体的流量测量普遍存在温压补偿问题。在仪表的设计或对旧设备的改造中,气体流量测控系统应尽可能采用微机化仪表,根据被测气体及仪表类型,选用合适的数学模型,实施温压自动补偿。

气体吸附原理及过程

气体吸附原理及过程 一切物质都是由原子组成的。气态的原子和分子可以自由地运动。相反,固态时原子由于相邻原 子间的静电引力而处于固定的位置。但固体最外层(或表面)的原子比内层原子周围具有更少的相邻 原子。为了弥补这种静电引力不平衡,表面原子就会吸附周围空气中的气体分子。整个固体表面吸附 周围气体分子的过程称为气体吸附。事实证明,监测气体吸附过程能够得到丰富的关于固体特征的有 用信息。 在进行气体吸附实验之前,固体表面必须清除污染物,如水和油。表面清洁(脱气)过程,大多 数情况下是将固体样品置于一玻璃样品管中,然后在真空下加热。图1 展示了预处理后的固体颗粒表 面,其含有裂纹和不同尺寸和形状的孔。 样品一旦清洁后,就要转移至外置的杜瓦瓶(或其它恒温浴或高温炉)中使其处于恒温状态。然 后,使少量的气体(被吸附物,即吸附质)逐步进入被抽真空的样品管。进入样品管的吸附质分子很 快便到达固体样品(即吸附剂)上每一个孔的表面。这些分子要么从表面弹回,要么粘着于固体表面。 气体分子被粘着于固体表面的现象就称为被吸附。通过被吸附分子与表面间的相互作用力的大小可以 判定吸附过程本质上是物理吸附(作用力弱)还是化学吸附(作用力强)。

物理吸附 物理吸附是最普通的一种吸附类型。被物理吸附的分子可以相当自由地在样品表面移动。随着越 来越多的气体分子被导入体系,吸附质分子会在整个吸附剂表面形成一个薄层。根据著名的BET 理 论,假设被吸附分子为单分子层,我们可以估算出覆盖整个吸附剂表面所需的分子数Nm(见图2)。 被吸附分子数Nm 与吸附质分子的横截面积的乘积即为样品的表面积。 继续增加气体分子的通入量则会导致多层吸附。多层吸附过程与毛细管凝聚过程(见图3)是同 时进行的。后一过程可由开尔文方程进行充分的描述。该方程量化了剩余(或平衡)气体压力与能凝 聚气体的毛细管尺寸的比例。利用Barrett, Joyner and Halenda (BJH) 法等计算方法可以根据平衡气体 压力计算孔径。所以我们可以做出被吸附气体的体积与相对饱和平衡气压之间的实验曲线

气体吸附原理及过程

2005.1
气体吸附原理及过程
The Gas Sorption Process ABC in 30 minutes 一切物质都是由原子组成的。气态的原子和分子可以自由地运动。相反,固态时原子由于相邻原 子间的静电引力而处于固定的位置。但固体最外层(或表面)的原子比内层原子周围具有更少的相邻 原子。为了弥补这种静电引力不平衡,表面原子就会吸附周围空气中的气体分子。整个固体表面吸附 周围气体分子的过程称为气体吸附。事实证明,监测气体吸附过程能够得到丰富的关于固体特征的有 用信息。 在进行气体吸附实验之前,固体表面必须清除污染物,如水和油。表面清洁(脱气)过程,大多 数情况下是将固体样品置于一玻璃样品管中,然后在真空下加热。图 1 展示了预处理后的固体颗粒表 面,其含有裂纹和不同尺寸和形状的孔。 样品一旦清洁后,就要转移至外置的杜瓦瓶(或其它恒温浴或高温炉)中使其处于恒温状态。然 后,使少量的气体(被吸附物,即吸附质)逐步进入被抽真空的样品管。进入样品管的吸附质分子很 快便到达固体样品(即吸附剂)上每一个孔的表面。这些分子要么从表面弹回,要么粘着于固体表面。 气体分子被粘着于固体表面的现象就称为被吸附。 通过被吸附分子与表面间的相互作用力的大小可以 判定吸附过程本质上是物理吸附(作用力弱)还是化学吸附(作用力强) 。
4)
图1 图2 图3 图4
放大的固体颗粒的横截面 饱和度大约为 15%时的单分子吸附层 饱和度大约为 70%时的多层吸附/毛细管凝聚状态 饱和度大约为 100%时的所有孔(总孔)体积填充状态

物理吸附 物理吸附是最普通的一种吸附类型。被物理吸附的分子可以相当自由地在样品表面移动。随着越 来越多的气体分子被导入体系,吸附质分子会在整个吸附剂表面形成一个薄层。根据著名的 BET 理 论,假设被吸附分子为单分子层,我们可以估算出覆盖整个吸附剂表面所需的分子数 Nm(见图 2) 。 被吸附分子数 Nm 与吸附质分子的横截面积的乘积即为样品的表面积。 继续增加气体分子的通入量则会导致多层吸附。多层吸附过程与毛细管凝聚过程(见图 3)是同 时进行的。后一过程可由开尔文方程进行充分的描述。该方程量化了剩余(或平衡)气体压力与能凝 聚气体的毛细管尺寸的比例。利用 Barrett, Joyner and Halenda (BJH) 法等计算方法可以根据平衡气体 压力计算孔径。所以我们可以做出被吸附气体的体积与相对饱和平衡气压之间的实验曲线(即等温 线) ,再对其进行转换,就可以得到累积的或微分孔径分布图。 随着平衡吸附质压力趋于饱和,孔就被吸附质完全填充(见图 4) 。如果知道吸附质的密度,就 可以计算出其所占的体积,然后就可以相应地计算出样品的总孔体积。如果此时我们将吸附过程逆向 操作,从体系中逐步减少气体量,也可以得到脱附等温线。由于吸附和脱附机理不同,吸附和脱附等 温线很少能够重叠。等温线的迟滞现象与固体颗粒的孔形有关。 与物理吸附不同,化学吸附是因为吸附质分子和表面特定位置,即化学活性部位,形成了强的化 学键。因此,化学吸附的基本用途是计算可能引起化学和催化反应的表面活性部位的数量。 附:一些吸附剂的孔结构照片
粉煤灰
天然沸石分子筛
放射虫类
刺金
炭黑

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