layered double hydroxide supported on Syagrus coronata biochar

Journal Pre-proof Adsorption of anti-inflammatory drug diclofenac by MgAl/ layered double hydroxide supported on Syagrus coronata biochar

Grazielle Emanuelle de Souza dos Santos, Alessandra Honjo Ide, José Leandro Silva Duarte, Gordon McKay, Antonio Osimar Sousa Silva, Lucas Meili PII:

S0032-5910(20)30096-6

DOI:

https://doi.org/10.1016/j.powtec.2020.01.083

Reference:

PTEC 15152

To appear in:

Powder Technology

Received date:

9 December 2019

Revised date:

23 January 2020

Accepted date:

28 January 2020

Please cite this article as: G.E. de Souza dos Santos, A.H. Ide, J.L.S. Duarte, et al., Adsorption of anti-inflammatory drug diclofenac by MgAl/layered double hydroxide supported on Syagrus coronata biochar, Powder Technology(2019), https://doi.org/ 10.1016/j.powtec.2020.01.083

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© 2019 Published by Elsevier.

Journal Pre-proof

Adsorption of anti-inflammatory drug diclofenac by MgAl/layered double hydroxide supported on Syagrus coronata biochar

Grazielle Emanuelle de Souza dos Santos1, Alessandra Honjo Ide1, José Leandro Silva Duarte1,2, Gordon McKay3, Antonio Osimar Sousa Silva4, Lucas

oo

f

Meili1*

1

pr

Laboratório de Processos, Centro de Tecnologia, Universidade Federal de

2

Laboratorio

de

Eletroquímica

e-

Alagoas, Maceió-AL, Brazil

Aplicado,

Instituto

de

Química

e

Pr

Biotecnologia, Universidade Federal de Alagoas, Maceió-AL, Brazil 3

Division of Sustainable Development, College of Science and Engineering,

Qatar Laboratório

de

Síntese

Jo u

4

rn

al

Hamad Bin Khalifa University, Education City, Qatar Foundation, Doha,

de

Catalisadores,

Universidade

Federal

de

Alagoas, Maceió-AL, Brazil

Corresponding author. *Laboratório de Processos, Centro de Tecnologia, Universidade Federal de Alagoas, Av. Lourival Melo Mota, Tabuleiro dos Martins, Maceió-AL, 57072970, Brazil. E-mail address: [email protected] (L. Meili)

Journal Pre-proof 1. Introduction The

development

of

modern analytical

techniques

has permitted

the

detection of the so-called emerging pollutants in the environment. These compounds are present in a variety of commercial products such as food, beverages, medicines, personal care products, among others, and, after their consumption, they are discarded into the aquatic environment [1]. Pharmaceuticals

are a class of

emerging pollutants that

have been

concentrations,

their

continuous

oo

f

causing many concerns. Although they are found in water matrices in low consumption

generates

a

high

pr

occurrence in the environment in the long term, since many conventional

e-

wastewater treatments are inefficient to achieve the complete removal of

Pr

these contaminants [2]. Diclofenac sodium (DS), a non-steroidal drug, is widely consumed as anti-inflammatory and analgesic. DS is one of the widely

detected

pharmaceuticals

in

wastewater,

biosolids

and

al

most

rn

superficial waters. It has been reported that this compound has a low

Jo u

biodegradability and is not easily removed in conventional water and wastewater treatment plants. DS concentration in the inlet of wastewater treatment plants is reported to be 250 ng.L -1. However, only 14% of concentration

reduction

is

obtained

using

conventional

treatments,

reaching 215 ng.L-1 at the outlet of the plants [3–6]. For this reason, adsorption processes provide a suitable alternative for the removal of emerging pollutants from water [7–22]. In this context, the use of layered double hydroxides (LDHs) has been studied due to their high porosity, large surface area and good ion exchange capacity, making these materials significantly potential adsorbents. LDHs are anionic clays

Journal Pre-proof which are not found abundantly in the environment, but they are easily synthesized

in the

laboratory.

LDHs consist

of

piled positive layers

separated by inter-layered regions formed by anions and water. The general formula is [M 1−x+2Mx+3 (OH)2]+x Ax/n-n·mH2O. M+2 is a divalent metal, M+3 is a trivalent metal and A−n is an n valent anion. The ratio between M+2/M+3 molecules is usually 0.1≤x≤0.5 [23,24]. When supported on

larger

particles,

as

an

example,

charcoal

and

biochar,

their

oo

f

effectiveness is increased in the adsorptive process [25]. Several studies have been reported in the literature using LDHs and

pr

activated carbons as adsorbents to remove emerging pollutants, including

modified

wheat-straw

biochar

has

been used

for

nitrate

Pr

MgFe-LDH

e-

DS. Composites formed by LDH and biochar are reported in the literature:

adsorption[26]; LDH-biochar composites produced by pyrolysis of Ni/Feand precipitation of LDHs onto pristine

al

LDH-modified pine feedstock,

hydroxides

modified

sugarcane

leaves

biochar

were

used

to

Jo u

double

rn

biochar, both were used for the sorption of arsenic [27]; Mg/Al-layered

remove phosphate from aqueous solution [28]; an oil-tea Camellia shells biochar/MnAl-LDH composite was used for Cu(II) adsorption; hierarchical CuAl/sisal carbon fiber layered double hydroxide was applied to remove phosphates from water [29]; and MgFe-LDH/pine cone flakes biochar composite was used for the sorption of aquatic phosphorus [30]. In our previous work, the synthesis of LDH-bovine bone biochar composites was prepared in different molar ratios of Mg:Al (2:1, 3:1 and 4:1) using the coprecipitation method and these were used to remove an organic dye from aqueous

solutions

by adsorption.

The characterization guaranteed the

Journal Pre-proof effectiveness of synthesis and the material presented a good feasibility in dye adsorption under basic solution conditions [31]. The same material was applied as an alternative adsorbent for caffeine removal from water. The composite showed an attractive potential for caffeine adsorption, being

an

interesting

material

for

water

treatment

applications

[32].

