Intrusion/Extrusion of water into organic grafted SBA-15 silica materials for energy storage.

Mesoporous SBA-15 silica materials were grafted with trialkylsilyl compounds having short (C1) and long (C8) carbon chain and characterized by XRD, N2 physisorption analysis, 29Si MAS-NMR and contact angle (CA) measurements. A drastic enhancement of the hydrophobic property after grafting was observed by forced intrusion water; it occurred in two steps and with quite high intrusion pressures (mean values - 10 and - 15 MPa). The hydrophobic nature of both internal and external surface area was confirmed by 29Si MAS-NMR and CA measurements, respectively.

Thermodynamics of water intrusion in nanoporous hydrophobic solids.

We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement.

Pure silica chabazite molecular spring: a structural study on water intrusion-extrusion processes.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer.