Structural and energetic properties of carbosils hydrothermally treated in the classical autoclave or the microwave reactor

Carbon/silica adsorbents (carbosils) prepared by pyrolysis of CH₂Cl₂ at 823 K and the reaction time from 0.5 to 6 h on the mesoporous silica gel surface (Si-60, Merck, granule size 0.2–0.5 mm) and then hydrothermally treated at 473 K with steam or liquid water by using the classical autoclave with traditional heating way or in the microwave reactor were studied by means of TG, adsorption and Q-TG methods. Changes in the structural characteristics of hybrid adsorbents before and after hydrothermal treatment were analyzed on the basis of nitrogen adsorption. Thermal properties of initial and modified samples as well as concentration of carbon deposit were studied using thermogravimetry (TG) in the range of 293–1273 K. The adsorbed water layers were investigated by means of thermodesorption of water under the quasi-isothermal conditions (Q-TG) in the range of 293–573 K. Concentration of weakly and strongly adsorbed water and the surface free energy on the interphase of adsorbent/water were calculated. It was stated that hydrothermal treatment in the microwave reactor, contrary to that in the classical autoclave, allows to obtain adsorbents with noticeably higher values of total pore volume in relation to the initial adsorbents and in majority with a higher specific surface area. Application of microwave energy allows to obtain adsorbents with lower values of surface free energy in relation to the initial adsorbents and those modified in the autoclave.