Preparation and application of activated carbon fibers derived from cellulose and polyester-derived residues for the removal of Pb2+ ions from aqueous solution

(1)

Activated carbon ﬁ bers prepared from cellulose and polyester – derived residues and their application on removal of Pb

²

ions from

aqueous solution

Patrícia S. Carraro

^a,

⁎ , Lucas Spessato

^a

, Lucas H.S. Crespo

^a

, Jéssica T.C. Yokoyama

^a

, Jhessica M. Fonseca

^a

, Karen C. Bedin

^a

, Amanda Ronix

^a

, André L. Cazetta

^a

, Taís L. Silva

^b

, Vitor C. Almeida

^a,

⁎

aLaboratory of Environmental and Agrochemistry, Department of Chemistry, State University of Maringá, 5790 Colombo Avenue, Maringá 87020-900, Paraná, Brazil

bFederal University of Technology–Paraná, 635 Marcílio Dias Street, Apucarana 86812-460, Paraná, Brazil

a b s t r a c t a r t i c l e i n f o

Article history:

Received 17 April 2019

Received in revised form 4 June 2019 Accepted 6 June 2019

Available online 09 June 2019

In the present work, cellulose and cellulose/polyester-derived denim residues were successfully used as carbon precursors for preparation of H3PO4-activated carbonfibers (ACFs), which were applied on removal of Pb²ions from aqueous solutions. ACFs were prepared under conditions of slow pyrolysis, leading to the obtaining of materials with high BET surface area values (SBET). The materials were characterized from several analytical techniques and the results showed that they have well-developed porous structures, with SBETof 1714 and 1743 m²g⁻¹, for ACFs obtained from the cellulose (ACFC) and cellulose/polyester denim residues (ACFCP), respectively. Additionally, the materials showed a well-developed mesoporous structure. The thermogravimetric analysis confirmed the thermal stability of materials, while SEM images attested thefibrous character. The surface groups were explored viaFTIR, Boehm titration andpHPZC, which demonstrated the predominance of acidic groups on the surface of both materials. The Pb²adsorption efficiency from aqueous solution was investigated, evaluating the effect of solution pH, time, adsorbate initial concentration and temperature. The results confirmed the good performances of materials for Pb²removal, showing monolayer adsorption capacities of 361.54 and 385.77 mg g⁻¹for ACFCand ACFCP, respectively. Additionally, the thermodynamic studies confirmed the spontaneity and exothermic nature of adsorption, suggesting a synergistic mechanism with influence of chemisorption and ion exchange.

Keywords:

Denim residues Chemical activation Heavy metal Adsorption

1. Introduction

The inappropriate disposal of inorganic pollutants (like metallic ions) in the environment may conﬁgure several risks to the living organisms. Contrary of organic pollutants, which are susceptible to bio- logical degradation, the metallic ions are not biodegradable and conse- quently, they can be ingested/absorbed by different organisms (e.g.

plants or animals). As consequence, the metals are incorporated into the alimentary cycle, causing the development of different diseases due their accumulations in the receiving bodies. Metallic ions like cad- mium, chromium, mercury, iron, copper, nickel and lead are considered toxics and the necessity of their monitoring and removal from environment has been highlighted by several researchers [1]. The lead is considered one of the most toxic metal, and when ingested by humans, it is accumulated in the organism causing several and irreversible damages to the muscles, kidneys, reproductive and nervous systems; being

responsible for development of anemia, encephalopathies, hepatitis, nephritic syndrome, nervous and behavioral syndromes; and in extreme cases leading to death [2]. The main pollution sources of lead are the combustion of fossil fuels, mineral foundry and other industrial activities [1]. According to the United State Environmental Protection Agency (EPA), the acceptable limit of Pb² disposal in wastewater is 0.05 mg L⁻¹[3], while for the World Health Organization (WHO) the value is 0.01 mg L⁻¹[4]. These low values of acceptable limits demonstrate the necessity to perform effective treatments of residues containing Pb². In this sense, several treatment methods have been reported in the literature, such as chemical precipitation [5], membrane separation [6], ion exchange [7] and vacuum distillation [8]. However, these methods may present some disadvantages as: relatively high cost, incomplete removal of metallic ions and generation of sludges that needs to be subsequent treated [1]. In this way, the adsorption process emerges as an alternative for removal of metallic ions from aqueous solution, since it is considered a relatively simple, efﬁcient and low- cost method. Additionally, it is considered an environmental-friendly method, especially when the adsorbent materials are obtained from renewable and low-cost sources. Different materials have been applied

⁎ Corresponding authors.

E-mail addresses:[email protected](P.S. Carraro),[email protected] (V.C. Almeida).

Contents lists available atScienceDirect

Journal of Molecular Liquids

j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / m o l l i q

(2)

as precursors of adsorbent materials for removal of metallic ions, such as potato peels [9],Caryota urensseeds [10], guava seeds, Dindé stones, tropical almond shells [11],etc.

The activated carbons (ACs) can be considered the most used materials in adsorption processes. These materials have well-developed porous structures, making them suitable for adsorption of a wide range of pollutants [11]. The ACs can be prepared from different meth- odologies, providing materials with varied features, which allow apply- ing them in other processes as electrocatalysis, catalysis,etc. [12]. In the last few years, the preparation ofﬁbrous activated carbons (ACFs) has also been proposed. These materials have as main feature, theﬁbrous structures with nanopores, that when applied in adsorption processes of chemical species, can promote a decrease in the intraparticle diffu- sion resistance [13].

The ACFs can be prepared from a wide range of precursors, such as pineapple plant leaves [14], silkworm cocoon [15], cotton denim residues [16], cotton [17], rayon [18] and polyacrylamide [19]; using different activation methods to develop the porous structure. The choice of cellulosic and lignocellulosic precursors to prepare ACFs has driven the application of chemical activation processviaH3PO4[17]. During the chemical activation with H3PO4, occurs the dehydration of biomass and an expressive number of linkages are broken, while others are formed into the structure of the precursor. These changes in the bio- polymer chains occur at low temperatures and involve the depolymer- ization of cellulosic structure followed by substitution of hydrogen for polyphosphates groups. During the pyrolysis step, the effect of temperature leads to the expansion/dilatation of the material and formation of phosphate esters and aromatic rings. The phosphates–derived groups inhibit the ash formation during the pyrolysis, enhancing the yield of carbon material; while the expansion of structure favors the development of pores with larger diameters [20,21].

