PHOTOCATALYSIS - CHALLENGES AND

POTENTIALS

Prof. B. ViswanathanDepartment of chemistry

Indian Institute of Technology -Madras

Photocatalysis

Conventional redox reaction

Oxidizing agent should have more positive potential

Photocatalysis - simultaneous oxidation and reduction

The redox couple capable of promoting both the reactions can act as photocatalyst

Metals, Semiconductors and Insulators

reaction assisted by photonscatalyst

2

MetalsNo band gapOnly reduction or oxidationDepends on the band position

InsulatorsHigh band gapHigh energy requirement

Metals

VB

CB

VB

CB

VB

CBH+/H2

H2O/O2

Insulators

SC

E

WHY SEMICONDUCTOR ?

3

For conventional redox reactions, one is interested in either reduction or oxidation of a substrate.

For example consider that one were interested in the oxidation of Fe2+ ions to Fe 3+ ions then the oxidizing agent that can carry out this oxidation is chosen from the relative potentials of the oxidizing agent with respect to the redox potential of Fe2+/Fe3+ redox couple.

The oxidizing agent chosen should have more positive potential with respect to Fe3+/Fe2+ couple so as to affect the oxidation, while the oxidizing agent undergoes reduction spontaneously. This situation throws open a number of possible oxidizing agents from which one of them can be easily chosen.

Concepts –Why semiconductors are chosen as photo-catalysts?

4

Water splitting - carry out both the redox reactions simultaneously - reduction of hydrogen ions (2H+ + 2e- → H2) as well as (2OH- + 2h+ → H2O + 1/2O2 ) oxygen evolution from the hydroxyl ions.

The system that can promote both these reactions simultaneously is essential.

Since in the case of metals the top of the valence band (measure of the oxidizing power) and bottom of the conduction band (measure of the reducing power) are almost identical they cannot be expected to promote a pair redox reactions separated by a potential of nearly 1.23 V.

where the top of the valence band and bottom of the conduction band are separated at least by 1.23V in addition to the condition that the potential corresponding to the bottom of the conduction band has to be more negative with respect to be more negative with respect to while the potential of the top of the valence band has to be more positive to the oxidation potential of the reaction 2OH- + 2h+ → H2O + ½ O2.

5

This situation is obtainable with semiconductors as well as in insulators.

Insulators are not appropriate due to the high value of the band gap which demands high energy photons to create the appropriate excitons for promoting both the reactions. The available photon sources for this energy gap are expensive and again require energy intensive methods. Hence insulators cannot be employed for the purpose of water splitting reaction.

Therefore, it is clear that semiconductors are alone suitable materials for the promotion of water splitting reaction.

6

Criterion one has to use for the selection of the semiconductor materials and also how one can fine tune the material thus chosen

for the water splitting reaction.

Essentially for photo-catalytic splitting of water, the band edges (the top of valence band and bottom of the conduction band or the oxidizing power and reducing power respectively) have to be sifted in opposite directions so that the reduction reaction and the oxidation reactions are facile.

7

Ionic solids as the ionicity of the M-O bond increases, the top of the valence band (mainly contributed by the p- orbitals of oxide ions) becomes less and less positive (since the binding energy of the p orbitals will be decreased due to negative charge on the oxide ions) and the bottom of the conduction band will be stabilized to higher binding energy values due to the positive charge on the metal ions which is not favourable for the hydrogen reduction reaction.

More ionic the M-O bond of the semiconductor is, the less suitable the material is for the photo-catalytic splitting of water. The bond polarity can be estimated from the expression

Percentage ionic character (%) = 100)1( 4)( 2

BA

e

8

The percentage ionic character of the M-O bond for some of the semiconductors

Semiconductor

M-O Percentage ionic character

TiO2SrTiO3Fe2 O3ZnOWO3CdSCdSeLaRhO3LaRuO3PbOZnTeZnAsZnSeZnSGaPCuSeBaTiO3MoS2FeTiO3 KTaO3MnTiO3SnO2Bi2O3

Ti-OTi-O-SrFe-OZn-OW-OCd-SCd-SLa-O-RhLa-O-RuPb-OZn-TeZn-AsZn-SeZn-SGa-PCu-SeBa-O-TiMo-SFe-O-TiK-O-TiMn-O-TiSn-OBi-O

59.568.547.355.557.517.616.553.053.526.5 5.06.818.419.53.510.070.84.353.572.759.042.239.6

9

The oxide semiconductors though - suitable for the photo-catalytic water splitting reaction in terms of the band gap value which is greater than the water decomposition potential of 1.23 V.

