Science & Technology Indonesia 
p-ISSN: 2580-4405 e-ISSN: 2580-4391 
Sci. Technol. Indonesia 2 (2017) 1-8 
 

Article http://sciencetechindonesia.com 

 

@2017 Published under the terms of the CC BY NC SA 4.0 license 

 
1 

PREPARATION OF POLYOXOMETALATE COMPOUND (NH4)6(β-P2W18O62)/SiO2 BY SOL-GEL METHOD AND 
ITS CHARACTERIZATION  

 

Osin R Tambunan1*, Risfidian Mohadi1 
 
1Department of Chemistry, Faculty of Mathematic and Natural Science, Univeristas Sriwijaya. Jl. Palembang Prabumulih, Km. 32, Indralaya, Ogan 

Ilir, Sumatera Selatan 
*Corresponding Author E-mail : osintambunan@yahoo.com 

 

ABSTRACT 
Preparation of polyoxometalate compound of (NH4)6(β-P2W18O62)nH2O supported with silica derived from the hydrolysis of 
tetraethyl orthosilicate by sol-gel method has been conducted. The compound was synthesized and characterized using FT-IR 
spectrophotometer, crystallinity using XRD analysis and the determination of acidity via quantitatively and qualitatively. Qualitative 
analysis was performed using ammonia and pyridine adsorption and quantitative analysis using potentiometric titration. FT-IR 
spectrum of (NH4)6(β-P2W18O62)nH2O appeared in wavenumber 786.96 cm-1 (W-OC-W), 918.12 cm-1 (W-Oe-W), 964.41 cm-1 
(W=O), 1087.85 cm-1 (P-O), 3572.17 cm-1 (O-H),  1404.18 cm-1 (N-H) reinforced with wavenumber 1612.49 cm-1 with show vibration  
NH dari NH+, and to  (NH4)6(β-P2W18O62)nH2O/SiO2 appears in wavenumbers 794.67 cm-1 (W-Oc-W), 918.12 cm-1 (W-Oe-W), 
1049.28 cm-1 (W=O), 1087.85  cm-1 (P-O), 3564.15 cm-1 (O-H), 470.63 cm-1 (Si-O). Diffraction pattern of (NH4)6(β-P2W18O62)nH2O 
and (NH4)6(β-P2W18O62)nH2O/SiO2 compound show high crystanillity. The acidic properties showed (NH4)6(β-
P2W18O62)nH2O/SiO2 more acidic than (NH4)6(β-P2W18O62)nH2O. Analysis of the effect of temperature on the stability of the 
compounds polyoxometalate (NH4)6(β-P2W18O62)nH2O/SiO2 show that the temperature of 600ºC the shift in  wavenumbers of the 
compounds caused by vibration  W=O, W-OC-W,  W-Oe-W has been lost. This shows that at a temperatures of 600ºC on heating 
can cause changes in the structure of polyoxometalate (NH4)6(β-P2W18O62)nH2O/SiO2.  

 

Keywords : (NH4)6(β-P2W18O62).nH2O, Polyoxometalate, SiO2 

 

INTRODUCTION 
Polyoxometalate is a metal-oxygen  cluster compound 

having acid-base properties, has various structural variations and 
oxidation rates so it is very effective for both acid base and 
oxidation reaction catalyst. In general, polyoxometalate 
compounds can be classified into two groups: 
isopolyoxometalate and heteropolioxometale (Yamase et al, 
2002). 

Polyoxometalate compounds have many benefits, as a 
catalyst and basic ingredients of macromolecular synthesis. Its 
utilization as a catalyst because it has a high acidity that exceeds 
sulfuric acid and is not toxic (Okuhara et al,1996).  Research on 
polyoxometalate compounds is primarily intended in terms of 
its superiority as a catalyst which can be performed in 
homogeneous and heterogeneous system depending on the 
medium used. In heterogeneous system, polyoxometalate 
compounds may be used repeatadly of catalytic reaction. 
Polyoxometalate compounds have attracted attention to 
continue to be developed due to flexible properties as acid and 
base as well as an adjustable oxidation rate according to the 
desired application recruitments (Kozhevnikov, 2002). 

