Microporous and Mesoporous Materials 198 (2014) 45–49

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Microporous and Mesoporous Materials

journal homepage: www.elsevier .com/locate /micromeso

Preparation and characterization of activated carbon from plant wasteswith chemical activation

http://dx.doi.org/10.1016/j.micromeso.2014.07.0181387-1811/� 2014 Elsevier Inc. All rights reserved.

⇑ Corresponding author. Tel.: +90 442 231 40 04; fax: +90 442 236 09 55.E-mail address: ahmetgu@yahoo.com (A. Gürses).

Metin Açıkyıldız a, Ahmet Gürses b,⇑, Semra Karaca c

a Kilis 7 Aralık University, Faculty of Science and Art, Department of Chemistry, Kilis, Turkeyb Atatürk University, K.K. Education Faculty, Department of Chemistry, Erzurum, Turkeyc Atatürk University, Faculty of Science and Art, Department of Chemistry, Erzurum, Turkey

a r t i c l e i n f o

Article history:Received 18 February 2014Received in revised form 10 July 2014Accepted 13 July 2014Available online 21 July 2014

Keywords:Activated carbonChemical activationPlant wastesZinc chloride

a b s t r a c t

Activated carbon has been widely used in the sorption of chemical species from aqueous solutions as aversatile adsorbent with optimal sorption properties. However, production and regeneration of commer-cial activated carbons are still expensive and so the importance of activated carbon production by usinglow-cost raw materials and methods are still up to date. In this study, a one-step chemical activation pro-cess by zinc chloride was used to obtain activated carbon from plant wastes (PWs) such as pine sawdust(PS), rose seed (RS), and cornel seed (CS). The effect of activation parameters such as carbonization tem-perature, impregnation (ZnCl2/PW) ratio, and impregnation time on the properties of final products wereinvestigated. The produced activated carbons were characterized by nitrogen adsorption isotherms at77 K. The present results showed that the surface area and methylene blue index of activated carbons,which were determined by adsorption tests, were achieved as high as 1825 m2/g and 300 mg/g in theirhighest value, respectively.

� 2014 Elsevier Inc. All rights reserved.

1. Introduction or even better characteristics than the conventional ones [9,10].

The adsorption has been found to be superior as compared toother traditional treatment methods for wastewater treatmentdue to its low-cost, easy availability, simplicity of design, high effi-ciency, ease of operation and ability to treat dyes and metal ions[1,2]. The most widely used adsorbent to remove of wastes byadsorption is activated carbon. Activated carbon is a water indus-try’s standard adsorbent which has highly developed porosity, spe-cific surface area of more than 400 m2/g, surface functional groups,especially oxygen groups and relatively high mechanical strength[3–5]. Therefore, it has been extensively used for separation ofgases, recovery of solvents, removal of organic pollutants fromdrinking water and a catalyst support. As environmental pollutionis becoming a more serious problem, the need for activated carbonis growing [6]. However, production and regeneration of commer-cial activated carbons are still expensive [2] and there are manycontinuing researches for potential materials and methods so theimportance of production of activated carbon by using low-costraw materials and methods is still up to date [7,8]. Thus, it is ofextreme relevance to find suitable low-cost raw materials thatare economically attractive and at the same time present similar

Currently, there are many studies on the production of activatedcarbons from industrial or agricultural products, by-productsand/or wastes [9]. Basically, there are two different processes forthe preparation of activated carbons which have developed porenetwork and so high adsorption capacity: physical activation andchemical activation. In comparison with physical activation, thereare two important advantages of chemical activation. One is thelower temperature in which the process is accomplished. The otheris that the global yield of the chemical activation tends to begreater since burn-off char is not required [11].

The aim of this study is to evaluate the utility of some plantwastes, pine sawdust (PS), rose seed (RS) and cornel seed (CS) asabundant and/or cheap precursors for activated carbon production.The influence of the experimental parameters such as carboniza-tion temperature, impregnation ratio and impregnation time onthe carbon characteristics was evaluated. The surface areas of thesamples prepared in this study were compared with the resultspublished in the literature.

