Activated carbon from durian shell: Preparation and characterization

Thio Christine Chandra a, Magdalena Maria Mirna a, Jaka Sunarso b,Yohanes Sudaryanto a, Suryadi Ismadji a,*a Department of Chemical Engineering, Widya Mandala Surabaya Catholic University Kalijudan 37, Surabaya 60114, Indonesiab Division of Chemical Engineering, The University of Queensland, St. Lucia, Qld 4072, Brisbane, Australia

Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462

A R T I C L E I N F O

Article history:

Received 11 August 2008

Received in revised form 13 October 2008

Accepted 13 October 2008

Keywords:

Activated carbon

Pore structure

Durian shell

Activation

A B S T R A C T

Activated carbons were prepared from durian shell by chemical activation with potassium hydroxide. In

order to find the optimum pore characteristics, different KOH to durian shell ratio (0.25–1.0) and

activation temperature (673–923 K) was employed. The adsorption isotherm of activated carbons

produced within these range of temperature and impregnation ratio is a mixture of type I and type IV

isotherms. While activated carbons obtained at low chemical impregnation ratio of 0.25 were essentially

microporous, with higher impregnation ratio, they become predominantly mesoporous. KOH to durian

shell ratio of 0.5 and activation temperature of 773 K can be pinpointed as the optimum condition to

obtain high surface area activated carbon.

� 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Journal of the Taiwan Institute of Chemical Engineers

journa l homepage: www.e lsev ier .com/ locate / j t i ce

1. Introduction

Activated carbons are still in wide-use for adsorption ofpollutants within gaseous and liquid phases. Numerous economicand industrial sectors, such as food and beverage processing,chemical, pharmaceutical, petroleum, mining, nuclear, automo-bile, and vacuum manufacturing employ this material within theirprocessing units. Some of these applications are very demandingwith regard to the surface chemistry and characteristics of thesecarbon adsorbents (Stavropoulos and Zabaniotou, 2005). Ingeneral, activated carbons with high surface area and porevolumes can be prepared from a variety source of carbonaceousmaterials such as coal (Chattopadhyaya et al., 2006; Jibril et al.,2007; Li et al., 2007; Pietrzak et al., 2007), coconut shell (Achaw andAfrane, 2008), sawdust (Ismadji et al., 2005), agricultural wastesand plant materials (Asadullah et al., 2006; Cao et al., 2006; Cuerda-Correa et al., 2008; Deiana et al., 2008; Elizalde-Gonzalez andHernandez-Montoya, 2007; Gercel et al., 2007; Soleimani andKaghazchi, 2007) including agricultural industrial by-products(Bouchelta et al., 2008; Li et al., 2008; Lua and Yang, 2005; Nabaiset al., 2008; Olivares-Marin et al., 2007; Stavropoulos andZabaniotou, 2005; Sudaryanto et al., 2006; Suzuki et al., 2007).Among these precursors, coal and coconut shell are the two mainsources within industrial practice.

* Corresponding author. Tel.: +62 31 3891264; fax: +62 31 3891267.

E-mail addresses: suryadi@mail.wima.ac.id, suryadiismadji@yahoo.com

(S. Ismadji).

1876-1070/$ – see front matter � 2008 Taiwan Institute of Chemical Engineers. Publis

doi:10.1016/j.jtice.2008.10.002

The pore structure and pore size distribution of activatedcarbon commonly varies based on the nature of raw materials andactivation method. Activated carbons are generally obtained usingtwo main steps, e.g. carbonization of the raw materials below1000 8C in an inert atmosphere followed by activation of theresulting char in the presence of suitable oxidizing agents. Incarbonization, most of the non-carbon elements like hydrogen andoxygen are being removed onto gaseous form by pyrolyticdecomposition resulting in a carbon with fixed mass and arudimentary pore structure. The following activation step is thenemployed to enlarge the diameter of fine pores and also create newpores so that the adsorptive power of the carbonization product isenhanced (Hu et al., 2001).

