morphologic and surface characterization of different types of activated carbon fibres

355

Morphologic and Surface Characterization of Different Types of ActivatedCarbon Fibres

Jo Anne G. Balanay1* and Claudiu T. Lungu2 (1) Environmental Health Sciences Program, Department

of Health Education and Promotion, College of Health and Human Performance, East Carolina University, Greenville,

NC 27858, U.S.A. (2)School of Public Health, University of Alabama at Birmingham, RPHB 530, 1530 3rd Avenue S.

Birmingham, AL 35294, U.S.A.

(Received 25 January 2012; revised form accepted 13 March 2012)

ABSTRACT: This study provides a comparison of different types ofcommercially available activated carbon fibres (ACFs). Thus, ACFs in cloth(ACFC) and felt forms (ACFF) with three different surface areas were eachanalyzed for their pore volumes, pore sizes and pore-size distributions. The fibremorphology and organization was visualized using scanning electron microscopy(SEM). The microporosity of the ACF materials based on nitrogen isotherms, thepercentage of micropores by area and volume, the average pore size and the pore-size distribution were also determined. An increase in the surface areas of theACFC types led to an increase in the total pore volume, micropore volume,micropore area and pore width, but led to a decrease in the percentage ofmicropores by area and volume. The nitrogen isotherms demonstrated that thesurface area dictated the amount of adsorption onto the ACF regardless of the formof the latter. The difference in the volume of smaller micropores between theACFC and ACFF types may be attributed to the difference in the adsorbent densityand the accessibility of the fibre surface to the activating gas during the activationprocess. An understanding of the pore structure of ACFs by form and surface areais crucial in determining the appropriate specific applications of such adsorbents.

1. INTRODUCTION

Activated carbon has been historically used in the adsorption of gases and vapours (Fontana 1777;Cheremisinoff and Ellerbusch 1978; Hall and King 1988). Its various important applicationsinclude the separation of mixtures, purification of liquids, recovery of gaseous components andcatalysis (Bansal et al. 1988). It has been recognized that the role of surface area and porosity inactivated carbon and other carbonaceous porous materials is important in the adsorption process(de Saussure 1814; Mitscherich 1843). Adsorption is considered a surface phenomenon and, thus,the extent of adsorption is proportional to the specific surface area, which represents the portionof the total surface area that is available for adsorption. Hence, the more porous the solid is, thegreater the adsorption per unit weight of adsorbent (Weber Jr. 1972).

Individual pores may vary greatly in size and shape within a given adsorbent and betweendifferent adsorbents (Sing 1989). Pores are characterized by their width, w, which represents thediameter of a cylindrical pore or the distance between the sides of a slit-shaped pore. Accordingto the International Union of Pure and Applied Chemistry (IUPAC), pores are classified as

*Author to whom all correspondence should be addressed. E-mail:[email protected].

follows: macropore, having a pore width greater than 50 nm; mesopore, with a pore widthbetween 2 to 50 nm; and micropore, with a pore width of less than 2 nm.

In turn, surface area and porosity are influenced by several factors, such as the nature of theprecursor materials, the method of activation and the heat-treatment temperature (Ryu et al. 2000;Rong et al. 2003). An increase in the degree of activation of the activated carbon results in anincreased specific surface area, pore volume and pore diameter (Suzuki 1994). Different types ofactivation methods (i.e. chemical and physical) determine the dominant pore types of theadsorbent (Ryu et al. 2000). Thus, the degree of activation must be controlled for the selectiveadsorption of variously sized molecules.

