ti 1243 - titanium dioxide as photocatalyst

8/19/2019 TI 1243 - Titanium Dioxide as Photocatalyst

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AEROXIDE®, AERODISP® and AEROPERL®Titanium Dioxide as PhotocatalystTechnical Information


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Contents

1. 4

2. Fume Titanium Dioxi e 4

2.1 Production 4

2.2 Fundamental Properties 5

2.3 Properties of AEROXIDE® TiO2 P 25 5

2.4 Properties of AEROXIDE® TiO2 P 90 5

2.5 Properties of VP AEROPERL® P25 / 20 5

2.6 Properties of AERODISP® Fumed Titanium Dioxide Dispersions 6

3. 8

3.1 Fundamentals 8

3.2 Photomineralisation 9

3.3 Photosterilization 9

3.4 Photoinduced Super Hydrophilicity 10

3.5 Example Applications 10

4. Literature 11


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1. Introduction

Titanium ioxi e is wi e y use as a pigment or paints,

printing in s, p astics, cosmetics an oo . Typica titanium

ioxi e pigments are c aracterize y a primary partic e

size o etween 0.2 an 0.5 µm. In contrast to pigmentary

titanium ioxi e, t e nanostructure titanium ioxi e pro -

ucts o Evoni In ustries ave an average primary partic e

size o etween 14 an 21 nanometers an consequent ya most no pigmentary properties. However, t e primary

partic e size is on y mentione to in icate t e app ication

properties o a given pro uct T e supp ie pro uct oes

not come in t is orm, ut rat er as tig t y on e aggre-

gates o t e primary partic e, varying in size an s ape to

impart speci c app ication properties. T ese aggregates

orm agg omerates uring pro uction usua y into t e pow-

er or granu ate orm t at is supp ie to customers.

T e nanostructure titanium ioxi e pro ucts o Evoniare so un er t e tra e names AEROXIDE anAEROPERL an inc u e t e we - nown AEROXIDE

P25. AEROXIDE TiO P25 is wi e y use as acata yst, cata yst support, an eat sta i izer or si iconeru er. In terms o p otocata ysis AEROXIDE TiO P25

as een su ject o many stu ies over t e years, inc u -ing its use in wastewater treatment, t e re uction o NOxin ex aust gases, an t e manu acture o anti- acteria ,se -c eaning or anti ogging sur aces. Because o its igp otoactivity, AEROXIDE TiO P25 is oen recognizeas the “gold standard” in photocatalysis [1].

In or er to provi e you wit t e est so ution or eacapp ication, t e port o io o AEROXIDE TiO2 a so

inc u es a ig y isperse ume titania, AEROXIDETiO P 90, VP AEROPERL® P 25/20 granulated fumedtitania an AERODISP ispersions t ereo .

T is Tec nica In ormation escri es t e properties anapp ications o our various nanostructure titanium ioxi epro ucts as p otocata ysts. I you ave any urt er ques-tions, p ease contact our tec nica personne at any time.

2. Fumed Titanium Dioxide

Titanium ioxi e occurs in nature in t e mo i cationsruti e, anatase, an roo ite. Ruti e an anatase arepro uce in ustria y, eit er y t e su ate or c ori eprocess, in arge quantities an are use as pigments ancata ysts, an in t e pro uction o ceramic materia s.Titanium ioxi e is o outstan ing importance as a w itepigment ecause o its scattering properties, its c emicasta i ity, an ac o toxicity.

Titanium ioxi e is t e most important inorganic pigmentin terms o quantity, severa mio. tons are pro uce peryear [2] by two different processes. The older sulfate pro-

cess epen s on t e rea own o t e titanium-containingaw materia i menite or titanium s ag wit concentrate

su uric aci . In t e c ori e process, t e titanium-contain-ng raw materia s i menite, eucoxene, natura an synt et-c ruti e, titanium s ag, an anatase are c orinate .

2.1 Productionvoni s titanium ioxi es are pro uce in a simi ar

anner to t e AEROSIL process y uti izing titaniumc ori es as raw materia : TiC 4, a ig -purity iqui , isaporize , mixe wit air an y rogen. Imme iate yereaer t e gases are reacte at temperatures etween

1000 an 2400 °C in a urner ea ing to t e ormationo pure an nanostructure titanium ioxi e accor ing to

e o owing reaction:

TiCl4 + 2 H2 + O2 → TiO2 + 4 HCl

e properties o ume titania pro ucts can e variei e y y a justing t e process parameters.

