以共價有機框架TpBu或TpPa(OH)2移除水中之銅離子並利用pH響應釋放銅離子

Abstract

此研究中，第一次利用溶劑熱法成功合成新穎的2D共價有機框架TpBu。TpBu的主架有著胺基鍵結與羰基。TpBu被設計為可允許局部性氮原子周圍單鍵轉動，所以該共價有機框架於結構上有能力形成更多氫鍵。在pH -0.2的環境下，即使承受質子攻擊，TpBu仍然維持完整的堆疊層狀結構。TpBu吸附銅離子的同時也吸熱，於pH 7下(分別於25、35與45度C有23.4、29.2與37.9 mg/g)及於pH -0.2下(分別於25、35與45度C有17.1、21.0與31.2 mg/g)。於pH -0.2下僅有稍微減少的Langmuir 吸附量(與於pH 7下相比)，可推估出競爭吸附伴隨著吸熱減少。質子攻擊影響了外層TpBu，但堆疊層並未剝落。 於此研究中仍是首次將TpPa(OH)2 作為pH-響應吸附材料應用於銅離子移除。Langmuir吸附量分別於25、35與45度C為56.2、84.8、109.9 mg/g，為吸熱吸附過程。於pH -0.2下，35度C時的吸附量為11.3mg/g，減少了86.7%。堆堆疊的層狀結構於pH -0.2下被質子攻擊而毀壞，且無法於pH 7下恢復層狀結構。於pH-swing(7, -0.2, then 7)的實驗中35度C時的吸附量升至114.9mg/g，與原先的TpPa(OH)2相比有著35.5%的增加。這表示該層狀結構於極酸性環境下不被破壞，但是堆疊層會剝落，而增加了銅離子的可吸附點位。重複試驗得出，TpPa(OH)2可用作為pH-響應吸附材料，於pH 7下吸附了109.5±3.2 mg Cu(II)/g，並於pH -0.2下釋放90.5±4.6 mg Cu(II)/g

Abstract We synthesized a novel two-dimensional covalent organic framework (COF) TpBu via solvothermal method in this study. The TpBu possesses amine linkages and carbonyl functional groups on the backbone, and it is designed to permit local rotations of bonds around the nitrogen atoms on amine linkages; therefore, the yielded two-dimensional COF layers are flexible in structure. This design allows excess formation of the H-bonds between the neighboring layers. Upon proton attacks at pH -0.2, the so-synthesized TpBu remains intact in stacked structure. The TpBu can endothermically adsorb Cu(II) ions from water at both pH 7 (23.4, 29.2, and 37.9 mg/g, at 25, 35 and 45 oC, respectively) and pH -0.2 (17.1, 21.0, and 31.2 mg/g, at 25, 35 and 45 oC, respectively) by complexation reactions. At pH -0.2, compared to pH 7, excess protons only mildly reduce the Langmuir adsorption capacities of Cu(II) by TpBu. It can be 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. In this study, also for the first time, applied the covalent organic framework (COF) TpPa(OH)2 as a pH-responsive adsorbent for Cu(II) ions removal from waters. The Langmuir adsorption capacities at 25 oC, 35 oC, and 45 oC are 56.2 mg/g, 84.8 mg/g, and 109.9 mg/g, respectively. The process is an endothermic, entropy-driven adsorption process. The adsorption capacity of TpPa(OH)2 on Cu(II) at pH -0.2 and 35 oC is reduced to 11.3 mg/g, with an 86.7% loss. The layered structures of TpPa(OH)2 are deteriorated by proton attacks at pH -0.2, which cannot be recovered as pH is resumed to neutral. Compared to the pristine TpPa(OH)2, the pH-swing (7, -0.2, then 7), conversely, increases the Langmuir capacity at 35oC to 114.9 mg/g, a 35.5% increase. The TpPa(OH)2 can remain in COF layers structures intact in the highly acidic environment, while the exfoliated layers lead to additional sites for Cu(II) adsorption. TpPa(OH)2 can also be used as a pH-responsive adsorbent, adsorbing 109.5±3.2 mg Cu(II)/g at pH 7, and releasing 90.5±4.6 mg Cu(II)/g at pH -0.2.