Chemical Engineering Journal 225 (2013) 880–886

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Chemical Engineering Journal

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TiO2 based photocatalytic coatings: From nanostructure to functionalproperties

1385-8947/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2013.04.037

⇑ Corresponding author. Tel.: +39 0546 699718.E-mail address: anna.costa@istec.cnr.it (A.L. Costa).

Anna Luisa Costa a,⇑, Simona Ortelli a, Magda Blosi a, Stefania Albonetti b, Angelo Vaccari b, Michele Dondi a

a National Research Council of Italy, Institute of Science and Technology for Ceramics (CNR-ISTEC), Via Granarolo, 64, 48018 Faenza, Italyb Department of Industrial Chemistry and Materials, Bologna University, Viale del Risorgimento 4, 40136 Bologna, Italy

h i g h l i g h t s

� Direct ceramization of textilesubstrates with commercial derivedTiO2 nanosols.� Five nanosols, differing for starting

pH and relative aggregates size.� Correlations between physico-

chemical nano-macro scale propertiesand performances.� Industrially scalable application.� Inputs for the control of material

performance by design experiments.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Available online 21 April 2013

Keywords:TiO2

NanosolsNanocoatingsZ potentialHydrophilicityPhotocatalytic efficiency

a b s t r a c t

The present study shows the results of direct ceramization of textile substrates with commercial derivedTiO2 nanosols. A deep investigation on relationship between TiO2 based nanosols and nanocoatings prop-erties and their performances in term of hydrophilicity and photocatalytic efficiency was performed. Fivenanosols, differing for starting pH and relative agglomerates size were analyzed. The hydrophilic behav-ior and the catalytic performance of TiO2 coatings supported on different substrates (fabric, glass andceramic) were assessed and related to physicochemical characterization results. The described correla-tions between TiO2 nanoscale properties (nanostructure or surface chemistry), macroscale properties(hydrophilicity), as well as functional properties (photocatalytic activity), represents a first attempt toprovide sound criteria for the control of material performance by design experiments. The pH dependentaggregation state, is correlated to an increase of surface acidity as the shift of i.e.p. towards acid pHreveals. Such increase of acidity justifies an increase of hydrophilicity, consequent to stronger interactionwith water molecules, that occurs when a higher amount of Ti�O� sites are available. As well, the pho-tocatalytic performances and the hydrophilic behavior, resulted in a good agreement: the higher thehydrophilicity, the better the self-cleaning activity, so providing useful indications for the scale-upexploitation of such application.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

The functionalization of substrates through the application ofnanostructured coatings allows to create new materials, in whichthe properties of nanoparticles are transferred to the surface [1].The functionalization of surfaces may be exploited for many

applications: barrier coatings [2], self-cleaning hydrophobic [3]or photocatalytic coatings [4,5], antistatic coatings [6,7], super-paramagnetic coatings [8] with consequently very important tech-nological feedback. The type of support, the nature of the coatingand the way to interact affect the final properties of material.

The metal oxides coatings have been extensively studied; inparticular, TiO2-based coatings have attracted a huge attentiondue to the exploitation of their photocatalytic properties. Newmaterials in the field of textiles, constructions and plastics, with

A.L. Costa et al. / Chemical Engineering Journal 225 (2013) 880–886 881

self-cleaning, antibacterial and self-decontaminating propertieshave been developed by coupling different substrates with TiO2

based coatings. [9–16]. Recently, the application of nano-TiO2 intextile finishing has become an important area of research becauseof the self-cleaning effect provided by nano-TiO2 coatings to textilesubstrates. The application of TiO2 to textile, in fact, may result inefficient levels of self-cleaning activity, with the actual capabilityto degrade stains, bacteria, volatile organic compounds (VOCS) ad-sorbed onto fibres and transform them into CO2 and H2O. There-fore, a deep study of the process of preparation and applicationof the coating is of significant importance in the manufacturingprocess of high quality and performance end products.

