Abstract— position of peaks was not affected by

   Abstract— In this
study, nanoparticles of undoped titanium dioxide were prepared using precursor
Titanium tertbutoxide  via Sol gel
technique. Using a single process, Co, Cu, Fe, Ni and Zn doped TiO2
nanoparticles were prepared by simply changing the precursor dopant metal salt.
The nanostructures  were characterised by
a Scanning Electron Microscope, XRD, Ultraviolet visible Spectroscopy. SEM
confirmed the size of nanoparticles nearly 9 to 20 nm. XRD analysis proved that
the position of peaks was not affected by doping. The band gap for undoped and
doped samples are  estimated using the (?Ephot)^2 versus Ephot plots. Metal
doping decreases the band gap of anatase titatnium dioxide nanoparticles is
confirmed with our results.

 

Index Terms— Titanium dioxide nanoparticles, SEM, band gap,
transition metal doped

 

I  INTRODUCTION

 

Titanium dioxide is very useful because of its resistance
to photochemical erosion. It is convinient to handle and is comparatively
cheaper. It is used in photocatalytic application as it can be prepared easily.
Its photostability is high. Its holes have strong oxidizing power. Large
surface area increases amount of photon generated electron hole pairs.Titanium
dioxide is most suitable catalyst for organic contaminants.

 

Titanium dioxide has been used for the photodegradation of
organic dyes and decolorization of wastewater. Using TiO2 as photocatalyst  has one drawback that it has a wide energy
band and its band gap (3.2 eV for anatase phase ) falls nearly in the UV range
of electromagnetic spectrum. Only UV light forms electron hole pair required
for photocatalytic process.

 

Since UV light is only 3-5% of the solar spectrum,
scientist are trying to decrease its band gap so that electron hole formation
should occur at the incidence visible light. Undoped titanium
dioxide is sensitive nm, it can be doped with variety of  metal and nonmetal impurities 1.

 

One of the way to shift optical response of TiO2 to the
visible range   is by adding a transition
metal oxide such as that of copper, zinc, cobalt, nickel and
iron
in an adequate amount. 1 2 4 6. The recombination of electron hole
pairs (photo generated)  is reduced due
to this doping  and causes red shift.

 

 

II   MATERIALS AND METHODS

 

2.1 Materials:

 

All Analytical grade purity reagents were used without any
further purification. Titanium tert-butoxide (98% purity)was the titanium
precursor precursor used obtained from Sigma Aldrich. Hydrochloric acid HCl
was supplied by Highmedia and Analytical reagent grade ethanol was obtained
from Changshu Yangyuan Chemical, China.

 

De-ionized water was used for preparing all standard
solution. Loba Chemie supplied Anhydrous ferric chloride (FeCl3), copper
sulphate pentahydrate (CuSO4.5H2O), Cobalt Chloride hexahydrate (CoCl2.6H2O),
Nickel Chloride hexahydrate (NiCl2.6H2O) and Zinc Acetate dehydrate
(Zn(CH3COO)2.2H2O) of 99% purity.

 

 

2.2
Method of Preparation :

 

Undoped sample is prepared
using sol gel method described in 1013. Solution A is prepared with 2.5 mL
of Titanium tert-butoxide , 25 mL ethanol added together with constant
stirring. Solution B is prepared with 1.25 l. of distilled water ,0.25 mL of
Hydrochloric acid and 25 mL ethanol added together with constant stirring.
Solution A and B were mixed with continuous stirring for 2 hrs. A sol is
allowed to transform into gel which was dried under 80°C for 1 hr. The dry gel
was then sintered at 450°C for 3 hrs. to obtain desired undoped TiO2 Nano
crystalline particles.

 

Extra solution ‘C’ was
prepared for  metal doped TiO2
nanoparticles,. Solution C was a 0.73 M solution of the dopant metal precursor
salt in distilled water. 1 mL of solution ‘C’ was added to solution B and rest
of the procedure is same as above. The amount of metal salt solution used was
calculated for a Ti:Metal atomic ratio of 0.05.

