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Journal of Analytical and Applied Pyrolysis 89 (2010) 129–136

Contents lists available at ScienceDirect

Journal of Analytical and Applied Pyrolysis

journa l homepage: www.e lsev ier .com/ locate / jaap

haracterization and application of activated carbon produced fromak cups pulp

erkan Timura, Ismail Cem Kantarli b, Sermin Onenca, Jale Yanika,∗

Faculty of Science, Department of Chemistry, Ege University, 35100, Bornova, Izmir, TurkeyAtaturk Medical Technology Vocational Training School, Ege University, 35100, Bornova, Izmir, Turkey

r t i c l e i n f o

rticle history:eceived 12 February 2010ccepted 2 July 2010vailable online 31 July 2010

eywords:ak cups pulpctivated carbon

a b s t r a c t

Activated carbons have been prepared from a lignocellulosic waste material by chemical activation. Phos-phoric acid and zinc chloride have been used as activating agent. The influence of process variables on thecarbons’ surface area was studied to optimize these parameters. The textural properties of active carbonswere characterized by N2 adsorption at 77 K and SEM analysis, while Boehm titration and Fourier trans-form infrared (FTIR) analysis were conducted to determine the surface groups of the activated carbons.Under optimum conditions, activated carbons with a maximum surface area of 1000 and 1152 m2 g−1

for the activating agent phosphoric acid and zinc chloride, respectively, were obtained. Zinc chloride

hemical activationdsorption

produced the activated carbon having higher micropore volume compared to phosphoric acid activation.The results obtained showed that oak cups pulp is an economically promising material as a precursor inthe activated carbon production, based on the combination of yield, surface area and raw material cost.

The application of activated carbons was studied by the aqueous adsorption tests using different kindof dyes (acidic and basic), phenol and Cr(VI) as adsorbates. The aqueous adsorption tests showed thatthe surface chemistry of the activated carbons also played important role in dye adsorptions as well astextural properties.

. Introduction

Activated carbons are the most widely used adsorbents for theemoval of organic and inorganic compounds from air and watertreams. As environmental pollution is becoming a more seriousroblem, the need for activated carbon is growing. Activated car-ons can be prepared from a wide range of carbonaceous rawaterials. Commercial activated carbons are produced from coal,ood and coconut shells. However, utilization of agricultural and

orestry wastes as raw materials for the production of activatedarbon has increased notably in recent years because they areery cheap and readily available. In literature, a lot of researchas been reported on activated carbons from agricultural wastes1–6].

Activated carbons have specific properties depending on thetarting materials and activation methods. Activated carbons can be

roduced from lignocellulosic materials by physical and chemicalctivation. The physical activation method involves carbonizationf the raw material and the subsequent activation at high tem-erature in a carbon dioxide or steam atmosphere. The chemical

∗ Corresponding author. Tel.: +90 232 388 82 64; fax: +90 232 388 82 64.E-mail address: jale.yanik@ege.edu.tr (J. Yanik).

165-2370/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.jaap.2010.07.002

© 2010 Elsevier B.V. All rights reserved.

activation method involves the carbonization of the raw materialpreviously impregnated with a chemical agent such as zinc chlo-ride, phosphoric acid, potassium hydroxide etc. It is known thatZnCl2 and H3PO4 are able to catalyze dehydration reactions. Dur-ing the hold of impregnated biomass at 110 ◦C, the dehydrationof the lignocellulosic material can occur. Dehydration is not theonly means of some mechanism as for acid catalyzed dehydrationof alcohols. Jagtoyen et al. showed that there is a very significantrelease of methane, CO2 and CO beginning at around 100 ◦C inpyrolysis of white oak in presence of H3PO4 [7]. The advantage ofchemical activation over physical activation is to be performed inonly one step and at a relatively low temperature [8]. In addition,chemical activation produces a much higher yield than the physi-cal activation and led to a decrease in the mineral matter content[9]. However, there also are some disadvantages of the chemicalactivation process, such as the corrosiveness of the process and thewashing steps.

The removal of organic and inorganic toxic contaminants hasgreatly increased because of the ecological awareness of their

role in the environment. Phenol and its derivatives are invariablypresent in the effluents from industries engaged in the manufac-ture of a variety of chemical compounds such as plastics, dyes andplants used for coal gasification, and petrochemical units. On theother hand, industrial wastewater rich in heavy metal ions and

130 S. Timur et al. / Journal of Analytical and A

Table 1Properties of oak cups pulp.

Proximate analysis (as received, wt%)Moisture 11.5Ash 6.7Volatile matter 71.0

Ultimate analysis (dry, wt%)C 48.91H 6.85N 1.31S 0.12Oa 42.81

diaaddttctdgfcip

trctcelnob

pbawbtfio

2

2

apcfrw

by dissolving potassium dichromate in distilled water. Methy-lene Blue (MB), phenol and potassium dichromate were purchased

a Calculated from difference.

yes remains as an important environmental issue. Chromium(VI)s used in various industries including metallurgy, leather tanning,nd electroplating. Therefore, it is a major pollutant of the wastew-ters rejected by these industries. On the other hand, in textileyeing processes, a large volume of dye-contaminated effluent isischarged. These dyes are designed to be resistant to environmen-al conditions like light, effects of pH and microbial attack. Amonghe several treatment technologies developed to remove theseontaminants, adsorption has been found to be superior to otherechniques for wastewater treatment in terms of cost, simplicity ofesign, ease of operation and insensitivity to toxic substances. Ineneral, activated carbons are broadly applied effective adsorbentsor wastewater treatment. Adsorption from solutions by activatedarbon is influenced by the nature of the carbon surface includ-ng its surface area, porous and chemical structure, and its surfaceroperties as well as the chemistry of adsorbate.

