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© University of Peradeniya 2013
Ceylon Journal of Science (Physical Sciences) 17 (2013) 19-29 Chemistry
Breadfruit (Artocarpus altilis) Waste for Bioremediation of Cu (II) and Cd(II) Ions from Aqueous Medium
Namal Priyantha1,2*, Linda B.L. Lim3, D.T.B. Tennakoon3, Nur Hakimah Mohd Mansor3,
MuhdKhairud Dahri3 and HeiIng Chieng3
1Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka. 2Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka
3Department of Chemistry, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, BE 1410, Negara Brunei Darussalam. (*Corresponding author’s email: [email protected])
Received: 17 September2012 / Accepted after revision: 14 January 2013
ABSTRACT
The skin and the core of breadfruit (Artocarpus altilis) show great affinity toward
Cd(II) and Cu(II), showing high extent of removal. Consequently, the metal ion – bread-
fruit waste system reaches adsorption equilibrium within a short period of time. It is
found that both breadfruit skin and core are able to adsorb Cu(II) more easily than
Cd(II), and further, the extent of sorption of each metal by both the skin and the core is
approximately equal. Acidification of the solution phase decreases the extent of mass
transfer of each metal ion from the solution phase to the solid biosorbent phase. Nev-
ertheless, acidification of the solid phase (each adsorbent) shows no impact on Cd(II)
removal, while the Cu(II) removal is improved by 20%. Further, it is determined that
both Cu(II) and Cd(II) obey the Langmuir adsorption isotherm with a high regression
coefficient.
INTRODUCTION
Expansion of industrialization and ur-
banization has resulted in the generation of
large quantities of toxic materials, including
heavy metals and dyes, due to the extensive
use of these materials in industry. For in-
stance, cadmium and its compounds are
widely used for batteries, ceramics, alloys,
and in mining and metal plating industries,
while copper metal and its compounds are
used in industries, including pulp and paper,
fertilizer, petroleum refinery and aircraft
plating (Gupta et al., 2006; Bazrafshan et al.,
2006). Cadmium is considered to be one of
the more toxic heavy metals found in indus-
trial effluents, while copper is not as toxic as
cadmium (Rao and Khan, 2009). Free aqua
forms of metal ions are biologically active as
compared to other chemical forms, and
hence toxic metal ions, such as heavy metal
ions, cause health effects. Among them,
cadmium is carcinogenic and causes lung
fibrosis, kidney failure and bone softening,
while copper causes gastrointestinal ca-
tarrh, cramps in calves and hemochrometo-
sis (Anirudhan and Radhakrishnan, 2008).
Moreover, continuous drinking of beverages
containing Cu (II) leads to harmful diseases,
such as necrotic changes in the liver and
kidney, lung cancer and capillary damage
(Naughton et al., 2011). Contamination of
water by these heavy metals thus causes
harmful effects to living organisms and to
the environment, which has already become
a major global issue. It is therefore a re-
sponsibility of the human to find ways to
minimize pollution and to help improve the
quality of human life.
Methods successful in removing heavy
metals from waste water include chemical
precipitation, ion-exchange, osmosis, elec-
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
20
trolytic processes and membrane separa-
tion (Srivastava et al., 2008; Vimala and Das,
2009; Rathinam et al., 2010; Xiao et al.,
2010; Ahmaruzzaman, 2011; Masoudzadeh
et al., 2011). These techniques produce
large volumes of sludge, and further they
are not economical. Therefore, adsorption
has become an attractive alternative in re-
moving heavy metals from waste water.
Although activated carbon is an effective
adsorbent (Ahmaruzzaman, 2011; Ma-
soudzadeh et al., 2011; Budinova et al.,
2009), its use has been limited due to eco-
nomic factors. In an attempt to search for
economical adsorbents, much research has
focused, in recent years, on the use of bio-
mass, such as bacteria, fungi, yeast, fruit and
plant materials, to remove heavy metals
(Ahluwalia and Goyal, 2007; Naughton et al.,
2011). Biosorption, in general, provides en-
vironmentally-friendly and low-cost ap-
proaches for the removal of pollutants from
waste water.
