Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Synthes of Highly Ordered,Hydrothermally Stable, Mesoporous Silica Structures
Dongyuan Zhao,†,‡Qisheng Huo,†,‡Jianglin Feng,‡Bradley F.Chmelka,‡,§and
Galen D.Stucky*,†,‡
Contribution from the Department of Chemistry,Materials Rearch Laboratory,and Department of Chemical Engineering.Uni V ersity of California,Santa Barbara,California93106
Recei V ed No V ember25,1997
Abstract:A family of highly ordered mesoporous(20-300Å)silica structures have been synthesized by the u of commercially available nonionic alkyl poly(ethylene oxide)(PEO)oligomeric surfactants and poly-(alkylene oxide)block copolymers in acid media.Periodic arrangements of mescoscopically ordered pores with cubic Im3h m,cubic Pm3h m(or others),3-d hexagonal(P63/mmc),2-d hexagonal(p6mm),and lamellar (L R)symmetries have been prepared.Under acidic conditions at room temperature,the nonionic oligomeric surfactants frequently form cubic or3-d hexagonal mesoporous silica structures,while the nonionic triblock copolymers tend to form hexagonal(p6mm)m
esoporous silica structures.A cubic mesoporous silica structure (SBA-11)with Pm3h m diffraction symmetry has been synthesized in the prence of C16H33(OCH2CH2)10OH (C16EO10)surfactant species,while a3-d hexagonal(P63/mmc)mesoporous silica structure(SBA-12)results when C18EO10is ud.Surfactants with short EO gments tend to form lamellar mesostructured silica at room temperature.Hexagonal mesoporous silica structures with d(100)spacings of64-77Åcan be synthesized at100°C by using oligomeric nonionic surfactants.Highly ordered hexagonal mesoporous silica structures (SBA-15)with unusually large d(100)spacings of104-320Åhave been synthesized in the prence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(PEO-PPO-PEO)copolymers.SBA-15 mesoporous structures have been prepared with BET surface areas of690-1040m2/g,pore sizes of46-300Å,silica wall thickness of31-64Å,and pore volumes as large as2.5cm3/g.A novel cubic(Im3h m)cage-structured mesoporous silica structure(SBA-16)with a large cell parameter(a)176Å)has been synthesized using triblock copolymers with large PEO gments.The EO/PO ratio of the copolymers can be ud to control the formation of the silica mesopha:lowering this ratio of the triblock copolymer moieties promotes the formation of lamellar mesostructured silica,while higher ratios favor cubic mesostructured silica.Cubic mesoporous structures are also obtained when star diblock copolymers are ud as structure-directing agents. The calcined ordered mesoporous silicas reported in this paper are therm
ally stable in boiling water for at least48h.The asmbly of the inorganic and organic periodic composite materials appears to take place by a hydrogen bonding(S0H+)(X-I+)pathway.The asmbly rate r increas with increasing concentration of [H+]and[Cl-],according to the kinetic expression r)k[H+]0.31[Cl-]0.31.
Introduction
Nonionic alkyl poly(oxyethylene)surfactants and poly(oxy-alkylene)block copolymers are important families of surfactants that are widely ud in emulsifying,defoaming/antifoaming, coating,thickening,solubilizing,cleaning,lubricating,wetting, pharmaceutical,1coal and petrochemical industries,and hou-hold applications.2-4They display excellent interfacial stabi-lization properties and are low-cost,nontoxic,and biodegradable.
In composite materials synthesis,nonionic block copolymers are an interesting class of structure-directing agents who lf-asmbly characteristics lead to kinetically quenched structures. Block copolymers have the advantage that their ordering properties can be nearly continuously tuned by adjusting solvent composition,molecular weight,or copolymer architecture. Moreover,they permit solution organization of larger structural features than is possible with low-molecular-weight surfacta
nts, and they achieve this from lower solution concentrations.Novel morphologies and material properties can be produced by exploiting kinetically hindered microdomain parations in such systems,using as a guide insight on the existence and quence of mesoscopic morphologies obtained in cloly related co-polymer/homopolymer blends.5Clo analogies also exist in strictly organic systems,in which heterogeneous nanoscale structures have been controllably produced and stabilized as block copolymer composites containing polymerizable additives.
