Molybdenum-doped BiVO4 powders were prepared by Sol-gel method. Monoclinic scheelite phase was confirmed by X-ray diffraction (XRD) patterns and micro-Raman vibrational bands. Substitution of molybdenum in crystal sites of BiVO4 was evidenced from XRD by higher angle 2θ shift of the characteristic peak (-121) and from Raman showing lower frequency shift of dominant peak from 831 to 822 cm-1 which corresponds to V-O symmetric stretching mode. The morphological properties were analyzed by FE-SEM which confirmed the formation of homogeneous spherical shaped particles with size around 200-300nm. Optical properties were analyzed by Diffuse Reflectance Spectra which show higher absorption in the range of 550-850nm. Optical band gap energies were calculated by using Kubelka-Munk formula, i.e, 2.46 eV for 2 wt% Mo-BiVO4 and 2.47eV for undoped BiVO4. This confirms that Mo-BiVO4 particles have the same band gap but induce higher absorption in the visible light region compared to BiVO4

1. Structural and optical properties of molybdenum
doped BiVO4 powders
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V.I. Merupo 1.2, S. Velumani 1 and A. Kassiba 2 M. A. García-Sánchez3
1Department of Electrical Engineering- SEES, CINVESTAV – IPN, Zacatenco, Mexico D.F, C.P. 07360, Mexico.
2Institute of Molecules & Materials of Le Mans (IMMM) UMR CNRS 6283, Université du Maine, Le Mans, France.
3Department of Chemistry,Universidad Autónoma Metropolitana-Iztapalapa, Vicentina, México ,D. F. 09340, Mexico.

2. Content
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 Introduction about Photocatalyst
 Introduction of BiVO4
 Sol-gel technique
 Results and discussion
 Conclusions

3. 5/22/2018 CCE 2014 3
Photocatalysis
Fig3. The plot shows the experimentally determined quantum efficiency (QE),
against the wavelength of incident photons
Basic features of photocatalyst
 Able to absorb visible and/or
UV light
 Chemically and biologically inert
photo stable
 Inexpensive and
 nontoxic.
Fig2. A schematic
illustration of the
generation of electron-hole
pairs and the
corresponding redox
reactions taking place on
the semiconductor surface.
http://payneresearch.org/research/photo-electrochemical-pec-water-splitting/
Fig.1. Photosynthesis by green plants
and photocatalytic water splitting as an
artificial photosynthesis.

4. Why BiVO4?
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Choice of photocatalyst:
 Appropriate Band gap(Eg) and Band edge positions
 Efficiency of charge transfer
 Large life time of photo generated carriers (n)
 Surface area of particles
BiVO4 -2.4eV
TiO2 – 3.2eV
ZnO -3.4 eV
TiO2
4-6%
Solar
energy
>15%
Solar
energy
BiVO4
-Visible light utilization

5. Bismuth vanadate (BiVO4)
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Fig[2]: Phys. Chem. Chem. Phys., 2011, 13, 4746–4753Fig[1]:RSC Adv., 2014, 4, 6920-6926.
BiVO4 : Visible light driven photocatalysis. Appears in main three Crystalline forms: Monoclinic
scheelite, Tetragonal scheelite & zircon.
Monoclinic (~2.4 eV) (space group I2/b, space group number=15)
(high temp synthesis , stable at 670K – 770K ).
N- type direct band semi conductor.
Water splitting
Yellow pigment
Degradation of
organic pollutant
Solid Electrolyte
for SOFC
Applications
a(Ao) b(Ao) c(Ao) (o)
5.195 5.108 11.707 90.38

6. How to improve the
efficiency BiVO4?
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Importance of doping
 Doping will enhance separation of excited electron-
hole pairs in the semiconductor is suggested by DFT
calculations[1]
 Doping of W or Mo into the V site of BiVO4
strengthens the n-type characteristics by supplying
additional free electrons[2].
To improve the photocatalytic activity ,considering doping BiVO4
with metal ions will modulate the electronic structure.
[1]Z. Zhao et al. / Physics Letters A 374 (2010) 4919–4927, [2] Weifeng Yao, Dalton Trans., 2008, 1426–1430
[3] Phys.Chem.Chem.Phys.,2014, 16, 13465
According to effective mass evaluation from the DFT
calculations theory[3] Mo causes lowering the meff
meff   * 

7. Synthesis technique(Solgel)
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0.002 mol of Bi2O3 in 50 mL of
10% (w/w) HNO3.
0.002 moles of V2O5 in 80 °C of
50ml distilled water
0.004 mol of citric acid 0.004 mol of citric acid
Solution A add into solution B drop wise,
called solution C.
Doping BiVO4
Adding dopant in to the
Solution C
pH ~ 6.5
Stirring at 80oC until gel formation and dry,
calcination at 500oC.

8. Results and discussion
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9. X-Ray powder diffraction
analysis r diffraction
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Figure 1: XRD pattern of Mo- BiVO4 by sol gel method in comparison with undoped BiVO4. Fig 2: shows
characteristic peak shift to higher angle 2 position

10. 5/22/2018 CCE 2014 10
Crystallographic parameters
sample a(Å) b(Å) c(Å) (o)
Volume of cell (106
pm3)
BiVO4 5.195 5.093 11.704 90.38 309.74
2wt%Mo-
BiVO4
5.173 5.087 11.661 90.32 307.58
sample Bi V O1 O2
BiVO4 0, 0.25, 0.6337 0 0.25 0.1352
0.149, 0.506,
0.210
0.258 0.379
0.451
2wt%Mo-
BiVO4
0, 0.25, 0.6275
0.05, 0.255,
0.104
0.121, 0.483,
0.184
0.249, 0.414,
0.450
samples FWHM
2 position (-
121)
Crystallite
size(nm)
Band gap
Eg(eV)
BiVO4 0.2540 28.92 41.89 2.47
2wt%Mo-
BiVO4
0.2660 29.01 36.53 2.46
Table 1: Refined lattice dimensions of 2wt% Mo-BiVO4 and BiVO4 respectively
Table 2: Atomic positions of 2wt% Mo-BiVO4 and BiVO4 samples from rietveld refinement
Table 3: Crystallite size and energy band gaps of Mo-BiVO4 and undoped BiVO4 samples respectively

11. Raman analysis
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Raman spectra has a asymmeric stretching bond of Mo-O-Mo at 871cm-1 Shift in dominant peak at
822cm-1 (streching mode V-O) Clear shift in bending modes VO4 at 326, 364cm-1 .

12. SEM
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SEM images of Mo doped BiVO4 and undoped BiVO4 with EDAX composition in inset

13. UV-Vis Abs Spectroscopy
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DRS spectra of 2wt% Mo-BiVO4 along with BiVO4. In insert, the calculated energy band gaps from
Kubelka-Munk model.

14. Conclusions
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• Mo doped BiVO4 powders were successfully synthesized by Sol-
Gel technique.
• Mo substitutional doping has been confirmed by XRD and micro-
Raman analysis.
• Higher absorption in the range of 550 -850 nm is observed ,but
the band gap remains unchanged.
• Mo-BiVO4 has shown smaller size particles compared to BiVO4
particles which leads higher surface area able to enhance the
photocatalytic performance.
• The photocatalytic activity of Mo doped BiVO4 are underway

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