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International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 15 No: 04 10

153204-9191-IJCEE-IJENS ©August 2015 IJENS

I J E N S

Physicochemical Investigation of DYE Adsorption

By Brazilian Water Hyacinth (EICHORNIA

CRASSIPES) Rivadávia Tavares Martins Filho

a, Haroldo C.B Paula*

a, Regina C.M. Paula

b, Ronaldo F Nascimento

a ,

Ari Clecius Alves de Limaa, Diego de Quadros Melo

a,c

a Department of Analytical and Physical Chemistry, Federal University of Ceará, 60451-970, Fortaleza, CE-Brazil b Department of Organic and Inorganic Chemistry, Federal University of Ceará, 60455-760, Fortaleza, CE-Brazil

c Department of Chemistry, Federal Institute of Education and Science of Piauí, Rodovia Br 407, S/N, Campus Paulistana CEP:

64750-000, Paulistana, PI, Brazil. *email : [email protected]

Abstract-- A full and detailed study was conducted with

different parts of Brazilian water hyacinth (Eichornia crassipes),

in order to investigate plant physicochemical properties and

adsorption mechanism of a model dye (methylene blue) in

aqueous solution. Different plant parts were evaluated by

infrared spectroscopy and thermal analysis techniques. Several

adsorption experimental parameters were analyzed such as

contact time, effect of adsorbent dose, dye initial concentration,

pH and temperature effect. The adsorption thermodynamics and

kinetics were also investigated. The Langmuir, Freundlich,

Temkin and B.E.T. isotherms were used to determine parameters

such as the maximum adsorption capacity (qmáx), using linear

and non-linear models, whereby it was found that there is great

discrepancy between qmáx values obtained by linear and non

linear isotherms of aforementioned models, which seems to point

out to the inadequacy of these linear models for MB adsorption

on WH plant parts. Thermodynamic data revealed that MB

adsorption is exothermic and thermodynamically favored, being

ruled by physical connections, likely involving weak Van der

Waals forces.

Index Term-- Adsorption; Water hyacinth; Dyes; Isotherms;

nonlinear model 1.0 INTRODUCTION

In recent years, much have been spoken by the

academia in Brazil and worldwide, on waste, its disposal,

accumulation and final destination, mainly because different

wastes produced by humans pose serious environmental

problems. Among them, it can be refer to those from textile,

paint and plastic industries, which are highly colored effluents,

presenting troublesome treatments and final disposals [1]. It is

well known that uncontrolled waste disposal would change the

dynamics of natural water reservoirs, leading to disturbances

in an ecological system [2].

There are more than 10,000 commercially available

dyes [3], mostly having complex chemical structures [4],

being usually very difficult to decompose [5]. Methylene blue

is a dye with chemical formula C16H18N3SCl, having several

harmful effects on humans, although not highly dangerous. It

is harmful when it is ingested and when inhaled or in contact

with skin. Moreover, it causes eye irritation [6].

Conventional methods of wastewater treatment such as

coagulation, photobleaching and ozonation, are not very

effective in removing stains, and the method of adsorption on

activated charcoal is more frequently employed, being more

efficient, although more expensive [7]. Hence the great

interest on different low cost biosorbents which could be

applied to replace activated carbon on adsorption process.

Several biosorbents have been used, including the bark of the

wood [8], rice husk [8], banana peel [9], bamboo-based

activated carbon [10], hazelnuts shell [11], water hyacinth

[12,13], corncobs [14], sawdust [15] and treads of tire [16].

Water hyacinth (WH ) has also been used as biosorbent after

chemical treatments [17], after washing in acid medium [18],

treated with nitric acid [19], treated with phosphoric acid [20]

and together with activated carbon, after treatment with

phosphoric acid [21].

The water hyacinth (Eichornia crassipes) plant is a

noxious weed roots present in fresh water and is listed as one

of the worst aquatic weeds in the world [22]. Its high

productivity and tolerance to variation of nutrients,

temperature and pH levels have led to many of the

environmental and economic problems such as biodiversity

loss, interference with navigation, irrigation and power

generation [22].

Notwithstanding some studies carried out on this plant,

there is a lack of full information on infrared spectroscopy,

thermogravimetric analysis and differential scanning

calorimetry of water hyacinth from northeastern Brazil. This

claims to a more detailed characterization, focusing on its

potential use as a dye adsorbent.

In this sense, this study aimed to carry out a

comprehensive investigation encompassing all parts of the

water hyacinth of Northeastern Brazil, in order to evaluate its

potential as a dye adsorbent, specifically, of methylene blue,

in order to compare its properties with those of plants of

different countries.