Previous research has been done on the development of 
polyoxometalate compounds using carriers as TiO2, ZrOCl2, 
TaCl5 (Fatimah, 2009). Yang (2011) has also carried on  

 

Article History 
Received: 23 September 2016 
Accepted: 3 November 2016 
 
DOI: 10.26554/sti.2017.2.1.1-8 

(NH4)6(β-P2W18O62).nH2O with SiO2 sourced from tetraethyl 
orthosilica (TEOS) and using alcohol as a medium. In his 
research, TEOS hydrolys was used as a source of SiO2 by using 
microemulsion medium derived from sodium bis(2-ethylhexsil) 
sulfosuccinate with cyclohexane (Kim et al, 2006). According to 
Eriksson et al (2004) miccroemulsion is a liquid derived from a 
mixture of water, hydrocarbons, and surfactants. Sari and 
Situngkir (2016) reported metal oxide from reduction of TEOS 
(tetra ethyl ortho silicate) supported polyoxometalate.  
Polyoxometalate compounds embedded with SiO2 using 
microemulsions and sol-gel techniques are expected to have 
characteristics as catalysts having uniform pore sizes and can 
improve the acidity side of polyoxometalate compounds. In this 
research, synthesis and characterization of Dawson-type 
polyoxometalate compound (NH4)6(β-P2W18O62) were carried 
out with SiO2. The process of loading is done by sol-gel 
technique. To know the functional groups of polyoxometalate 
compound and to know whether or not a SiO2 carried by 
polyoxometalate compounds is characterized using FT-IR 
spectrofotometr and XRD. This characterization is perfomed 
both before and after the silica is carried by the polyoxometalate 
compounds. The acidity of the compound (NH4)6(β-
P2W18O62).nH2O/SiO2 was studied through quantitative and 
qualitative studies through potentiometric titration and 
identification using an FT-IR spectrometer followed by thermal 
stability test.  

 

EXPERIMENTAL SECTION 
The XRD Shimidzu lab X Type 6000, spectofotometer FT-

IR Shimidzu prestige 21 were used for characterizatio of the 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 2 

polyoxometalate compounds in this research. The materials 
used in this research were sodium tungsten, ortho phosphoric 
acid, aquades, ammonia, ammonium chloride, tetraethyl 
orthosilicals, bis(2-ethylhexsil)sulfosuccinate, n-butilamin, 
pyridin, cyxlohex-ane and  acetonitrile.  

 

Synthesis of Dawson-Type Polyoxometalate 
compounds (NH4)6(β-P2W18O62).nH2O and its 
characteritation. 

A total amount of 31.25 g of sodium tungsten was dissolved 
in water 62.5 mL and added 26.25 mL ortho phosphoric acid 
while stirred with a magnetic stirrer.The obtained solution was 
refluxed for 4 hoursand obtained a greenish solution. The 
solution was cooled and added 12.5 g ammonium chloride while 
stirring for  10 minutes to obtain a pale yellow solid. The 
obtainedsolid was filtered, dissolved with  75 mL aquades and 
the obtain filtrate was added with 12.5 g ammonium chloride to 
obtain a white solid. The white solid was filtered and dissolved 
with 31.25 mL of distilled water. The obtained solution was left 
for 5 days for polyoxometalate compound (NH4)6(β-
P2W18O62).nH2O according to (Contant, 1990). The poly-
oxometalate  (NH4)6(β-P2W18O62).nH2O obtained is 
characterizes by spectrophotometer FT-IR and XRD. 

 

Preparation Polyoxometalate compounds (NH4)6(β-
P2W18O62).nH2O/SiO2 by Sol-Gel Method (Newman et 
al, 2006) 

Preparation polyoxometalate compound (NH4)6(β-
P2W18O62).nH2O/SiO2 was modified  from the Kim et al (2006) 
procedure. The compound (NH4)6(β-P2W18O62).nH2O/SiO2 
was synthesized with 0.5 g sodium bis(2-ethylhexyl) 
sulfosuccinate dissolved with  1 mL siclohexane (Solution A). 
Compound  (NH4)6(β-P2W18O62).nH2O of 0.76 g was dissolved 
with 1 mL of aquadest ( Solution B).Solution B was added to 
solution A while distirer. A total 2 mL tetraethyl ortosilica 
(TEOS) was added dropwise. Stirred with a magnetic stirrer and 
heated 60°C. The mixture will form a hydrogel ang heated to 
100°C while stirring with a glass spatula. The white solid formed 
is a compound. (NH4)6(β-P2W18O62).nH2O/SiO2. The 
compound  (NH4)6(β-P2W18O62).nH2O/SiO2 was characterized 
by a FT-IR spectrofotometer, and an XRD diffractometer. 

 

Acidity Test of the Compound (NH4)6[β-
P2W18O62].nH2O/SiO2 qualitatively 

The acidity test was qualitatively modified from the 
Maksimov et al (2001) procedure by saturation of 
polyoxometalic compounds using ammonia and also pyridine. 
For saturation with ammonia as much as 0.5 g of compound 
(NH4)6(β-P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/ 
SiO2  inserted into vials and 1 mL of ammonia (NH3) 25% Into 
a beaker. A vial bottle is inserted into a beaker containing 
ammonia and tightly sealed with a plastic kreb. The compound 
is allowed one day in order to adsorption between ammonia and 
polyoxometalic compound. For saturation using a pyridine 
compound, the same work was done. A total of 0.5 g of each 
compound (NH4)6(β-P2W18O62).nH2O and (NH4)6(β-P2W18O62) 
.nH2O/SiO2 were inserted into vials and 1 mL of pyridine 25% 
were fed into beaker. A vial bottle is inserted into a beaker 
containing ammonia and tightly sealed with a plastic kreb. The 
compound was allowed for one day to allow adsorption between 

pyridine and polyoxometalate compounds. Compound 
(NH4)6(β-P2W18O62).nH2O and  (NH4)6(β-P2W18O62).nH2O/ 
SiO2 results in saturation with ammonia and pyridine were 
qualitatively tested by characterization using a FT-IR spectro-
photometer.  

