potential use of activated carbon derived from persea species under alkaline conditions for removing cationic dye from wastewaters

Catedra´tico Jose´ Beltra´n, 2, 46980 Paterna, Valencia, Spain Received 22 August 2016; revised 14 January 2017; accepted 15 January 2017 KEYWORDS Activated carbon; Adsorption; Basic Yel

Potential use of activated carbon derived from

Persea species under alkaline conditions for

removing cationic dye from wastewaters

Abdelmajid Regtia, My Rachid Laamaria, Salah-Eddine Stiribab,c,

a

Equipe de Chimie Analytique & Environnement, Faculte´ Poly-disciplinaire, Universite´ Cadi Ayyad, BP 4162, 46000 Safi, Morocco b

Equipe de Chimie Mole´culaire, Mate´riaux et Mode´lisation, Faculte´ Poly-disciplinaire, Universite´ Cadi Ayyad, BP 4162, 46000 Safi, Morocco

c

Instituto de Ciencia Molecular/ICMol, Universidad de Valencia, C/ Catedra´tico Jose´ Beltra´n, 2, 46980 Paterna, Valencia, Spain Received 22 August 2016; revised 14 January 2017; accepted 15 January 2017

KEYWORDS

Activated carbon;

Adsorption;

Basic Yellow 28;

Kinetics;

Persea americana species;

Thermodynamic studies

Abstract The use of Persea americana has been studied as an alternative source of activated car-bon for the removal of dyes from wastewater Chemical activation using phosphoric acid was employed for the preparation of the activated carbon (C-PAN) The BET surface area and the total pore volumes were found to be 1593 m2/g and 1.053 cm3/g, respectively This study investigates the effect of some parameters like, dye concentration, adsorbent dose, contact time and pH for the best comprehension of the adsorption manner Adsorption kinetic follows pseudo-second order kinetic model Langmuir and Freundlich isotherms models were used to analyze the adsorption equilibrium data and the best fits to the experimental data were provided by Langmuir model Maximum adsorption capacity is equal to 400 mg/g of Basic Yellow 28 onto the activated carbon derived from Persea americana Thermodynamic parameters, such as standard Gibbs free energy (DG0

), standard enthalpy (DH0

) and standard entropy (DS0

) has been calculated The adsorption process was found

to be spontaneous and exothermic process

This study shows that the activated carbon provided from Persea americana can be an alternative

to the commercially available adsorbents for dyes removal from liquid solutions

Ó 2017 University of Bahrain Publishing services by Elsevier B.V This is an open access article under the

CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

1 Introduction Among the different pollutants of aquatic ecosystems, dyes are

a large and important group of industrial chemicals for which world production in 1978 was estimated at 640,000 tons of which about 20–30% are wasted in industrial effluents during the textile dyeing and finishing processes (Clarke and Anliker,

* Corresponding author Fax: +212 524 669 516.

E-mail address: elhaddad71@gmail.com (M El Haddad).

Peer review under responsibility of University of Bahrain.

University of Bahrain

Journal of the Association of Arab Universities for

Basic and Applied Sciences www.elsevier.com/locate/jaaubas

www.sciencedirect.com

http://dx.doi.org/10.1016/j.jaubas.2017.01.003

1980) Moreover, most of these dyes can cause allergy,

der-matitis, skin irritation and also provoke cancer and mutation

Perenich, 1988) Also, the presence of very small amounts of

dyes in water less than one ppm for some dyes is highly visible,

very difficult to biodegrade, extremely difficult to eliminate in

natural aquatic environments and undesirable (Banat et al.,

1996; Robinson et al., 2001) Currently, much attention has

been paid to the removal of dyes from industrial wastewater

(Gupta et al., 2013, 2012a; Jain et al., 2003; Mittal et al.,

2010a, 2009a)

