Adsorption kinetics and isotherms of pesticides onto activated carbon-cloth

Adsorption kinetics and isotherms of pesticides onto activated carbon-cloth

Chemosphere 60 (2005) 1600–1607 www.elsevier.com/locate/chemosphere Adsorption kinetics and isotherms of pesticides onto activated carbon-cloth Erol ...

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Chemosphere 60 (2005) 1600–1607 www.elsevier.com/locate/chemosphere

Adsorption kinetics and isotherms of pesticides onto activated carbon-cloth Erol Ayranci *, Numan Hoda Chemistry Department, Akdeniz University, 07058 Antalya, Turkey Received 25 September 2004; received in revised form 7 February 2005; accepted 14 February 2005 Available online 9 April 2005

Abstract Adsorption of pesticides ametryn, aldicarb, dinoseb and diuron from aqueous solution onto high specific area activated carbon-cloth was studied. Kinetics of adsorption was followed by in situ UV-spectroscopy and the data were treated according to various rate models. The extent of adsorption was determined at the end of 125 min adsorption period. Rate constants and the extent of adsorption for the four pesticides were found to follow the order: dinoseb > ametryn > diuron > aldicarb. Adsorption isotherms were derived at 25 C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined. The types of interactions between the surface and pesticide molecules were discussed.  2005 Elsevier Ltd. All rights reserved. Keywords: Adsorption; Ametryn; Aldicarb; Dinoseb; Diuron; Carbon-cloth; Water treatment

1. Introduction Pollution of surface and ground waters causes risk to human health because of the potential health hazards of their contents of inorganic and organic compounds. Pesticides are group of hazardous compounds that may pollute water due to their extensive application in agriculture as rodenticides, insecticides, larvacides, miticides (acaricides), mollucides, nematocides, repellants, synergists, fumigants, fungicides, algicides, herbicides, defoliants, desiccants, plant growth regulators and sterilants. Although much benefit is obtained from their uses, they have some undesirable side effects such as toxicity, carcinogenity and mutagenity (Becker and Wilson, 1980; Kouras et al., 1998). Adsorption is one of the well* Corresponding author. Tel.: +90 242 310 23 15; fax: +90 242 227 89 11. E-mail address: [email protected] (E. Ayranci).

known methods used in removal of such hazardous compounds from polluted waters. Activated carbon is the most widely used adsorbent material for this purpose due to its efficiency and economic feasibility (Yoshida et al., 1993; Zhao et al., 1998). Utilization of activated carbon can be in the form of powder, granular and fiber or cloth. Activated carbon-cloth having very high specific surface area, adsorption capacity and mechanical strength, has gained increasing attention in recent years. Activated carbon-cloth or fiber is used for the removal of many pollutants from waste water by adsorption. For example Brasquet and Le Cloirec (1997) studied the adsorption of some aromatic organic compounds on the activated carbon fiber and at the granular activated carbon in relation to water treatments. They have found that kinetic coefficients obtained with the activated carbon fiber are 5–10 times greater than those obtained with granular activated carbon. In another study Faur-Brasquet et al. (2002) investigated the removal of

