Polymer based materials, polyimides (PI) were synthesized by direct thermal condensation of melamine and pyromellitic dianhydride and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy, N2 adsorption/desorption isotherms and X-ray photoelectron spectroscopy. The materials were then applied as catalysts for organic dye degradation under visible light irradiation in the presence of peroxymonosulfate (PMS). The results revealed that the metal-free catalysts can activate PMS to generate reactive radicals under visible light irradiation, leading to the efficient degradation of acid orange 7 (AO7) and other organic dyes in aqueous solution. Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, suggesting the good stability of metal-free polymeric photocatalysts. The intermediate products after AO7 degradation were analyzed by UV-vis spectra, ESI-MS and GC/MS. The effect of operation parameters such as the concentration of the catalyst, PMS and organic dye, and initial solution pH on the catalytic activity was also investigated. This study demonstrated a promising polymer material for organic dye degradation with PMS under visible light irradiation.