†Department of Chemistry.
‡Materials Rearch Laboratory.
§Department of Chemical Engineering.
(1)Schmolka,I.R.In Polymers for Controlled Drug Deli V ery;Tarcha, P.J.,Ed.;CRC Press:Boston,1991;Chapter10.
(2)Chu,B.;Zhou,Z.In Nonionic Surfactants:Polyoxyalkylene Block Copolymers;Nace,V.M.,Ed.;Surface Science Series Vol.60;Marcel Dekker:New York,1996.
(3)Sjo¨blom,J.;Stenius,P.;Danielsson,I.In Nonionic Surfactants: Physical Chemistry;Nace,V.M.,Ed.;Su
rface Science Series Vol.23;
Marcel Dekker:New York,1987.
(4)Meziani,A.;Tourand,D.;Zradba,A.;Pulvin,S.;Pezron,I.;Claus, M.;Kunz,W.J.Phys.Chem.B1997,101,3620.
(5)Matn,M.W.Macromolecules1995,28,5765.Matn,M.W.; Schick,M.Curr.Opin.Colloid Interface Sci.1996,1,329.
监视设备
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S0002-7863(97)04025-0CCC:$15.00©1998American Chemical Society
Published on Web06/09/1998
An excellent example of this is the work of Hillmyer et al.in which they lectively incorporated and cross-linked a thermo-tting epoxy resin in the PEO domains of a poly(ethylene oxide)-poly(ethylethylene)(PEO-PEE)diblock copolymer.6 The overall strategy of using block copolymers in materials synthesis is thus applicable not only to composites containing hydrophilic-hydrophobic cop
olymers,such as the silica-poly-(alkylene oxide)system,7but more generally to any lf-asmbling surfactant or copolymer system in which a network-forming additive is lectively partitioned among different mesostructured components.An enormous variety of nanopha-parated composite materials can be envisioned in which variations in the choice of blocks,copolymer compositions, solvents,or chain architecture are ud to tune lf-asmbly, while processing variables such as temperature,pH,aligning fields,etc.,are manipulated to regulate fixation of the resultant structure(s).
Pinnavaia and co-workers8,9ud nonionic surfactants in aqueous solutions to synthesize wormlike disordered mesopo-rous silica and alumina in neutral media asmbled by hydrogen-bonding interactions.8-10Attard et al.11have synthesized hexagonal mesoporous silica phas using concentrated(∼50 wt%)C12EO8solutions and suggested that the formation of mesoporous silica under the conditions occurs by a“real”liquid crystal template route.It should be noted,however,that the methanol produced by hydrolysis of tetramethyl orthosilicate (TMOS)initially destroys the liquid crystalline order formed by the surfactant.This,along with the varying concentration of water during the hydrolysis of TMOS and condensation of silica species under acid synthesis conditions,make the pres-ervation of the liquid crystalline order throughout the composite asmbly process questionable.12,13
Templin et al.14have ud high concentrations of poly-(isoprene-b-ethylene oxide)diblock copolymers(PI-b-PEO)to make lamellar and hexagonal aluminosilicate-polymer meso-structures that are highly ordered on length scales to∼40nm. The synthes were carried out in an acidic and nonaqueous solution(a mixture of CHCl3and tetrahydrofuran).The thermal stability of the materials and removal of the organic pha to create mesoporous structures has not yet been described. Mesoporous silica materials organized with nonionic surfac-tant species that display periodic structural order and that are made under neutral or basic synthesis conditions have not yet been reported.Of considerable interest in this regard is the report by Voegtlin et al.15of the synthesis of ordered mesopo-rous silica that gives an improved X-ray diffraction pattern by using nonionic surfactants in the prence of fluoride anions under near-neutral conditions.They postulate that the F-ions are coordinated to silica intermediates,S0H+(F-I0),which apparently provide sufficient electrostatic shielding and effective hydrogen bonding to form mesoporous silica structures that yield relatively narrow(100)Bragg diffraction peaks(full width at half-maximum(fwhm))0.15-0.5with Cu K R radiation). For veral reasons,including product cost,environmental, and biomimetic considerations,we have sought to u dilute aqueous organic concentrations in silica composite and meso-porous materials synthes.Built into this has been the idea of cooperative lf-asmbly16-18of the molecular inorganic and organic species,which together influence the final morphology and
mesoscopic ordering obtained and both of which can be controlled kinetically and via inorganic-organic interface interactions.