The Anatolian vegetation is very rich on account of species ofrees. The oak trees are widely found and distributed on the Aegeanegion of Anatolia. The acorn cups of Turkish oak [Quercus aegilops]ontaining high percentage of hydrolysable (pyrogallol) group ofannin are internationally called as “Valonea”. The matured acornups are picked between October and March, dried and sent to thextract factory. The valonea is treated with hot water in order toeach the tannin. The vegetable extract obtained from Valonea isamed as “Valex” and used in leather manufacture as tanner. On thether hand, the residue from extraction (oak cups pulp) is disposedy incineration.

Although preparation of activated carbon using chemical andhysical activation has been widely studied using various low-costiomass materials, there has not been any report on preparation ofctivated carbon from oak cups pulp. The objective of the presentork was to investigate the feasibility of producing activated car-

ons from a forestry industry waste by chemical activation andheir ability to remove dyes, phenol and hexavalent chromiumrom dilute aqueous solutions. The chemical recovery which is themportant from the point of view of environment and process econ-my in the chemical activation process was also investigated.

. Materials and methods

.1. Materials biomass

The oak cups pulp was supplied by Valex plant in Salihli/Izmirnd was air-dried for several days and ground below 1 mm. Someroperties of this material are given in Table 1. Because of low ashontent and high volatile matter, oak cups pulp is a good feedstock

or activated carbon production. The chemicals, such as zinc chlo-ide (99.99%), phosphoric acid (85%), and hydrochloric acid (37%),ere purchased from Aldrich and used as received.

pplied Pyrolysis 89 (2010) 129–136

2.2. Production of activated carbon

Air-dried biomass (150 g) was mixed in a beaker with 250 mLof H3PO4 or ZnCl2 solution with varying concentrations. H3PO4or ZnCl2 solution was used in impregnation ratios of 0.4:1, 0.6:1,0.8:1 and 1:1 of weight of impregnation reagent/weight of biomass(referred to as 40, 60, 80 and 100 wt% loading). The slurry was thendried in an oven at 105 ◦C for a predetermined time.

The impregnated biomass sample was pyrolyzed in a fixed beddesign and stainless steel reactor. In a typical run, impregnatedbiomass samples were placed into the reactor. The system washeated at a rate of 7 ◦C min−1 to 600 ◦C, and held at that tempera-ture for 2 h. The reactor was continuously purged with nitrogen ata flow rate of 25 mL min−1. After pyrolysis, the furnace was cooleddown to room temperature in nitrogen atmosphere. The char wasboiled with 200 mL of 10% HCl solution for 60 min, filtered in a vac-uum flask and washed with hot water and finally cold water toremove the chloride ions and other inorganics. After washing, acti-vated carbon samples were dried at 110 ◦C for 24 h and weighted.The yield of activated carbon was calculated by

yield(%) =(

m

M

)× 100

where M is the initial mass of oak cups pulp (g); m is the mass ofresultant activated carbon (g).

For comparison, the char obtained from oak cups pulp withoutchemical activator was subjected to washing with acid and water.

In a series of experiments, first 500 mL of filtrate was collectedand its chemical content was determined to reuse as impregnationsolution. The amounts of phosphate and zinc in filtrates were deter-mined by the gravimetric method, by precipitation as magnesiumammonium phosphate and as zinc pyrophosphate.

2.3. Characterization of activated carbons

The BET surface area was calculated from the adsorptionisotherms by using Brunauer–Emmett–Teller (BET) equation. TheBET surface area measurements were obtained from nitrogenadsorption isotherms at 77 K using a Micrometrics FlowSorb II-2300 Surface Area Analyzer. Automatic equipment (TriStar 3000)was used to obtain the nitrogen adsorption isotherms. To determinethe micropore volumes and the external area, the t-plot approachhas been applied. The surface morphology of activated carbonwas visualized via scanning electron microscopy (SEM, JEOL-FEG).Fourier transform infrared (FTIR) spectra of some of the activatedcarbons was obtained using a spectrophotometer (Spectrum 100,PerkinElmer) in order to qualitatively identify the chemical func-tionality of activated carbons. Pellets were prepared by mixing 1 mgof dried sample with 500 mg of KBr (Merck, for spectroscopy). Theamount of surface oxygen groups on the activated carbons has beendetermined by Boehm titration method [10].

2.4. Aqueous adsorption characteristics

Three dyes from different classes, phenol and Cr(VI) were usedas adsorbates to evaluate the adsorption capacity of the preparedactivated carbons. Cr(VI) adsorption was investigated via monitor-ing CrO4

2− ion on the activated carbons and it will be mentioned asCr(VI) in throughout the manuscript. Commercial-grade Basic Red18 and Acid Red 111 were used as received (Bayer). Their chemicalstructures are given in Fig. 1. The Cr(VI) solutions were prepared

from Merck as analytical reagent grade. Adsorption isotherms werederived from batch experiments. Procedure was as follows. Testsolutions (100 mL) of various concentration (ranging between 15

S. Timur et al. / Journal of Analytical and Applied Pyrolysis 89 (2010) 129–136 131

cture of investigated dyes.

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3

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Table 2Variances in BET surface area of activated carbons with impregnation time.

Impregnation time (h) BET surface area (m2 g−1)

H3PO4 ZnCl2

2 481 6954 597 8108 598 814

efficiency. Impregnation with ZnCl2 or H3PO4 increased the yieldof resulting carbon due to the inhibition of the formation of tar andvolatiles by chemical agents, hence enhancing the carbon yield.This result is in agreement with the observations of other work-

Table 3Variances in the yield and some properties of activated carbons with the concentra-tion of impregnation agent.

