Metal-oxides and Carbon NanoMaterials for Energy Applications
Dr S K Samdarshi
Department of Energy
Tezpur University, Tezpur
E-mail: drsksamdarshi@rediffmail.com
Polytypism in Metal Oxides:
Advantage Visible Photocatalysis
Dr S K Samdarshi
Centre For Energy Engineering
Central University of Jharkhand
University, Ranchi 835205
Jharkhand
E-mail: drsksamdarshi@rediffmail.com
Contents
A. Energy & Materials
B. Novel Energy Materials
C. Photo-catalysis
D. Novel Applications
E. Conclusion
A. Energy and Materials
Energy Application Materials




Energy utilization, conversion, and
storage
Macroscale  nanoscale
Structural and functional properties of
active materials and their interfaces at
nanoscale.
Applications:



Batteries, Supercapacitors, Fuel Cells:
Electrodes, electrolytes
Photocatalysis, and Photovoltaics:
Nanoparticles, nanostructured systems, Films
Other novel apps. Nanogenerators, Bio-energy ?
B. Novel Energy Materials
Materials and Dimensions

Material with novel structural and
functional properties
0-D structures
• Metal oxide nanoparticles(<5nm ?)
• Fullerene

1-D structures
• Metal oxide nanotubes/nanorods
• Carbon nanotubes/nanorods
• Carbon microtubes

2-D structures
• Graphene

3-D structures ?
C. Photo-catalysis
Photocatalytic Materials

Direct Photocatalytic Applications
• Environmental-Detoxification, Disinfection
• Energy - Solar Hydrogen Production
• Environmental + energy - CO2 valorization

Indirect/Alternative Applications:
• Photo-electrochemical Cell
• Solar Photovoltaic Application- OPV, and
DSSC
• Spin-offs



Photonics/optoelectronics
Spintronics
Piezoelectric nanogenerators
Industrial Applications








Paints with self-cleaning characteristics
Ordnance factory effluent treatment
Dyeing, dairy, tanning industries
Pharmaceuticals industries, Nursing
homes
Cosmetics Industries
Optoelectronics
Sensors; Nanogenerators
Spintronic devices; High density
memory chips
Photocatalysis
Fujishima and Honda, Nature, 1972
i) semiconductor photocatalyst
ii) initiator
iii) in the presence of light
Photocatalysis: Basic Mechanism
Photon
2
3
Electron
Hole
O2
1
Conduction band
Photocatalyst
Eg
Valance band
Reduction
O2-
H2O
.OH + H
Oxidation
+
Applications
Solar detoxification (Air, Water, Soil)
Solar disinfection (Air, Water, Soil)
Solar hydrogen production (Water)
Solar Carbon valorization(Air, Water)
Photocatalyst Materials
Sl.
No
Materi
al
Band
Gap
(eV)
Wavelengt
h (nm)
1.
CdO
2.1
590
2.
CdS
2.5
497
3.
CdSe
1.7
730
4.
Fe2O3
2.2
565
5.
GaAs
1.4
887
6.
GaP
2.3
540
7.
SnO2
3.9
318
8.
TiO2
3.0
390
9.
WO3
2.8
443
10.
ZnO
3.2
390
11.
ZnS
3.7
336
Advantages of Titania: Photostable, cheap & reusable, chemically &
biologically inert, high activity at ambient temperature.
Direct Photocatalytic Application

Problems and Issues
• Photon harvesting/Absorption (Red-shift)
• Carrier generation and separation
• Carrier transport/migration
• Utilization / photocatalytic activity
• Reusability
Structure and Band gap of TiO2
Anatase
Brookite
Rutile
S. Phase
No
Structure
Band
gap
1
Anatase
Tetrahedral
3.2eV
2
Rutile
Tetrahedral
3.0eV
3
Brookite
Octahedral
3.2eV
Active Phase: Anatase
Problems of titania

Low absorption wavelength (< 380 nm)

Recombination of charge carriers(Rutile)

