Accepted Manuscript

Title: Removal of Acetaminophen and Ibuprofen fromAqueous Solutions by Activated Carbon Derived fromQuercus Brantii (Oak) Acorn as a Low-cost Biosorbent

Authors: Heshmatollah Nourmoradi, Kobra FarokhiMoghadam, Ali Jafari, Bahram Kamarehie

PII: S2213-3437(18)30658-4DOI: https://doi.org/10.1016/j.jece.2018.10.047Reference: JECE 2732

To appear in:

Received date: 25-8-2018Revised date: 9-10-2018Accepted date: 21-10-2018

Please cite this article as: Nourmoradi H, Moghadam KF, Jafari A, KamarehieB, Removal of Acetaminophen and Ibuprofen from Aqueous Solutions byActivated Carbon Derived from Quercus Brantii (Oak) Acorn as a Low-cost Biosorbent, Journal of Environmental Chemical Engineering (2018),https://doi.org/10.1016/j.jece.2018.10.047

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1

Removal of Acetaminophen and Ibuprofen from Aqueous Solutions by Activated

Carbon Derived from Quercus Brantii (Oak) Acorn as a Low-cost Biosorbent

Heshmatollah Nourmoradi a, b, Kobra Farokhi Moghadam c, Ali Jafari c, Bahram Kamarehie c,*

a Department of Environmental Health Engineering, School of Health, Ilam University of Medical Sciences,

Ilam, Iran. b Biotechnology and Medicinal Plants Research Center, Ilam University of Medical Sciences, Ilam, Iran. c Department of Environmental Health Engineering, School of Health and Nutrition, Lorestan University of

Medical Sciences Khorramabad, Iran.

Corresponding Author: Department of Environmental Health Engineering, School of Health, Lorestan

University of Medical Sciences, Ilam, Iran. Tel: +089161603292 E-mail: b.kamarehie@gmail.com.

Graphical abstract

Abstract

Acetaminophen (ACT) and ibuprofen (IBP) are two of the drugs which consume a lot in

different countries. These compounds are not completely metabolized in the body and enter

into the environment, especially aquatic environments, through urine and feces. In this study,

activated carbon (AC) activated with basic and acidic solutions (NaOH, KOH, NH4Cl, and

H3PO4) were used to remove ACT and IBP from aqueous solutions. Different factors

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including activator type, contact time, pH, adsorbent dose, pollutant content, solution ion

strength and temperature were used to evaluate the sorption. The results showed that AC-

KOH and AC-H3PO4 had the maximum sorption ability for ACT and IBP, respectively. The

maximum sorption capacity for ACT (45.45 mg/g) and IBP (96.15 mg/g) was obtained at

contact times of 150 min and 120 min and pH 3, respectively. The findings of kinetics and

isotherms study also showed that the pseudo-second order kinetic and Freundlich isotherm

models best fitted the data than other models. As well as, thermodynamic study showed that

the sorption of ACT and IBP by the sorbent had an endothermic nature. On the basis of the

results, this agricultural waste (oak acorn) can be effectively used as an alternative adsorbent

for the removal of ACT and IBP in the aqueous phase.

Keywords: Adsorption, Activated carbon, Acetaminophen, Ibuprofen, Aqueous media.

1. Introduction

Pharmaceuticals compounds are known as emerging pollutants that have been extensively

applied for human and animals' treatment [1]. These chemicals due to irregular consumption

have been detected in the environment [2]. In spite of the consumption, pharmaceutical

industrial effluents and disposal of unused and expired drugs have an important role to

introduce the drugs into the environment [3]. Nowadays, the presence of pharmaceuticals as a

potential source of water and wastewater has become an important concern [4]. Although, the

concentration of pharmaceuticals in wastewater are frequently found in µg/L levels, but in

wastewater treatment plants with influent from pharmaceutical factories, the amount of these

chemicals has been reported up to several mg/L [5]. Conventional water and wastewater

treatment procedures have no substantial effects on the removal of the pharmaceuticals and

subsequently remain intact in aqueous environments [4]. Acetaminophen (ACT) and

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ibuprofen (IBP) are two of the drugs that are being consumed abundantly. Acetaminophen

has been extensively used as pain killer, antipyretic and also a main component of anti-flu

drugs all over the world which is accessible without physician's order [6, 7]. Unfortunately,

acetaminophen is not metabolized in the body; hence, it can be entered in the environment by

urine and feces [8]. It is so toxic and has potential danger to living organisms (animals and

people) and can cause liver and kidney damage, genotoxicity and hormone production

disrupter [9-11]. Ibuprofen also is the third most widely used drug in the world [12]. It is

consumed for muscle, head and tooth aches, rheumatic disorders, fever and migraine [13, 14].

