Exploring Functional Polymers in the Synthesis of Luminescent ZnO Quantum Dots for the Detection of Cr⁶⁺, Fe²⁺, and Cu²

The main aim of this work is to demonstrate that well-defined methacrylate-based copolymers with oligoethylene glycol side chains and functional groups such as thiol and glycidyl, obtained by photo-initiated reversible addition-fragmentation chain transfer (RAFT) in ethanol, are highly suitable as templates in the synthesis and protection of ZnO quantum dots (ZnO QDs) with remarkable photoluminescent properties. While the affinity of thiol groups to metallic surfaces is well established, their interaction with metal oxides has received less scrutiny. Furthermore, under basic conditions, glycidyl groups could react with hydroxyl groups on the surface of ZnO, representing another strategy for hybrid synthesis. The size and crystalline morphology of the resulting hybrids were assessed using DLS, TEM, and XRD, indicating that both polymers, even with a low proportion of functional groups (5% mol) are appropriate as templates and ligands for ZnO QDs synthesis. Notably, thiol-containing polymers yield hybrids with ZnO featuring excellent quantum yield (up to 52%), while polymers with glycidyl groups require combination with the organosilane aminopropyl triethoxysilane (APTES) to achieve optimal results. In both cases, these hybrids exhibited robust stability in both ethanol and aqueous environments. Beyond fundamental research, due to the remarkable photoluminescent properties and affordability, these hybrid ZnO QDs are expected to have potential applications in biotechnology and green science; in particular, in this study, we examined their use in the detection of environmental contaminants like Fe²⁺, Cr⁶⁺, and Cu²⁺. Specifically, the limit of detection achieved at 1.13 µM for the highly toxic Cr⁶⁺ underscores the significant sensing capabilities of the hybrids.