Low surface area
Options to red-shift the absorption
wavelength
Red-shift
Pristine
Anatase TiO2
Doping (anions/cations)
 Co-doping
 Metal oxide Complexes
 Sensitization (Dye/Plasmonic Resonance)

Options available to reduce
recombination



Mixed oxide complex
Multi-phasic MOx with homojunction
Sensitization (with Noble metals/dyes/graphene)
Y
Eg TiO2
Eg
MOx
Mixed oxide
complex
Eg TiO2
Eg TiO2
Eg
TiO2
Sensitization
Mixed phase complex
Options to increase specific
surface Area
Templating
 Nanoscale synthesis
 Templating (Surfactant/Bio)
Research Activities
 Silver sensitized V doped Titania Nanoparticles
 Vanadium doped Titania Nanoparticles
 Mixed Phase(MF) Titania Nanoparticles
 Nitrogen doped Titania Nanoparticles
 Bio-templated Hierarchical superstructures
 Metastable zinc oxide based systems
 Black titania systems
Synthesis



Sol-gel method(Hydrolytic/Non-hydrolytic)
Hydrothermal method
Solution combustion method
Organometallics
Hydrolysis
+
Calcination
Metal Salt +
Oxidant
Heat
Organometallic + M-OH
Autoclave
+
Calcination
Metal oxide
Metal oxide
Metal oxide
Sol-gel method
Solution Combustion
Hydrothermal
1.6
1.4
Absorbance (a.u.)
1.2
1.0
0.8
TiV oxide
0.6
0.4
Ag/TiV oxide
0.2
Degussa P25
0.0
300
A. Ag/TiV oxide
TEM
B. TiV oxide
400
500
600
Wavelength (nm)
700
800
UV-DRS
HRTEM
SAED Pattern
Detoxification
MB
Phenol
A. Methylene Blue
Sample
B. Phenol
Rate Constant(min-1)
Ag/TiV oxide
0.029
TiV oxide
0.015
Degussa P25
0.005
Solar Energy Materials and Solar Cells, Elsevier, 94, 2379-2385, 2010
Disinfection
Ag/TiV oxide (30 min)
TiV oxide (30 min)
Ag/TiV oxide (60 min)
TiV oxide (60 min)
Disinfection of E-Coli Bacteria
Ag/TiV oxide (Light)
TiV oxide (Light)
Degussa P 25 (Light)
Ag/TiV oxide (Dark)
TiV oxide (Dark)
Degussa P 25 (Dark)
Light Control
1.0
0.8
C/C0
0.6
0.4
0.2
0.0
0
10
20
30
40
50
60
Time (min)
Colloids and Surfaces B: Biointerfaces (Elsevier), 86, 7–13.
Microbicidal Photonic Efficiency
 mpe
V .C

J . A.t 
Photonic efficiency
mb
N

( J . Ap .t )
( I . )
J
( N A .h.c)
V=volume (l); ∆C= change in concentration (M); J = flux of photons (Einstein/m2/sec); A= illuminated area (m2);
∆t=change in time (sec). ∆N – Change in CFU count, Ap = effective plating area; NA =Avogadro’s constant
Why DP25 shows visible activity ?
AnataseHeat