Many treatment processes have been applied for the

removal of dyes from wastewater such as: Fenton process

(Behnajady et al., 2007), photocatalytic degradation (Gupta

et al., 2012b, 2011; Saleh and Gupta, 2012; Saravanan et al.,

2016, 2015a,b, 2014), sono-chemical degradation (Abbasi

and Asi, 2008), photo-Fenton processes (Garcia-Montano

et al., 2007), chemical coagulation/flocculation, ozonation,

cloud point extraction, oxidation, nano-filtration, chemical

precipitation, ion exchange, reverse osmosis and

ultra-filtration (Lorenc-Grabowsk and Gryglewic, 2007; Malik and

Saha, 2003; Malik and Sanyal, 2004; Banat et al., 1996;

Tawfik et al., 2012) Adsorption techniques have gained favor

due to their simplicity in operation, cost-effectiveness and

effi-ciency in the removal of pollutants too stable for conventional

methods (Mittal et al., 2010b, 2009b; Gupta and Nayak, 2012;

Gupta et al., 2015a,b, 2012b; Saleh and Gupta, 2014) More

recently, new researches on the effect of the ultrasound on

the adsorption–desorption process have been reported

(Asfaram et al., 2017; Alipanahpour Dil et al., 2017; Ghaedi

et al., 2015; Mazaheri et al., 2016) Almost all the work related

to adsorption techniques for color removal from industrial

effluents was based on studies using natural and abundant

materials Activated carbon (Regti et al., 2016a,b, 2017;

Gupta et al., 1997, 2013; Saleh and Gupta, 2014) is still the

most popular and widely used adsorbent Activated carbon

can be prepared using a variety of chemical (Attia et al.,

2008) and physical (Heibati et al., 2015) activation methods

and in some cases using a combination of both types of

meth-ods (Albero et al., 2009) Chemical activation is the process

where the carbon precursor is firstly treated with aqueous

solu-tions of dehydrating agents such as phosphoric acid, zinc

chlo-ride, sulfuric acid, and potassium hydroxide Afterwards, the

carbon material is dried at 373–393 K to eliminate the water

traces followed by its heating between 673 K and 1073 K under

nitrogen atmosphere (Faria et al., 2008) The physical

activa-tion consists of a thermal treatment of previously carbonized

material with suitable oxidizing gases, such as air at

tempera-tures comprised between 623 K and 823 K by using steam and/

or carbon dioxide (Heibati et al., 2015)

We have already used the potential efficiency of animal

bone meal material (El Haddad et al., 2012, 2013a,b), calcined

mussel shells (El Haddad et al., 2014a,b), calcined eggs shells

(Slimani et al., 2014) and activated carbon derived from

Med-lar nuts (Regti et al., 2016c) as new low cost adsorbents to

remove anionic and cationic dyes from aqueous solutions

For ongoing our program research for the decolourization

solutions, we have used activated carbon derived from natural

and low cost materials (Persea americana Nuts) Other studies

have been performed using activated carbon prepared from

agricultural wastes for the removal of dyes from aqueous

solu-tion (Gupta et al., 2015a,b)

In this current study, the removal of Basic Yellow 28 dye from aqueous solutions onto activated carbon derived from Persea americana nuts was investigated The choice of this agricultural wastes returns to the increased consumption of avocado fruit In this fact, the effect of different parameters such as pH, contact time, adsorbent dose, initial dye concen-tration and temperature were investigated The removal rate kinetics, thermodynamics and isotherms for Basic Yellow 28 adsorption onto treated Persea americana were also studied

2 Materials and methods 2.1 Materials

Persea americanaNuts (PAN) used for the preparation of the activated carbon, was collected, washed with distilled water and dried at room temperature for several dyes The dried material was then milled and separated by manually shaking stainless steel mesh screens with the opening of standard 0.45 mm an appropriate weight of PAN was immersed in

