Journal of Photochemistry and Photobiology A: Chemistry 280 (2014) 2731

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Journal of Photochemistry and Photobiology A:Chemistry

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Photoc ithpowde

Claudia L StucSara Mora Universit deb Universit de TM-Uc GranitiFiandr

a r t i c l

Article history:Received 21 OReceived in reAccepted 1 FebAvailable onlin

Keywords:PhotocatalysisLiquid phaseDyesMicro-sized TiO2Photocatalytic tile

he iniationially potoc(rho

n reaphot

1. Introdu

Titaniumthe best semdegradationand chargesbyRazavi etparticles wiMost of theric TiO2 mapuricationloadsmetalunderlineduse and expcan penetrawhen theyon materialpowder can

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dioxide (TiO2) is worldwide considered as one oficonductor to be used as photocatalyst for pollutants. Exposition under UV light promotes redox reactionsseparation that lead to oxidative processes as reportedal. [1]. TiO2 is oftenused inpowdery formasnano-sizedth high surface area, so as to enhance its photoactivity.literature reports consequently the use of nanomet-

terials for many purposes, from disinfection [2] and air[3] to decomposition of organic matter [4] or heavy

s inwastewaters [5].However, somerecentpapershavethe possible side-effects on human health due to bothosure to nanoparticles [6,7], as the ultra-small particleste inside human body from skin and nose especiallyare used in products like paints or simply cold-coateds surfaces for air purication and a loss of photoactivenot be neglected.s can be observed in liquid phase as well, where nano-er can affect the catalyst recovering at the end of thendering an industrial use of TiO2 nanopowders, due to

dingauthorat:Universitdegli StudidiMilano,DipartimentodiChim-9, 20133, Milano, Italy. Tel.: +39 0250314253.ress: Claudia.bianchi@unimi.it (C.L. Bianchi).

the extreme difculty in the nal ltering necessary to separatephotocatalytic powder and the cleaned solution, as reported bySchulze et al. [8].

On this basis, a great attention is focused on the potential of TiO2micro-sized powders to be used as photocatalyst for the degrada-tion of organic contaminants. Recent results for both NOx and VOCdegradation in gas phase seem to be very promising [9] but no dataare available for the degradation of pollutants in liquid phase yet.

Main target of the present work is to investigate the perfor-mance of a commercial micro-sized TiO2 (1077 by Kronos) usedas photocatalyst in the degradation of three different dyes (rho-damine B, crystal violet and methylene blue) in water. Micro-sizedsample was used as received, so to compare the obtained resultswith the classical nano-sized commercial P25 by Evonik, alwaysused as photocatalyst reference material.

Previously Marcos et al. [10] reported the deposition of TiO2layers on common ceramic glazed tiles using the screen-printingprocess, which is a low cost and common technique used for dec-oration in the ceramic industry. Labrincha et al. [11] depositedseveral commercial titania powders by jet spray on ceramic tiles,then red to stabilize the layers. In both cases a good activity ofnano-sized TiO2 photocatalytic layers on ceramic tiles was demon-strated in the degradation of Orange II dye. In the present case,micro-sized 1077 was industrially hot-coated at the surface of aporcelain-grs tile (Orosei ActiveTM). Tests using photoactive tileswere carried out to verify the efcacy of the coated catalyst to

see front matter 2014 Elsevier B.V. All rights reserved.rg/10.1016/j.jphotochem.2014.02.002atalytic degradation of dyes in water wr or coated on porcelain-grs tiles

. Bianchia,, Enrico Colomboa, Sara Gattoa, Martaandib, Valentino Capucci c

gli Studi di Milano, Dipartimento di Chimica & Consorzio INSTM-UdR, Milano, Italygli Studi di Torino, Dipartimento di Chimica & NIS Centre of Excellence & Consorzio INSe SpA, Castellarano, MO, Italy

e i n f o

ctober 2013vised form 24 January 2014ruary 2014e 10 February 2014

a b s t r a c t

Some particular drawbacks due to tcatalytic processes for water remedmicro-sized TiO2 powder and industrgrs tiles hot-coated with the same phthe degradation of three organic dyeswere achieved. Photocatalytic tiles cathe way for the fully industrial use ofocate / jphotochem

micro-sized TiO2 as

chia, Giuseppina Cerratob,

dR, Torino, Italy

dustrial use of nano-sized TiO2 (safety, recovery) in photo-can be avoided choosing micro-sized TiO2. Tests on bothrepared photocatalytic tiles, having the surface of porcelain-atalyst, were performed. Good photocatalytic performance indamine B, crystal violet and methylene blue) in water phaselly represent a good alternative to TiO2 suspensions and paveocatalysis in environmental remediation.