However, there are no reports regarding the use of layered double hydroxides

supported

on

biochar

for

diclofenac

sodium

adsorption.

oo

f

Besides, the fabrication and characterization of MgAl/LDH supported in Syagrus coronata biochar has not been explored

pr

Syagrus coronata, known as ouricuri, is an abundant plant in the semi-

e-

arid region of Brazil, frequently used to recover degraded areas. Despite

Pr

the oil as the most important derived product, its endocarp has received only limited study, therefore, its use as an adsorbent could significantly

al

contribute to provide added value to this native plant [33–36].

rn

Therefore, the present work is aimed to synthesize the MgAl layered

Jo u

double hydroxide supported on Syagrus coronata biochar in order to evaluate its potential as an adsorbent agent to remove DS from water media. This material could be both interesting and attractive, if a high adsorption capacity is achieved, due to the abundant and easy local access of the biomass, resulting in a greater economic viability. A new material with the best features of the biochar and LDH to improve emerging pollutants removal would be novel and a significant contribution to

environmental

protection.

For

this

purpose,

the

ouricuri

endocarp

biochar was produced by the pyrolysis process and the MgAl/LDH and the composite materials were synthesized by the co-precipitation method.

Journal Pre-proof The

adsorbents

produced

were

characterized

and

batch

adsorption

assays were performed. Kinetic, equilibrium and thermodynamic studies have been performed and are fully discussed.

2. Experimental 2.1 Adsorbate preparation The DS stock solution was prepared with a concentration of 1000 mg.L-1,

oo

f

using deionized water (18.2 MΩ). Working solutions were appropriately

pr

diluted in different concentrations to perform the adsorption assays.

e-

2.2 Adsorbents preparation

Pr

2.2.1 Biochar

Biochar was produced using the ouricuri (Syagrus coronata) endocarp as

al

the raw material and it was collected in the city of Maceio, state of

rn

Alagoas, Brazil. The preparation consisted of the separation of endocarp

Jo u

and almond. The endocarp was pyrolyzed using a tubular furnace (Jung model LT6 2010) heated by resistances, coupled with a cooling system and temperature controller. The pyrolysis process was carried out with a heating rate of 10ºC.min-1, a residence time of 120 min and the bath temperature was maintained at 3ºC [37]. The use of low temperatures, long

residence

pyrolysis

times

process

temperature

used

and

which in

small

heating

favours

the

the

process

rates characterized a slow production

was

400ºC,

of

biochar.

The

determined

by

thermogravimetric analysis (TGA) of the raw ouricuri endocarp, which guarantees

the

biochar

formation.

Moreover,

at

lower

pyrolysis

Journal Pre-proof temperatures, a higher biochar yield is obtained, which is the desirable product [38]. The biochar produced was crushed and sieved to obtain particle sizes between 0.208 mm and 0.250 mm.

2.2.2 MgAl/LDH The MgAl/LDH was synthesized by the co-precipitation method in which 0.030 mol of magnesium (6.10 g of MgCl2.6H2O) and 0.015 mol of

oo

f

aluminium (3.62 g of AlCl3.6H2O) were added to 20 mL of deionized water (18.2 MΩ) and stirred for 30 min until the complete dissolution of the

pr

components. Subsequently, a solution of NaOH (3 mol.L-1) was added

e-

dropwise until the solution reached pH 10. This step was carried out in

Pr

two hours and the mixture remained under stirring for another two hours [24]. The product obtained was centrifuged for five minutes at 3000 rpm,

al

then the solid phase was washed with deionized water until the pH was

rn

around 7.0. The material was placed in Petri dishes, dried in an oven for

Jo u

18 h at 60°C and, finally, crushed and sieved to obtain particles sizes between 0.208 and 0.589 mm.

2.2.3 Composite

The procedure to synthesize the composite was similar to the LDH synthesis described before, but 1.0 g of biochar was added after the dissolution of the salts in order to support the LDH in the porous material.

2.2.4 Synthesis yield

Journal Pre-proof The initial biomass of ouricuri and the biochar obtained were weighed by an analytical balance to determine the pyrolysis yield. The composite yield was also obtained through the mass balance. In both cases, the yields obtained were based on Equation 1, where Mfinal is the final mass of adsorbents, M initial is the initial mass.

M final M initial

x100

(1)

oo

f

R=

pr

2.3 Adsorbents characterization

The materials were characterized by thermogravimetric analysis (TGA

(BET),

(EDXRF),

XRPD

dispersive

energy

x-ray

Pr

method

e-

and DTGA), nitrogen adsorption by the Brunauer, Emmett and Teller

powder

diffraction,

fluorescence Fourier

spectroscopy

transform

infrared

al

spectroscopy (FT-IR) and scanning electron microscopy (SEM). TGA was

rn

performed using a term scale model Shimadzu DTG-60H, in which 10 mg

Jo u

of the adsorbent was heated to 1000º C at the rate of 10ºC.min-1 in an inert atmosphere (nitrogen gas) with a flow rate of 20 mL/min. BET analysis was performed using the micromeritics equipment ASAP 2020. The sample was degassed for 12 h (2 μmHg) at 350° C in order to remove all contaminants on the surface before nitrogen adsorption and desorption

measurements

were

performed.

EDXRF

analyses

were

conducted using a Shimadzu EDX 8000 equipment. XRD analysis was performed using a Shimadzu XRD 7000 diffractometer. The samples were added in powder form and analysed from 3 to 90° with a range of 0.02° (2θ) using copper radiation as the x-ray source, which corresponds

Journal Pre-proof to the wavelength of 0.15406 Å, voltage of 30 kV and current of 30 mA. The lamellar distances were obtained by comparing the values of the distances of the first basal peaks present in the diffractogram, calculated according to Equation 2, the Bragg's Law [39]:

nλ = 2dsenθ

(2)

oo

f

where n is the reflection order of the peaks, λ is the wavelength of the xrays used in the analysis, d is the interlayer spacing and θ is the Bragg

pr

angle determined by the diffraction peak.

of

layered

materials.

Thus,

the

basal

spacing

was

Pr

characteristic

e-

The repetition of the interlayer distance of the material n times is

calculated according to the mean of the values obtained for the first peaks

1

nλ

The

FT-IR

Jo u

d = n ∑ni= 1 2senθ

rn

al

observed in the diffractogram, according to Equation (3).

analyses

were

(3)

performed

using

a

spectrophotometer

Shimadzu IRPrestige-21 model by the ATR method in the range of 4000 to 400 cm-1. The surface morphology of the adsorbent material was analysed by

a SEM

Shimadzu SSX-550 model.

LDH samples were

sputter coated with gold particles for 6 min (10 mA) using a Sanyu Electron Quick Coater SC-701 model and biochar was placed directly over the carbon tape.

