織構(gòu)可控多孔炭納米纖維的制備及其室溫脫除低濃度氮氧化物

王明璽，郭澤宇，黃正宏，康飛宇

(1.武漢工程大學 化學與環(huán)境工程學院，綠色化工過程教育部重點實驗室，湖北 武漢430074；2.清華大學 材料學院，北京100084；3.內(nèi)蒙古農(nóng)業(yè)大學 材料科學與藝術(shù)設(shè)計學院，內(nèi)蒙古 呼和浩特010010)

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織構(gòu)可控多孔炭納米纖維的制備及其室溫脫除低濃度氮氧化物

王明璽1，2，郭澤宇2，3，黃正宏2，康飛宇2

(1.武漢工程大學 化學與環(huán)境工程學院，綠色化工過程教育部重點實驗室，湖北 武漢430074；2.清華大學 材料學院，北京100084；3.內(nèi)蒙古農(nóng)業(yè)大學 材料科學與藝術(shù)設(shè)計學院，內(nèi)蒙古 呼和浩特010010)

采用靜電紡絲法制備聚丙烯腈纖維，經(jīng)預氧化、炭化和活化，得到具有孔徑發(fā)達和比表面積大的多孔炭納米纖維?？刂萍徑z液的濃度和活化條件，可制得織構(gòu)可控的多孔炭納米纖維。將所制備的纖維用于室溫低濃度NO(20 ppm)的脫除，脫除效果主要基于吸附和催化氧化作用。纖維的織構(gòu)影響其脫除NO的性能，直徑越小、微孔越豐富、比表面積越大，對NO的吸附與催化氧化效果越好。當NO進口濃度為20 ppm時，在900 ℃下活化的平均直徑為175 nm的多孔炭納米纖維脫除NO率可高達29.7%。

多孔炭納米纖維；NO脫除；織構(gòu)可控；催化氧化

1　Introduction

Nitrogen oxides (NOx) emitted from industries and automobiles result in numerous environmental problems,such as the depletion of stratospheric ozone,formation of photochemical smog and acid rain,even several ppm of NOx(mostly 90% NO and other NO2) in the air are sufficient to jeopardize the health of human being and other creatures[1,2].Then it is urgent to develop remediation technologies for removing NOx.Many technologies have been established and employed to eliminate NOx,for examples,selective catalytic reduction (SCR)[3,4]，direct decomposition[5],NOxstorage reduction (NSR)[6,7].Unfortunately,the most developed techniques,selective catalytic reduction (SCR)[4]and NOxstorage/reduction (NSR)[7]can not be applied to remove NOxin the air due to their high working temperatures (generally above 300 ℃).Therefore,novel room-temperature de-NOxapproaches need to be explored.A promising alternative is to adsorb NOxat room temperature because adsorption requires a small space for installing the related equipment and consumes low electric energy.However,NO is extremely hard to be adsorbed owing to its supercriticality[8]and chemically inactivity[9]at room temperature.It is optional to oxidize NO into NO2for achieving a high NOxremoval efficiency at room temperature,the key issue is to find a highly efficient material that can catalytically oxide NO into NO2at room temperature.

The most-studied material that catalytically oxidize NO into NO2at room temperature is carbonaceous materials[10],including activated carbon[11,12]，activated carbon fibers (ACF)[13-15]，carbon xerogels[2],and carbon nanotubes and carbon nanofibers[16].Carbonaceous materials can be used as either catalyst or catalyst supports for oxidation NO into NO2.Among the carbonaceous materials,porous carbon nanofibers (PCNFs) are the most promising materials for oxidizing NO into NO2at room temperature,which are ascribed to their high length-to-diameter ratio,nanoscale diameter,high specific surface area and well-developed pore structure.Because PCNFs possess these properties,they have drawn a great deal of interests in recent years in many fields such as energy storage and conversion devices,chemical sensors,environmental remediation[17].The pore structure and surface area are crucial to their applications,for instance,desirable surface area and open pore structure are favorable for high rate capability and cycle performance[18-21].To obtain PCNFs,various methods have been exploited including template-derived method[22,23],thermal decomposition[24,25]，electrospinning[26-28]and CNF activation[18,29].Electrospinning method has been the most popular method for preparing CNFs[30]owing to its simple process,good repeatability and large-scale production.

In our previous work,we have ascertained basically that PCNFs are able to oxidize low concentration of NO (20 ppm) into NO2at room temperature[31].In the current work,we fabricated PCNFs with various textural structures by electrospinning combined with activation,and investigated the influence of texture on the oxidation efficiency of NO at low initial concentrations at room temperature.

