Fast Adsorption of Methylene Blue, Basic Fuchsin, and Malachite Green by a Novel Sulfonic-grafted Triptycene-based Porous Organic Polymer

In this study, a novel triptycene-based porous polymer grafted with sulfonic acid (TPP-SOH) was successfully synthesized by the post-synthetic modification of the non-functionalized polymer TPP. The polymer TPP-SOH was well-characterized and was found to be a fast and effective absorbent for the cationic dyes methylene blue (MEB), basic fuchsin (BF), and malachite green (MG), with over 95% removal being observed within 10 min from initial concentrations of 100 mg L, 100 mg L, and 300 mg L, respectively. The adsorption process for MEB, BF, and MG was pH-dependent. The adsorption behaviours for MEB, BF, and MG follow pseudo-second-order kinetics and fit the Langmuir model. Moreover, the maximum adsorption capacities of MEB, BF, and MG at room temperature were 981.8 mg g, 586.2 mg g, and 1942.5 mg g, respectively. It is worth noting that the values of the MEB, BF, and MG adsorption capacities on TPP-SOH were 5.5, 3, and 1.8 times that of the non-functionalized polymer TPP based on the same adsorbent weight. It is suggested that (i) there are strong electrostatic attractions between the sulfonic groups of the TPP-SOH and cationic dyes and (ii) the higher surface area and good porosity may contribute to the high dye adsorption capacity. Furthermore, TPP-SOH exhibited good cyclic stability, which can be regenerated at least five times without a significant loss of adsorption capacity. Therefore, the facile strategy synthesis, as well as the excellent adsorption capacity and reusability, make polymer TPP-SOH an attractive adsorbent for wastewater treatment.