Surface Modification of Powdered Maize Husk with Sodium Hydroxide for Enhanced Adsorption of Pb(II) Ions from Aqueous Solution

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

https://doi.org/10.47277/JETT/9(1)104

Surface Modification of Powdered Maize Husk with

Sodium Hydroxide for Enhanced Adsorption of

Pb(II) Ions from Aqueous Solution

Chidi E. Duru * Margaret C. Enedoh , Ijeoma A. Duru

¹Surface Chemistry and Environmental Technology (SCENT) Research Unit, Department of Chemistry, Imo State University, Owerri, PMB 2000, Imo

State, Nigeria.

Federal University of Technology Owerri, Department of Chemistry, PMB 1526, Imo State Nigeria

Received: 06/08/2020

Accepted: 13/10/2020

Published: 20/03/2021

Abstract

The impact of sodium hydroxide pretreatment of maize husk on its lead ion removal efficiency was investigated. Pretreatment of maize

husk with this alkali increased its surface area and porosity from 528.74 m /g and 0.477 cm /g to 721.54 m /g and 0.642 cm /g,

respectively. Batch adsorption studies were carried out to evaluate the effects of initial pH, adsorbent dose, initial lead ion concentration,

initial solution temperature, and contact time on the adsorption process. The maximum removal efficiency of maize husk at pH 5 and

adsorbent dose 2 g/L was 62.85 %, which increased to 82.84 % after pretreatment and was attained in 15 min. The adsorption data for the

natural and pretreated maize husk were best fitted in the Freundlich isotherm model, with their adsorption intensity (n) having values >1,

which indicated that lead ion adsorption onto the adsorbent types was a favorable physical process. The adsorption of lead ions onto the

adsorbents followed the pseudo-first-order kinetic model. The experimental adsorption capacities of maize husk (31.43 mg/g) and its

modified form (41.22 mg/g) were very close to those obtained from this model (31.03 mg/g and 40.65 mg/g respectively). The ΔH and ΔG

values of the adsorption process showed that the adsorption of lead ions by both adsorbents was an endothermic process and occurred

spontaneously. Alkali pretreated maize husk can therefore be used as a cheap adsorbent to remove lead ions from aqueous solution.

Keywords: Lead, maize husk, adsorbent, pretreatment, isotherm

lowered intelligence quotient, anemia, increased blood pressure,

damage to the brain and kidneys, miscarriage, reduction in male

fertility, blood disorders, and death [3].

Introduction

The various industrial activities going on in different parts of

the world are the primary sources of soil and water pollution by

heavy metals. Toxic metals like mercury, chromium, cadmium,

arsenic, nickel, and lead have been reported to be in high

concentrations in industrial wastewater due to different

manufacturing activities [1]. The presence of lead in both

surface and borehole water above regulated concentrations has

been observed even though its widespread use was discontinued

in many countries of the world [2]. It is still used in many

industrial production processes like smelting, refining, car

repair, battery manufacturing, and many others. It is highly

poisonous and can affect almost every organ in the body,

especially the nervous system. Its toxicity in children has a more

significant impact than in adults because they have softer

tissues, internal and external organs. It has resulted in severe

health conditions like behavioral problems, learning deficits,

Conventional treatment techniques like chemical

precipitation, ion exchange, membrane process, crystallization,

and electrochemical treatment have been used to remove toxic

metals from polluted water [4]. These processes are expensive

and inefficient when the heavy metal ions are contained in the

water at concentrations below 100 mg/L [5]. Researchers are

currently exploring the potentials of agro-waste materials in the

adsorption of metal ions from polluted water [6, 7, 8, 9]. The

findings from these studies have been very promising. The

merits of using plant wastes in wastewater treatment include

availability, low cost, selective adsorption of heavy metal ions,

good adsorption capacity, and regeneration potential.

Most adsorption studies have focused on the use of untreated

plant wastes in heavy metal removal from water. Recently, the

pretreatment of plant waste to extract soluble organic

compounds introduced into the treated water and enhance their

chelating efficiencies has been applied by many researchers

Coresponding author: Chidi E. Duru, Surface Chemistry and

Environmental Technology (SCENT) Research Unit,

Department of Chemistry, Imo State University, Owerri, PMB

[

10,11]. Pretreatment methods involving the use of different

modifying agents like mineral and organic acid solutions

hydrochloric acid, nitric acid, sulphuric acid, tartaric acid, citric

acid, etc.), base solutions (sodium hydroxide, calcium

(

000, Imo State, Nigeria. E-mail: chidiedbertduru@gmail.com,

Tel: +2348037131739

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

hydroxide, sodium carbonate), oxidizing agent (hydrogen

peroxide), organic compounds (ethylenediamine, formaldehyde,

methanol), to eliminate coloration of the aqueous solution,

remove soluble organic compounds and increase metal

adsorption efficiency have been applied in many studies

2.2 Preparation of Metal Solutions

All the chemicals used were of analytical reagent grade and

were prepared with distilled water in all the experiments. The

metal stock solution was prepared by dissolving appropriate

3 2

amounts of lead (II) nitrate, Pb(NO ) (M.W: 331.21 g/mol;

[

12,13,14]. Chemical modification can sometimes improve the

Assay: 99.0 %, Loba Chemie, India) in distilled water. Working

standards were prepared by progressive dilution of the stock lead

solution with distilled water.

adsorption efficiency of biomass by increasing the number of

binding sites, providing better ion-exchange properties, and

forms new functional groups that favor metal uptake.

