titania - photocatalyst for waste water decontamination · titania as a photocatalyst - application...
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Titania as a photocatalyst - Application in water cleaning
Titania - photocatalyst for waste water decontamination
Titania as a photocatalyst - Application in water cleaning
Table of contents
1. Introduction
2. State of art in waste water decontamination
3. Titania as a photocatalyst
4. Chemical modification of titania thin films
5. Laser modification of titania thin films
6. Experimental details
7. Photocatalytic tests
Titania as a photocatalyst - Application in water cleaning
Global Aim – Environmental protection
Water emission of organic substances in 1000 tons per year
Water emission of heavy metals in tons per year
Heavy metalsOrganic substancesNitrogen substances
BASF Annual report for 2003
Titania as a photocatalyst - Application in water cleaning
Waste water decontamination –state of art
Waste water decontamination methods
Mechanical method
Biological method
Physical method
Chemical method
H2O2 / UV
O3 / UV
Fenton - Reaction
Heterogeneous photocatalysis
Commercialmethods
Advanced Oxidation-Processes (AOP)
Titania as a photocatalyst - Application in water cleaning
• Irradiation of semiconductors having a band gap (2 - 4 eV) with UV light energy ≥ energy of the band gap Eg
• Generation of charge carriers
TiO2 hν TiO2 ( e- + h+)
• Formation of active radicals (OH*, O2*)
OH- + h+ OH•
O2- + e- •O2-
• Recombination process
e- + h+ Heat
hν
λ ≤ 390 nmE = 3,00 eV
Titania as a photocatalyst
Titania as a photocatalyst - Application in water cleaning
Photocatalysis
• Fujischima, Honda (1972) : Hydrogen synthesis via water photolysis in the presence of TiO2 electrode
• Bahnemann et al. (1984): Charge carriers generation via flash photolysis
and radicals formation on the surface of the photocatalyst
• Dibble, Dong (1991): Patent of the photocatalytic air decontamination
• Hoffman et al. (1995) : Application of the photocatalysis in the environment
• Linsebigler et al. (1995) : Photocatalysis on the TiO2 surface:
mechanism and experimental results
Titania as a photocatalyst - Application in water cleaning
Titania as a photocatalyst
Metal Semiconductor
Conduction band, CBfree free
Valence band, VB occupiedpartialy occupied
EF
EF
occupiedoccupied
Energy band of the internal shell
electrons
Electron energy levels in solid state - EF is the Fermi level
Titania as a photocatalyst - Application in water cleaning
Photocatalysts
• Semiconductors with band gap Eg = 2 – 4eV
• Oxides of the transition metals - ZnO, TiO2, Fe2O3
chalogenides - CdS, CdSe, ZnS
• Requirements for the catalysts
high specific surface area and porosity
chemical and UV resistance
nontoxical
photocorrosion – ZnO, CdS
toxic ions – Cd, S
reactive at different pH – Fe ions
Titania as a photocatalyst - Application in water cleaning
Why TiO2 ?
Advantages of ТiO2
• nontoxic• chemical resistant• photocorrosion resistant• cheap
Disadvantages of ТiO2
• Absorption in the UV wavelength range (3.2 eV)• High recombination rate
Solid state form - nanoparticles- thin films
Agglomeration affinity and filtration process necessary - nanoparticles Low specific surface area – thin films
TiO2photocatalyst
Titania as a photocatalyst - Application in water cleaning
Titania as a photocatalyst
Nanoparticles Thin films
Adv: high specific surface area
high adsorption ability
Adv: Stability at pH 6 -8
Smooth separation
Disadv: Agglomeration affinity by
pH - changes
Filtration and regeneration step
necessary
Disadv: low specific surface area,
low thermal stability,
cracks during the calcination
Literature: Kamat et al. (1983)
Gabera et al. (1996)
Illis, Andras (1999), Yu (2001
Literature: Mattews (1987)
Chang (2000)
Sakkas (2003)
Titania as a photocatalyst - Application in water cleaning