25 mL of concentrated phosphoric acid with a mass ratio (1:4) for 12 h and then dried in an oven for 24 h at 105°C The PAN was placed in a sealed ceramic oven and pyrolysed

at 500°C and remained constant for 2 h The resulting acti-vated carbon (C-PAN) was filtered and rinsed with distilled water until the washings were free of excess acid The final pro-duct of C-PAN was dried at 105°C for 24 h, crushed to get the particles size of 200–300mm and kept in desiccators for further study

Adsorption–desorption isotherms of nitrogen at
196 °C were measure with an automatic gas sorption analyzer (NOVA-1000, Quanta Chrome Corporation, USA) in order

to determine surface areas and total pore volumes

The Characterization of C-PAN was achieved by FT-IR spectroscopy and X-ray powder diffraction measurements FT-IR spectra (4000–450 cm
1range) were recorded with a Nicolet 5700 FT-IR spectrometer (Thermo Corp, USA) on samples prepared as KBr pellets The polycrystalline sample

of adsorbent was lightly ground in an agate mortar, pestle and filled into 0.5 mm borosilicate capillary prior to being mounted and aligned on an Empyrean PANalytical powder

(k = 1.54056 A˚) Three repeated measurements were collected

at room temperature in the 10° < 2h < 60° range with a step size of 0.01° Scanning Electronic Microscopy (SEM) images were obtained with (HITACHI-S4100, JAPAN) equipment operated at 20 kV

De-ionized water was used throughout the experiments for solutions preparation The adsorption studies for evaluation of the C-PAN adsorbent for the removal of the Basic Yellow 28 dye from aqueous solutions were carried out in triplicate using the batch contact adsorption method Basic Yellow 28 dye used in this study abbreviated as BY28 was purchased from Sigma–Aldrich (Germany) Chemical structure of BY28 is shown inFig 1

2.2 Adsorption experiments

For the adsorption experiments, fixed amounts of adsorbents (0.2 g/L–1.0 g/L) were placed in a 100 mL glass Erlenmeyer

concentrations (40–100 mg/L), which were stirred during a

suitable time (5–65 min) from 303 to 333 K The pH of the

dye solutions ranged from 2 to 12 was adjusted by 0.1 M

HCl or 0.1 M NaOH to investigate the effect of pH on

adsorp-tion processes Subsequently, in order to separate the

centrifuged at 3600 rpm for 10 min, and aliquots of 1–10 mL

of the supernatant were taken At predetermined time, the

residual dye concentration in the reaction mixture was

ana-lyzed by centrifuging the reaction mixture and then measuring

the absorbance by UV–Visible spectroscopy of the supernatant

at the maximum absorbance wavelength of the sample at

436 nm (Zermane et al., 2010)

The amount of equilibrium adsorption qe(mg/g) was

calcu-lated using the following expression:

qe¼C0
Ce

where Ce(mg/L) is the liquid concentration of dye at

equilib-rium, C0(mg/L) is the initial concentration of the dye in

solu-tion V is the volume of the solution (L) and W is the mass of

biosorbent (g) The BY28 removal percentage (%) can be

cal-culated as follows:

%Removal ¼C0
Ce

where C0is the initial dye concentration and Ce(mg/L) is the

concentrations of dye at equilibrium

3 Results and discussion

3.1 Characterization of C-PAN adsorbent

In order to investigate the surface characteristic of C-PAN

adsorbent, FT-IR and XRD spectrums were recorded As

shown in FT-IR spectrum in Fig 2, the frequencies of the

absorption bands of C-PAN are 876, 1074, 1149, 1563, 2916

and 3415 cm
1 The absorption band at 3415 cm
1is

attribu-ted to the hydroxyl groups (OAH) vibration, bands at 2916

and 1563 cm
1are assigned for P‚O group, while bands at

1149 and 1074 cm
1are attributed for PAO group and finally

band at 876 cm
1is attributed for PAH group (Liu et al., 2012

Wang et al., 2011) These function groups are due to the

pre-sent of H3PO4acid as an activation agent in the preparation

of C-PAN

Fig 3 shows an X-ray powder diffraction pattern of

C-PAN An amorphous peak with the equivalent Bragg angle

at 2h = 24.6 was recorded, together with other peaks recorded

at 2h = 17.5°, 31.2° and 47.5° Thus, as presented inFig 3, a

wide and high intensity peak between 20 and 30° centered at

25° indicates the amorphous nature of C-PAN adsorbent

Fur-thermore, XRD data gave clear evidence to the high purity of

the amorphous C-PAN

The surface morphology of the C-PAN adsorbent was examined.Fig 4shows the SEM image indicating that the sur-face contains many pores of different size and different shape could be observed, revealing the potential adsorption power

N

, CH3S O4 -+

Figure 1 Chemical structure of Basic Yellow 28

Figure 2 FT-IR spectrum of C-PAN adsorbent

Figure 3 XRD spectrum of C-PAN adsorbent

Figure 4 SEM image of C-PAN adsorbent

and suggesting that dyes were adsorbed on the mesopore or

microspore The BET surface area and the total pore volumes

of the obtained Persea americana activated carbon were found

to be 1593 m2/g and 1.053 cm3/g, respectively

3.2 Effect of C-PAN dosage on the adsorption capacity

The effect of the C-PAN dosage on the uptake (mg/g) is shown

inFig 5 The adsorbent dosage was varied from 0.2 g/L to 1 g/

L using V = 50 mL of BY 28 (100 mg/L) at ambient

tempera-ture The adsorption capacities increases with increasing time

and the response becomes constant for all amounts studied

The maximum uptake (q = 325 mg/g) was observed with the

dosage of 0.2 g/L The capacity of adsorption decreased

slightly with the higher dosage of the adsorbent The reason

may be the interparticle interaction, such as aggregation,

resulting from high adsorbent dose, aggregation would lead

to a decrease in the total surface area of the adsorbent and

on an increase in diffusional path length, while, at equilibrium,

the adsorption efficiency (%) increases from 65% to 98% by

increasing the C-PAN dose from 0.2 g/L to 1 g/L due to the

increase in the number of sites available for dye adsorption,

this is in agreement with our previous observations on BY28

dye removal by calcined bones biosorbent (El Haddad et al.,

2013a,b)

3.3 Effect of contact time and BY28 dye concentration

In order to achieve the effect of contact time and initial dye

concentration (40–100 mg/L) with 0.2 g/L of C-PAN and

tem-perature fixed at 25°C on the adsorption capacity of BY28 by

C-PAN, different experiments were realized Fig 6 depicts

these results It was observed that the adsorption capacity of

BY28 is increased with increasing the contact time of all initial

dye concentrations Furthermore, the adsorption capacity dye

is increased with the increase of initial dye concentration

Therefore, at higher initial dye concentration, the number of

molecules competing for the available sites on the surface of

C-PAN was high, hence, resulting in higher basic yellow

adsorption capacity

Through these results, it appears that for the first 15 min,

the adsorption capacity uptake was rapid then it proceeds at

a slower adsorption rate and finally it attains saturation at

30 min The obtained removal curves were single, smooth and continuous, indicating monolayer coverage of dye on the surface of adsorbent Analogue results are shown in many works (Mittal et al., 2013; El Haddad et al., 2012)

3.4 Effect of pH on the removal of BY28 dye onto C-PAN

Fig 7shows the variation of dye removal versus pH In this fact, to study the effect of initial pH of aqueous dye solution,

we have used a concentration of BY28 dye at 100 mg/L and 0.4 g/L of C-PAN adsorbent, keeping the temperature at

25°C and at different pH values in the range 2–12 The amount of dye adsorbed onto C-PAN was found to be con-stant for all pH values being studied The experiments carried out at different pH show that there was no significant change

in the percent removal dye over the entire pH range This indi-cates the strong affinity of the dye to C-PAN and that either

