Designed Construction of 2D Honeycomb Cationic MOF Materials for Selective Removal of Sulfonic Anionic Dyes

Various carcinogenic dyes in water bodies are difficult to degrade due to their stability to light and oxidants, causing extended pollution. In this study, MOF 1 ({[Co(tib)2]center dot (H2O)2 center dot SO4}n) and MOF 2 ({[Cu(tib)2]center dot(H2O)2 center dot SO4}n) (tib = 1,3,5-tirs(1-imidazolyl)benzene) were synthesized by the solvothermal method. MOFs 1 and 2 were successfully characterized by single-crystal X-ray diffraction (XRD) and powder X-ray diffraction (PXRD). Based on the structural characteristics of MOFs 1 and 2, we designed two cationic MOF material skeletons, namely, MOFs I and II ([Co(tib)22+]n and [Cu(tib)22+]n), which were obtained by calcination in combination with the thermogravimetric curve to remove the free components in the lattice. As expected, MOFs I and II showed an excellent adsorption effect on sulfonic anionic dyes. Notably, the adsorption capacity of MOF I can reach 2922.8 mg g-1 for Congo Red (CR) at room temperature (RT). The adsorption process fits the pseudo-second-order kinetic model and Freundlich isotherm model. Moreover, zeta potential tests and quantum chemical calculations indicate that electrostatic interactions and hydrogen bond between the hydroxyl group on the sulfonic acid group and the N atom on the imidazole ring mainly promote the adsorption of CR dyes on MOF I. MOFs I and II are revealed as a promising novel adsorption material to remove hazardous organic aromatic pollutants with high efficiency in future endeavors.

Automated summary

It was found that various carcinogenic dyes in water bodies are difficult to degrade due to their stability, causing extended pollution. To tackle this issue, two metal-organic framework materials (MOF 1 and MOF 2) were synthesized and characterized. Based on their structural characteristics, two cationic MOF material skeletons (MOFs I and II) were designed and obtained through calcination to remove free components. The adsorption capacity of MOF I for Congo Red was found to be 2922.8 mg g-1. The adsorption process follows the pseudo-second-order kinetic model and Freundlich isotherm model. Electrostatic interactions and hydrogen bond were identified as the main factors promoting the adsorption of Congo Red dyes on MOF I. Therefore, MOFs I and II are considered as promising adsorption materials for efficient removal of hazardous organic aromatic pollutants.