T. MARY JEEVA, J. JUDES: DEVELOPMENT AND CHARACTERIZATION OF METAL-DOPANT-BASED ZIRCONIA ...
751–761
DEVELOPMENT AND CHARACTERIZATION OF
METAL-DOPANT-BASED ZIRCONIA NANOFIBRES VIA AN
ELECTROSPINNING PROCESS FOR SCIENTIFIC APPLICATIONS
RAZVOJ IN KARAKTERIZACIJA KOVINSKIH DOPANTOV NA
OSNOVI NANOVLAKEN CIRKONIJEVEGA OKSIDA PREKO
ELEKTROSPINING POSTOPKA ZA ZNANSTVENO UPORABO
Mary Jeeva Thomas, John Judes
Department of Physics, University VOC College of Engineering, Anna University: Thoothukudi Campus, Thoothukudi – 628008,
Tamil Nadu, India
maryjeevat@gmail.com
Prejem rokopisa – received: 2018-01-29; sprejem za objavo – accepted for publication: 2018-06-28
doi:10.17222/mit.2018.013
Nanofibres and their composites are some of the emerging materials used in versatile applications due to their better compatible
performance. Zirconia nanofibres are examples of such materials. Though zirconia nanofibres have better performance, their
conductivity is inferior and to boost their performance, doping with metals is required. Thus, the present study deals with the
development of zirconia nanofibres doped with copper and iron in different concentrations and hybrid combinations using the
electrospinning method with polyvinyl alcohol as a precursor. The developed materials are subjected to a thermal treatment to
develop the properties. Both the thermally treated and untreated fibres were characterized using thermogravimetric analysis,
Fourier-transform infrared spectroscopy, X-Ray diffraction, scanning electron microscopy coupled with energy-dispersive
analysis, viscosity and conductivity measurements. It was concluded that doping thermally treated zirconia nanofibres with a
hybrid combination of copper and iron was beneficial.
Keywords: nanofibres, zirconia, copper, iron, calcination, polyvinyl alcohol
Nanovlakna in njihovi kompoziti so obetavni moderni materiali, ki se uporabljajo v razli~nih aplikacijah zaradi svojih pri-
merjalnih prednosti; nanovlakna cirkonijevega oksida so ena izmed njih. ^eprav imajo cirkonijeva nanovlakna dobre lastnosti,
je njihova naravna prevodnost pomanjkljivost, ki jo lahko izbolj{amo z legiranjem (dopiranjem) s kovinami. Tako se pri~ujo~a
{tudija ukvarja z razvojem cirkonijevih nanovlaken, ki so legirana (dopirana) z bakrom in `elezom v razli~nih koncentracijah in
hibridnih kombinacijah. Pri tem so za izdelavo vlaken uporabljali elektrospining postopek in polivinil alkohol kot prekurzor
(izhodi{~e). Razvite materiale so potem termi~no obdelali in s tem razvili njihove lastnosti. Tako termi~no obdelana kot
neobdelana vlakna so okarakterizirali s termogravimetri~no analizo (TGA; angl.: Thermo Gravimetric Analyser), Fourierjevo
transformacijsko Infrarde~o kromatografijo (FTIR chromatography), rentgensko difrakcijo, vrsti~no elektronsko mikroskopijo
(SEM) z energijsko disperzijsko spektroskopijo (EDS), meritvami viskoznosti in prevodnosti. Avtorji {tudije ugotavljajo, da ima
dopiranje s hibridno kombinacijo bakra in `eleza ugoden vpliv na termi~no obdelana nanovlakna cirkonijevega oksida.
Klju~ne besede: nanovlakna, cirkonijev oksid, baker, `elezo, kalcinacija, polivinil alkohol
1 INTRODUCTION
Nanofibres are some of the best choices due to their
important advantages, resulting from their nano-level
diameter with better properties. They are widely used in
the field of engineering, health sciences and environ-
mental aspects. Some of the applications include tissue
engineering, drug delivery, sensors, etc.
1
Achieving the
nanometre range depends on the various conditions and
methods for producing the fibres. The nanofibres are
produced by different methods, namely, thermal induced
phase separation, drawing, electrospinning and self-
assembly synthesis.
2
Electrospinning is considered as
one of the better synthesis methods due to its versatility,
inexpensive fabrication, simple construction and ability
to be used for various polymers.