Ibuprofen causes toxic impacts into the environment [15]. The concentration of ibuprofen in

effluents from wastewater treatment plants has been reported up to 25 mg/L [16]. Because of

the harmfully influences of the above-mentioned drugs on the environment and also on the

human health, the removal of them in the ecosystem especially in water bodies by appropriate

technique is necessary [17]. Various treatment technologies such as ultrasonic irradiation

[18], electrochemical degradation [19], adsorption [20-22], photocatalytic degradation [10],

advanced oxidation processes [8, 9, 23], biological treatment [24] and adsorption [1, 4, 5, 25-

29] have been carried out for the removal of acetaminophen and ibuprofen from water and

wastewater. Of these methods, adsorption is an effective procedure that strongly used to

remove numerous organic and inorganic pollutants from aqueous bodies. Regeneration of the

adsorbent is one of the important advantages of this process [30]. Activated carbon is one of

the most popular sorbent that because of high uptake capacity, large specific surface area and

porosity extensively applied for many organics in water and wastewater [30, 31]. But, high

production cost is the main limit for further applications [26]. Therefore, to solve this

problem, low-cost material including agricultural residues have been used for the production

of cheaper activated carbon [31]. Many activated carbon adsorbents originated from low-cost

agricultural wastes including pine [26], lotus stalk [32], olive-waste cake [33], wood and

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peach stones [34], Sisal waste [35], coconut shell [36], cork [13], Aegle marmelos correa

fruit shell [3], pomegranate wood [37] have been effectively used for the adsorption of

various pharmaceuticals in aqueous solutions. Oak (Quercus) is the most important plant

genus in western, central and northern Iran with predominant species of Q. Brantii (known as

Persian oak). It is native of various countries including in Iran, Iraq, Syria and Turkey [38].

More than 8 million hectares of the forests in Iran is covered by numerous oak species [39,

40]. In this research, activated carbon from Quercus Brantii (oak) acorn was used for the

removal of acetaminophen and ibuprofen in aqueous solutions. The influences of different

factors such as chemical activator type, contact time, solution pH, pollutant concentration,

adsorbent dose, solution ion strength and temperature were performed on the sorption.

2. Materials and Methods

2.1. Materials

Quercus Brantii acorns, oak fruits, were collected from the mountains around Ilam city (Iran).

The drugs of acetaminophen (≥99%) and ibuprofen (sodium salt, ≥98%) were provided by

Sigma-Aldrich Co (USA). Other chemicals including H2SO4 (96%), NaOH, KOH, NH4Cl,

ZnCl2 and H3PO4 and CaCl2 were purchased from Merck Co (Germany). Table 1 shows the

various properties of acetaminophen and ibuprofen. The ACT and IBP standard solutions of

200 mg/L were weekly prepared by distilled water and kept at 4 oC. The standard solutions at

desired concentrations were diluted by distilled water and used in the experiments.

2.2. Preparation of activated carbon

The oak fruits were firstly cut into pieces with the size of 0.5-1 cm and the activated carbon

(AC) production process was then carried out in three steps of dehydration, carbonization and

activation. In the dehydration stage, the crushed material was placed into the oven at 105 ºC

for 24 h. The carbonization was also conducted in an air sealed electrical furnace at 600 ºC

for 1 h. Finally, the activation step was done by chemical-thermal method. Four chemicals of

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NaOH, KOH, NH4Cl, ZnCl2 and H3PO4 at the mass ratio of 1/1 and 2/1 (chemical to carbon)

were used for chemical activation and after that the temperatures of 700 and 900 ºC were

applied for thermal activation as follows; 4 and 8 grams of each above-mentioned chemicals

were separately dissolved into a 50 mL falcon tube containing 20 mL of distilled water. Then,

4 grams of the carbonized sorbent were added to the solutions. In order to soak the material,

the suspensions were held at room temperature (25 ºC) for 24 hours and then the liquids were

discharged. The materials were eventually poured into crucible and entered an air sealed

furnace at 700 and 900 °C for 2 h. Finally, the AC was grinded by a mill, sieved to obtain

particle sizes in the range 200-500 µm (mesh size of 37-70), washed several times with

deionized water and then dried at 105 °C for 2 h.

