A photocatalytic dye-degradation study on methylene blue by graphitic nitride based polyimides synthesized via a facile thermal-condensation approach

The frequent use of methylene blue (MB) and other organic dyes pose serious environmental concerns subjected to their resistance towards traditional degradation procedures. Therefore, it is important to develop efficient degradation treatments to degrade such dyes. We report a facile thermal condensation methodology to synthesize graphitic nitride (GN) and its derived polyimides by using three different dianhydrides. The obtained results from physicochemical characterization; FTIR, XRD, XPS, and BET/BJH confirmed the formation of GN and its derived polyimides. The synthesized photocatalyst materials were tested for MB degradation under light irradiation for 60 min. Interestingly, the superior photocatalytic performance (96% MB degradation efficiency) despite of decreased surface area of polyimide, GN-FDA (6.78 m(2) g(-1)) has been attributed to its relatively improved degree of crystallinity, greater HOMO-LUMO charge separation, high quaternary nitrogen content, and appropriate porosity. This study can be concluded as follows; firstly the pi conjugated polyimides surprisingly undergo significant shrinkage in surface area probably due to pi-pi interactions. Secondly, derived polyimides exhibited essential features of photocatalytic materials viz greater HOMO-LUMO charge separation evidenced by DFT studies, improved hydrophilicity, appropriate surface area/porosity, and surface nitrogen functionalities that improve their degradation efficiency. Quantum mechanical calculations reveal that modification of GN results in improved electronic properties and enhanced dye degradation attributed to modified charge transfer. This work may open new opportunities to develop efficient metal-free photocatalysts based on GN that are a significant contribution in designing suitable photocatalyst materials for degradation of other organic dyes/contaminants.