Surface modification of cellulose isolated from sesamun indicum underutilized seed a means of enhancing cellulose hydrophobicity

This study has shown that hydrophobicity can be improved in cellulose via surface modification.. So, replacing the hydroxyl functional groups at the surface of cellulose via sur-face modi

Original Article

underutilized seed: A means of enhancing cellulose hydrophobicity

Adewale Adewuyia,b,*, Fabiano Vargas Pereirab

a Department of Chemical Sciences, Faculty of Natural Sciences, Redeemer's University, Ede, Osun State, Nigeria

b Department of Chemistry, Federal University of Minas Gerais, Av Ant^onio Carlos, 6627, Pampulha, CEP 31270-901 Belo Horizonte, MG, Brazil

a r t i c l e i n f o

Article history:

Received 25 May 2017

Received in revised form

10 July 2017

Accepted 20 July 2017

Available online xxx

Keywords:

Cellulose

Hydrophobicity

Modification

Sesamum indicum

Underutilized seed

a b s t r a c t

Cellulose (SC) isolated from sesame seed (SS) was surface modified with the introduction of an ester functional group via a simple reaction to produce the modified product (SA) SS, SC and SA were char-acterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), particle size distribution (PSD), zeta potential and scanning electron microscopy (SEM) SC and SA were evaluated for their water holding capacity (WC), oil holding capacity (OC), swelling capacity (SW) and their ability to adsorb heavy metals The FTIR revealed peaks corresponding to the formation of the ester functional group at the surface of SA The crystallinity of SC was 28.02% but after the modification it increased to 77.03% in SA The PSD of SC and SA was both monomodal with sizes of 10.1305mm in SC and 10.2511mm in SA The adsorption capacity of SC towards Pb (II) and Cu (II) ions was higher than that of

SA However, SA was unable to adsorb Cu (II) ions SA exhibited the lower WC and SW values as compared to SC which suggested an improved hydrophobicity after the modification This study has shown that hydrophobicity can be improved in cellulose via surface modification

© 2017 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an

open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

With the recent increase in demand for products made from

renewable and sustainable non-petroleum based resources,

cellu-lose is gaining significant recognition for diverse applications due

to its renewability, biodegradability, non-toxicity and molecular

structure It represents the most abundant renewable polymer

which is mostly used in the form offibers or derivatives Cellulose

has been reported from a number of conventional sources, which

are of both plant and microorganism origins[1] However, there is

still a need to search for better alternatives as most of the

previ-ously identified conventional sources are expensive On the other

hand, these sources have found other applications

Sesame seed (Sesamum indicum) is an underutilized plant

ma-terial in Nigeria which can serve as a source of cellulose This plant

belongs to the Pedaliaceae family[2] It is about 60e120 cm tall and

the fruit is a dehiscent capsule held close to the stem When ripe,

the capsule shatters to release a number of small seeds The seeds

are ovate, slightlyflattened and thin The seed oil has been reported

as an important source of phytonutrient for applications in food and pharmaceutical industries[3] The seed is an important source

of oil and after oil is extracted from the seed, the seed cake left is usually discarded as waste Presently, the seed cake is considered as waste with no specific use The essence of this work is to find application for this discarded seek cake in Nigeria

Due to the wide range of potential applications and important inherent properties of cellulose, there is a continuous effort on how

to improve and optimize the properties of cellulose-based natural fibers Among these important inherent properties of cellulose, the hydrophobicity plays an important role in water repellency, self-cleaning, corrosion prevention, friction reduction and antifouling

[4] The poor hydrophobicity of cellulose has limited its application

in a few areas of research such as in waste water treatment or purification Previous studies have shown that the properties of cellulose can be improved by surface modification[5] So, replacing the hydroxyl functional groups at the surface of cellulose via sur-face modification might be an effective means of improving on its hydrophobicity

In this regard, the present study is aimed at finding a cheap source of cellulose, which can be surface modified in order to improve its hydrophobicity This was achieved by isolating,

* Corresponding author Department of Chemical Sciences, Faculty of Natural

Sciences, Redeemer's University, Ede, Osun State, Nigeria.

E-mail address: walexy62@yahoo.com (A Adewuyi).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

http://dx.doi.org/10.1016/j.jsamd.2017.07.007

2468-2179/© 2017 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license ( http:// creativecommons.org/licenses/by/4.0/ ).

characterizing and surface modifying cellulose from a sesame seed.

