preparation and characterisation of biodegradable pollen–chitosan microcapsules and its...

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Preparation and characterisation of biodegradable pollen-chitosan microcap-sules and its application in heavy metal removal

İdris Sargın, Murat Kaya, Gulsin Arslan, Talat Baran, Talip Ceter

PII: S0960-8524(14)01669-1DOI: http://dx.doi.org/10.1016/j.biortech.2014.11.067Reference: BITE 14273

To appear in: Bioresource Technology

Received Date: 31 August 2014Revised Date: 14 November 2014Accepted Date: 15 November 2014

Please cite this article as: Sargın, İ., Kaya, M., Arslan, G., Baran, T., Ceter, T., Preparation and characterisation ofbiodegradable pollen-chitosan microcapsules and its application in heavy metal removal, Bioresource Technology(2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.11.067

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http://dx.doi.org/10.1016/j.biortech.2014.11.067

http://dx.doi.org/http://dx.doi.org/10.1016/j.biortech.2014.11.067

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Preparation and characterisation of biodegradable pollen-chitosan microcapsules and

its application in heavy metal removal

İdris Sargına*

, Murat Kayab, Gulsin Arslan

c, Talat Baran

d, Talip Ceter

e

aSelcuk University, Faculty of Science, Department of Chemistry, 42075, Konya, Turkey.

bAksaray University, Faculty of Science and Letters, Department of Biotechnology and

Molecular Biology, 68100, Aksaray, Turkey.

cSelcuk University, Faculty of Science, Department of Biochemistry, 42075, Konya, Turkey.

dAksaray University, Faculty of Science, Department of Chemistry, 68100, Aksaray, Turkey.

eDepartment of Biology, Faculty of Arts and Sciences, Kastamonu University, 37100

Kastamonu, Turkey.

*Corresponding Author: İdris Sargın, Department of Chemistry, Faculty of Science, Selcuk

University, 42075 Konya, Turkey.

Tel: +90-332-2233852 Fax: +90-332-2412499 E-mail address: [email protected]

Abstract

Biosorbents have been widely used in heavy metal removal. New resources should be

exploited to develop more efficient biosorbents. This study reports the preparation of three

novel chitosan microcapsules from pollens of three common, wind-pollinated plants (Acer

negundo, Cupressus sempervirens and Populus nigra). The microcapsules were characterized

(Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron

microscopy and elemental analysis) and used in removal of heavy metal ions: Cd(II), Cr(III),

Cu(II), Ni(II) and Zn(II). Their sorption capacities were compared to those of cross-linked

chitosan beads without pollen grains. C. sempervirens-chitosan microcapsules exhibited better

performance (Cd(II): 65.98; Cu(II): 67.10 and Zn(II): 49.55 mg g−1

) than the other

2

microcapsules and the cross-linked beads. A. negundo-chitosan microcapsules were more

efficient in Cr(III) (70.40 mg g−1

) removal. P. nigra-chitosan microcapsules were found to be

less efficient. Chitosan-pollen microcapsules (except P. nigra-chitosan microcapsules) can be

used in heavy metal removal.

Keywords: pollen; chitosan; microcapsule; biosorbent; heavy metal

Introduction

Heavy metal ions are discharged into water bodies via industrial operations such as

mining, metal finishing, plating, tannery and fertilizer production. Water bodies that have

been contaminated with heavy metal ions are posing risks to the environment (Bilal et al.,

2013). Certain heavy metal ions, even in small amounts, are capable of bio-accumulating in

the tissues of living organisms and are responsible from developing various diseases and

disorders (Abou El-Reash et al., 2011). Many attempts employing various techniques (e.g. co-

precipitation, solid phase extraction, ion-exchange separation and adsorption) have been made

to remove or recover heavy metal ions from waste waters. However, amongst the techniques

mentioned, adsorption manifests itself as an effective and simple method (Sarkar &

Majumdar, 2011). Many studies have shown biosorbents are excellent adsorbents (Wan Ngah

et al., 2011).