Southeastern Nigeria and many other parts of the world

produce millions of tons of maize kernel annually. The

enormous amounts of maize husk waste generated after the

harvest have posed serious disposal challenges in the towns and

cities. Recently, it has been shown that this plant waste is rich in

minerals like calcium, sulphur, potassium, and many

phytochemicals with medicinal value [15]. Studies on applying

this biomass as an adsorbent for zinc, iron, and copper uptake

have given very promising results [16, 17, 18, 19]. There has

been no attempt to use maize husk in the past or recent times,

whether in natural or pretreated forms, to adsorb lead from

aqueous solutions. In this study, the effect of initial solution pH,

biomass load, initial metal concentration, and contact time on

the adsorption of lead onto a natural and sodium hydroxide

pretreated maize husk were determined. Isotherm and kinetic

models were used to give a better insight into the mechanisms of

the adsorption process.

2.3 Experimental Procedure

2.3.1 Analysis of physical and chemical properties of

adsorbents

The adsorbents’ surface areas and pore sizes were

determined at 77 K from nitrogen adsorption isotherms using a

High-Speed Surface Area and Pore Size Analyzer, Model: Nova

4200e (Quantachrome Instruments, USA). Before analysis, the

adsorbents were dried and degassed at 110 C until a residual

vacuum of less than 0.02 mbar. The multi-point BET plot

method was used to determine the specific surface areas, and the

t-plot method was used to assess the microporosity of the

adsorbent samples. The determination of the mineral element

composition of H and HP was carried out using EDX3600B X-

ray fluorescence spectrophotometer. The samples were

pulverized to a fine homogenous size, and the resulting powder

pelletized. The fluorescence spectrophotometer was calibrated

using pure silver standard and the working curve for the sample

selected before the samples’ energy dispersive X-ray spectra

were obtained. Chemical analysis of the adsorbents was

performed using Chesson-Datta gravimetric method [20, 21]. 1 g

of the powdered adsorbent (v) was added into 150 mL of

deionized water in a beaker, and the mixture was heated in a

Materials and Methods

.1 Adsorbent collection, preparation, and modification

Maize seeds (genus Oba super II) from the National

Agriculture Food Council, Umudike, Abia State Nigeria, were

collected and planted by the researchers. At maturity, the husks

were collected, thoroughly washed with tap water, and then

rewashed with deionized water. They were sun-dried for two

water bath at 100 C for 1 h. After this period, the mixture was

allowed to cool, and the residue was obtained by filtration and

rinsed with 300 mL warm deionized water. This residue was

oven-dried to constant weight (w). It was then mixed with 150

days and then oven-dried at 100 C for 4 h. The dried husks

mL of 1 M H

and heated in a water bath at 100 C for 1 h.

were ground into powder using an electric grinder and sieved to

a particle size of 30 mesh using American Society for Testing

and Materials (ASTM) standard sieves. Maize husk powder (H)

was then pretreated using NaOH solution. This process was

carried out by soaking 10 g of H in 500 mL of 1 M solution of

the alkali. The mixture was stirred for several minutes and

allowed to stand for 24 hours. It was filtered, washed severally

with deionized water until the filtrate was neutral to litmus, and

then allowed to dry at room temperature for a few days. The

dried crumbs of the modified maize husk (HP) were ground to a

fine powder (Figure 1) and stored in a desiccator [19].

The mixture was filtered, and the residue was rinsed with 300

mL of deionized water and dried (x). It was immersed in 10 mL

of 72 % H SO at ambient temperature for 4 h, and then 150 mL

I M H SO was added into the mixture and refluxed in a water

bath for 1 h. The solid obtained after refluxing was rinsed with

400 mL of deionized water and heated in an oven at 105 C and

weighed until a constant weight was achieved (y). The solid was

finally heated in a kiln at 600 C till the attainment of ash. The

ash obtained was cooled and weighed (z). The cellulose,

hemicelluloses, and lignin content of H and HP were estimated

as follows:

푥−푦

Cellulose =

× 100

(1)

(2)

(3)

푣

푤−푥

× 100

푣

Hemicellulose =

푦−푧

× 100

푣

Lignin =

.3.1 Adsorption studies

The batch process was used in all the adsorption

Figure 1: Conversion of maize husk into the pretreated form

experiments in a thermostatic water bath shaker set at 30 C. 0.2

g of adsorbent was placed in 250 mL Erlenmeyer flasks with

100 mL solution of metal ions of the desired concentration.

After agitation on the shaker water bath at 120 rpm over a

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

predetermined operation time, the liquid phase was taken out

and filtered using 0.45 µm membrane filters (Millipore

Corporation, USA). The final concentration of metal ions in the

filtrates was analyzed by a fast sequential flame atomic

absorption spectrometer (AAS), model 240FS AA (Agilent

Technologies, USA). All the instrumental conditions were

optimized for maximum sensitivity, and measurements were

performed in triplicates. The number of metal ions adsorbed at

equilibrium per unit mass of adsorbent was calculated from Eq.

given concentration and agitated for 30 min, at 30 C. An aliquot

was collected from the flask after this time, filtered, and the

concentration of lead ions in the filtrate determined.