Activation can be carried out by chemical or physical means.Generally within chemical activation process, carbonization andactivation take place simultaneously as facilitated by chemicalactivating agents, i.e. dehydrating agents and oxidants. On theother hand for physical activation, carbonization of a precursoroccurs in priori followed by their activation at elevated tempera-ture in the presence of suitable activating agents, i.e. carbondioxide or steam. It has been noticed that chemical activationprocess normally takes place at a temperature lower the physicalactivation process (Ahmadpour and Do, 1997). The impregnationof precursor materials with chemical agents such as ZnCl2, H3PO4,and KOH can inhibit tar formation while also reduce the volatilematter evolution resulting in high precursor to carbon conversion.Therefore, the development of a porous structure is improved withchemical activation process (Ahmadpour and Do, 1997). Amongthe chemical activating agents, zinc chloride (ZnCl2) in particular is

hed by Elsevier B.V. All rights reserved.

Table 1Proximate and ultimate analysis of durian shell.

Analysis wt% Variation (%)

Proximate

Moisture 5.53 1.0

Volatile matter 69.59 1.2

Fixed carbon 22.36 0.8

Ash 2.52 1.5

Ultimate

Carbon 60.31 1.4

Nitrogen 3.06 1.4

Hydrogen 8.47 1.4

Oxygen 28.06 1.4

Sulphur 0.10 1.4

Table 2Fixed carbon content from several kinds of raw materials.

Raw material Fixed carbon (% wt)

Cassava peel (Sudaryanto et al., 2006) 28.90

Durian shell (this work) 22.36

Palm shell (Daud and Ali, 2004) 18.70

Coconut shell (Daud and Ali, 2004) 18.60

Teak sawdust (Ismadji et al., 2005) 23.38

T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462458

the most frequently used chemical in activated carbon preparation.Nowadays however, zinc chloride is less employed as it causeenvironmental problem. In addition, activated carbons from zincchloride are not suitable in pharmaceutical and food industries dueto its possibility to contaminate products. Another more favorableagent, KOH has been claimed to be the most effective alkali salt foractivated carbons production (Ahmadpour and Do, 1997).

Shell of durians is a major agricultural waste in Indonesia.Production of durians in Indonesia reached 562,710 tones per yearat 1998, which is likely to be increased during the next few years asdurian can be harvested several times in a year. Furthermore,increasing rate of durian (also called king of fruits) consumption isevident as most people like it which more or less would guaranteetheir availability as disposed products. While their waste disposalor pilings has become a common observation, it can bring aboutmore problems such as respiratory diseases, apart from theirpungent smell. These durian shells can therefore be employed ascarbon precursor to derive more economic value while at the sametime overcome the problem.

To obtain very specific materials with a given pore sizedistribution from low cost precursors at low temperature isconsidered a challenge. In our previous work, we have utilizedactivated carbon made from durian shell for methylene blueremoval however only a short description about the preparationwas given while its emphasis was on adsorption (Chandra et al.,2007). Within this work, preparation details including the effect ofvarious parameters onto surface development and characteristicsare given.

2. Experimental

2.1. Materials

Durian shell (Montong variety) was collected from local durianprocessing industry in Surabaya. The pristine durian shells havehigh water content (40%), hard shell texture and also strong durianflavor. As an initial step, the size of these materials was reduced to�1 � 1 cm. Prior to the process, durian shell was repeatedly washedwith distilled water in order to remove dust and other inorganicimpurities, then oven-dried for 24 h at 393 K to reduce its moisturecontent until less than 6%. Subsequently, as-dried durian shell wasgrounded in micro hammer mill until it became powder (40/60 mesh)and then stored in desiccators for further use. Potassium hydroxide,KOH (ACS reagent) with purity�85% (Sigma–Aldrich) was purchasedfrom Kurniajaya Pty Ltd.

The proximate analysis of durian shell was carried outaccording to ASTM standard E 870-82, while the ultimate analysiswas conducted according to ASTM D3176-89 (2002). Theproximate and ultimate analysis of the durian shell is given inTable 1. The C, H, N, O and S elements content in the ultimateanalysis were determined by an elemental analyzer (Heraeus,CHN-O-RAPID). Table 1 reveals that durian shell has high carbonand low ash content. In comparison with other materials (Table 2),Table 1 shows that durian shell has a quite high carbon contentwhich justifies its suitability as activated carbon precursor.

