Photocatalytic Performance of Hybrid SiO2-TiO2 Films

Samuele Gardin,† Raffaella Signorini,*,† Anna Pistore,‡ Gioia Della Giustina,‡

Giovanna Brusatin,‡ Massimo Guglielmi,‡ and Renato Bozio†

Department of Chemical Science, UniVersity of PadoVa, Via Marzolo 1, 35131, PadoVa, Italy, and Departmentof Mech. Eng.-Materials Section, UniVersity of PadoVa, Via Marzolo 9, 35131, PadoVa, Italy

ReceiVed: December 3, 2009; ReVised Manuscript ReceiVed: March 16, 2010

In this paper, we have investigated the properties of a composite SiO2-TiO2/TiO2 nanoparticle system. Hybrid filmshave been prepared using a sol-gel process, starting from tetraisopropoxy titanate and 3-glycidoxipropyltrimethoxysilaneas precursors and performing the synthesis at room temperature. The spin-coated films have been thoroughly characterizedwith UV-vis and FT-IR spectroscopies, TEM analysis, profilometry, and ellipsometry to evaluate their physical andstructural properties. Particular attention has been devoted to the study of their photocatalytic action.

1. Introduction

Among different existing photocatalysts, titanium dioxidebased films have been intensively investigated for their promis-ing mechanical, chemical, electrical, and optical properties. Inparticular, great attention has been devoted to the study of thephotocatalytic properties of TiO2 powders and thin films usefulfor the purification of air and water and the provision of self-cleaning surfaces.1-3 This activity can be obtained due to itsability to mineralize a wide range of organic contaminants, suchas aromatics, alkanes, alcohols, haloalkanes, dyes, insecticides,and surfactants, and to the photoinduced superhydrophilic effect.TiO2 works as a catalyst for the photodecomposition of organiccompounds; the oxidation reaction is represented by the equation

where mineral acids are generated when heteroatoms, such asS, N, and Cl, are present in the organic components.

In semiconductor photocatalysis, photons of energy abovethe band gap generate electron-hole pairs that can eitherrecombine or react with surface species. In the second case,the photogenerated electrons reduce the oxygen, while thephotogenerated holes mineralize the organic. The latter processprobably involves the initial oxidation of surface OH- groupsto hydroxyl radicals that then oxidize the organic and anysubsequent intermediates.4

It has been demonstrated that the photocatalytic activity stronglydepends on the physical properties of the TiO2, such as the crystalstructure (amorphous, anatase, rutile, or brookite), the surface area,the particle size, the surface hydroxyls, and so on. In particular,the crystalline structure seems to be the crucial parameter todetermine the photocatalytic activity: anatase seems to be the mostactive phase, whereas amorphous TiO2 shows negligible activity.5

The specific surface area also plays an important role in determiningthe catalytic activity: smaller TiO2 nanoparticles show a largersurface area and possess greater activity.

Different methods have been employed to prepare thenanoparticles, such as chemical precipitation, microemulsion,hydrothermal crystallization, and sol-gel synthesis.6-10 In thesol-gel processes, TiO2 is usually prepared by hydrolysis andpolycondensation reactions of titanium alkoxides, Ti(OR)n, toform oxopolymers, which are then transformed into an oxidenetwork. Because of the high reactivity of titanium alkoxides,some chelating reagents, such as diols, carboxylic acids, ordiketonate compounds, are added during the hydrolysis step.After the condensation step, a calcination treatment at 400 °Cor more is then required for removing the organic moleculesfrom the final products and completing the crystallization.11,12

By this way, it is possible to obtain films showing highphotocatalytic efficiency.13 A different alternative approachconsists in the ex situ synthesis of TiO2 nanoparticles, performedat low temperature.14-16

Here, we propose a new method for the synthesis of filmscontaining nanocrystalline TiO2 particles. This process isperformed at room temperature, without any calcination step,and allows obtaining films of nanoparticles embedded in asilica-titania amorphous and hybrid organic-inorganic net-work. By exposing them to the UV light, it is possible to obtaintransparent, homogeneous, and crack-free purely inorganic films,having a thickness of hundreds of nanometers.

