Effect of hydrothermal modification on the porous structure and thermal properties of carbon–silica adsorbents (carbosils)

Characterisation of porous structure and thermal properties of unmodified and hydrothermally modified (using H2O2, under high pressure conditions) carbon–silica adsorbents (carbosils) prepared by dichloromethane pyrolysis (under dynamic conditions) on the surface of narrow pore silica were discussed. The analysis was made based on the data of low-temperature nitrogen adsorption/desorption isotherms, transmission electron microscopy (TEM) and the results of differential thermal analysis. It was stated that both porous structure and thermal properties of tested samples are in correlation with the morphology and topography of the carbon deposit. This deposit forms globules and aggregates whose size and position on the inner and outer surface of silica depends on the time of its carbonisation. It was stated that hydrothermal treatment (HTT) of the carbosils changes both the porous structure and thermal properties of the tested samples. As a result of HTT of silica, decondensation and recondensation of orthosilic acid on large particles of silica takes place. Then a decrease in the specific surface area and increase in the radius of pores are observed. In the case of carbosils these changes are smaller and depend on the accessibility of the silica surface, which is connected with topography of carbon deposit.