2　Experimental

2.1Materials

The following chemical reagents were used as received without further purification:polyacrylonitrile (PAN,Mw=150 000 g/mol) from SP2Scientific Polymer Products.Inc.(USA); N,N-dimethylformamide (DMF) from Sigma-Aldrich.

2.2Preparation of PCNFs

The polymer solution for electrospinning was prepared by dissolving a certain amount of PAN in DMF at 60 ℃ under gentle stirring for 12 h to obtain a homogenous solution.The PAN concentration of the solution was adjusted from 10 to 16 wt% for fabricating fibers with different diameters.The experimental apparatus used for the electrospinning was self-designed.The polymer solution was put in a 50 mL syringe with a capillary tip (ID=0.6 mm),the distance between the tip of needle and grounded aluminum foil collector was 18-20 cm,the applied voltage of 15 kV was used to achieve a stable Taylor cone and the flow rate was at a constant of 1 mL/h.

The electrospun fibers were stabilized by heating to 280 ℃ at a rate of 5 ℃/min in air and then holding at this temperature for 2 h.The stabilized fibers were carbonized by heating to 800-900 ℃ at a rate of 5 ℃/min for 30 min under nitrogen.Finally,the carbonized fibers were activated by supplying steam for 30 min at different temperatures.To obtain PCNFs with different surface areas and pore structures,activation temperature was kept at 800,850 and 900 ℃,distilled water for steam was supplied by syringe,nitrogen was controlled by mass flow controller and the ratio of water/nitrogen was adjusted to 20 vol%,and total flow was fixed at 200 sccm.The PCNFs obtained at activation temperatures of 800,850 and 900 ℃ were designed as PCNF10-800,PCNF10-850 and PCNF10-900,respectively.The PCNFs activated at 850 ℃ under PAN concentrations of 12,15 and 16 wt% were labeled as PCNF12-850,PCNF15-850 and PCNF16-850.

2.3Characterization

The structures and morphologies of PCNFs were characterized by a field emission scanning electron microscope (FESEM,LEO-1530).The specific surface area,pore size distribution and pore volume were analyzed by N2adsorption/desorption at 77 K in volumetric adsorption systems (BELSORP-max,BEL,Japan).To remove impurities,all the samples were degassed prior to the adsorption measurements at 200 ℃ under nitrogen for 12 h.The pore structure of PCNFs were evaluated by applying quenched solid density functional theory (QSDFT)[32,33]to the N2adsorption isotherms assuming slit-shaped pores,the specific surface areas of samples were calculated byαsmethod[34],forαsis more suitable to evaluating the surface area of samples that show typical I-type adsorption-desorption isotherms.The surface chemical compositions of PCNFs were determined by a X-ray photoelectron spectroscope (XPS) (Thermo Scientific ESCALAB 250Xi) using monochromatized AL-KX-ray source.Wide-scan spectra were recorded in a 1 eV step size with pass energy of 20 eV.All the binding energies (BE) of XPS spectra were calibrated using the C 1s electron bond energy of 284.6 eV as a reference.Temperature-programmed decomposition (TPD) experiments were conducted in a commercial ChemBet PULSAR TPR/TPD (Quantachrome,USA) unit with a TCD detection.Samples (ca.0.02 g) were loaded in a U-shaped quartz reactor and ramped from room temperature to 1 000 ℃ (10 ℃/min),in a pure He or NO or NO-O2atmosphere (100 mL/min) for TPD experiments.In all the TPD tests,PCNFs were firstly outgassed at 200 ℃ in He atmosphere (100 mL/min) for 1 h,then cooled to room temperature.For the NO/O2TPD experiments,NO/O2(60 sccm) passed through a U-shaped reactor filled with PCNFs for 60 min,then PCNFs were flushed with He at the same temperature for 30 min.Finally,the samples were subsequently subjected to TPD under He flow (100 sccm).

2.4NO removal measurement

The NO removal tests were performed in a fixed-bed quartz micro-reactor with an inner diameter of 6 mm,100 mg of PCNF samples were used in each test and the packing length of samples in the reactor was about 35 mm.The reaction temperature was monitored at 30 ℃ with a thermostatic water bath through dipping the reactor in the water bath.The typical reactant gas composition was 20 ppm NO,21 vol% O2and balance N2,and the total flow rate was controlled at 200 sccm by a mass flow control system.The concentrations of NO and NO2in the inlet and outlet of the reactor were measured by a NOxchemiluminescence analyzer of NO-NO2-NOx(Thermo Electron Co.,USA,model 42i).The NO removal ratio (R) and NO oxidation efficiency (Rc) were calculated using equation (1) and (2),in which CNO,inand CNO,outdenote the NO concentrations in the inlet and outlet gases,and CNO2,inand CNO2,outdenote the NO2concentrations in the inlet and outlet gases,respectively.

