Adsorption Isotherm of Methylene Blue on KNbO3 Compound

Journal <strong>of</strong> Metals, Materials and Minerals, Vol.20 No.3 pp.77-79, 2010
<strong>Adsorption</strong> <strong>Isotherm</strong> <strong>of</strong> <strong>Methylene</strong> <strong>Blue</strong> on KNbO3 Compound
Juthathip SINTHAO 1,2 , Sitthisuntorn SUPOTHINA 3 and Sittinun TAWKEAW 2,4*
1 International Postgraduate Programs in Environmental Management (Hazardous Waste Management),
Graduate School, Chulalongkorn University, Bangkok, 10330, Thailand
2 National Center <strong>of</strong> Excellence for Environmental and Hazardous Waste Management,
Thammasat University, Pathumtani, 12120, Thailand
3 National Metal and Materials Technology Center, 114 Thailand Science Park, Paholyothin Rd.,
Klong 1, Klong Luang, Pathumthani, 12120, Thailand
4 Department <strong>of</strong> Chemical Engineering, Faculty <strong>of</strong> Engineering, Srinakharinwirot University,
107 Rangsit-Nakhonnayok Rd., Khong 16, Ongkharak, Nakhonnayok 26120, Thailand
Abstract
KNbO3 was prepared from Nb2O5 powder in 10 M KOH solution under hydrothermal treatment at
200°C for 12 hours. The equilibrium adsorption isotherm <strong>of</strong> methylene blue at pH 1 followed both Langmuir
and Freundlich isotherms. The maximum absorption capacity (qm) <strong>of</strong> methylene blue on Nb2O5 and KNbO3
were 0.4476 and 1.4749 mg/g, respectively. The Langmuir adsorption constant (KL) on Nb2O5 and KNbO3
were 1.2384 and 0.1799 L/mg, respectively.
Key word: <strong>Adsorption</strong> isotherm, KNbO3, <strong>Methylene</strong> blue
Introduction
<strong>Methylene</strong> blue dye is usually used in
coloring paper and dyeing textile fabrics. (1) The
methylene blue is not strongly hazardous but it is
resistant to breakdown by chemical, physical and
biological treatments. It can be chelated with metal
ions and produced a toxic compound that is harmful to
living organisms. Removal methods <strong>of</strong> dye in
wastewater usually employ the adsorption process.
Adsorbents are usually used such as activated clay,
activated carbon, natural clay, and zeolite.
KNbO3 is one the niobate compounds that can
decompose water to produce hydrogen and oxygen
gases via its photodecomposition property under
UV-light irradiation. (2) Based on its photodecomposition
property, the KNbO3 may be employed to decompose
methylene blue. However, the methylene blue
adsorption data with KNbO3 is less published. This
paper aims to study adsorption behavior <strong>of</strong>
methylene blue on the KNbO3 compound.
Materials and Experimental Procedures
Chemicals
All chemicals are analytical grade and
were used without further purification.
Preparation <strong>of</strong> KNbO3
KNbO3 was synthesized by following
Wang, et al. (3) method. The Nb2O5 powder (20g)
was dispersed in 160 ml <strong>of</strong> 10 M KOH aqueous
solution, and then subjected to hydrothermal
treatment in a 316-type stainless steel autoclave at
200°C for 12 hours. The autoclave was taken out
from the oven and cooled down to room temperature.
The product was filtered, washed with deionized
water three times, and dried at 110°C overnight.
Absorption <strong>Isotherm</strong> Study
A 0.25 g <strong>of</strong> the prepared powder was
suspended in 250 ml <strong>of</strong> methylene blue solution
with initial concentrations <strong>of</strong> 2 - 10 mg/L at room
temperature and shaking at 150 rpm for 24 hours
in the dark condition to prevent photodecomposition
<strong>of</strong> the methylene blue. The pH <strong>of</strong> the solutions was
adjusted to pH 1 with 6 M H2SO4. A 20 mL <strong>of</strong>
aliquot <strong>of</strong> liquid solution was sampled after
shaking for 24 hours and filtered with 0.45 μm
polycellulose acetate membrane. The concentration
<strong>of</strong> methylene blue in the supernatant solution
after and before adsorption was determined by
measuring the absorbance <strong>of</strong> solution at λmax <strong>of</strong>
663 nm with Shimadsu UV-1610 Spectrophotometer
(Japan).
* Corresponding author Tel: +66 2649 5000 ext. 2069; Fax: +66 3732 2608; E-mail: sittinun@swu.ac.th