Activated carbon fibres (ACF) are fibrous carbonaceous adsorbents obtained by thecarbonization and activation of polymeric fibres that can be prepared from various precursors.Novoloid, poly(acrylonitrile) (PAN), pitch and rayon precursors, with diameters in the range 10–20µm, are a few examples (Lo 2002). The small fibre diameter allows the homogeneous activation ofthe fibres, thus yielding a material with a narrow pore-size distribution composed mainly ofmicropores (Feng et al. 2005). Micropores in ACFs are known to be straight and uniform in size,and are directly accessible from the external surface of the fibre. Because of this, the adsorptionsites in ACFs can be accessed more easily than in other forms of activated carbon; hence, theadsorption kinetics are obviously faster than that of granular activated carbon (GAC) (Lo 2002).ACFs are unique as compared to traditional activated carbon adsorbents such as GAC because oftheir larger surface areas (1000–2400 m2/g), larger adsorption capacities (as high as 250% of thatof GAC) and faster heat and mass transfer properties (Petkovska et al. 1991; Lo 2002). ACFs canbe manufactured in various forms, such as woven cloth and unwoven felt, and are easy to handle(Huang et al. 2002).

Several studies have been conducted to assess the usefulness of ACFs in air pollution controldevices (Takeuchi et al. 1993; Huang et al. 2003; Cheng et al. 2004; Das et al. 2004; Hashishoand Rood 2005; Lorimier et al. 2005). In such applications, ACFs have been shown to be veryeffective adsorbents for capturing water vapour and organic vapours, such as benzene, toluene andxylene, from gas streams over a wide range of concentrations (Ramirez et al. 2004; Sullivan et al.2004; Fournel et al. 2005; Mallouk et al. 2010). Filters composed of a mat of ACFs have also beenused in the capture of toxic gases emanating from industrial processes and gasoline vapours fromautomobile tanks (Kohata et al. 1980; Fukuda et al. 1989). Other applications of ACFs includeenvironmental cleaning, the recovery of sulphur dioxide and nitric oxide in flue gas, energy savingand storage such as methane storage, carbon dioxide (CO2) capture, and air separation (Kitagawa1993; Kisamori et al. 1994; Mochida et al. 1994; Lozano-Castello et al. 2002).

The aim of the present study was to characterize different types of commercially availableACFs and compare their properties such as surface area, porosity and fibre morphology. Thesephysical characteristics are associated with the adsorption characteristics of activated carbons, andmay be important when considering the use of these adsorbent materials for specific applications.

2. MATERIALS AND METHODS

2.1. Materials

Two forms of ACFs, i.e. cloth and felt, were used as adsorbents and characterized in this study.The thickness of the ACF cloth (ACFC) was 0.0625 cm while that of the ACF felt (ACFF) rangedfrom 0.2 cm to 0.3 cm, which was 3–5-times greater than that of the ACFC. For each form, three

356 J.G. Balanay and C.T. Lungu/Adsorption Science & Technology Vol. 30 No. 4 2012

different manufacture-specified surface areas (ranging from 1000 m2/g to 2000 m2/g) were tested.Thus, six types of ACF were analyzed in this study. Table 1 lists the notation for each ACF basedon its form and surface area.

ACFC1000, ACFC1500, ACFF1500 and ACFC2000 are manufactured from phenol aldehyde-based, or novoloid, fibre precursors by American Kynol, Inc., Pleasantville, NY, U.S.A. Thenovoloid fibres contained approximately 76% carbon, 18% oxygen and 6% hydrogen. ACFF1000and ACFF1800 are manufactured from viscose rayon fibres by Beijing Evergrow Resources Co.,Beijing, P. R. China; their chemical composition was not disclosed by the manufacturer. The ACFswere cut into 4-cm diameter discs and degassed in an oven (Thermo Electron Corporation,Waltham, MA, U.S.A.) overnight at 200 °C prior to testing, in order to desorb any volatileimpurities and moisture from the ACF materials.

