1. BiVO4 and WO3 nanophotocatalysts:
water-splitting and environmental applications
Dr. Chandrappa G T
Department of Chemistry, Bangalore University
Bangalore
6th International Conference and Exhibition on Materials Science
and Engineering,
Atlanta, September , 2016

2. Objectives Materials Investigated BiVO4 WO3
Materials synthesis: Solution combustion method
Materials characterization: PXRD, TGA, UV-Vis, SEM, EDX and TEM
Properties study: Photocatalytic activity of materials for hydrogen evolution and degradation of dyes

3. Synthesis methods Building-up process Breaking-down process
Hydrothermal synthesis Inert gas condensation
Chemical vapor deposition Ion beam technique
Combustion synthesis Laser ablation
Co-precipitation Lithography
Micelles Mechanical attrition
Microwave technique Plasma pyrolysis
Sol-gel method Sputtering

4. Advantages of combustion synthesis
It is a self-sustained, short duration exothermic reaction
Volatalize low boiling point impurities and, therefore, result in higher purity products
High temperatures results in the direct formation of phases
No need of expensive processing facilities and equipment
The high thermal gradients and rapid cooling rates can give rise to new non-equilibrium or metastable phases

5. Methodology of solution combustion synthesis
Fuel
Oxidizer
Water
Aqueous redox mixture in a pre-heated muffle furnace (350 ⁰C ⁰C)
Combustion
Nanocrystalline powder

6. Bismuth vanadate (BiVO4)
Bismuth vanadate (BiVO4) is an n-type semiconductor and has been identified as one of the most promising photoanode materials.
It crystallizes either in a scheelite or a zircon-type structure. The scheelite phase has either tetragonal crystal structure or a monoclinic crystal structure while the zircon-type has tetragonal structure.
(a)Monoclinic scheelite
(b) Scheelite tetragonal
(c) Zircon-tetragonal

7. Monoclinic phase shows better photocatalytic activity compared to tetragonal phase.
Synthesis
Solution A:
Bi(NO3) ml HNO g MA
Solution B:
NH4VO g MA + 5ml Water +
Solution B was mixed with solution A with vigorous stirring to avoid precipitation of Bi2O3.
MA-Malic acid

8. Small volume combustion (SVC-BiVO4) : 2. 0-2
Small volume combustion (SVC-BiVO4) : ml precursor solution in 100 ml beaker
Bulk volume combustion (BVC-BiVO4) : more than 2.5 ml precursor solution in 100 ml beaker
Solid combustion (SC-BiVO4) : wet powder/solid obtained after evaporation of aqueous medium over hot plate

9. PXRD patterns of (a) SVC-BiVO4, (b) BVC-BiVO4 and (c) SC-BiVO4

10. TEM images of SVC-BiVO4
EDX pattern of SVC-BiVO4 d c
0.26nm
(200)
0.254 nm
(002) a b
Lattice spacing of 0.26 nm and nm correspond to (2 0 0) and (0 0 2) crystalline planes respectively for monoclinic scheelite BiVO4.

11. Nitrogen adsorption– desorption isotherms and the corresponding pore-size distribution curves (inset) of SVC-BiVO4
surface area of SVC-BiVO4 (13.86 m2 g−1) is nearly 20 times as larger as that of conventional solid state synthesised BiVO4 (0.7m2 g−1).
(a) Band gap for SVC-BiVO4 and (b) Potential energy diagram for photochemical reaction of SVC-BiVO4. a b
There is a shift in CB to more negative redox potential of H+/H2 (0 V vs NHE)

12. Time course of H2 evolution under UV-light irradiation.
489 μ mole/ 2.5 h of H2 evolution from UV photolysis of water-ethanol in the presence of SVC-BiVO4 was determined by gas chromatography

13. Degradation of MB under solar light
At various concentration
At various catalyst loading

14. MB absorption at 664 nm.

15. Carbon source for combustion Photocatalytic activity
Synthesis of BiVO4 by different carbon source and their physicochemical properties
Carbon source for combustion
Particle size in nm
surface area in m2/g
Photocatalytic activity
Urea
3.1
Phenol and Cr(VI)
Urea and citric acid
2.8
Methylene Blue
Sodium carboxymethylcellulose
50-200
3.0
Rhodamine B
DL-Malic acid
10-20
13.86
H2 generation and Methylene Blue
Comparison of hydrogen generation by BiVO4
 No
Material
Irradiation conditions
Reactant solution
Activity (μmol/h)
H O2 1
BiVO4
300 W Xe at >520 nm
aqueous AgNO3
----- 31 2
BiV0.98Mo0.02O4
Xe lamp (l>420 nm)
------
370 3
BiVO4-RGO
visible light,0.8 external bias
0.1M Na2SO4
0.75
0.21 4
PO4-doped BiVO4 50 5
UV light
Water- ethanol
195.6

