Harnessing of Newly Tailored Poly (Acrylonitrile)-Starch Nanoparticle Graft Copolymer for Copper IonRemoval via Oximation Reactionkhaled Mostafa  ( kh_mostafa@hotmail.com )

National Institute of Standards https://orcid.org/0000-0002-5512-5471H. Ameen 

National institute of standardsA. Ebessy 

National institute for standardsA. El-Sanabary 

National Research center

Research Article

Keywords: Poly (AN)-SNPs graft copolymer, oximation, heavy metal ions, adsorption, kinetic study

Posted Date: April 19th, 2021

DOI: https://doi.org/10.21203/rs.3.rs-412347/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.  Read Full License

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Harnessing of Newly Tailored Poly (Acrylonitrile)-Starch Nanoparticle Graft

Copolymer for Copper Ion Removal via Oximation Reaction

By

Kh M Mostafa1*, H. A. Ameen1 A. El- Ebessy1 and A. A. El-Sanabary2

1-Textile Metrology Laboratory, Chemical Metrology Division, National Institute of Standards

(NIS), B.O. Box 136, Giza, Code No. 12211, Egypt.

2- Polymer & Pigment Department, Chemical Industries Research Division, National Research

Center, Dokki, Cairo, Egypt.

Correspondent author: kh_mostafa@hotmail.com

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Abstract:

Our recently tailored and fully characterized poly (AN)-starch nanoparticle graft copolymer

having 60.1 G.Y. % was used as a starting substrate for copper ions removal from waste water

effluent after chemical modification with hydroxyl amine via oximation reaction. This was done

to change the abundant nitrile groups in the above copolymer into amidoxime one and the

resultant poly (amidoxime) resin was used as adsorbent for copper ions. The resin was

characterized qualitatively via rapid vanadium ion test and instrumentally by FT-IR spectra and

SEM morphological analysis to confirm the presence of amidoxime groups. The adsorption

capacity of the resin was done using the batch technique, whereas the residual copper ions

content in the filtrate before and after adsorption was measured using atomic adsorption

spectrometry. It was found that the maximum adsorption capacity of poly (amidoxime) resin was

115.2 mg/g at pH 7, 400ppm copper ions concentration and 0.25 g adsorbent at room

temperature. The adsorption, kinetics and isothermal study of the process is scrutinized using

different variables, such as pH, contact time, copper ion concentration and adsorbent dosage.

Different kinetics models comprising the pseudo-first-order and pseudo-second-order have been

applied to the experimental data to envisage the adsorption kinetics. It was found from kinetic

study that pseudo-second-order rate equation was better than pseudo-first-order supporting the

formation of chemisorption process. While, in case of isothermal study, the examination of

calculated correlation coefficient (R2) values showed that the Langmuir model provide the best

fit to experimental data than Freundlich one.

Keywords: Poly (AN)-SNPs graft copolymer; oximation, heavy metal ions; adsorption; kinetic

study.

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1- Introduction

Worldwide growth and rapid expansion of industrialization mainly for pollutant one likes textile,

mining, metal plating, leather tanning and pesticides; results a massive release of the sewages

embracing toxic substance especially heavy metal ions into the environment [1]. Heavy metal

ions, when existing in higher quantities than acceptable limits, are dangerous for human and

aquatic life at which various damage and disorders have been observed due to their toxicity [2].

Examples of such toxic heavy metal ions that cause serious challenge to health and are persistent

during treatment of waste water include; mercury, cadmium, zinc, lead, chromium, nickel and

copper [3]. Copper as in our case is considered as one of the most vital elements in activities of

the human body, however, if it was swallowed in more amount than required can lead to serious

health problems such as; tremor, vomiting, cramps and finally may be lead to the death [4]. Due

to the toxicity and carcinogenic effect of the above effluents; discharge of toxic waste in the

environment should be controlled [1]. So, numerous techniques have been developed for the

removal and recovery of metal ions from sewage and industrial wastewater such as precipitation,

ion exchange, membrane filtration, coagulation, flocculation, flotation, electrochemical

treatment, and adsorption [2, 3, 5-11]. The adsorption is consider as one of the low cost, simple, and

effective methods for the removal of heavy metal ions in wastewater with small and high

concentrations of contamination without leaving any unwanted residue. Besides, the process is

convenient to various adsorbents or bio sorbents which are effective and cheap as compared with

other processes [12]. On the other hand, poly acrylonitrile as a reactant synthetic resin is widely

used for adsorption of heavy metal ions due to its distinctive structures that embrace hardness,

chemical resistance, consistency and permeability with other polar materials [13]. Besides, the

presence of a large number of nitrile groups along the polymer backbone structure that could be

converted into other functional groups via chemical modification with various reagents such as

ethylene diamine, hydrazine, thioamide and imidazoline as well as amidoxime to develop new

moieties that are vital for the removal of cationic metal ions in wastewater treatment [14-16]. So, a

number of articles have been published for describing the synthesis of adsorbent using

amidoxime functional group via incorporating the nitrile group into a polymer matrix, followed

by the conversion of the nitrile group into amidoxime one by treatment with an alkaline solution

of hydroxylamine. In this regards, Egawa et al. [17] prepared a chelating resin encompassing

amidoxime by reacting acrylonitrile co-divinyl benzene copolymer beads as a synthetic one with

