介孔碳纳米材料的制备与改性

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介孔材料简介

介孔材料简介

介孔材料简介摘要:介孔材料作为一种新兴的材料在光化学、催化及分离等领域具有十分重要的应用,是当今研究的热点之。

本文阐述了介孔材料的研究进展,概述了介孔材料的分类及合成机理,并展望了介孔材料的应用前景,并简要介绍了孔径调节以及改性方法。

关键词:介孔材料,模板法,溶胶-凝胶法,合成机理,孔径调节Research development of mesoporous materials Abstract:Mesoporousmaterial is of much use in the fields of photochemistry, catalyst and separationetc, and it is one of hot spots of research. The research p rogress of the mesoporous materials is reviewed in this paper. And the classification and synthesis mechanism of the mesoporousmaterials are also outlined. The potential application foreground of the mesoporousmaterial is discussed as well.And briefly describes the aperture adjustment and modification methods.Key words:mesoporousmaterials; template method; sol - gel methods synthesis mechanism ;aperture adjustment1 前言人类社会的进步与材料科学的发展密切相关[ 1, 2 ],尤其是近几十年中,出现了许多具有特殊功能的新材料,其中介孔材料就是一种。

介孔材料简介及其制备方法

介孔材料简介及其制备方法

增刊1介孔材料简介及其制备方法宋磊(新疆有色金属研究所乌鲁木齐830000)摘要介孔材料是一类具有均匀孔道,孔径在2~50nm之间的吸附剂或薄膜类物质,它们在精细化工、石油及天然气加工、吸附与分离等领域均有广泛的应用。

由于有优越的性能,介孔材料已成为研究的热点。

孔材料的许多优异性能使其成为材料研究的热点。

本文综述了近年来介孔材料的制备方法,包括模板法、溶胶-凝胶法、水热法、沉淀法、硬模板法等;同时简要介绍了其在吸附、催化、电极、电客、信息储运和医药基因工程方面的应用。

关键词介孔材料制备1引言无机多孔材料是具有较大比表面积和孔容的材料,在精细化工、石油及天然气加工、吸附与分离等领域均有着广泛的用途,其中介孔材料在工业生产过程中有较好的应用前景。

典型介孔材料有普通的SiO2气凝胶、微晶玻璃、沸石分子筛、M41S系列介孔材料等,它们的孔径范围较大,是良好的催化剂载体和研究介孔吸附的模型化合物。

多孔材料是20世纪发展起来的崭新材料体系,其显著特点是:具有规则排列、大小可调的孔道结构及高的比表面积和大的吸附容量。

按照国际纯粹与应用化学联合会(IUPAC)的定义,孔径<2nm的多孔材料为微孔材料,>50nm的多孔材料为大孔材料,介于2~50 nm的多孔材料为介/中孔材料。

微孔材料孔径太小,限制了较大分子进入其孔隙或在孔腔内形成的大分子不能快速逸出,从而大大限制了其实际应用范围;对于大孔材料,虽然其孔径尺寸大,但同时存在着孔道形状不规则、尺寸分布过宽等缺点;而介孔材料不仅孔径适中、具有较大的比表面积和壁厚、且具有较高的热稳定性和水热稳定性。

在性能上,由于其量子限域效应、小尺寸效应、表面效应、宏观量子隧道效应、以及介电限域效应而体现出许多新的性质,因而在催化分离和吸附等方面以及在光电子学、电磁学、材料学、环境学等领域具有广阔的应用前景。

2介孔材料简介介孔分子筛是一类具有均匀微孔,孔径与一般分子相当的吸附剂或薄膜类物质,具有分子筛作用的物质很多,其中应用最广的是沸石。

原位限域生长策略制备有序介孔碳负载的超小MoO_(3)纳米颗粒

原位限域生长策略制备有序介孔碳负载的超小MoO_(3)纳米颗粒

Vol.42 2021年5月No.51589~1597 CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高等学校化学学报原位限域生长策略制备有序介孔碳负载的超小MoO3纳米颗粒王常耀,王帅,段林林,朱晓航,张兴淼,李伟(复旦大学化学系,上海200433)摘要采用原位限域生长策略制备了一系列有序介孔碳负载的超小MoO3纳米颗粒复合物(OMC-US-MoO3).其中,有序介孔碳被用作基质来原位限域MoO3纳米晶的生长.依此方法制备的MoO3纳米晶具有超小的晶粒尺寸(<5nm),并在介孔碳骨架内具有良好的分散度.制得的OMC-US-MoO3复合物具有可调的比表面积(428~796m2/g)、孔容(0.27~0.62cm3/g)、MoO3质量分数(4%~27%)和孔径(4.6~5.7nm).当MoO3纳米晶的质量分数为7%时,所得样品OMC-US-MoO3-7具有最大的孔径、最小的孔壁厚度和最规整的介观结构.该样品作为催化剂时,表现出优异的环辛烯选择性氧化性能.关键词有序介孔碳;氧化钼纳米晶;纳米材料;限域生长中图分类号O611.4文献标志码AIn situ Confinement Growth Strategy for Ordered Mesoporous CarbonSupport Ultrasmall MoO3NanoparticlesWANG Changyao,WANG Shuai,DUAN Linlin,ZHU Xiaohang,ZHANG Xingmiao,LI Wei*(Department of Chemistry,Fudan University,Shanghai200433,China)Abstract Ultrasmall particle sizes and excellent dispersity of the MoO3active species on support majorly dominate their catalytic performances.Herein,a series of ordered mesoporous carbon support ultrasmall mo⁃lybdena nanoparticles(OMC-US-MoO3)composites was synthesized through an in situ confinement growth strategy.Ordered mesoporous carbon was used as the matrix to in situ confine the growth of MoO3nanocrystals. The obtained MoO3nanocrystals show ultrasmall particle sizes(<5nm)and excellent dispersity on the meso-porous carbon frameworks.The obtained OMC-US-MoO3exhibits tunable specific surface areas(428―796 m2/g),pore volumes(0.27―0.62cm3/g),MoO3contents(4%―27%,mass fraction)and uniform pore sizes (4.6―5.7nm).As a typical example,the obtained sample with7%MoO3(denoted as OMC-US-MoO3-7)shows the largest pore size,smallest thickness of pore wall and most regular mesostructures.When being used as a catalyst,the OMC-US-MoO3-7exhibits an excellent catalytic activity for selective oxidation of cyclooctene with a high stability.Keywords Ordered mesoporous carbon;MoO3nanocrystal;Nanomaterials;Confinement growthdoi:10.7503/cjcu20200303收稿日期:2020-05-28.网络出版日期:2020-09-24.基金项目:国家自然科学基金(批准号:21975050)、国家重点研发计划纳米科技重点专项(批准号:2016YFA0204000, 2018YFE0201701)和中国博士后科学基金(批准号:2019M651342)资助.联系人简介:李伟,男,博士,教授,主要从事介孔材料的合成及应用研究.E-mail:*******************.cn1590Vol.42高等学校化学学报Epoxides,an important industrial chemicals,has been widely used in the fields of food additives,phar⁃maceutical intermediates,etc.[1,2].Catalytic epoxidation of olefin is one of the essential route to produce epo-xides,which oxygenation of carbon-carbon double bond to form cyclic epoxide groups.The kind of catalyst plays a key role on the epoxidation reaction.Among all catalysts,precious metal of gold based one illustrates high activity for olefin epoxidations[3,4].However,gold is limited resource and very expensive,even though it shows high conversion efficiency.Molybdenum oxide(MoO3),as one of the low cost,non-toxic and environ⁃mentally benign transition metal oxides,is widely used as heterogeneous catalysis for Friedel-Crafts alkyla⁃tion[5],hydrogenation reaction[6,7],epoxidation reaction[8,9],hydrogen evolution reaction[10],electrochemical energy storage for lithium-ion batteries[11,12],and gas sensors[13,14],etc..Gratifyingly,MoO3has been reported by several groups which have high activity for epoxidation of olefins in recent years[15,16].It is obvious that the size and morphology of MoO3active species are critical factors that affect their prop⁃erties for application[17~20].However,the synthesis and reaction process often easily causes serious sintering,migration and agglomeration of the MoO3nanoparticles,leading to the degradation of catalytic activity.Sup⁃ports are necessary for the immobilization of active species.Carbon has been widely used as an outstanding matrix to control the size and dispersity of supported metal oxides attributing to its advantages of intrinsical chemical inertness,high thermal stability,non-toxic and wide-sources[21~23].Molybdena supported carbon have been reported and show excellent performance as the catalyst for cyclooctene epoxidation[24,25].Recently,Chen group[26]fabricatedγ-Fe2O3@C@MoO3core-shell structured nanoparticles as a magnetically recyclable catalyst for the epoxidation reaction of olefins.The coated carbon layer play an efficient role for the stabiliza⁃tion of magnetic core.Biradar group[8]also reported a carbon microspheres-supported molybdena nanoparticles catalyst which also show outstanding effect for the epoxidation of olefins.However,above-mentioned catalysts are less porosity.Porous supports,especially,mesoporous carbon have been reported on many catalytic areas because of its large surface area,pore volume and pore size,which can not only improve the load capacity but also enlarge the reaction progress,where the diffusion process may be the rate-limiting step[26~28].Up to now,it is still urgent to fabricate mesoporous carbon supported MoO3catalyst with ultrasmall particle size and excel⁃lent dispersity.Herein,we construct an ordered mesoporous carbon support ultrasmall MoO3nanoparticles(OMC-US-MoO3)composites via an in situ confinement growth strategy.In this strategy,the ordered mesoporous carbon works as a matrix to in situ confine the growth of MoO3nanocrystals.The obtained MoO3nanocrystals show ultrasmall particle size(<5nm)and excellent dispersity on the mesoporous carbon frameworks.The content (mass fraction)of MoO3can be tuned from4%to27%.The obtained OMC-US-MoO3shows tunable specific surface areas(428―796m2/g),pore volumes(0.27―0.62cm3/g)and uniform pore size(4.6―5.7nm).As a typical example,the obtained sample with7%MoO3(denoted as OMC-US-MoO3-7)shows largest pore size,smallest thickness of pore wall and most regular mesostructures.When being used as a catalyst,the OMC-US-MoO3-7exhibits an excellent catalytic activity for selective oxidation of cyclooctene with a high stability.1Experimental1.1Chemicals and MaterialsPluronic F127(EO106PO70EO106,M w=12600)was purchased from Aldrich.All others chemicals were obtained from Aladdin company and used directly.Deionized water was used in all experiments.1.2Synthesis of Ordered Mesoporous Carbon Support Ultrasmall Molybdena NanoparticlesIn detail synthesis procedure,1.0g of Pluronic F127powders was added into10.0g of ethanol solution and stirred to a homogeneous clear solution at40℃.Afterwards,5.0g of20%(mass fraction)preformedNo.5王常耀等:原位限域生长策略制备有序介孔碳负载的超小MoO 3纳米颗粒phenolic resins ethanol solution and 1.0mL of peroxomolybdenum precursor solution were added into the ho⁃mogeneous system (5—200mg/mL ).The preformed phenolic resins was synthesized based on the reported method [27,28].Peroxomolybdenum precursor solution [29]was prepared by dissolving different contents of molyb⁃denum trioxide into 10.0mL of 30%hydrogen peroxide.The mixture solution was poured into dishes after 2h and then the dishes were heat treated at 40and 100℃for 8and 20h ,respectively ,forming the as -made com⁃posites consisting of Pluronic F127,phenolic resins ,and Mo species (denoted as as -made sample ).Then ,the calcination of as -made sample was implemented in a tubular furnace under N 2atmosphere.The temperature program was set from 25℃to 350℃with a ramp of 1℃/min ,maintenance for 3h ,and then to 600℃with 1℃/min ,maintenance for 2h.The obtained sample after pyrolysis was named as ordered mesoporous carbon support ultrasmall molybdena nanoparticles (OMC -US -MoO 3-x ),wherein x represent the actual mass fraction of MoO 3.1.3Activity Test The selective oxidation reaction of cyclooctene was carried out in the round -bottom flask (50mL ).In which ,40.0mmol of cyclooctene ,40.0mmol of 5.5mol/L TBHP in decane ,10mg of OMC -US -MoO 3-7cata⁃lyst (0.0048mmol/L of MoO 3),6.0g of 1,2-dichloroethane as solvent ,and 15.0mmol of chlorobenzene as internal standard.The reaction temperature is 80℃.At different time intervals ,conversion was calculated by sampling.The samples were analyzed on an Agilent 7890A gas chromatograph equipped with a HP -5column and products were confirmed by GC -MS.TOF values (mol of reacted cyclooctene per mol of catalyst and hour )was calculated at about half conversion of the reaction.The catalyst was reused after washing by water and drying.The test condition was kept same to the first time on the cyclic test.2Results and Discussion2.1Synthesis and CharacterizaitonThe developed in situ confinement growth strategy is employed to the preparation of ordered mesoporous carbon support ultrasmall molybdena nanoparticles (OMC -US -MoO 3)composites (Fig.1).In the synthesis sys⁃tem ,Pluronic F127is used as the structure -directing agent (soft -template ),preformed phenolic resins is used as carbon resource ,peroxomolybdenum solution is used as precursor ,and ethanol/H 2O is used as co -solvent ,respectively.The as -made sample and product OMC -US -MoO 3composites can be obtained after heat -treatment at 100and 600℃,respectively.The mass content of MoO 3in the OMC -US -MoO 3composites can be well tuned through adjusting the amount of peroxomolybdenum precursor in the synthesis system.TGA curves (Fig.2)show that the mass fractions of MoO 3species in the OMC -US -MoO 3composites areFig.1Illustration of the construction of OMC ⁃US ⁃MoO 3composites via the in situ confinementgrowth strategy Fig.2TGA curves of the OMC ⁃US ⁃MoO 3composites with different MoO 3contents obtained afterpyrolysis at 600℃,respectivelyMass fraction of MoO 3(%):a .4;b .7;c .10;d .16;e .27.1591Vol.42高等学校化学学报4%,7%,10%,16%and 27%(Table 1),respectively ,when adjusting the amount of molybdenum precursors in the synthesis system.The mass loss below 100℃is caused by the volatilization of adsorbed water in the composites.A slight mass increasement can be detected between 100and 300℃,demonstrating the existence of trace amount of MoO 2and abundant MoO 3in the composites.The mass increasement can be attributed to the oxidation of the trace amount MoO 2.Subsequently ,the huge mass loss above 300℃can be observed attribu -ting to the remove of carbon species in the composites.The mass loss between 100and 600℃is approximate to the mass fraction of MoO 3species in the composites.The SAXS patterns [Fig.3(A )]of OMC -US -MoO 3-4and OMC -US -MoO 3-7composites show two scatteringdiffraction peaks at 0.391and 0.782nm −1,and 0.412and 0.824nm ‒1,respectively ,indexing to the (100)and (200)reflections of a hexagonal mesosturtures with space group P 6mm .With the increasement of MoO 3content ,the q values of the (100)diffraction peaks shift to 0.532,0.617,and 0.678nm −1,for samples OMC -US -MoO 3-10,OMC -US -MoO 3-16,and OMC -US -MoO 3-27,respectively.The corresponding cell parame⁃ters of five composites are calculated to be about 18.5,17.6,13.6,11.7,and 10.7nm with the increased MoO 3content ,respectively.WAXRD patterns [Fig.3(B )]of five composites all show no diffraction peaks of MoO 3phase ,suggesting the ultrasmall particle size of MoO 3nanocrystals in the frameworks.This result demonstrates that the ordered mesoporous carbon frameworks can confine the size of MoO 3nanocrystals to an ultrasmall size even at a high MoO 3content effectively.Nitrogen adsorption -desorption isotherms of five OMC -US -MoO 3composites obtained after calcined at 600℃in N 2all display representative type -Ⅳcurves with H2hysteresis loops [Fig.4(A )],in agreement with the previously reported ordered mesoporous materials [30~32].Sharp capillary condensation steps in the relative pressure (p /p 0)of 0.41―0.70are observed for five composites ,demonstrating the narrow pore size distribu⁃tion.The Brunauer -Emmett -Teller (BET )surface area and pore volume of five composites are calculated and listed on Table 1.The surface area and pore volume decrease with the increased MoO 3content ,which can be attributed to the partial destroy and disappear of pore structures.The average pore sizes of five composites are also calculated and listed on Table 1from their pore size distribution curve [Fig.4(B )]derived from the adsorption branch based on BJH model.The average pore sizes are 4.7,5.7,5.5,5.4,and 4.6nm ,Table 1Structural and textural parameters for OMC -US -MoO 3with different content Sample No.12345MoO 3content (%,mass fraction )47101627S BET /(m 2·g -1)796693652574428V /(cm 3·g -1)0.620.540.490.410.27D /nm 4.75.75.55.4 4.6Fig.3SAXS(A)and WA ⁃XRD(B)patterns of the OMC ⁃US ⁃MoO 3composites with differentMoO 3contents obtained after pyrolysis at 600℃Mass fraction of MoO 3(%):a .4;b .7;c.10;d .16;e .27.1592No.5王常耀等:原位限域生长策略制备有序介孔碳负载的超小MoO 3纳米颗粒respectively.According to the cell parameters results ,the pore walls of five composites are calculated to be 14.1,11.9,8.1,6.3,and 6.1nm ,respectively.SEM images (Fig.5)show that OMC -US -MoO 3-4and OMC -US -MoO 3-7composites own the most regular mesostructures.Notably ,the regular [100]and [110]directions can be clear observed from the SEM images of OMC -US -MoO 3-7composites [Fig.5(B )and (F )].In addition ,the mesopores are opened and no obvious big metal nanoparticles can be observed from the surface.With further increasement of MoO 3content ,the reg⁃ular mesostructures is partial destroyed.TEM images of OMC -US -MoO 3-7composites [Fig.6(A )—(C )]taken along the [100]and [110]directions manifest a well -defined 2D hexagonal mesostructures in agreement with the result of the SAXS pattern [Fig.2(A )].The lattice spacing is measured to be 0.35nm from the HRTEM image [Fig.6(D )],attributing to the (040)crystalline planes of α-MoO 3[33].The average size of MoO 3nano⁃crystals is estimated to be (4.1±1.0)nm from the size statistics diagram.The survey spectrum of the OMC -US -MoO 3-7composites shows the presence of only Mo ,O and C elements [Fig.7(A )].The high -resolution Mo 3d core level XPS spectra [Fig.7(B )]show four peaks at 230.5,232.7,233.6,and 235.9eV ,demon⁃strating the co -existence of Mo 4+and Mo 6+species [34~36].The ratio of Mo 4+/Mo 6+is calculated to be about 13%.Only a few Mo 4+signals can be detected from the spectrum ,in agreement with the TGAresults.Fig.4N 2adsorption⁃desorption isotherms(A)and pore size distributions(B)of the OMC⁃US⁃MoO 3composites with different MoO 3contents obtained after pyrolysis at 600℃Mass fraction of MoO 3(%):a .4;b .7;c.10;d .16;e .27.Fig.5SEM images of OMC⁃US⁃MoO 3composites with different MoO 3contents obtained afterpyrolysis at 600℃Mass fraction of MoO 3(%):(A)4;(B)7;(C)10;(D)16;(E)27.1593Vol.42高等学校化学学报2.2Formation Mechanism Studies Based on the above results ,we propose that the in situ confinement growth strategy show significant impact on the formation of final OMC -US -MoO 3composites.The obtained MoO 3nanocrystals show ultrasmall particle size (<5nm )and excellent dispersity on the mesoporous carbon frameworks.This structure can be retained even the mass fraction of MoO 3is increased to 27%.However ,the regular mesostructures can be partial destroyed with the increased MoO 3mass content.According to the results that no large MoO 3nanocrys⁃tals can be detected from samples obtained after pyrolysis at 600℃,the unregular mesostructures can be attributed to the uncontrollable origin co -assembly process.2.3Selective Oxidation of Cyclooctene The selective oxidation reaction of cyclooctene with high catalytic performance and stability is still highly desired.However ,the stability of active nanoparticles in catalytic reaction is a major challenge ,especially for active nanoparticles with ultra -small size.For our case ,the OMC -US -MoO 3-7composites show most regular mesostructures ,largest pore sizes ,appropriate hole wall size ,MoO 3content and dispersity.So ,the obtained OMC -US -MoO 3-7composites catalyst is selected as the catalyst for cyclooctene epoxidation.The reactions were carried out using 1,2-dichloroethane as solvent in flask with chlorobenzene as internal standard at 80℃.The OMC -US -MoO 3-7composites catalyst shows a high TOF value of 2163h ‒1which is calculated on the basis of the experimental data at 2h.Meanwhile ,a high conversion (100%)of cyclooctene ,and selectivity (>99%)to 1,2-epoxycyclooctane at 8h can also be parison with the reported heterogeneous Mo -based catalyst using similar conditions was shown in Table 2.The present OMC -US -MoO 3-7catalystshowsFig.7Survey XPS spectrum(A)and high⁃resolution XPS spectra of Mo 3d (B)for OMC⁃US⁃MoO 3⁃7composites obtained after pyrolysis at 600℃Fig.6TEM images of OMC⁃US⁃MoO 3⁃7composites obtained after pyrolysis at 600℃Viewed along the hexagonal (A )and columnar (B ,C )directions and HRTEM image (D )of a representative MoO 3nanoparticle.1594No.5王常耀等:原位限域生长策略制备有序介孔碳负载的超小MoO 3纳米颗粒a higher TOF value than MoO 3/C [8],MoO 3/SiO 2[37],Mo -MOFs [9],Mo -MCM -41[38],Mo -SBA -15[38],[Pipera⁃zinCH 2{MoO 2(Salen )}]n [39],and MNP 30-Si -inic -Mo [40]as previous reported.It should be noted that cyclooc⁃tene still gave about 18%conversion [Fig.8(A )]in the absence of catalyst owing to the presence of strong TBHP oxidants ,which is consistent with previous reports [41,42].Further ,two other substrates ,cyclohexene and styrene were also tested under the same conditions to test the versatility of OMC -US -MoO 3-7as an epoxida⁃tion catalyst.Surprisingly ,the conversion of cyclohexene to 1,2-epoxyclohexane can reach 54%in 8h.Inaddition ,the conversion of styrene to styrene oxide can reach 95%in 36h ,respectively (Fig.S1,see the Sup⁃porting Information of this paper ).Beside the efficient conversion of catalyst and high TOF values ,the stability of catalyst is also very impor⁃tant ,especially for heterogeneous catalysis.Here ,the hot filtration test was used to assess the presence of active Mo species in solution.When the reaction lasted for 2h ,we removed the catalyst by hot filtration and let the mother liquid for reacting another 6h.The results showed that there was only a slight increase in con⁃version [Fig.8(A )],which is proof of a heterogeneous catalysis.For the recycling study ,cyclooctene epoxida⁃tion was performed maintaining the same reaction conditions except using the recovered catalyst.It can be clearly found that obvious changes are undetected for catalytic performance after five runs [Fig.8(B )].It indi⁃cates that ultrasmall MoO 3nanoparticles supported on ordered mesoporous carbon is highly stable and can be reused ,demonstrates its potential for industrial applications.The high conversion ,selectively ,and the TOF value for the cyclooctene epoxidation reaction can be attributed to the unique structure of the OMC -US -MoO 3-7composites.The high surface area ,volume ,andTable 2Calculating TOF value for epoxidation of cyclooctene and comparing with other catalysts *Catalyst OMC -US -MoO 3-7MoO 3/C MoO 3/SiO 2Mo -MOFs Mo -MCM -41Mo -SBA -15[PiperazinCH 2{MoO 2(Salen )}]n MNP 30-Si -inic -MoTime/h 2267331224Conv.(%)5280909397999546Epoxide sel.(%)>9910010099959398100TOF/h -1216353[8]72[35]270[9]22[36]40[36]16[37]2[38]*.TOF values(mol of reacted cyclooctene per mol of catalyst and hour)were calculated at abouthalf conversion of the reaction.Fig.8Time course plots of cyclooctene epoxidation(A)and reusability(B)by using OMC⁃US⁃MoO 3⁃7com⁃posites as catalystReaction conditions :40.0mmol of cyclooctene ,40.0mmol of 5.5mol/L TBHP in decane ,10mg of OMC -US -MoO 3-7catalyst (0.0048mmol/L of MoO 3),6.0g of 1,2-dichloroethane as solvent ,and 15.0mmol of chlorobenzene as internalstandard.The reaction temperature is 80℃.15951596Vol.42高等学校化学学报uniform mesopores can not only enrichment the reaction substrate but also in favor to the diffusion of sub⁃strates.The ultrasmall MoO3nanocrystals size and its excellent dispersity in the frameworks can expose more active sites.All these features are beneficial to the rapid conversion of substrate molecular with high selective⁃ly and conversion.3ConclusionsIn summary,an in situ confinement growth strategy was developed to the construction of ordered mesopo⁃rous carbon support ultrasmall molybdena nanoparticles(OMC-US-MoO3)composites.Ordered mesoporous carbon was used as an effective matrix to in situ confine the growth of MoO3nanocrystals.The obtained MoO3 nanocrystals show ultrasmall particle size(<5nm)and excellent dispersity on the mesoporous carbon frame⁃works.In addition,a serious of OMC-US-MoO3composite can be obtained with controllable specific surface areas(428―796m2/g),pore volumes(0.27―0.62cm3/g),MoO3contents(4%―27%,mass fraction)and uniform pore size(4.6―5.7nm).The mesostructures can be retained even the MoO3content as high as27%. 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EISA方法制备介孔碳及杂化介孔碳研究进展

EISA方法制备介孔碳及杂化介孔碳研究进展

EISA方法制备介孔碳及杂化介孔碳研究进展安娟娟;杨丽娜;李剑【摘要】溶剂挥发诱导自组装(EISA)法具有操作容易、成本低廉、结构和孔径易于控制、适用性强等特点.综述了以EISA法制备介孔碳材料的基本原理和合成方法.重点综述了EISA方法制备杂化介孔碳材料的研究进展,论述了掺杂型介孔碳和复合型介孔碳材料的性能优势,并对EISA方法在介孔碳材料制备中的发展趋势进行了展望.%The synthesis of ordered mesoporous carbon materials using the solvent evaporation induced self-assembly (EISA) method has many advantages, such as easy operation, low cost, easy control of channel structure and pore size and strong applicability. The fundamental and research progress of synthesizing ordered mesoporous carbon materials by EISA method are reviewed, with emphasis on the synthesis of functionalized ordered mesoporous carbons. The performance advantages of functionalized mesoporous carbon and composite mesoporous carbon are presented. The development trend of the synthesis of mesoporous carbon materials by EISA method is also discussed.【期刊名称】《天然气化工》【年(卷),期】2018(043)003【总页数】6页(P115-120)【关键词】溶剂挥发诱导自组装法;介孔碳材料;模板剂;杂化介孔碳【作者】安娟娟;杨丽娜;李剑【作者单位】辽宁石油化工大学化学化工与环境学部,辽宁抚顺 113001;辽宁石油化工大学化学化工与环境学部,辽宁抚顺 113001;辽宁石油化工大学化学化工与环境学部,辽宁抚顺 113001【正文语种】中文【中图分类】TQ426.6;TQ424介孔碳材料因具有较高的比表面积、可调的孔道结构而受到广泛关注,此外介孔碳还具有较高的机械强度、良好的导电能力和较强的吸附能力,是一种良好的电极材料[1,2]、吸附剂[3-5]和催化剂载体[6]。

纳米材料的制备方法

纳米材料的制备方法

纳米/微米三维结构的制备纳米材料是指在三维空间中至少有一维处于纳米尺度范围(1-100nm)或由它们作为基本单元构成的材料,这大约相当于10~100个原子紧密排列在一起的尺度。

纳米级结构材料简称为纳米材料(nano material),是指其结构单元的尺寸介于1纳米~100纳米范围之间。

由于它的尺寸已经接近电子的相干长度,它的性质因为强相干所带来的自组织使得性质发生很大变化。

并且,其尺度已接近光的波长,加上其具有大表面的特殊效应,因此其所表现的特性,例如熔点、磁性、光学、导热、导电特性等等,往往不同于该物质在整体状态时所表现的性质。

纳米颗粒材料又称为超微颗粒材料,由纳米粒子(nano particle)组成。

纳米粒子也叫超微颗粒,一般是指尺寸在1~100nm间的粒子,是处在原子簇和宏观物体交界的过渡区域,从通常的关于微观和宏观的观点看,这样的系统既非典型的微观系统亦非典型的宏观系统,是一种典型的介观系统,它具有表面效应、小尺寸效应和宏观量子隧道效应。

当人们将宏观物体细分成超微颗粒(纳米级)后,它将显示出许多奇异的特性,即它的光学、热学、电学、磁学、力学以及化学方面的性质和大块固体时相比将会有显著的不同。

纳米技术的广义范围可包括纳米材料技术及纳米加工技术、纳米测量技术、纳米应用技术等方面。

其中纳米材料技术着重于纳米功能性材料的生产(超微粉、镀膜、纳米改性材料等),性能检测技术(化学组成、微结构、表面形态、物、化、电、磁、热及光学等性能)。

纳米加工技术包含精密加工技术(能量束加工等)及扫描探针技术。

纳米材料具有一定的独特性,当物质尺度小到一定程度时,则必须改用量子力学取代传统力学的观点来描述它的行为,当粉末粒子尺寸由10微米降至10纳米时,其粒径虽改变为1000倍,但换算成体积时则将有10的9次方倍之巨,所以二者行为上将产生明显的差异。

纳米粒子异于大块物质的理由是在其表面积相对增大,也就是超微粒子的表面布满了阶梯状结构,此结构代表具有高表面能的不安定原子。

碳纳米管

碳纳米管

碳纳米管的制备及其在催化领域的应用摘要:碳纳米管,是一种具有特殊结构的一维量子材料,具有优异的催化性能,其优异的催化性能主要是由碳纳米管具有的巨大的长径比、超大的比表面积、极高的热稳定性和化学惰性以及其独特的电导性能决定的,并且由于纳米粒子作为催化剂具有表面凸凹不平、表面能高、晶内扩散通道短、表面催化活性位多等优点,使碳纳米管在催化领域有极大的发展前景。

用本文主要讨论了碳纳米管的制备、结构及其性质,并简要介绍了碳纳米管在催化领域中的一些重要应用。

关键词:碳纳米管;制备方法;催化作用引言:人们对碳元素的认识经历了很长的时间,到目前为止,已经发现了很多不同种类的碳元素组成的物质。

在18世纪时,人们就已经确定了两种碳的同素异形体:石墨和金刚石。

到了1924年人们又确定了石墨的结构。

但仅仅是由单质碳构成的物质远不止这两种,在1985年,C60的发现使人们对碳的认识提高到了一个新的阶段。

后来日本电子显微镜专家S.Iijima于1991年在高分辨电子显微镜下检测C60时发现阴极炭黑中含有一些针状物,这些针状物是由纳米级的同轴碳原子构成的管状物,相邻两管的层间距约为0.34mn,近似于C60的半径。

Iiijma将它命名为碳纳米管。

碳纳米管,是一种具有特殊结构——其外径为1-50nm,长度为几μm-几百μm,管壁可以是单层、双层、多层的一维量子材料,它的管子两端基本上都封口,重量轻,六边形结构且连接完美,具有许多优异的力学、电学和化学性能。

虽然碳纳米管到目前为止仅被发现20几年,但它已经已经显示出巨大的应用前景并且已经广泛地影响了化学、物理、材料等众多科学领域。

本文将对碳纳米管的制备方法及其在催化领域中的应用做出重点介绍。

正文:一、碳纳米管的结构和形貌碳纳米管是由类似石墨的六边形网格所组成的管状物,其中每个碳原子和相邻的三个碳原子相连,形成六边形网格结构,因此碳纳米管中的碳原子以SP2杂化为主,但碳纳米管中六边形网络结构中会产生一定的弯曲,其中可形成一定的SP3杂化键。

电化学传感器用碳材料的制备及应用综述

电化学传感器用碳材料的制备及应用综述

电化学传感器用碳材料的制备及应用综述摘要:近年来电化学传感器由于对痕量物质检测敏感,被广泛应用于环境保护监测及医学检测等相关领域,由于碳材料具有成本低廉、检测灵敏度高、操作简单等优势,使其在电化学传器的制备过程脱颖而出。

本文综述了新型碳纳米材料、改性碳材料的制备及其修饰电极用作电化学传感器在痕量检测方面的作用。

关键词:传感器、改性、氮良好的导电、导热性,比表面积大是新型碳纳米材料具有的显著特征,使其能满足电化学传感器的性能需求,为了提高进一步碳纳米材料的电催化活性、稳定性、检测灵敏度等高性能电化学传感器需求,研究者采用不同类型的原子、分子等对碳材料进行掺杂,发现改性后的碳材料性能有明显的提升。

相比于传统化学的测定方法,成本低,操作简单,灵敏度高等优势成为改性碳材料修饰电极的一大特点。

目前关于改性碳材料的研究很多,普遍应用于一些环境或人体体液中微量物质含量的测定。

本文对新型碳纳米材料(碳纳米管、石墨烯和多孔碳)的制备方法,单独氮掺杂碳材料和复合材料掺杂碳材料的制备及其修饰电极作为电化学传感器在微量物质含量测定方面的应用进行详细的介绍。

1、改性碳材料在电化学传器的制备过程的应用应用于电化学传感器中的碳材料能够促进电子的移动和降低电化学氧化还原中的过电位作用[1]。

由于通过物理化学的方法对原型碳材料(新型碳纳米材料如碳纳米管、石墨烯、多孔碳等)进行改性掺杂其他类型的原子、分子等,使之提高电化学传感器的性能。

1.1碳纳米管碳纳米管具有高比表面积,良好的导电和机械性能,在电化学领域前景广阔。

碳纳米管的制备有两种方法:一是电弧放电、激光烧蚀法等热处理法,二是化学气相沉积法[2]。

电弧放电、激光烧蚀法是利用电弧放电或激光烧蚀将石墨加热到3000-4000℃,使碳原子挥发,从而生成碳纳米管[2]。

但热处理的方法制得的碳纳米管副产物较多,为了解决这个问题,在使用电弧法的过程中,Ebbesen[3]等人发现采用在空气中加热的方法可以除去副产物,制得纯的多壁碳纳米管。

介孔材料研究进展

介孔材料研究进展

介孔材料研究进展雷瑞【摘要】介孔材料是指孔径为(2~50) nm的多孔材料,具有孔道结构规则有序、孔径分布窄、比表面积大和孔隙率高等特点,在催化、电、磁、传感器、纳米材料合成、光学器件和色谱载体等领域具有潜在的应用价值,是近年来国际上跨学科的研究热点.介孔材料的合成采用水热合成法,为液晶模板和协同自组装机理,在介孔材料中引入灿、Co、Cr、Cu、Fe、Ga、Mn、Mo、Nb、Ti、V和Zr等可提高反应活性和表面吸附能,主要应用于分离与吸附、光学以及作为催化剂使用.如何在保持介孔结构的基础上提高材料的结晶性及功能性,利用低成本模板剂制备结构稳定、高孔隙率和高比表面积的介孔材料已成为研究热点.【期刊名称】《工业催化》【年(卷),期】2014(022)007【总页数】5页(P505-509)【关键词】催化化学;介孔材料;形成机理;应用现状【作者】雷瑞【作者单位】陕西煤业化工技术研究院有限责任公司,陕西西安710065【正文语种】中文【中图分类】TQ426.65;O643.36多孔材料因具有较高的比表面积和孔体积,经常用作吸附剂、催化剂及催化剂载体。

多孔材料根据孔径大小可分为微孔材料(孔径<2 nm)、介孔材料[孔径(2~50) nm]和大孔材料(孔径>50 nm)[1]。

1992年,美孚公司首次以烷基季铵盐阳离子表面活性剂为模板剂,成功合成了M41S系列有序介孔分子筛,将分子筛的规则孔径从微孔范围扩展到介孔领域[2-3]。

有序介孔材料是新型无机纳米结构材料,具有较大的比表面积,相对大的孔径以及规整的孔道结构,在催化反应中适用于活化较大的分子或基团,显示出优于沸石分子筛的催化性能,并成为研究热点,在分离提纯、生物材料、催化和新型组装材料等方面具有巨大的应用潜力。

本文通过介孔材料的结构特点、合成方法、形成机理及应用现状,综述介孔材料的研究现状及其发展前景。

1 介孔材料特点及分类1.1 特点介孔材料的结构和性能介于无定形无机多孔材料和具有晶体结构的无机多孔材料之间,主要特点[4]:(1) 规则的孔道结构,可在微米尺度保持高度的孔道有序性;(2) 孔径分布窄,在(2~50) nm可调;(3) 比表面积大(1 000 m2·g-1),孔隙率高;(4) 经过优化合成条件或后处理,具有较好的水热稳定性。

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介孔碳纳米材料的制备与改性摘要:介孔碳纳米材料因具有快速传输通道、优异的导电性、极高的比表面积和出色的化学稳定性在众多领域受到广泛关注。

本文分析总结了这类材料的制备和改性方法,并讨论了存在的问题和未来研究方向。

关键词:介孔碳;纳米材料;制备;杂原子掺杂;石墨化0 引言多孔碳纳米材料是一类由封闭或者相互贯通的孔结构组建而成的具有不同维度的材料。

基于其孔径大小,可以被分为微孔(孔径d<2nm)、介孔(2nm≤d≤50 nm)和大孔(d>50 nm)碳纳米材料。

介孔碳纳米材料拥有快速传输通道和非常高的比表面积,使其备受关注(图1),被广泛用于超级电容器和电池的电极材料、催化剂及生物医药的载体。

大部分介孔碳纳米结构用五元环、七元环部分取代六元环或者引入其它缺陷促使碳原子层在空间上发生扭曲,进而形成介孔。

其表征方法有三种:第一种是用气体吸附仪进行表征,吸附特征曲线反映了气体在不同表面吸附状态的差异,可以被用来研究孔道的结构类型和相关性质。

第二种方法使用透射电子显微镜(TEM)和扫描电子显微镜(SEM),其中,SEM景深大,成像具有立体感,从而可以获得孔隙结构的多维度信息。

与之相比,TEM的分辨率高很多,在观察尺寸较小的介孔结构时非常有优势。

此外,小角度X射线衍射、扫描探针显微镜和核磁共振波谱等技术也可以用于分析碳纳米材料的介孔结构。

本文主要介绍介孔碳纳米材料的制备方法,包括碳化法、模板法、化学气相沉积(CVD)法,以及利用这些方法在调控材料孔道结构和化学组成方面所取得的研究进展。

在此基础之上,从杂原子掺杂和石墨化研究两方面对介孔碳纳米材料的改性方法进行总结。

1介孔碳纳米材料的制备制备介孔碳纳米材料的方法主要包括碳化法、模板法、CVD法。

1.1碳化法该方法涉及3个阶段:(1)脱水过程(200℃下),前驱体的化学组成没有出现明显变化;(2)热解过程(200~600℃),化学成分逐渐发生改变,碳骨架基本形成;(3)碳骨架的强化过程(600~1 000℃),产物的结构确定。

该方法主要问题在于解决前驱体的选择问题,金属有机框架(MOFs)和共价有机框架(COFs)等前驱体制备介孔碳纳米材料,具有均匀的孔道分布和极大的比表面积,MOFs材料在受热过程中,能保持其介孔骨架结构。

在特定气氛中,无机金属节点会转化为金属氧化物/碳化物或被还原为单质金属,该过程可进一步增加衍生碳材料的孔隙率。

例如,Sheng等[1]以碳纳米管负载的含氮ZIF-8材料作为前驱体,经碳化处理制备了原子级分散的Fe-N-C催化剂,表现出优异的氧气还原催化性能。

1.2模板法通过碳化法制备的介孔碳纳米材料往往存在孔结构无序和孔径不均匀等问题。

模板法则可以对目标产物中的孔道结构进行精准调控,包括孔径大小和孔道形状等。

基于模板本身特征和限域能力的差别,模板法可以被划分为2种:硬模板法和软模板法。

1.2.1硬模板法硬模板法多采用具有刚性结构的材料作为模板。

由硬模板法制备介孔碳纳米材料一般包含以下4步:(1)选择模板材料;(2)将前驱体填充至模板的孔隙中;(3)利用碳化法获得产物;(4)使用酸或碱刻蚀模板。

例如,2015年,Huang课题组[2]以介孔SiO,作为模板,结合CVD法,制备了有序的氮掺杂介孔碳纳米材料,碳层数低于5(图2a)。

如图2b所示,优化的产物中含有多级孔道结构,分别位于1.8nm和4 nm附近,其比表面积高达2800 m/g。

基于该材料组装的超级电容器的比容量为855 F/g,超过文献[3-5]中报道的数值。

在使用硬模板法时,模板的刻蚀通常需要涉及强腐蚀性的化学试剂。

此外,模板材料的加工艺复杂、生产成本高,限制了其大范围应用。

1.2.2软模板法软模板法是基于液晶模板机理,以两亲性分子作为模板的方法。

借助碳源与模板剂分子之间的相互作用,自组装形成孔道有序的前驱体,后续经高温退火转化为介孔碳纳米材料。

软模板法操作简单,具有良好的可控性,常用于制备介孔碳纳米材料1.3化学气相沉积法石墨烯和碳纳米管可以形成各种三维宏观组出色的力学及电学性能,应用潜力大。

CVD是制备这些三维碳纳米材料的常用方法,下文以石墨烯泡沫和碳纳米管海绵为例进行介绍。

1.3.1石墨烯泡沫的制备2011年,Chen等[6]报道了三维石墨烯泡沫的合成,研究人员以泡沫镍和甲烷分别作为模板和碳源,在1000℃下进行反应,甲烷发生裂解并均匀沉积在泡沫镍表面生成石墨烯,随后用酸将模板刻蚀。

石墨烯片层之间相互连接形成立体网络的多孔通道,加速载流子的迁移,电导率得以提高。

此外,所得石墨烯泡沫比表面积大、质量轻,具有很好的机械性能。

1.3.2碳纳米管海绵的制备碳纳米管海绵是由单根碳纳米管之间通过π-π作用相互搭接,组装为连通的三维多孔结构,其孔隙率高(>99%),并且拥有独特的压缩和回弹特征。