2.3.6 Thermodynamic studies

The effect of temperature on the uptake of lead ions was

conducted by contacting 0.2 g of each adsorbent with 100 mL of

lead ion solution at pH 5, and an initial concentration of 100

mg/L. the mixtures were agitated for 30 min in a water bath at

. The percentage removal of lead ions from aqueous solution

different temperatures (30, 35, 40, 45, and 50 C). The data

(

% r) at a given time t, was calculated from Eq. 5.

were used to compute and compare the adsorption process’s

thermodynamics by the two adsorbent systems.

(

퐶 −퐶 ).푉

표 ꢀ

푞_푒=

(4)

(5)

푚

.3.7 Mechanistic and surface morphology studies

The functional groups on the adsorbent surfaces were

(퐶_표−퐶_푡)

푟 =

퐶표

detected using Agilent Cary 630 Fourier transform infrared

FTIR) spectrophotometer. The adsorbent sample was mixed

(

with a spatula full of KBr in an agate mortar and ground to a

fine powder using a pestle. The powder was pressed to form thin

transparent pellets before the infrared spectrum of the adsorbent

was taken. Equal loads of H and HP (0.2 g) were stirred in 50

mL of equimolar solutions of lead ions (50 mg/L) for 30 min.

They were filtered, washed with deionized water, and dried in a

desiccator. The surface morphology of the adsorbents was

examined with a scanning electron microscopy (SEM) model

Phenom ProX by phenomWorld Eindhoven, The Netherlands.

The samples were placed on a double adhesive in a sample stub

and then coated with a sputter coater by Quorum Technologies

Model Q150R, with 5 nm of gold. After that, they were taken to

the chamber of the SEM machine, where they were viewed via

Navcam. The brightness contrasting was automatically adjusted,

and afterward, the morphologies of different magnification were

store in a USB 2.0 flash drive (USB stick).

where q

adsorbent (mg/g), C

(

time t, V is the volume of the solution (L) and m is the mass of

adsorbent (g).

is the quantity of metal adsorbed at equilibrium by the

is the initial concentration of metal

mg/L), C is the equilibrium concentration of the adsorptive

mg/L) in solution, C is the concentration of the metal at

.3.2 Effect of pH

To determine the effect of pH on the adsorption of lead by

the adsorbent, 100 mL of test solutions containing 100 mg/L of

lead ions at different pH levels (2, 3, 4, and 5) were prepared by

adjusting the pH to the desired value using 1 M HCl or 1 M

NaOH before adding the adsorbent. The pH measurements were

done using a Checker plus pH tester by HANNA. 0.2 g of

adsorbent was mixed with the test solution at a given pH, and

the mixture agitated for 30 min, at 30 C. The lead ion

concentration in the solution after this period was then

determined.

3 Results and Discussion

The multi-point BET plots for H and HP are shown in

Figure 2. The data from these plots showed that H possessed a

.3.3 Effect of adsorbent dose

The effect of the dose of adsorbent on the adsorption of lead

very large surface area (528.74 m /g), which increased to 721.54

ions was studied using different biomass concentrations (0.1,

m /g after modification. This is about 36 % increase in the

.2, 0.4, 0.8, 1.2, and 1.4 g) in 100 mL of 100 mg/L of metal

surface area of this biomass after it was modified with alkali.

The t-plots for H and HP are shown in Figure 3. The data from

ions at initial pH of 5 [22]. After mixing a given weight of

adsorbent with the metal solution, the mixture was agitated for

these plots showed that both H and HP were highly

microporous.

0 min, at 30 C and the concentration of lead ions in the

solution determined.

Table 1: Physical and chemical characteristics of H and HP

Adsorbent

BET surface area (m /g)

Pore volume (cm /g)

Micropore volume (cm /g)

.3.4 Adsorption kinetics

Adsorption kinetic experiments were conducted to assess the

528.74 721.54

0.325

0.477

2.80

0.62

3.80

3.11

6.17

0.94

0.21

74.22

20.17

5.61

0.368

0.642

3.00

0.55

2.25

0.26

6.11

0.93

0.20

96.83

3.41

0.24

rate of Pb(II) ion uptake onto H and HP. The effect of contact

time on the adsorption of lead ions by the adsorbent was

determined at 3 min intervals for 30 min, with an initial lead ion

concentration of 100 mg/L and solution initial pH of 5 at 30 C.

in each flask and agitated. The flasks were withdrawn at the

specified time intervals and the lead ion’s concentration at a

given time determined.

Pore diameter (Å)

.2 g of adsorbent was mixed with 100 mL of the metal solution

Mineral element analysis (wt %) K

Cellulose

Lignocellulose composition (%) Hemicellulose

Lignin

.3.5 Equilibrium and isotherm studies

The impact of the initial concentration of lead ions (100, 50,

5, and 12.5 mg/L) at initial solution pH of 5, on the adsorption

of this metal by the adsorbents, were studied. 0.2 g of a given

adsorbent was mixed with 100 mL solution of the metal ion at a

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

.1 Effect of pH

The pH of an aqueous solution is an essential factor in the

adsorption of metal ions. The effect of pH on the adsorption of

Pb ions onto H and HP was studied at pH 2–5 because

precipitation of Pb ions from the solution started at pH 5.5 [24,

25]. The adsorbents’ Pb ion removal efficiency directly

correlated with initial solution pH (Figure 5). The removal

efficiency of H at pH 2 was 13.4 %, which increased to 27.1 %

after modification. This increase continued from 25.1 % to 37.7

at pH 3, 33.9 % to 61.7 % at pH 4, and 52.9 % to 73.9 % at

pH 5. At lower pH values, H and HP’s surface potential were

largely positively charged due to their protonation by the high

+ +

concentration of H and H O ions in the solution [26].