 

Acidity Test of the compound (NH4)6(β-
P2W18O62).nH2O/SiO2 Quantitatively (Reddy et al, 
2006) 

A total of  0.1 g of each compound (NH4)6(β-
P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/SiO2 were 
dissolved in 8 mL acetonitrile and stirred for 6 hours with a 
magnetic stirrer. The suspension was titrated with 0.05 M n-
butylamine which was monitored by glass electrode as a pH 
sensor. Each droplet of potential titrant pervolume was 
generated, and recorded and linked potentiometric titration 
curves between the titrant volume and the resulting potential. 
The classification of the seams from the acidity side was 
classified on a scale: E> 100 mV (very acidic); 0> E> 100 mV 
(acid side); -100 <E <0 mV (weak acid side); and E <-100 mV 
(acid side is very weak). 

 

The Impact of Temperature on the Stability of the 
compound (NH4)6(β-P2W18O62).nH2O/SiO2 

The compound (NH4)(β-P2W18O62).nH2O/SiO2 was heated 
at various temperature 200oC, 300oC, 400oC, 500oC, and 600oC 
for 3 hours in he furnance. The combustion compound was 
cooled and analyzed by using FT-IR spectrofotometer.  

 

RESULTS AND DISCUSSION  

Synthesis of Dawson-Type Polyoxometalate compound 
(NH4)6(β-P2W18O62).nH2O and characterization  

The synthesis of dawson type polyoxometalate compound 
(NH4)6(β-P2W18O62).nH2O based on the  procedure performed 
by Contant (1990) using sodium tungsten as the base material. 
The forming polyoxometalate compound were characterized by 
functional group analysis using a FT-IR spectrophotometer and 
christanility analysis using XRD analysis. The reaction of 
polyoxometalate compound formation as follows: 

 

18(WO4)2- + 32H3PO4 + 6(NH4)+  (NH4)6(β-P2W18O62) + 
18H2O + 30H2PO4- 

 

The identification was carried out on a polyoxometalate 
(NH4)6(β-P2W18O62).nH2O  compound using a FT-IR 
spectrophotometer in the range of 200-4000 cm-1 wave numbers 
is shown in Figure 1. The spectrum FT-IR polyoxometalate 
(NH4)6(β-P2W18O62).nH2O in Figure 1 shows some significant 
absorption bands located at the wave number of 786 cm-1 
showing the vibration of the W-Oc-W group (oxygen in the 
middle of the polyoxometalic compound) And the numbers in 
918 cm-1 denote the vibration of the W-Oc-W group (the oxygen 
at the edge of the polyoxometalate compound). The wave 
number at 964 cm-1 shows the vibration of the W = O group, 
and the wave number at 1087 cm-1  denotes the vibration of the 
P-O group. The wave number at 1404 cm-1 denotes the vibration 
of the N-H group which is amplified by the 1612 cm-1 number 
indicating the NH vibration NH4+  (Finke et al, 1987). The 
compound (NH4)6(β-P2W18O62).nH2O was analyzed using 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 3 

XRD. Diffractogram of compound (NH4)6(β-P2W18O62).nH2O. 
presented in figure 2.  

 

 

 
Figure 1.  FT-IR spectra polyoxometalate compound (NH4)6 

(β-P2W18O62).nH2O 

 

  

 
Figure 2.  XRD Diffraction pattern of polyoxometalate 

compound (NH4)6(β-P2W18O62).nH2O 

 

The diffractogram in figure. 2 shows the diffraction for the 
highest intensity of the polyoxometalate compound (NH4)6(β-
P2W18O62).nH2O complexes appearing at the diffraction angles 
of 8°, 17°, 27°. According to Yang et al (2011) the diffraction for 
polyoxometalate compounds was found in some diffraction 
regions at 6-10°, 15-20°, 22-25°, and 35-40°. The diffraction that 
appears below 10° in region 2θ shows that the polyoxometalate 
compound has a very high crystallinity. Diffractogram of 
polyoxometalate compound (NH4)6(β-P2W18O62).nH2O shows 
the sharp diffraction peaks indicating polyoxometalate 
(NH4)6(β-P2W18O62).nH2O compounds have very high 
crystalline properties in which the atoms of the polyoxometalic 
compound (NH4)6(β-P2W18O62).nH2O is arranged regularly 
based on the length and angle of the regular bond. 