2.2. Determination of surface characteristics

The surface area, pore size and pore volume of the ACF samples were measured by nitrogenadsorption at –196 °C over a range of relative pressure (P/P0) from 0.02 to 1.0 using aMicromeritics ASAP 2020 automatic physisorption analyzer (Micromeritics Corp., Norcross,GA, U.S.A.). High-purity nitrogen (99.99%) (Airgas Inc., Radnor, PA, U.S.A.) was used in themeasurements. All samples underwent both the degassing and analysis processes in thephysisorption analyzer. The degassing process pre-treated the adsorbent sample by applying acombination of heat, vacuum and/or flowing gas to remove adsorbed contaminants acquiredfrom exposure to the atmosphere, and was performed at 300 °C for 1 h prior to the analysis.The analysis process involved the incremental dosing of nitrogen to the adsorbent samples.The quantity of nitrogen required to form a monolayer over the external surface of theadsorbent and its pores was determined at particular pressures. Knowing the area covered byeach adsorbed nitrogen gas molecule, it was possible to calculate the surface area. Threeanalyses (n = 3) were performed for each ACF type, giving a total of 18 physisorptionanalyses. The actual BET surface area was specifically measured to verify the surface areaspecified by the manufacturer of the ACF (nominal surface area).

The pore-size distribution of each ACF material was obtained in order to determine thepercentage of micropores, mesopores and macropores in the adsorbent. For pore-size distributionanalysis, the ACF materials were sent to the Instituto de Física Aplicada, Consejo Nacional deInvestigaciones Científicas y Técnicas – Universidad Nacional de San Luis (Institute of AppliedPhysics, National Council of Scientific and Technical Research – National University of San Luis)in Argentina. The Density Functional Theory (DFT) method was also used to calculate themicropore size distribution of the samples in particular; this method is based on a molecular modelof adsorption of nitrogen in porous solids (Ryu et al. 2000).

Morphologic and Surface Characterization of Different Types of Activated Carbon Fibres 357

TABLE 1. Notation of ACF Types Based on ACF Characteristics

Form Nominal surface area (m2/g)

1000 1500 1800 2000

Cloth ACFC1000 ACFC1500 – ACFC2000Felt ACFF1000 ACFF1500 ACFF1800 –

2.3. Scanning electron microscopy (SEM) images

Scanning electron microscopy (SEM) images of the different ACF samples were obtained for thepurpose of visualizing the organization, structure and texture of the fibres of the ACF. SEM imagesobtained from the Department of Material Science and Engineering, School of Engineering,University of Alabama at Birmingham were taken at 40.8 × and 5450 × magnifications. SEM imagesobtained from the Department of Metallurgical and Materials Engineering, College of Engineering,University of Alabama in Tuscaloosa were taken at 6000 × and 100,000 × magnification.

3. RESULTS

3.1. Characterization by form, surface area and porosity

Table 2 summarizes the surface characteristics of each ACF type, including the average surfacearea, pore volume and pore size (n = 3). The results demonstrate that the measured surface areaof the each ACFC was similar to that of its ACFF counterpart (i.e. ACFC1000 versus ACFF1000and ACFC1500 versus ACFF1500). Moreover, the ACFC2000 sample had a measured surfacearea comparable to that of the ACFF1800 sample. Thus, the samples ACFC2000 and ACFF1800can be considered as counterparts and may be compared against each other.

For both cloth and felt forms, as expected, the total pore volume increased as the surface areaincreased. The average pore sizes across all the ACF types were very similar, ranging from 1.67nm to 1.84 nm. For the ACFC types, as the surface area increased, the micropore area and volumealso increased, but the percentage of micropores by area and volume decreased. This trend wasnot observed in the ACFF types, which may imply that factors other than surface area affected theporosity of the materials. Furthermore, ACFC2000 and ACFF1800 were relatively similar withrespect to surface area and pore size, but had very different micropore areas and volumes, which


TABLE 2. Average Surface Area, Pore Volume and Pore Size by ACF Type (n = 3)

Parameters ACF type

ACFC1000 ACFC1500 ACFC2000 ACFF1000 ACFF1500 ACFF1800

Nominal surface 1000 1500 2000 1000 1500 1800area (m2/g)