Activating agent Reagentconcentration(wt%)

Yield (wt%) Ash (wt%) BET surfacearea (m2 g−1)

None – 30 12.0 150

H3PO4

40 40 11.0 59760 43 20.8 93180 42 21.0 977

Fig. 1. Chemical stru

nd 75 mg L−1 for Acid Red 111, 150 and 200 mg L−1 for Basic Red8, 50 and 100 mg L−1 for phenol, 100 and 400 mg L−1 for MB and5 and 300 mg L−1 for Cr(VI)) were added to the adsorbent (0.1 g)

n flasks and suspensions were shaken for an equilibrium timeetermined with preliminary studies (24 h for Basic Red 18 andB and 2 h for the other adsorbates). The pH of each solution was

djusted to optimum values of 2, 3 and 10 for Cr(VI), Acid Red 111nd Basic Red 18, respectively. No pH adjustment was done forhenol and MB solutions. The filtrates were analyzed for residualcid Red 111, MB, Basic Red 18 and phenol concentration using theV–visible spectrophotometer (UV-160A, Shimadzu) at 504, 665,84 and 269 nm, respectively. For residual Cr(VI) concentration, theltrates were analyzed by reaction with 1,5-diphenylcarbazide fol-

owed by absorbance measurement at 540 nm using the UV–visiblepectrophotometer.

. Results and discussion

.1. Influence of impregnation time on surface area of activatedarbon

Although, predrying of impregnated materials plays a criticalole in determining the characteristics of the produced activatedarbon [11], impregnation time has not received attention in liter-ture. The 24 h had been used as impregnation time in many studieselating to chemical activation process [8,12–18]. In this study, wenvestigated the effect of the impregnation time on the surface areaf activated carbon. For this, the oak cups pulp impregnated with0% impregnating agent was dried in a moisture oven at 110 ◦C forifferent periods (between 2 and 24 h) and then pyrolyzed.

Regardless of the type of impregnating agent, the surface area ofctivated carbons increased by increasing the impregnation timerom 2 to 4 h and remained almost constant for higher periodsTable 2). The impregnation time of 4 h was determined to be

ptimum and was used as impregnation time for all experiments.lthough, Suarez-Garcia et al. did not investigate the effect of

mpregnation time, they also used the impregnation time of 4 hn chemical activation of apple pulp with phosphoric acid [19]. Ithould be noted that the shorter impregnation time than those

12 601 81616 604 81524 606 818

used in the literature has an advantage from the point of processeconomy.

3.2. Influence of impregnation ratio

Table 3 summarizes the effects of impregnation agent loadingon the yield, BET surface area and the ash content of the activatedcarbon. As known, the yield is one of the indicators of the process

100 43 20.5 1002

ZnCl2

40 32 4.3 81060 40 7.0 95880 41 7.0 1045

100 42 13 1152

1 and Applied Pyrolysis 89 (2010) 129–136

eectwl

stmtrlvttzatcttp

vAsFioa

iThobu7oht3om

3

muiewTfvr

Table 4BET surface areas of activated carbons prepared using recovered impregnation solu-tion washing liquids.

Chemical content ofimpregnation solution (wt%)

Activatedcarbon type

BET surfacearea (m2 g−1)

PO4

57.60 AC1 100246.08 AC2 98033.83 AC3 925

Zn

TC

32 S. Timur et al. / Journal of Analytical

rs [7,19,20]. From Table 3, it looks that impregnation ratio has noffect on the yield of activated carbon from oak cups pulp. But, byonsidering the ash contents, it is clear that the lowest impregna-ion ratio gave the highest carbon yield. This result is in agreementith literature [1,21,22]. High amount of chemical agents led to the

arger evolution of volatiles [22].The ash contents of activated carbons obtained using ZnCl2 were

ignificantly lower than that of obtained using H3PO4 and evenhan that of char obtained from non-impregnated biomass. The

etal salts and water soluble components are easily removed inhe washing stage for the activated carbon obtained with zinc chlo-ide, and this is due to the high solubility of zinc salts (ZnO, ZnCl2)eft in the carbon mass [7,23]. The fact that the ash content in acti-ated carbon obtained with zinc chloride impregnation was lowerhan that in char obtained without chemical impregnation confirmshat the inorganic constituent of the raw material combined withinc chloride giving soluble components. The high ash content ofctivated carbons obtained with H3PO4 impregnation may be dueo two reasons [24]; (1) the formation of insoluble phosphates byombination of phosphoric acid and the inorganic constituent ofhe raw material, (2) phosphates are connected and cross linkedo the carbon matrix. Similar results have been observed for otherrecursors [24,25].

For both impregnating agents, the surface area of derived acti-ated carbons versus the impregnation ratio showed similar trend.s the impregnation ratio was increased from 40% to 60%, the BETurface area of the activated carbons showed a significant increase.rom the results presented in this section, we concluded that anmpregnation ratio of 80% can be taken as the optimum value forak cups pulp, considering the process economics, the BET surfacerea and the ash content of activated carbon.

Comparison of the surface areas found for oak cups pulp usedn this study with other lignocellulosic materials may be made.he activated carbons obtained from pine sawdust using H3PO4ad surface area ranging from 1559 to 1767 m2 g−1 [26], while thatbtained from eucalyptus bark [6], pecan shell [27], woody biomassirch [13], olive mill waste [24], flax [25] and chestnut wood [14]sing H3PO4 had surface area of 1239, 1130, 761, 336, 1290 and83 m2 g−1, respectively. On the other hand, the activated carbonsbtained from macadamia nutshell [7] and wood [28] using ZnCl2ad a surface area of 1718 and 1450 m2 g−1, respectively, whilehat obtained from olive kernels using KOH had a surface area of049 m2 g−1[3]. The differences between the results this study andthers studies were due to the differences in the type of startingaterials.