Journal Pre-proof 2.4 Adsorption experiments In order to evaluate the applicability of the adsorbent materials for DS removal, adsorption studies were performed in duplicate using a Dubnoff bath with orbital agitation at 140 rpm. In a typical adsorption assay, 0.1 g of the adsorbent was added to an Erlenmeyer with 25 mL of adsorbate solution.

The

contact

time,

temperature

and

adsorbate

initial

concentration were determined according to each specific test. At the end

oo

f

of the adsorption process, the samples were centrifuged for 5 min at 3000 rpm using a 320R universal centrifuge and, when necessary, the samples

pr

were diluted for analysis on the UVmini-1240 spectrophotometer.

e-

In order to evaluate the adsorption capacity of the adsorbents, the

%R=

m

C0 −Ce C0

∗V

rn

( C0 − Ce )

Jo u

qt =

al

using equations 4 and 5.

Pr

adsorbed amount (qt) in mg.g-1 and the removal capacity were calculated

∗ 100

(4)

(5)

where C0 and Ce are initial and concentration values (mg/L), m is the mass (g) of the adsorbent and V the volume (L) of the adsorbate solution.

2.4.1 Affinity assays A preliminary test was performed to evaluate the affinity of the adsorbate with the adsorbents. For this purpose, 0.1 g of adsorbent was added to 25 mL of DS solution (30 mg/L) and the samples were stirred at 30°C for 24

Journal Pre-proof h. The influence of pH on adsorption was also performed, using the same conditions but adjusting the solution pH to 2.0; 5.5; 7.0; 9.5 and 12.0 using HCl and NaOH solutions (0.1 M).

2.4.2 Kinetic studies The kinetic studies were performed at 30oC using the optimum pH value obtained in the previous assay and for different DS initial concentrations

oo

f

(50 and 200 mg.L-1). Samples were collected at 5, 10, 15, 30, 60, 120, 180, 240, 300, 360 and 420 min for the construction of the kinetic curve. experimental

data

were

correlated

with

pr

The

the

pseudo-first

order

optimum

parameters

were

found

using the non-linear

regression

Pr

the

e-

(Equation 6) and pseudo-second (Equation 7) models [40,41][41–44] and

model by the Statistica 13.3 software and applying the Quasi-Newton

rn

al

method.

qt =

k 2 tqe2

Jo u

qt = qe (1 − exp −𝑘1 t )

(1 +k 2 tqe)

(6)

(7)

where k1 and k2 are first and second order adsorption kinetic rate constants (min-1 and g.mg-1.h-1) respectively, qt and qe are the adsorbed adsorbent (mg.g-1) in time equilibrium, respectively.

2.4.3 Equilibrium studies

Journal Pre-proof Equilibrium studies were performed using the contact time obtained in the kinetic studies, at 30, 40, 50 and 60°C and DS concentrations of 50, 100, 200, 500, 750 and 1000 mg.L-1. The experimental data obtained were correlated by

the nonlinear regression module of the Statistica 13.3

software using the Quasi-Newton method with the Langmuir (Equation 8) [45], the Freundlich (Equation 9) [46], the Redlich-Peterson (Equation 10)

CeQ KL 1+ (CeKL )

e-

1

Pr

qe = Kf Ce nf

CeKrp

(1+arp Ce brp )

(9)

(10)

qS (KS Ce ) mS 1+ (KS Ce ) mS

(11)

Jo u

𝑞𝑒 =

rn

al

qe =

(8)

pr

qe =

oo

f

[47] and the Sips (Equation 11) [48] models.

where Q is the maximum adsorption capacity (mg.g-1), KL is the Langmuir constant (L/mg), KF is the Freundlich constant (mg.g-1)(mg.L-1) -1/nf, 1/nf is the heterogeneity factor, Krp (L.mg-1), arp (L.mg-1) and brp are RedlichPeterson constants, qS is the maximum adsorption capacity from the Sips model (mg.g-1), KS is the Sips constant (L.mg-1) and mS is the exponent of the Sips model.

2.4.4 Statistical evaluation

Journal Pre-proof In order to determine the accuracy of the models, the experimental data were evaluated by different statistical tools such as correlation coefficient (R2), relative mean error (ARE), adjusted coefficient of correlation (R2adj) and Akaike Information Criterion (AIC) presented in Equations 12 to 16, respectively [49].

∑n i =1 ( yi,exp −yi,mod ) ∑n ̅̅̅̅̅̅̅̅̅̅ i,mod ) i =1 ( yi,exp −y

2

(12)

2

∑ ni=1 |

SSE n

yi ,exp

) + 2np +

|

(13)

2np ( np +1) n− ( np + 1)

(14)

2

al

AIC = nln (

yi,exp −yi ,mod

pr

n

e-

100

Pr

ARE =

oo

f

R2 = 1 −

(15)

rn

SSE = ∑ni=1 (yi ,exp − yi ,mod )

where

yexp

( 1−R2 )(n−1)

Jo u

R2ajus = 1 −

(16)

n−np − 1

is

the

value

obtained

experimentally,

y mod

is

the

value

predicted by the model, np is the number of parameters of the model and n is the number of experimental points.

3. Results and Discussion 3.1 Synthesis yield

Journal Pre-proof The yields of the pyrolysis as well as the synthesis of the MgAl/LDH and the

MgAl/LDH-biochar

balances

and

the

composite

results

were

obtained

calculated

were

through

38.9,

68.7

the

and

mass 71.8%,

respectively. The pyrolysis process produced gaseous, liquid and solid products. Lower heating rates favour the production of biochar, as well as a lower final temperature. Gai et al. [50] evaluated the temperature influence in the pyrolysis of different materials and observed that the yield

oo

f

decreased with the temperature increase, due to the fact that higher temperatures favour more solid degradation and a greater amount of

pr

volatile materials. Therefore, the pyrolysis conditions, such as the heating

e-

rate of 10ºC/min and the final temperature at 400ºC, were chosen in order

Pr

to favour the biochar production, based in studies carried out by Meili et al. [38]. In the MgAl/LDH synthesis, it is important to note that the yield

al

may vary according to the manipulation in the process operation, since

rn

several losses in the handling can occur, mainly in the washing of the

Jo u

material.

