Al3+ enhanced room temperature phosphorescence of Pd-porphyrin resided in hybrid supramolecular gels and used for detection of trace Hg2+ ions

Abstract

Micelle-hybridized supramolecular hydrogels were constructed through the self-assembly of gelator N,N-dibenzoyl-L-cystine (DBC) and micelles formed from a Gemini surfactant (G12-8-12). A phosphor, palladium meso-tetra (4-carboxyphenyl) porphyrin (Pd-TCPP) and Al3+ ions were loaded within the hybrid system. Interestingly, the room temperature phosphorescence (RTP) of Pd-TCPP can be efficiently enhanced and modulated by the concentration of Al3+ ions. The enhancement effect could be attributed to the interactions between Al3+ and DBC as well as porphyrin, which verified by 1H NMR analysis. The study of transmission electron microscopy and scanning electron microscopy indicated that a more compact 3D network structure of the gel system was formed upon the addition of Al3+. In addition, measurement of critical micelle concentration indicated that Al3+ ions increase the surface activity of G12-8-12 to promote micelle formation, thereby increasing the dispersion of Pd-TCPP in the hybrid gels. Based on the synergistic effect of these results, the non-radiative transition of Pd-TCPP was efficiently inhibited, resulting in highly efficient RTP. Furthermore, the enhanced RTP of as-prepared gel system shows potential application to detect trace Hg2+ ions because the RTP can be quenched by Hg2+. A linear relationship between RTP against the logarithmic concentration of Hg2+ was found over the range of 6 × 10−8 and 1 × 10−6 mol/L. The detection limit was found to be 0.017 nmol/L.