Artocarpus altilis (breadfruit) is an Arto-
carpus variety which is grown in many
Asian countries. Traditionally, the leaves of
breadfruit have been used in the treatment
of liver cirrhosis, hypertension and diabetes
(Amarasinghe et al., 2008). Although many
equilibrium and kinetics studies have been
reported on the biosorption of heavy met-
als, especially Cd (II) and Cu(II), by different
types of biomass (Gupta et al., 2006; Rao
and Khan, 2009; Panda et al., 2006; Solisio
et al., 2008; Cojocaru et al., 2009; Luo et al.,
2010; Areco and Afonso, 2010), studies of
Artocarpus fruit biomass are very limited.
Among them, biosorption ability of Tarap
(Artocarpus odaratissimus), Jackfruit (Arto-
carpus hetorophyllus) and Cempedak (Arto-
carpus champeden), all of which belong to
the Artocarpus family, have been investigat-
ed recently (Inbaraj and Sulochana, 2004;
Lezcano et al., 2010; Lim et al., 2011). Fur-
ther, the chemical characterization of bread-
fruit has recently been reported (Amara-
singhe et al., 2008; Nwokocha and Williams,
2011; Maxwell et al., 2011) although its be-
havior in removing heavy metals has not
been reported to the best of our knowledge.
Despite many advantages in using bio-
mass in removing heavy metals, some com-
plications arise at research level and in fu-
ture applications. The same type of fruit ob-
tained from different places would have dif-
ferent texture, leading to variations in the
chemical composition, the structure, and the
chemistry of the biomass (Lim et al., 2011).
Due to these factors, accuracy and the preci-
sion of the final outcome would be of doubt
unless necessary precautions are practiced.
Proper sampling techniques, parameter op-
timization, and pre-treatment and pro-
cessing of the biomass are some steps re-
quired to address the above issues and to
enhance the efficiency of biosorption.
The aim of this research is to investigate
the feasibility of using breadfruit biomass,
in particular, its peel and core, for the re-
moval of cadmium and copper species from
aqueous solution under equilibrium condi-
tions. Effect of shaking time, settling time,
acidification and medium pH, on the extent
of biosorption was monitored in order to
optimize experimental conditions for the
most efficient removal. Additionally, the va-
lidity of adsorption isotherm models was
tested in order to obtain more information
on the interaction of the two metal ions with
breadfruit waste.
MATERIALS AND METHODS
Stock solutions of Cd (II) and Cu (II) of
concentrations ranging from 5 ppm up to
500 ppm were prepared by dissolving the
analytical grade nitrate of the respective
metal in deionized water. Solutions used for
acidification of the biomass and solutions of
different pH were prepared using NaOH
(Univar) and HNO3 (AnalaR). Samples of
breadfruit skin and core were dried in an
oven at 80 °C for about one week. Dried
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
21
samples were blended and sieved to obtain
particle sizes in the range of 355 - 850 µm.
Cadmium and copper ion concentra-
tions were determined using Atomic Ab-
sorption Spectrophotometer (NOVAA 300)
at the wavelengths of 228.8 nm and 324.8
nm, respectively. Thermo-Scientific pH me-
ter (Orion 2-Star Bench-top model) was
used in monitoring pH, and an electric shak-
er (Thermo-Scientific MaxQ) was used in
agitating the metal ion solutions at a speed
of 250 rpm. FTIR spectra were recorded on
Shimadzu spectrophotometer (IRPrestige-
21), which had the wavelength range be-
tween 750 cm-1 and 4000 cm-1, with a reso-
lution of 2 cm-1. X-ray fluorescence (XRF)
spectra were recorded using XRF
spectrophotometer (PANalytical Axios), and
morphological characteristics of the adsor-
bent surface were carried out using Scan-
ning Electron Microscope (SEM) (Tescan
Vega XMU).
Optimization of experimental parameters
A series of suspensions consisting of
0.100 g of each biosorbent and 50.0 mL of
10 ppm each metal ion solution was shaken
at a speed of 250 rpm. The filtrate of each
suspension at different shaking time peri-
ods up to 4 h was analyzed for the metal ion
content to determine the optimum shaking
time. Another series of suspensions of the
same composition was allowed to shake for
the optimum period and then each suspen-
sion was allowed to stand for different set-
tling time periods up to 4 h to determine the
optimum value. Many trials were conducted
for each experiment and the average was
reported.