3,4
Ceramic-based nano-
fibres possess good mechanical strength, thermal
strength, electrical and thermal insulation. In particular,
zirconia-based nanofibres possess this quality. To in-
crease their application suitability and to enhance their
conductive nature, it is mandatory to include dopants in
the fibre. Zirconium is a transition metal with very good
properties that is used in a variety of applications, such
as high-temperature applications, corrosion resistant ma-
terials, dental implants, knee replacements, prosthetic
applications and lotions for poison ivy.
5,6
Zirconia is
blended with the precursor matrix and then made into
fibres. Jing et al. developed ultrathin ZrO
2
nanofibres
using PVP as a precursor by the electrospinning process
and proved that calcinated nanofibres have a crystalline
phase and it could be used for fibre template
applications.
7
To improve the application range of the
zirconia fibres doping was introduced. Zirconia nano-
fibres doped with erbium was prepared using a modified
chemical vapour deposition technique in combination
with solution doping to incorporate the glass modifiers
and a nucleating agent. Then it was annealed and drawn
into the fibres before all the characterisations. It was
Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761 751
UDK 620.1:620.3:549.514 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(6)751(2018)

found to possess the ability for multi-wavelength gene-
ration and was suitable for the production of compact
lasers.
8
Poly(vinyl) alcohol/zirconium-yttrium acetate
(PVA/Zr-Y) nanofibers were prepared with and without
boron doping using the electrospinning method. It was
proved that boron-doped nanofibres increased the
conductivity and produced needle-shaped nanofibres.
9
It
is very clear from the literature that doping enhances the
properties like conductivity, diameter, stability, etc.
However, there is no research work related to the
development of metal-dopants-based zirconia nanofibres
with different concentrations and hybridisation. So, the
present study deals with the development of zirconia
nanofibres with metal dopants of different concentra-
tions, hybridisation, and then calcination of the deve-
loped fibres and a comparison with undoped, uncalci-
nated fibres.
2. MATERIALS AND METHODS
2.1. Materials
Granular polyvinyl alcohol (PVA, average molecular
weight 72,000 g/mol) diluted in distilled water was used
as a precursor. Zirconium oxychloride with sodium
hydroxide was used to make the zirconia fibres. Copper
sulphate (Cu dopant), ferric chloride (Fe dopant), and
sodium borohydride were used for the preparation of the
copper- and iron-based nanofibres. All the above mate-
rials, possessing the highest purity, were procured from
Sigma Aldrich Suppliers and used as received from the
supplier.
2.2. Equipment used for the synthesis
A magnetic stirrer with a hot plate (capable of a
maximum operating temperature of 100 °C) was used for
stirring the solution. An electrospinning machine was
used for producing the nanofibres. The electrospinning
apparatus possesses a syringe pump with a maximum
capacity of 20 mL. The spinning parameters considered
in this study were 1 mL/h for the dispending rate with a
spinning rate of 0.02 mL. The collector was covered with
aluminium foil. A voltage is supplied to the syringe and
the collector. The anode [positive (+)] voltage was
applied to the syringe needle, and the cathode [negative
(-)] voltage was applied to the back side of the collector
(aluminium foil). At the anode, the high voltage applied
was 20 kV, with the equipment that was capable of
producing a voltage of 50 kV. After spinning of the total
solution, the fibres were peeled off from the aluminium
foil. The distance between the syringe and the collector
was 13 cm. A schematic representation and a photograph
of the electrospinning apparatus are shown in Figure 1.
2.3. Procedure for the preparation of the sol and
development of the fibres
The PVA solution was prepared by dissolving granu-
lar PVA in 100 mL of distilled water and then stirred
using a magnetic stirrer at 70 °C for two hours to obtain
8 % of the PVA solution. In order to obtain undoped zir-
conia fibres, zirconium oxychloride of8%w a s
dissolved in 100 mL of distilled water and stirred using a
magnetic stirrer. The 8 % sodium hydroxide was dis-
solved in 100 mL of distilled water, stirred and titrated
with the zirconium oxychloride solution. Then the
solution was added drop by drop to the PVA solution at
room temperature. Finally, it was stirred for two hours
continuously to obtain the homogenous hybrid polymer
solution.
Dopant-based zirconia fibres were obtained by
following the procedure given below. In order to make
8 % of copper-dopant-based zirconia nanofibres,8%of
copper sulphate was dissolved in 100 mL of distilled
water using a magnetic stirrer. Then the 8 % of sodium
borohydride was dissolved in 100 mL of distilled water,
stirred and titrated against the copper sulphate solution.
