Ion-exchangeable layered niobates as photocatalysts

Catalysis Today, 16 (1993)479-466 Elsevier SciencePublishers B.V., Amsterdam

lon-exchangeable

K. Domen, and

Y.

layered

Ebina,

479

niobates

T.

Sekine,

as photocatalysts

A. Tanakaa,

J. Kondo,

C. Hirose

Research

Laboratory

of Technology,

aNikon

1-10-l

Co.,

of Resources

4259

Utilization,

Tokyo

Nagatsuta,

Midori-ku,

Yokohama

Asamizodai,

Sagamihara

228,

Institute 227,

Japan

Japan

Abstract Silica

pillared-niohates

layered

perovskite,

swelling

as

reagents.

expanded

by

m*/g

obtained

was

was

ca.

used.

The

revealed

and that

when

the

with

BET

the

with

proton-exchanged

photocatalytic

precursor

of these

silica

of the

original It was

derivative.

pillared-niobates

spacing

of 'ca. 200

intercalated

those

ions

interlayer area

activities

compared

a, so called,

alkylammonium

surface

an octylammonium

were the

from

by using

photocatalytic

silica

characteristic

prepared

A product

1.2 nm and

pillared-niobates KCazNb3010

were

KCazNbaOlo,

showed

a high

and

activity.

1. INTRODUCTION Recently niobates instance, metal HZ

we

02

reaction

found

that

interlayer from

that

(A

that

quantum

the

water

to

For

Ni Hz0

or Pt into

10 % under

steady

catalysts,

it was

were

of which

photocatalysts

ultrafine

decomposes

In these

molecules

mechanism

of conventional

up

layered

activities.

with

spaces

efficiency [l-33.

intercalated

ion-exchangeable

loaded

interlayer

condition

spaces,

some

photocatalytic

K, Rb)

q

at the

at high

state

found

interesting

A4Nbs017

particles

and

have

exhibit

was such

decomposed very

at

different

as TiOz.

OQZO-5861/93/$6.00 0 1993Elsevier SciencePublishers B.V. All rights reserved.

the

480 Another in the metal are

example

of

layered

family

of

layered

cations

at

the

generally

perovskite

interlayer

formulated

M = di

or trivalent

equals

to the

thickness

accumulation

A schematic

number

structure

In a concentrated metal

cations

replaced The at

by

Hi

ions

H+-exchanged the

are

family nm)

r51.

example,

however, and

the

activity layered

the

light

proved

to

we

compounds

only

visible

length which

region

(>

ultraviolet

to have light

seems

a

irradiation

of water

introduce

catalyst

of

into

suitable to be

In this we

preparation

of a pillaredperovskite

type

KCazNbs 010

because

to prepare

photocatalytic been

some

decomposition

in the

for

was

as a starting

material easy

sites

c-axis

molecules

photocatalytic

niobate. chosen

was

modification

oxidation

therefore,

examined

an overall

the

absorb

structure.

water

in visible

02 under

1.

to be

layer

reasons

is that

compounds

and

possible

the

the

RbPbzNb301o

Hz

further

indispensable. study,

materials

in Figure

intercalate

of

i.e.

direction.

100 % of alkali

are

as a result One

niobate

To accomplish OZ,

and

nm

to

photoresponse

most

to evolve

reduction

and

spaces - 0.2

almost

of n

sheet,

in c-axis

degradating

is known

number

macroanion

space

compounds

(A = alkaline The

unit

found

alkaline

These

3 is represented

q

without

exhibit

For

potential

NbOs

solution,

in these

while

photons.

and

0.1

interested

this 400

by

niobate

of the

are

contains

[4].

cation).

interlayer

form

inter-layer

increases

metal

of n

the

which

space

of the

acidic

at

photocatalysts

as A(Mn-lNbnOsn+l)

metal,

the

niobate

studied

although ultraviolet

it was and

the

activity in detail

it absorbed photons.

had [43,

only

0

A

.

M

@

NbOs

Figure 1. Schematic structure of a layered perovskite, AM2Nb&,.

HP

481 2. EXPERIMENTAL

KCazNbs01o

was

prepared

stoichiometric

mixture

10 h in air.

Photocatalytic

closed

gas

reaction

3. RESULTS

3.1.

of KzCO~,

circulation The

cell.

AND

in a platinum and

CaC03

reactions

system detail

with

was

an

crucible NbzOs

were inner

described

from at

1473

carried

out

irradiation

previously

a K for in a type

111.

DISCUSSION

Preparation

and

characterization

of

silica

pillared-

KCazNb3010

The

procedure

pillared-niobate This

1.

except

the

treatment.

adopted from

the

KCazNbaOlo

is following repetition

for

the of

KCa2Nb3010

preparation precursor

method

tetraethyl was

reported

of

is shown by

in Scheme

Landis

orthosilicate

ion-exchanged

silica

et al. [61

(TEOS)

in an aqueous

HN03

IKCazNb-JOlol

P t-

,t-

5M HNOJ aq. Stirring for 72 h at r.t.

