The oversolubility of methane gas in nano-confined water in nanoporous silica materials

The oversolubility of the non-polar methane (CH4) gas in nano-confined liquid in nanoporous silica materials is investigated. A series of mesoporous silica materials with different pore sizes, pore volumes, and different amounts of nano-confined water (H2O) are prepared using a pore-expanding reagent and surfactants of different chain-lengths, and the CH4 absorption by the silica nano-materials is studied at 298 K under low CH4 gas pressures. Analysis of the CH4 absorption data reveals unequivocal evidence for oversolubility of CH4 in the nano-confined H2O of all the hydrated nano-materials. The solubility enhancements are several hundred fold relative to the CH4 solubility in bulk H2O. Interestingly, the enhancements are 25-30% higher when a tricopper cluster complex capable of efficient selective CH4 oxidation under ambient conditions is immobilized into the nano-channels of the silica materials. This dramatic enhancement of the CH4 solubility is attributed to specific CH4 binding to the tricopper cluster complexes embedded within the mesopores of the nanoporous materials.