.3. The recovery of the activating agents

In the preparation of activated carbon by chemical activation,ain problem is the environmental contamination concerns of

sing chemical agents. To investigate the recovery of the activat-ng agents, a series of experiments was carried out. In this group ofxperiments; a part of the filtrate from the washing with acid and

ater of activated carbon was used as activating agent solution.

hus, the biomass was impregnated with the first 250 mL of filtraterom washing of activated carbon (AC1) obtained with 100 wt% acti-ating agent (H3PO4 and ZnCl2). Then the slurry was pyrolyzed. Theesulted activated carbon (AC2) was demineralized with acid and

able 5haracteristics of activated carbons prepared from oak cups pulp with chemical activatio

BET surfacearea (m2 g−1)

Langmuir surfacearea (m2 g−1)

External surfacearea (m2 g−1)

Micropore area(m2 g−1)

M(

VR-P 1002 1547 830 172 0VR-Z 1152 1763 756 395 0

28.80 AC1 115222.09 AC2 106017.01 AC3 949

water. The first 250 mL of filtrate was impregnated on the biomassand the slurry was pyrolyzed. Then the resulted activated carbon(AC3) was washed with acid and water.

The BET surfaces areas of oak cups pulp activated by recov-ered impregnation solution activated carbons are given in Table 4.The concentration of phosphate and zinc, which were gravimetri-cally determined, in impregnation solutions are also presented inTable 4. Approximately 75–80% of used activating agent could berecovered in 250 mL of filtrate independent of the type of activatingagent and impregnation ratio. In a previous study [29], the reagentrecovery of 90% by collecting of wash waters was reported, butre-utilization of recovered acid was not investigated. On the otherhand, Toles et al. observed that there was a dramatic decrease insurface area development with recycled acid in phosphoric acidactivation of nutshells [30]. The surface area of activated carbondecreased from 1070 to 852 m2 g−1 by using of recycled acid. How-ever, in this study, it is noted that for both H3PO4 and ZnCl2, the BETsurface areas of activated carbon (AC2 and AC3) prepared with fil-trates are only slightly less than that of activated carbons preparedwith the fresh impregnation solutions at the same concentrations. Itis clear that the impregnation solutions can be prepared by mixingof filtrate and fresh impregnation agent. The fact that the chem-icals used in production of activated carbon can be recovered isimportant from the point of environment and process economy.

3.4. Surface properties and adsorption isotherms of activatedcarbons

The most important property of activated carbon is its adsorp-tive capacity relating to the pore surface area and pore volume.Surface structures of the activated carbons obtained from oak cupspulp are shown in Table 5. The activated carbons obtained with80 wt% ZnCl2 and H3PO4 were donated as VR-Z and VR-P, respec-tively.

It is known that the microporosity of the activated carbondepends on the precursor and the activation conditions [7]. Tengand Yeh stated that the micropore fraction of the total pore volumeincreases after washing, indicating that the blocking by chemi-cals mainly occurs on micropore entrances [31]. As mentioned inliterature [18,19], the porosity is generated with chemical agent

remaining intercalated in the internal structure of lignocellulosicmaterials, hindering their shrinkage. In the case of activation withH3PO4, not only H3PO4, but also a mixture of polyphosphate com-pounds was present [18]. Since the polyphosphate compounds are

n.

icropore volumecm3 g−1)

Percentage ofmicropore

Total acidic sites(mmol H+/g AC)

Total basic sites(mmol OH−/g AC)

.0913 17.1 2.16 1.32

.2158 34.3 1.46 1.20

S. Timur et al. / Journal of Analytical and Applied Pyrolysis 89 (2010) 129–136 133

bssu

opaaaamaHo

tbZeitbtsdi

Fig. 2. Nitrogen adsorption isotherms of activated carbons.

igger in size than zinc chloride, they occupy a wide range of poreizes, resulting in larger pore size. On the other hand, the smallize of the ZnCl2 or its hydrates led to the formation of small andniform size of the micropores.

The observations in this study are in agreement with the resultsf other studies. Molina-Sabio and Rodriguez-Reinoso [21], inreparation of activated carbons from peach stones with H3PO4nd ZnCl2, observed that ZnCl2 developed both wide microporesnd low mesopores, whereas H3PO4 developed large mesoporesnd even macropores. It was also demonstrated that ZnCl2 was suit-ble for the production of activated carbons which are essentiallyicroporous [32]. On the other hand, Guo and Lua prepared the

ctivated carbons from oil-palm stones impregnated with ZnCl2,3PO4 or KOH. The degree of microporosity was in the followingrder; ZnCl2 > H3PO4 > KOH [33].

Figs. 2 and 3 show the N2 adsorption isotherms and pore size dis-ributions of the activated carbons, respectively. As seen from Fig. 2,oth isotherms of activated carbons obtained by impregnation withnCl2 and H3PO4 are type I b (materials with wide micropores). Byxamining these results together with the data given in Table 5, its seen that the degree of microporosity is higher with ZnCl2 activa-ion. As seen from Fig. 3, shows that the activated carbon preparedy ZnCl2 activation has shows higher differential pore volume in

he pore size range 9–23.4 Å. On the other hand, in the mesoporeize range, the activated carbon prepared by H3PO4 shows higherifferential pore volume indicating its more developed mesoporos-

ty.

Fig. 3. Pore size distribution of activated carbons.

Fig. 4. SEM images of activated carbons. (a) VR-Z, (b) VR-P.

Scanning electron micrographs (SEMs) of the external structuresof activated carbons are given in Fig. 4. It can be seen from themicrographs that the activated carbons prepared from oak cupspulp with H3PO4 impregnation has an intact external structure.However the external surface area of the activated carbon obtainedfrom oak cups pulp with ZnCl2 is full of cavities. According to themicrograph, it seems that the cavities resulted from the removal ofthe zinc compounds, leaving the space previously occupied by theZnCl2.