Supported TiO2 films can be prepared by many methods, suchas anodic oxidation [17–22], sputtering [23,24] and sol–gel process[11,25–33], nevertheless sol–gel deriving processes such as dip- orspray-coating are the most widely employed. The cited sol–gelmethods describe the preparation of TiO2 nanosol by sol–gel syn-thesis from precursors or by colloidal dispersion from commercialpowder. Both these procedures present some disadvantages in aview of a large scale application. In particular, the first suffers fromthe complexity and low reproducibility of wet chemicals processesand the second from problems related to the stability and the de-gree of transparency of the nanopowder dispersion. The presentwork overcomes these problems describing a method of producingself-cleaning photocatalytic textile by dip-pad-dry-cure methodstarting from TiO2 commercial nanosols, with stabilized character-istics and a guaranteed reproducibility. The characteristics andperformance of sols differing for synthesis post treatment werecompared and information collected exploited for a first semi-industrial sampling.

The photocatalytic activity of TiO2 is induced by UV light exci-tation, with consequent formation of electron�/hole+ pairs. The re-leased electrons are able to react with water and oxygen moleculeson the surface to form free radicals O��2 and �OH [29]. These radicalsare very reactive species that are able to decompose most organicstains as well as biological contaminants present in aqueous media[34]. Interphase domain plays a crucial role in governing the pho-tocatalytic activity of TiO2 coated materials, and macroscopic prop-erties, such as surface hydrophilicity, affect directly thephotocatalytic performances [35–37]. The common effort of nano-material scientist community towards the development of newmaterials by design and engineering at nanoscale level, requiresan increasing knowledge of structure–reactivity relationships, inorder to get the wished control on final properties.

This work represent a first attempt to correlate TiO2 nanoscaleproperties, such as nanostructure or surface chemistry, to macro-scale properties, such as hydrophilicity, as well as to functionalproperties, such as photocatalytic activity. The hydrophilic behav-ior and the catalytic performance of TiO2 coatings supported ondifferent substrates (fabric, glass and ceramic) were assessed andrelated to physicochemical characterization results. The depositionof TiO2 coatings on glass substrates and ceramic tiles was carriedout by dip-coating [38], while the fabrics were covered by a dip-pad-dry-cure method [39].

Table 1Chemical–physical characteristics of the nanosol samples: hydrodynamic diameter byDLS (dDLS), pH of isoelectric point (pHi.e.p.) and specific surface area by BET (SSABET).

Sample pH dDLS (nm) pHi.e.p SSA BET (m2 g�1)

TAC 1.5 36 7.7 237.2TACF3.5 3.5 66 6.3 –TACF4.0 4.0 96 6.1 190.2TACF4.2 4.2 119 5.9 –TN 6.0 44 <2.0 36.4

2. Experimental (materials and methods)

2.1. Materials

Acid TiO2 nanosol (TAC, pH 1.5) with a solid loading of 6 wt.%,was purchased by Colorobbia (Italy). The fabric used in this studywas a Jacquard textile and its composition was: 62% cotton and38% polyester. It belonged to soft furnishings (specific weight of360 g/m2). It was characterized by abrasion resistance of 22.000cycles (Martindale BS2543/BS5690). The glass support used was

soda-lime flat glass and the ceramic tiles used were unglazed por-celain stoneware.

The direct application of acid nanosol (TAC) has to be avoideddue to its very low pH and to the occurrence of synthesis byprod-ucts (organics, salts) that decrease the photocatalytic activity ofTiO2. For this reason, the TAC sol was treated by ultrafiltration be-fore the use (TACF). Ultrafiltration was carried out using polymericfilters with a pore size of 100 kDalton, which enable the retentionof TiO2 nanoparticles; by this way the pH increased while synthesisby-products were removed. The vessel refilled with water for sev-eral times allows the achievement of wished characteristics. Bychanging the washing degree, three nanosols samples were pre-pared with different pH values: 3.5, 4.0 and 4.2 (called TACF3.5,TACF4.0 and TACF4.2 respectively). As an alternative to ultrafiltra-tion process the commercial sol acidity was also decreased by add-ing citrate salt (TiO2:citrate weight ratio ffi 1:1) obtainingneutralized sample (TN, pH 6). Pristine and modified commercialsols were diluted with distilled water, in order to reach a solid con-tent of 3 wt.%. The chemical–physical properties of these sols sam-ples are reported in Table 1.

2.2. Preparation of TiO2-coated supports

Before catalyst deposition, glass samples were immersed in ace-tic acid solution for 7 h and then air dried for 24 h, while ceramictiles were washed with EtOH:water solution (10:90 v/v) underultrasounds for 15 min and then air dried for 24 h.