BET surface area 891.8 ± 7.8 1470.8 ± 8.9 2052.8 ± 6.2 979.9 ± 19.0 1407.3 ± 14.8 1861.1 ± 7.4(m2/g)

Micropore areaa (m2/g)840.2 ± 7.5 1336.9 ± 2.4 1726.7 ± 18.9 876.8 ± 27.3 1277.9 ± 11.3 1041.8 ± 54.3% Micropores by area 94.2 ± 0.6 90.9 ± 0.5 84.1 ± 0.7 89.5 ± 1.39 90.8 ± 0.2 56.0 ± 3.1Pore volumeb (cm3/g) 0.39 ± 0.00 0.62 ± 0.00 0.86 ± 0.01 0.43 ± 0.01 0.59 ± 0.01 0.86 ± 0.01Micropore volumea 0.36 ± 0.01 0.54 ± 0.00 0.69 ± 0.01 0.36 ± 0.01 0.51 ± 0.01 0.42 ± 0.02

(cm3/g)% Micropores by 92.0 ± 0.8 87.5 ± 0.7 78.2 ± 1.5 83.9 ± 3.3 87.4 ± 0.3 49.2 ± 3.1

volumePore sizec (nm) 1.74 ± 0.01 1.69 ± 0.01 1.71 ± 0.01 1.74 ± 0.08 1.67 ± 0.01 1.84 ± 0.02

aBy t-plot method. bSingle-point adsorption total pore volume estimated at a relative pressure ≥0.95. cAdsorptionaverage pore width (4V/A by BET).

were much lower for ACFF1800. This may be due to the fact that different precursors were usedin manufacturing these ACFs, thus resulting in a different pore structure.

3.2. Nitrogen adsorption isotherms

Nitrogen adsorption isotherms have been widely used as a standard tool for characterizing theporosity of materials. Important information about the surface area and pore structure ofadsorbents can be obtained from the adsorption isotherm. The adsorption and desorptionisotherms of nitrogen for each ACF type at a temperature of –196 °C are shown in Figure 1.


Relative pressure, P/P0

Qua

ntity

ads

orbe

d [c

m3 /

g (S

TP

)]

600

ACFC1000

ACFC1500

ACFC2000

ACFF1000

ACFF1500

ACFF1800

500

400

300

200

100

00 0.2 0.4 0.6 0.8 1

Figure 1. Nitrogen adsorption/desorption isotherms at –196 °C for different ACF types.

The shape of isotherms for all ACF types indicates that they were of Type I or of the Langmuirtype according to the IUPAC classification (Gregg and Sing 1982). Such an isotherm typeindicates that the materials were essentially microporous. It is apparent that most of the porevolumes of the ACFs, except ACFF1800, were filled below P/P0 � 0.1, showing that thesematerials were highly microporous. For ACFF1800, most of the pore volume was filled belowP/P0 � 0.3, as shown in Figure 2, which indicates that some larger pores (e.g. small mesopores)may have still existed. After a sharp increase to P/P0 = 0.1, the isotherms gradually levelled off,indicating smaller increments in further adsorption. The ACFCs, in general, had a slightly highernitrogen adsorption uptake than the ACFFs with a similar surface area, except for samplesACFC1000 and ACFF1000 where the felt material exhibited a higher nitrogen uptake than thecloth material.

Generally, an adsorption isotherm rises as the relative pressure is increased and reversing theprocedure – known as desorption – by reducing the relative pressure leads to a re-tracing ofthe adsorption curve. However, the adsorption curve of certain adsorbents is not re-traced bythe desorption curve, resulting in a loop on the isotherm. This phenomenon is known ashysteresis, being typical of mesoporous and macroporous materials with pores that are likely tohave a wide range of sizes and shapes. Hysteresis loops were observed for the isotherms ofACFF1000 and ACFF1800, which were both manufactured by Beijing Resources (see Figure

3). These hysteresis loops closed in the pressure region near saturation, which shows that theACF types concerned contained mesopores with an upper size restriction (Webb and Orr 1997).This unique characteristic may be attributed to the fibre precursor and the activation processused (which was different from those employed for the rest of the ACF types) resulting in adifferent pore structure.



