Cobalt MOF-Starbon Hybrids for Synergistic Chemosensing and Adsorption of Tetracycline

Pervasive tetracycline (TC) residues underscore the necessity for precise monitoring and efficient remediation. Starbon features a hierarchical architecture and rich surface functionality to support sensing and adsorption applications. Starbon has been extensively studied with metal oxides, but its integration with metal-organic frameworks (MOFs) for chemosensing and adsorption remains largely unexplored. The current study reports the synthesis of a novel MOF (PUC-13) and its composite with an S-350 starbon designated as SPU-10. SPU-10 was employed as a dual-functional chemosensor for tetracycline recognition and capture. A comprehensive suite of characterization methods was used to meticulously examine and validate the structural framework, surface characteristics, and thermal resilience of the composite. Mechanistic understanding of sensing and adsorption behaviors was reinforced through integrated spectroscopic analyses and surface characterization techniques. The developed system showcases adaptive capabilities in detecting tetracycline, reflected by a high Stern-Volmer quenching constant (K_sv = 0.62 × 10⁶ M^-1) along with excellent adsorption performance (98.2% removal efficiency). It exhibits a substantially maximum capacity of adsorption (q_max) of 112.21 mg g^-1. A notably low limit of detection, i.e., 0.35 μM, underscores the remarkable sensitivity and selectivity of the SPU-10 nanocomposite. Smartphone-assisted on-site monitoring was also carried out to validate the detection limit (LOD) for tetracycline. Pertaining to a surface area of 39.53 m² g^-1, the material exhibits a pseudo-second-order kinetic profile and aligns closely with the Langmuir adsorption isotherm, indicating monolayer coverage of tetracycline molecules. Mechanistic exploration through X-ray Photoelectron Spectroscopy (XPS), time-resolved fluorescence spectroscopy, and ζ-potential analysis provided crucial insight into both detection and adsorption pathways. Initially, tetracycline binds to the adsorbent via chemisorption followed by multilayer physisorption. Static interactions and the inner filter effect (IFE) primarily govern the fluorescence quenching of SPU-10. Recyclability was retained over four successive cycles, and the real-world applicability was validated in milk and water matrices.