3.2 Characterization

In order to characterize the materials produced, several analysis were performed, such as TGA, BET, EDXRF, XRPD, FT-IR and SEM. In the thermogravimetric materials

was

decomposition observed

along

analysis, the

the

thermal

temperature

stability

increase.

The

of

the mass

decreased due to chemical reactions such as decomposition, transitions and oxidation. Thus, it was possible to observe the temperature bands in which the decomposition was more pronounced. TGA and DTGA (Figure

Journal Pre-proof 1) indicated the mass loss and the differential thermal analysis, both as a function of time. By analysing the DTGA curve, it is possible to observe two main bands of mass losses. The first range occurs at temperatures up to 120ºC and refers to the moisture present in the biochar. The second range, which occurs in the range of 320 to 800°C, is related to the organic matter that has not been completely carbonized. According to Cortez et al. [51], the

hemicellulose,

a

lignocellulosic

cellulose

and

material,

lignin

and

which

consists

mainly

f

is

oo

endocarp

the

decomposition

of

of

these

pr

products occurs in different temperatures. In accordance with Yang et al.

e-

[52], the decomposition of hemicellulose occurs easily with greater mass

Pr

loss mainly between 220 to 315ºC, with maximum degradation at 268ºC. Cellulose degradation occurred in the range of 315 to 400ºC, reaching the

al

maximum at 355ºC. Lignin, due to its complex structure, was the most

rn

difficult to decompose, with slow degradation up to 900°C. Although

Jo u

hemicellulose and lignin were not completely carbonized in the pyrolysis process at 400ºC, this temperature was chosen in order to contribute to the solid fraction (biochar) formation, instead of gases and oils. The LDH has in its composition magnesium and aluminium cations and chloride

(Cl-)

anions

in

the

interlayered

region.

In

the

thermal

decomposition of the MgAl/LDH and the MgAl/LDH-biochar composite, shown in Figure 1 (b) and (c), respectively, it is possible to observe that the endothermic peaks of 100ºC and 240ºC relate to the evaporation of the water adsorbed on the LDH surface as well as the water intercalated in the layer together with the anions of Cl-. The third peak was observed

Journal Pre-proof at 390°C, which can be attributed to the structural dehydroxylation of the octahedral

layers

and,

consequently,

the

release

of

the

intercalated

anions [53]. The BET analysis was performed to obtain the surface properties of the materials. Table 1 presents the results obtained by adsorption of N2, in which the composite surface area was higher than that of the biochar, while the pore volume decreased. According to He et al. [54], if the pore

f

and consequently, the surface area increases, this

oo

volume decrease,

phenomenon is related to the impregnation of the biochar with the LDH.

pr

By analysis, it is possible to observe that both adsorbents presented a

e-

pore size range around 3.4-4.2 nm, and therefore are classified as materials

analysis,

was possible to construct the adsorption and desorption

it

[55].

From

the

data

obtained

from

the

BET

Pr

mesoporous

al

curves for all adsorbents, which are presented in Figure 2. According to

rn

IUPAC classification, the biochar isotherm can be classified as type II.

nonporous unrestricted

Jo u

Sing et al. [55] state that the reversible type II isotherm is in the form of a or

macroporous

adsorbent

multilayer-monolayer

material,

adsorption

which

presents

characteristic.

As

an the

adsorption and desorption curves presented in Figure 2 did not show the typical hysteresis

loop of

porous materials,

therefore

the biochar is

classified as nonporous according to the type of isotherm determined in the BET analysis. However, bio-carbons are porous materials and the result can be attributed to the fact that the biochar had no activation treatment. Therefore, the biochar pores were blocked, and this analysis could not identify them accurately.

Journal Pre-proof The adsorption and desorption isotherms presented in Figure 2 (a) and (b) correspond to type IV, according to IUPAC classification [55], in which the hysteresis cycles are associated to the condensation that occurs in the mesopores. The initial part of the isotherm is attributed to the monolayer-multilayer

adsorption,

since

it

behaves

similarly

to

the

corresponding one of a Type II isotherm. Then, there is the multilayer strip, which forms the hysteresis, characteristic of mesoporous structures.

oo

f

The present observed hysteresis can be classified as type H2, according to IUPAC, which is attributed to materials that are often disordered and pore

size

distribution

and

shape

are not

pr

the

well defined

[55,56].

e-

According to Crepaldi and Valim [23], the interlayer domain of LDHs

Pr

presents natural disorder due to the physical characteristics, such as ion exchange property and changes in hydration state.

results elements

and

chloride

in

the

MgAl/LDH

and

biochar/MgAl layered double hydroxide composite.

Jo u

coronata

aluminium

rn

magnesium,

al

X-ray fluorescence spectroscopy was performed to quantify the ions

obtained, for

the

LDH

synthesized

formation,

related to the cationic

layer

materials

where

presented

magnesium

and

the

Syagrus From the predicted

aluminium

are

and chlorine to the intercalated anion.

Moreover, for both samples, the percentage of magnesium was higher when compared to aluminium, as expected, due to the proportion of these ions added during the synthesis. Therefore, we can conclude that the materials were successfully synthesized. Figure 3 shows the results obtained from the XRPD analysis. According to the biochar X-ray pattern, there is the predominant characteristic of an

Journal Pre-proof amorphous solid, due to its wide form in the diffractogram [57]. The characteristic 22º peak has been described in several previous studies as being related to the biochar obtained from pyrolysis processes [58–60]. Shaaban et al. [59] stated that the peak 2θ = 22° is characteristic of the cellulose that is attributed to the crystallinity in the organized structure of the biochar source material. Mohanty et al. [58] obtained the broad peak for most of their studied biochars and related it to the formation of

oo

f

turbostratic carbon crystallites. The same behaviour was observed by Kim et al. [60] that when performing the pyrolysis of wood, observed the loss

pr

of the characteristic peaks of the cellulose and displacement of peaks to

e-

2θ between 22-24o, affirming that these results of the broad peaks are

al.

[61],

the

turbostratic

Pr

characteristic of turbostratic carbon crystallites. According to Gonçalves et character

of

a carbonaceous material can

al

originate from the structure of highly oriented pyrolytic graphite.

rn

The low height and large base width peaks in the LDH materials X-ray

particle

Jo u

spectrum are characteristic of materials with low crystallinity and small size

[62].

MgAl-LDH

and

the

composite

demonstrated

the

characteristics of layered compounds due to the repetition of the basal peaks

presented

in the

diffractogram

[63].