The spin-coated films have been characterized by means ofUV-vis and FT-IR spectroscopies, TEM analysis, profilometry,and ellipsometry to evaluate their physical and structuralproperties. FT-IR spectroscopy has been first exploited toobserve the evolution of the film microstructure with increasingUV treatment time. Moreover, stearic acid has been used,combined with FT-IR measurements, to measure the photo-catalytic activity of the preirradiated films toward the photo-degradation of organic compounds.

The obtained photoactivity does not reach the highest valuesreported in the literature for sol-gel films but is comparable tothat of commercial films.17 However, the absence of anycalcination process and the soft conditions for the preparationof samples make this material a suitable candidate for a low-cost coating on thermally unstable substrates.

2. Experimental Section

2.1. Materials. Basic catalyzed hybrid silica-titania sols(G7Ti3) were prepared employing tetraisopropoxytitanate (Ti-

* To whom correspondence should be addressed. Fax: +39 049 8275239.Tel: +39 049 8275118. E-mail: raffaella.signorini@unipd.it.

† Department of Chemical Science, University of Padova.‡ Department of Mech. Eng.-Materials Section, University of Padova.

organic + O298hν g Eg(TiO2)

CO2 + H2O + mineral acids

J. Phys. Chem. C 2010, 114, 7646–76527646

10.1021/jp911495h 2010 American Chemical SocietyPublished on Web 04/13/2010

ISOP) and 3-glycidoxipropyltrimethoxysilane (GPTMS) asprecursors. They are all purchased from Aldrich and usedwithout further purification. 2-Metoxyethanol (2-MeOEtOH)was employed as solvent, bidistilled water for hydrolysis, andsodium hydroxide (1M) as catalyst.

The sol was prepared in two different steps. In the first one,GPTMS was mixed with water (H2O/GPTMS ) 3) and thesolution was stirred at room temperature for one night. Thisprehydrolysis step is necessary to compensate for the higherreactivity of titanium alkoxides, with respect to that of siliconalkoxides. In the second step, 2-MeOEtOH and NaOH (0.3%M in GPTMS) were added in that order. Separately, TiISOPwas added to 2-MeOEtOH at a 1:1 volume ratio, and the solutionwas stirred for about 10 min. 2-MeOEtOH plays two differentroles, acting as solvent as well as stabilizer of titanium alkoxidetoward the hydrolysis-precipitation reaction.18,19 In fact, it hasthe ability to coordinate TiISOP, decreasing its hydrolysis rate.The two solutions were then mixed, reaching a concentrationof 150 g/L SiO2 + TiO2 (that is, the oxide content if the solwas dried and calcined); then, 2-MeOEtOH was added to reacha sol concentration of 100 g/L SiO2 + TiO2. Finally, the solwas sonicated for 30 min and then left to react under stirringfor 5 h at room temperature. The final Si/Ti molar ratio is 70:30.

All the sols were filtered with a microporous membrane (0.2µm Millipore) before use. Cleaned silicon wafers and soda-lime or quartz slides were used as substrates.

Hybrid silica-titania coating films were obtained from theprepared sol by spin-coating and drying in an oven at 60 °Cfor 30 min (RT sample). Before the photocatalytic activity tests,the film has been exposed for 10 min to the UV radiation todecompose the organic components present inside the film andobtain a completely inorganic SiO2-TiO2 network.

