Synergistic Catalysis and Sensing: Oxacalix[4]arene-Stabilized Rhodium Nanoparticles for Dye Degradation, Nitroaromatic Reduction and Al³⁺ Ion Detection.

The use of rhodium nanoparticles (RhNPs) in biomedical, environmental and industrial applications is highly significant due to their unique catalytic, physical and chemical properties. Further, NPs encapsulated within macrocyclic structures with inherent hollow cavities are able to boost their catalytic activity. Here we are reporting for the first time, a versatile, non-toxic, third-generation supramolecule, calixarene, stabilised RhNPs. The novel sulphonic-acid functionalized oxacalix[4]arene derivative satbilized RhNPs (DSOC@RhNPs) were synthesised by a simple one-pot NaBH reduction method at room temperature. The resulting DSOC@RhNPs were successfully characterized using UV-Vis, FT-IR, PXRD, HRTEM and EDX. The self-assembled, well-dispersed and spherical (average size of 6-8 nm) DSOC@RhNPs exhibited heterogeneous catalytic activity in the reduction of three, cationic, anionic and neutral carcinogenic azo dyes (methylene blue, methyl orange and neutral red). DSOC@RhNPs has the potential to reduce hazardous pollutants Like 4-nitrophenol (4-NP), retaining its catalytic efficiency across four consecutive cycles. The catalytic reduction of 4-NP and the formation of 4-AP were confirmed by UV-Vis and ESI-MS data. Further, newly systhesized DSOC@RhNPs exhibited excellent sensitivity in detecting Al³⁺ ions (LOD 9 µM). Therefore, the newly developed DSOC@RhNPs represent a versatile nanomaterial with potential for synergistic catalytic and sensing applications across diverse fields.