POTENTIAL OF Ti-W-Zn

MIXED METAL OXIDES FOR

PHOTOVOLTAIC AND

PHOTOCATALYTIC

APPLICATIONS

Dr Paul Franklyn

Dr S Durbach, L Hlekelele, R. Carnie

N Driver, Pfano, A Narrandes

Aims

� Synthesize a range of both ternary and quaternary mixed metal oxides of titanium, zinc and tungsten

� Characterise the samples

� Test each material for photocatalyticand photovoltaic applications

2

Anatase

• Distorted Octahedra

• a=b = 3.7845 Ȧ• c=9.5143 Ȧ

• Band gap of 3.2 eV

• Large, open structure

3

Mixed Metal Oxides

� Creating a single crystal structure◦ But with multiple metals in the structure

◦ Try not to disrupt the host crystal

◦ Add the metal ions after or during formation

� Ternary Oxides◦ Titanium-Tungsten oxide

◦ Titanium-Zinc oxide

� Quaternary Oxides◦ Titanium-Tungsten-Zinc oxide

4

Why the interest?

5

We want to remove this physical gap

and still reduce the bandgap

but yet maintain the redox suface

and keep the interior electrical behaviours

Our Approach

� Incorporation of tungsten/zinc ions into the anatase structure

� Titanium- 0.745Ȧ

� Tungsten- 0.740Ȧ

� Zinc- 0.740Ȧ

6

Crystallography justification

7

Anatase with 40% TungstenAnatase with 20% TungstenPure Anatase

Experimental approaches

� Hydrothermal

� Co-precipitation

� Resin gel

8

The Results

� Titanium-Tungsten Mixed Metal Oxides

9

0

500

1000

1500

2000

2500

0 20 40 60 80

Inte

nsi

ty (

A.U

)

2θ(°)

Ti60-W40

Ti70-W30

Ti80-W20

Ti90-W10

Ti95-W5

Titanium-Tungsten-Zinc MMOs

Calcined at 500° for 1 hour

Distortion of unit cells

11

c parameter

b parameter

� Calculation of b and c parameters

� Determined using PXRD 2θ (in radians)

� The calculated parameters are then

compared to the literature parameters

Distortion of the unit cells

12

� Ti-W b parameter c parameter

� Ti-W-Zn

Ti95-W5

Ti90-W10

Ti80-W20

Ti60-W40

0

0,005

0,01

0,015

0,02

0,025

0,03

0,035

0 20 40 60 80 100

Dif

fere

nce

betw

een li

tera

ture

and

exp

eri

menta

l

Percentage of Titanium

Ti95-W5

Ti90-W10

Ti80-W20Ti60-W40

-0,18

-0,16

-0,14

-0,12

-0,1

-0,08

-0,06

-0,04

-0,02

0

0 20 40 60 80 100

Dif

fere

nc

e b

etw

ee

n l

ite

ratu

re a

nd

ex

pe

rim

en

tal

Percentage of Titanium

Ti70-W10-

Zn20(a-c)

Ti70-W20-

Zn10(a-c)

Ti50-W25-

Zn25(a-c)

Ti40-W30-

Zn30(a-c)

0

0,005

0,01

0,015

0,02

0,025

0,03

0,035

0 20 40 60 80

Dif

fere

nce

be

twe

en

lit

era

ture

an

d

exp

eri

me

nta

l

Percentage of titanium

Ti70-W10-

Zn20(a-c)

Ti70-W20-

Zn10(a-c)

Ti50-W25-

Zn25(a-c)

Ti40-W30-

Zn30(a-c)

-0,08

-0,07

-0,06

-0,05

-0,04

-0,03

-0,02

-0,01

0

0 10 20 30 40 50 60 70 80

Dif

fere

nce

be

twe

en

lit

era

ture

an

d

exp

eri

me

nta

l

Percentage of titanium

TEM Analysis: Ti70-W10-Zn20

(001)

Zone-axis of anatase

13

TEM Analysis: Ti70-W10-Zn20

(100)

Zone-axis of anatase

14

Elemental analysis

� Small area EDS

confirmed

individual

particle

composition

15

Testing the photocatlysts

16

� The first sample

tested decomposed

20ml of water in 12

hours.

� When retested it only

decomposed 2ml

� Retested it did 5ml

� Other samples

showed similar

behaviour

In conclusion

� The synthesis of all the samples was confirmed - characterised using PXRD, TEM and EDS

� The testing of the catalysts was inconclusive◦ Reproducibility proved a problem

◦ Despite reproducible structural data

17

Future Work

� The synthesis of clean, carbon free ternary and quaternary mixed metal oxides

� The set up of a more reliable testing system

� Exploring the complete phase diagram of composition and temperature

18

Acknowledgements

� Pfano (vac student)

� Robyn Carnie (4th year)

� Lerato Hlekelele (PhD)

� Nicholas Driver (MSc)

� Ashvir Narrandes (PhD)

� National Research Foundation of South Africa for the grant, 87885◦ Any opinion, finding and conclusion or recommendation expressed in this material is that of the

author(s) and the NRF does not accept any liability in this regard.