Nitrogen-rich covalent triazine frameworks for high-efficient removal of anion dyes and the synergistic adsorption of cationic dyes.

Abstract Efficient adsorption of organic dyes from effluent has great importance for ecological and environmental protection. Herein, covalent triazine frameworks (CTFs) were constructed via the polycondensation of melamine and cyanuric chloride directly. Due to the numerous basic nitrogen atoms as high as 58.98 wt%, high BET surface area (670.2 m g−1), and hierarchical pore structure, CTFs demonstrated selective adsorption of anionic dyes in high capacity (e.g., a maximum adsorption capacity of 1581 mg g−1 for Congo red at 30 °C). The mechanism of the outstanding adsorption performance was carefully verified and ascribed to the electrostatic attraction and hydrogen bonding between CTFs and anionic dyes. The amine groups linking two adjacent triazine rings have primary responsibility for the superior performance. Unexpectedly, CTFs expressed a tuning synergetic effect for removing cationic dyes in aqueous solution coexisting with anionic dyes, exhibiting a great superiority in the specific and comprehensive treatment of organic dyes contaminated water. Furthermore, CTFs were stable and had long-periodic availability for more than 6 times, ensuring the adsorption rate higher than 90%. For better operation, hybrid monolithic aerogels were constructed by incorporating CTFs into polyvinylidene fluoride then casting in melamine resin foams. The obtained aerogels expressed high-efficient removal of anionic dyes coupled with convenient operation. This well-established metal-free porous material is a promising adsorbent candidate for anionic dyes selectively and even synergetic adsorption of cationic dyes in water remediation.