2.2. Activated carbon preparation

Chemical activation of durian shell was performed using KOH.Different carbonization temperatures and impregnation ratioswere employed to find the optimal conditions resulting in highsurface area activated carbons from durian shell. The activationwas performed as follows namely 25 g of durian shell in the form ofpowder was mixed with KOH solution (50%) with differentimpregnation ratio for 5 h at room temperature (around 303 K).

The impregnation was conducted in 250 mL round bottle flaskequipped with stirrer. During the impregnation period, themixture was stirred at 200 rpm. The mass ratio of chemicalactivating agent to durian shell was in the range of 1:4 to 1:1. Theresulting homogeneous slurry was then poured onto porcelain discand dried at 383 K for 24 h in a forced circulating oven. The driedproduct was later placed on horizontal tubular furnace andcarbonized at desired temperatures (673, 723, 773, 823, 873 and923 K). The activation was performed under nitrogen flow rate of150 cm3/min. The activation process was initiated by heating thesample at ramp rate of 10 K/min from room temperature (around303 K) until the desired temperature was reached. Samples wereheld at desired temperature for 1 h before cooling down undernitrogen flow. Sudaryanto et al. (2006) and Diao et al. (2002) intheir studies found that the activation time does not causesignificant change on the activated carbon. Therefore, 1 h waschosen as the activation time. The resulting carbons have particlesizes between 60 and 120 meshes. These activated carbons werewashed sequentially with a 0.5 N HCl solution. Consecutively,carbon powders were repeatedly washed with hot distilled wateruntil the pH of solution reach 6.5 and finally washed with colddistilled water. After that, these powders were dried at 383 K for24 h and stored in dessicator.

2.3. Characterization

The pore structure characteristics of activated carbons weredetermined using N2 adsorption, X-ray diffraction (XRD), andscanning electron microscope (SEM). Nitrogen adsorption wasconducted at 77 K using an automatic Micromeritics ASAP-2010volumetric sorption analyzer. Prior to gas adsorption measure-ments, the carbon was degassed at 573 K in a vacuum condition for24 h. Nitrogen adsorption isotherms were measured over a relativepressure (P/Po) range from approximately 10�5 to 0.995. The BETsurface area, micropore volume and micropore surface area of theactivated carbons were determined by application of theBrunauer–Emmett–Teller (BET) and Dubinin–Asthakov (DA) ana-lysis software available with the instrument, respectively. The BETsurface area was measured by means of the standard BET equationapplied in the relative pressure range from 0.06 to 0.3. The pore

Fig. 2. Effect of carbonization temperatures on the yield of activated carbon.

T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462 459

size distribution of the carbons was ascertained using theMicromeritics density functional theory (DFT) software, withmedium regularization.

SEM images were recorded using JEOL JSM-6400F field emissionSEM. A thin layer of platinum was sputter-coated on the samplesfor charge dissipation during FESEM imaging. The sputter coater(Eiko IB-5 Sputter Coater) was operated in an argon atmosphereusing a current of 6 mA for 3 min. The coated samples were thentransferred to the SEM specimen chamber and observed at anaccelerating voltage of 5 kV, spot size of 8, aperture of 4 and 15 mmworking distance. TGA–DSC curve was obtained using TGA/DSC 1star system (Mettler toledo) with ramping and cooling rate of10 K/min from room temperature to 1173 K under 20 mL/minnitrogen flow with gas controller GC200.

3. Results and discussion

A series of activated carbons were prepared from durian shell asprecursor with chemical activation using KOH as activating agent.The effects of different preparation variables on the porecharacteristic of activated products were also studied. Detailsare discussed as follows.