To the best of our knowledge, there is no report on the isolation and

surface modification of cellulose from the sesame seed source from

Nigeria

2 Experimental

2.1 Materials

SS was obtained from a local market in Ibadan, Oyo state,

Nigeria This was later identified at the Department of Botany and

Microbiology, University of Ibadan, Ibadan, Oyo state, Nigeria The

seeds were air dried, ground in an industrial mill and stored in an

airtight container Sodium chlorite, sodium hydroxide, acetic acid,

chloroacetic acid, suberic acid, thionylchloride, ethylenediamine

and all other chemicals used in this study were purchased from

SigmaeAdrich (Brazil)

2.2 Isolation of cellulose from SS

The isolation of cellulose from SS was achieved following the

method described by Flauzino Neto et al.[6] Briefly, 200 g of SS was

transferred into a 2 L beaker containing alkali solution (2 wt%

NaOH) This was heated at 80
C for 5 h with continuous stirring

using a Fisatom mechanical stirrer The beaker with its content was

cooled,filtered, washed continuously with deionized water several

times until alkali free and oven dried at 50
C The residue obtained

was bleached with a mixture of solution, which was made up of

equal volumes (1:1) of acetate buffer (27 g NaOH and 75 mL glacial

acetic acid, diluted to 1 L of distilled water) and aqueous sodium chlorite (1.7 wt% NaClO2in deionized water) The mixture was then stirred at 80
C for 5 h The resultingfibers were washed repeatedly

in deionized water until the pH of thefiber became neutral The bleaching step was repeated twice until the fiber became completely white and dried in an air-circulating oven at 50
C for

24 h giving rise to SC of an estimated yield of about 25%

2.3 Modification of SC Chloroacetylchloride was synthesized by stirring a mixture of chloroacetic acid (0.03 mol), thionylchloride (0.04 mol) and chlo-roform at 75
C for 30 min SC (7.50 g) was added to the chlor-oacetylchloride (after the removal of excess thionylchloride under reduced pressure); this was allowed to react for 5 h under constant stirring at 80
C andfinally cooled in ice Suberic acid (50 mL) was added and stirred for 6 h at 80
C under reflux Cold distilled water was added to the mixture and centrifuged thrice for 10 min at

8500 rpm to remove excess suberic acid Thefinal product was dried at 50
C for 24 h giving rise to an SA yield of about 80% 2.4 Characterization

The functional groups in SS, SC and SA were determined using FTIR (Perkin Elmer, spectrum RXI 83303) SS, SC and SA were blended with KBr, pressed into pellets and analyzed in the range of

400e4500 cm1 The X-ray diffraction pattern was obtained using

X-ray diffractometer (XRD-7000X-Ray diffractometer, Shimadzu) withfiltered Cu Karadiation at 40 kV and 40 mA XRD pattern was

Fig 1 FTIR spectra of the sesame seed (a), the sesame cellulose (b) and the modified sesame cellulose (c).

recorded from 10 to 80
C of 2q/s with a scanning speed of 2.00
/

min Thermal stability and fraction of volatile components of SS,

SC and SA were monitored by DTA-TG apparatus (SHIMADZU,

C30574600245) under nitrogen atmosphere, while the surface

morphology was studied using FEI quanta 200 (model EDAX EDS)

that operates on Genesis software (version 5.21) The PSD was

carried out using a zeta potential analyzer (DT1200, Dispersion

technology) at 25
C, while observing a general calculation

model for irregular particles Several measurements were taken

using Dispersion technology-AcoustoPhor Zetasize 1201 software

(version 5.6.16)

2.5 Water holding capacity

A known weight (0.5 g) of SC and SA was separately dispersed in

10 mL of distilled water in a pre-weighed, clean centrifuge tube (W)

placed in a water bath at 37
C for 30 min These were centrifuged

for 15 min at 4000 rpm; the supernatant was removed and the

centrifuge tube with the distilled water soaked SC and SA was

weighed (W2) WC was estimated as[7]:

WC

g g1

¼ðW2 ðW þ W1ÞÞ

2.6 Oil holding capacity

This was determined by weighing 0.2 g (W) of SC and SA

separately into a calibrated centrifuge tube containing 5 mL (V1) of

Picralima nitida seed oil The mixture was properly stirred for

10 min after which it was centrifuged for 30 min at 5000 rpm The supernatant oil (V2) was gently removed, while the absorbed oil was estimated as the difference between V1 and V2 OC was calculated as described by Lu et al.[8]:

OC

mL g1

¼V1 V2

2.7 Swelling capacity

SW was determined by placing 0.5 g (W) of SC and SA in a calibrated tube, the initial bed volume (V1) was measured, mixed with 10 mL of distilled water and shaken vigorously The tube with its content was placed in a water bath at 25
C for 24 h and thefinal volume (V2) measured SW was calculated as[9]:

SW

mL g1

¼V2 V1

2.8 Heavy metal adsorption capacity Lead nitrate (Pb(NO3)2) and copper sulfate (Cu(SO4).5H2O) salts were used in the preparation of the salt solutions in de-ionized water Metal adsorption study was carried out by separately shaking 0.1 g of SC and SA with a 50 mL solution (100 mg/L) of metal

in different beakers at 25
C and 200 rpm for 3 h This was later centrifuged for 10 min at 5000 rpm, and the metal concentration before and after adsorption were determined using Atomic

Fig 2 TG curves of the sesame seed (a), the sesame cellulose (b) and the modified sesame cellulose (c).

Absorption Spectrometer (Varian AA240FS) The metal ions

adsorption capacity of SC and SA was calculated as

qe¼ðCo CeÞV

where qeis the adsorption capacity in mg/g, Coand Ceare initial and

final concentrations (mg/L) of adsorbate (Pb and Cu) in solution

respectively; while V and M are volumes (L) of metal ion solution

and weight (g) of SC and SA used

3 Results and discussion

3.1 Characterization

The FTIR result is presented inFig 1 The spectra revealed peaks

corresponding to the OH functional group at 3320 cm1 The band

at 1745 cm1only found in SS was assigned to the C]O stretching

of the acetyl group and the uranic ester groups of the hemicellulose,

which may also be due to the ester linkage of the carboxylic group

in the lignin and hemicelluloses The band at 1745 cm1

dis-appeared in SC which may be due to the removal of hemicellulose

and lignin from SS but reappeared in SA which suggests the

for-mation of the ester functional group in SA Bands corresponding to

the amorphous characteristics of the cellulosic materials were seen

at 354 cm1in SS, SC and SA while the band at 2911 cm1 was

assigned to the CeH stretching of CH2in SS, SC and SA The peaks at

1094 and 1155 cm1was attributed to the deformation of the CeH

rocking vibration and the CeOeC pyranose ring skeleton, while the peak at 894 cm1was assigned to the symmetric CeOeC stretching

of theb-1,4-glycosidic linkages of the glucopyranose units of the cellulose in SS, SC and SA

Cellulose and its derivatives tend to carbonize under heating through dehydration and cross-linking reactions, which can be described as the rearrangement of a cellulose structure that pro-motes thefinal production of char residue SS, SC and SA were pyrolyzed in order to investigate their effects of temperature and thermal stability as shown inFig 2 Loss in mass wasfirst noticed in the temperature range of 85e115
C, which was attributed to the

loss of internal water molecules in SS, SC and SA There was another loss in mass within the temperature range of 115e162
C that may

be assigned to the loss of volatile organic compounds The loss in mass in the range of 189e320
C may be attributed to the loss of

hemicellulose Loss in mass at temperatures above 450
C in SS and

SC were assigned to losses of lignin and char[10] There was steady loss in mass in SA at temperatures above 320
C, which can be described as the loss in mass at 320e450
C, 450e600
C and

600e715
C This steady loss in mass was considered as being due

to the chain length of the suberic acid involved in the modification This increase in the decomposition temperature of SA may be an indication of the thermal stability of the cellulose that was increased with the modification

The diffraction pattern presented in Fig 3 with 2q peaks is typical of cellulose I structure The crystallinity index (Ic) was determined using the height of 200 peak (I002, 2q¼ 21.65
) and the

minimum intensity between the 200 and 110 peaks (IAM,

2q¼ 17.75
) which can be expressed as:

Fig 3 X-ray diffraction patterns of the sesame seed (a), the sesame cellulose (b) and the modified sesame cellulose (c).