In the present work, denim residues composed by cellulose and cellulose/polyester were used as carbon-precursors to prepare H3PO4– activated carbonsﬁbers. The textile industry is among the biggest pol- luters of the environment, especially in terms of water resources, due to the high volume of water used in its various processes. Additionally, this sector generates expressive amounts of solid wastes, among them the denim fabric residues from the garment manufacturing processes.

According to Brazilian Textile and Apparel Industry Association (Abit), the garment Brazilian industries generate around 170,000 tons per year of solid waste. Denim fabric residues are constituted mainly of cot- tonfibers, which in turn can be used as precursors for the preparation of activated carbonfibers (ACFs). The resulting materials herein prepared were characterized from several analytical techniques and applied on removal of Pb²ions from aqueous solution. The effects of initial solution pH, concentration of adsorbate, time and temperature were properly investigated and the theoretical modelsfitted to the experimental data, aiming to evaluate the adsorption process.

2. Materials and methods 2.1. Chemicals and reagents

All chemicals and reagents were purchased from Sigma-Aldrich or local suppliers with analytical grade and used without further puriﬁca- tion. The stock solution of Pb²ions (1000 mg L⁻¹) was prepared by dis- solution of Pb(NO3)2 in deionized water acidiﬁed with HNO3

(0.10 mol L⁻¹) and stored in glassﬂask. All other solutions were prepared from dilution of required volumes from the stock solution, while the pH (when necessary) was adjusted with HNO3or NaOH aqueous solutions (0.10 mol L⁻¹).

2.2. Precursors and preparation of ACFs

Denim fabric residues constituted of cellulose- (100%) and cellulose/

polyester (25% of polyester and 75% of cellulose) were supplied by a

clothing industry of Maringá city, Paraná State, Brazil. The precursors were received in the laboratory, cut into pieces around 1 cm²and dried in oven at 60 °C by 24 h. The determinations of moisture, ash, volatile matter andﬁxed carbon contents were carried out according to ASTM D1762-84 methodology [22].

ACFs from the denim fabric residues constituted of cellulose (ACF_C) and cellulose/polyester (ACFCP) were prepared. For this, 1.00 g of precursor was mixed, within a stainless-steel reactor (with lid and holes to inlet and outlet gases), with 1.00 mL of phosphoric acid (85%), giving an impregnation ratio of 1:1 (wt.:v.). Then, the mixture was kept in oven at 80 °C for 12 h. The pyrolysis of resulting material was carried out in N2atmosphere (100 mL min⁻¹) from a two-step procedure: in theﬁrst step, the furnace (EDG3P 7000) temperature was raised up to 300 °C, with heating rate of 5 °C min⁻¹, and kept in this temperature for 2 h. In the second step, the temperature was increased up to 500

°C (5 °C min⁻¹) and kept for 1 h. Then, the furnace was let to cool down untilca. 150 °C under the same N2ﬂow. The resulting material was ground into powder, using a mortar and pestle, and then washed with aqueous NaOH solution (0.1 mol L⁻¹) under stirring. The solid material was separated using a vacuumﬁltration system (using Millipore®

membrane of 0.45μm), and washed several times with distilled water until the supernatant's pH reached≈6.5. Finally, the material was dried in oven at 110 °C for 12 h.

2.3. Characterization of precursors and ACFs

Textural properties of ACFs were evaluated from N2adsorption and desorption isotherms, which were obtained at 77 K, using a QuantaChrome®, Nova 1200e equipment. The surface area values (SBET) were calculated from the linearﬁt of Brunauer, Emmett and Teller (BET) equation to the relative pressure range (p/p°) of 0.05–0.20 [23].

The total pore volume (V_t) was ascribed as the maximum amount of N2adsorbed atp/p°of 0.99. The micropore volume (V_μ) was estimated fromα-plot method, while the mesopores volume (Vm) was obtained from BJH method [24,25]. The average pore size (Aps) was calculated from the relation4VT/SBET, while the pore size distribution was estimated using the Non-Local Density Functional Theory (NLDFT) [26].

The crystallinity of as-prepared materials was evaluated using a Brüker, D8 Advance equipment, operating with a monochromatic Cu Kα(λ= 1.5406 Å) radiation source at voltage and current of 40 kV and 35 mA, respectively. The diffraction angle, 2θ, ranged from 10 to 80° with step size of 0.015° min⁻¹and acquisition time of 1.7 s. The functional groups of ACFs were analyzed from Fourier transform infrared spectroscopy (FTIR)viaa Thermo Scientiﬁc Nicolet IS10 spectrometer operating in the ATR mode. The spectra of the precursors and ACFs were recorded in the wavenumber range of 4000 to 400 cm⁻¹with a resolution of 4 cm⁻¹and acquisition rate of 32 scans min⁻¹. Additionally, the functional groups and pH of the surface of ACFs were also evaluated from Boehm titration and pH in the point of zero charge (pHPZC) [27,28]

(videSupplementary Material). The morphological features of the materials were investigated from Scanning Electron Microscopy (SEM). The samples were metallized with gold and analyzed in a Quanta 250 equipment (FEI Company), operating with resolution of 1.2 mm and acceler- ation of 20 kV. The Raman spectra of ACFs were acquired using a Brüker, Senterra II spectrometer investigating the wavenumber range of 2500 to 500 cm⁻¹. Thermal stability of precursors was evaluated by thermogravimetric analysis (TGA)viaa Netzsch STA 409 PC analyzer, operating from room temperature up to 850 °C under N2 atmosphere (100 mL min⁻¹) and heating rate of 10 °C min⁻¹.

2.4. Batch adsorption studies

For adsorption studies, 25.0 mL of adsorbate solutions and 25.0 mg of adsorbent were placed in contact inside polypropylene tubes (total volume of 50 mL), which were shaken at 150 rpm, using a thermo- shaker, under pre-determined times and temperature of 25 °C. Then,

(3)

the solutions wereﬁltered using a vacuum system and Millipore®

membrane (0.45μm). The remaining concentrations of Pb²ions were determined by Flame Atomic Absorption Spectrometry (F AAS) using an Analytik Jena, Nova AA300 equipment and air/acetyleneﬂame. The analytical curve was built from acid solutions of Pb²with concentration of 2.50 to 25.0 mg L⁻¹, which provided a linear regression equation of Abs = 0.0237[Pb²] 0.0071 and R²= 0.9979.