2.2 Fundamental Propertiesvoni s titanium ioxi e pro ucts are w ite pow ersit ig speci c sur ace areas. T e pro ucts are pure

itanium ioxi e wit an anatase content o 80 – 90 yeig t wit a sma portion o ruti e. T ey are not sur ace

reate . As mentione a ove, Evoni s titanium ioxi esare exce ent p otocata ysts. T is is ue to t e very igsur ace area an t e mixe anatase an ruti e crystastructure. Accor ing to Hurum et a t e ruti e acts as anantenna to exten t e p otoactivity into visi e wave-engt s an t e structura arrangement o t e simi ari y

size TiO2 crysta ites creates cata ytic „ ot spots at t e

utile-anatase interface“ 3 .

As can e seen rom Figure 1 t e pigmentary proper-ies white pigments have primary particle sizes around

200 – 500 nm are no longer relevant for nanostructuredartic es.

Pigmentransparen

Primary particle size [nm]

Figure 1 Influence of the primary particle size in nm on theransparency o t tan um ox e


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TEM HRTEM

5 nm

Figure 2 mages o 2 P25 depicting the primary crystals right graph and their aggregates and agglomerates left graph .

Figure 3 - mages o 2 P25 left and AEROXIDE® TiO P 90 right

2.3 Properties of AEROXIDE® TiO2 P 25AEROXIDE TiO P25 is a ne w ite pow er wit

y rop c c aracter cause y y roxy groups on t esurface [4]. It consists of aggregated primary particles.

e aggregates are severa un re nm in size an t erimary partic es ave a mean iameter o approx. 21 nm.article size and density of ca. 4 g / cm lead to a spe-

cific surface of approx. 50 m /g. Due to the formation

o aggregates an agg omerates, t e tampe ensity oAEROXIDE TiO P25 is only about 130 g / l (determinedacc. to DIN ISO 787 XI . The weight ratio of anataseand rutile is approximately 80 20. Both crystal forms areetragona ut wit i erent imensions o t e e emen-ary ce . At 300 °C, a s ow conversion o anatase to t eore sta e ruti e structure egins. At temperatures

ig er t an 00 °C, t e conversion runs aster com ineit a re uction o t e speci c sur ace. AEROXIDE TiO25 is suita e or many app ications t at require a ig

otoactivity.

2.4 Properties of AEROXIDE® TiO2 P 90W ereas t e average primary partic e size rom

s nm, von eve ope yariation o t e pro uction parameters anot er gra e in

or er to increase t e p otocata ytic properties: T e resu ts AEROXIDE TiO2 P 90, a pro uct wit an average

primary partic e size o 14 nm. Figure 3 s ows t e pri-mary partic e sizes o AEROXIDE TiO2 n contrast

o AEROXIDE TiO P25.

2.5 Properties of VP AEROPERL® P25 / 20As a ust ree a ternative to AEROXIDE TiO2 P25 weoffer a product grade named VP AEROPERL® P25 20.

s spec a granu ate t tan um ox e w t an averageparticle size of 20 µm (Figure 4) enables easy separation

ue to goo se imentation. Moreover VP AEROPERL25 20 allows improved handling properties due to

exce ent owa i ity an a ig tampe ensity.


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Figure 4 Images of VP AEROPERL® P25 20

Table 1ys co-c em ca ata o , 2 P 90 and VP AEROPERL® P25 20

Parameter (test method) Unit AEROXIDE® TiO2 P25 AEROXIDE® TiO2 P 90 VP AEROPERL® P25 / 20

Specific surface area BET 2 g ± 1 ± ± 1

pin 4 % dispersion

. – . . – . . – .

ampe ens tyacc. to DIN EN ISO 787

g l approx. 1 approx. 1 approx.

o sture2 hours at 105 °C

wt.- ≤1. ≤ . ≤ .

gnt on oss2 hours at 1000 °C based on material dried

for 2 hours at 105 °C

wt.- ≤ . ≤ . ≤ .

2 contentbased on ignited material

wt.- > . > . > .

Average particle size SEM µm

T e ata represent typica va ues an not pro uction parameters.

Deveopmenta pro ucts are a e e wit t e VP esignation. T eir commerciaization epen s on mar et response.