Upon vigorous stirring, the copper nanoparticle solution
was formed. After that the solution was titrated against
the zirconia oxychloride-PVA solution. Finally, 8 %
copper-doped zirconia-PVA solution was formed by
stirring it for two hours at room temperature. Then, the
prepared solution was loaded into a syringe pump and
spun based on the conditions provided in the above
sections. In the case of the 8 % iron-doped solution, in-
stead of titrating against copper sulphate, ferric chloride
was used. The other procedures remained the same.
The hybrid dopant-based zirconia nanofibres were
formed by following the above procedure with 4 % each
of copper sulphate and ferric chloride mixed with
T. MARY JEEVA, J. JUDES: DEVELOPMENT AND CHARACTERIZATION OF METAL-DOPANT-BASED ZIRCONIA ...
752 Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761
Figure 1: Electrospinning apparatus: a) schematic view and b) photo-
graph

sodium borohydride. The various % concentration solu-
tions were prepared by varying the respective chemical
solution (e.g., for 6 % copper-doped zirconia nanofibres,
6 % copper sulphate was considered, titrated and
spinned, similarly, for the iron-doped zirconia nano-
fibres, ferric chloride was considered).
To make heat-treated/calcinated nanofibres, the ob-
tained nanofibres were calcinated at 500 °C for1hina
muffle furnace. The 10 % iron-doped zirconia nanofibres
were not developed in this current study due to the
viscous nature of the solution that leads to problems in
the development of fibres. Based on the above procedure,
16 nanofibres were made (eight calcinated fibres and
eight uncalcinated fibres) and were designated as U1 to
U8 and C1 to C8, as shown in Table 1. In order to check
the calcinated nature of the PVA fibres, it was heat
treated at 150 °C for half an hour only, since prolonged
calcination and high temperature will lead to melting of
the PVA. The PVA will be removed from the C2 to C8
fibres upon calcination at 500 °C.
Table 1: Designation and developed nanofibre details
Developed Sample Details Uncalcinated Calcinated
PVA U1 C1
PVA-Zr U2 C2
PVA-Zr-Cu (6 %) U3 C3
PVA-Zr-Cu (8 %) U4 C4
PVA-Zr-Cu (10 %) U5 C5
PVA-Zr-Fe (6 %) U6 C6
PVA-Zr-Fe (8 %) U7 C7
PVA-Zr-Cu (4 %)-Fe (4 %) U8 C8
2.4. Characterization of the developed nanofibres
The conductivity and viscosity of the developed solu-
tion were measured using a conductivity meter with
built-in standard conductance and a A&D SV-10 visco-
meter, the standard allowable error is 5 % as per indus-
trial practice. Fourier-transform infrared spectroscopy
(FTIR) was used to obtain the information about the
absorption/emission by studying the stretching nature of
the samples (PerkinElmer, Spectrum-2). FTIR spectra
were acquired in the range of 4000 cm
–1
to 500 cm
–1
with
ten scans. A sample of weight 5 mg was used for each
measurement. The thermal stability of the developed
nanofibres was measured using a thermo gravimetric
analyser (TGA) (TGA 50, Shimadzu, Japan). The test
conditions were a nitrogen environment, possessing a gas
flow rate of 20 mL/min with the temperature ranging
from room temperature to 800 °C. The heating rate
considered was 5 °C/min, the sample weight considered
was 5 mg and a platinum pan was used. An X-Ray
diffractometer (XRD) was used to find the crystal
structure of the developed nanofibres (Rigaku Ultima III
XRD). Scanning electron microscopy (SEM) coupled
with energy-dispersive analysis (EDX) was used to study
the fibre diameter morphology and the composition
(Tescan VEGA 3LMU SEM of Czech Republic). The
morphological analysis of the fibres was made using
Image J software.
3 RESULTS AND DISCUSSION
The various characterisations carried out are reported
and discussed in the following sections in a detailed
manner.
3.1 Physical Properties
The viscosity of the solution plays an important role
in determining the diameter of the spun nanofibres. The
results show that an increase in the conductive dopants’
concentration increased the viscosity level. For instance,
the viscosity of PVA-Zr-Cu (8 %) is 2.89, while it is 3.13
for PVA-Zr-Cu (10 %). This increase in viscosity will
lead to an increase in diameter. It is also a postulate that
a drastic increase in viscosity will have a significant
effect on the jet breakup during spinning, leading to
small droplets and beads during the electrospinning, as
shown in the U5 and U2 composites. These are as per the
findings of Tahira Pirzada et al., 2012,
10
in their study of
hybrid silica-PVA nanofibres processed via electro-
spinning. The optimal percentage of viscosity could
overcome this. Adding dopants increased the viscosity,
and similar behaviour is seen in the current study, as
shown in Table 2.
