酮-亞胺共價有機框架在極端 pH 條件下的穩定性

Abstract

本研究基於由三醛基間苯三酚(triformylphloroglucinol, TP) 合成出具有酮烯胺鍵結键的共價有機框架材料，其由二維層組成的超結構可以透過π-π作用堆疊機制形成。研究的目的是比較在pH應力條件下三種Tp-COFs（TpPa(OH)2、TpPaSO3Na和TpBu）對於銅離子的堆疊穩定性及相應吸附性能。 這三種Tp-COFs在25攝氏度的中性水中均具有高度穩定性。然而，pH -0.2的應力條件會大幅破壞TpPa(OH)2的層堆疊，使其在pH 7和-0.2條件下的吸附能力分別為93.92 mg g-1和80.57 mg g-1。對於具有鈉離子的TpPaSO3Na結構，在極酸的環境下，過多的質子會取代鈉離子。導致吸附量 qe 較低，中性吸附為 101.56 mg g-1，酸性吸附的 qe 值為 58.54 mg g-1。而對於具有最高穩定性的TpBu，pH應力條件對其影響極小，其吸附能力約為84 mg g-1。 COF的穩定性與酰胺基和胺基堆積形成的層間氫鍵有關。 根據結構分析，推測層間氫鍵量順序為TpBu>TpPaSO3Na>TpPa(OH)2。經過實驗確認以確定穩定性程度。 此外，pH波動實驗表明，COF在回到中性環境後不會恢復到原來的狀態。

This study is based on synthesizing covalent organic framework (COF) materials with keto-enamine linkages derived from triformylphloroglucinol (TP). These COFs, composed of two-dimensional layered structures, can form superstructures through π-π stacking interactions. The research compares the stacking stability and corresponding adsorption performance of three Tp-COFs (TpPa(OH)2, TpPaSO3Na, and TpBu) under pH stress conditions concerning copper ions. All three Tp-COFs exhibit high stability in neutral water at 25oC. However, under pH -0.2 stress conditions, TpPa(OH) 2's layer stacking is significantly exfoliated, resulting in adsorption capacities of 93.92 mg g-1 and 80.57 mg g-1 at pH 7 and -0.2, respectively. For TpPaSO3Na, which incorporates sodium ions, the structural effects under acidic stress conditions result in protons substituting Na ions. It causes a low qe value for 101.56 mg g-1 for neutral adsorption, 58.54 mg g-1 for acidic adsorption. The most stable structure, TpBu, is minimally affected by pH stress conditions, with an adsorption capacity of approximately 84 mg g-1. The stability of COFs is related to the interlayer hydrogen bonds formed by the stacking of amide and amine groups. Based on structural analysis, it is inferred that the order of interlayer hydrogen bond abundance is TpBu > TpPaSO3Na > TpPa(OH)2. This is experimentally confirmed to determine the stability levels. Furthermore, the pH-swing experiment reveals that COFs do not revert to their original state after returning to a neutral environment.