100 µm10 µm


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2.6 Properties of AERODISP® Fumed Titanium Dioxide Dispersions

Figure 5 ua ty o spersons can vary s gn cant y

n or er to meet t e customer requirements Evoniapp ies severa posttreatment an an ing tec no ogies.

voni s ispersion tec no ogy a ows pro ucing sta eater ase ispersions wit particu ate istri utions

e e ow 0.1 µm aggregate sizes. To ac ieve t esesma iameters a ig energy mi ing step is app ie .

ese tai or-ma e ispersions are pre erre in app ica-ions in w ic a very ig transparency an a very ig

p otoactivity are require .

Table 2ys co-c em ca ata o an sp.

Parameter (test method) Unit AERODISP® W 740 X VP Disp. W 2730 X

con enbased on material ignited at 1000 °C

t. ± ±

p

DIN EN ISO 787 9

– –

scos tyBrookfield 50 rpm, 20 °C

m a s < <

ggregate s zed-50 value

< . < .

Density 20 °C g / cm³ . 1.

e ata represent typica va ues an not pro uction parameters.

Deveopmenta pro ucts are a e e wit t e VP esignation. T eir commerciaization epen s on mar et response.


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3. Photocatalytic Applications

3.1 FundamentalsIn or er to un erstan semicon uctor p otoc emistry,t ree mo es o action nee to e iscusse : P otomin-era ization, p otosteri ization an p otoin uce superhydrophilicity 5, 6, 7 .

Titanium ioxi e is a ig t-sensitive semicon uctor, ana sor s e ectromagnetic ra iation in t e near UV region.T e energy i erence etween t e va ence an t econ uctivity an s in t e so i state is 3.05 eV or ruti ean 3.29 eV or anatase, correspon ing to an a sorption

an at < 415 nm or ruti e an < 385 nm or anatase8, 9 .

A sorption o ig t energy causes an e ectron to e pro-mote rom t e va ence an to t e con uction an(Figure 6). This electron and the simultaneously createdpositive e ectron o e can move on t e sur ace o t e

an

an

–⋅

–

Figure 6 as c pr nc p e o t e p otoact v ty o t tan um ox e

solid where it can take part in redox reactions 10 .or examp e, water mo ecu es can e oxi ize , w ic are

common y a sor e onto t e titanium ioxi e sur ace,generat ng ra ica s. T ese ra ica s are a ar stron-ger oxi izing agent t an eit er ozone or c orine, ot

nown as strong oxi ants. On t e ot er an , re uctionof oxygen forming superoxide anions O -• and in asecond reduction step peroxide anions O 2- can occur.

ese anions ear interme iate oxi izing power. Aese oxi izing species can cause comp ete oxi ation o

organic compounds to carbon dioxide and water [11].

e anatase orm requires ig er ig t energy t an t euti e orm, ut s ows a stronger p otoactivity. T is cane exp aine wit t e onger i etime o t e excite state

n anatase an t e etter a sorption o oxygen in anionicorm at the anatase surface 12 .


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3.2 Photomineralisationepen ing on t e reaction con itions, organic compoun s

can e u y minera ize to t e o owing en pro ucts:

organic molecules → CO2 + H2O

organic N-compounds → HNO3 + CO2 + H2O

organic S-compounds→

H2SO4 + CO2 + H2O

organic Cl-compounds → HCl + CO2 + H2O

i usion to t e cata yst sur ace is t e rate- eterminingstep. In iqui p ase reactions, t e generation o variousnterme iate ecomposition pro ucts occurs. In some

cases, t ese interme iate pro ucts inactivate t e cata-lyst surface [13]. Reactions found in the literature usingAEROXIDE TiO P25 an UV- ig t inc u e t e comp etedecomposition of phenol 14, 15 , chlorophenols 16 ,nitroaromates 17 , aromatic amines 18 , agriculturaleffl uents 19 , and crude oil in water 20 .

Figure 7 s ows typica ecomposition rates o 4-c oro-p eno an ic oroacetic aci using AEROXIDE TiO2

25 irra iate wit a 500 W ig -pressure mercuryapor lamp concentrations: 1 g l titanium dioxide cata-

lyst; 120 mg / l chlorohydrocarbon; TOC= total organiccarbon).