H+or OH
ions could influence the dye adsorption capacity Whatever the pH of the dye solution, the dye removal % is constant and equal to 98% The constant removal efficiency

of BY28 dye by C-PAN adsorbent indicates that the ion exchange between the moieties of BY28 and C-PAN was not

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40 45 50 55 60 65

q t

Time (min)

0.2 g/L

0.4 g/L

0.6 g/L

0.8 g/L

1.0 g/L

Figure 5 Effect of C-PAN adsorbent dosage and contact time on

adsorption capacity of BY 28 from aqueous solution Initial dye

concentration: 100 mg/L; V = 50 mL and temperature: 25°C

0 50 100 150 200 250 300 350

0 5 10 15 20 25 30 35 40 45 50 55 60 65

q t

Time (min)

40 mg/L

60 mg/L

80 mg/L

100 mg/L

Figure 6 Effect of initial dye concentration and contact time on the removal of BY 28 from aqueous solution C-PAN: 0.2 g/L;

V= 50 mL and temperature: 25°C

0 20 40 60 80 100

Figure 7 Effect of pH on the removal of BY 28 from aqueous solution onto C-PAN Initial dye concentration: 100 mg/L,

m= 0.4 g/L, V = 50 mL and temperature: 25°C

the only one mechanism for dye removal in this system Other

type of interactions may involve too In this fact, the C-PAN

can also interact with BY28 dye molecules by hydrogen

bond-ing and van der Waals interactions A similar result was

obtained and previously achieved

3.5 Thermodynamic study

Thermodynamic data reflect the feasibility and favorability of

the adsorption process Parameters such as free energy change

(DG0

), enthalpy change (DH0

) and entropy change (DS0

) can

be determined by the change of equilibrium temperature

The free energy change of the adsorption reaction is given by

(Smith and Van Ness, 1987; Khormaei et al., 2007):

whereDG0

is the free energy change (kJ/mol), R is the

univer-sal gas constant (8.314 J/mol K), T is the absolute temperature

(K) and KCstates the equilibrium constants (qe/Ce) The values

ofDH0

andDS0

can be calculated from the following equation:

LnðKCÞ ¼
DH

0

0

where KCis plotted against 1/T, a straight line with the slope

(
DH0

/R) and intercept (DS0

/R) are given The calculated thermodynamic parameters are presented inTable 1

The positive values of DG0

(0.367 kJ/mol, 0.442 kJ/mol, 0.499 kJ/mol and 0.570 kJ/mol) at all temperatures (303 K,

313 K, 323 K and 333 K respectively) confirmed the

thermody-namic feasibility The increasing temperature from 303 to

333 K causes increasing of values ofDG0indicating a decrease

in feasibility of adsorption at higher temperatures

Values ofDH0

andDS0

were obtained as
3.81 kJ/mol and

15.38 J/mol K, respectively The negative value of DH0

shows that the adsorption is exothermic in nature The

nega-tive value ofDS0

suggests that the degree of randomness state

at the solid/solution interface increased during the BY28 dye

onto C-PAN

3.6 Adsorption isotherms

Adsorption isotherms are basic requirements for the design of

adsorption systems It can express the relationship between the

amounts of adsorbate (BY28) by unit mass of adsorbent

(C-PAN) at a constant temperature Herein, we analyzed our

experimental data by Langmuir and Freundlich isotherms

models The best-fitting model was evaluated using the

corre-lation coefficient In this case, Langmuir and Freundlich

iso-therm models are applied for giving the experimental data

during the isothermal adsorption studies The linear form of

Langmuir isotherm is expressed as (Safa and Bhatti, 2011):

