Dimethyl Methylphosphonate Adsorption Capacities and Desorption Energies on Ordered Mesoporous Carbons

In this study, we determine effective adsorption capacities and desorption energies for DMMP with highly ordered mesoporous carbons (OMCs), 1D cylindrical FDU-15, 3D hexagonal CMK-3, 3D bicontinuous CMK-8, and as a reference, microporous BPL carbon. After exposure to DMMP vapor at room temperature for approximately 70 and 800 h, the adsorption capacity of DMMP for each OMC was generally proportional to the total surface area and pore volume, respectively. Desorption energies of DMMP were determined using a model-free isoconversional method applied to thermogravimetric analysis (TGA) data. Our experiments determined that DMMP saturated carbon will desorb any weakly bound DMMP from pores >2.4 nm at room temperature, and no DMMP will adsorb into pores smaller than 0.5 nm. The calculated desorption energies for high surface coverages, 25% DMMP desorbed from pores ≤2.4 nm, are 68-74 kJ mol^-1, which is similar to the DMMP heat of vaporization (52 kJ mol^-1). At lower surface coverages, 80% DMMP desorbed, the DMMP desorption energies from the OMCs are 95-103 kJ mol^-1. This is overall 20-30 kJ mol^-1 higher in comparison to that of BPL carbon, due to the pore size and diffusion through different porous networks.