EFFECT OF SYNTHESIS CONDITIONS OF CARBON XEROGELS ON THEIR SURFACE CHEMISTRY, PORE TEXTURE AND METHYLENE BLUE ADSORPTION CAPACITY.

Resorcinol?formaldehyde organic xerogels (OXs) were synthesized by the polycondensation of resorcinol (R) and formaldehyde (F) using two different techniques [microwave (MW) - induced synthesis and conventional (C) synthesis methods]. For the MW-induced synthesis of OXs, five samples variable in their R-F solutions pH values [in the range 3.0-7.2] were synthesized. These samples were pyrolyzed at 750 oC under N2 flow to give five carbon xerogel (CX) samples. To study the effect of the carbonization temperature, the OX sample prepared at R-F solution pH value of 6.5 was selected and carbonized at different temperatures in the range 600 - 800oC, to produce four CX samples. To investigate the effect of the synthesis method on the CX characteristics, another OX sample was prepared by the conventional method at R-F solution pH value of 6.5 and was carbonized at 750oC under N2 flow to give the last CX sample. The effect of the synthesis conditions on the physicochemical and surface chemistry characteristics of the products was performed using different techniques, such as elemental analysis, determination of the surface acidic and basic active sites by the Boehm method, identification of surface functional groups by FTIR, XRD analysis, SEM and TEM investigations. Pore texture characteristics were evaluated by analysis of the respective N2/77K adsorption-desorption isotherms. The methylene blue (MB) number (Xm (mg/g)) and surface areas accessible to MB (SMB) were calculated using the Langmuir and Freundlich adsorption isotherm equations. The Langmuir adsorption isotherm model gives better fit as compared to Freundlich model. Ratios of methylene blue surface area to nitrogen surface area (SMB / SN2) were evaluated and discussed. Removal of MB from aqueous solution is governed by the chemical nature of the CX surface as well as the diffusion through the intricate internal porosity.