From pollutant to solution of wastewater pollution: Synthesis of activated carbon from textile sludge for dye adsorption

    From Pollutant to Solution of Wastewater Pollution: Synthesis of Activated Carbon from Textile Sludge for Dyes Adsorption Syieluing Wong, Nurul Atiqah Najlaa Yac’cob, Norzita Ngadi, Onn Hassan, Ibrahim M. Inuwa PII: DOI: Reference:

S1004-9541(17)30748-6 doi:10.1016/j.cjche.2017.07.015 CJCHE 889

To appear in: Received date: Revised date: Accepted date:

16 June 2017 17 July 2017 21 July 2017

Please cite this article as: Syieluing Wong, Nurul Atiqah Najlaa Yac’cob, Norzita Ngadi, Onn Hassan, Ibrahim M. Inuwa, From Pollutant to Solution of Wastewater Pollution: Synthesis of Activated Carbon from Textile Sludge for Dyes Adsorption, (2017), doi:10.1016/j.cjche.2017.07.015

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ACCEPTED MANUSCRIPT Energy, Resources and Environmental Technology From Pollutant to Solution of Wastewater Pollution: Synthesis of Activated Carbon from Textile Sludge for Dyes Adsorption Syieluing Wong1, Nurul Atiqah Najlaa Yac’cob1, Norzita Ngadi1*, Onn Hassan1, Ibrahim M. Inuwa2 Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia,

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1

Department of Industrial Chemistry, Kaduna State University, Kaduna Nigeria.

Corresponding

Author:

Tel:

+6075535480,

Fax:

+6075581463,

Email

address:

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[email protected] (N.Ngadi)

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2

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81310 Skudai, Johor, Malaysia

Abstract

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Adsorption is an important process in wastewater treatment, and conversion of waste materials to adsorbent offers a solution to high material cost related to the use of commercial activated carbon. This study investigated the adsorption behaviour of Reactive Black 5 (RB5) and

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Methylene Blue (MB) onto activated carbon produced from textile sludge (TSAC). The activated

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carbon was synthesized through chemical activation of precursor followed with carbonization at 650 ºC under nitrogen flow. Effects of time (0-200 min), pH (2-10), temperature (25-60 °C), initial dye -1

), and adsorbent dosage (0.01-0.15 g) on dyes removal efficiency were

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concentration (0-200 mg·L

investigated. Preliminary screening revealed that TSAC synthesized via H2SO4 activation showed higher adsorption behaviour than TSAC activated by KCl and ZnCl2. The adsorption capacity of -1

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TSAC was found to be 11.98 mg·g (RB5) and 13.27 mg·g (MB), and is dependent on adsorption

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time and initial dye concentration. The adsorption data for both dyes were well fitted to Freundlich isotherm model which explains the heterogeneous nature of TSAC surface. The dyes adsorption obeyed pseudo-second order kinetic model, thus chemisorption was the controlling step. This study reveals potential of textile sludge in removal of dyes from aqueous solution, and further studies are required to establish the applicability of the synthesized adsorbent for the treatment of waste water containing toxic dyes from textile industry. Keywords: Activated carbon; textile sludge; Reactive black 5; Methylene blue; adsorption

1.

Introduction

Remediation of industrial wastewater has become an important issue in scholar research, as the pollutant contained in the wastewater, when flow into river bodies, creates negative impacts on the ecosystem and human health, which are irreversible in some cases. The current strategy applied

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ACCEPTED MANUSCRIPT in wastewater treatment focused on removal of pollutants through various means prior to its discharge. Despite the advancement of latest technologies in wastewater treatment (e.g., membrane technology [1], advanced oxidation process [2] etc), adsorption remains a popular method, due to its simplicity in operation and process control, high efficiency, as well as low material and operational

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costs when compared to other methods [3]. Following the establishment of wastewater treatment

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using commercial activated carbon, the current research interested lies in the development of activated carbons (AC) from cheap sources, especially waste materials. Conversion to AC also adds

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values to such waste, which otherwise requires extra costs for disposal. Therefore, there is an increasing demand to from different industries to seek the possibility to convert their waste to ACs.