(

Figure 2: Multi-point BET plots for (a) H (b) HP at 77 K

The micropore volume of H (0.447 cm /g) increased to

.642 cm /g, which is about a 44 % increase in porosity due to

modification. The X-ray fluorescence scans of H and HP are

shown in Figure 4. The main mineral elements in the biomass

were calcium, sulphur, potassium, iron, phosphorus, and zinc.

Pretreatment had minimal effect on the mineral composition of

the biomass (Table 1). The gravimetric analysis of maize husk

(

showed that it contained 74.22

% cellulose, 20.17 %

hemicelluloses, and 5.61 % lignin. After alkali pretreatment, the

cellulose yield increased to 96.83 %, with a drop in the

hemicelluloses and lignin content to 3.41 % and 0.24 %,

respectively. A large amount of hemicellulose and lignin in the

maize husk lignocellulose dissolved in the alkali pretreatment

solution and washed off with deionized water during the rinsing

of the biomass. These observations are in agreement with

findings from previous studies [23].

Figure 3: t-plots for (a) H (b) HP at 77 K

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

.3 Adsorption kinetics

Adsorption kinetic experiments were conducted to determine

(

the adsorption rate of Pb ions onto H and HP, and the results are

shown in Figure 7.

Energy (eV)

(

Energy (eV)

Figure 4: X-ray fluorescence scan of (a) H (b) HP

0.1

0.2

0.4

0.8

1.2

1.4

Dose (g)

Figure 6: Effect of adsorbent dose on Pb ion adsorption by H and HP

initial pH = 5; C = 100 mg/L; T = 30 C)

(

Figure 5: Effect of pH on Pb ion adsorption by H and HP (C

= 100

mg/L; m = 2 g/L; T = 30 C)

These charges reduce the attraction of Pb ions in the solution

by the surfaces of H and HP. In contrast, an increase in pH

created more negatively charged surfaces on H and HP, which

facilitated Pb ions’ uptake from the solution. These results are in

agreement with findings from previous studies [27].

t (min)

Figure 7: Rate of adsorption of Pb ions by H and HP (initial pH = 5; C

= 100 mg/L; m = 2 g/L; T = 30 C)

.2 Effect of adsorbent dose

e t t

The plots of In (q – q ) vs t and t/q vs t for pseudo-first-

The effect of different amounts of H and HP on the removal

order and pseudo-second-order kinetic models are shown in

Figure 8. The mathematical and kinetic parameters from the

models are summarized in Table 4. These results showed that

the data were well fitted in the two kinetic models with the

pseudo-first-order model, giving a better fitting as observed in

of Pb ions from aqueous solution is shown in Figure 6. The

results demonstrated higher removal efficiencies for Pb ions

with an increase in the two adsorbents’ doses. HP showed a

marked increase in its removal efficiency as its load increased in

the solution due to the enhanced surface area of this adsorbent

the linear regression correlation coefficient values (R ) for H and

[

28,29]. The removal efficiencies of H and HP were almost the

HP. Also, the experimental adsorption capacity (q ) of the two

same at 0.2 g and 0.1 g, 0.4 and 0.2 g, and 0.8 g and 0.4 g doses

respectively, indication a 50 % enhancement in efficiency for

HP over H. These results showed that pretreatment of H with

NaOH could have increased the microporous structure of the

biomass thereby creating more adsorption sites for Pb ion

uptake. The solubilization of lignin in the alkali pretreatment

solution can bring about this adsorption site exposure on the

biomass [13].

biomass materials were very similar to those obtained from the

models (qe(cal)). In other words, the adsorption of lead ions onto

H and HP is a pseudo-first-order kinetic process. Also, the

pseudo-first-order rate constant for HP was 1.6 times the value

obtained for H, suggesting a faster uptake of lead ions by HP.

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

Table 2: Literature reports on biomass based adsorbents for Pb ion

uptake from aqueous solution

Table 5: Adsorption isotherm models used in this study

Initial

Isotherm Linearized forms of

Parameters

solution

References

concentration (mg/g)

mg/L)

model

equations

Biomass

Modifier

C (mg/L): equilibrium concentration

(

of Pb ions

Sawdust

Formaldehyde

in Sulfuric

q_m(mg/g): maximum adsorption

capacity of the adsorbent

K (L/mg): Langmuir constant

q_e(mg/g): adsorption capacity at

equilibrium

(

Pinus

5.1

1 – 10

9.78 [30]

C_ꢅ

K q

^qꢇ

ꢇ

sylvestris) acid

Langmuir

Isotherm

^qꢅ

ꢆ

Formaldehyde

in sulfuric

acid

Walnut

sawdust

Not

stated

10 – 200

20 – 100

5 – 20

4.48 [31]

133.60 [32]

C (mg/L): initial concentration of Pb

Cucumber

peel

ions

ꢉ

ꢃ−

_g−ꢃ): relative

(mg

ꢊ

ꢃ

Imperata

cylindrica

leaf powder

Bean husk

Cashew nut

shell

Maize husk

Maize husk Oxalic acid

Maize husk

^F^r^e^uⁿ^d^lⁱ^c^h^lⁿ^qꢅ = In K + In C

Sodium

hydroxide

ꢅ adsorption capacity of the adsorbent

n: adsorption intensity

ꢈ

13.50 [33]

