π-π conjugation driving peroxymonosulfate activation for pollutant elimination over metal-free graphitized polyimide surface.

A novel metal-free catalyst consisting of typical flower-like graphitized polyimide (g-PI) is first synthesized via an enhanced hydrothermal polymerization process, and it exhibits excellent performance for pollutant removal through peroxymonosulfate (PMS) activation over a wide pH range (3-11). The catalyst is especially effective for attacking the endocrine disruptor bisphenol A (BPA), which can be completely degraded in a short time. Based on the results of characterization, g-PI is consisted of abundant aromatic frameworks with π conjugates based on C-O-C linkages and N-hybrid rings, which play essential roles in the subsequent degradation of pollutants. In the g-PI/PMS/BPA system, BPA (rich in π bonds) is preferentially adsorbed to the catalyst surface through π-π interactions, accompanied by a decrease in its activation energy to produce surface-adsorbed BPA*. This species can be directly attacked and degraded by PMS without the need for the radical processes, which saves the energy required for the intermediate activation process of PMS. On the other hand, the electrons obtained from pollutants are rapidly transferred to the O center, driving PMS activation to generate free radicals. The synergetic interface process offers excellent potential for practical wastewater purification.