Fluorine-Containing Triazole-Decorated Silver(I)-Based Cationic Metal–Organic Framework for Separating Organic Dyes and Removing Oxoanions from Water

Abstract

Four new triazole-decorated silver(I)-based cationic metal-organic frameworks (MOFs), {[Ag(L1)](BF₄)}_<i>n</i> (<b>1</b>), {[Ag(L1)](NO₃)}_<i>n</i> (<b>2</b>), {[Ag(L2)](BF₄)}_<i>n</i> (<b>3</b>), and {[Ag(L2)](NO₃)}_<i>n</i> (<b>4</b>), have been synthesized using two newly designed ligands, 3-fluoro-5-(4<i>H</i>-1,2,4-triazol-4-yl)pyridine (L1) and 3-(4<i>H</i>-1,2,4-triazol-4-yl)-5-(trifluoromethyl)pyridine (L2). When the fluorine atom was changed to a trifluoromethyl group at the same position, tremendous enhancement in the MOF dimensionality was achieved [two-dimensional to three-dimensional (3D)]. However, changing the metal salt (used for the synthesis) had no effect. The higher electron-withdrawing tendency of the trifluoromethyl group in L2 aided in the formation of higher-dimensional MOFs with different properties compared with those of the fluoro derivatives. The fluoride group was introduced in the ligand to make highly electron-deficient pores inside the MOFs that can accelerate the anion-exchange process. The concept was proved by density functional theory calculation of the MOFs. Both 3D cationic MOFs were used for dye adsorption, and a remarkable amount of dye was adsorbed in the MOFs. In addition, owing to their cationic nature, the MOFs selectively removed anionic dyes from a mixture of anionic, cationic, and neutral dyes in the aqueous phase. Interestingly, the present MOFs were also highly effective for the removal of oxoanions (MnO₄^- and Cr₂O₇^2-) from water.