Qua

ntity

ads

orbe

d [c

m3 /

g (S

TP

)]

600

ACFC1000

ACFC1500

ACFC2000

ACFF1000

ACFF1500

ACFF1800

500

400

300

200

100

00.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Figure 2. Nitrogen adsorption isotherms at –196 °C for different ACF types over the relative pressure range 0.0–0.4 P/P0.

0.0

Qua

ntity

ads

orbe

d [c

m3 g

/ (S

TP

)]

280

275

270

265

260

255

250

245

240

550

540

530

520

510

500

490

480

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0


ACFF1800

ACFF1000

Figure 3. Hysteresis loops in nitrogen adsorption/desorption isotherms at –196 °C for ACFF1000 and ACFF1800.

3.3. Pore-size distribution

Analyzing the entire pore-size distribution of adsorbent is important because differences in thepore size affect the adsorption capacity towards molecules of various shapes and sizes. The pore-size distribution is also one of the criteria by which carbon adsorbents are selected for a specificapplication.

The pore-size distributions of the ACF samples were determined using the DFT method. Asshown in Figure 4, the pore sizes of all the ACFs were less than 3 nm in diameter. All ACF typespossessed a large number of micropores; some types contained some mesopores, but nomacropores. Sample ACFC1000 exhibited a dominant peak at ca. 1 nm, which demonstrates that


0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

0.110.100.090.080.070.060.050.040.030.020.010.00

0.1 1 10 100

ACFC1500 ACFF1500

ACFF1000ACFC1000

ACFC2000 ACFF1800

Pore width (nm)

Por

e vo

lum

e (c

m3 /

g)

Figure 4. Pore-size distributions of different ACF types.

the pore-size distribution in this sample was more concentrated around this value than those forthe other ACF types. Most of the micropores in sample ACFC1500 had diameters of ca. 0.9 nm,but this sample also exhibited a secondary peak at ca. 1.2 nm. In addition to 0.9-nm micropores,ACFC2000 exhibited smaller peaks over the pore width range 1–2 nm. Thus, for the ACFC types,there was an increasing volume of larger micropores as the surface area increased. The pore-sizedistribution for sample ACFF1000 exhibited mainly micropores distributed from 0.9 to 2 nm, andhad a lower volume of micropores of 1 nm diameter. Sample ACFF1500 exhibited a highervolume of micropores than ACFF1000 but size range remained the same. Sample ACFF1800 hadthe highest pore volume amongst the ACFF types, and had a wider pore size range of 0.9–3 nm.This sample also contained some mesopores whose diameters ranged from 2 nm to 3 nm on thebasis of the pore-size distribution.

Comparing the ACF forms, all the ACFC types possessed a greater volume of micropores withsmaller diameters. Such a difference in micropore-size distribution may be attributed to thedensity of the ACF and the accessibility of the fibre surface to the activating gas during theactivation process. Since the ACFCs had tightly woven fibres compared to the ACFFs, some oftheir fibre surfaces would be less accessible to the activating gas that etched the pores away,resulting in pore widening and a decrease in the volume of smaller micropores. Irrespective of thetype of precursor employed in the ACFF types, all these ACF forms had a lower volume of smallermicropores compared to the ACFCs. Thus, the pore-size distribution may have been significantlyinfluenced by the physical form of the ACF.