2.3. Adsorption experiments

The experiments of ACT and IBP uptake by activated carbon were conducted in a batch

system. All the tests (except the one for temperature) were done at room temperature (25 ºC)

by 200 mL conical flasks with 100 mL of drug solution and were agitated by a rotary shaker

(200 rpm). After the sorption process, the suspensions were centrifuged (5000 rpm for 10

min) and the drug content in the supernatant was determined by UV-Vis spectrophotometer at

the specified wavelength. All the tests were performed in duplicates and the mean values

were considered. The AC capacity (mg/g) was calculated through Eq (1).

qe =(C0 − Ce)V

M (1)

Where qe (mg/g) is the sorption capability of AC, C0 and Ce (mg/L) are the original and

ultimate drug content in the solution, V (L) is the solution volume and M (g) is AC mass [30].

2.3.1. Effect of sorbent type on the sorption

The influences of sorption type on the adsorption were carried out by various carbons

activated with NaOH, KOH, NH4Cl, ZnCl2 and H3PO4 at different mass ratio (1:1 and 1:2)

and temperature (700 and 900 °C). For this aim, the amount of 0.1 g of the sorbent was

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separately entered into 100 mL of 100 mg/L ACT and IBP solutions at solution pH of 7 and

agitated by an orbital shaker for 240 min at room temperature (25 ºC). After that, the amount

of ACT and IBP of the centrifuged clear supernatants was measured by spectrophotometer at

the wavelengths of 243 nm and 220 nm, respectively. The AC with the highest sorption

capacity of the drugs was selected for the subsequent experiments.

2.3.2. Effect of other parameters on the sorption

The effects of other factors on the adsorption were carried out by the best selected adsorbent

in the previous step. The experimental runs were done from the first to the sixth stage,

respectively on the basis of Table 2.

2.4. Characterization and analysis

The Fourier transform infrared (FTIR) spectra of the AC were specified by a FTIR

spectrophotometer (Spectrum Two, PerkinElmer, USA) with diffuse reflectance technique

(DRIFT) at resolution of 1 cm−1 in the region of 450–4000 cm-1. The textural properties of

the sorbent were investigated by Brunauer–Emmett–Teller (BET) equation through N2

adsorption at 77 K using an Autosorb1-Quantachrome instrument (BElSORP Mini, Microtrac

Bel Corp, Japan). The concentrations of ACT and IBP in the solutions were determined at the

maximum absorbance wavelengths of 243 and 220 nm, respectively via an UV-Vis

spectrophotometer (DR5000, HACH, USA).

3. Results and discussion

3.1. Characterization of the sorbent

The FTIR spectra of AC-KOH and AC-H3PO4 are depicted in Fig 1. As observed, the band at

3428-3431 cm-1 may be pertained to hydroxyl (–OH) stretching vibration, because of

intermolecular hydrogen bonding of the chemicals such as alcohols, phenols and carboxylic

acids showing the attendance of free –OH groups onto the sorbent [41]. The peak at 2924 cm-

1 is assigned to C–H stretching of aliphatic carbon. Also, the band appearing at 1625 cm-1

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belongs to the C=O vibration of carboxyl or anhydride groups [42]. The band presenting at

1433 cm–1 represents O-H stretching. The peak at 1384 cm-1 shows symmetrical CO2

stretching and the broad bans appearing at 1100 cm–1 to 1300 cm–1 are due to CH2

deformation [43]. The band at 600-620 cm–1 is also assigned to hydroxyl ions on the sorbent

[44]. As seen from Fig 1, the O-H band at 3407 cm–1 spectrum was decreased in both active

activated carbon (AC-KOH and AC-H3PO4) compared with raw-AC, which indicates that the

activator has acted as an dewater agent.

The BET surface area (active site) and pore size distribution of the sorbent can be obtained by

nitrogen adsorption. These important textural properties manage the sorption uptake of the

activated carbon. The major textural data of the studied ACs obtained from N2 adsorption

isotherms are presented in Fig 2. As observed (Fig 2(a)), the nitrogen sorption isotherm study

showed an extensive knee at low p/p0 up to 0.15 and the sorption by the ACs was nearly

constant over a varied range of upper relative pressures. This expressed that AC-KOH and

AC-H3PO4 are related to microporous structure (type I in the IUPAC grouping) with a

hysteresis loop (H4 types) in the desorption branch at p/p0 above 0.3. The results of N2

adsorption also showed that the surface areas of AC-KOH and AC-H3PO4 were 298 and

234.6 m2/g, respectively. Fig 2(b) depicts the pore size distribution of both the sorbents. This

figure confirmed the results of N2 isotherm shape. As seen, the sorbents had an enormous

contribution of micropores between 0.5 to 1.2 nm. Indeed, the mean pore diameters of AC-

KOH and AC-H3PO4 were determined as 2.09 and 1.88 nm, respectively and these findings

showed that both the AC was in micropores (dp<2 nm).