12.66 [34]

Isotherm

(L/mg): Elovich equilibrium

Not

stated

10 – 100

10 – 50

ꢋꢌ

ꢋꢌ constant

Elovich

Isotherm

ln ⁼^Iⁿ^K^qꢇ

ꢁ

ꢍꢌ

ꢋꢎ

^qm^:^E^l^o^vⁱ^c^h^m^a^xⁱ^m^u^m^a^d^s^o^r^p^tⁱ^oⁿ

Sulfuric acid

8.3

[35]

capacity

(mg/g): sorption capacity

50 – 300

12.5 – 100

7.38 [36]

9.33 [36]

31.43 This study

ln q = ln q ꢁ βε β: activity coefficient related to mean

ꢅ

ꢏ

sorption energy

D–R

Isotherm

Sodium

hydroxide

Maize husk

12.5 – 100

41.22 This study

휀 (J/mol): Polanyi potential

휀 = RT ln(1 +

)

-1 -1

ꢐ_푒

R (Jmol K ): 8.314

T (K): 303

Table 3: Adsorption kinetic models used in this study

Linearized forms of

equations

Kinetic model

Parameters

t (min): the contact time

2.8

2.6

2.4

2.2

(min ): the pseudo-first

order rate constant.

q (mg/g): adsorption

capacity at time t.

(mg/g): adsorption

capacity at equilibrium.

(g/mg.min): the pseudo-

second order rate constant.

Pseudo-first-order

model

푙푛(푞 ꢁ 푞 )

푒

ꢂ

= 푙푛푞 ꢁ 푘 ꢄ

푒

ꢃ

ꢄ

+ ꢄ

Pseudo-second-

order model

1.6

푒

푞_ꢂ푘 푞

푞_푒

1.4

1.2

1.0

0.8

Table 4: Kinetic parameters obtained from the models

Pseudo-first order Pseudo-second order

Biomass

e(cal)

0.6

31.43 0.9966 0.14

41.22 0.8553 0.23

31.03 0.9894 3.11 E-3 40.08

40.65 0.8539 6.30 E-3 47.62

t (min)

.4 Equilibrium and isotherm studies

The adsorption equilibrium data obtained in this study were

0.50

evaluated using the Langmuir, Freundlich, Elovich, and

.45

.40

Dubinin-Radushkevich (D–R) isotherm models [37] (Table 5).

A comparison of the R values from these models indicated that

the equilibrium data for H and HP best fitted the Freundlich

isotherm model (Figures 9 and 10). The Freundlich isotherm

parameters for H and HP are shown in Table 6. The value of n in

this model indicates the degree of non-linearity between solution

concentration and adsorption as follows: if n = 1, the adsorption

is linear; if n > 1, the adsorption is a favorable physical process,

and if n < 1, the adsorption is by a chemical process [38].

Therefore, the uptake of lead ions by H and HP occurred on a

heterogeneous surface by multilayer adsorption, and the number

of ions adsorbed increased infinitely with an increase in

concentration [39].

0.35

.30

.25

0.20

.15

.10

t (min)

100

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

Figure 8: (a) Pseudo first-order (b) Pseudo second-order kinetic plots for

∆ꢒ^ꢓ

∆S^ꢓ

In K_ꢑ= ꢁ _ꢔ_ꢕ+ _ꢔ

H and HP (initial pH = 5; C

= 100 mg/L; m = 2 g/L; T = 30 C)

(6)

where R is the gas constant (8.3145 J/mol K), T is the absolute

3.5

3.0

2.5

2.0

1.5

temperature (K), and ΔH and ΔS were calculated from the slope

ꢃ

and intercept of the linear plots of In K

and (Figure 11). The

ꢕ

equilibrium constant (K ) was calculated from the equation:

ꢍAꢌ

^Kꢑ = _ꢍ_ꢌ

(7)

where C_ꢖ_ꢅand C are the equilibrium concentrations of lead ions

ꢅ

(

mg/L) on the adsorbent and in the solution, respectively.

3.0

1.0

1.5

2.0

2.5

3.0

3.5

4.0

In Ce

2.5

Figure 9: Freundlich isotherm plot for H (initial pH = 5; C

= 12.5-100

100 mg/L

50 mg/L

mg/L; m = 2 g/L; T = 30 C)

25 mg/L

4.0

3.5

3.0

2.5

2.0

1.5

0.00310

0.00315

0.00320

0.00325

0.00330

/T (K)

4.0

3.5

3.0

2.5

2.0

-1

00 mg/L

0 mg/L

In Ce

25 mg/L

Figure 10: Freundlich isotherm plot for HP (initial pH = 5; C = 12.5-

00 mg/L; m = 2 g/L; T = 30 C)

Table 6: Freundlich isotherm parameters for H and HP

1.5

Adsorbent

0.9866

0.9666

1.19

3.57

1.51

9.38

1.0

0.00310

0.00315

0.00320

0.00325

0.00330

/T (K)

The n values for H and HP were 1.19 and 3.57, respectively,

indicating that lead adsorption on these adsorbents was by a

favorable physical process, with the surface of HP favoring this

process more than that of H.