Researches on developing biodegradable and eco-friendly biosorbents demanding less

chemical treatment during production are on the rise in the last decades. Various sorbents with

biological origin, like fungi (Damodaran et al., 2014), algae (He & Chen, 2014), bacteria

(Kieu et al., 2011) and yeasts cells (Machado et al., 2010) have been developed for removal

and recovery of metal ions from aqueous solutions. Biosorbents have been proved to be

effective and, in some cases, superior to the chemical resins in some ways: they are effective,

3

low cost, available in large quantities and more importantly have already carry functional

groups including amino, carboxyl, hydroxyl and carbonyl (Wang & Chen, 2009).

Chitosan is a naturally occurring carbohydrate polymer which can meet the above

mentioned traits: it is biocompatible, biodegradable and nontoxic to human and environment

and shows antimicrobial and antioxidant activities (Muzzarelli, 2011). These excellent

physicochemical features have put chitosan in a unique position amongst the biopolymers: it

has found broader applications in a number of fields including pharmaceutics and medicine

(Ong et al., 2008), food industry (Aider, 2010), textile (Alonso et al., 2009) and water

treatment (Hu et al., 2013).

Chitosan also has high affinity towards metal ions due to metal ion binding groups

(e.g. –NH2 and –OH) on its polymeric chains (Wu et al., 2010). Chitosan, in raw (Paulino et

al., 2007) or functionalized (Wang et al., 2013) form, is one of the widely utilized biosorbents

in removal or recovery of heavy metal ions. Among the chitosan-based sorbents, chitosan

composites have gained attention and have been considered as an alternative to the

conventional biosorbents in recent years. Various chitosan composites with biological

materials (e.g. cellulose, cotton, oil palm ash, silk and alginate) have been prepared and used

in heavy metal removal (Wan Ngah et al., 2011; Wang & Chen, 2014). However, chitosan

composites adsorbents with pollen grains have not been reported in the literature.

This is the first study to report the preparation and use of pollen-chitosan composite

microcapsules in heavy metal removal. Pollen grains were preferred: (1) since pollens are

biomaterial, (2) they are already fine powder and therefore can be easily covered with

chitosan and (3) they can be harvested in large quantities when needed. Modification of

chitosan composites is easily achieved via crosslinking in glutaraldehyde solution by forming

Schiff base. On the other hand, azomethine formation from free amino groups on chitosan

4

polymer reduces metal sorption capacity of the polymer by eliminating coordination sites for

metal ions. This study aimed to find out whether pollen grains entrapped in chitosan matrice

are capable of counterbalancing this loss and enhancing metal binding capacity of cross-

linked chitosan by increasing metal sorption sites, surface area and the porosity of the

microcapsules. Chitosan composite microcapsules with pollen grains from three common

plant species were prepared: A. negundo, C. sempervirens and P. nigra. Pollen grains from

these plants can be harvested easily because these anemophilous plants are wind-pollinated

and therefore produce large quantities of pollen grains (Çeter et al., 2011). The present work

deals with (1) preparation of three different chitosan-pollen microcapsules, (2)

characterisation of the microcapsules employing Fourier transform infrared (FT-IR)

spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and

elemental analysis (EA) and (3) assessment of the heavy metal (Cd(II), Cr(III), Cu(II), Ni(II)

and Zn(II)) sorption capacities of the three biosorbents and glutaraldehyde cross-linked

chitosan beads without pollen grains.

2. Experimental

2.1. Pollen samples collection and identification

The male cones from P. nigra, C. sempervirens and A. negundo were collected in

Kastamonu, Turkey and were identified with reference to the guide book by Coden and

Cullen (Cooden, 1965). The cones were kept in an oven at 25°C for 1–2 days to release the

pollen grains. The pollen grains were sieved to remove any other material and 95% of pollen

purity was ensured. Then, the pollen grains were kept at -20°C.

The plant samples are kept at the palynology laboratory at Vocational College,

Kastamonu University. P. nigra L. (08.04.2013, Voucher: Ceter 56) and A. negundo L.

(30.03.2013, Voucher: Ceter 49) cones were collected from the garden of Kastamonu

5

University Vocational College and C. sempervirens L. (30.03.2013, Voucher: Ceter 50) cones

were from the garden of Kastamonu İlbank.

