Understanding trichloroethylene chemisorption to iron surfaces using density functional theory

Area of Science:

• Environmental Chemistry
• Materials Science
• Computational Chemistry

Background:

• Trichloroethylene (TCE) is a common environmental pollutant.
• Metallic iron is widely used for in-situ remediation of TCE.
• Understanding the adsorption mechanism is crucial for optimizing remediation strategies.

Purpose of the Study:

• To investigate the thermodynamic favorability and structural outcomes of TCE chemisorption on metallic iron.
• To elucidate the reaction pathways and identify the most stable adsorption configurations.
• To correlate computational findings with experimental observations of TCE degradation.

Main Methods:

• Periodic density functional theory (DFT) calculations were employed.
• Simulated adsorption of TCE on iron surfaces from various initial configurations.
• Analyzed binding energies, bond lengths, bond angles, and activation energies.

Main Results:

• The most energetically favorable adsorption occurred at the C-bridge site, forming C-Fe bonds and causing complete C-Cl bond scission.
• Adsorption at top or hollow sites led to partial C-Cl bond scission and weaker C-Fe bonding.
• The C-bridge site exhibited an activation energy of 49 kJ/mol with an early transition state, consistent with complete dechlorination.

Conclusions:

• Chemisorption at the C-bridge site is the dominant pathway for TCE degradation on iron, resulting in complete dechlorination.
• Alternative adsorption sites (top, hollow, Cl-bridge) explain the formation of byproducts like chloroacetylene.
• DFT calculations accurately predict experimental observations of TCE remediation by iron.