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hydroxylamine by suspension polymerization. While, Kobuke et al. [18] synthesized a poly

acryloamidoxime resin from various copolymers of acrylonitrile and cross-linking agents. On the

other hand, Faraj et al. [19] studied the preparation and characterization of poly amidoxime

chelating resin from rubber wood fiber-g-poly acrylonitrile. But, one of the major drawbacks on

the adsorption capacity of poly acrylonitrile in an aqueous solution exists due to non-

biodegradability and high cost as well as low yield. To solve this problem as one of main target

in this manuscript, developing cheaper, biodegradable, low cost and effective adsorbents based

on starch nanoparticles using acrylonitrile as a reactive monomer via graft copolymerization to

overcome the latter drawbacks of the synthetic nature of poly acrylonitrile as an adsorbent resin

was studied. Recently, our research team studied a green and efficient tool for grafting

acrylonitrile onto starch nanoparticles using microwave irradiation [20]. Besides, graft

copolymerization of acrylonitrile onto starch nanoparticles using peroxymonopersulphate/

mandelic acid redox pair to increase its utilization was also studied in details for maximizing the

graft yield % [21]. Therefore, our research team attempt to explore the adsorption behavior of

copper ions from aqueous solutions based on our newly tailored poly (AN)-starch nanoparticles

graft copolymer with higher graft yield 60.1 % after oximation reaction (a point that has not been

reported in the literature). This was done to change the abundant nitrile groups in the above

copolymer into amidoxime one and the resultant insoluble poly (amidoxime) resin was used as

adsorbent for copper ions from their solutions. Most of the published works using poly

(amidoxime) resin is focused on uranium extraction in sea water [17, 18]; while, there are very few

articles published on transition metal uptake by poly (amidoxime) resin [19, 22-24]. Therefore,

different factors affecting the adsorption, such as pH, treatment time, poly (amidoxime) resin

dose and copper ions concentration were deliberated in detail. Besides, various adsorption

kinetics like pseudo-first-order and pseudo-second-order rate equation as well as isothermal

models have been applied to the experimental data especially with respect to Langmuir and

Freundlich isotherm.

2. Experimental Part:

2.1 Materials:

Poly (AN) - starch nanoparticles graft copolymer as a starting substrate was prepared and fully

characterized according to our previous works [21]. Details of the conditions used and their main

characteristics are given in Table I. Hydroxylamine hydrochloride (Acros organics, USA) was

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used for chemical modification of the copolymer. Sodium hydroxide (analytical grade) was

supplied by R & M (U.K). Copper sulphate pentahydrate (CuSO4.5H2O) (99.8%, Merck) of

analytical grade was used as heavy metal ion contaminant in this work. Ethyl alcohol and

hydrochloric acid and other chemicals used were of analytical reagent grade.

Please insert Table I here.

2.2 Graft copolymerization technique:

Unless otherwise designated; the graft polymerization reaction was carried out in 100 ml

stoppered flask containing an aqueous solution of acrylonitrile. The flasks were stoppered and

placed in a thermostatic water-bath at 450C. Nitrogen gas was purged through this solution to

remove the dissolved oxygen. Starch nanoparticle (1.0 g) and calculated amounts of acrylonitrile

(2 ml), mandelic acid (8 m mol / l) and sulphuric acid (10 m mol / l) solutions were added and

the reaction mixture was mixed comprehensively. Material to liquor ratio 1:20 was used. To

initiate the reaction a known amount of peroxymonosulfate (30 m mol/l) was added. The

contents were shaken occasionally during the course of reaction for 2 hours. Poly acrylonitrile

(homopolymer) was removed completely from its physical mixtures of starch nanoparticles and

poly (AN) - starch nanoparticles graft copolymer according to the reported method [21].