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Despite the contribution of textile industry as an important income source in many countries, the environmental impacts brought by such industry cannot be overlooked. Textile industry has been recognized as the most significant source of wastewater pollution [4], mostly

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related to the discharge of dyes that are mostly highly recalcitrant and toxic [5]. When discharge into water bodies, dyes molecules persists for long time as their large and complex molecules structures resist degradation by natural means, such as light and microorganism actions. These dyes molecules

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hinders the penetration of sunlight into the water, hence reduce the photosynthesis activities of aquatic plants, the producer in aquatic food web. This is especially true for Methylene blue (MB)

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and Reactive black 5 (RB5), which are dark in colour at high concentration. This could lead to disastrous effects to the aquatic ecosystem. In addition, the safety of seafood is compromised due to

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biomagnification and bioaccumulation effects of dyes molecules in the marine ecosystem. Transfer of these compounds into human body though ingestion of seafood could lead to undesirable and irreversible effects to human nervous systems [6].

AC

In view of the hazards brought by dyes molecules to human health, dyes removal from textile wastewater via a great number of adsorbents, especially those synthesized from agricultural waste has been investigated. Pradhananga et al. [7] successfully synthesize AC from chemical activation of bamboo cane powder using H3PO4, which possess high adsorption capacity on Lanasyn -1

-1

orange (2600 mg·g ) and Lanasyn gray (3040 mg·g ) respectively. AC produced from cashew net -1

shell via ZnCl2 activation by Spagnoli et al. [8] recorded adsorption capacity of 476 mg·g

for

methylene blue. Orlandi et al. [9] also explored the potential of AC from residual sludge in cellulose and paper industry as adsorbent of methylene blue.

Nevertheless, little attention is given to textile sludge (TS), which is another source of pollution generated from textile industry. The sludge contains high amount of metal ions (especially aluminium and iron that originate from coagulant and flocculants depends on the treatment process) as well as phosphorus, nitrogen and potassium originating from the chemicals used in various steps of textile dying and processing [10]. Therefore, unregulated disposal of TS at dumpsites and landfills

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ACCEPTED MANUSCRIPT may cause land and water pollution. In Malaysia, TS is considered as scheduled waste, therefore treatment of such waste thought on-site facilities or licensed waste treatment company incur cost to the textile manufacturers. In view of such scenario, it is necessary to seek a better alternative to disposal of TS. There are very limited number of studies in literature that reports synthesis of AC

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from TS for removals of strontium [11], oil [12] and dyes [13] from wastewater. This paper presents

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the adsorption behaviour of methylene blue (MB) and reactive black 5 (RB5) onto activated carbon synthesized from textile sludge (TSAC), which is not reported previously. Preliminary study was

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conducted to compare the performance of adsorbents activated by different reagents (H2SO4, KCl, ZnCl2), and the TSAC with the best performance was selected for characterizations as well as

Materials and Methods

2.1

Materials

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isotherm, kinetic and thermodynamic studies.

TS was obtained from the textile industry in Batu Pahat, Johor, Malaysia. The sludge was

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dried at 105 °C for 24 h, then ground and sieved to obtain particles with average size of 0.5 mm. RB5 and MB were purchased from Sigma–Aldrich and HmbG Chemicals respectively.

Preparation of TSAC

AC

2.2

The procedure for TSAC synthesis was adapted from the work by Rozada et al. [14] . Firstly, TS was chemically activated by impregnation with sulfuric acid (H2SO4) as activating agent. The mass ratio of sulfuric acid with respect to TS was 1:1. The chemical activation lasted for 48 hours in a shaker at room temperature (30 °C). Samples were then dried in an oven at 105 °C for 24 hours to a constant weight. Next, the samples were carbonized in a furnace with nitrogen flow at -1

heating rate of 5 °C·min to 650 °C, then hold for 30 min. After that, the carbonized product was rinsed with 10 wt% solution of HCl to eliminate excess dehydrating agents and soluble ash. Next, the sample was rinsed with distilled water, and dried in an oven at 80 °C for 24 hours. ACs were also prepared using ZnCl2 and KCl (mass ratio of 1:1) as activating agents for comparison purpose in term of adsorption performance.

2.3

Preparation of RB5 and MB dyes solutions

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ACCEPTED MANUSCRIPT Aqueous RB5 and MB stock solutions with concentrations of 150 mg·L-1 were prepared by mixing the dyes with distilled water. To prevent decolourization by direct sunlight, the stock solutions were stored in dark place before being used. According to Beer-Lambert Law [15], linear relationship can be observed between FTIR absorbance and adsorbate concentrations, provided that

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low concentration of adsorbate is used. Such law is widely applied to quantify concentration of a

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solute in solution [16]. By utilizing such concept, measurement of absorbance of RB5 (at 598 nm) and MB (at 630 nm) at different concentrations were performed by Aquamate v4.60 UV-Vis

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Spectrophotometer, followed by generation of calibration curves that relate absorbance values of MB and RB5 dye solutions to their concentrations. Fig. 1 indicates the calibration curves for the

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dyes solutions.

Calibration curves for (a) RB5 and (b) MB

2.4

Screening of ACs treated with different activating reagents

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Fig. 1

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Removal of RB5 and MB onto ACs treated with different reagents were studied in a batch study with the method adapted from literature [17, 18]. For each AC, 0.1 g of AC was mixed with 50 ml dye solution (100 mg·L-1) in 125ml conical flasks. The mixtures were agitated for 60 minutes at -1

200 r·min

. After 60 minutes, the adsorbent was filtered and the concentrations for residual dye in

the filtered solutions were determined using UV-VIS spectrophotometer with the help of calibration curve (Fig. 1). Percentage removals of RB5 and MB in each solution were then calculated using Equation (1). AC with the highest removal performance was selected for further adsorption study and characterizations. Percentage removal of aspirin =

𝐶0 − 𝐶e × 100% 𝐶0 (1)

where C0 and Ce denote the initial and equilibrium concentration (mg·L-1) of MB and RB5 dyes respectively.

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Adsorbents Characterization The functional groups of TS and TSAC were characterized using Fourier Transform

Infrared (FTIR) Spectroscopy (IRTracer-100 Spectrophotometer, Shimadzu Cooperation, Japan).

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The spectra were recorded from 400 to 4000 cm-1. The surface morphologies of TS and TSAC were

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observed using Field Emission Scanning Electron Microscopy (FESEM) (Hitachi SU8020). The surface area and pore size of TS and TSAC were measured by Nitrogen Adsorption-Desorption

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Isotherm Analyser (NAD) model Micromeritics 3 Flex Surface Characterization Analyser. Samples were degassed at 77 K under nitrogen gas flow for 4 hours prior to analysis.

Batch mode adsorption study

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2.6

In order to determine the effect of reaction time on adsorption equilibrium, a study on batch mode adsorption was carried out by agitating TSAC in 20 ml of solutions containing RB5 and MB

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aqueous dyes with concentration of 50 mg·L-1 at room temperature (30 °C) for 200 minutes. After the adsorption process, the adsorbent was filtered from the aqueous dyes solution. The final concentrations of RB5 and MB in aqueous dyes solutions were calculated based on measurement

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result from UV-Vis Spectrophotometer. The experiment was also performed to study the effect of

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initial dyes concentration (10-200 mg·L-1) and temperature (30-60 °C).

Equation (2):

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The adsorption capacity of RB5 and MB dyes in the adsorption system, qe was calculated by

qe =

(C0 -Ce )V m (2)

2.7

AC

where m is the mass of the adsorbent (g); and V is the volume of the solution (L).

Adsorption isotherm Adsorption isotherms at 30, 50 and 60 ºC were studied respectively with RB5 and MB dyes

concentrations varying from 10 to 200 mg·L-1. The equilibrium data were fitted to Langmuir and Freundlich isotherm models. The Langmuir equation could be described as shown below: Ce 1 Ce = + qe Q0 KL Q0 (3) -1

where qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg·g ), Q0 and KL are Langmuir constants related to adsorption capacity and the rate of adsorption, respectively.

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ACCEPTED MANUSCRIPT Based on the analysis of the Langmuir model, the essential characteristics of the Langmuir equation can be expressed in terms of a dimensionless separation factor, RL as defined in Eq. (4). RL =

1 (1+KLC0 )

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(4)

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The value of the separation factor, RL indicates whether the nature of the adsorption process is

The Freundlich isotherm model is defined as

1 lg Ce n

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lg qe = lg KF +

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irreversible (RL = 0), favourable (0 < RL < 1), linear (RL = 1) or unfavourable (RL > 1).

