58 (2007) 349ndash357

Materials Characterization

Al2O3ndashTiO2 thin films on glass substrate by solndashgel technique

Erdal Celik Ibrahim Keskin Isil Kayatekin Funda Ak Azem Erhan Oumlzkan

Dokuz Eylul University Faculty of Engineering Department of Metallurgical and Materials Engineering 35160 Izmir Turkey

Received 15 March 2006 accepted 26 May 2006

Abstract

In the present research self-cleaning Al2O3ndashTiO2 thin films were successfully prepared on glass substrate using a solndashgeltechnique for photocatalytic applications We investigated the phase structure microstructure adhesion and optical properties ofthe coatings by using XRD SEM scratch tester and UVVis spectrophotometer Four different solutions were prepared bychanging AlTi molar ratios such as 0 007 018 and 073 Glass substrates were coated by solutions of Ti-alkoxide Al-chlorideglacial acetic acid and isopropanol The obtained gel films were dried at 300degC for 10min and subsequently heat-treated at 500degCfor 5min in air The oxide thin films were annealed at 600degC for 60min in air TiO2 Ti3O5 TiO Ti2O α-Al2O3 and AlTi phaseswere determined in the coatings The microstructural observations demonstrated that Al2O3 content improved surface morphologyof the films and the thickness of film and surface defects increased in accordance with number of dipping It was found that thecritical load values of the films with 0 007 018 and 073 AlTi molar ratios were found to be 11 15 22 and 28mN respectivelyFor the optical property the absorption band of synthesized powders shifted from the UV region to the visible region according tothe increase of the amount of Al dopant The oxide films were found to be active for photocatalytic decomposition of methylenebluecopy 2006 Elsevier Inc All rights reserved

Keywords Al2O3ndashTiO2 coatings Solndashgel Microstructure Adhesion Photocatalytic application

1 Introduction

Transparent super-hydrophilic self-cleaning titaniumdioxide (TiO2) coating films on glass substrates havehigh potentiality for practical applications such asmirrors window glasses windshields of automobilesetc The super-hydrophilic property of the surfaceallows water to spread completely across the surfacerather than remain as droplets thus making it anti-

Corresponding author Tel +90 232 412 7472 fax +90 232 4127452

E-mail address isilkayatekindeuedutr (I Kayatekin)

1044-5803$ - see front matter copy 2006 Elsevier Inc All rights reserveddoi101016jmatchar200605015

fogging and easy to wash Recently there have beensome research papers about the super-hydrophilicproperty of TiO2 coating films [1] Several researchers[23] have reported super-hydrophilic TiO2 photocata-lyst and the photogeneration of a highly amphiphilic(both hydrophilic and oleophilic) surface M Machidaet al [4] have also reported the effect of SiO2 additionon super-hydrophilic property of TiO2 photocatalyst Inaddition to these the super-hydrophilic property ofporous TiO2 coating films has been investigated by J Yuet al [1] It is well known that the wettability of solidsurfaces with liquids is governed by the chemicalproperties of TiO2 surfaces and their geometry As far asthe geometry of a surface is concerned the hydrophilic

Fig 1 Flow chart of solndashgel processing for Al2O3ndashTiO2 films

350 E Celik et al Materials Characterization 58 (2007) 349ndash357

properties are well known to be enhanced by fineroughness Therefore the control of the microstructureof the surfaces of coating films is a way to improve thehydrophilic property Of course the chemical propertyof the surfaces is another important factor whichaffects the hydrophilic property With the increase ofchemically absorbed ndashOH on the surface the hydro-philic property will be enhanced [1] K Tadanaga et al[5] have studied super-water-repellent Al2O3 coatingfilms with high transmittance by using solndashgeltechnique A good combination of Al2O3 and TiO2

materials has not been reported yet Nonetheless JELee et al [6] demonstrated the effect of Al dopant onthe phase composition and particle size by usingthermal plasma which is completely different fromsolndashgel technique The optical property of synthesizedTiO2 powder was evaluated on the UVVis absorptionspectra They modified the property of TiO2 byintroduction of Al dopant and demonstrate thefeasibility of improvement of photocatalytic activityof TiO2 under visible light [6]

In our study we combined super-water-repellent andself-cleaning properties of Al2O3 and TiO2 materials asthin films on glass substrates by using solndashgel methodDepending on this we have developed a very simpleefficient and cost-effective method for deposition ofAl2O3ndashTiO2 thin films on glass substrates by using thetitanium isoproxide as a Ti-precursor The advantages ofthe solndashgel method are it is very simple and easy foroperation films are easily anchored on the substrate andit can be used for the deposition of substrates which hascomplex surface or large surface area The method isalso suitable for deposition on other substrates likestainless steel plates alumina plates silicaglass rashigrings silicaglass helix and glass wool Due to coating ofseveral substrates usage of transparent super-hydro-philic self-cleaning Al2O3ndashTiO2 coating films indifferent applications has been increased its importance[7ndash9] Furthermore the interest in the use of solndashgelmethod is due to other advantages good homogene-ity ease of composition control low processingtemperature and good optical properties In particularthe solndashgel processes is efficient in producing thintransparent multicomponent oxide layers of manycompositions on various substrates including glass[8ndash14]

2 Experimental procedure

Al2O3ndashTiO2 films were synthesized on glass sub-strates (15mmtimes15mmtimes2mm) by solndashgel technique forphotocatalytic applications In these experiments the

precursors were first weighted out in chimney hood andthen aluminum chloride (AlCl3middot6H2O) powder wasdissolved in isopropanol and glacial acetic acid Theisopropanol and glacial acetic acid were respectivelyused as solvent and chelating agent Titanium isoprop-oxide was added into the mixture The obtainedsolutions was stirred for 1h in an open receptacle keptat room temperature in air in order to yield a transparentand homogeneous solution as seen in Fig 1 Afterpreparation of solution glacial acetic acid displaced twoisoproxide ligands to form the alcoxydechelate Ti(i-PrO)2middot(CH3COO)2 [15] Four different solutions wereprepared by changing AlTi molar ratios including 0007 018 and 073 After preparation of transparentsolutions pH values of the solutions were measured todetermine their acidic and basic characteristics using astandard pH meter with Mettler Tolede electrode