2.0 EXPERIMENTAL

2.1 Materials and methods

Methylene blue (MB) (CI 52015) of chemical formulae

C16H18N3SCl, sodium hydroxide and chloridric acid were

purchased from Reagen Products Laboratorios Ltda.



I J E N S

Water hyacinth (WH) (Figure 1a) used in this study was

collected in the Lagoon of Parangaba, in Fortaleza, state of

Ceará and a voucher specimen of the sample was deposited in

the Herbarium Prisco Viana, of the Biology Department of the

Federal University of Ceará-UFC, under number 49095. Plant

parts were thoroughly washed with water to remove sand and

mud and immersed in distilled water, then were cut and

separated into parts, and put to dry in an oven at 70 °C. After

that, they were crushed, ground, passed through 60 mesh sieve

and stored in proper location.

2.2 Characterization techniques

FT-IR, DSC and TGA were used to evaluate the

physicochemical characteristics of WH. Fourier transform

infrared (FTIR) spectroscopy of the different plant parts of

water hyacinth were recorded using KBr pellets on a Perkin

Elmer apparatus, with wavelengths ranging between 400 and

4000 cm-1

. Scanning electron microscopy (SEM) images of

the biosorbents were obtained with JEOL TSM 5800, 30 kV.

The WH thermal properties were evaluated by

thermogravimetric analysis (TGA) in a Shimadzu equipment,

model 50 TGA, using a heating ramp of 10 °C min-1 from 25

to 900 °C, and differential scanning calorimetry (DSC) in an

Shimadzu equipment model DSC 50 by heating about 5 mg of

samples from 25 to 900 °C, using a heating rate of 10 °C min-

1.

2.3 Adsorption/desorption tests of WH for methylene blue

A stock solution of concentration 500 mg L-1

dye was

prepared by dissolving the dye in distilled water and the

experimental solutions were obtained by diluting the stock

solution in exact proportions in order to obtain solution

concentrations in the range 10-250 mg L-1

. Adsorption

experiments were performed in duplicate (n=2) in a

refrigerated benchtop incubator,( CIENTEC), model CT-

712R, with rotation of 75 rpm and temperature between 25 °C

to 45 °C. Samples were placed in 50 mL beaker containing 30

mL of dye concentrations at different initial pH. The initial pH

of the solutions was adjusted with HCl and NaOH 0.1 mol L-1

using a pH meter (PHTEK), model PHS-3B. Biomass

concentrations in the range 0.3 to 3.0 g L-1

were added to each

beaker. After shaking the vials in predetermined time

intervals, samples were removed and separated from the

biomass of the dye solution by centrifugation.

The desorption experiments were performed in two

steps: adsorption and desorption . In the adsorption step, 60

mg of biosorbent was added to 30 mL of dye solution of

concentration 100 mg L-1

. The solutions were maintained at 25

° C in a refrigerated incubator (CIENTEC model CT- 712R) ,

at 75 rpm, for 24 h. In the desorption step, the biosorbent

containing the dye was placed in a 50 ml beaker containing 30

ml of the eluent ( 0.1 M HCl ) and maintained under constant

stirring (75 rpm) for a period of 24 h, at 25 ° C.

The concentrations of dye solution of the supernatant

were estimated by measuring absorbance at a maximum

wavelength (methylene blue, λmáx = 660 nm) in the Micronal

spectrophotometer, model B582, using a calibration curve.

3.0 RESULTS AND DISCUSSION 3.1. Physicochemical characteristics of WH

3.1.1FTIR spectroscopy

The FTIR spectroscopic analysis of parts of water

hyacinth components is shown in Figure 1b. The FTIR spectra

indicate that the samples have similar absortion pattern, with

common bands in the range of 1100 cm-1

, 1600 cm-1

and 3500

cm-1

. The bands at 900, 1060 and 1380 cm-1

are characteristic

of carbohydrate units [23]. Shoulders at 1710 cm-1

suggests

the possibility of intermolecular associations of carboxylic

functions [24]. The bands at 1635 cm-1

can be assigned to

stretching vibrations of the carboxylate anion [23] or O-H

stretch of water molecules links. The vibrations of O-H

stretching that appear with a broadband at 3410 cm-1

show the

presence of water and alcoholic hydroxyl groups [25] and a

small peak at 2924 cm-1

assigned to stretching vibrations of C-

H. These results are similar to those reported for

polysaccharides such as cellulose and hemicellulose and

lignin. Peaks of the lignin components are shown at 1030 cm-

1, 1160 cm

-1, 1230 cm

-1 for guaiacyl and 1110 cm

-1, 1320 cm

-1

for syringyl [26].

