Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydrothermal
and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types
of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on contrary,
breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface
area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples
show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, initial
and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the
same dye.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3515

Khalameida, S.

Leboda, R.

Skubiszewska-Zieba, J.

Sydorchuk, V.

Zazhigalov, V.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 2, 02PCN15(4pp) (2013) 
 
 
2304-1862/2013/2(2)02PCN15(4) 02PCN15-1  2013 Sumy State University 
Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and 
its Catalytic Properties 
 
S. Khalameida1,*, V. Sydorchuk1, J. Skubiszewska-Ziéba2, R. Leboda2, V. Zazhigalov1 
 
1 Institute of Sorption and Problems of Endoecology National Academy of Science of Ukraine, 13, Naumov Str., 
03164, Kyiv, Ukraine 
2 Faculty of Chemistry, Maria Curie-Sklodowska, 3, pl. Marie Curie-Sklodowska, 20031, Lublin, Poland  
 
(Received 28 May 2013; published online 31 August 2013) 
 
Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydro-
thermal and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types 
of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on con-
trary, breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface 
area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples 
show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, ini-
tial and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the 
same dye. 
 
Keywords: Nb2O5, Mechanochemical, Sonochemichal, Hydrothermal activation, Rhomanin B destruction. 
 
 PACS number: 42.70.Qs 
 
 
1. INTRODUCTION 
 
Niobium pentoxide Nb2O5 as typical semiconductor 
with a high band gap [1] has attracted great research 
interest due to its remarkable applications in gas sen-
sors, optical devices, and Li-ion batteries [2]. Besides, it 
is used as oxide, acid and photocatalyst [2, 3]. There-
fore, Nb2O5 is versatile material. The influence of syn-
thesis conditions on its physical-chemical characteris-
tics is well studied. The application of non-conventional 
techniques for regulation properties of commercial nio-
bium pentoxide powders is the aim of this work.  
 
2. EXPERIMENTAL 
 
2.1 Activation of Niobium Pentoxide 
 
Sintered ceramic and three powders with different 
specific surface area S (dispersity) and phase composi-
tion were subjected to various types of modification: 
mechanochemical, hydrothermal, microwave and ultra-
sound treatments (MChT, HTT, MWT and UST, re-
spectively). MChT (milling) was carried out in Pulver-
isette 6 planetary ball mill (Fritsch Gmbh) in air, etha-
nol and water at rotation speed of 300-850 rpm. HTT 
was performed using steel autoclaves with volume of 
45 ml at 200 C and the autogeneous pressure for 5 h. 
“NANO 2000” high-pressure reactor (Plazmatronika, 
Poland) with power of 650 W was used for MWT. In the 
latter case, treatment temperature and pressure were 
200 C and 4.5 MPa. UST was carried out in open reac-
tor using UZDN ultrasonic disperser (Selmi, Ukraine) 
under frequency 20 KHz and 80 С for 1. 
 
2.2 Physical-chemical Characterizations 
 
The starting reagents and products of their trans-
formations were studied by means of X-ray powder dif-
fraction (XRD) using Philips PW 1830 diffractometer 
with CuKα-radiation. The primary crystallites size Dhkl 
was calculated using the broadening of the most inten-
sive lines according to Sherrer’s equation. Diffuse re-
flectance UV-Vis spectra of powders were registered on 
Lambda 35 UV-Vis spectrometer (Labsphere RSA-PE-
20 diffuse reflectance and transmittance accessory, 
Perkin-Elmer Instruments). BaSO4 was used as a ref-
erence. All spectra are presented in coordinates of Ku-
belka-Munk equation. Parameters of porous structure 
(specific surface area S, mesopores volume Vme) were 
determined from isotherms of nitrogen adsorption-
desorption obtained with the help of ASAP 2405N ana-
lyzer (“Micromeritics Instrument Corp”). Outgassing 
temperature and duration before taking of measure-
ments were 150 C and 2 h, respectively.  
 