(1)

(2)

3　Results and discussion

The factors affecting the properties of nanofibers by electrospinning method are manifold[35-37],such as solution properties,processing conditions,ambient parameters.In this study,we found that the PAN concentration of the solution is the dominating factor that determines the flexibility and diameter of the fibers,so PAN solutions with different concentrations (10,12,15,16 wt%) were electrospun into fibers in order to achieve fibers with various fiber diameters.Fig.1 shows SEM images and fiber diameter distributions of PCNFs derived from PAN solutions with different PAN concentrations.The average diameters of PCNF10 are 175 to 235 nm,respectively.The PCNF12 is more uniform than PCNF10.But as the concentration rose to 15 and 16 wt%,the average diameters of fibers increased sharply to about 468 and 1 206 nm,respectively.The results manifested that the PAN concentration of the solution had prominent effects on the diameters of the electrospun-derived fibers,because an increase of PAN concentration will result in an increase of viscosity of the electrospun solutions,which can resist the tensile of spinning jet.

The applications of PCNFs in most cases depend on their textural structures including specific surface area,pore volume and pore size distribution,which can be evaluated by nitrogen adsorption/desorption at 77 K.The nitrogen adsorption isotherms and pore size distribution of PCNFs activated at different temperatures are shown in Fig.2,and the corresponding textural parameters are listed in Table 1.It is notably observed that the adsorbed amount of nitrogen increases with the activation temperature.All the isotherms belong to a typical I-type isotherm,which indicates that an increase of activation temperature leads to an increase of total pore volume and micropore volume.The pore size distributions reveal that most of the pores for all samples are micropore (<2 nm).

The activation temperature had prominent influences on the pore formation of carbon materials,because temperature dominates the dynamic behavior in the activation process.Generally speaking,a high activation temperature results in a high specific surface area,total pore volume and high burn-off.The detailed results are summarized in Table 1.It is seen that a high activation temperature facilitates the increase of specific surface area and total pore volume of PCNFs.As the activation temperature increases，the micropore volume ratio decreases while the burn-off increases.In particular,the burn-off reaches 92.3% at 900 ℃,which is far more than that of 850 ℃.So,the appropriate activation temperature is 850 ℃ for producing PCNFs.

Fig.1　SEM images of PCNFs from different PAN concentrations and their fiber diameter distributions: (a) 10 wt%,(b) 12 wt%,(c) 15 wt% and (d) 16 wt%.

As mentioned above,the fiber diameter can be tailored by adjusting the PAN concentration of the electrospinning solution,the average diameter increases from 175 to 1 206 nm as the concentration rises from 10 to 16 wt%.The fibers with different diameters were activated under the same activation temperature,amount of activating agent (steam) and activating time,and their nitrogen adsorption/desorption isotherms at 77 K and pore size distributions are displayed in Fig.3.From the isotherms,it is found that the PCNFs with various fiber diameters have different adsorption capacities of N2,the fiber with smaller diameter have the higher adsorption capacity,which indicates that the fiber with small diameter is easy to activation.

Fig.2　(a) Nitrogen adsorption/desorption isotherms and (b) pore size distributions of PCNFs obtained at different activation temperatures.

PCNFsActivationtemperatureburn-off(wt%)SSAa(m2/g)αsPorevolume(cm3/g)TPVbVcmicrocVdmesodMicroporevolumeratio(%)PCNF10-800800℃36.57780.2720.2510.02192.3PCNF10-850850℃56.48760.3150.2880.02791.4PCNF10-900900℃92.312060.5620.4630.09982.4

Note:a:Specific surface area (SSA) was calculated by theαs.b:TPV:total pore volume calculated by the quenched solid density functional theory (QSDFT) method .c:Vmicro:micropore (<2 nm) volume.d:Vmeso:mesopore (2-50 nm) volume.

Fig.3　(a) Nitrogen adsorption/desorption isotherms and (b) pore size distributions of PCNFs with different fiber diameters obtained under the same activation conditions.