2.2. Materials

Chitosan powder (medium molecular weight), Cd(NO3)2. 4H2O and NaOH were

obtained from Sigma–Aldrich. Glutaraldehyde solution (GA) (25% in water, v:v), the metal

salts (Ni(NO3)2. 6H2O, Cr(NO3)3. 9H2O, Zn(NO3)2. 4H2O, Cu(NO3)2. 3H2O), acetic acid and

HCl were purchased from Merck. Methanol was obtained from AnalaR Normapur.

2.3. Preparation of chitosan-pollen microcapsules and cross-linked chitosan beads

Chitosan (1.000 g) was dissolved and stirred in 50 mL of 2% acetic acid solution.

0.500 g of pollen grains was added to the chitosan solution. To ensure homogeneity, the

mixture was stirred for 2 h. Then, the mixture was transferred into a burette. The mixture was

dropped into a coagulation solution (100 ml of water, 150 ml of methanol and 30.0 g NaOH)

(Pal et al., 2013). The microcapsules were kept in the coagulation solution overnight. Then,

they were removed from the solution by filtration. The microcapsules were rinsed with plenty

of distilled water to neutrality. Then, the microcapsules in water were recovered by a sieve

and transferred into cross-linking reaction solution (mixture of 30 ml of methanol and 0.3 ml

of GA) and stirred gently under reflux at 70°C for 6 h. Finally, to remove any unreacted GA

molecules, cross-linked microcapsules were rinsed with ethanol and water and finally dried at

room temperature. Cross-linked chitosan beads without pollen grains were also prepared

following the same method.

2.4. Characterisation of the pollen-chitosan microcapsules

2.4.1. FT-IR spectroscopy

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The IR spectra of pollen-chitosan microcapsules were recorded with a Perkin Elmer

FT-IR Spectrometer over the frequency range of 4000–625 cm−1

.

2.4.2. Elemental Analysis

Elemental analysis of the pollen-chitosan microcapsules was performed using Thermo

Flash 2000.

2.4.3. SEM analysis

The pollen-chitosan microcapsules were coated with gold for SEM analysis by Sputter

Coater (Cressingto Auto 108). The surface characteristics of the samples were examined by a

QUANTA FEG 250 scanning electron microscope.

2.4.4. TGA analysis

Thermogravimetric analysis of the microcapsules were conducted using EXSTAR S11

7300 at a heating rate of 10°C min−1

. The samples were heated up to 650°C.

2.5. Heavy metal sorption experiments

The pollen-chitosan microcapsules or cross-linked chitosan beads (0.1000 g) were

added to metal solution (25 mL of 10 mg L−1

at metal solution pH; Cd(II): 5.35, Cr(III): 4.63,

Cu(II): 5.18, Ni(II): 5.34, Zn(II): 5.34) and agitated on a shaker (Heidolph Promax 2020) at

200 rpm for 4 h. Then, the sorbent was removed from the solution with a filter paper. The

metal ion concentration in the solutions was detected using a flame atomic absorption

spectrophotometer (ContrAA 300, Analytikjena). The amount of metal ions recovered per unit

mass of the sorbents was determined employing the equation given below:

qe = (Ci–Ce)V/W (1)

7

where qe is the metal sorption capacity of the microcapsules or the cross-linked chitosan beads

(mg g−1

), Ci and Ce are the initial and equilibrium of metal ion concentrations (mL−1

),

respectively; V is the volume of metal solution (L), and W is the mass of the sorbent (g).

The effects of amount of sorbent (0.0250–0.1250 g), contact time (60–300 min.),

metal ion solution pH (3.0, 4.0 and the pH of the metal ion solutions), initial metal ion

concentrations (2.5–12.5 mg L−1

) and temperature (25, 35 and 45oC) on sorption behaviour of

the microcapsules were studied.

