Partial sulfurization of ultrafine BaTiO3 particles for photocatalyst

Institute of Multidisciplinary Research for Advanced Materials Tohoku University

J. Cuya, N. Sato, K. Yamamoto, H. Takahashi, and A. Muramatsu

Introduction

BaTiO3 is used asDielectric material. Supported catalyst for CO2 reforming and partial oxidation of CH4 at higher temperatures.Catalyst for processing of hazard pollutants by non-thermal plasma reactors.

However, BaTiO3 is unknown photocatalyst due toHigh band energy of 3.27 eV (378 nm). Photoactivity in UV spectra.

Objective

To enhance the optical absorption of BaTiO3 in visible-light spectra by partial sulfurization of BaTiO3 particles. That is a partial replacement of sulfur atoms by oxygen sites in the original BaTiO3 structure.

Preparation of BaTiO3

De-carbonated water14.429 g TIPO* 14.949 g TEA*

Solution Stock SolutionArgon atm. Overnight

TIPO:TEA 0.05:0.1*TIPO: titanium tetra-iso-propoxide

TEA: tri-ethanol-amine

6.315 g Ba(OH)2

10 ml stock solution

Gel

10 ml de-carbonated water

Stirring 30 min

Teflon autoclave Heating: 3 hrs T: 250° C

BaTiO3BaTiO3Cleaning Centrifugation Drying at r. t.

Partial sulfurization of BaTiO3

Quartz tube

Sample:1 g BaTiO3

Quartz boat

Electric furnace

Thermocouple

Gas inlet

Gas outlet

Flow rate: 5/50 ml/min Heating : 3 ºC/minT: 100-500 ºC

BaTiO3 Sulfurization Purification

Evacuation N2 refilling

Toluene CS2/N2 gas

100 ºC Vacuum

Partially Sulfurized

BaTiO3

Schematic drawing of reaction tube

Characteristics of ultrafine BaTiO3 particles

BaTiO3 particles were obtained by using TIPO and TEA as precursors.Characteristics:•Phase: Cubic•Particle size: 95 nm •Lattice parameter: 4.0061 Å•Specific area:12.42 mg/m2

•H2O (%): 1.6

200 nm

TEM microphotograph of BaTiO3

Sulfurization behavior of BaTiO3

-5

0

5

10

15

20

25

0 100 200 300 400 500 600 700 800 900 1000

Temperature/°C

Wei

ght c

hang

e/%

BaTiS3

Gas flow: N2 50 mL/min CS2 5mL/minHeating Rate: 1°C/min

19.2 18.4

-0.6

Starting temperature of sulfurization

BaTiO3 reacts slowly with CS2 at around 400 ºC forming BaTiS3. Reaction: BaTiO3+1.5CS2 BaTiS3+1.5CO2

XRD patterns for partially sulfurized BaTiO3

10 20 30 40 50 60

2Θ/degree

Inte

nsity

/a.u

.

100 °C

Initial Material

200 °C

300 °C

400 °C

500 °C

BaTiO3 (cub., JCPDS 31-174)

BaTiS3 (hex., JCPDS 15-328)

Sulfide Sulfide

Peaks corresponding to BaTiS3 appears only when BaTiO3 is sulfurized at 500ºC

Variation of lattice parameter

4

4.005

4.01

4.015

4.02

0 100 200 300 400 500

Temperature/ºC

Latti

ce p

aram

eter

a/ Å Lattice parameter : 4.031 Å

JCPDS 31-174

Formation of hex. BaTiS3

Cubic BaTiO3

Lattice parameter increases with increasing the sulfurization temperature. However, it decreases with formation of sulfide.

XPS of S2p3/2 for partially sulfurized BaTiO3

158160162164166168170172174

Binding energy/eV

Inte

nsity

/a.u

.

200 ºC

100 ºC

Sulfate

Sulfite Sulfur

Sulfide

300 ºC

400 ºC

500 ºC

From 200 and 500 ºC, a peak assigned to sulfide appears at around 161.4 and 160.8 eV whose intensity increases with the temperature.

UV-Vis spectra for partially sulfurized BaTiO3

Increasing the sulfurization temperature, the absorption of visible light increases in sulfurized BaTiO3 samples.

Band gap of BaTiO3: 378 nm

0

20

40

60

80

100

200 300 400 500 600 700 800

Wave length/nm

R /%

BaTiO3

100 º

BaTiS3

200 ºC

300 ºC

400 ºC

500 ºC

C

Conclusions

Partially sulfurized BaTiO3 absorbed higher visible light than initial BaTiO3 sample.The absorption increased with increasing the temperature of sulfurization.Since sulfide as BaTiS3 is formed above 400 ºC, it is suggested that absorption of visible light is caused by replacement of sulfur by oxygen in the initial BaTiO3structure.