0045-6535/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2005.02.040

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metal ions from aqueous solution by adsorption on the activated carbon fiber. The use of high-area carboncloth electrodes has been investigated for adsorption and electrosorption behavior for various adsorbates such as inorganic S-containing anions (Ayranci and Conway, 2001a), ethyl xanthate and thiocyanate (Ayranci and Conway, 2001b; Conway et al., 2001), phenol, phenoxide and chlorophenols (Ayranci and Conway, 2001c), some aromatic heterocyclic compounds (Conway et al., 2003) and pyridine (Niu and Conway, 2002a) in relation to waste-water purification. Several workers have studied the adsorption of pesticides onto carbon fiber from aqueous solutions. Pelekani and Snoeyink studied on the competitive adsorption between atrazine and natural organic matter (1999), atrazine and methylene blue (2000), atrazine and congo red dye (2001) on several phenolic resin-based activated carbon fibers. They showed that the mechanism of competition is controlled by the activated carbon pore size distribution. Martı´n-Gullo´n and Font (2001) compared the activated carbon fiber and granular activated carbon for their effectiveness in removal of pesticides from aqueous solution by adsorption. They concluded that highly activated pitch-based activated carbon fibers are more effective in the removal of atrazine than granular activated carbon. Murayama et al. (2003) investigated a simple and convenient quantitative analytical method for the removal of organochlorine pesticides in water samples using activated carbon fiber filter. They applied the proposed method to determine organochlorine pesticides from rain, river water and seawater samples. Ayranci and Hoda (2004a,b) have found that the pesticides atrazine, bromacil, 2,4-D, metribuzin, bentazon and propanil can be removed from aqueous solution to a certain extent by adsorption at the carbon-cloth. They have also followed the kinetics of adsorption of these pesticides and determined rate constants for the adsorption processes. The purpose of the present study was to investigate the adsorption behavior of the pesticides ametryn [2(ethylamino)-4-isopropylamino-6-methyl-thio-s-triazine], aldicarb [2-methyl-2-(methylthio) propionaldehyde o-methylcarbamoyloxime], diuron [N-(3,4-dichlorophenyl)-N,N-dimethyl urea] and dinoseb [2-(sec-butyl)4,6-dinitrophenol] at the high area carbon-cloth from aqueous solutions and thus the possibility of removal of these pesticides from waters polluted by them.

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(determined by the manufacturer using Kr BET). The pesticides ametryn, aldicarb, dinoseb and diuron were obtained from Riedel-de Ha¨en (Germany). The chemical structures, molecular weights and solubilities in water of these pesticides are given in Table 1. Deionized water was used in adsorption experiments. 2.2. Treatment of the carbon-cloth It was found by Ayranci and Conway (2001a) that the carbon-cloth material provides spontaneously a small but significant quantity of ions into the conductivity water used, probably due to its complex structure originating from its somewhat unknown proprietary preparation procedure. A deionization cleaning procedure was therefore applied, as described previously (Ayranci and Conway, 2001a; Ayranci and Hoda, 2004a) to avoid desorption of ions during the adsorption measurements. In this procedure, a carbon-cloth sample was placed in a flow-through washing cup and eluted with 5 l of warm (60 C) conductivity water in a kind of successive batch operations for two days with N2 bubbling in order to avoid possible adsorption of CO2 that might have been dissolved in water. The outflow water from each batch was tested conductometrically for completeness of the washing procedure. The washed carbon-cloth modules were then dried under vacuum at 120 C, cut to desired dimensions (about 0.5 · 1.5 cm), weighed accurately and kept in a desiccator for further use. 2.3. Adsorption cell

2. Materials and methods

A specially designed cell was used to carry out the adsorption studies and simultaneously to perform in situ concentration measurements by means of UV absorption spectrophotometry. This cell, described in detail including a diagram in our previous works (Ayranci and Conway, 2001a; Ayranci and Hoda, 2004a), was V-shaped with one arm containing the carbon-cloth attached to a short Pt wire sealed to a glass rod and the other arm containing a thin glass tube through which N2 gas was passed for the purposes of mixing and eliminating any dissolved CO2. The two arms were connected to a glass joint leading to a vacuum pump at the upper part of the V-shaped cell in order to provide the opportunity for initial outgassing of the carbon adsorbent, and the cell and solution. A quartz spectrophotometer cuvette was sealed to the bottom of the adsorption cell.