2.2. Film Characterization. The film microstructure hasbeen analyzed by infrared absorption spectra, in the range of400-4500 cm-1, recorded by a Fourier transform infraredspectroscope (Jasco FT-IR-620), with the accuracy of (1 cm-1.TEM-EDS analysis has been performed in order to investigatethe film structure and the nature of the titania clusters. Theoptical properties of the G7Ti3 films have been analyzed bymeans of ellipsometry and UV-vis absorption spectroscopy.Ultraviolet-visible (UV-vis) absorption spectra from filmsdeposited on quartz slides were measured in the range of200-800 nm by a spectrophotometer (JASCO V-570), with theaccuracy of (0.3 nm.

The refractive index of the coatings on quartz substrates wasmeasured by ellipsometry, which allows also the determinationof the film morphology. The film thickness has been examinedalso with a Tencor T-10 profilometer.

2.3. Photocatalytic Performance Measurements. The pho-tocatalytic performances of the films toward the degradation oforganic compounds have been measured using stearic acid (SA)as model material. It is a well-known reference material, and itprovides a reasonable model compound for the type of solidorganic films that deposit on exterior glass surfaces, such ashouse or office windows.

When irradiated with UV light, stearic acid decomposesaccording to the following reaction

a process involving a transfer of 104 electrons.

A film of SA has been deposited on the photocatalyticsubstrate, under test, by spin-coating at 1500 rpm a solution8.8 × 10-3 M in methanol. This results in an initial stearic acidcoverage of approximately 1.8 × 1015 molecules/cm2, calculatedfrom the integrated area of the SA peaks in the 2800-3000cm-1 range in the FT-IR spectra.20,21 The SA has three peaksin this range: the peaks at 2958, 2923, and 2853 cm-1 due tothe asymmetric in-plane C-H stretching mode of the CH3

groups and to the asymmetric and symmetric C-H stretchingmodes of the CH2 groups, respectively.

From the integrated area under these peaks, it is also possibleto estimate the surface density of SA as a function of theincreasing UV exposure time and so to obtain its photodecom-position rate. A single 6 W UV lamp with a maximum emissionat 365 nm (∼1.5 mW/cm2) and a Hamamatsu LC5 UVmercury-xenon lamp with a large emission spectrum (with anemission intensity of 3500 mW/cm2 at a 1 cm distance or ∼30mW/cm2 at 20 cm) have been used as irradiation sources. Theemission profiles of these lamps are shown in Figure 1, togetherwith the absorption spectrum of the photocatalytic film.

3. Results and Discussion

3.1. FT-IR Spectra. The FT-IR spectra of the RT filmbefore and after 1-4 sequential 150 s steps of exposure tothe LC5 UV lamp (d ∼ 3.5 cm, E ∼ 450 mW/cm2) arereported in Figure 2.

A 30 min thermal treatment, at 500 °C on an unexposed film,and 600 s UV exposed samples are also reported for comparison.

The FT-IR spectra of all the samples show two frequencyranges of great interest. In the first interval, between 3500 and2500 cm-1, there are the large ν(O-H) band and the two peaksat 2930 and 2870 cm-1, relative to the νas(CH2) and νs(CH2),respectively.

The ν(O-H) band receives four main contributions,22 reportedin Figure 3. The type (a) silanol group is characterized by asharp absorption peak around ∼3740 cm-1, and it never appearsin any sample, indicating that the silanol groups are mainlyhydrogen-bonded.

The RT sample shows a narrower peak (with respect to theUV and 500 °C treated samples), indicating a narrowerdistribution of silanol groups (only (c) and (d) groups), probablywith predominance of type (c) at ∼3380 cm-1 over type (d)

Figure 1. UV absorption spectrum (green line) of the G7Ti3 sample,showing an absorption edge at around 300 nm. The emission profilesof the 6 W UV lamp (blue line) and Hamamatsu LC5 lamp (red line)are also reported. It can be clearly seen that the 6 W lamp emits outsideof the absorption wavelength of the active sample, whereas the LC5lamp presents some emission peaks below 325 nm, where the samplestill absorbs.

CH3(CH2)16CO2H + 26O298hν g Eg semic.