Figure 7Decomposition of 4-chlorophenol (4-CP) and dichloroacetic ac id (DCA) using AEROXIDE® TiO2

UV-irradiation time [min]

T O C / T O C

0

DCA 4-CP


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3.3 PhotosterilizationAs mentione a ove, ra ica s are orme on t e titanium

ioxi e sur ace w en it is irra iate wit UV ig t. T esera ica s can a so attac t e ce s o microorganisms, sot at nanostructure titanium ioxi e can e ective y euse to in i it t e growt o acteria, viruses, a gae,yeast, mo , an ot er microorganisms on sur aces or iniqui s. AEROXIDE TiO can a so e use in coatings or

sur aces e ping to prevent isco oration ue to extensivealgae e. g. gloeocapsa magma growth.

3.4 Photoinduced Super-HydrophilicityAnot er mec anism is iscusse or t e so-ca e p oto-in uce super y rop i icity o serve on sur acescoate wit t in TiO2 ms: UV excitation pro ucese ectron- o e pairs; t ese o es can oxi ize ri ging

-species to oxygen; t us creating oxygen vacancies .Fo owing a sorption o water a y roxy ation ta es

ace an t e sur ace properties are c anging to aconsi era y more y rop i ic e aviour. Water contactang es o ess t an 5 ° can e measure an suc sur acesare consi ere as eing super y rop i ic. T e processs reverse in t e ar .

e se c eaning an e ogging action o suc sur acesarises rom t e act t at irt an grime t at co ects on

e sur aces is rea i y was e away y water.

3.5 Example Applicationsere are severa opportunities or ma ing use o t eotocata ytic properties. An exce ent summary, espe-

cia y ta ing into account t e Japanese mar et is escri en a oo et entit e TiO2 P otocata ysis – Fun amenta s

and Applications”, Bkc, Inc. Tokyo 1999 by A. Fujishi-a, K. Has imoto an T. Watana e. In a ition a more

ecently published overview can be found at 1 .

Table 3otocata ytc e ects an examp e app cat ons

Effect Example

otomnera sat on • epo ut ng cement• e c ean ng pa nt• r water pur cat on• eo or sat on

otoster zat on • ntimicrobial surfaces e. g. roofings and tiles

oto n uce super y rop c t y • e c ean ng t es an g asses• nt ogg ng m rrors


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4 Literature 1 s, ., ee, .- .; . otoc emstry an oto o ogy :

Chemistry 152, 233 2002

mann‘s ncyc ope a o n ustr a emstry

urum, . ., gr os, . ., an ray, . ., a , . an ur-nauer, . ; . ys. em. , 1 ,

4 Boehm, H. P.; Kolloid Z. & Z. Polym. 227 1 – 2 , 17 1968

na e, ., ry , . awunyama et a ; . otoc em. oto o .: 137, 53 2000

atana e, ., a a ma, ., ang, . et a ; n o ms351, 260 (1999)

u s ma, ., ao, ., ry , .; . otoc em. oto o . . 1,1 2000

8 Benrath, A.; Z. Wiss. Phot. 14, 217 1915

9 Renz, C.; Helv. Chim. Acta 4, 962 1921

1 nse g er, . ., u, ., ates r., . .; em. ev. ,1995

11 Masaki, Y.; Sumitomo Metal M. 50, No.4, 26 1999

1 ca an , ., ermann, . .; . ys. em. 1 , 1

1996

13 Leimbach, J.; Diss. Univ. Regensburg (1995)

1 att ews, . ., c voy, . .; . otoc em. oto o . .Chem., 64, 231 1992

1 o o, ., arc, ., art n, ., a m sano, ., ves, ., ca -ani, A.; Applied Catalysis B. Environmental 20, 29 1999

16 Mills, A., Wang, J.; J. Photochem. Photobiol. A. 118 1 , 531998

17 Ferry, J. L., Glaze, W. H., J. Phys. Chem. B 102 12 , 22391998

1 re s, ., r c eys aya, ., arc en o, ; x . ec no .Wastewater Treat., Int. Conf., Paper 51, 9 1996

1 omero, . , a , ., en a , ., ra , .; . ys. , ,Pr3 283 1999

20 Nair, M., Luo, Z., Heller, A.; Ind. Eng. Chem., Res. 32 10 ,2318 1993


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+ - + [email protected]

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ti 1243 - titanium dioxide as photocatalyst

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