Figure 11: Van’t Hoff plot for (a) H (b) HP (initial pH = 5; C

mg/L; m = 2 g/L; T = 30-50 C)

The ΔG at 303 K was obtained from the relationship:

= 25-100

(8)

∆

G^ꢗ= ∆H^ꢗꢁ T∆ꢘ^ꢗ

.5 Thermodynamic studies

The thermodynamic parameters, including enthalpy change

ΔH), entropy change (ΔS), and free energy change (ΔG), were

considered to determine if the adsorptive process occurred

spontaneously. The values of ΔH and ΔS were obtained from the

Van’t Hoff equation:

The positive values of ΔH at the studied initial metal ion

(

concentrations (Table 7) indicated that the adsorption process

was endothermic. Lead ions were adsorbed more efficiently onto

H and HP at higher temperatures. Similar results have been

reported in other studies [40]. The adsorption of lead ions by H

101

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

was more favored by an increase in temperature than HP. The

free energy of adsorption (ΔG) of lead ions onto H and HP were

negative and indicated that the process was spontaneous, and

spontaneity increased with an increase in temperature. The

positive values of entropy change showed an increase in

randomness at the solid/solution interface on H and HP during

lead ion adsorption.

polymer shifted to 3488.43 cm^-¹in H and disappeared

completely in HP. This indicated that the complexation

mechanism was involved in the adsorption of lead ions by H and

HP. The modification exposed the –OH functional groups on HP

for better interaction with lead ions. The disappearance of the –

OH band on HP pointed to a greater metal ion adsorption

intensity by this adsorbent, which resulted in the shielding of the

hydroxyl functional group on it by the adsorbed lead.

Table 7: Thermodynamic parameters for the adsorption of lead ions onto

H and HP

.7 Surface morphology analysis

To predict the change in the adsorbents’ surface morphology

Adsorbent C

(mg/L)

ΔG

ΔH

(kJ/mol)

66.99

60.04

73.14

49.79

40.84

61.73

ΔS (kJ/mol K)

(

kJ/mol)

–0.58

–1.47

–2.00

–3.24

–4.00

–5.54

after modification, the SEM images (Figure 13) of H and HP

were taken at ×8000 magnification. The image obtained for H

showed a smooth and continuous crystalline surface, which can

be attributed to a high presence of lignin on the biomass. After

modification, numerous hollow cylindrical shaped pores

appeared on HP, which increased its heterogeneity substantially.

The highly porous nature of HP would result in an increased

surface area, which would create more potential sites for the

adsorption of lead ions when compared to H. This indicated that

the treatment of H with sodium hydroxide was highly effective

in the delignification of the biomass.

0.9735

0.9670

0.9620

0.9734

0.9755

0.9491

0.223

0.203

0.248

0.175

0.148

0.222

.6 Mechanistic studies

The superimposed infrared spectra of H and HP in their

natural forms and after lead ion adsorption are shown in Figure

12.

Figure 13: Surface morphology of (A) H (B) HP (C) H after Pb

adsorption (D) HP after Pb adsorption

The images of H and HP after the adsorption of lead ions

were observed at ×7000 magnification. The surface of H became

slightly rough due to the deposition of metal ions on it. The

heterogeneity of the surface of HP reduced due to the occupation

of the smaller pore spaces by the metal ions. The larger pores

remained significant because they had more room for the uptake

of metal ions. These observations were clear indications that

pretreatment of maize husk’s surface using sodium hydroxide

was very efficient in increasing its capacity for the uptake of

lead ions from aqueous solution.

Figure 12: FTIR spectra of (A) H and HP (B) H before and after

adsorption (C) HP before and after adsorption

The major bands observed on H were a strong band at

-1

396.56 cm corresponding to an aromatic –OH, a strong band

-1

at 1624.55 cm corresponding to a C=O stretch, a strong and

broadband at 3495.59 cm^-¹corresponding to an –OH from a

polymer and a weak band at 2883.62 cm^-¹corresponding to a C-

H stretch from alkanes [41]. The absorption peaks initially

observed on H became stronger and more prominent on HP,

with better separation of peaks at the multiplet bands. After

adsorption of lead ions, the absorption band of the –OH in the

102

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

S. Babel and T.A. Kurniawan, Low-cost adsorbents for heavy

metals uptake from contaminated water: a review, J. Hazard. Mater.,

Conclusion

The effect of pretreatment of maize husk on its lead ion

7 (2003) 219-243.

adsorption potentials was studied. The data from the multi-point

BET plots and t-plots for natural maize husk (H) and its

pretreated form (HP) showed that pretreatment significantly

J. Wang and C. Chen, Biosorption of heavy metals by

Saccharomyces cerevisiae: a review, Biotechnol Adv., 24(5) (2006)

427-51.

increased the surface area of the biomass from 528.74 m /g to

6. R. Foroutan, R. Mohammadi, S. Farjadfard, H. Esmaeili, M. Saberi,

S. Sahebi, S. Dobaradaran and B. Ramavandi, Characteristics and

performance of Cd, Ni and Pb bio-adsorption using Callinectes

sapidus biomass: real wastewater treatment, Environ. Sci. Pollut.

Res., 26(7) (2019) 6336-6347.

21.54 m /g, and its porosity from 0.447 cm /g to 0.642 cm /g.

