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: [email protected]

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). 

Re eferences 

O3 Compoundd 

79 

1. Sheng, S J., Xiee, 

Y. & Zhou, , Y. (2009). <strong>Adsorption</strong> A <strong>of</strong>f 

methyllene 

blue ffrom 

aqueous 

solutionn 

on pyrrophyllite. 

AAppl. 

Clay Sci. S 46(4) : 

422–4224. 

2. Liu, L J. W., Chhen, 

G., Li, Z. H. & Zhang, , Z.G. (2007). 

Hydrotthermal 

syntthesis 

and ph hotocatalytic 

propertties 

<strong>of</strong> ATaaO3 

and AN NbO3 (A=Naa 

and K) ). Int. J. Hyydrogen 

Ener rg. 32(13) : 

2269 – 2272. 

3. Wang, W Y., YYi, 

Z., Li, Y. ., Yang, Q. & Wang, D. 

(2007). Hydrothermmal 

synthesis <strong>of</strong> o potassiumm 

niobatee 

powders. CCeram. 

Int. 33 3(8) : 1611– – 

1615. 

4. Hong, H H., Jiaang, 

W.-T., Zhhang, 

X., Tie e, L. & Li, Z. 

(2008) . <strong>Adsorption</strong>n 

<strong>of</strong> Cr(VI) on STACmodifieed 

rectorite. AAppl. 

Clay Sci. S 42(1-2) : 

292–2999. 

5. Li, L J., Wang, L., Qi, T., Zhhou, 

Y., Liu, C., C Chu, J. & 

Zhang, , Y. (2008). Different N-containing 

N 

functioonal 

groups modified mesoporous 

adsorbeents 

for Cr(VII) 

sequestratio on: Synthesis, 

characterization 

andd 

comparison n. Micropor. 

Mesopoor. 

Mat. 1100(2-3) 

: 442–4 450.

Adsorption Isotherm of Methylene Blue on KNbO3 Compound

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template ?