2014 Elsevier B.V. All rights reserved.

28 C.L. Bianchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 280 (2014) 2731

degrade dyes inwatermedia to obtain a stable and very easyway toseparate the solutionat theendof the reaction fromthephotoactivecatalyst.

2. Experimental

2.1. Materials and characterization

TiO2 1077 by Kronos was chosen as micro-sized photocatalyst,commercially classied as pigment. Characterization of this samplewas previously carried out and elsewhere reported [12]. However,principal feXRD, specisurements)

1077 isporcelain-gindustriallyface, red inbrush to remreported [1

Rhodam409g/mol),PM 479g/C28H31ClN2dye (Sigma

Two difpaper: 11up. Themosin thephotomicro-sizedpared to ththe past [14solution, hiused to test

The soluwater and wspontaneou

1077 poinstrumentHR-SEM-EDActiveTM tilLEO 1525,mmined usin

2.2. Photoccatalysts

Dyesdegtor (Fig. 1ause of an exemitting inuated in theOHM, modean internal

Dye adscatalyst amtion ranged

: Con: UV lmp; E

tolysatalyegrathe dis sp

), usium a

otoc

lindtestpho

aticajack

n wePhilipwith

UVancesam

eportwas

zed worptlutions in dark conditions for six hours. To avoid any alter-f both irradiating conditions anduiddynamicof the system,ysis was performed with the tiles still inside the reactor bute active faces turned towards the dark side of the reactor,

reventing the photoactivation of the TiO2 catalyst. Duringatalytic tests the TiO2 active faces of the tiles were turneds the UV light.same dyes solution described in the Section 2.1 were usedresent setup at a concentration of 1105 M. Kinetics werered by UVvis spectrophotometric analysis as described in2.2.

Table 1Physicochem

Sample Crystallite size (nm)(XRD)

OH/OTOT(XPS)

P25 26 0.141077 110 0.32atures (crystallographic phase and crystallites size byc surface area (SSA) by BET, and OH/OTOT by XPS mea-are summarized in Table 1.also used in commercially available photoactive

rs tiles (named Orosei ActiveTM). TiO2 was mixedwith a silica-based compound, sprayed on the tiles sur-industrial kiln a680 Candcleanedwitha rotatingwireove the TiO2 weakly stuck at the tile surface, as already

3].ine B (RhB, dye content 95%, C25N3H30Cl, PMMethylene Blue (MB, dye content 97%, C28H31ClN2O3,mol) and Crystal Violet (CV, dye content 90%,O3, PM 479g/mol) were used as organic pollutant. EachAldrich) was used without further purication.ferent dye concentrations were used in the present04 M and 1105 M, depending on the reaction set-t concentrated solutionwasused toverify the efciencydegradation of organicmolecules inwater of powderedTiO2 as stressing conditions. These results were com-

e results already obtained by P25 by several authors in,15] and reconrmed in this text. The less concentratedgher than the one reported by Marcos et al. [10], werethe performance of Orosei ActiveTM tiles.tions were prepared by dissolving the dye in distilledithout any pH adjustment, but leaving them at their

s values.wder has been characterized by HR-TEM (Jeol JEM 3010, equipped with LaB6 lament and operating at 300kV).X analysis were performed on as received Oroseies (Field Emission Gun Electron Scanning Microscopyetallizationwith Cr. Elemental compositionwas deter-

g Bruker Quantax EDS.).

atalytic test using powdered nano and micro-TiO2

radation inwatermediawasperformed ina slurry reac-) of 0.5 L volume [16]. Irradiation was allowed by theternal UV lamp (500W, Jelosil, HG500, halide lamp),the range 315400nm and with a emitting power eval-middleof the reactorbya radiometer instrument (Deltal HD2102.2) of 75W/m2. The reactor was equipped byrefrigerating serpentine system.orption tests have been carried out in the dark using aount of 1 g/L at four different dyes solution (concentra-between 106 and 104 M) for six hours.

Fig. 1. astirrer; CD: UV la

PhophotocDyes dtion ofa UVvmentsmaxim

2.3. Ph

A cydationsurfaceschemcoolingsolutiolamp (sure),a 125Willumin

Thetests rsimplydeioni

Adsdyes soationophotolwith ththus pphotoctoward

Thein the pmonitoSection

ical features of either 1077 and P25 powders.