2.1. Materials

2.4. Optical absorbance measurements

The carbon-cloth used in the present work was obtained from Spectra Corp. (MA, USA) coded as Spectracarb 2225, having a specific area of 2500 m2 g1

A Shimadzu 160A UV/vis spectrophotometer was used for optical absorbance measurements. The absorbance measurements were conducted in situ for the

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Table 1 Chemical structures, molecular weights and solubilities of pesticides Pesticide

Chemical structure

Molecular weight (g/mol)

Solubility in water at 20 C (mg/l)

Ametryn

227.30

185

Aldicarb

190.27

6000

Dinoseb

240.22

52

Diuron

233.10

42

study of the kinetics of adsorption process as follows. In all experiments, the size and weight of the carbon-cloth was kept as constant as possible (about 18.0 ± 0.1 mg). Its weight was accurately measured and recorded each time for calculation of fractional coverage, h, or the amount of adsorption per unit area, M, of the carboncloth. Carbon-cloth pieces were pre-wetted by leaving in water for 24 h before use. The idea of using prewetted carbon-cloth originates from our previous findings that pre-wetting enhances the adsorption process (Ayranci and Conway, 2001a,b). Carbon-cloth was dipped into the adsorption cell initially containing only water and vacuum was applied to remove all air in the pores of the carbon-cloth. Then wetted and degassed carbon-cloth was removed from the cell for a short time and water in the cell was replaced with a known volume of sample solution (20 ml). The sliding door of the sample compartment of the spectrophotometer was left half-open and the quartz cuvette fixed at the bottom of the adsorption cell (which now contained

the sample solution) was inserted into the front sample compartment. A teflon tube connected to the tip of a thin N2-bubbling glass tube was lowered from one arm of the adsorption cell down the UV cell to a level just above the light path to provide effective mixing. Finally, the carbon-cloth, which was removed temporarily after wetting and degassing, was inserted from the other arm of the adsorption cell into the solution. Then, quickly, an opaque curtain was spread above the sample compartment of the spectrophotometer, over the cell, to prevent interference from external light. The program for monitoring the absorbance at the specific wavelength of maximum absorbance pre-determined by taking the whole spectrum of each pesticide was then run on the built-in microcomputer of the spectrophotometer. Absorbance data were recorded in programmed time intervals of 1 min over a period of 125 min. Absorbance data were converted into concentration data using calibration relations pre-determined at the wavelength of interest for each pesticide.

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2.5. Determination of adsorption isotherms

3.2. Adsorption kinetics of pesticides

The adsorption isotherms of pesticides on carboncloth were determined on the basis of batch analysis. Carbon-cloth pieces of varying weights were allowed to equilibrate with pesticide solutions of constant initial concentration at 25 C for 48 h. The initial concentrations of ametryn, aldicarb, dinoseb and diuron were 103.84, 103.96, 22.38 and 32.27 mg l1, respectively. Preliminary tests showed that the concentration of pesticide remained unchanged after 8–10 h contact with carboncloth. So, the allowed contact time of 48 h ensures the equilibration. The equilibrium concentrations of pesticide solutions were measured spectrophotometrically. The amount of pesticide adsorbed per unit mass of carbon-cloth, qe, was calculated by Eq. (1),

Adsorption of pesticides onto carbon-cloth was monitored spectrophotometrically by the procedure described above. Absorbance data of each pesticide obtained in one-minute intervals during the course of adsorption were converted into concentration data using the corresponding calibration curves. Then, the concentrations were plotted as a function of time. They are shown in Fig. 1 for the four pesticides. Initial concentration of each pesticide was adjusted to be the same (6.5 · 105 M) in order to make the comparison of their adsorption behaviors easily. The decrease in concentration of dinoseb is the fastest while that of aldicarb is the slowest during 125 min of adsorption onto the carbon-cloth. Although the adsorption rate of ametryn appears to be slower than that of dinoseb at the early stages, it approaches almost to the same rate toward the end of total adsorption period. Concentrations of pesticides ametryn, aldicarb, dinoseb and diuron in solution decreased to 9.6 · 106, 4.3 · 105, 8.5 · 106 and 3.3 · 105 M, respectively, from the initial concentration of 6.5 · 105 M by adsorption onto the carbon-cloth within 125 min. Concentrations of pesticides in aqueous solution were reduced by a factor of 6.8 for ametryn, 1.5 for aldicarb, 7.6 for dinoseb and 2.0 for diuron over the course of adsorption. The adsorption of various aromatic molecules including some pesticides onto the same carbon-cloth was found to follow pseudo-first order kinetics (Ayranci and Conway, 2001c; Conway et al., 2001; Niu and Conway, 2002a,b; Ayranci and Hoda,

