# Attachment of Tridentate Ligand onto the Polyhedral Oligomeric Silsesquioxanes as an Efficient Strategy to Capture La(III) Ions: A Comparative Study of Homogeneous and Heterogeneous Systems Using Potentiometric Titration

## TL;DR

This paper explores using modified silsesquioxane materials to efficiently capture lanthanide ions, offering a sustainable recovery method.

## Contribution

The study introduces a novel heterogeneous system using POSS-L1 with enhanced La(III) binding compared to free ligands.

## Key findings

- Ligand L1 showed higher formation constants (9.0 and 16.9) for La(III) complexes compared to L2 (4.37).
- POSS-L1 formed [LaPOSS-L1]3+ with 81.0% efficiency at pH 5.42 and La(OH)3POSS-L1 above pH 8.0.
- Modified silsesquioxane matrices are promising for sustainable lanthanide ion adsorption.

## Abstract

Developing sustainable methods for lanthanide ion recovery
is a
relevant area of research that seeks to promote the efficient reuse
of these valuable chemical elements present in several electronic
devices. Adsorption techniques using materials functionalized with
chelating groups, such as modified Polyhedral Oligomeric Silsesquioxanes
(POSS) matrices, may play a crucial role in capturing these metals.
This work investigates the coordination of the lanthanum­(III) ion
with two tridentate organic ligands: bis­(pyridin-2-ylmethyl)­amine
(L1) and (pyridin-2-ylmethyl)­(thiophen-2-ylmethyl)­amine (L2). The
results revealed stronger interactions for L1, with higher formation
constants (9.0 for [LaL1]3+ and 16.9 for [La­(L1)2]3+) compared to L2 (4.37 for [LaL2]3+). Further
studies on ligand L1 attached to silsesquioxane (POSS-L1) showed
significant metal ion interactions, showing the formation of [LaPOSS-L1]3+ (81.0%) at pH 5.42 and La­(OH)3POSS-L1 above pH
8.0, with a formation constant of 10.33, which is higher than that
for free L1. These results demonstrate the efficient binding of La­(III)
to the POSS-L1 in a heterogeneous system. The modified silsesquioxane
matrix presents a promising alternative for lanthanide ion adsorption,
contributing to sustainable metal recovery strategies.