18CO2 + 18H2O

Photocatalytic Performance of Hybrid SiO2-TiO2 Films J. Phys. Chem. C, Vol. 114, No. 17, 2010 7647

groups at ∼3280 cm-1. A contribution of the peaks comesprobably also from the ν(OH) group of 2-MeOEtOH thatabsorbs at 3420 cm-1.23

The UV exposure induces an initial (for the first two steps)increase of the band, due to the increase of Si-OH groups andto the molecular water released as a result of the decompositionof the organic components. After 450 s of UV exposure, whenthe organic component is almost entirely decomposed, the peakintensity then returns to the initial value, but there is an increaseof the (d) groups and a lower wavenumber shoulder appearsdue to the presence of (b) silanol groups.

The thermal treatment at 500 °C induces the analogouseffect of the 600 s UV exposure concerning the organiccomponent decomposition. However, in this case, the bandis less intense, probably because the water from the thermaloxidation of hybrid groups is quickly evaporated at thistemperature. The two sharp bands at 2930 and 2870 cm-1

can be used to control the organic chain evolution underdifferent UV and thermal treatments: it can be clearly seenthat the propylic chain becomes progressively weaker forlonger UV exposure times and completely disappears afterUV exposure for 600 s. The same effect can be obtainedwith 30 min thermal treatment at 500 °C.

The second representative region, in the 1300-700 cm-1

range, contains a great number of superimposed peaks. Toevaluate the different peak contributions to the resultingspectra, deconvolutions have been performed with a multi-peak Gaussian fitting, as shown in Figure 4, and the resultsare reported in Table 1. The RT spectrum is reported in thetop portion of Figure 4. The intense peak [4] at 1107 cm-1

is related to νAS(C-O-C) bonds of the propylic chain,whereas the sharp peak [1] at 1200 cm-1 is related to thesymmetric stretching vibration of the CH2 groups of the

Figure 2. FT-IR spectra of the RT sample before (red line) and afterdifferent UV exposure times with the LC5 lamp from a distance of 3.5cm, with a corresponding incident intensity (considering the entireemission spectrum) of ∼450 mW/cm2. The spectra of samples treatedat 500 and 800 °C are also reported (brown and dark green spectra,respectively).

Figure 3. Schematic representation of the four different possible silanolgroups, free (a) and linked with different hydrogen bonds (b-d): thelarge circle is a silicon atom, the shaded circle is an oxygen atom, andthe small circle is a hydrogen atom.

Figure 4. FT-IR absorption spectra in the region of 1300-800 cm-1 of the RT sample, 600 s UV exposed sample, UV + thermal 500 °C annealedsample, and 800 °C annealed sample. The black dotted lines are the recorded spectra, the green lines are the deconvoluted peaks, and the red linesare the curves resulting from the fitting.

7648 J. Phys. Chem. C, Vol. 114, No. 17, 2010 Gardin et al.

propilyc chain; both are related to the presence of the organiccomponent in the RT films.

These bands disappear after UV exposure or thermaltreatments, indicating a photo- or thermal decomposition ofthe organic components. The four shoulders at lower ([2],[3]) and higher ([5], [6]) frequencies, with respect to the mainband at 1110 cm-1, are assigned, respectively, to thelongitudinal (LO) and transverse (TO) optical componentsof the asymmetric Si-O-Si stretching vibrationsνAS(Si-O-Si).13 We fit the LO shoulder with a two-peakdeconvolution, and not with only one, as reported by someauthors, because a better fitting results. The LO/TO ratio canbe correlated with the volume fraction of the residualporosity. In fact, the longitudinal optical component bandof νAS(Si-O-Si) in normal incidence transmission spectros-copy is activated only thanks to the pore light scattering ofthe IR radiation, such that a fraction of the absorbed light iseffectively obliquely incident.24,25 According to this hypothesis,the LO/TO ratio increases from 0.22 for the RT sample to 0.65and 0.56 after the 450 and 600 s UV treatments, respectively, asa consequence of the decomposition of the organic component thatleaves pores inside the film.

With thermal treatment at 500 °C, the LO/TO ratiobecomes 0.41, indicating a film densification and decreasesto 0.30 for the 800 °C treatment. The C-H stretching of theepoxy ring and the presence of residual 2-MeOEtOH areevidenced by the presence of the shoulder [9] at 856 cm-1

that disappears after only one 150 s step of UV exposure.Finally, the broad peak [8] centered at 912 cm-1 is probablythe result of the superimposition of the Si-O-Ti, Si-OH,and Si-O- groups’ stretching vibrations and of the two2-MeOEtOH bands at 880 and 960 cm-1. After the UV orthermal treatment at 500 °C, this peak shifts to lowerfrequencies, probably because the solvent contribution disap-pears. The band is now well-fitted with two peaks, the firstone centered at 900 cm-1 and assigned to the Si-O-

stretching vibration, while the main one, at 940 cm-1, isassigned to the Si-O-Ti and Si-OH stretching vibrations.26-28

In the sample treated at 800 °C, this peak can be attributedonly to Si-O-Ti vibrations because Si-OH groups are nolonger present in the film, as confirmed from the disappear-ance of the band centered at 3400 cm-1.

After the thermal treatment, at 800 °C, the Si-O-Si bandshifts to 1070 cm-1 and increases significantly, while theSi-O-Ti band decreases. This means that the number ofSi-O-Si bonds has increased, while that of the Si-O-Tibonds has decreased, suggesting a segregation of the titaniumions, which moved away from the silicon ions and migratedinto a titania-rich region, allowing the formation of additionalsiloxane bridges. The remaining Si-O-Ti bonds are thenmostly located on the surface of the titania cluster. To estimate

the Si-O-Ti connectivity (Ti dispersion in the Si matrix), it isinteresting to use the parameter D(Si-O-Ti), defined as29,30

where S(Si-O-Ti) and S(Si-O-Si) are the deconvoluted peakarea of the ν(Si-O-Ti) at 940 cm-1 and νAS(Si-O-Si) at 1120and 1170 cm-1, respectively; �Si and �Ti are the molar propor-tions of Si and Ti. respectively. D(Si-O-Ti) gives a qualitativeestimate of the fraction of Si-O-Ti species over the total Ticontent and thus a sort of mixing efficiency. The results obtainedare 2.6, 3.4, and 1.8 for the sample irradiated with UV light for600 s and the samples with 500 and 800 °C thermal treatments,respectively. The higher D value seems to confirm the migrationof the Ti ions, suggested above, even if this result cannot beconsidered as quantitative because it is not possible to estimatethe Si-OH contribution to the Si-O-Ti peak.

3.2. Ellipsometric Measurements. The ellipsometric mea-surements of the RT sample and after different UV and thermaltreatments reported in Figure 5 confirm what is outlined above.The film thickness decreases and the refractive index increasesfor increasing UV exposure time, according to the organiccomponent decomposition and the film densification.

The film porosity for the 600 s UV and for the thermallytreated samples has been estimated from the Lorentz-Lorentzequation, assuming a pore refractive index of 131

TABLE 1: Peak Deconvolution for the RT Sample in Figure 4,a

peaks [1] [2] [3] [4] [5] [6] [7] [8] [9]

RT position max [cm-1] 1199 1171 1145 1107 1054 1045 968 912 856area 0.90 0.30 1.88 8.21 0.16 9.53 0.55 4.33 0.40

600 s UV position max [cm-1] 1172 1120 1045 943 898area 2.18 1.80 7.93 4.45 1.00

UV + 500 °C position max [cm-1] 1192 1133 1048 947 904area 1.20 2.24 8.31 5.05 1.31

800 °C position max [cm-1] 1190 1145 1072 954 916area 2.43 0.85 10.89 4.14 2.05

a The multiple peaks have been fitted as the accumulation of Gaussian functions. The resulting coefficient of determination R2 and reduced �2

are 0.99982 and 4.3 ·10-7, respectively. The peak positions are reported together with the integrated area, width, and height.

