Metal ion-assisted carboxyl-containing covalent organic frameworks for the efficient removal of Congo red

Abstract

Covalent organic frameworks (COFs) have been utilized as molecular sieves to adsorb or remove or separate a wide range of substances.

A Carboxyl‐Functionalized Covalent Organic Framework Synthesized in a Deep Eutectic Solvent for Dye Adsorption

“…No product was obtained after reaction at 30 °C for 12 h. When the temperature was raised to 90 °C, the yield of the solid product (termed as TpPa‐COOH) was given to be 70 % after reaction for 1 h. Both the yield and surface area were increased after reaction for 12 h, however, not enhanced obviously by further increasing the reaction time. Therefore, the TpPa‐COOH sample was typically synthesized at 90 °C for 12 h. In the FTIR spectrum of TpPa‐COOH (Figure 1 a), the disappearance of the C=O bond (1642 cm −1 ) and C−H bond (2891 cm −1 ) of Tp as well as the N−H stretching bands of Pa‐COOH (3064, 3376 cm −1 ) indicates the complete consumption of the starting materials [21, 33–35] . Meanwhile, the C=N stretching bands in the enol form did not appear, while the strong peaks at 1577 and 1265 cm −1 were corresponded to the C=C and C−N stretching bands in the keto form [23, 33–36] .…”

“…[21,33,35,41] The peak at 134.9 is assigned to the aromatic carbons near carboxyl and secondary amine groups, [21] while the broad peaks between 118.0 and 126.1 ppm could be ascribed to the other aromatic carbons due to the fact that they have similar chemical environment. [21,[33][34][35] Thermogravimetric analysis (TGA) measured under nitrogen atmosphere exhibited one-step loss of weigh up to 300 8C( Figure S2), implying the sole formation of TpPa-COOH without the Bu 4 NBr/Im-based DES inside pores and its thermal stability.…”

“…When compared with MB, the higher Q eq value for ST is due to hydrogen bonding between -COOH groups of TpPa-COOH and -NH 2 groups of the dye ST (Scheme 2). [21,46] The outstanding adsorption performance of TpPa-COOH for the two cationic dyes makes it potentially be used to adsorb organic dyes in the field of water pollution.…”

“…A triazine‐functionalized polyimide COF exhibited superior adsorption capacity for the cationic dye methylene blue (MB), which was ascribed to the intrinsic pore‐size effect and improved electrostatic interaction between MB and the nitrogen‐containing sites in the COF [20] . Metal ion‐assisted COFs were found to display excellent adsorption performance on Congo Red (CR) because of the metal cations providing a positive contribution to the electrostatic interaction [21] . The structural diversity of COFs holds great promise for developing novel adsorbents to effectively adsorb organic dyes.…”

“…[20] Metal ion-assisted COFs were found to display excellent adsorption performance on Congo Red (CR) because of the metal cations providing ap ositive contribution to the electrostatic interaction. [21] The structural diversity of COFs holds great promise for developing novel adsorbents to effectively adsorb organic dyes.…”