Unleashing the dye adsorption potential of polyaminoimide homopolymer: DFT, statistical physics, site energy and pore size distribution analyses

Abstract

The efficient removal of Congo Red (CR) dye from aqueous solutions is an important issue in environmental protection. This study presents the synthesis and optimization of a polyaminoimide homopolymer (PHP) adsorbent for the removal of CR dye. To optimize the synthesis of PHP, ten different compositions of maleic anhydride and ethylene diamine were tested, with PHP3 demonstrating the highest efficacy. The adsorption process was further enhanced by optimizing pH, temperature, adsorbent dose, and initial dye concentration. Isotherm and kinetic studies revealed that the Langmuir-Freundlich model and the pseudo-second-order kinetics best described the adsorption process. Moreover, PHP3 demonstrated significantly greater selectivity for CR compared to Synozol yellow, and Sulfasalazine. Advanced statistical models were used to analyze the adsorption data, and the single-layer model with single energy (M1) being the most suitable, suggesting that CR molecules were adsorbed onto PHP3 in a perpendicular position through a multimolecular process, the adsorption process is physical, endothermic, spontaneous and specific surface area of PHP3 increased from 54.31 to 115.74 m2 g−1 as temperature rose from 288 to 318 K. Site energy distribution and pore size distribution studies showed that PHP3 has a heterogeneous energy distribution on its surface, and that the adsorption of CR dye primarily takes place in the macropores of PHP3. Density Functional Theory analysis indicated that PHP3 has electron-rich amine groups that can interact with electron-deficient sulfonate groups in CR, while electron-poor amide groups in the polymer can interact with the electron-rich azo group in Congo Red. It also shows that the presence of NaF, Na2SO4, and KCl salts did not significantly affect the CR adsorption, indicating the potential affinity/selectivity of PHP3 towards CR dye. The findings suggest that PHP3 could be an effective and promising adsorbent for industrial applications in wastewater treatment.