Thermostable mesoporous binaphthol-azo aromatic polyester: structure–property relationships and high‑capacity cationic dye uptake

Abstract A rigid mesoporous aromatic polyester (PABn) was synthesized via interfacial polycondensation of 4,4′‑binaphthol with an azo diphenyl diacid chloride and investigated for its molecular structure, thermal properties, porosity, and functional adsorption behavior. FT‑IR, 1 H‑NMR, and mass spectrometry confirmed the binaphthol‑based structure. FT‑IR, wide‑angle X‑ray diffraction, and differential scanning calorimetry revealed a fully amorphous architecture with a high glass transition temperature of 310–320 °C, consistent with a rigid, disordered network. Thermogravimetric analysis showed excellent thermal stability, with a 5% weight-loss temperature of 326 °C and a char yield of about 65 wt% at 600 °C. Nitrogen sorption and electron microscopy indicated a mesoporous texture with abundant accessible domains. As a functional demonstration, batch adsorption experiments with model dyes revealed pronounced selectivity for the cationic species methylene blue and crystal violet, with maximum capacities of 273 and 307 mg g –1 , respectively, and removal efficiencies of 96–98% within 60–90 min, while anionic methyl red and Congo red were scarcely adsorbed. The pseudo-second-order model best described the kinetic data, and the equilibrium data obeyed the Freundlich isotherm, consistent with heterogeneous adsorption on a mesoporous polyester network involving multiple surface and diffusion processes.