Consistent with the results of Voegtlin et al.15and our earlier studies,17-19balanced Coulombic,hydrogen bonding,and van der Waals interactions with charge matching in aqueous synthes provide an effective means of enhancing long-range periodic order.Such interactions are particularly important at the inorganic-organic interface and can be realized by working with cationic silica species below the aqueous isoelectric point of silica(pH∼2).With cationic surfactants and synthes carried out in HCl media below the aqueous isoelectric point of silica,the key interactions are among the cationic surfactant, chloride anion,and the cationic silica species(designated as S+X-I+,where S+is the cationic surfactant,X-is the halide anion,and I+is a protonated Si-OH ,[SiO
H
H]+,and the overall charge balance is provided by association with an additional halide anion).19,20
Solubilization of nonionic poly(alkylene oxide)surfactants and block copolymers in aqueous media is due to the association of water molecules with the alkylene oxide moieties through hydrogen bondin
g.2This should be enhanced in acid media where hydronium ions,instead of water molecules,are associ-ated with the alkylene oxygen atoms,thus adding long-range Coulombic interactions to the coasmbly process.If carried out below the aqueous isoelectric point of silica,cationic silica species will be prent as precursors,and the asmbly might be expected to proceed through an intermediate of the form (S0H+)(X-I+).The anion may be coordinated directly to the silicon atom through expansion of the silicon atom’s coordina-tion sphere.Our goal in this rearch was to u this structure-directing route to create highly ordered structures with low-cost,nontoxic,and biodegradable nonionic organics under relatively dilute aqueous conditions.In particular,we cho to investigate the u of block copolymers in order to extend the range and control of inorganic-organic mesopha structures from nanometer to larger length scales.7
Here we report new mesoporous silica structures that include cubic(Im3h m and Pm3h m),three-dimensional hexagonal(P63/ mmc),two-dimensional hexagonal(p6mm),possibly continuous L3sponge and lamellar(L R)mesostructures synthesized by using low molecular weight nonionic ethylene oxide surfactants and poly(alkylene oxide)block copolymers in acid media via an (S0H+)(X-I+)synthesis route.21,22Under the conditions,our results show that the structure of ordered mesoporous silica
(6)Hillmyer,M.;Lipic,P.M.;Hajduk,D.A.;Almdal,K.;Bates,F.S. J.Am.Chem.Soc.1997,119,2749.
(7)Zhao,D.;Feng,J.;Huo,Q.;Melosh,N.;Fredrickson,G.H.;Chmelka,
B.F.;Stucky,G.D.Science1998,279,548.
(8)Bagshaw,S.A.;Prouzet,E.;Pinnavaia,T.J.Science1995,269,1242.
(9)Bagshaw,S.A.;Pinnavaia,T.J.Angew.Chem.,Int.Ed.Engl.1996, 35,1102.
(10)Prouzet,E.;Pinnavaia,T.J.Angew.Chem.,Int.Ed.Engl.1997, 36,516.
(11)Attard,G.S.;Glyde,J.C.;Go¨ltner,C.G.Nature1995,378,366.
(12)Go¨ltner,C.G.;Antonietti,M.Ad V.Mater.1997,9,431.
(13)Antonietti,M.;Go¨ltner,C.Angew.Chem.,Int.Ed.Engl.1997,36, 910.
(14)Templin,M.;Franck,A.;Chesne,A.D.;Leist,H.;Zgang,Y.;Ulrich, R.;Scha¨dler,U.;Wiesner,U:Science1997,278,1795.