The basal spacing was

calculated according to Equation 3 using the values of the first three characteristic peaks (Table 2). The mean basal spacing for the MgAl-LDH was 7.84 Å and for the MgA/LDH-biochar was 7.96 Å. According to Cavani et al. [62], the basal spacing of 7.86 Å refers to the intercalated Clion, which is in agreement with the LDH materials produced in this work. From the basal spacing, it is possible to obtain information of the

Journal Pre-proof interlayer spacing, through the value of the layer width. The basal spacing represents the interlayer distance together with the layer formed by diand trivalent cations. According to Liu et al. [64] and Moraes et al. [65], the distance from the brucite layer for MgAl is 4.8 Å. The interlayer spacing for MgAl/LDH is 3.04 Å and for the MgAl/LDH-biochar composite is 3.16 Å, both in accordance with the literature. Regarding the peaks presented in the spectrum, Heraldy et al. [66] stated that the symmetric

oo

f

peaks at 2θ = 11o; 23o; 33o and 61o are characteristics of the LDHs and both MgAl-LDH and the composite exhibited characteristic peaks close to

pr

those values. According to Bolbol et al. [30] a peak at 2θ= 45.42° (plane

e-

018) is typical of the structure of hydrotalcite-like compounds, which were

Pr

indexed as the rhombohedral 3R stacking sequence of LDH layers. Cavani et al. [62] also obtained similar peaks for the MgAlCl-LDH. The

al

same behaviour in the XRD spectra was obtained in studies conducted by

rn

Cardoso et al. [63], Zhang et al. [68], Zimmermann et al. [69] and Meili et

Jo u

al. [25], in which the Cl- anions interspersed the layer formed by the Mg2+ and Al3+ cations. Therefore, the formation of LDH in the synthesized compounds was proven. The unidentified peak (around 2θ=31°) emerged in the XRD pattern, suggesting the presence of a small amount of other minerals,

which are

commonly

detected

for

biochars produced from

agricultural sources at pyrolytic temperatures [68]. Another interesting fact displayed in Figure 3 is the difference in the peaks intensity shown in the red color (LDH) when compared with the blue curve (composite). The composite XRD pattern showed lower intensities for the LDH related

Journal Pre-proof peaks due the decrease in the overall mass of the LDH for the analysed sample. The FTIR spectra are shown in Figure 4. The adsorption bands at the wavelengths around 3380 and 1630 cm-1 present in the LDH samples are attributed

to

H-O-H and O-H stretching vibrations,

vibrations of

the

hydroxyl group are due to the water molecules in the middle layer and by the water physically adsorbed [28,68]. According to Abdellaoui et al. [70],

oo

f

the mean intensity range at 1630 cm-1 occurs due to the bending mode of the water molecules and the band caused by the vibration of the anion

pr

interspersed in the lamella.

e-

The biochar sample showed a small peak in the range of 1600 cm-1.

water,

Pr

According to studies by Fonts et al. [71], the O-H stretch is related to the alcohol, phenols and carboxylic acid present

in the pyrolyzed

al

samples and to the loss of water from the surface of the adsorbed solids

rn

on the outer surface of the crystallite. The band observed at 1360 cm-1 in

Jo u

the LDH sample corresponds to the asymmetric CO 32- stretching, which can be attributed to carbonate contamination from the environmental air in the intermediate layer of LDH [64,68,69]. The band around 1017 cm-1 in the biochar sample is related to the C-O-H binding, corresponding to the compounds present in the biomass that gave rise to the biochar [52]. Peaks around 650 cm-1 can be attributed to the stretching vibrations of AlO or Mg-O bands, the cations by which LDHs are formed [70,72]. SEM micrographs obtained for the biochar are shown in Figures 5a-c, in which it is possible to observe a porous material, although the pores are closed,

once the charcoal did not undergo any activation treatment.

Journal Pre-proof Figures 5d-f depict the SEM micrographs for the composite, showing the LDH particles supported on the biochar porosity.

3.3 Adsorption studies 3.3.1 Affinity assays and pH effect In a preliminary test, no interaction between the biochar and DS was observed, probably because the biochar was not activated, and the pores

oo

f

were not available. For MgAl/LDH and the composite, removal efficiencies close to 60% were obtained for 30 mg/L of DS initial concentration.

6

shows

that

adsorption

occurred

e-

Figure

pr

Subsequently, the pH influence on DS adsorption was studied. without

large

variations,

Pr

achieving approximately 60% of removal at pH values from 5 to 12. On the other hand, adsorption was inhibited at pH 2. Once the DS pKa is

al

4.15, the molecule is in its neutral form at pH values close to the pKa,

rn

decreasing its solubility in water and causing precipitation. At pH values

Jo u

above the pKa, the DS molecule is ionized, presenting negative charges. In this form, the electrostatic interaction with the adsorbent is favoured, increasing the adsorption process [74-77]. Llinàs et al. [76] also observed that precipitation starts at a pH value close to the DS pKa. As the stock solution pH was 5.65, subsequent assays were performed without pH adjustment.

3.3.2 Kinetic studies The

adsorption

kinetics

were

evaluated

in

order

to

measure

the

adsorption rate, determining the equilibrium time and the influence of the

Journal Pre-proof DS initial concentration. The study was carried out with DS concentrations of 50 and 200 mg.L-1 for MgAl/LDH and 30, 50, 100 and 200 mg.L-1 for the composite. Figure 7 shows the kinetic curves and the fit of the experimental data with the pseudo-first order and pseudo-second order models. It was observed that DS presents different behaviour patterns according to the initial adsorbate concentration. For MgAl/LDH (Figure 7a), at 50

oo

f

mg.L-1, the equilibrium was reached in 1 h of contact, removing 78% of the pollutant. Nevertheless, for an initial concentration of 200 mg.L-1,

pr

equilibrium was reached only after 6 hours of contact, achieving up to

e-

82% of removal. The slower reaction rate at higher concentration can be

Pr

explained by the uptake mechanism being limited by the diffusion of nonsteroidal drugs tiaprofenic acid, flurbiprofen and ketoprofen adsorption

al

on LDH, already described by Conterosito et al. [78]. By analysing the

rn

MgAl/LDH-biochar composite (Figure 7b), more DS initial concentrations

Jo u

were examined to confirm this behaviour. For the lower concentrations, the equilibrium time was reached in the first hour, whereas for 200 mg.L-1 the equilibrium time was reached in 6 h with a removal of 70%. Probably, in the initial hours the adsorption occurred by physisorption. For higher concentrations,

besides

the

physisorption,

chemical

interactions

also

occurred inside the pores. The statistical values obtained by the adjustments are shown in Table 3. A comparison of the kinetic models helped to explain the observed adsorbent

behaviour,

as well as

controls the adsorption process.