Most of these semiconductors have bond character more than 50-60 % and hence modulating them will only lead to increased ionic character and hence the photo-catalytic efficiency of the system may not be increased as per the postulates developed

Therefore from the model developed in this presentation the following postulates have been evolved.

10

The photo-catalytic semiconductors are often used with addition of metals or with other hole trapping agents so that the life time of the excitons created can be increased.

This situation is to increase the life time of the excited electron and holes at suitable traps so that the recombination is effectively reduced.

In this mode, the positions of the energy bands of the semiconductor and that of the metal overlap appropriately and hence the alteration can be either way and also in this sense only the electrons are trapped at the metal sites and only reduction reaction is enhanced.

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•Hence we need stoichiometrically both oxidation and reduction for the water splitting and this reaction will not be achieved by one of the trapping agents namely that is used for electrons or holes.

•Even if one were to use the trapping agents for both holes and electrons, the relative positions of the edge of the valence band and bottom of the conducting band may not be adjusted in such a way to promote both the reactions simultaneously

12

Normally the semiconductors used in photo-catalytic processes are substituted in the cationic positions so as to alter the band gap value.

Even though it may be suitable for using the available solar radiation in the low energy region, it is not possible to use semiconductors whose band gap is less than 1.23 V and any thing higher than this may be favourable if both the valence band is depressed and the conduction band is destabilized with respect to the unsubstituted system.

Since this situation is not obtainable in many of the available semiconductors by substitution at the cationic positions, this method has not also been successful.

13

In addition the dissolution potential of the substituted systems may be more favourbale than the water oxidation reaction and hence this will be the preferred path way.

These substituted systems or even the bare semiconductors which favour the dissolution reaction will undergo only preferential photo-corrosion and hence cannot be exploited for photo-catalytic pathway. In this case ZnO is a typical example.

14

Very low value of the ionic character also is not suitable since these semiconductors do not have the necessary band gap value of 1.23 V. - the search for utilizing lower end of the visible region is not possible for direct water splitting reaction.

If one were to use visible region of the spectrum, then only one of the photo-redox reactions in water splitting may be preferentially promoted and probably this accounts for the frequent observation that non-stiochiometric amounts of oxygen and hydrogen were evolved in the photo-assisted splitting of water.

15

Therefore it is deduced that the systems which has ionic bond character of about 20-30% with suitable positions of the valence and conduction band edges may be appropriate for the water splitting reaction.

This rationalization has given one a handle to select the appropriate systems for examining as photo-catalysts for water splitting reaction.

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There are some other aspects of photo-catalysts on which some remarks may be appropriate.

Though they have been derived from the solid state point of view like flat band potential , band bending, Fermi level pinning, these parameters also can be understood in terms of the bond character and the redox chemical aspects by which the water splitting reaction is dealt.

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PROCESSES ON THE PHOTO-EXCITED SEMICONDUCTOR SURFACE AND BULK

A. Millis and S. L. Hunte J. Photochem. Photobiol. A: Chem 180 (1997) 1 18

Photodecomposition of water

Photocatalytic formation of fuel

Photocatalysis in pollution abatement

TYPICAL PHOTOCATALYTIC PROCESS

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HYDROGEN PRODUCTIONThere are various methods and technologies that have been developed and a few of them have already been practiced. These technologies can be broadly classified as:

Thermo-chemical routes for hydrogen production

Electrolytic generation of hydrogen

Photolytic means of hydrogen formation

Biochemical pathways for hydrogen evolution and

Chemical (steam ) reformation of naphtha

20

Photo electrolysis of Water-Holy Grail of Electrochemistry

Historically, the discovery of photo-electrolysis of water directly into oxygen at a TiO2 electrode and hydrogen at a Pt electrode by the illumination of light greater than the band gap of TiO2 [3.1 eV] is attributed to Fujishima and Honda though photo catalysis by ZnO and TiO2 has been reported much earlier by Markham in 1955

