Ureasil gels as a highly efficient adsorbent for water purification

Ureasils are nanocomposite organic-inorganic materials based on a silica backbone covalently connected through urea bridges with poly( oxyalkylene) chains. Ureasil gels are synthesized by the sol-gel procedure. These gels can efficiently adsorb and retain dyes from aqueous solutions and, thus, can be employed as water purification agents. Anionic dyes bearing a sulfonate chemical group are most efficiently adsorbed, followed by hydrophobic dyes and, finally, by cationic dyes. The adsorption of anionic dyes is very impressive, because a densely colored water sample is transformed into crystal clear water by using only a small quantity of ureasil adsorbent. Variations of the adsorption efficiency have been detected by varying the poly( oxyalkylene) chain length or by using different catalysts of the sol-gel procedure. The most efficient adsorbents were gels made by the conventional sol-gel route, that is, by HCl catalysis.