Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye methylene blue from aqueous solution

Accepted Manuscript Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye Methylene blue from aqueous solution

Fuat Güzel, Hasan Sayğılı, Gülbahar Akkaya Sayğılı, Filiz Koyuncu, Cumali Yılmaz PII:

S0959-6526(17)30036-7

DOI:

10.1016/j.jclepro.2017.01.029

Reference:

JCLP 8776

To appear in:

Journal of Cleaner Production

Received Date:

27 September 2016

Revised Date:

05 January 2017

Accepted Date:

05 January 2017

Please cite this article as: Fuat Güzel, Hasan Sayğılı, Gülbahar Akkaya Sayğılı, Filiz Koyuncu, Cumali Yılmaz, Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye Methylene blue from aqueous solution, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.01.029

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Graphical abstract:

ACCEPTED MANUSCRIPT Highlights 

Weeds-char was oxidized by nitric acid.



More than two-fold increase in acidic sites was observed on its optimum oxidized.



The effect of different parameters on the MB adsorption process was explored.



The maximum MB sorption was found to increase fourfold than that of weeds-char.



The optimum oxidized char can remove MB in water systems effectively.

ACCEPTED MANUSCRIPT

1

1

Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its

2

application in removal of hazardous dye Methylene blue from aqueous solution

3 4

Fuat Güzela,*, Hasan Sayğılıb, Gülbahar Akkaya Sayğılıa, Filiz Koyuncua, Cumali

5

Yılmaza

6

aDepartment

of Chemistry, Faculty of Education, Dicle University, 21280 Diyarbakır, Turkey

7

bDepartment

of Petroleum and Natural Gas Engineering, Faculty of Engineering and Architecture,

8

Batman University, 72100 Batman, Turkey

9

*Corresponding

10

author: Tel.: +90 (412) 2488377; Fax: +90 (412) 2488257; E-mail adresses:

[email protected]; [email protected] (F. Güzel)

11 12

Abstract

13

In this study, the optimal oxidized weeds-based biochar (OWC) with HNO3 was used as a

14

sorbent to remove methylene blue (MB) dye from aqueous solution. The optimal oxidation

15

conditions were determined according to the MB index (MI) of samples. Weeds-based

16

biochar (WC) and its oxidized samples were characterized by their pore and chemical

17

properties. The results showed that the oxidized WCs have a lower BET (Brunauer-Emmett-

18

Teller) surface area, more oxygen functional groups, lower pHpzc and higher MI compared

19

with the WC. Optimum conditions were determined considering the effect of process

20

parameters such as the solution pH, initial MB concentration, agitation time and solution

21

temperature for MB removal by the optimal OWC. The kinetic data followed the pseudo-

22

second order kinetic model. The equilibrium data were best represented by the Langmuir

23

isotherm model. The maximum MB sorption capacities of WC and optimal OWC were

24

determined as 39.68 and 161.29 mg/g, respectively, under detected optimum conditions (pH

25

7.4, OWC dosage 0.1 g/50 mL, agitation time 480 min and temperature 50 oC).

26

ACCEPTED MANUSCRIPT 1

Keywords: Weeds; Biochar; Surface oxidation; Sorption; Methylene blue

2

1. Introduction

2

3

In the last decade, the amount of contaminated water is rapidly increasing in parallel with

4

the increasing industrialization and population growth. Major water contaminants are many

5

organic compounds, such as pesticides, organochlorines, polychlorinated biphenyls,

6

polycyclic aromatic hydrocarbons, and organic dyes (Zhang et al., 2013). Dyes with intense

7

color and high toxicity are mostly used in various industries, including the dyestuff, paper,

8

textile, leather and cosmetic industries. Therefore, the removal of dyes from aqueous medium

9

is an essential necessity. Lately, there is an increasing demand of efficient and economical

10

technologies for removing dyes from water environment in the World (Yang et al., 2011).

