One - Step Green Synthesis of V2O5 and VO2 Using Extract of Orange Peel: Effect of Calcination Atmosphere
Author(s) : Hanaa M. Abuzeid 1 , Aisha M. Moustafa 2 and Ahmed M Hashem 1
1 Department of Inorganic Chemistry , National Research Centre , Egypt
2 Department of Solid State Physics , National Research Centre , Egypt
Glob J Chem Sci
Article Type : Research Article
Figure
1: X-Ray diffraction patterns of vanadium oxides samples
prepared in (a) air, (b) vacuum at 450°C.
Property |
V2O5 |
||
x |
y |
z |
|
O1 4f |
0.1049 |
0.25 |
0.5322 |
O2 4f |
0.0718 |
0.25 |
-0.0012 |
O3 2a |
0.25 |
0.25 |
-0.0127 |
V 4f |
0.1008 |
0.25 |
0.8945 |
S.G. |
Pmmn |
||
a |
11.5114(1) |
||
b |
3.56327(4) |
||
c |
4.37510(4) |
||
?=?-? |
90 |
||
Volume |
179.459(3) Å3 |
||
Calculated Density |
3.36568 g/cm3 |
||
Microstrain |
0.4093(3) |
||
Crystallite size nm |
287(2) |
||
Rwp |
42.8 |
||
Rexp |
38.5 |
||
c2 |
1.235 |
||
(V – O1) |
1.58580(1) |
||
(V – O1) |
2.79040(3)Å |
||
(V – O2) |
2.03859(2) |
||
2 x (V – O2) |
1.87179(1) |
||
V-O3 |
1.76484(2) |
Table 1: Refined parameters of sample prepared in air at 450°C (V2O5). Goodness of fit index (c2)=(Rwp/Rexpected)2.
V2O5
crystallizes in primitive orthorhombic unit cell related to the space group Pmmn
no (59). The unit cell contains two formula units, the refined values of lattice
constants are a=11.5114(2) Å, b= 3.5633(1) Å and c = 4.3751(1) Å, that is in
assent with results of many authors [52, 53]. The orthorhombic distortion is
given by (a-b)/(a+b) was found to be 0.5272. The micro strain was found to
be=0.409(8), while the crystallite size = 287(1) nm as expected due to the high
intensity and sharp peaks as shown in (Figure
2).
Figure 2: Rietveld refinement profile fitting for the V2O5 sample prepared in air at 450°C.
In the crystal structure of Pmmn of V2O5, vanadium atom is a six-fold coordinated and forming octahedron with different oxygen atoms that have different types of bonding. The vanadium pentoxide is a layered compound, which bonded habitually by weak van der Waals (vdW) interactions. This weak interaction between V2O5 layers is easy to schism at the (001) plane [54, 55]. Moreover, vanadium atom has robustly correlated d electrons in its valence shell. (Figure 3a) shows a view along b axis of V2O5 Pmmn which composed of distorted VO6 octahedra structures. The vanadyl oxygen atom O1 (apical) and the VO6 octahedra linked from the brims by series of oxygen atoms (O2) and from the corners by bridging oxygen atoms (O3). The atomic positions and the crystal structure parameters are listed in table 1. (Figure 3b) shows the coordination polyhedral of O around which partake brinks to form tortuous double chains along [001] and are cross-linked along [100] through partake corners, thus forming slabs in the zz plane.
Figure 3a: A view along b axis of V2O5.
Figure
3b: A view along c axis of V2O5.
It is well known that, vanadium dioxide (VO2) exhibited the metal to insulator phase transition due to different phases with different crystal structures. So, the second sample heat treated under vacuum at 450°C contains different phases. (Figure 4) represents the Rietveld refinement fitting of the VO2 which has three phases as observed from the qualitative phase analysis. The obtained results of Rietveld refinement of VO2 are tabulated in (Table 2). From this table it is clear that c2 = 1.064 is close to unit which proves the quality of the refinement. From this table it is clear also that the quantitative phase analysis revealed the percentage of the two polymorphs of VO2. These percentages recorded for monoclinic insulator phase and (tetragonal) rutile metallic phase is 69.2% and 18.1%, respectively and the percentage of VO was 12.7%.