2. Material and methods

2.1. Materials

Pine (Pinus sylvestris) sawdust, rose (Rosa canina, Gümüs�su Inc.)seed, and cornel seed (Cornus mas L.) obtained from the east of

46 M. Açıkyıldız et al. / Microporous and Mesoporous Materials 198 (2014) 45–49

Turkey were selected as the precursor to production of activatedcarbon. The precursors were dried, crushed and sieved to a particlesize fraction of 1.7 mm (seeds) and 5 mm (sawdust). Elementalcomposition of materials (carbon, nitrogen, hydrogen, and sulfur)was determined by using the LECO CHNS-932 elemental analyzer.The oxygen content was estimated by difference [100 � (% C + %H + % N + % S)]. The proximate and elemental analyses of raw mate-rials are shown in Table 1. The high carbon, low ash and low sulfurcontent of the precursors are positive factors and therefore, thesePWs can be potential starting materials for the production of activecarbon [12,13]. Zinc chloride (98%) and methylene blue (MB) wereobtained from Sigma Aldrich and Park respectively. A commercialactivated carbon (Merck-2183) was used as a reference material.

2.2. Method

Different amounts of ZnCl2 (5, 7.5, 10, 15, and 20 g) were dis-solved in 150 mL of distilled water, and then 10 g of dried PWswas mixed with the zinc chloride solution and stirred at approxi-mately 85 �C for 2 h. The mixtures were dehydrated in an oven at110 �C for about 24 h. The ZnCl2 impregnated PWs were placedin a ceramic crucible and pyrolyzed in a horizontal tubular furnaceunder the nitrogen flow. The samples were heated to final temper-atures of 300–800 �C with 10 �C/min heating rate for residencetime of 1 h. The resultant activated carbon was washed with 3 MHCl solution by heating at around 90 �C for 30 min, filtered andrinsed by warm distilled water until neutral pH, dried at 105 �Cin an oven for about 12 h and weighed to calculate the yield [14].The activated carbon production yields were calculated from theweight of activated carbons divided by the weight of the driedPWs.

The adsorption capacities of the samples were evaluated bymethylene blue adsorption. A 100 mg amount of the carbon sam-ples was added to 50 mL vials with 25 mL of methylene blue at aconcentration of 1200 mg/L in 5% acetic acid-distilled water solu-tion [15]. Blanks not containing methylene blue (MB) were usedfor each series of experiments. The vials were shaken for 24 h at25 �C. The concentration of MB in the supernatant solution afterand before adsorption was determined with a 1.0 cm light pathquartz cells using Shimadzu 1201 UV spectrophotometer (Shima-dzu) at 664 nm (kmax). The amount of methylene blue adsorbedby per gram of adsorbent was calculated as following equation:

q ¼ ðC0 � CÞ � Vw

where q is methylene blue index (mg/g), V is the volume of solution(L), and w is the dry weight of the added adsorbent (g).

The surface characteristics were determined by N2 adsorption/desorption isotherms at 77 K using an analyzer MicromeriticsGemini V. Prior to the adsorption analyses, the samples werepre-degassed at 120 �C for 3 h under vacuum to remove moistureand other impurities. In these analyses, nitrogen was used asadsorbate at liquid nitrogen temperature. Single point surface area(S, mg/g) was determined at P/P0 < 0.35. The average pore widths

Table 1The proximate and elemental analyses results of raw materials.

Precursor Elemental

C H N S O

PS 46.41 6.27 0.06 0.03 47.23RS 41.36 6.03 1.20 0.10 51.31CS 43.67 6.43 0.40 – 49.50

* As received.

of samples were determined by Barrett-Joyner-Halenda (BJH)method.

2.3. Mathematical modeling

In this study, models were developed to predict surface areasand methylene blue indexes of activated carbon samples basedon their preparation conditions (carbonization temperature,impregnation ratio, and impregnation time). Firstly, the fitting ofexperimental data to various models such as linear, logarithmic,inverse, power, cubic, compound, growth, and exponential wasinvestigated for selecting the best equation. Then the final versionof the chosen model with further changes which will increase theR2 values was determined by non-linear regression using the SPSS11.5 package program. The coefficient of determination R2 was oneof the main criteria for selecting the best equation [16]. In thederived models, the carbonization temperature, impregnationratio, and impregnation time were coded as X1, X2, and X3,respectively.