11

Various techniques have been identified for the dye removal from industrial effluent include

12

sorption, ion exchange, flocculation, chemical oxidation, membrane filtration, ozonation,

13

electrolysis, photodegradation, anaerobic treatment and coagulation. Among the above-

14

mentioned techniques, sorption techniques for removal of polluting dyes from industrial

15

effluents are considered to be an attractive method for the treatment of wastewaters due to its

16

low cost, simplicity of design, ease of operation and insensitivity to toxic pollutants (Cengiz

17

et al., 2012). Porous materials, particularly activated carbon is the most popular sorbent and

18

has been used with great success, but it is limited due to its relatively high cost (Meshko et al.,

19

2001). This has led to an increasing interest in research on biochar preparation from easily

20

available and cheaper precursor. According to previous researches, the production cost of

21

biochars has been found to be more economical than activated carbons and their sorption

22

capacities were determined to be less. Thus, numerous studies have been conducted on

23

surface modification of sorbent in order to enhance its effectiveness for sorption of certain

24

contaminants. Acidic treatment, as a surface functional group modification, can be carried out

ACCEPTED MANUSCRIPT

3

1

commonly using HNO3, H2O2, (NH4)2S2O8, and H2SO4 as oxidizing agents (ShamsiJazeyi and

2

Kaghazchi, 2010).

3

Until now, the study on methylene blue (MB) dye sorption using biochar and its oxidized

4

form produced from weeds has not been reported in literature. The weeds hinder the efficient

5

agricultural production. Therefore, these bio-wastes are removed from their millions of tons

6

of fertile soil, and discarded into the environment. The aims of this work were as follows: (1)

7

to prepare the biochar (WC) from weeds (W); (2) to determine the optimal oxidation

8

conditions with HNO3 of the prepared WCs according to MI; (3) to optimize the MB sorption

9

onto the optimal oxidized weeds-biochar (OWC) according to the process parameter such as

10

solution pH, sorbent dosage, initial concentration, agitation time and solution temperature; (4)

11

to evaluate in terms of kinetic and equilibrium isotherm parameters to explain the MB

12

sorption mechanisms of the OWC.

13 14

2. Material and methods

15

2.1. Preparation of weeds-based biochar, chemical oxidation and characterization

16

The weeds were supplied from the campus of Dicle University in Diyarbakır, Turkey, and

17

then washed, dried and sized to 1-2 cm in length. The preparation of WC was performed in a

18

horizontal stainless-steel tubular reactor (7.0 cm diameter x 100 cm length) under nitrogen

19

atmosphere (99.99%) flow (100 mL/min) at the rate of 5 oC/min at 500 oC for 1h.

20

Subsequently, the char product was cooled to room temperature, washed with hot deionized

21

water and HCl of 0.1 M until the pH of the washing solution reached 6-7, and dried at 105 oC

22

for 12 h and then sieved between 80 and 40 mesh. The yield was calculated as the ratio of the

23

dry weight of produced WC to the weight of the air-dried of the weeds.

24

To enhance oxygen-containing functional groups on the WC, it was oxidized by HNO3

25

with different concentrations. For this, 1.0 g of dried WC powder was treated with 25 mL of

ACCEPTED MANUSCRIPT

4

1

20, 40, and 65% of HNO3 solution for 1 h in the 80 oC (reflux under continuous stirring).

2

After treatment, samples were washed thoroughly with ultrapure water until the pH was close

3

to 7, and dried at 105 °C to a constant weight. The oxidized WCs were named as WC20,

4

WC40, and WC65, respectively, based on the HNO3 concentration.

5

The WCs before and after oxidation were characterized by elemental analyses, pore

6

characteristics, Boehm titrations, pHpzc and MI measurements. The elemental analysis (C, H

7

and N) was determined with an elemental analyzer (Leco CHNS 932). The oxygen content

8

was calculated by the difference. Pore characteristics such as SBET, VT and Dp were

9

determined by nitrogen sorption-desorption at 77 K with a surface area and porosity analyzer

10

(Micromeritics, TriStar II). Oxygen-containing functional groups (carboxylic, phenolic and

11

lactonic) were determined by Boehm titration method with different alkali solutions (NaOH,

12

Na2CO3 and NaHCO3) (Liu et al., 2010). The total acidity and basicity were determined from

13

the amount of NaOH and HCl, respectively that reacted with the sample. The pHpzc was

14

determined using the pH drift method (Valdés et al., 2002). It reflects the influence of all the

15

surface functional groups of sample. Sorptive property of the samples was preliminarily

16

characterized by MI measuring. They were conducted as described in the China National

17

Standards (GB/T12496.10).

18 19

2.2. Batch sorption studies

20

The basic dye, MB (Type: cationic; C.A.S. number: 122965-43-9; Color index: 52015;

21

Chemical formula: C16H18ClN3S, Color index: Basic blue 9; Mw: 319.85 g/mol (anhydrous

22

basis); λmax: 665 nm) was used as sorbate.