3.2. Effect of sorbent type on the sorption

The effects of activators including various chemicals and temperatures were carried out on

the removal of ACT and IBP through 0.1 g of the adsorbent into 100 mL of 100 mg/L drugs

solution. The mixing time was 200 min and conducted through an orbital shaker (200 rpm).

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As seen from Table 3, AC activated with KOH (1:1 mass ratio) at 900 ºC had the maximum

sorption capacity (64.92 mg/g) for ACT drug. The highest sorption capacity for IBP occurred

by AC activated via H3PO4 (1:2 mass ratio) at 900 ºC.

3.3. Effect of contact time on the sorption

The amount of ACT and IBP adsorbed onto the AC was investigated as a function of mixing

time (0-200 min) by 1 g/L of adsorbent and solution pH 7 at 25 ºC. The findings are shown in

Fig 3(a). It is evident that the uptake of both the drugs was quickly enhanced at the starting

the process up to 30 min, because of the availability of more sorption active sites in this

period [30]. The removal rate was then gradually increased over time until it reached

equilibrium state at times of 120 min and 150 min for IBP and ACT, respectively. The

sorption capacity of AC for ACT and IBP at the equilibrium condition was 36.52 mg/g and

35.49 mg/g, respectively. Therefore, the above-mentioned equilibrium times were chosen for

the subsequent experiments as the optimum times.

3.3.1. Adsorption kinetics

Kinetic models are important factors to investigate the removal mechanism of pollutants by

the adsorbent. Three commonly used models including pseudo-first order, pseudo-second

order and intraparticle diffusion models were applied to data analysis. The pseudo-first order

kinetic model is presented by Eq (2):

ln(qe − qt) = ln qe − k1t (2)

In the equation, the values of qe (mg/g) and qt (mg/g) are the capacity of AC to ACT and IBP

uptake at the equilibrium state and at time (min), respectively. K1 (1/min) is the rate constant

of the kinetic model. The parameters of K1 and qe were obtained from the slope and intercept

of plotting ln(qe-qt) against t (min), respectively [30].

The following equation is used to determine the pseudo-second order kinetic model:

t

qt=

1

k2qe2

+t

qe (3)

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Where, the factors of qe and qt are the same as the pseudo-first order kinetic model. K2

(g/mg.min) is the rate constant of the model. The intercept and slope of the plotting t/qt

versus t (min) belong to K2 and qe, respectively. Fig 3(b) indicates pseudo-second order

kinetic model for the uptake of ACT and IBP by AC. Table 4 also listed various kinetic

models parameters. As can be observed, the pseudo-second order kinetic model best fitted the

experimental data. The R2 coefficient of the pseudo-second order kinetic model was greater

than of the pseudo-first order model (R2=0.996 for ACT and R2=0.976 for IBP). The

matching adsorption process to the pseudo-second order model indicated that various

mechanisms such as surface adsorption and diffusion into the pores were contributed in the

sorption of ACT and IBP onto active sites of the activated carbon [45]. Mestre et al. (2011)

reported the similar kinetic study for the removal of ACT and IBP by activated carbons from

sisal waste in aqueous solution [35].

The dissemination mechanism of any pollutant to the sorbent is determined through intra-

particle diffusion kinetic model. This model is expressed by Eq (4).

qt = kidt1/2 + C (4)

Where; Kid (g/mg.min) is the rate constant of intra-particle diffusion kinetic model. C and Kid

were calculated from the intercept and gradient of the linear plotting qt vs. t1/2, respectively

[30]. As listed in Table 4, the C values of the intra-particle diffusion kinetic model (6.96 for

ACT and 7.40 for IBP) did not cross from the beginning point (C≠0). Hence, it can be

expressed that the intra-particle diffusion was not the only rate-limiting step for the removal

of ACT and IBP by the sorbent.

3.4. Effect of solution pH on the sorption

The solution pH, due to the effect on the characteristics of both the sorbent and adsorbate, is a

vital parameter for the sorption. The effect of solution pH (3 to 9) on the sorption of ACT and

IBP by AC was conducted under the conditions given in Table 2 and the result is existed in

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Fig 4. As observed, the sorption capability of AC was declined by increasing solution pH for

both drugs. The sorption rate of ACT and IBP was reduced from 24.36 to 16.25 mg/g and

from 56.93 to 23.61 mg/g by increasing solution pH from 3 to 9, respectively. This

performance is associated with two factors including the charges on the activated carbon

surface at a stated solution pH and the ionization of the adsorbate [14]. The adsorbent surface

charge depends on the solution pH and point zero charge pH of the carbon surface (pHzpc).