3. Result and discussion

3.1. The effect of carbonization temperature

Effects of carbonization temperature on the methylene blueindex (q), surface area (S), and yield (%) of activated carbon wereevaluated under the conditions of the impregnation ratio of1.5 g/g and impregnation time of two hours (Table 2).

The carbonization temperature and impregnation ratio can beassumed as the most important process parameters affecting theyield of activated carbon. As seen from Table 2, the yield of acti-vated carbon decreased with the increasing of carbonization tem-perature for all the raw materials. This could be attributed to thepromotion of carbon burning-off, tar volatilization and the devola-tilization of biomass would be enhanced due to increase of temper-ature. Hence, the char yield was reduced and the volatile (liquidand gas) yield was increased [14,17].

The methylene blue indexes of the samples sharply increasedwith the increase of carbonization temperature from 300 to400 �C, whereas after 400 �C there was no significant change. Thesimilar results were also found for the surface area of activated car-bon prepared from PWs. For instance, the surface areas of the acti-vated carbons prepared from PS sharply increased withtemperature up to 400 �C and then slightly decreased. However,the highest surface areas for the produced activated carbon fromRS and CS are observed at 500 �C. It highlighted that there are threestages of pore development. They are: opening of previously inac-cessible pores, creation of new pores by selective activation andwidening of the existing pores [18]. Thus, it can be hypothesizedthat the first two stages are the dominant process on the poredevelopment until temperature where the surface area is maxi-mum. However, at the higher temperature, it can be concludedthe widening of the existing pores. Decrease in the surface areascan be attributed to widening of the existing pores as a resultof severe thermal treatment, which causes the breakdown of

Proximate*

Moisture Fixed carbon Volatile matters Ash

6.02 21.30 72.23 0.455.50 25.37 66.34 2.795.40 27.34 64.67 2.59

Table 2The effect of experimental parameters on the surface area, methylene blue index andyield of activated carbon samples.

Precursor Temperature(�C)

Imp.ratio (w/w)

Imp.time(h)

q (mg/g)

S (m2/g) Yield(%)

PS 300 1.50 2 181.78 4.47 53.41400 0.50 2 179.79 721.76 46.90400 0.75 2 292.05 782.36 48.38400 1.00 2 298.62 1297.39 49.83400 1.50 2 299.41 1824.71 45.57400 2.00 2 299.47 1004.89 46.67500 1.50 1 299.37 1503.32 45.64500 1.50 2 299.32 1677.67 46.09500 1.50 3 299.21 1728.69 41.59600 1.50 2 298.86 1603.75 40.63700 1.50 2 298.94 1313.09 38.51800 1.50 2 299.93 1344.52 39.09

RS 300 1.50 2 122.68 18.41 51.94400 0.50 2 149.34 522.46 48.11400 0.75 2 236.40 500.24 52.30400 1.00 2 272.19 856.70 50.04400 1.50 2 294.19 824.56 48.26400 2.00 2 295.77 1057.98 44.77500 1.50 1 288.01 1264.63 42.57500 1.50 2 291.76 1238.49 41.45500 1.50 3 296.99 1053.24 44.46600 1.50 2 291.96 1044.52 40.43700 1.50 2 282.54 1047.55 38.61800 1.50 2 292.46 986.93 38.13

CS 300 1.50 2 155.00 12.10 55.71400 0.50 2 238.91 477.70 54.01400 0.75 2 265.76 533.99 59.25400 1.00 2 292.37 729.08 52.20400 1.50 2 296.03 845.51 50.40400 2.00 2 294.34 779.12 42.68500 1.50 1 286.78 1079.75 51.91500 1.50 2 297.13 1355.09 42.96500 1.50 3 296.08 1291.67 47.72600 1.50 2 285.29 1044.80 42.30700 1.50 2 275.24 964.67 42.38800 1.50 2 298.55 1238.44 40.76

0

10

20

30

40

0.00 0.20 0.40 0.60 0.80 1.00

Am

ount

ads

orbe

d (m

mol

/g)

Relative pressure (p/p0)

300 400 500

600 700 800

Fig. 1. N2 adsorption isotherms of carbons prepared from PS at different carbon-ization temperature.