Crystal phases of titania
Phases Crystal type
Photocatal.Activity
Literature
Anatase (tetragonal) Energy band gap : 3,2 eVDensity : 3,91g/cm3
high
Marue Fox et al. (1995)
Yataka et al. (1999)
Brokit (orthorhombic)Energy band gap: 3,1eVDensity : 4,13 g/cm3
middleKominamia et al. (2000)
Rutile (tetragonal)Energy band gap : 3,0 eV Density : 4,27 g/cm3
lowMarue Fox et al. (1995)
Yataka et al. (1999)
Titania as a photocatalyst - Application in water cleaning
Technical photocatalysts
Literature : Cabrera et al. (1996), Chen und Ray (1998) and Lucarelli et al. (2000)
ProductAnatas part
in %Specific
surface areain m2/g
Pore diameterin nm
Extinctions-coefficient εTiO2
P-25Degussa
~ 70 50 no pores 5,5 · 103
Aldrich > 99 9,6 - 4,0 · 103
Hombikat > 99 > 250 5,6 2,5 · 103
Fisher ~ 95 8,8 - 1,0 · 103
AnatasBritish TiO2
> 99 105,8 5 -
RutilBritish TiO2
0 32,4 no pores -
Titania as a photocatalyst - Application in water cleaning
Photocatalytic activity of titania nanoparticles and thin films
Thin film modified with
Particlesdiameter
in nm
Specific surface area
in m2/g
Pore diameterin nm
Photoactivity in mol/g Catalyst
nonmodified 10,3 71 3,8 0,71
Polyethylen-glycol( PEG) 14,0 69 3,8 1,16
Ethyldiglycol-acetat (EEE) 8,1 89 4,3 1,59
PEG und EEE 7,8 76 4,1 0,34
NanoparticlesDegussa P-25
20,0 50 - 0,34
Literature : N.Negishi et al., Thin Solid Films 392 (2001) 249-253
Titania as a photocatalyst - Application in water cleaning
Photocatalytic activity : The ability of the catalyst to degrade the contaminant(A Decrease of the contaminat concentration a time limit)
Mills et al. (1993): Oxidation of pentachlorphenol
2 HOC6Cl5 + 7 O2hv (TiO2) 4 HCOOH + 8 CO2 + 10 HCl
Choi and Hoffman (1994): Reduction of tetrachlormethan
CCl4 + 2 H2O hv (TiO2) CO2 + H+ + Cl-
Others Contaminants: Aromatic hydrocarbons, aldehyds, ketons,nitrogen-substances, organic acids and alcohols, pesticide, herbicide
Photocatalytic degradation of organic model substances by titania
Titania as a photocatalyst - Application in water cleaning
Processes for thin films preparation
• Physical methods (expensive)
- Pulse laser deposition (PLD)- RF sputtering- Electron beam evaporation
• Chemical methods (easily accessible)
- Sol - gel method- Spray pyrolysis- Chemical Vapour Deposition (CVD)
Titania as a photocatalyst - Application in water cleaning
Sol - Gel process
1. Hydrolysis
(RO)3Ti-OR + H-OH (RO)3Ti-OH + ROH
2. Condensation with water separation
(RO)3Ti-OH + HO-Ti (RO)3 (RO)3Ti-O-Ti(OR)3 + H2O
3. Condensation with alcohol separation
(RO)3Ti-OH + RO-Ti(OR)3 (RO)3Ti-O-Ti(OR)3 + ROH
Titania as a photocatalyst - Application in water cleaning
• Chemical modification
• Laser modification
Modification of the morphology of
titania
The properties of the titania thin films can be changed via
Titania as a photocatalyst - Application in water cleaning
Chemical modification
Electron acceptors - Ag+ Fe2+, Cu2+
Electron donors - Nb5+, Та5+
Acceptors recombination centers -Cr3+, Ga3+
Donors recombination centers - Mo5+,V5+
Sato et al. (1980) doping with PtHermann et al. (1984) doping with Cr 3+
Butler et al. (1993) doping with Cu2+ and Fe2+
Arabatsiz et al. (2003) doping with Ag+
Trapalis et al. (2003) doping with Fe2+
Heidenau et al. (2003) doping with Cu2+
Sakkos et al. (2004) doping with Ag+Nb
Titania as a photocatalyst - Application in water cleaning
Chemical modification
CuO, CdS - shifts the absorption edge to lower energies
(λ > 390 nm)
Al2O3, SiO2 – increase the adsorption ability
of Titan (IV) oxides
Sclafani et al. (1991) CdS - modification
Yang et al. (1997) Al2O3 - modification
Chiang et al. (2002) CuO - modification
Titania as a photocatalyst - Application in water cleaning
Chemical modification
Modification with polymers (Polyethylenglycole) and
organic dyes (Erythrosine)
Goal:→ Control of the catalyst microstructure and
