rhodamine removal

Abstract

Bagasse pith (BP) has been utilized for activated carbon preparation using H3PO4 (BPH) or KOH (BPK)
as a chemical activating agent followed by carbonization at 500 ◦C. The physicochemical properties of
activated carbon were carried out. The effectiveness of carbon prepared in adsorption of Rhodamine B
(RhB) has been studied as a function of adsorbent type, pH, particle size, agitation time, temperature,
initial dye concentration, and desorption. The results obtained showed that the adsorb ability of (RhB) to
the BPH is higher than that of the BPK carbon by approximately 10 folds (198.6 and 21.5mgg−1, respectively).
Kinetic studies show that the adsorption of RhB proceeds according to the pseudo-second-order.
The intra-particle diffusion was identified to be the rate-limiting step in addition to the film diffusion.
The adsorption was analyzed using 5 isotherm models (Langmuir, Freundlich, Temkin, Harkins–Jura, and
Halsey isotherm equations). The highest values of r2 were obtained with Langmuir (0.997). The adsorption
capacity, qm, was 263.85 (mg g−1) at initial pH 5.7 for the particle size 0.25nm and equilibrium time of
240 min at a temperature of 20 ◦C and initial dye concentration range of 100–600 (mg l−1). Temperature
effect proves that the adsorption is endothermic with �H= 4.151 (kJ mol−1), �S = 65.786 (J mol−1 K−1)
and a decrease in Gibbs energy (�G=−7.939 to −26.729 kJ mol−1). Desorption studies were carried out
using water medium, HCl and NaOH with desorption of 2.7, 5.4 and 7.8%, respectively of adsorbed RhB
confirming the chemical adsorption mechanism of the dye. This adsorbentwas found to be both effective
and economically viable.

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Journal of Hazardous Materials
journal homepage: www.elsevier.com/locate/jhazmat
Activated carbon from agricultural by-products for the removal of
Rhodamine-B from aqueous solution
Hamdi M.H. Gad∗, Ashraf A. El-Sayed
Hot Laboratories and Waste Management Centre, Egyptian Atomic Energy Authority, P.O. 13759, Cairo, Egypt
article info
Article history:
Received 27 September 2008
Received in revised form 26 February 2009
Accepted 27 February 2009
Available online xxx
Keywords:
Activated carbon
Bagasse pith
Rhodamine B
Isotherm models
Desorption
abstract
Bagasse pith (BP) has been utilized for activated carbon preparation using H3PO4(BPH) or KOH (BPK)
as a chemical activating agent followed by carbonization at 500 ◦C. The physicochemical properties of
activated carbon were carried out. The effectiveness of carbon prepared in adsorption of Rhodamine B
(RhB) has been studied as a function of adsorbent type, pH, particle size, agitation time, temperature,
initial dye concentration, and desorption. The results obtained showed that the adsorb ability of (RhB) to
the BPH is higher than that of the BPK carbon by approximately 10 folds (198.6 and 21.5 mgg−1, respec-
tively). Kinetic studies show that the adsorption of RhB proceeds according to the pseudo-second-order.
The intra-particle diffusion was identified to be the rate-limiting step in addition to the film diffusion.
The adsorption was analyzed using 5 isotherm models (Langmuir, Freundlich, Temkin, Harkins–Jura, and
Halsey isotherm equations). The highest valuesof r2were obtained with Langmuir (0.997). The adsorption
capacity, qm, was 263.85 (mgg−1) at initial pH 5.7 for the particle size 0.25 nm and equilibrium time of
240 min at a temperature of 20◦C and initial dye concentration range of 100–600 (mg l−1). Temperature
effect proves that the adsorption is endothermic with H=4.151 (kJmol−1), S= 65.786 (J mol−1K−1)
and a decrease in Gibbs energy (G=−7.939 to −26.729 kJ mol−1). Desorption studies were carried out
using water medium, HCl and NaOH with desorption of 2.7, 5.4 and 7.8%, respectively of adsorbed RhB
confirming the chemical adsorption mechanism of the dye. This adsorbent was found to be both effective
and economically viable.
Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
1. Introduction
Color is the first contaminant to be recognized in water and has
to be removed from wastewater before discharging it into water
bodies. Residual dyes are the majorcontributors to color in wastew-
aters generated from textile and dye manufacturing industries, etc.
[1]. Color impedes light penetration, retards photosynthetic activ-
ity, inhibits the growth of biota and also has a tendency to chelate
metal ions which result in micro-toxicity to fish and other organ-
isms [2]. It should be noted that the contamination of drinking
water by dyes at even a concentration of 1.0mg l−1could impart
significant color, making it unfit for human consumption [1]. Most
of the used dyes are stable to photo-degradation, bio-degradation
and oxidizing agents [2]. Currently, several physical or chemical
processes are used to treat dye-laden wastewaters. However, these
processes are costly and cannot be used effectively to treat the
wide range of dye-laden wastewater. The advantages and disad-
vantages of some methods of dye removal from wastewaters are
given in Table 1 [3]. The adsorption process is one of the efficient
∗Corresponding author.
E-mail address: hmhgad1@yahoo.com (H.M.H. Gad).
methods to remove dyes from effluent and has an advantage over
the other methods due to the excellentadsorption efficiency of acti-
vated carbon (powdered or granular) for organic compounds even
from dilute solutions, but commercially available activated carbons
are very expensive.
Various carbonaceous materials, such as coal, lignite, coconut
shells, wood and peat are used in the production of commercial
activated carbons [4]. However, the abundance and availability of
agricultural by-products make them good sources of raw materials
for activated carbons. Agricultural by-products [5] are renewable
sources of raw materials for activated carbon production because
the development of methods to reuse waste materials is greatly
desired. Residues from agriculture and agro-industries are the
non-product outputs from the growing and processing of raw agri-
cultural products such as rice, corn, beans and peanuts [6]. Disposal
of agricultural by-products is currently a major economic and eco-
logical issue, and the conversion of by-products to adsorbents,
such as activated carbon, represents a possible outlet. A number
of agricultural waste materials are being studied for the removal of
different dyes from aqueous solutions at different operating con-
ditions (Table 2;[1]). Activated carbon prepared from bagasse pith
is a promising adsorbent for the removal of dyes from wastewa-
ter [28,44,45]. In Egypt, this agricultural by-product is produced
0304-3894/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jhazmat.2009.02.155

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Table 1
Advantages and disadvantages of the methods used for dye removal from industrial effluents [3].
Physical/chemical methods Advantages Disadvantages
Fentons reagent Effective decolorization Sludge generation
Ozonation No change in effluent volume Short half life (20 min)
Photochemical No sludge generation Formation of by-products
NaOCl Initiate azo-bond cleavage Release of aromatic amines
Electrochemical Non-hazardous end products High cost of electricity
Activated carbon Highly effective for various dyes Very expensive
Peat Good adsorbent Surface area is low
Silica gel Effective for basic dyes Side reactions in effluent
Membrane filtration Removes all dyes Concentrated sludge production
Ion exchange No adsorbent loss Not effective for all dyes
in huge amount continuously. This by-product is a carbonaceous,
and fibrous solid waste, which creates a disposal problem and
is generally used for its fuel value. Therefore, it was of inter-
est to prepare a higher value product, such as activated carbon,
from it.