3.5. Surface chemistry of activated carbons

Although it is well known that surface area and porous structuredetermine adsorptive properties of activated carbon, heteroatoms,especially oxygen, in its surface has also an appreciable effect onthe adsorptive properties.

Activated carbons have considerable amounts of heteroatomand the presence of these atoms, especially oxygen, in surfacegroups has an appreciable effect on the adsorptive properties ofthe activated carbon as well as surface area and porous struc-ture. Therefore, the activated carbons having the same surface areabut prepared by different methods may show different adsorptioncharacteristics due to their surface chemistry. In this study, theamount of surface oxygen groups on the activated carbons (VR-Z and VR-P) has been determined by Boehm titration method andthe results are shown in Table 5.

The results presented in Table 5 revealed that the predominantfunctions at the surface of the activated carbons are acidic. Acti-vated carbon prepared by using H3PO4 has the higher concentrationof surface groups than the activated carbon obtained by ZnCl2 acti-vation.

134 S. Timur et al. / Journal of Analytical and Applied Pyrolysis 89 (2010) 129–136

of ac

wocsoss

sbrTs9spbo[

3

vaai

toTureup

wr

Fig. 5. IR spectra

In addition to Boehm titration, FTIR spectra of activated carbonsere taken in order to qualitatively evaluate the chemical structure

f activated carbons. It should be noted that because of the darkolor of activated carbons, almost all of the radiation in the visiblepectrum was absorbed and the peaks obtained were usually a sumf the interactions of different types of groups. The results of FTIRpectra of activated carbons are presented in Fig. 5. The shape ofpectra obtained for both two samples was similar.

The small band around 1100 cm−1 is ascribable to either C–OHtretching in phenols or C–O stretching in cyclic ethers. The strongands appearing at 1602 and 1566 cm−1 are due to the aromaticing stretching coupled to highly conjugated carbonyl groups.he small broad band around 3600 cm−1 can be assigned to –OHtretching from phenolic and carboxylic groups. Between 450 and00 cm−1, there is a number of broad overlapping bands which areuperimposed. They cannot, therefore, be described in terms of sim-le motion of specific functional groups or chemical bonds. It muste noted that characteristic bands below 900 cm−1 are C–H out-f-plane bending absorption in aromatic ring and C–C stretching34].

.6. Aqueous adsorption characteristics

Aqueous adsorption tests were conducted on selected acti-ated carbons (VR-Z and VR-P) with the aim of assessing potentialpplications in the water treatment industry. The selected useddsorbates are the most common toxic compounds present inndustrial effluents.

In surface adsorption studies, the relationship between the solu-ion concentration and the species uptake can be described in termsf either a Langmuir-type or Freundlich-type isotherm, generally.he parameters in Freundlich and Langmuir equations are veryseful for predicting adsorption capacities and also for incorpo-ating into mass transfer relationships in the design of contactingquipment. In this study, the Langmuir and Freundlich models weresed to fit the adsorption isotherms and to evaluate the isothermarameters.

The Langmuir model is expressed as

Ceqe

= 1KLSM

+ CeSM

here SM (mg g−1) is the maximum amount of adsorption cor-esponding to complete monolayer coverage on the surface, qe

tivated carbons.

(mg g−1) is the amount of adsorbed adsorbate, KL (L g−1) is the Lang-muir constant and Ce is the equilibrium liquid phase concentrationsof adsorbate solution.

The Freundlich model is given as

qe = KFCe1/n

where KF is Freundlich constant and roughly an indicator of theadsorption capacity. 1/n gives an indication of the favorability ofadsorption. Heterogeneity becomes more prevalent as 1/n getscloser to zero.

Freundlich isotherm indicates that significant adsorption takesplace at low concentrations, but the increase in the amountadsorbed with concentration becomes less significant at higherconcentration. On the other hand, Langmuir model is used forhomogenous surfaces and demonstrate monolayer coverage of theadsorbate at the outer surface of the adsorbent.

3.6.1. PhenolFor phenol adsorption, VR-P showed a closer fit to the Lang-

muir model, whereas the adsorption data for the VR-Z was wellfitted with both models (Table 6). Because phenol (size of phe-nol ≈ 0.8 nm) is adsorbed mainly within the micropores, phenoladsorption capacity of VR-P was lower than that of VR-Z, as aresult of its less developed microporous structure. Similar resultwas obtained in literature. Altenor et al. produced the activated car-bons from vetiver roots with different H3PO4 concentrations havingmicropore volumes of 0.45, 0.39, and 0.22 cm3 g−1, surface areasof 1170, 1272, and 1004 m2 g−1 and phenol adsorption capacitiesof 122, 74, and 107 mg g−1, respectively [16]. And they mentionedthat the highest phenol adsorption capacity of activated carbon pro-duced was attributed to its having the highest micropore volumepercentage.

The other reason for lower phenol adsorption capacity of VR-P may be the higher amount of acidic surface groups. In additionto microporosity, the phenol adsorption is highly related to theoxygen-containing surface functional groups. It was reported thatthe presence of basic surface groups promotes phenol adsorp-tion while acidic surface groups reduced the adsorption of phenol

[17,35–37]. Gonzalez-Serrano produced the activated carbons fromlignin with H3PO4 at 425, 500, and 600 ◦C having micropore vol-umes of 0.82, 0.74, and 0.70 cm3 g−1, surface areas of 1459, 1372,and 1244 m2 g−1 and phenol adsorption capacities of 200, 227and 213 mg g−1, respectively [17]. It was also reported that the

S. Timur et al. / Journal of Analytical and Applied Pyrolysis 89 (2010) 129–136 135

Table 6Parameters of the Langmuir and Freundlich adsorption models of adsorbates.