The effect of solution pH on Pb²adsorption onto ACFs was investigated in the range of 2.0 to 6.0, using Pb² solution of 500 mg L⁻¹and shaking time of 120 min. The pH values of solutions were adjusted using NaOH (0.1 M) and HNO3(0.1 M) solutions. The kinetic study was carried out with Pb² solutions of 80, 300 and 500 mg L⁻¹ at pH 3.0, and shaking time ranging from 0 to 120 min. The adsorption equilibrium study was performed with Pb²solutions with concentrations ranging from 10 to 700 mg L⁻¹at pH 3.0 and shaking time of 120 min. The effect of temperature on Pb²adsorption onto ACFs was investigated at temperatures of 298, 308, 318 and 328 K, solutions with concentration of 500 mg L⁻¹at pH 3.0 and shaking time of 120 min.

Thermodynamic parameters (ΔG°,ΔH°andΔS°) were calculated from the equations listed in Table S1 (videSupplementary Material). The maximum amounts of Pb² ions adsorbed onto ACFs at equilibrium (qe) and timet(qt) were determined from Eq.(1):

q_e¼q_t¼C0−C_t;e V

W ð1Þ

where,C0,CeandCt(mg L⁻¹) correspond to initial concentrations, concentrations at the equilibrium and timet, respectively,V(L) is the volume andW(g) the mass of ACFs used.

2.5. Adsorption evaluation and theoretical models

In order to evaluate the interactions, dynamic and performances of ACFs to adsorb Pb² ions, the nonlinear kinetic models (videTable S1) of pseudo-ﬁrst order [29], pseudo-second order [30] and Elovich [31], as well as the nonlinear isotherm models of Freundlich [32], Langmuir [33] and Dubinin-Radushkevich [34] wereﬁtted to experimental data.

The nonlinearﬁts were performed using the software Origin® 8.5. The models that best described the experimental data were those showed the highestR²values and lowest normalized standard deviation (Δq) values [35], which can be estimated from Eq.(2).

Δqð Þ ¼% 100

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P q_exp−q_cal

=q_exp

h i2

n−1 vu

ut

ð2Þ

where,qexpis the experimental adsorption capacity at equilibrium or timet(mg g⁻¹),qcalis the calculated adsorption capacity at equilibrium or timet(mg g⁻¹) andnis the number of experimental points.

3. Results and discussion

3.1. Centesimal analysis, yield and thermal stability

The centesimal analysis of precursors showed that cellulose and cellulose/polyester residues have relatively low contents ofﬁxed carbon (3.59 and 8.17%) and high volatile matter contents (89.3 and 86.5%), respectively. Additionally, the yields of ACFCand ACFCPwere found to be 46.0 and 48.0%, respectively, which are in accordance with the results observed in the TG-DTG curves (Fig. S1).

According to the TG-DTG curves, cellulose-based precursor showed a ﬁrst mass loss (≈70%) centered at 350 °C, which can be ascribed to cellulose depolymerizationviatransglycosylation reactions and release of compounds with low molecular mass [36]. The same proﬁle is observed for cellulose/polyester-derived precursor, with mass loss of≈60%, which is associated to degradation of polyester [37,38]. The second mass loss

is observed around 500 °C for both precursors and a third one at≈670

°C for the cellulose/polyester-based precursor, which corresponds to the carbonization and release of aliphatic compounds [39].

3.2. Textural, morphological and structural characterization of materials

The porosimetric analysis was carried out and the adsorption/desorption isotherms are shown inFig. 1a. According to the International Union of Pure and Applied Chemistry (IUPAC), the isotherms of ACFC

and ACFCPcan be classiﬁed asType IV(a), characteristics of materials with well-developed mesoporous structure. The isotherms showed hys- teresis in the desorption branches, which can be classiﬁed asH4, characteristics of micro-mesoporous carbon structures [25].

The textural properties of ACFs were determined and the data displayed inTable 1. As can be seen, the BET surface area values (S_BET) of ACFC(1714 m²g⁻¹) and ACFCP(1743 m²g⁻¹) were similar and high.

Additionally, the use of phosphoric acid as activating agent induced the formation of mesopores instead micropores in the materials, giving Vmvalues of 0.67 cm³g⁻¹for ACFCand 0.58 cm³g⁻¹for ACFCP, which are around 4-fold higher than those found forV_μvalues. The results of mesoporous volumes herein found are in accordance with other works reported in the literature [40–42], which also prepared carbon- based adsorbent materialsviachemical activation with H3PO4. TheAps

values (Table 1) corroborate with the tendency of the materials present more mesopores than micropores, and this behavior can be seen from the distribution proﬁles of the pores showed inFig. 1b. The NLDFT- based distributions show that a high portion of the pores are distributed around 2.0 nm for both materials; however, there are signiﬁcant

150 300 450 600 750 900

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0

150 300 450 600 750 900

Adsorbed Volume at STP (cm3 g-1 )

ACF_C

(a)

ACF_CP

Relative Pressure (p/p°)

2.0 4.0 6.0 8.0 10.0 12.0

0.00 0.15 0.30 0.45 0.00 0.03 0.05 0.08 0.10

dVp

(

cm³ nm-1 g-1

)

Pore width (nm) ACF_C

ACF_CP (b)

Fig. 1.N2adsorption and desorption isotherms at 77 K (a) and NLDFT-based pore size distribution (b) of ACFCand ACFCP.

(4)

amounts of pores distributed between 2.2 and 8.0 nm, justifying the predominance of mesopores and theApsvalues.

The morphologies of the precursors and carbon-based materials were investigated from SEM images.Fig. 2a–b show the SEM images of cellulose- (Fig. 2a) and cellulose/polyester-based (Fig. 2b) precursors, from which it can clearly be seen the presence of well-definedfibers, characteristic of denim structures. After the activation with H3PO4and subsequent pyrolysis, thefibrous appearances were maintained, as can be seen inFig. 2c–d. The presence of cellulose in both precursors promoted specific reactions between the H3PO4 and precursors, preventing the complete decomposition of thefibers.

The structural features of materials were investigated from X-ray diffraction patterns and Raman spectra. Fig. S2 shows the diffraction patterns of precursors, whileFig. 3a shows the results for the prepared materials. As can be seen in Fig. S2, both precursors present similar peaks distribution. For the cellulose-based denim, the peaks are centered atca. 14°, 16°, 20° and 34°, corresponding to the crystallographic planes (101), (111), (021) and (310), while the peaks for cellulose/

polyester-based denim are centered atca. 14°, 16°, 22° and 34° and can be assigned to the crystallographic planes (101), (011), (110) and (104) according crystallographic database JCPDS 03-0289 and 50- 2275, respectively. On the other hand, the ACFs showed crystallographic proﬁles signiﬁcantly different of precursors, as showed inFig. 3a. In both materials, it is possible identify two peaks centered atca. 25° and 42°, corresponding to the crystallographic planes (002) and (101). The (002) plane can be ascribed to incomplete development of crystalline microstructure, while the plane (101) is related with disordered layers on graphitic domains [17]. The average diameters of the crystallite were calculated from Scherer Eq. [43], which were found to be 2.0 nm and 1.0 nm for ACFCand ACFCP, respectively.

The Raman spectra of ACFs displayed inFig. 3b show two well- deﬁned bands centered atca. 1340 and 1650 cm⁻¹, characteristics of

E2gandA1gmodes of the carbon structures, which are calledDandG bands, respectively. The D band is associated with sp³carbon disordered, while theGband indicates the presence of atoms with sp²-hibridization characteristic of graphitic layers [44]. The ratio Table 1

Textural properties of denim-derived carbon materials.

SBET(m²g⁻¹) Vt(cm³g⁻¹) Vμ(cm³g⁻¹) Vm(cm³g⁻¹) Aps(nm)

ACFC 1714 1.29 0.12 0.67 3.02

ACFCP 1743 1.22 0.19 0.58 2.80

Fig. 2.SEM images of cellulose- (a) and polyester-based (b) denim residues as well as ACFC(c) and ACFCP(d).

(002)(002) (101)

ACFC

Intensity (u.a.)

(a)

10 20 30 40 50 60 70 80

(101)

ACFCP

2θ (°)

D G

G 2D

ACF_C

500 1000 1500 2000 2500 3000

D

ACF_CP

Intensity (u.a.)

Raman Shift (cm^-1)

(b)

2D

Fig. 3.XRD patterns of ACFs (a) and Raman spectra (b) of ACFs.

(5)

between D and G bands provide information about the structural organization of materials; whose values can be obtained from the ratio between the areas of D and G bands of the Raman spectra, when the crystallites have diameters lower than 4.4 nm [45]. As showed in Fig. S3, the area for each band was obtained from deconvolution and the ratio (A_D/A_G) of both materials was found to be 3.0, indicating the same deformation degree of the structures. The 2D band at ca.

2850 cm⁻¹indicates graphene layers present on structure. Its intensity, position and shape will depend of the number of layers. With the increase of these layers, the band can be divided into diverse others overlapped modes due the reduction of symmetry on structure [45].

The deconvolutions (videFig. S3) showed the presence of two overlapped Gaussian bands (D₁andD₂), indicating that both materials have more than two graphene layers [46].

3.3. Surface groups of materials

The functional groups present on precursors and ACFs were investigated from FTIR spectra displayed inFig. 4a–b. As can be seen, the spectra of precursors have the same proﬁle (same bands' distribution). The broad band centered atca. 3273 cm⁻¹is associated with stretching vibration of O\\H groups. The band around 2885 cm⁻¹can be ascribed to symmetric and asymmetric stretching of\\CH2\\groups of aliphatic chains; while the band at 1716 cm⁻¹ is associated with vibration stretching of C_C linkages, and the band atca. 1627 cm⁻¹can be assigned to asymmetric stretching of carboxylate groups. Finally, the bands at 1253 and 1012 cm⁻¹are characteristics to stretching vibration of C\\O moieties in carboxylic groups [46].

On the other hand, after performing the activation and pyrolysis of precursors, the resulting materials showed signiﬁcant changes on bands' distribution, with decrease in the number and intensities of some of them. In theFig. 4b, the band atca. 3855 cm⁻¹can be ascribed to stretching vibration of O\\H linkages present in carboxylic, phenolic and alcohol groups [47]. The band centered around 1554 cm⁻¹ is

characteristic to stretching vibration of C_O groups, while the band at ca. 1218 cm⁻¹corresponds to stretching vibration of C\\O linkages of carboxylic groups [48]. Additionally, the bands between 1082 and 500 cm⁻¹can be assigned to symmetric vibration of ionized (P–O⁻) and polyphosphates (P\\O\\P) groups, respectively [48].

The semi-quantitative determination of the groups present on surface of prepared materials was carried from Boehm titration and the results are shown in Table S2. It can be observed similar results, being the acid groups predominant on both materials, with concentrations around of 1.81 mmol g⁻¹. These acidic groups are distributed on ACFCand ACFCPas carboxylic (1.04 and 0.9 mmol g⁻¹), lactonic (0.73 and 0.79 mmol g⁻¹) and phenolic (0.04 and 0.11 mmol g⁻¹) groups, respectively.

The surface pH values were evaluated from the pH in the point of zero charge (pHPZC) and the results are displayed in Fig. S4. ThepHPZC

values were found to be 3.27 and 4.84 for ACF_Cand ACF_CP, respectively;

corroborating with the acidic character of the surface predicted from Boehm titration, which infer that ACFs have chemical groups suitable to accommodate or lose protons, causing a change in the liquid charge of materials' surface from the pH variation. Additionally, the difference between thepHPZCvalues can be justiﬁed by the presence of higher con- tent of basic groups on ACFCPsurface (videTable S2).

4. Adsorption studies 4.1. Effect of solution pH

The solution pH has direct inﬂuence on adsorption efﬁciency in solid-liquid systems. The chemistry species of the metallic ions in solutions are dependent of solution pH, and in the case of Pb², the following species can be found: Pb², Pb(OH) , Pb(OH)2, Pb(OH)3−, Pb(OH)42−, Pb2

(OH)3and Pb3(OH)42 [49]. The Pb² is predominant specie for solutions with pH values below 5.5, while above this value, occurs the formation of hydroxide species [50]. The effect of solution pH on adsorption of Pb²onto ACFs was evaluated and the results are shown inFig. 5.

According to results (Fig. 5), the highestqevalues were obtained in pH values superior to 3.0 for both materials. At low pH values, besides the electrostatic repulsion between the metallic ions and protonated groups, there is excess of H3O species in solution, occurring a competi- tion to interact with the partially negative sites available. Additionally, the behavior ofqevalues in relation to pH (Fig. 5), can be understood evaluating thepHpzcvalues of ACFs. When the solution pH is lower thanpHPZCvalue, the surface of material will be positively charged, while for solution pH higher thanpHpzcvalue, the surface will be nega- tively charged. Evaluating the data compiled inFig. 5, the highest

Cellulose fiber (a)

4000 3500 3000 2500 2000 1500 1000 500

1012 16271253 2885 1716

Cellulose-polyester fiber

Transmitance (u.a.)

