Efficient adsorption of 1,4-naphthoquinone on covalent organic frameworks

Abstract

1,4-Naphthoquinone is a widely used intermediate in the fields of medicine and chemical engineering. However, it is moderately toxic and can cause serious pollution of water, soil, and air. Thus, the selective removal of 1,4-naphthoquinone from the environment has become an urgent issue. Covalent organic frameworks (COFs) have highly ordered structures, adjustable pore sizes, and customizable chemically functionalized surfaces, providing great potential to realize the adsorption of 1,4-naphthoquinone. However, the molecular recognition and separation performance of COFs largely depend on their physicochemical properties. Therefore, precise control of the physicochemical properties of COFs and exploration of their role mechanisms in target molecule recognition and separation are of great significance for enhancing the application performance of COF materials. In this work, three different COF nanostructures (COF_TF-DBD, COF_TFP-DBD, and COF_TMTF-DBD) are synthesized, and their adsorption performances for 1,4-naphthoquinone are investigated. It is found that the pore size and polar groups within the COF channels play decisive roles in their adsorption capacity. Among them, COF_TMTF-DBD demonstrates the best performance in adsorbing 1,4-naphthoquinone pollutants due to its stronger hydrophobicity, more suitable pore structure, and larger specific surface area, with an adsorption capacity of up to 150.65 mg g⁻¹. Moreover, in a 1,4-naphthoquinone solution with an initial concentration of 160 mg L⁻¹, COF_TMTF-DBD could remove over 55% of 1,4-naphthoquinone within 30 minutes and achieve a removal efficiency of 88% after 120 minutes. Further mechanistic studies reveal that the physicochemical properties of COF channels not only affect the adsorption rate of pollutants but also influence their adsorption capacity.