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

Abstract

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 × 103 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.