Oswald viscometer which is a simple device forcomparing the flow times of two liquids of knowndensity was used to determine viscosity values of theprepared solutions as shown in Fig 2 The mainprinciple in determining viscosity depends on measure-ment of flow time from a certain volume of fluidAccording to this method when the viscosity of oneliquid is known the viscosity of the other can becalculated After the reservoir is filled with a liquid it is

Fig 2 Figure of Oswald viscometer

351E Celik et al Materials Characterization 58 (2007) 349ndash357

pulled by suction above the upper mark The timerequired for the liquid to fall from mark 1 to mark 2 isrecorded Then the time required for the same volumeof a liquid for known viscosity to flow is recorded underidentical conditions and the viscosity is calculated withEq (1) According to this principle flow times of theprepared solutions were determined at 25 30 35 40 and45degC and then their viscosity values were calculated asfollows

g1g2

frac14 q1t1q1t2

eth1THORN

where ρ1 and ρ2 are densities of sample solution andreference solution respectively Also t1 and t2 flowtimes of sample solution and reference solutionrespectively In this study isopropanol solvent is takenas a reference fluid [16]

Prior to the coating process glass slide substrateswith dimension of 15mmtimes15mmtimes3mm were cleanedin ultrasonic cleaner with acetone The solutions weredeposited on glass slide substrates The solutiontemperature was kept at 25degC during the depositionThe substrates containing the deposited solutions weredried at 300degC for 10min in air The obtained gel filmswere dried at 300degC for 10min and subsequently heat-treated at 500degC for 5min in air We repeated this film-making process for six times The thick multilayeredfilms were annealed at 600degC for 60min in air to makethem polycrystalline

XRD patterns of thin films were determined bymeans of a Rigaku (DMAX-2200PC) diffractometerwith a Cu Kα irradiation (wavelength λ=015418nm)XRD results of the films were evaluated as a function of

Al content The surface topographies of Al2O3ndashTiO2

films were examined by using SEM (JEOL JSM 6060)Depending on SEM observations surface morphologiesand growth behaviours of the TiO2-based films wereinvestigated in details

Adhesion strength of the films was measured by aShimadzu Scanning Scracth Tester SST-W101 Scratchtest is carried out to determine and analyze the adhesionstrength of a coating to a substrate In the test a diamondstylus scratched over the coated surface with a constantspeed under progressing normal load until a criticalforce is reached at which adhesion failure is detectedThis critical load is used as a measurement of theadhesion between coating and substrate In this studyadhesion strength of coatings was evaluated by using ascanning scratch tester with a 15μm tip radius diamondstylus During the test a stylus was drawn on coatingsurface with a sliding speed of 5μm sminus1 keepingscanning amplitude of 10μmwhich perpendicular to thescratching direction at the same time Load was carriedout progressively to the stylus with a loading speed of2μm sminus 1 Friction on the stylus increases withincreasing load which causes a delay in movementbetween cartridge body and stylus This delay is definedas a cartridge output

UVVis absorption spectra of reaction products ofmethylene blue solutions photocatalyzed by TiO2-basedthin films on glass substrate were recorded by a doublebeam scanning spectrophotometer (V-530 UVVISSpectrophotometer JASCO) Since the methylene blue(C6H18N3ClSmiddot2H2O) is a dye used as an oxidationndashreduction indicator it can be activated by light to anexcited state which in turn activates oxygen to yieldoxidizing radicals as demonstrated in Zeman andTakabayashi [17] The produced TiO2 films wereimmersed in methylene blue solution of 2ppm for 3hunder sunshine The coating surface covered withmethylene blue was irradiated with visible light Thisprocess was repeated for both Al doped and undopedTiO2 films

3 Results and discussion

As to the key role of the solndashgel reaction in thepreparation of organicinorganic materials it is difficultto understand their preparation without a basic knowl-edge of the solndashgel process Many factors influence therate of hydrolysis and condensation in the solndashgelprocess such as temperature pH catalyst nature of thesolvent and the type of salt and alkoxide-basedprecursors [13] The pH value of the solutions is animportant factor among these parameters Because of

Fig 3 pH values of the solutions depending on AlTi molar ratios

Table 1Viscosity values of the solutions having different AlTi molar ratios

Temperature(degC)

Viscosity (cp)

Isopropanol AlTi=0

AlTi=0007

AlTi=018

AlTi=073

25 207 207 183 166 20030 174 191 174 157 18435 149 163 154 139 16340 129 130 135 121 14245 114 121 126 114 131

Fig 4 Relationship between temperature and viscosity in the solutionhaving different AlTi molar ratios

352 E Celik et al Materials Characterization 58 (2007) 349ndash357

this reason we investigated the pH values of thesolutions depending on AlTi ratios as demonstrated inFig 3 According to this result it is clear that acidity ofthe solutions increases with increasing AlTi molarratios It was estimated that Cl ions in AlCl3middot6H2Oprecursor caused to increase acidity of the solutionsowing to an increase of AlTi molar ratios The pHvalues of the solutions with 007 018 and 073AlTimolar ratios were found to be 396 330 276 and 178respectively Although the pH value of pure Ti-basedsolution is 396 the pH values of Al- and Ti-basedsolutions decrease with increasing amount of AlCl3middot6-H2O precursor Inasmuch as pH value of the solution isan important factor influencing the formation of thepolymeric three-dimensional structure of the gel duringthe gelation process it should be taken into considera-tion while preparing solutions While ramified structureis randomly formed in acidic conditions separatedclusters are formed from the solutions showing basiccharacters [1418] Notably Clminus ions favor smallpolymers with more crystalline structures Since poly-meric complexes formed from Clminus ions are ldquobuildingblocksrdquo of the solid the anions are much responsible forthe structure of a solndashgel [18] The other factor isdilution of the solution using solvent The excesssolvent physically affects the structure of the gelbecause the liquid phase during the aging proceduresmainly consists of the excess solvent The changes in thegel structure at this stage partly influence the structure ofthe final film [19]

