Efficient and selective recovery of palladium from acidic metallurgical wastewater is of great economic and environmental importance but remains challenging. Here, two novel ionic covalent organic frameworks (iCOFs), Tp-DG and BT-DG, were synthesized by reaction of 1,3-diaminoguanidine hydrochloride with 1,3,5-triformyphloroglucinol and benzene-1,3,5-triscarbaldehyde, respectively, and then applied to the recovery of Pd(II) from metallurgical wastewater. The maximum adsorption capacities of Tp-DG and BT-DG at pH 2.0 and 298.15 K were 342.1 mg g and 231.1 mg g, which are higher than the majority of similar reported adsorbents. The adsorption isotherms of Pd(II) on iCOFs were highly consistent with the Langmuir isotherm model. Furthermore, the kinetics of the adsorptions by Tp-DG and BT-DG conformed to the quasi-second-order kinetic model, indicating that the controlling step of adsorption is chemical adsorption. Thermodynamic studies revealed that elevated temperatures are beneficial for the recovery of Pd(II). At the same time, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, and density functional theory computational analysis confirmed that electrostatic attraction and coordination are the main mechanisms for Pd(II) adsorption on iCOFs. This work not only highlights that the prepared iCOFs can be used as effective reusable adsorbents to selectively adsorb Pd(II) but also opens the door for the practical application of iCOFs in recovering palladium from complex metallurgical wastewater.

中文翻译：

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胍功能化离子共价有机骨架用于从冶金废水中选择性高效回收钯(II)


从酸性冶金废水中高效、选择性地回收钯具有重大的经济和环境重要性，但仍然具有挑战性。在这里，通过 1,3-二氨基胍盐酸盐与 1,3,5-三甲酰间苯三酚和苯-1,3,5-三甲醛反应合成了两种新型离子共价有机框架（iCOF），Tp-DG 和 BT-DG，分别应用于冶金废水中Pd(II)的回收。 Tp-DG和BT-DG在pH 2.0和298.15 K下的最大吸附容量分别为342.1 mg g和231.1 mg g，高于大多数报道的类似吸附剂。 Pd(II)在iCOFs上的吸附等温线与Langmuir等温线模型高度一致。此外，Tp-DG和BT-DG的吸附动力学符合准二级动力学模型，表明吸附的控制步骤是化学吸附。热力学研究表明，升高温度有利于 Pd(II) 的回收。同时，傅里叶变换红外光谱、X射线光电子能谱、zeta电位和密度泛函理论计算分析证实静电吸引和配位是iCOFs上Pd(II)吸附的主要机制。这项工作不仅强调了所制备的iCOFs可以作为有效的可重复使用的吸附剂来选择性吸附Pd(II)，而且为iCOFs从复杂冶金废水中回收钯的实际应用打开了大门。