(15)Voegtlin, A. C.;Ruch, F.;Guth,J.L.;Patarin,J.;Huve,L. Microporous Mater.1997,9,95.
(16)Monnier,A.;Schu¨th,F.;Huo,Q.;Kumar,D.;Margole,D.; Maxwell,R.S.;Stucky,G.D.;Krishnamurty,M.;Petroff,P.;Firouzi,A.; Janicke,M.;Chmelka,B.F.Science1993,261,1299.
(17)Firouzi,A.;Kumar,D.;Bull,L.M.;Besier,T.;Sieger,P.;Huo, Q.;Walker,S.A.;Zasadzinski,J.A.;Glinka,C.;Nicol,J.;Margole,D.; Stucky,G.D.;Chmelka,B.F.Science1995267,1138.
(18)Firouzi,A.;Atef,F.;Oertli,A.G.;Stucky,G.D.;Chmelka,B.F. J.Am.Chem.Soc.1997,119,3596.
(19)Huo,Q.;Margole,D.I.;Stucky,G.D.Chem.Mater.1996,8, 1147.
(20)Huo,Q.;Margole,D.I.;Ciesia,Feng,P.;Gier,T.E.;Sieger,P.; Leon,R.;Petroff,P.M.;Schu¨th,F.;Stucky,G.D.Nature1994,368,317.
(21)Mercier,L.;Pinnavaia,T.J.Ad V.Mater.1997,9,500.
(22)Braun,P.V.;Onar,P.;Stupp,S.I.Nature1996,380,325.
Hydrothermally Stable,Mesoporous Silica Structures J.Am.Chem.Soc.,Vol.120,No.24,19986025
is controlled predominantly by the surfactant species lected and that each type of surfactant favors formation of a specific mesostructured silica pha.Under the reaction conditions ud here,nonionic oligomeric ethylene oxide surfactants often result in the formation of cubic phas,while triblock copolymers tend to yield hexagonal mesostructures at room temperature.X-ray diffraction,nitrogen adsorption/desorption isotherms,and trans-mission electron micrograph(TEM)data show that the meso-porous silica products are highly ordered,with BET surface areas up to1160m2/g.Importantly,after calcination the mesoporous products are thermally stable even in boiling water. High-quality hexagonal mesoporous silica(p6mm)synthesized by this approach has a much larger cell parameter(a)120-320Å),a larger uniform pore size(47-300Å),a larger pore volume(up to2.5cm3/g),and thicker silica walls(31-64Å) than MCM-41synthesized by using conventional low-molecular weight cationic surfactants.
南海战事Experimental Section
乡下英文Chemicals.All surfactants are commercially available from Aldrich, Fluka,and BASF and were ud as received,including the following: Brij52,C16H33(OCH2CH2)2OH,designated C16EO2,(Aldrich);Brij30, C12EO4,(Aldrich);Brij56,C16EO10,(Aldrich);Brij58,C16EO20, (Aldrich);Brij76,C18EO10,(Aldrich);Brij78,C16EO20,(Aldrich);Brij 97,C18H35EO10,(Aldrich);Brij35,C
12EO23,(Aldrich);Triton X-100, CH3C(CH3)2CH2C(CH3)2C6H4(OCH2CH2)x OH,x)10(av),(Aldrich); Triton X-114,CH3C(CH3)2CH2C(CH3)2C6H4(OCH2CH2)5OH(Aldrich); Tween20,poly(ethylene oxide)(20)sorbitan monolaurate(Aldrich); Tween40,poly(ethylene oxide)(20)sorbitan monopalmitate(Aldrich); Tween60,poly(ethylene oxide)(20)sorbitan monostearate(Aldrich); Tween80,poly(ethylene oxide)(20)sorbitan monooleate(Aldrich); and Span40,sorbitan monopalmitate(Aldrich).The structures are as follows:
Other surfactants ud include Tergitol TMN6,CH3CH(CH3)CH-(CH3)CH2CH2CH(CH3)(OCH2CH2)6OH(Fulka);Tergitol TMN10, CH3CH(CH3)CH(CH3)CH2CH2CH(CH3)(OCH2CH2)10OH(Fulka);block copolymers having a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(EO-PO-EO)quence centered on a(hydro-phobic)poly(propylene glycol)nucleus terminated by two primary hydroxyl groups;Pluronic L121(M av)4400),EO5PO70EO5(BASF); Pluronic L64(M av)2900),EO13PO30EO13(BASF);Pluronic P65(M av
)3400),EO
20
PO30EO20(BASF);Pluronic P85(M av)4600),EO26-PO39EO26(BASF);Pluronic P103(M av)4950),EO17PO56EO17 (BASF);Pluronic P123(M av)5800),EO20PO70EO20,(Aldrich); Pluronic F68(M av)8400),EO80PO30EO80(BASF);Pluronic F127(M av