Fig 4 (the plot inside the figure) also illustrates the pHzpc of the sorbent which is a proper

method to designate the mechanism of the sorption process over various primarily adjusted

pHs. As seen, the pHzpc of AC-KOH and AC-H3PO4 as the adsorbents of ACT and IBP was

10 and 2, respectively. The working solutions pHs in this study were as pH<pHzpc for ACT

and pH˃pHzpc for IBP adsorption. This indicated that the surface of the AC-KOH and AC-

H3PO4 were positively and negatively charged, respectively. On the other hand, as seen from

Table 1, the pKa for IBP and ACT was 4.95 and 9.38, respectively. Whenever the solution

pH is lower than pKa (pH<pKa), both the drugs are mostly in their non-ionized forms. Vice

versa (pH˃pKa), the drugs are in their ionized (negatively charged) forms [14]. So, ACT

mainly had a neutral charge in the working solution pH (2 to 9) in this study. But, IBP mostly

was in non-ionized forms up to solution pH 4.95 and after that the charge of it was negative

(from pH 4.95 up to 9). Eq (5) is used to determine the % of ionization chemicals in aqueous

solution [14].

Ionization % =100

1 + 10(pKa−pH) (5)

According to the above equation, the values of ionization for ACT at solution pHs 3, 5, 7 and

9 are 0.0004, 0.004, 0.4 and 30 %, respectively. These values for IBP at the noted pHs are

1.1, 52.87, 99.11 and 99.99 %, respectively. As seen, the amount of ionized form of the drugs

was substantially increased by raising solution pH. The reason for decreasing sorption

capacity of AC-H3PO4 in the removal of IBP can be due to the fact that at the pH<pKa, the

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negatively charged adsorbent can easier adsorb the mainly anionic form of IBP. But at

pH˃pKa, the negatively charged adsorbent because of an electrostatic repulsion between the

surface and the carboxylate IBP anions can result in the lower sorption. For ACT, the

ionization percent was increased by enhancing solution pH. But, the removal efficiency of it,

due to the competition of hydroxyl ions with ACT to sorption onto positively charged

adsorbent, was decreased by increasing pH. In this study, the pH 3 was subsequently applied

for the sorption of both drugs in the next experiment.

3.5. Effect of sorbent dosage on the sorption

The effects of various sorbent dosages (0.5 to 10 g/L) were studied on the removal of ACT

and IBP. As displayed in Fig 5, the removal efficiency (%) of ACT and IBP was increased

from 10.67 to 89.55% and from 36.24 to 100% by raising adsorbent dosage from 0.5 to 10

g/L, respectively. The increased removal percent of the drugs at high adsorbent dosages can

be because of the presence more available surface area and sites for an efficient adsorption

[45]. As seen, increasing adsorbent dosage from a certain value of more than 5.0 g/L for IBP

and more than 7.0 g/L for ACT, may be due to conglomeration of the sorbent particles,

caused a negligible increase in the drugs removal. In this study, because of the highest qe

obtained by adsorbent dosage of 1 g/L (Data on the figure not shown), the sorbent dosage of

1 g/L was used for the subsequent expriments.

3.6. Effect of drug content on the sorption

The influence of various initial ACT and IBP concentrations (5, 25, 50, 75, 100 and 150

mg/L) was carried out on the drugs removal. The experiments were done by 0.1 g of the

sorbent into 100 mL solution at contact time of 150 min for ACT and 120 min for IBP and at

the optimum solution pH. Fig 6(a) presents the effect of initial drug content on the sorption.

As can be seen, the sorption capacity of both the drugs was rapidly raised by the enhancing

the adsorbate content in the solution. The quantity of ACT and IBP uptaked by the sorbent

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was improved from 2.64 to 32.25 mg/g and from 4.53 to 81.71 mg/g with increasing

adsorbate concentration from 5 to 150 mg/L, respectively. The reason for this finding can be

due to the increment of driving force rate including Van der Waal’s force which dominates

the mass transfer resistance of the drugs to the active sites of the adsorbent [30].

3.6.1. Isotherm study

The adsorption isotherms are used to understand the pollutant molecules distribution between

liquid and solid phases at equilibrium condition. In this research, the experimental data were

fitted using isotherm models of Langmuir, Freundlich and Dubinin–Radushkevich (D-R).