The high adsorptive capacities of activated carbons are related
to properties such as surface area, porosity, and surface functional
groups. These unique characteristics are dependant on the type of
raw material employed and method of activation. Basically, there
are two different processes for the preparation of activated carbon:
physical and chemical activation [7]. Physical activation involves
carbonization of the carbonaceous precursor followed by activa-
tion of the resulting char in the presence of activating agents such
as carbon dioxide or steam. Chemical activation, on the other hand,
involves the carbonization of the precursorin the presence of chem-
ical agents. In physical activation, the elimination of a large amount
of internal carbon mass is necessary to obtain a well-developed
porous structure, whereas in chemical activation process, chemical
agents used are dehydrating agents that influence pyrolytic decom-
position and inhibit the formation of tar, thus enhancing yield of
carbon. Chemical activation has more advantages [8],overphysi-
cal activation with respect to higher yield, more surface area and
better development of porous structure in carbon. It also helps
to develop oxygenated surface complexes on the surface of acti-
vated carbon. Consequently, the aim of this work was to study
the feasibility of developing an efficient adsorbent from agricul-
tural by-product by H3PO4(or KOH) activation and to investigate
its adsorption capacity by removal of dye from aqueous solu-
tions.
RhB was selected for the adsorption experiment due to its
presence in the wastewaters of several industries (such as textile,
leather, jute and food industries). Detection of gamma rays is now a
days using the photosensitivedye, which changes its color with inci-
dent radiation. To evaluate the suitability of the prepared activated
carbon for its use in water and wastewater treatment systems, its
characterization has been done for physical, chemical and adsorp-
tion properties because these preliminary studies provide good
information about the applicability of the product in a treatment
system.
2. Experimental
2.1. Adsorbent raw material
In the manufacture of sugar, the sugar cane stalks are chopped
to small pieces by rotary knives, and juice is extracted by crushing
them through one or more roller mills. During this process more
than 95% of sucrose content of the cane is removed. The waste
residual material from this operation is termed bagasse pith. The
moisture content of bagasse pith was 14.5±0.5% [9], and it was
not subjected to any form of pretreatment prior to use. The Egyp-
tian bagasse pith was subjected to chemical analysis [10] and the
results obtained are given in Table 3.
2.2. Preparation of activated carbon
Bagasse pith (BP) was chosen as precursor for the production of
activated carbons by one-step chemical activation using H3PO4(or
KOH). In each experiment, 60g of crushed bagasse pith was soaked
in 100ml of 70% H3PO4(or KOH) solution to cover it completely,
slightly agitated to ensure penetration of the acid (or base) through-
out, then the mixture was heated to 80◦C for 1 h and left overnight
at room temperature to help appropriate wetting and impregnation
of the precursor. The impregnated mass was dried in an air oven
at 80 ◦C overnight, then, admitted into the reactor (ignition tube),
which was then placed in a tubular electric furnace open from both
ends. The temperature was raised at the rate of (50 ◦C/10 min.) to
the required end temperature. The carbonization process was car-
ried out at 500 ◦C for 80 min in limited air. The product – (BPH)
refers to H3PO4treatment, whereas (BPK) refers to KOH treatment
– was thoroughly washed with warm distilled water (70◦C) until
pH of the solution came close to the initial pH of the rinsing water.
Finally, the activated carbon was dried at 110◦C for 24 h and sieved
to different particle sizes and kept for use.
2.3. Characterization of prepared BPH activated carbon
The resulting carbon was then characterized with respect
to its pore structure and surface area using nitrogen
Table 2
Some agricultural wastes studies for dye(s) removal from aqueous solutions [1].
No. Agricultural waste Dye(s)
1 Maize cob Astrazon blue, Erionyl red
2 Coconut shell, groundnut shell Methylene blue
3 Silk, cotton hull, coconut tree sawdust, maize cob Rhodomine-B, congo red, methylene blue, methyl violet, malachite green
4 Rice husk Malachite green, basic, acid direct and disperse dyes, acid yellow 36, saframnine, methylene blue
5 Orange peel Acid violet 17
6 Coir pith Acid violet, acid brilliant blue, methylene blue, Rhodomine-B, congo red
7 Banana and orange peels Methylene orange, methylene blue, methyl violet, acid black, Congo red, Rhodamine-B, procion orange
8 Banana pith Congo Red, Rhodamine-B, acid violet, acid brilliant blue, acid brilliant blue
9 Groundnut shell powder Basic, direct and disperse dyes
10 Wheat straw, corncob, bark husk. Cibacron yellow C-2R, cibacron red C-2G, cibacron blue C-R, remazol black B, remazol red RB.

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Table 3
Physicochemical characterization of BPH activated carbon and chemical analysis of bagasse pith.
No. Parameters Values No. Parameters Values
1 Carbon yield (%) 95 15 Phenol number (mg) 150
2 Ash content (%) 6.5 16 Iodine number (mgg−1)740
3 Methylene blue number (mgg−1) 280 17 Particle size (mm) 1.0–0.25
4 Packed density (gml−1) 0.284 18 Matter soluble in water (%) 1.7
5 Apparent density (g ml−1) 0.17 19 Matter soluble in acid (%) 2.42
6 BET surface area (m2g−1) 522.7 20 Matter soluble in base (%) 2.31
7 Langmuir surface area (m2g−1) 797 21 Moisture content (%) 6
8 Average pore radius (Å) 15.04 22 C% 75.76
9 Half pore width (Å) 7.374 23 H % 3.56
10 Micropore surface area (m2g−1) 589.6 24 N % 2.1
11 Total pore volume (cm3g−1) 0.388 25 S % 0.6
12 Micropore volume (cm3g−1) 0.091 26 O % (by difference) 16.98
13 Mesopores volume (cm3g−1) 0.297 27 pH 3.5
14 Point of zero charge (pHPZC) 3.9 28
Chemical analysis of bagasse pith raw material %
1␣-Cellulose 53.7 4 Alcohol/benzene solubility 7.5
2 Pentosan 27.9 5 Ash 6.6
3 Lignin 20.2
adsorption/desorption at −196 ◦C which was conducted using
a gas sorption analyzer (Quantachrome, NOVA 1000e series, USA),
pH, elemental analysis, ash content, density, solubility in water,
acid and base.
2.4. Adsorption procedure
The sorption study was performed by batch sorption exper-
iments using RhB as an adsorbate and bagasse pith activated
carbon as an adsorbent. The properties of RhB are presented in
Table 4. The dye was made up in stock solutions of concentration
1000mgl−1and was subsequently diluted to required concentra-
tions (100–600 mg g−1). Calibration curve for dye was prepared
by recording the absorbance values for a range of known concen-
trations at the wavelength for maximum absorbance. This value,
max, was found to be 554 nm for RhB. The pH of the solution
was adjusted using HCl and NaOH and all pH measurements
were carried out using a digital pH meter. Temperature controlled
shaking thermostat was used to control the desired tempera-
ture. The effect of experimental parameters such as pH value,
temperature, different particle sizes of carbon and concentration
were studied. Blanks were run simultaneously without any sor-
bent.
Adsorption experiments were conducted by adding 100 mg of
activated carbons into a series of 250 ml Erlenmeyer each filled with
100ml of experimental solution with each initial concentration,
particle size of carbon, pH and temperature. All of the Erlenmeyer
were then covered with aluminum foil and placed to a thermo-
static shaker bath and shaken to eqilibrium. After equilibrium time
had been reached, activated carbon was separated from the solu-
tion by centrifugation at 3000 rpm for 5 min. The absorbance of
clarified supernatant solution was analyzed using a UV–vis spec-
trophotometer (Shimadzu 160-A Model). The amount of adsorbed
RhB [uptake (mg g−1) at time t,qt], was calculated from the mass
Table 4
Properties of Rhodamine-B.