The presence of hydroxyl biomass characterizes the

affinity for basic dyes, such as MB, thus serving as active sites

for adsorption.



I J E N S

4000 3500 3000 2500 2000 1500 1000 500

wavenumber / cm-1

Root

Stolon

Rhizome

Petiole

3410

2924

1635

1060

1030

1110

9001380

1160

1230

1320

1710

Fig. 1. (a) Eichornia crassipes plant parts: 1 – Rhizome (partially visible), 2 – stolon, 3 – Root, 4 – Petiole, 5 – Flower.; (b) FTIR spectrum of the different parts

of water hyacinth.

3.1.2 Thermal analysis

Biomasses have as main components polysaccharides

such as cellulose and hemicellulose, and other organic

polymers such as lignin and their main functional groups are

OH, CH, C-N, CH2OH, COOH [13,27]. Most lignocellulosic

materials have generally in their composition a mixture of 40-

80 % cellulose, 15-30 % hemicellulose and lignin 10-25 %

[27].

The thermogravimetric curves (TGA) of the different

parts of the water hyacinth are shown in Figure 2a. For the

root, only two stages of mass losses are observed while for the

rhizome, stolon and petiole three events are detected. The first

event in all samples is due to loss of residual moisture, which

follow the decreasing order rhizome > petiole > root > stolon.

The second event corresponds to hemicellulose degradation, at

300 °C, while cellulose and lignin start to decompose at

temperatures above 300 °C [27]. Thermograms revealed that

WH plant parts have stability in the order: petiole < root <

rhizome < stolon. Above 700 °C, root and petiole exhibit high

ash content.

0 200 400 600 800 10000

20

40

60

80

100

0 200 400 600 800 1000

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,0

0,1

d(m

/m0)d

T (

%/°

C)

Temperature (°C)

Wei

gh

t /

%

Temperature / °C

Root

Stolon

Rhizome

Petiole

(a) (b)



I J E N S

0 100 200 300 400 500 600-4

-3

-2

-1

0

1

2

3

4

exo

DSC

/ m

W

Temperature / °C

Root

Stolon

Rhizome

Petiole

Fig. 2. (a) Thermogravimetric and DSC (b) curves for the different parts of water hyacinth.

The peak decomposition temperatures (DTG) of WH

parts and ashes at 900 °C are shown in insert of Figure 2a and

listed in Table I. It can be seen that in the lower temperature

region, the highest DTG value was obtained for the root and

the lowest for stolon, while at temperatures above 700 °C,

high values were obtained for root and pethiole. This figures

are in good agreement with the fact that root and petiole have

high ash contents, in values higher than those previously

reported [21].

Table I Peak decomposition temperatures of the different parts of water hyacinth

Sample Peak temperatures (°C) Residue ( %)

Root 322 19.59

Stolon 287 1.57

Rhizome 303 16.23

Petiole 316 21.30

DSC curves obtained for different parts of the water

hyacinth are shown in Figure 2b. All plant parts present

endothermic peaks in the range 50 to 150 °C due to water

evaporation. Above 200 °C most of the thermal decomposition

was exothermic.

Double exothermic peaks were observed for WH root,

in the temperature range 250-350 °C, whereas the stolon

presents a single large peak in the same region. Similar data

were reported [28] and events were attributed to hemicellulose

and lignin decompositions in neem leaf powder. Rhizome and

petiole show much smaller exothermic peaks.

The region of thermal decomposition of biomass

depends on its main components, namely cellulose,

hemicellulose and lignin [29]. Hemicellulose has a

decomposition temperature lower than cellulose and lignin

[30]. Exothermic peaks at temperatures of approximately 175

°C are related to the hemicellulose degradation. Double

exothermic peaks in the range of 250-350 °C are attributed to

decomposition of hemicellulose and lignin. The

decomposition of cellulose is reported to start with an

endothermic peak around 300 °C and ends with exothermic

peaks near 370 °C.

3.2. Adsorption experiments

3.2.1Effect of dosage

The effects of the dosage of different parts of water

hyacinth on MB dye adsorption are shown in Figure 3a. The

percentage of dye adsorbed increased with increasing biomass

concentration in the range 0.3 to 3.0 g L-1

, likely due to the

fact that the greater the amount of biomass the greater is the

amount of available adsorption sites [31], but the maximum

adsorption capacity will decrease because there will be an

increased availability of adsorption sites, thus increasing the

interaction and aggregation of particles, as a consequence of

high adsorbent concentration [32]. Such aggregation would

result in a decrease in total surface area of the adsorbent [33].