3.1. TGA–DSC of durian shell

Fig. 1 depicts the TGA–DSC curve for carbonization of durianshell. The experiment was conducted at a ramping rate 10 K/minfrom 298 to 1173 K, dwelling at 1173 K for 10 min and than coolingdown at the same ramping rate to 298 K. The weight lost at thebeginning of the process (373 8C) was due to evaporation of freemoisture content. With further temperature increase, bound waterin durian shell also evaporated. Sharp decrease of weightevidenced at temperatures between 543 and 643 K was causedby the release of volatile matter from durian shell while above643 K, decomposition of some structure within durian shell stilltakes place.

3.2. Yield of activated carbon

For the production of commercial activated carbons, relativelyhigh product yields are expected. Activation temperature plays animportant role on the yield of activated carbon. Fig. 2 depicts theeffect of activation temperature on the yield of activated carbon atdifferent activation time and impregnation ratio. As seen in Fig. 2,activation temperature has quite significant effect on the yield ofcarbon. With increasing activation temperature, the yield ofactivated carbon decrease as the weight loss rate is higher

Fig. 1. TGA–DSC curve for durian shell.

primarily due to the initial large amount of volatiles that can beeasily released with higher temperature as well as the loss ofmoisture to a lesser extent. Lower yield that comes with higherKOH to durian shell ratio might be attributed to the enhancementof carbon burn-off by extra KOH widening (micropore intomesopore).

3.3. Pore structure of activated carbons

Identifying the pore structure of activated carbons by nitrogenadsorption at 77 K is an essential procedure before applying themonto liquid phase experiments. The N2 adsorption isotherms ofactivated carbons prepared at different impregnation ratios andactivation temperatures are shown in Fig. 3. The shape ofadsorption isotherm can provide preliminary qualitative informa-tion on the adsorption mechanism as well as on the porousstructure of carbon. These isotherms clearly show the predomi-nantly microporous nature of the carbons, with some mesoporesleading to gradual increase in adsorption after the initial filling ofthe micropores, followed by more rapid enhancement nearsaturation. Adsorption isotherm of these activated carbons atcarbonization temperature 673–923 K and impregnation ratio0.25–1.00 can be properly classified as a mixture of type I and typeIV isotherms (see Fig. 4). According to IUPAC classification, type Iisotherm can be associated with microporous structure while typeIV isotherm exhibited by mixture of microporous and mesoporousmaterial. The plateau of this isotherm commences at high relativepressures (P/Po) and toward the end of isotherm, steep gradientexist as a result of a limited uptake of nitrogen, indicating capillarycondensation in the mesopores. These features indicate thedevelopment of micro and mesoporous structure on this charduring activation process, further confirmed by the DFT (densityfunctional theory) pore size distributions as shown in Fig. 4 (KOHto durian shell ratio 0.25 and 0.5). The pore size distributiondelineates a model of solid internal structure, which assumes thatan equivalent set of non-interacting and regularly shaped modelpores can represent the complex void spaces within the real solid.The pore size distribution is closely related to both kinetic andequilibrium properties of porous material and perhaps is the mostimportant aspect for characterizing the structural heterogeneity ofporous materials employed in industrial application. It is apparentfrom Fig. 4 that the pore size distribution was largely dependent onthe KOH to durian shell ratio. Activated carbons obtained at lowchemical ratio (0.25) were essentially microporous and as thechemical ratio increases, the activated carbons become mostly

Fig. 3. Adsorption isotherms of nitrogen at 77 K on durian shell activated carbons. (For interpretation of the references to color in this figure legend, the reader is referred to

the web version of the article.)

T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462460

mesoporous. A similar tendency was also observed by Timur et al.(2006).

Table 3 shows the pore properties of all activated carbonsprepared from durian shell with KOH activation. The BET values(519–992 m2/g) are comparable to the commercially availableactivated carbon (Wu et al., 2005), e.g., 300–600 m2/g for ICIHydrodarco 3000, 1044 m2/g for Calgon Filtrasorb-400 and

Fig. 4. Pore size distributions of durian shell activated carbons. (a) KOH to durian

shell ratio 0.25 and (b) KOH to durian shell ratio 0.50.

