Silica gel is typically made from silica particles that form a gel-like structure. These particles have a high surface activity and a large surface area, which are essential for its adsorptive properties. The preparation process generally involves the sol-gel method, in which a silica precursor is dissolved in a solvent, undergoes hydrolysis and polymerization reactions, and ultimately forms a gel structure. The particle size and pore structure of silica gel can be adjusted according to the specific requirements for different applications.