The ratio of dye adsorbed by the root increased from

46.1 to 98.2 % for the petiole from 42.2 to 87.5 %, for the

rhizome from 50.1 to 93.2 % and for the stolon from 50.2 to

91.3 %. The highest dye adsorption was observed for the root.

For most plant parts, dye adsorption equilibrium was achieved

at adsorbent concentration above 2.0 g L-1

, below this value,

all plant parts exhibits statistically the same adsorption

(b)



I J E N S

figures. Thus, the concentration of adsorbent chosen for

further experiments was 2.0 g L-1

.

0 1 2 3

40

50

60

70

80

90

100

Dye

sor

bed

ratio

/ %

Sorbent dose / (g L-1)

Root

Stolon

Rhizome

Petiole

Fig. 3. Effect of dosage on the adsorption of methylene blue by water hyacinth biomass, dye concentration: 100 mg L-1, particle size: 60 mesh, contact time: 24

hours, pH 6.5 to 7.0, 25 °C.

3.2.2 Influence of initial dye concentration

The influence of dye concentration on WH adsorption

was investigated. As shown in Figure 4, when dye

concentration was increased from 50 to 250 mg L-1

, the

percentage of adsorption by the root decreased from 97.6 to

86.9 %, by the petiole from 86.1 to 75.7 %, by the rhizome

from 92.7 to 86.7 % and by stolon from 90.7 to 87.8 %. At

MB concentration range 50-250 mg L -1

, the lowest adsorption

was observed for petiole and the highest for root.

0 50 100 150 200 25070

80

90

100

Dy

e s

orb

ed

rati

o /

%

Dye concentration / (mg L-1)

Root

Stolon

Rhizome

Petiole

Fig. 4. Influence of dye concentration on methylene blue adsorption on different parts of water hyacinth biomass (adsorbent concentration: 2 g L-1, particle size:

60 mesh, contact time: 24 h, pH 6.5 to 7.0, 25 °C).

At low dye concentrations the adsorption ratio is high

because the biomass is able to adsorb large amount of dye

molecules, but at high dye concentrations, the adsorption sites

become progressively occupied, thus reducing the percentage

of dye adsorbed [27].



I J E N S

Gong et al [3] reported similar results using peanut

shells for MB adsorption, where by dye adsorption

percentages decreased from 95.97 to 62.11 %.

3.2.3 Effect of initial pH

The pH is a major factor in adsorption processes in

aqueous solutions, because it directly affects the surface

charge of adsorbents and the degree of ionization of the

adsorbate, thus contributing to the dissociation of functional

groups on the surface adsorption sites of adsorvent [11].

The effects of initial pH on the adsorption ratios of MB

dye were investigated at 25 °C in pH range from 2 to 12. As

shown in Figure 5, in pH 2, removal is minimal, for all plant

parts, taking values in the range 46.6 – 72.8 %. At pH 4-6,

adsorption remains fairly constant in the range 85 -95 %, for

all plant parts, being maximal for root.

2 4 6 8 10 1230

40

50

60

70

80

90

100

Dye

sorb

ed r

atio

/ %

Initial pH

Root

Stolon

Rhizome

Petiole

Fig. 5. Effect of initial pH on the adsorption of methylene blue with water hyacinth biomass as an adsorbent (adsorbent concentration: 2.0 g L-1, particle size: 60

mesh, contact time: 24 h);

In pH 12 the sorption is maximum for all plant parties,

reaching 99.4 % for the root. It is likely that the low

adsorption of methylene blue at low pH values indicates the

possibility of formation of positive charges on the adsorbent,

thus preventing the adsorption of methylene blue. In addition,

at that pH range the adsorption of methylene blue may have

been hindered, due to electrostatic repulsion between the

positively charged dye cations. It also may have been a

competition between H+ ions and protonated dye in the

adsorption sites [34].

According to Tarawou [13], using water hyacinth for

the adsorption of methyl red dye, there was a better adsorption

in alkaline medium, reaching the best values at pH 8.

3.2.4 Effect of temperature

The effect of temperature on the adsorption of

methylene blue on different parts of WH, in a temperature

range from 298 to 318 K, is shown in Figure 6. It can seen that

adsorption increases slightly (in the range 96.54 – 97.43 %)

with increasing temperature, for the root and rhizome, while

stolon and pethiole present decreasing adsorption ratios.

Maximal values were achieved for root at 298 K and least

figures were obtained for pethiole at 318 K. On studies of

adsorption of methylene blue on luffa cylindrica fibers it is

reported that the adsorption equilibrium was not significantlly

affected by temperature changes [35].