Adsorbates Activated carbon Langmuir model Freundlich model

SM (mg g−1) KL (L mg−1) R2 1/n KF R2

PhenolVR-Z 75.19 0.072 0.99 0.36 14.89 0.96VR-P 62.11 0.830 0.99 0.12 41.67 0.83

Methylene BlueVR-Z 384.60 0.107 0.99 0.17 196.60 0.88VR-P 454.50 0.880 0.99 0.11 281.80 0.87

Basic Red 18VR-Z 181.82 7.857 0.99 0.03 163.12 0.88VR-P 232.56 0.632 0.99 0.06 177.83 0.90

Acid Red 111VR-Z 40.48 0.058 0.95 0.49 4.72 0.98VR-P 34.84 0.097 0.99 0.33 8.34 0.99

paAtsfvabAgcccti

3

Rcaf

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imoVwf

Cr(VI)VR-Z 156.30VR-P 147.10

resence of carbon–oxygen surface groups of the non-acidic char-cter increased as the temperature increased. On the other hand,ygün et al. produced the activated carbon from several agricul-

ural wastes by chemical activation using ZnCl2 [36]. Although theurface area of all activated carbons was not very much differentrom each other, phenol adsorption capacities differed. The acti-ated carbons lacking of acidic functional groups had higher phenoldsorption capacity (145 and 126 mg g−1) than the activated car-ons having acidic functional groups of 0.33 and 0.13 mmol g−1.nd they proposed that the presence of acidic surface functionalroups hinders the ability of activated carbon to adsorb phenolicompounds by reducing the effectiveness of basic groups. As con-lusion, due to the higher acidic functional groups, the activatedarbons obtained from oak cups pulp showed lower phenol adsorp-ion than the activated carbons produced from agricultural wastesn literature.

.6.2. Basic dyesTwo kinds of basic dyes were used, Methylene Blue and Basic

ed 18. Former is a relatively large molecule and serves as a modelompound for adsorption of medium size organic compounds fromqueous solutions. Latter is widely used for acrylic and its blendedabric dyeing.

For Methylene Blue, both VR-Z and VR-P showed a closer fit tohe Langmuir model (Table 6). The Langmuir capacity, SM,, of acti-ated carbon prepared by ZnCl2 impregnation (VR-Z) was lowerhan that of activated carbon prepared by H3PO4 impregnationVR-P) which could be due to its less developed mesoporosity. Theesults obtained in this study were comparable with the results ofther workers, methylene blue adsorption capacities were foundo be in the range of 115–400 mg g−1 [3,16,38–41].

Although, pH had no influence on the adsorption of MB, thedsorption of Basic Red 18 increased with increasing pH from 7 to0 and further increase in pH had no considerable effect on adsorp-ion capacity (the dates are absent in text). It was also reported thathe adsorption of Basic Red 18 on activated sludge increased withH up to 6–10 [42]. The reason is the fact that negative surfaceharge of absorbent increased with increasing pH, which enhanceshe uptake of dye cations due to the electrostatic force of attraction.imilar observation was reported for adsorption of other cationicyes [17,43].

From Table 6, it can be seen that the Langmuir model resultednto a better fit than the Freundlich model for Basic Red 18. The

aximum adsorption capacity (SM) of VR-P was more than thatf VR-Z, although letter has larger surface area. This shows thatR-P surface has more active sites (positive ions) which can reactith the functional groups of Basic Red 18 leading to some complex

ormation. It may be mentioned that basic dye adsorption capacity

0.089 0.99 0.29 34.76 0.900.056 0.89 0.27 33.45 0.85

of activated carbon is depends on the not only BET surface area, andbut also interaction of positive ions with surface functional groupsof activated carbons.

Low uptake of Basic Red 18 than MB could be due to its chemi-cal structure which might lead to the formation of large aggregatedmolecules that hindered their free diffusion to the internal porosity[44]. For various types of basic dyes, comparison may be made ofthe adsorption capacity found for activated carbons prepared fromoak cups pulp with the activated carbons prepared from other lig-nocellulosic wastes. The adsorption capacities of activated carbonprepared from palm kernel shell [45], saw dust [46], apricot shell[47] and Bagasse [48] were found to be 333.33 mg g−1 (for Basic Blue9), 289.9 mg g−1 (for crystal violet), 181.5 mg g−1 (for Astrazon BlueFGRL) and 198.6 mg g−1 (for Rhodamine-B), respectively.

3.6.3. Acidic dyesAs in the case of Basic Red 18, the pH of the solution played an

important role on the adsorption capacity. As expected, the adsorp-tion of Acid Red 111 increased with decreasing pH. This is due to theexistence of significantly high electrostatic attraction between thepositively charged surface of the adsorbent and anionic dye belowpH 5. Maximum adsorption was observed at pH 2 and 3 for VR-Pand VR-Z, respectively. Similar behavior has also been reported byother researchers [49].

Comparing the results obtained for Basic Red 18 with Acid Red111, one can say that the adsorption capacity of activated carbonsobtained from oak cups pulp for basic dye is much more than acidicdye. This is due to the strong correlations between acidity/basicityof activated carbon and maximum adsorption capacity. Faria et al.reported that basic dyes might preferably adsorb onto activatedcarbons with acidic characteristics whereas acidic dyes preferablyadsorb on basic activated carbons [50]. According to Faria et al.,the presence of oxygen-containing functional groups in acidic car-bons, which are electron-withdrawing groups, reduce the electrondensity on the surface of the carbon leading to a decrease in theadsorption potential for the dye molecules. Simultaneously thereis an increase in repulsive electrostatic interactions between theanions of the dyes and the negatively charged surface of activatedcarbon.