2.3. Modification of poly (AN)-starch nanoparticles graft copolymer via oximation

reaction):

Poly (AN) - starch nanoparticles graft copolymer (0.25 g), ethyl alcohol (25 ml) and

hydroxylamine hydrochloride (3 g) were added into a 250 ml three-neck round-bottom flask with

a reflux condenser. The mixture was stirred at room temperature for 3.0 hour. Then sodium

hydroxide solution 6 ml of (1 M) was added to the reaction mixture to neutralize the

hydrochloric acid. The pH of the reaction mixture was attuned to pH 7. The reaction was

permitted to continue for 6 h at 70 °C under continuous stirring. At the end of the reaction, the

resultant amidoxime-modified poly (AN)-starch nanoparticles graft copolymer was then filtered

and washed carefully with 50 ml of ethanol and 100 ml of double distilled water. The chelating

copolymer was allowed to dry in a vacuum oven at 50 °C till a constant weight.

2.4. Adsorption in batch test:

An aqueous working standard stock solution of copper ions (406 ppm) was prepared by

dissolving cupric sulphate (CuSO4. 5H2O, 1.6 g) in 1000 ml double distilled water. The

amidoxime - modified poly (AN)-starch nanoparticles graft copolymer (0.1–2.0 g) was then

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added to the copper solution (100 ml), and the dispersion was stirred for 15 min at room

temperature (260C ± 0.5) using our calibrated data logger apparatus on the magnetic starrier to

form a complex with the copper ions. The amidoxime - modified poly (AN) - starch

nanoparticles graft copolymer-copper ions complex was then removed by filtration and the

filtrate was used for the residual metal analysis using Atomic Absorption type S Series (U.S.A).

The amount of adsorbed Cu (+2) at equilibrium, qe (mg/g) was calculated using the

following equation: 𝑞𝑒 = (𝐶0 − 𝐶𝑒)𝑉𝑊

Where Co and Ce (mg/L) are the initial copper concentration and copper concentration at

equilibrium, respectively; W (g) is the weight of adsorbent used, and V is the volume of Cu (+2)

solution (0.1 L).

2.4.1. Adsorption Kinetics:

2.4.1.1. Pseudo-first order model:

It can be generally expressed by the linear form as in equation 1 below: ln(𝑞𝑒 − 𝑞𝑡) = 𝑙𝑛𝑞𝑒 − 𝐾1𝑡 (1)

Where, qe is the equilibrium adsorption capacity of the adsorbent (mg/g), qt represents the

adsorption capacity (mg/g) at time t, while K1 (min−1) is the equilibrium rate constant of pseudo

first-order adsorption model.

2.4.1.2. Pseudo-second order model:

It can be generally expressed by equation 2. 𝑡𝑞𝑒 = 1𝐾2𝑞𝑒2 + 1𝑞𝑒 (2)

Where, qe is the equilibrium adsorption capacity of the adsorbent (mg/g), K2 (g mg−1 min−1) is

the equilibrium rate constants of pseudo second-order adsorption model.

N. B. The values of linear correlation coefficient regression (R2) are used to predict the most

suited isotherm and kinetic model for the adsorption process.

2.4.2. Adsorption isotherm:

2.4.2.1. Longmuir isotherm:

It can be expressed as shown below by equation 3: 1𝑞𝑒 = 1𝐾𝐿 𝑞𝑚𝑎𝑥 ∗ 1𝐶𝑒 + 1𝑞𝑚𝑎𝑥 (3)

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Where, Ce is the adsorption capacity at equilibrium concentration (mg/L), qmax represents the

maximum adsorption capacity (mg/g) and KL (L/mg) is the Langmuir's constant isotherm.

2.4.2.2. Freundlich isotherm:

It can be expressed as shown by equation 4. 𝐿𝑜𝑔 𝑞𝑒 = 𝑙𝑜𝑔 𝐾𝑓 + 1𝑛 𝑙𝑜𝑔 𝐶𝑒 (4)

Where, qe is the equilibrium adsorption capacity of the adsorbent (mg/g), Kf is the Freundlich

constant and used to measure the adsorption capacity, 1/n is the adsorption intensity and Ce is

the adsorption capacity at equilibrium concentration (mg/l).

2.5. Characterizations of amidoxime-modified poly (AN)-starch nanoparticles graft

copolymer functional group:

2.5.1. Qualitative vanadium ion test:

About 0.1 g of wet resin was shaken with vanadium (V) ion in dilute hydrochloric acid solution

and a purple colored complex on the resin beads was detected.

2.5.2. Instrumental analysis:

2.5.2.1. Fourier Transform Infrared Spectroscopy (FTIR):

Fourier transform infrared (FTIR) spectroscopy was carried out using a Nicolet 380

spectrophotometer (Thermo Scientific) and the IR spectra were scanned 32 times over the range

of wave number 4000–400 cm−1. The sample (0.002 g) was mixed with KBr to reach (0.2 g) to

form a round disk appropriate for measurements.