 

 Synthesis of Dawson-Type Polyoxometalate 
Compound (NH4)6(β-P2W18O62).nH2O/SiO2 And 
Characteritation. 

The preparation of Dawson- Type polyoxometalate 
compound (NH4)6(β-P2W18O62).nH2O  with SiO2  based on the 
procedure undertaken by Newman et al. (2006) in SiO2 is derived 
from tetraethyl orthosilicate in the form of a liquid. 
Identification using spectrophotometer FT-IR compound 
(NH4)6(β-P2W18O62).nH2O/SiO2  showed the presence of 
specific vibrations of polyoxometalate and SiO2 compounds 

presented in Figure 3. On FT-IR spectrum of compound 
(NH4)6(β-P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/ 
SiO2 noticeable differences before placement and after assuming 
SiO2. 

Figure. 3 shows the difference shown by FT-IR spectrum of 
polyoxometalate (NH4)6(β-P2W18O62).nH2O compound before 
being assumed with SiO2. According to Derick et al, (1999) the 
asymmetric stretching vibration of Si-O-Si is at the wave number 
1130-1000 cm-1. Smith (1999) reported that the Si-O-Si 
asymmetric stretch vibration was stronger at 1085 cm-1. The FT-
IR spectrum of compound (NH4)6(β-P2W18O62).nH2O/SiO2 
undergoes a shift of wave numbers for asymmetric Si-O-Si 
stretching vibration at 1103.28 cm-1. The shift of wave numbers 
occurs in vibration W = O. The W = O vibe before embodiment 
appears at 964.41 cm-1 wave numbers and the vibrations after 
being assumed with SiO2 appear at 1049.28 cm-1 wave numbers. 
According to Stuart (2004), the vibration -OH vibration in the 
presence of hydrogen bonding effect is in the range of 3500-
2500 cm-1 wavelengths characterized by a widened peak on the 
FT-IR spectrum. Figure 3B has a shift of wave numbers at the 
peak 3572.17 cm-1  identifies the -OH vibration by the presence 
of H2O in the compound (NH4)6(β-P2W18O62).nH2O and the 
wave number at peak 3464.15 cm-1 identifies the -OH by the 
presence of H2O in the compound (NH4)6(β-
P2W18O62).nH2O/SiO2  

 

 
Figure  3. FTIR spectrum of polyoxometalate (NH4)6(β-

P2W18O62).nH2O (A), (NH4)6(β-P2W18O62).nH2O/SiO2  (B) 

 

Figure 3A shows the spectra that appear at the wave numbers 
786, 918, 964, 1087, 1404 cm-1 for vibration of the W-Oc-W 
group (oxygen in the middle of the polyoxometalate 
compound), the vibration of the W-Oe-W group (The oxygen at 
the edges of the polyoxometalic compound), the vibration of the 
W = O group, the vibration of the PO group and the vibration 
of the NH group reinforced by the 1612 cm-1 indicate the NH 
vibration of NH4 (Finke et al. 1987). In Figure 3B the FT-IR 
SiO2 spectrum of the absorption band peak appears at wave 
number 470 for the vibration of the Si-O group. Figure 3A 
spectra of FT-IR compound (NH4)6(β-P2W18O62).nH2O/SiO2 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 4 

have the same absorption bands of both the polyoxometalate 
(NH4)6(β- P2W18O62).nH2O as well as the SiO2 absorption 
bands. This identifies the presence of polyoxometalate 
(NH4)6(β-P2W18O62).nH2O and SiO2 forming groups which 
show the success of SiO2 baffling process in the 
polyoxometalate (NH4)6(β-P2W18O62).nH2O. Table 1 shows 
wave numbers of polyoxometalate compound (NH4)6(β-
P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/SiO2. 
Further, polyoxometalate (NH4)6(β-P2W18O62).nH2O analysis 
using XRD. Comparison of the compound (NH4)6(β-
P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/SiO2 
presented in the Figure 4.  

 

Table 1. Wave numbers of polyoxometalate compound 
(NH4)6(β-P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/ 
SiO2 

(NH4)6(β-
P2W18O62).nH2O. 