Gelation occurs when aggregation of particles ormolecules takes place in a liquid under the action of vander Waals forces or via the formation of covalent ornoncovalent bonds This process can be investigatedusing rheological measurement techniques [20]Because of this reason viscosities of the solutions

were measured Fig 4 denotes viscosity values of thesolutions as function of temperature and AlTi molarratios as listed in Table 1 Viscosity values of thesolutions decrease with increasing temperature Accord-ing to the obtained results the highest viscosity valuewas found in the solution with AlTi=073 except AlTi=0 Besides the lowest viscosity value was deter-mined in the solution with AlTi=018 molar ratio

The phase identification of Al2O3ndashTiO2 films onglass slide substrates was performed by means of XRDtechniques after annealing process at 600degC for 1h inair The XRD patterns of the thin films are given in Fig5 with different AlTi ratios such as 0 007 018 and073 Inasmuch as gel coated samples were heat-treatedin the temperature range of 300 and 600degC amorphousand anatase phases were found Especially anatasephase of pure TiO2 having tetragonal structure wasstrongly observed at 600degC as explained elsewhere[2122] It can be seen that the peaks at 2θ of 25283808 4452 4792 5332 and 6266 are assigned to(101) (004) (112) (200) (106) and (215) lattice planesof TiO2 We have similar results with researches of XJiang et al [23] and YM Wang et al [24] regarding as

Fig 5 XRD patterns of Al2O3-TiO2 thin films produced on glasssubstrate depending on AlTi molar ratios such as 0 007 018 and073 The samples were annealed at 600 degC for 60 min in air

353E Celik et al Materials Characterization 58 (2007) 349ndash357

TiO2 peaks Additional peaks rutile TiO2 Ti3O5 TiOTi2O α-Al2O3 and AlTi were found as well as TiO2

anatase phase because of Al dopants As shown in Fig5 α-Al2O3 diffraction peak was obvious in 2θ 24deg plus adiffraction peak of anatase phase We could not found

Fig 6 SEMmicrographs of Al2O3-TiO2 films on glass substrate including Aldipping is 6 The scale bar is 5μm

the noticeable change in the phase by an introduction ofAl dopant at low molar ratios such as 0007 and 018We have a good agreement with the research of JE Leeet al [6] In the coating with 007 of CuTi molar ratioAlTi peak with low intensity was determined in 2θ 43degas well as Ti2O rutile and anatase TiO2 phases AnataseTiO2 and Ti3O5 peaks were found in the coatings with018 of AlTi molar ratio It was known that Al specieswell dissolved into the TiO2 crystal because the peakcorresponding to Al compounds did not included in theX-ray diffraction patterns [6] In spite of this realityTi3O5 and α-Al2O3 phases were found in the coatingwith 073 of AlTi ratio because Al2O3 content increasedin the coatings

Fig 6 shows SEM micrographs of Al2O3-TiO2 filmson glass glide substrate including different AlTi ratiosDepending on Al2O3 content of the coatings micro-structure of Al2O3ndashTiO2 films slightly changes Gen-erally speaking Al2O3 content improved surfacemorphology of the films The microstructure of thecoatings in Fig 6(a) reveals some pores and cracksthroughout the coatings In these coatings especially

Ti molar ratios such as (a) 0 (b) 007 (c) 018 and (d) 073 Number of

Fig 7 SEMmicrographs of Al2O3-TiO2 films prepared in AlTi=073 molar ratio including different numbers of dipping The numbers of dipping are(a) 1 (b) 2 (c) 3 (d) 4 (e) 5 and (f) 6 The scale bar is 10μm

354 E Celik et al Materials Characterization 58 (2007) 349ndash357

mosaic structures were observed As shown in Fig 6(b)(c) and (d) very large coating islands and small canalsamong them were found The sizes of coating islands arein the range of 05 and 2μm The size of small canal is05μm Namely as the AlTi molar ratio increases thecoating structure becomes more homogeneous (Fig 6

(d)) The application of thermal processes carried out athigh temperature results in some cracks inside thecoating However no flake of layers is observable Thenumbers of layers are six in all coatings Fig 7 denotesSEM micrographs of Al2O3ndashTiO2 films on glasssubstrate having different layers These films were

Fig 8 Cartridge percentage-test force curves for Al2O3-TiO2 filmswith different AlTi molar ratios

Fig 9 UVndashVis spectra of reaction product of methylene blue solutionphotocatalyzed by a thin film of Al2O3-TiO2 on glass substrate afterUV irradiation of sample (a) Absorbance-wavelength curves ofAl2O3-TiO2 film with AlTi=073 molar ratio depending on filmthickness (b) Absorbance-wavelength curves of Al2O3-TiO2 film withAlTi=0 0007 018 and 073 molar ratios The number of layer is six

355E Celik et al Materials Characterization 58 (2007) 349ndash357

prepared from the solutions having AlTi=073 molarratio As shown from microstructural observations aregular surface morphology forms as AlTi ratioincreases It was observed that coating island size ofthe top layer is larger than that of lower layers Thinfilms are obtained for the coatings which contain fewlayers The thickness of film and surface defectsincreases in accordance with number of dippingHowever more pores and homogeneous structurecould be obtained by changing viscosity of thesolutions Cracking was less extensive in thinner filmsand very thick films which were produced usingviscous solutions tended to peel off the substratecompletely In contrast the films fabricated usingdiluted solutions with solvent are extremely uniformdense crack-free and pinhole-free [25]