Figure 5. Ellipsometric determination of the refractive index of theRT and treated films in the range of 400-1200 nm. An enhancementin the refractive index for increasing UV exposure time is shown. Theindex increases even more with thermal treatment at 500 and 800 °C.

D(Si-O-Ti) )S(Si-O-Ti)

SSi-O-Si)·�Si

�Ti

(nf2 - 1)

(nf2 + 2)

)(1 - Vp)(nm

2 - 1)

(nm2 + 2)

Photocatalytic Performance of Hybrid SiO2-TiO2 Films J. Phys. Chem. C, Vol. 114, No. 17, 2010 7649

where Vp is the volume fraction of pores, nf is the measuredrefractive index, and nm is the effective index of an inorganicfully densified matrix, assumed to be 1.68 by extrapolation ofSchroeder data.32 These results are also reported in Table 2.

The sharp absorption band in the UV region (Figure 6) isindicative of the tendency of titania, in silica-titania sol-gelfilms, to form a separated phase, composed of titania ortitanium-oxo clusters of nanometric sizes.23,33 This band doesnot move to longer wavelengths after UV or thermal treatments,suggesting that the cluster size and nature do not change. TheUV-visible spectra of the RT and treated samples show noremarkable absorption in the 400-800 nm range (not reportedin Figure 6).

3.3. TEM Analyses. To investigate the presence and thenature of the TiO2 clusters, TEM analyses have been performed.Figure 7 reports TEM images of an unirradiated and a UV-irradiated film, where it is possible to see some crystallineparticles of titania, well-dispersed in an amorphous background.The particle diameter is in the range of of 2-6 nm. The energy-dispersive spectroscopy (EDS) analysis shows the presence ofa high amount of Ti and O in the nanoparticle-rich zone of the

sample, while the amount of Ti is much lower when a samplezone without nanoparticles have been analyzed. EDS hasconfirmed that the particles shown in the TEM micrographs areTiO2: the plane distance from the TEM picture corresponds toa brookite crystalline form of TiO2.

All particles with a crystalline nature together with the greatamount of hydroxyl groups and with the residual film porosityare responsible for the photocatalytic behavior of the filmreported below.

3.4. Photocatalytic Tests. The first test has been performedwith the 6 W UV lamp whose emission spectrum is shown inFigure 1 superimposed to the absorption spectrum of the G7Ti3.

From the absorption spectra, it is clear that G7Ti3 films donot absorb at the emission wavelength of the lamp, so it isreasonable to suppose that they do not show any photocatalyticaction toward the decomposition of the organic compounds. Thisfact is confirmed by the FT-IR spectra of the 600 s UV exposedfilm spin-coated with stearic acid (top panel of Figure 8). Noremarkable differences in the spectra are visible also after 8 hof exposure with the UV lamp.

Successive tests have been performed with the HamamatsuLC5 UV lamp, possessing several emission bands in a widespectral range, which enter also into the absorption band of theG7Ti3 photocatalytic film (see Figure 1). In particular, this lampshows four peaks (centered at 290, 297, 303, and 313 nm) inthe spectral region below 325 nm, where G7Ti3 film starts toabsorb. This lamp has been used at a distance of 10 cm fromthe sample, giving an irradiance of ∼12 mW/cm2. After only1 h of exposure time, the stearic acid IR peaks disappear,indicating the complete decomposition of the spin-coated acidfilm (center panel of Figure 8).

The trend of SA concentration as a function of UV exposuretime is reported in the bottom part of Figure 8. To confirm theG7Ti3 photocatalytic action, a stearic acid film spin-coateddirectly on a Si substrate has also been exposed to the sametreatment. In that case, also after 2 h of exposure, the AS peaksonly slightly decrease.