)12600),EO
106
PO70EO106(BASF):Pluronic F88(M av)11400), EO100PO39EO100(BASF);Pluronic25R4(M av)3600),PO19EO33PO19 (BASF);star diblock copolymers having four EO n-PO m chains(or in rever,the four PO n-EO m chains)attached to an ethylenediamine nucleus,and terminated by condary hydroxyl groups;Tetronic908 (M av)25000),(EO113PO22)2NCH2CH2N(PO113EO22)2(BASF);Tetron-ic901(M av)4700),(EO3PO18)2NCH2CH2N(PO18EO3)2(BASF);and Tetronic90R4(M av)7240),(PO19EO16)2NCH2CH2N(EO16PO19)2 (BASF).Tetraethoxysilane(TEOS)(Aldrich),tetramethoxysilane (TMOS)(Aldrich),and tetrapropoxysiliane(TPOS)(Aldrich)were ud as silica sources.
Synthes.Mesoporous silica phas were synthesized at room temperature(RT)by using nonionic s
urfactants as the structure-directing agents.In a typical preparation,4.0g of Brij76was dissolved in20 g of water and80g of2M HCl solution with stirring.Then8.80g of TEOS was added to that homogeneous solution with stirring at room temperature for20h.The solid product was recovered,washed,and air-dried at room temperature.Yields are typically∼95%(bad on silicon),which is similar to that obtained using low-molecular weight cationic surfactant species under acid conditions.19,20
Silica-block copolymer mesophas were synthesized by this procedure at35-60°C,except the synthesis using Pluronic F127which was reacted at room temperature.In a typical preparation,4.0g of Pluronic P123was dissolved in30g of water and120g of2M HCl solution with stirring at35°C.Then8.50g of TEOS was added into that solution with stirring at35°C for20h.The mixture was aged at 80°C overnight without stirring.The solid product was recovered, washed,and air-dried at RT.Yields are∼98%(bad on silicon), which is comparable to the synthes described above.Calcination was carried out by slowly increasing temperature from room temper-ature to500°C in8h and heating at500°C for6h.
Analys.X-ray powder diffraction(XRD)patterns were taken on a Scintag PADX diffractometer equipped with a liquid nitrogen cooled germanium solid-state detector using Cu K R radiation.The nit
rogen adsorption and desorption isotherms at77K were measured using a Micromeritics ASAP2000system.The sample was pretreated at200°C overnight in the vacuum line.The data were analyzed by the BJH (Barrett-Joyner-Halenda)method using the Haly equation for multilayer thickness.The pore size distribution curve came from the analysis of the adsorption branch of the isotherm.The pore volume was taken at the P/P0)0.985single point.High-resolution29Si MAS NMR spectra were recorded on a Chemagnetics CMX-500spectrometer operating at a29Si resonance frequency of59.71MHz under conditions of magic-angle spinning at3kHz at room temperature;π/2pul lengths of6-7µs were ud to acquire one-pul29Si spectra resulting from 100-300signal-averaged accumulations,employing a300s repetition delay between each scan.The29Si MAS spectra are referenced to tetramethylsilane,Si(CH3)4.Transmission electron micrographs(TEM) were taken on a2000JEOL electron microscope operating at200kV. The samples for TEM were prepared by dispersing a large number of particles of the products through a slurry in acetone onto a holey carbon film on a Ni grid.A Netzsch Thermoanalyzer STA409was ud for simultaneous thermal analysis combining thermogravimetry(TG), derivative thermogravity(DTG),and difference thermoanalysis(DTA) with a heating rate of5K min-1in air.
