Insights into the binding mechanism of 2D copper-tetrakis-(4-carboxyphenyl)-porphyrin metal-organic framework nanosheets with Rhodamine B: Spectroscopic and thermodynamics studies

Metal-organic frameworks (MOFs) of copper-tetrakis-(4-carboxyphenyl)-porphyrin (CuTCPP) were prepared by a solvothermal route. The two-dimensional (2D) ultrathin nanosheets with larger specific surface area show higher adsorption capacity for rhodamine B (RhB), compared with the bulk MOF of CuTCPP. The binding mechanism of the 2D nanosheets with RhB was investigated based on spectroscopic methods . The results reveal that the fluorescence of RhB is efficiently quenched by 2D CuTCPP nanosheets , and the quenching mechanism is totally the static quenching by forming a ground state RhB-CuTCPP nanosheets complex with an apparent association constant of 3.953 × 10 3  M −1 . The interaction between RhB and CuTCPP nanosheets leads to the H-aggregate of RhB in the complex. Higher-order aggregate may also be involved in the complexation. Thermodynamic studies demonstrate that RhB-CuTCPP nanosheets interaction is a spontaneous process and driven by electrostatic and hydrophobic forces . The 2D CuTCPP nanosheets can be regenerated from the complex and used repeatedly.