Monolayer adsorption on the homogenous surface of the adsorbent and the absence of

interaction among adsorbate molecules on the sorbent surface are the main hypothesis of

Langmuir isotherm model. The Langmuir isotherm is presented by Eq (6):

Ce

qe=

Ce

Qm+

1

bQm (6)

Where; Ce (mg/L) and qe are the concentration of adsorbate and sorption ability (mg/g) of the

sorbent at the equilibrium state, respectively. Qm (maximum uptake capacity, mg/g) and b

(the Langmuir constant, L/mg) are achieved by the slope and intercept of plotting Ce/qe

opposed to Ce, respectively [30].

The Freundlich isotherm model is on the basis of multilayer sorption onto the heterogeneous

surface of the adsorbent. The Freundlich isotherm model can be described by Eq (7):

lnqe = ln kf +1

n ln Ce (7)

Where; qe and Ce are same as the definition of the above. Kf (L/g) and n are the constants of

the isotherm and can be calculated via the intercept and gradient of plot of ln qe vs. ln Ce,

respectively. Table 5 indicates the results of the isotherms parameters. As listed, the

Freundlich isotherm best fitted the data than of other isotherms (R2= 0.993 for ACT and

0.990 for IBP). The value of n>1 obtained by the Freundlich model indicates the strong bond

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between the adsorbate and sorbent [30]. The amounts of n for the sorption of ACT and IBP

(Table 5) were found to be 1.52 and 1.72 in this study, respectively. Fig 6(b) also depicted the

Freundlich isotherm model plot for the sorption of the studied drugs.

The Dubinin–Radushkevich (D–R) isotherm model is used to determine the type of sorption

as physisorption, chemisorption or chemical ion exchange. This isotherm can be used via Eq

(8):

ln qe = ln qm-β ε2 (8)

Where; qm (mg/g) is the theoretical sorption ability of the sorbent in saturation condition, ß

(kJ/mol) is a invariable connected with sorption energy and Ɛ is the Polanyi potential

provided by Eq (9):

ε = RT ln (1 +1

Ce) (9)

Where; R (kJ/mol.K) is universal gas constant (8.314 J/mol.K) and T (K) is absolute

temperature of liquid. The intercept and slope of liner plot of ln qe vs. Ɛ2 in Eq (8) are used to

obtain qm and ß, respectively [30]. The E value (sorption energy, kJ/mol) acquired by Eq (10)

can be used to determine the sorption nature.

E =1

√2β (10)

The physisorption, chemical ion exchange and chemisorption occurred for E values of <8, 8-

16 and ˃16 kJ/mol, respectively. As shown in Table 5, the E values for the sorption of ACT

and IBP in this study were 0.107 and 0.357 kJ/mol, respectively. So, physical sorption

occurred for the uptake of the studied drugs by the AC.

3.7. Effect of solution ion strength on the sorption

The effect of solution ion strength on the sorption of ACT and IBP by AC is shown in Fig 7.

As displayed, the removal percent of ACT and IBP was slightly reduced from 21.61 to

17.25% and from 12.6 to 10.2% by increasing solution ionic strength (from 20 to 80 mg/L

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Ca+2), respectively. It may be due to reducing the electrostatic interactions between adsorbate

and sorbent by increasing the ionic strength in the solution. Behera et al. (2012) reported the

same results for the removal of IBP by various clays and AC [46].

3.8. Comparison of adsorption capacity with various adsorbents

Table 6 shows the sorption capacity of various adsorbents for ACT and IBP in the aqueous

solutions. As observed, a simple comparison indicates that AC derived from oak acorn (the

sorbent of our study) can be used as an alternative adsorbent for the removal of ACT and IBP

in the aqueous phase.

3.9. Effect of temperature on the sorption and thermodynamic study

The influences of temperatures (15 to 45 oC) were investigated on the sorption of ACT and

IBP by AC. Fig 8 shows the results of the sorption at the various temperatures. As seen, the

findings depicted that increasing solution temperature was a favorable factor on the removal

efficiencies for both the drugs. So, the removal uptake of ACT and IBP was enhanced from

32.57 to 55.55 mg/g and 15.96 to 23.16 mg/g as the solution temperature was enhanced from

15 oC to 45 oC, respectively. Solution temperature had a substantial influence on the sorption

of hydrophobic chemicals than hydrophilic one. In order hand, cold water can diminish the

dispersion rate of molecules and then prevent the entrance of them into the fine surface pores

of activated carbon. But, at high water temperature, the diffusion of hydrophobic molecules

into the small pore size of the sorbent is increased [4]. Moreover, the increase of the

adsorption capacity may be because of increment in the number of active sites onto the

sorbent at higher temperature [50]. Overall, these can explain the higher removal efficiency

of the drugs by raising solution temperature in our study. Galhetas et al. (2014) and Bahamon

et al. (2017) reported the same results for the removal of ACT and IBP by activated carbon,

respectively [26, 51].

