Removal of sudan dyes from water with C18-functional ultrafine magnetic silica nanoparticles

► C18-UMS NPs were successfully synthesized. ► C18-UMS NPs have small diameter and can be easily dispersed in aqueous samples. ► Sudan dyes in large volume of water samples were extracted by C18-UMS NPs. ► C18-UMS NPs can be recycled. ► The factors which can influence extraction efficiencies were investigated.