The functionalized silica has been an effective material for the removal of heavy metal from aqueous solutions and the support of nanoparticles. Silica substrates are usually synthesized from expensive precursors i.e., tetraethoxysilane or tetramethoxysilane. Almost processes used for the functionalization of silica are complicated and time consuming because they are conducted in organic solvents. The objective of this book is to introduce facile, eco-friendly, and cost-effective methods to functionalize silica that is synthesize via a sol-gel process using sodium silicate and sulfuric acid. The obtained functionalized silica could be used for the water purification.