The aim of scratch test is to evaluate the adhesionbetween coating and substrate In the test increasingnormal load is applied to the diamond stylus Simulta-neously diamond stylus is scratched over the surface ofthe coating with a constant speed The load at whichfailure occurs on the coating is defined as critical loadThe test load versus cartridge output () curves forTiO2-based films on glass substrates were given in Fig8 During the scratch test with increasing applied loadfriction of the stylus becomes large therefore delay inmovement of the stylus from that of the cartridge bodyalso becomes large This delay is given as a cartridgeoutput Critical load values of the TiO2 coatings werefound from Fig 8 when sudden increase takes place atthe cartridge output The critical load values of 0 007018 and 073 AlTi molar ratios were found to be 11 1522 and 28mN respectively Therefore the films having073 ratio have better adhesion strength to the glass

substrate among other coatings Improvement in adhe-sion properties was determined depending on Al content

The activity of the thin film catalyst was determinedby photo-oxidation of methylene blue Fig 9 depictsUVVis spectra of reaction product of methylene bluesolution photocatalyzed by thin films of Al2O3 dopedand undoped TiO2 on glass substrate after UVirradiation of sample Before UV irradiation thesamples in methylene blue solution were subjected tosun rays for 3h Generally photocatalytic activity can beclassified as three sections However here it wasdetermined depending on concentration variation ofsolutions at which photocatalytic material contains Inthis method absorbance of reaction product of methy-lene blue solution photocatalyzed by thin films of Al2O3

doped and undoped TiO2 on glass substrate after UVirradiation of sample was investigated as a function ofwavelength Generally all solutions including methy-lene blue show characteristic absorption bands at420nm This shows that the thin films deposited onglass catalyze the decomposition of the products

Table 3Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=00007 018 and 073 molar ratios on glass substrate after UVirradiation of sample

AlTi ratio Decomposition ()

0 060007 05018 05073 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h The number of layer is 6

Table 2Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UV irradiation ofsample

Number of layer Decomposition ()

First layer 06Second layer 11Third layer 14Fourth layer 18Fifth layer 08Sixth layer 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h

356 E Celik et al Materials Characterization 58 (2007) 349ndash357

solutions including methylene blue on exposure to UVradiation Similar effects were reported elsewhere [14]The oxide films exhibit an active behaviour forphotocatalytic decomposition of methylene blue Fig9(a) denotes absorbancendashwavelength curves of Al2O3ndashTiO2 film with AlTi=073 molar ratio depending onfilm thickness Table 2 shows decomposition percentageof reaction product of methylene blue solution photo-catalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UVirradiation of sample The highest decompositionpercentage having 18 was obtained from the coatingwith four layers Absorbancendashwavelength curves ofAl2O3ndashTiO2 film with 0 0007 018 and 073AlTimolar ratios are given in Fig 9(b) The number of layeris 6 which is constant for all coatings Table 3 showsdecomposition percentage of reaction product ofmethylene blue solution photocatalyzed by Al2O3ndashTiO2 thin films with 0 0007 018 and 073AlTi molarratios on glass substrate after UV irradiation of sampleAccording to these results the highest decompositionpercentage was seen in the coating with AlTi=0 Adecrease in decomposition percentage was observed inthe films with six layers as Al content increases

4 Conclusion

We have developed a very simple efficient and cost-effective method for deposition of Al2O3ndashTiO2 thinfilms on glass substrates by using the titaniumisoproxide as a Ti-precursor The following results canbe summarized below

(1) Acidity of the solutions increases with increasingAlTi molar ratios It was estimated that Cl ions inAlCl3middot6H2O precursor caused to increase acidityof the solutions owing to an increase of AlTimolar ratios

(2) Viscosity values of the solutions decreases withincreasing temperature According to the obtainedresults the highest viscosity value was found inthe solution with AlTi=073 except AlTi=0Besides the lowest viscosity value was deter-mined in the solution with AlTi=018 molarratio

(3) Because gel coated samples were heat-treated inthe temperature range of 300 and 600degCamorphous and anatase structures were foundEspecially anatase phase of pure TiO2 havingtetragonal structure was strongly observed at600degC Rutile TiO2 Ti3O5 TiO Ti2O α-Al2O3

and AlTi were found as well as TiO2 anatasephase

(4) Al2O3 content improved surface morphology ofthe films The application of thermal processescarried out at high temperature results in somecracks inside the coating In addition to thesemore pores and homogeneous structure couldbe obtained by changing viscosity of thesolutions

(5) The critical load values of 0 007 018 and073AlTi molar ratios were found to be 11 15 22and 28mN respectively Therefore the filmshaving 073 ratio have better adhesion strengthto the glass substrate among other coatingsImprovement in adhesion properties was deter-mined depending on Al content

(6) All solutions including methylene blue showcharacteristic absorption bands at 420nm Thisshows that the thin films deposited on glasscatalyze the decomposition of the productssolutions including methylene blue on exposureto UV radiation Moreover the highest decom-position percentage was seen in the coating withAlTi=0 A decrease in decomposition percentagewas observed in the films with six layers as Alcontent increases

357E Celik et al Materials Characterization 58 (2007) 349ndash357

Acknowledgements

The authors would like to express their gratitude toDept of Metallurgical and Materials Engineering ofDokuz Eylul University Also this study was partlysupported by Technological Research Project of DokuzEylul University

References

[1] Yu J Zhao X Zhao Q Wang G Mater Chem Phys200168253ndash9

[2] Fujishima A Rao TN Tryk DA J Photochem Photobiol CPhotochem Rev 200011ndash21

[3] Wang R Hashimoto K Fujishima A Chikuni M Kojima EKitamura A et al Nature 1997388431ndash5