0

10

20

30

0.00 0.20 0.40 0.60 0.80 1.00

Am

ount

ads

orbe

d (m

mol

/g)

Relative pressure (p/p0)

300 400 500

600 700 800

Fig. 2. N2 adsorption isotherms of carbons prepared from RS at different carbon-ization temperature.

0

10

20

30

0.00 0.20 0.40 0.60 0.80 1.00

Am

ount

ads

orbe

d (m

mol

/g)

Relative pressure (p/p0)

300 400 500

600 700 800

Fig. 3. N2 adsorption isotherms of carbons prepared from CS at different carbon-ization temperature.

M. Açıkyıldız et al. / Microporous and Mesoporous Materials 198 (2014) 45–49 47

cross-links in the carbon matrix, with a consequent rearrangementof carbonaceous aggregates and the collapse of pores. It is also pos-sible that there is a destruction of pore structures depending onextensive gasification at high temperatures [19].

The N2 adsorption isotherms on the carbons prepared from PWsat different carbonization temperatures are shown in Figs. 1–3. As

can be seen from these figures, there is a nearly horizontal plateauat higher relative pressures after the rapid increase in the adsorbedamount of N2 at low relative pressures. These isotherm character-istics point out the Type I isotherm based on the classification ofthe BDDT (Brunauer, Deming, Deming, and Teller) for low and highcarbonization temperatures [20]. The Type I isotherm represents amaterial with microporous structure. The major uptake occurs atlow relative pressures indicating the formation of highly porousmaterials for all carbonization temperatures. However, at the mid-dle carbonization temperatures, isotherm shapes show that thecarbons are mainly microporous, but with a significant mesopor-ous character. Average pore sizes of samples support these inter-pretations. The average pore width ranges were determined as23–31, 24–27, and 23–27 Å for PS, RS, and CS, respectively.

3.2. The effect of impregnation ratio

Effects of the impregnation ratio (ZnCl2/PW ratio, w/w) on themethylene blue index (q), surface area (S), and yield (%) of acti-vated carbon were evaluated under the conditions of carbonizationtemperature of 400 �C and impregnation time of 2 h (Table 2). Itcan be seen that methylene blue indexes for all samples increased

48 M. Açıkyıldız et al. / Microporous and Mesoporous Materials 198 (2014) 45–49

from 0.50 to 0.75 impregnation ratio; however, at other impregna-tion ratios (1.0–2.0), this index values exhibit the tendency to beconstant. Likewise, as seen from Table 2, when the impregnationratio was increased from 0.50 to 0.75, the yields for all samplesincreased. However, the yields decreased with continuing increaseof the impregnation ratio. These findings can be attributed to theactivating agents such as ZnCl2 may promote the formation ofcross-links, leading to the formation of a rigid matrix, and lessprone to volatile loss [21]. As can be seen from Table 2, when theimpregnation ratio was increased from 1.5 to 2, the fact thatdecrease of the yield and surface area values and constant of meth-ylene blue index can be attributed to new micropores did not growany longer while existing micropores were continuously enlargedinto mesopores. These results also suggested that ZnCl2 not onlydevelops new pores but also enlarges existing pores by choosingan appropriate impregnation ratio.

Caturla et al. [22] has reported that the large amount of organiccarbons is removed as CO, CO2, CH4 and tar coupling with O and Hatoms if activating agent is not used. The activated agent in theinterior of particles provides a dehydrating effect on the alreadytransformed components (cellulose, hemicellulose, and lignin)during the heat treatment. It is also possible that cross-linkingreactions are predominant in this step with the subsequent reduc-tion in the exit of volatile matter and tars, leading to high activecarbon yield observed [23–27]. In the current study, activationwith the low impregnation ratios resulted in a higher yield rangeof 48–54 since ZnCl2 selectively stripped H and O away from theimpregnated sample as H2O and H2 rather than hydrocarbons, COor CO2. These findings are compatible with previous reports[22,28]. In addition to these mechanisms as mentioned before,the reduction of weight loss or enhancing the carbon yield in theimpregnation with ZnCl2 can be due to the promoting effect ofZnCl2 on the Scholl condensation (polymerization) reactions. Thesereactions, which occur among the aromatic hydrocarbons and tar-forming compounds, result in the formation of larger molecules(polycyclic aromatics) in the structure of activated products andincrease in the carbon yield [29].