to understand

the mechanism that

Journal Pre-proof For both adsorbents, at lower concentrations, the contact time data were better fitted to the pseudo-first order model, since the determination coefficients (R2) were higher and a smaller average relative error (ARE) was obtained when compared to the pseudo-second order model. On the other hand, for the highest concentration (200 mg/L), it was evident that the pseudo-second order model fitted better, since the R2 was higher and the ARE decreased from 4.38 to 2.96% for MgAl/LDH and from 9.03 to

oo

f

5.83% for the composite. Thus, the kinetics tend to be more complex when using this material (composite), implying that adsorption may not naturally,

and

the

modification

of

pr

happen

some

parameters

was

e-

necessary to obtain the maximum adsorption potential [79,80]. At the

Pr

same time, the limiting mechanism in this process is chemical adsorption, involving valence forces through the sharing or exchange of electrons

al

between adsorbent and adsorbate, which are slower reactions, justifying

rn

the need of 6 h to reach the equilibrium [43].

Jo u

According to studies carried out by Ho and McKay [81], when the initial adsorbate concentration is very high, the best fit is usually with the pseudo-first

order

model,

while

for

lower

concentrations

the

best

correlation is to the pseudo-second order model. The same behaviour was

observed

by

Azizian [79].

However,

in the present

work,

the

behaviour was the opposite. Probably because DS adsorption occurred first

on

the

adsorbents

surface,

characterizing

faster

reactions.

Subsequently, through diffusion, adsorption became slower under higher concentrations. The kinetic study showed that the MgAl/LDH provided better

removal when compared to the composite.

This characteristic

Journal Pre-proof behaviour may be related to the lack of interaction between the biochar and LDH observed in preliminary tests. Therefore, the synergistic effect between them,

when in composite form,

results in lower values of

capacity of adsorption than the isolated clay. However, the LDH itself has a low mechanical resistance, which would not be feasible for applications in adsorption columns. The use of the composite would overcome these

oo

as well as the utilization of agricultural wastes.

f

mechanical problems, preserving the adsorption properties of MgAl/LDH,

pr

3.3.3 Equilibrium studies

e-

In order to determine the mechanism of interaction between adsorbent

Pr

and adsorbate, as well as the adsorption characteristics, isotherms were studied using the composite, since this material had better mechanical

al

stability and maintained the properties of the MgAl/LDH. The adsorption

rn

study was performed with initial DS concentrations of 50, 100, 200, 500,

Jo u

750, and 1000 mg.L-1, at 30, 40, 50 and 60ºC (Figure 8). From the results obtained, the temperature increase favoured the DS adsorption, indicating an endothermic process [82]. The experimental data were compared with theoretical models such as Langmuir, Freundlich, Redlich-Peterson and Sips and the fitting of the correlations was based on the statistical parameters obtained, such as the R2, ARE, R2adjus and AIC (Table 4). From the curves shown in Figure 8, adsorption occurs favourably at lower temperatures, whereas the ones with higher temperatures tend to be extremely

favourable.

However,

when

evaluating

the

values

of

the

equilibrium constants obtained by the Langmuir and Sips models, the K

Journal Pre-proof values

decreased

with

the

temperature

increase.

This

behaviour

is

characteristic of chemisorption processes, which can be justified from the results obtained in the thermodynamic studies. It was also evident that with the temperature increase, the Langmuir and Freundlich models did not show good correlation with the experimental data, probably because these models have only two parameters, working better for linear curves with little concavity. In addition, the Langmuir model implies that every

oo

f

adsorption is homogeneous, and each active site has equivalent energy and that adsorption occurs in monolayers. However, the material studied, presents

different

anions

intercalated

pr

MgAl/LDH-biochar,

in the layer,

e-

such as chlorides and hydroxyls, resulting in active sites with different

Pr

energies.

types

active

sites

increment.

and

Nevertheless,

increases this

type

exponentially of

process

with

the

is

not

Jo u

concentration

of

rn

several

al

According to the Freundlich model, adsorption occurs heterogeneously in

physically possible, so it can be concluded that the Freundlich model does not fit well when using high adsorbate concentrations, requiring the use of moderate concentrations [83]. Therefore, as the assays were performed in a wide range of concentrations, the Freundlich model did not present good adjustments. For the Langmuir model, the separation factor was also calculated (RL) for the initial concentrations at the different temperatures. The RL values ranged from 0.14 to 0.79, indicating that the adsorption process is favourable. By checking the heterogeneity factor of the Freundlich isotherm, it is noted that the values obtained are between

Journal Pre-proof 1.6 and 2.0. This implies a favourable adsorption, since the values are in a range between 1 and 10. For values of n equal to 1, the interaction between adsorbent and adsorbate tends to be linear. Moreover, very high values of n imply a stronger interaction. The separation factor and the heterogeneity factor confirmed the favourable behaviour for the isotherms and are presented in Figure 8. The Redlich-Peterson and Sips models are hybrids of the Langmuir and overcoming

some

of

their

limitations.

f

isotherms,

Thus,

as

oo

Freundlich

expected, the experimental data presented better correlation with these

pr

models. Moreover, they are three parameters isotherms, against two in

e-

the Langmuir and Freundlich models. Sips was the one with the best fit to

Pr

the experimental data, with R2 higher than 0.99 at all temperatures and lower relative mean errors. Analysing the R2adjus values, which reflects the

al

degree of freedom of the models and the number of experimental data,

As

the

Sips

Jo u

correlation.

rn

the values were close to 1 for the Sips model, proving once again the best model

is

a

combination of

Langmuir

and

Freundlich isotherms, it allows the prediction of the adsorption capacity of the isotherm monolayer

at high concentrations of adsorbate [84]. In

addition, as this model has three parameters, it can better describe the adsorption process on heterogeneous surfaces. So, it reduces to the Freundlich isotherm at

low concentrations and predicts the saturation

surface by the Langmuir isotherm at high concentrations, bypassing the limitations of these two parameter models [3]. Therefore, after confirming that Sips was the best fit model with the experimental

data,

it

was

used

to

predict

the maximum adsorption

Journal Pre-proof capacity

of

the

MgAl/LDH-biochar

composite,

which was 138.83 and

168.04 mg.g-1 at 30 and 60o C, respectively. This result was compared to other studies [4,74, 84 and 85] using several adsorbents to remove DS from

water

presented

in Table

5.