(5)

Both KF and n represent Freundlich constants, where n indicates the favourability of the adsorption -1

-1

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process and KF ((mg ·g )·( mg )1/n) indicates the adsorption capacity of the adsorbent.

Generally, the value of n should be between 1 and 10 to show a favourable adsorption process. The higher value of n (smaller value of 1/n) illustrates the stronger adsorption intensity [19].

equals to 1 [20].

Kinetic studies

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Linear adsorption that leads to identical adsorption energies for all sites exists when the value of 1/n

Sorption kinetic studies were conducted at 30 ºC using dyes solutions with initial concentration of 50 mg·L-1 using pseudo-first-order and pseudo-second-order kinetic models.

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Additionally, the intraparticle diffusion model was used to study the diffusion mechanism of dyes through the porous adsorbent.

The pseudo-first-order kinetic model is described by the formula lg (qe -qt ) = lg qe - k1 t (6) -1

where qt (mg·g ) are the amounts of adsorbate adsorbed at any time, t (min), respectively. The constant k1 (min-1) is the adsorption rate constant of the first order adsorption. The pseudo-second-order kinetic model is defined by the formula t 1 1 = + t 2 qt k2 qe qe (7) -1

-1

where k2 (g·mg ·min ) is the rate constant of the second-order adsorption.

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The intraparticle diffusion model is expressed by the equation 1

qt = kp t2 (8)

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where t1/2 (min1/2) is the half-life time in second, and kp is the intraparticle diffusion rate constant

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(mg·g-1·min-1/2).

3.

Results and Discussion

3.1

Removal performances of ACs from different activating agents

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Fig. 2 shows the performances of three different ACs prepared on the removal of anionic RB5 and cationic MB dyes. From the graph, it is clearly showed that the AC with H2SO4 activation possesses the highest percentage removal for both RB5 and MB. The superior effect of AC via

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H2SO4 activation is attributed to formation of stable C-O complexes during activation, which promotes development of the internal porosities of AC. Besides that, integration of sulphuric acid into the carbonaceous TS during activation retard the formation of tars and promote the introduction

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of oxygen functionalities according to the reaction [21]. Improvement of adsorption capacity of dyes

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on AC modified with sulphuric acid was also reported by Martin-Lara et al. [22]. Such improvement is the result of oxygenated groups’ introduction onto the AC surface by H2SO4, which is reported in several studies [23, 24]. Furthermore, the use of H2SO4 as a chemical activating agent is more

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attractive as it gives less impact to environment [25]. Therefore, TSAC via H2SO4 activation was

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used in the following part of this study.

Fig. 2

Removal of anionic RB5 and cationic MB dyes by three different ACs

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ACCEPTED MANUSCRIPT 3.2

Adsorbents Characterizations

3.2.1

FTIR

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The spectra for TS and TSAC showed a similar pattern of bands (Fig. 3). However, several differences were observed in the TSAC spectrum compared to the TS spectrum by the decrease of

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the peak intensities. These may be ascribed to the stretching vibration from the activation process of

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the TS. Both TS and TSAC samples showed strong and broad bands at 3434-3400 cm-1. These may assigned to the inter/intra-hydrogen bonding (O-H) stretching which is related to hydroxyl groups that can found in phenols, alcohols and carboxylic structures [12]. The spectra also illustrate the presence of N-H stretches [26]. A strong band observed at 2921 cm-1 and 2850 cm-1 for TS

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spectrum, and 2918 cm-1 for TSAC spectrum were assigned to the asymmetric C-H band, which is present in alkyl groups [16]. Stretching adsorption bands at 1651 cm-1 for TS spectrum may correspond to carboxyl group C=O present in esters, aldehydes, ketone groups and acetyl

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derivatives, and C=C stretching that is attributed to the aromatic C-C (1458 cm-1; 1409 cm-1) bands and COO- asymmetric stretching [26-28]. TSAC spectrum also showed the C-C stretching (in-ring) at 1403 cm-1. The band at 1116 cm-1 and 1035 cm-1 (TS spectrum) and 1068 cm-1 (TSAC spectrum)

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is ascribed to the strong band of C-O and C-N stretching [28, 29] and S=O stretching [30]. The

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presence of S=O group shows that surface chemistry of the TSAC was modified during activation of biomass precursor with H2SO4. Furthermore, broad peak of C-Cl stretching showed in both TS and TSAC spectrum at 616 cm-1 and 617 cm-1 respectively [31]. The presence of chlorine in the AC is

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probably due to the use of dyes and bleaching agents in the textile manufacturing process.

