Synthesis of a novel covalent organic framework TpBu: using as copper ion adsorbent from extremely acidic water

Backgrounds: The covalent organic framework (COF) is a porous matrix comprising light elements linked with covalent bonds. The COF Tp-family is widely studied. The purpose of this study is to propose and synthesize a novel Tp-COF that can remain structural stability at extremely acidic environment. Methods: This study synthesized a novel two-dimensional COF TpBu with amine linkages and carbonyl functional groups on the backbone, via the solvothermal method. Significant findings: TpBu is designed to permit local rotations of bonds around the nitrogen atoms on amine linkages, so the yielded two-dimensional COF layers are flexible in structure for excess formation of the H-bonds between the neighboring layers. The so-synthesized TpBu remains intact in stacked structure upon proton attacks at pH -0.2. As a demonstration for its use, the synthesized TpBu endothermically adsorbs Cu(II) ions from water at both pH 7 (23.4, 29.2, and 37.9 mg/g, at 25, 35 and 45 °C, respectively) and pH -0.2 (17.1, 21.0, and 31.2 mg/g, at 25, 35 and 45 °C, respectively) by complexation reactions. At pH -0.2, excess protons only mildly reduce the Langmuir adsorption capacities of Cu(II) by TpBu compared to pH 7, likely attributable to competitive adsorption with decreased changes in adsorption enthalpy. The proton attacks affect the outer layers of TpBu, but cannot exfoliate the stacked layers.