A (solvent-free) approach to metal-free photo-catalysts for methylene blue degradation

The hazardous industrial effluent, enriched in organic dyes, produces environmental alarms of being resistant to natural degradation processes. Therefore, the development of sustainable, and cost-effective degradation processes is a vital demand. Here, we present a simple, scalable, and cost-effective methodology to synthesize polyimides from melem and dianhydrides monomers through a solvent-free, thermal condensation approach for effective photo-catalytic dye degradation. The synthesized polyimides were systematically characterized to investigate their surface functionality, crystallinity, morphology, surface area, porosity, and elemental composition followed by their photocatalytic activity. The obtained results confirmed that polyimides derived from melem with 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (M-FDA) and 4,4'-oxydiphthalic dianhydride (M-ODPA) exhibited an efficient degradation of methylene blue up to 93 and 92%, respectively. Whereas, melem and naphthalene tetra-carboxylic dianhydride-based polyimide (M-NTDA) displayed relatively low-degradation ability after the same irradiation period of 75 min. The superior photocatalytic performances of M-FDA and M-ODPA polyimides have been attributed to their relatively low degree crystallinity, layered morphology, high nitrogen content; 26.07, 24.08%, respectively, with high pyridinic (N6) configurations; 69.48 and 64.14%, respectively; and improved surface areas of 2.6183 and 1.8441 m(2)g(-1) with sufficient pores which offer more reactive sites for interaction with dye molecules leading to superb photocatalytic activity. Hence, it can be concluded that besides extended pi network structure, photocatalysis may be improved in photocatalyst materials by improving their physicochemical characteristics. The current endeavor is a great contribution to research community for developing suitable photocatalysts to degrade various other dyes and pollutants efficiently.

Automated summary

The study presents a new method for synthesizing polyimides through solvent-free, thermal condensation approach, and the systematic characterizations and photocatalytic activity evaluation reveal that polyimides derived from M-FDA and M-ODPA exhibit high efficiency in degrading dyes.