Porous structure of NiO-based xerogels

NiO-based xerogels were prepared by sol-gel processing starting from the Ni Cl2-BuOH-H2O system. Structural features associated to the porosity of xero gels were studied by small-angle X-ray scattering. Xerogels heat-treated at low temperatures (423 and 573 K) are composed of hydrated NiCl2 small crys tals and exhibit an essentially single mode nanoporous structure with an av erage pore radius of approximate to 75 Angstrom. Xerogels heat- treated at 973 and 1173 K are composed of aggregates of NiO crystals which only contai n intergrain mesopores with radii exceeding 200 Angstrom. A mixture of phas es is observed in xerogels heat- treated at 773 K. Xerogels with a water co ncentration of 2 mol/(mol NiCl2) exhibit a narrow nanopore size distributio n. Water concentrations higher or lower than 2 mol promote the formation of nanoporous structures with wider size distributions.