3. Results and discussion

3.1. Characterisation of pollen-chitosan microcapsules

FT-IR

FT-IR spectra can provide an insight into the structure of chitosan polymer chains

after the cross-linking reaction has been accomplished. In the FT-IR spectrum of chitosan, an

absorption band at 1590 cm−1, which is corresponded to the NH2 groups, appears (Pawlak &

Mucha, 2003). This band and any other bands which can be ascribed to the stretching of

carbonyl groups (C=O, 1700–1750 cm−1) of glutaraldehyde were not observed in spectra of

the three pollen-chitosan microcapsules. Also, the bands appearing at 1650 (A. negundo),

1647 (C. sempervirens) and 1649 cm−1

(P. nigra) can be attributed imine (C=N) groups

(Vieira & Beppu, 2006). Furthermore, the bands at 1574 (A. negundo), 1575 (C.

sempervirens) and 1572 cm−1

(P. nigra) which can be corresponded to C–N stretching can

signify cross-linking of the chitosan polymer. These observations can confirm the

condensation of the amino groups of the chitosan with glutaraldehyde (Altun & Cetinus,

2007).

EA

8

Nitrogen (N), carbon (C) and hydrogen (H) contents of the pollen-chitosan

microcapsules were determined. N, C and H contents of A. negundo-chitosan microcapsules

were 5.9, 42.76 and 7.24%; C. sempervirens-chitosan; 5.25, 42.45, 7.18% and P. nigra-

chitosan; 6.75, 43.77, 7.16% and the cross-linked chitosan beads; 6.91, 42.95, 7.00%

respectively. C and H contents of the three microcapsules and the cross-linked chitosan beads

were close to each other. However, variations in the N content of the each sorbent was

significant and was in the following order: cross-linked chitosan>P. nigra>A. negundo>C.

sempervirens. This order may also represent the chemical compositions of the pollens in the

same way. However, average metal sorption capacity of the microcapsules followed the

opposite order: C. sempervirens>A. negundo>P. nigra (Table 1). It seems that there is

probably a negative correlation between the nitrogen containing groups of the pollen grains

and the metal binding sites on the biosorbents.

Surface morphology

SEM images showed that the pollen grains were entrapped in the chitosan matrice, but

they were randomly distributed on the surface. Pollen grains from A. negundo and P. nigra

were buried in the microcapsules and fewer grains were exposed to the surface. When

compared to the others, the microcapsules with C. sempervirens were more spherical and

more pollen grains were on the surface; therefore they had larger surface area than the others.

This may explain the higher metal sorption capacity of the C. sempervirens-chitosan

microcapsules (vide infra).

TGA

Crystallinity of chitosan determines its thermal stability (Guibal, 2004). Modification

of chitosan (i.e., Schiff bases formation) reduces number of pendant amino groups on the

polymer chains; this leads to the deformation of intermolecular hydrogen bonds and lowers

9

the crystallinity of the chitosan polymer. Maximum decomposition temperature (DTGmax) of

raw chitosan has been reported to be 302°C (Kaya et al., 2014), and a decrease in the DTGmax

values of the microcapsules was expectable after the cross-linking of the polymeric backbone.

As expected, lower DTGmax values were recorded for the pollen-chitosan microcapsules; A.

negundo-chitosan: 273, C. sempervirens-chitosan: 258 and P. nigra-chitosan: 269°C.

At end of the pyrolysis, 70.5% of A. negundo-chitosan, 84.5% of C. sempervirens-

chitosan and 75.7% of P. nigra-chitosan microcapsules decomposed. As mentioned,

microcapsules with A. negundo had the highest DTGmax value. These microcapsules also

exhibited the highest thermal stability but the lowest Cd(II) uptake capacity. C. sempervirens-

chitosan microcapsules, which had the lowest thermal stability and the highest total

decomposition rate, showed better performance in metal heavy sorption than the others (vide

infra).

3.2. Heavy metal sorption performances of the microcapsules

3.2.1. Adsorbent dosage

The minimum amount of the pollen-chitosan microcapsules that was required was

determined for each of the metal ions (Fig. 1). The increase in the amount of the sorbents led

to an increase in the amount of the metal ions removed until a saturation point. After this

point (close to the 0.1 g), the increment in the sorbent dosage did not contribute much to the

sorption of the metal ions. Similar trends were observed for the three types of the pollen-

chitosan microcapsules and the chitosan beads without pollen grains.

3.2.2. Contact time

Time that is required for the adsorption of the metal ions onto each of the pollen-

chitosan microcapsules to attain the equilibrium state was determined (Fig. 2). The studies

10

revealed that the sorption of Cd(II), Cr(III), Cu(II), Ni(II) and Zn(II) on the pollen-chitosan

microcapsules or the chitosan beads was slow in nature and an equilibrium state was observed

at around 240 min. for each metal ion regardless of the sorbent type. This could be attributed

to the diffusion resistance within the polymeric matrice. Additionally; it appears that the

incorporation of the pollen grains in chitosan did not significantly change the diffusion

characteristics of the microcapsules.