3.6.4. Cr(VI)The pH value of the solution is an important controlling param-

eter in the Cr(VI) adsorption process. The uptake of Cr(VI) increased

with a decrease in the solution pH. The pH dependence of the metaluptake is mainly related to the functional groups on the activatedcarbon and also on the metal solution chemistry. From pH 1 topH 6, most chromium species exist in solution in the form HCrO4

−,while from pH 6 to pH 10, the H2CrO4 species become predominant

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36 S. Timur et al. / Journal of Analytical

n solution [51]. Under acidic conditions, the surface of the acti-ated carbons becomes highly protonated and favors the uptakef Cr(VI) in the anionic form by ion exchange mechanism [52].he highest adsorption efficiency was obtained at pH 2.0. There-ore, the equilibrium adsorption measurement of Cr(VI) has beenarried out at pH 2.0. The equilibrium data fits both the Lang-uir and Freundlich equations well for VR-Z (Table 6). Langmuir

r(VI) adsorption capacities of VR-Z and VR-P are almost similar,lthough they have different surface area and micropore volume.he reason may be attributed to the simultaneous effect of surfacexygen groups, pore structure, and surface area of activated car-ons. It must be noted these activated carbons have higher Cr(VI)dsorption capacity than that of agricultural waste-derived acti-ated carbons. Comparatively, the maximum adsorption capacitiesf activated carbons obtained from sawdust by H3PO4 [49], fromerminalia arjuna nut by ZnCl2 [53], and from Casurina equisetifoliaeaves by ZnCl2 [54] were found to be 59.2, 28.43 and 35 mg g−1,espectively. The differences in adsorption capacities could be dueo the initial carbon content of the raw material and activationrocess which influences surface morphology and chemistry ofdsorbent.

. Conclusions

In this study, the activated carbons were prepared from oak cupsulp by chemical activation method. Phosphoric acid and zinc chlo-ide were used as activating agent. The chemical to biomass ratiof 80–100% (by mass) and the impregnation time of 4 h were to beound the best condition for the production of high surface area acti-ated carbons from lignocellulosic material by chemical activation.he maximum surface areas of the activated carbons were 1000nd 1152 m2 g−1 for phosphoric acid and zinc chloride, respectively.he micropore volume of activated carbon prepared by ZnCl2 wasigher than that of activated carbon obtained using H3PO4.

In addition, from the point of environment and process econ-my, the recovery of the activating agents was also investigated.pproximately 75–80% of used activating agent could be recoverednd was reused in impregnation of biomass.

The aqueous adsorption tests showed that the activated car-ons from oak cups pulp had a notable adsorption capacity forhromium, phenol and basic dyes. The results obtained from aque-us adsorption tests also revealed that the role of carbon surfacehemistry on adsorption capacity is as important as the roles ofurface area and porosity.

As conclusion the present investigation showed that oak cupsulp can be effectively used as a raw material for the preparationf activated carbon by chemical activation. The resulting activatedarbons may be used to effectively treat wastewater due to theirigh adsorption capacities. Cost analysis for the preparation of acti-ated carbons has not been carried out, but it is well known thathe manufacturing costs of activated carbons are based on the prod-ct yield, surface area and cost of starting materials [55]. Since thetarting material has zero cost and use of activating agent repeat-dly in activation process was proved to be efficient, the cost ofctivated carbon from oak cups pulp is expected to low.

cknowledgments

We would like to thank to Ege University for financial supportnder the contract 2004/Fen/057. It is a pleasure to thank Dr. Yunusnal for analysis support.

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pplied Pyrolysis 89 (2010) 129–136

References

[1] S. Yorgun, N. Vural, H.D. Yorgun, Microporous Mesoporous Mater. 122 (2009)189–194.

[2] I.H. Aljundi, N. Jarrah, J. Anal. Appl. Pyrolysis 81 (2008) 33–36.[3] A. Zabaniotou, G. Stavropoulos, V. Skoulou, Bioresour. Technol. 99 (2008)

320–326.[4] W. Li, L. Zhang, J. Peng, N. Li, X. Zhu, Ind. Crop. Prod. 27 (2008) 341–347.[5] M. Belhachemi, R.V.R.A. Rios, F. Addoun, J. Silvestre-Albero, A. Sepulveda-

Escribano, F. Rodriguez-Reinoso, J. Anal. Appl. Pyrolysis 86 (2009) 168–172.[6] P. Patnukao, P. Pavasant, Bioresour. Technol. 99 (2008) 8540–8543.[7] M. Jagtoyen, F. Derbyshire, Carbon 36 (1998) 1085–1097.[8] A. Ahmadpour, D.D. Do, Carbon 35 (1997) 1723–1732.[9] M.A. Lillo-Ródenas, D. Cazorla-Amorós, A. Linares-Solano, Carbon 41 (2003)

267–275.10] H.P. Boehm, E. Diehl, W. Heck, R. Sappok, Angew. Chem. Int. Ed. 3 (1966) 669.11] B.S. Girgis, M.F. Ishak, Mater. Lett. 39 (1999) 107–114.12] A.H. El-Sheikh, A.P. Newman, H.K. Al-Daffaee, S. Phull, N. Cresswell, J. Anal. Appl.

Pyrolysis 71 (2004) 151–164.13] A.C. Lua, T. Yang, J. Colloid Interface Sci. 274 (2004) 594–601.14] T. Budinova, E. Ekinci, F. Yardim, A. Grimm, E. Björnbom, V. Minkova, M. Gora-

nova, Fuel Process. Technol. 87 (2006) 899–905.15] V. Gomez-Serrano, E.M. Cuerda-Correa, M.C. Fernandez-Gonzalez, M.F.