3.4. Scanning election microscopy (SEM) images

The images obtained from SEM analysis basically illustrated the fibres of the ACF materials atlower magnifications, and the surface texture of the materials as an indication of porosity at highermagnifications. As shown in Figure 5, at the lowest SEM magnification (40.8×) the inter-fibrestructures of the cloth and felt forms were very different. The ACFC was composed of woven


Figure 5. SEM images of activated carbon fibres at 40.8 × magnification.

yarns of twisted fibres, while the ACFF was composed of non-woven, randomly distributed fibres.This characteristic gave the ACFC cloth a much denser form compared to the ACFF. For theACFC, the higher the surface area, the tighter the weave of the fibres (see Figure 5, micrographs1–3). An estimate of the weave tightness was undertaken by visually counting the number of knotsper cm2 on the SEM image. Samples ACFC1000, ACFC1500 and ACFC2000 had 99 knots, 104knots and 120 knots, respectively. With the ACFF, the higher the surface area, the more fibres perarea of the material were present (see Figure 5, micrographs 4–6).

At 5450 × magnification (Figure 6), individual fibres were clearly shown but the magnificationwas insufficient to visualize the pores. At this magnification, the fibres were seen to be ca. 6–8µm in diameter, cylindrical with apparently smooth surfaces, other than samples ACFF1000 and


Figure 6. SEM images of activated carbon fibres at 5450 × magnification.

ACFF1800 which exhibited ridged surfaces and thinner fibres (5–7 µm). It is interesting to notethat these two different ACF types were from the same manufacturer (Beijing) while the other fourACF types were from another company (American Kynol).

When the fibre end of each ACF type was magnified 6000 × (as shown in Figure 7), samplesACFF1000 and ACFF1800 were also shown to have ridged fibres, with smooth surfaces. The restof the ACFs with cylindrical fibres had more prominent pores on the fibre surfaces. This is alsodemonstrated in Figure 8 at 100,000 × magnification where ACFF1000 and ACFF1800 may beseen to have smoother surfaces compared to the other ACF types that had surface that wereobviously more porous. The surface areas of ACFF1000 and ACFF1800 may be attributed to theridges on the fibre and the space left between adjacent fibres due to these ridges, not to the poreson the surfaces of the fibres since the fibres were smoother (not very porous) compared to the otherACFs. At this magnification (100,000 ×), the surface states of the various ACF types were shownbut the micropores and mesopores were not visualized and, hence, cannot be described on the basisof the images depicted.

4. DISCUSSION

Based on the pore-size distributions and SEM images, the surface areas of the ACF materials mayhave been increased in two ways: (1) increasing the density of the material, and (2) increasing thedegree of activation. First, the density of the ACFs and the morphology and organization of the fibresis shown in the SEM images. As far as the ACF form was concerned, the surface area apparentlyincreased on increasing the density of the ACF, i.e. the fibre mass per volume. This was achieved bymaking the fibre weave closer for the ACFC and increasing the fibre packing for the ACFF.


Figure 7. SEM images of activated carbon fibres at 6000 × magnification.

Figure 8.SEM images of activated carbon fibres at 100,000 × magnification.

Secondly, increasing the degree of activation may also have resulted in increasing the surface areaas well as pore volume. The effect of increasing the length of the activation process resulted thewidening of the micropores as shown by the pore-size distributions, particularly of the ACFC types.The size range of the micropores increased while the volume of the larger micropores also increased.This phenomenon has also been observed in several other studies where it was noted that the surfacearea increased as the degree of activation increased (Foster et al. 1992; Suzuki 1994; Tanada et al.2000). Specifically, Tanada et al. (2000) showed that ACFs that had received the strongest activationpossessed the highest specific surface area and the largest pore volume, but the smallest microporevolume. In addition, Foster et al. (1992) demonstrated that the length of the activation process causesan enlargement of the micropores, shifting the pore distribution to higher pore sizes.

Increasing the surface area of the ACFC types apparently increased the total pore volume,micropore volume and micropore area, but decreased the percentage of micropores by area andvolume. This decrease in the micropore percentage may be attributed to pore widening resultingin the formation of some mesopores due to the increased degree of activation. Since they camefrom a common manufacturer, this trend was particularly notable in the ACFC forms whereseveral factors were controlled in the ACFs on which they were based, including the fibreprecursor, carbonization and activation process. On the other hand, this trend was not observed inthe ACFF forms because they came from two different manufacturing sources and thus, manyfactors, including the precursor, were not controlled amongst these ACF forms. In fact, this wasan important limitation in the present study. The use of ACF materials derived from a commonprecursor is highly recommended in future studies to confirm the effects of the above-mentionedmechanisms in increasing the ACF surface area.

