cpb-bentonite untuk adsorpsi asam benzoat

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Preparation, Characterization and Adsorption Performanceof Cetyl Pyridine Bromide Modified Bentonites

Xiaodong Xin Jian Yang Rui Feng

Jie Zhao Guodong Chen Qin Wei

Bin Du

Received: 20 April 2011 / Accepted: 15 October 2011 / Published online: 1 November 2011 Springer Science+Business Media, LLC 2011

Abstract Benzoic acid removal is important for the water

treatment and adsorption is an effective treatment process.Cetyl pyridine bromide-modified bentonites (CPB-Bent)

and hydroxy-aluminum-pillared bentonites (Al(OH)-Bent)

were prepared and characterized by XRD, FTIR and BET.

Adsorption experiments were conducted on the adsorption

of benzoic acid onto natural bentonites, sodium bentonites

(Na-Bent), Al(OH)-Bent and CPB-Bent in batch experi-

ments. Benzoic acid removal onto CPB-Bent is pH

dependent and the optimum adsorption is observed at

pH *3.5. The adsorption rate was fast and equilibrium

was established within 90-min. The adsorption rate of

benzoic acid on CPB-Bent fit a pseudo-second order

kinetics model well (R2 =0.999). The results were ana-

lyzed according to the Henry, Langmuir, Freundlich, and

Dubinin-Radushkevich isotherm model equations. The

adsorption data is well interpreted by the Langmuir iso-

therm model. Benzoic acid solution at a concentration of

0.5 mmol/L was adsorbed by CPB-Bent; and, the final

adsorption efficiency was greater than 90%. The results

show that benzoic acid adsorption capability of CPB-Bent

is high with the maximum adsorption capability of

94.34 mg/g, which suggests that CPB-Bent is an excellent

adsorbent for effective benzoic acid removal from water.

Keywords Bentonite Cetyl pyridine bromide

Adsorption Benzoic acid Langmuir isotherm

1 Introduction

Industrial wastewater contains many organic and inorganic

materials such as aromatic compounds, heavy metals and

dyes. Many organic compounds have been classified as

hazardous pollutants due to their potential toxicity to

humans. The excessive and uncontrolled use of chemical

preservatives, which are mainly composed of organic

compounds, is a major problem. Benzoic acid, as a

chemical preservative, is one of the more important addi-

tives in the food industry. Because of its toxicity, its usage

as food additive has been prohibited in many countries,

such as China, Japan and the European Union. However,

benzoic acid is still be detected in industrial sewage.

There are many methods for the removal of organic

pollutants from aqueous solutions, such as adsorption,

chemical precipitation, ion exchange, membrane processes,

biological degradation, chemical oxidation and solvent

extraction. Adsorption is one of the more popular methods.

There are many studies on the adsorption of organic pol-

lutants from aqueous solutions [14]. Activated carbon has

the advantage of high adsorption capacity [3,4]. However,

because of its relatively high cost, lower cost and naturally

occurring adsorbents to remove contaminants from waste-

water are sought [1,57].

Recently, the use of natural mineral adsorbents for

wastewater treatment has increased due to their abundance

and low price. Treatment of clays with quaternary amine

Presented in part at the 1st International Congress on Advanced

Materials held in Jinan, PRC, from May 1217, 2011.

X. Xin J. Yang R. Feng J. Zhao B. Du

School of Resources and Environment, University of Jinan,

Jinan 250022, China

X. Xin G. Chen Q. Wei B. Du (&)

Key Laboratory of Chemical Sensing & Analysis in Universities

of Shandong, School of Chemistry and Chemical Engineering,

University of Jinan, Jinan 250022, China

e-mail: [email protected]; [email protected]

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J Inorg Organomet Polym (2012) 22:4247

DOI 10.1007/s10904-011-9615-2


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cationic surfactants is the common synthetic method for

organoclays. Quaternary ammonium cations may be

retained by both the outer and interlayer surfaces of

expandable clay particles via ion-exchange; and, they are

not easily displaced by small cations such as H?, Na?, or

Ca2?. The exchanged mineral surfaces become more

organophilic, thus increasing their adsorption of non-ionic

organic compounds from water. Among different clays,bentonite has been extensively investigated as a host due to

its excellent properties, such as cationic exchangeability,

swelling behavior, adsorption capability and large surface

area [8]. There has been much interest in the use of mod-

ified bentonites as adsorbents to prevent and remediate

environmental contamination. Previous studies show that

modified bentonites have been widely used to adsorb heavy

metals [9], dyes [10], gases [11], organic pollutants

[1214] and other environmental pollutants [1518].