Wavenumber (cm^-1)

3273

ACF_C (b)

4000 3500 3000 2500 2000 1500 1000 500

500 1082 1218 1554 ACF_CP

Transmitance (u.a.)

Wavenumber (cm^-1)

3855

Fig. 4.FTIR spectra of cellulose- and polyester-denim precursors (a) and ACFs (b).

2 3 4 5 6

40 60 80 100 120 140 160 180 200

qm (mg g-1 )

pH ACFC

ACF_CP

Fig. 5.Inﬂuence of initial solution pH on Pb²ions adsorption onto cellulose- and polyester- based ACFs.

(6)

adsorption capacity for ACFCwas found at pH 4.0, while for ACFCPthe best pH was 5.0. In both cases, the highest adsorbed amounts were obtained in pH values slightly above to that ofpHPZC, evidencing the importance of electrostatic interactions in the adsorption process.

4.2. Adsorption kinetic

The effect of time in the adsorption process was investigated from Pb² initial concentrations of 80, 300 and 500 mg L⁻¹, and the experimental data are shown in Fig. S5. According to results, the adsorption equilibrium was reached around 5 min for all studied cases. This fast adsorption can be attributed to the high surface area values of the materials, making available a large number of binding sites to interact with Pb² ions.

Table 2displays the kinetic parameters estimated from nonlinearfits of theoretical models to the experimental data. The results indicated that all models well-fitted to the experimental data, since theR²values were higher than 0.99. However, evaluatingR²andΔq values, the pseudo-second order model was that bestfitted to the experimental data, showing the highestR²values (ranging from 0.9999 to 0.9993) and lowestΔqvalues (1.48 to 0.53). Additionally, theqe,calvalues for the pseudo-second order model were closest with those experimentally obtained (qe,exp) (Table 2).

The pseudo-second order kinetic model can be interpreted as a special kind of Langmuir kinetic model, assuming the adsorbate concentration constant in time and the total number of binding sites is dependent of adsorbate amount adsorbed at the equilibrium [51]. This interpreta- tion suggests that pseudo-second order model is based on monolayer formation, which is associated with chemisorption mechanism. The bestﬁt of pseudo-second order model to the experimental data has also been reported by several researchers that investigated the removal of Pb² by carbon-based materials [52,53].

The Elovich model is also useful to predict the nature of adsorption;

whose theαandβparameters are associated with initial adsorption and desorption rates, respectively [51]. As can be seen fromTable 2, theα values for both materials were very high (ranging from 1.04 × 10³³to 4.45 × 10⁴³), while theβvalues were very low (ranging from 1.28 to 0.27), indicating the efﬁcient and stable interactions between the ACFs and Pb²ions.

4.3. Adsorption isotherm

The adsorption isotherm is an useful tool to predict the feasibility of studied processes, as well as to describe the phenomenon that leads to the retention or mobility of a substance into porous materials [54]. Ad- ditionally, it is possible to estimate the maximum adsorption capacity;

and from theﬁt of the theoretical models, some assumptions about the interaction adsorbent-adsorbate can be done. In this sense, the non- linearﬁts of Langmuir, Freundlich and Dubinin-Radushkevich (D-R) were carried out and they are displayed in Fig. S6, while the calculated parameters, as well as theΔqevalues are shown in theTable 3.

The Langmuir model is suitable to describe the adsorption process over energetically homogenous surfaces, wherein each adsorbate mole- cule/ion interact with an adsorptive site. Additionally, the maximum adsorption capacity will be reached when the monolayer is completely formed [55]. On the other hand, the Freundlich model is an empiric equation that describes the adsorption process on an energetically heterogenous surface, wherein the adsorbate species can be distributed in multilayers throughout the surface. In addition, the equation predicts the exponential decrease of the energy with the increase of the number Table 2

Kinetic parameters, determination coefﬁcients and normalized standard deviations of the kinetic models for Pb²adsorption onto ACFCand ACFCP. Initial concentration (mg L⁻¹)

ACFC ACFCP

80 300 500 80 300 500

qe,exp(mg g⁻¹) 82.07 322.22 369.82 81.12 325.41 359.77

Pseudo-ﬁrst order

qe(mg g⁻¹) 80.94 316.80 366.17 80.62 324.88 356.89

k1(min⁻¹) 4.62 3.35 3.13 2.65 4.27 4.06

h0(mg g⁻¹min⁻¹) 373.98 1061.28 1146.11 213.64 1387.24 1448.97

R² 0.9991 0.9984 0.9989 0.9979 0.9993 0.9997

Δq (%) 0.93 1.62 1.68 2.55 0.92 0.77

Pseudo-second order

qe(mg g⁻¹) 81.16 319.39 369.18 81.58 326.36 358.03

k2(min⁻¹) 0.78 0.06 0.05 0.14 0.12 0.13

h0(mg g⁻¹min⁻¹) 5137.82 6125.60 6814.70 931.74 12,781.30 16,664.11

R² 0.9993 0.9996 0.9999 0.9996 0.9997 0.9998

Δq (%) 0.82 0.86 0.87 1.48 0.53 0.55

Elovich

α(mg g⁻¹min⁻¹) 5.54 × 10⁴³ 4.15 × 10⁴⁴ 9.17 × 10⁴² 1.04 × 10³³ 4.45 × 10⁴³ 3.36 × 10⁴³

β(g mg⁻¹) 1.28 0.33 0.27 0.98 0.31 0.28

R² 0.9986 0.9995 0.9992 0.9976 0.9994 0.9989

Δq (%) 1.04 0.82 0.96 1.73 0.66 0.92

Table 3

Parameters and determination coefﬁcients of the isotherm models for Pb²adsorption onto denim derived carbonﬁbers.

ACFC ACFCP

qe,exp(mg g⁻¹) 354.97 360.53

Langmuir

Qm(mg g⁻¹) 361.54 385.77

KL(L mg⁻¹) 0.36 0.14

R² 0.9701 0.9664

Δqe(%) 2.96 3.41

Freundlich

KF(L mg⁻¹) 135.95 121.82

nF 5.36 4.78

R² 0.8753 0.8776

Δqe(%) 5.81 5.79

Dubinin-Radushkevich

Qm(mg g⁻¹) 351.93 376.73

KDR(L mg⁻¹) 0.0008 0.002

E (kJ mol⁻¹) 25.0 16.0

R² 0.9451 0.9479

Δqe(%) 4.84 4.29

(7)

of species adsorbed on the surface [56]. The Dubinin-Radushkevich (D- R) model, in turn, was initially proposed to describe the adsorption of subcritical vapors in microporous solids composed by energetically het- erogeneous sites,viaa mechanism based on Gaussian distribution [54].