Suspensions of the biosorbent of the
same composition (50.0 mL of 10 ppm met-
al ion solution with 0.100 g biosorbent)
were used for the investigation of the effect
of pH on the extent of removal. For this pur-
pose, the pH of the suspension was con-
trolled at the desired value with 12 M solu-
tions of NaOH and/or HNO3.
Determination of the acid content of the
adsorbent
A mixture of a sample of breadfruit skin
(0.500 g) and 25.0 mL of distilled water was
stirred well and the initial pH of the solution
was measured. The solution was then titrat-
ed with a standardised NaOH solution
(0.010 M), and the pH of the solution was
monitored until it reached up to about 10.
The titration was repeated two more times.
The same titration was performed for
breadfruit core as well.
Acidification of the biosorbent
In order to investigate the effect of acid-
ification of breadfruit waste on metal ion
removal, 0.100 g of each adsorbent was
treated with 50.0 mL of 70 % nitric acid and
shaken for one hour. The resulting suspen-
sion was then filtered and washed with dis-
tilled water. The residue was oven dried at
80 °C for one day and used to investigate the
metal ion removal ability from 10 ppm met-
al ion solutions under optimized conditions.
The extent of removal of each metal ion by
the acidified adsorbent was then compared
with the untreated adsorbent.
Adsorption isotherms
A series of suspensions consisting of
0.100 g of each biosorbent and 50.0 mL of
each metal ion solution of concentration
varying from 5 ppm to 500 ppm was al-
lowed to reach equilibrium under optimized
conditions. The filtrate of each solution was
analyzed for the respective metal content.
The amount of each metal adsorbed by each
biosorbent was calculated using Equation
(1).
Mm
VCCq
fi
e
1000
)( )g (mmol 1-
(1)
where qe is the amount of metal being ad-
sorbed by the adsorbent at equilibrium, Ci is
the initial concentration of the metal ion (in
ppm), Cf is the final concentration of the
metal ion in solution after being adsorbed
(ppm), V is the volume of the solution used
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
22
(mL), m is the mass of adsorbent used (g)
and M is the molar mass of the metal (g mol-
1).
FTIR spectra
Dried samples of breadfruit skin and
core were separately crushed into a fine
powder, mixed with dried KBr solid in a ra-
tio of 1:100 and pellets were prepared for
recording FTIR spectra.
RESULTS AND DISCUSSION
Optimization of experimental parame-
ters
Contact time
Among many factors that govern the ex-
tent of biosorption of Cd (II) and Cu(II) on
breadfruit biomass, the contact time, which
includes both shaking time and settling
time, is an important parameter as it pro-
vides information on time scale to reach
equilibrium. Figure 1 shows the effect of
shaking time on the extent of each metal ion
removed, which can be used to determine
the time required to reach equilibrium. Re-
moval of Cu (II) by breadfruit skin and core
is greater as compared to that of Cd (II), and
further the skin samples show stronger af-
finity toward Cu (II). Nevertheless, Cu (II)
takes a longer time to reach equilibrium,
which is expected because a longer equili-
bration time period would be needed when
more adsorbate is transferred to the surface
of the solid adsorbent. By careful analysis of
the amount adsorbed – shaking time rela-
tionships, it is recommended that shaking
time periods of 180 - 210 min (skin – 180
min; core – 210 min) be needed to achieve
sorption equilibrium of Cu (II), while a
shorter time period of 120 min is sufficient
for Cd (II) on both skin and core.
Many natural adsorbents in raw or
modified forms, including Sri Lankan bread-
fruit, have shown stronger sorption toward
Cu (II) than Cd(II) (Chang and Huang, 2008;
Su et al., 2012; Mohapatra and Anand, 2010)
to support this observation. This can be
partly attributed to the smaller radius of
0.80 °A of the aqua complex of Cu(II) as
compared to that of Cd(II) (0.96 °A) (Per-
son, 2010).
It is observed that there is not much
change in the amount adsorbed of each
metal ion when the adsorbate–adsorbent
system is allowed to stand for up to 4 h,
demonstrating that the equilibrium has es-
tablished upon exposure to the shaking time
period selected (Figure 2). This behavior is
common for all four systems; Cd (II)-
breadfruit skin, Cd (II)-breadfruit core, Cu
(II)-breadfruit skin and Cu (II)-breadfruit
core. Although it is not necessary to opti-
mize settling time after optimization of
shaking time, it is recommended that a min-
imum settling time of one hour be used to
assure equilibrium characteristics of the
systems.