(NH4)6(β-
P2W18O62).nH2O/SiO2 

Vibration 
Type  

964.41 1049.28 W=O 

786.96 794.67 W-Oc-W 

918.12 918.12 W-Oe-W 

1087.85 1087.85 P-O 

3572.12 3464.15 O-H 

 

 
Figure  4. Difractions of (NH4)6(β-P2W18O62).nH2O (A) and 

(NH4)6(β-P2W18O62).nH2O/SiO2 (B) 

 

Polyoxometalate compound (NH4)6(β-P2W18O62).nH2O 
which was assumed by SiO2 was characterized using XRD. 
Characterization using XRD diffraction angle and crystallinity 
showed polioksometalate compounds dengan SiO2 (NH4)6(β-
P2W18O62).nH2O/SiO2. The comparison of XRD difraction of 
the compound (NH4)6(β-P2W18O62).nH2O with (NH4)6(β-
P2W18O62).nH2O/SiO2 were presented in Figure 4. Figure 4A 
shows the diffraction of (NH4)6 (β-P2W18O62) .nH2O that appear 
at 2θ area under 10º indicates that the compound 
polioksometalate (NH4)6(β-P2W18O62).nH2O possess extremely 

high crystallinity due atoms (NH4)6(β-P2W18O62).nH2O regularly 
by Length and angle of bond formed. Figure 4B shows the XRD 
pattern of compound (NH4)6(β-P2W18O62).nH2O/SiO2. The 
compound (NH4)6(β-P2W18O62).nH2O/SiO2 has a high 
crystallinity by the diffraction angle 2θ 8°, 18°, 27° and 34°, 
respectively which shows the characteristics of the compound 
polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2 where atoms 
polyoxometalate compound (NH4)6(β-P2W18O62).nH2O/SiO2 
arranged regularly based on the length and angle of a regular 
bond. In Figure 4B shows the XRD pattern of (NH4)6(β-
P2W18O62).nH2O/SiO2  indicates the diffraction angle changes  

. 

Acidity Test Of The compound (NH4)6(β-P2W18O62).nH2O  
and (NH4)6[β-P2W18O62].nH2O/SiO2  Quantitatively 

Acidity Test Of CThe compound (NH4)6(β-
P2W18O62).nH2O  Qualitatively 

Measurement of acidity in polyoxometalate compound 
(NH4)6(β-P2W18O62).nH2O done both qualitatively and 
quantitatively. Qualitatively, FT-IR spectrophotometer was used 
in which polyoxometalate (NH4)6(β-P2W18O62).nH2O was 
saturated with ammonia and with pyridine for one day resulting 
in adsorption on the surface of the compound adsorpsi 
(NH4)6(β-P2W18O62).nH2O. The saturation result is then 
compared before or after being saturated with ammonia or 
pyridine. The spectra of FT-IR compound (NH4)6(β-
P2W18O62).nH2O of saturation result is presented in Figure 5. 

 

 
Figure 5. FTIR spectrum of (NH4)6(β-P2W18O62).nH2O 
saturated with pyridine (A), (NH4)6(β-P2W18O62).nH2O 

saturated with ammonia (B), (NH4)6(β-P2W18O62).nH2O before 
saturated (C) 

FT-IR spectrum in Figure 5A and B did not find any 
absorption band at wave number 1400-1440 cm-1 on 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 5 

polyoxometalate (NH4)6(β-P2W18O62).nH2O. According to 
Dines et al, (1991) ammonia forms ammonium ions (NH4+) with 
the observed wave numbers being at 1400-1440 cm-1. In 
polyoxometalate compound (NH4)6(β-P2W18O62).nH2O 
saturated with ammonia and pyridine does not show the 
ammonium ion vibration (NH4+) in the 1400-1440 cm-1 wave 
numbers range. Ammonia can be adsorbed on the acid side of 
the heteropoly compound as well as on the metal cations which 
in this study is not observed as Figure 5A and 5B. 

 

Acidity Test Of Compound (NH4)6(β-P2W18O62).nH2O/ 
SiO2 Qualitatively   

The compound (NH4)6(β-P2W18O62).nH2O/SiO2 is 
saturated using ammonia and pyridine just as with section 3.3.1. 
Then the polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2 was 
characterized using a FT-IR spectrophotometer. The saturated 
FT-IR (NH4)6(β-P2W18O62).nH2O/SiO2 spectrum is presented 
in Figure 6. Figure 6A shows the spectrum of FT-IR 
polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2  before it is 
saturated. Figure 6B shows the FT-IR spectrum of 
polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2 saturated 
with pyridine. Dines et al, (1991) states that ammonia forms an 
ammonium ion (NH4+) with an observed wave number at 1400-
1440 cm-1. Seo et al (1988) states that ammonia can be adsorbed 
on the acid side of the heteropoly compound as well as on the 
metal cation. The compound (NH4)6 (β-P2W18O62) .nH2O / 
SiO2 exhibits the ammonium ion vibration (NH4)6(β-
P2W18O62).nH2O/SiO2 the saturation result is shown in the 
Figure 6. 

