Integration of Phosphotungstic Acid into Zeolitic Imidazole Framework-67 for Efficient Methylene Blue Adsorption

Abstract

To enhance the dye adsorption capacity of zeolitic imidazolate framework-67 (ZIF-67), phosphotungstic acid (HPW) was integrated into ZIF-67 to prepare composite adsorbents. Characterization results demonstrated that the electronegative HPW was uniformly and tightly deposited on the electropositive ZIF-67. Methylene blue (MB) was selected as a model contaminant to evaluate the adsorption performance of hybrid adsorbents. Results showed that HPW@ZIF-67 had excellent adsorption capacity toward cationic MB. The optimal ZIF-67-0.2 HPW sample with a HPW dosage of 9.9 wt % presented an adsorption capacity of 446.4 mg g –1 . ZIF-67-0.2 HPW displayed good reusability, and the adsorption data can be well described by pseudo-second order and Langmuir isotherm models. The adsorption mechanism was ascribed to the preferred electrostatic attraction and π–π stacking between MB and composite adsorbents. This work provides a route to enhance organic dye removal efficiency of ZIF materials through regulation of surface charge property and sheds light on the development of ZIF-based adsorbents.

Hollow Heteropoly Acid-Functionalized ZIF Composite Membrane for Proton Exchange Membrane Fuel Cells

“…Figure a exhibits the XRD patterns of pure ZIF-67 and HZF formed using various HPA contents. The pristine ZIF-67 nanoparticles exhibited well-defined crystalline diffraction peaks at 7.39, 10.42, 12.80, 14.76, 16.52, 18.08, 22.19, 24.55, and 26.73°, which correspond to the (011), (002), (122), (022), (013), (222), (114), (233), and (134) planes, respectively. ,,, As the HPA content in HZF increased during the synthetic process, the crystalline peak intensity of HZF gradually decreased, leaving only a few intense diffraction peaks. , In particular, the crystalline diffraction peaks of HZF4 almost disappeared, indicating that the ZIF-67 framework was destroyed because of the significantly reduced Co–N bond in HZF. , …”

“…30,37 In particular, the crystalline diffraction peaks of HZF4 almost disappeared, indicating that the ZIF-67 framework was destroyed because of the significantly reduced Co−N bond in HZF. 30,35 Figure 2b presents the N 2 adsorption−desorption isotherm measured at 77 K for pure ZIF-67 and HZF formed using various HPA contents. The BET surface area of the pristine ZIF-67 nanoparticles was approximately 1360 m 2 /g, which is similar to previously reported values.…”

“…37,40 The rhombic dodecahedral structure collapsed when the HPA was attached to the ZIF-67 nanoparticles, resulting in a hollow structure. 41 ZIF-67 nanoparticles have been used to develop hollow or core-shell nanostructures using the Ostwald ripening and Kirkendall effects. 42−45 The ZIF-67 nanoparticles underwent acid-etching because of the HPA functionalization on their surface, and their constructing components (cobalt metal ions and C 4 H 6 N 2 ) diffused from the core side to the shell side.…”

“…The peak intensity of the Co−N bond decreased with a slight shift when HPA became attached to the ZIF-67 nanoparticles, indicating that the metal ion−organic ligand framework collapsed slightly. 34,35 The HZF nanoparticles with the highest HPA content (i.e., HZF4) exhibited a further decrease in the peak intensity of the Co−N bond and a shift (blueshift) to high wavenumbers.…”

“…Figure S1 shows the TEM images of HZF formed using various HPA contents in order to compare their external morphology. The pure ZIF-67 nanoparticles had a traditional rhombic dodecahedral structure with a size of 300–500 nm. , The rhombic dodecahedral structure collapsed when the HPA was attached to the ZIF-67 nanoparticles, resulting in a hollow structure . ZIF-67 nanoparticles have been used to develop hollow or core-shell nanostructures using the Ostwald ripening and Kirkendall effects. − The ZIF-67 nanoparticles underwent acid-etching because of the HPA functionalization on their surface, and their constructing components (cobalt metal ions and C 4 H 6 N 2 ) diffused from the core side to the shell side. ,, Figure S2 shows the TEM images of HZF2 as a function of HPA functionalization time from 0 min to 24 h to demonstrate the structural evolution.…”