1000 m2/g for Westvaco Nuchar WL. Increased temperature from673 to 773 K results in higher BET surface area and microporevolume as indicated in Table 3. This phenomenon was due to therelease of volatile matters; however the continual decreases inthese two properties with increasing temperature from 773 to923 K were probably due to the sintering effect of the volatiles andthe shrinkage of the carbon structure, resulting in the narrowingand closing up of some of the pores. Table 3 also showed thatactivated carbons prepared at temperature of 773 K and impreg-nation ratio 0.5 yielded the largest BET surface area and microporevolume.

The effect of KOH to durian shell ratio on BET surface area andtotal pore volume can also be seen in Table 3. They suggestedthat KOH is not only responsible for the development of newmicropores but also for the enlargement of as-existing micro-pores to mesopores (see Fig. 4 and Table 3). At the sametemperature, the BET surface area as well as the total porevolume in general, enlarges with increase in KOH to durian shellratio. At KOH to durian shell ratio 0.25 and 0.5, a large amount ofmicropore was created, resulting in the increase of BET surfacearea and micropore volume. When KOH to durian shell ratioreaches 1, the widening of existing micropores and developmentof new micropores occurred simultaneously, leading to higherBET surface area and total pore volume as indicated in Table 3. Athigh ratio of KOH to durian shell, the microporosity developmentis mostly attributed to the intercalation of potassium metal inthe carbon structure. Pore widening normally begins when anumber of opened pore exists in the structure which is the casewhen the chemical ratio is reasonably high (Mohanty et al.,2006).

The surface morphology of the activated carbons produced wascharacterized using scanning electron microscope. Fig. 5 depictsthe SEM micrographs of pristine durian shell and activated carbonobtained at activation temperature of 723 K and impregnationratio 0.5 (773/0.5). The SEM micrograph showed that somemacropores were created on the external surface of the carbonduring the activation process. This phenomenon is mainlydue to the release of volatile matter and reaction betweenpotassium hydroxide and the carbon atom in the precursor(Ganan et al., 2004) in accordance to the reaction of6KOH + 2C ? 2K + 3H2 + 2K2CO3. The presence of metallic potas-sium then intercalates the carbon matrix resulting in thewidening of spaces between carbon atomic layers (Ahmadpourand Do, 1997).

Table 3Pore characteristic of durian shell activated carbon (DSAC).

Carbon code BET surface area (m2/g) Micropore surface area (m2/g) Micropore volume (cm3/g) Total pore volume (cm3/g)

673/0.25 560 199 0.160 0.198

723/0.25 579 283 0.308 0.347

773/0.25 900 681 0.367 0.402

823/0.25 717 334 0.285 0.413

873/0.25 541 319 0.130 0.341

923/0.25 520 278 0.284 0.345

673/0.50 674 521 0.342 0.381

723/0.50 872 551 0.326 0.374

773/0.50 992 849 0.368 0.411

823/0.50 927 765 0.324 0.378

873/0.50 866 779 0.297 0.331

923/0.50 467 291 0.137 0.172

673/1.00 663 480 0.211 0.328

723/1.00 890 533 0.337 0.389

773/1.00 979 805 0.349 0.423

823/1.00 934 731 0.309 0.392

873/1.00 780 592 0.241 0.329

923/1.00 674 450 0.218 0.304

T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462 461

4. Conclusion

Activated carbons were prepared from durian shell by KOHactivation method at different KOH to durian shell ratio andactivation temperatures. Pore properties of the carbons includingthe BET surface area, pore volume and pore size distribution werecharacterized using nitrogen adsorption. The KOH to durian shellratio of 0.5 and activation temperature of 773 K was found as theoptimum conditions to acquire high surface area activated carbonfrom durian shell. In addition, by adjusting the activation

Fig. 5. SEM images of (a) pristine durian shell and (b) activated carbon (773/0.5).

temperature and impregnation ratio, the pore structure of carboncan be tailored.

Acknowledgements

This research was financially supported by Sub-Project Manage-ment Unit Technological and Professional Skills Development SectorProject (ADB Loan No. 1792-INO) through Widya Mandala TPSDPStudent Grant 2006. Many thanks to Professor Joao C Diniz da Costafrom Division of Chemical Engineering, The University of Queens-land Australia for providing TGA-DSC analysis.