The objective of this study is to examine the feasibility of

using different kinds of bentonites (natural bentonites, sodium

bentonites, hydroxyaluminum-pillared bentonites (Al(OH)-Bent) and cetyl pyridine bromide-modified bentonites (CPB-

Bent)) as adsorbents for benzoic acid removal. In the present

study, Al(OH)-Bent and CPB-Bent were synthesized and

characterized by FTIR, XRD and BET analysis. Adsorption

capacities of different kinds of bentonites were investigated.

The benzoic acid adsorption properties (effect of operating

variables, adsorption kinetics, and adsorption isotherms) were

also evaluated utilizing batch experimental methods.

2 Materials and Methods

2.1 Apparatus and Reagents

The bentonites used in this study were purchased from the

Fangzi bentonite plant (Weifang, Shandong Province,

China). Cetyl pyridine bromide (CPB), NaCl, HCl, NaOH,

AlCl3, and AgNO3were of analytical grade, obtained from

Sinopharm Chemical Reagent Beijing Co., Ltd, China. All

of the reagents were used as received.

The concentration of benzoic acid was determined by

UVvis spectrophotometry (Lamda 35, PerkinElmer, USA).

FTIR spectra were recordedon a PerkinElmer SpectrumOne

FTIR spectrometer. XRD patterns of the prepared samples

were obtained with a Rigaku D/MAX 2200 X-ray diffrac-

tometer (Tokyo, Japan). Surface area measurements were

performed on Micromeritics ASAP 2020 surface area and

porosity analyzer (Quantachrome, United States).

2.2 Preparation of Modified Bentonites

The natural bentonites were converted to sodium bento-

nites (Na-Bent) before the synthesis of modified bentonites.

Natural bentonites (100 g) were dispersed in 2.0 L of

deionized water by vigorous shaking for 6-h. The\2 lm

fraction of the bentonites were collected according to

Stokes law. Then the bentonites were dispersed in NaCl

solution (500 mL, 0.5 mol/L) and stirred for 24-h. The

supernatant was removed after settling. This procedure was

repeated twice. After complete exchange, Na-Bent were

washed with deionized water repeatedly until free ofchloride ions as indicated by AgNO3solution. The product

was dried at 80 C, gently ground in an agate mortar to

200 mesh and kept in a sealed bottle. The cation exchange

capacity (CEC) of the bentonites was determined by the

methylene blue test (ANSI/ASTM C837-76). The CEC of

the Na-Bent is 82 mmol 100/g. The result is similar to that

of Yan et al. [19]. Na-Bent (20 g) were reacted with CPB

solution equivalent to the CEC, shook for 24-h. The clear

supernatant was discarded. The final organic-modified

bentonite mixture was washed several times with deionized

water until free of bromide ions as indicated by AgNO3

solution. The sample of CPB-Bent was dried at 80 C,activated for 1-h at 105 C, ground in an agate mortar to

pass through a 200 mesh sieve and kept in a sealed bottle.

2.3 Preparation of Al(OH)-Bent

A pillaring solution of hydroxy-aluminum oligomeric cations

was prepared by slowly adding NaOH solution (0.48 mol/L)

to AlCl3 solution (0.2 mol/L) under vigorous stirring at 60 C

until the OH-/Al3? molar ratio reached 2.4. The solution was

stored at 60 C for 24-h. Theresulting pillaring solutions were

added dropwise to a 1% by weight Na-Bent suspension with

stirring for 12-h at theratioof 10 mmol oligomericcations per

gram of Na-Bent. The slurry was stirred for 24-h at room

temperature andwashed repeatedly withdeionized water until

there was no chloride. The samples were dried at 80 C,

ground in an agate mortar to pass through a 200 mesh sieve

and kept in a sealed bottle. The inorganic-pillared bentonites

arre designated Al(OH)-Bent.

2.4 General Batch Adsorption Procedure

For the adsorptionof benzoicacid, a stocksolution of15 mg/L

was prepared by dissolving benzoic acid in deionized water.

Dilutions of the stock solution were used in subsequent

experiments. In the isotherm experiments, CPB-Bent (0.5 g)

and benzoic acid solution (10 mL, 0.2-5.0 mmol/L) were

mixed in a series of Teflon centrifuge tubes. An optimum pH

wasattainedbyaddingafewdropsofHClorNaOH.Thetubes

were capped and placed on an orbital shaker at 170 rev/min

for 90-min to ensure equilibrium. The suspension was sepa-

rated by filtration. Blank samples containing only deionized

water and CPB-Bent were monitored for the duration of the

experiment as a control.