21

2H + + 2e- H2 0.00V

O2 + 4e- + 4H+ 2H2O 1.229V

The band edges of the electrode must overlap with the acceptor and donor states – Minimum band gap 1.23 eV

Charge transfer from the surface of the semiconductor must be fast - prevent photo corrosion

Shift of the band edges resulting in loss of photon energy

CHALLENGES IN PHOTODECOMPOSITION OF WATER

22

PHOTO-ELECTROCHEMICAL CELL FOR THE PHOTO CLEAVAGE OF WATER

23

NHE0.00

1.23

OR Type – Oxidation & Reduction

R Type – Reduction

O Type – Oxidation

X type - None

H+/H2

H2O/O2

TYPES OF SEMICONDUCTORS BASED ON WATER ELECTOLYSIS – CHOICE OF MATERIALS

eV

Semiconductor materials that satisfy the band gap requirement (~1.4 eV) - susceptible for photo corrosion.

Stable materials with a wider band gap absorb light only in the UV region. 24

Conditions for photo electrolysis of water For the direct photo electrochemical decomposition of

water to occur, several key criteria have to be met with. These can be stated at the first level as follows:

The band edges of the electrode must overlap with the acceptor and donor states of water decomposition reaction, thus necessitating that the electrodes should at least have a band gap of 1.23 V, the reversible thermodynamic decomposition potential of water. This situation necessarily means that appropriate semiconductors alone are acceptable as electrode materials for water decomposition.

The charge transfer from the surface of the semiconductor must be fast enough to prevent photo corrosion and shift of the band edges resulting in loss of photon energy.

25

What modifications? various conceptual principles have been incorporated

into typical TiO2 system so as to make this system responsive to longer wavelength radiations. These efforts can be classified as follows:

Dye sensitization Surface modification of the semiconductor to improve

the stability Multi layer systems (coupled semiconductors) Doping of wide band gap semiconductors like TiO2 by

nitrogen, carbon and Sulphur New semiconductors with metal 3d valence band

instead of Oxide 2p contribution Sensitization by doping. All these attempts can be understood in terms of

some kind sensitization and hence the route of charge transfer has been extended and hence the efficiency could not be increased considerably. In spite of these options being elucidated, success appears to be eluding the researchers.

26

Conditions to be satisfied? The band edges of the electrode must overlap

with the acceptor and donor states of water decomposition reaction, thus necessitating that the electrodes should at least have a band gap of 1.23 V, the reversible thermodynamic decomposition potential of water. This situation necessarily means that appropriate semiconductors alone are acceptable as electrode materials for water

The charge transfer from the surface of the semiconductor must be fast enough to prevent photo corrosion and shift of the band edges resulting in loss of photon energy.

27

without deterioration of the stability

should increase charge transfer processes at the interface

should improvements in the efficiency

ENGINEERING THE SEMICONDUCTOR ELECTRONIC STRUCTURES

28

Positions of bands of semiconductors relative to the standard potentials of several redox couples

29

Identifying and designing new semiconductor materials with considerable conversion efficiency and stability

Constructing multilayer systems or using sensitizing dyes - increase absorption of solar radiation

Formulating multi-junction systems or coupled systems - optimize and utilize the possible regions of solar radiation

Developing nanosize systems - efficiently dissociate water

THE AVAILABLE OPPORTUNITIES

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high surface area

morphology

presence of surface states

wide band gap

position of the VB & CB edge

CdS – appropriate choice for the hydrogen production

eV

ADVANTAGES OF SEMICONDUCTOR NANOPARTICLES

31

The opportunities

The opportunities that are obviously available as such now include the following:

Identifying and designing new semiconductor materials with considerable conversion efficiency and stability

Constructing multilayer systems or using sensitizing dyes so as to increase absorption of solar radiation.

Formulating multi-junction systems or coupled systems so as to optimize and utilize the possible regions of solar radiation.

Developing catalytic systems which can efficiently dissociate water.

32

Opportunities evolved Deposition techniques have been considerably

perfected and hence can be exploited in various other applications like in thin film technology especially for various devices and sensory applications.

The knowledge of the defect chemistry has been considerably improved and developed.

Optical collectors, mirrors and all optical analysis capability have increased which can be exploited in many other future optical devices.