The lead ion removal efficiency of H and HP increased with an

increase in pH (2 – 5) and adsorbent dose (1 g/L – 12 g/L). The

maximum lead ion removal efficiency of H and HP was 62.85 %

and 82.84 %, respectively, which was attained in 15 min at 30

N.K. Mondal, A. Samanta, P. Roy and B. Das, Optimization study

of adsorption parameters for removal of Cr(VI) using Magnolia leaf

biomass by response surface methodology, Sustain. Water Resour.

Manag., 5 (2019) 1627-1639.

C. The experimental equilibrium adsorption capacity of the

biomass was 31.43 mg/g, which increased to 41.22 mg/g after

modification. The pseudo-first-order kinetic model better

explained the rate of lead ion removal from aqueous solution by

both adsorbent types. The Freundlich isotherm model was

followed in the uptake of lead ions onto the modified and

unmodified adsorbent forms, indicating that adsorption of lead

occurred on a heterogeneous surface by multilayer adsorption.

The positive ΔH values and negative ΔG values for the

adsorption process at different initial lead ion concentrations (25

8. F. de Freitas, L.D. Battirola, R. Arruda and L.R.T. de Andrade,

Assessment of the Cu(II) and Pb(II) removal efficiency of aqueous

solutions by dry biomass Aguape: kinetic of adsorption, Environ.

Monit. Assess., 191(12) (2019) 751.

V.O. Njoku, A.A. Ayuk, E.N. Ejike, E.E. Oguzie, C.E. Duru and

O.S. Bello, Cocoa pod husk as a low cost biosorbent for the removal

of Pb(II) and Cu(II) from aqueous solutions, Aust. J. Basic Appl.

Sci., 5(8) (2011) 101-110.

10. Y. Ozudogru and M.J. Merdivan, Adsorption of U(VI) and Th(IV)

–

100 mg/L) and 2 g/L adsorbent dose showed that lead

ions from aqueous solutions by pretreatment with Cystoseira

adsorption onto the biomass types was an endothermic process

and occurred spontaneously. Complexation was the observed

mechanism followed during the uptake of lead ions onto maize

husk and its pretreated form.

barbata,

Radioanal.

Nucl.

Chem.,

(2019).

doi.org/10.1007/s10967-019-06943-6

1. W. Qu, D. He, Y. Guo, T. Yining and S. Ren-Jie,

Characterization of modified Alternanthera philoxeroides by

diethylenetriamine and its application in the adsorption of

copper(II) ions in aqueous solution, Environ. Sci. Pollut. Res.,

26(21) (2019) 21189-21200.

2. C.E. Duru, I.A. Duru, C.E. Ogbonna, M.C. Enedoh and P. Emele,

Adsorption of copper ions from aqueous solution onto natural and

pretreated maize husk: adsorption efficiency and kinetic studies, J.

Chem. Soc. Nigeria, 44 (5) (2019) 798-803.

3. G.T. Asere, V.C. Stevens and D.G. Laing, Use of (modified) natural

adsorbents for arsenic remediation: a review, Sci. Total Environ.,

676 (2019) 706-720.

14. W.S. Wan Ngah and M.A.K.M. Hanafiah, Removal of heavy metal

ions from wastewater by chemically modified plant wastes as

adsorbents: a review, Bioresour. Technol., 99 (2008) 3935-3948.

Funding

This research is funded by the Tertiary Education Trust

Fund of the Nigerian Government under grant number

TETFUND/DESS/UNI/OWERRI/2015/RP/VOL.I.

Ethical issue

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

(

avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements that

submitted work is original and has not been published elsewhere

in any language.

5. C.E. Duru, Mineral and phytochemical evaluation of Zea mays

husk, Scientific African, 7 (2020) e00224.

6. C.E. Duru and I.A. Duru, Studies of sorbent efficiencies of maize

parts in Fe(II) removal from aqueous solutions, Int. Lett. Chem.

Phys. Astron., 72 (2017) 1-8.

7. C.E. Duru and I.A. Duru, Adsorption capacity of maize biomass

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

parts in the remediation of Cu²⁺ion polluted water, WNOFNS, 12

(2017) 51-62.

8. C.E. Duru, I.A. Duru, F.C. Ibe and M.C. Enedoh, Profiling of Zn

ion sorption in modeled aqueous solutions by different parts of

maize biomass, IOSR JAC, 10(3–1) (2017) 70-75.

C.E. Duru, M.A. Nnabuchi and I.A. Duru, Adsorption of Cu onto maize

husk lignocelluloses in single and binary Cu-Zn solution systems:

equilibrium, isotherm, kinetic, thermodynamic and mechanistic

studies, Egypt. J. Chem., 62(7) (2019) 1695-1705.

Authors’ contribution

All authors of this study have a complete contribution for

data collection, data analyses and manuscript writing.

References

19. R. Datta, Acitogenic fermentation of lignocelluloses - acid yield and

conversion of components, Biotechnol. Bioeng., 23(9) (1981) 2167-

M.S. Abdel-Raouf and A.R.M. Abdul-Raheim, Removal of heavy

metals from industrial waste water by biomass-based materials: a

review, J. Pollu. Eff. Cont., 5(1) (2017) 180.

170.

0. P. Mahyati, A.R. Patong, M.N. Djide and D.P. Taba,

Biodegradation of lignin from corn cob by using a mixture of

Phanerochaete Chrysosporium, Lentinus Edodes and Pleurotus

Ostreatus, Int. J. Sci. Technol. Res., 2(11) (2013) 79-82.