Figure
4: Rietveld refinement profile fitting for the sample
prepared in vacuum at 450°C.
The obtained major monoclinic phase with space group C2/m (No.14), and refined unit cell parameters a = 12.0582(3)Å, b = 3.6893(1)Å, c = 6.4187(3)Å, ?° = 106.961(5)Å as given in table 2 are in agreement with the results of M. Saini et al and H. Qiu et al [56, 57]. Phase transition from the highly symmetrical quadrilateral structure, to the lower symmetry monoclinic structure was observed by W. Chen et al [58] during the synthesis of vanadium dioxide nanorods by hydrothermal method. Two differing V–V bond lengths are formed, 0.312 nm and 0.265 nm.
Property |
Polymorph 1 (Monoclinic)
VO2 |
Polymorph 2 (Rutil) (Tetragonal)VO2 |
VO |
Weight Percentage% |
69.2 |
18.1 |
12.7 |
a Å |
12.0582(3) |
4.5272(2) |
4.055(1) |
b Å |
3.6893(1) |
4.5272(2) |
4.055(1) |
C Å |
6.4187(3) |
2.8793(2) |
4.055(1) |
?° |
106.961(5) |
|
|
Volume Å3 |
273.130(2) |
59.013(5) |
66.676(4) |
Crystallite size nm |
79(3) |
653(8) |
76(1) |
Microstrain |
0.73(2) |
0.98(4) |
0.59(2) |
Rwp |
56.2 |
||
Rexp |
54.4 |
||
c2 |
1.068 |
Table 2: Refined parameters of sample prepared in vacuum at 450°C (VO2)
Refinement results of the first minor polymorph of VO2 (tetragonal) rutile metallic phase (R) are tabulated in table 2. Rutile VO2 with a space group of P42/mnm has refined unit cell parameters a = b = 4.5324(2) Å, c =2.7825(2) Å which agreed with results of Z. Shao et al [59]. In VO2 (R) crystal, the tetravalent vanadium ions reside at both of body centers of the tetragonal structure, and each V4+ ion besetment with 6O2- ions comprise an octahedral VO6 unit. The nearest V-V atoms distance is equal to 0.287 nm in the z-axis direction. Unique physical properties of VO2 by reason of its polymorphism due to the rearrangement of atoms inside the unit cell encourage M. A Rodriguez et al [60] to study the transformation temperature of insulator monoclinic to the metallic tetragonal rutile phase using In-Situ high temperature XRD and they obtained pure tetragonal VO2 Rutile single phase at 70°C. The third phase in the second sample was the low valence VO phase which crystallized in the rock salt structure, space group Fm-3m and the refined cubic unit cell parameter was a=4.055(1) Å. From the refined parameters of the second sample tabulated in table 2 it is clear that the micros train values of the three phases were, 0.73(2), 0.98(4) and 0.59(2), respectively which indicated that the tetragonal rutile metallic phase has a large number of defects due to the transformation from high symmetry to lower symmetry phase (Figures 5 and 6).
Figure 5: TEM images at two magnifications for V2O5 sample prepared in air at 450°C.
Figure 6: TEM images at two magnifications for VO2 sample prepared in vacuum at 450°C.
From (Figures 5 &
6) it is worth noting that the calcination atmosphere has an impact on the
shape and size of the particles of the prepared oxides. V2O5
oxide which synthesized in air at 450°C shows big particles
with laminar shape. The particles look arranged as layer over layer with sizes
exceed 200 nm. Going to figure 6 which display TEM images of VO2
samples prepared in vacuum at the same temperature we notice different shape
and size for its particles. The neutral atmosphere provided by vacuum not only
gives reduced form of vanadium oxides but also minimizes and changes their
particles size and shape, respectively. Unidentified shape of nano-sized
particles was observed for these reduced oxides. These particles have sizes
less than 100 nm and much lower than those observed for V2O5
particles.
*Corresponding author: Ahmed M. Hashem, National Research Centre, Inorganic Chemistry Department, Egypt
Copyright: © 2021 All copyrights are reserved by Ahmed M. Hashem, published by Coalesce Research Group. This This work is licensed under the terms of the Creative Commons Attribution License which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.