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All the thermodynamic factors of the process including entropy (∆Sº), enthalpy (∆Hº) and

standard free energy (∆Gº) were obtained by Eqs (11) to (14).

∆Gº = −RT ln k (11)

k =qe

Ce (12)

∆Gº = ∆Hº − T∆Sº (13)

ln k =∆Sº

R−

∆Hº

RT (14)

Where k is the equilibrium fixed values, determined by the Langmuir isotherm. The ∆Sº

(J/k.mol) and ∆Hº (kJ/mol) were also obtained by the intercept and gradient of plotting ln k

versus 1/T in Eq (14), respectively [30]. As presented (Table 7), the positive value of ∆Hº

(11.44 kJ/mol for ACT and 24.85 kJ/mol for IBP) proposes that the sorption of ACT and IBP

by AC from the aqueous phase is an endothermic nature. Also, the positive value of ∆Sº

showed a rising randomness at the solid/liquid interface happens in the interior structure of

the adsorbent [50]. The decrease of ΔGº value with an increase in temperature (Table 7)

specifies that the adsorption process becomes more favorable at higher temperatures.

Conclusion

In this study, activated carbon from Quercus Brantii (oak) acorn was applied for the removal

of acetaminophen (ACT) and ibuprofen (IBP) from aqueous media. The effects of different

factors such as chemical activator type, contact time, solution pH, pollutant concentration,

adsorbent dose, solution ion strength and temperature were performed on the sorption. The

best activated carbon for the removal of ACT and IBP was obtained by KOH and H3PO4

activation, respectively. The results indicated that the optimum contact times for ACT

sorption were achieved at 150 min and for IBP at 120 min at pH 3. Also, the sorption process

obtained by D-R isotherm showed the uptake of both the drugs was carried out as

physiosorption. As well as, the finding thermodynamic study showed that the sorption of

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ACT and IBP by the sorbent was favorable at higher temperature. On the basis of the results,

this agricultural waste (oak acorn) can be effectively applied as an alternative adsorbent for

the removal of ACT and IBP in the liquid media.

Acknowledgement

The authors appreciate the vice Chancellery for Research of Lorestan University of Medical

Sciences, Iran for financially support of the study (Grant No: A-10-1446-4).

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Fig 1. The FTIR spectra of the sorbents for the ACT and IBP removal.

Fig. 2. (a) N2 adsorption–desorption isotherms at 77 K and (b) Pore size distribution of the adsorbents.

0

20

40

60

80

100

120

400 1300 2200 3100 4000

Tran

smit

ance

(%

)

Wavelength (cm-1)

AC-KOH AC-H3PO4 Raw-AC

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Fig 3. (a) The effect of contact time on the removal of ACT and IBP by AC (ACT and IBP solution conc.=100

mg/L, pH =7.0 and AC dose =1g/L) and (b) Pseudo-second order kinetic model.

Fig 4. The effect of solution pH on the sorption of ACT and IBP by AC (contact time = 120 min for IBP and

150 min for ACT, 0.1 g of AC and 100 mg/L ACT and IBP in 100 mL solution at 25 ºC).

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Fig 5. The effect of sorbent dosage on the removal of ACT and IBP (contact time = 120 min for IBP and

150 min for ACT and 100 mg/L ACT, , pH=3, and IBP in 100 mL solution at 25 ºC).

Fig 6. (a) The effect of initial drug content on the sorption of ACT and IBP and (b) The Freundlich isotherm

model (contact time = 120 min for IBP and 150 min for ACT, pH=3, 0.1 g of AC and 100 mg/L ACT and IBP

in 100 mL solution at 25 ºC).

0

20

40

60

80

100

120

0 2 4 6 8 10 12

Re

mo

val (

%)

Adsorbent dose (g/L)

ACT

IBP

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Fig 7. The effect of solution ion strength on the sorption of ACT and IBP. (contact time = 120 min for IBP and

150 min for ACT, pH=3, 0.1 g of AC and 100 mg/L ACT and IBP in 100 mL solution at 25 ºC).

Fig 8. The effect of various temperatures on the uptake of ACT and IBP by AC.

0

5

10

15

20

25

30

0 20 40 60 80 100

Re

mo

val (

%)

Ionic strength (mg/L Ca+2)

ACT

IBP

0

10

20

30

40

50

60

0 10 20 30 40 50

qe

(mg/

g)

Temperature (ºC)

ACT

IBP

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Table 1. The chemical and structural characteristics of ACT and IBP.