Icð%Þ ¼I002 IAM

where I002 represents both crystalline and amorphous materials

while IAMrepresents the amorphous material The crystallinity of

SC was 28.02% but after the modification it increased to 77.03% in

SA The increase in crystallinity may be due to the introduction of

the ester group to the cellulose which may likely have reinforced

the crystalline nature of the cellulose The particle size distribution

of SC and SA was found to be monomodal The size distribution was found to be 10.1305mm for SC and 10.2511mm for SA The zeta potential is presented inFig 4 The values of the zeta potential increased in SC and SA just as the pH value increased The value of the zeta potential is suggestive that SC and SA are stable materials The SEM micrograph is presented inFig 5 The surface of SS ap-pears to have irregular shape and size which seemed to be composed of several microfibrils with each fiber having a compact structure Surface of SC is different from that of SS, it appeared smooth and flaky which may be due to the removal of

Fig 4 Zeta potentials of the sesame cellulose (a) and the modified sesame cellulose (b).

Fig 5 SEM images of the sesame seed (a), the sesame cellulose (b) and the modified sesame cellulose (c).

hemicellulose, lignin and some other non-cellulosic materials

while SA appears to be stacked particles of aggregated

macromol-ecules; it exhibited a lumpish structure which may be due to the

intramolecular interaction in the molecule The surface of SA is

completely different from those of SS and SC

3.2 Water holding, oil holding and swelling capacities of SC and SA

The values obtained for WC, OC and SW with respect to SC and

SA are presented inFig 6 WC was found to be 17.0372 g/g for SC

and 2.6116 g/g for SA WC estimates the ability of SC and SA to hold

water over a period of time, especially when subjected to an

external centrifugal gravity or compression forces The values

ob-tained for WC were lower in SA compared to SC, which may be due

to the modification that might have improved the hydrophobicity

of SA The value of WC for SA is also lower than those reported for

the red beanflour[11]and the white lupin[12], but higher than

that reported for the standardflour[13] OC can be related to the

adsorption of organic compounds to the surface of SC and SA, which

can be linked to the porosity of the structure of SC and SA[14] The

value obtained for SA (4.0302 mL/g) was higher than that of SC

(2.6165 mL/g) These values are lower than those reported for

Polythia longifolia[15]but higher than those for the cowpea[16]

and the white lupin[12] SW estimates the amount of water that

SC and SA can absorb at a given time The value was found to be

higher in SC (3.6860 mL/g) than in SA (1.9488 mL/g) This once

again shows an improved hydrophobicity in SA over SC These

values are lower than those reported for the coconut kernel[14]

and the cowpea[16]

3.3 Heavy metal adsorption capacity

Heavy metals have been known to enter the human body

through food chain and most time cause serious harm to human

health as a result of the disease they bring Exposure to polluted

water is one of the key sources of this problem in developing

countries[17,18] This may be caused by contamination from

ma-terials with strong affinity for heavy metal adsorption Use of

ma-terials with low affinity for heavy metal adsorption is of interest

during certain industrial applications like in the case of food and

cosmetic industries SC and SA were evaluated for their ability to

adsorb Cu (II) and Pb (II) ions from an aqueous solution The

adsorption capacities varied with SC showing the higher adsorption capacity towards the studied metals The results obtained for the adsorption capacities of SC and SA are presented inTable 1, these are also compared with those reported previously in the literature The adsorption capacity of SC towards Cu (II) was 5.695 mg/g, while

SA was unable to adsorb Cu (II) ions from the solution, probably due

to the inability of the modified surface to interact with the Cu (II) ions in the solution SA may not be able to interact with Cu (II) ions because of the conversion of the hydroxyl group at its surface to the ester functional groups as a result of the modification Moreover, the ester group lacks hydrogen atoms which could have been exchanged for the Cu (II) ion like in the case of the hydrogen atom

in the hydroxyl group This reduction in the metal adsorption ca-pacity of SA suggests that the modification has taken place This suggests that SA mayfind applications, where interference from Cu (II) is not required or of limited importance SC was also found to have the higher adsorption capacity for Pb (II) ion which was 20.681 mg/g while the value obtained for SA was 0.888 mg/g This also showed that SA has little attraction for Pb (II) ions The value obtained for SA was far lower than those reported in the literature

4 Conclusion Cellulose was isolated from SS with an estimated yield of 25%, thanks to the surface modified using the suberic acid In this case, the hydroxyl group at the surface of SC was found to be converted

to the ester functional group The improved hydrophobicity was indicated by the reduced WC and SW after the modification The SA exhibited the low adsorption capacity towards Pb (II) ions, but it was unable to adsorb Cu (II) ions from an aqueous solution This suggests that SA mayfind potential applications where interference from Cu (II) is not required or of limited importance

Acknowledgments This research was supported by TWAS-CNPq The authors are also grateful to TWAS-CNPq for awarding a postdoctoral fellowship

at Universidade Federal de Minas Gerais, Minas Gerais, Brazil References

[1] J George, S.N Sabapathi, Cellulose nanocrystals: synthesis, functional prop-erties, and applications, Nanotechnol Sci Appl 5 (2015) 45e54

[2] H Zebib, G Bultosa, S Abera, Physico-chemical properties of sesame (Ses-amum indicum L.) varieties grown in northern area, Ethiopia, Agr Sci 6 (2015) 238e246

Fig 6 WC, OC and SW of the sesame cellulose (a) and the modified sesame cellulose (b).

