Soluble Anionic Porphyrin for Detecting Hg(II), Cd(II), Pb(II), Cu(II), Fe(III), and Zn(II) Ions by Fluorescence and UV-Visible Spectral Studies

Optical sensors for detecting metal ion contaminants in the environment are being developed because of a growing need for timely, simple, and reliable techniques required for monitoring or controlling the presence of some toxic cations released. A water-soluble anionic porphyrin was synthesized by a simple and affordable procedure that entails sulfonation of meso-tetraphenylporphyrin and purification, using modified standard methods. The effect of the presence of 0.33 mM Ca2+, Cd2+, Pb2+, Hg2+, Cu2+, Zn2+, and Fe3+ ions on absorption and fluorescence spectra of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) was investigated at 25 °C within 25 minutes of interaction. Shifts in wavelength of fluorescence peaks (Hg2+ and Cd2+) and Soret absorption band (Cd2+ and Zn2+); emergence of new fluorescence peaks (Pb2+, Fe3+, and Zn2+); splitting of B band (Fe3+); and the reduction in the number of Q bands (Zn2+ and Hg2+) as well as outright fluorescence quenching or near quenching (in the case of Cu2+ and Hg2+ ions, respectively) have been used to describe the characteristic behaviour of the porphyrin in the presence of these metal ions. The techniques used were easy, sensitive, fast, and inexpensive, and the organic molecule was chemically stable. These selective and reversible interactions of the ligand with heavy metal ions in aqueous solution could be used to detect and monitor the presence of some toxic cations released into water bodies and the environment.