 Mixed PhaseHeat

 Rutile
XRD results
A/R
ratio
Calcination
Temperature
(oC)
Anatase
Rutile
Anatase
Rutile
1.
600
33.66
-
100
0
∞
2.
650
38.38
51.38
91.93
8.07
11.39
3.
675
41.60
45.20
87.52
12.48
7.01
4.
700
40.65
51.76
37.84
62.16
0.61
5.
750
47.27
60.60
23.60
76.40
0.31
6.
800
51.48
51.87
8.53
91.47
0.09
7.
850
-
55.32
0
100
0
Sl. No
Crystalline Size (nm)
Spurr’s Equation
Fraction (%)
Scherrer Formula
UV-Vis-DRS spectra
Activity dependence on A/R ratio and
irradiation spectrum
Visible
UV
Variation in rate constant in degradation of Phenol with
increase in rutile content under UV and Visible irradiation
Variation with A/R phase ratio and
Crystallite size
Jung et al, Catalysis Communications (2004)
Su et al, Journal of Physical Chemistry C, 2011
Photocatalytic model for Biphasic
Titania
Barrier
Potential
a.
3.0 eV
3.2 eV
c.
hν (λ 380 nm)
hν (λ > 380 nm)
Barrier
Potential
Barrier
Potential
b.
e
3.2 eV
h
h
e e
h
3.0 eV
Rutile Sink model (Beakley, UNM))
e
e
e
3.0 eV
3.2 eV
h
h
h
Rutile Antenna model (Gray, NWUniv)
Interface model for Biphasic TiO2
Barrier
Potential
a.
3.0 eV
3.2 eV
b.
c.
hν (λ > 380 nm)
Barrier
Potential
Barrier
Potential
hν (λ 380 nm)
e
3.2 eV
h
h
e e
h
3.0 eV
e
e
e
3.0 eV
3.2 eV
h
h
h
Biphasic/mixedphase charge separation
Size dependence of the electronic structure of several oxide nanocomposite systems.
Valence and conduction bands are represented by the corresponding top and bottom
edges, respectively. Blue/red arrows describe UV/visible light induced charge
transfer processes.
Kubacka et al, Chemical Reviews, 2012



Is it possible to further enhance the
activity ?
Increase the specific surface area
Bio-inspired systems
Bio-templating using Cotton(? ) Cellulose
(C6H10O5)n
Chemical composition of cotton fiber
Cellulose
= 95%
Protein
= 1.3%
Ash
= 1.2%
Wax
= 0.6%
Sugar
= 0.3%
Organic acids
= 0.8%
Other chemical compounds = 0.8%
Metal chlorides +
Ether/Alcohol(R-alkyl group)
[Ti]-Cl + ROH  [Ti]-OR + HCl
[Ti]-Cl + ROR  [Ti]-OR + RCl
[Ti]-Cl + [Ti]-OR  [Ti]-O- [Ti]
+ R-Cl
NH-TiO2 -XRD and BET
X-ray powder diffractograms of the
calcined materials.
N2 adsorption–desorption isotherms at -196oC of the
calcined materials derived from cotton wool (top) and
corresponding pore size distributions (bottom).
Boury et al, New Journal of Chemistry, RSC, 2012
Bio-template based hierarchical
superstructure
XRD, BET, Raman Analysis
BET, XRD, TEM Analysis
Sl.
No.
Sample
BET Analysis
Surface Pore
Pore
Area Volume Width
( m2/g) (cm3/g) (nm)
Crystallite Size (nm)
XRD
BET
TEM
1. Cel-TiO2-400
101
0.347
12.6
12
12
20-30
2. Cel-TiO2-700
23
0.150
31.7
26
42
35-50
UV-DRS and PL Analysis
Photo-catalytic Kinetics(UV)
Bio-templated Hierarchical
Superstructure
High specific surface area and photon harvesting features are probably
responsible for this( Boury and Samdarshi, Eur J of In Chem, 2013)
Mixed phase in other semiconductor systems?
ZnO phases
ZincblendeHeat