References

Achaw, O. W. and G. Afrane, ‘‘The Evolution of the Pore Structure of Coconut Shellsduring the Preparation of Coconut Shell-based Activated Carbons,’’ MicroporousMesoporous Mater., 112, 284 (2008).

Ahmadpour, A. and D. D. Do, ‘‘The Preparation of Activated Carbon from MacadamiaNutshell by Chemical Activation,’’ Carbon, 35, 1723 (1997).

Asadullah, M., M. A. Rahman, M. A. Motin, and M. B. Sultan, ‘‘Preparation andAdsorption Studies of High Specific Surface Area Activated Carbons Obtained fromthe Chemical Activation of Jute Stick,’’ Adsorp. Sci. Technol., 24, 761 (2006).

Bouchelta, C., M. S. Medjram, O. Bertrand, and J. P. Bellat, ‘‘Preparation and Char-acterization of Activated Carbon from Date Stones by Physical Activation withSteam,’’ J. Anal. Appl. Pyrolysis, 82, 70 (2008).

Cao, Q., K. C. Xie, Y. K. Lv, and W. R. Bao, ‘‘Process Effects on Activated Carbon with LargeSpecific Surface Area from Corn Cob,’’ Bioresour. Technol., 97, 110 (2006).

Chandra, T. C., M. M. Mirna, Y. Sudaryanto, and S. Ismadji, ‘‘Adsorption of Basic Dyeonto Activated Carbon Prepared from Durian Shell: Studies of Adsorption Equili-brium and Kinetics,’’ Chem. Eng. J., 127, 121 (2007).

Chattopadhyaya, G., D. G. Macdonald, N. N. Bakhshi, J. S. Soltan, and A. K. Dalai,‘‘Preparation and Characterization of Chars and Activated Carbons from Saskatch-ewan Lignite,’’ Fuel Process. Technol., 87, 997 (2006).

Cuerda-Correa, E. M., A. Macias-Garcia, M. A. D. Diez, and A. L. Ortiz, ‘‘Textural andMorphological Study of Activated Carbon Fibers Prepared from Kenaf,’’ Micro-porous Mesoporous Mater., 111, 523 (2008).

Daud, W. and W. S. W. Ali, ‘‘Comparison on Pore Development of Activated CarbonProduced from Palm Shell and Coconut Shell,’’ Bioresour. Technol., 93, 63 (2004).

Deiana, C., D. Granados, R. Venturini, A. Amaya, M. Sergio, and N. Tancredi, ‘‘ActivatedCarbons Obtained from Rice Husk: Influence of Leaching on Textural Parameters,’’Ind. Eng. Chem. Res., 47, 4754 (2008).

Diao, Y. L., W. P. Walawender, and L. T. Fan, ‘‘Activated Carbons Prepared fromPhosphoric Acid Activation of Grain Sorghum,’’ Bioresour. Technol., 81, 45 (2002).

Elizalde-Gonzalez, M. P. and V. Hernandez-Montoya, ‘‘Characterization of Mango Pit asRaw Material in the Preparation of Activated Carbon for Wastewater Treatment,’’Biochem. Eng. J., 36, 230 (2007).

Ganan, J., C. M. Gonzalez-Garcia, J. F. Gonzalez, E. Sabio, A. Macias-Garcia, and M. A.Diaz-Diez, ‘‘Preparation of Activated Carbons from Bituminous Coal Pitches,’’ Appl.Surf. Sci., 238, 347 (2004).

Gercel, O., A. Ozcan, A. S. Ozcan, and H. F. Gercel, ‘‘Preparation of Activated Carbon froma Renewable Bio-Plant of Euphorbia rigida by H2SO4 Activation and Its AdsorptionBehavior in Aqueous Solutions,’’ Appl. Surf. Sci., 253, 4843 (2007).

Hu, Z. H., M. P. Srinivasan, and Y. M. Ni, ‘‘Novel Activation Process for Preparing HighlyMicroporous and Mesoporous Activated Carbons,’’ Carbon, 39, 877 (2001).