Figure 1: Effect of shaking time on the extent of adsorption of Cu(II) (■) and Cd(II) () on bread-fruit skin (top) and core (bottom) [50.0 mL of 10 ppm metal ion solution, 0.100 g of biosorbent].
Other Artocarpus species are also re-
ported to have comparable shaking and set-
tling times for biosorption of Cu (II) and Cd
(II) (Lim et al., 2011). However, Punicgran-
atum (pomegranate) required an equilibra-
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
23
tion period of 10 h for biosorption of Ni (II)
(Bhatnagar and Minocha, 2010).
Figure 2: Settling time of Cu(II) (■) and Cd(II)
() on breadfruit skin (top) and core (bottom) [50.0 mL of 10 ppm metal ion solution, 0.100 g of biosorbent, shaking times are as given in the text].
Solution pH
The extent of removal of both metal
ions, Cd (II) and Cu (II), is much decreased
when the solution is acidified with HNO3,
probably due to the competition with H+
ions, as reported earlier (Priyantha and
Bandaranayaka, 2011). Increase in the pH of
the solution beyond 6.0 does not significant-
ly increase the extent of removal as com-
pared to that at ambient pH (Table 1). As
additional interference would result in due
to the presence of ionic constituents in
HNO3 and NaOH used for pH adjustments, it
is recommended that the biosorption of Cd
(II) and Cu(II) be carried out under ambient
conditions without any pH adjustment.
Determination of the acid content of
breadfruit skin and core
Determination of the acid content of the
sorbent is useful to gain information on the
mechanism of metal ion uptake by exploring
the type of interaction between each metal
ion and each biosorbent. The pH-titration
curve and its first order derivative plot the
titration of breadfruit skin which can be
used to quantify the acidic content are
shown in Figure 3. The total amount of acid-
ic protons present in breadfruit skin, based
on the equivalence point of the titration, is
estimated to be 2.4 10-4mol per gram of
adsorbent (Vend = 12.0 mL of NaOH). Fur-
ther, the presence of two types of acidic or-
ganic functional groups with ionizable hy-
drogen can be identified by observing two
maxima in the derivative plot shown in Fig-
ure 3. Subsequently, the pKa values of the
two types of acidic groups are determined
to be approximately 5.8 and 7.4 from the
pH-titration curve based on the fact that the
pH at the half-equivalence point during a
pH-titration is equal to the corresponding
pKa value. A similar pH-titration curve and a
derivative plot were observed for breadfruit
core as well. The smaller pKa value would
correspond to carboxylic acid groups while
the larger value corresponds to alcohol or
phenolic groups in comparison with the pKa
values of aliphatic and aromatic carboxylic
acids, and those of alcohols and phenols
(http://research.chem.psu.edu/brpgroup/p
Ka_compilation.pdf). The absence of well-
defined (sharp) peaks in the derivative plot
is due to the availability of many types of
carboxylic acid and phenolic groups in the
biosorbent, and the gradual change in pH in
the titration curve is due to the weak acidic
character of the constituents present.
Sorption of Cu (II) and Cd (II) on bread-
fruit skin and core
The presence of carboxylic acids and alco-
hols/phenolic compounds in breadfruit
waste is supported by FTIR spectra (Figure
4, Table 2). Changes in intensity observed in
the peaks between 1000 cm-1and 1750 cm-1
in the spectra recorded before and after
sorption of Cd(II) provide evidence for in-
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
24
volvement of carbonyl groups in the bond
formation with Cd(II). Cu (II) also results in
Figure 3: The pH-titration curve (top) and the first order derivative plot (bottom) for the reac-tion of a suspension of breadfruit skin with a solution of 0.010 M NaOH.
similar changes in the FTIR spectrum. In-
corporation of the two metal ions to the-
breadfruit matrix is further evidenced by
observing a significant enhancement in the
intensity of the peak for each metal in the
XRF spectrum when metal ion solutions are
treated with each of breadfruit skin and
core. A sample XRF spectrum for Cu (II)-
treated breadfruit skin is shown in Figure 5.