The understanding of the electronic structure of materials has been advanced and this has helped to our background in materials chemistry.

Many electrodes have been developed, which can be a useful for all other kinds of electrochemical devices.

33

Limited success – Why?The main reasons for this limited success in all these directions

are due to: The electronic structure of the semiconductor controls the

reaction and engineering these electronic structures without deterioration of the stability of the resulting system appears to be a difficult proposition.

The most obvious thermodynamic barriers to the reaction and the thermodynamic balances that can be achieved in these processes give little scope for remarkable improvements in the efficiency of the systems as they have been conceived and operated. Totally new formulations which can still satisfy the existing thermodynamic barriers have to be devised.

The charge transfer processes at the interface, even though a well studied subject in electrochemistry has to be understood more explicitly, in terms of interfacial energetics as well as kinetics. Till such an explicit knowledge is available, designing systems will have to be based on trial and error rather than based on sound logical scientific reasoning.

34

Nanocrystalline (mainly oxides like TiO2, ZnO, SnO and Nb2O5 or chalcogenides like CdSe) mesoscopic semiconductor materials with high internal surface area If a dye were to be adsorbed as a monolayer, enough can be retained on a given area of the electrode so as to absorb the entire incident light.

Since the particle sizes involved are small, there is no significant local electric field and hence the photo-response is mainly contributed by the charge transfer with the redox couple.

Two factors essentially contribute to the photo-voltage observed, namely, the contact between the nano crystalline oxide and the back contact of these materials as well as the Fermi level shift of the semiconductor as a result of electron injection from the semiconductor.

35

Another aspect of thee nano crystalline state is the alteration of the band gap to larger values as compared to the bulk material which may facilitate both the oxidation/reduction reactions that cannot normally proceed on bulk semiconductors.

The response of a single crystal anatase can be compared with that of the meso-porous TiO2 film sensitized by ruthenium complex (cis RuL2 (SCN)2, where L is 2-2’bipyridyl-4-4’dicarboxlate).

The incident photon to current conversion efficiency (IPCE) is only 0.13% at 530 nm ( the absorption maximum for the sensitizer) for the single crystal electrode while in the nano crystalline state the value is 88% showing nearly 600-700 times higher value.

36

This increase is due to better light harvesting capacity of the dye sensitized nano crystalline material but also due to mesoscpic film texture favouring photo-generation and collection of charge carriers .

It is clear therefore that the nano crystalline state in combination with suitable sensitization is one another alternative which is worth investigating.

37

The second option is to promote water splitting in the visible range using Tandem ells. In this a thin film of a nanocrystalline WO3 or Fe2O3 may serve as top electrode absorbing blue part of the solar spectrum. The positive holes generated oxidize water to oxygen

4h+ + 2H2O --- O2 + 4 H+

The electrons in the conduction band are fed to the second photo system consisting of the dye sensitized nano crystalline TiO2 and since this is placed below the top layer it absorbs the green or red part of the solar spectrum that is transmitted through the top electrode. The photo voltage generated in the second photo system favours hydrogen generation by the reaction

4H+ + 4e- --- 2H2

The overall reaction is the splitting of water utilizing visible light. The situation is similar to what is obtained in photosynthesis

38

Dye sensitized solid hetero-junctions and extremely thin absorber solar cells have also been designed with light absorber and charge transport material being selected independently so as to optimize solar energy harvesting and high photovoltaic output. However, the conversion efficiencies of these configurations have not been remarkably high.

Soft junctions, especially organic solar cells, based on interpenetrating polymer networks, polymer/fullerene blends, halogen doped organic crystals and a variety of conducting polymers have been examined. Though the conversion efficiency of incident photons is high, the performance of the cell declined rapidly. Long term stability will be a stumbling block for large scale application of polymer solar cells.

39

New Opportunities

1. New semi-conducting materials with conversion efficiencies and stability have been identified. These are not only simple oxides, sulphides but also multi-component oxides based on perovskites and spinels.

2. Multilayer configurations have been proposed for absorption of different wavelength regions. In these systems the control of the thickness of each layer has been mainly focused on.

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New Opportunities

3. Sensitization by dyes and other anchored molecular species has been suggested as an alternative to extend the wavelength region of absorption.