Based on the nitrogen adsorption/desorption isotherms,the specific surface area calculated byαs-plot method,the pore parameters and burn-off of PCNFs derived from various PAN concentrations of the electrospinning solutions are summarized in Table 2.The specific surface area byαsdecreases from 876 to 674 m2/g,the total pore volume and micropore volume all decreases ,while the micropore volume ratio increases from 91.4% to 97.7% with the concentration from 10 to 16 wt%.

Table 2　Surface area and pore parameters of PCNFs with various diameters activated under the same activation conditions.

Up to now,the most widely investigated carbon material is activated carbon fibers (ACFs) that is applied in removing NOxat low temperature[13-15,38,39]，but the existing researches almost focused on removing NOxof high concentrations more than 500 ppm,rare researches on NOxremoval of low concentrations less than 100 ppm,because NO of low concentrations below 0.1% is very inactive at room temperature[40,41],and the conventional catalysts can not oxidize NO into NO2or reduce NO into N2.For comparison,0.100 g ACFs were used to remove NO of 20 ppm under the same conditions as PCNFs,and the breakthrough curves of NOxover ACFs are shown in Fig.4.As depicted in Fig.4,the outlet concentrations of NO and NOxis slightly lower than that of inlet in the initial 40 h,while NO2outlet concentration remains almost at 0 before 90 h,then it rises slowly to 1 ppm and keeps at this value after 90 h.The outlet concentration of NOxarrives at 20 ppm after 100 h,which was the same as the inlet NO concentration.The results indicate that ACFs have a low adsorption capability and low catalytic activity for NO of 20 ppm at room temperature,although they possess abundant micropores and high specific surface area.

Fig.4　Breakthrough curves of NOx over activated carbon fibers (ACFs) at 30 ℃.

Our previous work has confirmed that nonporous CNFs can catalytically oxide NO of 20 ppm into NO2to a certain extent at room temperature[31],but the oxidation efficiency was not ideal.NO with low concentrations cannot be removed efficiently at room temperature by ACFs having high surface area and abundant micropores alone or CNFs without pores.Therefore,it is necessary to combine the advantages of ACFs and CNFs for removing low concentration NO at room temperature.

Firstly,we investigated the effects of surface area and pore volume of PCNFs on the NO removal,PCNF10 activated at different temperatures were used to remove NO at room temperature.The textural parameters of PCNF10 are summarized in Table 1.PCNFs contain abundant micropores and have high surface areas,thus they have strong adsorption capability for NOx,especially for NO.The breakthrough curves of NOxover PCNFs are displayed in Fig.5.The breakthrough times of NO are 1,2 and 3 h over PCNF10-800,PCNF10-850 and PCNF10-900,respectively,which reveal that the increase of surface area and micropore volume is beneficial to the adsorption of NO.The outlet concentrations of NO2over PCNF10-800,PCNF10-850 and PCNF10-900 at steady state are 3.2,6.0 and 6.5 ppm,respectively,which are much higher than that over ACFs.The breakthrough curves of NO2confirm that NO oxidation is enhanced with the increase of the surface area and micropore volume.Based on the equation (1) and (2),the calculated NO removal ratios (R) over PCNF10-800,PCNF10-850 and PCNF10-900 are 11.4%，27.6%，29.7%,and NO oxidation efficiencies (Rc) are 9.2%，24.3%，27.0%,respectively,which demonstrate that the removal and oxidation efficiency of NO are strongly dependent on the specific surface area and micropore volume.

Fig.5　NO removal over PCNF10 derived from different activation temperatures: (a) PCNF10-800,(b) PCNF10-850 and (c) PCNF10-900.

It is worth noting that the breakthrough time of NO2is shortened from 80 to 50 h as the surface area and pore volume rise.This can be explained by the following two aspects.NO2competes with NO in adsorption,the rapid increase of NO adsorption amount might result in the decrease of NO2adsorption as the surface area and pore volume increase.NO can be also oxidized more readily and rapidly to produce a large amount of NO2,so it is fast to reach equilibrium adsorption for NO2,resulting in the reduction of breakthrough time of NO2.This further proves that the increase of surface area and pore volume can improve the catalytic activity of NO oxidation at room temperature.