Polyoxometalate compound  (NH4)6(β-P2W18O62).nH2O/ 
SiO2 saturated ammonia does not exhibit absorption bands at 
1400-1440 cm-1 wave numbers. In this case it is possible that the 
ammonia is not adsorbed on the polyoxometalate (NH4)6(β-
P2W18O62).nH2O/SiO2. Khalifah and Prasetyoko (2008) explain 
that pyridine molecules bound to Lewis acid sites are absorbed 
over the 1400-1700 cm-1 wave range. Figure 6C shows that the 
pyridine molecule has been adsorbed by the polyoxometalate 
(NH4)6(β-P2W18O62).nH2O/SiO2 compound shown in the wave 
number 1481.33 cm-1. This shows the polyoxometalate 
compound (NH4)6(β-P2W18O62).nH2O/SiO2  having Lewis acid 
properties. 

 

Acidity Test of the Compound  (NH4)6(β-
P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/SiO2  
Quantitatively 

Potentiometric titration method is an analytical technique 
based on the potential measurement of a sensor or electrode. 
The electrodes used are glass-containing glassy electrode, the 
liquid having the potential difference properties between the 
membrane and the electrolyte in contact with the membrane is 
determined by the activity of the particular ion. The membrane 
electrode used is a glass electrode. These glass electrodes are said 
to be ion-selective because they are specific to H+  ions only. 

The acidity measurements of  

(NH4)6(β-P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O 
/SiO2 were carried out quantitatively by measurement using 
potentiometric titration with n-butylamine as titrant and 
acetonitrile as solvent. Acetonitrile is an aprotic solvent as a 
solvent in compound (NH4)6(β-P2W18O62).nH2O and  (NH4)6(β-
P2W18O62).nH2O/SiO2 so measurable only acidity (NH4)6(β-

P2W18O62).nH2O and (NH4)6(β-P2W18O62).nH2O/SiO2. Accor-
ding to Pecchi et al (1985) the use of benzene, acetonitrile, and 
iso-octane solvents as solvents in potentiometric titration as a 
polar solvent to avoid the occurrence of acid or proton 
adsorption of n-butylamine and acetonitrile as an inert solvent. 
The measurement by potentiometric method can determine the 
total acidity and acidity side of a polyoxometalic compound. The 
initial potential value (Ei) identifies acidity strength from the 
surface side and classifies the acidity strength based on the span 
divided into scales: Ei> 100 mV (acid side is very strong), 0 <Ei 
<100 mV (strong acid side), -100 <Ei <0 mV (weak acid side), 
Ei <-100 mV (acid side is very weak) (Romanelli et al, 2004). 

 

 
Figure 6. FTIR spectrum of (NH4)6(β-P2W18O62).nH2O/SiO2 
saturated with pyridine (A), (NH4)6(β-P2W18O62).nH2O/SiO2. 
saturated with ammonia (B), (NH4)6(β-P2W18O62).nH2O/SiO2 

before saturated (C) 

 

The first and second derivative curves are made to see where 
the titration equivalent point is shown in Figures 7B and 7C. 
Equivalent point is performed to see the condition where the 
base of n-butylamine is added precisely reacts with the 
compound (NH4)6(β-P2W18O62).nH2O being titrated. In 
addition, an equivalence point is performed to determine the 
amount of base volume of n-butylamine needed to neutralize the 
(NH4)6(β-P2W18O62).nH2O/SiO2 compound which is consi-
dered to be acidic. Figure 7A shows the result of measurement 
of compound (NH4)6(β-P2W18O62).nH2O has an initial potential 
value of 61.96 mV. Based on the potential value range 0 <Ei 
<100 polyoxometalate (NH4)6(β-P2W18O62).nH2O has a strong 
acid side. The titration equivalent point is at 0.8 mL of n-



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 6 

butylamine volume reinforced by the first derivative curve and 
the second derivative of potentiometric titration data. The 
titration equivalent point can be observed with sharp potential 
changes (Mulja and Suharman, 1995). Figures 7B and 7C show 
the first derivative curves and the second derivative curves of 
the polyoxometalate  (NH4)6(β-P2W18O62).nH2O. 

 

 
Figure  7. Titration curves of polyoxometalate compound of 
(NH4)6(β-P2W18O62).nH2O (A), Titration curve first derivate 

(B), Titration curve second derivate (C) 

 

The measurement of the acidity of the polyoxometalate 
(NH4)6(β-P2W18O62).nH2O/SiO2 quantitatively is also carried 
out through potentiometric titration. From the titration curve 
presented in Figure 7, the titration equivalent point is obtained 
when the titration volume is 0.8 mL n-butylamine. Based on 
equivalence point data, it is found that polyoxometalate 
(NH4)6(β-P2W18O62).nH2O/SiO2 compounds require more n-
butylamine base volume to neutralize the polyoxometalate 
compound (NH4)6(β-P2W18O62).nH2O/SiO2. This indicates that 
(NH4)6(β-P2W18O62).nH2O/SiO2  is more acidic than the 
polyoxometalate compound  (NH4)6(β-P2W18O62).nH2O. This is 
also supported by looking at the potential initial value 
comparison. The initial potential value of polyoxometalate 
compound (NH4)6(β-P2W18O62).nH2O/SiO2  is 76.16 mV 
whereas the initial potential value of polyoxometalate (NH4)6(β-
P2W18O62).nH2O amount 61,96 mV. The compound  (NH4)6(β-
P2W18O62).nH2O/SiO2 is included in the acid classification 
having a strong acid side based on the potential acid strength 
value range. Increasing the safety of the polyoxometalate 
(NH4)6(β-P2W18O62).nH2O/SiO2 compound due to the 
compound (NH4)6(β-P2W18O62).nH2O  interacts with the carrier 
SiO2 derived from tetraethyl orthosilicate. The titration curve of 
potentiometric compound (NH4)6(β-P2W18O62).nH2O/SiO2  
can be seen in Figure 8. 