Conductivity is another important aspect of the
electrospinning process. Viscosity and conductance are
interdependent in many cases. The higher the viscosity
the higher will be the conductance. This postulate was
true for all the dopant-based composites in which higher
viscosity enhanced the conductance, since the gap
between the materials is reduced. Another point noted is
the higher the viscosity in case of sample 2, the poorer
the conductance. Thus, it is clear that conductance is
purely dependent on the conductive nature of the
constituent ingredients, as shown in Table 2. It is also
worth noting that the higher the conductance, the lower
will be the diameter, as per the findings of Seeram et
al.,
11
but in the current study it is the opposite. The metal
dopants present with the fibres excite the electrons and
increase the diameter. Similar behaviour was visualised
by Selda Keskin et al.,
12
in their study on neody-
mium-doped PVA/Zr-Ce oxide nanocrystalline com-
posites.
Table 2: Viscosity and conductivity of the samples
Sample
no
Composite
Conducti-
vity (S/m)
Viscosity
(Pa)
1 PVA 1.15 1.67
2 PVA-Zr 41.1 2.82
3 PVA-Zr-Cu (6 %) 43.5 2.76
4 PVA-Zr-Cu (8 %) 45.7 2.89
5 PVA-Zr-Cu (10 %) 49.2 3.13
6 PVA-Zr-Fe (6 %) 44.6 2.83
7 PVA-Zr-Fe (8 %) 61 2.91
8 PVA-Zr-Cu (4 %)-Fe (4 %) 90.09 2.97
T. MARY JEEVA, J. JUDES: DEVELOPMENT AND CHARACTERIZATION OF METAL-DOPANT-BASED ZIRCONIA ...
Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761 753

3.2 XRD Studies
X-Ray diffraction (XRD) was carried out to study the
crystal structures and the amorphous-crystalline phase
vibrations.
13
Figures 2a and 2b show the X-Ray diffrac-
tograms of the uncalcinated and calcinated specimens.
From Figure 2 it is clear that three peaks are observed
around ~39°, ~45°, ~66 ° and ~79°, which denote the
peaks for PVA, copper (Cu), iron (Fe) and zirconia (Zr)
respectively. From Figure 2 it is clear that the calcinated
specimens show more intense peaks when compared
with the uncalcinated samples, which were found in
accordance with the findings of Ohtaki et al.,
14
and
Abbas et al.
15
From Figure 2a, the sample U1 shows the XRD
diffractograms for PVA. Only two peaks are formed,
which correspond to the amorphous and crystalline
structures of PVA at 15.37° and 22.42° respectively.
Thus, representing the crystalline structures of the car-
bon and hydrogen, while U2 shows the intensity peaks of
PVA and Zr at 2 = 38.41° and 78.51°, respectively. The
intensity peaks of Cu rise with a rate corresponding to
the percentage of Cu 6 %, 8 % and 10 % added to the
composite, where Zr and PVA are kept constant. Thus
we can see from the composites U3, U4 and U5 that the
intensity peak of Zr decreases, concerning the increase in
the percentage of Cu and this eventually gives rise to the
crystal peaks of Zr at 78.09°, 78.10°, and 78.34°, res-
pectively. The same aspect was found in accordance with
the findings of Yeh et al.
16
This phenomenon is attributed
to the bonding of Cu atoms with Zr.
From the diffractograms of U3, U4, U5 it is clear that
the crystal intensity of Cu increases, which suppresses
the intensity peak of the zirconia. The intense peak
appeared due to the strong intermolecular attractions
between the polymer chains and the intermolecular
hydrogen bond. The diffractograms of U6 and U7 denote
the peaks of Fe and Cu at 2 = ~66 and ~79, respect-
ively. It is clear that the intensity peak of Fe increases in
U7 due to the increase in the w/% of Fe, while the Zr and
PVA are kept constant at 8 %. The U8 diffractograms
have three peaks at 2 = 44.92°, 65.27° and 78.42°,
respectively, for copper, iron and zirconia. The peaks
show that the crystallinity index of Zr rises when Cu and
Fe are added at 4 %, respectively. This phenomenon
occurs due to the high intermolecular bonding between
the hydrogen and carbon atoms.
15,17
Figure 2b shows the calcinated diffractograms of the
same eight samples. The samples were calcinated at
500 °C. The diffractograms observed are similar to
Figure 2a due to the same composition, but the intensity
peaks are much higher when compared to Figure 2a.
This is because the monoclinic Fe and face-centred cubic
Cu exhibit a strong intermolecular bond with orthogonal
crystals of Zr when subjected to heat.