Results and Discussion
1.Oligomeric Alkyl-Ethylene Oxide Surfactants.(a) C16EO10Surfactant.The powder XRD pattern(Figure1 (bottom))of as-synthesized mesoporous silica SBA-11prepared in the prence of oligomeric nonionic surfactant species C16-EO10shows evidence of three reflections at2θvalues between 1and2°(one strong peak and two shoulder peaks)with d spacings of∼56.6Å.Calcination at500°C for6h yields a
6026J.Am.Chem.Soc.,Vol.120,No.24,1998Zhao et al.
better-resolved XRD pattern(Figure1(top)),in which a third shoulder peak is obrved with a slight decrea of d values,as expected.19,20,23-25In addition,two new peaks are resolved at 2θvalues between3and4°.After calcination,the intensities of the XRD peaks are substantially greater than tho measured from the as-synthesized products,suggesting that SBA-11is stable and the siloxane condensation promoted during the calcination process improves the long-range mesoscopic order-ing of the pores.The XRD patterns of as-synthesized SBA-11 can be indexed as a cubic mesopha belonging to the Pm3h m (221)space group(or others such as P23(195),Pm3h(200), P432(207),P4h32(215)).U of C16EO10as structure-directing species yields products with unit cell parameters(a)of127and 106Åfor as-synthesized and calcined SBA-11,respectively. Further evidence for a cubic mesostructure is provided by the TEM images prented in Figure2,which are reprenta
tive of mesoporous silica prepared with C16EO10.The micrograph shows well-ordered mesopore structures viewed along the[111], [011],and[001]directions,suggesting that the mesoporous silica is a highly ordered three-dimensional cubic mesostructure. The binary pha diagrams of nonionic surfactants,such as C16EO8and C16EO12,in water contain cubic(I),hexagonal(H1), cubic(V1),and lamellar(L R,L2)phas,respectively,with increasing surfactant concentration.3,26,27In addition,two cubic phas have been reported at relatively low surfactant concen-trations(I1′and I1′′).28,29One of the structures is Pm3h n,which is the same as that found by Mitchell et al.,while the other is different but not clearly defined.28,29A cubic Pm3h m(diffraction symmetry)or possibly distorted cubic mesostructured silica film made by using cationic(C16H33N(CH3)3Br,CTAB)surfactant species under acidic conditions has recently been obrved by Brinker and co-workers.30The results here suggest that the C16-EO10surfactant species yield a cubic Pm3h m mesoporous silica pha under the acid synthesis conditions ud.
The N2adsorption-desorption isotherm(Figure3(main plot) for SBA-11is type IV without hysteresis31,32and shows a well-defined step in the adsorption and desorption curve between partial pressures P/P0of0.2-0.4.Such adsorption behavior is indicative of the filling of framework-confined mesopores with an average BJH pore size of25Å.32-34The fwhm of5Åmeasured for the po
re-size distribution(Figure3,int)indicates that SBA-11has well-defined uniform pore dimensions.It is similar to that obrved for mesoporous silica prepared with surfactant species containing an alkylammonium head group (5Å).19,32The pore-size distribution is narrower than that of the wormlike disordered materials produced by S0I0templating using nonionic surfactant species under neutral conditions(9Å).8-10Calcined SBA-11has a N2BET surface area of1070 m2/g and a pore volume of0.68cm3/g(Table1). Thermogravimetic(TGA)and differential thermal(DTA) analys of SBA-11show three weight loss steps in the TGA curve,with a total weight loss of55wt%,and one endothermic
(23)Kresge,C.T.;Leonowicz,M.E.;Roth,W.J.;Vartuli,J.C.;Beck, J.S.Nature1992,359,710.