TiO2 films were deposited at room conditions (namely temper-ature = 21 �C and humidity of air = 45%) onto glass and ceramicsamples by dip coating, as follows: dipping for 5 s in the colloidalsolution, withdrawal from the solution at constant velocity(2 mm/s). The coated samples were air dried and subsequentlytreated in oven for 10 min at 130 �C to promote adhesion to thesupport. Otherwise fabric samples were washed by ultrasoundsfor 30 min, 15 min with soap and water and 15 min with wateronly. Pretreated fabrics samples were dipped in the titania nanosol,soaked for 3 min, and passed through a two-roller laboratory pad-der. The padded fabric samples were then dried in oven at 100 �Cfor 10 min, cured at 130 �C for 3 min and then washed in waterby ultrasounds for 15 min in order to remove the nanoparticlesnot physical-chemically adsorbed onto the surface.

The TiO2 amount absorbed on the fabric substrates was evalu-ated by weighting the solid residue after burning at 800 �C for30 min, with a heating rate of 100 �C/h (burn-out), and resulted3 wt.% of the coated sample, coherent with the capacity of testedcotton fabrics to adsorb an amount of sol equivalent to theirweight. The burn-out was also applied to fabrics washed at 40 �Cfor 90 min with washing machine for ten and twenty cycles in or-der to detect TiO2 coating stability after several washing.

The coating processes of glass, ceramic and fabric samples areshown in Scheme 1.

2.3. Characterization

The phase composition of the TiO2 nanopowders was deter-mined by X-ray powders diffraction (XRD). Diffraction patterns

Dip-Coating Dip-padding-curing

Glass substrates and Ceramic tiles

Preparation of TiO2-coated supports

(a) (b)Fabric substrates

Scheme 1. Coating process of glass and ceramic supports by dip-coating (a) and of fabric supports by dip-padding-curing (b).

Scheme 2. Discoloration efficiency percentage (DE�%).

882 A.L. Costa et al. / Chemical Engineering Journal 225 (2013) 880–886

were collected on the dried powders of the samples TAC, TACF4.0and TN: each suspension was dried for 24 h at room temperature(r.t.) in air, washed several times with absolute ethanol and driedin oven at 130 �C for 10 min. Analyses were performed by aBragg–Brentano diffractometer (Bruker D8 Advance, Germany)operating in h/2h configuration, with a XCeleretor detector (10–60� 2h range, 0.02 stepsize, 0.5 s time-per-step).

The specific surface area measurements were determinate byBrunauer-Emmett-Teller (BET) method. It is a well-recognized ap-proach to determine the specific surface area of nanoporous mate-rials which is based on physical adsorption of gas molecules ontothe material interface [40,41]. The specific surface area (BET) mea-surements were carried out using N2 as adsorptive gas Sorpty 1750(Carlo Erba, Italy). The measurements were performed on the driedpowders of the samples TAC, TACF4.0 and TN.

Nanosol particle size distribution was determined at r.t. using aZetasizer Nanoseries (Malvern Instruments, UK), able to calculatethe hydrodynamic diameter of suspended particles by dynamiclight scattering (DLS) technique. AcoustoSizer II (Colloidal Dynam-ics, Australia) equipped with an automatic titrating system wasused to determine the Zeta potential of nanosols as a function ofpH (experimental uncertainty: 3 mV for Z potential and 0.03 forpH). The measurements were carried out on sols at low concentra-tion (0.5 wt.%) to prevent precipitation due to pH changes. Thetitration for samples at pH < 4.5 was performed by addition of1 M KOH solution, while the titration for sample at pH 6 was per-formed by adding 1 M HCl solution.

The homogeneity of coating were verified by performing hydro-philicity and photodegradation measurements on a set of ten sam-ples for each type. After that a selection of samples were chosen tocomplete characterization measurements.

Hydrophilicity was evaluated by the sessile drop method, mea-suring the contact angle of a water drop on the coated glass orceramic surface with an optical tensiometer OCA plus (DataPhysicsInstruments, Germany). For each sample five measurements wereperformed and the average value was considered. Despite thatthe hydrophilicity of TiO2 modified fabrics depends both on hydro-philicity of TiO2 coatings and on characteristics of textile support,such as structure, composition and water content, it was possibleto make a sound extrapolation between contact angles-basedhydrophilicity of ceramic/glass samples and that of textile samples,because the characteristics of textile support were the same for allsample investigated.

