Understanding Dimethyl Methylphosphonate Adsorption and Decomposition on Mesoporous CeO₂

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Growing global risks of chemical warfare agent (CWA) use necessitate advanced materials for CWA detection and degradation.
• Dimethyl methylphosphonate (DMMP) is a key simulant for sarin (GB) in laboratory studies.
• Mesoporous cerium oxide (CeO2) is a promising high-surface-area material for adsorbing and decomposing hazardous substances.

Purpose of the Study:

• To investigate the interaction and decomposition mechanisms of DMMP on as-synthesized mesoporous CeO2.
• To elucidate the role of CeO2 surface properties in DMMP dissociation.
• To computationally model DMMP interaction with different CeO2 surfaces using density functional theory (DFT).

Main Methods:

• Mass spectrometry (MS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study DMMP interaction with mesoporous CeO2.
• Density functional theory (DFT) modeling was employed to simulate DMMP adsorption and dissociation on pristine and hydroxylated CeO2 (110) and (111) surfaces.
• Characterization of the as-synthesized mesoporous CeO2 material.

Main Results:

• Experimental evidence shows DMMP dissociates on mesoporous CeO2 at room temperature via two distinct pathways.
• DFT calculations reveal an exceptionally low activation energy barrier for DMMP dissociation on the pristine CeO2 (111) surface.
• DMMP decomposition on hydroxylated CeO2 surfaces exhibits a significantly higher activation energy barrier compared to pristine surfaces.

Conclusions:

• Mesoporous CeO2 demonstrates high efficacy in decomposing DMMP at ambient temperatures, likely due to facile dissociation on pristine (111) surfaces.
• The observed dual dissociation pathways are potentially linked to interactions with both pristine and hydroxylated CeO2 sites.
• The findings suggest that pristine CeO2 surfaces are crucial for low-temperature DMMP decomposition, with hydroxylated sites playing a role at higher temperatures or after saturation.