Engineering Phosphogypsum into a Fluorescent Nanosensor Based on Functionalized Nano-CaCO3 for Selective Hg2+ Detection

Phosphogypsum (PG) is a major solid by-product generated during wet-process phosphoric acid production. Its stockpiling poses significant environmental risks due to the potential leaching of harmful substances. Therefore, conversion of PG into high-value-added products is urgent. In this work, nano-calcium carbonate (Nano-CaCO3) was synthesized from PG via a phase-transfer precipitation method. The surface of the as-prepared product was then modified for Hg2+ detection. Initially, the nanoparticle surface was functionalized with (3-aminopropyl)triethoxysilane (APTES), followed by grafting with a synthesized rhodamine B-based derivative (RhoB-NCS). The acquired product was denoted as CaCO3@RhoB-NCS. Physical characterization demonstrated its successful fabrication. The product is an effective sensor for Hg2+ detection, exhibiting enhanced fluorescence emission at 600 nm with a detection limit as low as 1.0 × 10−6 M. Moreover, the CaCO3@RhoB-NCS was used as a filler for Hg2+ test paper. This work demonstrates a promising approach for valorizing solid waste into high-value-added product.