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lndo. J. Chem.,2010,10 (2),143 -

148

143

POLYMORPHIC TRANSFORMATION OF

TITANIUM

DTOXIDE

CAUSED BY HEAT

TREATMENT OF PROTONIC

LEPTDOCROCITE

TITANATE

Hari

Sutrisno.

and

Sunarto

Depaftment of Chemical Education, Faculty of Mathematix and Natural Science, Yogyakarfa State University (YSU), Kampus Karangmalang, Yogyakarta 55281, lndonesia

Received March 15, 2010; Accepted tilay 6,2010

ABSTRACT

The polymorphic phases

of

titanium dioxide yvere successfully prepared

by

heat treatmenfs

of

protonic titanate, Ho.dtTiLa6sDotssO{0.5HzO at various temperatures. Ihe prepared powders were characterized EDX (Energy Dispersive X-ray), Scanning Hectron Microscopy (SEM), X-rays Diffractometer (XRD), Raman

',

and

High

Resolution Transmission Electron Microscopy (HRTEM).

The

etrect

of

calcination on the phase structure and morphology of the heated samples wasinvestigated. The research indicated

lc

protonic titanate, Ho.slTh.ass?o.nsO{A.5HzO (D = vacancy), lost the interlayer water by being heated up to

T

to produce a dehydrated phase, Hs.saTils65?s.1s5Oa. Above 300 "C, the dehydrated phase, Ho.slTil,.s65tro.fis0$

transformed to TiOz@) and anatase was obtained as pure phase at 6A0 "C. The phase transformed as

fuwing

process.' Ho.stTh.ws&.rssOi0.#1za

-+

Hs.5aTh.s6sils.tesO{0.25H2

-+

Hs.saTh.s6s&.tss0t

)

TiOz@) -+

layered compound, titanium dioxide, lepidocrocite, phase transformation, heattrcatment

Titianium dioxide (TiO2) is considered to be one of mos.t promising materials

due

to

its

excellent

stability,

high

oxidation

affinity, hardness, superior photo-reactivity and optoelectronic properties. lt is widely used as wtite

in paints, cosmetics, photoelectrobhEmistry and canier in industry [1]. Titanium dioxide as an n-semiconductor with a wide energy band gap is

well-for its

potential applications

in

the

fteld

of devices [2-6], superhydrophilic

and

light-amphiphilic surfaces f/-101

and

antibacterial 111-131.

lt

can

be

also

applied

in photocatalysis [141.

The

photocatalytic

of

TiO2

is

markedly influenced

-by

ihe polymorphic phases, particle shape, size, crystallinity, and specific surface area. nanoparticles show high photocatalytic activities they have

a

large surface area per unit mass rolume, and hence facilitate the diffusion of excited and holes towards the surface before their This process involves

a

large yariety of

for

example,

partial

or

total

oxidation,

h$rogen

transfer, metal deposition, detoxification, or gaseous pollutant removal

[1$

Titanium dioxide has eleven polymorphic phases: (tetragonal,

Allamdl

[20t, rutile

(tetragonal,

)

121-221, brookite (orthorombic, Pbcal 1231,

author. Ttl/Fax i +62-274-548/;0g address : sutrisnohari@uny.ac.id

TiOz(B) (monoclinic,

C2lm) [24],

TiO2(H)-hollandite

(tetragonal,

Alm) [25],

TiO2(R[ramsdellite (orthorombic, Pbnml [26], TiO2-columbite type o-PbO2

(TiOrll) (orthorombic, Pbnm) 127-287, TiO2 baddeteyite

type

(TiO2-Ml) (monoclinic,

nlc,

[29-301,

TiOr

orthorombik

ffiOrOl)

(ortorombik, Pbca) [31], TiO2

fluorite

type

CaF2

(cubic,

Fm3m)

I32l dan

TiOz cotunnite type (orthorombic, Pnma) t33]. Rutile

is

a

stable phase, while

anatase

and

brookite

are

metastable

and

will

be

transformed

into

a thermodynamically most stiable rutile phase

at

higher

temperature

after

thermal

treatment.

The

low

,

ternperature anatiase phase is ineversibly transformed to rutile phase on heat treatment above 450

'C.

The

.

transformation from anatase to rutile is metastable-tc.

stable

transformation

and there

is

no

equilibrium temperature of the transformation. The transformation ternperature range varies from 400

"C

to

1200 "C, depending on the grain size, presence

of

impurities, dopants, precursor material and synthesis method [34].

The photocatalytic performance of TiO2 can be

optimized

by

microstructural

and

macrostructural control on the morphology of the material because of

the intimately morphology-dependent characteristic of

the

photocatalytic properties.

lt

is

interesting and necessary to investigate the process of the TiO2 phase transformation,

both

from

a

scientific

and

from

a technological

point

of

view.

Nanostruc'tured TiOz materials can be prepared by dry and wet processes. ln this work, the TiO2 polymorphic phases are prepared

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