ð1Þ

where V is the volume of pesticide solution in l, c0 and ce are the initial and equilibrium concentrations, respectively, of the pesticide solutions in mg l1 and m is the mass of the carbon-cloth in g. Eq. (1) gives qe in mg pesticide adsorbed per g carbon-cloth.

3. Results and discussions 3.1. Absorption characteristics of pesticides Absorption properties and calibration data for the four pesticides studied are given in Table 2. In order to obtain the calibration curve of each pesticide, absorbances were measured at the corresponding kmax as a function of concentration and the data were fitted to Lambert–Beer law by the method of least square analysis. The resulting correlation coefficients given in the last column of Table 2 show that the fit to Lambert–Beer law is excellent. These calibration curves were used to convert absorbances into concentrations in kinetic and equilibrium studies.

Table 2 Spectrophotometric pesticides

b 4 d

2

and calibration parameters for the

Pesticides

kmax (nm)

e (au cm1 M1)a

rb

Ametryn Aldicarb Dinoseb Diuron

224 245 270 211

36 300 1800 10 300 28 700

0.9996 0.9999 0.9986 0.9999

a

6

-5

V  ðc0  ce Þ m

cx10 (M)

qe ¼

e is the molar absorptivity and au stands for absorbance unit. b r is the correlation coefficient for fit of data to Lambert– BeerÕs law.

c a 0 0

50

100

150

time (min) Fig. 1. Adsorption behaviors of pesticides (a) dinoseb, (b) aldicarb, (c) ametryn and (d) diuron from aqueous solutions on the carbon-cloth. Initial concentration of each pesticide was 6.5 · 105 M and the carbon-cloth used for the adsorption was 18.0 mg.

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2004a,b). In order to make a detailed analysis for the adsorption data of the present work, some probable kinetic models were applied. These models include intraparticle diffusion which can be formulated as qt ¼ k i t1=2

ð2Þ

pseudo-first order which can be formulated as ln c  ln c0 ¼ k 1 t

ð3Þ

and pseudo-second order which can be formulated as ð1=cÞ  ð1=c0 Þ ¼ k 2 t

ð4Þ

where qt is the amount of adsorbate adsorbed at any time, c0 is the initial concentration of adsorbate, c is the concentration of adsorbate at any time, t is time and ki, k1 and k2 are rate constants for diffusion, pseudo-first order and pseudo-second order models, respectively. qt is obtained from c0 and c values by the following equation: qt ¼

ðc0  cÞ  V m

ð5Þ

where V is the volume of adsorbate solution and m is the mass of the carbon-cloth. The applicability of the three models was checked by constructing linear plot of qt versus t1/2 for intraparticle diffusion, of ln c versus t for pseudo-first order and of 1/c versus t for pseudo-second order models. The rate constants ki, k1 and k2 obtained from the slopes of corresponding linear plots are given in Table 3 together with correlation coefficients, r. When the regression coefficients of the three models are compared for each pesticide, it can be seen that all of them are greater than 0.97. So, it is very difficult to predict a certain kinetic model to fit the adsorption data of all four pesticides. It is clear that the smallest regression coefficients are for the intraparticle diffusion model. It is to be noted that qt versus t1/2 lines of this model do not pass from the origin although the model predicts to do so. If the data are forced to pass from the origin for this model, even smaller regression coefficients are obtained. So, intraparticle diffusion model does not seem to be successfully applicable for the present adsorption data. The first order and the second order models seem to

be applicable almost in equal success. The decreasing order of rate constants of pesticides for these two models is the same: dinoseb > ametryn > diuron > aldicarb. The extent of adsorption was quantified by calculating, M, the amount of adsorbate adsorbed per unit area of the carbon-cloth using Eq. (6) and the percentage of coverage on carbon-cloth surface, h, using Eq. (7): M ¼ ðc0  cÞV =2500 m