The investigated correlation between hydrophilicity of TiO2

modified fabrics with their photocatalytic activity depends bothon hydrophilicity of TiO2 coatings and on characteristics of textilesupport, such as structure, composition and water content. Never-theless, in order to evaluate hydrophilicity of TiO2 coatings andcorrelate it to photocatalytic efficiency we could only apply the

sessile drop method to ceramic/glass substrates, such making asound extrapolation on hydrophilic behavior of textile samples, be-cause the characteristics of textile support were the same for allsample investigated.

2.4. Photocatalytic activity measurements

The pristine fabric sample and the titania-coated samples werestained by dropping 0.2 mL of an aqueous solution of rhodamine B(0.07 g/L) or red wine.

Rhodamine B dye was selected because its degradation repre-sent an important goal, as far as decontamination of textile indus-try wastewaters is concerned. The red wine photodegration wasinvestigated in order to identify a more common application ofproposed self-cleaning textile, exploitable by home furnishing tex-tile sector. Furthermore, the very complex chemical nature of redwine, justifies the use of rhodamine B, as simple target moleculeto study photodegradation mechanism, also thanks to several dataavailable in literature [42].

After staining, the samples were irradiated from a distance of25 cm using a 300 W lamp simulating sunlight radiation (OsramULTRA-Vitalux, Italy). The UV radiation intensity was 1.3 mW/cm2. Rhodamine B and red wine stained samples were irradiatedfor 30 min and 24 h, respectively; to assess the degree of discolor-ation, the samples underwent color measurements before and afterUV exposure. All color measurements were performed by diffusereflectance spectroscopy (Miniscan MSXP4000, HunterLab, USA)in the 400–700 nm range (illuminant D65, observer 10�) taking alight trap and a white glazed tile as references. Color is expressedas CIELab parameters: brightness (L�: 100 = white 0 = black) andchroma (a�: red +, green �; b�: yellow +, blue �). TiO2 photocata-lytic performance was expressed as discoloration efficiency per-centage; the measurements on stained fabrics, both before andafter exposure, were scaled with the unstained sample. In particu-lar, the color difference (DE�) between samples before and afterexposure, calculated as follows,

0

2

4

6

8

10

1 10 100 1000 10000Diameter [nm]

Inte

nsity

(%)

TACTACF3.5TACF4.0TACF4.2TN

Fig. 1. The influence of pH on the hydrodynamic diameter of nanosols.

Fig. 2. XRD diffractograms of (a) TAC, (b) TACF4.0 and (c) TN powders.

-60

-30

0

30

60

90

120

1 3 5 7 9

pH

Zeta

Pot

entia

l [m

V]

TACTACF3.5TACF4.0TACF4.2

-3

0

3

5.8 6.1

Fig. 3. The influence of pH on dispersion zeta potential of nanosols.

A.L. Costa et al. / Chemical Engineering Journal 225 (2013) 880–886 883

DE� ¼ ½ðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2�1=2

was referred to the pristine sample by subtracting the backgroundcolor of the fabric (Scheme 2).

Fig. 4. Schematic representation of surface properties of TiO2 dispersed nanopar-ticles as a function of pH and agglomeration state.

3. Results and discussion

3.1. Nanoscale properties

The DLS hydrodynamic diameters of TiO2 nanosols are reportedin Fig. 1. Excepting the sample TN, the higher is the pH of nanosol(going from TAC to TACF4.2) the larger is the hydrodynamic diam-eter, because the degree of agglomeration progressively increases.The sample TN results well dispersed because agglomeration ishindered by the presence of a citrate capping agent.

The XRD patterns (Fig. 2) confirms that starting pH does not af-fect the crystalline phases. The broad peaks typical of nano-sizedcrystallites are detected for all samples. The main phase detectedis anatase with a small amount of brookite (about 16 wt.%). BET re-sults on dried powders, reported in Table 1, are coherent with DLSsize values; in fact, the highest surface area of the most acid sampleTAC, corresponds to the smallest particle size. When the pHreaches the value of 4 by ultrafiltration, agglomeration occursand the surface area decreases. Sample TN, due to its differentpreparation, shows another trend; although even having a verysmall particle size (44 nm), exhibits the lowest surface area, maybe due to the presence of carbon residues after powder drying thatis detrimental for the surface area. The measurement of f potentialas a function of pH (Fig. 3), let to identify the isoelectric point, i.e.the pH at which f potential sets to zero (pHi.e.p.). As evidenced inequations 1–3, TiO2 shows in water the typical behavior of ampho-teric hydroxylated metal oxides, being protonated and positivelycharged at pH lower than pH of zero charge (pHpzc), while is

negatively charged at pH higher than pHpzc. If no specific adsorp-tion of solubilized species occurs, pHpzc equals pHi.e.p. [43].