2.3 Photocatalytic Activity 
 
The testing of photocatalytic activity was carried 
out using degradation of textile dye rhodamine B (Rh 
B) in aqueous medium (0.5·10 – 5 mol L – 1 solution). This 
reaction was performed in glass reactor with magnetic 
stirrer. The illumination was realized using high-
intensity discharge Na lamp GE Lucalox (Hungary) 
with power 70 W which irradiates solely in visible re-
gion. The ratio catalyst / dye solution was 
100 mg / 150 ml. The initial solution and that after dye 
degradation was analyzed spectrophotometrically at 
max  555 nm (Lambda 35, PerkinElmer Instruments) 
after centrifugation of reaction mixture (10 min at 
8000 rpm). The calculation of photodegradation rate 
constants Kd was based on the concentration change of 
the solution after establishment of adsorp-
tion / desorption equilibrium. 
 
3. RESULTS AND DISCUSSION 
 
3.1. Modification of Low-dispersed Nb2O5 
 
Diffractograms of initial and modified Nb2O5 with 
S  2 m2g – 1 which is orthorhombic phase (JCPDS N 
30-873) are depicted on Fig. 1. One can see that its 
phase composition does not changed as a result of 
 S.KHALAMEIDA, V. SYDORCHUK, J. SKUBISZEWSKA-ZIEBA, ET AL. PROC. NAP 2, 02PCN15 (2013) 
 
 
02PCN15-2 
MChT during 1 h in different media (ethanol, water, 
air) and UST in water. However, intensity of reflexes 
Ihkl decreases and their width, on contrary, increases.  
 
 
 
Fig. 1 – XRD patterns for low-dispersed Nb2O5: initial (a), 
after UST 1 h (b), MChT at 600 rpm 1 h in ethanol (c), water 
(d) and air (f) 
 
Thus, I001 (2Θ  22.72º) reduces in 1.5-1.8 times (max-
imum after dry milling). Crystallites size D001 also de-
creases: from 28.7 to 19.8-24.3 nm (Table, column 7). At 
the same time, UST of this sample for 1 h does not cause 
any changes in crystal structure (Fig. 1, curve b) which 
can be explained by small intensity of UST. UV-Vis spec-
tra for samples milled on air also do not show considerable 
alteration in structure: main band is centered about 310-
325 nm and absorption edge  – at 380-380 nm (band gap 
Eg ~ 3.25 eV) which is agreed with literature data [4]. 
Samples prepared via MChT in water reveal certain bath-
ochromic shift of  to 393 nm which corresponds to values 
of Eg  3.15 eV as in [5], for example.  
The particles of low-dispersed Nb2O5 powder are 
practically non-porous which can be seen from calcula-
tions based on adsorption data. MChT and UST (first of 
all, short-time) promote increasing in specific surface 
area. At MChT, it is obviously caused by de-
aggregation of polycrystalline particles and breaking of 
primary crystallite. The latter is confirmed by calcula-
tions based on XRD data indicated above. Only first 
process takes place during UST since D001 value does 
not changed. Besides, pore volume increases as result 
of all types of modification which is associated with 
formation of phase contact between crystallites. 
 
3.2. Modification of high-dispersed Nb2O5 
 
 High-dispersed Nb2O5 (S  355 m2·g – 1) is X-ray 
amorphous. Their modification results in improvement 
of crystal structure, namely, formation of orthorhombic 
phase (Fig. 2). It takes place under severe hydrother-
mal conditions: milling in water at 850 rpm or MWT at 
200 ºС. Value of D001 equals 23.5 and 22.7 nm, respec-
tively. 
 
 
Fig. 2 – XRD patterns for high-dispersed Nb2O5: initial (a), after 
MChT at 850 rpm in water (b), MWT at 200 °C in water (c) 
 
As can be seen on Fig. 3, UV-Vis spectrum for high-
dispersed sample contain band at 275 nm while that for 
low-dispersed – at 319 nm (Fig. 3). This discrepancy 
can be explained by different dispersity and crystal 
structure of both Nb2O5. UST of high-dispersed samples 
also leads hypsochromic shift of absorption edge i.e.  
 
