Fast adsorption of methylene blue, basic fuchsin, and malachite green by a novel sulfonic-grafted triptycene-based porous organic polymer

Abstract

In this study, a novel triptycene-based porous polymer grafted with sulfonic acid (TPP-SO₃H) was successfully synthesized by the post-synthetic modification of the non-functionalized polymer TPP. The polymer TPP-SO₃H 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⁻¹, 100 mg L⁻¹, and 300 mg L⁻¹, 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⁻¹, 586.2 mg g⁻¹, and 1942.5 mg g⁻¹, respectively. It is worth noting that the values of the MEB, BF, and MG adsorption capacities on TPP-SO₃H 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-SO₃H and cationic dyes and (ii) the higher surface area and good porosity may contribute to the high dye adsorption capacity. Furthermore, TPP-SO₃H 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-SO₃H an attractive adsorbent for wastewater treatment.