Fig. 3

FTIR spectra of (a) TS and (b) TSAC

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3.2.2

Surface Morphology FESEM micrographs (Fig. 4) convey different morphology of TS and TSAC surfaces. The

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examination of the initial raw TS showed an uneven surface with no pores. On the other hand,

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uneven surface with pores openings was observed on the surface of TSAC. Such observations indicate that chemical activation by H2SO4 and the carbonization processes at high temperature led

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to development of porosity on TSAC surface. This surface characteristic of TSAC would definitely

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substantiate to higher adsorption capacity of RB5 and MB dyes onto the TSAC.

Fig. 4

FESEM images of (a) TS and (b) TSAC

3.2.3

Nitrogen adsorption-desorption isotherm The nitrogen adsorption-desorption curve [Fig. 5(a) and 5(b)] provides qualitative

information on the TS and TSAC samples. From the figure, the best-fit for nitrogen adsorptiondesorption curve for TS is type V isotherm, which refers to small adsorbate-absorbent interaction potentials and is associated with pores in the range of 1.5 to 100 nm. Similar to type III, the adsorption of type V adsorbent proceeds, as the adsorbate’s interaction with an adsorbed layer is greater than the interaction with the adsorbent surface. For TSAC, large amount of nitrogen was adsorbed at relatively higher pressure. This implies isotherm type IV for TSAC adsorbent, whereas

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ACCEPTED MANUSCRIPT the slope showed increased uptake of adsorbate at a higher pressure as pores are filled. The inflection point reached near completion of the first monolayer. Type V isotherm also signified the porous structure of TSAC in the range of 1.5 to 100 nm.

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The surface physical parameters obtained from the N2 adsorption-desorption isotherms are

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summarized in Table 1. From the data, it is marked that the BET surface area of TSAC was greatly improved (from 90.65 to 221.52 m2 ·g-1), implying pore development during the chemical activation

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with H2SO4 and carbonization at 650 ºC. According to Smith et al. [25], high carbonization temperature can maximize the BET surface area as a consequence of increased aromatization, which occurred at high temperatures. HCl washing at the end of the synthesis of TSAC also resulted

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in the increase of TSAC’s surface area as it lowers down the inorganic contents of the carbonaceous material through realizing the partial dissolution of the inorganic fraction [25].

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The structural heterogeneity is generally characterized in terms of pore size distribution. According to the classification of IUPAC-pore dimensions, the pores of adsorbents were grouped into micropore (d < 2 nm), mesopore (d = 2–50 nm) and macropore (d > 50 nm). The pore

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distribution data were determined by BJH method for both samples [Fig. 5(c)]. From the plotted curves, the pore size distributions curves showed the highest peaks at pore widths of 3.8205 nm for

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TS sample and 1.2154 nm for TSAC sample. Thus, the TS was identified as a mesoporous material, whereas the TSAC as microporous material. The expansion of pores in the activation process

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showed positive results of the micropore growth in the TSAC adsorbent.

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(a) Nitrogen adsorption/desorption isotherms for (a) TS and (b) TSAC, as well as (c) pore

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Fig. 5

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size distribution of TS and TSAC

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Table 1. Characteristic of samples. Parameters

Total surface area, SBET /m2 ·g-1 2

Micropore surface area /m ·g 3

Microporous volume /cm ·g 3

Mesoporous volume /cm ·g

-1

-1

-1

TS

TSAC

BET

90.65

221.52

t-plot

N.A.

124.48

t-plot

N.A.

0.1832

BJH adsorption

0.1988

0.1075

Note: The micropore surface area and micropore volume are below the detection limit of the instrument.