The

MgAl/LDH-biochar

composite

presented higher adsorption capacity over other adsorbents. Therefore, the LDH supported in the Syagrus coronata biochar is a promising material for DS adsorption, since it presented a very satisfactory removal

oo

f

efficiency and a good maximum capacity of adsorption when compared

pr

with other adsorbents.

e-

3.3.4 Thermodynamics

Pr

The free energy values of Gibbs (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were determined using equations 17 and 18 to evaluate the mechanism

al

involved in the adsorption process. The slope and angular coefficients of

rn

the curve ΔG° (kJ.mol-1) as a function of (Ke) provided the values of ΔH°

Jo u

and ΔS°, respectively. Ke values were obtained from the Sips model, which was the isotherm model that best fitted the equilibrium data.

Table

6 shows the results of the thermodynamic parameters obtained.

 G    R .T . ln K e

 G    H   T . S 

(17)

(18)

where R is the universal gas constant (8.314 J.mol-1.K-1), T is the temperature (K) and Ke is the thermodynamic equilibrium constant.

Journal Pre-proof From the negative values of ΔG o it is possible to state that the adsorption process occurred spontaneously and the negative values of ΔHo indicated an exothermic process. The magnitude of ΔHo (-111.61 kJ.mol-1, between 80 and 450 kJ.mol-1) confirmed the equilibrium results, that adsorption occurred

by

a

process

of

chemisorption

[49].

The

system

entropy

increase indicated by the positive value of ΔSo, suggested that a change occurs in the structure of the adsorbent. Furthermore, it can be assumed

oo

f

that a random fixation of adsorbate occurred at the active sites present on the adsorbent surface. These results have been corroborated by several

e-

pr

works found in the literature [25,86,90,91]. 4. Conclusions

Pr

In this contribution we proposed for the first time the removal of DS from

composite

as

al

water using the Syagrus coronata biochar/MgAl layered double hydroxide an

adsorbent.

For

this

purpose,

the

material

was

rn

successfully synthesized, which was demonstrated through the several

Jo u

characterization analyses performed. From the adsorption study, it was evident that the layered materials achieved a high efficiency for DS removal (≈ 82% for the MgAl/LDH-biochar composite at the concentration of 200mg/L and 6 h of contact time). The kinetic studies showed that the equilibrium time was dependent on the adsorbate initial concentration. For low

concentrations,

physisorption,

whereas,

the

predominant

with

the

mechanism

increase

of

DS

would

be

concentration

the the

adsorption tended to be more complex and, consequently, slower. In order to study the adsorption isotherm, several models were adjusted to the experimental data and it was observed that the Sips model was the

Journal Pre-proof one that presented the best fit, according to the statistical parameters. In short,

Syagrus

composite

coronata

demonstrated

biochar/MgAl very

good

layered

double

performance

in

hydroxide

DS

removal,

especially when compared with other adsorbents from the literature, being a potential adsorbent to remove this emerging pollutant from water.

Acknowledgments

e-

pr

oo

f

The authors thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/Brazil) and Fundação de Amparo à Pesquisa do Estado de Alagoas (FAPEAL/ Brazil).

[1]

Pr

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Removal of sodium diclofenac from aqueous solution by adsorbents

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derived from cocoa pod husks, J. Environ. Chem. Eng. 5 (2017) 1465– 1474. doi:10.1016/j.jece.2017.02.018.

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Journal Pre-proof FIGURES

Figure 1. Thermogravimetric degradation curves of the biochar (a), the MgAl/LDH (b)

e-

pr

oo

f

and the MgAl/LDH-biochar composite (c).

Jo u

rn

al

Pr

(a)

(c)

(b)

Journal Pre-proof Figure 2. N2 Adsorption/desorption curves of the biochar (a), the MgAl/LDH (b) and

oo

f

the MgAl/LDH-biochar composite (c).

Jo u

rn

al

Pr

e-

pr

(a)

(c)

(b)

Journal Pre-proof Figure 3. XRPD of the adsorbents under study.

22.23º

Intensity

11.20º 22.59º

Biochar

34.66º 45.42º

60.81º

11.04º

f

MgAl/LDH

34.62º

20

40

60.64º

pr

0

45.42º

oo

22.42º

60

Jo u

rn

al

Pr

e-

2

MgAl/LDH-biochar

80

Journal Pre-proof Figure 4. Infrared spectroscopy of the adsorbents under study.

Biochar

1602

Transmittance

1631

1360

MgAl/LDH-biochar

f

oo 3000

e-

pr

3384

3500

640

1627 1366

3384

2500

2000

-1

rn

al

Pr

Wavenumber (cm )

Jo u

4000

1017

MgAl/LDH

1500

651 1000

Journal Pre-proof Figure 5. SEM micrographs of the biochar (a, b, c: 200x, 500x, 2000x)

Jo u

rn

al

Pr

e-

pr

oo

f

and the MgAl/LDH-biochar composite (d, e, f: 200x, 500x, 2000x).

Journal Pre-proof Figure 6. Effect of pH on DS adsorption onto MgAl/LDH-biochar

Jo u

rn

al

Pr

e-

pr

oo

f

composite.

Journal Pre-proof

Figure 7. DS adsorption kinetics onto the MgAl/LDH (a) and the MgAl/LDH-biochar

e-

pr

oo

f

composite (b).

Jo u

rn

al

Pr

(a)

(b)

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Figure 8. DS adsorption isotherms onto the MgAl/LDH-biochar composite.

