Synthesis of Hydrophilic and Hydrophobic High Surface Area Xerogels at pHs below Silica Iso-electric Point

The synthesis of hydrophilic and hydrophobia high surface area (up to 1087 m²/cc) silica xerogels at pHs below 2 is demonstrated in this work. High surface area xerogels exhibit extremely fine microstructural features and fast gelation times (less than one hour). Contrary to conventional generalization that xerogels synthesized at low pH are polymeric, it is demonstrated that particulate xerogels can also be synthesized at pHs below 2. These xerogels are synthesized by the addition of large amounts of NH₄OH and have relatively lower surface areas. The particulate nature of these xerogels is indicated by their opacity and from their coarse microstructural features as observed by TEM.