3.2.3. pH

Metal solution pH can affect not only metal ion speciation in the solution but

physicochemical nature of the sorbent. Chitosan itself exhibits pH depending solubility

nature; its structure in the solution is subject to changes especially through

protonation/deprotonation of the amino and hydroxyl groups on it. The lower sorption

capacities observed for each of the microcapsules at more acidic conditions could be resulted

from the decrease in the electron-donating ability of N and O atoms and the repulsion forces

upon protonation of the binding sites on the sorbents (Fig. 3). Also, possible competition of

hydronium ions with the metal cations for sorption sites could weaken the chelation ability of

the sorption sites on the sorbents.

3.2.4. Thermodynamic analysis

The effect of the temperature on the uptake of the metal ions was studied and higher

sorption capacities for the three microcapsules were accomplished at elevated temperatures.

By using the linear van’t Hoff plot of log KC versus 1/T, changes in standard free energy

(∆G°), enthalpy (∆H°), and entropy (∆S°) were calculated.

∆G°=−RT lnKC (2)

∆G°= ∆H°−T∆S° (3)

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log KC = (∆S°/2.303R) − (∆H°/2.303RT) (4)

where KC is the equilibrium constant, R is universal gas constant (8.314 J mol−1

K−1

) and T is

the temperature (K). The value of ∆S° and ∆H° were obtained from the slope (∆H◦/2.303R)

and the intercept (∆S◦/2.303R) of van’t Hoff plot, log KC versus 1/T of log KC versus 1/T plot.

The thermodynamic analysis (Table 2) revealed the exothermic nature of the

adsorption of the metal ions onto pollen-chitosan microcapsules. However adsorption process

for chitosan beads was found to be endothermic. With the exception of two processes,

chitosan beads-Zn(II) and A. negundo-Cr(III), randomness was increased. Cd(II), Ni(II) and

Zn(II) sorption on chitosan beads was nonspontaneous, while the sorption of other metal ions

was observed to be spontaneous. As for Gibb’s free energy changes of the sorption system of

pollen-chitosan microcapsules, it appears that the metal uptake process of the microcapsules

was spontaneous. The observed discrepancies in some data have been reported in earlier

studies (Liu & Lee, 2014). A recent study addressed this issue and the authors recommended

further detailed studies on thermodynamic evaluation of adsorption of heavy metal ions.

3.2.5. Isotherm models

Adsorption equilibrium studies of the chitosan-based sorbents have been usually

conducted using two isotherms models; the Langmuir and the Freundlich adsorption isotherm

models. These mathematical models make it possible to quantify performance of the

biosorbent (Wang & Chen, 2014) and their linearized isotherm expressions are employed

(Foo & Hameed, 2010):

i. The Freundlich Model: log qe= log KF+(1/n) logCe (5)

12

with qe,, amount of solute adsorbed in mmol g−1

, Ce, the equilibrium concentration of

the adsorbate in mM L−1

and KF and n Freundlich constants denoting adsorption

capacity and intensity of adsorption.

ii. The Langmuir model: Ce/qe = Ce/Q0+1/Q0

b (6)

with qe, amount of solute adsorbed in mmol g−1

, Ce, the equilibrium concentration of

the adsorbate in mmol L−1

, Q0(in mmol g

-1) and b(in L mmol

-1) Langmuir constants

related to adsorption capacity and energy of adsorption.

Table 3 lists the parameters and the correlation coefficients obtained from the plots of

Langmuir (Ce/qe vs. Ce) and Freundlich (log qe vs. log Ce). It appears that adsorbate-

adsorbent system can be better explained by the Langmuir model for the microcapsules C.

sempervirens-chitosan and P. nigra-chitosan and the chitosan beads. On the other hand, the

Freundlich model gave higher correlation coefficients (R2) for the adsorption of the metal ions

on A. negundo-chitosan microcapsules. This may demonstrate the heterogeneous surface

characteristics of the A. negundo-chitosan microcapsules.