23

Batch sorption experiments were conducted in 50 mL Erlenmeyer flasks. They were stirred

24

at 120 rpm for the time required in a water bath shaker (Daihan-WSB-30). To optimize the

25

sorption conditions, the effects of various operating parameters such as initial solution pH (2-

ACCEPTED MANUSCRIPT

5

1

10), sorbent dosage (0.1-0.5 g), initial MB concentration (50-400 mg/L), agitation time (5-480

2

min) and solution temperature (20-50 oC) were studied. After each process, the samples were

3

centrifuged (5000 rpm, 10 min) for solid-liquid separation and the residual MB concentration

4

in solution was analyzed by a UV-vis spectrophotometer (Perkin Elmer-Lambda 25) at its

5

λmax (665 nm).

6 7

3. Results and discussion

8

3.1. Effect of oxidant concentration on the some physical and chemical properties of WC and

9

selection of optimum oxidation condition

10

3.1.1. Effect on the pore structure

11

As can be seen in the Table 1, the pore characteristics such as SBET, VT and DP of prepared

12

WC and OWCs decreased with increasing HNO3 concentration. This reduction may be due to

13

either narrowing of the pore entrances of oxygen groups formed on the entrance and walls of

14

pores or to the destruction of pore walls and the conversion of micro- and mesopores to

15

macropores because of the strong oxidation conditions. Similar observations were stated by

16

some other researchers (Shim et al., 2001; Gökçe and Aktaş, 2014).

17 18

3.1.2. Effect on the elemental compositions

19

Table 1 shows the changes in the elemental compositions of WCs by oxidation with

20

various concentrations of HNO3. As seen in this table, while acid concentration increases, the

21

carbon and hydrogen contents decrease, and also the oxygen and nitrogen contents increase.

22

The decrease of carbon and increase of nitrogen and oxygen may be due to the destruction of

23

the pore walls, the formation of aromatic compounds containing nitrogen and the formation of

24

carbon-oxygen functional groups on the surface, respectively.

25

ACCEPTED MANUSCRIPT 1

6

3.1.3. Effect on the surface chemical properties

2

Table 1 shows the changes in the surface functional, total acidic and basic groups of WC

3

by oxidation with various HNO3 concentrations. As seen in this table, oxidation treatment

4

processes increased the total acidity of the surface that resulted from the increase in surface

5

acidic functional groups, such as carboxylic, lactone and phenol groups. These changes also

6

support the decrease in the pHpzc value in same table with increased oxidant concentrations.

7 8

3.1.4. Effect on the MI

9

The measured MI values of WC, WC20, WC40 and WC65 are 1.08, 17.04, 39.65 and

10

49.05 mg/g, respectively (Table 1). According to this order, the WC65 shows the highest MI

11

value. These results are also endorsed by the increased the ΔpHpzc values. From the above-

12

mentioned surface chemical analysis results and the MI values, the WC65 was selected as

13

optimal OWC sample. It was used in the sorption experiment of MB dye from the aqueous

14

phase in this study.

15

Table 1

16 17 18

3.2. Effect of various operating parameters on the Methylene blue dye adsorption

19

3.2.1. Effect of solution pH

20

The effect of pH on the adsorption of MB by WC65 was investigated over the pH range

21

from 2.0 to 9.0 (Table 2). It was observed that an increase in the amount sorbed of MB from

22

11.90 to 21.55 mg/g occurred when the pH values changed from 2.0 to 7.4. This can be on the

23

basis of a decrease in competition between positively charged H+ and MB for surface sites

24

and also by decrease in positive surface charge on the sorbent, which results in a lower

25

electrostatic repulsion between the sorbent surface and MB dye ions. The effect of pH can

ACCEPTED MANUSCRIPT

7

1

also be elucidated in terms of the pHpzc of the WC65. It is a suitable indicator when the

2

surface of sorbent becomes either positively or negatively charged as a function of pH (Chen

3

et al, 2011a). The surface charge of the sorbent is positive at pH
4

pH>pHpzc (Yau et al., 2009). The pHpzc of WC65 was determined as 4.0 (Table 1). Thus,

5

below pH 4.0, WC65 was positively charged and did not favor adsorption of positively

6

charged MB dye ions due to electrostatic repulsion. The optimum pH for MB adsorption onto

7

WC65 was found to be in the range of 7.4-10.0 (Table 2), which was higher than the pHpzc

8

value of 4.0. Thus, the WC65 acts as a negative surface and attracts the cationic MB. A

9

similar behavior has been reported by other MB adsorption studies (Vadivelan and Kumar,

10

2005; Ncibi et al., 2007). Therefore, pH 7.4 was used as the optimum pH for further studies.