Table 1 Comparison of the adsorption of Pb (II) and Cu (II) ions on SC and SA with other adsorbents reported in the literature.

Adsorbent Pb (II) Cu (II) Reference Adansonia digitata 54.417 9.349 [19]

Banana peel 89.286 5.720 [22]

Bionanocomposite 224.97 169.817 [23]

Modified polyamineepolyurea 109.90 73.50 [25]

Coconut tree sawdust 25.00 3.89 [26]

Cicer arietinum 20.69 17.77 [27]

Chitosan-coated bentonite 13.49 12.14 [29]

Modified silica 65.54 104.12 [30]

Note: Values are in mg/g.

[3] K.R Anilakumar, N.S Nagaraj, K Santhanam, Effect of coriander seeds on

hexachlorocyclohexane-induced lipid peroxidation in rat liver, Nutr Res 21

(2001) 1455e1462

[4] P Wang, D Zhang, R Qiu, B Hou, Super-hydrophobic film prepared on zinc as

corrosion barrier, Corros Sci 53 (2011) 2080e2086

[5] J Chen, M Su, X Zhang, R Chen, J Hong, L Yang, Z Yang, The role of cations in

homogeneous succinoylation of mulberry wood cellulose in salt-containing

solvents under mild conditions, Cellulose 21 (2014) 4081e4091

[6] W.P Flauzino Neto, H.A Silverio, N.O Dantas, D Pasquini, Extraction and

characterization of cellulose nanocrystals from agro-industrial residue-soy

hulls, Ind Crops Prod 42 (2013) 480e488

[7] M Zhang, C.J Zhang, S Shrestha, Study on the preparation technology of superfine

ground powder of Agrocybe chaxingu Huang, J Food Eng 67 (2005) 333e337

[8] H Lu, Y Gui, L Zheng, X Liu, Morphological, crystalline, thermal and

physi-cochemical properties of cellulose nanocrystals obtained from sweet potato

residue, Food Res Int 50 (2013) 121e128

[9] E Lecumberri, R Mateos, M Izquierdo-Pulido, P Ruperez, L Goya, L Bravo,

Dietary fibre composition, antioxidant capacity and physico-chemical

prop-erties of a fibre-rich product from cocoa (Theebroma cacao L.), Food Chem 104

(2007) 948e954

[10] M.E Babiker, A.R.A Aziz, M Heikal, S Yusup, M Abakar, Pyrolysis

charac-teristics of phoenix dactylifera date palm seeds using thermo-gravimetric

analysis (TGA), Int J Environ Sci Dev 4 (2013) 521e524

[11] S Ashraf, S.M.G Saeed, S.A Sayeed, R Ali, Impact of microwave treatment on

the functionality of cereals and legumes, Int J Agric Biol 14 (2012) 365e370

[12] H Tizazu, S.A Emire, Chemical composition, physicochemical and functional

properties of lupin (Lupinus albus) seeds grown in Ethiopia, Afr J Food Agric.

Nutr Dev 10 (2010) 3029e3046

[13] L Menon, S.D Majumdar, U Ravi, Mango (Mangifera indica L.) kernel flour as a

potential ingredient in the development of composite flour bread, Ind J Nat.