TiIV þH2O! TiIV � OHþHþ ð1Þ

TiIV � OHþHþ ! TiIV � OHþ2 ð2Þ

TiIV � OH! TiIV � O� þHþ ð3Þ

On the basis of above consideration pHi.e.p. reflects the surfaceacidity and a shift of pHi.e.p. towards acid pH is expected by moreacid surface. The strong shift of TN sol pHi.e.p. of TN sol at values <2,compared with pH range (5–7) reported in literature for colloidaltitania [44], is justified by the presence of citrate capping agentsthat transfer a negative net charge on the surface. The behavior isdifferent for bare TiO2 sols (samples TAC and TAFC); in this case aslight shift of pHi.e.p. towards acid pH from TAC sample to TAFCsample, increasing starting pH (pHi.e.p. TAFC3.5 > TAFC4 > -TAFC4.2) may be related only to different nanostructures. As al-ready discussed in literature [44,45], due to the high surfacereactivity of nanomaterials, small changes in surface chemistry,presence of contaminants or synthesis by-products, as well as mor-phological differences (due to agglomeration phenomena) may af-fect the pHi.e.p. In particular, the observed different surfaceacidity of TAC and TAFC sample, as well as small differences withinTAFC samples set, may be justified by different agglomeration de-gree, as hydrodynamic diameters size reported in Table 1 reveal.In fact, as schematized in Fig. 4, a complex aggregated structurehas most chances to stabilize negative charges arising from surfacede-protonation.

Table 2Burn-out test results. Weight loss of the coated fabrics after burning: before washing,after ten and twenty washing. Experimental conditions: temperature = 800 �C,heating rate = 100 �C/h and residence time = 15 min.

Sample % TiO2 beforewashing

% TiO2 after 10washings

% TiO2 after 20washings

TAC 3.0 - -TACF3.5 3.2 2.8 2.7TACF4.0 3.7 - -TACF4.2 3.6 - -TN 2.9 - -

Table 3Contact angle measurements and relative standard deviation (r) on TiO2 thin filmssupported on glass substrates and ceramic tile.

Sample pH Contact angle (�) ± standard deviation (r)

Glass substrate Ceramic tile

Pristine – 57.3 ± 2.3 60.0 ± 2.0TAC 1.5 44.2 ± 2.2 45.8 ± 3.9TACF3.5 3.5 34.2 ± 3.6 40.8 ± 2.7TACF4.0 4.0 20.7 ± 1.4 28.3 ± 3.3TN 6.0 7.0 ± 1.5 9.2 ± 2.1

Table 4Photocatalytic test: discoloration of (a) rhodamine B stain and (b) red wine stain.Experimental conditions: exposure time = (a) 30 min, and (b) 24 h.

Sample pH Efficiency%

(a) Rhodamine B (b) Red wine

Pristine – 49.2 37.5TAC 1.5 84.6 46.8TACF3.5 3.5 92.5 81.5TACF4.0 4.0 94.7 95.2TACF4.2 4.2 97.8 95.9TN 6.0 68.7 57.2

884 A.L. Costa et al. / Chemical Engineering Journal 225 (2013) 880–886

The formation of an homogenous coating of nano-TiO2 is con-firmed by burn-out test. The amount of TiO2 (about 3 wt.%) iscoherent with the capacity of tested cotton fabrics to adsorb anamount of sol equal to their weight. The adhesion of coating wasassessed by burn-out test results after washing at 40 �C for tenand twenty cycles on TACF3.5 sample. All results are shown inTable 2.

Pristine TAC TACF3.5

TNTACF4.0 TACF4.2

3.2. Hydrophilicity

As evidenced by hydrophilicity data reported on Table 3 andFig. 5, the surface acidity trend affects the hydrophilicity of TiO2

coated supports. Both glass and tile surfaces, in fact, show adecreasing of contact angles as increasing starting pH of TiO2.The high concentration of Ti–O� sites, present on more acidic sur-faces, promotes the formation of hydrogen bonds with water mol-ecules, with an improved hydrophilicity.