Table 1 – Porous structure parameters of Nb2O5  
 
N Treatment conditions S, m2·g – 1 Vs, cm3·g – 1 VΣ, cm3·g-1 Vme, cm3·g – 1 Ds, nm D001, nm 
1 2 3 4 5 6 7 8 
1 Initial low-dispersed 2.0 0.005 – 0.005 650 28.7 
2 MChT air 300 rpm 2.8 0.01 – 0.01 470 24.3 
3 MChT air 600 rpm 4.9 0.01 0.11 0.01 270 22.4 
4 MChT water 600 rpm 6.0 0.02 0.15 0.02 220 19.8 
5 MChT ethanol 600 rpm 3.0 0.01 0.05 0.01 445 21.9 
6 UST 0.5 h 4.4 0.04 0.10 0.04 300 28.0 
7 UST 1 h 2.8 0.03 0.06 0.03 470 29.2 
8 HTT 200 ºС 1.8 0.02 0.02 0.02 725 32.3 
9 Initial high-dispersed 355 0.29 0.30 0.12 4.0 – 
10 MChT air 600 rpm 46 0.02 0.05 0.02 31 – 
11 MChT air 850 rpm 14 0.06 0.07 0.06 100 – 
12 MChT water 850 rpm 8.0 0.02 0.80 0.02 175 22.4 
13 MWT 200 °C 55 0.07 0.48 0.07 24 25.1 
14 UST 0.5 h 321 0.30 0.31 0.14 4.5 – 
15 UST 1 h 333 0.32 0.32 0.17 4.5 – 
16 HTT 200 °C 144 0.39 0.41 0.36 9.0 10.3 
 
 MECHANOCHEMICAL, SONOCHEMICAL AND HYDROTHERMAL ACTIVATION… PROC. NAP 2, 02PCN15 (2013) 
 
 
02PCN15-3 
 
 
Fig. 3 – UV-Vis spectrum for high-dispersed Nb2O5: 
amorphous phase (a), the same after UST 1 h (b), 
orthorhombic phase after UST 1 h (c)  
 
narrowing of band gap. Although high-dispersed 
sample is powder (free-dispersed state), its particles, 
are micro-mesoporous (Table). Modification of this 
sample, using all kinds of treatment, causes reduction 
of specific surface area which is maximal as a result of 
MChT and MWT. Modification in water promotes 
formation of porous framework through consolidation of 
particles. There is secondary porosity represented by 
macropores (total pore volume VΣ  sorption pore 
volume Vs), as a result. Thus, value of macropores 
volume equals 0.32 cm3·g – 1 or 80 % of total pore 
volume VΣ for sample modified via MWT. 
 
3.3. Photocatalytic Activity 
 
Nb2O5 samples subjected to MChT and UST show 
higher absorption of visible light which is main reason of 
their photocatalytic activity (rate constant of Rh B degra-
dation Kd) in this region. Clear relationship has been es-
tablished: the values of specific surface area S and absorp-
tion in visible range is higher, the Kd magnitude is more. 
For example, kinetic curves of Rh B degradation 
under visible irradiation in the presence of different 
modified samples are depicted on Fig. 4. Noteworthy 
that niobium pentoxide contributes to the rapid (during 
10 min) deethylation of rhodamine B to rhodamine 110 
(shift of band 555 towards 498-500 nm) and following 
decrease of intensity of this band (Fig. 5). 
 
 
 
Fig. 4 – Kinetic curves for low-dispersed Nb2O5 after MChT in 
air at 300 rpm (1), 600 rpm (2), HTT at 200 °C (3), UST 1 h (4) 
 
 
Fig. 5 – UV-Vis spectral changes of Rhodamin B aqueous solu-
tion in the presence of high-dispersed Nb2O5 after visible irradi-
ation  
 
The latter indicated destruction of chromophore 
ring in dye molecule. Value of Kd for this process, calcu-
lated using intensity of band 500 nm, equals 3.28·10 – 4 
and 4.22·10 – 4 s – 1 under UV- and visible irradiation, 
respectively. It is known that using of TiO2 photocata-
lyst leads to slower stepwise diethylation of Rh B [6].  
Five samples of Nb2O5 (with S  0.1, 2, 3, 355 and 
474 m2·g – 1) were studied for mechanocatalytic degra-
dation of RhB in aqueous solutions. It has been estab-
lished the same antibate dependence between values of 
Kd and S for initial catalyst as for the titania samples 
[7]. The obtained relationship can be satisfactorily ap-
proximated by two nearly straight segments that are 
intersected, i.e. broken line (Fig. 6). 
 