2.5.2.2. Scanning Electron Microscopy (SEM):

SEM images for surface morphology of the samples were taken using (Joel GM4200, Quanta

200, Holland). The surfaces of all the samples were coated with a gold thin layer under vacuum

before SEM studies at an accelerating voltage of 20 kV.

2.6. Statistical analysis and metrological precision:

All of the tests were conducted in triplicate. The data were analyzed and expressed as mean

values ± standard deviations as well as error bars. This was done to insure about the high

precision of metrological measurements all over the work when using our calibrated instruments

in our institute either by primary standard apparatus or certified reference materials used

especially for this purpose.

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3. Results and discussion:

3.1. Formation of poly (AN)-starch nanoparticles graft copolymer:

Our previously tailored and fully characterized poly (AN)-starch nanoparticles graft copolymer

(60.1 % graft yield) was obtained via grafting of acrylonitrile onto starch nanoparticles using

free-radical initiating process.

3.2. Formation of poly (amidoxime) resin via Oximation reaction:

The conversion of abundant nitrile groups in our newly tailored poly (AN)-starch nanoparticles

graft copolymer designated as PANSNGC-CN to amidoxime was carried out by the treatment of

the copolymer with hydroxylamine (NH2OH) in an alkaline medium. The existence of

amidoxime functional groups in the resin was confirmed firstly by vanadium ion as a simple

rapid qualitative analysis test through the formation of characteristic purple color complex and,

secondly by FTIR and SEM as other instrumental tools. Details of the conditions used are given

in the text. The proposed reaction mechanism is shown in scheme 1 below:

NaOH NH2 Vanadium ion

PANSNPGC-C≡N + NH2OH PANSNPGC-C purple color complex

NOH

Scheme 1: Formation of amidoxime-modified poly (AN) - starch nanoparticles graft copolymer.

Where, PANSNPGC-CN represents poly (AN)-starch nanoparticles graft copolymer, NH2OH,

represents hydroxylamine, while, the product represents amidoxime modified poly (AN)-starch

nanoparticles graft copolymer i.e. poly (amidoxime) chelating resin.

3.3. Suggested adsorption mechanism:

Adsorption of copper ions (Cu2+) on the active functional groups of poly (amidoxime)

chelating resin occurred between the amidoxime groups and copper cations, at which a certain

possible chelation mechanism for the complexation takes place as shown below in scheme 2.

HN NH

PANSNPGC−C Cu2+ C-CGPNSNAP

N O O N

Scheme 2: Proposed mechanism of complex formation of amidoxime-modified poly (AN)-starch

nanoparticles graft copolymer and Cu2+ions.

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3.4. Adsorbent characterization:

3.4.1. Qualitative test of amidoxime functional groups:

It is well known that, several approaches have been applied for confirmation of the formation of

amidoxime groups in the resin. Several metal ions bind with amidoxime to yield a visual color in

the resin bead. Consequently, the manifestation of amidoxime groups in the resin was confirmed

by rapid vanadium ion test through the formation of a purple color complex [25].

3.4.2. FT-IR spectra:

Figure 1 parades the FTIR spectra of (a) poly (AN)-starch nanoparticles graft copolymer, (b)

amidoxime modified poly (AN)-starch nanoparticles graft copolymer and (c) amidoxime

modified poly (AN) - starch nanoparticles graft copolymer loaded copper ions. Details of the

conditions used are given in the text. With respect to the FT-IR spectra of poly (AN)-starch

nanoparticles graft copolymer Fig. 1(a); the main characteristic new absorption stretching band

of poly acrylonitrile at 2248 cm-1 are shown due to the presence of nitrile groups. This revealed

that the graft copolymerization of acrylonitrile onto starch nanoparticles had successfully taken

place. While, in case of amidoxime modified poly (AN)-starch nanoparticles graft copolymer

Fig. 1(b), the formed nitrile band at 2248 cm-1 disappeared and a new stretching vibrations band

of amidoxime (C=N) appeared at around 1650 cm-1 confirming the formation of the amidoxime

group in the poly(amidoxime) resin [24]. Besides, the formation of the N–O band at 912 cm-1 of

the oxime group [22]. Furthermore, the broad and intense band observed at 3428 cm–1 is due to

absorptions arising from both the N–H and O–H groups in the amidoxime resin [19]. Furthermore,

a weakening of the nitrile group peak at 2248 cm-1 in fig. 1(b) clearly designate the conversion of

nitrile groups into the oxime groups through treatment with hydroxylamine.