Parameters Values Parameters Values
Suggested name Rhodamine-B Solubility in water 0.78%
C.I. number 45170 Solubility in ethanol 1.47%
C. I. name Basic violet 10 Absorption maximum 56.5
Class Rhodamine Empirical formula C28 H31N2O3Cl
Ionization Basic Formula weight 479.029
Color Red
balance equation:
qt=Ce−Ct×V
M(1)
when tis equal to the equilibrium contact time, Ct=Ce,qt=qe, and
the amount of adsorbed at equilibrium, qe, is calculated using Eq.
(1).
2.5. Desorption studies
After adsorption experiments the RhB laden carbon was sepa-
rated out by filtration using Whattman filter paper no. 42 and the
filtrate was discarded. The RhB loaded carbon was given a gentle
wash with double-distilled water to remove the unadsorbed RhB if
present. Desorption studies were carried out using several such car-
bon samples. They were agitated with distilled water, NaOH or HCl
solution of 0.1N concentration. The desorbed RhB in the solution
was separated by centrifugation and analyzed as before.
3. Results and discussion
Neither changes appeared in the absorption spectrum nor addi-
tional peaks formed for the dye solution after shaking it with the
adsorbent. This indicated that there was no breakdown product(s)
of the dye and also supported the fact that the dye removal from
the solution in this study was through the mechanism of adsorption
[11].
In activated carbon–liquid phase interactions,it has been known
that the adsorption capacity depends on a number of factors
namely: (a) the physical natureof the adsorb ent-pore structure, ash
content and functional groups; (b) the nature of the adsorbate, its
pKa, functional groups present, polarity, molecular weight and size;
(c) the solution conditions such as pH, ionic strength and the adsor-
bate concentration. In the following sections we will investigate
some of these factors.
3.1. Characterization of BPH activated carbon
Pore characteristic of the activated carbon was determined by
N2adsorption. The nitrogen adsorption/desorption isotherms of
BPH activated carbon is illustrated in Fig. 1. The activated carbon
possessed combination of type I and type II of IUPAC isotherm,
indicating simultaneous presence of micropores and mesopores.
This isotherm also exhibited a type H4 hysteresis loop, character-
istic of slit-shaped pores. The pore characteristics of BPH activated

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Fig. 1. Nitrogen adsorption/desorption isotherm of BPH activated carbon.
carbon are given in Table 3. The presence of micropores and meso-
pores in the activated carbon prepared from bagasse pith were also
indicated by the pore size distribution as depicted in Fig. 2.Aprox-
imate analysis of the BPH was carried out, using the recommended
standard methods of analysis. The physicochemical characteriza-
tion of BPH activated carbon and its precursor (bagasse pith) is
summarized in Table 3.
3.2. The effect of adsorbent surface change
The BP treated with H3PO4has larger capacity compared to the
BP treated with KOH, as shown in Fig. 3. The treatments with acid
produce three types of surface oxides: acidic, basic, and neutral
[12]. Fixation of the acidic groups on the surface of the activated
carbon makes it more hydrophilic and decreases its pH of the
point of zero charge [13]. Puri and Mahajan [14] have reported
that the replacement of alkaline ions with H+on charcoal causes
the hydrophobicity of the surface of the carbon to increase. So,
in our study, the adsorbability of RhB to the BPH carbon is higher
than that of the BPK carbon by approximately 10 folds (198.6
and 21.5 mg g−1, respectively). Two agents (H3PO4and KOH) can
produce different surface properties. Higher adsorption capacity of
BPH indicates two possibilities; one is that the hydrophobicity and
hyrophilicty of the carbon surface have no effect on the adsorption;
Fig. 2. Pore size distribution of BPH activated carbon.
Fig. 3. Effect of activating agent on the adsorption of RhB.
the other is that they are all fit for the adsorption process, as
the RhB ions have different functional groups. From the obtained
results, the BPH carbon was used in the further investigation of the
factors affecting of on the adsorption of RhB.
3.3. Effect of pH
The effect of pH on the adsorption of RhB ions onto BPH carbon
was determined. The result is shown in Fig. 4. The experimental
data showed that the uptake of RhB at pH 2.45 was 190.8 (mgg−1)
and it has been observed that the uptake decreases with increase
in pH. As shown, at pH 3.44 the uptake was 187.9(mg g−1) where,
at pH 10 the RhB uptake was 168.7 (mgg−1). The influence of pH
on the pronounced sorption of RhB on the surface of the carbon
at low pH ranges leads to the assumption that chemisorptions
dominates in this range and chemisorptions along with physisorp-
tion occurs at higher pH ranges [15]. In addition, it appears that
a change in pH of the solution results in the formation of dif-
ferent ionic species, and different carbon surface charge. At pH
values lower than 4, the RhB ions are of cationic and monomeric
molecular form [16], thus theyRhB can enter into the pore struc-
ture. At a pH value higher than 4, the zwitterionic form of RhB
in water (Fig. 5) may increase the aggregation of RhB to form a
larger molecular form (dimer) and become unable to enter into the
pore. Ghanadzadeh et al. [17] have studied the aggregation of RhB
in the microporous solid hosts. Lopez Arbeloa and Ruiz Ojeda [18]
determined the equilibrium constant for the dimer↔monomer
transition of RhB in aqueous solution. The greater aggregation of
the zwitterionic form is due to the attractive electrostatic interac-
tions between the carboxyl and xanthene groups of the monomers
[19].
3.4. Effect of contact time and initial dye concentration
Very rapid adsorption was found during the adsorption time
of 4 h. However, the amount of RhB adsorbed increases with time
and reaches a constant value after 5h. After the equilibrium time,
the amount of RhB adsorbed did not alter with time. Thus, the
mixing time for the rest of adsorption studies was set to be 5 h
to ensure the equilibrium in adsorption and kinetic studies. The
amount of RhB dye adsorbed per unit mass of BPH activated car-
bon increased with increase in dye concentration in test solution. It
increased from 100 to 264mg g−1as the RhB concentration in the
test solution was increased from 100 to 600 mgl−1. Maximum dye
was sequestered from the solution within 4h after the start of every
experiment. After that, the concentration of RhB in liquid phase
remained almost constant. In the process of dye adsorption initially
dye molecules have to first encounter the boundary layer effect and

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Fig. 4. Effect of initial pH solution on the adsorption of RhB onto BPH activated carbon.
Fig. 5. Molecular form of RhB (cationic and zwitterionic form).
then they have to diffuse from boundary layer film onto adsorbent
surface and then finally, they have to diffuse into the porous struc-
ture of the adsorbent. For higher initial concentration studied, it
was found that there was no significant change on the equilibrium
time at the observed initial RhB concentration range. The uptake
(mg g−1) of dye removal versus time curves is single, smooth and
continuous leading to saturation(Fig. 6), suggesting the possibil-
ity of monolayer coverage of RhB on the outer surface of the BPH
activated carbon[20]. These observations are consistent with the
Fig. 6. Effect of contact time and initial dye concentration on the adsorption of RhB
onto BPH activated carbon.
observations of other results [21,22] for the biosorption of basic
dyes by water hyacinth, duckweed and sawdust.
3.5. Kinetic of adsorption of RhB onto BPH activated carbon
In order to investigate the mechanism of sorption and potential
rate-controlling steps such as mass transport and chemical reaction
processes, kinetic models have been used to test experimental data.