 
 
Fig. 6 – Dependence between the values of the rate constant 
of degradation and specific surface area of the catalyst 
 
Therefore, Kd magnitude is maximal for the most 
low-dispersed sample (1.4∙10 – 3 s – 1). On the contrary, 
value of Kd steadily increases within 1.1∙10 – 4- 
1.1∙10 – 3 s – 1 when specific surface area of Nb2O5 cata-
lyst rises from 2 to 355 m2·g – 1 under ultrasound deg-
radation of Rh B. 
 
4. CONCLUSION 
 
Modification of low-dispersed Nb2O5 via mecha-
nochemical and sonochemical treatments causes par-
tial destruction of its crystal structure and increase 
of dispersity (specific surface area). Porous network 
is formed in aqueous medium. On contrary, crystal 
structure of high-dispersed Nb2O5 is improved as 
results of all types of modification. All modified sam-
 S.KHALAMEIDA, V. SYDORCHUK, J. SKUBISZEWSKA-ZIEBA, ET AL. PROC. NAP 2, 02PCN15 (2013) 
 
 
02PCN15-4 
ples show higher absorption of visible light. Increase 
of photo-, mechano-, and sonocatalytic activity of 
modified Nb2O5 in process of rhodamine B degrada-
tion takes place. 
 
AKNOWLEDGEMENTS. 
 
This work was supported by the State Science 
Technology Program “Nanotechnology and nano-
materials” Project No 6.22.1.9. 
 
REFERENCES 
 
1. K. Hara, T. Horiguchi, T. Kinoshita, et al., Sol. Energ. 
Mater. Sol. C. 64, 115 (2000). 
2. A.M. Aegerter, Sol. Energ. Mater. Sol. C 68, 401 (2001). 
3. K. Tanabe, Catal. Today 78, 65 (2003). 
4.  F. Dolci, M. Di Chio, M. Baricco, E. Giamello, J. Mater. 
Sci. 42, 7180 (2007). 
5. B. Zielinska, E. Borowiak-Palen, R.J. Kalenzuk, J. Phys. 
Chem. Solids 69, 236 (2008). 
6. P. Wilhelm, D. Stephan, J. Photochem. Photobiol. A. 185, 
19 (2007). 
7. S. Khalameida, V. Sydorchuk, V. Zazhigalov, Chem. Phys. 
Technol. Surf. 2, 253 (2011). [in Ukrainian]. 
 