4. The coupled systems, thus giving rise to multi-junctions is another approach which is being pursued in recent times with some success

5. Activation of semiconductors by suitable catalysts for water decomposition has always fascinated scientists and this has resulted in various metal or metal oxide (catalysts) loaded semi conductors being used as photo-anodes

41

New opportunities (Contd) Recently a combinatorial electrochemical synthesis

and characterization route has been considered for developing tungsten based mixed metal oxides and this has thrown open yet another opportunity to quickly screen and evaluate the performances of a variety of systems and to evolve suitable composition-function relationships which can be used to predict appropriate compositions for the desired manifestations of the functions.

It has been shown that each of these concepts, though has its own merits and innovations, has not yielded the desired levels of efficiency. The main reason for this failure appears to be that it is still not yet possible to modulate the electronic structure of the semiconductor in the required directions as well as control the electron transfer process in the desired direction.

42

PREPARATION OF CdS NANOPARTICLES

1 g of Zeolite (HY, H, HZSM-5)

1 M Cd(NO3)2 , stirred for 24 h, washed with water

Cd / Zeolite

1 M Na2S solution, stirred for 12 h, washed with water

CdS / Zeolite

48 % HF, washed with water

CdS Nanoparticles

43

XRD PATTERN OF CdS

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)44

Debye Scherrer Equation

d SPACING AND CRYSTALLITE SIZE

0.89cos

T

= diffraction angle T = Crystallite size = wave length = FWHM

d-spacing (Å)Catalyst (0 0 2) (1 0 1) (1 1 2)

CrystalliteSize(nm)

CdS (bulk) 1.52 1.79 2.97 21.7

CdS (bulk)(HF treated)

1.52 1.79 2.93 21.7

CdS-Y 1.53 1.79 2.96 8.8

CdS- 1.52 1.78 2.93 8.6

CdS-Z 1.52 1.79 2.97 7.2

45

UV –VISIBLE SPECTRA OF CdS SAMPLES

Samples Band Gap (eV)

CdS – Z

CdS – Y

CdS -

Bulk CdS

2.38

2.27

2.21

2.13

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)46

PHOTOCATALYTIC PRODUCTION OF HYDROGEN

35ml of 0.24 M Na2S and 0.35 M Na2SO3 in Quartz cell

0.1 g CdS400 W Hg lamp

N2 gas purged before the reaction and constant

stirring

Hydrogen gas was collected overwater in the gas burette

47

AMOUNT OF HYDROGEN EVOLVED BY CdS PHOTOCATALYST

48

TEM IMAGE OF CdS NANOPARTICLES

Catalyst Particle Size (nm)

Surfacearea (m2/g)

Rate of hydrogenproduction ( moles /h)

CdS - Y 8.8 36 102

CdS - Z 6 46 68

CdS - 11 26 67

CdS - Bulk 23 14 45

CdS-Z

CdS-

100 nm100 nm

CdS-Z

49

SCANNING ELECTRON MICROGRAPHS

50

CdS-Z CdS-Y

CdS- CdS- bulk

PHOTOCATALYSIS ON Pt/TiO2 INTERFACE

Electrons are transferred to metal surface

Reduction of H+ ions takes place at the metal surface

The holes move into the other side of semiconductor

The oxidation takes place at the semiconductor surface

TiO2Pt

Vacuum level

Aq. Sol Aq. Sol

pH=0

pH = 7H+/H2

C.B

V.B

EF

T.Sakata, et al Chem. Phys.Lett. 88 (1982) 5051

MECHANISM OF RECOMBINATION REDUCTION BY METAL DOPING

Conduction Bande- e- e- e- e- e- e- e- e- e- e- e-

Valence Bandh+ h+ h+ h+ h+ h+ h+ h+ h+ h+

Electron/hole pairrecombination

Electron/hole pair generation

e-(M) <-- M+e-

Eg

Metallic promoter attracts electrons from TiO2 conduction band and slows recombination reaction

52

Activity of the catalyst is directly proportional to work function of the metal and M-H bond strength.