11

The possible adsorption mechanisms of MB dye ions at this pH may be electrostatic

12

interaction of the negative adsorption sites of the WC65 (-COOH groups) (SOWC-COOH) with

13

positively charge dye ions and hydrogen bonding interactions between the reactive -OH

14

(SOWC -C6H5-OH) on the WC65 surface and the amine groups (-NR2) of the MB dye ions.

15

Thus adsorption mechanisms for MB dye can be described by the following expressions:

16 17

SWC65-COO- + R2N+ → SWC65-COO-NR2

(1)

18

SWC65-C6H5-O- + R2N+ → SWC65 - C6H5-O-NR2

(2)

19 20

3.2.2. Effect of WC65 dosage

21

The dependence on dosage of MB adsorption was studied by varying the amount of WC65

22

in the medium from 0.1 to 0.5 g/50 mL, while keeping other parameters constant such as

23

initial concentration of 100 mg/L, pH 7.4, agitation rate of 120 rpm, contact time of 1 h and

24

temperature of 20 oC (Table 2). As presented in Table 2, the amount of MB adsorbed was

25

found to decrease from 18.11 to 9.64 mg/g with increasing sorbent dosage from 0.1 g to 0.5 g.

ACCEPTED MANUSCRIPT

8

1

This may be attributed to the decrease in total adsorption surface area available to dye ions

2

resulting from overlapping or aggregation of adsorption sites. Similar observations were

3

previously reported by some researchers (Chakraborty et al., 2011). Based on this

4

observation, optimum dosage of WC65 for subsequent studies was chosen as 0.1 g/50 mL.

5 6

3.2.3. Effect of contact time/initial dye concentration

7

Fig.1 illustrates the adsorption capacity for the contact time at varying initial MB

8

concentrations between 50 and 400 mg/L of dye at a fixed pH 7.4, 0.1 g of WC65 and

9

temperature of 20 oC. It was found that the adsorption process was fast at initial stage of 420

10

min, thereafter it became slower until it reached a constant value where no more MB dye can

11

be removed from the solution. The rapid adsorption at the initial contact time is due to the

12

highly negatively charged surface of the WC65 for adsorption of MB in the solution at pH

13

7.4. The adsorption equilibrium was established in about 480 min. After this time, the amount

14

of adsorbed MB has not changed significantly with time. This time was selected as optimum

15

contact time for isotherm studies.

16

Furthermore, as seen in Fig. 1, the amount of MB adsorbed onto WC65 increased from

17

27.21 to 77.77 mg/g with increase in initial MB concentration from 50 to 400 mg/L. This may

18

be caused to an increase in the driving force between the aqueous and solid phases and

19

increase the number of collisions between MB dye ions and WC65. Similar results have been

20

reported by some other researchers (Tan et al., 2008; Han et al., 2011). Fig. 1

21 22

3.2.4. Effect of solution temperature

23

The effect of temperature was investigated by the addition of 0.1 g of sorbent in 50 mL of

24

various initial concentrations (100-700 mg/L) prepared from 1000 mg/L stock solution of MB

25

dye for 440 min at 20-50oC and pH 7.4. The results are displayed in Fig. 2. As seen in this

ACCEPTED MANUSCRIPT

9

1

figure, the sorbed amount of MB with increase from 20 to 50oC of temperature was found to

2

increase from 67.57 to 161.29 mg/g. The increase in the adsorption capacity might be due to

3

the possibility of increase in the number of active sites for the adsorption with the increase of

4

temperature. This may also be a result of an increase in the mobility of the MB dye ions with

5

the rise of temperature (Güzel et al., 2015). This proves that the adsorption process is

6

endothermic in nature. Fig. 2

7 8

3.3. Kinetic and equilibrium data modeling

9

For kinetic modeling, two famous kinetic models namely, pseudo-first order and pseudo-

10

second order were tested to find the best-fitted model for the kinetic data. The best-fit model

11

was selected based on the R2 and Δq(%) values. The linearized forms of two kinetic models

12

are given in Table 3. The kinetic plots were drawn from the kinetic data at different initial MB