The model has been reported as a useful tool to understand the adsorption of metallic ions and organic molecules in porous solids. The nature of adsorption can be evaluated from theKDRconstant, which is associated with free mean adsorption energy (E).

From the data compiled inTable 3, for both materials, the Langmuir model showed the highestR²values and lowestΔqevalues, suggesting the monolayer formation as the main adsorption mechanism. Addition- ally, the determined monolayer adsorption capacity values (Qm) are close to the experimental adsorption capacity values (q_e,exp). For the ACFC, theqe,expandQmvalues were 354.97 mg g⁻¹and 361.54 mg g⁻¹, while for ACFCPwere 360.53 and 385.77 mg g⁻¹, respectively. The Lang- muir separator factors (R_L) were calculated for both systems and results were displayed in Fig. S6. According to model, the adsorption mechanism will be unfavorable forRLb1, favorable for 0bRLb1, linear for R_L= 1 and irreversible forR_L= 0 [57]. Considering the range of initial Pb² concentration evaluated herein (10–700 mg L⁻¹), theRLvalues ranged from 0.004 to 0.220 for ACFC, and from 0.010 to 0.424 for ACFCP; indicating a favorable interaction between ACFs and Pb²ions.

The parameter1/nFof Freundlich model provides information about the adsorption intensity or surface heterogeneity. The surface of material becomes more heterogenous when1/nFvalues are close to zero. Ad- ditionally, values below unit indicate chemisorption, while values above one indicate cooperative adsorption [54]. The1/nFvalues for ACFCand ACFCPwere found to be 0.19 and 0.21, indicating a high heterogeneity degree of the surfaces. Furthermore, chemisorption plays a signiﬁcant role on adsorption mechanism.

The D-R model provides parameters that allowing to calculate free mean adsorption energy (E) of the process. As can be seen from Table 3, the estimated values ofEfor ACFCand ACFCPwere 25.0 and 16.0 kJ mol⁻¹, respectively.Evalues ranging from 8 to 16 kJ mol⁻¹have been described as characteristic of ion exchange process [58]. Consider- ing the data herein reported, the adsorption mechanisms involve the ion exchange processes (replacement of protons by Pb² ions) and chemisorption.

Table 4shows the monolayer adsorption capacity values (Qm) of various materials similar to those herein reported and applied on adsorption of Pb² ions from aqueous solution. As can be seen, theQmvalues of ACFCand ACFCPwere higher than those reported in the literature, demonstrating the efﬁciency of the adsorbents' materials prepared from denim residues activated with phosphoric acid. Additionally, should be reported thatQmvalues of different materials are related to SBETvalues and surface chemistry features, as well as the kind of carbon material precursor used.

4.4. Thermodynamic of adsorption

The thermodynamic parameters are important to evaluate the adsorption spontaneity from the analysis of involved energy and degree of randomness in the interface. Fig. S7 shows the van't Hoff plots

obtained from correlation between lnKcvs.1/Tfor ACFCand ACFCP, while the calculated parameters are displayed in Table S3. As can be seen, the Gibbs free energy change (ΔG°) ranged from −19.43 to

−13.27 kJ mol⁻¹for ACFCand from−19.18 to−12.42 kJ mol⁻¹for ACFCP, indicating the spontaneity and feasibility of Pb² ions adsorption onto ACFs. The negative values of enthalpy change (ΔH°) demonstrate the exothermic nature of interaction between the Pb² ions and active sites over ACFs' surface. According to literature,ΔH°values ranging from 80 to 200 kJ mol⁻¹are associated with chemisorption [59]. As displayed in Table S2, theΔH°values for ACFCand ACFCPwere−75.93 and−82.03 kJ mol⁻¹, respectively; evidencing the importance of chemisorption on adsorption mechanism. Finally, the entropy change (ΔS°) is associated with the degree of randomness in the solid/liquid interface, and the obtained values for ACFC(−193.54 J K⁻¹mol⁻¹) and ACFCP

(−231.72 J K⁻¹mol⁻¹) suggest the decrease on randomness,i.e., occurred an increase on organization in the solid/liquid interface.

5. Conclusion

ACFs were successfully prepared using cellulose- and cellulose/

polyester-based denim residues as carbon precursorviachemical activation with H3PO4. The results showed similarity in the textural properties for both materials, which suggest the noninfluence of precursors' composition in this property. Additionally, the surface chemistry composition of the ACFs also presented similarity, attested from Boehm titration andpHpzcvalues. The ACFs were applied on removal of Pb² ions from aqueous solution and the results demonstrated its high efficiency in the adsorption processes. The kinetic study showed the quasi-instantaneous adsorption (highhovalues), which can be associated with the high surface area values. Additionally, the bestfits of pseudo-second order model suggest the chemical nature of the adsorbent-adsorbate interactions. The adsorption isotherms were also evaluated and the Langmuir model was that better described the experimental data, indicating the monolayer adsorption of Pb²ions on ACFs surface; while the free mean adsorption energy estimated from D-R equation also demonstrate the chemical nature of interactions, corroborating with thermodynamic parameters. As result, the adsorption of Pb² ions onto ACFs occurs in monolayerviaa spontaneous and exothermic process with decrease on randomness in the solid/liquid interface. Addi- tionally, the chemisorption and ion exchange play a significant and synergistic role in the adsorption mechanism. Thus, the materials herein reported have great potential to be used as sustainable adsorbents for removal of Pb² ions from aqueous solution.

Acknowledgements

The authors acknowledge theﬁnancial support provided by CAPES, CNPq and Fundação Araucária - Brazil.

Appendix A. Supplementary data

Supplementary data to this article can be found online athttps://doi.

org/10.1016/j.molliq.2019.111150.

References

[1] S.Z. Mohammadi, M.A. Karimi, D. Afzali, F. Mansouri, Removal of Pb(II) from aqueous solutions using activated carbon from Sea-buckthorn stones by chemical activation, Desalination 262 (2010) 86–93.

[2] M. Bahrami, M.J. Amiri, F. Bagheri, Optimization of the lead removal from aqueous solution using two starch based adsorbents: design of experiments using response surface methodology (RSM), J. Environ. Chem. Eng. 7 (2019), 102793.

[3] EPA, Basic Information about Lead in Drinking Water, United States Environ, Prot.

Agency (2019).

[4] World Health Organization (WHO), Lead in Drinking-water, Diss. Abstr. Int. Sect. B Sci. Eng. 57 (2011) 6562,https://doi.org/10.1155/2013/959637.