With the increase in the impregnation ratio, the initial effect ofZnCl2 is to inhibit the release of volatile matter, which results inhigher yield and MB adsorption of activated carbon. Subsequently,with the further increase in the impregnation ratio, the zinc chlo-ride chemical assumed a dehydration agent role during activation.It inhibits the formation of tars and any other liquids that couldclog up the pores of the sample, the movement of the volatilesthrough the pore passages would not be hindered, and volatileswill be subsequently released from the carbon surface during acti-vation [30–32].

In the present study, our results showed that methylene blueindexes of activated carbons exhibit the tendency to be constantat high impregnation ratios (1.0–2.0) (Table 2), although surfaceareas of the materials showed maximum values. On the otherhand, after 1:1 ratio for RS, surface area decreased while the meth-ylene blue index is increasing with increasing impregnation ratioand methylene blue indexes of other raw materials exhibit the ten-dency to be constant. This is attributed to widening of microporeswhich also cause to the decreasing of surface area and increasing ofmethylene blue index due to size difference. However, the openingof new pores becomes the dominant with the increasing of theimpregnation ratio for PS and CS.

3.3. The effect of impregnation time

The effect of impregnation time on the methylene blue index(q), surface area (S), and yield (%) of activated carbon were evalu-ated under the conditions of carbonization temperature of 500 �Cand impregnation ratio of 1.5:1 (w/w) (Table 2). It can be deduced

from these data that the raw materials exhibited the differentresponse to impregnation time. The methylene blue indexes ofactivated carbon samples produced from PS did not significantlychange with increasing time; however, their surface areasincreased with increasing time. The surface area and methyleneblue indexes of activated carbon samples produced from CSenhanced with increasing time up to 2 h and then they reduced.The methylene blue index of the activated carbons prepared fromRS constantly increased with impregnation time whereas their sur-face area decreased with impregnation time. The activated carbonyield values for the PS did not change until 2 h, but after itdecreased. The activated carbon yields for the RS and CS decreasedfor the first 2 h and then they increased with the increase ofimpregnation time. In the view of the present results, it can be saidthat the impregnation time has a considerable effect to access ofthe ZnCl2 to the interior of the PS to develop of the new micropores[33]. For the CCS, it can be concluded that the increase of impreg-nation time causes to the porosity along with the loss of mass. Onthe other hand, for the RHS, the pore widening becomes dominantto creation of the new pores with increasing impregnation time.Based on the current results, it can be also said that the diffusionof activating agent for the PS and CS is more effective than RS.

Effect of carbonization temperature (X1), impregnation ratio(X2), and impregnation time (X3) on the methylene blue indexes(q) and surface areas (S) of activated carbon samples were deter-mined with non-linear regression analysis. Obtained final empiri-cal models after some modifications in the equations withdetermination coefficients (R2) were expressed by the followingequations for each precursor:

PS activated carbon:

q ¼ 6:506 � x1 þ 541:007 � x2 � 0:003 � x21 � 100:719 � x2

2

þ 0:00816 � x23 �

2:994 � 108

x21

� 266:576x2

2

þ 2:157 � 106

x1

þ 875:862x2

� 6:438 � 103 ðR2 ¼ 1:000Þ

S ¼ �770 � x1 þ 9:548 � 103 � x2 þ 542 � x3 þ 0:289 � x21 � 3085 � x2

2

� 113:95 � x23 þ

1:021 � 1011

x21

þ 476:8x2

2

� 4:087 � 108

x1þ 453:99

x2

� 1:001 � 1013

x31

þ 7:954 � 105 ðR2 ¼ 0:998Þ

RS activated carbon:

q ¼ �49 � x1 � 113 � x2 þ 1:53 � x3 þ 0:018 � x21 þ 16:4 � x2

2

þ 0:740 � x23 þ

6:866 � 109

x21

þ 5:4x2

2

� 2:697 � 107

x1� 183

x2

� 6:874 � 1011

x31

þ 5:258 � 104 ðR2 ¼ 1:000Þ

S ¼ 739 � x1 � 19630 � x2 þ 212:5 � x3 � 0:267 � x21 þ 4220 � x2

2

� 79:6 � x23 �

1:059 � 1011

x21

þ 4902x2

2

þ 4:187 � 108

x1� 21691

x2

þ 1:03 � 1013

x31

� 7:657 � 105 ðR2 ¼ 1:000Þ

CS activated carbon:

q ¼ �1:44 � x1 � 4609 � x2 þ 32:67 � x3 þ 0:001 � x21 þ 921:7 � x2

2

� 7:00 � x23 �

1:298 � 108

x21

þ 1350:35x2

2

þ 5:256 � 105

x1� 5717:86

x2

þ 8:175 � 103 ðR2 ¼ 0:999Þ

Table 3Literature reports of activated carbon samples produced from similar precursors and/or activating agent.

Precursor Experimental conditions Surface area (m2/g) Refs.

Rose seeds Impregnation with ZnCl2 and carbonization at 500 �C 1265 This studyRose seeds Chemical activation with 3 M ZnCl2 at 500 �C 800 [34]Cornel seeds Impregnation with ZnCl2 and carbonization at 500 �C 1355 This studyCornel seeds Steam activation at 700–800 �C 766 [35]Cornel stones Impregnation with concentrated H2SO4 and carbonization at 200 �C 449 [36]Pine sawdust Impregnation with ZnCl2 and carbonization at 400 �C 1825 This studyPine sawdust Impregnation with 8 M H3PO4 and carbonization at 450 �C 1767 [37]Pine sawdust Physical activation with CO2 at 800 �C 352 [38]Paulownia wood Impregnation with ZnCl2 and carbonization at 400 �C 2736 [28]Cattle-manure compost Impregnation with ZnCl2 and carbonization at 400 �C 2170 [14]Corn cob Impregnation with ZnCl2 and carbonization at 500 �C 1563 [24]Dates’ stones Impregnation with ZnCl2 and carbonization at 700 �C 1215 [39]Coir pith Impregnation with ZnCl2 and carbonization at 700 �C 752 [40]

M. Açıkyıldız et al. / Microporous and Mesoporous Materials 198 (2014) 45–49 49

S ¼ 485 � x1 � 2467 � x2 þ 783 � x3 � 0:156 � x21 þ 354 � x2

2

� 169:4 � x23 �

8:655 � 1010

x21

þ 1127x2

2

þ 3:237 � 108

x1� 4601:7

x2

þ 8:769 � 1012

x31

� 5:689 � 105 ðR2 ¼ 1:000Þ

where x1 (�C) is the carbonization temperature, x2 (w/w) is theimpregnation ratio, x3 (h) is the impregnation time; q (mg/g) isthe methylene blue index, and S (m2/g) is the surface area ofsamples.

According to the regression coefficients, derived equations verywell express the effect of carbonization temperature, impregnationratio, and impregnation time onto both surface areas and methy-lene blue indexes of samples.

The properties of activated carbon samples prepared in thisstudy were also compared with the results published in the litera-ture (Table 3) and commercial activated. The surface areas of thenew presented samples were much higher than some activatedcarbon samples produced with similar precursors and/or activatingagent (Table 3) and the commercial ones which its surface area islower than 1000 m2/g except for those paulownia wood and cat-tle-manure compost.

4. Conclusions

In the view of the experimental results, it concluded thatthe selected precursors can be efficiently used for productionof the activated carbon samples. The best adsorptive propertiesof the samples prepared from pine sawdust, rose seed, and cornelseed by a one-step chemical activation with zinc chloride wereobtained at the carbonization temperature of 400–500 �C, theimpregnation ratio of 1.5, and the impregnation time of 1–2 h.The highest surface areas were found to be 1825, 1265, and1355 m2/g and the maximum methylene blue indexes were foundas 300, 297, and 299 mg/g for PS, RS, and CS, respectively. Theseresults show that the produced samples have superior surfaceproperties. Therefore it can be concluded that these activatedcarbon samples can be employed as effective adsorbents to removeof undesirable chemicals.

Acknowledgments

The authors thank TUBITAK (108T986) for financial support andM. Açıkyıldız is grateful to TUBITAK (BIDEB 2211) for thefellowship.

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