Prod Res 5 (2014) 75e82

[14] L.L.W.C Yalegama, D.N Karunaratne, R Sivakanesan, C Jayasekara, Chemical

and functional properties of fibre concentrates obtained from by-products of

coconut kernel, Food Chem 141 (2013) 124e130

[15] A Adewuyi, F.V Pereira, Cellulose nanocrystals from underutilized Polythia

longifolia seed, Period Tche Quim 14 (2017) 10e18

[16] V Benítez, S Cantera, Y Aguilera, E Molla, R.M Esteban, M.F Díaz,

M.A Martin-Cabrejas, Impact of germination on starch, dietary fiber and

physicochemical properties in non-conventional legumes, Food Res Int 50

(2013) 64e69

[17] F Asadi, H Shariatmadari, N Mirghaffari, Modification of rice hull and

sawdust sportive characteristics for remove heavy metals from synthetic

so-lutions and wastewater, J Hazard Mater 154 (2008) 451e458

[18] P.C Okafor, P.U Okon, E.F Daniel, E.E Ebenso, Adsorption capacity of coconut

(Cocos nucifera L.) shell for lead, copper, cadmium and arsenic from aqueous

solutions, Int J Electrochem Sci 7 (2012) 12354e12369

[19] A Adewuyi, F.V Pereira, Nitrilotriacetic acid functionalized Adansonia digitata biosorbent: preparation, characterization and sorption of Pb (II) and Cu (II) pollutants from aqueous solution, J Adv Res 7 (2016) 947e959

[20] M Mohapatra, L Mohapatra, P Singh, S Anand, B.K Mishra, A comparative study on Pb(II), Cd(II), Cu(II), Co(II) adsorption from single and binary aqueous solutions on additive assisted nano-structured goethite, Int J Eng Sci Tech-nol 2 (2010) 89e103

[21] M.G.A Vieira, A.F de Almeida Neto, M.G Carlos da Silva, C.C Nobrega, A.A Melo Filho, Characterization and use of in natura and calcined rice husks for biosorption of heavy metals ions from aqueous effluents, Braz J Chem Eng 29 (2012) 619e633

[22] R.M Salim, A.J.K Chowdhury, R Rayathulhan, K Yunus, Md Z.I Sarkar, Bio-sorption of Pb and Cu from aqueous solution using banana peel powder, Desal Water Treat 57 (2016) 303e314

[23] R Ahmad, A Mirza, Adsorption of Pb(II) and Cu(II) by alginateeAuemica bionanocomposite: kinetic, isotherm and thermodynamic studies, Process Saf Environ Prot 109 (2017) 1e10

[24] A.L.G Paulino, A.J.D Cunha, R.V.D.S Alfaya, A.A.D.S Alfaya, Chemically modified natural cotton fiber: a low-cost biosorbent for the removal of the Cu(II), Zn(II), Cd(II), and Pb(II) from natural water, Desal Water Treat 52 (2013) 4223e4233

[25] C Ozer, F Boysan, M Imamoglu, Adsorption of Cu(II), Ni(II) and Pb(II) ions onto polyamine-polyurea polymer modified with pyromellitic dianhydride: kinetic, isotherm and thermodynamic studies, Desal Water Treat 57 (2015) 11173e11183

[26] W.P Putra, A Kamari, S.N.M Yusoff, C.F Ishak, A Mohamed, N Hashim, I Md Isa, Biosorption of Cu(II), Pb(II) and Zn(II) Ions from aqueous solutions using selected waste materials: adsorption and characterisation studies, J Encap Ads Sci 4 (2014) 25e35, http://dx.doi.org/10.4236/jeas.2014.41004 [27] D.K.V Ramana, K Jamuna, B Satyanarayana, B Venkateswarlu, M.M Rao,

K Sehaih, Removal of heavy metals from aqueous solutions using activated carbon prepared from Cicer arietinum, Toxicol Environ Chem 92 (2010) 1447e1460, http://dx.doi.org/10.1080/02772241003614312

[28] H.A Sani, M.B Ahmad, M.Z Hussein, N.A Ibrahim, A Musa, T.A Saleh, Nanocomposite of ZnO with montmorillonite for removal of lead and cop-per ions from aqueous solutions, Process Saf Environ Prot 109 (2017) 97e105

[29] W Tsai, M.D.G de Luna, H.L.P Bermillo-Arriesgado, C.M Futalan, J.I Colades,

M Wan, Competitive fixed-bed adsorption of Pb(II), Cu(II), and Ni(II) from aqueous solution using chitosan-coated bentonite, Int J Polym Sci 2016 (2016), http://dx.doi.org/10.1155/2016/1608939

[30] S Radi, S Tighadouini, M Bacquet, S Degoutin, J Dacquin, D Eddike,

M Tillard, Y.N Mabkhot,b-Keto-enol tethered pyridine and thiophene: syn-thesis, crystal structure determination and its organic immobilization on silica for efficient solideliquid extraction of heavy metals, Molecules 21 (2016) 888e891