These kinetic models included the pseudo-first order, the pseudo-
second-order and the Elovich equations.
Fig. 7. Plot of logkcagainst reciprocal temperature for RhB sorption onto BPH acti-
vated carbon.

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Table 5
Kinetic of adsorption of RhB onto BPH activated carbon: first-order constants for the effect of pH, particle sizes, concentration and temperature.
Parameter Values First-order equation log (qe−qt) = log (qe)−k1/2.303.t
qe, exp. mg g−1qeCalcu. mg g−1K1(min−1)r2Slope X10−3
pH
2.45 192.5 219.8 16.1×10−30.965 6.96
3.44 188.7 283.9 18.7×10−30.957 8.16
6.03 183.9 319.3 20.9×10−30.951 9.08
8.47 176.8 277.1 17.6×10−30.960 7.65
10.33 169.9 214.9 16.4 ×10−30.965 7.13
Particle size (mm)
<0.25 200.0 355.2 20.8 ×10−30.961 9.06
<0.50 192.5 261.5 18.8×10−30.971 8.20
<1.00 188.7 280.3 18.2×10−30.978 7.92
Concentration (mgl−1)
100 100.0 46.60 14.6 ×10−30.928 6.35
200 198.6 337.1 18.9 ×10−30.958 7.10
300 213.8 345.2 18.2×10 −30.947 7.90
400 235.0 419.9 19.2 ×10−30.955 8.24
500 258.0 330.4 18.4 ×10−30.952 8.33
600 264.0 373.8 19.7 ×10−30.972 8.55
Temperature (◦C)
20 192.6 364.1 21.8 ×10−30.945 9.48
35 195.9 350.3 20.4×10 −30.959 8.87
50 199.6 280.7 18.1 ×10−30.965 7.87
70 218.8 196.12 11.9 ×10−30.974 5.17
3.5.1. Pseudo-first order reaction
The pseudo-first order equation of Lagergren [23] is generally
expressed as follows:
log(qe−qt)=log(qe)−k1
2.303.t (2)
where qeand qtare the sorption capacities at equilibrium and at
time t, respectively (mgg−1) and k1(min−1) is the rate constant.
The equation applicable to experimental results generally differs
from a true first order equation in two ways [24]: (i) the parameter
log (qe−qt) does not represent the number of available sites and
(ii) the parameter log (qe) is an adjustable parameter and often it
is found not equal to the intercept of a plot of log (qe−qt) against t,
whereas in a true first order log (qe) should be equal to the intercept
of a plot of log (qe−qt) against t. In order to fit Eq. (2) to experimen-
tal data, the equilibrium capacity, qe, must be known. In many cases
qeis unknown and as chemisorption tends to become immeasur-
ably slow, the amount sorbed is still significantly smaller than the
equilibrium amount [25]. In over 50% of literature references, based
on analyzing sorption kinetics, authors did not measure an equilib-
rium isotherm [26].
The data for the sorption of RhB onto BPH activated carbon
were plotted according to Eq. (2) and the results are summarized in
Table 5. The equilibrium capacity qewas obtained by trial and error
and the correlation coefficients are shown in Table5 for the ef fect of
pH, particle size, concentration and temperature. Numerous appli-
cations of the Lagergren equation (pseudo-first order systems) have
been reported. Boyd et al. [27] proposed that: (i) if the film diffu-
sion is rate controlling, the slope of the plots of Eq. (9) will vary
inversely with the particle size, the film thickness and with the
distribution coefficient, k; (ii) if the sorption rate-controlling step
is chemical exchange, the slope will be independent of particle
diameter and flow rate and will depend only on the concentra-
tion of the sorbate in solution and the temperature. In the case of
the sorption of RhB onto BPH activated carbon, the rate constant
is independent of concentration but dependent on temperature.
Table 6
Kinetic of adsorption of RhB onto BPH activated carbon: pseudo-second-order parameters for the effect of pH, particle sizes, concentration and temperature.
Parameter Values Second-order equation t/qt=1/kq2
e+1/qet
qeexp. mg g−1qecalcu. mg g−1kg mg−1min−1r2h=kq2
e
pH
2.45 192.5 224.2 8.6×10 −50.994 4.323
3.44 188.7 223.2 8.6×10 −50.992 4.284
6.03 183.9 219.3 8.4×10 −50.992 4.039
8.47 176.8 208.3 8.3×10 −50.993 3.601
10.33 169.9 199.6 8.2 ×10−50.993 3.266
Particle size (mm)
<0.25 200.0 239.2 7.4×10 −50.994 4.234
<0.50 192.5 230.9 7.3×10 −50.994 3.892
<1.00 188.7 229.9 6.8×10 −50.993 3.594
Concentration (mg l−1)
100 100.0 104.8 5.9 ×10−40.998 6.479
200 198.6 242.7 5.7 ×10−50.992 3.357
300 213.8 264.6 5.0 ×10−50.997 3.501
400 235.0 295.9 4.8 ×10−50.995 4.203
500 258.0 312.5 4.6 ×10−50.997 4.492
600 26 4.0 319.6 4.4 ×10−50.996 4.494
Temperature (◦C)
20 192.6 234.2 6.7 ×10−50.994 3.675
35 195.9 235.3 6.9 ×10 −50.994 3.820
50 199.6 236.6 7.9 ×10−50.994 4.311
70 218.8 258.4 6.5 ×10 −50.995 4.340

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The mechanism of RhB sorption onto BPH may be chemically rate
controlling.
3.5.2. Pseudo-second-order reaction
If the rate of sorption is a second-order mechanism, the pseudo-
second-order chemisorption kinetic rate equation is expressed as:
t
qt
=1
kq2
e
+1
qet(3)
where qeand qtare the sorption capacities at equilibrium and at
time t, respectively (mgg−1) and kis the rate constant of pseudo-
second-order sorption (g mg−1min−1). where hcan be regarded as
the initial sorption rate as qt/t→0, hence:
h=kq2
e(4)
Eq. (3) can be written as:
t
qt
=1
h+1
qet(5)
Eq. (3) does not have the disadvantage of the problem with
assigning an effective qe. If pseudo-second-order kinetics are appli-
cable, the plot of t/qtagainst tof Eq. (3) should give a linear
relationship, from which qe,kand hcan be determined from the
slope and intercept of the plot and there is no need to know any
parameter beforehand.
The application of second-order equation to the experimental
results of adsorption of RhB onto BPH activated carbon, gives the
highest values of the correlation coefficient of the three kinetic
models under investigation: (i) Effect of initial pH: The highest value
of correlation coefficient and initial sorption rate are obtained at
the value of 2.45 of initial pH and decreased as the pH of solu-
tion increased confirming the experimental results obtained, where
sorption capacity decreased from 224.2 to 199.6 mg g−1when the
pH of the dye solution was increased from 2.45 to 10.33. (ii) Effect
of particle size of the adsorbent: Table 6 illustrated that increasing
the particle size of adsorbent from < 0.25 to <1.00 mm leading
to the decrease in adsorption capacity, adsorption rate, correlation
coefficient and initial rate of adsorption. (iii) Effect of initial dye con-
centration: Table 6 shows the constants of Eq. (2) that were obtained
from slope and intercept. All the fits show very good correlation
coefficients. HO and McKay presented similar results for the sorp-
tion systems of basic and acid dyes onto pith [28]. The equilibrium
sorption capacity qeincreased from 104.8 to 319.6 mg g−1when
the initial concentration of RhB increased from 100 to 600 mgl−1.
But, the values of the rate constant were found to decrease from
5.9 ×10−4−− to 4.4 ×10−5gmg
−1min−1for an increase in the ini-
tial concentration and this is may be due to strike hindrance of
higher concentration of dye. (iv) Effect of temperature:Table 6 shows
the sorption kinetics of RhB removal at 20, 35, 50 and 70 ◦C at the
initial dye concentration of 250mg l−1. Increasing the temperature
from 20 to 70◦C, the removal of the dye increased from 234.2 to
258.4 mg g−1. This may be due to a tendency for the dye molecules
to escape from the bulk phase to the solid phase with an increase
in temperature of the solution [29]. The temperature dependence
of dye sorption by BPH activated carbon shows a good compliance
with the pseudo-second-order equation, which is reflected by high
coefficients of correlation as shown in Table 6.Fig. 7 shows a linear
relationship between the logarithm of rate constant and the recip-
rocal of temperature. The activation energy (E) for the sorption of
RhB by BPH sorbent was calculated using the Arrhenius equation
[30]:
k=k0exp −E
RT (6)
where k(g mg−1min−1) is pseudo-second-order constant of sorp-
tion, k0is the temperature independent factor (gmg−1min−1), R
Table 7
Kinetic of adsorption of RhB onto BPH activatedcarbon: Elovich equation parameters
for the effect of pH, particle sizes, concentration and temperature.
Parameter Values Elovich Equation qt=ˇln (aˇ)+ˇln (t)
ˇ˛ r2
pH
2.45 45.08 0.00653 0.982
3.44 44.69 0.00592 0.980
6.03 44.11 0.00588 0.979
8.47 41.61 0.00564 0.981
10.33 39.45 0.00558 0.982
Particle size (mm) <0.25 48.48 0.00433 0.982
<0.50 47.29 0.00427 0.977
<1.00 48.22 0.00362 0.976
Concentration (mg l−1)
100 9.58 0.00101 0.949
200 50.95 0.00226 0.983
300 55.37 0.00270 0.974
400 62.69 0.00277 0.971
500 61.21 0.00363 0.994
600 62.11 0.00401 0.989
Temperature (◦C)
20 48.94 0.00358 0.985
35 48.29 0.00401 0.985
50 46.69 0.00515 0.986
70 51.58 0.00518 0.988
is the gas constant (8.314J mol−1K−1), and Tis the solution tem-
perature (K).From this equation, the rate constant of sorption, k0
is 3.865 ×10 −4gmg
−1min−1and the activation energy of sorption
Eis 62.03 kJ mol−1.These findings show that dye adsorption pro-
cess by BPH activated carbon is chemisorptions and endothermic
process.
3.5.3. Elovich model
The Elovich equation is generally expressed as follows [31]:
qt=ˇln(˛ˇ)+ˇln(t) (7)
Where qtis the sorption capacity at time t(mg g−1), ˛is the
initial sorption rate (mgg−1min−1) and ˇis the desorption con-
stant (g mg−1) during any experiment. Thus, the constants can be
obtained from the slope and the intercept of a straight line plot of
qtagainst ln (t).
Table 7 lists the kinetic constants obtained from the Elovich
equation. It will be seen from the data that the value of ˛and ˇ
varied as function of the pH, particle size of the adsorbent, initial
dye concentration and temperature.(a) Ef fectof initial pH of solution:
The values of ˛and ˇdecrease as the pH of the solution increases,
this is in agreement with the experimental results obtained. (b)
Effect of particle size of adsorbent: As the particle size decreases the
initial adsorption rate, ˛, increases, this is because higher surface
area with smaller particle leads to higher initial adsorption rate
confirming the results obtained from the second-order reaction
listed in Table 6. (c) Effect of initial dye concentration: On increas-
ing the initial dye concentration, the value of ˛, initial adsorption
rate, increases and the value of ˇ, desorption constant, decreases
with the concentration more than 400 mgl−1. (d) Effect of tempera-
ture: As the temperature increases from 20 to 70 ◦C, the value of ˛
increases from 35.8×10−4to 51.8 ×10−4.
3.5.4. Intra-particle diffusion
Sorption of sorbate on sorbent proceeds in several steps, involv-
ing transport of the solute molecules from the aqueous phase to the
surface of the solid particulates (film diffusion) and diffusion of the
solute molecules into the interior of the pores, which is usually a
slow process. The intra-particle diffusion rate constant (kid)isgiven
by the Weber–Morris equation [32]:
qt=k0.5
idt+I (8)

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Fig. 8. Intra-particle diffusion of RhB through adsorption onto BPH activatedcarbon.
where kid is the rate constant of intra-particle transport in
mg g−1min1/2 and I, is the boundary layer (film diffusion). When
intra-particle diffusion plays a significant role in controlling the
kinetics of the sorption process, the plots of qtversus t0.5 yield a
straight line passing through the origin and the slope gives the rate
constant, kid.
The sorption of RhB onto the BPH activated carbon depends on
film diffusion and intra-particle diffusion, and the more rapid one
will control the overall rate of transport. Thus, the concentration of
the sorbed RhB, qt(mg g−1) was plotted against time applying the
Weber–Morris equation as shown in Fig. 8. According to the intra-
particle diffusion model, a linear plot indicates a rate controlled by
intra-particle diffusion. This is due to the fact that fractional uptake
will vary with the function kid (t)0.5. In contrast, the plot obtained
from this study shows multi-linearity with 2 steps. The first part of
the multi-linear plot is attributed to boundary layer diffusion, the
second to the intra-particle diffusion and the chemical reaction. The
multi-linearity curve indicates that intra-particle diffusion is not a
fully operative mechanism in the sorption of RhB by the BPH.
The diffusion rate was found high in the initial stages
(kid =10.47mgg
−1min−1) and decreased on passage of time
(kid = 0.074mg g−1min−1), indicating that the rate of the adsorp-
tion step is film diffusion at the early stage of removal of dye. The
value of kid indicated that intra-particle diffusion step could be a
rate-controlling step. The change in the slope may be due to the
existence of different pore sizes [33]. This behavior was also con-
firmed from the linear plot of Btversus time employing Reichenburg
equation [34]:
Bt=−0.4977 −2.303 log(1 −F) (9)
Where Btis a mathematical function (F)ofqt/qe. The plot was linear
up to 120min and does not pass through the origin (correlation
coefficient, r2= 1).
3.6. Sorption isotherm studies
Adsorption isotherms are important for the description of how
adsorbates will interact with an adsorbent and are critical in opti-
mizing the use of adsorbent. Thus, analysis of the results obtained
from the equilibrium isotherm studies is fundamental to evaluate
the affinity of the adsorbent for a particular adsorbate. Equilib-
rium studies are described by a sorption isotherm characterized by
certain constants whose values express the surface properties and
affinity of the adsorbent. Consequent upon this, the results obtained
from these studies were tested with 5 different isotherm equa-
tions (i.e. Langmuir, Freundlich, Temkin, Halsey, and Harkins–Jura
isotherm equations): (1) The monolayer coverage of the adsorbate
on the adsorbent surface at constant temperature is represented
by the Langmuir isotherm. The Langmuir isotherm hints towards
surface homogeneity. The linearized form of the equation can be
represented thus [35];
Ce
qe
=1
kqm
+x
qmCe(10)
where Ceis the concentration of the adsorbate at equilibrium
(mg l−1), qeis the amount of adsorbate adsorbed at equilibrium
per unit mass of adsorbent (mg g−1), qmis the monolayer sorption
capacity at equilibrium (mg g−1), and kis the Langmuir equilibrium
constant (l mg−1). A plot of Ce/qeversus Cegives a straightline, if the
sorption process is described by the Langmuir isotherm equation.
The values of qmand kare obtained from the slope and intercept
of the straight line plot. (2) The Freundlich isotherm is regarded
as an empirical isotherm. It indicates the surface heterogeneity of
the adsorbent. The linearized form of the isotherm is expressed
thus;
ln qe=ln Kf+1
nln Ce(11)
Where kfand nare Freundlichcoefficients, obtainable from the plots
of ln qeversus ln Ce.kfand nare Freundlich adsorption constants,
related to adsorption capacity and sorption intensity, respectively.
(3) Temkin and Pyzhev [36] studied the heat of adsorption and
the adsorbent–adsorbate interaction on surfaces [36]. The Temkin
isotherm equation is given as:
qe=B1ln KT+B1ln Ce(12)
where B1=RT/b,T(K) is the absolute temperature, Ris the uni-
versal gas constant (8.314 J mol−1), KTis the equilibrium binding
constant (l mg−1), and B1is related to the heat of adsorption. The
Temkin constants are obtained from the plot of qeversus ln Ce. (4)
The Harkin–Jura[37] adsorption isotherm can be expressed as:
1
q2
e
=B
A−1
Alog Ce(13)
the isotherm equation accounts for multilayer adsorption and can
be explained by the existence of a heterogeneous pore distribution.
(5) The Halsey adsorption isotherm (Halsey) [38] can be given as:
ln qe=1
nln k−1
nln Ce(14)
this equation is suitable for multilayer adsorption and the fitting of
the experimental data to this equation attest to the heteroporous
nature of the adsorbent.
Results of adsorption isotherms showed the shape of type L
(Fig. 9) according to the classification of Giles et al. [30]. The L (or
Langmuir) shape of the isotherms means that there is no strong
Fig. 9. Adsorption isotherm of RhB dye onto BPH activated carbon.

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Table 8
Langmuir parameters at different conditions.
Langmuir parameters at different temperatures
and constants concentration (200 mgl−1).
Langmuir parameters at different
concentrations and constant temperatures
20 ◦C35
◦C50
◦C70
◦CAt20
◦CRL[RL= 1/1 + bC0]C0(mg l−1)
qm(mg g−1) 93.1 98.23 103.6 119.3 263.85 0.072 100
b(l mg−1) 0.142 0.1862 0.258 0.0616 0.1286 0.025 300
r20.982 0.983 0.979 0.991 0.9970 0.013 600
Table 9
Parameters of different isotherms of adsorption of RhB onto BPH activated carbon.
Freundlich isotherm Temkin isotherm Harkins–Jura isotherm Halsey isotherm
Kf= 158.5 (l g−1)B= 14.1 A=0.5835 n=11.33
n=10 KT= 172.7 (l mg−1)B= 3.095 K= 154.58
r2= 0.9595 r2= 0.9656 r2= 0.922 r2=0.989
competition between the solvent and the adsorbate to occupy the
adsorbent sites. In this case, the longitudinal axes of the adsorbed
molecules are parallel to the adsorbent surface [30]. The results
obtained were analyzed using 5 different isotherm equations. In
order to understand the mechanism of RhB adsorption onto BPH,
the experimental data were fitted to the aforementioned equilib-
rium isotherm equations and the different isotherm parameters,
obtained from the different plots, are presented in Tables 8 and 9.
An error function is required to evaluate the fitness of each isotherm
equation to the experimental data obtained from the optimiza-
tion process employed. In the present study the linear coefficient
of determinations, r2, was used. The values of the linear correla-
tion, r2, of each isotherm equation, when fitted to the experimental
data are presented in Tables 8 and 9. The highest values of r2were
obtained when the experimental data were fitted into Langmuir
and Halsey isotherm equations. The description of the sorption of
RhB onto BPH by the Langmuir isotherm equations is a pointer to:
(i) the monolayer coverage of the sorbate on a sorbent surface at
constant temperature, (ii) homogeneity of the surface of the BPH.
and (iii) qmand bwere determined from the slope and intercept
of the plot (Figs. 10 and 11) and are presented in Table 8. Their
values were found to be 263.85−and 0.1286 (lmg−1), respectively.
RLvalues between 0.0 and 1.0 at different concentrations indicate
favorable adsorption of dye onto BPH activated carbon (Table 10).
Halsey isotherm hints towards the aggregation (or agglomeration)
of the zwitterionic form of RhB in water to form a larger molec-
ular form (dimer) (Fig. 5) at the surface of the BPH activated
carbon.
Fig. 10. Linear from of Langmuir equation of adsorption of RhB onto BPH adsorbent
at different concentrations and constant temperatures.
Fig. 11. Linear from of Langmuir equation of adsorption of RhB onto BPH adsorbent
at different temperatures and constant concentrations.
3.7. Effect of particle size
It is clear that with the decrease in particle size, the sorption
increases because the sorption capacity is directly proportional to
the total exposed surface and inversely proportional to particle
diameter for a non-porous sorbent [15]. This is due to the fact that
sorption being a surface phenomenon; the smaller sorbent sizes
offered comparatively larger surface area and hence higher RhB
removal at equilibrium as shown in Fig. 12. This can be explained
by the fact that for smaller particles, large external surface area is
presented to the RhB molecules in the solution which results in
a lower driving force per unit surface area for mass transfer than
when larger particles used [39].
3.8. Effect of temperature
The plot of adsorption capacity as a function of temperature
(Fig. 13) shows an increasing amount of adsorbed RhB with temper-
ature from 20 to 70◦C indicating that adsorption capacity depends
Table 10
Constant parameter, RL.
RLValue Type of isotherm
RL> 1.0 Unfavorable
RL= 1.0 Linear
RL= 0.0 Irreversible
0.0 < RL< 1.0 Favorable

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Fig. 12. Effect of particle size on the adsorption of RhB onto BPH activated carbon.
on temperature. The molecular size of RhB [13] (L: 1.8nm; B:
0.7 nm) and the average pore size of the carbon are near to 2nm.
Therefore, after the pore has adsorbed RhB molecules at the open-
ing, it will hinder the subsequent entrance of RhB molecules. The
intra-particle diffusion rate of sorbate into the pores will be inten-
sified as temperature increases, as diffusion is an endothermic
process [40]. So the adsorption increases with temperature.
3.8.1. Thermodynamic studies
The uptake of RhB dye by the BPH increases on raising the tem-
perature confirming the endothermic nature of the adsorption step.
The change in standard free energy (G0), enthalpy (H0) and
entropy (S0) of adsorption were calculated from the following
equations:
G =−RT ln KC(15)
where Ris the gas constant, KCthe equilibrium constant and Tthe
temperature in K. The KCvalue is calculated from Eq.;
KC=CA
CS
(16)
Where CAand CSare the equilibrium concentrations of dye ions
on adsorbent (mg l−1) and in the solution (mg l−1), respectively.
Standard enthalpy (H) and entropy (S), of adsorption can be
estimated from van’t Hoff equation given in:
ln KC=−H
RT +S
R(17)
Fig. 13. Effect of temperature on the adsorption of RhB onto BPH activated carbon.
Fig. 14. Plotoflnkcagainst reciprocal temperature for RhB sorption onto BPH acti-
vated carbon.