16
This, in turn,
plays a vital role in forming the strong crystal structures
in the lattice plane. C8 shows a good crystal structure
when compared to the other specimens. Another aspect
is that the calcination of PVA in the case of C2 gives rise
to a peak at 44.33, as per the literature.
18
The pheno-
menon was due to the dehydration during the calcination
and altered the crystal structure in the presence of Zr.
T. MARY JEEVA, J. JUDES: DEVELOPMENT AND CHARACTERIZATION OF METAL-DOPANT-BASED ZIRCONIA ...
754 Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761
Figure 2: XRD diffractograms: a) uncalcinated nanofibres (U1-U8),
b) calcinated nanofibres (C1-C8)

3.3 FTIR Studies
The Fourier-transform infrared spectroscopic images
of uncalcinated and calcinated specimens are shown in
Figures 3a and 3b.
From Figure 3a U1 shows the spectrogram peaks of
PVA at 606 cm
–1
, 850 cm
–1
, which were due to the
stretching of the C-H alkene. Later, a peak was seen at
1093 cm
–1
due to the C-O alkoxy stretch. Further, it
shows small bumps at 1242 cm
–1
, which are due to the
SP
3
C-H bending. And then a peak was seen at 1444
cm
–1
, due to the presence of the C=C aromatic stretch. A
small bump is observed at 2472 cm
–1
due to S-H thiol
stretch. Some small peaks are observed at 2907 cm
–1
, due
to the O-H carboxylic acid stretch. This is followed by a
small bump at 3332 cm
–1
, due to the presence of the 2°
N-H bond
17
.
U2 spectrograms from Figure 3a show the presence
of Zr and PVA. The first peak was seen at 839 cm
–1
and
the second U-shaped peak was at 1083 cm
–1
, which
denote the presence of the C-H alkene and C-O alkoxy
stretch, respectively. The next concurrent peaks are seen
at 1422 cm
–1
and 1666 cm
–1
, which denote the presence
of N-H bending and C≡ N stretching. The next con-
sequent peaks are observed at 2650 cm
–1
, 2940 cm
–1
and
3268 cm
–1
, which corresponds to C-H aldehyde stretch-
ing, O-H carboxylic acid stretch and the 2° N-H stretch,
respectively. The number of intense peaks is reduced,
while new peaks such as 1666 cm
–1
and 2059 cm
–1
are
formed, which denote the presence of Zr.
19
The next consecutive specimens U3, U4 and U5 show
the spectrograms that corresponds to the presence of Cu
that has been doped with PVA and Zr at a rate of 6 %,
8 % and 10 %, respectively. From the spectrograms of
U3 and U5 the peaks observed are 627cm
–1
, 828 cm
–1
and 945 cm
–1
, which correspond to the presence of the
C-H alkene stretch,
20
while U7 does not show the
presence of the C-H alkene bond because U7 is doped
with 10 % CuSO
4
. So the inter-lattice spaces are filled
with sulphate and copper atoms, thus lowering the
concentration of PVA. This results in a low penetration
of IR rays. The next corresponding peak for U3 is found
at 1072 cm
–1
, which shows the presence of the C-O
alkoxy stretch. The next consecutive peaks of U3 are
found at 1412 cm
–1
, 1634 cm
–1
, 1719 cm
–1
, 2918 cm
–1
and 3278 cm
–1
, which correspond to the presence of the
C=C aromatic stretch, N-H bending, C=O stretch, O-H
carboxylic acid and 2° N-H stretching, respectively. The
specimen U4 shows the intensity peak at 1465 cm
–1
,
which is due to the C=C aromatic stretch. The next peak
is formed at 1740 cm
–1
due to the vibration of C=O. The
next consecutive peaks are found at 2059 cm
–1
and 2302
cm
–1
, which correspond to C≡N. The next peak is formed
at 2918 cm
–1
, which denotes the O-H carboxylic acid,
and the last peak is found at 3438 cm
–1
, which denotes
the presence of the O-H alcoholic stretch. From Figure
3a the U5 specimen shows the spectrogram recorded for
10 % copper doped with Zr and PVA. There are lesser
peaks in U5 when compared to U1, U2, U3 and U4
because the 10 % copper doping prevents the IR from
passing through the specimens, thus showing better
quality.
