Fabrication of monodisperse micron-sized and aldehyde-functionalized microspheres coating with covalent organic framework for efficient and rapid removal of copper ions from wastewater

Covalent organic frameworks (COFs) possess an excellent ability for absorbing heavy metals, but their uneven particle size, difficult separation, and poor dispersion limit their wide application in the treatment of heavy metal pollution. In this paper, a monodisperse poly(4-allyloxybenzaldehyde-co-divinylbenzene) microsphere (denoted as PAD) was prepared with 4-allyloxybenzaldehyde as a functional monomer and divinylbenzene (DVB) as a crosslinker by one-step seed swelling polymerization. Subsequently, oxalyldihydrazide (ODH) and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) were chosen as the precursors for coating the COF layer onto the surface of PAD through a one-pot method. The resulting monodisperse particles (diameter = 6.3 mu m) with a core-shell structure were assigned as PAD@COF and possessed excellent dispersibility in water along with a high specific surface area of 163.8 m2 g-1. In isothermal and dynamic adsorption experiments, the maximum adsorption capacity of Cu2+ reached 270.9 mg g-1, with the adsorption amount reaching 93 mg g-1 after only 10 min. The Langmuir isothermal adsorption model and pseudo-second-order kinetic model were consistent with the adsorption process, indicating that the adsorption of Cu2+ on PAD@COF occurred as a monolayer and that the adsorption process was controlled by chemical processes.