3.2

Effect of reaction time on adsorption equilibrium Adsorption of RB5 from its aqueous solution (50 mg·L-1, 20 ml) at room temperature (30

°C) by 0.2 g of TSAC was analysed as a function of reaction time [Fig. 6(a)]. It was observed that the amount of RB5 dyes adsorbed increased with reaction time until the equilibrium was reached. Initially, the rate of adsorption increased rapidly before showing a constant line (qe = 5.00 mg ·g-1) at

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ACCEPTED MANUSCRIPT a reaction time of 90 minutes onward. The rapid increase of adsorption was due to higher vacant surface sites available during the initial stage of adsorption process. A similar pattern is shown in the adsorption of MB onto TSAC as a function of adsorption time [Fig. 6(b)]. The rate of adsorption was initially increasing rapidly before it became constant (qe= 3.65 mg ·g-1) when the equilibrium was

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reached. The equilibrium time showed that the TSAC adsorbent reached saturation in approximately

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120 minutes. Therefore, equilibrium time was set conservatively at 120 min for further experiments

min (2 h) to standardize the experimental condition.

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in adsorption of both MB dyes; the equilibrium time for adsorption of RB5 was prolonged to 120

Effects of iron- and aluminium- loaded adsorbents on performance of adsorbents were

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investigated in several works [32, 33]. Thus, it is reasonable to believe that the performance of dye adsorption onto TSAC is affected by the presence of impurities, including metal ions contained in TS (due to use of chemicals during textile dyeing and processing as mentioned in the introduction).

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This is the most possible reason that leads to deviation of data points from the fitted lines as shown in Fig. 6(b), although some other possible factors, including precision of spectrophotometer readings may also contribute to the deviation. However, Nevertheless, more studies are needed to draw

Fig. 6

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conclusive links between presence of multiple metals on TSAC and the adsorption performance.

Effect of adsorption time on adsorption of (a) RB5; (b) MB (0.2 g TSAC; 20 ml aqueous

solution; room temperature; pH 6.5 (original pH of RB5 aqueous solution) and pH 6.2 (original pH of MB aqueous solution)) 3.3

Effect of initial dye concentration on the adsorption equilibrium The effect of initial concentration of aqueous dye solution on the amount adsorbed (qe) of

RB5 and MB dyes on TSAC are shown in Fig. 7. The curve indicates that the qe values increase with the increment of the initial dye concentration. A rapid increase in the amount of dyes absorbed onto TSAC adsorbent was spotted at the initial concentration of dye solution. The adsorption processes then showed only a slight change at a higher initial concentration of dye solution. These results were attributed to the increase of driving force of dyes molecule due to concentration gradient [34], which

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ACCEPTED MANUSCRIPT resulted in a higher number of collisions between RB5 and MB dyes molecules with TSAC

Fig. 7

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adsorbent surface. Thus, the adsorption capacities of both dyes were increased.

Effect of initial dye concentration on adsorption of (a) RB5 and (b) MB (0.2 g TSAC; 2

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hours adsorption time; 20 ml aqueous solution; pH 6.5 (original pH of RB5 aqueous solution) and 6.2 (original pH of MB aqueous solution)).

Adsorption equilibrium isotherms

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Fig. 8 shows that the resulting isotherms at three different temperatures are positive, both

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linear and curved plots in relation to the concentration axis, which indicates complete monolayer saturation of the dye covering the surfaces of TSAC at all examined temperatures. The adsorption

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isotherms were also characterized by a very favourable shape, which the initial slope of the curve was inclined, indicating a great affinity of the material for the dye molecules [35].

The linearized Langmuir and Freundlich isotherm plots for both RB5 and MB dyes

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adsorption onto TSAC are shown in Fig. 9. Table 2 summarizes the Langmuir and Freundlich isotherm parameters calculated from the adsorption process. High correlation coefficients, R2 for the Freundlich isotherm model at various temperatures were observed for both dyes. These high correlation coefficients strongly support the fact that the cationic and anionic dye adsorption onto TSAC closely followed the Freundlich isotherm model, which explains the heterogeneous nature of the TSAC surface. Moreover, the Q0 values obtained from the Langmuir plot were higher than the value of qmax in experimental values (9.017 and 10.320 mg ·g-1 for RB5 and MB, respectively). Such observation indicated suitability of the Freundlich isotherm model to represent the adsorption process of RB5 and MB onto TSAC, which can further be examined from Freundlich constant of the equation. Freundlich constant KF showed the adsorption capacity of the adsorbent, which are 0.260, 0.168 and 0.134 for adsorption of RB5, and 0.141, 0.165 and 0.163 for the adsorption of MB. Higher values of KF suggest the highest adsorption capacity. The value of Freundlich constant n also gives a measure of favourability of adsorption [36]. The n value between 1 and 10 showed the favourability of the adsorption process. The adsorption is more favourable at the smaller value of n with n value

