Modeling of Adsorption Isotherms of Caffeine onto Groundnut Shell as a Low Cost Adsorbent

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1191-1195

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

https://doi.org/10.47277/JETT/8(3)1195

Modeling of Adsorption Isotherms of Caffeine onto

Groundnut Shell as a Low Cost Adsorbent

Abdoulaye Demba N’diaye ¹* and Mohamed Sid’Ahmed Kankou¹

Unité de Recherche Eau, Pollution et Environnement, Département de Chimie, Faculté des Sciences et Technique, Université de Nouakchott Al Aasriya,

BP 880, Nouakchott, Mauritanie

Laboratoire de Chimie, Service de Toxicologie et de Contrôle de Qualité, Institut National de Recherches en Santé Publique, BP 695, Nouakchott,

Mauritanie

Received: 29/06/2020

Accepted: 05/08/2020

Published: 20/09/2020

Abstract

Caffeine is a chemical compound that has been detected in the environment and belongs to some of the most popular emerging pollutants

that may cause serious environmental and human health problems. In this study, the adsorption of caffeine on groundnut shell as low cost

adsorbent was investigated using the batch equilibrium method. Three adsorption isotherms namely the Langmuir, Freundlich and Redlich–

Peterson isotherms in their non-linear forms were applied to the adsorption equilibrium data. Both the Langmuir and Redlich–Peterson models

were found to fit the adsorption isotherm data well. The retention of caffeine on the groundnut shell showed a relatively significant adsorption

with a maximal quantity of 4.21 mg g . The present study showed that the powdered groundnut shell is a promising and alternative adsorbent

for the removal of caffeine from aqueous solutions.

Keywords: Caffeine, Groundnut shell, Adsorbent, Isotherms

Introduction

adsorbents are preferred for their biodegradable, non-toxic nature,

low commercial value and highly cost-effective nature. In order

to decrease the cost of treatment and expand its use in wastewater

treatment, we have used groundnut shell considered as solid waste

of agriculture. Groundnut is cultivated in over 100 nations around

the world. Main producers are China, India, Nigeria, Senegal and

Sudan [16].

The aim of this study was to describe the modeling of

adsorption isotherms of caffeine from aqueous solutions using

groundnut shell as a low cost adsorbent. Three adsorption

isotherms such as the Langmuir, Freundlich and Redlich–

Peterson isotherms in their non-linear forms were applied to the

equilibrium data of adsorption of caffeine by groundnut shell.

Caffeine (1, 3, 7-Trimethyl-3,7-dihydro-1H-purin-2,6-dion)

is a methylxanthine alkaloid with chemical formula C

1]. Caffeine acts as psychostimulant and analeptic [2]. Many

10 4 2

H N O

[

drugs contain caffeine: analgesics, antihistamines, diet pills, cold

remedies, and stimulants of psychophysical activity. A potentially

toxic dose is considered to be above 10 mg kg [3]. Caffeine has

high water solubility and low octanol–water partition

coefficient. Due to the low efficiency of conventional wastewater

treatment process, caffeine has been detected in many surface

water and ground water [4; 5]. Several methods have been applied

for treatment of pharmaceutical products like photocatalytic

degradation [6], micro extraction [7], oxidation [8],

biodegradation [9], chlorination [10], biofiltration [11],

nanofiltration and reverse osmosis [12], electrochemical

oxidation [13], and adsorption [14]. Adsorption process has been

a prominent method of treating aqueous effluent in industrial

processes for a variety of separation and purification purposes.

Besides, adsorption on activated carbon is very widely used for

achieving high water purification. However, although activated

carbon is a preferred adsorbent, its widespread use is restricted

due to its cost. Commercially available activated carbons are still

expensive due to the use of non-renewable and relatively high-

cost starting material [15].

Materials and methods

.1 Adsorbate, adsorbent and experimental procedures

Caffeine, in analytical purity and used in the experiments

directly. The caffeine solutions were prepared by diluting stocks

solution to appropriate concentrations when needed [4; 5]. The

used groundnut shell (Figure 1) was collected from the local

market of Nouakchott City in Mauritania. Details on the

preparation of the groundnut shell as adsorbent, as well as some

characterization parameters of the groundnut shell have been

reported in previous studies [16].

In this reason, researchers have concentrated on finding

alternative natural adsorbents to activated carbon. Natural

Corresponding author: Abdoulaye Demba N’diaye, (a) Unité de Recherche Eau, Pollution et Environnement, Département de Chimie, Faculté des Sciences

et Technique, Université de Nouakchott Al Aasriya, BP 880, Nouakchott, Mauritanie and (b) Laboratoire de Chimie, Service de Toxicologie et de Contrôle

de Qualité, Institut National de Recherches en Santé Publique, BP 695, Nouakchott, Mauritanie. E-mail : abdoulndiaye1974@gmail.com

191

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1191-1195

caffeine per g of dried groundnut shell) was calculated using the

equation (1):

^C^^Ce

 

(1)

q 

where q is the caffeine concentration in groundnut shell as

-1 -

adsorbent (mg g ), C is the initial caffeine concentration (mg L

-1

); C is the caffeine concentration at equilibrium (mg L ); V is

the solution volume (L) and m is the mass of the groundnut shell

used (g).

