Pressure-induced hydration

Pressure-induced hydration (PIH), also known as “super-hydration”, is a special case of pressure-induced insertion whereby water molecules are injected into the pores of microporous materials. In PIH, a microporous material is placed under pressure in the presence of water in the pressure-transmitting fluid of a diamond anvil cell.^[1][2]

Early physical characterization^[3] and initial diffraction experiments^[4] in zeolites were followed by the first unequivocal structural characterization of PIH in the small-pore zeolite natrolite (Na₁₆Al₁₆Si₂₄O₈₀·16H₂O), which in its fully super-hydrated form, Na₁₆Al₁₆Si₂₄O₈₀·32H₂O, doubles^[5] the amount of water it contains in its pores.

PIH has now been demonstrated in natrolites containing Li, K, Rb and Ag as monovalent cations^[6][7] as well as in large-pore zeolites,^[8] pyrochlores,^[9] clays^[10] and graphite oxide.^[11]

Using the noble gases Ar, Kr, and Xe as well as CO₂ as pressure-transmitting fluids, researchers have prepared and structurally characterized the products of reversible, pressure-induced insertion of Ar^[12] Kr,^[13] and CO₂^[14] as well as the irreversible insertion of Xe^[13] and water.^[15]