SEM images obtained before and after sorp-
tion of 500 ppm Cu (II) solution provide ad-
ditional support for strong affinity of Cd (II)
on breadfruit skin (Figure 6). Similar chang-
es in SEM images were observed for Cu (II)
as well.
Stronger interaction of Cu (II) as com-
pared to Cd (II), and complexation being the
principal mode of mass transfer (bioreme
diation) are further evidenced from the
formation constants (Kf) of the two metals
with organic functionalities (Bunting and
Thong, 1970). For example, log (Kf) for the
Cu(II)-benzoic acid complex is 1.51, while
that for Cd(II)-benzoic acid is 1.15. These
values are 1.76 and 1.30, respectively, for
acetic acid.
Figure 4: FTIR spectrum of breadfruit core be-fore () and after sorption of Cd (II) (---).
Figure 5: XRF spectra of breadfruit skin before ( ) and after treatment with 100 ppm Cu (II) ( ) and 500 ppm of Cu (II) ( ).
Table 2: Assignment of FTIR peaks for bread-fruit core
Peak locations (cm-1)
Assignment
Untreated Treated with Cd(II)
1736 1736 C=O stretching
1635 1635 C=O stretching
1416 1416 C=C stretching
1153 1155 C-O stretching
Stronger interaction of Cu (II) as compared
to Cd (II), and complexation being the prin-
cipal mode of mass transfer (bioremedia-
tion) are further evidenced from the for-
mation constants (Kf) of the two metals with
organic functionalities (Bunting and Thong,
1970). For example, log (Kf) for the Cu (II)-
benzoic acid complex is 1.51, while for Cd
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
25
(II) )-benzoic acid is 1.15. These values are
1.76 and 1.30, respectively, for acetic acid.
Table 1: Extent of removal of each metal at ambient pH (50.0 mL of 10 ppm metal ion solution, 0.100 g of biosorbent).
Biosorbent Adsorbate Ambient pH Extent of
removal (mmol g-1)
Before metal ion addition
After metal ion addition
Breadfruit skin Cu(II) 5.60 4.89 0.060 Breadfruit skin Cd(II) 5.60 4.81 0.040 Breadfruit core Cu(II) 5.18 4.84 0.058 Breadfruit core Cd(II) 5.18 4.77 0.040
Figure 6: SEM images (approximately 525x magnification) of breadfruit skin (i) before and (ii) after
treatment with 500 ppm Cd (II).
Acidification of the biosorbent
Analysis of the suspension of the acidi-
fied adsorbent and each metal ion solution
indicates that the extent of removal is better
with the acidified adsorbent as compared to
the untreated adsorbent. However, the per-
centage difference of the extent of removal
of Cd (II) is only 2-3 %, while that for Cu (II)
is greater than 20%. This is indicative of the
fact that protonation of the surface of the
biosorbent have no impact on the interac-
tion of Cd (II) and the biosorbent surface.
Hence, the principal mode of mass transfer
from the solution phase to the biosorbent
phase is not ion-exchange, which further
supports the complex formation between Cd
(II) and organic functional groups, as indi-
cated in earlier sections. Nevertheless, ion-
exchange of Cu (II) with H+ contributes to
about 20% of the overall mass transfer pro-
cess, and the remainder is mainly complex
formation. The stronger affinity of Cu (II)
over Cd (II) for ion-exchange with H+ has
already been reported in many instances in
support of the above findings (Chang and
Huang, 1998, Su et al., 2012).
Sorption isotherms
Biosorption of heavy metals on the sur-
face of biomass is mainly due to the chemi-
cal or physical binding between the adsorb-
ate and the biosorbent. The mechanism of
biosorption depends on the type of func-
tional groups present in the surface of the
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
27
biosorbent although the complete mecha-
nism of removal would have many other
contributions.