Besides the surface area and pore volume of PCNFs,thefiber diameter also plays an important role on the NOxremoval efficiency,which can be known from the results of NOxremoval over ACFs and PCNF10.To further explore the effects of fiber diameter on NOxremoval,PCNFs with different fiber diameters were obtained by adjusting the PAN concentration of electrospinning solution under the same activating conditions.The breakthrough curves of NOxover PCNFs with different fiber diameters are presented in Fig.6.The outlet concentrations of NO are zero at the initial stage for all PCNFs,whereas the breakthrough times of NO decrease from 3 to 1.5 h with the increase of fiber diameters.The breakthrough time of NO over PCNF12-850 is close to that over PCNF10-850,for their fiber diameter difference is small.After NO breakthrough,its concentration rises gradually until the steady state is attained,and the steady-state NO outlet concentration over PCNF12-850,PCNF15-850 and PCNF16-850 are 15.8,17.8 and 18.2 ppm,respectively.Obviously,the breakthrough time and outlet concentration of NO2at steady state also decreases with the increase of PCNFs’ fiber diameter.These results suggest that thin fiber diameter and developed micropore structure are in favor of the NO removal through the adsorption and oxidation.In other words,the thinner the fiber diameter of PCNFs is,the higher the adsorption capability and catalytic activity are,which is correlated with their micropore structure.On one hand,the micropores in the PCNFs with smaller fiber diameter are more uniform and most of them are shallow pores,but the pores in PCNFs with larger fiber diameter are heterogeneous and the depth of pores is greater,leading to reduction of the actual available micropores and surface area[42].On the other hand,the NO removal over PCNFs relies on adsorption and catalytic oxidation involving mass transfer,deeper pores and deep path in the pores are detrimental to mass transfer due to bigger mass transfer resistance.Correspondingly,the adsorption capability and catalytic activity will be weakened as the fiber diameter rises.

Fig.6　NOxbreakthrough curves over PCNFs derived from different PAN concentrations: (a)PCNF12-850 (12 wt%),(b) PCNF15-850 (15 wt%) and (c) PCNF16-850 (16 wt%).

To explore the species adsorbed on PCNFs during the NO adsorption and oxidation,TPD tests were conducted for PCNF10-850 after adsorption for 60 min in a gas of 10 vol% NO balanced with He,or pure O2,or a gas mixture of 10 vol% NO,21 vol% O2and 69 vol% N2.Fig.7 presents the desorption spectra of PCNF10-850 after adsorption of above gas mixtures.The thermal decomposition analyses in He is shown in Fig.7a,the TPD signal presents a main broad peak in the temperature interval 785-980 ℃,with Tmax≈918 ℃.The broad peak is contributed to the overlap of carbon oxides (CO and CO2) decomposed from different oxygen complexes.The TPD spectra were deconvolved by Gaussian functions to determine the contribution of each type of surface oxygen groups,which are inserted in Fig.7a.As shown in this figure,the broad peak is consisted of three peaks located at 797，860 and 922 ℃.It is controversy in the literature and difficult to assign each of the deconvolved peaks to specific groups[43].Generally speaking,the CO peak results from phenolic,carbonyl,anhydride,ether and quinine groups,while the CO2peak results from carboxylic acids or lactones[44].The NO-TPD spectra are shown in Fig.7b,another two peaks located at 250 and 515 ℃ appears,the mass spectra of NO-TPD shown in Fig.8 demonstrate that the peak at 250 ℃ is deconvolved into two peaks centered at 150 and 248 ℃,which are assigned to the desorption of NO[45].To further study the NO adsorption and oxidation on PCNFs,NO and O2simultaneously passed into the bed flled with PCNFs in the U-shape reactor,then TPD experiments were conducted and the results are presented in Fig.7c.It is noted that the peak of NO desorption is enhanced and the peak of CO (M/Z=28) decomposition is shifted to higher temperature,which indicate that the presence of O2facilitates the adsorption of NO.

Fig.7　TPD profiles of PCNF10-850: (a)He,(b) NO and (c)NO/O2.

XPS was performed to investigate the surface elemental compositions,the change of nitrogen functional groups,and the results are shown in Fig.9.For the N1s spectra before adsorption of NO/O2,the broad peak in the (BE) range of 395-403 eV could be deconvolved into two peaks centered at 398 and 401 eV,which are ascribed to the surface pyridine functional groups and pyrrole functional groups.But for the N1s spectra after adsorption of NO/O2,another new broad peak is observed clearly,which is the overlap of two peaks located at 405.9 and 407.2 eV for —NO2,—NO3group,respectively[46].Furthermore,by comparing the XPS spectra of Fig.9a and 9b,it is easy to find that the two peaks at 398 and 401 eV shift toward right,their relative strength also change prominently,the peak at 398 eV is weakened while the peak at 401 eV is enhanced,indicating an increase of the relative amount of pyrrole functional groups.This confirms that the adsorbed NO is oxidized into NO2over PCNFs in the presence of O2,because a chemical shift toward high BE results from an increase of oxidation state for an element.

