Matrix Implications on the Photochemical Degradation of

Chlorinated Aromatics using Ceria Nanoparticles

April Meeks, Nguyen Nguyen, Delana A. Nivens and Will E. Lynch

Department of Chemistry and PhysicsAASU

11935 Abercorn St.Savannah, GA 31419

Halogenated aromatics have long been known as Persistent Bioaccumulative Toxic Pollutants (PBTs) - Defined

• Not biodegradable, highly toxic • travel long distances in the environment and easily transferred

– a half-life in water greater than two months– soil and sediment half-lives greater than six months

• target organs: – central nervous systems-causes tremors and seizures– reproductive organs

» Slow maturation in children and birth defects» abnormal fetal development» passed in mother’s milk

– chromosomes» Liver, breast and other cancers

Background--Environmental Remediation

Presented are recent studies on the use of cerium oxide nanoparticles for the degradation of halogenated aromatics. Nanometer scale ceria particles are prepared and investigated for their ability to dehalogenate aromatic substrates in the presence of light greater than 330 nm. Photodegradation studies are carried out on EPA priority pollutants (such as hexachlorobenzene). The degradation products are analyzed by SPME/GC-MS. In the case of hexachlorobenzene, a stepwise dechlorination of the compound is observed. The effects of salts commonly found in environmental samples have also been investigated. The competing or enhancing effects on the dechlorination rates will also be presented.

Abstract

Background-- Environmental Remediation• Examples

• DDT (dichlorodiphenyltrichloroethane) - banned from use as a pesticide by the EPA in the 1970’s

– Pesticide– Plants that were exposed to this compound were either eaten by

animals or humans. – DDT builds up in the fatty tissues of animals.

• Hexachlorobenzene*– Pesticide– Fungicide– Fireworks and ammunition

• Studies on degradation of these compounds may have applications to environmental systems

Establish the ability of CeO2 nanoparticles to dechlorinate hexachlorobenzene in lab samples

Examine the effects of common inorganic ions found in the environment on the catalysis

The ions studied include:chloride, bromide, iodide, fluoride, bicarbonate, sulfate, dihydrogenphosphate, ammonium

Purpose

•CeO2 nanoparticles

•Used to photodegrade chlorinated compounds•Monitor by SPME-GC/MS

•0.7µM PDMS fiber•GC conditions:

•250ºC inlet•60ºC for 6 min•40ºC/min to 120ºC •15ºC/min to 300ºC

Photochemical Dehalogenation

Cl

Cl

ClCl

Cl

Cl Cl

ClCl

Cl

Cl

ClCl

Cl

Cl

ClCl

Cl

-Cl--Cl--Cl-

Experimental Method Production of and Photochemical Studies on Cerium

Dioxide Nanoparticles

• CeO2 produced from Ce(NO3)3 and hexamethylenetetramine 2.0 X 10-3 M HCB

• Photocatalytic Studies• 2.0 X 10-5 M Cerium Dioxide NP• 0.10 M salt concentration (if appropriate)• Light > 330 nm exposure• Lamp Power: 7.8 & 17.6 mW/cm2

re

mmrhEE

ohegnp πεε4

8.1118

2

**2

2−

⎥⎥⎦

⎤

⎢⎢⎣

⎡++=

CeO2 bulk band gap: 3.15 eVEffective Band-Gap: 3.54 eVParticle size is: 5.7 nmElectron and hole

effective masses = 0.42 me

Particle Size via Brus Equation

nm0.2

0.3

0.4

0.5

0.6

200 300 400 500 600

Photodegradation of HCB by CeO2

0

2550

75

100

0 50 100

Time (hours)

(Are

a C

l-)/(

Are

a C

l- +

A

rea

HC

B) HCB

PCB

TCB

TriCB

Photodegradation of HCB by CeO2

0.E+00

6.E+05

1.E+06

2.E+06

2 5 8 11 14

Time (min)

Abu

ndan

ce

-Cl6

-Cl5

-Cl4

-Cl3-Cl2

Degradation Products --24 h No Matrix•2.0 X 10-3 M HCB•2.0 X 10-5 M Cerium dioxide

No Salts

0

5

10

15

20

25

30

hexa penta tetra tri di mono benz

Compound

% C

ompo

sitio

n

No Salts

Degradation Products 24 h Halide Anion Matrix (0.10M)

0

15

30

45

60

75

hexa penta tetra tri di mono benz

Compound

% C

ompo

sitio

n NaClNo SaltsNaFNaBrNaI

Degradation Products24 h Oxyanions (0.10 M)

0

10

20

30

40

50

60

70

hexa penta tetra tri di mono

Compound

% C

ompo

sitio

n

No SaltsSulfateHydrogen phosphateCarbonate

Degradation Products24 h Ammonium Ion (0.10 M)

0

10

20

30

40

50

60

70

80

hexa penta tetra tri di mono

Compound

% C

ompo

sitio

n

AmmoniumNo Salts

Degradation Products24 h Cyanide Ion (0.10 M)

0

10

20

30

40

50

60

70

80

90

100

hexa penta tetra tri di mono

Compound

% C

ompo

sitio

n

CyanideNo Salts

Degradation Products24 h Sulfide Ion (0.10 M)

0

20

40

60

80

hexa penta tetra tri di mono benz

Compound

% C

ompo

sitio

n

SulfideNo Salts

Results and Conclusions

• CeO2 effective as catalysts for light induced dechlorination processes.

• Majority of inorganic ions have positive or no effect

• Significantly Depress Rate – CN-

• Depress Rate – I-, Br-

• No effect – NH4+, HCO3

-

• Enhancement – Cl-, SO42-, HPO4

2-, S2-

Conclusions

1. NPs are effective catalysts for dehalogenation of EPA priority pollutants.

2. Matrix effects generally enhance catalytic activity

Only I-, Br- and CN- depress the rate significantly.

Acknowledgements

•National Science Foundation Division of Undergraduate Education: Nanotechnology in Undergraduate Education Grant CHE/NUE 0303994

•National Science Foundation Course Curriculum and Improvement Grant DUE/CCLI - 9952343

•USG Matching Grant

•AASU College of Arts and Sciences, Department of Chemistry and Physics

•AASU Research and Scholarship Grant / Gignilliat Scholarship