Amount adsorbed – initial concentra-
tion relationships for a biosorption system
provide information on the type of the iso-
therm, the concentration range for mono-
layer coverage, and the concentration at
which the multilayer coverage begins. The
amount of each metal ion adsorbed on
breadfruit skin and core at different concen-
trations ranging from 5 ppm to 500 ppm
indicates that biosorption leads to a mono-
layer initially up to about 100 ppm of each
metal ion, and the sorption process then
slowly continues (Figure 7). This is a signifi-
cant finding because this demonstrates the
potential of breadfruit waste to be used in
bioremediation of waste water containing
high levels Cu (II) and Cd(II). Howeverinitial
concentrations beyond 500 ppm would not
provide reliable information due to possible
precipitation.
As Figure 7 indicates, the Langmuir iso-
therm, which assumes a monolayer uptake
of an adsorbate on a homogeneous surface,
was tested for both metal ions on each bio-
sorbent surface. The Langmuir model is
represented by Equation (2),
e
ee
CK
CKqq
1
max (2)
Where qe is the amount of the adsorbate be-
ing adsorbed, qmax is the maximum adsorp-
tion capacity, K is the Langmuir constant
and Ce is the concentration of the adsorbate
at sorption equilibrium. Equation (2) is lin-
earized to the form,
maxmax
1
qKq
C
q
C e
e
e
(3) Although this model is empirical, reasona-
bly reliable results can be obtained for the
extent of surface coverage under various
experimental conditions.
Figure 8 shows the linearized Langmuir
adsorption isotherm model for biosorption
of each meal on each biosorbent. Having the
R2 value close to 1.0 suggests that biosorp-
tion of Cu (II) and Cd (II) leads to monolayer
coverage initially (Table 3). Further, it is
evident from the results given in the table
that the Langmuir constant, which is a
measure of the strength of sorption, for
Cu(II) sorption is higher for both skin and
core, further supporting the fact that Cu(II)
is more strongly removed by each bio-
sorbent.
Table 3: Regression coefficients and isotherm constant for biosorption of Cu (II) and Cd(II) on breadfruit skin and core.
Adsorbent Adsorbate Langmuir model
R2 b Breadfruit skin
Cd(II) 0.9823 0.0489
Cu(II) 0.9847 0.0361
Breadfruit core
Cd(II) 0.9245 0.0264
Cu(II) 0.9254 0.0617
Figure 7: Amount of sorption of Cd (II) () and
Cu (II) (■) on breadfruit core.
Thorough mixing of metal ion adsorbed
breadfruit waste with deionized water is
not able to release them to the solution
phase, further demonstrating the strong af-
finity on the biosorbent. Treatment with
strong mineral acids would not be a good
option as certain compounds present in the
biosorbent would denature and mix with
metal ions released. Thus, electrochemical
Priyantha et al., /Ceylon Journal of Science-Physical Sciences 17 (2013) 19-29
28
reduction under mild acidic conditions
would be a possible approach for the recov-
ery of adsorbed metal ions.
Figure 8: Langmuir adsorption isotherm for biosorption of Cu (II) (■) and Cd (II) () on breadfruit skin (top) and core (bottom).
CONCLUSION
Biosorption ability of both breadfruit
skin and core toward heavy metals ions, Cd
(II) and Cu (II), is so strong that sorption
equilibrium attains efficiently. The optimum
shaking and settling times for Cd (II) are
determined to be 120 min and 60 min for
both skin and core, while the optimum
shaking time for Cu (II) is 180 – 210 min,
with the same settling time period of 60
min. Complexation of Cd (II) and Cu (II)
with acidic functional groups present in
breadfruit waste would probably provide
the principal contribution to the mass trans-
fer of Cd (II) and Cu (II) from aqueous solu-
tion. The maximum removal under opti-
mized conditions from a 10 ppm solution is
0.040 mmol g-1 for Cd (II) by both skin and
core of breadfruit. The corresponding val-
ues for Cu (II) are 0.060 mmol g-1 and 0.058
mmol g-1, respectively. Stronger interaction
of Cu(II) and breadfruit waste is further ev-
idenced by greater Langmuir adsorption
constant (K) for Cu(II) as compared to that
of Cd(II) for both skin and core, and further,
K is greater on skin than core for both met-
als.
Acknowledgements
The authors would like to thank the Gov-
ernment of Negara Brunei Darussalam and
the Universiti Brunei Darussalam for their
financial support. The authors would also
like to thank the Energy Research Group
and Biology Department at the Universiti
Brunei Darussalam for allowing the use of
SEM and XRF instruments.
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