Titania - photocatalyst for waste water decontamination · Titania as a photocatalyst - Application in water cleaning Titania - photocatalyst for waste water decontamination

Titania as a photocatalyst - Application in water cleaning

Titania - photocatalyst for waste water decontamination


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


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


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)


• 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


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



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


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


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


TiO2 applications

TiO2 application



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)


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)


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 -


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


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


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)


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


• Chemical modification

• Laser modification

Modification of the morphology of

titania

The properties of the titania thin films can be changed via


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



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



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


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


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


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.


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)


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


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


HRTEM analysis of the laser modified TiO2 thin films

a b

Brightfield mode Dakrfield mode


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. %


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


Morphology of the laser modified TiO2 and silver-doped TiO2 thin films

a b

c d

TiO2

TiO2-Ag


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


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


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%


Photocatalytic reactors

UV- Lamp, λ=365 nm,

PTiO2 – thin filmsH2O + organic

pollution


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


TiO2 virgin TiO2_Ag virgin

15 %

39%


0 100 200 300 4000.12

0.16

0.20

Conc

entra

tion

of M

B.10

-5 in

mol

/l


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


pH 6 pH 2 pH 9

TiO2_Ag thin films Laser irradiated

65%

17%

30%


Different pH


0 100 200 300 400

0.12

0.14

0.16

0.18

MB

degr

adat

ion.

10-5 in

mol

/l


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


TiO2 Nanoparticles TiO2 thin film virgin TiO2 thin film laser modified

same concentration pH 6-7



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




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


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

Titania - photocatalyst for waste water decontamination · Titania as a photocatalyst - Application in water cleaning Titania - photocatalyst for waste water decontamination

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