Water vapor adsorption properties of Ti-containing mesoporous silica

Materials enabling intelligent humidity control were synthesized using fume d silica, tetraethylorthotitanate and quaternary alkylammonium surfactant ( decyl-, dodecyl-, tetradecyl- and hexadeeyltrimethylammonium chlorides) as a liquid-crystal template under hydrothermal conditions. X-ray diffraction profiles and transmission electron micrographs indicated that a homogeneous hexagonal structure of SiO2-TiO2 was formed from those products. The mesos tructured products had high BET surface areas from 540 to 863 m(2)/g, with uniform pore diameters of 1.5-3 nm. These physical quantities were controll ed by varying the size of the organic template. Water vapor adsorption isot herms for these materials experienced a sharp increase in adsorption when t he relative water vapor pressure (P/P-0) was in the range of 0.4-0.6. Over this range of pressures, the maximum amount of adsorbed mater was between 2 0 and 50 mass%, The isotherms were classified as type V in the IUPAC notati on, showed an unusually large hysteresis, The large hysteresis could be exp lained by the difference in contact angle between adsorption and desorption , For both the 2nd and 3rd water vapor adsorption-desorption isotherms, any morphological change was not observed in the isotherms, meaning that these materials have high durability in their humidity control ability, A small shift of the broad Q(4) Si-29-MAS/NMR spectra indicated that a wider distri bution of the Si-O-Si angles in the SiO4 tetrahedra when titanium was incor porated into the silica matrix.