LDiaz-Torres Mex-Kor 2014 UANL

8/11/2019 LDiaz-Torres Mex-Kor 2014 UANL

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Photoluminescent andPhotocatalytic Properties of TiO2

decorated Bismuth doped

Strontium AluminatesL.A. Daz-Torres1

Carlos R. Garca1, P. Salas2, M. Guzmn1

1.Centro de Investigaciones en ptica A. C. Len Mxico2. Centro de Fsica Aplicada y Tecnologa Avanzada. Universidad

Nacional Autnoma de Mxico.June 2014


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Introduction

Funct ional

materials

OpticalMagnetic

Electrical

Catalytic

Chemical

Luminescence

Photocatalysis

Multifunctional

TiO2 decorated Bi

doped Strontium

aluminates

Phosphorescent materials (PMs)Emergency signaling.Compact fluorescet lamps.

Lasting for hours. 1

1) Materials 2010, 3, 2536-2566.

TiO2is one of the best photocatalyst.

SrAl2O4:Eu2+,Dy3+and Sr4Al14O25:Eu

2+,Dy3+

show long persistence time.

PMs improve the photocatalyc of the TiO2

in composites.2

Bismuth enhance the photocatalytic

activity of some crystalline lattices.3

2) J. Mater Chem A, (2013), 1, 1123-1126.

3) M Sc. and Eng. B (2011) 176, 13821387.


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Introduction

Sr4Al14O25: Eu,Dy can be used without irradiation to assist the Ag3PO4photocatalyst

in water solutions. 6

Persistent materials (PMs) create free carriers (electron or holes) which promote the

photocatalytic process.

Persistent materials have been proposed to help, with exciting light, the

photocatalyst to degrade some contaminants from water and environment.5

5) J. Mater Chem A, (2013), 1, 1123-1126.

6) J. Mol. Cat. A, (2012), 363-364, 129-133.


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Produ ce a decorated TiO2Bi-dop ed stront ium aluminate with a goo d

photo catalyt ic act iv i ty under UV irradiat ion (365 nm ).

That the deco rated TiO2 Bi-dop ed stront ium alum inate could degrade

methylene blue (MB) dye in water solut io ns .

That the Persistence of the stront ium alum inates im proves w ith Bism uth

concentrat ion.

Is it possible to ?


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MotivationDyes in wastewater are the major pollutants.7

Wastewater from

textile industry.

MB as pollutant in

water.

Methylene blue (MB)

contamination dye in a

lake.

7) Int. J. of Env. Sci. (2012),3,3, 940-955.

Object ives:

1 ) Syn thes ize Eu,Dy-s t ron t ium a luminate codoped wi th d i fferen t Bi mola r concent ra tions

betw een 0.0% and 15.0% mo l.

2) Then deco rate i t w i th TiO2at low tem perature.

2) Study the structura l , morp holog ica l and opt ica l proper t ies.

3) Evaluate the pho tocatalyt ic activ i ty of the TiO2decorated samples

in methylene blue degradat ion in so lut ions u nder UV (365 nm) irradiat ion.


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SynthesisWe use the combustion synthesismethod with urea as fuel.

1 2 3 4

Stage 1

Stage 2

1. Dissolved nitrates

in 15 ml of deionised

water.

2. Introduce the beaker

at 600C into the preheated

mufle.

3. Combustion ocurred

lasting 20-30 sec.

4. Green phosphorescent

foaming is obtained.

Sr(NO3)2 ,Al(NO3)3Eu(NO3)3 Dy (NO3)3Bi(NO3)3 .

Powders are pressed

with 2.5 t and disks of

1.0 g are produced.

The disks are annealed

at 1150C for 6h in a carbon

reducing atmosphere

56

(TiO2-SrAlO-Bi)Stage 3

Grind the disks for

Characterization of obtained

powders

7

SrAlO-Bi

Wet mixing in ethanol

1:1 in weight Mixture

TiO2 : SrAlO-Bi

Dry for 24 h and anneal

at 450C for 1h.

Grind and use

as a photocatalyst.

8

9 10


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Photocatalysis

At the beginning After 190 min

1) 0.5 mM solutions of methylene blue and 30 mg ofTiO2-SrAlO-Bi photocatalyst in water strongly

stirred for 1 h in darkness.

2) Then, the UV lamps (365 nm) are turned ON

keeping the stirring. Samples of 0.2 ml are extracted

in regular periods. Samples are centrifuged at 5000 rpm.

3) We measure the absorbance spectrum at regular periods.