ð6Þ

h ¼ ½ðc0  cÞVN A 100=ð4  1019  2500 mÞ

ð7Þ

where c0 and c are molar concentrations of the solutions at the beginning and at a specific time during the adsorption process, respectively. V is the volume of solution, m is the mass of the carbon-cloth piece and NA is AvogadroÕs number. M is the amount of pesticide adsorbed per unit area of carbon-cloth and h is the percent coverage of carbon-cloth at time t. The calculations are based on the known specific surface area of 2500 m2 g1 for the carbon-cloth provided by the manufacturer, corresponding to an approximate value of 4 · 1019 carbon sites per m2 of the surface determined by the atomic radius of carbon but dependent on the actually unknown geometry of surface carbon-atom packing (Ayranci and Conway, 2001b). The M and h values calculated at 125 min of adsorption of pesticides are given in the third and the forth columns of Table 4. The M and h values of adsorption of pesticides onto the carbon-cloth follow the same order obtained for pseudo-first order rate constants (k1) given above. Dinoseb has the largest M and h values and aldicarb has the smallest. It is clear from these results that

Table 4 M and h values defined by Eqs. (6) and (7), respectively, for the adsorption of pesticides Pesticides

c0 (mol l1)

M (108 mol (m2 C-cloth)1)

h

Ametryn Aldicarb Dinoseb Diuron

6.5 · 105 6.5 · 105 6.5 · 105 6.5 · 105

2.46 0.97 2.51 1.42

0.037 0.015 0.038 0.021

Table 3 Rate constants and regression coefficients obtained from treatment of adsorption data according to the three kinetic models Pesticides

Kinetic model Pseudo-first order

Ametryn Aldicarb Dinoseb Diuron

Pseudo-second order

Intraparticle diffusion

k1

r

k2

r

ki

r

0.0156 0.0035 0.0163 0.0051

0.9993 0.9985 0.9884 0.9916

669.7 67.17 868.6 115.3

0.9769 0.9990 0.9951 0.9990

1.49 0.54 1.47 0.83

0.9945 0.9868 0.9798 0.9987

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3.3. Adsorption isotherms of pesticides In order to assess the potential adsorption capacity of the carbon-cloth toward the pesticides studied, its adsorption isotherms at 25 C were derived on the basis of batch analysis as described in Section 2.5. The isotherm data were treated according to the well-known Langmuir and Freundlich isotherm models. The Langmuir model assumes uniform energy sites on the surface. The linearized Langmuir isotherm equation can be written as follows: ce 1 ce ¼ þ ð8Þ qe bqm qm where qe (in mg g1) is the amount of solute adsorbed per unit mass of adsorbent, ce (in mg l1) the equilibrium concentration of solute, qm (in mg g1) the amount of solute adsorbed per unit mass of adsorbent required for monolayer coverage of the surface, b (in l mg1) a constant related to the heat of adsorption. When ce/qe is plotted against ce and the data are regressed linearly, qm and b constants are calculated from the slope and the intercept. On the other hand the Freundlich isotherm equation in linearized form can be given as follows:

(mg1(1/n) l1/n g1) is related to the adsorption capacity of the carbon-cloth and 1/n is another constant related to the surface heterogeneity. When ln qe is plotted against ln ce and the data are treated by linear regression analysis, 1/n and K constants are determined from the slope and intercept. The value of 1/n is known as the heterogeneity factor and ranges between 0 and 1; the more heterogeneous the surface, the closer 1/n value is to 0 (Al Duri, 1995). The parameters of Langmuir and Freundlich equations for the adsorption of four pesticides onto the carbon-cloth obtained as described above are given in Table 5. The isotherms obtained using these parameters are presented in Figs. 2, 3, 4 and 5 for ametryn, aldicarb, dinoseb and diuron, respectively, together with experimental data points. The fit of experimental isotherm data to Langmuir and Freundlich equations seems to be quite good when correlation coefficients (r) obtained from linear regression analysis are examined (r values are not given but all are greater than 0.98). However, it is very difficult to decide which model represents the experimental data best just on the basis of regression

400

qe (mg/g)

there is no direct relation between the solubilities of these pesticides (Table 1) and the extents of their adsorption onto the carbon-cloth. The structure of the pesticide is believed to play an important role in determining the order of extents of adsorption. The main force of adsorption is expected to be the dispersion forces between the p electrons in pesticide structure and p electrons in the carbon-cloth surface. An aromatic ring in the pesticide structure increases the possibility of such interactions due to the delocalization of p electrons over the ring. Thus, the lowest rate and the extent of adsorption observed for aldicarb is probably due to the absence of an aromatic ring in its structure. The branched alkyl substituent of aromatic ring of dinoseb causes the rate and extent of adsorption of this pesticide to be the highest by providing hydrophobicity to the structure.

200

0 0

1 ln qe ¼ ln K þ ln ce n

ð9Þ

where qe and ce have the same definitions as in Langmuir equation above. Freundlich constant, K, in unit of

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20

40

Ce (mg/l) Fig. 2. The fit of experimental adsorption data (m) to Langmuir (- - -) and Freundlich (—) models for ametryn.

Table 5 The parameters of Langmuir and Freundlich isotherm equations for the adsorption of pesticides Pesticides

Ametryn Aldicarb Dinoseb Diuron

Langmuir

Freundlich

qm (mg/g)

b (l/mol)

P

K (mg1(1/n) l1/n g1)

1/n

P

354.61 421.58 301.84 213.06

0.80 0.13 0.20 1.89

14.0739 4.3000 1.4198 6.5764

200.95 102.03 49.09 128.41

0.152 0.347 0.7764 0.4412

2.7841 3.0921 2.4854 0.1502

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200

qe (mg/g)

qe (mg/g)

400

200

100

0 0

20

40

Ce (mg/l)

0 0

Fig. 3. The fit of experimental adsorption data (m) to Langmuir (- - -) and Freundlich (—) models for aldicarb.

2

Ce (mg/l) Fig. 5. The fit of experimental adsorption data (m) to Langmuir (- - -) and Freundlich (—) models for diuron.

qe (mg/g)

100

50

0 0

2

4

Ce (mg/l) Fig. 4. The fit of experimental adsorption data (m) to Langmuir (- - -) and Freundlich (—) models for dinoseb.

coefficients. A better criterium is to introduce a parameter known as normalized percent deviation (Juang et al., 1996) or in some literature percent relative deviation modulus, P, (Ayranci and Dalgic, 1992; Ayranci, 1995) given by the following equation: X P ¼ ð100=N Þ ðjqeðexptÞ  qeðpredÞ j=qeðexptÞ Þ ð10Þ where qe(expt) is the experimental qe at any ce, qe(pred) is the corresponding predicted qe according to the equation under study with best fitted parameters, N is the number of observations. It is clear that the lower the P value, the better is the fit. The P values calculated for the fit of isotherm data of the four pesticides to the Langmuir and Freundlich equations are given in Table 5. The fit ac-

