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Supplementary Material

Mesoporous activated carbon fibers synthesized from denim fabric waste: efficient

adsorbents for removal of textile dye from aqueous solutions

Taís L. Silvaa,b, André L. Cazettaa, Patricia S.C. Souzaa, Tao Zhangc, Tewodros Asefac,d,

and Vitor C. Almeidaa*

a Laboratory of Environmental and Agrochemistry, Department of Chemistry, State

University of Maringá, Av. Colombo 5790, CEP 87020-900 – Maringá, Paraná, Brazil.

b Federal University of Technology – Paraná, 635 Marcilio Dias Street, Apucarana,

Paraná, Brazil.

c Department of Chemical and Biochemical Engineering, Rutgers, The State University

of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854, USA.

d Department of Chemistry and Chemical Biology, Rutgers, The State University of New

Jersey, 610 Taylor Road, Piscataway, New Jersey 08854, USA.

*Corresponding author: Tel.: + 55 44 3011 4500; Fax: + 55 44 3011 4449

E-mail address: vcalmeida@uem.br

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Fig. S1 Molecular structure of RBBR dye.

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2 3 4 5 6 7 8 9 10

2.0

2.4

2.8

3.2

3.6

0

2

4

6

pH

pH

fin

al

pHinitial

Fig. S2 Graph of pHPZC for ACFs.

Fig. S3. TEM images of ACFs.

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Fig. S4. EDS spectrum (a) and elemental mapping image (b) of ACFs.

(a)

(b)

(a)

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Table S1. Nonlinear models of adsorption isotherm and kinetic, and equations of

thermodynamic and intra-particle diffusion.

Kinetic model Equations

Pseudo-first order qt = qe[1 − e−𝑘1t]

Pseudo-second order qt = 𝑘2 qe

2 t

1 + 𝑘2 qe t

Intra-particle diffusion qt = kidt0.5 + C

Isotherm model

Langmuir qe = Qm 𝐾𝐿 Ce

1 + 𝐾𝐿 Ce

Freundlich qe = 𝐾𝐹Ce1/𝑛𝐹

Dubinin Radushkevich 𝑞𝑒 = 𝑞𝑚𝑒𝑥𝑝−𝐾𝐷𝑅𝜀2

𝜀 = 𝑅𝑇𝑙𝑛 (1 +1

𝐶𝑒)

𝐸 = 1

√2𝐾𝐷𝑅

Thermodynamic equations

∆G = ∆H – T∆S ∆G = −RTlnKc

Kc = qe

Ce lnKc =

∆S

R−

∆H

RT

k1 = rate constant of pseudo-first order; k2 = rate constant of pseudo-second order; kid = rate constant of

intra-particle diffusion (mg g-1 min-0.5); Ci = constant associated with the layer boundary thickness (mg g-

1); h0 = initial adsorption rate; KF and nF are constant and exponent of Freundlich model, respectively; Qm

= maximum adsorption capacity; KL = Langmuir constant. KDR is Dubinin-Radushkevich constant; ε is the

Polanyi potential; R is the universal gas constant (8.314 J K-1 mol-1); T is the absolute temperature in Kelvin

(K); E is the mean free energy of adsorption (kJ mol-1); Kc is the adsorbate distribution coefficient between

the solid and liquid phases at equilibrium.

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Table S2. Kinetic parameters determined from nonlinear fits of the pseudo-first order and

pseudo-second order models to the experimental data.

qe = mg g-1, k1 = min-1, h0 = mg g-1 min-1, k2 = g mg-1 min-1, and ∆qe = %.

Initial

concentration (mg

L-1)

qe,exp (mg g-1) Pseudo-first order Pseudo-second order

100 120 qe = 112 qe = 120

k1 = 1.11×10-1 k2 = 1.40 × 10-3

R2 = 0.918 R2 = 0.972

Δqe = 4.58 Δqe = 2.72

200 200 qe = 172 qe = 194

k1 = 4.85 × 10-3 k2 = 3.00 × 10-4

R2 = 0.922 R2 = 0.968

Δqe = 7.46 Δqe = 3.29

300 244 qe = 217 qe = 246

k1 = 4.36 × 10-3 k2 = 2.00 × 10-4

R2 = 0.900 R2 = 0.951

Δqe = 6.73 Δqe = 3.37

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Table S3. Isothermal parameters determined from the nonlinear fits of models to

experimental data.

Langmuir Freundlich Dubinin-Radushkevich

Qm = 253 mg g-1 kF = 156 mg g-1 Qm = 257 mg g-1

Ka = 7.10 L mg-1 nF = 8.67 KDR = 1 × 10-4

R2 = 0.853 R2 = 0.955 R2 = 0.710

Δqe = 7.49% Δqe = 1.55% Δqe = 6.76%

Table S4. Thermodynamic parameters for adsorption of RBBR on ACFs.