Alexandre-Franco, A. Macias-Garcia, Mater. Lett. 59 (2005) 846–853.16] S. Altenor, B. Carene, E. Emmanuel, J. Lambert, J.-J. Ehrhardt, S. Gaspard, J. Haz-

ard. Mater. 165 (2008) 1029–1039.17] E. Gonzalez-Serrano, T. Cordero, J. Rodriguez-Mirasol, L. Cotoruelo, J.J.

Rodriguez, Water Res. 38 (2004) 3043–3050.18] E. Demirbas, M. Kobya, M.T. Sulak, Bioresour. Technol. 99 (2008) 5368–5373.19] F. Suarez-Garcia, A. Martinez-Alanso, J.M.D. Tascon, J. Anal. Appl. Pyrolysis 63

(2002) 283–301.20] C. Namasivayan, K. Kadirvelu, Bioresour. Technol. 62 (1997) 123–127.21] M. Molina-Sabio, F. Rodriguez-Reinoso, Colloids Surf. A 241 (2004) 15–25.22] R. Malik, D.S. Ramteke, S.R. Wate, Waste Manage. 27 (2007) 1129–1138.23] W.T. Tsai, C. Chang, S.L. Lee, Bioresour. Technol. 64 (1998) 211–217.24] C. Moreno-Castilla, F. Carrasco-Marin, M.V. Lopez-Ramon, M.A. Alverez-

Merino, Carbon 39 (2001) 1415–1420.25] P.T. Williams, A.R. Reed, J. Anal. Appl. Pyrolysis 71 (2004) 971–986.26] Y. Munoz, R. Arriagada, G. Soto-Garrido, R. Garcia, J. Chem. Technol. Biotechnol.

78 (2003) 1252–1258.27] Y. Guo, D.A. Rockstraw, Bioresour. Technol. 98 (2007) 1513–1521.28] C. Hu, J. Zhou, S. He, Z. Luo, K. Cen, Fuel Process. Technol. 90 (2009) 812–817.29] C. Srinivasakannan, M.Z. Abu Bakar, Biomass Bioenerg. 27 (2004) 89–96.30] C.A. Toles, W.E. Marshall, M.M. Johns, J. Chem. Technol. Biotechnol. 72 (1998)

256–263.31] H. Teng, T.S. Yeh, Ind. Eng. Chem. Res. 37 (1998) 58–65.32] R.F. Rodriguez-Reinoso, A.L. Solano, in: P.A. Thrower (Ed.), Chemistry and

Physics of Carbon, vol. 21, Marcel Dekker, New York, 1989, pp. 2–146 (Chapter1).

33] J. Guo, C. Lua, J. Porous Mater. 7 (2000) 491–497.34] C. Moreno-Castilla, M.V. Lopez-Ramon, F. Carrasco-Marina, Carbon 38 (2000)

1995–2001.35] H. Oda, M. Kishida, C. Yokokawa, Carbon 19 (1981) 243–248.36] A. Aygün, S. Yenisoy-Karakas, I. Duman, Microporous Mesoporous Mater. 66

(2003) 189–195.37] C. Moreno-Castilla, J. Rivera-Utrilla, M.V. Lopez-Ramon, F. Carrasco-Marin, Car-

bon 33 (1995) 845–851.38] B.H. Hameed, I.A.W. Tan, A.L. Ahmad, J. Hazard. Mater. 158 (2008) 324–332.39] G. Duman, Y. Onal, C. Okutucu, S. Onenc, J. Yanik, Energy Fuels 23 (2009)

2197–2204.40] S. Timur, I.C. Kantarli, E. Ikizoglu, J. Yanik, Energy Fuels 20 (2006) 2636–2641.41] H. Deng, L. Yang, G. Tao, J. Dai, J Hazard. Mater. 166 (2009) 1514–2152.42] O. Gulnaz, A. Kaya, F. Matyar, B. Arikan, J. Hazard. Mater. 108 (2004) 183–188.43] S. Preethi, A. Sivasamy, S. Sivanesan, V. Ramamurthi, G. Swaminathan, Ind. Eng.

Chem. Res. 45 (2006) 7627–7632.44] V.K. Gupta, I. Ali, V.K. Saini, J. Colloid Interface Sci. 315 (2007) 87–93.45] A. Jumasiah, T.G. Chuah, J. Gimbon, T.S.Y. Choong, I. Azni, Desalination 186

(2005) 57–64.46] S. Chakraborty, S. De, S.D. Gupta, J.K. Basu, Chemosphere 58 (2005) 1079–1086.47] B. Karagozoglu, M. Tasdemir, E. Demirbas, M. Kobya, J. Hazard. Mater. 147

(2007) 297–306.48] H.M.H. Gad, A.A. El-Sayed, J. Hazard. Mater. 168 (2009) 1070–1081.49] M.M. Mohamed, J. Colloid Interface Sci. 272 (2004) 28–34.50] P.C.C. Faria, J.J.M. Orfao, M.F.R. Pereira, Water Res. 38 (2004) 2043–2052.

51] L. Yang, J.P. Chen, Bioresour. Technol. 99 (2008) 297–307.52] T. Karthikeyan, S. Rajgopal, L.R. Miranda, J. Hazard. Mater. 124 (2005) 192–199.53] K. Mohanty, M. Jha, B.C. Meikap, M.N. Biswas, Chem. Eng. Sci. 60 (2005)

3049–3059.54] K. Ranganathan, Bioresour. Technol. 73 (2) (2000) 99–103.55] G.G. Stavropoulos, A.A. Zabaniotou, Fuel Process. Technol. 90 (2009) 952–957.