I J E N S

80

85

90

95

Dy

e so

rbed

rat

io /

%

Temperature / °C

Root

Stolon

Rhizome

Petiole

298 308 318

Fig. 6. Effect of temperature on removal of methylene blue with different parts of the water hyacinth (dye concentration: 100 mg L-1, adsorbent concentration: 2.0

g L-1, particle size: 60 mesh, contact time: 24 h)

On the other hand, the adsorption of methylene blue

dye on diatomite showed that increasing temperature promotes

an increase in the maximum adsorption capacity and

according to the authors, this should result in an increase the

intraparticle diffusion [36].

Khattri and Singh [37] reported that a temperature

increase in the process of adsorption of crystal violet dye on

sawdust, affects the solubility and chemical potential of the

adsorbate and that the solubility of the adsorbate increases

with rising temperature. These effects were due to the drop of

chemical potential, thus causing a reduction in adsorption

ratio.

3.3 Adsorption isotherms

The amount of methylene blue adsorbed at equilibrium

on different adsorbent parts of water hyacinth, qe (mg g-1

) was

calculated by mass balance according to Equation 1 [9,28].

W

VCCq eoe

(1)

Where Co is the concentration of methylene blue (mg L-1

), in

the liquid phase; Ce MB equilibrium concentration (mg L-1

) in

the liquid phase, V volume (L) of solution and W the mass (g)

of water hyacinth.

To determine the mechanisms related to the adsorption of MB

onto MH, Langmuir and Freundlich, isotherm models were

tested with the experimental data with the parameters being

obtained using linear and nonlinear regression [38]. The

adsorption isotherms obtained are shown in Figure 7( for the

Root), and the parameters calculated for the models used are

presented in Table II and III.

0 5 10 15 20 25 30 35

0

40

80

120

160

200

Experimental Linear Non-Linear

qe(m

g/g

)

Ce(mg/L)

Root

(a)

Fig. 7. Comparison of the Langmuir (a) and Freundlich (b) adsorption isotherms using linear and non-linear models for the methylene blue dye at 298K adsorption

on WH biomass (root).

Figure 7 shows that Langmuir non linear isotherm

was found to fit better to the experimental data than linear one,

at equilibrium concentrations larger than 10 mg. L-1

, whereas

Freundlich isotherm fitted satisfactorily to both linear and non

0 5 10 15 20 25 30 35

0

20

40

60

80

100

120

Experimental Linear Non linear

qe(

mg.g

-1)

Ce(mg.L

-1)

Root

(b)



I J E N S

linear models. Similar behavior was observed for other plant

parts (data not shown).

3.3.1 Langmuir Isotherm Model

A Langmuir model assumes that adsorption occurs at

specific homogenous sites within the adsorbent (monolayer

adsorption), Equation 2[38]:

eL

eLmáxe

CK

CKqq

1 (2)

Where Ce is the solute concentration at equilibrium

(mg.L−1

), qe is the amount of ions metals adsorbed at

equilibrium (mg.g−1

), kL is the Langmuir adsorption constant

(L.mg−1

) and qmax is the monolayer capacity of the adsorbent

(mg.g−1

). Efficient adsorbents are expected to have high kL and

qmax values. The values of qmax followed the order: Stolon >

Rhizome > Petiole > Root, Table II.

Table II

Parameters of Langmuir isotherms at 298, 308 and 318 K for different WH plant parts.

Tempe-

rature(K) Model

Parameters

Root Stolon Rhizome Petiole

298

Linear

qmáx(mg/g) 819.7 202.4 305.8 80.0

kL (L/mg) 0.0096 0.014 0.0099 0.067

R² 0.995 0.998 0.997 0.996

SSE 10421.8 4762.3 2233.8 1198.8

Non-

Linear

qmáx(mg/g) 129.0 603.7 301.4 239.3

kL (L/mg) 0.1312 0.007 0.0157 0.010

R² 0.985 0.993 0.979 0.989

SSE 110.7 50.8 159.1 62.4

308

Linear

qmáx(mg/g) 1030.9 292.4 367.6 96.9

kL (L/mg) 0.0085 0.012 0.0095 0.055

R² 0.999 0.999 0.998 0.999

SSE 1576.4 176.8 744.5 279.1

Non-

Linear

qmáx(mg/g) 137.0 322.1 183.8 267.2

kL (L/mg) 0.1217 0.0106 0.0339 0.0108

R² 0.985 0.956 0.994 0.994

SSE 70.9 175.8 22.9 19.7

318

Linear

qmáx(mg/g) 1020.4 296.7 490.2 117.8

kL (L/mg) 0.0077 0.011 0.0082 0.027

R² 0.998 0.999 0.998 0.999

SSE 866.8 82.6 610.9 156.7

Non-

Linear

qmáx(mg/g) 145.9 816.4 129.5 271.8

kL (L/mg) 0.095 0.0035 0.052 0.008

R² 0.983 0.986 0.989 0.987

SSE 79.4 54.5 41.3 41.5

SSE= sum of squared errors

The essential characteristics of Langmuir isotherm can

be expressed by a dimensionless parameter called the

equilibrium constant RL, which is defined by equation 3 [39]:

oL

LCk

R

1

1

( 3)

Where kL is the Langmuir constant (L mg-1

) and Co the

methylene blue initial concentration (mg L-1

) in the liquid

phase.

