Electrocatalytic Oxidation of Organic Pollutants:

Kinetic Considerations for Environmental Applications

Dr. Ronald Vargas

Electrochemistry LaboratoryChemistry Department

Universidad Simón BolívarCaracas - Venezuela

UNIVERSIDAD SIMÓN BOLÍVAR

INTRODUCTION

ENVIRONMENTAL ELECTROCHEMISTRY

ELECTROCHEMISTRY OF OXYGEN TRANSFER

NEW DEVELOPMENTS

CONCLUSIONS

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ELECTROCHEMISTRY

… Electrochemistry is about reducing tensions, as the French callthe voltage, and being aware of current events …

Thermodynamics

Kinetics:

dn/dt = i / (nF)

1 molecule is around 0.1 nm, and

under 1 V implies:

100 MV/cm of potential gradient!Fig 1. Electrochemical cell

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Fig 2. Key steps forenvironmental goal usingEOTR.

ELECTROCHEMICAL OXYGEN TRANSFER REACTION (EOTR)

Vargas. R., et al. J. Solid. Stated. Electrochem. 20(4) (2016) 875

is any pollutant molecule

How does affect the molecularstructure of the organic compound?

THE CHARGE TRANSFER INTERMEDIATE!

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Fig 3. Spectroelectrochemical observation of the charge transfer intermediate.

Case: p-metoxiphenol on PbO2-Bi

From the temperaturedependence we obtained the free energy of activation! Δ‡G200 300 400 500 600

0

/ nm

R/R = 0,02

to=0s

tf=1s

Vargas. R., et al. J. Solid. Stated. Electrochem. 20(4) (2016) 875

account the driven force!

MATHEMATHICAL MODEL OF THE ELECTROCHEMICAL PROCESS

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Vargas. R., et al. Electrochim. Acta. 80 (2012) 326

Current equation (new reaction rate model)

Langmuir – Hinshelwood equation Levich diffusion length

Convective - diffusive equation

kKc

1 + Kc

From appropiate kinetic experiments thecharacteristic constants (k and K) can be evaluated!

VOLCANO PLOT AND LINEAR FREE ENERGY CORRELATIONS

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Fig 5. Volcano plot on PbO2-Bi

Vargas. R., et al. J. Solid. Stated. Electrochem. 20(4) (2016) 875

The stability conditionsat the interface can beredefined!

kinetics thermodynamics

Fig 6. Structure – reactivity relationships on PbO2-Bi

Phenolic family:

p-nitrophenol, p-cyanophenol,

Phenol,p-methylphenol, p-methoxyphenol

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1) A new structure – reactivity relationships have been envisaged.

2) The charge transfer reaction rate and the adsorption propertiesat the electrode are decoupled using a new kinetic model.The transport phenomena with surface reaction model.

3) The chemical kinetic of an organic compound family caninvolves a volcano plot in the EOTR.

CONCLUSIONS

THANK YOU

Dr. Ronald Vargas

Electrochemistry LaboratoryChemical DepartmentUniversidad Simón BolívarOfc. QYP-215Correo: ronaldvargas@usb.ve

Research interests:

Fundamental ElectrochemistryPhysical ChemistryEnergy and EnvironmentChemical Sciences

@labequsbhttp://www.labeq.usb.ve/

Acknowledgments:

TWAS-TYAN / ICSU ROLAC / TWAS ROLAC

Patricia Zancan and the organizing committee

Satisfactory results in many water polluted systems:

- Insecticides, pesticides, herbicides

- Phenols, poly aromatic heterocyclic compounds, chlorinated compounds

- Municipal wastewaters: urea, surfactant, e-coli

- Highly polluted biphasic media (oil from petroleum wastes / water)

ELECTROLYSIS TIMEFig A1. Petroleum residual dissolve with surfactant in water media

OBSERVATIONS AND POSIBILITIES

Fig A2. Spectral signal decay as a function of experimental parameters

Potential and temperature increment

EXPERIMENTAL VALIDATION FOR PHENOLIC COMPOUNDS

EXPERIMENTAL VALIDATION FOR PHENOLIC COMPOUNDS

Vargas. R., et al. Electrochim. Acta. 80 (2012) 326

Méndez. D., et al. App. Catal. B:Environ. 166-167 (2015) 529

Fig A3. (A) (reaction rate) -1 vs. (matter flux) -1/2 plot for two electrodes. (B) Reaction rate results envisage the structure – reactivity relationships

Phenolic family:p-nitrophenol, p-cyanophenol, phenolp-methylphenol, p-methoxyphenol

(matter flux) -1/2 (rad/s) -1/2

(re

ac

tio

n r

ate

) -1

(m

ol / s

) -1

no

rma

lize

d r

ea

cti

on

ra

te

concentration (M)

(A) (B)

x

K and k accounts the chemical effects

1,2 1,4 1,6 1,8 2,00

1

2

3

4

E / V vs. ECS

kobs / s

-1

1,2 1,4 1,60

2

4

6

8

10

12

14

E / V vs. ECS

kobs / s

-1

a) b)

Fig A4. Potential effect.

PMF

PNF

PMF

PNF

a) PbO2-Bi b) SnO2-Sb

EXPERIMENTAL VALIDATION FOR PHENOLIC COMPOUNDS