Structure of silica gel Si-60 and pyrocarbon/silica gel adsorbents thermally and hydrothermally treated

Characteristics of porous structure of silica gel Si-60 (pristine and cover ed by different amounts of pyrocarbon prepared by pyrolysis of acenaphthene , acetylacetone, and glucose, then heated at 500 degreesC in air or hydroth ermally treated (HTT) at 150 or 200 degreesC, and also heated at 500 degree sC) were analyzed by using TEM, H-1 NMR, and adsorption-desorption of nitro gen at 77.35 K. The structural parameters were estimated by the direct mini mization method or the overall isotherm approximation with a regularization procedure. Pyrolysis of different organics on Si-60 is accompanied by mark ed changes in the pore structure depending on the nature of precursors. Hyd rothermal treatment of silica gel and carbosils at 150-200 degreesC for 6 h results in a strong modification of both pores and outer surfaces of silic a gel particles in contrast to heating of pristine Si-60 or carbosils (afte r HTT) at 500 degreesC in air for 24 h. Computations of the distributions o f the pore size and nitrogen adsorption energy, as well as 1H NMR spectra o f the interfacial water, reveal an increase in the adsorbent nonuniformity due to hydrothermal treatment, but heating of silica gel and pyrocarbon/sil ica in air gives the opposite result.