Determining the pore structure of ACF types by form and surface area is crucial inunderstanding the usefulness of an ACF in a specific application. One example is determiningwhether an ACF type is best for the adsorption of a particular gaseous component, taking accountof the porosity of the adsorbent. Several studies have shown that gases or vapours are betteradsorbed into sorbents having an extensive micropore structure, with pores that have dimensionscomparable to those of the adsorbed molecules. The capture of larger molecules may not beappropriate for ACFs with smaller micropores. A study by Tanada et al. (2000) found it wasimpossible for nonafluorobutyl methyl ether (NFE) to move into the pores when adsorbed onto anACF with micropores of diameter less than 1.5 nm, simply because the pores were too narrow toallow access to the adsorbate molecule. Moreover, another study has shown that highlymicroporous ACFs exhibited higher adsorption affinities to low molecular weight aromaticorganic compounds than carbon nanotubes with higher mesopore and macropore volumes(Kisamori et al. 1994). Adsorbents with larger pores would be expected to be more efficient in theadsorption of large size molecules, which may move more readily into these larger pores. Hence,the width of micropores in the adsorbent must be matched to the dimensions of gas or vapourmolecules to be adsorbed.

5. CONCLUSIONS

On the basis of the corresponding nitrogen adsorption isotherm type (Type I), it was shown thatall the ACF materials investigated were mainly composed of micropores, with variations in thepercentage of micropores by area (ranging from 56.0–94.2%) and by volume (ranging from49.2–92.0%), the average pore size (ranging from 1.67–1.84 nm) and the pore-size distribution(most pores have a width less than 2 nm).


The surface areas of the ACFs were increased by increasing the bulk density and degree ofactivation of the adsorbents. Particularly for ACFCs, the increase in surface area also increasedthe total pore volume, micropore volume, micropore area and pore width, but decreased thepercentage of micropores by area and volume. Based on the nitrogen isotherms, it would appearthat the surface area dictates the amount of adsorption onto a given ACF, regardless of its form.

ACFCs possessed a greater volume of smaller micropores in comparison to ACFFs. This maybe attributed to the difference in the density of the materials and the accessibility of the fibresurface to the activating gas during the activation process. Thus, the physical form of an ACF mayinfluence the pore-size distribution of the adsorbent. Knowing the pore structure of an ACF typebased on its form and surface area, it should be possible to appropriately match its characteristicsto a specific application.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Karim Sapag of the Institute of Applied Physics, NationalCouncil of Scientific and Technical Research, National University of San Luis, Argentina. Thisstudy was supported by Grant # 2T42OH008436-03 and ROI Grant No. OH 008080 from theNational Institute for Occupational Safety and Health (NIOSH).

REFERENCES

Bansal, R.C., Donnet, J.B. and Stoeckli, F.S. (1988) Active Carbon, CRC Press, New York.Cheng, T., Jiang, Y., Zhang, Y. and Liu, S. (2004) Carbon 42, 3081.Cheremisinoff, P.N. and Ellerbusch, F. (1978) Carbon Adsorption Handbook, Ann Harbor Science

