Effects of pre-adsorbed water on methane adsorption onto blends with hydrophobic and hydrophilic nanosilicas

Abstract

The effects of water pre-adsorbed onto hydro-compacted hydrophilic nanosilica A-300 and its blend with hydrophobic AM1 (dimethyldichlorosilane hydrophobized A-300) on methane adsorption depend on the amounts of water (h = 0.005−0.25 g per gram of dry solids) and the AM1/A-300 ratio (1:1, 3:1, and 5:1), as well on the pretreatment conditions. The interfacial and temperature behaviors of co-adsorbed water and methane were analyzed using low-temperature 1H NMR spectroscopy (for static samples), cryoporometry, and quantum chemistry. The structural, morphological, and textural characteristics of the materials were studied using 1H MAS and 29Si CP/MAS NMR spectroscopy, infrared spectroscopy, SEM, TEM, and nitrogen adsorption. It is unexpected that 1H NMR signal of methane increases with increasing temperature. This could be occurred due to enhanced molecular mobility and structure changes in mobile water and ice clusters bound in voids between silica nanoparticles in their aggregates, as well because of changes in the textural characteristics of the pretreated blends. The maximal adsorption of methane (38 mg/g at 285 K) is observed for AM1/A-300 (3:1) hydrated at h = 0.1 g/g. An increase or decrease in the content of hydrophobic nanosilica AM1 in the blends, as well the bound water amount, results in a decrease in the methane adsorption, but hydro-compaction of the blends results in increased methane adsorption.