The specimens U6 and U7 show spectrograms of Fe
doped with Zr and PVA at the level of 8 % and 10 %,
respectively. From Figure 3a U6 shows intensity peaks
at 1259 cm
–1
, which denotes the presence of C-O alkyl
groups. The peak is formed at 1454 cm
–1
, representing
the vibration of the C=C aromatic presence. The next
peak formed at 1632 cm
–1
, is due to the bending of the
N-H medium peak, and next one is observed at 2304 cm
–1
,
which is attributed to the presence of C≡ N stretching. It
is then followed by two consecutive peaks at 2492 cm
–1
and 3343 cm
–1
, which were due to the molecular vib-
ration and stretching of S-H Thiol and N-H 2°, res-
pectively.
Figure 3a U8 shows the spectrograms of copper and
iron-doped with Zr and PVA, only three peaks are
observed at 1430 cm
–1
, 1621 cm
–1
and 3322 cm
–1
, which
is due to the vibrational intensities due to the C=C aro-
matic stretching, bending of N-H bond and 2° N-H
stretching, respectively. So from the Figure 3a,w ec a n
observe that specimen U8 shows better results by pre-
venting more transmittance of IR rays.
21
Figure 3b shows the spectrogram of the calcinated
eight samples, namely, C1, C2, C3, C4, C5, C6, C7 and
C8. Sample C1 in Figure 3b shows intensity peaks for
PVA at 943 cm
–1
, which were due to the bending of sp
2
C-H. The next consecutive peaks are observed at 2053
cm
–1
and 2485 cm
–1
, because of the stretching of C≡ C
and C≡N, respectively. It is then followed by the stretch-
ing of S-H thiol at an intensity of 2652 cm
–1
and then
T. MARY JEEVA, J. JUDES: DEVELOPMENT AND CHARACTERIZATION OF METAL-DOPANT-BASED ZIRCONIA ...
Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761 755
Figure 3: FTIR spectrum of: a) uncalcinated nanofibres, b) calcinated
nanofibres

followed by small bumps at 2925 cm
–1
and 3365 cm
–1
,
which were due to the presence of O-H carboxylic acid
and stretching of O-H alcohol, respectively. Specimen
C2 shows intensity peaks that start at 1030 cm
–1
, which
is due to the stretching of the C-O alkoxy. The next peak
is observed at 1316 cm
–1
, due to the stretching of C-O
(alkyl) and C=C, which indicates that the aromatic
stretch was found at 1435 cm
–1
. The next intensity peak
was due to the bending of N-H at 1637 cm
–1
, which is
then followed by the stretching of C-H aldehyde at 2898
cm
–1
. A small bump is observed at 3356 cm
–1
due to 2 °
N-H stretching. Further, the C3 and the C4 specimens in
Figure 3b show intensity peaks in the same manner. The
first intensity peak is observed at 605 cm
–1
and 604 cm
–1
,
which is due to the bending of the SP
2
aromatic alkene.
The second consecutive intensity peaks are observed at
768 cm
–1
and 782 cm
–1
, which are attributed to the bend-
ing of the C-H alkene. The third, consecutive intensity
peaks are observed at 1030 cm
–1
and 1032 cm
–1
, which
are due to C-O alkoxy stretch. The last intensity peaks
are observed at 3438 cm
–1
and 3421 cm
–1
, which are
attributed to the stretching of the O-H alcohol.
17,19
The C5 specimen shows only three intensity peaks
when compared with the other specimens. The peaks are
recorded at 943 cm
–1
, 1632 cm
–1
, and 3355 cm
–1
, which
are due to the bending of the C-H alkene, bending of the
N-H and stretching of the SP
2
C-H respectively.
Specimen C6 shows the spectrograms of Fe doped
with Zr and PVA and also calcinated at 500 °C. The peak
is observed at 606 cm
–1
, which specifies the bending of
the SP
2
aromatic alkene. The second intensity peak is
found at 788 cm
–1
, which is due to the bending of the
C-H alkene. The third intensity peak is observed at
1038 cm
–1
, which is due to the alkoxy stretching of C-O.
The fourth intensity peak is observed at 3439 cm
–1
and
3522 cm
–1
, which is attributed to the stretching of the
O-H alcohol. The specimen C7 shows the first intensity
peak at 1022 cm
–1
, which is due to the alkoxy stretching
of C-O. The second intensity peak is observed at
1621 cm
–1
, which is due to the bending of N-H. The last
intensity peak is recorded at 3414 cm
–1
, which is due to
the stretching of the O-H alcohol.
Specimen C8 shows the spectrograms of the calci-
nated specimen Fe and Cu doped with PVA and Zr. Only
three intensity peaks are formed. The first peak was at
1429 cm
–1
due to the bending of SP
3
C-H. The second
peak is due to the aromatic stretching of C=C at
1631 cm
–1
. The last peak was observed at 3349 cm
–1
, due
to the stretching of the alcohol O-H.