Publishers, Inc., Ann Harbor, MI, U.S.A.Das, D., Gaur, V. and Verma, N. (2004) Carbon 42, 2949.de Saussure, N.T. (1814) Gilbert’s Ann. Phys. 47, 113.Feng, W., Kwon, S., Borguet, E. and Vidic, A. (2005) Environ. Sci. Technol. 39, 9744.Fontana, F. (1777) Memorie Mat. Fis. Soc. Ital. Sci. 1, 679.Foster, K.L., Fuerman, R.G., Economy, J., Larson, S.M. and Rood, M.J. (1992) Chem. Mater. 4, 1068.Fournel, L., Mocho, P., Fanlo, J.L. and Le Cloirec, P. (2005) Environ. Technol. 26, 1277.Fukuda, T., Omori, S., Asakura, S. and Matsumoto, K. (1989) Kagaku Souchi 31, 55 (in Japanese).Gregg, S.J. and Sing, K.S.W. (1982) Adsorption, Surface Area and Porosity, 2nd Edn, Academic Press,

London.Hall, C.R. and King, K.S.W. (1988) Chem. Br. 24, 670.Hashisho, Z. and Rood, M. (2005) Environ. Sci. Technol. 39, 6851.Huang, Z.H., Kang, F., Liang, K.M. and Hao, J. (2003) J. Hazard. Mater. B 98, 107.Huang, Z.H., Kang, F., Zheng, Y.P., Yang, J.B. and Liang, K.M. (2002) Carbon 40, 1363.Kisamori, S., Kurod, K., Kawano, S., Mochida, I., Matsumura, Y. and Yoshikawa, M. (1994) Energy Fuels

8, 1337.Kitagawa, H. (1993) Proc. Nippon Kagakukai, 65th Spring Meeting, p. 153.Kohata, T., Fukuda, T., Ishizaki, N., Omori, S. and Komagata, H. (1980) Kagaku Kogaku 44, 343 (in

Japanese).Lo, S.Y. (2002) MS Thesis, University of Illinois at Urbana-Champaign, Urbana, IL, U.S.A.Lorimier, C., Subrenat, A., Le Coq, L. and Le Cloirec, P. (2005) Environ. Technol. 26, 1217.Lozano-Castello, D., Cazorla-Amoros, D. and Linares-Solano, A. (2002) Energy Fuels 16, 1321.Mallouk, K.E., Johnsen, D.L. and Rood, M.J. (2010) Environ. Sci. Technol. 44, 7070.


Mitscherich, E. (1843) Pogg. Ann. 59, 94.Mochida, I., Kisamori, S., Hironaka, M., Kawano, S., Matsumura, Y. and Yoshikawa, M. (1994) Energy

Fuels 8, 1341.Petkovska, M., Tondeur, D., Grevillot, G., Granger, J. and Mitrovic, M. (1991) Sep. Sci. Technol. 26, 425.Ramirez, D., Sullivan, P.D., Rood, M.J. and James, K.J. (2004) J. Environ. Eng. 130, 231.Rong, H., Ryu, Z., Zheng, J. and Zhang, Y. (2003) J. Colloid Interface Sci. 261, 207.Ryu, Z., Zheng, J., Wang, M. and Zhang, B. (2000) J. Colloid Interface Sci. 230, 312.Sing, K.S.W. (1989) Adsorption: Science and Technology, Kluwer Academic Publishers, Dordrecht, The

Netherlands.Sullivan, P.D., Rood, M.J., Dombrowski, K.D. and James, K.J. (2004) J. Environ. Eng. 130, 258.Suzuki, M. (1994) Carbon32, 577.Takeuchi, Y., Shigeta, A. and Iwamoto, H. (1993) Sep. Technol. 3, 46.Tanada, S., Kawasaki, N., Nakamura, T., Araki, M. and Tachibana, Y. (2000) J. Colloid Interface Sci. 228,

220.Webb, P.A. and Orr, C. (1997) Analytical Methods in Fine Particle Technology, Micromeritics Instrument

Corp., Norcross, GA, U.S.A.Weber Jr., W.J. (1972) Physicochemical Processes: For Water Quality Control, Wiley Interscience, New

York.Zhang, S., Shao, T., Kose, H.S. and Karanfil, T. (2010) Environ. Sci. Technol. 44, 6377.


morphologic and surface characterization of different types of activated carbon fibres

Documents