The value of RL indicates the type of isotherm to be

unfavorable (RL> 1), linear (RL = 1), favorable (0 <RL <1) or

irreversible (RL = 0). Under the same conditions, the values

obtained for WH were 0.51, 0.42, 0.50, 0.13 for root, stolon,

rhizome and petiole, respectively. Usually the adsorption of



I J E N S

methylene blue on water hyacinth can be accepted as

appropriate when the RL values are close to zero [35].

3.3.2Freundlich Adsorption Isotherm

The Freundlich isotherm takes into account the

heterogeneity of the surface, the distribution of active sites and

their energies compared to the adsorbate [40]. Freundlich

isotherm equation is given by equation 4:

nefe CKq

1

(4)

Where is KF is the Freundlich constant, and 1/n is the

Freundlich exponent which is a constant related to the

intensity of adsorption, i.e., the distribution of active sites and

determines the heterogeneity of the surface and KF is a

constant that determines the adsorbent adsorption capacity on

the multilayer [41]. These values along with correlation

coefficients of our work are presented in Table III.

Table III

Parameters of Freundlich isotherms at 298, 308 and 318 K for different WH plant parts.

Temperatu

re(K)

Model

Parameters Root Stolon Rhizome Petiole

298

Linear

kF (L.mg-1

) 23.6 6.3 9.5 5.1

1/n 0.45 0.82 0.67 0.70

R² 0.987 0.995 0.985 0.997

SSE 264,8 59,5 163,6 20,8

Non-

Linear

kF (L.mg-1

) 22.2 5.1 6.9 4.6

1/n 0.46 0.89 0.77 0.72

R² 0.968 0.994 0.985 0.996

SSE 247,6 39,9 111,6 18,7

308

Linear

kF (L.mg-1

) 21.2 3,7 9.9 5.0

1/n 0.53 0.90 0.67 0.75

R² 0.983 0,987 0.999 0.999

SSE 162,3 179,3 49,8 8,6

Non-

Linear

kF (L.mg-1

) 19.2 4.4 8.5 4.4

1/n 0.57 0.84 0.71 0.79

R² 0.969 0.958 0.990 0.998

SSE 148,3 168,6 39,4 5,4

318

Linear

kF (L.mg-1

) 20.0 3.7 11.6 3.5

1/n 0.53 0.89 0.57 0.80

R² 0.997 0.992 0.994 0.990

SSE 117,1 47,9 70,3 23,6

Non-

Linear

kF (L.mg-1

) 16.4 3.4 10.1 3.6

1/n 0.61 0.92 0.61 0.79

R² 0.984 0.988 0.985 0.993

SSE 73,1 46,6 58,7 21,5

SSE= sum of squared errors

Freundlich isotherm exhibiting highest KF value (23.6

L mg-1

) for WH root and the minimal (5.1 L mg-1

) for petiole.

Algae42

present data in the range 4.2 – 13 L mg-1

. Mesocarp

and epicarp components of the babassu palm tree presented

maximum adsorption of the Turquoise Remazol dye of 1.44

and 2.38 mg g -1

[41]. Regarding to the correlation

coefficients of both Langmuir and Freundlich models, it can

be concluded that the WH experimental data applies well to

both models.

The temperature effect can be seen in Table 1 and 2,

revealing that maximum adsorption ratio increases with the



I J E N S

temperature for WH root. The Langmuir constant for WH root

decreases with the temperature, for the non linear model,

remaining fairly constant for the linear model, the later

meaning that the coverage of the adsorbate monolayer does

not change, in the temperature range investigated.

Khan et al [43] reported values for WH root maximum

adsorption capacity and Langmuir constant as being equal to

187 mg.g-1

and kL=0.116 L.mg-1

, respectively. Moringa seed

cake datafor chromium adsorption resulted in 3.191 mg g-1

and

kL value of 0.089 L.mg-1

[44], while microalga spirulina

platensis adsorbed the metal presenting adsorption capacity of

100.39 mg g-1

.

