Temperature (200–283 K) dependence of methane adsorption onto hydrophobic nanosilica/arginine composite at various hydration

Abstract

It has been assumed that nanoparticle/aggregate/agglomerate structure, texture and surface characteristics of hydrophobic nanosilica AM1 treated with certain amounts of arginine and water may provide better conditions for methane adsorption compared to AM1 alone. Nanosilica and composites are characterized using adsorption, desorption, microscopic, spectroscopic, XRD, SAXS, and quantum chemistry methods. The 1H NMR spectroscopy (at 200–283 K) and cryoporometry (T < 273 K) methods have been applied to AM1/arginine differently wetted and mechanically treated. The wetted blends have been studied in the methane atmosphere without or with addition of chloroform-d. In mechanically treated wetted blends, arginine (initially crystalline) is nanostructured and amorphous. In the powders wetted at 0.1–0.5 g of water per gram of dry solids, interaction energy of unfrozen water with nanoparticles depends nonmonotonically on the degree of hydration. The value of the free surface energy is maximal at the hydration of 0.3 g/g. Bound water, which partially fills interparticle voids and may remain liquid or forms amorphous ice nanoparticles at lower temperatures, provides enhanced nanoporosity in wetted composites. This is appropriate for the methane adsorption up to 7.3–4.9 wt% at 199–283 K.