13

concentrations under optimized sorption conditions determined in Table 2 for MB sorption

14

onto the WC65 (Fig. 1). The kinetic parameters, R2 and Δq(%) values determined from the

15

kinetic plots are presented in Table 3. The pseudo-second order kinetic model had the best-fit,

16

according to the high R2 and low Δq(%) (Figure not shown) values. The qe,cal values

17

calculated according to the pseudo-second order were closer to the qe,exp values, when

18

compared with the pseudo-first order. Therefore, the pseudo-second order kinetics model is

19

more appropriate to describe the sorption behavior of MB onto WC65. The pseudo-second-

20

order model is based on the assumption that the rate-determining step may be a chemical

21

sorption involving valence forces through sharing or exchange of electrons between sorbent

22

and sorbate (Bayramoglu et al., 2009).

23

For isotherm modeling, two commonly used isotherm models, namely the Langmuir and

24

Freundlich were fitted to the experimental equilibrium data for MB at different temperatures.

25

The linearized isotherm equations used are given in Table 3. The isotherms were drawn from

ACCEPTED MANUSCRIPT

10

1

the equilibrium data at different temperatures under optimized sorption conditions determined

2

in Table 2 for MB sorption onto the WC65 (Fig. 2). The calculated isotherm parameters and

3

R2 determined from the equilibrium isotherms are listed in Table 3. High R2 values obtained

4

from isotherm models revealed that the equilibrium data followed the Langmuir model (figure

5

not shown). As seen from Table 3, the Langmuir isotherm constants, qm and b increased with

6

increasing the temperature, indicating that the sorption density was higher at higher

7

temperatures (Güzel et al., 2014). The increasing of b values with temperature indicates that

8

there is a chemical interaction between WC65 and MB. The maximum sorption capacities, qm

9

obtained from the Langmuir equation for WC and WC65 at 50 oC were found as 39.68 and

10

161.29 mg/g, respectively (Table 3). The four-fold increase in value of the qm is due to effects

11

on the surface with the HNO3 oxidation as mentioned earlier. A comparison of maximum

12

sorption capacities of the WC65 with other reported values for some sorbents is listed in

13

Table 4. Table 2-4

14 15

4. Conclusions

16

Based on the obtained results, the following conclusions can be drawn:

17



The oxidation with different concentrations caused a decrease in the SBET and an

18

increase in the MI. The highest MI was found to be 49.05 mg/g onto WC oxidized

19

with 65% concentration of HNO3.

20



The kinetic and equilibrium data were well represented by the pseudo-second order

21

kinetic and Langmuir isotherm models, respectively. The maximum sorption

22

capacities for MB onto WC and WC65 were found to be 39.68 and 161.29 mg/g at 50

23

oC,

24 25

respectively.

Consequently, this study shows that WC65 acts as a potential and low-cost sorbent for the removal of hazardous dye MB from aqueous medium.

ACCEPTED MANUSCRIPT 1

List of abbreviations

2

b

Langmuir isotherm equilibrium constant representing the energy of sorption (L/mg)

3

C0

Initial dye concentration (mg/L)

4

Ce

Equilibrium concentration of dye (mg/L)

5

Dp

Average pore diameter (nm),

6

K

Freundlich constant representing sorption capacity ((mg/g) (L/mg)1/n)

7

k1

Pseudo-first order rate constant (1/min)

8

k2

Pseudo-second order rate constant (g/mg min)

9

MI

Methylene blue index (mg/g)

10

n

Freundlich isotherm constant representing sorption intensity

11

pHpzc

pH at the point of zero charge of surface

12

qe

Sorbed dye amount per gram of sorbent at equilibrium (mg/g)

13

qe,cal

Calculated amount of dye sorbed per gram of sorbent at equilibrium (mg/g)

14

qe,exp

Experimental amount of dye sorbed per gram of sorbent at equilibrium (mg/g)

15

qm

qe for complete monolayer sorption capacity (mg/g)

16

qt

Sorbed dye amount per gram of sorbent at time t (mg/g)

17

R2

Correlation coefficient

18

SBET

BET (Brunauer-Emmett-Teller) surface area (m2/g)

19

SWC65

Surface of the WC65.

20

t

Time (min)

21

T

Temperature (K)

22

VT

Total pore volume (cm3/g)

23

Δq (%) Normalized standard deviation

24

λmax

25

Maximum wavelength (nm)

11

ACCEPTED MANUSCRIPT

12

1

References

2

Bayramoglu, G., Altintas, B., Arica, M.Y., 2009. Adsorption kinetics and thermodynamic

3

parameters of cationic dyes from aqueous solutions by using a new strong cation-exchange

4

resin. Chem. Eng. J. 152, 339-346.

5

Cengiz, S., Tanrikulu, F., Aksu S., 2012. An alternative source of adsorbent for the removal

6

of dyes from textile waters: Posidonia oceanica (L.). Chem. Eng. J. 189-190, 32-40.

7

Chakraborty, S., Chowdhury, S., Saha, P.D., 2011. Adsorption of Crystal Violet from aqueous

8

solution onto NaOH-modified rice husk. Carbohydr. Polym. 86 (4), 1533-1541.

9

Chen, H., Zhao, J., Dai, G., 2011. Silkworm exuviae-A new non-conventional and low-cost

10

adsorbent for removal of methylene blue from aqueous solutions. J. Hazard.Mater. 186 (2-3),

11

1320-1327.

12

GB/T12496.10, China National Standard, Standard Test Method for Determination of

13

Methylene Blue Number of Activated Carbon, 1999.

14

Gökçe, Y., Aktaş, Z., 2014. Nitric acid modification of activated carbon produced from waste

15

tea and adsorption of methylene blue and phenol. Appl. Surf. Sci. 313, 352-359.

16

Güzel, F., Sayğılı, H., Sayğılı, G.A., Koyuncu, F., 2014. Elimination of anionic dye by using

17

nanoporous carbon prepared from an industrial biowaste. J. Mol. Liq. 194, 130-140.

18

Güzel, F., Sayğılı, H., Sayğılı, G.A., Koyuncu, F., 2015. New low-cost nanoporous

19

carbonaceous adsorbent developed from carob (Ceratonia siliqua) processing industry waste

20

for the adsorption of anionic textile dye: Characterization, equilibrium and kinetic modeling.

21

J. Mol. Liq. 206, 244-255.

22

Han, X., Wang, W., Ma, X., 2011. Adsorption characteristics of methylene blue onto low cost

23

biomass material lotus leaf. Chem. Eng. J. 171 (1), 1-8.

ACCEPTED MANUSCRIPT

13

1

Li, Y., Du, Q., Liu, T., Peg, X., Wang, J., Sun, J., Wang, Y., Wu, S., Wang, Z., Xia, Y., Xia,

2

L., 2013. Comparative study of methylene blue dye adsorption onto activated carbon,

3

graphene oxide, and carbon nanotubes. Chem. Eng. Res. Des. 91 (2), 361-368.

4

Liu, Z., Zhang, F.-S., Wu, J., 2010. Characterization and application of chars produced from

5

pinewood pyrolysis and hydrothermal treatment. Fuel 89 (2), 510-514.

6

Mahmoud, D.K., Salleh, M.A.M., Karim, W.A.W.A., Idris, A., Abidin, Z.Z., 2012. Batch

7

adsorption of basic dye using acid treated kenaf fibre char: equilibrium, kinetic and

8

thermodynamic studies. Chem. Eng. J. 18-182, 449-457.

9

Makrigianni, V., Giannakas, A., Deligiannakis, Y., Konstantinou, I., 2015. Adsorption of

10

phenol and methylene blue from aqueous solutions by pyrolytic tire char: Equilibrium and

11

kinetic studies. J. Environ. Chem. Eng. 3 (1), 574-582.

12

Meshko, V., Markovska, L., Mincheva, M., Rodrigues, A. E., 2001. Adsorption of basic dyes

13

on granular activated carbon and natural zeolite. Water Res. 35(14), 3357-3366.

14

Ncibi, M.C., Mahjoub, B., Seffen, M., 2007. Kinetic and equilibrium studies of methylene

15

blue biosorption by Posidoniaoceanica (L.) fibres. J. Hazard. Mater. 139 (2), 280-285.

16

ShamsiJazeyi, H., Kaghazchi, T., 2010. Investigation of nitric acid treatment of activated

17

carbon for enhanced aqueous mercury removal. J. Ind. Eng. Chem. 16 (5), 852-858.

18

Shi, L., Zhang, G., Wei, D., Yan, T., Xue, X., Shi, S., Wei, Q., 2014. Preparation and

19

utilization of anaerobic granular sludge-based biochar for the adsorption of methylene blue

20

from aqueous solutions. J. Mol. Liq. 198, 334-340.