Journal Pre-proof TABLES

Table 1. Surface areas, pore volumes and pore dimensions of the adsorbents under study. Surface area (m2/g)

Pore volume (cm3/g)

Pore size (nm)

Biochar

71.61

0.27

3.98

MgAl/LDH

212.89

0.24

4.18

Composite

168.02

0.16

3.50

Jo u

rn

al

Pr

e-

pr

oo

f

Material

Table 2. Basal Spacing of the layered materials under study. MgAl/LDH

Peaks 1 2 3 Average

Composite d (Å) 7.894 7.866 7.758 7.839

Peaks 1 2 3 Average

d (Å) 8.008 7.897 7.988 7.964

Journal Pre-proof

f

Table 3. Kinetic parameters for DS adsorption onto MgAl/LDH and MgAl/LDH-biochar

Pseudo-first order R2

R2

5.07

-8.54

0.9723

9.737

5.45

-6.15

4.38

15.23 0.9948

43.46

2.96

6.68

0.9788

9.349

200

0.9850

39.11

30

0.9839

50

0.9853

100

0.9609

200

0.9687

e-

50

qe (mg/g) ARE

AIC

5.42

4.83

-12.81 0.9764

5.74

5.31

-10.12

8.85

6.05

-11.37 0.9968

9.58

2.33

-25.03

18.97

14.53

11.33 0.9754

22.08

11.95

8.08

9.03

19.65 0.9853

39.46

5.83

12.87

al

rn Jo u

Pseudo-second order

AIC

qe (mg/g) ARE (%)

MgAl/LDH

Composite

pr

Concentration (mg/L)

Pr

Material

oo

composite.

33.03

Journal Pre-proof

Table 4. Equilibrium parameters for DS adsorption onto MgAl/LDH-biochar composite.

Sips

Jo u

rn

f

40°C 155.55 0.0056 0.9894 0.9823 0.7734 0.6302 0.4586 0.2519 0.1877 0.1441 24.01 27.15 1.8800 4.2931 0.9654 0.9423 40.74 34.28 0.8333 0.0040 1.0459 0.9896 0.9740 23.08 37.08 137.16 0.00330 1.1708 0.9909 0.9773 18.27 36.26

oo

al

RedlichPeterson

pr

Freundlich

30°C 116.52 0.0060 0.9929 0.9882 0.7546 0.6066 0.4393 0.2397 0.1762 0.1379 11.47 21.88 2.0104 3.9605 0.9844 0.9740 22.27 26.59 0.8946 0.0240 0.8280 0.9952 0.9880 11.60 29.53 135.83 0.00869 0.8593 0.9934 0.9835 12.48 30.87

e-

Langmuir

Parameters qmáx (mg/g) KL (L/mg) R2 R2adj 50 mg/L 100 mg/L 20 mg/L RL 500 mg/L 750 mg/L 1000 mg/L ARE AIC n KF [(mg/L)(L/g)1/n] R2 R2adj ARE AIC KR (L/mg), (L/mg)β β R2 R2 adj ARE AIC qmáx(mg/g) Ks (L/mg) mS R2 R2 adj ARE AIC

Pr

Models

50°C 201.47 0.0057 0.9741 0.9568 0.7608 0.6170 0.4839 0.2489 0.1856 0.1429 41.43 34.77 1.7596 4.7162 0.9320 0.8867 58.47 40.56 0.9928 0.0009 1.2692 0.9818 0.9545 37.06 42.65 144.91 0.00056 1.6909 0.9939 0.9848 18.07 36.06

60°C 269.09 0.0050 0.9479 0.9132 0.7902 0.6528 0.4853 0.2724 0.2026 0.1571 81.01 41.22 1.6135 4.6155 0.9039 0.8398 96.71 44.90 1.1333 0.0001 1.5478 0.9645 0.9113 70.60 48.92 168.04 0.00008 2.2005 0.9930 0.9825 25.90 39.16

52

Journal Pre-proof

Table 5. Comparison of maximum adsorbed DS onto different adsorbents. Temperatur Concentration e (mg/L) o ( C)

Adsorbent

Maximum adsorbed amount (mg/g)

Reference s

5–30

22

76.98

[70]

Activated carbon

25–100

25

83.0

[4]

0-50

25

22.22

[81]

Olive stones activated carbon

25–150

23

11.0

[82]

Activated carbon from cocoa pod husk

10-30

25

0.47411

[83]

MgAl/LDH-biochar composite

50–1000

30/60

135.83/168.05

This study

oo

Jo u

rn

al

Pr

e-

activated carbon

pr

Cyclamen persicum

f

Isabel grape bagasse

53

Journal Pre-proof

Table 6. Thermodynamics parameters for DS adsorption onto MgAl/LDH-biochar composite. ΔG°(kJ/mol) ∆H° ∆S° (kJ/mol) (kJ/mol) 303.15K 313.15K 323.15K 333.15K -24.71

-20.09

-111.61

-0.271

rn

al

Pr

e-

pr

oo

f

-28.57

Jo u

-29.6

54

Journal Pre-proof Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

oo

f

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

pr

Lucas Meili, Dr.

e-

Federal University of Alagoas

Jo u

rn

al

Pr

[email protected]

55

Journal Pre-proof Highlights MgAl/LDH composite and biochar from Syagruscoronata endocarp were produced.

-

Emerging pollutant Diclofenac sodium was successfully removed by the materials.

-

Materials were characterized by TGA/DTGA, adsorption of N2, XRD, XRPD, FT-IR, SEM.

-

Isotherms fit to the Sips model. Adsorption capacity of 168 mg.g-1 was achieved.

Jo u

rn

al

Pr

e-

pr

oo

f

-

56

Journal Pre-proof Abstract: The increasing levels of diclofenac sodium (DS) detection in aquatic environments have been causing great concern, thus the efficient removal of DS is of urgent importance. In this study, for the first time a composite

with

MgAl/layered

double hydroxide

supported on Syagrus

coronata biochar was fabricated, characterized and used for diclofenac sodium

adsorption.

The

physicochemical

characterizations,

including X-

ray, FT-IR, N2 adsorption and microscopy, confirmed the composite was

oo

f

successfully synthesized. Adsorption batch experiments demonstrated a high DS removal efficiency (higher of 82% for 200 mg.L -1 of DS). Kinetic

providing

maximum

adsorption

e-

chemisorption

pr

and equilibrium studies indicated the limiting adsorption mechanism was capacity

of

138.83

and

Pr

168.04 mg.g-1 at 30 and 60o C, respectively. Thermodynamics suggested DS adsorption was spontaneous, exothermic and created modification in

al

the adsorbent structure. All these findings suggested that the composite is

rn

an efficient and promising material for DS-contaminated water treatment,

Keywords:

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achieving superior adsorption capacity compared with other adsorbents. high

capacity

removal;

clays;

emerging

pollutants;

pharmaceuticals; wastewater

57