Matrix Implications on the Photochemical Degradation of...
19
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 Physics AASU 11935 Abercorn St. Savannah, GA 31419
Transcript of Matrix Implications on the Photochemical Degradation of...
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