Table 11
The thermodynamic parameters of the adsorption of RhB using BPH activated
carbon.
Temperature (K)−G(kJmol−1)H(kJ mol−1)S(J mol−1k−1)
293 7.939 4.151 65.786
308 9.902
323 12.361
343 26.729
The slope and intercept of the van’t Hoff plot is equal to −H/R
and S/R, respectively [30]. The van’t Hoff plot for the adsorption
of RhB onto BPH is given in Fig. 14. Thermodynamic parameters
obtained are summarized in Table 11.FromTable 11, the posi-
tive values of enthalpy change (H= 4.151 kJ mol−1) conform the
endothermic nature of the adsorption process. The positive value
of S(S= 65.786 J mol−1K−1) reflects the affinity of adsorbent
material towards RhB. Despiteb eing endothermic nature, the spon-
taneity of the adsorption process was decreased in the Gibbs energy
of the system. The Gvalues varied in range with the mean values
showing a gradual increase from −7.939 to −26.729 (kJ mol−1)in
the temperature rangeof 20–70 ◦C in accordance with the endother-
mic nature of the adsorption process.
3.9. Desorption studies of RhB dye
Desorption studies help to elucidate one mechanism of adsorp-
tion and recovery of the adsorbate and adsorbent. The regeneration
of the adsorbent may make the treatment process economical. If
the adsorbed dyes can be desorbed using neutral pH water, then
the attachment of the dye to the adsorbent is by weak bonds. If
acid or alkaline water desorps the dye then the adsorption is by
ion exchange. If organic acids, like acetic acid can desorp the dye,
then the dye is held by the adsorbent through chemisorption [41].
The effect of various reagents used for desorption studies indicates
that NaOH is a better reagent for desorption, because we could get
7.8, 5.4 and 2.7% removal of adsorbed dye for NaOH, HCl and H2O,
respectively after 24h of contact b etweenthe loaded matrix and the
desorbing agents. This is expected because desorption will depend
on the size of the molecule, number of contact points, surface con-
centration, temperature and concentration of adsorbed species in
solution [42]. In absence of competition from other adsorbates,
large adsorbed molecules are unlikely to desorp on dilution with
water [43]. Such molecules will have several contact points leading
to large net adsorption energy, although individual contacts may
be weak. It is therefore statistically and energetically improbable
that all segments will leave the surface simultaneously [42].In

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Table 12
The estimated costs of prepared BPH and commercial activated carbon.
No. Item Costs (pt.) US $
1 Raw material (transportation and crushing included). 50 0.09
2 Commercial H3PO4(L) =(1.167 L for 1kg) 240 ×1.167= 280 0.507
3 Power consumption (4h ×1.8 k W ×20pt.) 144 0.261
4 Water 30 0.05
5 Personnel 40 0.07
6 Total for 1kg of prepared activated carbon 544 $0.978 ≈1.00
7 Total for 1ton prepared activated carbon $1000
8 Total for 1kg of commercial activated carbon 2500 $4.55
9 Total for 1ton of commercial activated carbon $4550
Fig. 15. Adsorption and desorption curves of RhB by BPH activated carbon.
particular, adsorption on a porous substance such as activated
carbon may take place in pores of a diameter similar to that of
the adsorbing species. consequently, there could be many contact
points and a correspondingly high adsorption energy. For desorp-
tion to take place, a large energy barrier may need to be overcome
[43]. In conclusion, it may be noted that the kinetic tests suggested
the reversibility of the adsorption process is incomplete (Fig. 15).
So, the regeneration of activated carbon can be made by thermal
treatment at elevated temperatures.
3.10. Cost analysis
The relative cost of the material used in the present study is very
much lower than that of commercial activated carbons as shown
in Table 12. The bagasse pith is available abundantly; throughout
the year, free of cost, and after considering expenses like trans-
port, chemical, electrical energy and processing cost, the cost of
the material would be approximately US $ 1/kg (US $10 00/ton)[46].
This cost can be further brought down after successful regenera-
tion of used activated carbon. The cost of the activated carbon used
for water treatment in our country is more than US $4.55/kg (US
$4550/ton).
4. Conclusion
This study shows the application of activated carbon prepared
from bagasse pith for removal of Rhodamine B from aqueous solu-
tion. From the experimental results it was found that: (1) the
bagasse pith treated with phosphoric acid (BPH) showed higher
adsorption capacity for adsorption of Rhodamine B (RhB) than the
treated with potassium hydroxide (BPK). The maximum removal of
dye was observed at pH 2.45. The adsorption capacity increases
with the decrease in particle size due to the increase in the surface
area. The equilibrium time was 240min. The effect of temperature
revealed that the adsorption of the dye, RhB is an endothermic indi-
cating that the adsorption would be enhanced at temperature above
the ambient temperature. (2) According to Langmuir adsorption
isotherm, the adsorption capacity, qm, is 263.85 (mgg−1) at ini-
tial pH 5.7 for the particle size of 0.25 nm and equilibrium time
of 240 min at a temperature of 20 ◦C and initial dye concentration
range of 100–600 (mg l−1). (3) The adsorption of RhB from aqueous
solution onto BPH proceeds according to the pseudo-second-order
and the dye uptake process wasfound to be controlled by film diffu-
sion at earlier stages and by intra-particle diffusion at later stages.
(4) Desorption studies carried out in water medium, HCl and NaOH
with desorption of 2.7, 5.4 and 7.8% respectively of adsorbed RhB
confirming the chemical adsorption mechanism of the dye. This
adsorbent was found to be both effective and economically viable.
References
[1] R. Malik, D.S. Ramteke, S.R. Wate, Adsorption of malachite green on ground-
nut shell waste based powdered activated carbon, Waste Manag. 27 (9) (2007)
1129–1138.
[2] V.K. Garg, M. Amita, R. Kumar, R. Gupta, Basic dye (methylene blue) removal
from simulated wastewater by adsorption using Indian rosewood saw dust: a
timber industry waste, Dyes Pig. 63 (2004) 243–250.
[3] T. Robinson, G. McMullan, R. Marchant,P. Nigam, Remediation of dyes in textile
effluent: a critical review on current treatment technologies with a proposed
alternative, Bioresour. Technol. 77 (2001) 247–255.
[4] R.R. Bansode, J.N. Losso, W.E. Marshall, R.M. Rao, R.J. Portier,Adsorption of metal
ions by pecan shell based granular activated carbons, Bioresour. Technol. 89
(2003) 115–119.
[5] K. Ankur, G. Collin, J. Faujan, B.H. Ahmad, Z. Zulkarnian, Z.M. Hussain, H.A.
Abdullah, Preparation and characterization of activated carbon from Resak
wood (Vatika hulletti), Res. J. Chem. Environ. 5 (3) (2001) 21–24.
[6] W.T.Tsai, C.Y. Chang, S.Y. Wang, C.F. Chang, S.F. Chien, H.F. Sun, Cleaner produc-
tion of carbon adsorbents by utilizing agricultural waste corn cob Resources,
Conservation Recycling 32 (2000) 43–53.
[7] A. Ahmadpour, D.D. Do, The preparation of activecarbons from coal by chemical
and physical activation, Carbon 34 (4) (1996) 471–479.
[8] M.A. Lillo-Rodensas, D. Carzrola-Ameros, A. Linares-Solano, Chemical reactions
between carbons and NaOH and KOH—–an insight into chemical activation
mechanisms, Carbon 41 (2003) (2003) 265–267.