[4] Machida M Norimoto K Watanabe T Hashimoto K FujishimaA J Mater Sci 1993342569ndash74

[5] Tadanaga K Katata N Minami T J Am Ceram Soc1997801040ndash5

[6] Lee JE Oh S-M Park D-W Synthesis of nano-sized Al dopedTiO2 powders using thermal plasma Thin Solid Films2004457230ndash4

[7] Sonawane RS Hegde SG Dongare MK Preparation of titanium(IV) oxide thin film photocatalyst by solndashgel dip coating MaterChem Phys 200377744ndash50

[8] Kim DJ Hahn SH Oh SH Kim EJ Influence of calcinationtemperature on structural and optical properties of TiO2 thin filmsprepared by solndashgel dip coating Mater Lett 200257355ndash60

[9] Wang Z Hu X Fabrication and electrochromic properties ofspin-coated TiO2 thin films from peroxo-polytitanic acid ThinSolid Films 199935262ndash5

[10] Lucic-Lavcevic M Dubcek P Milat O Etlinger B Turkovic ASokcevic D et al Nanostructure of solndashgel derived TiO2 for thin

films on glass substrates measured by small angle scattering ofsynchrotron light Mater Lett 19983656ndash60

[11] Lin H Kozuka H Yoko T Preparation of TiO2 films on self-assembled monolayers by solndashgel method Thin Solid Films1998315111ndash7

[12] Gartner M Scurtu R Ghita A Zaharescu M Modreanu MTrapalis C et al Thin Solid Films 2004455ndash456417ndash21

[13] Brinker CJ Scherer GW Solndashgel science the physics andchemistry of solndashgel processing San Diego Academic Press1990 p 2656

[14] Sonowane RS Hedge SG Dongare MK Mater Chem Phys200277744ndash50

[15] Guillard C Beaugiraud B Dutriez C Hermann J-M JaffrezicH Jaffrezic-Renault N et al Appl Catal B Environ200239331ndash42

[16] wwwchemuiceduchem343343Viscositypdf[17] Zeman P Takabayashi S Surf Coat Technol 200215393ndash9[18] Pierre AC Introduction to solndashgel processing Boston Kluwer

Academic Publishers 1998 p 36[19] Dumeignil F Sato K Imamura M Matsubayashi N Payen E

Shimada H Appl Catal A Gen 2003241319ndash29[20] Phonthammachai N Rumruangwong M Gulari E Jamieson

AM Jitkarnka S Wongkasemjit S Colloids Surf A Physico-chem Eng Asp 200424761ndash8

[21] Ahn YU Kim EJ Kim HT Hahn SH Mater Lett2003574660ndash6

[22] Liu W-M Chen Y-X Kou G-T Xu T Sun DC Wear2003254994ndash1000

[23] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[24] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[25] Xu B Li D Chen Y Chem Soc Faraday Trans 1998941905ndash6

Fig 8 Cartridge percentage-test force curves for Al2O3-TiO2 filmswith different AlTi molar ratios

Fig 9 UVndashVis spectra of reaction product of methylene blue solutionphotocatalyzed by a thin film of Al2O3-TiO2 on glass substrate afterUV irradiation of sample (a) Absorbance-wavelength curves ofAl2O3-TiO2 film with AlTi=073 molar ratio depending on filmthickness (b) Absorbance-wavelength curves of Al2O3-TiO2 film withAlTi=0 0007 018 and 073 molar ratios The number of layer is six

355E Celik et al Materials Characterization 58 (2007) 349ndash357

prepared from the solutions having AlTi=073 molarratio As shown from microstructural observations aregular surface morphology forms as AlTi ratioincreases It was observed that coating island size ofthe top layer is larger than that of lower layers Thinfilms are obtained for the coatings which contain fewlayers The thickness of film and surface defectsincreases in accordance with number of dippingHowever more pores and homogeneous structurecould be obtained by changing viscosity of thesolutions Cracking was less extensive in thinner filmsand very thick films which were produced usingviscous solutions tended to peel off the substratecompletely In contrast the films fabricated usingdiluted solutions with solvent are extremely uniformdense crack-free and pinhole-free [25]

The aim of scratch test is to evaluate the adhesionbetween coating and substrate In the test increasingnormal load is applied to the diamond stylus Simulta-neously diamond stylus is scratched over the surface ofthe coating with a constant speed The load at whichfailure occurs on the coating is defined as critical loadThe test load versus cartridge output () curves forTiO2-based films on glass substrates were given in Fig8 During the scratch test with increasing applied loadfriction of the stylus becomes large therefore delay inmovement of the stylus from that of the cartridge bodyalso becomes large This delay is given as a cartridgeoutput Critical load values of the TiO2 coatings werefound from Fig 8 when sudden increase takes place atthe cartridge output The critical load values of 0 007018 and 073 AlTi molar ratios were found to be 11 1522 and 28mN respectively Therefore the films having073 ratio have better adhesion strength to the glass

substrate among other coatings Improvement in adhe-sion properties was determined depending on Al content

The activity of the thin film catalyst was determinedby photo-oxidation of methylene blue Fig 9 depictsUVVis spectra of reaction product of methylene bluesolution photocatalyzed by thin films of Al2O3 dopedand undoped TiO2 on glass substrate after UVirradiation of sample Before UV irradiation thesamples in methylene blue solution were subjected tosun rays for 3h Generally photocatalytic activity can beclassified as three sections However here it wasdetermined depending on concentration variation ofsolutions at which photocatalytic material contains Inthis method absorbance of reaction product of methy-lene blue solution photocatalyzed by thin films of Al2O3

doped and undoped TiO2 on glass substrate after UVirradiation of sample was investigated as a function ofwavelength Generally all solutions including methy-lene blue show characteristic absorption bands at420nm This shows that the thin films deposited onglass catalyze the decomposition of the products