  

 
 

Figure 8.  Titration curves of polyoxometalate compound of 
(NH4)6(β-P2W18O62).nH2O/SiO2  (A), Titration curve first 

derivate (B), Titration curve second derivate (C) 

 

The Effect of Temperature on the Stability of the 
Compound (NH4)6(β-P2W18O62).nH2O/SiO2. 

The compound (NH4)6(β-P2W18O62).nH2O/SiO2 was 
heated at various temperatures to see the effect of temperature 
on the stability of the compound (NH4)6(β-
P2W18O62).nH2O/SiO2. The heating results of the compound  
(NH4)6(β-P2W18O62).nH2O/SiO2 at various temperatures were 
characterized by an FT-IR spectrophotometer. Figure 9 shows 
the spectrum of FT-IR polyoxometalate compound (NH4)6(β-
P2W18O62).nH2O/SiO2 without heating and heated at various 
temperatures from 200-600°C.   

In Figure 9 shows the difference shown by FT-IR spectrum 
of polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2 before and 
after heated at the temperature range 200-600ºC. Based on the 
FT-IR spectrum of compound (NH4)6(β-P2W18O62).nH2O/ 
SiO2 which is warmed up the vibrations appear to have shifted 
wavenumbers. 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 7 

 
Figure  9. FTIR spectrum of of (NH4)6(β-

P2W18O62).nH2O/SiO2 at various temperatures (A) 600ºC, (B) 
500ºC, (C) 400ºC, (D) 300ºC, (E) 200ºC, (F) (NH4)6(β-

P2W18O62).nH2O/SiO2 before heated. 

 

Figure 9 shows the presence of -OH groups in the presence of 
H2O observed in the range of 3400-3500 cm-1. Vibration of 

polyoxometalate compound (NH4)6(β-P2W18O62). nH2O/SiO2 
in the wavenumber 800-1000 cm-1 at 600ºC indicates a 
difference caused by vibration W = O, W-Oe-W vibration and 
vibration W- Oc-W has been lost. This indicates that on the 
increase of temperature on heating can cause structure change 
of polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2.  At a 
temperature of 200ºC shows little difference due to vibration W 
= O that overlap with vibration W-Oe-W and W-Oc-W, 
whereas with temperature 300ºC vibration W = O and W-Oe-
W was disappeared. This indicates an increase in the heating 
temperature which may cause changes in the structure of the 
polyoxometalate (NH4)6(β-P2W18O62).nH2O/SiO2.  

 

CONCLUSION  
Polyoxometalate compound (NH4)6(β-P2W18O62).nH2O  

and (NH4)6(β-P2W18O62).nH2O/SiO2 has been succesfuly 
prepared which is characterized by the vibration of the 
polyoxometalate group as results of the characterization of the 
FT-IR spectrofotometer. Vibration of the polyoxometalate 
compound (NH4)6(β-P2W18O62).nH2O shows the presence of 
vibration  W=O appear on the area  964.41 cm-1, W-Oc-W 
appear on the area 786.96 cm-1, W-Oe-W appear on the area  
918.12 cm-1, P-O appear on the area 1087.85 cm-1, and 
polyoxometalate compound    (NH4)6(β-P2W18O62).nH2O/SiO2   
shows the presence of vibration W=O appear on the area 
1049.28 cm-1, W-Oc-W appear on the area 794.67 cm-1, W-Oe-
W appear on the area  918.12 cm-1, P-O appear on the area 
1087.85 cm-1,O-H appear on the area 3464.15 cm-1, Si-O appear 
on the area 470 cm-1. XRD diffraction patterns show 
polyoxometalate compound (NH4)6(β-P2W18O62).nH2O and 
(NH4)6(β-P2W18O62).nH2O/SiO2  has a high crystallinity with an 
angle of diffraction 2θ each of them 8°-34°.  Compound 
(NH4)6(β-P2W18O62).nH2O/SiO2 has high acidity compared 
with the compound (NH4)6(β-P2W18O62).nH2O acidity test 
quantitatively. The impact temperature on the stability of the 
compound (NH4)6(β-P2W18O62).nH2O/SiO2 shows of the 
temperature 600ºC there is a shift of compound wavenumbers 
(NH4)6(β-P2W18O62).nH2O/SiO2. 