C8H1,NHz/ heptane Reflux for 24 h

Si(OEt), Stirring for 72 h at SOT

Si(OEt)4:(CsH~,NHJ)CazNbjOlo

I L

/+Calcination

for 4 h

,

Silica pillared-(C~H~7NH3)Ca2NbjOlo Scheme 1. Preparation of Silica pillared-niobate.

28 I degree Figure 2. XRD pattern of modified KCa2Nb3010.

solution

(5 N) to substitute The degree

temperature.

H+ for K* ions for 72 h at room

of ion exchange

was more than 90 % which was determined analysis

of R+ concentration

The X-ray diffraction Figure

The c-axis

2(a).

the hydration

eluted

(XRD) pattern

into the aqueous af HCazNb3Olo

length was estimated

of the interlayer

was then swelLed

by a long-chain

to be 1.57 nm HCa2&bsOlo

alkylammonium

ion in heptane.

of the sample swelled

shown in Figure

2(b) which

by octyl~mmonium

shows the expanded

This sample was treated

c-axis

twice as mentioned

By this treatment

to intercalate

space

TEOS is expected

filled with alkyf-chains

The final pillared-niobate K for 9 h in air, only once,

was produced

same with that of HCazNbsO ~0 which of intercalated spacing.

into the ions.

by calcination

suggested

at 773

was carried

length after calcinetion

at

above.

of ammonium

When the TEOS treatment

the c-axis

is length of

in a neat TEOS solution

353 K for 72 h, which was repeated interlayer

solution.

is shown in

space occurred.

The XRD pattern 3.26 nm.

by this treatment

by atomic absorption

out

was almost

the

that the amount

TEOS was too small to expand the interlayer

Repeating

good reproducibility

the TEOS treatment for preparing

twice resulted

in a

the pillared-niobate.

Table 1 Comparison of c-axis lengths and BET surface areas of some pillared-niobates.

precursor

c-axis length

(nm)

surface area

before celcination

after Cal&nation


KVb~~)~a2Nb3010

3.26

2.93

200

G&$bSH3~Ca2Nb3010

3.92

3.36

180

5.00

4.31

50

After

the

calcination

was

thoroughly

burnt

was

diminished

by

octylammonium than was

that

to

to

the

silica

873

K and

the

collapsed

at

nm comparing sample When K,

respectively.

at the

K.

the

c-axis

of Thus,

all

the

samples

lengths

and

the

using and

after

the

measured of

the

that

volume

length

shows

the

although

atomic

temperature

surface

the

the

the of

in the

c-axis

the

alkylammonium The of

before

surface with

area the

This

increase

suggests

silica-pillared increse

length

of Si/Nb

ions.

and

BET

of the

increases.

were

Table 2 The composition of silica pillared-niobates

between

alkyl Table

2

determined 15 and

25 %

determined by EDX K

Si

Nb

Ca

GHl~dCm~dh

0.16

1.0

0.54

0.05

WdkdH3)Ca2~3010

0.22

1.0

0.70

0.07

(GsH37NJJ3)Ca2~3Olo

0.23

1.0

0.65

0.08

precursor

1

of

samples

silica-pillared-niobates

ratios

was

of alkyl-chain

77 K decreased

with

at

In Table areas

different

length for

indicates

to sinter

below.

of pillared-niobates.

decreases

composition The

at

of micropores

spaces

chane

EDX.

length

the

both

nm

completely

octadecilammmonium

However,

NZ adsorption

c-axis

the

with ions

calcination. by

interlayer

by

increased

1.36

were

This

was

BET

three

by

lengths

calcination

nm which

temperature

begins

pillar

described

prepared

ammonium

c-axis

interlayer

dodecil,

length

the

silica

ions,

intercalated

longer

973

pillared-niobates

c-axis

was

alkylammonium 2.93

of the

calcination

nm,

K for

octy1,

but

the

1.47

pillar

was

to that

K or

773

i.e.

length

or

structure 973

4 h, by which

c-axis

873

2.50

that

is shown

0.33

K for

the

intercalated

increased

at

773

of HCazNbaOlo.

decreased

fixed

at out,

484 which

increased X-ray

with

photoelectron

silica-pillared extent

of the

latter

sample.

observed that

but

of Ca

silica-

the

pillared

niobate

surface in the

aqueous

activity

In Table

methanol

intercalate

activity

water

solution at

the

are

very

the

low

for

was

of the

comparing

with

those

product

niobates

niobates and from

an

does

reaction

rate of Hz evolution / prnol*ti’ precursor

alone

Pt-loadedC)

KCazNbJ 010

14

100

HCazNb3 010

2200

8700

500

10800

-

9700

pillared-niobate

CsHlTNH3

pillared-niobate

C12H25NH3

pillared-niobate

C1sH3,NH3

not

occurs

Table 3 Comparison of rates of Hz evolution from an aqueous methanol solution a) catalystb)

of

niobate.