Table 3Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=00007 018 and 073 molar ratios on glass substrate after UVirradiation of sample

AlTi ratio Decomposition ()

0 060007 05018 05073 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h The number of layer is 6

Table 2Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UV irradiation ofsample

Number of layer Decomposition ()

First layer 06Second layer 11Third layer 14Fourth layer 18Fifth layer 08Sixth layer 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h

356 E Celik et al Materials Characterization 58 (2007) 349ndash357

solutions including methylene blue on exposure to UVradiation Similar effects were reported elsewhere [14]The oxide films exhibit an active behaviour forphotocatalytic decomposition of methylene blue Fig9(a) denotes absorbancendashwavelength curves of Al2O3ndashTiO2 film with AlTi=073 molar ratio depending onfilm thickness Table 2 shows decomposition percentageof reaction product of methylene blue solution photo-catalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UVirradiation of sample The highest decompositionpercentage having 18 was obtained from the coatingwith four layers Absorbancendashwavelength curves ofAl2O3ndashTiO2 film with 0 0007 018 and 073AlTimolar ratios are given in Fig 9(b) The number of layeris 6 which is constant for all coatings Table 3 showsdecomposition percentage of reaction product ofmethylene blue solution photocatalyzed by Al2O3ndashTiO2 thin films with 0 0007 018 and 073AlTi molarratios on glass substrate after UV irradiation of sampleAccording to these results the highest decompositionpercentage was seen in the coating with AlTi=0 Adecrease in decomposition percentage was observed inthe films with six layers as Al content increases

4 Conclusion

We have developed a very simple efficient and cost-effective method for deposition of Al2O3ndashTiO2 thinfilms on glass substrates by using the titaniumisoproxide as a Ti-precursor The following results canbe summarized below

(1) Acidity of the solutions increases with increasingAlTi molar ratios It was estimated that Cl ions inAlCl3middot6H2O precursor caused to increase acidityof the solutions owing to an increase of AlTimolar ratios

(2) Viscosity values of the solutions decreases withincreasing temperature According to the obtainedresults the highest viscosity value was found inthe solution with AlTi=073 except AlTi=0Besides the lowest viscosity value was deter-mined in the solution with AlTi=018 molarratio

(3) Because gel coated samples were heat-treated inthe temperature range of 300 and 600degCamorphous and anatase structures were foundEspecially anatase phase of pure TiO2 havingtetragonal structure was strongly observed at600degC Rutile TiO2 Ti3O5 TiO Ti2O α-Al2O3

and AlTi were found as well as TiO2 anatasephase

(4) Al2O3 content improved surface morphology ofthe films The application of thermal processescarried out at high temperature results in somecracks inside the coating In addition to thesemore pores and homogeneous structure couldbe obtained by changing viscosity of thesolutions

(5) The critical load values of 0 007 018 and073AlTi molar ratios were found to be 11 15 22and 28mN respectively Therefore the filmshaving 073 ratio have better adhesion strengthto the glass substrate among other coatingsImprovement in adhesion properties was deter-mined depending on Al content

(6) All solutions including methylene blue showcharacteristic absorption bands at 420nm Thisshows that the thin films deposited on glasscatalyze the decomposition of the productssolutions including methylene blue on exposureto UV radiation Moreover the highest decom-position percentage was seen in the coating withAlTi=0 A decrease in decomposition percentagewas observed in the films with six layers as Alcontent increases

357E Celik et al Materials Characterization 58 (2007) 349ndash357

Acknowledgements

The authors would like to express their gratitude toDept of Metallurgical and Materials Engineering ofDokuz Eylul University Also this study was partlysupported by Technological Research Project of DokuzEylul University

References

[1] Yu J Zhao X Zhao Q Wang G Mater Chem Phys200168253ndash9

[2] Fujishima A Rao TN Tryk DA J Photochem Photobiol CPhotochem Rev 200011ndash21

[3] Wang R Hashimoto K Fujishima A Chikuni M Kojima EKitamura A et al Nature 1997388431ndash5

[4] Machida M Norimoto K Watanabe T Hashimoto K FujishimaA J Mater Sci 1993342569ndash74

[5] Tadanaga K Katata N Minami T J Am Ceram Soc1997801040ndash5

[6] Lee JE Oh S-M Park D-W Synthesis of nano-sized Al dopedTiO2 powders using thermal plasma Thin Solid Films2004457230ndash4

[7] Sonawane RS Hegde SG Dongare MK Preparation of titanium(IV) oxide thin film photocatalyst by solndashgel dip coating MaterChem Phys 200377744ndash50

[8] Kim DJ Hahn SH Oh SH Kim EJ Influence of calcinationtemperature on structural and optical properties of TiO2 thin filmsprepared by solndashgel dip coating Mater Lett 200257355ndash60

[9] Wang Z Hu X Fabrication and electrochromic properties ofspin-coated TiO2 thin films from peroxo-polytitanic acid ThinSolid Films 199935262ndash5

[10] Lucic-Lavcevic M Dubcek P Milat O Etlinger B Turkovic ASokcevic D et al Nanostructure of solndashgel derived TiO2 for thin

films on glass substrates measured by small angle scattering ofsynchrotron light Mater Lett 19983656ndash60

[11] Lin H Kozuka H Yoko T Preparation of TiO2 films on self-assembled monolayers by solndashgel method Thin Solid Films1998315111ndash7

[12] Gartner M Scurtu R Ghita A Zaharescu M Modreanu MTrapalis C et al Thin Solid Films 2004455ndash456417ndash21

[13] Brinker CJ Scherer GW Solndashgel science the physics andchemistry of solndashgel processing San Diego Academic Press1990 p 2656

[14] Sonowane RS Hedge SG Dongare MK Mater Chem Phys200277744ndash50

[15] Guillard C Beaugiraud B Dutriez C Hermann J-M JaffrezicH Jaffrezic-Renault N et al Appl Catal B Environ200239331ndash42

