A new nitrogen-rich imine-linked neutral covalent organic framework: Synthesis and high-efficient adsorption of organic dyes

Nowadays, water pollution caused by organic dyes has received increasing attentions due to serious harm to public health and ecosystem, and it is of great significance to design new porous materials with high adsorption capacity to remove organic dye pollutants from wastewater. Herein, a new two-dimensional N-rich imine-linked covalent organic framework (termed as BPA-TAPA COF) has been constructed through Schiff-base reaction between 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPA) and tri(4-aminophenyl)amine (TAPA) under solvothermal conditions, and showed good crystallinity, high thermal stability and certain porosity. Then, it was used as a functional adsorbent for removal of organic dyes, which exhibited good adsorption performances for both cationic and anionic dyes, namely malachite green (MG), Janus green B (JGB), Congo red (CR), and acid orange (AO). Significantly, the adsorption capacities of BPA-TAPA COF for MG and CR reached up to 1070 and 2016 mg.g(-1), in which the latter ranked as the highest in comparison to those of the other documented functional COFs. The removal efficiency of BPA-TAPA COF toward CR (100 ppm) in aqueous solution reached to 99.0% within 180 min. Hydrogen bonds and pi-pi stacking attractions between COF and dye molecules played crucial roles in adsorption of organic dyes. This work uncovers that neutral COFs with nitrogen-rich functional sites can be used as new adsorbents for removal of both cationic and anionic organic dyes and might provide new information for developing effective adsorbents with high adsorption capacity.