Crystallographic phase SSA(m2 g1)

75/25 anatase/rutile 50Anatase 12tinuous stirred slurry reactor; A: refrigerating serpentine system; B:amp. b: cylindrical batch reactor used for photocatalytic experiments:: Orosei ActiveTM tiles; F: cooling jacket; G: magnetic stirrer.

is tests have been performed for six hours; the same forsis performed using fresh 0.1 g/L TiO2 in powder form.dation was checked every 60min. Analytic determina-yes concentrations in water solution was performed byectrophotometer analyzer (T60 UVvis PG LTD instru-ng water as the reference. Pure CV has an absorbancet 590nm, RhB at 555nm and MB at around 670nm.

atalytic test using photoactive TiO2 tiles

rical batch reactor of 1 L volumewas used for dye degra-s in presence of ten photoactive tiles (0.03m2 totaltoactive area) immersed into the liquid solution, aslly shown in Fig. 1b. Refrigeration was allowed by aet. Two different lamps directly immersed into the dyere used with this setup: a typical germicidal 9W UV-Cs TUV BL-S, model AEPL-7913 mercury vapor low pres-a UV-A illuminance at the tiles surface of 1W/m2 and-A lamp (Jelosil, mercury vapor low pressure), with anof 65W/m2.e batch of Orosei ActiveTM tiles was used for all theed in the present paper; after each test the tiles werehed using deionized water and acetone and then left inater all night long.

ion tests were carried out by dipping the tiles into the

C.L. Bianchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 280 (2014) 2731 29

3. Results and discussion

3.1. Powders and tiles characterization

Conventional and HR-TEM investigations indicate that (almost)no ultrane crystallites are evident for the plain 1077 powder(see Fig. 2a, left-hand section): in particular, all particles exhibitwell-ordered crystallographic terminations (see Fig. 2a, right-handsection), all belonging to the anatase phase (mostly to the (101)family of planes), as also reported in [12], referring to XRD anal-ysis performed on the same sample. HR-SEM images of Orosei

tiles show a homogeneous distribution of TiO2 crystallites in themicro-sized range without ultrane particles [13].

A further magnication (Fig. 2b) reveals the particles dimensionthat ranges between 100 and 125nm as already obtained by XRD(Table 1). By EDX analysis it was possible to determine the quantityof TiO2 coated on the tiles surface as 1.1 g/m2. Related to the tentiles used in our tests with the total photoactive surface of 0.03m2,a quantity of 0.033g/L of TiO2 was estimated to work during thephotocatalysis tests.

3.2. Photocatalytic degradation of dyes in presence of TiO2powders

Experimental dark tests have shown a very low adsorption of allthe dyes on both P25 and 1077 catalyst at the spontaneous pH wehave in our working conditions. Notwithstanding P25 has specicsurface area double than 1077 (25m2/g and 12m2/g, respectively)photolysis of CV and MB are almost negligible for both the catalysts

(6% for both dyes for P25, 9% and 4% for CV and MB, respectively, for1077). 12% of dye degradation for simple photolysis (10% for P25)was achieved for RhB.

The dye molecules here considered are all cationic organic-basedoneswith a several benzene rings andhighmolecularweight,being thus quite complex systems to be degraded.

Photocatalytic tests showgood results indyes abatement.Nano-sized powder shows the best results for all the considered dyesachieving the complete decolorizing of the water solution in 6h inthe case of CV (Fig. 5SI), but also micro-sized sample are able todegrade the pollutants with a good efciency (ranging from 48 to58% depending on the dye in six hours) (Fig. 3).

A study on the reaction rate has been done by elaborating thekinetic constants for both 1077 and P25 samples. Photocatalysisgenerally follows a LangmuirHinshelwood mechanism [17]:

r = K = kKC1 + KC (1)

where r is the reaction rate for the oxidation of the reactant, k is thetrue kinetic constant, including the mass of catalyst and the ux ofefcient photons, is the coverage fraction of the material, C is thedye concentration in solution and K is the adsorption equilibriumconstant.

Eq. (1) can be approximated to a pseudo-rst order kinetic withrespect to the negligible adsorption of the dyes by the micrometercatalyst used:

r = dCdt

= kappC (2)

es ofFig. 2. a: TEM images of pure 1077 in powder form. b: HR-SEM imag Orosei ActiveTM tiles refer to 100.00K X.

30 C.L. Bianchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 280 (2014) 2731

Fig. 3. Photoccrystal violet;

where kappThe integraand the sloThe rate conand for all t(data in Tapowders exlikely becaudespite the

The posssimply ltefunnel equilaboratory s

For 107recover all ttimes in detest (CV dishand, no recing the solulter papertion remain

The loweof dyes in wthe facilitythe end of tsimple was

3.3. Photocactivated til

Accordinsized TiO2onto porcelsetup verifyimmersed i

Controlthe tiles weand MB, whHowever, d

Photocatalysis with OroseiTM active tiles and UV-light irradiation (9Won UV lamp); crystal violet; methylene blue; rhodamine B.