[5] M. Ye, G. Li, P. Yan, J. Ren, L. Zheng, D. Han, S. Sun, S. Huang, Y. Zhong, Removal of metals from lead-zinc mine tailings using bioleaching and followed by sulﬁde precipitation, Chemosphere 185 (2017) 1189–1196.

Table 4

Values of monolayer adsorption capacity of Pb²ions onto different related adsorbents.

Precursor Activating agent SBET

(m²g⁻¹) Qm

(mg g⁻¹)

References

Guava seeds CO2 1201 114.8 [11]

Dindé stones CO2 1029 53.1 [11]

T-Almond shells CO2 1074 92.9 [11]

Lemna minor H3PO4 531 170.9 [58]

Tire KOH 265 49.70 [53]

Pine H3PO4 1094 27.53 [52]

Cellulose H3PO4 1714 361.54 Present study

Cellulose/polyester H3PO4 1743 385.77 Present study

(8)

[6] I. Hajdu, M. Bodnár, Z. Csikós, S. Wei, L. Daróczi, B. Kovács, Z. Gyori, J. Tamás, J.

Borbély, Combined nano-membrane technology for removal of lead ions, J. Memb.

Sci. 409–410 (2012) 44–53.

[7] A. Murray, B. Örmeci, ScienceDirect use of polymeric sub-micron ion-exchange resins for removal of lead, copper, zinc, and nickel from natural waters, J. Environ.

Sci. (2018) 1–8.

[8] X. Li, Y. Gao, H. Ding, Removing lead from metallic mixture of waste printed circuit boards by vacuum distillation: factorial design and removal mechanism, Chemosphere 93 (2013) 677–682.

[9] G.Z. Kyzas, G. Bomis, R.I. Kosheleva, E.K. Efthimiadou, E.P. Favvas, M. Kostoglou, A.C.

Mitropoulos, Nanobubbles effect on heavy metal ions adsorption by activated carbon, Chem. Eng. J. 356 (2019) 91–97.

[10] S. Ravulapalli, K. Ravindhranath, Removal of lead (II) from wastewater using active carbon of Caryota urens seeds and its embedded calcium alginate beads as adsorbents, J. Environ. Chem. Eng. 6 (2018) 4298–4309.

[11]L. Largitte, T. Brudey, T. Tant, P.C. Dumesnil, P. Lodewyckx, Comparison of the adsorption of lead by activated carbons from three lignocellulosic precursors, Micropor. Mesopor. Mater. 219 (2015) 265–275.

[12] P. Serp, B. Machado, Carbon (Nano)materials for Catalysis, 2015 1–45,https://doi.

org/10.1039/9781782622567-00001.

[13] C. Hsiu-Mei, C. Ting-Chien, P. San-De, H.L. Chiang, Adsorption characteristics of Or- ange II and Chrysophenine on sludge adsorbent and activated carbonﬁbers, J. Haz- ard. Mater. 161 (2009) 1384–1390.

[14]K.K. Beltrame, A.L. Cazetta, P.S.C. de Souza, L. Spessato, T.L. Silva, V.C. Almeida, Ad- sorption of caffeine on mesoporous activated carbonﬁbers prepared from pineapple plant leaves, Ecotoxicol. Environ. Saf. 147 (2018) 64–71.

[15] J. Li, D.H.L. Ng, P. Song, C. Kong, Y. Song, P. Yang, Preparation and characterization of high-surface-area activated carbonﬁbers from silkworm cocoon waste for Congo red adsorption, Biomass Bioenergy 75 (2015) 189–200.

[16] T.L. Silva, A.L. Cazetta, P.S.C. Souza, T. Zhang, T. Asefa, V.C. Almeida, Mesoporous activated carbonﬁbers synthesized from denim fabric waste: efﬁcient adsorbents for removal of textile dye from aqueous solutions, J. Clean. Prod. 171 (2018) 482–490.

[17] X. Duan, C. Srinivasakannan, X. Wang, F. Wang, X. Liu, Synthesis of activated carbon ﬁbers from cotton by microwave induced H3PO4activation, J. Taiwan Inst. Chem.

Eng. 70 (2017) 374–381.

[18] Y.N. Prajapati, B. Bhaduri, H.C. Joshi, A. Srivastava, N. Verma, Aqueous phase adsorption of different sized molecules on activated carbonﬁbers: effect of textural properties, Chemosphere 155 (2016) 62–69.

[19] M.A.A. Zaini, Y. Amano, M. Machida, Adsorption of heavy metals onto activated carbons derived from polyacrylonitrileﬁber, J. Hazard. Mater. 180 (2010) 552–560.

[20] M. Jagtoyen, F. Derbyshire, Some considerations of the origins of porosity in carbons from chemically activated wood, Carbon 31 (1993) 1185–1192.

[21] M. Jagtoyen, F. Derbyshire, Activated carbons from yellow poplar and white oak by H3PO4activation, Carbon 36 (1998) 1085–1097.

[22] ASTM D 1762-84, Standard test method for chemical analysis of wood charcoal, ASTM Int. 84 (2011) 1–2,https://doi.org/10.1520/D1762-84R07.2.

[23] S. Brunauer, P.H. Emmett, E. Teller, Adsorption of gases in multimolecular layers, J.

Am. Chem. Soc. 60 (1938) 309–319.

[24]E.P. Barrett, L.G. Joyner, P.P. Halenda, The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms, J.

Am. Chem. Soc. 73 (1951) 373–380.

[25] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution, Pure Appl. Chem. 87 (2015) 1051–1069.

[26]J. Landers, G.Y. Gor, A.V. Neimark, Density functional theory methods for characterization of porous materials, Colloids Surfaces A Physicochem. Eng. Asp. 437 (2013) 3–32.

[27] H.P. Boehm, Some aspects of the surface chemistry of carbon blacks and other carbons, Carbon 32 (1994) 759–769.

[28] D. Prahas, Y. Kartika, N. Indraswati, S. Ismadji, Activated carbon from jackfruit peel waste by H3PO4chemical activation: pore structure and surface chemistry characterization, Chem. Eng. J. 140 (2008) 32–42.

[29] S. Lagergren, Zur theorie der sogenannten adsorption gelöster stoffe, K. Sven.

Vetenskapsakademiens Handl. 24 (1898) 1–39.

[30] Y.S. Ho, G. McKay, Pseudo-second order model for sorption processes, Process Biochem. 34 (1999) 451–465.