On the other hand, the FTIR spectra of amidoxime modified poly (AN)-starch

nanoparticles graft copolymer loaded copper ions fig. 1 ( c) shows a peak for elemental copper at

790 cm-1 which confirming the adsorption of Cu +2 ions onto the surface of adsorbent. Moreover,

a small shift in the absorbance peaks compared with the other two substrates was observed. The

broadband observed at 3442 cm−1 shifts to 3428 cm−1 and 3425 cm-1, while the peaks at 1673

shift to 1650 and 1648 cm−1, respectively. Such shifts may be contributed to the coordination of

Cu (II) ions as shown by other researchers [23].

Please insert figure 1 here.

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3.4.2. SEM topographic analysis:

Figure 2 pageants the SEM topographic analysis of (a) poly (AN)-starch nanoparticles graft

copolymer, (b) amidoxime modified poly (AN)-starch nanoparticles graft copolymer and (c)

amidoxime modified poly (AN) - starch nanoparticles graft copolymer loaded copper ions. By

comparing the SEM morphology surface of poly (AN)-starch nanoparticles graft copolymer (Fig.

2a) with that of amidoxime modified poly (AN)-starch nanoparticles graft copolymer as a

reactant resin (Fig. 2b); the latter revealed the presence of disordered and agglomerated materials

in addition to cavities on the surface of adsorbent, that causes the entrapment and the adsorption

of copper ions. While, after adsorption(Fig. 2c), the SEM micrograph of amidoxime modified

poly (AN)-starch nanoparticles graft copolymer loaded copper ions showed nearly the same

topographic surface of amidoxime poly (AN)-starch nanoparticles graft copolymer but with more

compact surface. The latter observed compact surface provided primary evidence of adsorption

by the above aforementioned resin which is also confirmed by other researchers [12, 26], who have

observed the presence of cavities or pores on the surface of the compact adsorbent, that causes

the entrapment and the adsorption of metal ions on such compact adsorbent.

Please insert figure 1 here.

4. Factors affecting Cu2+ adsorption onto amidoxime modified poly(AN)-starch

nanoparticles graft copolymer:

4.1. Effect of pH on adsorption:

Figure 3 signifies the influence of changing pH on the residual copper ions content

removal and adsorption capacity of amidoxime modified poly (AN)-starch nanoparticles graft

copolymer (resin). Details of the conditions used are given in the text. The studied test of pH

were limited to the pH 7 due to, it is well known that Cu (OH) 2 will be precipitated in alkaline

medium. It is seen Figure 3 that, the residual copper ion concentration in the filtrate decreased

and adsorption capacity increased by increasing pH value from 1 to 7. For more elaboration, at

pH 7 the residual metal ion content decreases from 406 ppm as a starting concentration of copper

in absence of amidoxime modified poly (AN)-starch nanoparticles graft copolymer to 130 ppm.

While, the other residual copper ion contents in the filtrate decreases from 406 ppm to 386, 370,

224, 180, 146, and 136 ppm when 1, 2, 3, 4, 5, 6 pH values were used respectively. The

decrement in the residual metal ion concentration follows the order: pH 7 > pH 6 > pH 5 > pH 4

> pH 3 > pH 2 > pH 1. Furthermore, the adsorption capacity (mg/g) of Cu +2 ions on the

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adsorbent resin increases from 8.0 (mg/g) to 110.4 (mg/g) by increasing the pH values from 1-7.

This can be elucidated by the fact that at lower pH value most of the amino groups in the

amidoxime modified poly (AN)-starch nanoparticles graft copolymer (resin) are protonated.

Then cationic repulsion can occur between copper ion species Cu+2 and protonated ploy

amidoxime resin which lead to lower adsorption value. The opposite holds true at higher pH

values. On the other word, most of the amino groups in the ploy amidoxime resin are less

protonated which lead to strong complexation between the ploy amidoxime resin and metal ion

in question i.e. higher adsorption capacity. This is in full agreement by the results published by

other researchers [9.27].

Pease insert figure 3 here.

4.2. Effect of contact time:

Figure 4 spectacles the effect of contact time on the copper ions removal and adsorption capacity

using the amidoxime modified poly (AN) - starch nanoparticles graft copolymer at pH 7. Details

of the conditions used are given in the text. It is seen from Fig. 4 that, the residual copper ions

content in the filtrated decreases from 406 ppm to 118 ppm and adsorption capacity increases

from 0.0 to 115.2 (mg/g) by increasing the contact time from 0 - 45 min., then leveled off

thereafter. Based on the above, and from the economic point of view, the copper ions removal

was completed within the first 45 min induction period, which indicates that the copper ions

rapidly form chelates or interaction with the oxime groups to form a ligand with copper ions as

shown in the scheme 2. This relative fast interaction will be valuable for practical application,

i.e. the amidoxime modified poly (AN)- starch nanoparticles graft copolymer could be used as a

filtering biopolymer resin for a short period of treatment of wastewater during filtration process

[9, 28].