(24)Beck,J.S.;Vartuli,J.C.;Roth,W.J.;Leonowicz,M.E.;Kresge,
C.T.;Schmitt,K.T.;Chu,C.T.-W.;Olson,
D.H.;Sheppard,迷迭香种苗
E.W.; McCullen,S.B.;Higgins,J.B.;Schlenker,J.L.J.Am.Chem.Soc.1992, 114,10834.
(25)Huo,Q.;Leon,R.;Petroff,P.M.;Stucky,G.D.Science1995,268, 1324.
(26)Mitchell,D.J.;Tiddy,G.J.T.;Waring,L.;Bostock,T.;McDonald, M.P.J.Chem.Soc.,Faraday Trans.11983,79,975.
(27)Danino,D.;Talmon,Y.;Zana,R.J.Colloid Interface Sci.1997, 186,170.
(28)Jahns,E.;Finkelmann,H.Colloid.Polym.Sci.1987,265,304.
(29)Funari,S.;Rapp,G.J.Phys.Chem.B1997,101,732.
(30)Lu,Y.;Ganguli,R.;Drewien,C.A.;Anderson,M.T.;Brinker,J.
C.;Gong,W.;Guo,Y.;Soyez,H.;Dunn,B.;Huang,M.H.;Zink,J.I. Nature1997,389,364.
(31)Sing,K.S.W.;Everett,D.H.;Haul,R.A.W.;Moscou,L.;Pierotti, R.A.;Rouque´rol,J.;Siemieniewska,T.Pure Appl.Chem.1985,57,603.
(32)Schmidt,R.;Hann,E.W.;Sto¨cker,M.;Akporiaye,D.;Ellestad, O.H.J.Am.Chem.Soc.1995,117,4049.
(33)Branton,P.J.;Hall,P.G.;Sing,K.S.W.;Reichert,H.;Schu¨th,F.; Unger,K.K.J.Chem.Soc.,Faraday Trans.1994,90,2965.
(34)Llewellyn,P.L.;Grillet,Y.;Schu¨th,F.;Reichert,H.;Unger,K.K. Microporous Mater.1994,3,345.
Figure1.Powder X-ray diffraction patterns of the cubic mesoporous silica structure SBA-11prepared by using C16EO10surfactant species at room
temperature.Figure2.Transmission electron micrographs with different orientations (top,[110];middle,[111];bottom,[001])of calcined cubic mesoporous silica SBA-11prepared by using C16EO10surfactant species at room temperature.
Hydrothermally Stable,Mesoporous Silica Structures J.Am.Chem.Soc.,Vol.120,No.24,19986027
李叔正
and two exothermic peaks in the DTA curve.The endothermic loss near80°C(7wt%loss)is assigned to water desorption,35,36 whereas the exothermic weight loss at210°C(25wt%loss) and310°C(23wt%loss)are assigned to desorption and decomposition of surfactant species.35,36By320°C,esntially all of the nonionic organic surfactant species have been removed from the SBA-11channels,which occurs at a much lower temperature than that(∼460°C)needed for removal of the cationic surfactant agents such as CTAB ud under basic conditions to prepare MCM-41mesoporous silica.35,36This is consistent with the weaker interactions expected between the nonionic surfactant and inorganic silica wall,compared to that of cationic CTAB with silica under basic MCM-41synthesis conditions.The thicker silica walls obrved for materials prepared with PEO-PPO-PEO species7are thought to result from a combination of such weaker PEO-silica interactions and the weaker micropha-parating tendency of PEO-PPO, relative to the MCM-41system.
The solid-state one-pul29Si MAS NMR spectrum(e Supporting Information Figure I)of as-synthesized SBA-11 prepared at RT shows three broad peaks at92,99,and109 ppm,corresponding to Q2,Q3,and Q4silica species,respec-tively.The ratio Q3/Q4is about0.92,suggesting incomplete silica condensation,while the broad peaks are consistent with a locally disordered silica framework.