T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462462

Ismadji, S., Y. Sudaryanto, S. B. Hartono, L. E. K. Setiawan, and A. Ayucitra, ‘‘ActivatedCarbon from Char Obtained from Vacuum Pyrolysis of Teak Sawdust: Pore Struc-ture Development and Characterization,’’ Bioresour. Technol., 96, 1364 (2005).

Jibril, B. Y., R. S. Al-Maamari, G. Hegde, N. Al-Mandhary, and O. Houache, ‘‘Effects ofFeedstock Pre-Drying on Carbonization of KOH-mixed Bituminous Coal in Pre-paration of Activated Carbon,’’ J. Anal. Appl. Pyrolysis, 80, 277 (2007).

Li, D. Y., H. L. Zhou, Y. J. Tian, L. Q. Wei, X. F. Wu, W. J. Li, and Y. F. Chen, ‘‘High-Specific-Surface-Area Activated Carbon from Anthracite,’’ Rare Met. Mater. Eng., 36, 583(2007).

Li, W., L. B. Zhang, J. H. Peng, N. Li, and X. Y. Zhu, ‘‘Preparation of High Surface AreaActivated Carbons from Tobacco Stems with K2CO3 Activation Using MicrowaveRadiation,’’ Ind. Crop Prod., 27, 341 (2008).

Lua, A. C. and T. Yang, ‘‘Characteristics of Activated Carbon Prepared from Pistachio-Nut Shell by Zinc Chloride Activation under Nitrogen and Vacuum Conditions,’’ J.Colloid Interface Sci., 290, 505 (2005).

Mohanty, K., D. Das, and M. N. Biswas, ‘‘Preparation and Characterization of ActivatedCarbons from Sterculia alata Nutshell by Chemical Activation with Zinc Chloride toRemove Phenol from Wastewater,’’ Adsorption, 12, 119 (2006).

Nabais, J. V., P. Carrott, M. Carrott, V. Luz, and A. L. Ortiz, ‘‘Influence of PreparationConditions in the Textural and Chemical Properties of Activated Carbons from a NovelBiomass Precursor: The Coffee Endocarp,’’ Bioresour. Technol., 99, 7224 (2008).

Olivares-Marin, M., C. Fernandez-Gonzalez, A. Macias-Garcia, and V. Gomez-Serrano,‘‘Porous Structure of Activated Carbon Prepared from Cherry Stones by ChemicalActivation with Phosphoric Acid,’’ Energy Fuel, 21, 2942 (2007).

Pietrzak, R., H. Wachowska, P. Nowicki, and K. Babel, ‘‘Preparation of Modified ActiveCarbon from Brown Coal by Ammoxidation,’’ Fuel Process. Technol., 88, 409 (2007).

Soleimani, M. and T. Kaghazchi, ‘‘Agricultural Waste Conversion to Activated Carbonby Chemical Activation with Phosphoric Acid,’’ Chem. Eng. Technol., 30, 649 (2007).

Stavropoulos, G. G. and A. A. Zabaniotou, ‘‘Production and Characterization of Acti-vated Carbons from Olive-Seed Waste Residue,’’ Microporous Mesoporous Mater.,82, 79 (2005).

Sudaryanto, Y., S. B. Hartono, W. Irawaty, H. Hindarso, and S. Ismadji, ‘‘High SurfaceArea Activated Carbon Prepared from Cassava Peel by Chemical Activation,’’Bioresour. Technol., 97, 734 (2006).

Suzuki, R. M., A. D. Andrade, J. C. Sousa, and M. C. Rollemberg, ‘‘Preparation andCharacterization of Activated Carbon from Rice Bran,’’ Bioresour. Technol., 98, 1985(2007).

Timur, S., I. C. Kantarli, E. Ikizoglu, and J. Yanik, ‘‘Preparation of Activated Carbons fromOreganum Stalks by Chemical Activation,’’ Energy Fuel, 20, 2636 (2006).

Wu, F. C., R. L. Tseng, and C. C. Hu, ‘‘Comparisons of Pore Properties and AdsorptionPerformance of KOH-activated and Steam-activated Carbons,’’ Microporous Meso-porous Mater., 80, 95 (2005).