Efficiently improving the adsorption capacity of the Rhodamine B dye in a SO3H-functionalized chromium-based metal–organic framework

Abstract

A metal–organic framework containing metal sites of chromium, termed BUT-8(Cr), was successfully fabricated via a solvothermal procedure, which is capable of excellent uptake of the Rhodamine B (RhB) dye from the solution. The removal of the RhB dye using BUT-8(Cr) was studied in terms of solution pH, material content, adsorption isotherms, and kinetics to identify the most favorable conditions. Accordingly, the maximum adsorption capacity of 811.7 mg g⁻¹ is well-fitted by the Langmuir isotherm model, which is much higher than those of previously reported MOF materials. Furthermore, the kinetic data for the RhB adsorption fit with the pseudo-second order model. This indicates that RhB uptake is a chemical process. The recycling test result shows that an efficiency of 94.5% is retained over seven recycles. The comparison of the results of FT-IR and Raman spectroscopy, and PXRD, and TGA-DSC analyses of RhB⊂BUT-8(Cr) reveals the presence of electrostatic and π–π interactions between the RhB⁺ ions and negatively charged SO₃⁻ moieties within the MOF architecture, leading to RhB removal with an ultra-high adsorption capacity. These findings show that the sulfonic-functionalized Cr-based MOF could be a promising candidate for removing organic dyes in a real polluted environment.