improve the adsorption ability
Kamat et al.(1983) modification with erythrosine
Negischi et al.(2001) modification with PEG and EEE
Magalhanes et al.(2004) modification with PEG
Titania as a photocatalyst - Application in water cleaning
Laser modification
• Excimer laser modificationinduces:
• High specific surface area and porosity
• Control of the phase transition
• Absorption edge shift to lower energies (bigger wavelength range)
• Separation of the elemental phase and decreasing of the recombination rate
Titania as a photocatalyst - Application in water cleaning
Experimental detailsStarting solution 6 Ma. % - Tetraisopropylorthotitanat Solvent Isopropanol, Peptisator : 65 % HNO3
Reaction parameters 25° C, continuous stirringArt of the substrates Glas (Calcium - sodiumsilicate)Deposition techniques Spin Coating, Dip CoatingLayer number 10 bis 15Thermal treatment 120°C und 350°CLaser modification KrF+ Excimer - Laser (λ=248 nm),
Energy density 140 mJ/cm2 bis 720 mJ/cm2
Pulse number 1 to 5
Titania as a photocatalyst - Application in water cleaning
Morphology of the laser modified TiO2 thin films
virgin
Scanning electron microscopy analysis
1µm 1µm1µm1µm
1 Pulse
2 Pulses
5 Pulses
1µm
1µm
1µm
1µm
1µm
1µm
Ed= 160 mJ /cm2
Ed= 450 mJ/cm2
Ed= 720 mJ/cm2
Ed= 300 mJ /cm2
Laser-modifiedTiO2 thin films
248,4 m2/g. 278,5 m2/g.
187,8 m2/g.307,8 m2/g.
164,7 m2/g.
Titania as a photocatalyst - Application in water cleaning
Morphology of the laser modifiedTiO2 and silver-doped TiO2 thin films
a
b
c
Atomic force microscopy of the virgin and laser modified structures
virgin (a),
laser modified:
with 1 Pulse (b),
with 5 Pulses (c)
Titania as a photocatalyst - Application in water cleaning
Optical spectra of titania
Results:Decreases of the transmission Absorption edge shifts to the visible range (400 – 450 nm )
200 300 400 500 600 700 8000
20
40
60
80
100
Wavelength in nm
virgin
160 mJ/cm2
480 mJ/cm2
720 mJ/cm2
Tran
smiss
ion
in %
200 300 400 500 600 700 8000
20
40
60
80
100
Tra
nsm
issi
on in
%
Wavelength in nm
virgin 1 pulse 2 pulses 5 pulses
Titania as a photocatalyst - Application in water cleaning
ТЕМ images of the lasermodified TiO2 – crystalphase (а,b), transitionfrom crystal toamorphous (с) andamorphous phase (d, e)
а c d
TEM and SAED pictures of laser modified titania
Titania as a photocatalyst - Application in water cleaning
HRTEM analysis of the laser modified TiO2 thin films
a b
Brightfield mode Dakrfield mode
Titania as a photocatalyst - Application in water cleaning
Elemental analysis of the laser modified TiO2 thin film
Analysis O Na Mg Al Si Ti Ca Notices
Probe with 1 Pulse
56.1 3.0 - - - 31.4 - rest C in the films
Probe with5 Pulses
56,3 2,6 - - 1,2 26,6 - rest C in the films
Table 1. EDAX elemental analysis of the samples laser modified with 1 and 5 Pulses in atom. %
Titania as a photocatalyst - Application in water cleaning
Preparation of silver-doped TiO2 thin films
Тi(OC3H7)4 +C3H7ОН65 % HNO3
Thermal treatmentDrying - 120° C
Calcination - 350° C
АgNO3C3H7ОН
Dip Coating v = 0,08 сm/s
Spin Coating 3000 prm/ 30 s
Excimer laser modificationEd = 240 mJ/cm2
1 Pulse
Titania as a photocatalyst - Application in water cleaning
Morphology of the laser modified TiO2 and silver-doped TiO2 thin films
a b
c d
TiO2
TiO2-Ag
Titania as a photocatalyst - Application in water cleaning
200 300 400 500 600 700 8000
20
40
60
80
100IRVIS
d
b
a
Tran
smiss
ion
in %
Wavelength in nm
TiO2 calcinated - a TiO2 laser modified - b TiO2/Ag calcinated - c TiO2/Ag laser modified -d
Comparision of the optical spectraof undoped and and silver doped titania
Titania as a photocatalyst - Application in water cleaning
X-ray analysis of the silverdoped TiO2 thin films
20 30 40 50 60 70 80
Anatase [200]
Ag [200]
Rutile
Ag [111]
Anatase [103]
47,77
44,00
38,59
37,96
29,95
22,92In
tens
ity [a
.u.]
2θ
TiO2_Ag laser irradiated yellow sol
20 30 40 50 60 70
64,42o
46,30o44,33o38,21o
27,88o
32,25o
31,78o
TiO2/Ag non irradiated TiO2/Ag laser irradiated
Inte
nsity
a.u
.
2θ
Ag [200]Ag [111] Ag [220]Ag2O [211]
Rutile [110]
Anatase [004] Ag2O [111]
WAXRD Wide angle X-ray diffractometry
LAXRD - Low angle
X-ray diffractometry
Titania as a photocatalyst - Application in water cleaning
Control photocatalytical test
Experimental details:
MB Concentration 2.0 х 10-6mol/lUV - 365 nm,6.0 WTime - 6 hSpectrophotometry
of Methylene blue - 660 nm
0 50 100 150 200 250 300 350 4000.190
0.195
0.200
Conc
entra
tion
of m
ethy
lene
blu
e *1
0-5 m
ol/l
Irradiation time in min
methylene blue UV irradiated TiO2 thin film virgin without UV TiO2 thin film laser modified without UV
2%
1%
0,3%
Titania as a photocatalyst - Application in water cleaning
Photocatalytic reactors
UV- Lamp, λ=365 nm,
PTiO2 – thin filmsH2O + organic
pollution
Titania as a photocatalyst - Application in water cleaning
Comparison of the photocatalytic activity of pure and silver doped TiO2 thin films
0 100 200 3000,08
0,09
0,10
0,11
0,12
0,13
0,14
0,15
0,16
Conc
entra
tion
of M
B .1
0-5 in
mol
/l
Irradiation time in min
TiO2 virgin TiO2_Ag virgin
15 %
39%
Titania as a photocatalyst - Application in water cleaning
0 100 200 300 4000.12
0.16
0.20
Conc
entra
tion
of M
B.10
-5 in
mol
/l
Irradiation time in min
pH 6 pH 2 pH 9
TiO2 thin films laser modified31%
21%
17%
0 100 200 300 400
0.04
0.08
0.12
0.16
0.20
Conc
entra
tion
of M
B.10
-5 in
mol
/l
Irradiation time in min
pH 6 pH 2 pH 9
TiO2_Ag thin films Laser irradiated
65%
17%
30%
Comparison of the photocatalytic activity of pure and silver doped TiO2 thin films
Different pH
Titania as a photocatalyst - Application in water cleaning
0 100 200 300 400
0.12
0.14
0.16
0.18
MB
degr
adat
ion.
10-5 in
mol
/l
Irradiation time in min
TiO2laser modified TiO2 _Ag laser modified TiO2 Nanoparticles
catalysts concentration 0.1g/L
0 100 200 300 4000.06
0.08
0.10
0.12
0.14
MB
conc
entra
tion
.10-5
in m
ol/l
Irradiation time in min
TiO2 Nanoparticles TiO2 thin film virgin TiO2 thin film laser modified
same concentration pH 6-7
Comparison of the photocatalytic activity of pure and silver doped TiO2 thin films
Titania as a photocatalyst - Application in water cleaning
0 50 100 150 200 250 3000.04
0.06
0.08
0.10
0.12
0.14
0.16
(a) TiO2 calcinated (b) TiO2/Ag calcinated (c) TiO2laser modified (d) TiO2/Ag laser modified
(d)
(c)
(b)
(a)
C o of m
ethy
lene
blu
e .1
0-5 m
ol/l
Irradiation time in min
Comparison of the photocatalytic activity of pure and silver doped TiO2 thin films
Titania as a photocatalyst - Application in water cleaning
Antibacterial activity of the pure and silver doped TiO2 thin films
E. Coli DH5α cultivated in LuriaBertani (1 Liter consist of 10g Bactotrypton, 5g exstract of yeast, 5g NaCl).
Ag/TiO2-thin film
TiO2/Ag-thin film
TiO2-thin film
TiO2/Ag-Thin film
control
UV Fluorescence Sun
Darkness UV -2 hrs
4 hours
Titania as a photocatalyst - Application in water cleaning
Conclusions
• A new approach for design of the morphology and properties of thin films for purpose of waterdecontamination is proposed
Excimer laser modification induces:
• Surface roughness increase
• Spectral sensibilisation to infrared wavelength range
• Formation of the most photocatalytic active crystal phases
• Two fold increasing of the inherent photocatalytic activity of the samples studied