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 covered by different amounts of pyrocarbon prepared by pyrolysis of acenaphthene, acetylacetone, and glucose, then heated at 500 °C in air or hydrothermally treated (HTT) at 150 or 200 °C, and also heated at 500 °C) were analyzed by using TEM, 1 H NMR, and adsorption−desorption of nitrogen at 77.35 K. The structural parameters were estimated by the direct minimization method or the overall isotherm approximation with a regularization procedure. Pyrolysis of different organics on Si-60 is accompanied by marked changes in the pore structure depending on the nature of precursors. Hydrothermal treatment of silica gel and carbosils at 150−200 °C for 6 h results in a strong modification of both pores and outer surfaces of silica gel particles in contrast to heating of pristine Si-60 or carbosils (after HTT) at 500 °C in air for 24 h. Computations of the distributions of the pore size and nitrogen adsorption energy, as well as 1 H NMR spectra of the interfacial water, reveal an increase in the adsorbent nonuniformity due to hydrothermal treatment, but heating of silica gel and pyrocarbon/silica in air gives the opposite result.