1. Chao-Wei.H and Wu. J. C. S Chi-Hung. L, Catalysts 2, 490 (2012)
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Sing. K.S.W. Gregg.S.J., Adsorption, Surface Area and Porosity, 2nd ed. (1982)
D. Zhao, Huo, Q., Feng, J., Chemlka, B. F. and Stucky, G. D., JACS 120 (24) (1998).
Catalysis Today 51 (1999) 233-254
Porous
Materials
Microporous
<2nm
Mesoporous
2-50nm
Macroporous
>50nm
Background
Motivation
TiO2 is the most researched and used photocatalyst but its bandgap energy is
in the UV region.
Requirements for good photocatalyst:
•1.23 eV is the minimum band gap.
•Hydrophilic
•Slow recombination
•High specific surface area
Bandgap modification of photocatalysts into visible region can improve the
efficiency of photocatalyst.
Hypothesis
Material Synthesis
(TiO2)x(SiO2)1-x x=0.04,0.08,0.1
Characterization
Results
Conclusion
• The surface and bulk of nanoporous materials have different thermal
expansion coefficient.
• Stress in nanoporous glass can be manipulated using this thermal
expansion mismatch.
• We developed a physical method of manipulating the bandgap of
nanoporous glasses for photocatalytic applications.
References
Bandgap Manipulation of Nanoporous Photocatalyst
Mayur Sundararajan and Gang Chen
Department of Physics and Astronomy, Ohio University, Athens, OH 45701
Valence Band
Conduction Band
Reactants
Reduce
Oxidize
Photocatalyst
e
-
e
-
h
+
Bandgap
Energy
Sunlight
CO2
H2O
O2
Starch
Photosynthesis
Photocatalysis: Chemical reaction induced by photoirradiation in the
presence of a photocatalyst.
H2
Photocatalyst
Application:
Water-splitting by solar energy
Ex. TiO2,, ZnS, SrTiO3, CdS, GaP
Mesoporous
glass
Mesopores
Porewall
• The porewalls are amorphous
• High Specific Surface Area
• High Porosity
• The pores may be ordered or disordered
Zeolites
0 100 200 300 400 500 600
0.19140
0.19145
0.19150
0.19155
0.19160
0.19165
0.19170
0.19175
SAXS_peak_position(Å-1)
WAXS_peak_position(Å-1)
Temperature(°C)
SAXS_peak_position(Å-1)
1.562
1.564
1.566
1.568
1.570
1.572
1.574
WAXS_peak_position(Å-1)
Along the pores
Expansion
Perpendicular
to the pores
Contraction
Inter-poredistance(Å-1)
Strainintheporewall(Å-1)
Anisotropic Thermal Expansion
Stress Relaxation
Temperature
Time
RT
Synthesis Temperature
We propose that this stress manipulation
by annealing can be used to modify the
bandgap of a wide bandgap amorphous
material.
M(OR)4
OH
𝐻2 𝑂+
M
OH
𝐻2 𝑂+
𝑂−
OH
M
OH
𝑂−
Basic
Acidic
Metal
Precursor
Condensation
with template
Surfactant
Micelle
Surfactant
Self-assembly
Liquid crystal
Template
Condensation with
metal precursor
Template
Removal
Mesoporous
material
Inorganic Component
Organic
Component
Aging
Metal Precursor
TEOS – Tetra Ethyl Ortho Silicate
Ti(OPr)4 – Titanium Iso-Propoxide
Gas-sorption
• Pore size
• Pore volume
• Surface area
X-ray Scattering
WAXS
(10-50°)
SAXS
(0.1-10°)
X-ray film
d10
60°
Inter-pore
distance
Pore wall
Pore
SAXS WAXS
UV-vis Spectroscopy
Tauc Plot
Tauc Equation
(Abs*E)2 = k(hv-E)
3.50 3.75 4.00 4.25 4.50 4.753.50 3.75 4.00 4.25 4.50 4.753.50 3.75 4.00 4.25 4.50 4.753.50 3.75 4.00 4.25 4.50 4.75
eV
600C - (3.74eV)
(Abs*E)^2
700C - (3.94eV)
900C - (3.87eV)
800C - (4.02eV)
SEM-Energy Dispersive X-ray Spectroscopy
Element
Line
Atom % Atom %
Error
O K 54.28 +/- 1.20
Si K 41.66 +/- 0.43
Ti K 4.06 +/- 0.27
Total 100.00
Bandgap – Tauc Plot
Sample 600C –AS 700C 800C
Surface Area(m2/g) 830 786 796
Pore width(A) 27 27.5 27
Pore wall(nm) 1.8 1.7 1.5
Pore volume(cm3/g) 0.6 0.5 0.5
Bandgap Manipulation Method
Surfactant
CTAB – Cetyl Trimethyl Ammonium Bromide
Sol-gel synthesis:
Cuvette:capitolscientific.com,Gas-sorption:micromerirtics.com,SEM:guillermocapilla.wordpress.com.UV-vis Spectroscopy:nordiscientific.com,Bones:Smithsonian National Museum of Natural History,Zeolites:http://www.zeolite-collection.eu/
600 650 700 750 800 850 900
3.84
3.88
3.92
3.96
4.00
Bandgap(eV)
Temperature(c)
Bandgap vs Temp
Amorphous Crystalline
Intensity(arb.units)
q(nm-1
)
Periodic Pores
SAXS
First sharp diffraction peak(FSDP)
WAXS
Log(Intensity(arb.Units)
4 8 12 16 20 24 28
2.5
3.0
3.5
4.0
4.5
5.0
Intensity(arb.units)
q(nm-1
)
800C
700C
10 15 20 25
Intensity(arb.units)
q(nm-1
)
800C
700C
1.0 1.5 2.0 2.5
Intensity(arb.units)
q(nm-1
)
800C
700C
SAXS/WAXS –Stress Indicator
Log(Intensity(arb.Units)