FT-IR and FT-NMR Study of Organophosphorus Surface Reactions

Abstract

Fourier transform infrared (FT-IR) and Fourier transform nuclear magnetic resonance (FT-NMR) methods were used to examine the adsorption and reaction of diisopropyl fluorophosphate (DFP) on various solid adsorbents. Static and flow system experiments were monitored with the use of FT-IR to determine DFP adsorption rates and isotherms on silica, coated silicas, γ-alumina, coated aluminas, and activated charcoal. The adsorption of DFP(g) onto the solid adsorbents was generally very rapid, with a half-life of 20 s for 1 mg DFP onto 25 mg of 350 m²/g silica. The DFP adsorption isotherm on silica indicated chemisorption to a monolayer at P/P₀ < 0.6, followed by increased coverage that appears to be physical adsorption. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, photoacoustic spectroscopy (PAS), and solid-state ³¹P NMR of adsorbed DFP showed chemisorption on silica and on alumina. Bonding at the P=O of DFP was indicated by a −41 cm⁻¹ shift in the v(P=O) and a 1-ppm upfield shift in the ³¹P resonance. DRIFT, PAS kinetics, and ³¹P NMR showed that DFP hydrolyzed after the initial adsorption on alumina and some coated materials but not on silica or activated charcoal. The rate of hydrolysis increased on alumina with addition of water and varied with different aluminas and coated silicas.