 Mixed PhaseHeat

Wurtzite ?
Wurtzite
Intensity (a.u.)
Zincblende
20
25
30
35
40
45
50
55
60
65
70
2 (degree)
Rocksalt
Mixed phase ?
ZnO naostructures
Nanohelix
Nanopyramid
Nanotetrapod
Gao et al, Science, 2005
Lu et al, Adv Func Mat, 2008
All Wurtizite ?
Lazzarini et al ACS Nano, 2009
ZnO naostructures
St - Stearate
Yang et al, JACS, 2010
All Wurtizite ?
(101)
ZnO and Co doped ZnO- Mixed
Phase ?
(103)
100
(101)
ZnO
40
(103)
(102)
(110)
60
(002)
80
(100)
Intesity (a.u)
(110)
Co-ZnO
(102)
120
(002)
(100)
140
20
0
30
40
50
60
2degree)
Co doped ZnO – Wurtzite (SG: P63MC) (JCPDS)
Sample
Grain size (nm)
ZnO
32.78
a= 3.179
Co-ZnO
48.66
a= 3.176
d(101)(A0)
Peak intensity
(100)/(200)
c=5.0847
1.589
1.028
c=5.0761
1.588
1.065
Lattice constant
Hydrothermal Synthesis
ZnO/Co-ZnO:Visible Kinetics
PL
1100
1000
900
Intensity (a.u)
800
700
600
500
400
300
ZnO
200
Co-ZnO
100
0
360 380 400 420 440 460 480 500 520 540 560 580 600
wavelength (nm)
Visible - Phenol
Visible - MB
1.0
1.0
0.9
MB
ZnO (MB)
Co-ZnO
0.8
C/Co
C/Co
0.8
0.6
Blank
Co-ZnO
ZnO
0.7
0.6
0.4
0.5
0.2
0.4
0
20
40
60
Time (min)
80
100
120
0
20
40
60
Time(min)
80
100
120
ZnO phases
Zincblende
Intensity (a.u.)
Wurtzite
35
40
45
50
55
60
65
70
2 (degree)
100
90
20
Mixed Zincblende and Wurtzite
phase in Co doped ZnO
(101)
(222)
110

25
*
* (002)
120
*
130

ZnO
10
*

*
5
·



(112)
20
10
(103)
30

(110)
40
·
Co-ZnO (S)
Co-ZnO(M)

*
50

15
(102)
60
(210)
70
*(100)
* (111) *
* (200) *
80
*
30
Intensity (a.u)
25
Intensity (a.u)
20
0
30
35
40
40
50
45
2degree)
2(degree)
60
50
55
70
60
Co-ZnO-Mixed phase
1.6
1.4
1.2
Absorbance
1.0
0.8
Co-ZnO (M)
Co-ZnO (S)
0.6
0.4
ZnO
0.2
0.0
350
400
450
500
Wavelength (nm)
Particle size of the samples
SL No
Sample
Particle size (nm)
1
ZnO
11.3 (WZ)
2
Co-ZnO (S)
13.3(WZ)
3
Co-ZnO(M)
16.4 (WZ), 29 (ZB)
550
600
Co-ZnO mixed phase:Visible
kinetics
MB(blank)
ZnO
S.P
M.P
MB
1.0
Phenol
Blank
ZnO
M.P
S.P
1.0
0.9
0.8
0.8
C/Co
C/Co
0.6
0.7
0.4
0.6
0.2
0.5
0.4
0.0
0
10
20
30
40
50
60
0
20
40
60
80
100
120
140
Time (min)
A
Photocatalytic degradation rate constant and photonic efficiency of the samples
Catalyst sample
ZnO
Co-ZnO (S)
Co-ZnO(M)
Rate constant (min-1) Stand.deviat
n of rate
MB
Phenol
constant for
phenol
0.013
0.025
0.045
0.0016
0.0049 ±0.0011
0.0074 ±0.0016
Photonic efficiency (%)
MB
Phenol
0.014
0.021
0.027
0.002
0.007
0.008
Mn-ZnO (M)
XRD

MnZn45 is a mixed phase of
wurtzite and zinc-blende ZnO

MnZn50 is a single phase ZnO
TEM
Photocatalytic activity of Co-ZnO(M)and Mn-ZnO(M)
for the degradation of MB
High activity of mixed Phase Co-ZnO(M) and Mn-ZnO(M)
compared to pristine and doped single phase ZnO