Data in Table 3 reveal that Freundlich constant

1/n is smaller for WH root, pointing out to its low surface

heterogeneity compared to other plant parts while the n

constant is greater than 1 for petiole, stolon, root and rhizome.

Moring seed cake used as adsorbent yielded similar values for

n constant.44

On the other hand 1/n increases with temperature

for Freundlich non linear model and remains constant for

linear model. kF constant is larger for the root in the

temperature range investigated, demonstrating its better

adsorption capacity.

3.4 Kinetics of adsorption

Figure 8 illustrates the adsorption kinetics of methylene

blue on different biomasses of water hyacinth at 298 K. The

removal rates of the dye during the first hour of adsorption

were very fast, adsorbing about 80 % of the dye. It was also

observed that the sorption is practically the same for different

plant parts, during the first three hours. After a very fast

sorption, the removal increased slightly reaching about 95 %

by the root, reaching equilibrium in about 4 h for all

biomasses, probably due to saturation of their surface. This

fact was also observed for the adsorption of methylene blue on

peanut hull [3].

0 1 2 3 4 560

70

80

90

100

Dy

e S

orb

ed r

atio

/ %

Time / h

Root

Stolon

Rhizome

Petiole

Fig. 8. Kinetics of adsorption of methylene blue with different adsorbents of water hyacinth (dye concentration: 100 mg L-1 concentration of the adsorbent: 2 g L-1,

particle size: 60 mesh, pH 6.5 to 7.0, 298 K).

Kinetic studies were also performed with water

hyacinth using different dyes such as Methyl Orange and

Indigo Carmine, both acid dyes, and data did not result in

good figures (data not shown), thus confirming the fact that

WH has affinity for basic dyes, in good agreement with

previously published data [46]. Experimental data were fitted

to a Langergren equation of pseudo-first order according to

Equation 5[28,45].

tkqqq ete 1 lnln (5)

Where qt is the amount of methylene blue adsorbed at a given

time (mg g-1

) and k1 the adsorption equilibrium constant of

pseudo first-order (h-1

).

A plot of ln (qe - qt) versus t gives the adsorption

equilibrium constant of pseudo-first order. The MB adsorption

data was also applied to a pseudo-second order model

according to Equation 6. A plot of t / qt versus t shows a linear

relationship if the experimental data fit well to the kinetics of

pseudo-second order [45,46].

eet qt

qkqt

2

2

1 (6)

Where k2 is the adsorption equilibrium constant of pseudo-

second order (g mg-1

h-1

).

For example, the root adsorption kinetics data at

temperatures of 298, 308 and 318 K, were treated with the

models of pseudo-first order and pseudo-second order and the

results are presented in Table IV. The data show that the

values of qe calculated for the model of pseudo-first order are



I J E N S

not in agreement with the experimental data, thus proving the

inadequacy of the model. On the other hand, the calculated

values fitted to the model of pseudo-second order, with

appropriate correlation coefficients and thus justify its

applicability.

The kinetic model of pseudo-second order was also reported

as the most suitable for adsorption of methylene blue on wheat

shells [47] and bamboo-based activated carbon [10]. Table IV

shows that the adsorption kinetic constant increases with the

temperature, in good agreement with literature.

Table IV

Kinetic parameters of adsorption of methylene blue on WA root.

Parameters Temperature (K)

298 308 318

qe (mg g-1

) 46.1 44.6 44.7

Pseudo-first order

k1 (h-1

) 1.07 1.46 2.07

qecal (mg g-1

) 9.3 5.3 4.8

R2 0.988 0.878 0.912

Pseudo-second order

k2 (h-1

) 0.25 0.59 0.92

qecal (mg g-1

) 47.7 45.3 45.2

R2 0.998 0.999 0.999

3.5 Desorption study

It can be seen, table V, that WA plant parts present

satisfactory desorption values in the range 60.0 – 70.8 %, the

maximal figure being obtained by root. Orange peel employed

for removal of an acid dye presented maximum desorption of

60% [49].

Table V

Methylene blue desorption on different WA plant parts

WA plant part Adsorption

(%)

Desorption

(%)

Root 92.5 70.8

Stolon 81.9 61.7

Rhizome 87.2 65.5

Petiole 84.4 60.0

3.4 Thermodynamic study

The thermodynamic parameters of adsorption

processes are important because they enable the determination

of their spontaneity through the free energy (G°), the

absorption or release of energy by their enthalpy change (H°)

and the possibility of the molecules to organize themselves or

not, by the change of entropy (S°) [50].

