Novel MOF (Fe)-on-MOF (Co) adsorbent for efficient removal of Congo red from water media

Abstract

Congo red (CR) poses a significant threat to ecosystems and bodily safety due to its toxicity, stability, and the difficulty of natural degradation. The adsorption technique offers the benefits of high efficiency, simplicity, and a wide application range, and is often used for wastewater restoration. This study was based on the metal-organic framework (MOF)-on-MOF strategy and adopted in-situ growth to prepare an efficient and rapid adsorption material, MIL-88A(Fe)-on-ZIF-67 (MOZ), for adsorbing CR. The kinetic experiments demonstrated that MOZ could achieve an approximately 80% removal rate of CR within 60 minutes, and the pseudo-second-order kinetic model could achieve the peak fitting degree (R2 = 0.9984) for the experimental results. Isothermal adsorption and thermodynamic experiments revealed that the adsorption of CR by the MOZ is a spontaneous endothermic process, and this process follows the Langmuir model (Qm = 1,579.78 mg/g, R2 = 0.9997). After undergoing 5 cycles of the adsorption-desorption process, the adsorption material maintained a removal rate of 92.48% for CR, indicating its outstanding recyclability. π-π stacking, electrostatic attraction, hydrogen bonds, and pore filling are the key factors for efficient adsorption of CR. The adsorption materials prepared in this paper, which are highly efficient, fast, low-cost, and environmentally friendly, have certain prospects in the area of industrial wastewater treatment on a large scale.