According to the breakthrough curves of NOxover PCNFs,the outlet concentration of NO in the initial stage of several hours was very low even 0,then it ascended rapidly to a maximum value and kept at this value for a long time,finally it dropped and arrived at a steady state after NO2broke.It can be deduced that the adsorption of NO over PCNFs was divided into two stages.In the first stage,NO was adsorbed on PCNFs by physisorption,after some time,it reached adsorption saturation due to the limit of PCNFs’ adsorption capacity,the surface adsorption sites for NO were completely occupied,leading to the breakthrough of NO.In the second stage,the adsorbed NO reacted with O2in the gas phase to produce adsorbed NO2(—NO2) and the adsorption sites for NO were released,the outlet concentration of NO decreased and reached a new steady state.

Fig.8　NO-TPD/MS profiles of PCNF10-850:(a)M/Z=30 and (b)M/Z=28.

Fig.9　Deconvolved XPS spectra of nitrogen groups (N1s) on PCNF10-850: (a) before adsorption of NO/O2and (b) after adsorption of NO/O2.

4　Conclusions

PCNFs with controlled textural structures were obtained through pre-carbonization of PAN-based electrospun nanofibers,followed by physical activation with steam in N2atmosphere.The PAN concentrations of electrospinning solution and steam activation conditions have significant effects on the fiber size and porosity of the PCNFs.A lower PAN concentration of electrospinning solution generated fibers with a thinner diameter,and a higher activation temperature led to formation of developed pores with a higher specific surface area and pore volume.The as-prepared PCNFs were used to remove NO with low concentrations at room temperature through adsorption and catalytic oxidation.It was found that the diameter of fiber,surface area and pore volume play major roles in NO removal.The breakthrough time of NO over PCNF10 and NO oxidation efficiency increased with the specific surface area and pore volume,the highest NO removal ratio (R) and NO oxidation efficiency (Rc) can reach 29.7% and 27%,respectively,when the inlet concentration of NO was 20 ppm.The textural structure of PCNFs can be adjusted effectively by changing the spinning and activation conditions,and their textural structures have prominent effects on their NO removal performance.

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Preparation of porous carbon nanofibers with controllable pore structures for low-concentration NO removal at room temperature

WANG Ming-xi1,2,GUO Ze-yu2,3,HUANG Zheng-hong2,KANG Fei-yu2

(1.Key Laboratory for Green Chemical Process of Ministry of Education,School of Chemical and Environmental Engineering, Wuhan Institute of Technology,Xiongchu Avenue 693,Wuhan430074,China;2.Lab of Advanced Materials,School of Materials Science and Engineering,Tsinghua University,Beijing100084,China;3.School of Materials Science and Art Design,Inner Mongolia Agriculture University,Hohhot010010,China)

Porous carbon nanofibers (PCNFs) with controllable pore structures for removing low-concentrations of NO at room temperature were prepared from electrospun polyacrylonitrile nanofibersby oxidative stabilization,carbonization and steam activation.The PCNFs had high surface areas and abundant micropores,which were favorable for the adsorption and catalytic oxidation of NO at ambient temperature.The diameter of the fibers and their pore structure were tailored by adjusting the concentrations of polyacrylonitrile,and the spinning and activation parameters.Their performance in the removal of low-concentration NO was strongly dependent on their pore structure and fiber diameter.The highest NO removal ratio for PCNFs activated at 900 ℃,which had an average diameter of 175 nm,reached 29.7% when the inlet NO concentration was 20 ppm.

Porous carbon nanofibers (PCNFs); NO removal; Controllable texture; Catalytic oxidation

date:2016-05-08;Revised date:2016-06-04

Cooperative Project JST-MOST (2011DFA50430,2008DFA51410).

HUANG Zheng-hong,Associate Professor.E-mail:zhhuang@mail.tsinghua.edu.cn

1007-8827(2016)03-0277-10

TQ127.1+1

A

中日國際科技合作項目JST-MOST (2011DFA50430，2008DFA51410).

黃正宏，博士，副研究員.E-mail:zhhuang@mail.tsinghua.edu.cn

English edition available online ScienceDirect ( http:www.sciencedirect.comsciencejournal18725805 ).

10.1016/S1872-5805(16)60013-6