cepted to be good when P is below 5. The fit of experimental data to Freundlich equation seems to be excellent for all pesticides with P values well below 5. On the other hand Langmuir model is also good for aldicarb and dinoseb with P < 5. In general one can say that Freundlich equation represents the isotherm data of the pesticides studied better than Langmuir equation. The K parameter of Freundlich equation is a measure of adsorption capacity of the carbon-cloth. According to the K values listed in Table 5 the adsorption capacities of the pesticides studied follow the order: ametryn > diuron > aldicarb > dinoseb. According to the classification of Giles et al. (1960), the slope of the initial curvature of the adsorption isotherm gives the characteristics of the adsorption process. The adsorption of the four pesticides may be classified as L-type suggesting that carbon-cloth has a high affinity for these pesticides and there is no competition from the solvent for adsorption sites. The dimensionless constant known as separation factor (RL) was calculated from the following equation using Langmuir b parameter (Bayat, 2002): RL ¼

1 1 þ bc0

ð11Þ

where b (in l mg1) is the Langmuir constant and c0 (in mg l1) the initial concentration. Isotherm is considered to be unfavorable, linear, favorable or irreversible depending on the value of RL. It was found that RL is 0.0076 for ametryn, 0.0013 for aldicarb, 0.0087 for dinoseb and 0.0554 for diuron. Since all these RL values are between 0 and 1, the adsorption of these four pesticides onto carbon-cloth is considered to be favorable.

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4. Conclusion It was found that ametryn, aldicarb, dinoseb and diuron could be removed to a certain extent from aqueous solutions by adsorption onto the high area activated carbon-cloth. The adsorption processes were found to follow the pseudo-first order or the pseudo-second order kinetics over a period of 125 min. The rate constants for both models decreased in the order: dinoseb > ametryn > diuron > aldicarb. The isotherms at 25 C were found to fit almost equally well to Langmuir and Freundlich models. Acknowledgments Authors thank to Scientific Research Projects Unit of Akdeniz University for the support of this work through the project 2001.01.0121.016, to the Spectra Corp. (MA, USA) for providing the activated carbon-cloth and to the Central Laboratory Unit of Faculty of Agriculture of Akdeniz University for the use of their facilities. References Al Duri, B., 1995. Adsorption modeling and mass transfer. In: McKay, G. (Ed.), Use of Adsorbents for the Removal of Pollutants from Wastewaters. CRC Press, Florida, pp. 133– 173. Ayranci, E., 1995. Equilibrium moisture characteristics of dried eggplant and ocra. Nahrung 38, 228–233. Ayranci, E., Conway, B.E., 2001a. Adsorption and electrosorption at high-area carbon felt electrodes for waste-water purification: systems evaluation with inorganic, S-containing anion. J. Appl. Electrochem. 31, 257–266. Ayranci, E., Conway, B.E., 2001b. Adsorption and electrosorption of ethyl xanthate and thiocyanate anions at higharea carbon-cloth electrodes studied by in situ UV spectroscopy: development of procedures for wastewater purification. Anal. Chem. 73, 1181–1189. Ayranci, E., Conway, B.E., 2001c. Removal of phenol, phenoxide and chlorophenols from waste-waters by adsorption and electrosorption at high-area carbon felt electrodes. J. Electroanal. Chem. 513, 100–110. Ayranci, E., Dalgic, A.C., 1992. Moisture sorption isotherms of pistacia terebinthus L. and its protein isolate. Lebensm-Wiss. Technol. 88, 143–152. Ayranci, E., Hoda, N., 2004a. Studies on removal of metribuzin, bromacil, 2,4-D and atrazine from water by adsorption on high area carbon cloth. J. Hazard. Mater. B 112, 163–168. Ayranci, E., Hoda, N., 2004b. Adsorption of bentazon and propanil from aqueous solutions at the high area activated carbon-cloth. Chemosphere 57, 755–762. Bayat, B., 2002. Comparative study of adsorption properties of Turkish fly ashes I. The case of nickel(II), copper(II) and zinc(II). J. Hazard. Mater. B 95, 251–273. Becker, D.L., Wilson, S.C., 1980. Carbon Adsorption Handbook. In: Cheremisinoff, P.N., Ellebush, F. (Eds.), The Use

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