Iron-based metal–organic framework as an effective sorbent for the rapid and efficient removal of illegal dyes

Abstract

A metal organic framework (MOF-235) was fabricated by a simple solvothermal method and utilized as an adsorbent for the selective removal of electron-rich conjugated dyes. Parameters that influenced the adsorption process were investigated and the excellent adsorption properties of MOF-235 toward Congo red (CR) and lemon yellow (LY) are also exhibited in a wide range of pH 3–9. Moreover, the adsorption kinetics and thermodynamics were determined, indicating that the Langmuir model can well describe the adsorption isotherm and the pseudo-second order model can satisfactorily describe the adsorption kinetics. Thanks to the large hydrophobic effect between electron-deficient MOF and electron-rich conjugated dye molecules, the ultrahigh maximum adsorption capacity for CR and LY calculated by the Langmuir model is up to 1250 and 250 mg g⁻¹, respectively, which surpass that of most reported adsorbents. Notably, the maximum adsorption capacity of adsorption of CR and LY is up to 1131 and 209 mg g⁻¹ in fruit juice, respectively. Additionally, the synthesized MOF-235 has a high adsorptive selectivity and fast adsorption rate and can be regenerated for removal by washing with ethanol containing NaOH solution. These results demonstrated that MOF-235 would be an effective and easily reusable adsorbent for the adsorptive removal of CR and LY from fruit juice.