C. sempervirens-chitosan microcapsules exhibited nearly two times higher affinity for

Cd(II) (65.98 mg g−1

) than the other sorbents. Also, this sorbent was more efficient in Cu(II)

(67.10 mg g−1) and Zn(II) (49.55 mg g−1) removal. In Cr(III) removal, A. negundo-chitosan

microcapsules were more effective than all the other adsorbents (70.40 mg g−1). As for Ni(II)

removal, pollen microcapsules adsorbed slightly more ions than the chitosan beads. P. nigra-

chitosan microcapsules were observed to have lower adsorption capacity than the other

sorbents including cross-linked chitosan beads (Table 1). Chitosan-pollen microcapsules

(except P. nigra-chitosan microcapsules) can be used in heavy metal removal. Affinity of the

each sorbent for the metal ions were in the order: A. negundo:

Cr(III)>Cu(II)>Cd(II)>Ni(II)>Zn(II); C. sempervirens: Cu(II)>Cr(III)>Cd(II)>Zn(II)>Ni(II)

13

and P. nigra: Cu(II)>Cr(III)>Cd(II)>Zn(II)>Ni(II). W.S. Wan Ngah et al. reported metal

adsorption capacity of some chitosan composites in their review paper; chitosan-cotton fibres:

Cu(II): 24.78, Ni(II):7.63, Cd(II):15.74 mg g−1

, chitosan-cellulose: Cu(II): 26.50, Zn(II):

19.81, Ni: 13.21 and chitosan-alginate; Cu(II): 67.66 mg g−1

. In case of Cd(II) ions, all the

pollen-chitosan microcapsules were more efficient than the chitosan-cotton fibres adsorbents.

In sorption of Cu(II), Zn(II) and Ni(II) ions, C. sempervirens-chitosan microcapsules were

more effective than the two adsorbent; chitosan-cotton fibres and chitosan-cellulose

composite sorbents. Chitosan-alginate composite showed slightly better performance than C.

sempervirens-chitosan sorbent.

4. Conclusions

Only C. sempervirens-chitosan microcapsules exhibited higher affinity for Cd(II) than

the chitosan beads. C. sempervirens-chitosan microcapsules removed more Cu(II), Cd(II) and

Zn(II) ions and can be tested for other metal ions. C. sempervirens-chitosan microcapsules

had (1) the lowest thermal stability, (2) the highest pyrolysis rate, (3) the lowest N content and

(4) the largest surface. These findings demonstrate that further studies on pollen-chitosan

microcapsules can aim to develop more efficient biosorbents using different pollen grains

with different surface morphology and chemical composition. Chitosan/pollen ratio,

deacetylation degree and molecular weight of chitosan can be manipulated to target various

metal ions.

Conflict of Interests

The authors declare no conflict of interests.

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Supplementary materials

FT-IR spectra, TGA thermogram and SEM images of the pollen-chitosan microcapsules are

given in supplementary materials.

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Figure Legends

Fig 1. Effect of pollen-chitosan microcapsules (a: A. negundo-chitosan, b: C. sempervirens-

chitosan, c: P. nigra-chitosan) amount on the adsorption of metals on pollen-chitosan

microcapsules at initial pH; metal concentration 10 mg L-1; volume of solution 25 mL;

temperature 20°C.

Fig. 2. Effect of contact time on the sorption of metals by pollen-chitosan microcapsules (a:

A. negundo-chitosan, b: C. sempervirens-chitosan, c: P. nigra-chitosan) at initial pH; amount

of pollen-chitosan microcapsules 0.1 g; temperature 20°C; initial metal concentration 10 mg

L-1; volume of metal solution, 25 mL.

Fig. 3. Effect of pH on the sorption of metals by pollen-chitosan microcapsules (a: A.

negundo-chitosan, b: C. sempervirens-chitosan, c: P. nigra-chitosan). Amount of pollen-

chitosan microcapsules 0.1 g; temperature 20°C; initial metal concentration 10 mg L-1

;

volume of metal solution, 25 mL.

19

Table Legends

Table 1. Metals sorption capacity of the pollen-chitosan microcapsules.

Table 2. Thermodynamic parameters for the adsorption of metals on pollen-chitosan

microcapsules.

Table 3. Parameters of Freundlich and Langmuir isotherms for sorption of metals on pollen-

chitosan microcapsules.

23

Table 1

Metals

Sorbents Cd (pH:5.35) Cr (pH:4.63) Cu (pH:5.18) Ni (pH:5.34) Zn (pH:5.34)

% mg g-1

% mg g-1

% mg g-1

% mg g-1

% mg g-1

chitosan beads 26.60 26.64 58.80 58.80 40.80 40.66 16.20 16.20 21.10 21.11

A. negundo-

chitosan 25.13 32.82 63.77 70.40 48.45 50.58 22.81 22.42 22.24 27.78

C.

sempervirens-

chitosan

52.46 65.98 58.46 64.63 64.37 67.10 22.81 22.42 39.91 49.55

P. nigra-

chitosan 25.77 30.91 38.34 41.54 41.07 31.01 17.25 20.43 21.62 28.23

24

Table 2

Isotherms Freundlich Langmuir

Metal ions Sorbents k n R2

Q0 b R

2

Cd(II)

chitosan beads 0.321 2.119 0.917 0.152 0.827 0.959

A. negundo-chitosan 19.861 0.654 0.981 0.281 0.466 0.692

C. sempervirens-chitosan 1.159 5.181 0.842 0.678 135.593 0.938

P. nigra-chitosan 2.891 9.709 0.325 0.330 25.404 0.938

Cr(III)

chitosan beads 2.723 2.198 0.941 1.164 38.805 0.988



P. nigra-chitosan 1.531 4.464 0.568 0.999 66.600 0.916

Cu(II)

chitosan beads 5.888 1.706 0.990 1.456 60.650 0.916



P. nigra-chitosan 1.365 30.303 0.247 0.750 149.925 0.867

Ni(II)

chitosan beads 1.153 1.362 0.910 0.813 2.398 0.949



P. nigra-chitosan 2.163 6.452 0.274 0.398 19.881 0.968

Zn(II)

chitosan beads 0.552 3.205 0.890 0.246 10.690 0.954



P. nigra-chitosan 2.124 2.328 0.221 0.471 67.259 0.982

25

Table 3

Metals Sorbents

∆H°(J mol−1

)

∆S°(J K−1

mol−1

)

∆G° (J mol−1

)

T=298.15 (K) T=308.15 (K) T=318.15 (K)

Cd(II)

chitosan beads 6933.527 7.927 4569.999 4490.725 4411.452

A. negundo-chitosan -6632.900 31.460 -16012.800 -16327.400 -16642.000

C. sempervirens-chitosan -512.595 2.256 -1186.260 -1208.850 -1231.450

P. nigra-chitosan -6789.920 31.862 -16289.700 -16608.300 -16927.000

Cr(III)

chitosan beads 275.924 1.762 -249.304 -266.921 -284.573

A. negundo-chitosan -4951.500 -11.987 -1377.860 -1257.990 -1138.130


P. nigra-chitosan -748.308 31.862 -10248.100 -10566.700 -10885.300

Cu(II)

chitosan beads 2364.790 15.835 -2356.560 -2514.910 -2673.270



P. nigra-chitosan -685.119 0.708 -896.352 -903.437 -910.521

Ni(II)

chitosan beads 385.834 -8.578 2943.469 3029.252 3115.036



P. nigra-chitosan -233.798 13.825 -4355.700 -4493.950 -4632.200

Zn(II)

chitosan beads 2814.771 -2.068 3431.343 3452.023 3472.703



P. nigra-chitosan -995.701 14.016 -5174.690 -5314.860 -5455.620

26

Highlights

Preparation of biodegradable, biocompatible and nontoxic pollen-chitosan microcapsule

Characterisation of pollen-chitosan microcapsules by SEM, FTIR, TGA and EA

Application in heavy metal removal: Cd(II), Cr(III), Cu(II), Ni(II) and Zn(II)

The novel pollen-chitosan biosorbents showed higher performance in Cd(II) removal

C. sempervirens pollen-chitosan microcapsules showed the highest removal performance

preparation and characterisation of biodegradable pollen–chitosan microcapsules and its...

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