f the ceramic pieces, i.e. in the surfaces uncovered by theatalytic layer.ect photolysis highlights different results depending on theamp: a percentage degradation of 64% for CV, 70% for MB% for RhB was achieved for 9W immersion lamp, a very highin comparison to the photolysis tests reported in Section 2.2.er inon inotolyer rehe ahotoforgeynamultsted mor 9Wradan facobtai

Table 2Rate constant

Sample

1077P25atalysis of dyesperformedwithpowderedmicro-TiO2 catalyst (1077):methylene blue; rhodamine B.

is the apparent rst order rate constant and t is the time.l form in functionof timeof the Eq. (1) canbewithdrawnpe of the straight line interpolated represents the kapp.stants were consequently calculated for both samples

he tested dyes and are all in the 103 magnitude order.ble 2). It is worth noting that both nano- and micro-hibit k values in the same order of magnitude, mostse the photocatalytic process follows a similar pathwaydimensions of the TiO2 powder.ibility to recover the powdered catalystwas checked byring the nal degraded solution in a standard Bcknerpped with a lter paper or directly centrifuging it in acale equipment working at 10,000 rpm.7 sample the simple centrifugation was sufcient tohe used photocatalyst. The powder was washed severalionized water and reused in the same dye degradationcoloration) with no loss of photoactivity. On the otherovery of P25was possible neither ltering or centrifug-tion. The nano-powder passed completely through theand it was not separated by the solution by centrifuga-ing very well-dispersed in water.r efciencyof 1077micro-sizedTiO2 in thedegradationater than nano-sized photocatalyst is fully rewarded byto recover the photoactive powder from the solution athe purication reaction and reuse it eventually after ahing in water.

atalytic degradation of dyes in presence of TiO2es

Fig. 4.immersi

sides ophotoc

Dirused land 14resultHowevemissithe ph

Lowlamp. Tpure pnot toow d

Resthe coaFig. 4 f

Degtiles; ivalueg to the previous results obtained by the use of micro-catalyst, the activity of 1077 industrially hot-coatedain-grs tiles was evaluated in another experimentaling the material efciency with two different UV lampsnside the dyes solution.experiments of photolysis and adsorption of dyes onre carried out. Dark tests shown a 25% adsorption of CVile RhB adsorption is on the contrary almost negligible.yes were exclusively xed in the backside and lateral

Fig. 5. Attenuand UV-light i

calculated for both 1077 and P25 samples.

RhB rate constant 103 (min1) MB constant rate 1.78 1.785.0 5.1this case this was a germicidal lamp and therefore anthe UV-C region is present and is probably enhancingsis process.sults were obtained using the 125W UV-A immersionbsence of UV-C allows to have dyes degradation due tolysis within 30% for CV and MB, 10% for RhB (we havet that tiles are already immersed not to alter the reactoric and therefore adsorption process is still present).obtained by photocatalytic tests, carried out by using

icro-TiO2 catalyst onto the tiles surface are showed inlamp.

tion of dyes is improved by the use of the photoactivet after a six hours reaction, the percentage degradationned is 78% for CV, 88% for MB, and the 30% for RhB,ation of the 590nm absorbance peak of CV by OroseiTM active tilesrradiation (125W immersion UV-A lamp).

103 (min1) CV constant rate 103 (min1)2.648.2

C.L. Bianchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 280 (2014) 2731 31

revealing an increase of about 15% of degradation on all dyes incomparison to the simply photolysis tests.

Tests with the 125W UV-A lamp lead to the complete degra-dation of CV (Fig. 5) and MB in less than three hours and thedisappearance of 71% RhB in 6h.

4. Conclusions

Main target of the present work was thus to verify the possibil-ity to usemicro-sized TiO2, instead of the classical nanopowders, inthe degradation of organic molecules in water phase. The obtainedresults have tobe consideredwith great importance asusingmicro-sized TiO2 the health risks related to nano-sized particles can beavoided; moreover such a micro-sized powder can be easily l-tered and recovered, in order to be immediately reused for furtherphotodegradation reactions, opening the way of a fully industrialuse of photocatalysis in environmental remediation.

A further improvement can be achieved coating micro-TiO2on porcelain-grs tiles surfaces. The photocatalytic materialsdescribed here can be reused, just after mere rinsing of the tilesin distilled water, and without affecting the photocatalytic activ-ity. In fact all the tests performed in the present work were doneusing the samebatch of ten samples obtained from industrially pre-pared tiles (Orosei ActiveTM), and no loss in their photoactivity wasmonitored.

This indicates that the TiO deposited layers are not deactivatedduring the rcan be reut

These neing alternatapplicationprocess.

Acknowled

The authversit di Ptiles.

Appendix A

Supplemfound, inj.jphotoche

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