C.E. Duru, M.C. Enedoh and I.A. Duru, Physicochemical

assessment of borehole water in a reclaimed section of Nekede

mechanic village, Imo State, Nigeria, Chemistry Africa, 2(4) (2019)

1. S. Rajoriya, A. Haquiqi, B. Chauhan, G. Tyagi, A.S. Pundir and

A.K. Jain, Influence of adsorption process parameters on the

removal of hexavalent chromium (Cr(VI)) from wastewater: a

review, J. Environ. Treat. Tech., 8(2) (2020) 597-603.

89-698.

A.L. Wani, A. Ara and A.J. Usmani, Lead toxicity: a

review, Interdiscip. Toxicol., 8(2) (2015) 55-64.

103

Journal of Environmental Treatment Techniques

2021 Volume 9, Issue 1, Pages: 95-104

2. H. Shuhaida and K.G. Soh, Effect of sodium hydroxide pretreatment

on rice straw composition, Ind. J. Sci. Technol., 9(21) (2016) 1-9.

3. G. Blazque, M. Carlero, F. Hernainz, G. Tenorio and M.A. Martin-

Lara, Equilibrium biosorption of lead(II) from aqueous solutions by

solid waste from olive-oil production, Chem. Eng. J., 160 (2010)

15-622.

4. A. Mlayah and S. Jellali, Study of continuous lead removal from

aqueous solutions by marble wastes: efficiencies and mechanisms,

Int. J. Environ. Sci. Technol., 12 (2015) 2965-1978.

5. K.M. Nguyen, B.Q. Nguyen, H.T. Nguyen and H.T.H. Nguyen,

Adsorption of arsenic and heavy metals from solutions by

unmodified iron-ore sludge, Appl. Sci., 9 (2019) 619-633.

6. B.S. Zadeh, H. Esmaeili, R. Foroutan, S.M. Mousavi and S.A.

Hashemi, Removal of Cd from aqueous solution using Eucalyptus

sawdust as a bio-adsorbent: kinetic and equilibrium studies, J.

Environ. Treat. Tech., 8(1) (2020) 112-118.

7. S. Rajoriya, A. Haquiqi, B. Chauhan, G. Tyagi, A.S. Pundir, A.K.

Jain and D. Agarwal, Adsorption Studies on the removal of

hexavalent chromium (Cr (VI)) from aqueous solution using black

gram husk, J. Environ. Treat. Tech., 2020 8(3) (2020) 1144-1150.

8. N. Arumugam, S. Chelliapan, S.T. Thirugnana and A.B. Jasni,

Optimisation of heavy metals uptake from leachate using red

seaweed Gracilaria changii, J. Environ. Treat. Tech., 8(3) (2020)

089-1092.

9. V.C. Taty-Costodes, H. Fauduet, C. Porte and A. Delacroix,

Removal of Cd(II) and Pb(II) ions from aqueous solutions by

adsorption onto sawdust of Pinus sylvestris, J. Hazard. Mater., 105

(2003) 121-142.

0. Y. Bulut and Z. Tez, Removal of heavy metal ions by modified

sawdust of walnut, Fresenius Environ. Bull., 12 (2003) 1499-1504.

1. M. Basu, A.K. Guha and L. Ray, Adsorption of lead on cucumber

peel, J. Clean. Prod., 151 (2017) 603-615.

2. M.A.K. Hanafiah, S.C. Ibrahim and M.Z.A. Yahya, Equilibrium

adsorption study of lead ions onto sodium hydroxide modified

Lalang (Imperata cylindrica) leaf powder, J. Appl. Sci. Res., 2

(2006) 1169-1174.

3. C.T. Onwordi, C.C. Uche, A.E. Ameh and L.F. Petrik, Comparative

study of the adsorption capacity of lead (II) ions onto bean husk and

fish scale from aqueous solution, J. Water Reuse Desal., 9(3) (2019)

49-262.

4. K. Nuithitikul, R. Phromrak and W. Saengngoen, Utilization of

chemically treated cashew-nut shell as potential adsorbent for

removal of Pb(II) ions from aqueous solution, Sci. Rep., 10(1)

(2020) 3343.

5. A.I. Adeogun, M.A. Idowu, A.E. Ofudje, S.O. Kareem and S.A.

Ahmed, Comparative biosorption of Mn(II) and Pb(II) ions on raw

and oxalic acid modified maize husk: kinetic, thermodynamic and

isothermal studies, Appl. Water Sci., 3 (2013) 167-179.

6. H.N. Tran, S. You and H.A. Hosseini-Bandegharaei Chao, Mistakes

and inconsistencies regarding adsorption of contaminants from

aqueous solutions: a critical review, Water Res., 120 (2017) 88-116.

7. A.N.A. El-henday, Surface and adsorptive properties of carbons

prepared from biomass, Appl. Surf. Sci., 252 (2005) 287-295.

8. H. Freundlich, About adsorption in solutions, Z. Phys. Chem.,

7U(1) (1907) 385-470.

9. F. Gorzin and M.M.B.R. Abadi, Adsorption of Cr(VI) from aqueous

solution by adsorbent prepared from paper mill sludge: Kinetics and

thermodynamics studies, Adsorp. Sci. Technol., 36(1-2) (2017) 149-

69.

0. B.D. Mistry, Handbook of spectroscopic data Chemistry, Oxford

Book Company, 2009.

104