The thermodynamic parameters for the adsorption of

methylene blue were investigated for the root of water

hyacinth, as it has exhibited the best results for MB

adsorption. The data were used for calculation of adsorption

free energy (G°), enthalpy change of adsorption (H°) and

entropy change of adsorption (S°). These parameters were

calculated at temperatures of 298, 308 and 318 K. The free

energy (G°) was calculated using the following equation [50-

52]:

LkRTG ln (7)

Where kL is the equilibrium constant of adsorption

(Langmuir model) and R is the universal gas constant (8.314 J

mol-1

K-1

).

The values of H° and S° were respectively

determined from the slope and the intersection of the graph of

G° versus T plotted from Equation 6 [52]. Table 6 presents

the thermodynamic parameters for the adsorption at

equilibrium of methylene blue on water hyacinth root. STHG (8)

Table VI

Thermodynamic parameters for equilibrium adsorption of methylene blue on water hyacinth root

Temperature/K kL (L mg-

1)

∆H° (kJ mol-

1)

∆S° (J mol-

1K

-1)

∆G° (kJ mol-

1)

R²

298 0.0096 - 8.8 -19.0 - 3.17 0.993

308 0.0085 - 2.96

318 0.0077 - 2.79



I J E N S

The change in Gibbs free energy (ΔG°) is the

fundamental criterion of spontaneity of the process. A given

process occurs spontaneously at a given temperature if ΔG° <

0 [52].

Data obtained revealed that for all temperatures

studied, the negative values of ΔG show that MB adsorption is

thermodynamically favored and that there is an increase in

Gibbs free energy with decrease temperature, confirming the

improved viability of the adsorption process at lower

temperatures and the water hyacinth-dye interactions occurred

spontaneously. These facts have also been reported by

Hameed, Din and Ahmad [10] and Bulut and Aydin [53]. The

apparent Gibbs free energy of sorption for methyl red, was

reported as 15.55 kJ/mol, revealing a non spontaneous

processs [54]. The negative value of entropy (S°) reflects the

decreased randomness at solid-liquid interface, i.e. a more

ordered structure is obtained after adsorption.

The negative value of H° indicates that the adsorption

of methylene blue on the WH root is an exothermic reaction.

An adsorption process is generally considered to be physical35

when H° < 25 kJ mol-1

and chemical when H° > 40 kJ mol-

1 therefore, MB adsorption on WH roots is due to be ruled by

physical connections, likely involving weak Van der Waals

forces.

Studies of adsorption of methylene blue on luffa

cylindrica fibers [35] resulted in an exothermic and

spontaneous process, as well as on Brazil nut shells [55] the

later yielded values of H° = -5.22 kJ mol-1

, ΔG° = -2.27 kJ

mol-1

and ΔS° = -112.23 J mol-1

K-1

, thus demonstrating

similarity of the obtained results. Activation energies also was

calculed for MB adsorption on WH plant parts from Arrhenius

equation using the pseudo-second order kinetic constants at

different temperatures through a plot of ln k versus 1/T as

shown in figure 9. The calculated activation energies are

19.6, 36.9, 24.8 and 18.6 kJ.mol-1

for root, stolon, rhizome and

petiole, respectively, revealing that adsorption processes occur

through physical interactions.

0,00310 0,00315 0,00320 0,00325 0,00330 0,00335

-3

0

3

Root

Stolon

Rhizome

Petiole

ln k

1/T

Fig. 9. Thermodynamic parameters of MB dye sorption by WH.

4.0 CONCLUSIONS

It has been showed that different WH plant parts have

distinct adsorption characteristics and can be used as

adsorbent material for basic dyes such as methylene blue,

yielding maximum adsorption values of 603.7mg g-1

, for the

stolon, non linear model, at room temperature. For acid dyes

such as methyl orange and indigo carmine the adsorption

ratios were not significant.

The adsorption isotherms were well fitted to the

Langmuir and Freundlich models, presenting satisfactorily

values for their coefficient of determination, being slightly

better for the Langmuir isotherm. Maximum adsorption ratio

was found to be considerably higher than previously reported

ones in countries such as Philippines and Egypt. Kinetic

studies showed a good data experimental match to a pseudo-

second order model. WH thermal properties were found to be

similar to those of biomasses such as wheat shells, peanut hull

and palm tree fibers.

Thermodynamic studies revealed that MD adsorption

on WH was an exothermic and spontaneous process, ruled by

physical connections, likely involving weak Van der Waals

forces.

Due to the abundance of water hyacinth in the aquatic

environment and the consequent low cost and the hereby

reported properties, it seems to become a viable candidate to

be used as a dye bioadsorbent.

ACKNOWLEDGMENTS

Authors are thankful to CNPQ and CAPES for financial

support.



I J E N S

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