Sulfonate-modified calixarene-based porous organic polymers for electrostatic enhancement and efficient rapid removal of cationic dyes in water

Developing of fast and efficient adsorbents for removal of low concentration refractory organics in water is significant. Herein, a novel calix[4]arene-based porous organic polymer CaPy is constructed through Sonogashira-Hagihara cross-coupling polycondensation. The strong polar sulfonate is further anchored onto the polymer skeleton of CaPy and three sulfonate-modified anionic polymers CaPy-S1, CaPy-S2, and CaPy-S3 were obtained and fully characterized. The adsorption isotherms showed that the maximum adsorption capacities of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward methylene blue (MB) were 270, 1454, 558 and 1381 mg g-1, whereas those for Rhodamine B (RhB) were 183, 2653, 1132, and 1796 mg g-1, respectively. The maximum adsorption capacity toward RhB was the highest reported vale among the currently used synthetic adsorbents. In addition, the pseudo-second-order rate constants of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward MB were 0.00572, 0.488, 2.24, and 0.192 g mg-1 min-1, respectively, and those toward RhB were 0.000234, 0.138, 0.0819, and 0.203 g mg-1 min-1, respectively. The pseudo-second-order rate constant of CaPy-S2 toward MB was 2.24 g mg-1 min-1 indicating one of the highest adsorption speeds. The activation energy of CaPy-S1 for RhB and MB were 121 and 109 kJ mol-1, respectively, demonstrating that the adsorption of both dyes on CaPy-S1 was chemisorption process. Further, the obtained values of Gibbs free energy were negative, revealing that the adsorption process was spontaneous. This work provides an effective approach for improving adsorption performance via post-modification.