Procedure

UV lamps

(365 nm)

Quartz beakerfilled with the solution

magnetic

stirrer plate

Reactor design

Agilent UV-Vis cary 60 spectro photometer

Uti l ised to measure the absorb ance spectra


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Results


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20 30 40 50 60 70

SrAl2O

4JCPDS 34-0379

15.0%

10.0%

5.0%

2.0%

1.0%

2tetha ()

0.0%

Bi, mol.%

Structural analysis by X-ray difraction

of the SrAlO-Bi powders.

For low conc entra tions o f Bi

(x= 0.0%, 1.0%, 2.0% and

5.0 %) the pow ders are

composed

Mainly of the phases: SrAl2O4

and

Sr4Al14O25.

For high concentrat ions of Bi

( x = 10.0 % and 15.0%) the

same stront ium alum inates

phases appear but Bi2O3phase

also appear in theXRD patterns.


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Morphology of the SrA lO-B i powders

0%

2.0%5.0%

10% 15%

1.0%Micrograins of irregular shapes

are observe for all samples afterthe annealed in carbon reduced

atmosphere.

The sample without Bi codoping

show particles with

larger sizes than the othersamples.


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400 450 500 550 600 650

PL

(a.u.)

Wavelength (nm)

0.0%

1.0%

2.0%

5.0%

7.0%

10.0%15.0%

= 380nmexc510 nm

463 nm

Bi mol.%

0.0 2.5 5.0 7.5 10.0 12.5 15.0

PL

Intensity(a.u.)

Bi concentration, mol.%

510 nm band:SrAl2O4:Eu,Dy

0.0 2.5 5.0 7.5 10.0 12.5 15.0

PL

Intensity(a.u.)

Bi concentration, mol.%

463 nm band: Sr4Al

14O

25:Eu,Dy

Photo lum inescence of the SrA lO-B i

powders.

The samp le codop ing w ith the 1.0 % of Bi

show the h ighest luminescence when is

exci ted with 380 nm UV l ight .

As B i concentrat ion increases the

lum inescence intensi ty decreases and

a shi f t to the blue region is ob served.

Tendenc ies of the 510 nm and 463 nm

lumin escence bands as a funct ion of B i

codoping.


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For photocatalysis we select the 0%, 2.0 %, 15.0%and pure TiO2 in order to

evaluate the methylene blue degradation.

These samples were decorated with TiO2 and then the photocatalysis experimentwas made for each sample.

TiO2- decorated SrAlO-B i fo r pho tocatalysis

20 30 40 50 60 70

0

50

100

150

200

250

300

350

counts

2 )

TiO2Anatase phase JCPDS 84-1286

20 30 40 50 60 700

20

40

60

80

100

120

140

**

*

* *

***

*

**

**

**

counts

2

strontium aluminates phasesTiO

2anatase phase

*

XRD pattern of the 2.0 % sample after decorated with TiO2

Pure commercial TiO2 Decorated TiO2-SrAlO-Bi-2.0 %

powder sample


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TiO2- decorated SrAlO-B i fo r pho tocatalysis

Morphology of the pure TiO2and the TiO2-decorated SrAlO-Bi 2.0%

Pure TiO2 TiO2- decorated SrA lO Bi 2.0%

Aparent ly the TiO2nanop art ic les are attached to th e surface of the

large micro grains o f the SrAlO-Bi 2.0 % samp le.

This fact is benef icial for the photo catalyt ic act iv i ty because the su rface

area is enhanc e.


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0 50 100 150 2000

25

50

75

100

%D

egradation

Exposure time (min)

0.0% Bi

2.0% Bi15.0% Bi

Reference Only TiO2

Photocatalyt ic degradat ion of of methylene blue

under UV (365 nm ) ligh t.

The 2.0 % B i TiO2decorated SrAlO sample reach almost a complete

degradat ion after 210 m in o f UV irradiation .


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ConclusionsLong persistent green and grenish blue materials were produced bythe combustion synthesis method followed by annealing in a reducingcarbon atmosphere.

The persistent powders were decorated with TiO2and the photocatalyticactivity was evaluated for the concentrations of x= 0.0%, 2.0%, 15.0%and pure TiO

2.

The decorated TiO2SrAlO 2.0 % Bi-codoping sample show goodphotocatalytic activity, the degradation was 97 % after 210 min underUV (365 nm) irradiation.

The 2.0 % sample show the long lasting persistence time and thePhotocatalytic activity probably due to the Bi levels into the strontiumaluminates lattices which creates electron or holes traps.

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LDiaz-Torres Mex-Kor 2014 UANL