Pease insert figure 4 here.

4.3. Effect of sorbent dosage:

Figure 5 spectacles the effect of varying adsorbent dosage (0.1 - 0.5 g) on the residual copper

ions content in the filtrate and adsorption capacity using the adsorbent resin. This was done by

using 400 ppm of Cu+2 ions concentration and pH 7. More details about the conditions used are

given in the text. It was seen from the figure 5 that, both the residual copper ions content in the

filtrate and adsorption capacity were decreased from 300 ppm to 113 ppm and from 106 mg/g to

73.25 mg/g respectively as the amount of amidoxime-modified poly (AN) - starch nanoparticles

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graft copolymer was increased from 0.1 g to 0.5 g, respectively. This was most probably, due to

higher concentration of sorbent leads to the accumulation of sorbent particles that decreased the

surface area and availability of the active sites to form ligand or complex with copper ion cations

[23].

Pease insert figure 5 here.

4.4. Effect of initial copper concentration:

The effect of copper ions concentration was studied by varying the initial concentration

of copper ions from 50- 400 ppm. Figure 6 shows the effect of varying initial concentration with

respect to the residual copper ion content in the filtrate and adsorption capacity on the

amidoxime-modified poly (AN) - starch nanoparticles graft copolymer. It reveals from figure 6

that, the residual copper ions content in the filtrate and adsorption capacity of amidoxime-

modified poly (AN) - starch nanoparticles graft copolymer increased by increasing the initial

concentration from 50 ppm to 400 ppm. This implies that the adsorption of copper ions is

dependent on the initial concentration of heavy metal ions. For more details, the adsorption

capacity increased as the number of possible binding sites increased and this is mainly due to the

presence of more available copper ions and electrostatic interactions between them and the

adsorbent active sites [23, 27].

Pease insert figure 6 here.

5- Adsorption kinetics:

It is well known that, the kinetic adsorption isotherm models have been extensively explored to

study the rate determining step of the adsorption process [29]. The kinetic experiments design of

Cu+2 ions adsorption was achieved at pH 7 and 400 mg/g Cu+2 ions as an optimum pH and

copper ions concentration respectively at room temperature. In current study, the adsorption

kinetic was compared using pseudo-first order and pseudo-second order kinetic models as the

commonly used models as described below:

Unless otherwise indicated, figure 7 (a, b) display the pseudo-first order and pseudo-second

order plot of ln (qe - qt) against (t) and (1/qt) against (t) respectively of Cu (+2) ions solution and

their calculated data. The rate constant k1 and k2 were calculated from the slope while the

theoretical value of qe (mg/g) was calculated from the intercept. As shown in Table II, the

correlation coefficient (R2) of the pseudo-second order kinetic (0.99631) is higher than that

obtained from the pseudo-first order kinetic (0.64291). Hence, the pseudo-second order kinetic

13

model is better to signify the experimental data than that of the pseudo-first order kinetic model.

Therefore, the pseudo-second order kinetic model is preferred to reflect the chemical process

during adsorption of Cu (+2) ions towards amidoxime-modified poly (AN)-starch nanoparticles

graft copolymer. Besides, other similar published results have been confirmed the bio sorption of

Cu(+2) ions into sugar beet pulp [30] and H3PO4- activated rubber wood sawdust [31], that obey the

second order kinetic equation also.

Please insert figure 7 (a, b) and table II here.

6. Adsorption isotherm:

Usually, the importance of adsorption isotherms is to deliver evidence on how the adsorbate

molecules dispersed between solution and the adsorbent molecule at a given equilibrium

conditions [32]. The effect of copper ion concentration on the adsorption capacity and the sorption

isotherm provided useful information about metal ions uptake by the adsorbent resin. Different

concentrations of copper ions were adsorbed by amidoxime-modified poly (AN)-starch

nanoparticles graft copolymer. The initial copper ion concentration was increased from 50 to 400

ppm, while the other parameters like resin dosage, pH, period and temperature were kept

constant. The results showed that the residual copper ion content in the filtrate increased (i.e.

adsorption capacity increased) with increasing copper ions concentration. The equilibrium data

of the adsorption from aqueous media was scrutinized by using the Langmuir and Freundlich

isothermal model.

For Langmuir isotherm model that uses the rules of a monolayer adsorption and a certain

number of identical active sites (active sites distributed consistently on the surface of the

adsorbent), assuming zero interaction between the adsorbents.