J Inorg Organomet Polym (2012) 22:4247 43

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3 Results and Discussion

3.1 Characterization of Bentonites

X-ray diffraction (XRD) was performed on dried natural

bentonites, Na-Bent, Al(OH)-Bent and CPB-Bent

(Table1). For natural bentonites, the main counter cations

were calcium and magnesium, which was in agreementwith the observedd001 distance of 14.7 A. The d001 value

decreased to 12.2 A when one Ca2? or Mg2? ion was fully

exchanged by two Na? ions. After hydroxy-aluminum

polycations exchange, thed001increased to 19.03 A. After

CPB cation exchange, the d001 increased to 19.0 A. BET

surface area, pore volume and average pore diameter for

different samples are given in Table1. The BET surface

area of Al(OH)-Bent and CPB-Bent is larger than that of

Na-Bent and natural bentonites.

FT-IR spectra have been widely used to probe the

aggregation of adsorbed organic cations on clay minerals.

The FT-IR spectra of natural bentonites, Na-Bent and CPB-Bent from 4,000 to 300/cm are shown in Fig. 1. A band at

3,438/cm shows HOH hydrogen bonded water. The

intensive band at 1,045/cm is assigned to the SiO

stretching vibration. The SiOAl and SiOSi bending

vibrations appear at 525 and 467/cm, respectively. The

small band at 1,635/cm corresponds to the d(SiOH)

deformation [20]. The bands at 2,925 and 2,845/cm

(Fig.1c) correspond to CH2 asymmetric [ms(CH2)] and

symmetric stretching [ms(CH2)], respectively [21,22]. The

splitting of the methylene scissoring mode at 1,485/cm is

diagnostic of the packing density increase of the interca-

lated surfactants within the clay gallery [23]. The results

indicate that the CPB molecules are impregnated into the

interlayer space of the bentonites.

3.2 Effect of Operating Variables on the Adsorption

of Benzoic Acid by CPB-Bent

To understand the adsorption of benzoic acid onto CPB-

Bent, the influence of initial pH, adsorbent concentration,

equilibrium time, and adsorption isotherms on benzoic acid

adsorption were studied. The adsorption of benzoic acid

onto natural bentonites, Na-Bent, Al(OH)-Bent and CPB-

Bent were carried out on a 10 mL, 0.5 mmol/L benzoic

acid solution at various pH values to examine the effect of

pH (Fig.2). Benzoic acid is hardly adsorbed by natural

bentonites, Na-Bent and Al(OH)-Bent; therefore, the

adsorption properties of these materials are no longer dis-cussed. However, pH exerts a significant impact on the

adsorption of benzoic acid onto CPB-Bent by affecting the

surface charge of the adsorbents and the degree of ioni-

zation of organic compounds. Benzoic acid adsorption of

CPB-Bent has a high removal efficiency at pH 34, and

appears to peak at about pH 3.5, while the uptake of ben-

zoic acid decreases with increasing pH. Benzoic acid is

mostly present in neutral form when the pH is less than the

pKa (pKa,benzoic acid =4.19). At the pKa, 50% of benzoic

Table 1 The d001 value, BET surface area, total pore volume andaverage pore diameter for natural bentonites, Na-Bent, Al(OH)-Bent

and CPB-Bent

Adsorbent d001(A)

BET surface

area (m2/g)

Pore volume

(cm3/g)

Average pore

diameter (nm)

Natural

bentonites

14.7 10.2 0.0307 3.52

Na-Bent 12.2 31.7 0.0608 7.67

Al(OH)-Bent 19.03 159.2 0.1131 8.425

CPB-Bent 19.0 167 0.122 8.79

3600 3000 2400 1800 1200 600

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

c

b

Transmittance

Wavenumber (cm-1)

Natural Bentonites

Na-Bent

CPB-Bent

a

Fig. 1 FT-IR spectra ofa natural bentonites, b Na-Bent, and c CPB-

Bent

0 2 4 6 8 100

10

20

30

40

50

60

70

80

90

100

Removalefficiency%

pH

CPB-Bent

Na-Bent

Natural Bent

Al(OH)-Bent

Fig. 2 Effect of pH on the adsorption of benzoic acid onto natural

bentonites, Na-Bent, Al(OH)-Bent and CPB-Bent

44 J Inorg Organomet Polym (2012) 22:4247

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acid is present as the anion; at pH[pKa, anions predomi-

nate. Lower adsorption at higher pH may be due to the

abundance of OH- ions competing with the anions of

organic compounds for the adsorption sites, and the ionic

electrostatic repulsions between the negatively charged

bentonites surface and the ionic organic compounds.