21

Shim, J.W., Park, S.J., Ryu, S.K., 2001. Effect of modification with HNO3 and NaOH on

22

metal adsorption by pitch-based activated carbon fibers. Carbon 39 (11), 1635-1642.

23

Stavropoulos, G.G., Zabaniotou, A.A., 2005. Production and characterization of activated

24

carbons from olive-seed waste residue. Micropor. Mesopor. Mater. 82 (1-2), 79-85.

ACCEPTED MANUSCRIPT

14

1

Sun, L., Wan, S., Luo, W., 2013. Biochars prepared from anaerobic digestion residue, palm

2

bark, and eucalyptus for adsorption of cationic methylene blue dye: characterization,

3

equilibrium, and kinetic studies. Bioresour. Technol. 140, 406-413.

4

Tan, I.A.W., Ahmad, A.L., Hameed, B.H., 2008. Adsorption of basic dye on high-surface area

5

activated carbon prepared from coconut husk: equilibrium, kinetic and thermodynamic

6

studies, J. Hazard. Mater. 154 (1-3), 337-346.

7

Vadivelan, V., Kumar, K.V., 2005. Equilibrium, kinetics, mechanism, and process design for

8

the sorption of methylene blue onto rice husk. J. Colloid Interf. Sci. 286 (1), 90-100.

9

Valdés, H., Sánchez-Polo, M., Rivera-Utrilla, J., Zaror, C., 2002. Effect of ozone treatment on

10

surface properties of activated carbon. Langmuir 18 (6), 2111-2116.

11

Yang, Y., Wang, G., Wang, B., Li, Z., Jia, X., Zhou, Q., Zhao, Y., 2011. Biosorption of Acid

12

Black 172 and Congo Red from aqueous solution by nonviable Penicillium YW 01: kinetic

13

study, equilibrium isotherm and artificial neural network modeling. Bioresour. Technol. 102

14

(2), 828-834.

15

Yau, Z., Wang, L., Qi, J., 2009. Biosorption of methylene blue from aqueous solution using a

16

bioenergy forest waste: Xanthoceras sorbifolia seed cost. Clean-Soil Air Water 37 (8), 642-

17

648.

18

Yenisoy-Karakaş, S., Aygün, A., Güneş, M., Tahtasakal, E., 2004. Physical and chemical

19

characteristics of polymer-based spherical activated carbon and its ability to adsorb organics.

20

Carbon 42 (3), 477-484.

21

Zhang, Y.-R., Wang, S.-Q., Shen, S.-L., Zhao, B.-X., 2013. A novel water treatment magnetic

22

nanomaterial for removal of anionic and cationic dyes under severe condition. Chem. Eng. J.

23

233, 258-264.

ACCEPTED MANUSCRIPT Figure captions Fig.1. The kinetic plots related to the MB sorption onto WC65 at different initial concentration and contact time (pH 7.4, WC65 dosage 0.1 g/50 mL, and temperature 293 K). Fig.2. Sorption isotherms of MB onto WC65 at different temperatures (pH 7.4, WC65 dosage 0.1 g/50 mL, initial concentrations 100-700 mg/L and agitation time 480 min).

ACCEPTED MANUSCRIPT 90

50 ppm 100 ppm 200 ppm 400 ppm

qe(mg/g)

74

58

42

26

10

0

300

600

900

t (min) Fig. 1

1200

1500

ACCEPTED MANUSCRIPT 200

293 K-WC65 303 K-WC65 313 K-WC65 323 K-WC65

qe(mg/g)

160

323 K-WC

120

80

40

0

0

170

340

510

Ce (mg/L)

Fig. 2

680

850

ACCEPTED MANUSCRIPT Weeds-chars

WC

WC20

WC40

WC65

40.46

25.56

17.56

5.138

Pore characteristics SBET (m2/g) VT (cm3/g)

0.036

0.019

0.016

DP (nm)

5.14

3.74

3.66

3.57

65.96

55.41

54.16

51.14

Hydrogen

2.53

2.07

1.64

1.05

Nitrogen

3.12

4.95

5.16

5.61

Oxygena

28.39

38.59

39.04

41.18

Yield

42.80

-

-

-

Carboxylic group (meq/g)

0.522

0.569

0.539

0.610

Phenolic group (meq/g)

0.073

0.208

0.387

0.940

Lactonic group (meq/g)

0.480

0.595

0.639

0.724

Total acidic group (meq/g)

1.075

1.372

1.565

2.274

Total basic group (meq/g)

1.111

0.931

0.764

0.578

pHpzc

8.00

4.50

4.25

4.00

ΔpHpzc

0.00

3.50

3.75

4.00

1.08

17.04

0.006

Elemental compositions (wt. %) Carbon

Surface chemical characteristics

Sorptive characteristic MI (mg/g) aby

39.65

difference

Table 1 Variation in some physical and chemical characteristics of unoxidized and oxidized WCs.