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ACCEPTED MANUSCRIPT between 1 and 10 [37]. The n values were found to be 1.573, 1.224 and 1.073 for the adsorption of RB5, and 1.331, 1.280 and 1.259 for the adsorption of MB. These values indicate favourable adsorption processes for the adsorption of both dyes onto TSAC governed by physisorption. Similar results were reported for the adsorption of MB and Reactive Red 222 (RR222) dyes onto composite

Fig. 8

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beads, activated clay, and chitosan beads [38].

Adsorption isotherms of RB5 and MB by TSAC adsorbent obtained at difference

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temperatures

Fig. 9

Linearized (a) Langmuir and (b) Freundlich isotherm plots for anionic RB5 adsorption by

TSAC; and linearized (c) Langmuir and (d) Freundlich isotherm plots for anionic MB adsorption by TSAC.

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ACCEPTED MANUSCRIPT Table 2. The Langmuir and Freundlich isotherms parameters for the adsorption of RB5 dye onto TSAC. Langmuir

Freundlich n

R2

0.636

1.573

0.969

0.817

1.224

0.942

0.932

1.073

0.997

0.141

0.752

1.331

0.965

0.969

0.165

0.781

1.280

0.983

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Temperature

0.163

0.794

1.259

0.981

/ºC

KL

Q0

RL

R

303

0.014

9.017

0.890

323

0.007

17.953

333

0.001

303

2

KF

1/n

0.992

0.260

0.886

0.791

0.168

90.090

0.890

0.680

0.134

0.009

10.320

0.919

0.941

323

0.006

16.639

0.906

333

0.006

17.825

0.904

0.954

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Adsorption kinetic study

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MB

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RB5

The kinetics of adsorption describes the rate of adsorption at the solid-liquid interface. The kinetics of RB5 and MB adsorption onto TSAC adsorbent was analysed using two kinetic models,

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namely Pseudo-first order model and Pseudo-second order model (Fig. 10). The value of correlation

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coefficient, R2 as well as slope and intercept obtained from the plots are tabulated in Table 3. The comparison of qe data shows that the calculated qe values of the pseudo-second order are closer to the experimental values as compared to those from the pseudo-first order. The agreement on

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experimental and calculated qe values indicates that the adsorption system follows the pseudosecond order kinetic model. Moreover, the correlation coefficient, R2 of the pseudo-second order model showed higher values for both dyes which indicate that the adsorption of the dyes onto TSAC

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were classified as chemisorption as the rate-limiting step, which involves valence forces of electrons between adsorbate and adsorbent [39].

The solute transfer in a solid/liquid adsorption process is generally divided into three categories: external mass transfer (boundary layer diffusion), intraparticle diffusion or both [40]. Three consecutive steps involved in the adsorption diffusion includes, the external mass transfer as the first step, where the diffusion occurs between the liquid films to the adsorbent surface. The second step is the intraparticle transport, which involves the diffusion of the liquid contained in the pores and/or along the pore walls. The third step is the reaction at phase boundaries, where the adsorption and desorption between the adsorbate and active sites are generally controlled by the kinetics of bond formation [41]. The intraparticle diffusion model (Fig. 11) represents the diffusion mechanism of RB5 and MB dyes adsorbed through the TSAC adsorbent. From the figure, it is apparent that the multi linear with three distinct regions existed from the data plotted, which indicates three different kinetic mechanisms. The initial slope represents the film diffusion, the

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ACCEPTED MANUSCRIPT second slope represents intraparticle as the rate-limiting step, whereas the last section is the final equilibrium stage. The sorption of RB5 and MB dyes onto TSAC adsorbent may be controlled by film diffusion at earlier stages and as the TSAC particles were loaded with RB5 and MB dyes ions, the sorption process may be controlled by intraparticle diffusion [40]. Thus, the intraparticle

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diffusion was not the only rate-determining factor. The intercept values represent the thickness of the

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boundary layer. Larger intercept values propose that the surface diffusion has a larger contribution as

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D

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the rate-limiting step.