Generic name Chemical

formula Chemical structure

Molecular

weight (g/mol) pKa Log kow λ max (nm)

Acetaminophen C8H9NO2

151.16 9.38 0.46 243

Ibuprofen

(Na-Salt) C13H17O2Na

228.26 4.95 3.97 220

Table 2. The experimental set up for the adsorption of ACT and IBP by AC.

No Exprimental Run Contact Time

(min) pH

Adsorbent

Dose (g/L)

ACT Conc.

(mg/L)

IBP Conc.

(mg/L)

Ion strength

(mg/L Ca+2)

Temp

(ºC)

1 Effect of contact time 0-200 7 1 100 100 - 25

2 Effect of solution pH a* 3-9 1 100 100 - 25

3 Effect of sorbent dose a* 3 0.5-10 100 100 - 25

4 Effect of drug conc a* 3 1 5-150 5-150 - 25

5 Effect of ion strength a* 3 1 100 100 20-80 25

6 Effect of temperature a* 3 1 100 100 20 15-45

a* = 120 min for IBP and 150 min for ACT.

Table 3. Sorption capacity of the various types of the adsorbent for ACT and IBP.

Adsorbent Chemical

Activator

Activation

Temp (ºC)

AC (g) to

Chemical (g) Ratio

ACT IBP

qe (mg/g) qe (mg/g)

AC NaOH 700 1 to 1 22.42 6.66 1 to 2 15.39 0.00 900 1 to 1 28.91 11.38

1 to 2 19.61 6.54

AC KOH 700 1 to 1 19.18 3.71 1 to 2 28.00 1.23

900 1 to 1 64.92 15.97 1 to 2 44.59 2.88

AC NH4Cl 700 1 to 1 59.61 19.99 1 to 2 38.91 7.48

900 1 to 1 33.09 4.77 1 to 2 38.18 0.00

AC ZnCl2 700 1 to 1 63.32 11.14

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1 to 2 43.79 4.42

900 1 to 1 44.73 6.89 1 to 2 35.50 6.54

AC H3PO4 700 1 to 1 31.75 7.96 1 to 2 46.87 22.00

900 1 to 1 40.45 20.23

1 to 2 42.18 22.71

Table 4. Kinetic parameters for the sorption of ACT and IBP by AC.

Kinetic type Adsorbate

ACT IBP

Pseudo-first order qe (mg/g) 24.78 21.99

K 0.018 0.015

R2 0.962 0.880

Pseudo-second order

qe (mg/g) 40.00 38.46

K (g/mg.min) 0.001 0.001

R2 0.996 0.976

Intraparticle diffusion

C (mg/g) 6.96 7.40

K (mg/g.min1/2) 2.540 2.530

R2 0.923 0.944

Table 5. Isotherm parameters for the sorption of ACT and IBP onto the adsorbents.

D-R isotherm

Freundlich isotherm

Langmuir isotherm Adsorbate

R2 E (kJ/mol) qm(mg/g) R2 n Kf R2 b(L/mg) Qm(mg/g)

0.896 0.107 26.44 0.993 1.529 1.582 0.975 0.02 45.45 ACT

0.781 0.357 58.30 0.990 1.724 7.743 0.953 0.06 96.15 IBP

Table 6. Comparison of various studies for the adsorption ACT and IBP.

Adsorbent Adsorbate pH Equilibrium time

(min)

Maximum sorption

capacity (mg/g) Ref.

AC derived from cattail fiber ACT Independent

in 2-9 540 59.85 [47]

AC from Dende coconut ACT 2.0 240 70.62 [48]

AC from Babassu coconut ACT 2.0 240 71.39 [48]

AC from pinewood IBP 2.5 600 16.84 [49]

AC from agricultural by-product IBP 2.0 1560 12.60 [33]

AC from Artemisia vulgaris IBP 2.0 300 16.94 [22]

AC from oak acorn ACT 3.0 150 45.45 This study

AC from oak acorn IBP 3.0 120 96.15 This study

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Table 7. Thermodynamic parameters for the adsorption of ACT and IBP by AC.

Adsorbate qe (mg/g) ΔG (kJ/mol) ΔH ΔS

288 K 298 K 308 K 318 K 288 K 298 K 308 K 318 K (kJ/mol) (J/mol.K)

ACT 15.96 19.51 21.24 23.16 3.90 3.64 3.38 3.11 11.44 26.16

IBP 32.57 41.87 51.68 55.55 1.66 0.85 0.05 -0.76 24.85 80.50

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