Organophospate adsorption on nanosized silica and silica/alumina: Surface interactions and behavior of adsorbents

Organophosphate compounds (OPs) are common in pesticides and can be highly toxic. Negative environmental impacts resulting from the release of OPs can be reduced with rapid detection, which relies on sensitive sampling techniques. In this work, nanosized silica and silica/alumina were tested for their ability and behavior in adsorbing gas-phase dimethyl methylphosphonate (DMMP). Surface interactions were probed using Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflectance (ATR) to establish correlations between surface properties and adsorption behavior. Adsorption characteristics were also investigated by gas chromatography (GC) equipped with a flame ionization detector (FID). Silica and silica/alumina adsorbents were exposed to DMMP in a flow system. FT-IR spectroscopy revealed that physical interactions between the adsorbents and DMMP were attributed to the presence of surface silanol. GC-FID results showed that adsorption onto both silica and silica/alumina followed Langmuir isotherm behavior. Silica demonstrated superior adsorption behavior as compared to silica/ alumina. The following Langmuir isotherm constants are representative of the data: 0.88 for silica and 0.82 for silica/alumina.