Temperature (K) ΔG (kJ mol-1) ΔH (kJ mol-1) ΔS (J mol-1 K-1)

303 -0.403 -5.19 -15.7

318 -0.260

328 -0.107

X-ray diffraction and Raman spectroscopy

X-ray diffraction (XRD) analysis was carried out to investigate the crystallinity of

the ACFs. Fig. S5a shows the XRD pattern of ACFs, which shows two peaks located at

around 2-theta of 23° and 44°. The broad peak at 2-theta of 23° is assigned to the (002)

diffraction of disordered carbon phase, and the peak at 2-theta of 44° is attributed to the

(100/101) diffraction peaks of graphitized carbon (Tao et al., 2015). The results overall

reveal the presence of some stacked graphitic layers along with an amorphous structure

of activated carbon.

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10 20 30 40 50 60 70 80

Inte

nsi

ty (

a.u

.)

2 (°)θ

(a)

600 800 1000 1200 1400 1600 1800 2000

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

(b)G-band

D-band

Fig. S5. XRD pattern (a) and Raman spectrum of ACFs (b).

Raman spectrum of ACFs shown in Fig. S5b displays two peaks at around 1340

and 1590 cm-1. The band at 1340 cm-1 is called a D band and is associated with structural

defects or disordered structures in the sp2 domains of the carbon materials, while the band

at 1590 cm-1 is called a G band and corresponds to the E2g vibration mode of graphitic sp2

carbon (Tao et al., 2015). Thus, the ID/IG ratio (ratio of the intensity of the two Raman

peaks) can be used to evaluate the degree of graphitization in carbon materials. The ID/IG

ratio determined from integrated peak area of ACFs was 1.20, indicating the presence of

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defects in the graphite structure of the material. This means, despite its low ash content,

the cellulose material can give rise to defective graphite, most likely due to the

phosphorus dopant atoms making it into its structure. These results corroborate those

obtained by XRD analyses and FTIR spectroscopy.

Adsorption mechanism from intra-particle diffusion model

The intra-particle diffusion model proposed by Weber and Morris (1963) assumes

that the adsorption process may occur from some mechanistic steps, such as: diffusion of

the solute from the solution to the film surrounding to the particle, external diffusion, pore

diffusion, and solute uptake (Asuquo and Martin, 2016).

The linear fits of the intra-particle diffusion model (Table S1) to the experimental

kinetic data (RBBR initial concentrations of 100, 200 and 300 mg L-1) are displayed in

Fig. S6.

0 2 4 6 8 10 12 14 16

0

50

100

150

200

250

100 mg L-1

200 mg L-1

300 mg L-1

qt

(mg g

-1)

t0.5 (min0.5)

Figure S6. Linear fits of the intra-particle diffusion model to the experimental kinetic

data.

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According to Fig. S6, the plots of (mg g-1) vs. t0.5 have multi-linear profiles for

three concentrations studied, suggesting processes of three-steps for the adsorption of

RBBR onto ACFs. Additionally, it can be seen the linear section of qt versus t0.5 does not

pass through the origin (Ci ≠ 0), indicating that intra-particle diffusion is not the rate-

limiting step of the adsorption process (Mitrogiannis et al., 2015). The first linear section

is related to the instantaneous adsorption or external surface adsorption (film diffusion),

while the second stage is associated with the gradual adsorption, where the intra-particle

diffusion is the rate-limiting step. The third linear section represents the equilibrium stage,

where the intra-particle diffusion starts to slow down, and the apparent saturation of

adsorption sites occurs (Li et al., 2013; Mitrogiannis et al., 2015). The parameters (kid and

Ci) calculated from the linear fit of the model to the experimental data are shown in Table

S5. It can be seen the intra-particle rate constant (kid,2) increased (7.05 to 15.4 mg g-1 min-

0.5) with increase RBRB initial concentration, showing a faster intra-particle diffusion at

higher concentrations.

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Table S5. Parameters calculated from linear fit of intra-particle diffusion model to the

experimental kinetics data.

Initial concentration (mg L-1)

100 200 300

First stage

kid,1 (mg g-1 min-0.5) 25.8 27.2 35.9

C1 (mg g-1) 1.95 0.65 1.18

R² 0.9614 0.9961 0.9924

Second stage

kid,2 (mg g-1 min-0.5) 7.05 13.5 15.4

C2 (mg g-1) 50.5 34.1 47.1

R² 0.9492 0.9825 0.9920

Third stage

kid,3 (mg g-1 min-0.5) 0.61 6.70 1.95

C3 (mg g-1) 110.8 94.3 213.6

R² 0.9714 0.9807 1.0

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