SBA-11can be synthesized over a wide composition range (1:0.036-0.6:0.4-20:97-650TEOS:C16EO10:HCl:H2O)at RT. TMOS and TPOS can also be ud as sources of silica.The mesopha symmetry is not changed by varying the surfactant-to-silica ratio(<0.6)at RT,and only cubic SBA-11is formed. At higher surfactant/silica ratios(>0.6),a poorly ordered unstable lamellar-like mesopha is formed,possibly becau the C16EO10is not completely dissolved.Lower surfactant/silica ratios(<0.036)induce only partial precipitation of the silica species.The results indicate that at RT,the C16EO10surfactant favors a cubic mesopha.At higher temperatures,a hexagonal mesoporous silica structure(p6mm)is formed,consistent with molecular packing considerations.17,37Figure4shows the XRD patterns of as-synthesized and calcined hexagonal mesoporous silica prepared using the same composition as that for cubic SBA-11(1:0.144:2:85TEOS:C16EO10:HCl:H2O),but after20 h of reaction at RT and subquent heating at100°C without stirring for3days.This mesostructured silica synthesized at a higher temperature(100°C)shows three well-defined peaks at 2θvalues between1and8°(Figure4)that can be indexed as (100),(110),and(200)Bragg reflections,typical of hexagonal (p6mm)SBA-15,mesoporous silica.7This material is thermally stable after calcination at500°C,as evidenced by retention of
(35)Huo,Q.;Margole,D.I.;Ciesla,U.;Demuth,D.G.;Feng,P.; Gier,T.E.;Sieger,P.;Firouzi,A.;Chmelka,B.F.;Schu¨th,F.;Stucky,G.
D.Chem.Mater.1994,6,1176.
(36)Chen,C.;Li,H.;Davis,M.E.Microporous Mater.1993,2,17.
(37)Israelachvili,J.N.In Physics of Amphiphiles:Micelles,Vesicles and Microemulsions;Societa Italiana di Fisica;Bologna,Italy,1985;pp 24-58.
Table1.Physicochemical Properties of Mesoporous Silica(SBA)Prepared Using Nonionic Alkyl Poly(ethylene oxide)Surfactants surfactant reaction temp mesopha d a(Å)BET surface area(m2/g)pore size b(Å)pore vol(cm3/g) C16EO2RT lamellar64.3
C12EO4RT cubic45.3(44.7)670220.38
C12EO4RT lamellar45.7570
C12EO460°C L3(?)42.4610240.39
C16EO10RT cubic56.6(47.6)1070250.68
C16EO10100°C hexagonal64.1(62.8)91035 1.02
C16EO20RT cubic63.7(49.6)600220.29
C18EO10RT P63/mmc63.5(51.0)1150310.83
C18EO10100°C hexagonal77.4(77.0)910400.92
C18H35EO10RT P63/mmc49.1(47.7)1000270.59
C12EO23RT cubic54.8(43.3)500160.24 Tween20RT cubic55.1(46.8)800190.37 Tween40RT cubic52.4(49.6)700200.36 Tween60RT cubic63.8(53.9)720240.52 Tween60RT lamellar38.7
Tween80RT cubic62.2(53.9)710250.43
Span40RT lamellar55.5
Triton X100RT cubic41.8(35.5)780170.35
Triton X114RT cubic42.2(36.7)990160.45 Teritor TMN6RT cubic44.3(39.9)1160230.57 Teritor TMN10RT cubic42.3(36.5)800200.38
a d(100)spacing or d value of characteristic reflection of the as-synthesized products;the number insi
风骚秘书de brackets is the d value after calcination at500°C for6h.
b Calculated from adsorption branch.
Figure3.Nitrogen adsorption-desorption isotherm plots and pore
扮演英语size distribution curve from the adsorption branch of calcined cubic
(Pm3m)mesoporous silica SBA-11prepared by using C16EO10sur-
月经能吃芒果吗factant species at room temperature.
6028J.Am.Chem.Soc.,Vol.120,No.24,1998Zhao et al.