[16] wwwchemuiceduchem343343Viscositypdf[17] Zeman P Takabayashi S Surf Coat Technol 200215393ndash9[18] Pierre AC Introduction to solndashgel processing Boston Kluwer

Academic Publishers 1998 p 36[19] Dumeignil F Sato K Imamura M Matsubayashi N Payen E

Shimada H Appl Catal A Gen 2003241319ndash29[20] Phonthammachai N Rumruangwong M Gulari E Jamieson

AM Jitkarnka S Wongkasemjit S Colloids Surf A Physico-chem Eng Asp 200424761ndash8

[21] Ahn YU Kim EJ Kim HT Hahn SH Mater Lett2003574660ndash6

[22] Liu W-M Chen Y-X Kou G-T Xu T Sun DC Wear2003254994ndash1000

[23] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[24] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[25] Xu B Li D Chen Y Chem Soc Faraday Trans 1998941905ndash6

Table 3Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=00007 018 and 073 molar ratios on glass substrate after UVirradiation of sample

AlTi ratio Decomposition ()

0 060007 05018 05073 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h The number of layer is 6

Table 2Decomposition percentage of reaction product of methylene bluesolution photocatalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UV irradiation ofsample

Number of layer Decomposition ()

First layer 06Second layer 11Third layer 14Fourth layer 18Fifth layer 08Sixth layer 009

Before UV irradiation the samples in methylene blue solution weresubjected to sun rays for 3h

356 E Celik et al Materials Characterization 58 (2007) 349ndash357

solutions including methylene blue on exposure to UVradiation Similar effects were reported elsewhere [14]The oxide films exhibit an active behaviour forphotocatalytic decomposition of methylene blue Fig9(a) denotes absorbancendashwavelength curves of Al2O3ndashTiO2 film with AlTi=073 molar ratio depending onfilm thickness Table 2 shows decomposition percentageof reaction product of methylene blue solution photo-catalyzed by Al2O3ndashTiO2 thin films with AlTi=073 onglass substrate depending coating thickness after UVirradiation of sample The highest decompositionpercentage having 18 was obtained from the coatingwith four layers Absorbancendashwavelength curves ofAl2O3ndashTiO2 film with 0 0007 018 and 073AlTimolar ratios are given in Fig 9(b) The number of layeris 6 which is constant for all coatings Table 3 showsdecomposition percentage of reaction product ofmethylene blue solution photocatalyzed by Al2O3ndashTiO2 thin films with 0 0007 018 and 073AlTi molarratios on glass substrate after UV irradiation of sampleAccording to these results the highest decompositionpercentage was seen in the coating with AlTi=0 Adecrease in decomposition percentage was observed inthe films with six layers as Al content increases

4 Conclusion

We have developed a very simple efficient and cost-effective method for deposition of Al2O3ndashTiO2 thinfilms on glass substrates by using the titaniumisoproxide as a Ti-precursor The following results canbe summarized below

(1) Acidity of the solutions increases with increasingAlTi molar ratios It was estimated that Cl ions inAlCl3middot6H2O precursor caused to increase acidityof the solutions owing to an increase of AlTimolar ratios

(2) Viscosity values of the solutions decreases withincreasing temperature According to the obtainedresults the highest viscosity value was found inthe solution with AlTi=073 except AlTi=0Besides the lowest viscosity value was deter-mined in the solution with AlTi=018 molarratio

(3) Because gel coated samples were heat-treated inthe temperature range of 300 and 600degCamorphous and anatase structures were foundEspecially anatase phase of pure TiO2 havingtetragonal structure was strongly observed at600degC Rutile TiO2 Ti3O5 TiO Ti2O α-Al2O3

and AlTi were found as well as TiO2 anatasephase

(4) Al2O3 content improved surface morphology ofthe films The application of thermal processescarried out at high temperature results in somecracks inside the coating In addition to thesemore pores and homogeneous structure couldbe obtained by changing viscosity of thesolutions

(5) The critical load values of 0 007 018 and073AlTi molar ratios were found to be 11 15 22and 28mN respectively Therefore the filmshaving 073 ratio have better adhesion strengthto the glass substrate among other coatingsImprovement in adhesion properties was deter-mined depending on Al content

(6) All solutions including methylene blue showcharacteristic absorption bands at 420nm Thisshows that the thin films deposited on glasscatalyze the decomposition of the productssolutions including methylene blue on exposureto UV radiation Moreover the highest decom-position percentage was seen in the coating withAlTi=0 A decrease in decomposition percentagewas observed in the films with six layers as Alcontent increases

357E Celik et al Materials Characterization 58 (2007) 349ndash357

Acknowledgements

The authors would like to express their gratitude toDept of Metallurgical and Materials Engineering ofDokuz Eylul University Also this study was partlysupported by Technological Research Project of DokuzEylul University

References

[1] Yu J Zhao X Zhao Q Wang G Mater Chem Phys200168253ndash9

[2] Fujishima A Rao TN Tryk DA J Photochem Photobiol CPhotochem Rev 200011ndash21

[3] Wang R Hashimoto K Fujishima A Chikuni M Kojima EKitamura A et al Nature 1997388431ndash5

[4] Machida M Norimoto K Watanabe T Hashimoto K FujishimaA J Mater Sci 1993342569ndash74

[5] Tadanaga K Katata N Minami T J Am Ceram Soc1997801040ndash5

[6] Lee JE Oh S-M Park D-W Synthesis of nano-sized Al dopedTiO2 powders using thermal plasma Thin Solid Films2004457230ndash4

[7] Sonawane RS Hegde SG Dongare MK Preparation of titanium(IV) oxide thin film photocatalyst by solndashgel dip coating MaterChem Phys 200377744ndash50

