Zr-based MOF @ carboxymethylated filter paper: Insight into construction and methylene blue removal mechanism

Abstract

A novel and flexible paper-based filtration material, namely Zirconium-based metal-organic framework @ carboxymethylated filter paper (CMP-UiO-66), was synthesized in this work. The CMP-UiO-66 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS mapping), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA). The removal performance and corresponding mechanisms were evaluated with the help of a batch experiments under different conditions, FTIR, isotherm models and thermodynamics studies. The Langmuir isotherm model can accurately describe the removal process under the initial concentrations from 10 to 50 mg/L. The values of thermodynamics parameters were positive standard entropy (ΔS) and standard enthalpy (ΔH) values, but negative standard Gibbs free energy (ΔG), indicating a random, endothermic and spontaneous process. The removal mechanisms which were made of physical interactions (fibers obstruction and pores filling) and chemical interactions (hydrogen bonding, electrostatic attraction, π-π and n-π interactions), synthetically played a role in the removal process. The CMP-UiO-66 exhibited the excellent removal efficiencies and partition coefficients toward methylene blue (MB) dye for a wide range of pH via simple filtration. Compared with powder-type absorbents, CMP-UiO-66 which possessed the favorable reusability, simplicity and rapidity can be considered as a promising adsorbent for effectively capturing the MB dye molecules. It could also be reused after a simple washing process. This work may provide an effective method for capturing the MB dye molecules by a simple filtration step of the dye solution in the short time, without causing secondary pollution.