Anthracene and pyrene appended Schiff bases having a (N,N) donor for the synthesis of highly stable colloidal silver nano-particles: application in selective sensing and nitroarene reduction

Abstract

Ligands bis(anthracen-9-ylmethylene)ethane-1,2-diamine (L1)/bis(anthracen-9-ylmethylene)hexane-1,6-diamine (L2)/bis(pyren-1-ylmethylene)ethane-1,2-diamine (L3)/bis(pyren-1-ylmethylene)hexane-1,6-diamine (L4) have been synthesized and structurally characterized using ¹H and ¹³C{¹H} NMR and IR spectroscopy. These ligands have been used to stabilize silver nanoparticles (Ag-NPs) in the colloidal state, and their size was found to be in the range of 20–27 nm as revealed by TEM studies. The Ag-NPs are highly stable and can be stored in a refrigerator for at least two months without precipitation. The NPs stabilized with L1 showed selective colorimetric sensing for Hg(II) and Cl⁻ ions, whereas L2-stabilized NPs showed sensing for Hg(II), Bi(III) and I⁻ ions. Similarly, NPs stabilized with L3 showed selective naked-eye sensing for Hg(II) and HSO₄⁻ ions, whereas L4-stabilized NPs showed sensing for Hg(II), Bi(III), Cr(III) and HSO₄⁻ ions. The data indicate that the spacer unit has a significant effect in governing the selectivity, i.e. the ligands with 2-C spacer units are more selective than those with 6-C spacer units. Furthermore, to determine the catalytic potential of these NPs, L1-stabilized Ag-NPs have been tested for nitroarene reduction, the second-largest organic pollutant. These NPs act as excellent catalysts for reducing toxic nitro-aromatics to valuable amines in a very short reaction time at very low catalyst loading. Kinetic studies suggest that the reaction follows pseudo-first-order with a rate constant of 0.2554 min⁻¹. The negative Hammett slope and data obtained from zeta potential indicate the involvement of a cationic intermediate.