以共價有機框架 EB-COF:Br 吸附水中之磷酸鹽或砷酸鹽

Abstract

共價有機框架（COF）是由輕元素所組成的共價網。這項研究進行了合成和表徵，並首次將生產的EB-COF：Br 作為吸附劑用於從中性的水中去除磷酸鹽和砷酸鹽，以及從極低pH 的溶液中去除磷酸。首先證明了合成的COF 在6 M HCl 或6 M NaOH 溶液中的結構穩定且在75%磷酸中維持主要[1 0 0] 的平面。 首先，磷酸鹽在EB-COF：Br 上的吸附是一個吸熱過程，在25、35 和45°C 下的最大吸附容量分別為25.3、34.7 和35.3 mg / g COF。相應的砷酸鹽吸附過程是放熱過程，最大吸附量分別為53.1、27.5 和5.1 mg / g。合成的COF 還可以有效地吸附河水（pH 7.45）中的磷酸鹽和砷離子，但吸附能力降低。磷酸根或砷酸根離子上的負電荷與COF 的正電荷（=N+–）之間的靜電相互作用，以及磷酸根或砷酸根離子上的氫原子與COF 的（–C=O）基團之間的氫鍵為主要的吸附機制。25°C 下，砷酸鹽的強靜電相互作用使其吸附能力高於磷酸鹽。但是，砷酸根離子尺寸不匹配以及被（= N +–）和（–C=O）基團包圍的吸附位點引起的氫鍵受干擾，降低了砷酸根對溫度和外部陰離子挑戰的穩定性。 此外，來自常規濕法蝕刻工藝的廢混合酸流還含有高含量的磷酸，因此需要回收利用。這項研究是首次使用共價有機框架EB-COF：Br 作為吸附劑來吸附不同濃度的磷酸。 EB-COF：Br 在極酸性溶液中具有很高的吸附磷酸的能力。 EB-COF：Br 在25、35 和45°C 下對廢混合酸的最大吸附容量（qmax）分別為6649、6885 和 6522 mg-H3PO4 / g，這表明吸附過程與溫度無關。COF（–NH–）上的氫原子與磷酸上的氫原子之間的氫鍵與磷酸之間的強氫鍵是吸附過程的主要機制。

The covalent organic framework (COF) is made light elements linked by covalent networks. This study synthesize and characterized, and for the first time applied the produced EB-COF:Br as adsorbent for phosphate and arsenate removal from nearly neutral waters and for phosphoric acid from extremely low pH solution. The synthesized COF was first proven structurally stable in solutions of 6 M HCl, or 6 M NaOH and can maintain the main [1 0 0] planes under 75% phosphoric acid immersion. Then the phosphate adsorption onto the EB-COF:Br was shown to be an endothermic process with maximum adsorption capacity at 25, 35 and 45 °C as 25.3, 34.7 and 35.3 mg/g COF, respectively; and the corresponding arsenate adsorption process being an exothermic process with maximum adsorption capacity as 53.1, 27.5 and 5.1 mg/g, respectively. The synthesized COF could also effectively adsorb phosphate and arsenate ions from river water (pH 7.45) but at reduced adsorption capacities. The electrostatic interactions between the negative charge on phosphate or arsenate ions and the positively charged (=N+–) of COF, and the hydrogen bondings between H atom on phosphate or arsenate ions and the (–C=O) group of COF were the dominating mechanisms for the present adsorption process. The strong electrostatic interactions for arsenate contributed to its higher adsorption capacity than noted for phosphate at 25 °C. However, the disturbed hydrogen bonding induced by mismatched sizes of arsenate ion and the adsorption sites surrounded by the (=N+–) and the (–C=O) groups reduced the stability of arsenate to against temperature and external anion challenges. In addition, streams of waste mixed acids from conventional wet etching processes contain high levels of H3PO4, which warrant recycling. This investigation is the first to use covalent organic framework EB-COF:Br as adsorbent to adsorb phosphoric acid from waste mixed acids from the world’s largest semiconductor foundry. The EB-COF:Br has very high capacities to adsorb H3PO4 in extremely acidic solutions. The maximum adsorption capacities (qmax’s) of EB-COF:Br for waste mixed acids at 25, 35 and 45°C are 6649, 6885 and 6522 mg-H3PO4/g, respectively, suggesting that the adsorption process is temperature-independent. The hydrogen bonding between H atom on (–NH–) of COF and H atom on phosphorous acid and strong hydrogen bonding for phosphoric acid each other were the dominating mechanisms for the present adsorption process.