Novel synthesized covalent organic framework and determination of its adsorption capacity for coumarin dyes

Using a solvothermal Schiff-base condensation technique, a novel nitrogen-rich covalent organic framework (COF_DFFT-PDKA) was created and its ability to adsorb coumarin-based dyes from aqueous solutions was assessed. FT-IR, XRD, SEM, and TEM investigations verified the successful development of the crystalline and porous framework. Fluorescence spectroscopy was used to conduct adsorption experiments of Coumarin 6, Coumarin 7, and Coumarin 30 under various pH, temperature, contact time, and metal-ion conditions. The Langmuir, Freundlich, and Temkin isotherm models were used to examine the adsorption equilibrium data. The findings showed that while Coumarin 6 exhibited heterogeneous surface interactions consistent with the Freundlich model, adsorption of Coumarin 7 and Coumarin 30 followed the Langmuir model, indicating dominant monolayer adsorption. The maximum adsorption capacities of COF_DFFT-PDKA for C6, C7, and C30 were 51.33, 826.45, and 362.32 mg/g, respectively. According to kinetic investigations, a pseudo-second-order model best described the adsorption process, suggesting a mechanism regulated by chemisorption. In the three dyes, the ΔG and ΔH values were negative, while the ΔS values were positive. This demonstrated that adsorption operates spontaneously and is exothermic in nature. COF_DFFT-PDKA has the potential to be an effective and selective adsorbent for wastewater treatment, as evidenced by its strong adsorption of Coumarin 7.