Mesoporous Copper Nanoparticle/TiO₂ Aerogels for Room-Temperature Hydrolytic Decomposition of the Chemical Warfare Simulant Dimethyl Methylphosphonate

Mesoporous copper-titanium dioxide (Cu/TiO₂) composite aerogels with <5-nm-diameter copper (Cu) nanoparticles hydrolyze the chemical warfare (CW) simulant dimethyl methylphosphonate (DMMP) under aerobic and anaerobic conditions. After Cu/TiO₂ is exposed to DMMP in an in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) reaction chamber, hydrolysis products (i.e., methoxy groups) are bound to the surface, while no intact DMMP is observed. In contrast, DMMP degradation is not observed under our DRIFTS reactor conditions at native TiO₂ aerogels, CuO, or Cu₂O nanoparticles. We attribute the hydrolytic activity of Cu/TiO₂ aerogels to a high surface concentration of OH species that form at Cu||TiO₂ junctions. Neither hydrolysis of DMMP nor excess surface OH is observed on Au/TiO₂ aerogels. The poor ability of the Au||TiO₂ interface to activate water relative to that of the Cu||TiO₂ interface suggests that a readily reducible supporting oxide is insufficient to promote an excess population of surface OH species - the supported nanoparticle must be sufficiently redox-active as well. Under aerobic conditions, DMMP hydrolysis is accelerated on Cu/TiO₂, suggesting that O₂ promotes the formation and turnover of surface OH sites. The general materials design demonstrated here of a Cu nanoparticle/reducing oxide aerogel is a promising route to CW decontamination as well other surface-mediated chemistries requiring the activation of water.