English

Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 2, 02PCN15(4pp) (2013)   2304-1862/2013/2(2)02PCN15(4) 02PCN15-1  2013 Sumy State University Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties  S. Khalameida1,*, V. Sydorchuk1, J. Skubiszewska-Ziéba2, R. Leboda2, V. Zazhigalov1  1 Institute of Sorption and Problems of Endoecology National Academy of Science of Ukraine, 13, Naumov Str., 03164, Kyiv, Ukraine 2 Faculty of Chemistry, Maria Curie-Sklodowska, 3, pl. Marie Curie-Sklodowska, 20031, Lublin, Poland   (Received 28 May 2013; published online 31 August 2013)  Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydro-thermal and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on con-trary, breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, ini-tial and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the same dye.  Keywords: Nb2O5, Mechanochemical, Sonochemichal, Hydrothermal activation, Rhomanin B destruction.   PACS number: 42.70.Qs   1. INTRODUCTION  Niobium pentoxide Nb2O5 as typical semiconductor with a high band gap [1] has attracted great research interest due to its remarkable applications in gas sen-sors, optical devices, and Li-ion batteries [2]. Besides, it is used as oxide, acid and photocatalyst [2, 3]. There-fore, Nb2O5 is versatile material. The influence of syn-thesis conditions on its physical-chemical characteris-tics is well studied. The application of non-conventional techniques for regulation properties of commercial nio-bium pentoxide powders is the aim of this work.   2. EXPERIMENTAL  2.1 Activation of Niobium Pentoxide  Sintered ceramic and three powders with different specific surface area S (dispersity) and phase composi-tion were subjected to various types of modification: mechanochemical, hydrothermal, microwave and ultra-sound treatments (MChT, HTT, MWT and UST, re-spectively). MChT (milling) was carried out in Pulver-isette 6 planetary ball mill (Fritsch Gmbh) in air, etha-nol and water at rotation speed of 300-850 rpm. HTT was performed using steel autoclaves with volume of 45 ml at 200 C and the autogeneous pressure for 5 h. “NANO 2000” high-pressure reactor (Plazmatronika, Poland) with power of 650 W was used for MWT. In the latter case, treatment temperature and pressure were 200 C and 4.5 MPa. UST was carried out in open reac-tor using UZDN ultrasonic disperser (Selmi, Ukraine) under frequency 20 KHz and 80 С for 1.  2.2 Physical-chemical Characterizations  The starting reagents and products of their trans-formations were studied by means of X-ray powder dif-fraction (XRD) using Philips PW 1830 diffractometer with CuKα-radiation. The primary crystallites size Dhkl was calculated using the broadening of the most inten-sive lines according to Sherrer’s equation. Diffuse re-flectance UV-Vis spectra of powders were registered on Lambda 35 UV-Vis spectrometer (Labsphere RSA-PE-20 diffuse reflectance and transmittance accessory, Perkin-Elmer Instruments). BaSO4 was used as a ref-erence. All spectra are presented in coordinates of Ku-belka-Munk equation. Parameters of porous structure (specific surface area S, mesopores volume Vme) were determined from isotherms of nitrogen adsorption-desorption obtained with the help of ASAP 2405N ana-lyzer (“Micromeritics Instrument Corp”). Outgassing temperature and duration before taking of measure-ments were 150 C and 2 h, respectively.   2.3 Photocatalytic Activity  The testing of photocatalytic activity was carried out using degradation of textile dye rhodamine B (Rh B) in aqueous medium (0.5·10 – 5 mol L – 1 solution). This reaction was performed in glass reactor with magnetic stirrer. The illumination was realized using high-intensity discharge Na lamp GE Lucalox (Hungary) with power 70 W which irradiates solely in visible re-gion. The ratio catalyst / dye solution was 100 mg / 150 ml. The initial solution and that after dye degradation was analyzed spectrophotometrically at max  555 nm (Lambda 35, PerkinElmer Instruments) after centrifugation of reaction mixture (10 min at 8000 rpm). The calculation of photodegradation rate constants Kd was based on the concentration change of the solution after establishment of adsorp-tion / desorption equilibrium.  