An amine-rich porous organic polymer with flexible diarylmethane moieties for adsorptive removal of anionic dyes

Abstract

Developing porous organic polymers (POPs) as efficient adsorbents for wastewater treatment began a new era in environmental remediation. In the current paper, an amine-rich triazine-based POP with excellent flexibility, denoted as MDA-POP, was synthesized using a facile method from accessible building blocks. The prepared MDA-POP was thoroughly characterized using various analytical techniques and its application in removing Congo red and Scarlet 4BS, two widely used textile colors, was investigated. The optimal conditions for the adsorption process were determined by studying different effective parameters, including pH, temperature, adsorbent dosage, and contact time. By optimizing the adsorption conditions, the dye removal efficiency reached up to 99%, with maximum adsorption capacities of 71.43 mg g⁻¹ for Congo red and 136.97 mg g⁻¹ for Scarlet 4BS. The adsorption isotherms of both the dyes were best fitted to the Langmuir model, which indicates monolayer adsorption. Moreover, the study on the kinetic aspects of adsorption shows that the pseudo-second-order model is the best model for describing the adsorption process; thus, the chemical interactions play a vital role in the rate-determining step of the adsorption. The thermodynamic studies show that the standard enthalpies of adsorption (ΔH°) are −178.8 kJ mol⁻¹ for Congo red and −75.4 kJ mol⁻¹ for Scarlet 4BS, indicating that the nature of adsorption is chemisorption. Also, the negative standard free Gibb's energy (ΔG°) values reveal a spontaneous adsorption process. This paper provides a facile and efficient method for synthesizing POPs as adsorbents for water treatment applications.