Synthesis of RGO-TiO2 (M) nanocomposites
XRD
UV-DRS
TEM
Raman
Hydrogenated Ag/TiO2
X-ray diffraction analysis
X-ray diffraction patterns of pristine,
Ag/TiO2 and H-Ag/TiO2.
The relative intensity of the (101) peak of
pristine, Ag/TiO2 and H-Ag/TiO2.
 All the sample found to be anatase phase with average particle
size of about 20 nm
 The relative intensity (RI) of Ag/TiO2 is decreased.
 Further decrease in RI is observed in H-Ag/TiO2.
Hydrogenated Ag/TiO2
TEM micrograph analysis
(a)
Ag
TiO2
(b)
Ag
10 nm
(c)
TiO2
(d)
Ag
Ag
Unhydrogenated titania (a, b) and hydrogenated titania (c, d)
1. The Ag particles are
found to be about 8
nm.
2. The inter planner
spacing of titania and
Ag are found 3.3 and
2.3 Ao, respectively
3. The surface of the
hydrogenated titania
get distorted (show
arrowhead Fig. d).
Hydrogenated Ag/TiO2
Photocatalytic performance analysis
 Ag/TiO2 shows 3.6 times and H-Ag/TiO2
shows 18 times more activity over
pristine titania under visible light.
 The large part of enhancement in the
activity (about 5 times further) is seen
after hydrogenation of the catalyst.
Reason:
i)
SPR induce local field enhancement
near the Ag/TiO2 interface.
ii) Formation of mid-gap/band-tail states
in the band gap of titania due to crystal
distortion
Photocatalytic
degradation of MB
activity under visible
light
D. Novel Energy
Applications Materials
•
•
•
•
Peizoelectric nanogenerators
CO2 valorizaton
Catalysts and Anti-oxidants
Anti-oxidant grafted MWCNT
ZnO Piezoelectric Nanogenerators
For one nanowire
Output voltage on the
load = 8 mV.
PZ energy output by
one NW in one
discharge event is
=0.05 fJ,
NW of typical
resonance frequency 10
MHz, the output power
of the NWwould be
=0.5 pW.
If the density of NWs per unit area on the substrate is 20/mm2, the output
power density is =10 pW/mm2.
Wang et al, Science, 2006
CO2 Valorization

The 2008 atmospheric CO2 level of 385 ppm,
business as usual, will reach 450100 ppm by
2100
STRATEGIES for Mitigation




CO2 emitted may be sequestered through
carbon capture and storage (CCS), in geological
formation would require an additional fuel input
of 25 to 80% - Leakage
May be recycled through biomass to bio-fuel
production through plant products(bioethanol/
bio-diesel) or microalgae - solar-fuel ~ 1%
Thermo-chemical route – Energy intensive
Electrochemical Conversion–Catalyst deactivate
CO2 Valorization


In 1979, Inoue et al used semiconductor s TiO2,
ZnO, CdS, SiC, and WO3, for photo-reduction
of
suspended
in
CO2-saturated
water
illuminated by a Xe lamp.
Small amounts of formic acid, formaldehyde,
methyl alcohol, and methane were produced.





CO2 + 2H++ 2eCO2 + 2H++ 2eCO2 + 4H++ 4eCO2 + 6H++ 6eCO2 + 8H++ 8e-
• Roy et al, ACS Nano, 2010;
 CO + H2O
 HCOOH
 HCHO
 CH3OH
 CH4
Kunacka et al, Chemical Review, 2012
CNT based anti-oxidants charge
carrier in OPV

Butylated hydroxytoluene (BHT)
TEM image of Pristine and BHT Grafted MWCNT
Iron oxide nanoparticles as
antioxidants

Antioxidant potency of Iron oxide
nanoparticles were tested using a
modified DPPH method
Contributors

All the research scholars of S&EM Lab
• Dr. P J Lahkar, Dr. S Paul, and Mr. R G
Nair, Dr M Husain, Dr P S Patil, Dr S R
Patil, Ms B Rajbongshi, Mr A Ramchiary,
Ms R Verma

Project students of S&EM Lab
• Mr A M Tripathi, Ms. S Ojah, Mr. B Borah,
Mr. P Bhardwaj, Mr P Bora, Ms B Boro, S
Bharali

Collaborators
• Dr P H Mutin, Director, CNRS lab; Prof
Bruno Boury, University of Montepellier,
France