3. RESULTS AND DISCUSSION  3.1. Modification of Low-dispersed Nb2O5  Diffractograms of initial and modified Nb2O5 with S  2 m2g – 1 which is orthorhombic phase (JCPDS N 30-873) are depicted on Fig. 1. One can see that its phase composition does not changed as a result of  S.KHALAMEIDA, V. SYDORCHUK, J. SKUBISZEWSKA-ZIEBA, ET AL. PROC. NAP 2, 02PCN15 (2013)   02PCN15-2 MChT during 1 h in different media (ethanol, water, air) and UST in water. However, intensity of reflexes Ihkl decreases and their width, on contrary, increases.     Fig. 1 – XRD patterns for low-dispersed Nb2O5: initial (a), after UST 1 h (b), MChT at 600 rpm 1 h in ethanol (c), water (d) and air (f)  Thus, I001 (2Θ  22.72º) reduces in 1.5-1.8 times (max-imum after dry milling). Crystallites size D001 also de-creases: from 28.7 to 19.8-24.3 nm (Table, column 7). At the same time, UST of this sample for 1 h does not cause any changes in crystal structure (Fig. 1, curve b) which can be explained by small intensity of UST. UV-Vis spec-tra for samples milled on air also do not show considerable alteration in structure: main band is centered about 310-325 nm and absorption edge  – at 380-380 nm (band gap Eg ~ 3.25 eV) which is agreed with literature data [4]. Samples prepared via MChT in water reveal certain bath-ochromic shift of  to 393 nm which corresponds to values of Eg  3.15 eV as in [5], for example.  The particles of low-dispersed Nb2O5 powder are practically non-porous which can be seen from calcula-tions based on adsorption data. MChT and UST (first of all, short-time) promote increasing in specific surface area. At MChT, it is obviously caused by de-aggregation of polycrystalline particles and breaking of primary crystallite. The latter is confirmed by calcula-tions based on XRD data indicated above. Only first process takes place during UST since D001 value does not changed. Besides, pore volume increases as result of all types of modification which is associated with formation of phase contact between crystallites.  3.2. Modification of high-dispersed Nb2O5   High-dispersed Nb2O5 (S  355 m2·g – 1) is X-ray amorphous. Their modification results in improvement of crystal structure, namely, formation of orthorhombic phase (Fig. 2). It takes place under severe hydrother-mal conditions: milling in water at 850 rpm or MWT at 200 ºС. Value of D001 equals 23.5 and 22.7 nm, respec-tively.   Fig. 2 – XRD patterns for high-dispersed Nb2O5: initial (a), after MChT at 850 rpm in water (b), MWT at 200 °C in water (c)  As can be seen on Fig. 3, UV-Vis spectrum for high-dispersed sample contain band at 275 nm while that for low-dispersed – at 319 nm (Fig. 3). This discrepancy can be explained by different dispersity and crystal structure of both Nb2O5. UST of high-dispersed samples also leads hypsochromic shift of absorption edge i.e.   Table 1 – Porous structure parameters of Nb2O5   N Treatment conditions S, m2·g – 1 Vs, cm3·g – 1 VΣ, cm3·g-1 Vme, cm3·g – 1 Ds, nm D001, nm 1 2 3 4 5 6 7 8 1 Initial low-dispersed 2.0 0.005 – 0.005 650 28.7 2 MChT air 300 rpm 2.8 0.01 – 0.01 470 24.3 3 MChT air 600 rpm 4.9 0.01 0.11 0.01 270 22.4 4 MChT water 600 rpm 6.0 0.02 0.15 0.02 220 19.8 5 MChT ethanol 600 rpm 3.0 0.01 0.05 0.01 445 21.9 6 UST 0.5 h 4.4 0.04 0.10 0.04 300 28.0 7 UST 1 h 2.8 0.03 0.06 0.03 470 29.2 8 HTT 200 ºС 1.8 0.02 0.02 0.02 725 32.3 9 Initial high-dispersed 355 0.29 0.30 0.12 4.0 – 10 MChT air 600 rpm 46 0.02 0.05 0.02 31 – 11 MChT air 850 rpm 14 0.06 0.07 0.06 100 – 12 MChT water 850 rpm 8.0 0.02 0.80 0.02 175 22.4 13 MWT 200 °C 55 0.07 0.48 0.07 24 25.1 14 UST 0.5 h 321 0.30 0.31 0.14 4.5 – 15 UST 1 h 333 0.32 0.32 0.17 4.5 – 16 HTT 200 °C 144 0.39 0.41 0.36 9.0 10.3   MECHANOCHEMICAL, SONOCHEMICAL AND HYDROTHERMAL ACTIVATION… PROC. NAP 2, 02PCN15 (2013)   02PCN15-3   Fig. 3 – UV-Vis spectrum for high-dispersed Nb2O5: amorphous phase (a), the same after UST 1 h (b), orthorhombic phase after UST 1 h (c)   narrowing of band gap. Although high-dispersed sample is powder (free-dispersed state), its particles, are micro-mesoporous (Table). Modification of this sample, using all kinds of treatment, causes reduction of specific surface area which is maximal as a result of MChT and MWT. Modification in water promotes formation of porous framework through consolidation of particles. There is secondary porosity represented by macropores (total pore volume VΣ  sorption pore volume Vs), as a result. Thus, value of macropores volume equals 0.32 cm3·g – 1 or 80 % of total pore volume VΣ for sample modified via MWT.  3.3. Photocatalytic Activity  Nb2O5 samples subjected to MChT and UST show higher absorption of visible light which is main reason of their photocatalytic activity (rate constant of Rh B degra-dation Kd) in this region. Clear relationship has been es-tablished: the values of specific surface area S and absorp-tion in visible range is higher, the Kd magnitude is more. For example, kinetic curves of Rh B degradation under visible irradiation in the presence of different modified samples are depicted on Fig. 4. Noteworthy that niobium pentoxide contributes to the rapid (during 10 min) deethylation of rhodamine B to rhodamine 110 (shift of band 555 towards 498-500 nm) and following decrease of intensity of this band (Fig. 5).    Fig. 4 – Kinetic curves for low-dispersed Nb2O5 after MChT in air at 300 rpm (1), 600 rpm (2), HTT at 200 °C (3), UST 1 h (4)   Fig. 5 – UV-Vis spectral changes of Rhodamin B aqueous solu-tion in the presence of high-dispersed Nb2O5 after visible irradi-ation   The latter indicated destruction of chromophore ring in dye molecule. Value of Kd for this process, calcu-lated using intensity of band 500 nm, equals 3.28·10 – 4 and 4.22·10 – 4 s – 1 under UV- and visible irradiation, respectively. It is known that using of TiO2 photocata-lyst leads to slower stepwise diethylation of Rh B [6].  Five samples of Nb2O5 (with S  0.1, 2, 3, 355 and 474 m2·g – 1) were studied for mechanocatalytic degra-dation of RhB in aqueous solutions. It has been estab-lished the same antibate dependence between values of Kd and S for initial catalyst as for the titania samples [7]. The obtained relationship can be satisfactorily ap-proximated by two nearly straight segments that are intersected, i.e. broken line (Fig. 6).    Fig. 6 – Dependence between the values of the rate constant of degradation and specific surface area of the catalyst  Therefore, Kd magnitude is maximal for the most low-dispersed sample (1.4∙10 – 3 s – 1). On the contrary, value of Kd steadily increases within 1.1∙10 – 4- 1.1∙10 – 3 s – 1 when specific surface area of Nb2O5 cata-lyst rises from 2 to 355 m2·g – 1 under ultrasound deg-radation of Rh B.  4. CONCLUSION  Modification of low-dispersed Nb2O5 via mecha-nochemical and sonochemical treatments causes par-tial destruction of its crystal structure and increase of dispersity (specific surface area). Porous network is formed in aqueous medium. On contrary, crystal structure of high-dispersed Nb2O5 is improved as results of all types of modification. All modified sam- S.KHALAMEIDA, V. SYDORCHUK, J. SKUBISZEWSKA-ZIEBA, ET AL. PROC. NAP 2, 02PCN15 (2013)   02PCN15-4 ples show higher absorption of visible light. Increase of photo-, mechano-, and sonocatalytic activity of modified Nb2O5 in process of rhodamine B degrada-tion takes place.  AKNOWLEDGEMENTS.  This work was supported by the State Science Technology Program “Nanotechnology and nano-materials” Project No 6.22.1.9.  REFERENCES  1. K. Hara, T. Horiguchi, T. Kinoshita, et al., Sol. Energ. Mater. Sol. C. 64, 115 (2000). 2. A.M. Aegerter, Sol. Energ. Mater. Sol. C 68, 401 (2001). 3. K. Tanabe, Catal. Today 78, 65 (2003). 4.  F. Dolci, M. Di Chio, M. Baricco, E. Giamello, J. Mater. Sci. 42, 7180 (2007). 5. B. Zielinska, E. Borowiak-Palen, R.J. Kalenzuk, J. Phys. Chem. Solids 69, 236 (2008). 6. P. Wilhelm, D. Stephan, J. Photochem. Photobiol. A. 185, 19 (2007). 7. S. Khalameida, V. Sydorchuk, V. Zazhigalov, Chem. Phys. Technol. Surf. 2, 253 (2011). [in Ukrainian].  

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Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties

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