Facile synthesis of silica monolith doped with meso-tetra(p-carboxyphenyl)porphyrin as a novel metal ion sensor.

Abstract A novel metal ion sensor was prepared using silica monolith doped with meso -tetra( p -carboxyphenyl)porphyrin. The doped material was prepared using TEOS:EtOH:H 2 O:HCl:porphyrin molar ratios of 1:5:7:3.1 × 10 −2 :2.3 × 10 −5 , respectively. The mixture was kept 16 days for the gelation process and then the wet gel was dried at 55–60 °C for 3 days. The porphyrin-doped monolith obtained was kept in 1 M metal salt solution for 2 days. The visible spectrum of the metal-coordinated porphyrin-doped monolith was compared with the uncoordinated porphyrin-doped monolith. The spectra show the characteristic maxima for Cu 2+ at 543 nm, for Zn 2+ at 522, 559, and 596 nm, for Pb 2+ at 531 and 559 nm, and for Ni 2+ at 522 and 551 nm. The metal coordinated to the silica monolith could be removed by washing with 1 M HNO 3 . However the Cu 2+ could not be eluted by acidic solution due to its strong bonding to the porphyrin. The results show that this porphyrin-doped monolithic biomaterial is a promising sensor for metal ions in wastewater and other harsh environments.