[9] G. Mckay, Application of surface diffusion model to the adsorption of dyes on
bagasse pith, Adsorption 4 (1998) (1998) 361–372.
[10] S.M. Saad, A.M. Nasser, M.T. Zimaity, H.F. Abdel-Maged, J. Oil Colour Chem. Ass.
61 (1978) 43.
[11] H. Lata, V.K. Garg, R.K. Gupta, Removal of a basic dye from aqueous solution by
adsorption using parthenium hysterophorus: an agricultural waste, Dyes Pig.
74 (2007) 653–658.
[12] C. Moreno-Castilla, M.A. Ferro-Garcia, Activated carbon surface modifications
by nitric acid, hydrogen peroxide, and ammonium peroxydisulfate treatments,
Langmuir 11 (11) (1995) 4386–4392.
[13] Y. Guo, J. Zhao, H. Zhang, S. Yang, J. Qi, Z. Wang, H. Xu, Use of rice husk-based
porous carbon for adsorption of Rhodamine B from aqueous solutions, DyesPig.
66 (2005) 123–128.
[14] B. Puri, O. Mahajan, Soil Sci. 94 (1962) 162.
[15] S.N. Preeti, B.K. Singh, N. Siddarth, Equilibrium, Kinetic and thermodynamic
studies on phenol sorption to clay, J. Environ. Prot. Sci. 1 (2007) 83–91.
[16] A.V. Deshpande, U. Kumar, Effect of method of preparation on photophysical
properties of Rh-B impregnated sol–gelhosts, J. Non-Cryst. Solids 306 (2) (20 02)
149–159.
[17] A. Ghanadzadeh, M.A. Zanjanchi, R. Tirbandpay, The role of host environment
on the aggregative properties of some ionic dye materials, J. Mol. Struct. 616
(1e3) (2002) 167–174.

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Rhodamine-B from aqueous solution, J. Hazard. Mater. (2009), doi:10.1016/j.jhazmat.2009.02.155
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[18] I. Lopez Arbeloa, P. Ruiz, Ojeda, Dimeric states of Rhodamine B, Chem. Phys.
Lett. 87 (6) (1982) 556–560.
[19] C. Lin, A.R. James, N.P. Branko, Correlation of double-layer capacitance with the
pore structure of sol–gel derived carbon xerogels, J. Electrochem. Soc. 146 (10)
(1999) 3639–3643.
[20] K.S. Low, C.K. Lee, L.L. Heng, Sorption of basic dyes by Hydrilla verticillata,
Environ. Technol. 14 (1993) 115–124.
[21] V.K. Garg, A. Moirangthem, R. Kumar, R. Gupta, Basic dye (methylene blue)
removal from simulatedwastewater by adsorption using Indian rosewood saw-
dust: timber industry waste, Dyes Pig. 63 (2004) 243–250.
[22] C. Namasivayam,J.S.E. Arasi, Removal of Congo red from wastewaterby adsorp-
tion onto waste red mud, Chemosphere 34 (1997) 401–417.
[23] S. Lagergren, About the theory of so-called adsorption of soluble sub-
stances, Kungliga Svenska Vetenskapsakademiens. Handlingar24 (4) (1898) 1–
39.
[24] C. Aharoni, D.L. Sparks, Kinetics of soil chemical reactions-a theoretical treat-
ment, in: D.L. Sparks, D.L. Suarez (Eds.), Rates of Soil Chemical Processes, Soil
Science Society of America, Madison, WI, 1991, pp. 1–18.
[25] M. Ungarish, C. Aharoni, Kinetics of chemisorption: deducing kinetic lawsfrom
experimental data, J. Chem. Soc.-Faraday Trans. 77 (1981) 975–985.
[26] Y.S. Ho, G. Mckay, A comparison of chemisorption kinetic models applied to
pollutant removal on various sorbents, Trans. IChemE 76 (B) (1998).
[27] G.E. Boyd, A.W. Adamson Jr., L.S. Myers, The exchange adsorption of ions from
aqueous solutions by organic zeolites. II. Kinetics, J. Am. Chem. Soc. 69 (1947)
(1947) 2836–2848.
[28] G. Mckay, M.S. El guendi, M.M. Nassar, Equilibrium studies for the adsorption
of dyes on bagasse pith, J. Adsorption Sci. Technol. 15 (1997) 251–270.
[29] Y.S. Ho, C.C. Chiang, Sorption studies of acid dye by mixed sorbent, Adsorption
J. Int. Adsorption Soc. 7 (2001) 139–147.
[30] C.H. Giles, T.H. MacEwan, S.N. Nakhwa, D. Smith, Studies in adsorption. Part
XI. A system of classification of solution adsorption isotherms, and its use in
diagnosis of adsorption mechanisms and in measurements of specific surface
areas of solids, J. Chem. Soc. 10 (1960) 3973–3993.
[31] M.J.D. Low, Kinetics of chemisorption of gases on solids, Chem. Rev. 60 (1960)
267–312.
[32] W.J. Weber, J.C. Morris, J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 90 (SA3) (1964) 70.
[33] S.L.C. Ferreira, H.C. Dos Santos, M.S. Fernandes, J. Anal. Atom. Spectrom. 17
(2002) 115.
[34] D. Reichenburg, J. Am. Chem. Soc. 75 (1972) 589.
[35] N.A. Oladoja, I.O. Asia, C.O. Aboluwoye, Y.B. Oladimeji, A.O. Ashogbon, Studies
on the sorption of basic dye by rubber (hevea brasiliensis) seed shell, Turk. J.
Eng. Env. Sci. 32 (2008) 1–10.
[36] M.I. Temkin, V. Pyzhev, Kinetic of ammonia synthesis on promoted iron cata-
lysts, Acta Physiochim. URSS 12 (1940) 327–356.
[37] W.D. Harkirns, G.J. Jura, The decrease of free surface energy as a basis for the
development of equations for adsorption isotherms; and the existence of two
condensed phases in films on solids, J. Chem. Phys. 12 (1944) 112–113.
[38] J. Halsey, Chem. Phys. 16 (1948) 931.
[39] M. Ozacar, I.A. Sengil, Adsorption of acid dyes from aqueous solutions by cal-
cined alunite and granular activated carbon, Adsorption 8 (2002) 301–308.
[40] G.N. Manju, M.C. Giri, Indian J. Chem. Technol. 6 (1) (1999) 134–140.
[41] S. Arivoli, M. Thenkuzhali, Kinetic, mechanistic, thermodynamic and equilib-
rium studies on the adsorption of Rhodamine B by acid activated low cost
carbon, E-J. Chem. 5 (2) (2008) 187–200.
[42] Th. Tadros,Polymers in Colloid Systems: Adsorption, Stability and Flow,Elsevier,
Amsterdam, 1998.
[43] A.A.M. Daifullah, B.S. Girgis, H.M.H. Gad, A study of the factors affecting the
removal of humic acid by activated carbon prepared from biomass material,
Colloids Surf. A: Physicochem. Eng. Aspects 235 (2004) 1–10.
[44] N.K. Amin, Removal of reactive dye from aqueous solutions by adsorption onto
activated carbons prepared from sugarcane bagasse pith, Desalination 223
(2008) 152–161.
[45] G. Mckay, M. El Geundi, M.M. Nassar, Pore Diffusion during the adsorption of
dyes onto bagasse pith, Process Safety Environ. Prot. 74 (4) (1996) 277–288.
[46] http://www.financialexpress.com/news/phosphoric-acid-report-an-acid-test-
for-manufacturers/159377/.