 

 

2.3  Characterisation:

 

D8
Advance X-ray diffraction meter(Bruker AXS, Germany) was used to characterize
the crystalline structure (room temperature, 30 KV,  30 mA), using Cu Ka radiation (=0.15406 nm).
The crystal Field Emission Scanning Electron Microscopy (JEDL JSM-7600F) was
used to study the morphology and structure of the particles.

 

Size of nanoparticles was measured.
UV/Vis spectrophotometer  Perkin Elmer
Lambda XLS+ was used to study the absorption spectra of the TiO2 samples.

 

III  RESULTS

 

3.1  SEM
Analysis:

 

“Fig.
1,” (a) and (f) shows the SEM images along with the
particle size distribution of the synthesized undoped  and doped TiO2.
SEM imaging of all six samples showed
spherical nature of nanoparticles with particle size nearly 11nm to 24nm.  Sample1(Undoped), Sample 2(Co doped), Sample
3(Cu doped), Sample 4(Fe doped), Sample 4(Fe doped), Sample 5(Ni doped), Sample
6(Zn doped) 3.2
UV-Visible
spectra

 

The band gap calculations are done as per procedure 1415. The graph
is ploted between  (?Ephot)^2
versus Ephot for a direct transition which is most suitable for anatse
TiO2 paricles, where Ephot is the photon energy, Ephot= (1239/?) eV, ? is the wavelength in nm and ? is the
absorption coefficient . An absorption energy is given by the  value of Ephot extrapolated to ? = 0, which corresponds to a bandgap Eg. The bandgaps of all the six
samples were calculated as tabulated below. Our calculated bandgap values are
compared with values mentioned in the literature.2

 

The results showed the band gap of Titanium dioxide was narrowed
due to metal doping which improves the
photo reactivity of TiO2. Our results matches with the literature i.e. band gap
decreases due to metal doping.3.3 XRD analysis : JCPDS-84-1286  was referred to compare the peaks of samples
which confirmed its anatase structure at 2? = 25.4o. Also it is
noted that  our sample’s diffractograms do
not have any peak assigned to rutile phase (2? = 27.36 o). The crystallite size was
determined with the help of the Scherrer formula below: G = 0.9? / ?(2?) cos ?  where
? is the Cu K? radiation wavelength and ?(2?) is peak width at
half-height. The calculated sizes are mentioned below. XRD of all samples
showed the peaks are occurring at the
same angle that means doping did not cause any effect on anatase nature of TiO2
nanoparticles. 

ed
due to metal doping which improves the
photo reactivity of TiO2. Our results matches with the literature i.e. band gap
decreases due to metal doping.IV  CONCLUSIONS: 

SEM pictures of samples show uniform morphology with spherical
particles.
The
particle size 11 nm-24 nm which matches with the size calculated using
XRD.
The
prepared  TiO2 sample’s absorption
spectra exhibited strong absorptions below 370 nm for undoped, Cu doped
and Co doped samples, below 380 for Zn doped, below 480 for Fe doped,
below 650 for Ni doped.
The
band gap of 3.4eV of the prepared sample confirmed its nano crystallite
size as larger band gap have  smaller crystallite size. Bulk sample of
TiO2 has band gap of 3.2 eV.
XRD
pattern revealed  that the prepared
titania composed of predominantly anatase phase . The position of peaks
was not affected by doping.
Band
gap decreases due to metal doping in Anatase TiO2 nano particles. ACKNOWLEDGMENT

 

The
author is thankful to Mumbai University for funding this project  under Minor Research Grant and S.I.E.S.
Graduate School of Technology for supporting this research work.

Thanks
are due to SAIF, Indian Institute of  Technology,
Mumbai for  helping in characterizing the
samples.

 

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