HF-Free Synthesis of Nanoscale Metal-Organic Framework NMIL-100(Fe) as an Efficient Dye Adsorbent

A hydrofluoric acid (HF)-free solvothermal method was used to synthesize nanoscale metal-organic framework NMIL-100(Fe), which exhibited comparable physicochemical properties as those prepared by traditional methods, but with a mild and environmentally benign synthesis condition. XRD, TGA, N₂ adsorption, FT-IR, SEM, and TEM were employed to characterize the as-prepared NMIL-100(Fe), which was further applied as an effective adsorbent for dye adsorption, including two cationic dyes, rhodamine 6G (R6G) and rhodamine B (RB), and an anionic reactive red 120 (RR 120) with high adsorption efficiencies and capacities. The adsorption process can be well described by pseudo-second-order kinetic model and Langmuir isotherm model. Hydrogen bonding and electrostatic interaction were revealed for the adsorption of the two cationic dyes and one anionic dye onto NMIL-100(Fe), respectively, as investigated by mechanism studies. Thermodynamic analyses indicate that adsorption processes for cationic and anionic dyes are entropy-driven endothermic and enthalpy-driven exothermic processes, respectively. This environmental-benign synthetic strategy for NMIL-100(Fe), as well as its high adsorption efficiency and capacity, might be used for the fabrication of other nanoscale metal-organic frameworks, and the potential applications of NMIL-100(Fe) in real wastewater treatment.