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Instead of using organic solvents, a deep eutectic solvent (DES) composed of tetrabutylammonium bromide and imidazole (Bu4 NBr/Im) was employed as a solvent for the first time to synthesize covalent organic frameworks (COFs). Due to the low vapor pressure of the Bu4 NBr/Im-based DES, a new carboxyl-functionalized COF (TpPa-COOH) was synthesized under environmental pressure. The as-synthesized TpPa-COOH has open channels, and the DES can be removed completely from the pores. The dye adsorption performance of TpPa-COOH was examined for three organic dyes with similar molecular sizes: one anionic dye (eosin B, EB) and two cationic dyes (methylene blue, MB and safranine T, ST). TpPa-COOH showed an excellent selective adsorption effect on MB and ST. The electronegative keto form in TpPa-COOH might help to form electrostatic and π-π interactions between the π-stacking frameworks of TpPa-COOH and the positive plane MB and ST molecules. The adsorption isotherms of MB and ST on TpPa-COOH were further investigated in detail, and the equilibrium adsorption was well modeled by using a Langmuir isotherm model. Together with hydrogen bonding, TpPa-COOH showed higher adsorption capacity for ST than for MB (1135 vs. 410 mg g-1 ). These results could provide a guidance for the green synthesis of adsorbents in removing organic dyes from wastewater.

In this work, an aromatic nitrile containing the pyrimidine moiety and bisimidazolium cations (PyImCl) was synthesized and subsequently employed to prepare a bisimidazolium-based cationic covalent triazine framework (PyImCl-cCTF) through the ionothermal trimerization reaction. The chemical composition and structure of PyImCl-cCTF were carefully revealed by a series of techniques. As examined by N2 sorption isotherms at 77 K, PyImCl-cCTF exhibited large surface area and abundant microporous structures. Together with the high content of imidazolium cations derived from the bisimidazolium-based monomer, PyImCl-cCTF showed high CO2 uptake capacity of 235 and 133 mg/g at 1 bar under 273 and 298 K, respectively, superior to the previously reported cCTFs. The dye adsorption performance of PyImCl-cCTF was performed for commonly used dyes. Surprisingly, PyImCl-cCTF exhibited a certain removal effect on both anionic and cationic dyes. Moreover, PyImCl-cCTF with the positively charged skeleton can quickly remove anionic dyes through electrostatic interactions, showing almost 100% removal efficiency within 20 min. These results demonstrate that PyImCl-cCTF can behave as an efficient adsorbent for both CO2 capture and dye removal to solve environmental problems.

A covalent triazine framework (FL-CTF) consisting of electron-donating thiophene units and electron-accepting benzothiadiazole units was synthesized using Suzuki polycondensation. The successful polymerization and chemical structure of FL-CTF were revealed by a combination of FTIR, solid-state 13C NMR, and XPS. The as-prepared FL-CTF with donor–acceptor structure shows fluorescence property in DMF. A series of fluorescent measurements were performed to ascertain the sensing property of FL-CTF toward metal ions. The fluorescence quenching appears upon addition of Fe3+ and the fluorescence intensity recovers facilely after the addition of a chelating agent tetrabutylammonium fluoride. To understand the fluorescence quenching and recovery process, UV–Vis absorption spectra and XPS were further measured. The electron transfer from FL-CTF to electron-deficient Fe3+ and the interaction between Fe3+ and nitrogen sites in FL-CTF may lead to fluorescence quenching. The interference experiments indicated that FL-CTF can selectively detect Fe3+ in the presence of other metal ions or different counter anions. Moreover, FL-CTF can detect Fe3+ with high sensitivity with the detection limit of 0.78 μM. These results demonstrate that FL-CTF has high selectivity and sensitivity toward Fe3+ and thus is expected to be a fluorescent sensor in practical applications.