21
In Figures 3a and 3b the intensity peaks are reduced
because calcination disintegrates the PVA molecules.
This leads to better adhesion of the Fe and Cu with the
Zr, providing good structural stability. The phenomenon
is proved by less transmittance of the IR rays by the
calcinated specimens.
3.4 TGA studies
The thermal stability of the developed nanofibres was
found by measuring the weight loss related to tempera-
ture using TGA. The TGA curves for the uncalcinated
and calcinated nanofibres are given in Figure 4a and 4b.
When the U1 nanofibres are subjected to heat, a
drastic weight loss occurred, as shown in Figure 4a,
mainly at three stages. The first stage is from 60 °C to
155 °C, which is due to the weight loss due to moisture
content. Followed by 155 °C to 200 °C, which is mainly
due to the dehydration process, which is the loss of
internal water molecules. Then from 230 °C to 445 °C,
this is mainly due to the breakage and evaporation of the
polymer molecule chain. After 445 °C it may be due to
the semi-crystalline nature of PVA. While in case of C1,
as shown in Figure 4b, there is a slight deviation in the
temperature range, since it is calcinated (150 °C). So it
showed dehydration of the internal water molecule struc-
ture until 230 °C, followed by the polymer chain break-
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Figure 4: TGA curves of: a) uncalcinated nanofibres, b) calcinated
nanofibres

age and evaporation until 440 °C. The weight loss of C1
is 98 %, while it is 99 % for U1.
In the case of U2, it had very little weight loss, which
is mainly due to the PVA and internal water molecules
from adjacent OH groups. This is in accordance with the
findings of Sigwadi et al.
22
While in the case of the C2
composites the weight loss is much less when compared
to U2, due to the removal of water molecules during
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Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761 757
Figure 6: SEM images of uncalcinated fibres: a) U1, b) U2, c) U3, d) U4, e) U5, f) U6, g) U7, h) U8
Figure 5: Typical TG-DTA curves of: a) U2, b) C2

calcination. To study in detail the weight loss of Zr-PVA,
the DTA curves were analysed as shown in Figure 5a
and 5b for the U2 and C2 composites. The U2
composites showed two endothermic peaks, which are
due to the moisture dehydration and then the second one
is due to the polymer chain breakage. The C2 composites
showed that the only one which is mainly due to the
internal polymer chain breakage is in accordance with
the findings of Pessoa et al.
23
The weight losses of the
U2 and C2 nanofibres are 5 % and 6 %. The TGA curves
for the doped fibres showed different trends. The
dopant-based nanofibres showed broader curves due to
the presence of dopants, which interrupt the heat through
it. The copper-dopant-based zirconia nanofibres showed
better thermal resistance, while the iron-dopant-based
zirconia nanofibres showed more stability. This is mainly
due to the crystallisation structure. It is very clear from
the C8 composites as shown in Figure 4b, where the
weight loss is much less when compared to the other
fibres, which are mainly due to the homogenous distri-
bution and optimal percentage of copper and iron. Also,
upon calcination, the materials are stabilised, as shown
in the XRD. This nature plays a crucial role in with-
standing the thermal resistance behaviour of the fibres.
The weight loss of C8 is much less, i.e., 3.7 %, only
when compared to the other fibres. It is now clear that
the calcinated, dopant-based nanofibres are the potential
materials for thermal stability, which is also due to the
conductive and higher melting temperatures of the
dopants.
3.5 Morphological studies of the developed nanofibres
SEM studies were used to study the morphology of
the developed nanofibres. The SEM images of the uncal-
cinated nanofibres are given in Figure 6a to 6h in which
the fibre diameter is greater than the calcinated one. The
prime reasons for such behaviour are mainly due to the
presence of PVA in the composition. Generally, the cal-
cination of fibres removes the PVA from its composition,
which leads to the reduction in the diameter. It is stated
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758 Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761
Figure 7: SEM images of calcinated fibres: a) C1, b) C2, c) C3, d) C4, e) C5, f) C6, g) C7, h) C8

in the literature that PVA provides a good surface finish
and smoothness to the structure, but upon calcination,
this nature is changed, which is visible from Figures 6f
and 7f. It is also stated in the literature that PVA plays
the role of the template during spinning. If it is removed,
then there will be an abrupt change in the diameter. The
degradation of PVA is also justified from the SEM
images (Figures 6a and 7a in which there is a drastic
change in diameter of the fibres. To justify the removal
of the smoothness, the surface roughness was measured,
which is shown as 112 nm for U6 composite, while it is
145 nm for the C6 composite. This is in accordance with
the findings of Dharmaraj et al.