Similar behaviour was reported by Yldz et al . [2] for

benzoic acid adsorption by organobentonites, and by Banat

et al. [24] for the adsorption of phenol by bentonites.

Natural bentonites, Na-Bent, Al(OH)-Bent and CPB-

Bent of different concentrations were combined with a

fixed 10 mL, 0.5 mmol/L benzoic acid solution at theoptimum pH, respectively. As shown in Fig.3, the

adsorption of benzoic acid increased with the increase of

absorbent concentration at lower concentration, and

reached to a plateau at the appropriate concentration of

adsorbent of 0.05 g/mL. The adsorption of benzoic acid

onto CPB-Bent was much higher than that of natural

bentonites and Na-Bent. Although the removal efficiencies

of natural bentonites, Na-Bent and Al(OH)-Bent also

increased with the increase of adsorbent concentration, the

efficiencies remained at a low level. Therefore, the

adsorption properties of natural bentonites, Na-Bent and

Al(OH)-Bent are not discussed further.

3.3 Adsorption Kinetics

The adsorption of benzoic acid increased with time and

reached equilibrium at about 90 min (Fig.4). The

adsorption kinetics data of benzoic acid were determined

by testing pseudo-first order kinetic model and pseudo-

second order kinetic model. The results were shown in

Table2. The measured kinetic data of benzoic acid

adsorbed on CPB-Bent fit pseudo-second order kinetic

model well with a correlation coefficient of 0.999, which

suggested that the chemisorption process could be a rate-

limiting step [25].

3.4 Adsorption Isotherms

Based on the above optimized conditions, the adsorp-

tion isotherms of benzoic acid onto CPB-Bent were

studied. The Henry, Langmuir, Freundlich and Dubinin-

Radushkevich equations were used for modeling these

adsorption isotherm data, as shown in Fig.5. TheR2 value

obtained for the Langmuir isotherm was 0.9975, indicating

a very good mathematical fit by the model. The adsorption

of benzoic acid onto CPB-Bent is monolayer uniform

adsorption. From the Langmuir model, the maximum

adsorption capability of benzoic acid onto CPB-Bent is

94.34 mg/g.

4 Conclusions

Al(OH)-Bent and CPB-Bent were prepared, characterized

and used to remove benzoic acid from aqueous solution.

Natural bentonites, Na-Bent, Al(OH)-Bent and CPB-Bent

were used to remove benzoic acid from aqueous solution.

The benzoic acid adsorption capabilities of natural

Fig. 3 Effect of adsorbent concentration for the adsorption of

benzoic acid onto natural bentonites, Na-Bent, Al(OH)-Bent and

CPB-Bent

0 50 100 150 200 250 300

0

10

20

30

40

50

60

70

80

90

100

Remova

lefficiency%

t(min)

CPB-Bent

Natural Bentonites

Na-Bent

Fig. 4 Effect of adsorption time on the adsorption of benzoic acid

onto natural bentonites, Na-Bent, Al(OH)-Bent and CPB-Bent

Table 2 Kinetic parameters for benzoic acid adsorption

Kinetic model R2 qe k

Pseudo-first order kinetic model 0.004 0.199 0.0005

Pseudo-second order kinetic model 0.999 7.943 0.0013


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bentonites, Na-Bent and Al(OH)-Bent are low, but high for

CPB-Bent. The pH effect, adsorbents concentration, equi-

librium time, adsorption isotherms and kinetics, were

examined. The pseudo-second order model accurately

described the benzoic acid adsorption kinetics for CPB-

Bent. The adsorption isotherm data agree well with the

Langmuir adsorption isotherm model. Benzoic acid solu-

tion of 0.5 mmol/L was adsorbed onto CPB-Bent. The final

adsorption efficiency was higher than 90% suggesting that

CPB-Bent is an excellent adsorbent for effective removal

of benzoic acid from water.

Acknowledgments This study was supported by the Natural Sci-

ence Foundation of China (No. 21075052), the Natural Science

Foundation of Shandong Province (No. ZR2010BM030,

ZR2010EM063), the Science and Technology Key Plan Project of

Shandong Province (No. 2010GSF10628), Special Research and

Development Environmental Protection Industry of Shandong Prov-

ince (2011), National Major Projects on Water Pollution Control

and Management Technology (No. 2008ZX07422), and the Science

and Technology Development Plan Project of Jinan City (No.

201004015).

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cpb-bentonite untuk adsorpsi asam benzoat

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