16. Conclusion
We demonstrated a novel synthetic strategy to produce highly effective visible-light-driven photocatalyst m-BiVO4 and investigated H2 evolution under UV-light in water/ethanol system.
Control over the solution preparation, amalgamation and the quantity of precursor used for the reaction.
The amount of precursor solution used for combustion reaction plays an important role in achieving the impurity free product
G. P. Nagabhushana, G.Nagaraju, G. T. Chandrappa , Journal of Materials Chemistry A, 2013, 1,

17. Tungsten trioxide (WO3)
WO3 is a material of great interest, due to its applications in electrochromic, photocatalytic, photoluminescent, and gas sensing materials.
Synthesis
0.2 g of tungsten metal + 3 ml H2O2
1:1 mol ratio of sucrose was added +
hot plate was maintained at 170±5 °C.
Vigorous flammable reaction with
bluish black product

18. (b) calcined at 500 °C for 30 min and
PXRD patterns of WO3 a b c
(a) as synthesised WO3
(b) calcined at 500 °C for 30 min and
(c) calcined at 500 °C for 2 hours
Phase : Monoclinic

19. TGA of as synthesised WO3
Weight loss of 3.03 wt % up to 150 °C due to adsorbed water
Weight loss of wt % in the range of 150 °C and 470 °C is due to the oxidation of carbon to carbon dioxide.

20. SEM images of (a) as synthesized WO3 and (b) WO3 sample in muffle furnace after 30 min at 500 °C
The porous nature is very much evident from the SEM images
Nitrogen adsorption-desorption isotherms (inset is the corresponding pore-size distribution curve) of WO3
BET surface area = M2/g

21. Band gap for WO3 calcined sample at 500 °C for 30 min
The band gap calculated for WO3 using Mott–Schottky plot is found to be eV.
CB and the VB are found to be at eV and eV respectively.

22. TEM images of WO3 (a and b) WO3 sample calcined at 500 °C for 30 min
HRTEM of the same sample ( inset -SAED pattern)
Size distribution histogram

23. Irradiation conditons
Time course of Hydrogen evolution under UV-light irradiation
WO3 nanoparticles showing hydrogen evolution of about 457 μ mol per 2.5 h, in the absence of either coupling oxides or doping metals. No
Materials
Irradiation conditons
Reactant solution
Activity (μ mol/h) H2
References 1
Bi2W2O9; Pt as Co-catalyst
400–450W Hg lamp
Aq.Methanol 18 26 2
(NaBi)0.5WO4; Pt as Co-catalyst
300 W Xe lamp 7 27 3
(AgBi)0.5WO4; Pt as Co-catalyst
0.1 4
WO3;Pt as Co-catalyst
300–500 W Xe lamp with a cut-off filter (L42)
28-29 5
PbWO4;RuO2 as Co-catalyst
200 W Hg–Xe lamp
Water 24
30-31 6
WO3
240 W Hg-Xe lamp
Water-Ethanol
182.8
Present work
Comparison of hydrogen generation by tungsten trioxide and other tungsten based oxides reported in the literature

24. Degradation of MB under UV-light
At various catalyst loading
At various concentration
The highest photocatalytic activity for the degradation of 10 PPM MB of about 97% within 60 min was exhibited by 100 mg of the photocatalyst.

25. Conclusion
We have demonstrated a simple green process for the synthesis of highly crystalline tungsten oxide.
The high surface area and the average particle size, ~5 nm, of WO3 has shown the excellent photocatalytic activity under UV-light.
The reactants as well as the process is eco-friendly.
The present method is the most cost effective compared to any of the reported ones till date.
Chosing suitable oxidant & fuel in combustion is boundless and hence one can synthesize nanomaterials with unexpected properties.

26. Acknowledgements
University Grants Commission for financial support

27. Thank you