[8] Kim DJ Hahn SH Oh SH Kim EJ Influence of calcinationtemperature on structural and optical properties of TiO2 thin filmsprepared by solndashgel dip coating Mater Lett 200257355ndash60

[9] Wang Z Hu X Fabrication and electrochromic properties ofspin-coated TiO2 thin films from peroxo-polytitanic acid ThinSolid Films 199935262ndash5

[10] Lucic-Lavcevic M Dubcek P Milat O Etlinger B Turkovic ASokcevic D et al Nanostructure of solndashgel derived TiO2 for thin

films on glass substrates measured by small angle scattering ofsynchrotron light Mater Lett 19983656ndash60

[11] Lin H Kozuka H Yoko T Preparation of TiO2 films on self-assembled monolayers by solndashgel method Thin Solid Films1998315111ndash7

[12] Gartner M Scurtu R Ghita A Zaharescu M Modreanu MTrapalis C et al Thin Solid Films 2004455ndash456417ndash21

[13] Brinker CJ Scherer GW Solndashgel science the physics andchemistry of solndashgel processing San Diego Academic Press1990 p 2656

[14] Sonowane RS Hedge SG Dongare MK Mater Chem Phys200277744ndash50

[15] Guillard C Beaugiraud B Dutriez C Hermann J-M JaffrezicH Jaffrezic-Renault N et al Appl Catal B Environ200239331ndash42

[16] wwwchemuiceduchem343343Viscositypdf[17] Zeman P Takabayashi S Surf Coat Technol 200215393ndash9[18] Pierre AC Introduction to solndashgel processing Boston Kluwer

Academic Publishers 1998 p 36[19] Dumeignil F Sato K Imamura M Matsubayashi N Payen E

Shimada H Appl Catal A Gen 2003241319ndash29[20] Phonthammachai N Rumruangwong M Gulari E Jamieson

AM Jitkarnka S Wongkasemjit S Colloids Surf A Physico-chem Eng Asp 200424761ndash8

[21] Ahn YU Kim EJ Kim HT Hahn SH Mater Lett2003574660ndash6

[22] Liu W-M Chen Y-X Kou G-T Xu T Sun DC Wear2003254994ndash1000

[23] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[24] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[25] Xu B Li D Chen Y Chem Soc Faraday Trans 1998941905ndash6

357E Celik et al Materials Characterization 58 (2007) 349ndash357

Acknowledgements

The authors would like to express their gratitude toDept of Metallurgical and Materials Engineering ofDokuz Eylul University Also this study was partlysupported by Technological Research Project of DokuzEylul University

References

[1] Yu J Zhao X Zhao Q Wang G Mater Chem Phys200168253ndash9

[2] Fujishima A Rao TN Tryk DA J Photochem Photobiol CPhotochem Rev 200011ndash21

[3] Wang R Hashimoto K Fujishima A Chikuni M Kojima EKitamura A et al Nature 1997388431ndash5

[4] Machida M Norimoto K Watanabe T Hashimoto K FujishimaA J Mater Sci 1993342569ndash74

[5] Tadanaga K Katata N Minami T J Am Ceram Soc1997801040ndash5

[6] Lee JE Oh S-M Park D-W Synthesis of nano-sized Al dopedTiO2 powders using thermal plasma Thin Solid Films2004457230ndash4

[7] Sonawane RS Hegde SG Dongare MK Preparation of titanium(IV) oxide thin film photocatalyst by solndashgel dip coating MaterChem Phys 200377744ndash50

[8] Kim DJ Hahn SH Oh SH Kim EJ Influence of calcinationtemperature on structural and optical properties of TiO2 thin filmsprepared by solndashgel dip coating Mater Lett 200257355ndash60

[9] Wang Z Hu X Fabrication and electrochromic properties ofspin-coated TiO2 thin films from peroxo-polytitanic acid ThinSolid Films 199935262ndash5

[10] Lucic-Lavcevic M Dubcek P Milat O Etlinger B Turkovic ASokcevic D et al Nanostructure of solndashgel derived TiO2 for thin

films on glass substrates measured by small angle scattering ofsynchrotron light Mater Lett 19983656ndash60

[11] Lin H Kozuka H Yoko T Preparation of TiO2 films on self-assembled monolayers by solndashgel method Thin Solid Films1998315111ndash7

[12] Gartner M Scurtu R Ghita A Zaharescu M Modreanu MTrapalis C et al Thin Solid Films 2004455ndash456417ndash21

[13] Brinker CJ Scherer GW Solndashgel science the physics andchemistry of solndashgel processing San Diego Academic Press1990 p 2656

[14] Sonowane RS Hedge SG Dongare MK Mater Chem Phys200277744ndash50

[15] Guillard C Beaugiraud B Dutriez C Hermann J-M JaffrezicH Jaffrezic-Renault N et al Appl Catal B Environ200239331ndash42

[16] wwwchemuiceduchem343343Viscositypdf[17] Zeman P Takabayashi S Surf Coat Technol 200215393ndash9[18] Pierre AC Introduction to solndashgel processing Boston Kluwer

Academic Publishers 1998 p 36[19] Dumeignil F Sato K Imamura M Matsubayashi N Payen E

Shimada H Appl Catal A Gen 2003241319ndash29[20] Phonthammachai N Rumruangwong M Gulari E Jamieson

AM Jitkarnka S Wongkasemjit S Colloids Surf A Physico-chem Eng Asp 200424761ndash8

[21] Ahn YU Kim EJ Kim HT Hahn SH Mater Lett2003574660ndash6

[22] Liu W-M Chen Y-X Kou G-T Xu T Sun DC Wear2003254994ndash1000

[23] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[24] Jiang X Ding G Lou L Chen Y Zheng X Catal Today200493ndash95811ndash8

[25] Xu B Li D Chen Y Chem Soc Faraday Trans 1998941905ndash6