[31] S. Roginsky, Y.B. Zeldovich, The catalytic oxidation of carbon monoxide on manga- nese dioxide, Acta Physicochim. U.S.S.R. 1 (1934) 554.

[32] H.M.F. Freundlich, Over the adsorption in solutions, J. Phys. Chem. 57 (1906) 385–471.

[33] I. Langmuir, The constitution and fundamental properties of solids and liquids. Part I solids, J. Am. Chem. Soc. 38 (1916) 2221–2295.

[34]M.M. Dubinin, L.V. Radushkevich, The equation of the characteristic curve of activated charcoal, Dokl. Akad. Nauk SSSR 55 (1947) 327–329.

[35] F.-C. Wu, R.-L. Tseng, R.-S. Juang, Kinetic modeling of liquid-phase adsorption of re- active dyes and metal ions on chitosan, Wat. Res. 35 (2001) 613–618.

[36] F. Shaﬁzadeh, A.G.W. Bradbury, W.F. Degroot, T.W. Aanerud, Role of inorganic addi- tives in the smoldering combustion of cotton cellulose, Ind. Eng. Chem. Prod. Res.

Dev. 21 (1982) 97–101.

[37] Winter Roman, Effect of sulfate groups from sulfuric acid hydrolysis on the thermal degradation behavior of bacterial cellulose, Biomacromolecules 5 (2004) 1671–1677.

[38]Z. Yuan, Z. Xu, D. Zhang, W. Chen, Y. Huang, T. Zhang, D. Tian, H. Deng, Y. Zhou, Z.

Sun, Mesoporous activated carbons synthesized by pyrolysis of waste polyester tex- tiles mixed with Mg-containing compounds and their Cr(VI) adsorption, Colloids Surfaces A Physicochem. Eng. Asp. 549 (2018) 86–93.

[39] F. Fang, X. Chen, X. Zhang, C. Cheng, D. Xiao, Y. Meng, X. Ding, H. Zhang, X. Tian, En- vironmentally friendly assembly multilayer coating forﬂame retardant and antimi- crobial cotton fabric, Prog. Org. Coatings. 90 (2016) 258–266.

[40]B.S. Girgis, M.F. Ishak, Activated carbon from cotton stalks by impregnation with phosphoric acid, Mater. Lett. 39 (1999) 107–114.

[41]A. Reffas, V. Bernardet, B. David, L. Reinert, M.B. Lehocine, M. Dubois, N. Batisse, L.

Duclaux, Carbons prepared from coffee grounds by H3PO4activation: characterization and adsorption of methylene blue and nylosan red N-2RBL, J. Hazard. Mater.

175 (2010) 779–788.

[42]T. Vernersson, P.R. Bonelli, E.G. Cerrella, A.L. Cukierman, Arundo donax cane as a precursor for activated carbons preparation by phosphoric acid activation, Bioresour. Technol. 83 (2002) 95–104.

[43]A.C. Ferrari, D.M. Basko, Raman spectroscopy as a versatile tool for studying the properties of graphene, Nat. Nanotechnol. 8 (2013) 235–246.

[44] F. Tuinstra, J.L. Koenig, Raman spectrum of graphite, J. Chem. Phys. 53 (1970) 1126–1130.

[45] M. Szybowicz, A.B. Nowicka, A. Dychalska, Characterization of Carbon Nanomaterials by Raman Spectroscopy, Elsevier Ltd, 2018https://doi.org/10.1016/

B978-0-08-101973-3.00001-8.

[46] J. Xu, L. Chen, H. Qu, Y. Jiao, J. Xie, G. Xing, Preparation and characterization of activated carbon from reedy grass leaves by chemical activation with H3PO4, Appl. Surf.

Sci. 320 (2014) 674–680.

[47] E. Smidt, K. Meissl, The applicability of Fourier transform infrared (FT-IR) spectroscopy in waste management, Waste Manag. 27 (2007) 268–276.

[48] A.M. Puziy, O.I. Poddubnaya, A. Martínez-Alonso, A. Castro-Muñiz, F. Suárez-García, J.M.D. Tascón, Oxygen and phosphorus enriched carbons from lignocellulosic material, Carbon 45 (2007) 1941–1950.

[49] Q. Liu, Y. Liu, Distribution of Pb(II) species in aqueous solutions, J. Colloid Interface Sci. 268 (2003) 266–269.

[50] S. Duan, R. Tang, Z. Xue, X. Zhang, Y. Zhao, W. Zhang, J. Zhang, B. Wang, S. Zeng, D.

Sun, Effective removal of Pb(II) using magnetic Co0.6Fe2.4O4micro-particles as the adsorbent: synthesis and study on the kinetic and thermodynamic behaviors for its adsorption, Colloids Surfaces A Physicochem. Eng. Asp. 469 (2015) 211–223.

[51] S.S. Gupta, K.G. Bhattacharyya, Kinetics of adsorption of metal ions on inorganic materials: a review, Adv. Colloid Interf. Sci. 162 (2011) 39–58.

[52] M. Momčilović, M. Purenović, A. Bojić, A. Zarubica, M. Randelovid, Removal of lead (II) ions from aqueous solutions by adsorption onto pine cone activated carbon, De- salination 276 (2011) 53–59.

[53]A. Nieto-Márquez, A. Pinedo-Flores, G. Picasso, E. Atanes, R. Sun Kou, Selective adsorption of Pb², Cr³and Cd²mixtures on activated carbons prepared from waste tires, J. Environ. Chem. Eng. 5 (2017) 1060–1067.

[54] K.Y. Foo, B.H. Hameed, Insights into the modeling of adsorption isotherm systems, Chem. Eng. J. 156 (2010) 2–10.

[55]F.W. Clarke, B. Langmuir, Constitution of solids and liquids, J. Am. Chem. Soc. 38 (1916) 2221–2295.

[56] H. Freundlich, Über die Adsorption in Lösungen, Zeitschrift Für Phys. Chemie. 57U (1907)https://doi.org/10.1515/zpch-1907-5723.

[57] K. Mahapatra, D.S. Ramteke, L.J. Paliwal, Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal, J. Anal. Appl. Pyrolysis 95 (2012) 79–86.

[58] Y. Huang, S. Li, H. Lin, J. Chen, Fabrication and characterization of mesoporous activated carbon from Lemna minor using one-step H3PO4activation for Pb(II) removal, Appl. Surf. Sci. 317 (2014) 422–431.

[59] Y. Liu, Y.J. Liu, Biosorption isotherms, kinetics and thermodynamics, Sep. Purif.

Technol. 61 (2008) 229–242.