Simultaneous adjustment of the main chemical variables to fine-tune the porosity of carbon xerogels

The objective of this study was to assess the effect of the resorcinol–formaldehyde molar ratio of precursor solutions with pH values ranging from 5.0 to 7.0 and dilution ratios between 5 and 10 upon the final porous properties of carbon xerogels synthesized by microwave heating, using an optimal design of response surface methodology. It was found that when the resorcinol–formaldehyde molar ratio was decreased the microporosity was enhanced as the addition reaction was favored. Hence, the micropore volume of carbon xerogels not only depends on the conditions used during carbonization, but also on the synthesis conditions. Mesoporosity was also increased when the resorcinol–formaldehyde molar ratio decreased while macroporosity was only influenced by the initial pH of the precursor solutions. The simultaneous variations of the three chemical variables allowed an exhaustive control of the final porous properties of carbon xerogels, which exhibited pore sizes and pore volumes that could not be obtained by modifying just the pH and the dilution ratio.