Cu(ii) and Zn(ii) frameworks constructed by directional tuning of diverse substituted groups on a triazine skeleton and supermassive adsorption behavior for iodine and dyes

Abstract

The controllable design, synthesis and functional properties of a series of triazine tetratopic carboxylic MOFs have always been hotspots and challenges for research. Based on the characterization of the C–Cl bond on the triazine skeleton being easily substituted by some functional groups, we designed and synthesized a series of triazine tetratopic carboxylic Cu(II) and Zn(II) MOFs via the reaction of Cu(NO₃)₂·2.5H₂O and ZnSO₄·7H₂O, as well as triazine tetratopic carboxylic H₄TDBA-Cl (H₄TBDA-Cl = 5,5′-((6-chloro-1,3,5-triazine-2,4-diyl)bis(azanediyl))diisophthalic acid) under hydrothermal conditions. During the process of synthesizing, the C–Cl bond on the triazine skeleton of the ligand was substituted with different groups, which formed the complexes ([Cu₂(TBDA-Cl)(H₂O)·10DMF·30H₂O]_n) (DMF = N,N-dimethylformamide) (1), N(Me)₂ -[(CH₃)₂NH₂]₄·[Zn₃(HTBDA-N)₂(SO₄)₂]_n (2) and H ([Cu₂(TBDA-H)(H₂O)]_n) (3), respectively. It is worth noting that the in situ substitution reaction occurred for complexes 2 and 3 during the process of synthesis. Also, the structural analysis showed that the molecules in complexes 1–3 were connected with different building blocks to form different three-dimensional structures. We performed iodine adsorption experiments on the three complexes and found that there was a significant relationship between the structural configuration and adsorption behaviour. The results showed that the complex 1 with the Cl atom on the triazine skeleton could have a boosting effect on adsorption with iodine. It displayed a remarkable adsorption effect for iodine (in the solution of water: 7.6 g g⁻¹ and in the solution of cyclohexane: 548.2 mg g⁻¹). In addition, it also displayed the adsorption effect for JGB dye (204.9 mg g⁻¹). For complex 2, it displayed an uptake effect for iodine in the solution of cyclohexane (529 mg g⁻¹). The possible adsorption mechanism was also investigated. By comparison, we found that chlorine atoms could play an important role in the adsorption processes. The adsorption capacity of complex 1 (containing the chlorine atom in the structure) was much higher than that for complex 3.