Gui等[7]选择二氯苯和二茂铁分别作为碳源和催化剂前驱体,在Ar/NH3混合气氛中生长得到三维碳纳米管海绵。

该结构由多壁碳纳米管搭接而成,其外径为20-40 nm,长度达数百微米,其电阻率为6x10-3Ω·m,同时具有优异的热稳定性。

2介孔碳纳米材料的掺杂在经历高温合成时,碳材料表面的大多数含氧基团会被消除,表现出化学惰性和疏水性,限制了其在诸多领域的应用。

为了提高介孔碳纳米材料的各方面性能,需要对其进行改性研究。

常用的策略有2类:一类是通过活化来调控孔隙结构;另一类是进行杂原子掺杂,通过改变介孔碳纳米材料的电子结构和表面性质,进而改善材料的导电性、润湿性和吸附性。

如图4所示,碳材料中常见的掺杂原子有N、B、P和S。

本文主要介绍氮掺杂。

2.1氮掺杂氮与碳元素原子半径接近,与碳成键后对碳纳米材料的晶格畸变影响较小。

氮含有孤对电子,在碳骨架中可以形成离域的π键,促进电子传输。

此外,氮和碳元素电负性的差异会导致电荷密度的不均匀性分布,进而改变材料的表面物理性质和化学反应活性。

碳材料中掺杂氮原子主要有4种存在形式:吡啶型氮(pyridinic N)、吡咯型氮(pyrrolie N)、氧化型氮(Oxidized N)和石墨型氮(graphitic N)。

氮掺杂介孔碳纳米材料的制备方法可以分为原位法和后处理法。

原位法一般对富氮前驱体进行热处理,在其碳化阶段将氮原子掺入碳晶格中。

该方法得到的产物结构稳定,并且可以实现较高氮含量的掺杂。

Yang等[8]将ZIF-8纳米颗粒和聚丙烯腈的复合纤维作为复合前驱体,分别经过冷冻干燥和碳化处理(1000 ℃,1 h),制备了蜂窝状的氮掺杂碳纳米纤维气凝胶,具有很好的重复压缩性。

基于该电极材料组装的超级电容器比容量为279 F·g-1(电流密度为0.5A·g-1) 后处理法是在已经合成的介孔碳纳米材料表面引入含氮物质,然后通过高温处理或化学嫁接等方法实现氮原子的掺杂。

常用的含氮物质主要包括湿法改性剂和干法氨化剂。

如图5a所示,Oh等[9]将介孔碳球(MCS)与苯二硫醇(硫源)以及尿素(氮源)混合在一起,对该体系进行退火(900℃,2 h),制备了硫和氮共掺杂的介孔碳微球(NSMCS,氮物种主要以石墨氮和吡啶氮形式存在)。

在碱性条件下,这种不含金属的碳材料表现出和商业Pt/C催化剂相媲美的氧还原催化活性。

3介孔碳纳米材料的石墨化大多数报道的介孔碳纳米材料缺陷较多,主要为无定形碳,具有较低的电子电导率、较差的结构稳定性和力学性能。

此外,在电化学能量存储与转换应用中容易发生电化学腐蚀,致使各项性能出现明显衰减。

为了进一步提升介孔碳纳米材料的综合性能,增加其石墨化程度是关键。

如图7a所示,Cao等[10]在惰性气氛中对炭黑依次进行1600和2 800℃的高温处理,制备了石墨化程度很高的介孔碳笼结构。

产物的孔径为15~30 nm,碳层数为10~20(图7b)。

将其作为钾离子电池的负极材料时表现出超越石墨的循环稳定性。

这是因为在钾离子反复嵌入/脱出过程中,相比于平面层状的石墨结构,笼状的介孔结构具有更好的张力应变能力。

通过高温处理所获得的碳材料石墨化程度得以增强,但是生产中所需的设备成本高且反应能耗大,限制了其大范围制备与应用。

由此可见,发展高效节能的方法来实现高石墨化程度的介孔碳纳米材料的制备是当前的研究重点。

Feng等[11]以坏血酸为碳源,通过铁基催化剂合成了石墨化介孔碳材料,产物中的铁物种用盐酸去除(图7c)。

从图7d可以得知,产物的孔壁厚度为5~10 nm,呈现出清晰的碳品格条纹,碳层间距为0.34 nm,对应着石墨材料的(002)晶面。

类似地,Alshareef课题组[12]基于镍催化剂实现了介孔碳纳米材料的合成(图7e)。

实验中通过改变反应的温度可以调控产物的石墨化程度。

研究发现,当温度由600℃升高至800℃,制备的介孔碳具有最好的晶化结构(图7f),更低温度下所得产物中的很多碳原子通过sp3杂化方式参与成键。

引入过渡金属催化剂可以显著提高介孔碳纳米材料的石墨化程度,然而,目前获得的产物中依旧存在如下问题:(1)孔径分布不均匀;(2)碳层数不可控;(3)通常残留大量催化剂颗粒。

可见,高质量的石墨化介孔碳材料的合成依旧具有挑战性,仍需更加深入的研究4结论与展望介孔碳纳米材料表现出多方面突出的理化特性,具体包括:(1)高电导率和比表面积、大量的缺陷结构能够赋予材料充足的活性位点;(2)介孔结构提供畅通的传输通道,加速反应动力学过程;(3)化学修饰性强,通过引入杂原子调节电子结构,进而提升电学性能、润湿性能和吸附性能;还可以与其它活性材料通过化学作用力复合,进而提高电化学性能;(4)出色的热力学和电化学稳定性,提高石墨化程度可以拓宽工作的电压和温度区间。

因此,介孔纳米材料在电化学能量存储与转换、生物医药、环境等研究领域得到广泛应用。

通过上述总结和评述可知,介孔碳纳米材料在制备方法的发展、结构和组成的调控以及改性研究方面已经取得了很多进展。

与此同时,我们也意识到该研究领域依旧面临一些问题。

一方面,本文总结到各种制备方法都有着各自的优点和局限性,因此发展普适性的合成方法很重要,同时可以调控材料的结构和组成。

今后的研究还应该注重发展大规模制备的方法,以适用于工业化批量生产。

在改性研究方面,需要灵活运用活化、杂原子掺杂、缺陷工程和结构复合等策略,来调节介孔碳纳米材料的孔隙、组成和电子结构,进一步提升各方面性能。

为了推进介孔碳纳米材料的实际应用进程,还应该深入调查结构一性能之间的构效关系。

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