78
Analysis
Crystal structure and microstructure <strong>of</strong> the
samples were measured by using an X-ray
diffractometer (XRD, JDX-03530, JEOL, Japan),
and a scanning electron microscope (SEM, JEM-
2010, JEOL, Japan), respectively. Specific surface
area was measured by means <strong>of</strong> nitrogen
adsorption method (BET, Quantachrome Autosorb
Automated Gas Sorption).
Results and Discussion
Figure 1 shows XRD patterns <strong>of</strong> the starting
powder and the hydrothermal product. The starting
powder showed the XRD pattern corresponding
to the Nb2O5 phase (JCPDF # 37-1468). The
hydrothermal product showed the XRD pattern
corresponding to KNbO3 phase (JCPDF # 71-2171).
Intensity Intensity (a.u.) (a.u)
0 10 20 30 40 50 60 70
Figure 1. XRD patterns <strong>of</strong> the KNbO3 product and
starting Nb2O5 powder.
Figure 2 shows SEM images <strong>of</strong> the Nb2O5
powder and KNbO3 product. The Nb2O5 morphology
is a brick-shape particle (Figure 2 (a)). The KNbO3
product showed the brick-like morphology (Figure 2 (b)),
similar to that reported by Wang, et al. (3) The
specific surface area <strong>of</strong> the KNbO3 is 4.02 m 2 /g
which is ~ 3 times higher than that <strong>of</strong> the starting
Nb2O5 (Table 1).
Absorbent
2theta (degree)
KNbO3
Nb2O5
Table 1. <strong>Adsorption</strong> parameters and specific surface area.
SINTHAO, J. et al.
Figure 2. SEM images <strong>of</strong> the KNbO3 product and
starting Nb2O5 powder.
The equilibrium adsorption isotherms <strong>of</strong>
methylene blue onto the adsorbents were determined
by Langmuir and Freundlich isotherms. The Langmuir
equation assumes a finite number <strong>of</strong> coordination
sites on the surface <strong>of</strong> an adsorbent, whereas the
Freundlich equation is an empirical equation. (4) The
Langmuir isotherm is expressed as follow. (5)
q
e
qmK
LCe
=
1+
K C
L
e
(1)
where qe is the equilibrium adsorption capacity
(mg/g), Ce is the equilibrium concentration <strong>of</strong> the
methylene blue solution (mg/L), qm is the maximum
capacity <strong>of</strong> methylene blue (mg/g), and KL is the
Langmuir constant (L/mg).
The Freundlich isotherm is expressed as follow. (5)
q
e
= K C
(2)
F
1/
n
e
where KF is the Freundlich constant (mg/g (mg/L) n )
and 1/n is the heterogeneity factor.
Langmuir isotherm Freundlich isotherm
R 2 qm (mg/g) KL (L/mg) R 2 n KF (L/mg)
Nb2O5
KNbO3
BET (m 2 /g)
Nb2O5 0.993 0.4476 1.2384 0.935 5.6180 0.5798 1.33
KNbO3 0.914 1.4749 0.1799 0.912 1.6077 0.5428 4.02
3µm
3µm

Figgure
3 showss
the adsorpttion
isothermm
<strong>of</strong>
methylene blue absorbbed
by Nb2OO5
and KNbbO3
absorbents ffollowing
booth
Langmuirr
and Freunddlich
isotherms, rrespectively.
. Both isotheerms
fitted wwith
the adsorpttion
data. Taable
1 showws
the resultss
<strong>of</strong>
the calculaated
isothermm
constants <strong>of</strong> Nb2O5 and
KNbO3 forr
methylene blue adsorption.
The vaalue
<strong>of</strong> n was grreater
than 1 indicating thaat
the methyllene
blue was prreferred
to aadsorb
on botth
adsorbentts.
The value o<strong>of</strong>
the maximmum
adsorpttion
capacity
KNbO3 is hhigher
than the value o<strong>of</strong>
Nb2O5 <strong>of</strong>
starting maaterial
because
the specific
surface a
<strong>of</strong> KNbO3 is higher thhan
the valuue
<strong>of</strong> Nb2O5
about 3 timmes.
(4)
y <strong>of</strong>
the
area
for
Figure 3. LLangmuir
ploots
(a) and Freundlich pplots
(b) for the addsorption
<strong>of</strong> mmethylene
bluue
at
different initiaal
concentratioons
using Nbb2O5
(�) and KNbbO3
(Δ) adsorbbents.
Conclusioons
A<strong>Adsorption</strong>
I<strong>Isotherm</strong>
<strong>of</strong> M<strong>Methylene</strong>
Bl lue on KNbO
Thiis
study invvestigated
tthe
equilibriium
adsorption <strong>of</strong> methyleene
blue onnto
Nb2O5 and
KNbO3 adssorbents.
Thee
methylene blue adsorpttion
on both abbsorbents
folllowed
both Langmuir and
Freundlich isothermss.
Maximuum
adsorpttion
capacity (qqm)
<strong>of</strong> the KKNbO3was
3.3
times higgher
than that <strong>of</strong>f
the Nb2O5.
(a)
(b)
Ac cknowledgeemonts
The auuthors
are ggrateful
to the
National
me etal and Matterials
Technnology
Cent ter (MTEC)
for r financial suupport
<strong>of</strong> thiss
work (MT-B-52-CER-
17- -257-G).
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