Ce

qe ¼ 1

qmKL

where Ce(mg/L) is the equilibrium concentration of BY28 dye,

qe (mg/g) is the amount of BY28 adsorbed par unit mass of adsorbent KL(L/mg) and qm(mg/g) are Langmuir constants related to rate of adsorption and adsorption capacity, respec-tively A straight line with slope of 1/qm and intercept of 1/qmKLis obtained when Ce/qe is plotted against Ce.Table 2 shows the values of these parameters The essential character-istics of Langmuir equation can be expressed in terms of dimensionless separation factor, RLdefined as:

1þ KLC0

ð6Þ where C0is the initial concentration of BY28 dye, the RLvalue implies whether the adsorption is:

Unfavorable: RL> 1 Linear: RL= 1 Favorable: 0 < RL< 1 Irreversible: RL= 0

As depicted inTable 2, RLvalues versus the initial dye con-centration at ambient temperature are calculated It was observed that all the RL values obtained were comprised between 0 and 1, showing that the adsorption of BY28 onto C-PAN was favorable The RLvalues decrease upon increasing the initial dye concentration, which indicates that the adsorp-tion was more favorable at higher BY28 concentraadsorp-tion The maximum adsorption capacity was calculated (400 mg/g) under ambient temperature

The linear form of Freundlich isotherm is expressed as (Deniz and Karaman, 2011):

logðqeÞ ¼ logðKfÞ þ1

where Kfand n are Freundlich isotherm constants Kf(mg/g) (L/g) is an indication of the adsorption capacity, while 1/n is the adsorption intensity The plot of log (qe) versus log (Ce) that should give a straight line with a slope of (1/n) and inter-cept of log (Kf) and all data are shown inTable 2 In this case, the value found for n was superior to 1, which proves that the adsorption of BY28 onto C-PAN is favorable The best fit of experimental data was obtained with the Langmuir model with

r2value 0,997 This result suggests the monolayer and homoge-nous adsorption

3.7 Adsorption kinetic

The adsorption kinetics gives the idea about mechanism of adsorption, from which efficiency of process estimated In order to investigate the adsorption process of BY28 onto C-PAN adsorbent, the data obtained from adsorption kinetic experiments were simulated first order and pseudo-second order models The pseudo-first order equation is gener-ally represented as follows (Ozcan et al., 2007):

logðqe
qtÞ ¼ logðqeÞ
k1

where, qeis the amount of dye adsorbed at equilibrium (mg/g),

qtis the amount of dye adsorbed at time t (mg/g), k1is the first-order rate constant (min
1) and t is time (min)

Table 1 Thermodynamic data for the adsorption of BY 28

onto C-PAN

Temperature (K) DG 0

(kJ/mol) DH 0

(kJ/mol) DS 0

(J/mol K)

The values of k1, qe calculated from the equation and the

correlation coefficient (r2) values of fitting the pseudo-first

order rate model at different concentrations are presented in

Table 3 The linearity plots of log (qe–qt) versus time at

differ-ent initial dye concdiffer-entrations (Fig 8) suggested that the

pro-cess of dye adsorption did not follow the pseudo-first order

rate kinetics Also fromTable 3, it is indicated that the values

of the correlation coefficients are not high for the different dye

concentrations Furthermore, the estimated values of qe

calcu-lated from the equation qe(cal) differ substantially from those

measured experimentally qe(exp) That gives confirmation that

the adsorption process of BY28 onto C-PAN did not obey the

pseudo-first order model

The pseudo-second order equation is generally represented

as follows (Moussavi and Mahmoudi, 2009):

t

qt¼ 1

k2q2þ 1

where, k2is the pseudo-second order rate constant (g/mg.min)

A plot of t/qt and t should give a linear relationship if the

adsorption follows pseudo-second order model To understand the applicability of the model, a linear plot of t/qtversus time under different dye concentrations were plotted inFig 9 The values of k2, qeand correlation coefficients (r2) were calculated from the plot and are given inTable 3 The qe(cal) determined from the model along with correlation coefficients indicated that qe(cal) is very close to qe(exp) and correlation coefficient

is also greater than 0.99 As a matter of consequence, the sys-tem BY28-C-PAN could be well described by the pseudo-second order model

