Bismuth Metal Organic Frameworks for the Ultra-Sensitive Detection of Cd ²⁺ in Water

The reliable and ultrasensitive detection of cadmium ions (Cd 2+ ) remains a critical challenge due to their high toxicity and persistence in aquatic environments. Herein, we report the synthesis of bismuth-pyromellitic acid metal–organic framework (Bi-PMA MOF) via a facile solvothermal approach and its application as an efficient electroactive material for sensitive and precise electrochemical detection of Cd 2+ utilizing square-wave anodic stripping voltammetry (SW-ASV). Unlike conventional bismuth-based materials, the Bi-PMA MOF integrates the high coordination versatility of Bi 3+ with the electron-rich, carboxylate-based pyromellitic linker, forming a robust and conductive framework with slab-like morphology as revealed by scanning electron microscopy (SEM). This unique structural architecture provides abundant accessible sites and rapid ion diffusion pathways, facilitating efficient charge transfer and preconcentration of Cd 2+ at the electrode surface. The synthesized Bi-PMA drop-cast onto an in-house-fabricated PCE to form a disposable sensing platform. The SW-ASV sensing parameters were optimized with respect to preconcentration potential, time, and electrolyte conditions. The fabricated Bi-PMA/PCE sensor revealed linear performance with dual-level concentration profiles: 0.1–1 μg L –1 and 1–120 μg L –1, having an ultralow detection limit of 0.008 μg L –1 and excellent sensitivities of 878.2 μA L cm –2 μg –1 (0.1 μg L –1 to 1 μg L –1 ) and 31.87 μA L cm –2 μg –1 (1 μg L –1 to 120 μg L –1 ), respectively. The developed sensor exhibited strong selectivity in the coexistence of potential competing ions and exhibited good reproducibility, repeatability, and stability over time. Real-sample validation was performed by analyzing a spiked tap water specimen, demonstrating its suitability for practical environmental surveillance of cadmium.