The linear form of the Langmuir isotherm equation is given by Eq. 3 as shown in the

experimental part section, 1𝑞𝑒 = 1𝐾𝐿𝑞𝑚𝑎𝑥 × 1𝐶𝑒 + 1𝑞𝑚𝑎𝑥

Where qe is the adsorption capacity (mg/g), Ce is the equilibrium concentration of the adsorbate

(mg/ L), qmax represents the maximum adsorption capacity of adsorbents (mg/ g), and KL is the

Langmuir adsorption constant (L/mg). The regression of 1/qe against 1/Ce was plotted according

to the Langmuir sorption isotherm model (linear regression), as in Fig. 8 (a).

Please insert figure 8 (a) here.

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The values of qmax and KL were calculated from the slope (1.23651) and the intercept

(0.0026545) of the linear plot of 1/qe and 1/Ce. The calculated data for the maximum sorption

capacity (qmax) and the sorption coefficient (KL) are presented in Table III.

Please insert table III here.

While, the in case of Freundlich isotherm, which is described by Eq. 4, log 𝑞𝑒 = log 𝐾𝑓 + 1𝑛 𝑙𝑜𝑔𝐶𝑒

Where, Kf is the Freundlich constant and used to measure the adsorption capacity and 1/n is the

adsorption intensity. Figure 10 shows a corresponding plot of the data. The values of Kf (mg/g)

and 1/n were calculated from the slope (1.05604) and intercept (0.1691) of the linear plot of log

qe versus log Ce (Fig. 8 (b). The calculated data for the Kf and 1/n were shown in (Table III).

Please insert figure Fig. 8 (b) here.

As shown above in tables III, the Freundlich isotherm graph provided lower correlation

coefficient (R2=0.99526) values as compared to that of Longmire isotherm (R2=0.99956). This

indicates that the sorption of Cu (+2) onto amidoxime-modified poly (AN)-starch nanoparticles

graft copolymer is tailored well with the Langmuir isotherm model which suggest a higher

manifestation of a multilayer adsorption process for the studied copper ions.

Conclusion:

Amidoxime modified poly (AN)-starch nanoparticles graft copolymer as adsorbent resin was

successfully prepared from poly (AN)-starch nanoparticles graft copolymer with a graft yield %

of 60.1 as a starting substrate via oximation reaction. The obtained resin was characterized by

quantitative rapid vanadium ion test and FT-IR spectral analysis as well as SEM topography

before and after adsorption of Cu (+2) ions to confirm the oximation reaction. The obtained results

showed that; the residual Cu (+2) ions contents in the filtrate increased (a) by increasing pH values

with the range studied; (b) by increasing the contact time up to 45 min. then leveled off

thereafter, (c) increased by increasing copper ions concentration within the range studied and (d)

by increasing resin dosage up to 1.0 g then leveled off after that. On the other hand, kinetic study

was found that pseudo-second-order rate equation was better than pseudo-first-order supporting

the formation of chemisorption process. While, in isothermal kinetic study, the examination of

R2 values showed that the Langmuir model afford the best fit to experimental data than

Freundlich one.

15

Figure captions

Figure 1: FT-IR spectra of (a) Poly (AN) - starch nanoparticles graft copolymer; (b) Amidoxime

modified Poly (AN)-starch nanoparticles graft copolymer and (c) Amidoxime modified Poly

(AN) –starch nanoparticles graft copolymer loaded Cu+2 ions.

Reaction conditions:

Details of the conditions used are given in the text.

Figure 2: SEM of (a) poly (AN)-starch nanoparticles graft copolymer, (b) amidoxime modified

poly (AN)- starch nanoparticles graft copolymer and (c) amidoxime modified poly (AN)- starch

nanoparticles graft copolymer loaded copper ions.

Reaction conditions:

Details of the conditions used are given in the text.

Figure 3: Effect of changing pH value on the residual copper ions concentration and adsorption

capacity using amidoxime modified poly (AN) - starch nanoparticles graft copolymer.

Reaction Conditions:

[Amidoxime modified poly (AN) - starch nanoparticles graft copolymer], (0.25 g); [Initial

copper ion concentration], 406 ppm; total volume, 100 ml; time, 30 min; temperature, 26◦C ±1.

Figure 4: Effect of changing contact time on the residual copper ions concentration and

adsorption capacity using amidoxime modified poly (AN)- starch nanoparticles graft copolymer.

Reaction Conditions:

[Amidoxime modified poly (AN) - starch nanoparticles graft copolymer], (0.25 g); [Initial

copper ion concentration], 406 ppm; pH, 7; total volume, 100 ml; temperature, 26◦C ±1.

Figure 5: Effect of changing resin dosage on the residual copper ions concentration and

adsorption capacity using amidoxime modified poly (AN) - starch nanoparticles graft copolymer

Reaction conditions:

[Initial copper ion concentration], 406 ppm; pH, 7; reaction time, 45 min., total volume, 100 ml;

temperature, 26◦C ±1.

