钴镍双金属氢氧化物/石墨烯电控分离膜排异性回收废水中低浓度磷酸盐

采用滴涂结合电化学沉积两步法制备了一种具有优良电活性的三维花状钴镍双金属氢氧化物/石墨烯(CoNi-LDH/G)杂化膜，用于电控离子交换过程(electrically switched ion exchange，ESIX)吸附水溶液中低浓度的磷酸根(PO₄^3-)离子。结合 X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等对CoNi-LDH/G杂化膜进行形貌、组成及结构表征。采用电化学方法考察了该杂化膜在不同吸附电压、不同初始浓度、共存离子及不同pH值条件下对PO₄^3-吸附性能的影响。实验结果表明：通过调节氧化还原电位，即使在低浓度下，杂化膜对 PO₄^3-也具有良好的吸附性能，且可以在较宽的pH 值(4~10)范围内使用，同时受共存离子及其浓度变化影响甚小。此外，G 对 PO₄^3-的吸附容量为 1.10 mg·g^-1，CoNi-LDH 对PO₄^3-的吸附容量为11.74 mg·g^-1，二者吸附容量之和小于CoNi-LDH/G对PO₄^3-的吸附容量(16.25 mg·g^-1)。同时，结合O1s的XPS数据分析发现，CoNi-LDH/G杂化膜对PO₄^3-的吸附过程除了层间阴离子交换、PO₄^3-与层板金属离子配位的配体交换外，还存在G与CoNi-LDH之间的协同效应。

Exclusionary recovery of phosphate anions with low concentration from wastewater using a CoNi-layered double hydroxide/graphene electronically controlled separation film

A high electroactive hybrid film of CoNi-layered double hydroxide grown on graphene (CoNi-LDH/G) with a three-dimensional (3D) flower-like structure was successfully prepared by using two-step coating and electrodeposition method, and applied to separate and recover low concentrated phosphate anions from wastewater via electrically switched ion exchange. The morphology, composition, and structure of the CoNi-LDH/G hybrid film were demonstrated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The effect of absorption potentials, initial phosphate concentrations, co-existing anions, and pH on the phosphate electrochemistry adsorption performance of the hybrid film was also investigated. The experimental results indicated that the hybrid film had a high adsorption performance by adjusting the redox potential, even at low concentrations. In addition, it can be used in a wide pH range (4-10), and its adsorption capacity for PO₄^3- was little affected by coexisting ions and their variations in concentration. Furthermore, the adsorption capacity of G and CoNi-LDH for PO₄^3- was 1.10 and 11.74 mg·g^-1, respectively. Moreover, the sum of these two was also lower than that of the CoNi-LDH/G hybrid film (16.25 mg·g^-1). Combined with O1s XPS analysis, it was found that PO₄^3- adsorption on CoNi-LDH/G hybrid film aside from interlayer ion exchange, complexation ligand exchange between PO₄^3- and layer-plate metal ions, the synergistic effects between G and CoNiLDH also existed.