Fig. 10 Plots of Pseudo-first order kinetic model for adsorption of (a) RB5 and (b) MB, as well as

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Pseudo-second order kinetic model for adsorption of (c) RB5 and (d) MB by TSAC.

Fig. 11 Intraparticle diffusion plots for (a) RB5 and (b) MB adsorption by TSAC

Table 3.

Kinetic parameter of the pseudo-first order, pseudo-second order and intraparticle

diffusion for the adsorption of RB5 and MB dyes.

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ACCEPTED MANUSCRIPT Kinetic equation

RB5

MB

qe (exp) /mg ·g-1

5.000

3.660

4.44E-02

4.12E-02

k1 /min-1 -1

R

6.850

2

0.9704

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Pseudo-second order k2 /g·mg-1·min-1 qe (theor.) /mg ·g-1 R

2

kp /mg·g-1·min-1/2

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C /mg ·g-1 2

5.973

0.8198

7.13E-03

9.52E-03

5.784

4.156

0.9879

0.9835

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Intraparticle Diffusion Model

R

IP

qe (theor.) /mg ·g

T

Pseudo-first order

4.49E-02

1.18E-01

4.458

2.307

0.91

0.99

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Table 4 shows the comparison of the maximum adsorption capacity of dyes onto various adsorbents. The TSAC prepared in this study provided a relatively low RB5 and MB dyes adsorption

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capacity, whereas the value is comparable to other adsorbents reported in literature. Nevertheless, application of TSAC is an interesting option for textile industry when considering the elimination of

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treatment cost of TS as scheduled waste. Moreover, previous research on the use of AC for the adsorption of strontium by Kaçan and Kütahyali (2012) shows the BET surface area (SBET) of 135 m2 ·g-1 and the adsorption capacity was reported to be 12.11 mg ·g-1. Thus, it shows that the TSAC

AC

prepared in this study was improved from the previous research with higher SBET of 221.52 m2 ·g-1.

Table 4. Comparison of the maximum monolayer adsorption capacity of dyes onto various adsorbents Adsorbent

qe /mg ·g-1

Dyes

Reference

RB5

11.98

This work

MB

13.27

This work

AC from medical cotton

MB

476.2

[3]

AC from Plantain peels

MB

47.3

[42]

AC from Karanj (Pongamia Pinnata) fruit hulls

MB

154.8

AC from the edible fungi residue

RB5

172.43

TSAC

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[43] [44]

ACCEPTED MANUSCRIPT Acid Red 18

52

Basic Violet 4

91

AC from sewage sludge

4.

[45]

Conclusions

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TSAC was successfully synthesized from TS as an alternative for low-cost adsorbent.

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TSAC prepared via H2SO4 treatment exhibited higher adsorption performance than TSAC treated with KCl and ZnCl2. FTIR result confirmed the existence of important hydroxyl and carboxyl

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functional groups in TSAC which are absent in TS. Increased porosity on the surface of TSAC by 144% from TS surface was indicated from BET analysis result. The microporous character of TSAC was attributed to the activation process during the synthesis process. Comparison of surface morphology through FESEM indicates development of porosity on TSAC during chemical

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activation. Adsorption study results showed that optimum conditions for equilibrium adsorption time were different for RB5 and MB dyes. Similar adsorption behaviour was observed for both anionic

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RB5 and cationic MB dyes as a response to initial dye concentration. The adsorption isotherms showed that the adsorption of RB5 and MB dyes onto TSAC fits well to the Freundlich model while kinetic studies showed that the adsorption of both dyes onto TSAC is best described by pseudosecond order model. In conclusion, this study demonstrates the possibility to transform TS as a

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source of pollution to adsorbents of dye from wastewater, and more studies are needed to improve

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Acknowledgments

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the adsorption performance of TSAC.

The authors extend their sincere gratitude to the Ministry of Higher Education Malaysia (MOHE) for the financial supports received under University Grant (08H05) and Fundamental

AC

Research Grant Scheme (4F489).

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