To compare this result with others present in the literature,the formal quantum efficiency (FQE) and the quantum yield(QY) have also been calculated and reported in Table 3.8,34,35

The quantum yield of the G7Ti3 film is comparable with thatof the ActivTM film (0.01-0.02), but is lower with respect tothe pure titania sol-gel film (0.15-0.18).36 This extraordinaryhigh photoactivity of sol-gel films can probably be ascribedto their great porosity that determines an increase of the contactarea between the active film and the organic component to bedestroyed.

Nevertheless, it should be considered that only a small fractionof our film is constituted of active titanium clusters, while thegreat part is a SiO2-like or mixed SiO2-TiO2 inert matrix.

TABLE 2: RT Sample Film Thicknessa

samplethickness

(nm)shrinkage

(%)porosity

(%)

RT 800 /300 s UV 393 51600 s UV 281 65 10500 °C × 30 min 261 67 7600 s UV + 500 °C × 30 min 231 71 6800 °C × 30 min 203 75 3.7

a The changes in thickness and porosity after different treatmentsare also reported. All the data are obtained from the ellipsometricanalysis.

Figure 6. UV-visible spectra of the RT sample and 600 s UV andthermal annealed films.

Figure 7. TEM analysis of the unexposed sample (left panel) and 600 s UV exposed sample, showing the titanium clusters or radius ranging from2 to 6 nm (right panel).

7650 J. Phys. Chem. C, Vol. 114, No. 17, 2010 Gardin et al.

By increasing the relative amount of titania in this film, itwill be probably possible to improve its photocatalytical activity,approaching or even reaching the value reported above.Moreover, the great advantage of this film is the absence of athermal annealing; by this way, they can be spin-coated evenon thermally unstable substrates.

4. Conclusions

We have reported the room-temperature synthesis of hybridSiO2-TiO2 sol-gel films with nanocrystalline TiO2 clustershomogeneously dispersed inside the amorphous matrix. Thestructure of these films has been characterized with TEMmicrographs and the induced UV edge absorption changes,confirming the presence of crystalline nanoparticles.

Moreover, we have tested their photocatalytic activities usingstearic acid as the reference material. This system seems to bereally promising for future applications, such as UV-treatedinorganic films or photocatalytic coatings, to be deposited onthermally degradable substrates.

Acknowledgment. This work was supported by the grantPRIN 2007 (2007LN873M) and the CNR-INSTM agreementproject “PROMO”.

References and Notes

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TABLE 3: Formal Quantum Efficiency (FQE) and theQuantum Yield (QY) Calculated for the G7Ti3 Sample

incidentintensity × 1018

photon/cm2/minrate, Ri × 1013

mol/cm2/minFQEa × 10-4

mol/photon

fractionof light

absorbed, f b QYc × 10-2

1.11 2.05 0.18 0.138 0.013

a FQE (δ) calculated as δ ) rate of stearic acid destruction(molecules removed/cm2)/incident light intensity (photons cm-2).b Fraction of light absorbed (f) calculated using f ) (1 - 10-Abs(λ))for the four main peaks, from an analysis of the overlap of theUV-vis spectra of the film with that of the emission spectrum ofthe lamp (using the data in Figure 1). c QY (�) calculated as �) δ/f.

Figure 8. Photocatalytic test performed with a 6 W UV lamp (witha maximum emission at 365 nm, I ∼1.5 mW/cm2) (top). Theirradiation up to 8 h on the RT and on the preirradiated active filmspin-coated with stearic acid does not produce any remarkabledifference in the FT-IR band intensity. Photocatalytic test performedwith a LC5 lamp, at a distance of ∼10 cm between the samplepreirradiated and the lamp, giving I ∼ 12 mW/cm2 energy (center).The decomposition of the AS is complete after 100 min of UVexposure (bottom).

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