24
in which the zirconium
oxide nanofibres upon calcination gave a higher surface
roughness. This is because of the crystallisation of
zirconia at elevated temperature though the temperature
of calcination is not so high in the present study, but
there is a slight modification in the structure, which
could be confirmed from the XRD studies in Figure 2b.
It is said in the literature that a change in the diameter is
not only due to the precursor, but also due to the shrink-
age of the fibres due to structural changes.
25
The same is also confirmed using the EDX, as shown
in Figure 8b, in which there is an increase in the Cu and
Zr % than in Figure 8a. Another possible reason could
also be due to the presence of metal dopants, which en-
hances the conductive nature and allows the heat to per-
colate to it, leading to such a nature. Figures 9a and 9b
show the frequency distribution of the diameter in uncal-
cinated and calcinated copper (6 %) doped zirconia
nanofibres, in which the average diameter is less for the
calcinated (C3) sample. It is a postulate that the doped
nanofibres have a larger diameter than the undoped one,
which is also found in our study, where the average
diameter of C3 is 1.71 times higher than C2. This is a
concept as per the findings of Uslu et al.
3
in their study
on boron-doped alumina-stabilised zirconia nanofibres
produced by electrospinning.
3
The dopant-based zirconia
nanofibres showed good round and even shaped fibres
with an appreciable diameter, as per the literature. The
undoped nanofibres showed a needle-like structure with
beads, as visualised in the SEM images in Figures 6b
and 7b, which is mainly due to the poor viscosity, which
was due to the rough surface and some defects.
26
Similarly, in case of Figure 6e, which possess high
viscosity, it leads to form more net-shaped structures that
interrupt the homogenous distribution of fibres, forming
a good structure. The good diameter properties are
shown in Figures 6h and 7h, which is mainly due to the
conductance of the fibres. Better conductance, which
will be helpful for the dispending of good diameter
based fibres without the formation of any beads and
defects, is in accordance with the studies of Cui et al.
26
It
is also stated that the conductance is based on the do-
pants available
27
as well as on its mechanical behaviour.
The mean diameter on the nanometre scale is given in
Table 3. This is in line with the discussion above. The
EDX of the other samples also showed a similar trend
concerning their composition, so only the U3 and C3
fibres are alone discussed. This diameter change and
surface roughness will be very helpful for the application
aspects of the developed fibres.
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Materiali in tehnologije / Materials and technology 52 (2018) 6, 751–761 759
Figure 9: Frequency of diameter distribution in U3 and C3 nanofibres
Figure 8: EDX spectrum of: a) U3 Sample, b) C3 Sample

Table 3: Mean diameter of the uncalcinated and calcinated nanofibres
on the nanoscale
Sample
Uncalcinated
(U)/nm
Calcinated
(C )/nm
1 243 225
2 273 259
3 441 385
4 503 411
5 609 512
6 570 526
7 758 628
8 856 710
4 CONCLUSIONS
The doped and undoped zirconia nanofibres were
synthesised using the electrospinning technique, further
calcinated at elevated temperatures and characterised.
Based on the test results the following conclusions were
drawn:
• Zirconia doped with copper and iron showed two
times higher conductance than the other dopant-based
samples.
• XRD of the calcinated dopant-based nanofibres
showed good crystalline peaks and structures since
monoclinic Fe and face-centred cubic Cu exhibited a
strong intermolecular bond with orthogonal crystals
of Zr upon calcination.
• Calcinated zirconia nanofibres doped with metals
showed good bond stretching in the FTIR spectra and
the calcinated zirconia nanofibres doped with copper
and iron (hybrid) showed a better structural stability
than the other composites.
• Calcinated zirconia nanofibres doped with copper
and iron showed less weight loss (3.7 %), which
proved its better thermal stability.
• SEM studies showed that the diameter characteristics
of the calcinated nanofibres are less compared to the
uncalcinated samples, i.e., 0.83 times lower than the
uncalcinated sample in the case of zirconia doped
with iron and copper. It also showed good diameter
characteristics. EDX showed there was reduced
levels of C and O % due to the removal of the PVA
from the surface.
• Thus, from the above results, it is clear that calci-
nated zirconia nanofibres doped with copper and iron
are the positive solution for better conductance. The
future work is to develop a polymer composite using
dopant-based zirconia nanofibres and to characterise
them.
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