49.05

ACCEPTED MANUSCRIPT Run ____

Operating parameters ____________________________________________________ m (g) pH Co (mg/g) t (min) T (oC) Effect of solution pH 1 0.1 2.0 100 60 20 2 " 3.0 " " " 3 " 4.0 " " " 4 " 5.0 " " " 5 " 6.0 " " " 6 " 7.0 " " " 7 " 8.0 " " " 8 " 9.0 " " " 9 " 10.0 " " " Effect of adsorbent dosage 10 0.1 7.4 100 60 20 11 0.2 " " " " 12 0.3 " " " " 13 0.4 " " " " 14 0.5 " " " " Effect of initial dye concentration 15 0.1 7.4 50 390 20 16 " " 100 430 " 17 " " 200 450 " 18 " " 400 480 " Effect of solution temperature 19 0.1 7.4 100-700 480 20 20 " " " " 30 21 " " " " 40 22 " " " " 50

Table 2 The experimental run and conditions for optimal MB sorption onto WC65.

q (mg/g) 11.90 16.32 17.63 18.79 19.32 20.39 21.82 22.67 22.80 18.11 16.12 14.06 11.88 9.64 27.21 50.55 57.40 77.77 67.57 92.59 138.89 161.29

ACCEPTED MANUSCRIPT Kinetic models:

Pseudo-first order

Pseudo-second order

Equations:

ln(qt - qe) = lnqe - k1t

t/qt = 1/(k2qe ) + t/qe

______________________________________

qe,cal

k1.10-3 R2

_______________________________________________

k2.10-4

R2

C0

qe,exp

Δq

qe,cal

(%)

(mg/g) (g/(mg min))

Δq

(mg/mL)

(g/mg) (mg/g) (1/min)

50

27.71

16.38 7.30

0.9762 3.09

26.88 11.50

0.9883

0.12

100

50.55

43.41 7.25

0.9606 0.89

52.91

3.10

0.9851

0.41

200

57.40

48.64 7.20

0.9691 0.87

60.61

2.60

0.9807

0.49

400

77.77

66.98 7.20

0.9647 0.87

81.97

2.00

0.9909

0.47

(%)

Isotherm models:

Freundlich

Langmuir

Equations:

lnqe = lnKF + (1/nF) lnCe

Ce/qe = 1/ (qmb) + Ce/qm

____________________________ K

1/n

R2

(mg/g) (L/mg)1/n

_______________________ qm

b

(mg/g)

(L/mg)

R2

293-WC65

11.14

0.280

0.9139

65.57

0.019

0.9976

303-WC65

23.81

0.216

0.9464

92.59

0.034

0.9981

313-WC65

23.76

0.291

0.9229

138.89

0.033

0.9979

323-WC65

27.96

0.301

0.9075

161.29

0.042

0.9982

2.37

0.417

0.9181

39.68

0.007

0.9872

323-WC

Table 3 Kinetic and isotherm parameters for MB sorption onto WC65.

ACCEPTED MANUSCRIPT Carbonaceous sorbents Weeds char

qmax (mg/g)

References

39.68

This study

161.29

This study

Palm bark char

2.66

Sun, 2013

Eucalyptus char

2.06

Sun, 2013

Optimal oxidized weeds char

Acid treated kenaf fibre char

18.18

Mahmoud et al., 2012

Anaerobic granular sludge char

90.91

Shi et al., 2014

Tire char

65.81

Makrigianni et al., 2015

Commercial activated carbon

14.00

Yenisoy-Karakaş., 2004

Commercial activated carbon

240.00

Stavropoulos and Zabaniotou, 2005

Carbon nanotubes

188.68

Li et al., 2013

Graphene oxide

243.90

Li et al., 2013

Table 4 Comparisons of the maximum sorption of MB dye onto various carbonaceous sorbents.