PHOTOCATALYTIC HYDROGEN EVOLUTION OVER METAL LOADED CdS NANOPARTICLES

53

MetalRedox

potential(E0)

Metal- hydrogen bond energy (K cal mol-1)

Work function

(eV)

Hydrogen evolution rate*(µmol h-1 0.1g-1)

PtPdRhRu

1.1880.9510.7580.455

62.864.565.166.6

5.655.124.984.71

60014411454

HYDROGEN PRODUCTION ACTIVITY OF METAL LOADED CdS PREPARED FROM H-ZSM-5

*1 wt% metal loaded on CdS-Z sample. The reaction data is presented after 6 h under reaction condition.

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)54

Pt, Pd & Rh show higher

activity

High reduction potential.

Hydrogen over voltage is less for Pt, Pd & Rh

EFFECT OF METALS ON HYDROGEN EVOLUTION RATE

Ru

Ni

Pt

Pd

Ag

Fe

Cu

RhAu

10

100

1000

3 %55

EFFECT OF SUPPORT ON THE CdS PHOTOCATLYTIC ACTIVITY

2, 5,10 and 20 wt % CdS on support - by dry impregnation method

MgO support has higher photocatalytic activity - favourable band position

Alumina & Magnesia supports enhance photocatalytic activity

56

Pb2+/ ZnS Absorption at 530nm (calcinations at 623-673K) Formation of extra energy levels between the band gap by Pb 6s orbital Low activity at 873K is due to PbS formation on the surface (Zinc blende to wurtzite)

(a) 573 K, (b) 623 K, (c) 673 K, (d) 773 K, and (e) 873K Band structure of ZnS doped with Pb.

Eg

I. Tsuji, et al J. Photochem. Photobiol. A. Chem 622 (2003) 1 57

250 ml of 5 mM Na2S solution

250 ml of 1 mM Cd(NO3)2

Rate of addition 20 ml / h

Ultrasonic waves

= 20 kHz

The resulting precipitate was washed with distilled water

until the filtrate was free from S2- ions

PREPARATION OF MESOPOROUS CdS NANOPARTICLE BY ULTRASONIC MEDIATED PRECIPITATION

58

The specific surface area and pore volume are 94 m2/g and 0.157 cm3/g respectively

The adsorption - desorption isotherm – Type IV (mesoporous nature)

Mesopores are in the range of 30 to 80 Å size

The maximum pore volume is contributed by 45 Å size pores

N2 ADSORPTION - DESORPTION ISOTHERM

59

XRD pattern of as-prepared CdS -U shows the presence of cubic phase

The observed “d” values are 1.75, 2.04 and 3.32 Å corresponding to the (3 1 1) (2 2 0) and (1 1 1) planes respectively - cubic

The peak broadening shows the formation of nanoparticles

The particle size is calculated using Debye Scherrer Equation

The average particle size of as- prepared CdS is 3.5 nm

X- RAY DIFFRACTION PATTERN

M. Sathish and R. P. Viswanath Mater. Res. Bull (Communicated)60

The growth of fine spongy particles of CdS-U is observed on the surface of the CdS-U

The CdS-bulk surface is found with large outgrowth of CdS particles

The fine mesoporous CdS particles are in the nanosize range

The dispersed and agglomerated forms are clearly observed for the as-prepared CdS-U

CdS-U CdS - BulkTEM SEM

ELECTRON MICROGRAPHS

61

CdS-U

100 nm

Metal CdS-U CdS-Z CdSbulk

-

Rh

Pd

Pt

73

320

726

1415

68

114

144

600

45

102

109

275

1 wt % Metal loaded CdS – U is 2-3 times more active than

the CdS-Z

PHOTOCATALYTIC HYDROGEN PRODUCTION

Na2S and Na2SO3 mixture used as sacrificial agent

Amount of hydrogen (µM/0.1 g)

62

Difficulties on controlling the semiconductor electronic structure without deterioration of the stability

Little scope on the thermodynamic barriers and the thermodynamic balances for remarkable improvements in the efficiency

Incomplete understanding in the interfacial energetic as well as in the kinetics

LIMITED SUCCESS – WHY?

63

Deposition techniques -thin film technology, for various devices

and sensory applications.

Knowledge of the defect chemistry has been considerably improved and developed.

Optical collectors, mirrors and all optical analysis capability have increased

Understanding of the electronic structure of materials

Many electrodes have been developed- useful for all other kinds of electrochemical devices.

THE OTHER OPPORTUNITIES EVOLVED

64

Thank you all foryour kind attention