As KCazNb3010 the

for

segregation

of KCazNbs010

space,

for

preferentially

of Hz evolution

listed.

interlayer

to Nb

those

silica-pillared

rates

the was

of Ca and

silica-pillared

of

the

Si peak

same

silica

space

with

3, the

surface

no noticeable

but

of

the

niobate

was

and

to examine

intensities

that

interlayer

in comparison

HCazNbsOlo .

on

almost

occurred

photocatalytic

examined

were

indicates

Photocatalytic

were

intensity the

of HCazNb301o

measured

silica

Actually

This

The

of

signal

silica

on the

(XPS)

also

a silica-pillared

or Nb.

incorporated

were

segregation On

length.

spectra

niobate

HCatNb3Olo.

3.2

the c-axis

6600

a) CHsOH 50 ml + Hz0 300 ml, b) catalyst 1 g, Hg lamp (450 W) c) 0.1 wt%

485 only

at the

activity

external

of

HCanNb3Olo,

surface,

it.

When

the

activity

to

water.

is a typical

layered

lower any

that

silica

spaces. however,

the

to poison

activity,

Pt was

activity

to be a catalyst the

The

catalyst

is attached

When

for

by

onto

the

Hz evolution

between

is shown

in Table

HCazNb3010, when

methanol

than

two

As

are

rate

replaced

by ethanol

it was

in the

cases

sites interlayer

of

Pt

and

the

decreased

of magnitude

exhibit

is known

is considered

compared.

and

silica

rates For

lower

by

1-propanol

evolution ratesa) / pmol=h-’ HCazNbjO1ob’

pillared-niobate CSHI~NH~

MeOH

4670

8100

EtOH

384

5500

PrOH

43

1100

BuOH

30

1060

a) Pt 0.1 wt% loaded b) &-exchange degree > 95%

of Hz

drastically

Table 4 Dependence of Hz evolution rates from several alcohol solutions on KCazNb3Olo and silica pillared-niobate. alcohol

rather

sheet.

HCazNbsOlo

of HZ evolution

the

orders

alcohols

not

the

silica

4 where

from

pillared-catalyst,

on a niobate

difference

several

at

as

was

catalytic

sheets silica

site,

sites

A remarkable

from

does

the

completely.

pillared-niobate evolution

Pt-loading

silica

i.e.

of

as well

of HZ evolution

niobate

recovered

orders

rate without

low

ions,

ion-exchangeable

As

on

very H+

of

it blocks

loaded

HZ evolution

three

of methanol

of HCazNb3010.

photocatalytic

when

by

behavior

[4].

pillared-niobate than

the

replaced

intercalation

photocatalysts

silica

explains

were

increased

magni.t~tde due This

the

which

Ii+ ions

more and

l-

486 This

butanol. on

the

species

the

of

difficult other

although

these

for

of HZ

an aqueous

alcohol

silica

than

the

alcohols

for

attributed

to

the

pillaring.

silica

In summary, KCa2Nb3010

solution

effect spacing

which

30 times

longer the

with

comparing

was

attributed the

HZ

with to

of the

alkyl

pronounced rate

for

silica

increase

chains

should

spacing

for

rate

alkyl

longer

be to

Hz

even

chains

HCazNb3010. the

due

of

from

activity

evolution

intercalation

from

This

prepared

longer

On

chain.

less

higher

is

structural

evolution

interlayer

high

of alcohols

facilitated

the

photocatalytic

rather

extent

alkyl

HCazNb3010.

with of

HZ

activity

intercalation

is much

pillared-niobate

or butanol

of pillaring

for

a good

It showed

as propanol

was

that

silica

to the

the

longer

Actually

increase

exhibited

evolution. an aqueous

the

with

activity

solution

pillared-niobate

i.e.

pillared-niobate

remains.

butanol

activity

is attributed

evolution

it still

of photocatalytic

alcohols,

for the

hand,

dependence

dependence

of alcohols

intercalation more

strong

in such

This interlayer

of those

alcohols.

4. REFERENCES 1 2 3 4 5 6

A. Kudo, K. Sayama, A. Tanaka, K. Asakura, K. Domen, K. Maruya and T. Onishi, J. Catal., 120 (1989) 337. K. Sayama, A. Tanaka, K. Domen, K. Maruya and T. Onishi, J. Catal., 124 (1990) 541. K. Sayama, A. Tanaka, K. Domen, K.Maruya and T. Onishi, J. Phys. Chem., 95 (1991) 1345. K. Domen, J. Yoshimura, T. Sekine, A. Tanaka and T. Onishi, Catal. Lett., 4 (1990) 339. J. Yoshimura, Y. Ebina, A. Tanaka, J. Kondo and K. Domen, J. Phys. Chem., accepted for publication. M. E. Landis, B. A. Aufdembrink, P. Chu, I. D. Johnson, G. W. Kirker and M. K. Rubin, J. Am. Chem. Sot., 113 (1991) 3189.