Pristine TAC TACF3.5

3.3. Photocatalytic activity measurements

The photocatalytic activity was assessed as discoloration of rho-damine B aqueous solution and red wine stains on pristine andcoated fabrics. Both tests prove an increase in the photocatalyticperformances by increasing the starting pH of the nanosol (Table 4).

0

10

20

30

40

50

1 2 3 4 5 6pH

Con

tact

Ang

le (d

egre

e)

Ceramic TileGlass substrate

Fig. 5. The influence of nanosol pH on the contact angle values.

The good agreement between the photocatalytic performances andthe hydrophilic behavior is explained considering that the highhydrophilicity of the surfaces maximizes the contact between stainand active phase. Moreover, the presence of adsorbed water mole-cules, promoted by the hydrophilic feature, promotes the produc-tion of hydroxyl radical, �OH, involved in the photocatalyticreaction mechanism.

Under UV irradiation (Fig. 6), a total discoloration is achievedwith the samples TACF4.0 and TACF4.2, a partial discoloration isobtained with samples TAC, TACF3.5 and TN, whilst the pristinesample shows a visible stain, even if attenuated. Similar resultsare obtained with the self-cleaning tests of red wine stain(Fig. 7). The expected efficiency increase, as starting pH increases,actually is not verified for the TN sample that shows a decreasingof efficiency percentage, with a value similar to that of TAC sample(Fig. 8a). TN sample represents, also in this case, an exception. Infact, due to its different surface chemistry, despite its high startingpH value and its good acid and hydrophilic behaviors (Fig. 8b), it

TACF4.0 TACF4.2 TN

Fig. 6. Rhodamine B stain discoloration on the fabric samples under UV irradiation.t = 0 (up) t = 30 min (under).

Pristine TAC TACF3.5

TN

Pristine TAC TACF3.5

TACF4.0

TACF4.0

TACF4.2

TACF4.2

TN

Fig. 7. Red wine stain discoloration on the fabric samples under UV irradiation. t = 0(up) t = 30 min (under).

0

20

40

60

80

100

1 2 3 4 5 6pH

Effic

ienc

y %

Rhodamine B

Red wine

0

10

20

30

40

50

1 2 3 4 5 6pH

Con

tact

Ang

le (d

egre

e)

0

2

4

6

8

Isoe

lect

ric p

oint

Contact Angle

Isoelectric point

(a)

(b)

Fig. 8. (a) Efficiency values as function of pH (b) Influence of pH on contact anglevalues (on glass substrates) and pHi.e.p.

A.L. Costa et al. / Chemical Engineering Journal 225 (2013) 880–886 885

exhibits a low photocatalytic activity, due to the detrimental effectthat organic capping molecules have on photocatalytic reactivity[36].

4. Conclusions

The present study shows the results of direct ceramization oftextile substrates with commercial derived TiO2 nanosols. Thecharacteristics and performance of sols differing for synthesis posttreatment were compared and information useful for a first semi-industrial sampling provided.

A deep investigation on relationship between TiO2 based nano-sols and nanocoatings properties and their performances in term ofhydrophilicity and photocatalytic efficiency was performed.

Five nanosols, differing for starting pH and relative agglomer-ates size were analyzed, finding an increase of particle size and asurface area decrease as starting pH increases. The exceptionshown by TN nanosol was attributed to the stabilization providedby anionic surfactant molecules.

The pH dependent aggregation state, is correlated to an increaseof surface acidity as the shift of i.e.p. towards acid pH reveals. Suchincrease of acidity justifies an increase of hydrophilicity, conse-quent to stronger interaction with water molecules, due to the ex-pected higher amount of Ti�O� sites available.

As well, the photocatalytic efficiency trend may be correlated tosurface hydrophicity that can promote the formation of an higheramount of �OH radicals and maximizes the contact between stainand active phase.

The described correlations between TiO2 nanoscale properties,(nanostructure or surface chemistry), macroscale properties,(hydrophilicity), as well as functional properties, (photocatalyticactivity) represents a first attempt to provide sound criteria forthe control of material performance by design experiments. A mul-tiscale modelling applied to described materials and properties isforeseen, in order to confirm the hypothesis based on the experi-mental data.

Acknowledgement

Authors gratefully thank Novaresin spa for the financialsupport.

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