3.8 Comparison with other derived activated carbon

The value of maximum adsorption capacity qm(mg/g) is of importance to identify which adsorbent shows the highest adsorption capacity and is useful in scale-up considerations Some studies have been conducted using various types of acti-vated carbon derived from many materials for removing dyes from aqueous solutions.Table 4depicts a comparison of the adsorption capacity of C-PAN with that reported for other

Table 2 Adsorption isotherm constants for removal of BY 28 onto C-PAN adsorbent at ambient temperature

Table 3 Pseudo-first order and pseudo-second order kinetic parameters for BY 28 removal using C-PAN adsorbent

Concentration of BY 28 (mg/L) Pseudo-first order Pseudo-second order

k 1 (min
1) q e (cal) (mg/g) q e (exp) (mg/g) r2 k 2  10
4 (g/mg.min) q e (cal) (mg/g) r2

0

1

2

3

Time (min)

40 mg/L

60 mg/L

80 mg/L

100 mg/L

Figure 8 Pseudo-first order plots for different initial dye

concentrations removal using C-PAN adsorbent C-PAN

adsor-bent: 0.2 g/L; temperature 25°C

0 0.1 0.2 0.3 0.4

Time (min)

40 mg/L

60 mg/L

80 mg/L

100 mg/L

Figure 9 Pseudo-second order plots for different initial dye concentrations removal using C-PAN adsorbent C-PAN adsor-bent: 0.2 g/L; temperature 25°C

adsorbents It can be seen from the Table 4that the C-PAN

adsorbent show a comparable adsorption capacity with the

respect to other adsorbents, revealing that the C-PAN is

suit-able for the removal basic dye from aqueous solutions

3.9 Regeneration of C-PAN

The economic aspect and environmental of the use of

adsor-bent materials, makes important the reuse of biosoradsor-bents,

(Fig 10) displays the difference in adsorption capacity(mg/g)

of first and five cycles, the adsorption capacity was reduced

from 235 to 37.3 mg/g, its due to the reduction in the specific

surface of this material Therefore, C-PAN shows excellent

adsorption performance and regeneration, and its use can be

extended to environmental applications for wastewater

treatment

4 Conclusion

The results of this study show that C-PAN obtained from the

nuts of Persea americana can be successfully used as a low cost

and eco-friendly adsorbent for the removal of basic yellow 28

(BY28) from aqueous solution and The following conclusions

have been drawn from the above investigations:

– The adsorption process was influenced by a number of

fac-tors such as adsorbent dose, pH, contact time, and the

ini-tial BY28 concentration

– The uptake (mg/g) was observed to increase with increasing

initial dye concentration and decrease with increasing

adsorbent dose The adsorption parameters for the

Lang-muir and Freundlich isotherms were determined and the equilibrium data were best described by the Langmuir iso-therm model with acceptable r2, which indicates that a homogeneous adsorption takes place between BY28 dye and C-PAN

– The pseudo-second order equation was best described for the kinetics of the C-PAN adsorption system due to its high

r2 In addition, the theoretical qegenerated by the pseudo-second order equation is in good agreement with the exper-imental qevalue

– Thermodynamic studies indicate that the adsorption pro-cess is exothermic and spontaneous in nature

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Table 4 Comparison of maximum monolayer adsorption

capacities of C-PAN with those of various AC adsorbents

AC adsorbent q m (mg/g) Reference

Rambutan peel 215.05 Njoku et al (2014)

Stricta algae-based 526.00 Attouti et al (2013)

Pomelo skin 501.10 Foo and Hameed (2011)

Pomegranate peel 370.86 Mohd et al (2014)

Persea americana 400.00 This study

0

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Cycle number

Figure 10 Effect of regeneration cycles on the adsorption

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