A mesoporous silica functionalized by a covalently bound naphthalene-based receptor for selective optical detection of fluoride ion in water

The naphthalene urea fluorescent receptor 1 immobilized mesoporous silica (FMS) and the fluorescent receptor 1 immobilized silica particles (FSP) were prepared via sol–gel reaction. The sensing ability of FMS and FSP was studied by addition of the anions F–, Cl–, Br–, I– and HSO4- to water suspensions of the assayed solid. Of all the anions tested, addition of fluoride ion to a suspension of FMS resulted in the largest decrease in the fluorescence intensity of naphthalene of FMS. Thus, fluoride ions bind with four urea N–H protons of receptor 1 onto FMS. On the other hand, addition of Cl–, I–, Br– and HSO4- did not reduce the fluorescence of FMS. In case of FSP, the sensitivity for fluoride ion was 8 times lower than that of FMS due to immobilization of smaller amounts of receptor 1 in silica particles. The result implies that mesoporous silica with its large surface area is useful as a supporting material.