Results and Discussion

The analysis of the isotherm data by fitting them to different

isotherm models is an important step to find the suitable model

that can be used for design purpose. Typically, the mathematical

correlation, which constitutes an important role towards the

modeling analysis, operational design and applicable practice of

the adsorption systems, is usually depicted by graphically

expressing the solid-phase against its residual concentration [17].

Over the years, a wide variety of equilibrium isotherm models

such as Langmuir, Freundlich, Brunauer–Emmett–Teller,

Redlich– Peterson, Dubinin– Radushkevich, Temkin, Toth,

Koble–Corrigan, Sips, Khan, Hill, Flory–Huggins and Radke–

Prausnitz isotherm, have been formulated in terms of three

fundamental approaches [18]. Kinetic consideration is the first

approach to be referred. Hereby, adsorption equilibrium is

defined being a state of dynamic equilibrium, with both

adsorption and desorption rates are equal [19]. Whereas,

thermodynamics, being a base of the second approach, can

provide a framework of deriving numerous forms of adsorption

isotherm models, and potential theory, as the third approach,

usually conveys the main idea in the generation of characteristic

curve [20]. However, an interesting trend in the isotherm

modeling is the derivation in more than one approach, thus

directing to the difference in the physical interpretation of the

model parameters [21]. In this work, Langmuir, Freundlich ad

Redlich-Peterson isotherms in their non-linear forms were applied

to the equilibrium data of adsorption of caffeine by groundnut

shell. The Langmuir adsorption isotherm assumes that the

adsorption takes place at specific homogeneous surface sites

within the adsorbent and has found successful application in many

adsorption processes of monolayer adsorption [22]. The nonlinear

Langmuir model can be expressed by equation (2):

Figure 1: Collected groundnut shell

The results of physicochemical characteristics of the

groundnut shell are shown in Table 1 [16].

Table 1: physicochemical characteristics of groundnut shell

Parameters

pHpzc

Moisture (%)

Ash (%)

Mean

5.8±0.10

4.7±0.36

2.7±0.17

67.1±1.57

0.57±0.03

< 100

Volatile matter (%)

Bulk density (g mL )

Particle size (µm)

The value of the pHpzc revealed that the studied groundnut

shell possess predominantly acidic nature. From the proximate

analysis, it was observed that moisture, ash and volatile matter

was slightly high which may be due to its plant origin. The X-Ray

fluorescence results show that the potassium, calcium,

magnesium and silica oxides are major component of the

groundnut shell. The Fourier Transform Infra-Red spectroscopy

analyses of the groundnut shell showed some functional groups

content in groundnut shell can act as proton donor and

consequently coordination is possible with the positively charged

caffeine [16].

q K C

(2)

q_e

^^K^Ce

.2 Adsorption isotherms

The adsorption isotherms at ambient temperature are obtained

where q is the amount of caffeine adsorbed per unit mass of

-1

groundnut shell (mg.g ), k

-1

is the Langmuir constant related to

by mixing (70 rpm), for 6 hours, 0.5 g of groundnut shell

adsorbent with 50 mL of caffeine solutions with different

concentrations varying from 0 to 100 mg L . At the end of each

experiment the agitated solution mixture was micofiltered using

micro filter and the residual concentration of caffeine was

determined by High Performance Liquid Chromatography

the adsorption capacity (L g ), C is the concentration of caffeine

-1

in the solution at equilibrium (mg L ), q

is the maximum uptake

per unit mass of groundnut shell (mg.g ). The factor of separation

of Langmuir, R , which is an essential factor characteristic of this

-1

isotherm is calculated by equation (3):

(

HPLC). Ultra pure water and methanol (70:30 V/V) were used

(3)

-1

as a mobile phase at a flow rate of 1 mL min at a selected wave

length of 254 nm [4; 5]. The caffeine uptake amount q (mg of

R 

(1 k C )

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Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1191-1195

where C

the Langmuir constant. The R

defavourable (R >1), linear (R

irreversible (R =0). The Freundlich isotherm is an empirical

is the higher initial concentration of caffeine and K

value implies the adsorption to be

=1), favourable (0<R <1), or

adsorption studies of pharmaceutical products on various

adsorbents follow the Langmuir isotherm model [26-35].

equation employed to describe heterogeneous systems [22]. The

nonlinear representation of the Freundlich model is as in equation

0,9

(

4):

Experimental data

Langmuir

/ n

q  K C

(4)

0,4

0,2

Freundlich

-1 -1 n

Where K (mg g ) (L mg ) and 1/n are the Freundlich constants

Redlich-Peterson

related to adsorption capacity and adsorption intensity,

respectively. The Redlich–Peterson isotherm model combines

elements from both the Langmuir and Freundlich equation and

the mechanism of adsorption is a hybrid one and does not follow

ideal monolayer adsorption. It is used as a compromise to improve

the fit by Langmuir or Freundlich [23]. The nonlinear

representation of the Redlich–Peterson model is as in equation

100

₍_m_g_L-1₎

Figure 2: Comparison between the experimental and predicted isotherms

for the adsorption of caffeine by groundnut shell

Table 2: Parameters isotherm model for caffeine retention on the

Groundnut Shell

(

5):

Parameters

Values

4.21

K C_e

(5)

^qe ^

 C_e

K_L

SSE

R )%(

0.0031

0.76

0.00065

99.87

0.87

0.018

0.0018

99.63

0.0125

0.00018

0.96

Langmuir

Freundlich

-1

where KRP (L g ) and αRP (L mol ) are the Redlich-Peterson

isotherm constants, while n is the exponent, which lies between 0

and 1. Two errors functions including the Sum of the Squares of

the Errors (SSE) and the correlation coefficient (R ) were used to

verify the model for the adsorption systems [24; 25]. The SSE and

K_F

SSE

R )%(

R values, by using the Solver Excel, are determined respectively

by following equations (6) and (7):

Redlich-Peterson

SSE=



q  q



mod

(6)

(7)

SSE

R )%(

0.00034

99.93

exp











q -q

mod

Table 3: Adsorption capacities of different adsorbents for the uptake of

different pharmaceutical products from their aqueous solutions

exp

R =100 1-



q -q

exp

−1

avr

Adsorbate

Carbamazepine

Ibuprofen

Adsorbent

q (mg g ) Ref.



0.37

0.32

0.12

0.037

1.74

0.77

0.99

3.8

Cork

[36]

[37]

[38]

where qexp (mg g ) is equilibrium capacity from the experimental

data, qavr (mg g ) is equilibrium average capacity from the

Sugar Can Bagasse

Vegetable Sponge

Grape Stalk

Yonimbe Bark

Cork Bark

Parthenium weed

Posidonia Oceanica

Dehydrated Sewage

Sludge

Paracetamol

experimental data and qmod (mg.g ) is equilibrium from model.

So that R ≤ 100 – the closer the value is to 100, the more perfect

Paracetamol

Ibuprofen

is the fit. Figure 2 shows the experimental data fitted to non-linear

forms of the three isotherms, using Solver Excel, for caffeine

adsorption by groundnut shell. The isotherms constants related to

Langmuir, Freundlich and Redlich–Peterson models determined

from the plots shown in Figure 2 are listed in Table 2. The values

[39]

1.638

[

40]

Paracetamol

.956

of R

favorability of the adsorption of caffeine onto groundnut shell. It

is interesting to note that the value of K < 0.1 is a sign of low

surface energy, which indicates stronger bonding between

caffeine and the groundnut shell as adsorbent.

, K

and 1/n are in between 0 and 1 give an indication of the

Aspirin

Caffeine

Banana peel

Grape stalk

2.29

0.938

[41]

[42]

Present

study

Caffeine

Groundnut shell

4.21

As can be clearly seen from Table 2, the Langmuir and

The monolayer adsorption capacity, q , was found to be 4.21

-1

Redlich–Peterson models gave the highest R and low SSE value

mg g . A list showing the adsorption capacity of different low

cost adsorbents for the adsorption of different pharmaceutical

products from their aqueous solutions is given in Table 3. From

Table 3, it is observed that the adsorption capacities of groundnut

shell adsorbent for pharmaceutical product uptake are superior

with other low cost adsorbents. It can be concluded that the

groundnut shell without any treatment applied in this work can be

showing that the adsorption isotherms of caffeine by groundnut

shell were best described by these two models. The suitability of

the Langmuir isotherm to fit the data was confirmed by the

exponent value of the Redlich– Peterson model, n, which was

near to one. It should be noted that most of the isotherm

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Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1191-1195

considered a promising material to be used for caffeine

adsorption.

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The equilibrium data were analyzed using non-linear method

by fitting them to the Langmuir, Freundlich and Redlich–Peterson

model equations. Both the Langmuir and Redlich–Peterson

isotherms represent well the experimental adsorption data. The

maximum adsorption capacity was found to be 4.21 mg g .

Groundnut shell could be considered as potential low cost

adsorbent for caffeine removal from aqueous solution. For future

studies, the usability of groundnut shell for pharmaceutical

products removal from real wastewater will be tested and as

comparison, a fixed bed column will be employed to investigate

the effect of reactor design.

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Authors are aware of, and comply with, best practice in

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The authors declare that there is no conflict of interest that

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