16

Figure 6: Effect of changing copper ions concentrations on the residual copper ions

concentration and adsorption capacity using amidoxime modified poly (AN) - starch

nanoparticles graft copolymer

Reaction conditions:

[Amidoxime modified poly (AN) - starch nanoparticles graft copolymer], (0.25 g); pH, 7;

reaction time, 45 min., total volume, 100 ml; temperature, 26◦C ±1.

Figure 7 (a): Pseudo-first -order rate for the adsorption of Cu(+2) ions by by amidoxime-modified

poly (AN)-starch nanoparticles graft copolymer.

Reaction conditions:

Details of the conditions used are given in the text.

Figure 7 (b): Pseudo-second-order rate for the adsorption of Cu (+2) ions by amidoxime-modified

poly (AN)-starch nanoparticles graft copolymer resin.

Reaction conditions:

Details of the conditions used are given in the text.

Figure 8 (a): Langmuir isotherm for the adsorption of Cu (+2) by amidoxime-modified poly

(AN)- starch nanoparticles graft copolymer.

Reaction conditions:

Details of the conditions used are given in the text.

Figure 8 (b): Freundlich isotherm for the adsorption of Cu(II) by amidoxime-modified

poly(AN)- starch nanoparticles graft copolymer.

Reaction conditions:

Details of the conditions used are given in the text.

17

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Figures

Figure 1

FT-IR spectra of (a) Poly (AN) - starch nanoparticles graft copolymer; (b) Amidoxime modi�ed Poly (AN)-starch nanoparticles graft copolymer and (c) Amidoxime modi�ed Poly (AN) –starch nanoparticles graftcopolymer loaded Cu+2 ions. Reaction conditions: Details of the conditions used are given in the text.

Figure 2

SEM of (a) poly (AN)-starch nanoparticles graft copolymer, (b) amidoxime modi�ed poly (AN)- starchnanoparticles graft copolymer and (c) amidoxime modi�ed poly (AN)- starch nanoparticles graftcopolymer loaded copper ions. Reaction conditions: Details of the conditions used are given in the text.

Figure 3

Effect of changing pH value on the residual copper ions concentration and adsorption capacity usingamidoxime modi�ed poly (AN) - starch nanoparticles graft copolymer. Reaction Conditions: [Amidoximemodi�ed poly (AN) - starch nanoparticles graft copolymer], (0.25 g); [Initial copper ion concentration], 406ppm; total volume, 100 ml; time, 30 min; temperature, 26C ±1.

Figure 4

Effect of changing contact time on the residual copper ions concentration and adsorption capacity usingamidoxime modi�ed poly (AN)- starch nanoparticles graft copolymer. Reaction Conditions: [Amidoximemodi�ed poly (AN) - starch nanoparticles graft copolymer], (0.25 g); [Initial copper ion concentration], 406ppm; pH, 7; total volume, 100 ml; temperature, 26C ±1.

Figure 5

Effect of changing resin dosage on the residual copper ions concentration and adsorption capacity usingamidoxime modi�ed poly (AN) - starch nanoparticles graft copolymer Reaction conditions: [Initial copperion concentration], 406 ppm; pH, 7; reaction time, 45 min., total volume, 100 ml; temperature, 26C ±1.

Figure 6

Effect of changing copper ions concentrations on the residual copper ions concentration and adsorptioncapacity using amidoxime modi�ed poly (AN) - starch nanoparticles graft copolymer Reaction conditions:[Amidoxime modi�ed poly (AN) - starch nanoparticles graft copolymer], (0.25 g); pH, 7; reaction time, 45min., total volume, 100 ml; temperature, 26C ±1.

Figure 7

(a): Pseudo-�rst -order rate for the adsorption of Cu(+2) ions by by amidoxime-modi�ed poly (AN)-starchnanoparticles graft copolymer. Reaction conditions: Details of the conditions used are given in the text.(b): Pseudo-second-order rate for the adsorption of Cu (+2) ions by amidoxime-modi�ed poly (AN)-starchnanoparticles graft copolymer resin. Reaction conditions: Details of the conditions used are given in thetext.

Figure 8

(a): Langmuir isotherm for the adsorption of Cu (+2) by amidoxime-modi�ed poly (AN)- starchnanoparticles graft copolymer. Reaction conditions: Details of the conditions used are given in the text.(b): Freundlich isotherm for the adsorption of Cu(II) by amidoxime-modi�ed poly(AN)- starchnanoparticles graft copolymer. Reaction conditions: Details of the conditions used are given in the text.