 

REFERENCES 
Contant, R., Abbessi, M., Thouvenot, R., Herve., 2004, 

Syntheses and 31P, 51V,and 183W NMR Structural 
Investigation of Octadeca (molybdo−tungsto−vanado) 
diphosphates Related to the [H2P2W12O48]12- Anion. Inorganic 
Chemistry, 43, 3597. 

Dines, T. J., Colin H. R., and Andrew M. W., 1991. Infrared and 
Raman Study of the Adsorption of NH3, Pyridine, NO and 
NO2 on Anatase. Journal Chemical Society, 87, 643-651. 

Fatimah, I, 2009, Peningkatan Aktivitas Katalitik TiO2 dan ZrO2 
melalui Pengembanan pada Matriks Al2O3-Montmorillonit. 
Laporan Akhir Kegiatan Hibah Penelitian untuk Mahasiswa 
Program Doktor, UGM. 

Finke, R.G, Droege, M.W, Domaille, P.J, 1987, Trivacant 
Heropoly tungstate Deviratives. 3.1. Rational Syntheses, 
Characterization, Two-Dimentional183W NMR, and 
Properties of P2W18M4(H20)2O6210- and 
P2W30M4(H20)2O11216- (M= Co, Cu, Zn), Inorganic Chemistry, 
26,3886-3896.. 

Khalifah, S.N., and Prasetyoko, D, 2008, Sintesis dan Karakterisasi 
ZSM-5 Mesoporous Dengan Variasi Rasio SiO2/Al2O3. Surabaya 



Tambunan et al. / Science and Technology Indonesia 2(1) 2017:1-8 

@2017 Published under the terms of the CC BY NC SA 4.0 license 8 

: Jurusan Kimia Fakultas MIPA Institut Teknologi Sepuluh 
Nopember 

Kim. H. J, Shul. Y. G, and Han. H, 2006, Synthesis of 
Heteropolyacid (H3PW12O40)/SiO2 Nanoparticles and Their 
Catalytic Properties, Applied Catal. A: General, 299, 46-51. 

Kozhevnikov, I., Robert, M R., Derouane, E, 2002, Catalyst for 
Chemical Synthesis, Vol. 2: Catalysis by Polyoxometalates. John 
Willey & Sons: Liverpool. 

Mulja, Muhammad & Suharman, 1995, Analisis Instrumental. 
Airlangga University Press, Surabaya. 

Newman, A., Brown D R., Siril, P., Lee, AF.,Wilsom, K, 2006, 
Structural Studies of High Dispersion (H3PW12O40)/SiO2 
Solid Acid Catalyst Physical Chemistry. Chemical Physics, pp 8, 
2893-2902. 

Okuhara.T.; Mizuno. N.; Misono. M, 1996, Advances in 
Catalysis Vol 41: Catalytic Chemistry of Heteropoly Compounds. 
113-252.  

Pecchi, G and Ruby Cid., 1983. Potentiometric Method for 
Determining The Number and Relative Strength of Acid Site 
in Colored Catalysts. Applied Catalysis, 14 : 15-21 

Reddy, K. M, N. Lingaiah, P. S Sai Prasad, and I. Suryanarayana., 
2006, Acidity Constants of Supported Salts of Heteropoly 
Acids Using a Methodology Related to the Potentiometric 
Mass Titration Technique. Journal of Solution Chemistry, 35, 3. 

Romanelli, G., P. Vázquez., L. Pizzio., N. Quaranta., J. Autino., 
M. Blanco., C. Cáceres., 2004, Phenol 
Tetrahydropyranylation Catalyzed by SilicaAlumina 
Supported Heteropolyacids with Keggin Structure. Applied 
Catalysis , 261, 163-170. 

Sari M A, Y., & Situngkir, M. (2017). Synthesis, Characterization, 
and Thermal Stability of K8[SiW11O39]nH2O/SiO2. 
Science & Technology Indonesia, 1(1), 8-15. 

Seo, Gon., Jeong Woo Lim., Jong Taik Kim., 1988, Infrared 
Study on the Adsorbed State of Ammonia on Heteropoly 
Compounds. Journal of Catalysis, 114, 469-472. 

Smith, B. 1999. Infrared Spectral Interpretation : A sytematic 
Approach . CRC Press, New York. 

Yamase, T.;Pope, M. T. Eds, 2002, Polyoxometalate Chemistry For 
Nano-Composite Design; Kluwer: Dordrecht. The Netherlands. 

Yang, Shuijin. Yongkui Huang., and Li Yu, 2011, Catalytic 
Application of H4SiW12O40/SiO2 in Synthesis of Acetals and 
Ketals. Advanced Materials Research, 284-286, 2374-237